Science.gov

Sample records for determining micromechanical strain

  1. Determining Micromechanical Strain in Nitinol

    SciTech Connect

    Strasberg, Matthew; /SLAC

    2006-09-27

    Nitinol is a superelastic alloy made of equal parts nickel and titanium. Due to its unique shape memory properties, nitinol is used to make medical stents, lifesaving devices used to allow blood flow in occluded arteries. Micromechanical models and even nitinol-specific finite element analysis (FEA) software are insufficient for unerringly predicting fatigue and resultant failure. Due to the sensitive nature of its application, a better understanding of nitinol on a granular scale is being pursued through X-ray diffraction techniques at the Stanford Synchrotron Radiation Laboratory (SSRL) at the Stanford Linear Accelerator Center (SLAC). Through analysis of powder diffraction patterns of nitinol under increasing tensile loads, localized strain can be calculated. We compare these results with micromechanical predictions in order to advance nitinol-relevant FEA tools. From this we hope to gain a greater understanding of how nitinol fatigues under multi-axial loads.

  2. Implementation of Fiber Substructuring Into Strain Rate Dependent Micromechanics Analysis of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    2001-01-01

    A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were incorporated into a mechanics of materials based micromechanics method. In the current work, the micromechanics method is revised such that the composite unit cell is divided into a number of slices. Micromechanics equations are then developed for each slice, with laminate theory applied to determine the elastic properties, effective stresses and effective inelastic strains for the unit cell. Verification studies are conducted using two representative polymer matrix composites with a nonlinear, strain rate dependent deformation response. The computed results compare well to experimentally obtained values.

  3. Strains at the myotendinous junction predicted by a micromechanical model

    PubMed Central

    Sharafi, Bahar; Ames, Elizabeth G.; Holmes, Jeffrey W.; Blemker, Silvia S.

    2011-01-01

    The goal of this work was to create a finite element micromechanical model of the myotendinous junction (MTJ) to examine how the structure and mechanics of the MTJ affect the local micro-scale strains experienced by muscle fibers. We validated the model through comparisons with histological longitudinal sections of muscles fixed in slack and stretched positions. The model predicted deformations of the A-bands within the fiber near the MTJ that were similar to those measured from the histological sections. We then used the model to predict the dependence of local fiber strains on activation and the mechanical properties of the endomysium. The model predicted that peak micro-scale strains increase with activation and as the compliance of the endomysium decreases. Analysis of the models revealed that, in passive stretch, local fiber strains are governed by the difference of the mechanical properties between the fibers and the endomysium. In active stretch, strain distributions are governed by the difference in cross-sectional area along the length of the tapered region of the fiber near the MTJ. The endomysium provides passive resistance that balances the active forces and prevents the tapered region of the fiber from undergoing excessive strain. These model predictions lead to the following hypotheses: (i) the increased likelihood of injury during active lengthening of muscle fibers may be due to the increase in peak strain with activation and (ii) endomysium may play a role in protecting fibers from injury by reducing the strains within the fiber at the MTJ. PMID:21945569

  4. Implementation of Laminate Theory Into Strain Rate Dependent Micromechanics Analysis of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    2000-01-01

    A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were implemented into a mechanics of materials based micromechanics method. In the current work, the computation of the effective inelastic strain in the micromechanics model was modified to fully incorporate the Poisson effect. The micromechanics equations were also combined with classical laminate theory to enable the analysis of symmetric multilayered laminates subject to in-plane loading. A quasi-incremental trapezoidal integration method was implemented to integrate the constitutive equations within the laminate theory. Verification studies were conducted using an AS4/PEEK composite using a variety of laminate configurations and strain rates. The predicted results compared well with experimentally obtained values.

  5. High Strain Rate Deformation Modeling of a Polymer Matrix Composite. Part 2; Composite Micromechanical Model

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Stouffer, Donald C.

    1998-01-01

    Recently applications have exposed polymer matrix composite materials to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under these extreme conditions. In this second paper of a two part report, a three-dimensional composite micromechanical model is described which allows for the analysis of the rate dependent, nonlinear deformation response of a polymer matrix composite. Strain rate dependent inelastic constitutive equations utilized to model the deformation response of a polymer are implemented within the micromechanics method. The deformation response of two representative laminated carbon fiber reinforced composite materials with varying fiber orientation has been predicted using the described technique. The predicted results compare favorably to both experimental values and the response predicted by the Generalized Method of Cells, a well-established micromechanics analysis method.

  6. Micromechanics-Based Permeability Evolution in Brittle Materials at High Strain Rates

    NASA Astrophysics Data System (ADS)

    Perol, Thibaut; Bhat, Harsha S.

    2016-08-01

    We develop a micromechanics-based permeability evolution model for brittle materials at high strain rates (≥ 100 s^{-1}). Extending for undrained deformation the mechanical constitutive description of brittle solids, whose constitutive response is governed by micro-cracks, we now relate the damage-induced strains to micro-crack aperture. We then use an existing permeability model to evaluate the permeability evolution. This model predicts both the percolative and connected regime of permeability evolution of Westerly Granite during triaxial loading at high strain rate. This model can simulate pore pressure history during earthquake coseismic dynamic ruptures under undrained conditions.

  7. Ultrahigh-Q Micromechanical Resonators by Using Epitaxially Induced Tensile Strain in GaNAs

    NASA Astrophysics Data System (ADS)

    Onomitsu, Koji; Mitsuhara, Manabu; Yamamoto, Hideki; Yamaguchi, Hiroshi

    2013-11-01

    We fabricated micromechanical resonators using epitaxially grown GaNAs, in which in-plane tensile strain is induced by the growth on GaAs substrates. The resonators show significant improvement in resonance frequency and quality factor (Q) compared with those made of unstrained GaAs. The optimization of nitrogen concentration provides a resonator with the highest room-temperature Q value so far reported for III-V materials: the obtained Q of 1.2×105 is about 30 times higher than that of resonators made of GaAs. The ultrahigh-Q GaNAs mechanical resonators are suitable for various sensing applications to unveil phenomena that have not yet been possible to examine.

  8. Incorporation of Mean Stress Effects into the Micromechanical Analysis of the High Strain Rate Response of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

    2002-01-01

    The results presented here are part of an ongoing research program, to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. A micromechanics approach is employed in this work, in which state variable constitutive equations originally developed for metals have been modified to model the deformation of the polymer matrix, and a strength of materials based micromechanics method is used to predict the effective response of the composite. In the analysis of the inelastic deformation of the polymer matrix, the definitions of the effective stress and effective inelastic strain have been modified in order to account for the effect of hydrostatic stresses, which are significant in polymers. Two representative polymers, a toughened epoxy and a brittle epoxy, are characterized through the use of data from tensile and shear tests across a variety of strain rates. Results computed by using the developed constitutive equations correlate well with data generated via experiments. The procedure used to incorporate the constitutive equations within a micromechanics method is presented, and sample calculations of the deformation response of a composite for various fiber orientations and strain rates are discussed.

  9. Micromechanical Model for Deformation in Solids with Universal Predictions for Stress-Strain Curves and Slip Avalanches

    SciTech Connect

    Dahmen, Karin A.; Ben-Zion, Yehuda; Uhl, Jonathan T.

    2009-05-01

    A basic micromechanical model for deformation of solids with only one tuning parameter (weakening {epsilon}) is introduced. The model can reproduce observed stress-strain curves, acoustic emissions and related power spectra, event statistics, and geometrical properties of slip, with a continuous phase transition from brittle to ductile behavior. Exact universal predictions are extracted using mean field theory and renormalization group tools. The results agree with recent experimental observations and simulations of related models for dislocation dynamics, material damage, and earthquake statistics.

  10. Strain rate-dependent deformation and strength modeling of a polymer matrix composite utilizing a micromechanics approach

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert Keith

    1999-11-01

    Potential gas turbine applications will expose polymer matrix composites to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under extreme conditions. Specifically, analytical methods designed for these applications must have the capability of properly capturing the strain rate sensitivities and nonlinearities that are present in the material response. The Ramaswamy-Stouffer constitutive equations, originally developed to analyze the viscoplastic deformation of metals, have been modified to simulate the nonlinear deformation response of ductile, crystalline polymers. The constitutive model is characterized and correlated for two representative ductile polymers, Fiberite 977-2 and PEEK, and the computed results correlate well with experimental values. The polymer constitutive equations are implemented in a mechanics of materials based composite micromechanics model to predict the nonlinear, rate dependent deformation response of a composite ply. Uniform stress and uniform strain assumptions are applied to compute the effective stresses of a composite unit cell from the applied strains. The micromechanics equations are successfully verified for two polymer matrix composites, IM7/977-2 and AS4/PEEK. The ultimate strength of a composite ply is predicted with the Hashin failure criteria that were implemented in the composite micromechanics model. The failure stresses of the two composite material systems are accurately predicted for a variety of fiber orientations and strain rates. The composite deformation model is implemented in LS-DYNA, a commercially available transient dynamic explicit finite element code. The matrix constitutive equations are converted into an incremental form, and the model is implemented into LS-DYNA through the use of a user defined material subroutine. The deformation response of a bulk polymer and a polymer matrix composite are predicted by finite element analyses. The results

  11. Foam Micromechanics

    SciTech Connect

    Kraynik, A.M.; Neilsen, M.K.; Reinelt, D.A.; Warren, W.E.

    1998-11-03

    Foam evokes many different images: waves breaking at the seashore, the head on a pint of Guinness, an elegant dessert, shaving, the comfortable cushion on which you may be seated... From the mundane to the high tech, foams, emulsions, and cellular solids encompass a broad range of materials and applications. Soap suds, mayonnaise, and foamed polymers provide practical motivation and only hint at the variety of materials at issue. Typical of mukiphase materiaIs, the rheoIogy or mechanical behavior of foams is more complicated than that of the constituent phases alone, which may be gas, liquid, or solid. For example, a soap froth exhibits a static shear modulus-a hallmark of an elastic solid-even though it is composed primarily of two Newtonian fluids (water and air), which have no shear modulus. This apparent paradox is easily resolved. Soap froth contains a small amount of surfactant that stabilizes the delicate network of thin liq- uid films against rupture. The soap-film network deforms in response to a macroscopic strain; this increases interracial area and the corresponding sur- face energy, and provides the strain energy of classical elasticity theory [1]. This physical mechanism is easily imagined but very challenging to quantify for a realistic three-dimensional soap froth in view of its complex geome- try. Foam micromechanics addresses the connection between constituent properties, cell-level structure, and macroscopic mechanical behavior. This article is a survey of micromechanics applied to gas-liquid foams, liquid-liquid emulsions, and cellular solids. We will focus on static response where the foam deformation is very slow and rate-dependent phenomena such as viscous flow can be neglected. This includes nonlinear elasticity when deformations are large but reversible. We will also discuss elastic- plastic behavior, which involves yield phenomena. Foam structures based on polyhedra packed to fill space provide a unify- ing geometrical theme. Because a two

  12. On consistent micromechanical estimation of macroscopic elastic energy, coherence energy and phase transformation strains for SMA materials

    NASA Astrophysics Data System (ADS)

    Ziółkowski, Andrzej

    2016-09-01

    An apparatus of micromechanics is used to isolate the key ingredients entering macroscopic Gibbs free energy function of a shape memory alloy (SMA) material. A new self-equilibrated eigenstrains influence moduli (SEIM) method is developed for consistent estimation of effective (macroscopic) thermostatic properties of solid materials, which in microscale can be regarded as amalgams of n-phase linear thermoelastic component materials with eigenstrains. The SEIM satisfy the self-consistency conditions, following from elastic reciprocity (Betti) theorem. The method allowed expressing macroscopic coherency energy and elastic complementary energy terms present in the general form of macroscopic Gibbs free energy of SMA materials in the form of semilinear and semiquadratic functions of the phase composition. Consistent SEIM estimates of elastic complementary energy, coherency energy and phase transformation strains corresponding to classical Reuss and Voigt conjectures are explicitly specified. The Voigt explicit relations served as inspiration for working out an original engineering practice-oriented semiexperimental SEIM estimates. They are especially conveniently applicable for an isotropic aggregate (composite) composed of a mixture of n isotropic phases. Using experimental data for NiTi alloy and adopting conjecture that it can be treated as an isotropic aggregate of two isotropic phases, it is shown that the NiTi coherency energy and macroscopic phase strain are practically not influenced by the difference in values of austenite and martensite elastic constants. It is shown that existence of nonzero fluctuating part of phase microeigenstrains field is responsible for building up of so-called stored energy of coherency, which is accumulated in pure martensitic phase after full completion of phase transition. Experimental data for NiTi alloy show that the stored coherency energy cannot be neglected as it considerably influences the characteristic phase transition

  13. Strain Rate Dependent Deformation and Strength Modeling of a Polymer Matrix Composite Utilizing a Micromechanics Approach. Degree awarded by Cincinnati Univ.

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    1999-01-01

    Potential gas turbine applications will expose polymer matrix composites to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under extreme conditions. Specifically, analytical methods designed for these applications must have the capability of properly capturing the strain rate sensitivities and nonlinearities that are present in the material response. The Ramaswamy-Stouffer constitutive equations, originally developed to analyze the viscoplastic deformation of metals, have been modified to simulate the nonlinear deformation response of ductile, crystalline polymers. The constitutive model is characterized and correlated for two representative ductile polymers. Fiberite 977-2 and PEEK, and the computed results correlate well with experimental values. The polymer constitutive equations are implemented in a mechanics of materials based composite micromechanics model to predict the nonlinear, rate dependent deformation response of a composite ply. Uniform stress and uniform strain assumptions are applied to compute the effective stresses of a composite unit cell from the applied strains. The micromechanics equations are successfully verified for two polymer matrix composites. IM7/977-2 and AS4/PEEK. The ultimate strength of a composite ply is predicted with the Hashin failure criteria that were implemented in the composite micromechanics model. The failure stresses of the two composite material systems are accurately predicted for a variety of fiber orientations and strain rates. The composite deformation model is implemented in LS-DYNA, a commercially available transient dynamic explicit finite element code. The matrix constitutive equations are converted into an incremental form, and the model is implemented into LS-DYNA through the use of a user defined material subroutine. The deformation response of a bulk polymer and a polymer matrix composite are predicted by finite element analyses. The results

  14. Micromechanical thermogravimetry

    NASA Astrophysics Data System (ADS)

    Berger, R.; Lang, H. P.; Gerber, Ch.; Gimzewski, J. K.; Fabian, J. H.; Scandella, L.; Meyer, E.; Güntherodt, H.-J.

    1998-09-01

    We demonstrate a new method for thermal analysis of nanogram quantities of material using a micromechanical thermogravimetric technique. The cantilever-type device uses an integrated piezoresistor to sense bending and simultaneously to ramp the temperature and control temperature cycles. It has a mass resolution in the picogram range. A quantitative analysis of the dehydration of copper-sulfate-pentahydrate (CuSO 4·5H 2O) is presented. The technique outperforms current thermogravimetric approaches by five orders of magnitude.

  15. Micromechanical Oscillating Mass Balance

    NASA Technical Reports Server (NTRS)

    Altemir, David A. (Inventor)

    1997-01-01

    A micromechanical oscillating mass balance and method adapted for measuring minute quantities of material deposited at a selected location, such as during a vapor deposition process. The invention comprises a vibratory composite beam which includes a dielectric layer sandwiched between two conductive layers. The beam is positioned in a magnetic field. An alternating current passes through one conductive layers, the beam oscillates, inducing an output current in the second conductive layer, which is analyzed to determine the resonant frequency of the beam. As material is deposited on the beam, the mass of the beam increases and the resonant frequency of the beam shifts, and the mass added is determined.

  16. Electrostatically controlled micromechanical gyroscope

    NASA Technical Reports Server (NTRS)

    Hawkey, Timothy (Inventor); Torti, Richard (Inventor); Johnson, Bruce (Inventor)

    1994-01-01

    An integrated electrostatically-controlled micromechanical gyroscope with a rotor encompassed within a rotor cavity and electrostatically spun within the cavity. The gyroscope includes a plurality of axial electrostatic rotor actuators above and below the rotor for controlling the axial and tilt position of the rotor within the cavity, and a plurality of radial electrostatic actuators spaced circumferentially around the rotor for controlling the radial and tilt position of the rotor within the cavity. The position of the rotor within the cavity is then resolved to determine the external forces acting on the rotor.

  17. Micromechanical Study of Metals

    NASA Technical Reports Server (NTRS)

    Velikov, P. A.; Stchapov, N. P.; Lorenz, W. F.

    1945-01-01

    The Institut Scientifique Experimental des Transports at Moscow established toward the end of 1925 had since its inception included in its program the study of the mechanism of plastic deformation and the problems associated with it with reference to the materials of the means of transport. Before the program thus determined upon could be carried out, it was necessary to adopt a method of research, or, more exactly, a system of such methods. Because of the modest equipment of the laboratory of the recently established institute, the choice of any particular method was determined not only by the advantages it offered but also by the resources available. As a result of a series of studies and investigations, a method was determined upon which in this paper will be denoted as the micromechanical method. The underlying basis of this method is already known. As will be seen from the description that follows, the micromechanical method is merely a combination of the micrographic study of plastic deformations with mechanical tests on small specimens. It is a well-known fact that a number of investigators have largely employed and still are employing these two procedures and have thereby obtained good results. The authors of the present paper have found it useful to combine the two methods, by making the two studies simultaneously on the sane specimen.

  18. Micromechanics of shear banding

    SciTech Connect

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  19. Determination of residual strains in ceramic-fiber reinforced composites using fluorescence spectroscopy

    SciTech Connect

    Yang, X.; Young, R.J.

    1995-06-01

    The dependence of the positions of the R{sub 1} and R{sub 2} fluorescence lines upon fiber strain has been determined for the PRD-166 alumina-zirconia fiber. It is found that the wavenumbers of both lines increase with increasing strain. The approximately linear relationship between line shift and fiber strain has been used to map the distribution of thermal residual strain along the fibers in Pyrex and soda-lime silicate (SLS) glass-matrix model single-fiber composites. It has been shown that the values of thermal strain in the fibers are close to those expected from theoretical analyses. The interfacial shear stress has been derived from the point-to-point variation of the fiber strain along the fibers. It has also been found that the distribution of strain along a fully embedded fiber is close to that predicted by conventional shear-lag analysis. It has been demonstrated that fluorescence spectroscopy is a powerful method of following the micromechanics of deformation in ceramic fibers and composites.

  20. Micromechanical damage and fracture in elastomeric polymers

    NASA Astrophysics Data System (ADS)

    Heyden, Stefanie

    This thesis aims at a simple one-parameter macroscopic model of distributed damage and fracture of polymers that is amenable to a straightforward and efficient numerical implementation. The failure model is motivated by post-mortem fractographic observations of void nucleation, growth and coalescence in polyurea stretched to failure, and accounts for the specific fracture energy per unit area attendant to rupture of the material. Furthermore, it is shown that the macroscopic model can be rigorously derived, in the sense of optimal scaling, from a micromechanical model of chain elasticity and failure regularized by means of fractional strain-gradient elasticity. Optimal scaling laws that supply a link between the single parameter of the macroscopic model, namely the critical energy-release rate of the material, and micromechanical parameters pertaining to the elasticity and strength of the polymer chains, and to the strain-gradient elasticity regularization, are derived. Based on optimal scaling laws, it is shown how the critical energy-release rate of specific materials can be determined from test data. In addition, the scope and fidelity of the model is demonstrated by means of an example of application, namely Taylor-impact experiments of polyurea rods. Hereby, optimal transportation meshfree approximation schemes using maximum-entropy interpolation functions are employed. Finally, a different crazing model using full derivatives of the deformation gradient and a core cut-off is presented, along with a numerical non-local regularization model. The numerical model takes into account higher-order deformation gradients in a finite element framework. It is shown how the introduction of non-locality into the model stabilizes the effect of strain localization to small volumes in materials undergoing softening. From an investigation of craze formation in the limit of large deformations, convergence studies verifying scaling properties of both local- and non-local energy

  1. Compound floating pivot micromechanisms

    DOEpatents

    Garcia, Ernest J.

    2001-04-24

    A new class of tilting micromechanical mechanisms have been developed. These new mechanisms use compound floating pivot structures to attain far greater tilt angles than are practical using other micromechanical techniques. The new mechanisms are also capable of bi-directional tilt about multiple axes.

  2. Micromechanics of cellularized biopolymer networks

    PubMed Central

    Jones, Christopher A. R.; Cibula, Matthew; Feng, Jingchen; Krnacik, Emma A.; McIntyre, David H.; Levine, Herbert; Sun, Bo

    2015-01-01

    Collagen gels are widely used in experiments on cell mechanics because they mimic the extracellular matrix in physiological conditions. Collagen gels are often characterized by their bulk rheology; however, variations in the collagen fiber microstructure and cell adhesion forces cause the mechanical properties to be inhomogeneous at the cellular scale. We study the mechanics of type I collagen on the scale of tens to hundreds of microns by using holographic optical tweezers to apply pN forces to microparticles embedded in the collagen fiber network. We find that in response to optical forces, particle displacements are inhomogeneous, anisotropic, and asymmetric. Gels prepared at 21 °C and 37 °C show qualitative difference in their micromechanical characteristics. We also demonstrate that contracting cells remodel the micromechanics of their surrounding extracellular matrix in a strain- and distance-dependent manner. To further understand the micromechanics of cellularized extracellular matrix, we have constructed a computational model which reproduces the main experiment findings. PMID:26324923

  3. Micromechanisms with floating pivot

    DOEpatents

    Garcia, Ernest J.

    2001-03-06

    A new class of tilting micromechanical mechanisms have been developed. These new mechanisms use floating pivot structures to relieve some of the problems encountered in the use of solid flexible pivots.

  4. Critique of Macro Flow/Damage Surface Representations for Metal Matrix Composites Using Micromechanics

    NASA Technical Reports Server (NTRS)

    Lissenden, Cliff J.; Arnold, Steven M.

    1996-01-01

    Guidance for the formulation of robust, multiaxial, constitutive models for advanced materials is provided by addressing theoretical and experimental issues using micromechanics. The multiaxial response of metal matrix composites, depicted in terms of macro flow/damage surfaces, is predicted at room and elevated temperatures using an analytical micromechanical model that includes viscoplastic matrix response as well as fiber-matrix debonding. Macro flow/damage surfaces (i.e., debonding envelopes, matrix threshold surfaces, macro 'yield' surfaces, surfaces of constant inelastic strain rate, and surfaces of constant dissipation rate) are determined for silicon carbide/titanium in three stress spaces. Residual stresses are shown to offset the centers of the flow/damage surfaces from the origin and their shape is significantly altered by debonding. The results indicate which type of flow/damage surfaces should be characterized and what loadings applied to provide the most meaningful experimental data for guiding theoretical model development and verification.

  5. A Micromechanical RF Channelizer

    NASA Astrophysics Data System (ADS)

    Akgul, Mehmet

    The power consumption of a radio generally goes as the number and strength of the RF signals it must process. In particular, a radio receiver would consume much less power if the signal presented to its electronics contained only the desired signal in a tiny percent bandwidth frequency channel, rather than the typical mix of signals containing unwanted energy outside the desired channel. Unfortunately, a lack of filters capable of selecting single channel bandwidths at RF forces the front-ends of contemporary receivers to accept unwanted signals, and thus, to operate with sub-optimal efficiency. This dissertation focuses on the degree to which capacitive-gap transduced micromechanical resonators can achieve the aforementioned RF channel-selecting filters. It aims to first show theoretically that with appropriate scaling capacitive-gap transducers are strong enough to meet the needed coupling requirements; and second, to fully detail an architecture and design procedure needed to realize said filters. Finally, this dissertation provides an actual experimentally demonstrated RF channel-select filter designed using the developed procedures and confirming theoretical predictions. Specifically, this dissertation introduces four methods that make possible the design and fabrication of RF channel-select filters. The first of these introduces a small-signal equivalent circuit for parallel-plate capacitive-gap transduced micromechanical resonators that employs negative capacitance to model the dependence of resonance frequency on electrical stiffness in a way that facilitates the analysis of micromechanical circuits loaded with arbitrary electrical impedances. The new circuit model not only correctly predicts the dependence of electrical stiffness on the impedances loading the input and output electrodes of parallel-plate capacitive-gap transduced micromechanical device, but does so in a visually intuitive way that identifies current drive as most appropriate for

  6. Micromechanics of hearing

    NASA Astrophysics Data System (ADS)

    Hudspeth, A. J.

    2015-12-01

    The following summarizes the key points addressed during a tutorial session on the Micromechanics of Hearing that took place at the 12th International Workshop on the Mechanics of Hearing held at Cape Sounio, Greece, in June 2014. The tutorial was intended to present an overview of basic ideas and to address topics of current interest relevant to the Workshop. The session was recorded, and the audio file and accompanying visual content of the presentation can be found in the Mechanics of Hearing Digital Library (www.mechanicsofhearing.org).

  7. A Micromechanical RF Channelizer

    NASA Astrophysics Data System (ADS)

    Akgul, Mehmet

    The power consumption of a radio generally goes as the number and strength of the RF signals it must process. In particular, a radio receiver would consume much less power if the signal presented to its electronics contained only the desired signal in a tiny percent bandwidth frequency channel, rather than the typical mix of signals containing unwanted energy outside the desired channel. Unfortunately, a lack of filters capable of selecting single channel bandwidths at RF forces the front-ends of contemporary receivers to accept unwanted signals, and thus, to operate with sub-optimal efficiency. This dissertation focuses on the degree to which capacitive-gap transduced micromechanical resonators can achieve the aforementioned RF channel-selecting filters. It aims to first show theoretically that with appropriate scaling capacitive-gap transducers are strong enough to meet the needed coupling requirements; and second, to fully detail an architecture and design procedure needed to realize said filters. Finally, this dissertation provides an actual experimentally demonstrated RF channel-select filter designed using the developed procedures and confirming theoretical predictions. Specifically, this dissertation introduces four methods that make possible the design and fabrication of RF channel-select filters. The first of these introduces a small-signal equivalent circuit for parallel-plate capacitive-gap transduced micromechanical resonators that employs negative capacitance to model the dependence of resonance frequency on electrical stiffness in a way that facilitates the analysis of micromechanical circuits loaded with arbitrary electrical impedances. The new circuit model not only correctly predicts the dependence of electrical stiffness on the impedances loading the input and output electrodes of parallel-plate capacitive-gap transduced micromechanical device, but does so in a visually intuitive way that identifies current drive as most appropriate for

  8. Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson's ratios and fluid expulsion under tensile loading.

    PubMed

    Ahmadzadeh, Hossein; Freedman, Benjamin R; Connizzo, Brianne K; Soslowsky, Louis J; Shenoy, Vivek B

    2015-08-01

    As tendons are loaded, they reduce in volume and exude fluid to the surrounding medium. Experimental studies have shown that tendon stretching results in a Poisson's ratio greater than 0.5, with a maximum value at small strains followed by a nonlinear decay. Here we present a computational model that attributes this macroscopic observation to the microscopic mechanism of the load transfer between fibrils under stretch. We develop a finite element model based on the mechanical role of the interfibrillar-linking elements, such as thin fibrils that bridge the aligned fibrils or macromolecules such as glycosaminoglycans (GAGs) in the interfibrillar sliding and verify it with a theoretical shear-lag model. We showed the existence of a previously unappreciated structure-function mechanism whereby the Poisson's ratio in tendon is affected by the strain applied and interfibrillar-linker properties, and together these features predict tendon volume shrinkage under tensile loading. During loading, the interfibrillar-linkers pulled fibrils toward each other and squeezed the matrix, leading to the Poisson's ratio larger than 0.5 and fluid expulsion. In addition, the rotation of the interfibrillar-linkers with respect to the fibrils at large strains caused a reduction in the volume shrinkage and eventual nonlinear decay in Poisson's ratio at large strains. Our model also predicts a fluid flow that has a radial pattern toward the surrounding medium, with the larger fluid velocities in proportion to the interfibrillar sliding. PMID:25934322

  9. Probabilistic Fiber Composite Micromechanics

    NASA Technical Reports Server (NTRS)

    Stock, Thomas A.

    1996-01-01

    Probabilistic composite micromechanics methods are developed that simulate expected uncertainties in unidirectional fiber composite properties. These methods are in the form of computational procedures using Monte Carlo simulation. The variables in which uncertainties are accounted for include constituent and void volume ratios, constituent elastic properties and strengths, and fiber misalignment. A graphite/epoxy unidirectional composite (ply) is studied to demonstrate fiber composite material property variations induced by random changes expected at the material micro level. Regression results are presented to show the relative correlation between predictor and response variables in the study. These computational procedures make possible a formal description of anticipated random processes at the intra-ply level, and the related effects of these on composite properties.

  10. A numerical method for determining the strain rate intensity factor under plane strain conditions

    NASA Astrophysics Data System (ADS)

    Alexandrov, S.; Kuo, C.-Y.; Jeng, Y.-R.

    2016-07-01

    Using the classical model of rigid perfectly plastic solids, the strain rate intensity factor has been previously introduced as the coefficient of the leading singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. Since then, many strain rate intensity factors have been determined by means of analytical and semi-analytical solutions. However, no attempt has been made to develop a numerical method for calculating the strain rate intensity factor. This paper presents such a method for planar flow. The method is based on the theory of characteristics. First, the strain rate intensity factor is derived in characteristic coordinates. Then, a standard numerical slip-line technique is supplemented with a procedure to calculate the strain rate intensity factor. The distribution of the strain rate intensity factor along the friction surface in compression of a layer between two parallel plates is determined. A high accuracy of this numerical solution for the strain rate intensity factor is confirmed by comparison with an analytic solution. It is shown that the distribution of the strain rate intensity factor is in general discontinuous.

  11. A Micromechanical INS/GPS System for Small Satellites

    NASA Technical Reports Server (NTRS)

    Barbour, N.; Brand, T.; Haley, R.; Socha, M.; Stoll, J.; Ward, P.; Weinberg, M.

    1995-01-01

    The cost and complexity of large satellite space missions continue to escalate. To reduce costs, more attention is being directed toward small lightweight satellites where future demand is expected to grow dramatically. Specifically, micromechanical inertial systems and microstrip global positioning system (GPS) antennas incorporating flip-chip bonding, application specific integrated circuits (ASIC) and MCM technologies will be required. Traditional microsatellite pointing systems do not employ active control. Many systems allow the satellite to point coarsely using gravity gradient, then attempt to maintain the image on the focal plane with fast-steering mirrors. Draper's approach is to actively control the line of sight pointing by utilizing on-board attitude determination with micromechanical inertial sensors and reaction wheel control actuators. Draper has developed commercial and tactical-grade micromechanical inertial sensors, The small size, low weight, and low cost of these gyroscopes and accelerometers enable systems previously impractical because of size and cost. Evolving micromechanical inertial sensors can be applied to closed-loop, active control of small satellites for micro-radian precision-pointing missions. An inertial reference feedback control loop can be used to determine attitude and line of sight jitter to provide error information to the controller for correction. At low frequencies, the error signal is provided by GPS. At higher frequencies, feedback is provided by the micromechanical gyros. This blending of sensors provides wide-band sensing from dc to operational frequencies. First order simulation has shown that the performance of existing micromechanical gyros, with integrated GPS, is feasible for a pointing mission of 10 micro-radians of jitter stability and approximately 1 milli-radian absolute error, for a satellite with 1 meter antenna separation. Improved performance micromechanical sensors currently under development will be

  12. Micromechanics of Drosophila Audition

    NASA Astrophysics Data System (ADS)

    Göpfert, M. C.; Robert, D.

    2003-02-01

    An analysis is presented of the auditory micromechanics of the fruit fly Drosophila melanogaster. In this animal, the distal part of the antenna constitutes a resonantly tuned sound receiver, the vibrations of which are transduced by a chordotonal sense organ in the antenna's base. Analyzing the mechanical behavior of the antennal receiver by means of microscanning laser Doppler vibrometry, we show that the auditory system of wild-type flies exhibits a hardening stiffness nonlinearity and spontaneously generates oscillations in the absence of external stimuli. According to the deprivation of these mechanical properties in mechanosensory mutants, the receiver's nonlinearity and oscillation activity are introduced by chordotonal auditory neurons. Requiring the mechanoreceptor-specific extracellular linker protein No-mechanoreceptor-potential-A (NompA), NompC mechanosensory transduction channels, Beethoven (Btv), and Touch-insensitive-larva-B (TilB), nonlinearity and oscillation activity of the fly's antennal receiver depend on prominent components of the auditory transduction machinery and seem to originate from motility of auditory receptor cilia.

  13. Micromechanics and anatomical changes during early ontogeny of two lianescent Aristolochia species.

    PubMed

    Köhler, L; Speck, T; Spatz, H C

    2000-04-01

    The mechanical properties of young stems of Aristolochia macrophylla Lam. and Aristolochia brasiliensis Mart. et Zucc. were studied during elongation growth and primary differentiation. Data for the modulus of elasticity, for the viscoelastic behaviour caused by longitudinal tension and for the shear modulus resulting from torsion around a longitudinal axis were related to the underlying structural changes by quantitative analysis of stem anatomy, tissue distribution, ultrastructure, and cell wall biochemistry. The orientation of cellulose microfibrils was determined by light microscopy and small-angle X-ray diffraction, and the lignin content was determined by thioglycolic acid derivatization and spectroscopic quantification. It was demonstrated that the increase in stability during early development is due to the complementary effects of increase in cell wall material, lignification, and cellulose microfibril alignment. A detailed micromechanical model, considering internal prestresses, is proposed to explain the characteristic biphasic stress-strain behaviour as well as the strain-hardening observed.

  14. Micromechanics and anatomical changes during early ontogeny of two lianescent Aristolochia species.

    PubMed

    Köhler, L; Speck, T; Spatz, H C

    2000-04-01

    The mechanical properties of young stems of Aristolochia macrophylla Lam. and Aristolochia brasiliensis Mart. et Zucc. were studied during elongation growth and primary differentiation. Data for the modulus of elasticity, for the viscoelastic behaviour caused by longitudinal tension and for the shear modulus resulting from torsion around a longitudinal axis were related to the underlying structural changes by quantitative analysis of stem anatomy, tissue distribution, ultrastructure, and cell wall biochemistry. The orientation of cellulose microfibrils was determined by light microscopy and small-angle X-ray diffraction, and the lignin content was determined by thioglycolic acid derivatization and spectroscopic quantification. It was demonstrated that the increase in stability during early development is due to the complementary effects of increase in cell wall material, lignification, and cellulose microfibril alignment. A detailed micromechanical model, considering internal prestresses, is proposed to explain the characteristic biphasic stress-strain behaviour as well as the strain-hardening observed. PMID:10805439

  15. Micromechanics for particulate reinforced composites

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.; Goldberg, Robert K.; Mital, Subodh K.

    1996-01-01

    A set of micromechanics equations for the analysis of particulate reinforced composites is developed using the mechanics of materials approach. Simplified equations are used to compute homogenized or equivalent thermal and mechanical properties of particulate reinforced composites in terms of the properties of the constituent materials. The microstress equations are also presented here to decompose the applied stresses on the overall composite to the microstresses in the constituent materials. The properties of a 'generic' particulate composite as well as those of a particle reinforced metal matrix composite are predicted and compared with other theories as well as some experimental data. The micromechanics predictions are in excellent agreement with the measured values.

  16. Micromechanics Analysis Code (MAC) User Guide: Version 1.0

    NASA Technical Reports Server (NTRS)

    Wilt, T. E.; Arnold, S. M.

    1994-01-01

    The ability to accurately predict the thermomechanical deformation response of advanced composite materials continues to play an important role in the development of these strategic materials. Analytical models that predict the effective behavior of composites are used not only by engineers performing structural analysis of large-scale composite components but also by material scientists in developing new material systems. For an analytical model to fulfill these two distinct functions it must be based on a micromechanics approach which utilizes physically based deformation and life constitutive models and allows one to generate the average (macro) response of a composite material given the properties of the individual constituents and their geometric arrangement. Here the user guide for the recently developed, computationally efficient and comprehensive micromechanics analysis code, MAC, who's predictive capability rests entirely upon the fully analytical generalized method of cells, GMC, micromechanics model is described. MAC is a versatile form of research software that 'drives' the double or triple ply periodic micromechanics constitutive models based upon GMC. MAC enhances the basic capabilities of GMC by providing a modular framework wherein (1) various thermal, mechanical (stress or strain control), and thermomechanical load histories can be imposed; (2) different integration algorithms may be selected; (3) a variety of constituent constitutive models may be utilized and/or implemented; and (4) a variety of fiber architectures may be easily accessed through their corresponding representative volume elements.

  17. Micromechanics Analysis Code (MAC). User Guide: Version 2.0

    NASA Technical Reports Server (NTRS)

    Wilt, T. E.; Arnold, S. M.

    1996-01-01

    The ability to accurately predict the thermomechanical deformation response of advanced composite materials continues to play an important role in the development of these strategic materials. Analytical models that predict the effective behavior of composites are used not only by engineers performing structural analysis of large-scale composite components but also by material scientists in developing new material systems. For an analytical model to fulfill these two distinct functions it must be based on a micromechanics approach which utilizes physically based deformation and life constitutive models and allows one to generate the average (macro) response of a composite material given the properties of the individual constituents and their geometric arrangement. Here the user guide for the recently developed, computationally efficient and comprehensive micromechanics analysis code's (MAC) who's predictive capability rests entirely upon the fully analytical generalized method of cells (GMC), micromechanics model is described. MAC is a versatile form of research software that 'drives' the double or triply periodic micromechanics constitutive models based upon GMC. MAC enhances the basic capabilities of GMC by providing a modular framework wherein (1) various thermal, mechanical (stress or strain control) and thermomechanical load histories can be imposed, (2) different integration algorithms may be selected, (3) a variety of constituent constitutive models may be utilized and/or implemented, and (4) a variety of fiber and laminate architectures may be easily accessed through their corresponding representative volume elements.

  18. Micromechanics of brittle creep in rocks

    NASA Astrophysics Data System (ADS)

    Brantut, N.; Baud, P.; Heap, M. J.; Meredith, P. G.

    2012-08-01

    In the upper crust, the chemical influence of pore water promotes time dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail at stresses well below their short-term failure strength, and even at constant applied stress (“brittle creep”). Here we provide a micromechanical model describing time dependent brittle creep of water-saturated rocks under triaxial stress conditions. Macroscopic brittle creep is modeled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of cracks in compression are derived from the sliding wing crack model of Ashby and Sammis (1990), and the crack length evolution is computed from Charles' law. The macroscopic strains and strain rates computed from the model are non linear, and compare well with experimental results obtained on granite, low porosity sandstone and basalt rock samples. Primary creep (decelerating strain) corresponds to decelerating crack growth, due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep with apparently constant strain rate arises as an inflexion between those two end-member phases. The minimum strain rate at the inflexion point can be estimated analytically as a function of model parameters, effective confining pressure and temperature, which provides an approximate creep law for the process. The creep law is used to infer the long term strain rate as a function of depth in the upper crust due to the action of the applied stresses: in this way, sub-critical cracking reduces the failure stress in a manner equivalent to a decrease in cohesion. We also investigate the competition with pressure solution in porous rocks, and show that the transition from sub

  19. In-situ scanning electron microscopy and atomic force microscopy Young's modulus determination of indium oxide microrods for micromechanical resonator applications

    SciTech Connect

    Bartolomé, Javier; Hidalgo, Pedro; Maestre, David; Cremades, Ana Piqueras, Javier

    2014-04-21

    Electric field induced mechanical resonances of In{sub 2}O{sub 3} microrods are studied by in-situ measurements in the chamber of a scanning electron microscope. Young's moduli of rods with different cross-sectional shapes are calculated from the resonance frequency, and a range of values between 131 and 152 GPa are obtained. A quality factor of 1180–3780 is measured from the amplitude-frequency curves, revealing the suitability of In{sub 2}O{sub 3} microrods as micromechanical resonators. The Young's modulus, E, of one of the rods is also measured from the elastic response in the force-displacement curve recorded in an atomic force microscope. E values obtained by in-situ scanning electron microscopy and by atomic force microscopy are found to differ in about 8%. The results provide data on Young's modulus of In{sub 2}O{sub 3} and confirm the suitability of in-situ scanning electron microscopy mechanical resonance measurements to investigate the elastic behavior of semiconductor microrods.

  20. Micromechanical Analyses of Sturzstroms

    NASA Astrophysics Data System (ADS)

    Imre, Bernd; Laue, Jan; Springman, Sarah M.

    2010-05-01

    have been made observable and reproducible within a physical and a distinct element numerical modelling environment (DEM). As link between field evidence gained from the deposits of natural sturzstroms, the physical model within the ETH Geotechnical Drum Centrifuge (Springman et al., 2001) and the numerical model PFC-3D (Cundall and Strack, 1979; Itasca, 2005), serves a deterministic fractal analytical comminution model (Sammis et al., 1987; Steacy and Sammis, 1991). This approach allowed studying the effects of dynamic fragmentation within sturzstroms at true (macro) scale within the distinct element model, by allowing for a micro-mechanical, distinct particle based, and cyclic description of fragmentation at the same time, without losing significant computational efficiency. Theses experiments indicate rock mass and boundary conditions, which allow an alternating fragmenting and dilating dispersive regime to evolve and to be sustained long enough to replicate the spreading and run out of sturzstroms. The fragmenting spreading model supported here is able to explain the run out of a dry granular flow, beyond the travel distance predicted by a Coulomb frictional sliding model, without resorting to explanations by mechanics that can only be valid for certain, specific of the boundary conditions. The implications derived suggest that a sturzstrom, because of its strong relation to internal fractal fragmentation and other inertial effects, constitutes a landslide category of its own. Its mechanics differ significantly from all other gravity driven mass flows. This proposition does not exclude the possible appearance of frictionites, Toma hills or suspension flows etc., but it considers them as secondary features. The application of a fractal comminution model to describe natural and experimental sturzstrom deposits turned out to be a useful tool for sturzstrom research. Implemented within the DEM, it allows simulating the key features of sturzstrom successfully and

  1. Nondestructive Strain Measurement System Used to Determine Surface Strain on Fibers

    NASA Technical Reports Server (NTRS)

    Tuma, Margaret L.

    1999-01-01

    Small-diameter structural fibers are being considered as reinforcements for high temperature ceramic matrix composite materials, and thus they require characterization. At the NASA Lewis Research Center, a nondestructive optical technique was used to determine surface strain on a structural fiber, in real time, as it was pulled in a tensile test machine. With this technique, interference or speckle patterns from the laser illuminated fiber test specimen are recorded. As the fiber is pulled, its speckle pattern shifts in proportion to the strain, translation, and rotation components of the sample deformation. Shifting speckle patterns are detected in real time by two linear charge-coupled discharge (CCD) camera arrays, and the images are processed by a hardware correlator. Surface strain is selectively detected on fibers with diameters on the order of 100 mm and can be resolved to 19 microstrain. This system was designed to be robust and compact and generally does not require surface preparation of the structural fibers. For strain detection, two laser beams are positioned incident on the structural fiber being tested, as shown in the photograph, where the test specimen is mounted in a tensile test machine via two coupons. As the fiber is pulled, the speckle pattern produced from each laser beam is detected by one of two CCD arrays located inside the tube on the right side of the photograph.

  2. Micromechanics of ambient temperature cyclic fatigue loading in a composite of CAS glass ceramic reinforced with Nicalon fibers

    SciTech Connect

    Rousseau, C.Q.; Davidson, D.L.; Campbell, J.B. )

    1994-04-01

    The behavior of a Nicalon fiber reinforced glass ceramic composite cyclicly loaded has been evaluated at ambient temperature using high-resolution micromechanical test methods. On this basis, the events leading to fracture have been found to be similar to those accompanying fracture in unidirectional tension tests. Matrix strains were determined locally at the point of matrix fracture. Crack opening displacements (CODs) were measured as a function of loading cycles, and fiber strains were determined, in some cases. It is concluded that debonding of fibers begins at the point of matrix cracking and rapidly increases. Most of the cyclic lifetime of the material is spent with fibers debonded over large distances (fractions of a millimeter); these fibers are pulled out of the matrix on each loading cycle. Final debond length, as determined by fractography, is a function of the number of cycles to fracture, and of the applied stress level. 23 refs.

  3. An electrostatically rebalanced micromechanical accelerometer

    NASA Astrophysics Data System (ADS)

    Boxenhorn, Burton; Greiff, Paul

    The design and test performance of a low-cost micromechanical accelerometer (MA) with integral electrodes, developed for use with the vibratory micromechanical gyro described by Boxenhorn and Greiff (1988), are reported. The MA is a monolithic Si device of size 300 x 600 microns and comprises a torsional pendulum with capacitive readout and an electrostatic torquer. Data from 360-deg sweep tests performed in a g-field are presented in tables and graphs and discussed in detail. Results include bandwidth about 1 Hz, scale-factor error 480 ppm, stable bias of 260 microg over 203 min, and temperature effect 2100 microg/C on bias and -123 ppm/C on scale factor.

  4. Micromechanical Analyses of Sturzstroms

    NASA Astrophysics Data System (ADS)

    Imre, Bernd; Laue, Jan; Springman, Sarah M.

    2010-05-01

    have been made observable and reproducible within a physical and a distinct element numerical modelling environment (DEM). As link between field evidence gained from the deposits of natural sturzstroms, the physical model within the ETH Geotechnical Drum Centrifuge (Springman et al., 2001) and the numerical model PFC-3D (Cundall and Strack, 1979; Itasca, 2005), serves a deterministic fractal analytical comminution model (Sammis et al., 1987; Steacy and Sammis, 1991). This approach allowed studying the effects of dynamic fragmentation within sturzstroms at true (macro) scale within the distinct element model, by allowing for a micro-mechanical, distinct particle based, and cyclic description of fragmentation at the same time, without losing significant computational efficiency. Theses experiments indicate rock mass and boundary conditions, which allow an alternating fragmenting and dilating dispersive regime to evolve and to be sustained long enough to replicate the spreading and run out of sturzstroms. The fragmenting spreading model supported here is able to explain the run out of a dry granular flow, beyond the travel distance predicted by a Coulomb frictional sliding model, without resorting to explanations by mechanics that can only be valid for certain, specific of the boundary conditions. The implications derived suggest that a sturzstrom, because of its strong relation to internal fractal fragmentation and other inertial effects, constitutes a landslide category of its own. Its mechanics differ significantly from all other gravity driven mass flows. This proposition does not exclude the possible appearance of frictionites, Toma hills or suspension flows etc., but it considers them as secondary features. The application of a fractal comminution model to describe natural and experimental sturzstrom deposits turned out to be a useful tool for sturzstrom research. Implemented within the DEM, it allows simulating the key features of sturzstrom successfully and

  5. Micromechanics Analysis Code (MAC) Developed

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The ability to accurately predict the thermomechanical deformation response of advanced composite materials continues to play an important role in the development of these strategic materials. Analytical models that predict the effective behavior of composites are used not only by engineers in performing structural analysis of large-scale composite components but also by material scientists in developing new material systems. For an analytical model to fulfill these two distinct functions, it must be based on a micromechanics approach that uses physically based deformation and life constitutive models, and it must allow one to generate the average (macro) response of a composite material given the properties of the individual constituents and their geometric arrangement. Only then can such a model be used by a material scientist to investigate the effect of different deformation mechanisms on the overall response of the composite and, thereby, identify the appropriate constituents for a given application. However, if a micromechanical model is to be used in a large-scale structural analysis it must be (1) computationally efficient, (2) able to generate accurate displacement and stress fields at both the macro and micro level, and (3) compatible with the finite element method. In addition, new advancements in processing and fabrication techniques now make it possible to engineer the architectures of these advanced composite systems. Full utilization of these emerging manufacturing capabilities require the development of a computationally efficient micromechanics analysis tool that can accurately predict the effect of microstructural details on the internal and macroscopic behavior of composites. Computational efficiency is required because (1) a large number of parameters must be varied in the course of engineering (or designing) composite materials and (2) the optimization of a material's microstructure requires that the micromechanics model be integrated with

  6. Determining straining of Escherichia coli from breakthrough curves

    NASA Astrophysics Data System (ADS)

    Foppen, J. W. A.; Mporokoso, A.; Schijven, J. F.

    2005-02-01

    Though coliform bacteria are used world wide as an indication of faecal pollution, the parameters determining the transport of Escherichia coli in aquifers are relatively unknown, especially for the period after the clean bed collision phase brought about by prolonged infiltration of waste water. In this research, the breakthrough curves of E. coli after total flushing of 50-200 pore volumes were studied for various influent concentrations in various sediments at different pore water flow velocities. The results indicated that straining in Dead End Pores (DEPs) was an important process that dominated bacteria breakthrough in fine-grained sediment (0.06-0.2 mm). The filling of the DEP space with bacteria took 5-65 pore volumes and was dependent on concentration. Column breakthrough curves were modelled and from this the DEP volumes were determined. These volumes (0.21-0.35% of total column volume) corresponded well with values calculated with a formula based on purely geometrical considerations and also with values calculated with a pore size density function. For this function the so-called Van Genuchten parameters of the sediments used in the experiments were determined. The results indicate that straining might be a dominant process affecting colloid transport in the natural environment and therefore it is concluded that proper knowledge of the pore size distribution is crucial to an understanding of the retention of bacteria.

  7. Strain Gage Measurement System to Determine Cryogenic Propellant Tank Level

    NASA Technical Reports Server (NTRS)

    Figueroa, Fernando; St.Cyr, William W.; VanDyke, David; McVay, Greg; Mitchell, Mark; Langford, Lester

    2003-01-01

    Measurement of tank level, particularly for cryogenic propellants, has proven to be a difficult proposition. Current methods based on differential pressure, capacitance sensors, temperature sensors, etc.; do not provide sufficiently accurate or robust measurements, especially at run time. This paper describes a simple, but effective method to determine propellant volume by measuring very small deformations of the structure supporting the tank. Results of a laboratory study to validate the method, and experimental data from a deployed system are presented. A comparison with an existing differential pressure sensor shows that the strain gage system provides a very good quality signal even during pressurization.

  8. Adhesion, friction and micromechanical properties of ceramics

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1988-01-01

    The adhesion, friction, and micromechanical properties of ceramics, both in monolithic and coating form, are reviewed. Ceramics are examined in contact with themselves, other harder materials, and metals. For the simplicity of discussion, the tribological properties of concern in the processes are separated into two parts. The first part discusses the pull-off force (adhesion) and the shear force required to break the interfacial junctions between contacting surfaces. The role of chemical bonding in adhesion and friction, and the effects of surface contaminant films and temperature on tribological response with respect to adhesion and friction are discussed. The second part deals with abrasion of ceramics. Elastic, plastic, and fracture behavior of ceramics in solid state contact is discussed. The scratch technique of determining the critical load needed to fracture interfacial adhesive bonds of ceramic deposited on substrates is also addressed.

  9. Method for preventing micromechanical structures from adhering to another object

    DOEpatents

    Smith, J.H.; Ricco, A.J.

    1998-06-16

    A method for preventing micromechanical structures from adhering to another object includes the step of immersing a micromechanical structure and its associated substrate in a chemical species that does not stick to itself. The method can be employed during the manufacture of micromechanical structures to prevent micromechanical parts from sticking or adhering to one another and their associated substrate surface. 3 figs.

  10. Method for preventing micromechanical structures from adhering to another object

    DOEpatents

    Smith, James H.; Ricco, Antonio J.

    1998-01-01

    A method for preventing micromechanical structures from adhering to another object includes the step of immersing a micromechanical structure and its associated substrate in a chemical species that does not stick to itself. The method can be employed during the manufacture of micromechanical structures to prevent micromechanical parts from sticking or adhering to one another and their associated substrate surface.

  11. A micromechanical study of dilatancy of granular materials

    NASA Astrophysics Data System (ADS)

    Kruyt, N. P.; Rothenburg, L.

    2016-10-01

    In micromechanics of granular materials, relationships are investigated between micro-scale characteristics of particles and contacts and macro-scale, continuum characteristics. Dilatancy is an important property of granular materials, defined as volume changes (dilative or compressive) induced by shear deformation. To obtain detailed information at the micro-scale, two-dimensional Discrete Element Method simulations of isobaric tests with disk-shaped particles have been performed. The required information includes the fabric tensor which characterizes statistical properties of the contact network. The dependence of the dilatancy rate on the shear strength and the fabric tensor has been investigated, based on the results of the simulations employing a dense and a loose initial system. The dilatancy rate depends in a complex, non-unique way on the shear strength, while the dependence on the fabric tensor is more amenable to analytical description. Two micromechanical mechanisms of dilatancy have been identified: (i) dilatancy due to deformation of loops that are determined by the interparticle contact network and (ii) dilatancy due to topological changes in the interparticle contact network that correspond to the creation or disruption of contacts. For the first mechanism the anisotropy in the contact network is the primary parameter, while for the second mechanism the average number of contacts per particle is the primary parameter. A fabric-based micromechanical relation for the dilatancy rate has been formulated that describes these identified mechanisms. Parameters present in this relation are determined by fitting this relation to the results of the Discrete Element Method simulations, using combined data for the dense and the loose initial system. Employing these fitted coefficients, good agreement is obtained between the results of the simulations and the predictions of the micromechanical dilatancy relation.

  12. Micromechanical studies of composites by BEM

    NASA Technical Reports Server (NTRS)

    Banerjee, P. K.; Henry, D. P., Jr.; Dargush, G. F.

    1991-01-01

    Over the last five years BEM has been developed into a very effective tool for micromechanical studies of composites. The analyses developed range from static elastic analysis, steady state heat transfer, steady state and transient thermoelastic analysis, periodic and transient dynamic analysis. Currently some of these analyses are being extended to nonlinear micromechanical analyses involving viscoplasticity, elastoplasticity, combined plasticity fracture and creep. The paper describes some of the results for elastic analysis, heat transfer and thermoelastic analyses.

  13. Micromechanisms of thermomechanical fatigue: A comparison with isothermal fatigue

    NASA Technical Reports Server (NTRS)

    Bill, R. C.

    1986-01-01

    Thermomechanical Fatigue (TMF) experiments were conducted on Mar-M 200, B-1900, and PWA-1480 (single crystals) over temperature ranges representative of gas turbine airfoil environments. The results were examined from both a phenomenological basis and a micromechanical basis. Depending on constituents present in the superalloy system, certain micromechanisms dominated the crack initiation process and significantly influenced the TMF lives as well as sensitivity of the material to the type TMF cycle imposed. For instance, high temperature cracking around grain boundary carbides in Mar-M 200 resulted in short in-phase TMF lives compared to either out-of-phase or isothermal lives. In single crystal PWA-1480, the type of coating applied was seen to be the controlling factor in determining sensitivity to the type of TMF cycle imposed. Micromechanisms of deformation were observed over the temperature range of interest to the TMF cycles, and provided some insight as to the differences between TMF damage mechanisms and isothermal damage mechanisms. Finally, the applicability of various life prediction models to TMF results was reviewed. Current life prediction models based on isothermal data must be modified before being generally applied to TMF.

  14. Implementation of Improved Transverse Shear Calculations and Higher Order Laminate Theory Into Strain Rate Dependent Analyses of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Zhu, Lin-Fa; Kim, Soo; Chattopadhyay, Aditi; Goldberg, Robert K.

    2004-01-01

    A numerical procedure has been developed to investigate the nonlinear and strain rate dependent deformation response of polymer matrix composite laminated plates under high strain rate impact loadings. A recently developed strength of materials based micromechanics model, incorporating a set of nonlinear, strain rate dependent constitutive equations for the polymer matrix, is extended to account for the transverse shear effects during impact. Four different assumptions of transverse shear deformation are investigated in order to improve the developed strain rate dependent micromechanics model. The validities of these assumptions are investigated using numerical and theoretical approaches. A method to determine through the thickness strain and transverse Poisson's ratio of the composite is developed. The revised micromechanics model is then implemented into a higher order laminated plate theory which is modified to include the effects of inelastic strains. Parametric studies are conducted to investigate the mechanical response of composite plates under high strain rate loadings. Results show the transverse shear stresses cannot be neglected in the impact problem. A significant level of strain rate dependency and material nonlinearity is found in the deformation response of representative composite specimens.

  15. Bio-Inspired Micromechanical Directional Acoustic Sensor

    NASA Astrophysics Data System (ADS)

    Swan, William; Alves, Fabio; Karunasiri, Gamani

    Conventional directional sound sensors employ an array of spatially separated microphones and the direction is determined using arrival times and amplitudes. In nature, insects such as the Ormia ochracea fly can determine the direction of sound using a hearing organ much smaller than the wavelength of sound it detects. The fly's eardrums are mechanically coupled, only separated by about 1 mm, and have remarkable directional sensitivity. A micromechanical sensor based on the fly's hearing system was designed and fabricated on a silicon on insulator (SOI) substrate using MEMS technology. The sensor consists of two 1 mm2 wings connected using a bridge and to the substrate using two torsional legs. The dimensions of the sensor and material stiffness determine the frequency response of the sensor. The vibration of the wings in response to incident sound at the bending resonance was measured using a laser vibrometer and found to be about 1 μm/Pa. The electronic response of the sensor to sound was measured using integrated comb finger capacitors and found to be about 25 V/Pa. The fabricated sensors showed good directional sensitivity. In this talk, the design, fabrication and characteristics of the directional sound sensor will be described. Supported by ONR and TDSI.

  16. Micromechanical Modeling for Tensile Behaviour of Carbon Fiber - Reinforced Ceramic - Matrix Composites

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2015-12-01

    The stress-strain curves of fiber - reinforced ceramic - matrix composites (CMCs) exhibit obvious non-linear behaviour under tensile loading. The occurrence of multiple damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding and fibers fracture, is the mainly reason for the non-linear characteristic. The micromechanics approach has been developed to predict the tensile stress-strain curves of unidirectional, cross-ply and woven CMCs. The shear-lag model was used to describe the micro stress field of the damaged composite. The damage models were used to determine the evolution of micro damage parameters, i.e., matrix crack spacing, interface debonded length and broken fibers fraction. By combining the shear-lag model with damage models and considering the effect of transverse multicracking in the 90° plies or transverse yarns in cross-ply or woven CMCs, the tensile stress-strain curves of unidirectional, cross-ply, 2D and 2.5D woven CMCs have been predicted. The results agreed with experimental data.

  17. Micromechanics of TEMPO-oxidized fibrillated cellulose composites.

    PubMed

    Bulota, Mindaugas; Tanpichai, Supachok; Hughes, Mark; Eichhorn, Stephen J

    2012-01-01

    Composites of poly(lactic) acid (PLA) reinforced with TEMPO-oxidized fibrillated cellulose (TOFC) were prepared to 15, 20, 25, and 30% fiber weight fractions. To aid dispersion and to improve stress transfer, we acetylated the TOFC prior to the fabrication of TOFC-PLA composite films. Raman spectroscopy was employed to study the deformation micromechanics in these systems. Microtensile specimens were prepared from the films and deformed in tension with Raman spectra being collected simultaneously during deformation. A shift in a Raman peak initially located at ~1095 cm(-1), assigned to C-O-C stretching of the cellulose backbone, was observed upon deformation, indicating stress transfer from the matrix to the TOFC reinforcement. The highest band shift rate, with respect to strain, was observed in composites having a 30% weight fraction of TOFC. These composites also displayed a significantly higher strain to failure compared to pure acetylated TOFC film, and to the composites having lower weight fractions of TOFC. The stress-transfer processes that occur in microfibrillated cellulose composites are discussed with reference to the micromechanical data presented. It is shown that these TOFC-based composite materials are progressively dominated by the mechanics of the networks, and a shear-lag type stress transfer between fibers.

  18. Micromechanics of TEMPO-oxidized fibrillated cellulose composites.

    PubMed

    Bulota, Mindaugas; Tanpichai, Supachok; Hughes, Mark; Eichhorn, Stephen J

    2012-01-01

    Composites of poly(lactic) acid (PLA) reinforced with TEMPO-oxidized fibrillated cellulose (TOFC) were prepared to 15, 20, 25, and 30% fiber weight fractions. To aid dispersion and to improve stress transfer, we acetylated the TOFC prior to the fabrication of TOFC-PLA composite films. Raman spectroscopy was employed to study the deformation micromechanics in these systems. Microtensile specimens were prepared from the films and deformed in tension with Raman spectra being collected simultaneously during deformation. A shift in a Raman peak initially located at ~1095 cm(-1), assigned to C-O-C stretching of the cellulose backbone, was observed upon deformation, indicating stress transfer from the matrix to the TOFC reinforcement. The highest band shift rate, with respect to strain, was observed in composites having a 30% weight fraction of TOFC. These composites also displayed a significantly higher strain to failure compared to pure acetylated TOFC film, and to the composites having lower weight fractions of TOFC. The stress-transfer processes that occur in microfibrillated cellulose composites are discussed with reference to the micromechanical data presented. It is shown that these TOFC-based composite materials are progressively dominated by the mechanics of the networks, and a shear-lag type stress transfer between fibers. PMID:22181067

  19. Elongated Tetrakaidecahedron Micromechanics Model for Space Shuttle External Tank Foams

    NASA Technical Reports Server (NTRS)

    Sullivan, Roy M.; Ghosn, Louis J.; Lerch, Bradley A.; Baker, Eric H.

    2009-01-01

    The results of microstructural characterization studies and physical and mechanical testing of BX-265 and NCFI24-124 foams are reported. A micromechanics model developed previously by the authors is reviewed, and the resulting equations for the elastic constants, the relative density, and the strength of the foam in the principal material directions are presented. The micromechanics model is also used to derive equations to predict the effect of vacuum on the tensile strength and the strains induced by exposure to vacuum. Using a combination of microstructural dimensions and physical and mechanical measurements as input, the equations for the elastic constants and the relative density are applied and the remaining microstructural dimensions are predicted. The predicted microstructural dimensions are in close agreement with the average measured values for both BX-265 and NCFI24-124. With the microstructural dimensions, the model predicts the ratio of the strengths in the principal material directions for both foams. The model is also used to predict the Poisson s ratios, the vacuum-induced strains, and the effect of vacuum on the tensile strengths. However, the comparison of these predicted values with the measured values is not as favorable.

  20. Micromechanics of Spray-On Foam Insulation

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Arnold, Steven M.; Sullivan, Roy M.

    2007-01-01

    Understanding the thermo-mechanical response of the Space Shuttle External Tank spray-on foam insulation (SOFI) material is critical, to NASA's Return to Flight effort. This closed-cell rigid polymeric foam is used to insulate the metallic Space Shuttle External Tank, which is at cryogenic temperatures immediately prior to and during lift off. The shedding of the SOFI during ascent led to the loss of the Columbia, and eliminating/minimizing foam lass from the tank has become a priority for NASA as it seeks to resume scheduled space shuttle missions. Determining the nature of the SOFI material behavior in response to both thermal and mechanical loading plays an important role as any structural modeling of the shedding phenomenon k predicated on knowledge of the constitutive behavior of the foam. In this paper, the SOFI material has been analyzed using the High-Fidelity Generalized Method of Cells (HFGMC) micromechanics model, which has recently been extended to admit a triply-periodic 3-D repeating unit cell (RUC). Additional theoretical extensions that mere made in order to enable modeling of the closed-cell-foam material include the ability to represent internal boundaries within the RUC (to simulated internal pores) and the ability to impose an internal pressure within the simulated pores. This latter extension is crucial as two sources contribute to significant internal pressure changes within the SOFI pores. First, gas trapped in the pores during the spray process will expand or contract due to temperature changes. Second, the pore pressure will increase due to outgassing of water and other species present in the foam skeleton polymer material. With HFGMC's new pore pressure modeling capabilities, a nonlinear pressure change within the simulated pore can be imposed that accounts for both of these sources, in addition to stmdar&-thermal and mechanical loading; The triply-periodic HFGMC micromechanics model described above was implemented within NASA GRC's MAC

  1. Method of Manufacturing a Micromechanical Oscillating Mass Balance

    NASA Technical Reports Server (NTRS)

    Altemir, David A. (Inventor)

    1999-01-01

    A micromechanical oscillating mass balance and method adapted for measuring minute quantities of material deposited at a selected location, such as during a vapor deposition process. The invention comprises a vibratory composite beam which includes a dielectric layer sandwiched between two conductive layers.The beam is positioned in a magnetic field. An alternating current passes through one conductive layers, the beam oscillates, inducing an output current in the second conductive layer, which is analyzed to determine the resonant frequency of the beam. As material is deposited on the beam, the mass of the beam increases and the resonant frequency of the beam shifts, and the mass added is determined.

  2. Using micromechanical resonators to measure rheological properties and alcohol content of model solutions and commercial beverages.

    PubMed

    Paxman, Rosemary; Stinson, Jake; Dejardin, Anna; McKendry, Rachel A; Hoogenboom, Bart W

    2012-01-01

    Micromechanic resonators provide a small-volume and potentially high-throughput method to determine rheological properties of fluids. Here we explore the accuracy in measuring mass density and viscosity of ethanol-water and glycerol-water model solutions, using a simple and easily implemented model to deduce the hydrodynamic effects on resonating cantilevers of various length-to-width aspect ratios. We next show that these measurements can be extended to determine the alcohol percentage of both model solutions and commercial beverages such as beer, wine and liquor. This demonstrates how micromechanical resonators can be used for quality control of every-day drinks.

  3. Using Micromechanical Resonators to Measure Rheological Properties and Alcohol Content of Model Solutions and Commercial Beverages

    PubMed Central

    Paxman, Rosemary; Stinson, Jake; Dejardin, Anna; McKendry, Rachel A.; Hoogenboom, Bart W.

    2012-01-01

    Micromechanic resonators provide a small-volume and potentially high-throughput method to determine rheological properties of fluids. Here we explore the accuracy in measuring mass density and viscosity of ethanol-water and glycerol-water model solutions, using a simple and easily implemented model to deduce the hydrodynamic effects on resonating cantilevers of various length-to-width aspect ratios. We next show that these measurements can be extended to determine the alcohol percentage of both model solutions and commercial beverages such as beer, wine and liquor. This demonstrates how micromechanical resonators can be used for quality control of every-day drinks. PMID:22778654

  4. Micromechanical models for textile composites

    NASA Technical Reports Server (NTRS)

    Sankar, Bhavani V.; Marrey, Ramesh V.

    1995-01-01

    Numerical and analytical micromechanical models are presented to predict the thermoelastic behavior of a textile composite. In the numerical model, the unit-cell is discretized with finite elements, and periodic boundary conditions are imposed between opposite faces of the unit-cell. For a thin textile composite, stress gradients effects through the thickness are demonstrated. The consequent difference in the stiffness and strength behavior of thick and thin composites are discussed. The numerical model is implemented to predict 3-D thermo-elastic constants for a thick textile composite, and the plate thermo-mechanical properties for a thin textile composite. The numerical model is extended to compute the thermal residual microstresses due to processing to predict the composite failure envelopes. An analytical model - Selective Averaging Method (SAM) - is proposed, which is based on a judicious combination of stiffness and compliance averaging to estimate the 3-D elastic constants. Both the models are tested and verified for several examples by comparing the stiffness properties with elasticity solutions and available results.

  5. Computational micromechanical analysis of the representative volume element of bituminous composite materials

    NASA Astrophysics Data System (ADS)

    Ozer, Hasan; Ghauch, Ziad G.; Dhasmana, Heena; Al-Qadi, Imad L.

    2016-08-01

    Micromechanical computational modeling is used in this study to determine the smallest domain, or Representative Volume Element (RVE), that can be used to characterize the effective properties of composite materials such as Asphalt Concrete (AC). Computational Finite Element (FE) micromechanical modeling was coupled with digital image analysis of surface scans of AC specimens. Three mixtures with varying Nominal Maximum Aggregate Size (NMAS) of 4.75 mm, 12.5 mm, and 25 mm, were prepared for digital image analysis and computational micromechanical modeling. The effects of window size and phase modulus mismatch on the apparent viscoelastic response of the composite were numerically examined. A good agreement was observed in the RVE size predictions based on micromechanical computational modeling and image analysis. Micromechanical results indicated that a degradation in the matrix stiffness increases the corresponding RVE size. Statistical homogeneity was observed for window sizes equal to two to three times the NMAS. A model was presented for relating the degree of statistical homogeneity associated with each window size for materials with varying inclusion dimensions.

  6. Micromechanics of Brittle Creep Under Triaxial Loading Conditions

    NASA Astrophysics Data System (ADS)

    Meredith, P. G.; Brantut, N.; Baud, P.; Heap, M. J.

    2011-12-01

    In the upper crust, the chemical influence of pore water promotes time-dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail (i) at stresses far below their short-term failure strength, and (ii) even at constant applied stress ("brittle creep"). Here we provide a micromechanical model and experimental results describing time-dependent brittle creep of water-saturated granite under triaxial stress conditions. Macroscopic brittle creep is modeled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of microcracks in compression are derived from the sliding wing-crack model of Ashby and Sammis (1990). Crack length evolution is computed from Charles' law. The macroscopic strain and strain rates are then computed from the change in energy potential due to microcrack growth. They are non-linear, and compare well with complementary experimental results obtained on granite samples. Primary creep (decelerating strain) corresponds to decreasing crack growth rate , due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep with apparently constant strain rate arises as merely an inflexion between the two end-member phases.

  7. A new optical system for the determination of deformations and strains: calibration characteristics and experimental results.

    PubMed

    Derwin, K A; Soslowsky, L J; Green, W D; Elder, S H

    1994-10-01

    Many types of optical strain measurement systems have been used for the determination of deformations and strains in soft biological tissues. The purpose of this investigation is to report a new optical strain measurement system developed in our laboratory which offers distinct advantages over systems developed in the past. Our optical strain system has demonstrated excellent performance in calibration and experimental tests. Calibration tests illustrate the system's accuracy to 0.05% strain at 3.52% strain and 0.18% strain at 11.74% strain. Further, this system can measure strains to within 2% measurement error for strains in a 0-11.74% range when 100 microns increments of motion are used for calibration. The resolution of our system appears to be at least as good as the linear micrometer (2 microns) used as a calibrating standard. Errors in strain measurement due to whole specimen rotation or translation are quantified. Rotations about an in-plane axis perpendicular to the direction of strain and translations in/out of the plane of focus result in the largest sources of error. Finally, in an in vitro biomechanical study of the rabbit Achilles tendon, experimental failure strains are 4.3 +/- 0.9% using this system. PMID:7962015

  8. Micromechanics and constitutive modeling of connective soft tissues.

    PubMed

    Fallah, A; Ahmadian, M T; Firozbakhsh, K; Aghdam, M M

    2016-07-01

    In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical homogenization method with the help of ABAQUS software. The periodic boundary conditions and the proposed constitutive models are implemented into ABAQUS using the DISP and the UMAT subroutines, respectively. The existence of the solution and stable material behavior of proposed constitutive model for collagen fibers are investigated based on the poly-convexity condition. Results of the presented micromechanics model for connective tissues are compared and validated with available experimental data. Effects of geometrical and material parameters variation at microscale on macroscopic mechanical behavior of tissues are investigated. The results show that decrease in collagen content of the connective tissues like the tendon due to diseases leads 20% more stretch than healthy tissue under the same load which can results in connective tissue malfunction and hypermobility in joints. PMID:26807767

  9. Micromechanics and constitutive modeling of connective soft tissues.

    PubMed

    Fallah, A; Ahmadian, M T; Firozbakhsh, K; Aghdam, M M

    2016-07-01

    In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical homogenization method with the help of ABAQUS software. The periodic boundary conditions and the proposed constitutive models are implemented into ABAQUS using the DISP and the UMAT subroutines, respectively. The existence of the solution and stable material behavior of proposed constitutive model for collagen fibers are investigated based on the poly-convexity condition. Results of the presented micromechanics model for connective tissues are compared and validated with available experimental data. Effects of geometrical and material parameters variation at microscale on macroscopic mechanical behavior of tissues are investigated. The results show that decrease in collagen content of the connective tissues like the tendon due to diseases leads 20% more stretch than healthy tissue under the same load which can results in connective tissue malfunction and hypermobility in joints.

  10. Lorentz force magnetometer using a micromechanical oscillator

    NASA Astrophysics Data System (ADS)

    Li, M.; Ng, E. J.; Hong, V. A.; Ahn, C. H.; Yang, Y.; Kenny, T. W.; Horsley, D. A.

    2013-10-01

    This paper presents a Lorentz force magnetometer employing a micromechanical oscillator. The oscillator, actuated by both electrostatic force and Lorentz force, is based on a 370 μm by 230 μm silicon micromechanical resonator with quality factor (Q) of 13 000. This field-sensitive micromechanical oscillator eliminates the need for an external electronic oscillator and improves magnetometer's stability over temperature. The resonator uses no magnetic materials and is encapsulated using an epitaxial polysilicon layer in a process that is fully compatible with complementary metal-oxide-semiconductor manufacturing. The sensor has a magnetic field resolution of 128 nT/rt-Hz with 2.1 mA bias current.

  11. The Relationship Between Constraint and Ductile Fracture Initiation as Defined by Micromechanical Analyses

    NASA Technical Reports Server (NTRS)

    Panontin, Tina L.; Sheppard, Sheri D.

    1994-01-01

    initiation loads and to calculate the associated (critical) global fracture parameters. The loads are verified experimentally, and microscopy is used to measure pre-crack length, crack tip opening displacement (CTOD), and the amount of stable crack growth. Results for A516-70 steel indicate that the constraint-modified, critical strain criterion with a critical length approximately equal to the grain size (0.0025 inch) provides accurate predictions of crack initiation. The critical void growth criterion is shown to considerably underpredict crack initiation loads with the same critical length. The relationship between the critical value of the J-integral for ductile crack initiation and crack depth for SECT and SECB specimens has been determined using the constraint-modified, critical strain criterion, demonstrating that this micromechanical model can be used to correct in-plane constraint effects due to crack depth and bending vs. tension loading. Finally, the relationship developed for the SECT specimens is used to predict the behavior of circumferentially cracked pipe specimens.

  12. A micromechanical approach to elastic and viscoelastic properties of fiber reinforced concrete

    SciTech Connect

    Pasa Dutra, V.F.; Maghous, S. Campos Filho, A.; Pacheco, A.R.

    2010-03-15

    Some aspects of the constitutive behavior of fiber reinforced concrete (FRC) are investigated within a micromechanical framework. Special emphasis is put on the prediction of creep of such materials. The linear elastic behavior is first examined by implementation of a Mori-Tanaka homogenization scheme. The micromechanical predictions for the overall stiffness prove to be very close to finite element solutions obtained from the numerical analysis of a representative elementary volume of FRC modeled as a randomly heterogeneous medium. The validation of the micromechanical concepts based on comparison with a set of experiments, shows remarkable predictive capabilities of the micromechanical representation. The second part of the paper is devoted to non-ageing viscoelasticity of FRC. Adopting a Zener model for the behavior of the concrete matrix and making use of the correspondence principle, the homogenized relaxation moduli are derived analytically. The validity of the model is established by mean of comparison with available experiment measurements of creep strain of steel fiber reinforced concrete under compressive load. Finally, the model predictions are compared to those derived from analytical models formulated within a one-dimensional setting.

  13. Use of Ti Plasmid DNA Probes for Determining Tumorigenicity of Agrobacterium Strains

    PubMed Central

    Burr, Thomas J.; Norelli, John L.; Katz, Barbara H.; Bishop, Andrew L.

    1990-01-01

    Probes consisting of T-DNA genes from the Ti plasmid of Agrobacterium tumefaciens were used for determining tumorigenicity of strains. Two 32P-labeled probes hybridized with 28 of 28 tumorigenic strains of the pathogen but not with 20 of 22 nontumorigenic strains. One probe, pTHE17, consists of all but the far left portion of the T-DNA of strain C58. Probe SmaI7 consists of SmaI fragment 7 of pTiC58, including onc genes 1, 4, and 6a and most of 2. Another probe, pAL4044, consisting of the vir region of strain Ach-5, hybridized with several nontumorigenic as well as tumorigenic strains. Colony hybridizations were done with 28 tumorigenic and 22 nontumorigenic Agrobacterium strains. About 106 CFU of the different tumorigenic strains were detectable with this method. Southern analyses confirmed the presence or absence of Ti plasmids in strains for which tumorigenicity was questioned. Colony hybridization with the T-DNA probes provides a rapid and sensitive means for determining the tumorigenic nature of Agrobacterium strains. Images PMID:16348218

  14. Use of Ti plasmid DNA probes for determining tumorigenicity of agrobacterium strains

    SciTech Connect

    Burr, T.J.; Norelli, J.L.; Katz, B.H.; Bishop, A.L. )

    1990-06-01

    Probes consisting of T-DNA genes from the Ti plasmid of Agrobacterium tumefaciens were used for determining tumorigenicity of strains. Two {sup 32}P-labeled probes hybridized with 28 of 28 tumorigenic strains of the pathogen but not with 20 of 22 nontumorigenic strains. One probe, pTHE17, consists of all but the far left portion of the T-DNA of strain C58. Probe SmaI7 consists of SmaI fragment 7 of pTiC58, including onc genes 1, 4, and 6a and most of 2. Another probe, pAL4044, consisting of the vir region of strain Ach-5, hybridized with several nontumorigenic as well as tumorigenic strains. Colony hybridizations were done with 28 tumorigenic and 22 nontumorigenic Agrobacterium strains. About 10{sup 6} CFU of the different tumorigenic strains were detectable with this method. Southern analyses confirmed the presence or absence of Ti plasmids in strains for which tumorigenicity was questioned. Colony hybridization with the T-DNA probes provides a rapid and sensitive means for determining the tumorigenic nature of Agrobacterium strains.

  15. Micromechanical analysis of native and cross-linked collagen type I fibrils supports the existence of microfibrils.

    PubMed

    Yang, L; van der Werf, K O; Dijkstra, P J; Feijen, J; Bennink, M L

    2012-02-01

    The mechanical properties of individual collagen fibrils of approximately 200 nm in diameter were determined using a slightly adapted AFM system. Single collagen fibrils immersed in PBS buffer were attached between an AFM cantilever and a glass surface to perform tensile tests at different strain rates and stress relaxation measurements. The stress-strain behavior of collagen fibrils immersed in PBS buffer comprises a toe region up to a stress of 5 MPa, followed by the heel and linear region at higher stresses. Hysteresis and strain-rate dependent stress-strain behavior of collagen fibrils were observed, which suggest that single collagen fibrils have viscoelastic properties. The stress relaxation process of individual collagen fibrils could be best fitted using a two-term Prony series. Furthermore, the influence of different cross-linking agents on the mechanical properties of single collagen fibrils was investigated. Based on these results, we propose that sliding of microfibrils with respect to each other plays a role in the viscoelastic behavior of collagen fibrils in addition to the sliding of collagen molecules with respect to each other. Our finding provides a better insight into the relationship between the structure and mechanical properties of collagen and the micro-mechanical behavior of tissues. PMID:22301184

  16. A micromechanical device that monitors arterial pressure during general anesthesia and in intensive care units

    NASA Astrophysics Data System (ADS)

    Andreeva, A. V.; Luchinin, V. V.; Kuzmina, K. A.; Klyavinek, A. S.; Karelov, A. E.

    2015-12-01

    A vibroacoustic fiber optic system that consists of micromechanical components designated for use in medicine and biology is reviewed. A theoretical analysis of a fiber optic microphone is done and its optimal construction parameters are determined. The possibility of using the developed system with magnetic resonance tomography to noninvasively measure man's arterial pressure is specified.

  17. Micromechanical Modelling of Stress Waves in Rock and Rock Fractures

    NASA Astrophysics Data System (ADS)

    Resende, R.; Lamas, L. N.; Lemos, J. V.; Calçada, R.

    2010-11-01

    The goal of this paper is to simulate the interaction of stress waves and rock fractures in a particle micromechanical model. Stress waves travelling in fractured rock masses are slowed down and attenuated by natural heterogeneities, voids, microcracks and, above all, by faults and fractures. Considerable laboratory and theoretical investigation have uncovered the major aspects of this phenomenon, but models that cover the core mechanisms of the wave propagation in rock masses are necessary to investigate aspects of wave-fracture interaction, which are not completely clear, and in the future simulate full-scale real problems. The micromechanical model is based on the particle discrete element model that reproduces rock through a densely packed non-structured assembly of 2D disks with point contacts. The model of a hard rock core is developed and an irregular rock joint is generated at mid-height. A new contact constitutive model is applied to the particles in the joint walls. Numerical static joint compression tests are performed and a typical hyperbolic stress-displacement curve is obtained. Conditions for good quality wave transmission through non-jointed unorganized particulate media are determined, hybrid static-dynamic boundary conditions are established and plane waves are emitted into the compressed joint. The transmitted and reflected waves are extracted and analysed. Joint dynamic stiffness calculated according to the hypotheses of the Displacement Discontinuity Theory shows to increase with the static joint compression until the joint is completely closed. Still in its early stages of application, this rock micromechanical model enables the joint behaviour under static and dynamic loading to be analysed in detail. Its advantages are the reproduction of the real mechanics of contact creation, evolution and destruction and the possibility of visualizing in detail the joint geometry changes, which is hard to accomplish in the laboratory.

  18. Cyclic stress-strain curve determination for D6AC steel by three methods

    NASA Technical Reports Server (NTRS)

    Nachtigall, A. J.

    1977-01-01

    The room temperature cyclic stress-strain was determined for D6AC low alloy steel by three different methods. The method that involves the use of a single specimen monotonic tension test after cyclic straining provided the best agreement with the accepted basic method which requires a number of companion specimen tests. The single specimen test is also the simplest to conduct.

  19. Micromechanical Modeling of Woven Metal Matrix Composites

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Pindera, Marek-Jerzy

    1997-01-01

    This report presents the results of an extensive micromechanical modeling effort for woven metal matrix composites. The model is employed to predict the mechanical response of 8-harness (8H) satin weave carbon/copper (C/Cu) composites. Experimental mechanical results for this novel high thermal conductivity material were recently reported by Bednarcyk et al. along with preliminary model results. The micromechanics model developed herein is based on an embedded approach. A micromechanics model for the local (micro-scale) behavior of the woven composite, the original method of cells (Aboudi), is embedded in a global (macro-scale) micromechanics model (the three-dimensional generalized method of cells (GMC-3D) (Aboudi). This approach allows representation of true repeating unit cells for woven metal matrix composites via GMC-3D, and representation of local effects, such as matrix plasticity, yarn porosity, and imperfect fiber-matrix bonding. In addition, the equations of GMC-3D were reformulated to significantly reduce the number of unknown quantities that characterize the deformation fields at the microlevel in order to make possible the analysis of actual microstructures of woven composites. The resulting micromechanical model (WCGMC) provides an intermediate level of geometric representation, versatility, and computational efficiency with respect to previous analytical and numerical models for woven composites, but surpasses all previous modeling work by allowing the mechanical response of a woven metal matrix composite, with an elastoplastic matrix, to be examined for the first time. WCGMC is employed to examine the effects of composite microstructure, porosity, residual stresses, and imperfect fiber-matrix bonding on the predicted mechanical response of 8H satin C/Cu. The previously reported experimental results are summarized, and the model predictions are compared to monotonic and cyclic tensile and shear test data. By considering appropriate levels of porosity

  20. An engineering model of woven composites based on micromechanics

    NASA Technical Reports Server (NTRS)

    Carter, W. C.; Cox, B. N.; Dadkhah, M. S.; Morris, W. L.

    1993-01-01

    Composites with three-dimensional woven architectures exhibit large strains to failure when compared to composites made up of the same materials but not with three-dimensional interlocking tows. The fracture mechanics of such three-dimensional architectures is a subject requiring substantial investigation and experimental testing. Classical fracture mechanics concepts (for instance, an isolated defect in a homogeneous body) will not be applicable to the woven fracture test specimen. The use of an isolated singularity to characterize an entire specimen is inadequate when the density of defects is considerable and the material is heterogeneous. Modelling of such a complex system requires a great deal of insight and consideration as well as prudent choices of model sizes to make numerical schemes feasible. The purpose of this manuscript is to review our recently acquired knowledge of damage accumulation in woven composites and to describe a practicable model of the macroscopic behavior in these and other complex composite architectures based on such knowledge. In this manuscript, discussion will be limited to uniaxial compressive loading; considerations of general loading (monotonic and cyclic) will appear in a subsequent manuscript. Our modelling efforts may be briefly described as follows: the composite is subdivided into microstructural elements (microelements) in which the micromechanical modelling is either understood rigorously or can be represented adequately by statistical parameters. There can be microstructural elements for many different types of composite components, such as the various types of warp and weft and matrix for three-dimensional woven composites. The physical dimensions of microelements are made as large as possible while the response within the element can still be represented by a single micromechatlical calculation. The various elements are linked together(sometimes by associating distinct corners and edges, sometimes by superposition) in a

  1. Three-dimensional micromechanical models for the nonlinear analysis of pultruded composite structures

    NASA Astrophysics Data System (ADS)

    Kilic, Mustafa Hakan

    This study presents a new three-dimensional (3D) micromechanics-based nonlinear framework for the analysis of pultruded composite structures. The proposed material modeling framework is a nested micromechanical approach that explicitly recognizes the different composite systems within the cross-section of a pultruded composite member. The 3D lamination theory is used to generate a homogenized nonlinear effective response using a through-thickness representative stacking sequence. Different 3D micromechanical models can be used to represent the composite layers within the repeating stacking sequence, e.g. roving layer, continuous filament mat (CFM), and woven fabrics. The proposed modeling framework is applied for pultruded composite material systems made from roving and CFM. The roving layer is idealized using an existing 3D nonlinear micromechanics model for a unidirectional fiber reinforced material. A simple nonlinear micromechanical model for the CFM layer is introduced and implemented. The overall modeling approach is able to predict both the elastic and nonlinear response of the composite material based on the in-situ properties and response of the fiber and matrix constituents. Experimental data, from off-axis tests of pultruded plates, is used to verify the proposed modeling approach. The 3D modeling framework shows good prediction capabilities for the overall effective elastic constants, as well as the nonlinear multi-axial stress-strain response. In addition, a simple degradation and damage modeling is coupled with the proposed analysis framework. Several applications are performed for the nonlinear analysis of pultruded composite structures, such as progressive failure analysis of notched plates, bending of short beams, and damage analysis of pultruded FRP bolted connections.

  2. Strains from both Theiler's virus subgroups encode a determinant for demyelination.

    PubMed Central

    Fu, J; Rodriguez, M; Roos, R P

    1990-01-01

    The GDVII strain and other members of the GDVII subgroup of Theiler's murine encephalomyelitis viruses (TMEV) cause an acute lethal neuronal infection in mice, whereas the DA strain and other members of the TO subgroup of TMEV cause a chronic demyelinating disease associated with a persistent virus infection. We used GDVII/DA chimeric infectious cDNAs to produce intratypic recombinant viruses in order to clarify reasons for the TMEV subgroup-specific difference in demyelinating activity. We found that both the GDVII and DA strains contain a genetic determinant(s) for demyelinating activity. No demyelination occurs following GDVII strain inoculation because this strain produces an early neuronal disease that kills mice before white matter disease and persistent infection can occur. Images PMID:2243399

  3. Method for determining the hardness of strain hardening articles of tungsten-nickel-iron alloy

    DOEpatents

    Wallace, Steven A.

    1984-01-01

    The present invention is directed to a rapid nondestructive method for determining the extent of strain hardening in an article of tungsten-nickel-iron alloy. The method comprises saturating the article with a magnetic field from a permanent magnet, measuring the magnetic flux emanating from the article, comparing the measurements of the magnetic flux emanating from the article with measured magnetic fluxes from similarly shaped standards of the alloy with known amounts of strain hardening to determine the hardness.

  4. Stress-Transfer Micromechanics For Fiber Length with a Photocure Vinyl Ester Composite

    PubMed Central

    Petersen, Richard C.; Lemons, Jack E.; McCracken, Michael S.

    2014-01-01

    The objective was to test how increasing fiber length above the critical length would influence mechanical properties and fracture crack propagation. Micromechanics considering fiber/matrix stress-transfer was used to evaluate the results in addition to a shear debonding volume percent correction term necessary for the final analysis. Fiber lengths of 0.5, 1.0, 2.0, 3.0, and 6.0 mm with 9 μm diameters were added into a photocure vinyl ester particulate-filled composite at a uniform 28.2 vol%. Mechanical flexural testing was performed using four-point fully articulated fixtures for samples measuring 2 × 2 × 50 mm3 across a 40 mm span. Fiber length correlated with improved mechanical properties for flexural strength, modulus, yield strength, strain, work of fracture, and strain energy release, p < 0.001. In addition, sample fracture depth significantly decreased with increasing fiber lengths, p < 0.00001. All mechanical properties correlated significantly as predictors for fracture failure, p < 0.000001, and as estimators for each other, p < 0.0001. The stress-transfer micromechanics for fiber length were improved upon for strength by including a simple correction factor to account for loss of fiber volume percent related to cracks deflecting around debonded fiber ends. In turn, the elastic property of modulus was shown to exhibit a tendency to follow stress-transfer micromechanics. PMID:25382894

  5. Analysis of metal-matrix composite structures. I - Micromechanics constitutive theory. II - Laminate analyses

    NASA Technical Reports Server (NTRS)

    Arenburg, R. T.; Reddy, J. N.

    1991-01-01

    The micromechanical constitutive theory is used to examine the nonlinear behavior of continuous-fiber-reinforced metal-matrix composite structures. Effective lamina constitutive relations based on the Abouli micromechanics theory are presented. The inelastic matrix behavior is modeled by the unified viscoplasticity theory of Bodner and Partom. The laminate constitutive relations are incorporated into a first-order deformation plate theory. The resulting boundary value problem is solved by utilizing the finite element method. Attention is also given to computational aspects of the numerical solution, including the temporal integration of the inelastic strains and the spatial integration of bending moments. Numerical results the nonlinear response of metal matrix composites subjected to extensional and bending loads are presented.

  6. Micromechanics-Based Progressive Failure Analysis of Composite Laminates Using Different Constituent Failure Theories

    NASA Technical Reports Server (NTRS)

    Moncada, Albert M.; Chattopadhyay, Aditi; Bednarcyk, Brett A.; Arnold, Steven M.

    2008-01-01

    Predicting failure in a composite can be done with ply level mechanisms and/or micro level mechanisms. This paper uses the Generalized Method of Cells and High-Fidelity Generalized Method of Cells micromechanics theories, coupled with classical lamination theory, as implemented within NASA's Micromechanics Analysis Code with Generalized Method of Cells. The code is able to implement different failure theories on the level of both the fiber and the matrix constituents within a laminate. A comparison is made among maximum stress, maximum strain, Tsai-Hill, and Tsai-Wu failure theories. To verify the failure theories the Worldwide Failure Exercise (WWFE) experiments have been used. The WWFE is a comprehensive study that covers a wide range of polymer matrix composite laminates. The numerical results indicate good correlation with the experimental results for most of the composite layups, but also point to the need for more accurate resin damage progression models.

  7. A spider's biological vibration filter: micromechanical characteristics of a biomaterial surface.

    PubMed

    Young, Seth L; Chyasnavichyus, Marius; Erko, Maxim; Barth, Friedrich G; Fratzl, Peter; Zlotnikov, Igor; Politi, Yael; Tsukruk, Vladimir V

    2014-11-01

    A strain-sensing lyriform organ (HS-10) found on all of the legs of a Central American wandering spider (Cupiennius salei) detects courtship, prey and predator vibrations transmitted by the plant on which it sits. It has been suggested that the viscoelastic properties of a cuticular pad directly adjacent to the sensory organ contribute to the organ's pronounced high-pass characteristics. Here, we investigate the micromechanical properties of the cuticular pad biomaterial in search of a deeper understanding of its impact on the function of the vibration sensor. These properties are considered to be an effective adaptation for the selective detection of signals for frequencies >40 Hz. Using surface force spectroscopy mapping we determine the elastic modulus of the pad surface over a temperature range of 15-40 °C at various loading frequencies. In the glassy state, the elastic modulus was ~100 MPa, while in the rubbery state the elastic modulus decreased to 20 MPa. These data are analyzed according to the principle of time-temperature superposition to construct a master curve that relates mechanical properties, temperature and stimulus frequencies. By estimating the loss and storage moduli vs. temperature and frequency it was possible to make a direct comparison with electrophysiology experiments, and it was found that the dissipation of energy occurs within a frequency window whose position is controlled by environmental temperatures.

  8. Probabilistic micromechanics for high-temperature composites

    NASA Technical Reports Server (NTRS)

    Reddy, J. N.

    1993-01-01

    The three-year program of research had the following technical objectives: the development of probabilistic methods for micromechanics-based constitutive and failure models, application of the probabilistic methodology in the evaluation of various composite materials and simulation of expected uncertainties in unidirectional fiber composite properties, and influence of the uncertainties in composite properties on the structural response. The first year of research was devoted to the development of probabilistic methodology for micromechanics models. The second year of research focused on the evaluation of the Chamis-Hopkins constitutive model and Aboudi constitutive model using the methodology developed in the first year of research. The third year of research was devoted to the development of probabilistic finite element analysis procedures for laminated composite plate and shell structures.

  9. Micromechanical apparatus for measurement of forces

    DOEpatents

    Tanner, Danelle Mary; Allen, James Joe

    2004-05-25

    A new class of micromechanical dynamometers has been disclosed which are particularly suited to fabrication in parallel with other microelectromechanical apparatus. Forces in the microNewton regime and below can be measured with such dynamometers which are based on a high-compliance deflection element (e.g. a ring or annulus) suspended above a substrate for deflection by an applied force, and one or more distance scales for optically measuring the deflection.

  10. Flexible magnetic filaments as micromechanical sensors.

    PubMed

    Goubault, C; Jop, P; Fermigier, M; Baudry, J; Bertrand, E; Bibette, J

    2003-12-31

    We propose a new micromechanical approach to probe bending rigidity at molecular scale. Long flexible filaments made of magnetic colloids and linkers are shown to adopt under magnetic field a hairpin configuration. Measuring the hairpin curvature as a function of the field intensity and the linker length from diffracted light allows us to deduce the linker bending rigidity kappa. The technique is presented for two types of linkers: a spontaneously adsorbing polymer and a grafted biomolecular.

  11. Determination of Constant Strain Gradients of Elastically Bent Crystal Using X-ray Mirage Fringes

    NASA Astrophysics Data System (ADS)

    Jongsukswat, Sukswat; Fukamachi, Tomoe; Hirano, Kenji; Ju, Dongying; Negishi, Riichirou; Shimojo, Masayuki; Hirano, Keiichi; Kawamura, Takaaki

    2012-07-01

    Two experimental approaches are studied to determine a parameter of the strain gradient in an elastically bent crystal. In one approach, the parameter is determined by measuring the third peak of the X-ray mirage interference fringes and in the other, by measuring the region where no mirage diffraction beam reaches on the lateral surface of the crystal. Using the X-rays from synchrotron radiation, the mirage fringes have been observed in the 220 reflection of the Si crystal whose strain is controlled in cantilever bending. These two approaches both give accurate values of the parameter of the strain gradient, showing good agreement with the values calculated using elastic theory. In addition, the residual strain due to gravity is observed by measuring mirage fringes when the bending force becomes zero.

  12. Use of electron diffraction for determination of strain distribution in synthetic diamonds

    NASA Astrophysics Data System (ADS)

    Balovsyak, S.; Borcha, M.; Garabazhiv, Ya.; Fodchuk, I.; Tkach, V.

    2012-01-01

    In this paper we demonstrate possibilities of electron backscattering diffraction technique (Kikuchi method) for determination of strain distribution in local areas of synthetic diamond samples. To increase the precision of lattice parameter determination a correlation method and corresponding software were used for accurate identification of coordinates of Kikuchi lines intersections on the Kikuchi patterns. Consequently, subjective factors influencing on accuracy at determination of displacements of image details were minimized. Samples have been investigated by scanning electron microscope "Zeiss" EVO-50 using CCD detector. The complex analysis of location changes of Kikuchi lines intersections and Kikuchi line intensity profiles permits to specify peculiarities of strain distribution for diamonds grown by various methods.

  13. Use of electron diffraction for determination of strain distribution in synthetic diamonds

    NASA Astrophysics Data System (ADS)

    Balovsyak, S.; Borcha, M.; Garabazhiv, Ya.; Fodchuk, I.; Tkach, V.

    2011-09-01

    In this paper we demonstrate possibilities of electron backscattering diffraction technique (Kikuchi method) for determination of strain distribution in local areas of synthetic diamond samples. To increase the precision of lattice parameter determination a correlation method and corresponding software were used for accurate identification of coordinates of Kikuchi lines intersections on the Kikuchi patterns. Consequently, subjective factors influencing on accuracy at determination of displacements of image details were minimized. Samples have been investigated by scanning electron microscope "Zeiss" EVO-50 using CCD detector. The complex analysis of location changes of Kikuchi lines intersections and Kikuchi line intensity profiles permits to specify peculiarities of strain distribution for diamonds grown by various methods.

  14. Wild Sex in Zebrafish: Loss of the Natural Sex Determinant in Domesticated Strains

    PubMed Central

    Wilson, Catherine A.; High, Samantha K.; McCluskey, Braedan M.; Amores, Angel; Yan, Yi-lin; Titus, Tom A.; Anderson, Jennifer L.; Batzel, Peter; Carvan, Michael J.; Schartl, Manfred; Postlethwait, John H.

    2014-01-01

    Sex determination can be robustly genetic, strongly environmental, or genetic subject to environmental perturbation. The genetic basis of sex determination is unknown for zebrafish (Danio rerio), a model for development and human health. We used RAD-tag population genomics to identify sex-linked polymorphisms. After verifying this “RAD-sex” method on medaka (Oryzias latipes), we studied two domesticated zebrafish strains (AB and TU), two natural laboratory strains (WIK and EKW), and two recent isolates from nature (NA and CB). All four natural strains had a single sex-linked region at the right tip of chromosome 4, enabling sex genotyping by PCR. Genotypes for the single nucleotide polymorphism (SNP) with the strongest statistical association to sex suggested that wild zebrafish have WZ/ZZ sex chromosomes. In natural strains, “male genotypes” became males and some “female genotypes” also became males, suggesting that the environment or genetic background can cause female-to-male sex reversal. Surprisingly, TU and AB lacked detectable sex-linked loci. Phylogenomics rooted on D. nigrofasciatus verified that all strains are monophyletic. Because AB and TU branched as a monophyletic clade, we could not rule out shared loss of the wild sex locus in a common ancestor despite their independent domestication. Mitochondrial DNA sequences showed that investigated strains represent only one of the three identified zebrafish haplogroups. Results suggest that zebrafish in nature possess a WZ/ZZ sex-determination mechanism with a major determinant lying near the right telomere of chromosome 4 that was modified during domestication. Strains providing the zebrafish reference genome lack key components of the natural sex-determination system but may have evolved variant sex-determining mechanisms during two decades in laboratory culture. PMID:25233988

  15. Computational micromechanics of woven composites

    NASA Technical Reports Server (NTRS)

    Hopkins, Dale A.; Saigal, Sunil; Zeng, Xiaogang

    1991-01-01

    The bounds on the equivalent elastic material properties of a composite are presently addressed by a unified energy approach which is valid for both unidirectional and 2D and 3D woven composites. The unit cell considered is assumed to consist, first, of the actual composite arrangement of the fibers and matrix material, and then, of an equivalent pseudohomogeneous material. Equating the strain energies due to the two arrangements yields an estimate of the upper bound for the material equivalent properties; successive increases in the order of displacement field that is assumed in the composite arrangement will successively produce improved upper bound estimates.

  16. Micromechanics Modeling of Composites Subjected to Multiaxial Progressive Damage in the Constituents

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Amold, Steven M.

    2010-01-01

    The high-fidelity generalized method of cells composite micromechanics model is extended to include constituent-scale progressive damage via a proposed damage model. The damage model assumes that all material nonlinearity is due to damage in the form of reduced stiffness, and it uses six scalar damage variables (three for tension and three for compression) to track the damage. Damage strains are introduced that account for interaction among the strain components and that also allow the development of the damage evolution equations based on the constituent material uniaxial stress strain response. Local final-failure criteria are also proposed based on mode-specific strain energy release rates and total dissipated strain energy. The coupled micromechanics-damage model described herein is applied to a unidirectional E-glass/epoxy composite and a proprietary polymer matrix composite. Results illustrate the capability of the coupled model to capture the vastly different character of the monolithic (neat) resin matrix and the composite in response to far-field tension, compression, and shear loading.

  17. Determination of antibiotic resistance pattern and bacteriocin sensitivity of Listeria monocytogenes strains isolated from different foods in turkey

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study aimed to determine the antibiotic resistance pattern and bacteriocin sensitivity of Listeria monocytogenes strains isolated from animal derived foods. With disc diffusion assay, all fourteen L. monocytogenes strains were susceptible to the antibiotics, including penicillin G, vancomycin, ...

  18. Distribution of energy storage rate in area of strain localization during tension of austenitic steel

    NASA Astrophysics Data System (ADS)

    Oliferuk, W.; Maj, M.; Zembrzycki, K.

    2015-01-01

    The present work is devoted to experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using electron back scattered diffraction (EBSC) were performed.

  19. High-Fidelity Micromechanics Model Enhanced for Multiphase Particulate Materials

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Arnold, Steven M.

    2003-01-01

    This 3-year effort involves the development of a comprehensive micromechanics model and a related computer code, capable of accurately estimating both the average response and the local stress and strain fields in the individual phases, assuming both elastic and inelastic behavior. During the first year (fiscal year 2001) of the investigation, a version of the model called the High-Fidelity Generalized Method of Cells (HFGMC) was successfully completed for the thermo-inelastic response of continuously reinforced multiphased materials with arbitrary periodic microstructures (refs. 1 and 2). The model s excellent predictive capability for both the macroscopic response and the microlevel stress and strain fields was demonstrated through comparison with exact analytical and finite element solutions. This year, HFGMC was further extended in two technologically significant ways. The first enhancement entailed the incorporation of fiber/matrix debonding capability into the two-dimensional version of HFGMC for modeling the response of unidirectionally reinforced composites such as titanium matrix composites, which exhibit poor fiber/matrix bond. Comparison with experimental data validated the model s predictive capability. The second enhancement entailed further generalization of HFGMC to three dimensions to enable modeling the response of particulate-reinforced (discontinuous) composites in the elastic material behavior domain. Next year, the three-dimensional version will be generalized to encompass inelastic effects due to plasticity, viscoplasticity, and damage, as well as coupled electromagnetothermomechanical (including piezoelectric) effects.

  20. Wireless actuation of bulk acoustic modes in micromechanical resonators

    NASA Astrophysics Data System (ADS)

    Mateen, Farrukh; Brown, Benjamin; Erramilli, Shyamsunder; Mohanty, Pritiraj

    2016-08-01

    We report wireless actuation of a Lamb wave micromechanical resonator from a distance of over 1 m with an efficiency of over 15%. Wireless actuation of conventional micromechanical resonators can have broad impact in a number of applications from wireless communication and implantable biomedical devices to distributed sensor networks.

  1. Ex vivo determination of bone tissue strains for an in vivo mouse tibial loading model

    PubMed Central

    Carriero, Alessandra; Abela, Lisa; Pitsillides, Andrew A.; Shefelbine, Sandra J.

    2014-01-01

    Previous studies introduced the digital image correlation (DIC) as a viable technique for measuring bone strain during loading. In this study, we investigated the sensitivity of a DIC system in determining surface strains in a mouse tibia while loaded in compression through the knee joint. Specifically, we examined the effect of speckle distribution, facet size and overlap, initial vertical alignment of the bone into the loading cups, rotation with respect to cameras, and ex vivo loading configurations on the strain contour maps measured with a DIC system. We loaded tibiae of C57BL/6 mice (12 and 18 weeks old male) up to 12 N at 8 N/min. Images of speckles on the bone surface were recorded at 1 N intervals and DIC was used to compute strains. Results showed that speckles must have the correct size and density with respect to the facet size of choice for the strain distribution to be computed and reproducible. Initial alignment of the bone within the loading cups does not influence the strain distribution measured during peak loading, but bones must be placed in front of the camera with the same orientation in order for strains to be comparable. Finally, the ex vivo loading configurations with the tibia attached to the entire mouse, or to the femur and foot, or only to the foot, showed different strain contour maps. This work provides a better understanding of parameters affecting full field strain measurements from DIC in ex vivo murine tibial loading tests. PMID:24835472

  2. Time And Temperature Dependent Micromechanical Properties Of Solder Joints For 3D-Package Integration

    NASA Astrophysics Data System (ADS)

    Roellig, Mike; Meier, Karsten; Metasch, Rene

    2010-11-01

    The recent development of 3D-integrated electronic packages is characterized by the need to increase the diversity of functions and to miniaturize. Currently many 3D-integration concepts are being developed and all of them demand new materials, new designs and new processing technologies. The combination of simulation and experimental investigation becomes increasingly accepted since simulations help to shorten the R&D cycle time and reduce costs. Numerical calculations like the Finite-Element-Method are strong tools to calculate stress conditions in electronic packages resulting from thermal strains due to the manufacturing process and environmental loads. It is essential for the application of numerical calculations that the material data is accurate and describes sufficiently the physical behaviour. The developed machine allows the measurement of time and temperature dependent micromechanical properties of solder joints. Solder joints, which are used to mechanically and electrically connect different packages, are physically measured as they leave the process. This allows accounting for process influences, which may change material properties. Additionally, joint sizes and metallurgical interactions between solder and under bump metallization can be respected by this particular measurement. The measurement allows the determination of material properties within a temperature range of 20° C-200° C. Further, the time dependent creep deformation can be measured within a strain-rate range of 10-31/s-10-81/s. Solder alloys based on Sn-Ag/Sn-Ag-Cu with additionally impurities and joint sizes down to O/ 200 μm were investigated. To finish the material characterization process the material model coefficient were extracted by FEM-Simulation to increase the accuracy of data.

  3. 3D X-ray Strain Microscopy in Two-Phase Composites at Submicron Length Scale

    SciTech Connect

    Barabash, Rozaliya; Bei, Hongbin; Ice, Gene E; Gao, Yanfei; Barabash, Oleg M

    2011-01-01

    Author note: Part of this research summary is based on findings first reported in Refs. [3-5, 18]. Renewed interest in composite materials is driven by the fact that their mechanical properties can be superior to those of individual constituent phases. Interfaces between the phases are the key elements responsible for the unique micro-mechanisms of plastic deformation in composites. In this study the depth-dependent residual strain distributed in the two phases and partitioned across the composite interfaces is directly measured at submicron length-scale using X-ray microdiffraction and compared to a detailed simulation within the framework of micromechanical stress analysis. Interface strength is determined from the analysis of the so-called slip zone caused by the near-surface stress relaxation. Two examples are discussed including NiAl/Mo and Ni/Mo composites.

  4. An x-ray method for direct determination of the strain state and strain relaxation in micron-scale passivated metallization lines during thermal cycling

    SciTech Connect

    Besser, P.R. ); Brennan, S. ); Bravman, J.C. )

    1994-01-01

    We describe a method for directly determining the strain state of passivated metal lines. Synchrotron radiation in the grazing incidence geometry is used to directly measure the in-plane interplanar spacing along the length and width of the lines, while the strain normal to the surface of the line is measured using conventional diffraction methods. The entire strain state is thereby defined. Previous work has measured out-of-plane reflections, fit them to a straight line as a trigonometric function of the angle of orientation, and extrapolated to determine the principal strains. The equivalence of the two x-ray methods on the same sample is demonstrated at room temperature before and after thermal cycling. For short time strain relaxation experiments during thermal cycling, measurement of the three principal strains leads to the direct calculation of the stress relaxation. We apply the strain determination technique to Al--0.5%Cu lines passivated with Si[sub 3]N[sub 4] as the lines are thermally cycled from room temperature to 450 [degree]C and back. The strain state, stress state, and strain relaxation of the lines are calculated at several temperatures during thermal cycling.

  5. Micromechanics Analysis Code With Generalized Method of Cells (MAC/GMC): User Guide. Version 3

    NASA Technical Reports Server (NTRS)

    Arnold, S. M.; Bednarcyk, B. A.; Wilt, T. E.; Trowbridge, D.

    1999-01-01

    The ability to accurately predict the thermomechanical deformation response of advanced composite materials continues to play an important role in the development of these strategic materials. Analytical models that predict the effective behavior of composites are used not only by engineers performing structural analysis of large-scale composite components but also by material scientists in developing new material systems. For an analytical model to fulfill these two distinct functions it must be based on a micromechanics approach which utilizes physically based deformation and life constitutive models and allows one to generate the average (macro) response of a composite material given the properties of the individual constituents and their geometric arrangement. Here the user guide for the recently developed, computationally efficient and comprehensive micromechanics analysis code, MAC, who's predictive capability rests entirely upon the fully analytical generalized method of cells, GMC, micromechanics model is described. MAC/ GMC is a versatile form of research software that "drives" the double or triply periodic micromechanics constitutive models based upon GMC. MAC/GMC enhances the basic capabilities of GMC by providing a modular framework wherein 1) various thermal, mechanical (stress or strain control) and thermomechanical load histories can be imposed, 2) different integration algorithms may be selected, 3) a variety of material constitutive models (both deformation and life) may be utilized and/or implemented, and 4) a variety of fiber architectures (both unidirectional, laminate and woven) may be easily accessed through their corresponding representative volume elements contained within the supplied library of RVEs or input directly by the user, and 5) graphical post processing of the macro and/or micro field quantities is made available.

  6. Micromechanics of composite laminate compression failures

    NASA Technical Reports Server (NTRS)

    Guynn, E. Gail; Bradley, Walter L.

    1988-01-01

    The purpose of this annual progress report is to summarize the work effort and results accomplished from July 1987 through July 1988 on NASA Research Grant NAG1-659 entitled Micromechanics of Composite Laminate Compressive Failure. The report contains: (1) the objective of the proposed research, (2) the summary of accomplishments, (3) a more extensive review of compression literature, (4) the planned material (and corresponding properties) received to date, (5) the results for three possible specimen geometries, experimental procedures planned, and current status of the experiments, and (6) the work planned for the next contract year.

  7. Micromechanics of high temperature deformation and failure

    NASA Technical Reports Server (NTRS)

    Nasser, S. N.; Weertman, J. R.

    1985-01-01

    The micromechanics of the constitutive behavior of elastoplastic materials at high temperatures was examined. The experimental work focused on the development of microscopic defects in superalloys (Waspaloy), especially the formation of voids at grain boundary carbides, and slip induced surface cracks within grains upon cyclic loading at high temperatures. The influence of these defects on the life expectancy of the material was examined. The theoretical work consists of two parts: (1) analytical description of the mechanisms that lead to defects observed experimentally; and (2) development of macroscopic elastoplastic nonlinear constitutive relations based on mechanical modeling.

  8. Approximate Micromechanics Treatise of Composite Impact

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Handler, Louis M.

    2005-01-01

    A formalism is described for micromechanic impact of composites. The formalism consists of numerous equations which describe all aspects of impact from impactor and composite conditions to impact contact, damage progression, and penetration or containment. The formalism is based on through-the-thickness displacement increments simulation which makes it convenient to track local damage in terms of microfailure modes and their respective characteristics. A flow chart is provided to cast the formalism (numerous equations) into a computer code for embedment in composite mechanic codes and/or finite element composite structural analysis.

  9. Cryogenic transimpedance amplifier for micromechanical capacitive sensors.

    PubMed

    Antonio, D; Pastoriza, H; Julián, P; Mandolesi, P

    2008-08-01

    We developed a cryogenic transimpedance amplifier that works at a broad range of temperatures, from room temperature down to 4 K. The device was realized with a standard complementary metal oxide semiconductor 1.5 mum process. Measurements of current-voltage characteristics, open-loop gain, input referred noise current, and power consumption are presented as a function of temperature. The transimpedance amplifier has been successfully applied to sense the motion of a polysilicon micromechanical oscillator at low temperatures. The whole device is intended to serve as a magnetometer for microscopic superconducting samples.

  10. Micromechanics of saturated and unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Chateau, Xavier; Dormieux, Luc

    2002-07-01

    The homogenization method is used to determine the formulation of the behaviour of both saturated and unsaturated porous media. This approach makes it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale. Furthermore, the influence of the morphologies of the solid and fluid phases on the macroscopic behaviour is studied. The strain induced by drying is examined as a function of the morphological properties.

  11. Antibiotic Resistance Determinants in a Pseudomonas putida Strain Isolated from a Hospital

    PubMed Central

    Duque, Estrella; Fernández, Matilde; Molina-Santiago, Carlos; Roca, Amalia; Porcel, Mario; de la Torre, Jesús; Segura, Ana; Plesiat, Patrick; Jeannot, Katy; Ramos, Juan-Luis

    2014-01-01

    Environmental microbes harbor an enormous pool of antibiotic and biocide resistance genes that can impact the resistance profiles of animal and human pathogens via horizontal gene transfer. Pseudomonas putida strains are ubiquitous in soil and water but have been seldom isolated from humans. We have established a collection of P. putida strains isolated from in-patients in different hospitals in France. One of the isolated strains (HB3267) kills insects and is resistant to the majority of the antibiotics used in laboratories and hospitals, including aminoglycosides, ß-lactams, cationic peptides, chromoprotein enediyne antibiotics, dihydrofolate reductase inhibitors, fluoroquinolones and quinolones, glycopeptide antibiotics, macrolides, polyketides and sulfonamides. Similar to other P. putida clinical isolates the strain was sensitive to amikacin. To shed light on the broad pattern of antibiotic resistance, which is rarely found in clinical isolates of this species, the genome of this strain was sequenced and analysed. The study revealed that the determinants of multiple resistance are both chromosomally-borne as well as located on the pPC9 plasmid. Further analysis indicated that pPC9 has recruited antibiotic and biocide resistance genes from environmental microorganisms as well as from opportunistic and true human pathogens. The pPC9 plasmid is not self-transmissible, but can be mobilized by other bacterial plasmids making it capable of spreading antibiotic resistant determinants to new hosts. PMID:24465371

  12. Pattern recognition characterizations of micromechanical and morphological materials states via analytical quantitative ultrasonics

    NASA Technical Reports Server (NTRS)

    Williams, J. H., Jr.; Lee, S. S.

    1986-01-01

    One potential approach to the quantitative acquisition of discriminatory information that can isolate a single structural state is pattern recognition. The pattern recognition characterizations of micromechanical and morphological materials states via analytical quantiative ultrasonics are outlined. The concepts, terminology, and techniques of statistical pattern recognition are reviewed. Feature extraction and classification and states of the structure can be determined via a program of ultrasonic data generation.

  13. Determining a Prony Series for a Viscoelastic Material From Time Varying Strain Data

    NASA Technical Reports Server (NTRS)

    Tzikang, Chen

    2000-01-01

    In this study a method of determining the coefficients in a Prony series representation of a viscoelastic modulus from rate dependent data is presented. Load versus time test data for a sequence of different rate loading segments is least-squares fitted to a Prony series hereditary integral model of the material tested. A nonlinear least squares regression algorithm is employed. The measured data includes ramp loading, relaxation, and unloading stress-strain data. The resulting Prony series which captures strain rate loading and unloading effects, produces an excellent fit to the complex loading sequence.

  14. Simplified Micromechanics of Plain Weave Composites

    NASA Technical Reports Server (NTRS)

    Mital, Subodh K.; Murthy, Pappu L. N.; Chamis, Christos C.

    1996-01-01

    A micromechanics based methodology to simulate the complete hygro-thermomechanical behavior of plain weave composites is developed. This methodology is based on micromechanics and the classical laminate theory. The methodology predicts a complete set of thermal, hygral and mechanical properties of plain woven composites, generates necessary data for use in a finite element structural analysis, and predicts stresses all the way from the laminate to the constituent level. This methodology is used in conjunction with a composite mechanics code to analyze and predict the properties/response of a generic graphite/epoxy woven textile composite and a plain weave ceramic composite. The fiber architecture, including the fiber waviness and fiber end distributions through the thickness, is properly accounted for. Predicted results compare reasonably well with those from detailed three-dimensional finite element analyses as well as available experimental data. However, the main advantage of the proposed methodology is its high computational efficiency as compared with three-dimensional finite element analyses.

  15. Method for forming suspended micromechanical structures

    DOEpatents

    Fleming, James G.

    2000-01-01

    A micromachining method is disclosed for forming a suspended micromechanical structure from {111} crystalline silicon. The micromachining method is based on the use of anisotropic dry etching to define lateral features of the structure which are etched down into a {111}-silicon substrate to a first etch depth, thereby forming sidewalls of the structure. The sidewalls are then coated with a protection layer, and the substrate is dry etched to a second etch depth to define a spacing of the structure from the substrate. A selective anisotropic wet etchant (e.g. KOH, EDP, TMAH, NaOH or CsOH) is used to laterally undercut the structure between the first and second etch depths, thereby forming a substantially planar lower surface of the structure along a {111} crystal plane that is parallel to an upper surface of the structure. The lateral extent of undercutting by the wet etchant is controlled and effectively terminated by either timing the etching, by the location of angled {111}-silicon planes or by the locations of preformed etch-stops. This present method allows the formation of suspended micromechanical structures having large vertical dimensions and large masses while allowing for detailed lateral features which can be provided by dry etch definition. Additionally, the method of the present invention is compatible with the formation of electronic circuitry on the substrate.

  16. Determining horizontal displacement and strains due to subsidence. Rept. of Investigations/1991

    SciTech Connect

    Tandanand, S.; Powell, L.R.

    1991-01-01

    Horizontal displacements and ground strains induced by mine subsidence are significant information needed for calculating damage and developing precautions against subsidence effects on surface structures. To devise a simple method for determining the surface horizontal displacements and strains simultaneously with the subsidence prediction, the U.S. Bureau of Mines examined the significance of the tilt number, which is the proportionality constant in the relationship between the horizontal displacement and the slope of the subsidence profile. The ratio of the tilt number to the critical radius of the subsidence trough is identical to the ratio of the maximum possible horizontal displacement to the full subsidence, which is found to be constant in most European coalfields. If this ratio is known for a particular minesite in the United States, then horizontal displacement and ground strains can be readily obtained from the primary subsidence data.

  17. Determination of surfaces of constant inelastic strain rate at elevated temperature

    NASA Technical Reports Server (NTRS)

    Battiste, R. L.; Ball, S. J.

    1986-01-01

    An experimental effort to perform special exploratory multiaxial deformation tests on tubular specimens of type 316 stainless steel at 650 C (1200 F) is described. One test specimen was subjected to a time-independent torsional shear strain test history, and surfaces of constant inelastic strain rate (SCISRs) in an axial/torsional stress space were measured at various predetermined points during the test. A second specimen was subjected to a 14-week time-dependent (creep-recovery-creep periods) torsional shear stress histogram SCISRs determinations made at 17 points during the test. The tests were conducted in a high temperature, computer controlled axial/torsional test facility using high-temperature multiaxial extensometer. The effort was successful, and for the first time the existence of surfaces of constant inelastic strain rate was experimentally demonstrated.

  18. Primary Isolation Strain Determines Both Phage Type and Receptors Recognised by Campylobacter jejuni Bacteriophages

    PubMed Central

    Sørensen, Martine C. Holst; Gencay, Yilmaz Emre; Birk, Tina; Baldvinsson, Signe Berg; Jäckel, Claudia; Hammerl, Jens A.; Vegge, Christina S.; Neve, Horst; Brøndsted, Lone

    2015-01-01

    In this study we isolated novel bacteriophages, infecting the zoonotic bacterium Campylobacter jejuni. These phages may be used in phage therapy of C. jejuni colonized poultry to prevent spreading of the bacteria to meat products causing disease in humans. Many C. jejuni phages have been isolated using NCTC12662 as the indicator strain, which may have biased the selection of phages. A large group of C. jejuni phages rely on the highly diverse capsular polysaccharide (CPS) for infection and recent work identified the O-methyl phosphoramidate modification (MeOPN) of CPS as a phage receptor. We therefore chose seven C. jejuni strains each expressing different CPS structures as indicator strains in a large screening for phages in samples collected from free-range poultry farms. Forty-three phages were isolated using C. jejuni NCTC12658, NCTC12662 and RM1221 as host strains and 20 distinct phages were identified based on host range analysis and genome restriction profiles. Most phages were isolated using C. jejuni strains NCTC12662 and RM1221 and interestingly phage genome size (140 kb vs. 190 kb), host range and morphological appearance correlated with the isolation strain. Thus, according to C. jejuni phage grouping, NCTC12662 and NCTC12658 selected for CP81-type phages, while RM1221 selected for CP220-type phages. Furthermore, using acapsular ∆kpsM mutants we demonstrated that phages isolated on NCTC12658 and NCTC12662 were dependent on the capsule for infection. In contrast, CP220-type phages isolated on RM1221 were unable to infect non-motile ∆motA mutants, hence requiring motility for successful infection. Hence, the primary phage isolation strain determines both phage type (CP81 or CP220) as well as receptors (CPS or flagella) recognised by the isolated phages. PMID:25585385

  19. On the Finite Element Implementation of the Generalized Method of Cells Micromechanics Constitutive Model

    NASA Technical Reports Server (NTRS)

    Wilt, T. E.

    1995-01-01

    The Generalized Method of Cells (GMC), a micromechanics based constitutive model, is implemented into the finite element code MARC using the user subroutine HYPELA. Comparisons in terms of transverse deformation response, micro stress and strain distributions, and required CPU time are presented for GMC and finite element models of fiber/matrix unit cell. GMC is shown to provide comparable predictions of the composite behavior and requires significantly less CPU time as compared to a finite element analysis of the unit cell. Details as to the organization of the HYPELA code are provided with the actual HYPELA code included in the appendix.

  20. Micromechanical modeling of advanced materials

    SciTech Connect

    Silling, S.A.; Taylor, P.A.; Wise, J.L.; Furnish, M.D.

    1994-04-01

    Funded as a laboratory-directed research and development (LDRD) project, the work reported here focuses on the development of a computational methodology to determine the dynamic response of heterogeneous solids on the basis of their composition and microstructural morphology. Using the solid dynamics wavecode CTH, material response is simulated on a scale sufficiently fine to explicitly represent the material`s microstructure. Conducting {open_quotes}numerical experiments{close_quotes} on this scale, the authors explore the influence that the microstructure exerts on the material`s overall response. These results are used in the development of constitutive models that take into account the effects of microstructure without explicit representation of its features. Applying this methodology to a glass-reinforced plastic (GRP) composite, the authors examined the influence of various aspects of the composite`s microstructure on its response in a loading regime typical of impact and penetration. As a prerequisite to the microscale modeling effort, they conducted extensive materials testing on the constituents, S-2 glass and epoxy resin (UF-3283), obtaining the first Hugoniot and spall data for these materials. The results of this work are used in the development of constitutive models for GRP materials in transient-dynamics computer wavecodes.

  1. Haploid deletion strains of Saccharomyces cerevisiae that determine survival during space flight

    NASA Astrophysics Data System (ADS)

    Johanson, Kelly; Allen, Patricia L.; Gonzalez-Villalobos, Romer A.; Nesbit, Jacqueline; Nickerson, Cheryl A.; Höner zu Bentrup, Kerstin; Wilson, James W.; Ramamurthy, Rajee; D'Elia, Riccardo; Muse, Kenneth E.; Hammond, Jeffrey; Freeman, Jake; Stodieck, Louis S.; Hammond, Timothy G.

    2007-02-01

    This study identifies genes that determine survival during a space flight, using the model eukaryotic organism, Saccharomyces cerevisiae. Select strains of a haploid yeast deletion series grew during storage in distilled water in space, but not in ground based static or clinorotation controls. The survival advantages in space in distilled water include a 133-fold advantage for the deletion of PEX19, a chaperone and import receptor for newly- synthesized class I peroxisomal membrane proteins, to 77-40 fold for deletion strains lacking elements of aerobic respiration, isocitrate metabolism, and mitochondrial electron transport. Following automated addition of rich growth media, the space flight was associated with a marked survival advantage of strains with deletions in catalytically active genes including hydrolases, oxidoreductases and transferases. When compared to static controls, space flight was associated with a marked survival disadvantage of deletion strains lacking transporter, antioxidant and catalytic activity. This study identifies yeast deletion strains with a survival advantage during storage in distilled water and space flight, and amplifies our understanding of the genes critical for survival in space.

  2. Micromechanical Modeling of Metal Forming Operations

    NASA Astrophysics Data System (ADS)

    Van, Tung Phan; Jöchen, Katja; Böhlke, Thomas

    2011-05-01

    In this work, a ferritic stainless steel (DC04) is investigated in the following three steps. First, we use micropillar compression test data for the identification of a large strain single crystal plasticity model. In the second step the model is verified based on Electron Backscatter Diffraction (EBSD) measurements in a small specimen subjected to a large strain uniaxial tensile test. The two-dimensional EBSD data have been discretized by finite elements and subjected to homogeneous displacement boundary conditions for the second step. Finally, we apply a two-scale Taylor type model at the integration points of the finite elements to simulate the deep drawing process based on initial texture data. The texture data required for the specification of the two-scale model is determined based on the aforementioned EBSD data and by using a texture component method simultaneously to improve the computation time. The finite element simulations were performed with differently textured sheet metals and compared with experiment.

  3. Probing the micro-mechanical behavior of bone via high-energy x-rays.

    SciTech Connect

    Almer, J.; Stock, S. R.; X-Ray Science Division; Northwestern Univ.

    2006-01-01

    Bone is a highly-adaptive, particulate-reinforced composite which, through a complex hierarchical structure, achieves excellent mechanical performance. The composite preserves, to a large degree, the desirable properties of the individual components: high toughness of the bone matrix, collagen fibrils stabilized by water, and high stiffness of the reinforcing phase, nano-sized crystallites of carbonated apatite. Understanding bone fragility (osteoporosis) requires quantifying mechanical input to bone and identifying 'weak-link' microstructures. This mechanical input has been quantified in vivo with strain gages attached to cortical bone, but attached strain gages do not probe subsurface mechanical response. We addressed this shortcoming recently by appling wide- and small-angle x-ray scattering to canine fibula sections, to study the micro-mechanical response of bone on different length scales. These data provide a unique view of load partition between the constituent phases of bone, and here we extend these measurements to an entire rat tibia, where strain gradients due to bending are anticipated. Tibiae of 14 week old Sprague-Dawley rats were studied. A 3D microCT rendering of the sample and definitions of the loading (y) and transverse (x) directions appear in Fig.1, with the y-axis approximately parallel to the bone's longitudinal axis. Due to the curved shape of the tibia, significant sample bending in the x-direction was anticipated even under uniaxial compression, similar to that expected in vivo (there was little curvature in the y-z plane). The sample cross-section at y=0 was determined by microCT to be approximately 4 mm{sup 2}. The sample was potted in epoxy and compressed in a load frame designed for in situ x-ray scattering studies. Loading was in displacement control, at a rate of 0.06 {micro}m/sec. The aggregate macroscopic response was followed using a load cell combined with strain gages located on both the 'convex' (-x) and 'concave' (+x) sides of

  4. Method for identifying biochemical and chemical reactions and micromechanical processes using nanomechanical and electronic signal identification

    DOEpatents

    Holzrichter, John F.; Siekhaus, Wigbert J.

    1997-01-01

    A scanning probe microscope, such as an atomic force microscope (AFM) or a scanning tunneling microscope (STM), is operated in a stationary mode on a site where an activity of interest occurs to measure and identify characteristic time-varying micromotions caused by biological, chemical, mechanical, electrical, optical, or physical processes. The tip and cantilever assembly of an AFM is used as a micromechanical detector of characteristic micromotions transmitted either directly by a site of interest or indirectly through the surrounding medium. Alternatively, the exponential dependence of the tunneling current on the size of the gap in the STM is used to detect micromechanical movement. The stationary mode of operation can be used to observe dynamic biological processes in real time and in a natural environment, such as polymerase processing of DNA for determining the sequence of a DNA molecule.

  5. Method for identifying biochemical and chemical reactions and micromechanical processes using nanomechanical and electronic signal identification

    DOEpatents

    Holzrichter, J.F.; Siekhaus, W.J.

    1997-04-15

    A scanning probe microscope, such as an atomic force microscope (AFM) or a scanning tunneling microscope (STM), is operated in a stationary mode on a site where an activity of interest occurs to measure and identify characteristic time-varying micromotions caused by biological, chemical, mechanical, electrical, optical, or physical processes. The tip and cantilever assembly of an AFM is used as a micromechanical detector of characteristic micromotions transmitted either directly by a site of interest or indirectly through the surrounding medium. Alternatively, the exponential dependence of the tunneling current on the size of the gap in the STM is used to detect micromechanical movement. The stationary mode of operation can be used to observe dynamic biological processes in real time and in a natural environment, such as polymerase processing of DNA for determining the sequence of a DNA molecule. 6 figs.

  6. Readout of micromechanical cantilever sensor arrays by Fabry-Perot interferometry

    SciTech Connect

    Wehrmeister, Jana; Fuss, Achim; Saurenbach, Frank; Berger, Ruediger; Helm, Mark

    2007-10-15

    The increasing use of micromechanical cantilevers in sensing applications causes a need for reliable readout techniques of micromechanical cantilever sensor (MCS) bending. Current optical beam deflection techniques suffer from drawbacks such as artifacts due to changes in the refraction index upon exchange of media. Here, an adaptation of the Fabry-Perot interferometer is presented that allows simultaneous determination of MCS bending and changes in the refraction index of media. Calibration of the instrument with liquids of known refraction index provides an avenue to direct measurement of bending with nanometer precision. Versatile construction of flow cells in combination with alignment features for substrate chips allows simultaneous measurement of two MCS situated either on the same, or on two different support chips. The performance of the instrument is demonstrate in several sensing applications, including adsorption experiments of alkanethioles on MCS gold surfaces, and measurement of humidity changes in air.

  7. Micromechanics of intraply hybrid composites: Elastic and thermal properties

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1979-01-01

    Composite micromechanics are used to derive equations for predicting the elastic and thermal properties of unidirectional intraply hybrid composites. The results predicted using these equations are compared with those predicted using approximate equations based on the rule of mixtures, linear laminate theory, finite element analysis and limited experimental data. The comparisons for three different intraply hybrids indicate that all four methods predict approximately the same elastic properties and are in good agreement with measured data. The micromechanics equations and linear laminate theory predict about the same values for thermal expansion coefficients. The micromechanics equations predict through-the-thickness properties which are in good agreement with the finite element results.

  8. Micromechanics-Based Inelastic Finite Element Analysis Accomplished Via Seamless Integration of MAC/GMC

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Trowbridge, D.

    2001-01-01

    A critical issue in the micromechanics-based analysis of composite structures becomes the availability of a computationally efficient homogenization technique: one that is 1) Capable of handling the sophisticated, physically based, viscoelastoplastic constitutive and life models for each constituent; 2) Able to generate accurate displacement and stress fields at both the macro and the micro levels; 3) Compatible with the finite element method. The Generalized Method of Cells (GMC) developed by Paley and Aboudi is one such micromechanical model that has been shown to predict accurately the overall macro behavior of various types of composites given the required constituent properties. Specifically, the method provides "closed-form" expressions for the macroscopic composite response in terms of the properties, size, shape, distribution, and response of the individual constituents or phases that make up the material. Furthermore, expressions relating the internal stress and strain fields in the individual constituents in terms of the macroscopically applied stresses and strains are available through strain or stress concentration matrices. These expressions make possible the investigation of failure processes at the microscopic level at each step of an applied load history.

  9. Material Properties Test to Determine Ultimate Strain and True Stress-True Strain Curves for High Yield Steels

    SciTech Connect

    K.R. Arpin; T.F. Trimble

    2003-04-01

    This testing was undertaken to develop material true stress-true strain curves for elastic-plastic material behavior for use in performing transient analysis. Based on the conclusions of this test, the true stress-true strain curves derived herein are valid for use in elastic-plastic finite element analysis for structures fabricated from these materials. In addition, for the materials tested herein, the ultimate strain values are greater than those values cited as the limits for the elastic-plastic strain acceptance criteria for transient analysis.

  10. Determination of Dehydrogenase Activities Involved in D-Glucose Oxidation in Gluconobacter and Acetobacter Strains

    PubMed Central

    Sainz, Florencia; Jesús Torija, María; Matsutani, Minenosuke; Kataoka, Naoya; Yakushi, Toshiharu; Matsushita, Kazunobu; Mas, Albert

    2016-01-01

    Acetic acid bacteria (AAB) are known for rapid and incomplete oxidation of an extensively variety of alcohols and carbohydrates, resulting in the accumulation of organic acids as the final products. These oxidative fermentations in AAB are catalyzed by PQQ- or FAD- dependent membrane-bound dehydrogenases. In the present study, the enzyme activity of the membrane-bound dehydrogenases [membrane-bound PQQ-glucose dehydrogenase (mGDH), D-gluconate dehydrogenase (GADH) and membrane-bound glycerol dehydrogenase (GLDH)] involved in the oxidation of D-glucose and D-gluconic acid (GA) was determined in six strains of three different species of AAB (three natural and three type strains). Moreover, the effect of these activities on the production of related metabolites [GA, 2-keto-D-gluconic acid (2KGA) and 5-keto-D-gluconic acid (5KGA)] was analyzed. The natural strains belonging to Gluconobacter showed a high mGDH activity and low activity in GADH and GLDH, whereas the Acetobacter malorum strain presented low activity in the three enzymes. Nevertheless, no correlation was observed between the activity of these enzymes and the concentration of the corresponding metabolites. In fact, all the tested strains were able to oxidize D-glucose to GA, being maximal at the late exponential phase of the AAB growth (24 h), which coincided with D-glucose exhaustion and the maximum mGDH activity. Instead, only some of the tested strains were capable of producing 2KGA and/or 5KGA. In the case of Gluconobacter oxydans strains, no 2KGA production was detected which is related to the absence of GADH activity after 24 h, while in the remaining strains, detection of GADH activity after 24 h resulted in a high accumulation of 2KGA. Therefore, it is possible to choose the best strain depending on the desired product composition. Moreover, the sequences of these genes were used to construct phylogenetic trees. According to the sequence of gcd, gene coding for mGDH, Acetobacter and Komagataeibacter

  11. Determination of Dehydrogenase Activities Involved in D-Glucose Oxidation in Gluconobacter and Acetobacter Strains.

    PubMed

    Sainz, Florencia; Jesús Torija, María; Matsutani, Minenosuke; Kataoka, Naoya; Yakushi, Toshiharu; Matsushita, Kazunobu; Mas, Albert

    2016-01-01

    Acetic acid bacteria (AAB) are known for rapid and incomplete oxidation of an extensively variety of alcohols and carbohydrates, resulting in the accumulation of organic acids as the final products. These oxidative fermentations in AAB are catalyzed by PQQ- or FAD- dependent membrane-bound dehydrogenases. In the present study, the enzyme activity of the membrane-bound dehydrogenases [membrane-bound PQQ-glucose dehydrogenase (mGDH), D-gluconate dehydrogenase (GADH) and membrane-bound glycerol dehydrogenase (GLDH)] involved in the oxidation of D-glucose and D-gluconic acid (GA) was determined in six strains of three different species of AAB (three natural and three type strains). Moreover, the effect of these activities on the production of related metabolites [GA, 2-keto-D-gluconic acid (2KGA) and 5-keto-D-gluconic acid (5KGA)] was analyzed. The natural strains belonging to Gluconobacter showed a high mGDH activity and low activity in GADH and GLDH, whereas the Acetobacter malorum strain presented low activity in the three enzymes. Nevertheless, no correlation was observed between the activity of these enzymes and the concentration of the corresponding metabolites. In fact, all the tested strains were able to oxidize D-glucose to GA, being maximal at the late exponential phase of the AAB growth (24 h), which coincided with D-glucose exhaustion and the maximum mGDH activity. Instead, only some of the tested strains were capable of producing 2KGA and/or 5KGA. In the case of Gluconobacter oxydans strains, no 2KGA production was detected which is related to the absence of GADH activity after 24 h, while in the remaining strains, detection of GADH activity after 24 h resulted in a high accumulation of 2KGA. Therefore, it is possible to choose the best strain depending on the desired product composition. Moreover, the sequences of these genes were used to construct phylogenetic trees. According to the sequence of gcd, gene coding for mGDH, Acetobacter and Komagataeibacter

  12. Determination of Dehydrogenase Activities Involved in D-Glucose Oxidation in Gluconobacter and Acetobacter Strains.

    PubMed

    Sainz, Florencia; Jesús Torija, María; Matsutani, Minenosuke; Kataoka, Naoya; Yakushi, Toshiharu; Matsushita, Kazunobu; Mas, Albert

    2016-01-01

    Acetic acid bacteria (AAB) are known for rapid and incomplete oxidation of an extensively variety of alcohols and carbohydrates, resulting in the accumulation of organic acids as the final products. These oxidative fermentations in AAB are catalyzed by PQQ- or FAD- dependent membrane-bound dehydrogenases. In the present study, the enzyme activity of the membrane-bound dehydrogenases [membrane-bound PQQ-glucose dehydrogenase (mGDH), D-gluconate dehydrogenase (GADH) and membrane-bound glycerol dehydrogenase (GLDH)] involved in the oxidation of D-glucose and D-gluconic acid (GA) was determined in six strains of three different species of AAB (three natural and three type strains). Moreover, the effect of these activities on the production of related metabolites [GA, 2-keto-D-gluconic acid (2KGA) and 5-keto-D-gluconic acid (5KGA)] was analyzed. The natural strains belonging to Gluconobacter showed a high mGDH activity and low activity in GADH and GLDH, whereas the Acetobacter malorum strain presented low activity in the three enzymes. Nevertheless, no correlation was observed between the activity of these enzymes and the concentration of the corresponding metabolites. In fact, all the tested strains were able to oxidize D-glucose to GA, being maximal at the late exponential phase of the AAB growth (24 h), which coincided with D-glucose exhaustion and the maximum mGDH activity. Instead, only some of the tested strains were capable of producing 2KGA and/or 5KGA. In the case of Gluconobacter oxydans strains, no 2KGA production was detected which is related to the absence of GADH activity after 24 h, while in the remaining strains, detection of GADH activity after 24 h resulted in a high accumulation of 2KGA. Therefore, it is possible to choose the best strain depending on the desired product composition. Moreover, the sequences of these genes were used to construct phylogenetic trees. According to the sequence of gcd, gene coding for mGDH, Acetobacter and Komagataeibacter

  13. Determination of Dehydrogenase Activities Involved in D-Glucose Oxidation in Gluconobacter and Acetobacter Strains

    PubMed Central

    Sainz, Florencia; Jesús Torija, María; Matsutani, Minenosuke; Kataoka, Naoya; Yakushi, Toshiharu; Matsushita, Kazunobu; Mas, Albert

    2016-01-01

    Acetic acid bacteria (AAB) are known for rapid and incomplete oxidation of an extensively variety of alcohols and carbohydrates, resulting in the accumulation of organic acids as the final products. These oxidative fermentations in AAB are catalyzed by PQQ- or FAD- dependent membrane-bound dehydrogenases. In the present study, the enzyme activity of the membrane-bound dehydrogenases [membrane-bound PQQ-glucose dehydrogenase (mGDH), D-gluconate dehydrogenase (GADH) and membrane-bound glycerol dehydrogenase (GLDH)] involved in the oxidation of D-glucose and D-gluconic acid (GA) was determined in six strains of three different species of AAB (three natural and three type strains). Moreover, the effect of these activities on the production of related metabolites [GA, 2-keto-D-gluconic acid (2KGA) and 5-keto-D-gluconic acid (5KGA)] was analyzed. The natural strains belonging to Gluconobacter showed a high mGDH activity and low activity in GADH and GLDH, whereas the Acetobacter malorum strain presented low activity in the three enzymes. Nevertheless, no correlation was observed between the activity of these enzymes and the concentration of the corresponding metabolites. In fact, all the tested strains were able to oxidize D-glucose to GA, being maximal at the late exponential phase of the AAB growth (24 h), which coincided with D-glucose exhaustion and the maximum mGDH activity. Instead, only some of the tested strains were capable of producing 2KGA and/or 5KGA. In the case of Gluconobacter oxydans strains, no 2KGA production was detected which is related to the absence of GADH activity after 24 h, while in the remaining strains, detection of GADH activity after 24 h resulted in a high accumulation of 2KGA. Therefore, it is possible to choose the best strain depending on the desired product composition. Moreover, the sequences of these genes were used to construct phylogenetic trees. According to the sequence of gcd, gene coding for mGDH, Acetobacter and Komagataeibacter

  14. Strain-Based Damage Determination Using Finite Element Analysis for Structural Health Management

    NASA Technical Reports Server (NTRS)

    Hochhalter, Jacob D.; Krishnamurthy, Thiagaraja; Aguilo, Miguel A.

    2016-01-01

    A damage determination method is presented that relies on in-service strain sensor measurements. The method employs a gradient-based optimization procedure combined with the finite element method for solution to the forward problem. It is demonstrated that strains, measured at a limited number of sensors, can be used to accurately determine the location, size, and orientation of damage. Numerical examples are presented to demonstrate the general procedure. This work is motivated by the need to provide structural health management systems with a real-time damage characterization. The damage cases investigated herein are characteristic of point-source damage, which can attain critical size during flight. The procedure described can be used to provide prognosis tools with the current damage configuration.

  15. Genotype determination of three dengue type 2 virus strains from Myanmar by sequencing E/NSI gene junction.

    PubMed

    Kyaw-Zin-Thant; Khin-Mar-Aye; Soe-Thein; Than-Swe; Hasebe, F; Morita, K; Igarashi, A

    1995-12-01

    Genotype of three dengue-2 virus strains from Myanmar was determined as genotype II by sequencing 240 nucleotide long fragment across the E/NS1 gene junction by the primer extension dideoxy chain termination method, applying direct sequencing of the PCR product. These strains were isolated from a dengue shock syndrome (DSS) patient and two patients with dengue hemorrhagic fever (DHF) grade 1, in Yangon (Rangoon), Myanmar (Burma), in 1987. Sequence homology of all three strains were highest (96%) to New Guinea C strain (genotype II), lesser homology (93%) to Jamaican 1409 strain (genotype III), and the least homology (91%) to PR 159/S1 strain (genotype I). Two DHF strains revealed only 2 nucleotide and 3 nucleotide differences compared with DSS strain, all at the 3rd position of the codons which resulted in silent mutations.

  16. Determination of the ductile-brittle transition temperature from the microplastic-strain rate

    NASA Astrophysics Data System (ADS)

    Andreev, A. K.; Solntsev, Yu. P.

    2008-04-01

    The possibility of the determination of the tendency of cast and deformed steels to brittle fracture using the temperature dependence of the small-plastic-strain rate is studied. The temperature corresponding to the maximum in this curve is found to indicate an abrupt decrease in the steel plasticity, which makes it possible to interpret it as the ductile-brittle transition temperature depending only on the structure of a material.

  17. Micromechanical models for textile structural composites

    NASA Technical Reports Server (NTRS)

    Marrey, Ramesh V.; Sankar, Bhavani V.

    1995-01-01

    The objective is to develop micromechanical models for predicting the stiffness and strength properties of textile composite materials. Two models are presented to predict the homogeneous elastic constants and coefficients of thermal expansion of a textile composite. The first model is based on rigorous finite element analysis of the textile composite unit-cell. Periodic boundary conditions are enforced between opposite faces of the unit-cell to simulate deformations accurately. The second model implements the selective averaging method (SAM), which is based on a judicious combination of stiffness and compliance averaging. For thin textile composites, both models can predict the plate stiffness coefficients and plate thermal coefficients. The finite element procedure is extended to compute the thermal residual microstresses, and to estimate the initial failure envelope for textile composites.

  18. Coupling a Bose condensate to micromechanical oscillators

    NASA Astrophysics Data System (ADS)

    Kemp, Chandler; Fox, Eli; Flanz, Scott; Vengalattore, Mukund

    2011-05-01

    We describe the construction of a compact apparatus to investigate the interaction of a spinor Bose-Einstein condensate and a micromechanical oscillator. The apparatus uses a double magneto-optical trap, Raman sideband cooling, and evaporative cooling to rapidly produce a 87Rb BEC in close proximity to a high Q membrane. The micromotion of the membrane results in small Zeeman shifts at the location of the BEC due to a magnetic domain attached to the oscillator. Detection of this micromotion by the condensate results in a backaction on the membrane. We investigate prospects of using this backaction to generate nonclassical states of the mechanical oscillator. This work was funded by the DARPA ORCHID program.

  19. Shrinking the hammer: micromechanical approaches to morphogenesis.

    PubMed

    Milani, Pascale; Braybrook, Siobhan A; Boudaoud, Arezki

    2013-11-01

    Morphogenesis, the remarkable process by which a developing organism achieves its shape, relies on the coordinated growth of cells, tissues, and organs. While the molecular and genetic basis of morphogenesis is starting to be unravelled, understanding shape changes is lagging behind. Actually, shape is imposed by the structural elements of the organism, and the translation of cellular activity into morphogenesis must go through these elements. Therefore, many methods have been developed recently to quantify, at cellular resolution, the properties of the main structural element in plants, the cell wall. As plant cell growth is restrained by the cell wall and powered by turgor pressure, such methods also address the quantification of turgor. These different micromechanical approaches are reviewed here, with a critical assessment of their strengths and weaknesses, and a discussion of how they can help us understand the regulation of growth and morphogenesis.

  20. Micromechanical modeling of heterogeneous energetic materials

    SciTech Connect

    Baer, M.R.; Kipp, M.E.; Swol, F. van

    1998-09-01

    In this work, the mesoscale processes of consolidation, deformation and reaction of shocked porous energetic materials are studied using shock physics analysis of impact on a collection of discrete HMX crystals. High resolution three-dimensional CTH simulations indicate that rapid deformation occurs at material contact points causing large amplitude fluctuations of stress states having wavelengths of the order of several particle diameters. Localization of energy produces hot-spots due to shock focusing and plastic work near grain boundaries as material flows to interstitial regions. These numerical experiments demonstrate that hot-spots are strongly influenced by multiple crystal interactions. Chemical reaction processes also produce multiple wave structures associated with particle distribution effects. This study provides new insights into the micromechanical behavior of heterogeneous energetic materials strongly suggesting that initiation and reaction of shocked heterogeneous materials involves states distinctly different than single jump state descriptions.

  1. Apparatus for raising or tilting a micromechanical structure

    SciTech Connect

    Allen, James J.

    2008-09-09

    An active hinge apparatus is disclosed which can be used to raise a micromechanical structure (e.g. a plate or micromirror) on a substrate. The active hinge apparatus utilizes one or more of teeth protruding outward from an axle which also supports the micromechanical structure on one end thereof. A rack is used to engage the teeth and rotate the axle to raise the micromechanical structure and tilt the structure at an angle to the substrate. Motion of the rack is provided by an actuator which can be a mechanically-powered actuator, or alternately an electrostatic comb actuator or a thermal actuator. A latch can be optionally provided in the active hinge apparatus to lock the micromechanical structure in an "erected" position.

  2. Micromechanical modelling of partially molten and sand reinforced polycrystalline ice

    NASA Astrophysics Data System (ADS)

    Castelnau, O.; Duval, P.

    2009-12-01

    The viscoplastic behaviour of polycrystalline ice is strongly affected by the very strong anisotropy of ice crystals. Indeed, in the dislocations creep regime relevant for ice sheet flow, dislocation glide on the basal plane of ice single crystals leads to strain-rates ~6 order of magnitude larger than strain-rates that might be obtain if only non-basal glide is activated. At the polycrystal scale, this behaviour is responsible for a strong mechanical interaction between grains in the secondary (stationary) creep regime, and strain-rate is essentially partitioned between soft grains well-oriented for basal glide and hard grains exhibiting an unfavourable orientation for basal slip. As a consequence, the macroscopic flow stress at the polycrystal scale essentially depends on the resistance of the hardest slip systems or on the associated accommodation processes such as climb of basal dislocation on non-basal planes. Creep experiments performed on polycrystalline ices containing a small amount (less than 10% volume fraction) of liquid water show a dramatic increase of strain-rate, by more than one order of magnitude, compared to solid ice when deformed under similar thermo-mechanical conditions. Similarly, a strong hardening is observed when polycrystalline ice is reinforced by sand (which can be considered as a rigid phase here). This behaviour can be explained by micromechanical models, which aims at estimating the mechanical interactions between grains. For example, the presence of water releases stress concentrations at grain boundaries and therefore favours the inactivation of non-basal systems. To estimate such effect and to reach quantitative comparison with experimental data, we make use of the recent Second-Order homogenization mean-field approach of Ponte-Castaneda, based on self-consistent scheme. The advantage of this approach, which has been shown to provide excellent results when applied to many different non-linear composite materials, comes from the

  3. Some guidelines for determining foot-and-mouth disease vaccine strain matching by serology.

    PubMed

    Mattion, Nora; Goris, Nesya; Willems, Tom; Robiolo, Blanca; Maradei, Eduardo; Beascoechea, Claudia Perez; Perez, Alejandro; Smitsaart, Eliana; Fondevila, Norberto; Palma, Eduardo; De Clercq, Kris; La Torre, José

    2009-01-29

    The selection of matching strains for use in outbreaks of foot-and-mouth disease (FMD) virus can be assessed in vivo or by serological r-value determination. Sera from animals involved in vaccine potency and cross-protection trials performed using the "Protection against Podal Generalization" (PPG) test for two serotype A strains were collected and analyzed by the virus neutralization test (VNT) and liquid-phase ELISA (lpELISA) in three laboratories. The average VNT r-values for medium and high serum titer classes from the A(24) Cruzeiro vaccinated animals were in line with the A/Arg/01 heterologous PPG outcome for all testing laboratories, suggesting that the vaccine strain A(24) Cruzeiro is unlikely to protect against the field isolate A/Arg/01. The corresponding lpELISA r-values were slightly higher and indicate a closer relationship between both strains. Pooling of serum samples significantly reduced the inter-animal and inter-trial variation. The results suggest that a suitable reference serum for vaccine matching r-value experiments might be a pool or a medium to high VNT or lpELISA titer serum. Furthermore, the VNT seems to produce the most reproducible inter-laboratory results. More work is, however, needed in order to substantiate these claims. PMID:19041355

  4. Surface strain-field determination of tympanic membrane using 3D-digital holographic interferometry

    NASA Astrophysics Data System (ADS)

    Hernandez-Montes, María del S.; Mendoza Santoyo, Fernando; Muñoz, Silvino; Perez, Carlos; de la Torre, Manuel; Flores, Mauricio; Alvarez, Luis

    2015-08-01

    In order to increase the understanding of soft tissues mechanical properties, 3D Digital Holographic Interferometry (3D-DHI) was used to quantify the strain-field on a cat tympanic membrane (TM) surface. The experiments were carried out applying a constant sound-stimuli pressure of 90 dB SPL (0.632 Pa) on the TM at 1.2 kHz. The technique allows the accurate acquisition of the micro-displacement data along the x, y and z directions, which is a must for a full characterization of the tissue mechanical behavior under load, and for the calculation of the strain-field in situ. The displacements repeatability in z direction shows a standard deviation of 0.062 μm at 95% confidence level. In order to realize the full 3D characterization correctly the contour of the TM surface was measured employing the optically non-contact two-illumination positions contouring method. The x, y and z displacements combined with the TM contour data allow the evaluation its strain-field by spatially differentiating the u(m,n), v(m,n), and w(m,n) deformation components. The accurate and correct determination of the TM strain-field leads to describing its elasticity, which is an important parameter needed to improve ear biomechanics studies, audition processes and TM mobility in both experimental measurements and theoretical analysis of ear functionality and its modeling.

  5. Screening of lignocellulose-degrading superior mushroom strains and determination of their CMCase and laccase activity.

    PubMed

    Fen, Li; Xuwei, Zhu; Nanyi, Li; Puyu, Zhang; Shuang, Zhang; Xue, Zhao; Pengju, Li; Qichao, Zhu; Haiping, Lin

    2014-01-01

    In order to screen lignocellulose-degrading superior mushroom strains ten strains of mushrooms (Lentinus edodes939, Pholiota nameko, Lentinus edodes868, Coprinus comatus, Macrolepiota procera, Auricularia auricula, Hericium erinaceus, Grifola frondosa, Pleurotus nebrodensis, and Shiraia bambusicola) were inoculated onto carboxymethylcellulose agar-Congo red plates to evaluate their ability to produce carbomethyl cellulase (CMCase). The results showed that the ratio of transparent circle to mycelium circle of Hericium erinaceus was 8.16 (P < 0.01) higher than other strains. The filter paper culture screening test showed that Hericium erinaceus and Macrolepiota procera grew well and showed extreme decomposition of the filter paper. When cultivated in guaiacol culture medium to detect their abilities to secrete laccase, Hericium erinaceus showed the highest ability with the largest reddish brown circles of 4.330 cm. CMCase activity determination indicated that Coprinus comatus and Hericium erinaceus had the ability to produce CMCase with 33.92 U/L on the 9th day and 22.58 U/L on the 10th day, respectively, while Coprinus comatus and Pleurotus nebrodensis had the ability to produce laccase with 496.67 U/L and 489.17 U/L on the 16th day and 18th day. Based on the results, Coprinus comatus might be the most promising lignocellulose-degrading strain to produce both CMCase and laccase at high levels.

  6. Micromechanics model for predicting anisotropic electrical conductivity of carbon fiber composite materials

    NASA Astrophysics Data System (ADS)

    Haider, Mohammad Faisal; Haider, Md. Mushfique; Yasmeen, Farzana

    2016-07-01

    Heterogeneous materials, such as composites consist of clearly distinguishable constituents (or phases) that show different electrical properties. Multifunctional composites have anisotropic electrical properties that can be tailored for a particular application. The effective anisotropic electrical conductivity of composites is strongly affected by many parameters including volume fractions, distributions, and orientations of constituents. Given the electrical properties of the constituents, one important goal of micromechanics of materials consists of predicting electrical response of the heterogeneous material on the basis of the geometries and properties of the individual phases, a task known as homogenization. The benefit of homogenization is that the behavior of a heterogeneous material can be determined without resorting or testing it. Furthermore, continuum micromechanics can predict the full multi-axial properties and responses of inhomogeneous materials, which are anisotropic in nature. Effective electrical conductivity estimation is performed by using classical micromechanics techniques (composite cylinder assemblage method) that investigates the effect of the fiber/matrix electrical properties and their volume fractions on the micro scale composite response. The composite cylinder assemblage method (CCM) is an analytical theory that is based on the assumption that composites are in a state of periodic structure. The CCM was developed to extend capabilities variable fiber shape/array availability with same volume fraction, interphase analysis, etc. The CCM is a continuum-based micromechanics model that provides closed form expressions for upper level length scales such as macro-scale composite responses in terms of the properties, shapes, orientations and constituent distributions at lower length levels such as the micro-scale.

  7. The importance of anchorage in determining a strained protein loop conformation.

    PubMed Central

    Hodel, A.; Kautz, R. A.; Adelman, D. M.; Fox, R. O.

    1994-01-01

    We examine the role of the conformational restriction imposed by constrained ends of a protein loop on the determination of a strained loop conformation. The Lys 116-Pro 117 peptide bond of staphylococcal nuclease A exists in equilibrium between the cis and trans isomers. The folded protein favors the strained cis isomer with an occupancy of 90%. This peptide bond is contained in a solvent-exposed, flexible loop of residues 112-117 whose ends are anchored by Val 111 and Asn 118. Asn 118 is constrained by 2 side-chain hydrogen bonds. We investigate the importance of this constraint by replacing Asn 118 with aspartate, alanine, and glycine. We found that removing 1 or more of the hydrogen bonds observed in Asn 118 stabilizes the trans configuration over the cis configuration. By protonating the Asp 118 side chain of N118D through decreased pH, the hydrogen bonding character of Asp 118 approached that of Asn 118 in nuclease A, and the cis configuration was stabilized relative to the trans configuration. These data suggest that the rigid anchoring of the loop end is important in establishing the strained cis conformation. The segment of residues 112-117 in nuclease A provides a promising model system for study of the basic principles that determine polypeptide conformations. Such studies could be useful in the rational design or redesign of protein molecules. PMID:8003973

  8. Micromechanical evaluation of bone microstructures under load

    NASA Astrophysics Data System (ADS)

    Mueller, Ralph; Boesch, Tobias; Jarak, Drazen; Stauber, Martin; Nazarian, Ara; Tantillo, Michelle; Boyd, Steven

    2002-01-01

    Many bones within the axial and appendicular skeleton are subjected to repetitive, cyclic loading during the course of ordinary daily activities. If this repetitive loading is of sufficient magnitude or duration, fatigue failure of the bone tissue may result. In clinical orthopedics, trabecular fatigue fractures are observed as compressive stress fractures in the proximal femur, vertebrae, calcaneus and tibia, and are often preceded by buckling and bending of microstructural elements. However, the relative importance of bone density and architecture in the aetiology of these fractures is poorly understood. The aim of the study was to investigate failure mechanisms of 3D trabecular bone using micro-computed tomography (mCT). Because of its nondestructive nature, mCT represents an ideal approach for performing not only static measurements of bone architecture but also dynamic measurements of failure initiation and propagation as well as damage accumulation. For the purpose of the study, a novel micro-compression device was devised to measure loaded trabecular bone specimens directly in a micro-tomographic system. A 3D snapshot of the structure under load was taken for each load step in the mCT providing 34 mm nominal resolution. An integrated mini-button load cell in the compression device combined with the displacement computed directly from the mCT scout view was used to record the load-displacement curve. From the series of 3D images, failure of the trabecular architecture could be observed, and in a rod-like type of architecture it could be described by an initial buckling and bending of structural elements followed by a collapse of the overloaded trabeculae. A computational method was developed to quantify individual trabecular strains during failure. The four main steps of the algorithm were (i) sequential image alignment, (ii) identification of landmarks (trabecular nodes), (iii) determine nodal connectivity, and (iv) to compute the nodal displacements and

  9. Flavohaemoglobin HmpX: a new pathogenicity determinant in Erwinia chrysanthemi strain 3937.

    PubMed

    Favey, S; Labesse, G; Vouille, V; Boccara, M

    1995-04-01

    Unlike wild-type Erwinia chrysanthemi strain 3937, which fully macerates inoculated Saintpaulia plants, HmpX- mutants produce necrotic lesions or no symptoms. The hmpX gene was sequenced and the corresponding protein sequence analysed. We show that HmpX belongs to a family of flavohaemoproteins (HMP), previously identified in two yeasts and in Escherichia coli. Comparisons of protein sequences at the secondary structure level by hydrophobic cluster analysis have shown that HmpX possesses two functional regions, a haemoglobin domain in its N-terminal part and a flavin reductase domain in its C-terminal part. In an HmpX- strain, the synthesis of pectate lyases, which are pathogenicity determinants in E. chrysanthemi, was reduced in conditions of low oxygen tension. Using gus fusion in hmpX, it was shown that hmpX transcription was induced in coculture with tobacco cells. A putative function for HmpX is discussed. PMID:7773389

  10. Determining Sliding Velocity and Shear-Strain Magnitude From Basal Sediments of Past Ice Sheets

    NASA Astrophysics Data System (ADS)

    Iverson, N. R.; Hooyer, T. S.; Thomason, J. F.

    2004-12-01

    Ice sheets slide over their basal sediments and commonly deform them. Despite meticulous description of such sediments, they have not been used to estimate rates or magnitudes of basal motion. Thus, although a common assertion is that modeling of past ice sheets can benefit from studies of basal sediments, their actual utility in modeling studies has been minimal. We have developed methods for estimating sliding velocity and till shear-strain magnitude from basal sediments of past ice sheets. The first method involves balancing shear traction on clasts that have plowed through the bed surface with resistance to plowing provided by the bed. The shear traction on clasts is provided by the sliding theory of Lliboutry, and plowing resistance is estimated using a geotechnical theory of cone penetration. The result is an expression for sliding speed of a past ice sheet that depends only on the size distribution of clasts that plowed and the thermomechanical properties of ice and clasts. This method was applied to sizes of clasts that plowed through outwash near Peoria, Illinois, to estimate the sliding speed of the Illinoian ice sheet in that area: 60-170 m/a. The second method involves shearing till in laboratory experiments to study the evolution of till microstructural properties as a function of shear-strain magnitude. Microstructural anisotropy is quantified by collecting multiple intact samples (20 mm cubes) and determining the strength of fabric defined by principal directions of magnetic susceptibility. These directions depend on alignment of needle-shaped magnetite grains. Fabrics formed by directions of maximum susceptibility do not become steady until shear strains of 20-50. Therefore, laboratory calibrations of fabric strength to shear-strain magnitude allow the extent of bed deformation to be determined from susceptibility fabrics of basal till. These studies can provide quantitative inputs to ice-sheet models that have been unavailable previously.

  11. Simple method for direct determination of bending strains by use of digital holography.

    PubMed

    Hung, M Y; Lin, L; Shang, H M

    2001-09-01

    A computer-based technique is described for direct determination of bending strains in beam and plate structures. First a displacement-related phase-change map is constructed by digital holography and computer-vision techniques. Subsequently the computer generates an exact replica of the phase-change map, then overlays the two identical maps and, finally, rotates one of the maps through 180 degrees relative to the other in their planes about a point of interest. The local curvatures and the local twist of the bent surface at the point of interest are determined from the conic sections that are reconstructed from the algebraic sum of the phase changes at the vicinity of this point, thus permitting further calculation for determination of the local bending strains. When the need arises, bending moments and stresses may be determined concurrently. As the optical setup is simple, with computer-based data acquisition and processing, the entire system is user friendly, and rapid measurement is achieved.

  12. Effect of SiC reinforcement on the deformation and fracture micromechanisms of Al-Li alloys

    PubMed

    Poza; Llorca

    1999-11-01

    The effect of SiC reinforcement on the microstructure of a naturally aged 8090 Al alloy as well as on the deformation and fracture micromechanisms was investigated. To this end, the microstructural characteristics (grain and reinforcement morphology, precipitate structure) were determined in the unreinforced alloy and in the composite reinforced with 15 vol.% SiC particles. The materials were tested under monotonic tension and fully reversed cyclic deformation and then carefully analysed through scanning and transmission electron microscopy to find the dominant deformation and failure processes for each material and loading condition. It was found that the dispersion of the SiC particles restrained the formation of elongated grains during extrusion and inhibited the precipitation of Al3Li. As a result, the plastic deformation in the composite was homogeneous, while strain localization in slip bands was observed in the unreinforced alloy specimens tested in tension and in fatigue. The unreinforced alloy failed by transgranular shear along the slip bands during monotonic deformation, whereas fracture was initiated by grain boundary delamination, promoted by the stress concentrations induced by the slip bands, during cyclic deformation. The fracture of the composite was precipitated by the progressive fracture of the SiC reinforcements during monotonic and cyclic deformation.

  13. Atomic Force Microscopy Reveals Regional Variations in the Micromechanical Properties of the Pericellular and Extracellular Matrices of the Meniscus

    PubMed Central

    Sanchez-Adams, Johannah; Wilusz, Rebecca E.; Guilak, Farshid

    2014-01-01

    Regional variations in the composition and architecture of the extracellular matrix (ECM) and pericellular matrix (PCM) of the knee meniscus play important roles in determining the local mechanical environment of meniscus cells. In this study, atomic force microscopy was used to spatially map the mechanical properties of matched ECM and perlecan-labeled PCM sites within the outer, middle, and inner porcine medial meniscus, and to evaluate the properties of the proximal surface of each region. The elastic modulus of the PCM was significantly higher in the outer region (151.4±38.2 kPa) than the inner region (27.5±8.8 kPa), and ECM moduli were consistently higher than region-matched PCM sites in both the outer (320.8±92.5 kPa) and inner (66.1±31.4 kPa) regions. These differences were associated with a higher proportion of aligned collagen fibers and lower glycosaminoglycan content in the outer region. Regional variations in the elastic moduli and some viscoelastic properties were observed on the proximal surface of the meniscus, with the inner region exhibiting the highest moduli overall. These results indicate that matrix architecture and composition play an important role in the regional micromechanical properties of the meniscus, suggesting that the local stress-strain environment of meniscal cells may vary significantly among the different regions. PMID:23568545

  14. Complete genome sequence of a novel Plum pox virus strain W isolate determined by 454 pyrosequencing.

    PubMed

    Sheveleva, Anna; Kudryavtseva, Anna; Speranskaya, Anna; Belenikin, Maxim; Melnikova, Natalia; Chirkov, Sergei

    2013-10-01

    The near-complete (99.7 %) genome sequence of a novel Russian Plum pox virus (PPV) isolate Pk, belonging to the strain Winona (W), has been determined by 454 pyrosequencing with the exception of the thirty-one 5'-terminal nucleotides. This region was amplified using 5'RACE kit and sequenced by the Sanger method. Genomic RNA released from immunocaptured PPV particles was employed for generation of cDNA library using TransPlex Whole transcriptome amplification kit (WTA2, Sigma-Aldrich). The entire Pk genome has identity level of 92.8-94.5 % when compared to the complete nucleotide sequences of other PPV-W isolates (W3174, LV-141pl, LV-145bt, and UKR 44189), confirming a high degree of variability within the PPV-W strain. The isolates Pk and LV-141pl are most closely related. The Pk has been found in a wild plum (Prunus domestica) in a new region of Russia indicating widespread dissemination of the PPV-W strain in the European part of the former USSR.

  15. Horizontal strain field of the Bohemian Massif determined from GPS measurements

    NASA Astrophysics Data System (ADS)

    Schenkova, Z.; Talich, M.; Schenk, V.

    2011-12-01

    Permanent GNSS and campaign GPS data monitored on several geodynamic networks located in the territory of the Bohemian Massif, Central Europe, allowed site movements to be determined. To constrain the first image of regional strain field for this territory a 2-D numerical modeling based on the theory of continuum mechanics under an assumption of homogeneity of the area was applied and site movements, i.e. displacement vectors, were taken as calculation inputs. This approach represents a purely geometric solution. Further attention was paid to influences of regional geological discontinuities of the Massif, by means of an evaluation of their mechanical decoupling along major faults and/or fault zones that play an important role in the distribution of the regional and local motions and stress patterns. The particular analysis of the behavior of tectonic zones in the Bohemian Massif was performed. Fundamental source of the mobility of these zones depends directly on sizes and directions of existing northward movements of structural blocks of the Alpine orogenic system. It was found that common horizontal strain field of the Bohemian Massif displays significant E-W extensions in the eastern and western parts of the Massif and mild N-S compressions in its central part. Additional analyses of the strain field pattern and its numerical uncertainties will be discussed from the viewpoint of data processing and knowledge of geological structures.

  16. Homozygous diploid deletion strains of Saccharomyces cerevisiae that determine lag phase and dehydration tolerance

    NASA Technical Reports Server (NTRS)

    D'Elia, Riccardo; Allen, Patricia L.; Johanson, Kelly; Nickerson, Cheryl A.; Hammond, Timothy G.

    2005-01-01

    This study identifies genes that determine length of lag phase, using the model eukaryotic organism, Saccharomyces cerevisiae. We report growth of a yeast deletion series following variations in the lag phase induced by variable storage times after drying-down yeast on filters. Using a homozygous diploid deletion pool, lag times ranging from 0 h to 90 h were associated with increased drop-out of mitochondrial genes and increased survival of nuclear genes. Simple linear regression (R2 analysis) shows that there are over 500 genes for which > 70% of the variation can be explained by lag alone. In the genes with a positive correlation, such that the gene abundance increases with lag and hence the deletion strain is suitable for survival during prolonged storage, there is a strong predominance of nucleonic genes. In the genes with a negative correlation, such that the gene abundance decreases with lag and hence the strain may be critical for getting yeast out of the lag phase, there is a strong predominance of glycoproteins and transmembrane proteins. This study identifies yeast deletion strains with survival advantage on prolonged storage and amplifies our understanding of the genes critical for getting out of the lag phase.

  17. Pilot Screening to Determine Antimicrobial Synergies in a Multidrug-Resistant Bacterial Strain Library

    PubMed Central

    Kim, Si-Hyun; Park, Chulmin; Chun, Hye-Sun; Choi, Jae-Ki; Lee, Hyo-Jin; Cho, Sung-Yeon; Park, Sun Hee; Choi, Su-Mi; Choi, Jung-Hyun; Yoo, Jin-Hong

    2016-01-01

    With the rise in multidrug-resistant (MDR) bacterial infections, there has been increasing interest in combinations of ≥2 antimicrobial agents with synergistic effects. We established an MDR bacterial strain library to screen for in vitro antimicrobial synergy by using a broth microdilution checkerboard method and high-throughput luciferase-based bacterial cell viability assay. In total, 39 MDR bacterial strains, including 23 carbapenem-resistant gram-negative bacteria, 9 vancomycin-intermediate Staphylococcus aureus, and 7 vancomycin-resistant Enterococcus faecalis, were used to screen for potential antimicrobial synergies. Synergies were more frequently identified with combinations of imipenem plus trimethoprim–sulfamethoxazole for carbapenem-resistant Acinetobacter baumannii in the library. To verify this finding, we tested 34 A. baumannii clinical isolates resistant to both imipenem and trimethoprim–sulfamethoxazole by the checkerboard method. The imipenem plus trimethoprim–sulfamethoxazole combination showed synergy in the treatment of 21 (62%) of the clinical isolates. The results indicate that pilot screening for antimicrobial synergy in the MDR bacterial strain library could be valuable in the selection of combination therapeutic regimens to treat MDR bacterial infections. Further studies are warranted to determine whether this screening system can be useful to screen for the combined effects of conventional antimicrobials and new-generation antimicrobials or nonantimicrobials. PMID:26974861

  18. Read-out of micromechanical cantilever sensors by phase shifting interferometry

    SciTech Connect

    Helm, M.; Servant, J.J.; Saurenbach, F.; Berger, R.

    2005-08-08

    White light interferometry was applied to determine the bending of micromechanical cantilever sensors (MCS) with an error typically less than 1 per mille. Deflections smaller than 2 nm could be resolved at a lateral resolution of 2 {mu}m. Absolute values for curvatures can be determined and suitable reference points can be chosen on the MCS support. This was demonstrated in experiments using plasma polymerized polyallylamine films, which cross link upon ultraviolet light irradiation. The results suggest that 100 {mu}m long segments are sufficient to estimate reliable curvature radii of 450 {mu}m long microcantilever sensors.

  19. Micromechanics and constitutive models for soft active materials with phase evolution

    NASA Astrophysics Data System (ADS)

    Wang, Binglian

    Soft active materials, such as shape memory polymers, liquid crystal elastomers, soft tissues, gels etc., are materials that can deform largely in response to external stimuli. Micromechanics analysis of heterogeneous materials based on finite element method is a typically numerical way to study the thermal-mechanical behaviors of soft active materials with phase evolution. While the constitutive models that can precisely describe the stress and strain fields of materials in the process of phase evolution can not be found in the databases of some commercial finite element analysis (FEA) tools such as ANSYS or Abaqus, even the specific constitutive behavior for each individual phase either the new formed one or the original one has already been well-known. So developing a computationally efficient and general three dimensional (3D) thermal-mechanical constitutive model for soft active materials with phase evolution which can be implemented into FEA is eagerly demanded. This paper first solved this problem theoretically by recording the deformation history of each individual phase in the phase evolution process, and adopted the idea of effectiveness by regarding all the new formed phase as an effective phase with an effective deformation to make this theory computationally efficient. A user material subroutine (UMAT) code based on this theoretical constitutive model has been finished in this work which can be added into the material database in Abaqus or ANSYS and can be easily used for most soft active materials with phase evolution. Model validation also has been done through comparison between micromechanical FEA and experiments on a particular composite material, shape memory elastomeric composite (SMEC) which consisted of an elastomeric matrix and the crystallizable fibre. Results show that the micromechanics and the constitutive models developed in this paper for soft active materials with phase evolution are completely relied on.

  20. Experimental Characterization and Micromechanical Modelling of Anisotropic Slates

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Feng; Wei, Kai; Liu, Wu; Hu, Shao-Hua; Hu, Ran; Zhou, Chuang-Bing

    2016-09-01

    Laboratory tests were performed in this study to examine the anisotropic physical and mechanical properties of the well-foliated Jiujiang slate. The P-wave velocity and the apparent Young's modulus were found to increase remarkably with the foliation angle θ, and the compressive strength at any confining pressure varies in a typical U-shaped trend, with the maximum strength consistently attained at θ = 90° and the minimum strength at θ = 45°. The slate samples failed in three typical patterns relevant to the foliation angle, i.e. shear failure across foliation planes for θ ≤ 15°, sliding along foliation planes for 30° ≤ θ ≤ 60° and axial splitting along foliation planes for θ = 90°. The stress-strain curves at any given foliation angle and confining pressure display an initial nonlinear phase, a linear elastic phase, a crack initiation and growth phase, as well as a rapid stress drop phase and a residual stress phase. Based on the experimental evidences, a micromechanical damage-friction model was proposed for the foliated slate by simply modelling the foliation planes as a family of elastic interfaces and by characterizing the interaction between the foliation planes and the rock matrix with a nonlinear damage evolution law associated with the inclination angle. The proposed model was applied to predict the deformational and strength behaviours of the foliated slate under triaxial compressive conditions using the material parameters calibrated with the uniaxial and/or triaxial test data, with good agreement between the model predictions and the laboratory measurements.

  1. On the Micromechanisms of Anomalous Slip in BCC Metals

    SciTech Connect

    Hsiung, L L

    2005-09-06

    Dislocation substructures developed in high-purity Mo single crystals deformed under uniaxial compression at room temperature to a total strain of {approx} 0.5% with a strain rate of 1 s{sup -1} have been investigated using transmission electron microscopy (TEM) techniques in order to elucidate the underlying micromechanisms of the anomalous operation of {l_brace}0{bar 1}1{r_brace} slip systems, i.e. Schmid-law violation, in bcc metals. The crystals were oriented with the stress axis parallel to a nominal single-slip orientation of [{bar 2}920], in which the ({bar 1}01)[111] slip system is the only system having a maximum value of Schmid factor (m = 0.5). Nevertheless, the recorded stress-strain curve reveals no single-slip or easy-glide stage, and the anomalous slip occurs in both (011) and (0{bar 1}1) planes. TEM examination of the dislocation structure in the ({bar 1}01) primary slip plane reveals that in addition to the operation of the ({bar 1}01)[111] slip system, the coplanar ({bar 1}01)[1{bar 1}1] slip system that has a much smaller Schmid factor (m = 0.167) is also operative. Similarly, the (0{bar 1}1)[111] slip system (m = 0.25) is cooperative with the coplanar (0{bar 1}1)[{bar 1}11] system (m = 0.287), and the (011)[1{bar 1}1] slip system (m = 0.222) is cooperative with the coplanar (011)[11{bar 1}] system (m = 0.32). The occurrence of {l_brace}0{bar 1}1{r_brace} anomalous slip is accordingly proposed to be initiated from the cooperative dislocation multiplication and mutual trapping and blocking of 1/2[111] and 1/2[1{bar 1}1] coplanar dislocation arrays in the ({bar 1}01) plane. The resulted internal stresses render the propagation of both 1/2[111] and 1/2[1{bar 1}1] screw dislocations from the ({bar 1}01) plane onto the {l_brace}0{bar 1}1{r_brace} planes and subsequently result in the occurrence of anomalous slip.

  2. Micromechanical Modeling for the Deformation of Sand with Non-coaxiality Between Stress and Material Axes

    NASA Astrophysics Data System (ADS)

    Bennett, K. C.; Chang, C. S.; Borja, R. I.

    2011-12-01

    This research project has taken the micromechanics approach to model the strength and deformation behavior of inherently anisotropic sand subjected to stresses non-coaxial with the material axes. Asymmetric sand grains, such as elongated sand grains, are likely to develop a preferred orientation when deposited during the process of alluvial sedimentation, creating an inherently anisotropic material fabric with horizontally oriented bedding planes. Sand thus exhibits different strength and stress-strain behavior dependent on the direction of loading with respect to the axes of the soil. Accounting for non-coaxiality between the stress and material axes is paramount for the accurate prediction of soil's response to applied loads; however, despite the numerous advancements in constitutive models and numerical methods for geotechnical analysis, the problem of accounting for the effect of non-coaxiality between stress and material axes on soil behavior has not been satisfactorily addressed. Drained hollow cylinder torsional shear (HCTS) compression tests on Toyoura sand were simulated, where the direction of the major principal stresses were applied at various angles to the material axes ranging from 0° to 90° from vertical (i.e., ranging from normal to parallel with the bedding plane). Anisotropic behavior has been attributed to interlocking of the sand particles, where the interlocking is least and sliding occurs most easily on the bedding plane. The degree of interlocking was taken as a material property which varies in three dimensions with respect to the material axes, and has been shown to account for observed anisotropy of material strength. Anisotropy of elastic and plastic strain was accounted for, as was the volumetric strain behavior. The developed micromechanics model has been shown to be capable of predicting anisotropy of strength and stress-strain behavior resulting from non-coaxiality of the stress and material axes.

  3. Measuring the micromechanical properties of embryonic tissues.

    PubMed

    Chevalier, Nicolas R; Gazguez, Elodie; Dufour, Sylvie; Fleury, Vincent

    2016-02-01

    Local mechanical properties play an important role in directing embryogenesis, both at the cell (differentiation, migration) and tissue level (force transmission, organ formation, morphogenesis). Measuring them is a challenge as embryonic tissues are small (μm to mm) and soft (0.1-10 kPa). We describe here how glass fiber cantilevers can be fabricated, calibrated and used to apply small forces (0.1-10 μN), measure contractile activity and assess the bulk tensile elasticity of embryonic tissue. We outline how pressure (hydrostatic or osmotic) can be applied to embryonic tissue to quantify stiffness anisotropy. These techniques can be assembled at low cost and with a minimal amount of equipment. We then present a protocol to prepare tissue sections for local elasticity and adhesion measurements using the atomic force microscope (AFM). We compare AFM nanoindentation maps of native and formaldehyde fixed embryonic tissue sections and discuss how the local elastic modulus obtained by AFM compares to that obtained with other bulk measurement methods. We illustrate all of the techniques presented on the specific example of the chick embryonic digestive tract, emphasizing technical issues and common pitfalls. The main purpose of this report is to make these micromechanical measurement techniques accessible to a wide community of biologists and biophysicists.

  4. Frequency division using a micromechanical resonance cascade

    SciTech Connect

    Qalandar, K. R. Gibson, B.; Sharma, M.; Ma, A.; Turner, K. L.; Strachan, B. S.; Shaw, S. W.

    2014-12-15

    A coupled micromechanical resonator array demonstrates a mechanical realization of multi-stage frequency division. The mechanical structure consists of a set of N sequentially perpendicular microbeams that are connected by relatively weak elastic elements such that the system vibration modes are localized to individual microbeams and have natural frequencies with ratios close to 1:2:⋯:2{sup N}. Conservative (passive) nonlinear inter-modal coupling provides the required energy transfer between modes and is achieved by finite deformation kinematics. When the highest frequency beam is excited, this arrangement promotes a cascade of subharmonic resonances that achieve frequency division of 2{sup j} at microbeam j for j = 1, …, N. Results are shown for a capacitively driven three-stage divider in which an input signal of 824 kHz is passively divided through three modal stages, producing signals at 412 kHz, 206 kHz, and 103 kHz. The system modes are characterized and used to delineate the range of AC input voltages and frequencies over which the cascade occurs. This narrow band frequency divider has simple design rules that are scalable to higher frequencies and can be extended to a larger number of modal stages.

  5. Contact micromechanics in granular media with clay

    SciTech Connect

    Ita, S.L.

    1994-08-01

    Many granular materials, including sedimentary rocks and soils, contain clay particles in the pores, grain contacts, or matrix. The amount and location of the clays and fluids can influence the mechanical and hydraulic properties of the granular material. This research investigated the mechanical effects of clay at grain-to-grain contacts in the presence of different fluids. Laboratory seismic wave propagation tests were conducted at ultrasonic frequencies using spherical glass beads coated with Montmorillonite clay (SWy-1) onto which different fluids were adsorbed. For all bead samples, seismic velocity increased and attenuation decreased as the contact stiffnesses increased with increasing stress demonstrating that grain contacts control seismic transmission in poorly consolidated and unconsolidated granular material. Coating the beads with clay added stiffness and introduced viscosity to the mechanical contact properties that increased the velocity and attenuation of the propagating seismic wave. Clay-fluid interactions were studied by allowing the clay coating to absorb water, ethyl alcohol, and hexadecane. Increasing water amounts initially increased seismic attenuation due to clay swelling at the contacts. Attenuation decreased for higher water amounts where the clay exceeded the plastic limit and was forced from the contact areas into the surrounding open pore space during sample consolidation. This work investigates how clay located at grain contacts affects the micromechanical, particularly seismic, behavior of granular materials. The need for this work is shown by a review of the effects of clays on seismic wave propagation, laboratory measurements of attenuation in granular media, and proposed mechanisms for attenuation in granular media.

  6. Single coil bistable, bidirectional micromechanical actuator

    SciTech Connect

    Tabat, Ned; Guckel, Henry

    1998-09-15

    Micromechanical actuators capable of bidirectional and bistable operation can be formed on substrates using lithographic processing techniques. Bistable operation of the microactuator is obtained using a single coil and a magnetic core with a gap. A plunger having two magnetic heads is supported for back and forth linear movement with respect to the gap in the magnetic core, and is spring biased to a neutral position in which the two heads are on each side of the gap in the core. The single electrical coil is coupled to the core and is provided with electrical current to attract one of the heads toward the core by reluctance action to drive the plunger to a limit of travel in one direction. The current is then cut off and the plunger returns by spring action toward the gap, whereafter the current is reapplied to the coil to attract the other head of the plunger by reluctance action to drive the plunger to its other limit of travel. This process can be repeated at a time when switching of the actuator is required.

  7. Micromechanical structures and microelectronics for acceleration sensing

    SciTech Connect

    Davies, B.R.; Montague, S.; Smith, J.H.; Lemkin, M.

    1997-08-01

    MEMS is an enabling technology that may provide low-cost devices capable of sensing motion in a reliable and accurate manner. This paper describes work in MEMS accelerometer development at Sandia National Laboratories. This work leverages a process for integrating both the micromechanical structures and microelectronis circuitry of a MEMS accelerometer on the same chip. The design and test results of an integrated MEMS high-g accelerometer will be detailed. Additionally a design for a high-g fuse component (low-G or {approx} 25 G accelerometer) will be discussed in the paper (where 1 G {approx} 9.81 m/s). In particular, a design team at Sandia was assembled to develop a new micromachined silicon accelerometer which would be capable of surviving and measuring high-g shocks. Such a sensor is designed to be cheaper and more reliable than currently available sensors. A promising design for a suspended plate mass sensor was developed and the details of that design along with test data will be documented in the paper. Future development in this area at Sandia will focus on implementing accelerometers capable of measuring 200 kilo-g accelerations. Accelerometer development at Sandia will also focus on multi-axis acceleration measurement with integrated microelectronics.

  8. Micromechanical sensors for chemical and physical measurements

    SciTech Connect

    Wachter, E.A.; Thundat, T.

    1995-06-01

    The advent of inexpensive, mass-produced microcantilevers promises to bring about a revolution in the field of chemical and physical sensor design. In this paper, a novel class of highly sensitive sensors are discussed that are based on commercially available microcantilevers, such as those used in atomic force microscopy. When coated with a sensitizing overlayer, these microcantilevers show significant changes in two independent analyte-induced signals, resonance frequency and static bending, as the result of exposure to various chemical and physical phenomena. Resonance frequency shift has the particular advantage of being relatively insensitive to interference from external factors such as thermal drift. Examples of micromechanical sensors based on this approach that are capable of detecting mercury vapor (with a sensitivity of 1.25 Hz/pg and linear correlation of 0.998), relative humidity (55 Hz/%R.H., correlation=0.999), or optical irradiation (10 Hz/nJ response) are discussed in detail, along with the effects of coatings on sensitivity, linearity, and reversibility of response. Further, extension of this tremendously flexible concept into a universal detection paradigm for chemical and physical phenomena is examined.

  9. Computational micromechanics of bioabsorbable magnesium stents.

    PubMed

    Grogan, J A; Leen, S B; McHugh, P E

    2014-06-01

    Magnesium alloys are a promising candidate material for an emerging generation of absorbable metal stents. Due to its hexagonal-close-packed lattice structure and tendency to undergo twinning, the deformation behaviour of magnesium is quite different to that of conventional stent materials, such as stainless steel 316L and cobalt chromium L605. In particular, magnesium exhibits asymmetric plastic behaviour (i.e. different yield behaviours in tension and compression) and has lower ductility than these conventional alloys. In the on-going development of absorbable metal stents it is important to assess how the unique behaviour of magnesium affects device performance. The mechanical behaviour of magnesium stent struts is investigated in this study using computational micromechanics, based on finite element analysis and crystal plasticity theory. The plastic deformation in tension and bending of textured and non-textured magnesium stent struts with different numbers of grains through the strut dimension is investigated. It is predicted that, unlike 316L and L605, the failure risk and load bearing capacity of magnesium stent struts during expansion is not strongly affected by the number of grains across the strut dimensions; however texturing, which may be introduced and controlled in the manufacturing process, is predicted to have a significant influence on these measures of strut performance.

  10. Dissociation of immune determinants of outer membrane proteins of Chlamydia psittaci strain guinea pig inclusion conjunctivitis.

    PubMed

    Westbay, T D; Dascher, C C; Hsia, R C; Bavoil, P M; Zauderer, M

    1994-12-01

    Chlamydia trachomatis is an important human pathogen. Research to develop a Chlamydia vaccine has focused on the major outer membrane protein (MOMP). Determinants of this protein elicit serovar-specific neutralizing antibodies which are thought to play a critical role in protective immunity. MOMP-specific antibody responses are highly variable in the polymorphic population. Genetic factors which might influence the MOMP-specific immune response are consequently of particular interest. The C. psittaci strain guinea pig inclusion conjunctivitis (GPIC) is a natural pathogen of the guinea pig that causes both ocular and genital tract infections that closely resemble those caused by C. trachomatis in humans. As such, it provides an excellent model for disease. In this report, we explore the influence of major histocompatibility complex-linked genes on the MOMP-specific antibody response in mice immunized with either whole GPIC elementary bodies or recombinant GPIC MOMP. Our results indicate that the MOMP-specific antibody response is major histocompatibility complex linked such that mice of the H-2d haplotype are high responders while mice of the H-2k haplotype are low responders. We demonstrate that MOMP-specific B cells are present in H-2k strains which are, however, deficient in MOMP-specific helper T cells. Although immunization of low-MOMP-responder strains with whole chlamydial elementary bodies induces high levels of immunoglobulin G antibody specific for Omp2, the cysteine-rich outer membrane protein, MOMP-specific B cells are unable to receive help from Omp2-specific T cells. The failure of intermolecular help from Omp2-specific T cells and related observations raise important issues regarding the processing and presentation of chlamydial antigens and the design of optimal subunit vaccines.

  11. Analysis and prediction of particulate composite mechanical behavior using a nonlinear micromechanical theory

    NASA Astrophysics Data System (ADS)

    Wong, Franklin C.

    1997-12-01

    The objective of this study was to develop a micromechanical model that would account for material nonlinearity due to matrix nonlinear behavior and inclusion debonding in polymeric particulate composites. An existing model was improved by using a new modulus prediction routine based on the work of Mori-Tanaka and Ju-Chen. This routine accounted for particle interaction and described more accurately the effects of a debonded inclusion on overall mechanical properties. Predictions for glass bead/high density polyethylene (HDPE) and glass bead/polyurethane (PU) composite behavior showed that debonded particles modeled as vacuoles gave better results than those modeled as voids. This model could predict mechanical behavior of highly loaded composites if a representative value for adhesion energy was available. The final micromechanical model improved the previous model by characterizing the matrix as a nonlinear elastic material. A critical analysis using data from glass bead/hydroxl-terminated polybutadiene (HTPB) composites showed that debonding of largest to smallest particles throughout the monotonic strain history was a reasonable assumption. As well, particle interaction could be influenced by particle size and surface treatment. There were indications that particles did not fully debond. A sensitivity analyses revealed that overall behavior was controlled by particle-matrix adhesive characteristics. For glass bead/HTPB, glass bead/PU and glass bead/HDPE composites, the model was capable of predicting mechanical behavior as long as suitable adhesive characteristic values were available.

  12. Metal matrix composite micromechanics: In-situ behavior influence on composite properties

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Hopkins, D. A.; Chamis, C. C.

    1989-01-01

    Recent efforts in computational mechanics methods for simulating the nonlinear behavior of metal matrix composites have culminated in the implementation of the Metal Matrix Composite Analyzer (METCAN) computer code. In METCAN material nonlinearity is treated at the constituent (fiber, matrix, and interphase) level where the current material model describes a time-temperature-stress dependency of the constituent properties in a material behavior space. The composite properties are synthesized from the constituent instantaneous properties by virtue of composite micromechanics and macromechanics models. The behavior of metal matrix composites depends on fabrication process variables, in situ fiber and matrix properties, bonding between the fiber and matrix, and/or the properties of an interphase between the fiber and matrix. Specifically, the influence of in situ matrix strength and the interphase degradation on the unidirectional composite stress-strain behavior is examined. These types of studies provide insight into micromechanical behavior that may be helpful in resolving discrepancies between experimentally observed composite behavior and predicted response.

  13. Micromachined strain gauges for the determination of liquid flow friction coefficients in microchannels

    NASA Astrophysics Data System (ADS)

    Baviere, R.; Ayela, F.

    2004-02-01

    In this research program, we have performed and tested cupro-nickel (Cu-Ni) strain gauges micromachined on different sorts of silicon nitride (Si3N4) membranes. The design of the gauges obeys an electrical Wheatstone bridge configuration. We have found a good agreement between the expected electromechanical response of the bridge and the experimental signals. The results have displayed sensitivity to static pressure ranging from 50 to 100 µV V-1 bar-1 as a function of the thickness and of the diameter of the membranes. This is part of a study devoted to determining liquid flow friction coefficients in silicon-Pyrex microchannels. Preliminary attempts (Reynolds number up to 300) made using global pressure measurements and with very simple local pressure probes are discussed. Further experiments using Cu-Ni strain gauges are described. Their micromachining, characterization and integration along silicon microchannels are presented. These sensors permitted us to perform the first local and reliable pressure drop measurements in a 7.5 µm deep microchannel. The results are in good agreement with the classical laminar theory for a Reynolds number ranging from 0.2 to 3.

  14. A macro-micromechanics analysis of a notched metal matrix composite

    NASA Technical Reports Server (NTRS)

    Bigelow, Catherine A.; Naik, Rajiv A.

    1992-01-01

    Macro- and micromechanics analysis were conducted to determine the matrix and fiber behaviors near the notch in a center-notched metal-matrix composite. In this approach, the macrolevel analysis models the entire notched specimen using a 3D finite element program that uses the vanishing-fiber-diameter model to simulate the elastic-plastic behavior of the matrix and the elastic behavior of the fiber. The microlevel behavior is analyzed using a discrete fiber-matrix model containing one fiber and the surrounding matrix. The viability of this analysis is demonstrated using results for a boron/aluminum monolayer.

  15. Micromechanical simulation of damage progression in carbon phenolic composites

    NASA Technical Reports Server (NTRS)

    Slattery, Kerry T.

    1993-01-01

    Carbon/phenolic composites are used extensively as ablative insulating materials in the nozzle region of solid rocket motors. The current solid rocket motor (RSRM) on the space shuttle is fabricated from woven rayon cloth which is carbonized and then impregnated with the phenolic resin. These plies are layed up in the desired configuration and cured to form the finished part. During firing, the surface of the carbon/phenolic insulation is exposed to 5000 F gases from the rocket exhaust. The resin pyrolizes and the material chars to a depth which progresses with time. The rate of charring and erosion are generally predictable, and the insulation depth is designed to allow adequate safety margins over the firing time of the motor. However, anomalies in the properties and response of the carbon/phenolic materials can lead to severe material damage which may decrease safety margins to unacceptable levels. Three macro damage modes which were observed in fired nozzles are: ply lift, 'wedge out', and pocketing erosion. Ply lift occurs in materials with plies oriented nearly parallel to the surface. The damage occurs in a region below the charred material where material temperatures are relatively low - about 500 F. Wedge out occurs at the intersection of nozzle components whose plies are oriented at about 45 deg. The corner of the block of material breaks off along a ply interface. Pocketing erosion occurs in material with plies oriented normal to the surface. Thermal expansion is restrained in two directions resulting in large tensile strains and material failure normal to the surface. When a large section of material is removed as a result of damage, the insulation thickness is reduced which may lead to failure of the nozzle due to excessive heating of critical components. If these damage events cannot be prevented with certainty, the designer must increase the thickness of the insulator thus adding to both weight and cost. One of the difficulties in developing a full

  16. Micromechanical properties of keratin intermediate filament networks

    PubMed Central

    Sivaramakrishnan, Sivaraj; DeGiulio, James V.; Lorand, Laszlo; Goldman, Robert D.; Ridge, Karen M.

    2008-01-01

    Keratin intermediate filaments (KIFs) form cytoskeletal KIF networks that are essential for the structural integrity of epithelial cells. However, the mechanical properties of the in situ network have not been defined. Particle-tracking microrheology (PTM) was used to obtain the micromechanical properties of the KIF network in alveolar epithelial cells (AECs), independent of other cytoskeletal components, such as microtubules and microfilaments. The storage modulus (G′) at 1 Hz of the KIF network decreases from the perinuclear region (335 dyn/cm2) to the cell periphery (95 dyn/cm2), yielding a mean value of 210 dyn/cm2. These changes in G′ are inversely proportional to the mesh size of the network, which increases ≈10-fold from the perinuclear region (0.02 μm2) to the cell periphery (0.3 μm2). Shear stress (15 dyn/cm2 for 4 h) applied across the surface of AECs induces a more uniform distribution of KIF, with the mesh size of the network ranging from 0.02 μm2 near the nucleus to only 0.04 μm2 at the cell periphery. This amounts to a 40% increase in the mean G′. The storage modulus of the KIF network in the perinuclear region accurately predicts the shear-induced deflection of the cell nucleus to be 0.87 ± 0.03 μm. The high storage modulus of the KIF network, coupled with its solid-like rheological behavior, supports the role of KIF as an intracellular structural scaffold that helps epithelial cells to withstand external mechanical forces. PMID:18199836

  17. Squeezed light from a silicon micromechanical resonator.

    PubMed

    Safavi-Naeini, Amir H; Gröblacher, Simon; Hill, Jeff T; Chan, Jasper; Aspelmeyer, Markus; Painter, Oskar

    2013-08-01

    Monitoring a mechanical object's motion, even with the gentle touch of light, fundamentally alters its dynamics. The experimental manifestation of this basic principle of quantum mechanics, its link to the quantum nature of light and the extension of quantum measurement to the macroscopic realm have all received extensive attention over the past half-century. The use of squeezed light, with quantum fluctuations below that of the vacuum field, was proposed nearly three decades ago as a means of reducing the optical read-out noise in precision force measurements. Conversely, it has also been proposed that a continuous measurement of a mirror's position with light may itself give rise to squeezed light. Such squeezed-light generation has recently been demonstrated in a system of ultracold gas-phase atoms whose centre-of-mass motion is analogous to the motion of a mirror. Here we describe the continuous position measurement of a solid-state, optomechanical system fabricated from a silicon microchip and comprising a micromechanical resonator coupled to a nanophotonic cavity. Laser light sent into the cavity is used to measure the fluctuations in the position of the mechanical resonator at a measurement rate comparable to its resonance frequency and greater than its thermal decoherence rate. Despite the mechanical resonator's highly excited thermal state (10(4) phonons), we observe, through homodyne detection, squeezing of the reflected light's fluctuation spectrum at a level 4.5 ± 0.2 per cent below that of vacuum noise over a bandwidth of a few megahertz around the mechanical resonance frequency of 28 megahertz. With further device improvements, on-chip squeezing at significant levels should be possible, making such integrated microscale devices well suited for precision metrology applications. PMID:23925241

  18. Micromechanical aspects of failure in unidirectional fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Oguni, Kenji

    Micromechanical aspects of failure in unidirectional fiber reinforced composites are investigated using combined experimental and analytical methods. Results from an experimental investigation on mechanical behavior of a unidirectional fiber reinforced polymer composite (E-glass/vinylester) with 50% fiber volume fraction under quasi-static uniaxial and proportional multiaxial compression are presented. Detailed examination of the specimen during and after the test reveals the failure mode transition from axial splitting to kink band formation as the loading condition changes from uniaxial to multiaxial compression. Motivated by the experimental observations, an energy-based model is developed to provide an analytical estimate of the critical stress for axial splitting observed in unidirectional fiber reinforced composites under uniaxial compression in the fiber direction (also with weak lateral confinement). The analytic estimate for the compressive strength is used to illustrate its dependence on material properties, surface energy, fiber volume fraction, fiber diameter and lateral confining pressure. To understand the effect of flaws on the strength of unidirectional fiber reinforced composites, a fracture mechanics based model for failure is developed. Based on this model, failure envelope, dominant initial flaw orientation and failure mode for the composites under a wide range of stress states are predicted. Parametric study provides quantitative evaluation of the effect of various mechanical and physical properties on failure behavior and identifies their influence on strength. Finally, results from an experimental investigation on the dynamic mechanical behavior of unidirectional E-glass/vinylester composites with 30%, 50% fiber volume fraction under uniaxial compression are presented. Limited experimental results are also presented for the 50% fiber volume fraction composite under dynamic proportional lateral confinement. Specimens are loaded in the fiber

  19. An electrostatically suspended, micro-mechanical rate gyroscope

    NASA Technical Reports Server (NTRS)

    Hawkey, Timothy; Torti, Richard

    1992-01-01

    SatCon Technology has performed a study of micromechanical gyroscopes. The goals of this program were to define a baseline system configuration and establish technical feasibility for proof of principle and prototype fabrication. This report documents the research and presents the baseline mechanical design, sensors, control systems, and electronics. This section presents a project overview and specific technical objectives. Section 2 contains a background on micromechanical technology. Section 3 contains the microgyroscope specifications and configurations. Section 4 contains the electromechanical design. Section 5 outlines the control and electronics. Section 6 presents a preliminary sequence for microfabrication of the baseline design, and Section 7 contains conclusions and recommendations for further work.

  20. Effect of the anisotropy of monocrystalline silicon mechanical properties on the dynamic characteristics of a micromechanical gyroscope

    NASA Astrophysics Data System (ADS)

    Nesterenko, T. G.; Vtorushin, S. E.; Barbin, E. S.; Koleda, A. N.

    2015-04-01

    The aim of the research was to determine the effect of temperature on mechanical properties of a micromechanical gyroscope with the sensing element mounted on a silicon wafer, with the crystallographic orientation of (100) (110) (111). The research is of current relevancy since the metrological characteristics that depend on the eigenfrequencies over the full temperature range are to be controlled. The temperature-modal analysis of the micromechanical gyroscope model was performed with ANSYS program. The temperature dependence for eigenfrequencies was obtained. The dependence of the scale factor on temperature for the most temperature-independent variant of sensor positioning on the wafer was determined. The developed mathematical model was used to find the forms of the output oscillations of the gyroscope.

  1. Virulence Attributes and Host Response Assays for Determining Pathogenic Potential of Pseudomonas Strains Used in Biotechnology

    PubMed Central

    Tayabali, Azam F.; Coleman, Gordon; Nguyen, Kathy C.

    2015-01-01

    Pseudomonas species are opportunistically pathogenic to humans, yet closely related species are used in biotechnology applications. In order to screen for the pathogenic potential of strains considered for biotechnology applications, several Pseudomonas strains (P.aeruginosa (Pa), P.fluorescens (Pf), P.putida (Pp), P.stutzeri (Ps)) were compared using functional virulence and toxicity assays. Most Pa strains and Ps grew at temperatures between 28°C and 42°C. However, Pf and Pp strains were the most antibiotic resistant, with ciprofloxacin and colistin being the most effective of those tested. No strain was haemolytic on sheep blood agar. Almost all Pa, but not other test strains, produced a pyocyanin-like chromophore, and caused cytotoxicity towards cultured human HT29 cells. Murine endotracheal exposures indicated that the laboratory reference strain, PAO1, was most persistent in the lungs. Only Pa strains induced pro-inflammatory and inflammatory responses, as measured by elevated cytokines and pulmonary Gr-1 -positive cells. Serum amyloid A was elevated at ≥ 48 h post-exposure by only some Pa strains. No relationship was observed between strains and levels of peripheral leukocytes. The species designation or isolation source may not accurately reflect pathogenic potential, since the clinical strain Pa10752 was relatively nonvirulent, but the industrial strain Pa31480 showed comparable virulence to PAO1. Functional assays involving microbial growth, cytotoxicity and murine immunological responses may be most useful for identifying problematic Pseudomonas strains being considered for biotechnology applications. PMID:26619347

  2. Strain energy release rate determination of stress intensity factors by finite element methods

    NASA Technical Reports Server (NTRS)

    Walsh, R. M., Jr.; Pipes, R. B.

    1985-01-01

    The stiffness derivative finite element technique is used to determine the Mode I stress intensity factors for three-crack configurations. The geometries examined include the double edge notch, single edge notch, and the center crack. The results indicate that when the specified guidelines of the Stiffness Derivative Method are used, a high degree of accuracy can be achieved with an optimized, relatively coarse finite element mesh composed of standard, four-node, plane strain, quadrilateral elements. The numerically generated solutions, when compared with analytical ones, yield results within 0.001 percent of each other for the double edge crack, 0.858 percent for the single edge crack, and 2.021 percent for the center crack.

  3. Atrial fibrillation per se was a major determinant of global left ventricular longitudinal systolic strain

    PubMed Central

    Lee, Hung-Hao; Lee, Meng-Kuang; Lee, Wen-Hsien; Hsu, Po-Chao; Chu, Chun-Yuan; Lee, Chee-Siong; Lin, Tsung-Hsien; Voon, Wen-Chol; Lai, Wen-Ter; Sheu, Sheng-Hsiung; Su, Ho-Ming

    2016-01-01

    Abstract Atrial fibrillation (AF) may cause systolic abnormality via inadequate diastolic filling and tachycardia-induced cardiomyopathy. Global longitudinal strain (GLS) is a very sensitive method for detecting subtle left ventricular systolic dysfunction. Hence, this study aimed to evaluate whether AF patients had a more impaired GLS, AF was a major determinant of GLS, and determine the major correlates of GLS in AF patients. The study included 137 patients with persistent AF and left ventricular ejection fraction (LVEF) above 50% and 137 non-AF patients matched according to age, gender, and LVEF. Comprehensive echocardiography with GLS assessment was performed for all cases. Compared with non-AF patients, AF patients had a more impaired GLS, a larger left atrial volume index, higher transmitral E wave velocity (E), and early diastolic mitral velocity (Ea) (all P < 0.001) but comparable E/Ea. After adjustment for baseline and echocardiographic characteristics, the presence of AF remained significantly associated with impaired GLS (β = 0.533, P < 0.001). In addition, multivariate analysis of AF patients indicated that faster heart rates and decreased E, Ea, and LVEF were associated with more impaired GLS. This study demonstrated that AF patients had a more impaired GLS than non-AF patients, although LVEF was comparable between the 2 groups. AF was a major determinant of GLS even after adjustment for relevant clinical and echocardiographic parameters. PMID:27368031

  4. Use of the VNTR typing technique to determine the origin of Mycobacterium tuberculosis strains isolated from Filipino patients in Korea.

    PubMed

    Lee, Jihye; Tupasi, Thelma E; Park, Young Kil

    2014-05-01

    With increasing international interchange of personnel, international monitoring is necessary to decrease tuberculosis incidence in the world. This study aims to develop a new tool to determine origin of Mycobacterium tuberculosis strains isolated from Filipino patients living in Korea. Thirty-two variable number tandem repeat (VNTR) loci were used for discrimination of 50 Filipino M. tuberculosis strains isolated in the Philippines, 317 Korean strains isolated in Korea, and 8 Filipino strains isolated in Korea. We found that the VNTR loci 0580, 0960, 2531, 2687, 2996, 0802, 2461, 2163a, 4052, 0424, 1955, 2074, 2347, 2401, 3171, 3690, 2372, 3232, and 4156 had different mode among copy numbers or exclusively distinct copy number in VNTR typing between Filipino and Korean M. tuberculosis strains. When these differences of the VNTR loci were applied to 8 Filipino M. tuberculosis strains isolated in Korea, 6 of them revealed Filipino type while 2 of them had Korean type. Using the differences of mode or repeated number of VNTR loci were very useful in distinguishing the Filipino strain from Korean strain.

  5. 16S rDNA PCR-denaturing gradient gel electrophoresis in determining proportions of coexisting Actinobacillus actinomycetemcomitans strains.

    PubMed

    Ihalin, Riikka; Asikainen, Sirkka

    2006-06-01

    Certain serotypes of Actinobacillus actinomycetemcomitans seem to prefer coexistence in vivo. The 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) was tested for its capability to distinguish coexisting A. actinomycetemcomitans strains of different serotypes or genetic lineages and to determine their proportions in vitro. The migration pattern of the PCR amplicon from serotype c differed from those of the other serotypes. Contrary to the strains of serotypes c, d, and e, strains of serotypes a, b, and f consistently demonstrated intra-serotype migration patterns similar to each other. Since the migration patterns differed between serotype c and b strains a strain of each was used to determine their proportional representation in a strain mixture. The strains were distinguishable from each other above the 5% PCR-DGGE detection level (12.5 ng DNA/1.5 x 10(6) cells). DGGE provides a promising tool for in vitro studies on the coexistence of different genetic lineages of A. actinomycetemcomitans.

  6. Raman determination of layer stresses and strains for heterostructures and its application to the cubic SiC/Si system

    NASA Technical Reports Server (NTRS)

    Feng, Z. C.; Choyke, W. J.; Powell, J. A.

    1988-01-01

    A set of formulas for a generalized axial stress in diamond and zinc-blende semiconductors under axial stress is derived to calculate stress-related Raman shifts. By analyzing known Raman data on cubic SiC under hydrostatic pressures, one of the Raman-stress coefficients was obtained, and the existing elastic stiffness constants of cubic SiC were optimized. A method for calculating the stress and strain in SiC films on (100) Si is proposed. It is suggested that the stress and strain expressions and the method of the stress and strain determinations in heterostructures are quite general and may be used for other systems.

  7. Bandgap-customizable germanium using lithographically determined biaxial tensile strain for silicon-compatible optoelectronics.

    PubMed

    Sukhdeo, David S; Nam, Donguk; Kang, Ju-Hyung; Brongersma, Mark L; Saraswat, Krishna C

    2015-06-29

    Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial tensile strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in circular structures patterned within germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into a circular region. Biaxial tensile strains as large as 1.11% are observed by Raman spectroscopy and are further confirmed by photoluminescence measurements, which show enhanced and redshifted light emission from the strained germanium. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different germanium structures to be independently customized in a single mask process.

  8. Realistic micromechanical modeling and simulation of two-phase heterogeneous materials

    NASA Astrophysics Data System (ADS)

    Sreeranganathan, Arun

    This dissertation research focuses on micromechanical modeling and simulations of two-phase heterogeneous materials exhibiting anisotropic and non-uniform microstructures with long-range spatial correlations. Completed work involves development of methodologies for realistic micromechanical analyses of materials using a combination of stereological techniques, two- and three-dimensional digital image processing, and finite element based modeling tools. The methodologies are developed via its applications to two technologically important material systems, namely, discontinuously reinforced aluminum composites containing silicon carbide particles as reinforcement, and boron modified titanium alloys containing in situ formed titanium boride whiskers. Microstructural attributes such as the shape, size, volume fraction, and spatial distribution of the reinforcement phase in these materials were incorporated in the models without any simplifying assumptions. Instrumented indentation was used to determine the constitutive properties of individual microstructural phases. Micromechanical analyses were performed using realistic 2D and 3D models and the results were compared with experimental data. Results indicated that 2D models fail to capture the deformation behavior of these materials and 3D analyses are required for realistic simulations. The effect of clustering of silicon carbide particles and associated porosity on the mechanical response of discontinuously reinforced aluminum composites was investigated using 3D models. Parametric studies were carried out using computer simulated microstructures incorporating realistic microstructural attributes. The intrinsic merit of this research is the development and integration of the required enabling techniques and methodologies for representation, modeling, and simulations of complex geometry of microstructures in two- and three-dimensional space facilitating better understanding of the effects of microstructural geometry

  9. The rabies virus glycoprotein determines the distribution of different rabies virus strains in the brain.

    PubMed

    Yan, Xiuzhen; Mohankumar, Puliyur S; Dietzschold, Bernhard; Schnell, Matthies J; Fu, Zhen F

    2002-08-01

    The contribution of rabies virus (RV) glycoprotein (G) in viral distribution in the brain was examined by immunohistochemistry following stereotaxic inoculation into the rat hippocampus. Viruses used in this study include the highly neuroinvasive challenge virus standard strains (CVS-N2C and CVS-B2C) and the nonneuroinvasive attenuated SN-10 strain, as well as SN-10-derived recombinant viruses expressing the G gene from CVS-N2C (RN2C) or CVS-B2C (RB2C). The distribution of recombinant viruses in the brain was similar to those of the parental viruses from which the G was derived. For example, while CVS-B2C- and RB2C-infected neurons were seen preferentially in the hippocampus, cortex, and hypothalamus, CVS-N2C- and RN2C-infected neurons were preferentially found in the hippocampus, cortex, and thalamus. SN-10 infected efficiently almost all the brain regions. To further study the role of the RV G in virus spreading, we examined the distribution of RV antigen in brains infected with a recombinant RV in which the SN-10 G was replaced with vesicular stomatitis virus (VSV) G (SN-10-VG) was examined. The spreading of SN-10-VG to the cortex and the thalamus was drastically reduced, but the number of infected neurons in hippocampus and hypothalamus, particularly the paraventricular nucleus, was similar to the SN-10 virus. This pattern of spreading resembles that of VSV. Together, our data demonstrate that it is the G protein that determines the distribution pattern of RV in the brain.

  10. Micromechanical Aspects of Hydraulic Fracturing Processes

    NASA Astrophysics Data System (ADS)

    Galindo-torres, S. A.; Behraftar, S.; Scheuermann, A.; Li, L.; Williams, D.

    2014-12-01

    A micromechanical model is developed to simulate the hydraulic fracturing process. The model comprises two key components. Firstly, the solid matrix, assumed as a rock mass with pre-fabricated cracks, is represented by an array of bonded particles simulated by the Discrete Element Model (DEM)[1]. The interaction is ruled by the spheropolyhedra method, which was introduced by the authors previously and has been shown to realistically represent many of the features found in fracturing and communition processes. The second component is the fluid, which is modelled by the Lattice Boltzmann Method (LBM). It was recently coupled with the spheropolyhedra by the authors and validated. An advantage of this coupled LBM-DEM model is the control of many of the parameters of the fracturing fluid, such as its viscosity and the injection rate. To the best of the authors' knowledge this is the first application of such a coupled scheme for studying hydraulic fracturing[2]. In this first implementation, results are presented for a two-dimensional situation. Fig. 1 shows one snapshot of the LBM-DEM coupled simulation for the hydraulic fracturing where the elements with broken bonds can be identified and the fracture geometry quantified. The simulation involves a variation of the underground stress, particularly the difference between the two principal components of the stress tensor, to explore the effect on the fracture path. A second study focuses on the fluid viscosity to examine the effect of the time scales of different injection plans on the fracture geometry. The developed tool and the presented results have important implications for future studies of the hydraulic fracturing process and technology. references 1. Galindo-Torres, S.A., et al., Breaking processes in three-dimensional bonded granular materials with general shapes. Computer Physics Communications, 2012. 183(2): p. 266-277. 2. Galindo-Torres, S.A., A coupled Discrete Element Lattice Boltzmann Method for the

  11. Digital model for X-ray diffraction with application to composition and strain determination in strained InAs/GaSb superlattices

    SciTech Connect

    Meng, Yifei; Kim, Honggyu; Zuo, Jian-Min; Rouviére, Jean-Luc

    2014-07-07

    We propose a digital model for high quality superlattices by including fluctuations in the superlattice periods. The composition and strain profiles are assumed to be coherent and persist throughout the superlattice. Using this model, we have significantly improved the fit with experimental X-ray diffraction data recorded from the nominal InAs/GaSb superlattice. The lattice spacing of individual layers inside the superlattice and the extent of interfacial intermixing are refined by including both (002) and (004) and their satellite peaks in the fitting. For the InAs/GaSb strained layer superlattice, results show: (i) the GaSb-on-InAs interface is chemically sharper than the InAs-on-GaSb interface, (ii) the GaSb layers experience compressive strain with In incorporation, (iii) there are interfacial strain associated with InSb-like bonds in GaSb and GaAs-like bonds in InAs, (iv) Sb substitutes a significant amount of In inside InAs layer near the InAs-on-GaSb interface. For support, we show that the composition profiles determined by X-ray diffraction are in good agreement with those obtained from atom probe tomography measurement. Comparison with the kinetic growth model shows a good agreement in terms of the composition profiles of anions, while the kinetic model underestimates the intermixing of cations.

  12. Design and Implementation of a Micromechanical Silicon Resonant Accelerometer

    PubMed Central

    Huang, Libin; Yang, Hui; Gao, Yang; Zhao, Liye; Liang, Jinxing

    2013-01-01

    The micromechanical silicon resonant accelerometer has attracted considerable attention in the research and development of high-precision MEMS accelerometers because of its output of quasi-digital signals, high sensitivity, high resolution, wide dynamic range, anti-interference capacity and good stability. Because of the mismatching thermal expansion coefficients of silicon and glass, the micromechanical silicon resonant accelerometer based on the Silicon on Glass (SOG) technique is deeply affected by the temperature during the fabrication, packaging and use processes. The thermal stress caused by temperature changes directly affects the frequency output of the accelerometer. Based on the working principle of the micromechanical resonant accelerometer, a special accelerometer structure that reduces the temperature influence on the accelerometer is designed. The accelerometer can greatly reduce the thermal stress caused by high temperatures in the process of fabrication and packaging. Currently, the closed-loop drive circuit is devised based on a phase-locked loop. The unloaded resonant frequencies of the prototype of the micromechanical silicon resonant accelerometer are approximately 31.4 kHz and 31.5 kHz. The scale factor is 66.24003 Hz/g. The scale factor stability is 14.886 ppm, the scale factor repeatability is 23 ppm, the bias stability is 23 μg, the bias repeatability is 170 μg, and the bias temperature coefficient is 0.0734 Hz/°C. PMID:24256978

  13. Design and implementation of a micromechanical silicon resonant accelerometer.

    PubMed

    Huang, Libin; Yang, Hui; Gao, Yang; Zhao, Liye; Liang, Jinxing

    2013-01-01

    The micromechanical silicon resonant accelerometer has attracted considerable attention in the research and development of high-precision MEMS accelerometers because of its output of quasi-digital signals, high sensitivity, high resolution, wide dynamic range, anti-interference capacity and good stability. Because of the mismatching thermal expansion coefficients of silicon and glass, the micromechanical silicon resonant accelerometer based on the Silicon on Glass (SOG) technique is deeply affected by the temperature during the fabrication, packaging and use processes. The thermal stress caused by temperature changes directly affects the frequency output of the accelerometer. Based on the working principle of the micromechanical resonant accelerometer, a special accelerometer structure that reduces the temperature influence on the accelerometer is designed. The accelerometer can greatly reduce the thermal stress caused by high temperatures in the process of fabrication and packaging. Currently, the closed-loop drive circuit is devised based on a phase-locked loop. The unloaded resonant frequencies of the prototype of the micromechanical silicon resonant accelerometer are approximately 31.4 kHz and 31.5 kHz. The scale factor is 66.24003 Hz/g. The scale factor stability is 14.886 ppm, the scale factor repeatability is 23 ppm, the bias stability is 23 μg, the bias repeatability is 170 μg, and the bias temperature coefficient is 0.0734 Hz/°C.

  14. A reusable micromechanical energy storage/quick release system with assembled elastomers

    NASA Astrophysics Data System (ADS)

    Bergbreiter, Sarah; Mahajan, Deepa; Pister, Kristofer S. J.

    2009-05-01

    A reusable, elastomer-based energy storage/quick release system for MEMS has been designed, built and tested. Microrubber bands have been fabricated from silicone using two different methods, laser cut and molded, and assembled into silicon microstructures fabricated in a two-mask silicon-on-insulator (SOI) process. Using silicon hooks and force gauges designed in this process, these microrubber bands have been characterized as to their energy storage potential and efficiency by stretching them with a probe tip. These tests showed recovered energy efficiencies up to 92% at strains over 200% with a maximum stored energy over 19 µJ. In addition, a fully integrated micromechanical energy storage system to both store and release energy has been demonstrated using an electrostatic inchworm motor to stretch the elastomer band and release it. Using the inchworm motor, an estimated 4.9 nJ of energy was stored in the elastomer spring and quickly released.

  15. Simulation of micromechanical behavior of polycrystals: finite elements vs. fast Fourier transforms

    SciTech Connect

    Lebensohn, Ricardo A; Prakash, Arun

    2009-01-01

    In this work, we compare finite element and fast Fourier transform approaches for the prediction of micromechanical behavior of polycrystals. Both approaches are full-field approaches and use the same visco-plastic single crystal constitutive law. We investigate the texture and the heterogeneity of the inter- and intragranular, stress and strain fields obtained from the two models. Additionally, we also look into their computational performance. Two cases - rolling of aluminium and wire drawing of tungsten - are used to evaluate the predictions of the two mode1s. Results from both the models are similar, when large grain distortions do not occur in the polycrystal. The finite element simulations were found to be highly computationally intensive, in comparison to the fast Fourier transform simulations.

  16. Identification of microstructural characteristics in lightweight aggregate concretes by micromechanical modelling including the interfacial transition zone (ITZ)

    SciTech Connect

    Ke, Y.; Ortola, S.; Beaucour, A.L.; Dumontet, H.

    2010-11-15

    An approach which combines both experimental techniques and micromechanical modelling is developed in order to characterise the elastic behaviour of lightweight aggregate concretes (LWAC). More than three hundred LWAC specimens with various lightweight aggregate types (5) of several volume ratios and three different mortar matrices (normal, HP, VHP) are tested. The modelling is based on iterative homogenisation process and includes the ITZ specificities experimentally observed with scanning electron microscopy (SEM). In agreement with experimental measurements, the effects of mix design parameters as well as of the interfacial transition zone (ITZ) on concrete mechanical performances are quantitatively analysed. Confrontations with experimental results allow identifying the elastic moduli of LWA which are difficult to determine experimentally. Whereas the traditional empirical formulas are not sufficiently precise, predictions of LWAC elastic behaviours computed with the micromechanical models appear in good agreement with experimental measurements.

  17. An anisotropic micromechanical-based model for characterizing the magneto-mechanical behavior of NiMnGa alloys

    NASA Astrophysics Data System (ADS)

    Wang, Xingzhe; Li, Fang; Hu, Qiang

    2012-06-01

    As a typical ferromagnetic shape memory alloy (FSMA), NiMnGa alloy at room temperature is a heterogeneous material with martensitic variants and a high magnetic anisotropy property to produce a giant magnetic-induced strain and high frequency response. A theoretical model based on micromechanical and thermodynamic theory is proposed to describe the magneto-mechanical behavior of single-crystal FSMAs during the reorientation process of martensitic variants. It follows the well-established Eshelby equivalent inclusion method and the Mori-Tanaka scheme, and incorporates the influence of the material anisotropy and the variant inclusion morphology on the reorientation of the martensite variants. The modified micromechanical model is further applied to characterize the stress-strain behavior and magnetic-field-induced strain during the martensite variant rearrangement process in a single-crystal NiMnGa rod under applied magnetic field and/or mechanical loading. The simulation results show good agreement with the experimental data. The effects of the material anisotropy and inclusion morphology on the magnetoelastic constitutive behavior of FSMAs are discussed.

  18. Determination of Longwall Mining-Induced Stress Using the Strain Energy Method

    NASA Astrophysics Data System (ADS)

    Rezaei, Mohammad; Hossaini, Mohammad Farouq; Majdi, Abbas

    2015-11-01

    Extraction of the coal seam causes stress redistribution around the mined panel in longwall mining. The weight of bridging strata and strata that cantilevers over the destressed zone is shifted to adjacent gates, pillars, and abutments surrounding the longwall panel. Thus, knowledge of the mining-induced stress is very important to enable accurate design of gate supports and pillar dimensions. In this paper, an analytical model based on the strain energy balance in longwall coal mining is developed to determine the mining-induced stress over gates and pillars. In the proposed model, the height of the destressed zone above the mined panel, total induced stress, abutment angle, vertical component of induced stress, and coefficient of stress concentration over gates and pillars are determined analytically. As a case study, the proposed model is used to determine the coefficient of stress concentration over the gates and pillars in Tabas coal mine of Iran. In order to evaluate the effect of the proposed model's incorporated parameters on the coefficient of stress concentration, a sensitivity analysis is conducted based on the actual data of Tabas coal mine. Also, the proposed model is validated against the in-situ measurement as well as numerical and analytical models with the same boundary conditions. The validation results show that the proposed model is in agreement with the in-situ measurement and numerical model, but has differences compared with the available analytical models. Considering the obtained results, it can be concluded that the proposed analytical model can be used to calculate the mining-induced stress, aiming to reach the optimum design of gate supports and pillar dimensions.

  19. Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity

    PubMed Central

    Schwartz, Allison R.; Potnis, Neha; Timilsina, Sujan; Wilson, Mark; Patané, José; Martins, Joaquim; Minsavage, Gerald V.; Dahlbeck, Douglas; Akhunova, Alina; Almeida, Nalvo; Vallad, Gary E.; Barak, Jeri D.; White, Frank F.; Miller, Sally A.; Ritchie, David; Goss, Erica; Bart, Rebecca S.; Setubal, João C.; Jones, Jeffrey B.; Staskawicz, Brian J.

    2015-01-01

    Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type III effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of 67 Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Xg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type III effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion of AvrBsT and XopQ allows a host range expansion for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors. PMID:26089818

  20. Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity.

    PubMed

    Schwartz, Allison R; Potnis, Neha; Timilsina, Sujan; Wilson, Mark; Patané, José; Martins, Joaquim; Minsavage, Gerald V; Dahlbeck, Douglas; Akhunova, Alina; Almeida, Nalvo; Vallad, Gary E; Barak, Jeri D; White, Frank F; Miller, Sally A; Ritchie, David; Goss, Erica; Bart, Rebecca S; Setubal, João C; Jones, Jeffrey B; Staskawicz, Brian J

    2015-01-01

    Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type III effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of 67 Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Xg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type III effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion of AvrBsT and XopQ allows a host range expansion for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors. PMID:26089818

  1. An Efficient Implementation of the GMC Micromechanics Model for Multi-Phased Materials with Complex Microstructures

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Bednarcyk, Brett A.

    1997-01-01

    An efficient implementation of the generalized method of cells micromechanics model is presented that allows analysis of periodic unidirectional composites characterized by repeating unit cells containing thousands of subcells. The original formulation, given in terms of Hill's strain concentration matrices that relate average subcell strains to the macroscopic strains, is reformulated in terms of the interfacial subcell tractions as the basic unknowns. This is accomplished by expressing the displacement continuity equations in terms of the stresses and then imposing the traction continuity conditions directly. The result is a mixed formulation wherein the unknown interfacial subcell traction components are related to the macroscopic strain components. Because the stress field throughout the repeating unit cell is piece-wise uniform, the imposition of traction continuity conditions directly in the displacement continuity equations, expressed in terms of stresses, substantially reduces the number of unknown subcell traction (and stress) components, and thus the size of the system of equations that must be solved. Further reduction in the size of the system of continuity equations is obtained by separating the normal and shear traction equations in those instances where the individual subcells are, at most, orthotropic. The reformulated version facilitates detailed analysis of the impact of the fiber cross-section geometry and arrangement on the response of multi-phased unidirectional composites with and without evolving damage. Comparison of execution times obtained with the original and reformulated versions of the generalized method of cells demonstrates the new version's efficiency.

  2. Key determinants affecting sheep wool biodegradation directed by a keratinase-producing Bacillus subtilis recombinant strain.

    PubMed

    Zaghloul, Taha I; Embaby, Amira M; Elmahdy, Ahmed R

    2011-02-01

    OVAT (one variable at a time) approach was applied in this study to screen the most important physicochemical key determinants involved in the process of sheep wool biodegradation. The process was directed by a keratinase-producing Bacillus subtilis DB 100 (p5.2) recombinant strain. Data indicate that, sheep wool could be degraded efficiently in cultures incubated at 30°C, with initial pH of 7 with agitation at 150 rpm. Two times autoclaved alkali treated and undefatted chopped sheep wool is more accessible to biodegradation. B. subtilis recombinant cells could utilize sheep wool as a sole source of carbon and nitrogen. Sheep wool-based modified basal medium II, lacking NH₄Cl and yeast extract, could greatly support the growth of these bacterial cells. Sheep wool biodegradation was conducted efficiently in the absence of kanamycin consequently; high stability of the recombinant plasmid (p5.2) represents a great challenge upon scaling up this process. Three key determinants (sheep wool concentration, incubation time and inoculum size) imposing considerable constraints on the process are highlighted. Sheep wool-based tap water medium and sheep wool-based distilled water medium were formulated in this study. High levels of released end products, produced from sheep wool biodegradation are achieved upon using these two sheep wool-based water media. Data indicate that, sheep wool hydrolysate is rich in some amino acids, such as tyrosine, phenylalanine, lysine, proline, isoleucine, leucine, valine, aspartic acid and glutamic acid. Moreover, the resulting sheep wool hydrolysate contains soluble proteins of high and intermediate molecular weights. The present study demonstrates a feasible, cheap, reproducible, efficient and rapid biotechnological approach towards utilization of raw sheep wool waste through a recombinant bacterium.

  3. Computational micromechanics analysis of electron hopping and interfacial damage induced piezoresistive response in carbon nanotube-polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Chaurasia, A. K.; Ren, X.; Seidel, G. D.

    2014-07-01

    Carbon nanotube (CNT)-polymer nanocomposites have been observed to exhibit an effective macroscale piezoresistive response, i.e., change in macroscale resistivity when subjected to applied deformation. The macroscale piezoresistive response of CNT-polymer nanocomposites leads to deformation/strain sensing capabilities. It is believed that the nanoscale phenomenon of electron hopping is the major driving force behind the observed macroscale piezoresistivity of such nanocomposites. Additionally, CNT-polymer nanocomposites provide damage sensing capabilities because of local changes in electron hopping pathways at the nanoscale because of initiation/evolution of damage. The primary focus of the current work is to explore the effect of interfacial separation and damage at the nanoscale CNT-polymer interface on the effective macroscale piezoresistive response. Interfacial separation and damage are allowed to evolve at the CNT-polymer interface through coupled electromechanical cohesive zones, within a finite element based computational micromechanics framework, resulting in electron hopping based current density across the separated CNT-polymer interface. The macroscale effective material properties and gauge factors are evaluated using micromechanics techniques based on electrostatic energy equivalence. The impact of the electron hopping mechanism, nanoscale interface separation and damage evolution on the effective nanocomposite electrostatic and piezoresistive response is studied in comparison with the perfectly bonded interface. The effective electrostatic/piezoresistive response for the perfectly bonded interface is obtained based on a computational micromechanics model developed in the authors’ earlier work. It is observed that the macroscale effective gauge factors are highly sensitive to strain induced formation/disruption of electron hopping pathways, interface separation and the initiation/evolution of interfacial damage.

  4. Micromechanical properties of veneer luting resins after curing through ceramics.

    PubMed

    Oztürk, Elif; Hickel, Reinhard; Bolay, Sükran; Ilie, Nicoleta

    2012-02-01

    The aim of this study was to assess the performance of light-cured luting resin after curing under the ceramic restoration in comparison to dual-cured luting resin, by evaluating the micromechanical properties. Two hundred seventy thin luting composite films of ca. 170 μm in thickness were prepared by using two light-cured luting resins (Variolink Veneer, Ivoclar Vivadent; RelyX Veneer, 3M ESPE) and a dual-cured luting resin (Variolink II, Ivoclar Vivadent). The composites were cured by using a LED-unit (Bluephase®, Ivoclar Vivadent) with three different curing times (10, 20, and 30 s) under two ceramics (IPS e.max Press, Ivoclar Vivadent; IPS Empress® CAD, Ivoclar Vivadent) of different thicknesses (0, 0.75, and 2 mm). Forty-five groups were included, each containing six thin films. The samples were stored after curing for 24 h at 37°C by maintaining moisture conditions with distilled water. Micromechanical properties of the composites were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). For each sample, ten indentations were made, thus totalizing 60 measurements per group. Micromechanical properties of the luting resins were statistically analyzed (SPSS 17.0). Significant differences were observed between the micromechanical properties of the luting resins (p < 0.05). Variolink II showed the highest values in modulus of elasticity (E = 11 ± 0.5)* and Vickers hardness (HV = 48.2 ± 3.2)* and the lowest values in creep (Cr = 4.3 ± 0.1)* and elastic-plastic deformation (We/Wtot = 38.6 ± 0.7)* followed by RelyX Veneer (E = 6.9 ± 0.3, HV = 33 ± 2.5, Cr = 4.6 ± 0.2, We/Wtot = 41.8 ± 1.0)* and Variolink Veneer (E = 4.4 ± 0.4, HV = 20.1 ± 2.6, Cr = 5 ± 0.2, We/Wtot = 43.7 ± 1.3)*. Dual-cured luting resin expressed higher values in the micro-mechanical properties compared to the light-cured luting resins. The effect of luting resin type on the micromechanical properties of the luting resins was higher than the effect of

  5. Micromechanical properties of intercalated compounds of graphite oxide with dodecahydro- closо-dodecaboric acid

    NASA Astrophysics Data System (ADS)

    Karpenko, A. A.; Saldin, V. I.

    2016-08-01

    The micromechanical properties (Young's modulus, deformation, and adhesion) of the intercalated compound of graphite oxide with dodecahydro- closo-dodecaboric acid were studied by atomic force microscopy, transmission electron microscopy, and Raman spectroscopy and compared with the same characteristics of the starting graphite oxide. The significant difference in the micromechanical properties of the materials under study is dictated by differences in the topography and properties of their film surface, which, in turn, can be determined by their chemical composition. The introduction of dodecahydro- closo-dodecaboric acid in the interplanar space of graphite oxide affects the structuring of the latter. A considerable increase in the adhesion of the intercalated compound relative to that of oxide graphite is explained by high adhesive properties of the introduced acid, the Young's modulus of graphite oxide being higher than that of the intercalated compound. This was attributed to the high hydrophilicity of dodecahydro- closo-dodecaboric acid and the difficulty of water removal from the interplanar space; water plasticizes the material, which becomes softer than graphite oxide. The difference in the structure of the coating of the intercalated compounds and the starting graphite oxide was found to be also reflected by their Raman spectra, namely, by the increased intensity of the D line with the preserved position of the G line, which points to the impurity nature of the intercalate and the unchanged hexagonal lattice of graphite.

  6. Applicability of a Micromechanics Model Based on Actual Microstructure for Failure Prediction of DP Steels

    SciTech Connect

    Choi, Kyoo Sil; Soulami, Ayoub; Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2009-04-01

    In this paper, various micromechanics models based on actual microstructures of DP steels are examined in order to determine the reasonable range of martensite volume fraction where the methodology described in this study can be applied. For this purpose, various micromechanics-based finite element models are first created based on the actual microstructures of DP steels with different martensite volume fractions. These models are, then, used to investigate the influence of ductility of the constituent ferrite and martensite phases and also the influence of voids in the ferrite phase on the overall ductility of DP steels. The computational results indicate that there is a range of martensite volume fraction where the phase inhomogeneity between the ferrite and martensite phases has dominant effect on the overall ductility of DP steels, defeating the influence of the ductility of each phase and the voids in the ferrite phase, and that this phase inhomogeneity dominant region includes the range of marteniste volume fraction between 15% and 40%. Therefore, the methodology, adopted in this study, may be applied to DP steels within the phase inhomogeneity dominant region in tailoring the DP steel design for its intended purpose and desired properties.

  7. Micromechanical properties of intercalated compounds of graphite oxide with dodecahydro- closo-dodecaboric acid

    NASA Astrophysics Data System (ADS)

    Karpenko, A. A.; Saldin, V. I.

    2016-08-01

    The micromechanical properties (Young's modulus, deformation, and adhesion) of the intercalated compound of graphite oxide with dodecahydro- closo-dodecaboric acid were studied by atomic force microscopy, transmission electron microscopy, and Raman spectroscopy and compared with the same characteristics of the starting graphite oxide. The significant difference in the micromechanical properties of the materials under study is dictated by differences in the topography and properties of their film surface, which, in turn, can be determined by their chemical composition. The introduction of dodecahydro- closo-dodecaboric acid in the interplanar space of graphite oxide affects the structuring of the latter. A considerable increase in the adhesion of the intercalated compound relative to that of oxide graphite is explained by high adhesive properties of the introduced acid, the Young's modulus of graphite oxide being higher than that of the intercalated compound. This was attributed to the high hydrophilicity of dodecahydro- closo-dodecaboric acid and the difficulty of water removal from the interplanar space; water plasticizes the material, which becomes softer than graphite oxide. The difference in the structure of the coating of the intercalated compounds and the starting graphite oxide was found to be also reflected by their Raman spectra, namely, by the increased intensity of the D line with the preserved position of the G line, which points to the impurity nature of the intercalate and the unchanged hexagonal lattice of graphite.

  8. Draft Genome Sequence of Neisseria gonorrhoeae Strain NG_869 with Penicillin, Tetracycline and Ciprofloxacin Resistance Determinants Isolated from Malaysia.

    PubMed

    Ang, Geik Yong; Yu, Choo Yee; Yong, Delicia Ann; Cheong, Yuet Meng; Yin, Wai-Fong; Chan, Kok-Gan

    2016-06-01

    Gonorrhea is a sexually transmitted infection caused by Neisseria gonorrhoeae and the increasing reports of multidrug-resistant gonococcal isolates are a global public health care concern. Herein, we report the genome sequence of N. gonorrhoeae strain NG_869 isolated from Malaysia which may provide insights into the drug resistance determinants in gonococcal bacteria. PMID:27570316

  9. Molecular cloning and sequence determination of DA strain of Theiler's murine encephalomyelitis viruses.

    PubMed

    Ohara, Y; Stein, S; Fu, J L; Stillman, L; Klaman, L; Roos, R P

    1988-05-01

    Theiler's murine encephalomyelitis viruses (TMEV) belong to the Picornaviridae, and are divided into two subgroups. TO subgroup strains produce a persistent demyelinating central nervous system infection in mice, while GDVII subgroup strains cause acute polioencephalomyelitis. We generated three overlapping clones of the genome of DA strain, a member of TO subgroup. Sequence analysis revealed that the genome is 8093 nucleotides long with a poly(A) tail. The 5' noncoding region stretches from nucleotides 1 to 1065 and lacks a poly(C) tract. The open reading frame stretches from 1066 to 7968 and encodes 2301 amino acids. DA strain sequence is more closely related to members of the Cardiovirus genus than to members of other Picornavirus genera. Comparison with sequence of BeAn strain, another TO subgroup strain, showed that the P1 area has the greatest number of differences, while the noncoding regions are more well-conserved. The three overlapping clones will be important in recombinant infectious cDNA studies between strains of both subgroups.

  10. Determination of the strain rate dependent thermal softening behavior of thermoplastic materials for crash simulations

    NASA Astrophysics Data System (ADS)

    Hopmann, Christian; Klein, Jan; Schöngart, Maximilian

    2016-03-01

    Thermoplastic materials are increasingly used as a light weight replacement for metal, especially in automotive applications. Typical examples are frontends and bumpers. The loads on these structures are very often impulsive, for example in a crash situation. A high rate of loading causes a high strain rate in the material which has a major impact on the mechanical behavior of thermoplastic materials. The stiffness as well as the rigidity of polymers increases to higher strain rates. The increase of the mechanical properties is superimposed at higher rates of loading by another effect which works reducing on stiffness and rigidity, the increase of temperature caused by plastic deformation. The mechanical behavior of thermoplastic materials is influenced by temperature opposing to strain rate. The stiffness and rigidity are decreased to higher values of temperature. The effect of thermal softening on thermoplastic materials is investigated at IKV. For this purpose high-speed tensile tests are performed on a blend, consisting of Polybutylenterephthalate (PBT) and Polycarbonate (PC). In preliminary investigations the effects of strain rate on the thermomechanical behavior of thermoplastic materials was studied by different authors. Tensile impact as well as split Hopkinson pressure bar (SHPB) tests were conducted in combination with high-speed temperature measurement, though, the authors struggled especially with temperature measurement. This paper presents an approach which uses high-speed strain measurement to transpire the link between strain, strain rate and thermal softening as well as the interdependency between strain hardening and thermal softening. The results show a superimposition of strain hardening and thermal softening, which is consistent to preliminary investigations. The advantage of the presented research is that the results can be used to calibrate damage and material models to perform mechanical simulations using Finite Element Analysis.

  11. Determining displacement and strain maps immune from aliasing effect with the grid method

    NASA Astrophysics Data System (ADS)

    Sur, Frédéric; Blaysat, Benoît; Grédiac, Michel

    2016-11-01

    Spatial aliasing may affect methods based on grid image processing to retrieve displacement and strain maps in experimental mechanics. Such methods aim at estimating these maps on the surface of a specimen subjected to a loading test. Aliasing, which is often not noticeable to the naked eye in the grid images, may give spurious fringes in the strain maps. This paper presents an analysis of aliasing in this context and provides the reader with simple guidelines to minimize the effect of aliasing on strain maps extracted from grid images.

  12. Local strain distributions in partially recrystallized copper determined by in situ tensile investigation

    NASA Astrophysics Data System (ADS)

    Lin, F. X.; Ubhi, H. S.; Petrenec, M.; Zhang, Y. B.; Jensen, D. Juul

    2015-04-01

    A partially recrystallized copper sample produced by cold-rolling and annealing was deformed in situ by uniaxial tension in a scanning electron microscope, and electron backscatter diffraction data were collected before and after deformation to certain strains. The local strain distributions are quantified using digital image correlation. Distributions of the normal strain along the tensile direction (εxx) are shown in this paper. The recrystallized grains are found to deform more than the remaining unrecrystallized matrix. When εxx is averaged along lines perpendicular to the tensile direction, significant variation are observed, which may be related to the local recrystallized volume fraction.

  13. The nano-epsilon dot method for strain rate viscoelastic characterisation of soft biomaterials by spherical nano-indentation.

    PubMed

    Mattei, G; Gruca, G; Rijnveld, N; Ahluwalia, A

    2015-10-01

    Nano-indentation is widely used for probing the micromechanical properties of materials. Based on the indentation of surfaces using probes with a well-defined geometry, the elastic and viscoelastic constants of materials can be determined by relating indenter geometry and measured load and displacement to parameters which represent stress and deformation. Here we describe a method to derive the viscoelastic properties of soft hydrated materials at the micro-scale using constant strain rates and stress-free initial conditions. Using a new self-consistent definition of indentation stress and strain and corresponding unique depth-independent expression for indentation strain rate, the epsilon dot method, which is suitable for bulk compression testing, is transformed to nano-indentation. We demonstrate how two materials can be tested with a displacement controlled commercial nano-indentor using the nano-espilon dot method (nano-ε̇M) to give values of instantaneous and equilibrium elastic moduli and time constants with high precision. As samples are tested in stress-free initial conditions, the nano-ε̇M could be useful for characterising the micro-mechanical behaviour of soft materials such as hydrogels and biological tissues at cell length scales. PMID:26143307

  14. The nano-epsilon dot method for strain rate viscoelastic characterisation of soft biomaterials by spherical nano-indentation.

    PubMed

    Mattei, G; Gruca, G; Rijnveld, N; Ahluwalia, A

    2015-10-01

    Nano-indentation is widely used for probing the micromechanical properties of materials. Based on the indentation of surfaces using probes with a well-defined geometry, the elastic and viscoelastic constants of materials can be determined by relating indenter geometry and measured load and displacement to parameters which represent stress and deformation. Here we describe a method to derive the viscoelastic properties of soft hydrated materials at the micro-scale using constant strain rates and stress-free initial conditions. Using a new self-consistent definition of indentation stress and strain and corresponding unique depth-independent expression for indentation strain rate, the epsilon dot method, which is suitable for bulk compression testing, is transformed to nano-indentation. We demonstrate how two materials can be tested with a displacement controlled commercial nano-indentor using the nano-espilon dot method (nano-ε̇M) to give values of instantaneous and equilibrium elastic moduli and time constants with high precision. As samples are tested in stress-free initial conditions, the nano-ε̇M could be useful for characterising the micro-mechanical behaviour of soft materials such as hydrogels and biological tissues at cell length scales.

  15. Smart materials: strain sensing and stress determination by means of nanotube sensing systems, composites, and devices

    NASA Technical Reports Server (NTRS)

    Barrera, Enrique V. (Inventor); Nagarajaiah, Satish (Inventor); Dharap, Prasad (Inventor); Zhiling, Li (Inventor); Kim, Jong Dae (Inventor)

    2010-01-01

    The present invention is directed toward devices comprising carbon nanotubes that are capable of detecting displacement, impact, stress, and/or strain in materials, methods of making such devices, methods for sensing/detecting/monitoring displacement, impact, stress, and/or strain via carbon nanotubes, and various applications for such methods and devices. The devices and methods of the present invention all rely on mechanically-induced electronic perturbations within the carbon nanotubes to detect and quantify such stress/strain. Such detection and quantification can rely on techniques which include, but are not limited to, electrical conductivity/conductance and/or resistivity/resistance detection/measurements, thermal conductivity detection/measurements, electroluminescence detection/measurements, photoluminescence detection/measurements, and combinations thereof. All such techniques rely on an understanding of how such properties change in response to mechanical stress and/or strain.

  16. Determination of forming limit diagram for tube hydroforming based on the strain rate change criterion

    NASA Astrophysics Data System (ADS)

    Hu, Guolin; Yang, Lianfa; Liu, Jianwei

    2013-12-01

    Tube hydroforming (THF) is an attractive manufacturing process in automotive industry, and forming limit diagram (FLD) is a significant strategy to assess the formability of THF. In present study, a method of predicting the FLD for THF is developed based on finite element (FE) simulation with the strain rate change criterion (SRCC) as a failure criteria of identify localized necking. FE simulations under various linear loading paths are carried out to obtain the strain information. The equivalent strain rates at potential fracturing and its adjacent nodes are calculated and utilized with SRCC to distinguish the onset of fracturing in FE simulation. The fracture strains at the two nodes under various linear loading paths are abstracted for establishing FLD. Tube hydo-bulging experiments under the linear loading paths have been conducted to verify the prediction method of FLD, and the results show that this prediction method bears good agreement with experimental data.

  17. Residual strain gradient determination in metal matrix composites by synchrotron X-ray energy dispersive diffraction

    NASA Technical Reports Server (NTRS)

    Kuntz, Todd A.; Wadley, Haydn N. G.; Black, David R.

    1993-01-01

    An X-ray technique for the measurement of internal residual strain gradients near the continuous reinforcements of metal matrix composites has been investigated. The technique utilizes high intensity white X-ray radiation from a synchrotron radiation source to obtain energy spectra from small (0.001 cu mm) volumes deep within composite samples. The viability of the technique was tested using a model system with 800 micron Al203 fibers and a commercial purity titanium matrix. Good agreement was observed between the measured residual radial and hoop strain gradients and those estimated from a simple elastic concentric cylinders model. The technique was then used to assess the strains near (SCS-6) silicon carbide fibers in a Ti-14Al-21Nb matrix after consolidation processing. Reasonable agreement between measured and calculated strains was seen provided the probe volume was located 50 microns or more from the fiber/matrix interface.

  18. Micromechanical Model of a Surrogate for Collagenous Soft Tissues: Development, Validation and Analysis of Mesoscale Size Effects

    PubMed Central

    Reese, Shawn P.; Ellis, Benjamin J.; Weiss, Jeffrey A.

    2013-01-01

    Aligned, collagenous tissues such as tendons and ligaments are composed primarily of water and type I collagen, organized hierarchically into nanoscale fibrils, microscale fibers and mesoscale fascicles. Force transfer across scales is complex and poorly understood. Since innervation, the vasculature, damage mechanisms and mechanotransduction occur at the microscale and mesoscale, understanding multiscale interactions is of high importance. This study used a physical model in combination with a computational model to isolate and examine the mechanisms of force transfer between scales. A collagen-based surrogate served as the physical model. The surrogate consisted of extruded collagen fibers embedded within a collagen gel matrix. A micromechanical finite element model of the surrogate was validated using tensile test data that was recorded using a custom tensile testing device mounted on a confocal microscope. Results demonstrated that the experimentally measured macroscale strain was not representative of the microscale strain, which was highly inhomogeneous. The micromechanical model, in combination with a macroscopic continuum model, revealed that the microscale inhomogeneity resulted from size effects in the presence of a constrained boundary. A sensitivity study indicated that significant scale effects would be present over a range of physiologically relevant inter-fiber spacing values and matrix material properties. The results indicate that the traditional continuum assumption is not valid for describing the macroscale behavior of the surrogate, and that boundary-induced size effects are present. PMID:23400805

  19. Micromechanical model of a surrogate for collagenous soft tissues: development, validation and analysis of mesoscale size effects.

    PubMed

    Reese, Shawn P; Ellis, Benjamin J; Weiss, Jeffrey A

    2013-11-01

    Aligned, collagenous tissues such as tendons and ligaments are composed primarily of water and type I collagen, organized hierarchically into nanoscale fibrils, microscale fibers and mesoscale fascicles. Force transfer across scales is complex and poorly understood. Since innervation, the vasculature, damage mechanisms and mechanotransduction occur at the microscale and mesoscale, understanding multiscale interactions is of high importance. This study used a physical model in combination with a computational model to isolate and examine the mechanisms of force transfer between scales. A collagen-based surrogate served as the physical model. The surrogate consisted of extruded collagen fibers embedded within a collagen gel matrix. A micromechanical finite element model of the surrogate was validated using tensile test data that were recorded using a custom tensile testing device mounted on a confocal microscope. Results demonstrated that the experimentally measured macroscale strain was not representative of the microscale strain, which was highly inhomogeneous. The micromechanical model, in combination with a macroscopic continuum model, revealed that the microscale inhomogeneity resulted from size effects in the presence of a constrained boundary. A sensitivity study indicated that significant scale effects would be present over a range of physiologically relevant inter-fiber spacing values and matrix material properties. The results indicate that the traditional continuum assumption is not valid for describing the macroscale behavior of the surrogate and that boundary-induced size effects are present.

  20. Nonlinear Visco-Elastic Response of Composites via Micro-Mechanical Models

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.; Sridharan, Srinivasan

    2005-01-01

    Micro-mechanical models for a study of nonlinear visco-elastic response of composite laminae are developed and their performance compared. A single integral constitutive law proposed by Schapery and subsequently generalized to multi-axial states of stress is utilized in the study for the matrix material. This is used in conjunction with a computationally facile scheme in which hereditary strains are computed using a recursive relation suggested by Henriksen. Composite response is studied using two competing micro-models, viz. a simplified Square Cell Model (SSCM) and a Finite Element based self-consistent Cylindrical Model (FECM). The algorithm is developed assuming that the material response computations are carried out in a module attached to a general purpose finite element program used for composite structural analysis. It is shown that the SSCM as used in investigations of material nonlinearity can involve significant errors in the prediction of transverse Young's modulus and shear modulus. The errors in the elastic strains thus predicted are of the same order of magnitude as the creep strains accruing due to visco-elasticity. The FECM on the other hand does appear to perform better both in the prediction of elastic constants and the study of creep response.

  1. Microstructural and micromechanical characterization of IN718 theta shaped specimens built with electron beam melting

    DOE PAGESBeta

    Cakmak, Ercan; Kirka, Michael M.; Watkins, Thomas R.; Cooper, Ryan C.; An, Ke; Choo, Hahn; Wu, Wei; Dehoff, Ryan R.; Babu, Sudarsanam S.

    2016-02-23

    Theta-shaped specimens were additively manufactured out of Inconel 718 powders using an electron beam melting technique, as a model complex load bearing structure. We employed two different build strategies; producing two sets of specimens. Microstructural and micro-mechanical characterizations were performed using electron back-scatter, synchrotron x-ray and in-situ neutron diffraction techniques. In particular, the cross-members of the specimens were the focus of the synchrotron x-ray and in-situ neutron diffraction measurements. The build strategies employed resulted in the formation of distinct microstructures and crystallographic textures, signifying the importance of build-parameter manipulation for microstructural optimization. Large strain anisotropy of the different lattice planesmore » was observed during in-situ loading. Texture was concluded to have a distinct effect upon both the axial and transverse strain responses of the cross-members. In particular, the (200), (220) and (420) transverse lattice strains all showed unexpected overlapping trends in both builds. This was related to the strong {200} textures along the build/loading direction, providing agreement between the experimental and calculated results.« less

  2. Application of micromechanics to the characterization of mortar by ultrasound.

    PubMed

    Hernández, M G; Anaya, J J; Izquierdo, M A G; Ullate, L G

    2002-05-01

    Mechanical properties of concrete and mortar structures can be estimated by ultrasonic non-destructive testing. When the ultrasonic velocity is known, there are standardized methods based on considering the concrete a homogeneous material. Cement composites, however, are heterogeneous and porous, and have a negative effect on the mechanical properties of structures. This work studies the impact of porosity on mechanical properties by considering concrete a multiphase material. A micromechanical model is applied in which the material is considered to consist of two phases: a solid matrix and pores. From this method, a set of expressions is obtained that relates the acoustic velocity and Young's modulus of mortar. Experimental work is based on non-destructive and destructive procedures over mortar samples whose porosity is varied. A comparison is drawn between micromechanical and standard methods, showing positive results for the method here proposed.

  3. Computational methods for coupling microstructural and micromechanical materials response simulations

    SciTech Connect

    HOLM,ELIZABETH A.; BATTAILE,CORBETT C.; BUCHHEIT,THOMAS E.; FANG,HUEI ELIOT; RINTOUL,MARK DANIEL; VEDULA,VENKATA R.; GLASS,S. JILL; KNOROVSKY,GERALD A.; NEILSEN,MICHAEL K.; WELLMAN,GERALD W.; SULSKY,DEBORAH; SHEN,YU-LIN; SCHREYER,H. BUCK

    2000-04-01

    Computational materials simulations have traditionally focused on individual phenomena: grain growth, crack propagation, plastic flow, etc. However, real materials behavior results from a complex interplay between phenomena. In this project, the authors explored methods for coupling mesoscale simulations of microstructural evolution and micromechanical response. In one case, massively parallel (MP) simulations for grain evolution and microcracking in alumina stronglink materials were dynamically coupled. In the other, codes for domain coarsening and plastic deformation in CuSi braze alloys were iteratively linked. this program provided the first comparison of two promising ways to integrate mesoscale computer codes. Coupled microstructural/micromechanical codes were applied to experimentally observed microstructures for the first time. In addition to the coupled codes, this project developed a suite of new computational capabilities (PARGRAIN, GLAD, OOF, MPM, polycrystal plasticity, front tracking). The problem of plasticity length scale in continuum calculations was recognized and a solution strategy was developed. The simulations were experimentally validated on stockpile materials.

  4. Thermally induced micromechanical stresses in ceramic/ceramic composites

    SciTech Connect

    Li, Zhuang; Bradt, R.C.

    1992-11-01

    The internal micromechanical stresses which develop in ceramic-ceramic composites as a consequence of temperature changes and thermoelastic property differences between the reinforcing and matrix phases are addressed by the Eshelby method. Results for two whisker reinforced ceramic matrix composites and for quartz particles in porcelain are discussed. It is concluded that the stresses which develop in the second phase reinforcing inclusions are quite substantial (GPa-levels) and may be highly anisotropic in character. These stresses are additive to the macroscopic thermal stresses from temperature gradients which are encountered during heating and cooling, and also to externally apphed mechanical stresses (loads). These micromechanical stresses are expected to be highly significant for thermal cycling fatigue and other failure processes.

  5. Micromechanical characterization of nonlinear behavior of advanced polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.; Chen, J. L.; Sun, C. T.

    1994-01-01

    Due to the presence of curing stresses and oriented crystalline structures in the matrix of polymer matrix fiber composites, the in situ nonlinear properties of the matrix are expected to be rather different from those of the bulk resin. A plane stress micromechanical model was developed to retrieve the in situ elastic-plastic properties of Narmco 5260 and Amoco 8320 matrices from measured elastic-plastic properties of IM7/5260 and IM7/8320 advance composites. In the micromechanical model, the fiber was assumed to be orthotropically elastic and the matrix to be orthotropic in elastic and plastic properties. The results indicate that both in situ elastic and plastic properties of the matrices are orthotropic.

  6. Using dissipative particle dynamics to model micromechanics of responsive hydrogels

    NASA Astrophysics Data System (ADS)

    Alexeev, Alexander; Nikolov, Svetoslav; Fernandez de Las Nieves, Alberto

    2015-03-01

    The ability of responsive hydrogels to undergo complex and reversible shape transformations in response to external stimuli such as temperature, magnetic/electric fields, pH levels, and light intensity has made them the material of choice for tissue scaffolding, drug delivery, bio-adhesive, bio-sensing, and micro-sorting applications. The complex micromechanics and kinetics of these responsive networks however, currently hinders developments in the aforementioned areas. In order to better understand the mechanical properties of these systems and how they change during the volume transition we have developed a dissipative particle dynamics (DPD) model for responsive polymer networks. We use this model to examine the impact of the Flory-Huggins parameter on the bulk and shear moduli. In this fashion we evaluate how environmental factors can affect the micromechanical properties of these networks. Support from NSF CAREER Award (DMR-1255288) is gratefully acknowledged.

  7. Electromagnetic and nuclear radiation detector using micromechanical sensors

    DOEpatents

    Thundat, Thomas G.; Warmack, Robert J.; Wachter, Eric A.

    2000-01-01

    Electromagnetic and nuclear radiation is detected by micromechanical sensors that can be coated with various interactive materials. As the micromechanical sensors absorb radiation, the sensors bend and/or undergo a shift in resonance characteristics. The bending and resonance changes are detected with high sensitivity by any of several detection methods including optical, capacitive, and piezoresistive methods. Wide bands of the electromagnetic spectrum can be imaged with picoJoule sensitivity, and specific absorptive coatings can be used for selective sensitivity in specific wavelength bands. Microcantilevers coated with optical cross-linking polymers are useful as integrating optical radiation dosimeters. Nuclear radiation dosimetry is possible by fabricating cantilevers from materials that are sensitive to various nuclear particles or radiation. Upon exposure to radiation, the cantilever bends due to stress and its resonance frequency shifts due to changes in elastic properties, based on cantilever shape and properties of the coating.

  8. EDITORIAL: The 18th European Workshop on Micromechanics (MME 07)

    NASA Astrophysics Data System (ADS)

    Correia, J. H.

    2008-06-01

    This special issue of Journal of Micromechanics and Microengineering is devoted to the 18th European Workshop on Micromechanics (MME 07), which took place at the University of Minho, Guimarães, Portugal from 16-18 September 2007. Since the first workshop at the University of Twente in 1989 the field of micromechanics has grown substantially and new fields have been added: optics, RF, biomedical, chemistry, and in recent years the emergence of nanotechnology. This year an extensive programme was scheduled with contributions from new materials research to new manufacturing techniques. In addition, the invited speakers presented a review of the state-of-the-art in several main trends in current research, with the focus on micro/nanosystems in the ICT Work Programme in EC FP7. As ever, the two day workshop was attended by delegates from all over Europe, the USA, Brazil, Egypt, Japan and Canada. A total of 96 papers were accepted for presentation and there were a further five keynote presentations. The workshop provides a forum for young researchers to learn about new experimental methods and to enhance their knowledge of the field. This special issue presents a selection of 17 of the best papers from the workshop. The papers highlight fluidic and optical devices, energy scavenging microsystems, neural probe arrays and microtechnology fabrication techniques. All the papers went through the regular reviewing procedure of IOP Publishing, and I am grateful to all the referees for their excellent work. I would also like to extend my thanks to Professor Robert Puers for advice on the final selection of papers and to Ian Forbes of IOP Publishing for managing the entire process. My thanks also go to the editorial staff of Journal of Micromechanics and Microengineering. I believe that this special issue will provide a good overview of the topics presented at the workshop and I hope you enjoy reading it.

  9. Host Determinants of Prion Strain Diversity Independent of Prion Protein Genotype

    PubMed Central

    Crowell, Jenna; Hughson, Andrew; Caughey, Byron

    2015-01-01

    ABSTRACT Phenotypic diversity in prion diseases can be specified by prion strains in which biological traits are propagated through an epigenetic mechanism mediated by distinct PrPSc conformations. We investigated the role of host-dependent factors on phenotypic diversity of chronic wasting disease (CWD) in different host species that express the same prion protein gene (Prnp). Two CWD strains that have distinct biological, biochemical, and pathological features were identified in transgenic mice that express the Syrian golden hamster (SGH) Prnp. The CKY strain of CWD had a shorter incubation period than the WST strain of CWD, but after transmission to SGH, the incubation period of CKY CWD was ∼150 days longer than WST CWD. Limited proteinase K digestion revealed strain-specific PrPSc polypeptide patterns that were maintained in both hosts, but the solubility and conformational stability of PrPSc differed for the CWD strains in a host-dependent manner. WST CWD produced PrPSc amyloid plaques in the brain of the SGH that were partially insoluble and stable at a high concentration of protein denaturant. However, in transgenic mice, PrPSc from WST CWD did not assemble into plaques, was highly soluble, and had low conformational stability. Similar studies using the HY and DY strains of transmissible mink encephalopathy resulted in minor differences in prion biological and PrPSc properties between transgenic mice and SGH. These findings indicate that host-specific pathways that are independent of Prnp can alter the PrPSc conformation of certain prion strains, leading to changes in the biophysical properties of PrPSc, neuropathology, and clinical prion disease. IMPORTANCE Prions are misfolded pathogenic proteins that cause neurodegeneration in humans and animals. Transmissible prion diseases exhibit a spectrum of disease phenotypes and the basis of this diversity is encoded in the structure of the pathogenic prion protein and propagated by an epigenetic mechanism. In

  10. Micromechanics and Piezo Enhancements of HyperSizer

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Bednarcyk, Brett A.; Yarrington, Phillip; Collier, Craig S.

    2006-01-01

    The commercial HyperSizer aerospace-composite-material-structure-sizing software has been enhanced by incorporating capabilities for representing coupled thermal, piezoelectric, and piezomagnetic effects on the levels of plies, laminates, and stiffened panels. This enhancement is based on a formulation similar to that of the pre-existing HyperSizer capability for representing thermal effects. As a result of this enhancement, the electric and/or magnetic response of a material or structure to a mechanical or thermal load, or its mechanical response to an applied electric or magnetic field can be predicted. In another major enhancement, a capability for representing micromechanical effects has been added by establishment of a linkage between HyperSizer and Glenn Research Center s Micromechanics Analysis Code With Generalized Method of Cells (MAC/GMC) computer program, which was described in several prior NASA Tech Briefs articles. The linkage enables Hyper- Sizer to localize to the fiber and matrix level rather than only to the ply level, making it possible to predict local failures and to predict properties of plies from those of the component fiber and matrix materials. Advanced graphical user interfaces and database structures have been developed to support the new HyperSizer micromechanics capabilities.

  11. Continuum and micromechanics treatment of constraint in fracture

    SciTech Connect

    Dodds, R.H. Jr.; Shih, C.F.; Anderson, T.L.

    1993-07-01

    Two complementary methodologies are described to quantify the effects of crack-tip stress triaxiality (constraint) on the macroscopic measures of elastic-plastic fracture toughness, J and Crack-Tip Opening Displacement (CTOD). In the continuum mechanics methodology, two parameters, J and Q, suffice to characterize the full range of near-tip environments at the onset of fracture. A micromechanics methodology is described which predicts the toughness locus using crack-tip stress fields and critical J-values from a few fracture toughness tests. A robust micromechanics model for cleavage fracture has evolved from the observations of a strong, spatial self-similarity of crack-tip principal stresses under increased loading and across different fracture specimens. This report explores the fundamental concepts of the J-Q description of crack-tip fields, the fracture toughness locus and micromechanics approaches to predict the variability of macroscopic fracture toughness with constraint under elastic-plastic conditions. Computational results are presented for a surface cracked plate containing a 6:1 semi-elliptical, a = t/4 flaw subjected to remote uniaxial and biaxial tension.

  12. A micromechanical study of residual stresses in functionally graded materials

    SciTech Connect

    Dao, M.; Gu, P.; Maewal, A.; Asaro, R.J.

    1997-08-01

    A physically based computational micromechanics model is developed to study random and discrete microstructures in functionally graded materials (FGMs). The influences of discrete microstructure on residual stress distributions at grain size level are examined with respect to material gradient and FGM volume percentage (within a ceramic-FGM-metal three-layer structure). Both thermoelastic and thermoplastic deformation are considered, and the plastic behavior of metal grains is modeled at the single crystal level using crystal plasticity theory. The results are compared with those obtained using a continuous model which does not consider the microstructural randomness and discreteness. In an averaged sense both the micromechanics model and the continuous model give practically the same macroscopic stresses; whereas the discrete micromechanics model predicts fairly high residual stress concentrations at the grain size level (i.e., higher than 700 MPa in 5--6 vol% FGM grains) with only a 300 C temperature drop in a Ni-Al{sub 2}O{sub 3} FGM system. Statistical analysis shows that the residual stress concentrations are insensitive to material gradient and FGM volume percentage. The need to consider microstructural details in FGM microstructures is evident. The results obtained provide some insights for improving the reliability of FGMs against fracture and delamination.

  13. Mouse chromosome 11 harbors genetic determinants of hippocampal strain-specific nicotinic receptor expression.

    PubMed

    Rogers, Scott W; Weis, Janis J; Ma, Ying; Teuscher, Cory; Gahring, Lorise C

    2008-01-01

    Differences between isogenic mouse strains in cellular expression of the neuronal nicotinic acetylcholine (ACh) receptor subunit alpha 4 (nAChR alpha 4) by the dorsal hippocampus are well known. To investigate further the genetic basis of these variations, expression of the nAChR alpha 4 subunit was measured in congenic mouse lines derived from two strains exhibiting notable divergence in the expression of this subunit: C3H and C57BL/6. Congenic lines carrying reciprocally introgressed regions (quantitative trait loci; QTL) from chromosomes 4, 5, and 12 each retained the phenotype most closely associated with the parental strain. However, in congenic lines harboring the reciprocal transfer of a chromosome 11 QTL, a characteristic difference in the ratio of interneurons versus astrocytes expressing nAChR alpha 4 in the CA1 region is reversed relative to the parental strain. These finding suggest that this chromosomal segment harbors genes that regulate strain distinct hippocampal morphology that is revealed by nAChR alpha 4 expression.

  14. A chromosomal chloramphenicol acetyltransferase determinant from a probiotic strain of Bacillus clausii.

    PubMed

    Galopin, Sébastien; Cattoir, Vincent; Leclercq, Roland

    2009-06-01

    The mechanism of resistance to chloramphenicol was studied in four strains of Bacillus clausii included in a probiotic mixture, which is administered to humans for prevention of gastrointestinal side effects due to oral antibiotic therapy. By cloning experiments, a chloramphenicol acetyltransferase (CAT) gene, cat(Bcl), coding for a putative 228-amino acid CAT protein was identified in B. clausii SIN. The deduced amino acid sequence displayed from 31% to 85% identity with 56 CAT proteins from other Gram-positive bacterial strains. The cat(Bcl) gene was also detected by PCR in the three other B. clausii strains resistant to chloramphenicol, whereas it was absent in the three control strains susceptible to chloramphenicol. Pulse-field gel electrophoresis of total DNA digested by I-CeuI followed by hybridization with a cat-specific probe as well as unsuccessful repeated attempts of in vitro transfer of chloramphenicol resistance to various recipient cells indicated that cat(Bcl) was chromosomally located in all four resistant B. clausii strains. PMID:19459958

  15. Micromechanics analysis of space simulated thermal deformations and stresses in continuous fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Bowles, David E.

    1990-01-01

    Space simulated thermally induced deformations and stresses in continuous fiber reinforced composites were investigated with a micromechanics analysis. The investigation focused on two primary areas. First, available explicit expressions for predicting the effective coefficients of thermal expansion (CTEs) for a composite were compared with each other, and with a finite element (FE) analysis, developed specifically for this study. Analytical comparisons were made for a wide range of fiber/matrix systems, and predicted values were compared with experimental data. The second area of investigation focused on the determination of thermally induced stress fields in the individual constituents. Stresses predicted from the FE analysis were compared to those predicted from a closed-form solution to the composite cylinder (CC) model, for two carbon fiber/epoxy composites. A global-local formulation, combining laminated plate theory and FE analysis, was used to determine the stresses in multidirectional laminates. Thermally induced damage initiation predictions were also made.

  16. Strain determination in bone sections with simultaneous 3D digital holographic interferometry

    NASA Astrophysics Data System (ADS)

    Alvarez, Araceli Sánchez; De la Torre Ibarra, Manuel H.; Santoyo, Fernando Mendoza; Anaya, Tonatiuh-Saucedo

    2014-06-01

    A 3D digital holographic interferometer was used to measure the surface strain components in two different bovine's bone sections. The applied force on the sample was induced by a precisely controlled lateral micro compression. The simultaneous acquisition capability of the system helps to record a fast sequence of images, each one containing three independent holograms that result in three orthogonal displacement components u, v and w from which the surface strain components ɛx, ɛy and γxy over the bone's field of view were calculated. This research study was carried out in two different bone sections: the cortical bone and the medullary cavity/yellow marrow section. The resulting strain concentrators are of great importance to better understand the mechanical response of complex biological structures such as this bovine femoral bone.

  17. Markerless Escherichia coli rrn Deletion Strains for Genetic Determination of Ribosomal Binding Sites.

    PubMed

    Quan, Selwyn; Skovgaard, Ole; McLaughlin, Robert E; Buurman, Ed T; Squires, Catherine L

    2015-12-01

    Single-copy rrn strains facilitate genetic ribosomal studies in Escherichia coli. Consecutive markerless deletion of rrn operons resulted in slower growth upon inactivation of the fourth copy, which was reversed by supplying transfer RNA genes encoded in rrn operons in trans. Removal of the sixth, penultimate rrn copy led to a reduced growth rate due to limited rrn gene dosage. Whole-genome sequencing of variants of single-copy rrn strains revealed duplications of large stretches of genomic DNA. The combination of selective pressure, resulting from the decreased growth rate, and the six identical remaining scar sequences, facilitating homologous recombination events, presumably leads to elevated genomic instability. PMID:26438293

  18. Finite Element Modeling of Plane Strain Toughness for 7085 Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Karabin, M. E.; Barlat, F.; Shuey, R. T.

    2009-02-01

    In this work, the constitutive model for 7085-T7X (overaged) aluminum alloy plate samples with controlled microstructures was developed. Different lengths of 2nd step aging times produced samples with similar microstructure but different stress-strain curves ( i.e., different nanostructure). A conventional phenomenological strain-hardening law with no strain gradient effects was proposed to capture the peculiar hardening behavior of the material samples investigated in this work. The classical Gurson-Tvergaard potential, which includes the influence of void volume fraction (VVF) on the plastic flow behavior, as well as an extension proposed by Leblond et al.,[3] were considered. Unlike the former, the latter is able to account for the influence of strain hardening on the VVF growth. All the constitutive coefficients used in this work were based on experimental stress-strain curves obtained in uniaxial tension and on micromechanical modeling results of a void embedded in a matrix. These material models were used in finite element (FE) simulations of a compact tension (CT) specimen. An engineering criterion based on the instability of plastic flow at a crack tip was used for the determination of plane strain toughness K Ic . The influence of the microstructure was lumped into a single state variable, the initial void volume fraction. The simulation results showed that the strain-hardening behavior has a significant influence on K Ic .

  19. Micromechanical cohesion force between gas hydrate particles measured under high pressure and low temperature conditions.

    PubMed

    Lee, Bo Ram; Sum, Amadeu K

    2015-04-01

    To prevent hydrate plugging conditions in the transportation of oil/gas in multiphase flowlines, one of the key processes to control is the agglomeration/deposition of hydrate particles, which are determined by the cohesive/adhesive forces. Previous studies reporting measurements of the cohesive/adhesive force between hydrate particles used cyclopentane hydrate particles in a low-pressure micromechanical force apparatus. In this study, we report the cohesive forces of particles measured in a new high-pressure micromechanical force (MMF) apparatus for ice particles, mixed (methane/ethane, 74.7:25.3) hydrate particles (Structure II), and carbon dioxide hydrate particles (Structure I). The cohesive forces are measured as a function of the contact time, contact force, temperature, and pressure, and determined from pull-off measurements. For the measurements performed of the gas hydrate particles in the gas phase, the determined cohesive force is about 30-35 mN/m, about 8 times higher than the cohesive force of CyC5 hydrates in the liquid CyC5, which is about 4.3 mN/m. We show from our results that the hydrate structure (sI with CO2 hydrates and sII with CH4/C2H6 hydrates) has no influence on the cohesive force. These results are important in the deposition of a gas-dominated system, where the hydrate particles formed in the liquid phase can then stick to the hydrate deposited in the wall exposed to the gas phase.

  20. Micro-mechanical model for the tension-stabilized enzymatic degradation of collagen tissues

    NASA Astrophysics Data System (ADS)

    Nguyen, Thao; Ruberti, Jeffery

    We present a study of how the collagen fiber structure influences the enzymatic degradation of collagen tissues. Experiments of collagen fibrils and tissues show that mechanical tension can slow and halt enzymatic degradation. Tissue-level experiments also show that degradation rate is minimum at a stretch level coincident with the onset of strain-stiffening in the stress response. To understand these phenomena, we developed a micro-mechanical model of a fibrous collagen tissue undergoing enzymatic degradation. Collagen fibers are described as sinusoidal elastica beams, and the tissue is described as a distribution of fibers. We assumed that the degradation reaction is inhibited by the axial strain energy of the crimped collagen fibers. The degradation rate law was calibrated to experiments on isolated single fibrils from bovine sclera. The fiber crimp and properties were fit to uniaxial tension tests of tissue strips. The fibril-level kinetic and tissue-level structural parameters were used to predict tissue-level degradation-induced creep rate under a constant applied force. We showed that we could accurately predict the degradation-induce creep rate of the pericardium and cornea once we accounted for differences in the fiber crimp structure and properties.

  1. Micromechanical Modeling the Plastic Deformation of Particle-Reinforced Bulk Metallic Glass Composites

    NASA Astrophysics Data System (ADS)

    Jiang, Yunpeng; Shi, Xueping; Qiu, Kun

    2015-08-01

    A micromechanics model was employed to investigate the mechanical performance of particle-reinforced bulk metallic glass (BMG) composites. The roles of shear banding in the tensile deformation are accounted for in characterizing the strength and ductility of ductile particle-filled BMGs. For the sake of simplicity and convenience, shear band was considered to be a micro-crack in the present model. The strain-based Weibull probability distribution function and percolation theory were applied to describe the equivalent micro-crack evolution, which results in the progressive failure of BMG composites. Based on the developed model, the influences of shear bands on the plastic deformation were discussed for various microstructures. The predictions were in fairly good agreement with the experimental data from the literatures, which confirms that the developed analytical model is able to successfully describe the mechanical properties, such as yield strength, strain hardening, and stress softening elongation of composites. The present results will shed some light on optimizing the microstructures in effectively improving the tensile ductility of BMG composites.

  2. Micromechanical Prediction of the Effective Coefficients of Thermo-Piezoelectric Multiphase Composites

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob

    1998-01-01

    The micromechanical generalized method of cells model is employed for the prediction of the effective elastic, piezoelectric, dielectric, pyroelectric and thermal-expansion constants of multiphase composites with embedded piezoelectric materials. The predicted effective constants are compared with other micromechanical methods available in the literature and good agreements are obtained.

  3. Burkholderia pseudomallei strain type, based on pulsed-field gel electrophoresis, does not determine disease presentation in melioidosis.

    PubMed

    Cheng, Allen C; Day, Nicholas P J; Mayo, Mark J; Gal, Daniel; Currie, Bart J

    2005-01-01

    Melioidosis, the infection due to Burkholderia pseudomallei, may present with a spectrum of severity and may affect any site in the body. Differential strain virulence and tropism suggested by previous studies would have implications for virulence and vaccine work. We explored clinical correlations using pulsed-field gel electrophoresis (PFGE) typing in a well-characterised clinical collection. Two methods of analysis were used based on band-based similarity values: first, a conventional cluster analysis formed by the unweighted paired group mean analysis, and second, an analysis of the distribution of the "within-group" and "between-group" Dice coefficient. Clinical isolates from 114 cases of melioidosis occurring in the Northern Territory, Australia were studied; 71 strain types were defined with a Simpson's index of 0.91. No correlation was found between strain type and disease severity or site of melioidosis on presentation, with no differences in similarity values found when comparing within and between-groups. In particular, isolates from patients with neurological melioidosis were not clustered. There was evidence of geographical localisation. This study suggests that the variation in strain type may not be as important as host and environmental factors in determining the pattern of disease.

  4. Probing Micromechanical Properties of the Extracellular Matrix of Soft Tissues by Atomic Force Microscopy.

    PubMed

    Jorba, Ignasi; Uriarte, Juan J; Campillo, Noelia; Farré, Ramon; Navajas, Daniel

    2017-01-01

    The extracellular matrix (ECM) determines 3D tissue architecture and provides structural support and chemical and mechanical cues to the cells. Atomic force microscopy (AFM) has unique capabilities to measure ECM mechanics at the scale at which cells probe the mechanical features of their microenvironment. Moreover, AFM measurements can be readily combined with bright field and fluorescence microscopy. Performing reliable mechanical measurements with AFM requires accurate calibration of the device and correct computation of the mechanical parameters. A suitable approach to isolate ECM mechanics from cell contribution is removing the cells by means of an effective decellularization process that preserves the composition, structure and mechanical properties of the ECM. AFM measurement of ECM micromechanics provides important insights into organ biofabrication, cell-matrix mechanical crosstalk and disease-induced tissue stiffness alterations. J. Cell. Physiol. 232: 19-26, 2017. © 2016 Wiley Periodicals, Inc. PMID:27163411

  5. Probing Micromechanical Properties of the Extracellular Matrix of Soft Tissues by Atomic Force Microscopy.

    PubMed

    Jorba, Ignasi; Uriarte, Juan J; Campillo, Noelia; Farré, Ramon; Navajas, Daniel

    2017-01-01

    The extracellular matrix (ECM) determines 3D tissue architecture and provides structural support and chemical and mechanical cues to the cells. Atomic force microscopy (AFM) has unique capabilities to measure ECM mechanics at the scale at which cells probe the mechanical features of their microenvironment. Moreover, AFM measurements can be readily combined with bright field and fluorescence microscopy. Performing reliable mechanical measurements with AFM requires accurate calibration of the device and correct computation of the mechanical parameters. A suitable approach to isolate ECM mechanics from cell contribution is removing the cells by means of an effective decellularization process that preserves the composition, structure and mechanical properties of the ECM. AFM measurement of ECM micromechanics provides important insights into organ biofabrication, cell-matrix mechanical crosstalk and disease-induced tissue stiffness alterations. J. Cell. Physiol. 232: 19-26, 2017. © 2016 Wiley Periodicals, Inc.

  6. Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues.

    PubMed

    deBotton, Gal; Oren, Tal

    2013-01-01

    State of the art research and treatment of biological tissues require accurate and efficient methods for describing their mechanical properties. Indeed, micromechanics-motivated approaches provide a systematic method for elevating relevant data from the microscopic level to the macroscopic one. In this work, the mechanical responses of hyperelastic tissues with one and two families of collagen fibers are analyzed by application of a new variational estimate accounting for their histology and the behaviors of their constituents. The resulting close-form expressions are used to determine the overall response of the wall of a healthy human coronary artery. To demonstrate the accuracy of the proposed method, these predictions are compared with corresponding 3D finite element simulations of a periodic unit cell of the tissue with two families of fibers. Throughout, the analytical predictions for the highly nonlinear and anisotropic tissue are in agreement with the numerical simulations.

  7. Effective Young's Modulus Measurement of Thin Film Using Micromechanical Cantilever Sensors

    NASA Astrophysics Data System (ADS)

    Itakura, Akiko N.; Toda, Masaya; Miyake, Koji; Förch, Renate; Berger, Rüdiger

    2013-11-01

    Determination of mechanical properties of thin films, such as the Young's modulus, is of fundamental importance when the films are used for coating or for materials of microelectromechanical systems (MEMS). We show a simple method to calculate the effective Young's modulus of thin films by comparing lateral and vertical expansions. The stress of the film due to expansion in the lateral direction was measured using micromechanical cantilever sensor (MCS) techniques which allow for a calculation of the lateral expansion ratio of the film. The vertical expansion was measured using ellipsometry, surface plasmon resonance (SPR) and other film thickness meters. There is no limitation by the method for a measurement of Young's modulus, even if soft and thin polymer film. We detected the influence of humidity on effective Young's modulus of a polymer material by the method, as an example.

  8. Virulence determinants, antimicrobial susceptibility, and molecular profiles of Erysipelothrix rhusiopathiae strains isolated from China.

    PubMed

    Ding, Yi; Zhu, Dongmei; Zhang, Jianmin; Yang, Longsheng; Wang, Xiangru; Chen, Huanchun; Tan, Chen

    2015-11-01

    The aim of this study was to understand the epidemiology, serotype, antibiotic sensitivity, and clonal structure of Erysipelothrix rhusiopathiae strains in China. Forty-eight strains were collected from seven provinces during the period from 2012 to 2013. Pulse-field electrophoresis identified 32 different patterns which were classified into clonal groups A–D. Most pulsed-field gel electrophoresis (PFGE) patterns were observed in clonal complex A and B, suggesting high diversity of genetic characterization in these two predominant clonal complexes. Antibiotic sensitivity test shows that all the stains were susceptible to ampicillin, erythromycin, and cefotaxime, and resistant to kanamycin, cefazolin, sulfadiazine, and amikacin. Erythromycin and ampicillin are recommended as first-line antibiotics for treatment of E. rhusiopathiae in China. The high variation in PFGE pattern among the main clonal groups shows that the E. rhusiopathiae in China may originate from different lineages and sources instead of from expansion of a single clonal lineage across different regions. PMID:26975059

  9. Virulence determinants, antimicrobial susceptibility, and molecular profiles of Erysipelothrix rhusiopathiae strains isolated from China

    PubMed Central

    Ding, Yi; Zhu, Dongmei; Zhang, Jianmin; Yang, Longsheng; Wang, Xiangru; Chen, Huanchun; Tan, Chen

    2015-01-01

    The aim of this study was to understand the epidemiology, serotype, antibiotic sensitivity, and clonal structure of Erysipelothrix rhusiopathiae strains in China. Forty-eight strains were collected from seven provinces during the period from 2012 to 2013. Pulse-field electrophoresis identified 32 different patterns which were classified into clonal groups A–D. Most pulsed-field gel electrophoresis (PFGE) patterns were observed in clonal complex A and B, suggesting high diversity of genetic characterization in these two predominant clonal complexes. Antibiotic sensitivity test shows that all the stains were susceptible to ampicillin, erythromycin, and cefotaxime, and resistant to kanamycin, cefazolin, sulfadiazine, and amikacin. Erythromycin and ampicillin are recommended as first-line antibiotics for treatment of E. rhusiopathiae in China. The high variation in PFGE pattern among the main clonal groups shows that the E. rhusiopathiae in China may originate from different lineages and sources instead of from expansion of a single clonal lineage across different regions. PMID:26975059

  10. Determination of homozygous susceptible strain in Culex quinquefasciatus (Say), using single raft sib-selection method.

    PubMed

    Hidayati, H; Nazni, W A; Mohd, S A

    2008-04-01

    The standard laboratory strain was found to be heterozygous for susceptibility. Hence, an attempt was made to obtain a homozygous susceptible strain in Culex quinquefasciatus (Say) using single raft sib-selection method. Lab-bred females of Cx. quinquefasciatus from insectariums, Unit of Medical Entomology were used in the experiment. After blood feeding Cx. quinquefasciatus mosquitoes laid eggs in raft form, ten rafts selected randomly for the test. Each egg raft was introduced into a plastic tray from number one to number ten. Twenty-five third stage larvae from each tray were exposed to 17.5 microl from 500mg/l malathion in a paper cup label number 1 to number ten. In the bioassay, which had 100% mortality, the respective larva in that particular tray was bred to adult stage for the following generation. Less than 7days old female mosquitoes that emerged from F(0) were used in the test. The F(0) and the subsequent adult and larval stage generations were subjected to adult and larval bioassay. After selection for about 10 generations, a homozygous susceptible strain in Cx. quinquefasciatus was obtained.

  11. Determination of lattice parameters, strain state and composition in semipolar III-nitrides using high resolution X-ray diffraction

    SciTech Connect

    Frentrup, Martin Wernicke, Tim; Stellmach, Joachim; Kneissl, Michael; Hatui, Nirupam; Bhattacharya, Arnab

    2013-12-07

    In group-III-nitride heterostructures with semipolar or nonpolar crystal orientation, anisotropic lattice and thermal mismatch with the buffer or substrate lead to a complex distortion of the unit cells, e.g., by shearing of the lattice. This makes an accurate determination of lattice parameters, composition, and strain state under assumption of the hexagonal symmetry impossible. In this work, we present a procedure to accurately determine the lattice constants, strain state, and composition of semipolar heterostructures using high resolution X-ray diffraction. An analysis of the unit cell distortion shows that four independent lattice parameters are sufficient to describe this distortion. Assuming only small deviations from an ideal hexagonal structure, a linear expression for the interplanar distances d{sub hkl} is derived. It is used to determine the lattice parameters from high resolution X-ray diffraction 2ϑ-ω-scans of multiple on- and off-axis reflections via a weighted least-square fit. The strain and composition of ternary alloys are then evaluated by transforming the elastic parameters (using Hooke's law) from the natural crystal-fixed coordinate system to a layer-based system, given by the in-plane directions and the growth direction. We illustrate our procedure taking an example of (112{sup ¯}2) Al{sub κ}Ga{sub 1−κ}N epilayers with Al-contents over the entire composition range. We separately identify the in-plane and out-of-plane strains and discuss origins for the observed anisotropy.

  12. Influence of disease-suppressive strains of Streptomyces on the native Streptomyces community in soil as determined by the analysis of cellular fatty acids.

    PubMed

    Bowers, J H; Kinkel, L L; Jones, R K

    1996-01-01

    Analysis of cellular fatty acid profiles was used to distinguish among introduced pathogen- suppressive strains and indigenous strains of Streptomyces spp. isolated from soil of field plots established to test the efficacy of Streptomyces strains PonSSII and PonR in the biological control of potato scab. Reference libraries of fatty acid profiles were developed for a collection of known pathogenic strains and the introduced suppressive strains. Population densities of pathogen-related, suppressive, and saprophytic Streptomyces strains were determined from the relationship of field isolates to mean library profiles using cluster analysis and the unweighted pair-group method using arithmetic averages. Community diversity was similarly determined. Streptomyces strains PonSSII and PonR were distinguished from each other and from the pathogen group (which clustered together) based on fatty acid profiles. The introduced, suppressive strains successfully colonized the soil and represented 2-19% of the isolates sampled over 2 years. The introduction of the suppressive strains inhibited the population of strains related to the pathogen library at each sample date; the pathogen population was substantially lower in soil from treatments where the suppressive strains were introduced compared with the nonamended control. At harvest, the pathogen-related population was suppressed 85-93 and 36-44% in 1991 and 1992, respectively, in treatments with the suppressive strains compared with the nonamended control. Diversity of the community was not affected by the introduced strains, and diversity and equitability indices were similar among treatments at any sample time. The inhibition of the pathogen-related population was correlated with a reduction of scab symptoms observed in the field plots into which the suppressive strains were introduced. Implications of a fundamental shift in the pathogen-related population in response to the introduction of the suppressive strains for long

  13. Interfacial Micromechanics in Fibrous Composites: Design, Evaluation, and Models

    PubMed Central

    Lei, Zhenkun; Li, Xuan; Qin, Fuyong; Qiu, Wei

    2014-01-01

    Recent advances of interfacial micromechanics in fiber reinforced composites using micro-Raman spectroscopy are given. The faced mechanical problems for interface design in fibrous composites are elaborated from three optimization ways: material, interface, and computation. Some reasons are depicted that the interfacial evaluation methods are difficult to guarantee the integrity, repeatability, and consistency. Micro-Raman study on the fiber interface failure behavior and the main interface mechanical problems in fibrous composites are summarized, including interfacial stress transfer, strength criterion of interface debonding and failure, fiber bridging, frictional slip, slip transition, and friction reloading. The theoretical models of above interface mechanical problems are given. PMID:24977189

  14. Squeezing of Quantum Noise of Motion in a Micromechanical Resonator.

    PubMed

    Pirkkalainen, J-M; Damskägg, E; Brandt, M; Massel, F; Sillanpää, M A

    2015-12-11

    A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations that are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude 1.1±0.4  dB below the standard quantum limit, thus achieving a long-standing goal of obtaining motional squeezing in a macroscopic object. PMID:26705631

  15. A Micromechanical Contribution to Cochlear Tuning and Tonotopic Organization

    NASA Astrophysics Data System (ADS)

    Holton, Thomas; Hudspeth, A. J.

    1983-11-01

    The response properties of hair cells and nerve fibers in the alligator lizard cochlea are frequency selective and tonotopically organized with longitudinal position in the organ. The lengths of the hair-cell hair bundles also vary monotonically with longitudinal position. In this study, quantitative measurements were made of the motion of individual hair bundles in an excised preparation of the cochlea stimulated at auditory frequencies. The angular displacement of hair bundles is frequency selective and tonotopically organized, demonstrating the existence of a micromechanical tuning mechanism.

  16. Interfacial micromechanics in fibrous composites: design, evaluation, and models.

    PubMed

    Lei, Zhenkun; Li, Xuan; Qin, Fuyong; Qiu, Wei

    2014-01-01

    Recent advances of interfacial micromechanics in fiber reinforced composites using micro-Raman spectroscopy are given. The faced mechanical problems for interface design in fibrous composites are elaborated from three optimization ways: material, interface, and computation. Some reasons are depicted that the interfacial evaluation methods are difficult to guarantee the integrity, repeatability, and consistency. Micro-Raman study on the fiber interface failure behavior and the main interface mechanical problems in fibrous composites are summarized, including interfacial stress transfer, strength criterion of interface debonding and failure, fiber bridging, frictional slip, slip transition, and friction reloading. The theoretical models of above interface mechanical problems are given. PMID:24977189

  17. Micromechanical mass sensors for biomolecular detection in a physiological environment.

    PubMed

    Braun, Thomas; Barwich, Viola; Ghatkesar, Murali Krishna; Bredekamp, Adriaan H; Gerber, Christoph; Hegner, Martin; Lang, Hans Peter

    2005-09-01

    Micromechanical cantilever arrays are used to measure time-resolved adsorption of tiny masses based on protein-ligand interactions. Here, streptavidin-biotin interactions are investigated in a physiological environment. A measurement method is introduced using higher flexural modes of a silicon cantilever in order to enhance the sensitivity of mass detection. Modeling the cantilever vibration in liquid allows the measurement of absolute mass changes. We show time-resolved mass adsorption of final 7+/-0.7 ng biotinylated latex beads. The sensitivity obtained is about 2.5 pg/Hz measuring at a center frequency of 750 kHz.

  18. Micromechanical properties of hydrogels measured with MEMS resonant sensors.

    PubMed

    Corbin, Elise A; Millet, Larry J; Pikul, James H; Johnson, Curtis L; Georgiadis, John G; King, William P; Bashir, Rashid

    2013-04-01

    Hydrogels have gained wide usage in a range of biomedical applications because of their biocompatibility and the ability to finely tune their properties, including viscoelasticity. The use of hydrogels on the microscale is increasingly important for the development of drug delivery techniques and cellular microenvironments, though the ability to accurately characterize their micromechanical properties is limited. Here we demonstrate the use of microelectromechanical systems (MEMS) resonant sensors to estimate the properties of poly(ethylene glycol) diacrylate (PEGDA) microstructures over a range of concentrations. These microstructures are integrated on the sensors by deposition using electrohydrodynamic jet printing. Estimated properties agree well with independent measurements made using indentation with atomic force microscopy.

  19. Detection of electromagnetic radiation using micromechanical multiple quantum wells structures

    DOEpatents

    Datskos, Panagiotis G [Knoxville, TN; Rajic, Slobodan [Knoxville, TN; Datskou, Irene [Knoxville, TN

    2007-07-17

    An apparatus and method for detecting electromagnetic radiation employs a deflectable micromechanical apparatus incorporating multiple quantum wells structures. When photons strike the quantum-well structure, physical stresses are created within the sensor, similar to a "bimetallic effect." The stresses cause the sensor to bend. The extent of deflection of the sensor can be measured through any of a variety of conventional means to provide a measurement of the photons striking the sensor. A large number of such sensors can be arranged in a two-dimensional array to provide imaging capability.

  20. Anharmonic modal coupling in a bulk micromechanical resonator

    NASA Astrophysics Data System (ADS)

    Dunn, Tyler; Wenzler, Josef-Stefan; Mohanty, Pritiraj

    2010-09-01

    We present measurements of nonlinear coupling between various acoustic modes of a micromechanical resonator. Piezoelectric transduction allows measurement of both flexural and bulk longitudinal modes up to microwave frequencies, and we find that all modes of the device couple, regardless of type. This coupling thus provides a means of mechanical nonlinear signal processing across a wide range of frequencies. Through controlled simultaneous excitation, we quantify coupling strength by measuring the frequency shift in a detector mode in response to the known energy of a driven mode.

  1. Micromechanics of brittle creep and implications for the strength of the upper crust

    NASA Astrophysics Data System (ADS)

    Brantut, N.; Baud, P.; Heap, M. J.; Meredith, P. G.

    2012-04-01

    In the upper crust, the chemical influence of pore water or other aqueous solutions promotes time dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail at stresses far below their short-term failure strength, and even at constant applied stress ("brittle creep"). Here we present a new micromechanical model describing time dependent brittle creep of water-saturated rocks under triaxial stress conditions. Macroscopic brittle creep is modelled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of cracks in compression are derived from the sliding wing crack model of Ashby and Sammis (1990). Crack length evolution is computed from Charles' power law description of stress corrosion crack growth. The macroscopic strains and strain rates computed from the model are non-linear and compare well with experimental results obtained on granite, low porosity sandstone and basalt samples. Primary creep (decelerating strain rate) corresponds to decelerating crack growth, due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain rate as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep, with apparently constant strain rate, arises as merely an inflexion between these two end-member phases. The strain rate at the inflexion point can be estimated analytically as a function of model parameters, effective confining pressure and temperature conditions, which provides an approximate creep law for the process. The creep law is used to infer the long term differential stress as a function of depth in the upper crust for tectonic loading rates: sub-critical cracking induces an offset of the rock strength, which is equivalent to a decrease in cohesion. For porous rocks, the competition between sub

  2. Self-Determination as a Moderator of Demands and Control: Implications for Employee Strain and Engagement

    ERIC Educational Resources Information Center

    Parker, Stacey L.; Jimmieson, Nerina L.; Amiot, Catherine E.

    2010-01-01

    Does job control act as a stress-buffer when employees' type and level of work self-determination is taken into account? It was anticipated that job control would only be stress-buffering for employees high in self-determined and low in non-self-determined work motivation. In contrast, job control would be stress-exacerbating for employees who…

  3. Conduction band offset determination between strained CdSe and ZnSe layers using DLTS

    SciTech Connect

    Rangel-Kuoppa, Victor-Tapio

    2013-12-04

    The conduction band offset between strained CdSe layers embedded in unintentionally n-type doped ZnSe is measured and reported. Two samples, consisting of thirty Ultra Thin Quantum Wells (UTQWs) of CdSe embedded in ZnSe, grown by Atomic Layer Epitaxy, are used for this study. The thicknesses of the UTQWs are one and three monolayers (MLs) in each sample, respectively. As expected, the sample with one ML UTQWs does not show any energy level in the UTQWs due to the small thickness of the UTQWs, while the thickness of the sample with 3 ML UTQWs is large enough to form an energy level inside the UTQWs. This energy level appears as a majority trap with an activation energy of 223.58 ± 9.54 meV. This corresponds to UTQWs with barrier heights (the conduction band offset) between 742 meV and 784 meV. These values suggest that the band gap misfit between strained CdSe and ZnSe is around 70.5 to 74 % in the conduction band.

  4. Molecular determinants of azo reduction activity in the strain Pseudomonas putida MET94.

    PubMed

    Mendes, Sónia; Pereira, Luciana; Batista, Carlos; Martins, Lígia O

    2011-10-01

    Azo dyes are the major group of synthetic colourants used in industry and are serious environmental pollutants. In this study, Pseudomonas putida MET94 was selected from 48 bacterial strains on the basis of its superior ability to degrade a wide range of structurally diverse azo dyes. P. putida is a versatile microorganism with a well-recognised potential for biodegradation or bioremediation applications. P. putida MET94 removes, in 24 h and under anaerobic growing conditions, more than 80% of the majority of the structurally diverse azo dyes tested. Whole cell assays performed under anaerobic conditions revealed up to 90% decolourisation in dye wastewater bath models. The involvement of a FMN dependent NADPH: dye oxidoreductase in the decolourisation process was suggested by enzymatic measurements in cell crude extracts. The gene encoding a putative azoreductase was cloned from P. putida MET94 and expressed in Escherichia coli. The purified P. putida azoreductase is a 40 kDa homodimer with broad substrate specificity for azo dye reduction. The presence of dioxygen leads to the inhibition of the decolourisation activity in agreement with the results of cell cultures. The kinetic mechanism follows a ping-pong bi-bi reaction scheme and aromatic amine products were detected in stoichiometric amounts by high-performance liquid chromatography. Overall, the results indicate that P. putida MET94 is a promising candidate for bioengineering studies aimed at generating more effective dye-reducing strains.

  5. Determination of strain fields in porous shape memory alloys using micro-computed tomography

    NASA Astrophysics Data System (ADS)

    Bormann, Therese; Friess, Sebastian; de Wild, Michael; Schumacher, Ralf; Schulz, Georg; Müller, Bert

    2010-09-01

    Shape memory alloys (SMAs) belong to 'intelligent' materials since the metal alloy can change its macroscopic shape as the result of the temperature-induced, reversible martensite-austenite phase transition. SMAs are often applied for medical applications such as stents, hinge-less instruments, artificial muscles, and dental braces. Rapid prototyping techniques, including selective laser melting (SLM), allow fabricating complex porous SMA microstructures. In the present study, the macroscopic shape changes of the SMA test structures fabricated by SLM have been investigated by means of micro computed tomography (μCT). For this purpose, the SMA structures are placed into the heating stage of the μCT system SkyScan 1172™ (SkyScan, Kontich, Belgium) to acquire three-dimensional datasets above and below the transition temperature, i.e. at room temperature and at about 80°C, respectively. The two datasets were registered on the basis of an affine registration algorithm with nine independent parameters - three for the translation, three for the rotation and three for the scaling in orthogonal directions. Essentially, the scaling parameters characterize the macroscopic deformation of the SMA structure of interest. Furthermore, applying the non-rigid registration algorithm, the three-dimensional strain field of the SMA structure on the micrometer scale comes to light. The strain fields obtained will serve for the optimization of the SLM-process and, more important, of the design of the complex shaped SMA structures for tissue engineering and medical implants.

  6. A micromechanics-based nonlocal constitutive equation incorporating three-point statistics for random linear elastic composite materials

    NASA Astrophysics Data System (ADS)

    Drugan, W. J.; Willis, J. R.

    2016-06-01

    A variational formulation employing the minimum potential and complementary energy principles is used to derive a micromechanics-based nonlocal constitutive equation for random linear elastic composite materials, relating ensemble averages of stress and strain in the most general situation when mean fields vary spatially. All information contained in the energy principles is retained; we employ stress polarization trial fields utilizing one-point statistics so that the resulting nonlocal constitutive equation incorporates up through three-point statistics. The variational structure is developed first for arbitrary heterogeneous linear elastic materials, then for randomly inhomogeneous materials, then for general n-phase composite materials, and finally for two-phase composite materials, in which case explicit variational upper and lower bounds on the nonlocal effective modulus tensor operator are derived. For statistically uniform infinite-body composites, these bounds are determined even more explicitly in Fourier transform space. We evaluate these in detail in an example case: longitudinal shear of an aligned fiber or void composite. We determine the full permissible ranges of the terms involving two- and three-point statistics in these bounds, and thereby exhibit explicit results that encompass arbitrary isotropic in-plane phase distributions; we also develop a nonlocal "Milton parameter", the variation of whose eigenvalues throughout the interval [0, 1] describes the full permissible range of the three-point term. Example plots of the new bounds show them to provide substantial improvement over the (two-point) Hashin-Shtrikman bounds on the nonlocal operator tensor, for all permissible values of the two- and three-point parameters. We next discuss further applications of the general nonlocal operator bounds: to any three-dimensional scalar transport problem e.g. conductivity, for which explicit results are given encompassing the full permissible ranges of the

  7. Growth differences and competition between Listeria monocytogenes strains determine their predominance on ham slices and lead to bias during selective enrichment with the ISO protocol.

    PubMed

    Zilelidou, Evangelia; Manthou, Evanthia; Skandamis, Panagiotis

    2016-10-17

    Listeria monocytogenes strains are widespread in the environment where they live well mixed, often resulting in multiple strains contaminating a single food sample. The occurrence of different strains in the same food might trigger strain competition, contributing to uneven growth of strains in food and to bias during selective procedures. We tested the growth of seven L. monocytogenes strains (C5, 6179, ScottA, PL24, PL25, PL26, PL27) on ham slices and on nutrient-rich agar at 10°C, singly and in combinations. Strains were made resistant to different antibiotics for their selective enumeration. In addition, growth of single strains (axenic culture) and competition between strains in xenic cultures of two strains was evaluated in enrichment broth and on selective agar. According to ISO 11290-1:1996/Amd 1:2004 standard protocol for detection of L. monocytogenes, two enrichment steps both followed by streaking on ALOA were performed. Strain cultures were directly added in the enrichment broth or used to inoculate minced beef and sliced hams which were then mixed with enrichment broth. 180-360 colonies were used to determine the relative percentage of each strain recovered on plates per enrichment step. The data showed a significant impact of co-cultivation on the growth of six out of seven strains on ham and a bias towards certain strains during selective enrichment. Competition was manifested by: (i) cessation of growth for the outcompeted strain when the dominant strain reached stationary phase, (ii) reduction of growth rates or (iii) total suppression of growth (both on ham and in enrichment broth or ALOA). Outgrowth of strains by their competitors on ALOA resulted in limited to no recovery, with the outcompeting strain accounting for up to 100% of the total recovered colonies. The observed bias was associated with the enrichment conditions (i.e. food type added to the enrichment broth) and the strain-combination. The outcome of growth competition on food or

  8. Liquid chromatographic determination of toxigenic secondary metabolites produced by Fusarium strains.

    PubMed

    Mateo, J J; Mateo, R; Hinojo, M J; Llorens, A; Jiménez, M

    2002-05-10

    Various liquid chromatographic methods used in the analysis of mycotoxins (zearalenone, trichothecenes and fumonisins) produced by Fusarium species were compared in this work. The results demonstrate the suitability of modern clean-up procedures employing multifunctional MycoSep and immunoaffinity columns although these methods are more expensive than conventional methodologies for clean-up. HPLC with both fluorescence and photodiode array detection is a suitable technique for the analysis of toxic secondary metabolites produced by Fusarium species; different derivatisation strategies have been studied to improve the sensitivity of the technique because of the low concentration of these metabolites in contaminated food. The utility of the proposed methodology was assessed in cereal cultures of various Fusarium strains.

  9. Left Ventricular Diastolic Dysfunction in Dialysis Patients Assessed by Novel Speckle Tracking Strain Rate Analysis: Prevalence and Determinants

    PubMed Central

    de Bie, Mihály K.; Ajmone Marsan, Nina; Gaasbeek, André; Bax, Jeroen J.; Groeneveld, Marc; Gabreels, Bas A.; Delgado, Victoria; Rabelink, Ton J.; Schalij, Martin J.; Jukema, J. Wouter

    2012-01-01

    Background. Diastolic dysfunction is common among dialysis patients and is associated with increased morbidity and mortality. Novel echocardiographic speckle tracking strain analysis permits accurate assessment of left ventricular diastolic function, independent of loading conditions and taking all myocardial segments into account. The aim of the study was to evaluate the prevalence of diastolic dysfunction in chronic dialysis patients using this novel technique, and to identify its determinants among clinical and echocardiographic variables. Methods. Patients currently enrolled in the ICD2 study protocol were included for this analysis. Next to conventional echo measurements diastolic function was also assessed by global diastolic strain rate during isovolumic relaxation (SRIVR). Results. A total of 77 patients were included (age 67 ± 8 years, 74% male). When defined as E/SRIVR ≥236, the prevalence of diastolic dysfunction was higher compared to more conventional measurements (48% versus 39%). Left ventricular mass (OR 1.02, 95% CI 1.00–1.04, P = 0.014) and pulse wave velocity (OR 1.34, 95% CI 1.07–1.68, P = 0.01) were independent determinants of diastolic dysfunction. Conclusion. Diastolic dysfunction is highly prevalent among dialysis patients and might be underestimated using conventional measurements. Left ventricular mass and pulse wave velocity were the only determinants of diastolic dysfunction in these patients. PMID:22649726

  10. Exopolysaccharide Production and Ropy Phenotype Are Determined by Two Gene Clusters in Putative Probiotic Strain Lactobacillus paraplantarum BGCG11

    PubMed Central

    Zivkovic, Milica; Miljkovic, Marija; Ruas-Madiedo, Patricia; Strahinic, Ivana; Tolinacki, Maja; Golic, Natasa

    2014-01-01

    Lactobacillus paraplantarum BGCG11, a putative probiotic strain isolated from a soft, white, artisanal cheese, produces a high-molecular-weight heteropolysaccharide, exopolysaccharide (EPS)-CG11, responsible for the ropy phenotype and immunomodulatory activity of the strain. In this study, a 26.4-kb region originating from the pCG1 plasmid, previously shown to be responsible for the production of EPS-CG11 and a ropy phenotype, was cloned, sequenced, and functionally characterized. In this region 16 putative open reading frames (ORFs), encoding enzymes for the production of EPS-CG11, were organized in specific loci involved in the biosynthesis of the repeat unit, polymerization, export, regulation, and chain length determination. Interestingly, downstream of the eps gene cluster, a putative transposase gene was identified, followed by an additional rfb gene cluster containing the rfbACBD genes, the ones most probably responsible for dTDP-l-rhamnose biosynthesis. The functional analysis showed that the production of the high-molecular-weight fraction of EPS-CG11 was absent in two knockout mutants, one in the eps and the other in the rfb gene cluster, as confirmed by size exclusion chromatography analysis. Therefore, both eps and rfb genes clusters are prerequisites for the production of high-molecular-weight EPS-CG11 and for the ropy phenotype of strain L. paraplantarum BGCG11. PMID:25527533

  11. Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates

    NASA Astrophysics Data System (ADS)

    Meng, Qinghua; Wang, Zhenqing

    2016-05-01

    Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of ​​impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.

  12. Laser interferometric measurement of the micromechanics of the inner ear

    NASA Astrophysics Data System (ADS)

    Gummer, Anthony W.; Hemmert, Werner; Zenner, Hans-Peter

    1995-02-01

    Recent advances in optical techniques for vibration measurement have made it feasible to purchase commercially available laser Doppler velocimeters that, in combination with a light microscope, are capable of detecting velocities of poorly reflecting biological materials down to fractions of a micrometers s-1. Thus, in our particular application, the aim is to understand the micromechanics of the inner ear, particularly in the nanometer region where the ear is first able to detect sound. With currently available devices, it is now possible to make the necessary vibration measurements without need of introducing reflecting materials onto the object of interest. This not only avoids inertial loading, but also allows focusing through cellular layers onto otherwise inaccessible structures. Here we present the results of micromechanical experiments for the in vitro inner ear of the guinea pig, the most commonly used model in auditory physiology. Our experiments concentrate on the third and fourth cochlear turns because in this region the different cellular structures of the organ of Corti are optically accessible with present technology. The mechanical responses of all examined structures, including the basilar membrane, were equally frequency selective, but linear below 90 dB SPL, suggesting that active mechanical tuning is not as pronounced in the apex as in the base of the cochlea. This has important consequences for signal processing in the inner ear.

  13. Virtual mass effect in dynamic micromechanical mass sensing in liquids

    NASA Astrophysics Data System (ADS)

    Peiker, P.; Oesterschulze, E.

    2016-06-01

    Weighing individual micro- or nanoscale particles in solution using dynamic micromechanical sensors is quite challenging: viscous losses dramatically degrade the sensor's performance by both broadening the resonance peak and increasing the effective total mass of the resonator by the dragged liquid. While the virtual mass of the resonator was discussed frequently, little attention has been paid to the virtual mass of particles attached to the resonator's surface and its impact on the accuracy of mass sensing. By means of the in situ detection of a polystyrene microbead in water using a bridge-based microresonator, we demonstrate that the virtual mass of the bead significantly affects the observed frequency shift. In fact, 55 % of the frequency shift was caused by the virtual mass of the adsorbed bead, predicted by Stoke's theory. Based on the observed shift in the resonator's quality factor during particle adsorption, we confirm this significant effect of the virtual mass. Thus, a quantitative analysis of the mass of a single adsorbed particle is strongly diminished if dynamic micromechanical sensors are operated in a liquid environment.

  14. Micromechanical properties of tobacco mosaic viruses.

    PubMed

    Schmatulla, Alexander; Maghelli, Nicola; Marti, Othmar

    2007-03-01

    A tobacco mosaic virus (TMV) subject to local forces can be viewed as an uniform beam with local loads. We used a custom built Atomic Force Microscope (AFM) to determine the curvature induced in the TMV by concentrated load or by distributed forces. Local forces were created by the AFM tip. Distributed forces were applied to the virus via the surface tension of receding droplets. The experimental results of both methods can be described when we attribute a Young modulus of 6 +/- 3 GPa to the virus. Our value is about five times larger than published data. We compare our results to the literature and work out possible error sources in our experiment and in published one.

  15. Sequence determination of a mildly virulent strain (CU-2) of Gallid herpesvirus type 2 using 454 pyrosequencing.

    PubMed

    Spatz, Stephen J; Rue, Cary A

    2008-06-01

    The complete DNA sequence of the mildly virulent Gallid herpesvirus type 2 strain CU-2 was determined and consists of 176,922 bp with an overall gene organization typical of class E herpesviruses. Phylogenetically, this strain partitions in its own branch between the virulent strains RB-1B, Md11, and Md5, and the vaccine strain CVI988. Overall, the genome of CU-2 is more similar to that of CVI988, with identically sized unique short regions of 11,651 bp. As in CVI988, an insertion of 177 bp was identified in the overlapping genes encoding the Meq, RLORF6, and 23 kDa proteins within the repeat long region of the genome. A total of 15 single nucleotide polymorphisms (SNPs) common to both CU-2 and CVI988, and not occurring in virulent strains, were identified in the genes encoding UL29, UL45, UL50, UL52, LORF10, RLORF14a, RLORF12, Meq(RLORF7), 23kDa, ICP4, US3, and two hypothetical proteins MDV071.4 and MDV076.4. Each gene encoding UL29 and Meq contained two SNPs. Only one major open reading frame (ORF) encoding UL41, the virus host shutoff (VHS) ribonuclease, was disrupted in the CU-2 genome. An additional cytosine after the 25 codon is predicted to produce a truncated protein of 97 aa. Since GaHV-2 mutants lacking UL41 have been reported to retain their virulence, other factors are likely responsible for the low virulence of CU-2. It is largely suspected that SNPs in common with CVI988 along with the insertions in the Meq loci are responsible for its phenotype. Conversely, we identified 43 nonsynonymous mutations (within 23 genes) that may contribute to the virulence of CU-2. These SNPs are shared exclusively with all sequenced virulent strains (Md5, Md11, and RB-1B) and not present within the CVI988 genome. Although most occur in proteins of unknown function, a significant percentage is in proteins involved in virion assembly.

  16. Job Strain and Determinants in Staff Working in Institutions for People with Intellectual Disabilities in Taiwan: A Test of the Job Demand-Control-Support Model

    ERIC Educational Resources Information Center

    Lin, Jin-Ding; Lee, Tzong-Nan; Yen, Chia-Feng; Loh, Ching-Hui; Hsu, Shang-Wei; Wu, Jia-Ling; Chu, Cordia M.

    2009-01-01

    Little is known about the job strain of staff working in disability institutions. This study investigated the staff's job strain profile and its determinants which included the worker characteristics and the psychosocial working environments in Taiwan. A cross-sectional study survey was carried out among 1243 workers by means of a self-answered…

  17. Negative strain rate sensitivity in bulk metallic glass and its similarities with the dynamic strain aging effect during deformation

    SciTech Connect

    Dalla Torre, Florian H.; Dubach, Alban; Siegrist, Marco E.; Loeffler, Joerg F.

    2006-08-28

    Detailed investigations were carried out on the deformation behavior of Zr-based monolithic bulk metallic glass and bulk metallic glass matrix composites. The latter, due to splitting and multiplication of shear bands, exhibits larger compressive strains than the former, without significant loss of strength. Serrated flow in conjunction with a negative strain rate sensitivity was observed in both materials. This observation, together with an increase in stress drops with increasing strain and their decrease with increasing strain rate, indicates phenomenologically close similarities with the dynamic strain aging deformation mechanism known for crystalline solids. The micromechanical mechanism of a shear event is discussed in light of these results.

  18. Micromechanical model for self-organized secondary phase oxide nanorod arrays in epitaxial YBa2Cu3O7-δ films

    NASA Astrophysics Data System (ADS)

    Shi, Jack J.; Wu, Judy Z.

    2012-08-01

    A micromechanical model based on the theory of elasticity has been developed to study the configuration of self-assembled secondary phase oxide nanostructures in high-temperature superconducting YBa2Cu3O7-δ films. With the calculated equilibrium strain and elastic energy of the impurity doped film, a phase diagram of lattice mismatches vs. elastic constants of the dopant was obtained that predicts the energetically preferred orientation of secondary phase nanorods. The calculation of the nanorod orientation and the film lattice deformation has yielded excellent agreement with experimental measurements.

  19. The structure and micromechanics of elastic tissue

    PubMed Central

    Green, Ellen M.; Mansfield, Jessica C.; Bell, James S.; Winlove, C. Peter

    2014-01-01

    Elastin is a major component of tissues such as lung and blood vessels, and endows them with the long-range elasticity necessary for their physiological functions. Recent research has revealed the complexity of these elastin structures and drawn attention to the existence of extensive networks of fine elastin fibres in tissues such as articular cartilage and the intervertebral disc. Nonlinear microscopy, allowing the visualization of these structures in living tissues, is informing analysis of their mechanical properties. Elastic fibres are complex in composition and structure containing, in addition to elastin, an array of microfibrillar proteins, principally fibrillin. Raman microspectrometry and X-ray scattering have provided new insights into the mechanisms of elasticity of the individual component proteins at the molecular and fibrillar levels, but more remains to be done in understanding their mechanical interactions in composite matrices. Elastic tissue is one of the most stable components of the extracellular matrix, but impaired mechanical function is associated with ageing and diseases such as atherosclerosis and diabetes. Efforts to understand these associations through studying the effects of processes such as calcium and lipid binding and glycation on the mechanical properties of elastin preparations in vitro have produced a confusing picture, and further efforts are required to determine the molecular basis of such effects. PMID:24748954

  20. Probabilistic micromechanics of woven ceramic matrix composites

    NASA Astrophysics Data System (ADS)

    Goldsmith, Marlana

    Woven ceramic matrix composites are a special class of composite materials that are of current interest for harsh thermo-structural conditions such as those encountered by hypersonic vehicle systems and turbine engine components. Testing of the materials is expensive, especially as materials are constantly redesigned. Randomness in the tow architecture, as well as the randomly shaped and spaced voids that are produced as a result of the manufacturing process, are features that contribute to variability in stiffness and strength. The goal of the research is to lay a foundation in which characteristics of the geometry can be translated into material properties. The research first includes quantifying the architectural variability based on 2D micrographs of a 5 harness satin CVI (Chemical Vapor Infiltration) SiC/SiC composite. The architectural variability is applied to a 2D representative volume element (RVE) in order to evaluate which aspects of the architecture are important to model in order to capture the variability found in the cross sections. Tow width, tow spacing, and tow volume fraction were found to have some effect on the variability, but voids were found to have a large influence on transverse stiffness, and a separate study was conducted to determine which characteristics of the voids are most critical to model. It was found that the projected area of the void perpendicular to the transverse direction and the number of voids modeled had a significant influence on the stiffness. The effect of varying architecture on the variability of in-plane tensile strength was also studied using the Brittle Cracking Model for Concrete in the commercial finite element software, Abaqus. A maximum stress criterion is used to evaluate failure, and the stiffness of failed elements is gradually degraded such that the energy required to open a crack (fracture energy) is dissipated during this degradation process. While the varying architecture did not create variability in

  1. Micro-Raman probing of residual stress in freestanding GaN-based micromechanical structures fabricated by a dry release technique

    NASA Astrophysics Data System (ADS)

    Tripathy, S.; Lin, Vivian K. X.; Vicknesh, S.; Chua, S. J.

    2007-03-01

    In this study, the authors have employed micro-Raman scattering to characterize the residual stress in freestanding GaN-based micromechanical structures on (111)-oriented silicon substrates. Arrays of freestanding cantilevers and microbridges have been fabricated using a combination of dry etching techniques. The Si material beneath the GaN microstructures is removed by a nonplasma XeF2-based dry release technique. Two distinct sets of GaN-based layers on Si(111) with a different amount of growth-induced tensile stress are selected for the fabrication of freestanding cantilevers. The residual stress in these micromechanical structures is determined from the peak shift of the E2-high phonon mode of GaN. Such GaN mechanical structures on Si platforms may be useful for the fabrication of GaN-based microelectromechanical systems and sensors.

  2. Composite tube and plate manufacturing repeatability as determined by precision measurements of thermal strain

    NASA Astrophysics Data System (ADS)

    Riddle, Lenn A.; Tucker, James R.; Bluth, A. Marcel

    2013-09-01

    Composite materials often carry the reputation of demonstrating high variability in critical material properties. The JWST telescope metering structure is fabricated of several thousand separate composite piece parts. The stringent dimensional stability requirements on the metering structure require the critical thermal strain response of every composite piece be verified either at the billet or piece part level. JWST is a unique composite space structure in that it has required the manufacturing of several hundred composite billets that cover many lots of prepreg and many years of fabrication. The flight billet thermal expansion acceptance criteria limits the coefficient of thermal expansion (CTE) to a tolerance ranging between +/-0.014 ppm/K to +/-0.04 ppm/K around a prescribed nominal when measured from 293 K down to 40 K. The different tolerance values represent different material forms including flat plates and different tube cross-section dimensions. A precision measurement facility was developed that could measure at the required accuracy and at a pace that supported the composite part fabrication rate. The test method and facility is discussed and the results of a statistical process analysis of the flight composite billets are surveyed.

  3. Determination of high temperature strains using a PC based vision system

    NASA Technical Reports Server (NTRS)

    Mcneill, Stephen R.; Sutton, Michael A.; Russell, Samuel S.

    1992-01-01

    With the widespread availability of video digitizers and cheap personal computers, the use of computer vision as an experimental tool is becoming common place. These systems are being used to make a wide variety of measurements that range from simple surface characterization to velocity profiles. The Sub-Pixel Digital Image Correlation technique has been developed to measure full field displacement and gradients of the surface of an object subjected to a driving force. The technique has shown its utility by measuring the deformation and movement of objects that range from simple translation to fluid velocity profiles to crack tip deformation of solid rocket fuel. This technique has recently been improved and used to measure the surface displacement field of an object at high temperature. The development of a PC based Sub-Pixel Digital Image Correlation system has yielded an accurate and easy to use system for measuring surface displacements and gradients. Experiments have been performed to show the system is viable for measuring thermal strain.

  4. Mechanical behavior of Al-Li/SiC composites. Part 3: Micromechanical modeling

    SciTech Connect

    Poza, P.; Llorca, J.

    1999-03-01

    A micromechanical model is developed to compute the stress-strain curve of particle-reinforced metal-matrix composites under monotonic and cyclic deformation. The composite was modeled as a three-dimensional array of hexagonal prisms, each containing an intact or fractured reinforcement. The average stresses acting on the intact and damaged cells--as well as on the ceramic particles--were computed from the finite-element analysis of axisymmetric cylindrical cells, and the overall composite response was then calculated through an isostrain approach. The model was validated against the experimental results, reported in Parts 1 and 2 of this article, for an 8090 Al alloy reinforced with 15 vol pct SiC particles, where the matrix and reinforcement properties were obtain3ed from mechanical tests on the unreinforced alloy and from quantitative microscopy analyses of the fraction of broken reinforcements in the composite. The critical mechanisms which controlled the deformation and damage processes in the composite during monotonic and cyclic deformation are discussed in light of the model results.

  5. Creep lifetime prediction of oxide-dispersion-strengthened nickel-base superalloys: A micromechanically based approach

    NASA Astrophysics Data System (ADS)

    Heilmaier, M.; Reppich, B.

    1996-12-01

    The high-temperature creep behavior of the oxide-dispersion-strengthened (ODS) nickel-base superalloys MA 754 and MA 6000 has been investigated at temperatures up to 1273 K and lifetimes of approximately 4000 hours using monotonic creep tests at constant true stress σ, as well as true constant extension rate tests (CERTs) atdot \\varepsilon . The derivation of creep rupture-lifetime diagrams is usually performed with conventional engineering parametric methods, according to Sherby and Dorn or Larson and Miller. In contrast, an alternative method is presented that is based on a more microstructural approach. In order to describe creep, the effective stress model takes into account the hardening contribution σ p caused by the presence of second-phase particles, as well as the classical Taylor back-stress σ p caused by dislocations. The modeled strain rate-stress dependence can be transferred directly into creep-rupture stress-lifetime diagrams using a modified Monkman-Grant (MG) relationship, which adequately describes the interrelation betweendot \\varepsilon representing dislocation motion, and lifetime t f representing creep failure. The comparison with measured creep-rupture data proves the validity of the proposed micromechanical concept.

  6. Mechanical behavior of Al-Li/SiC composites: Part III. Micromechanical modeling

    NASA Astrophysics Data System (ADS)

    Poza, P.; Llorca, J.

    1999-03-01

    A micromechanical model is developed to compute the stress-strain curve of particle-reinforced metal-matrix composites under monotonic and cyclic deformation. The composite was modeled as a three-dimensional array of hexagonal prisms, each containing an intact or fractured reinforcement. The average stresses acting on the intact and damaged cells—as well as on the ceramic particles —were computed from the finite-element analysis of axisymmetric cylindrical cells, and the overall composite response was then calculated through an isostrain approach. The model was validated against the experimental results, reported in Parts I and II of this article, for an 8090 Al alloy reinforced with 15 vol pct SiC particles,[1,2] where the matrix and reinforcement properties were obtained from mechanical tests on the unreinforced alloy and from quantitative microscopy analyses of the fraction of broken reinforcements in the composite. The critical mechanisms which controlled the deformation and damage processes in the composite during monotonic and cyclic deformation are discussed in light of the model results.

  7. Micromechanical and macroscopic models of ductile fracture in particle reinforced metallic materials

    NASA Astrophysics Data System (ADS)

    Hu, Chao; Bai, Jie; Ghosh, Somnath

    2007-06-01

    This paper is aimed at developing two modules contributing to the overall framework of multi-scale modelling of ductile fracture of particle reinforced metallic materials. The first module is for detailed micromechanical analysis of particle fragmentation and matrix cracking of heterogeneous microstructures. The Voronoi cell FEM for particle fragmentation is extended in this paper to incorporate ductile failure through matrix cracking in the form of void growth and coalescence using a non-local Gurson-Tvergaard-Needleman (GTN) model. In the resulting enriched Voronoi cell finite element model (VCFEM) or E-VCFEM, the assumed stress-based hybrid VCFEM formulation is overlaid with narrow bands of displacement based elements to accommodate strain softening in the constitutive behaviour. The second module develops an anisotropic plasticity-damage model in the form of the GTN model for macroscopic analysis in the multi-scale material model. Parameters in this model are calibrated from results of homogenization of microstructural variables obtained by E-VCFEM analysis of microstructural representative volume element. Numerical examples conducted yield satisfactory results.

  8. Micromechanical analysis on tensile modulus of structured magneto-rheological elastomer

    NASA Astrophysics Data System (ADS)

    Chen, S. W.; Li, R.; Zhang, Z.; Wang, X. J.

    2016-03-01

    This paper proposed a micromechanical model to investigate the tensile modulus of structured magnetorheological elastomers (MRE) to understand its anisotropic properties. A three parameter representative volume element (RVE) model was presented to describe the microscopic structure, where particles could be organized in layer-like or chain-like structure. And the tensile modulus is defined as a ratio of stress to strain in the stretched direction. We then applied effective medium theory to derive a theoretical model for the modulus of MRE in the absence of magnetic field, considering the influence of particles configuration and volume fraction. In addition, the effect of magnetic field on magneto-induced stress inside MRE is evaluated to further establish a multi-scale model which explains the magneto-rheological effect of structured MRE. The proposed model was then compared with finite element analysis and ‘free energy’ model. It demonstrated that the proposed model match better with the finite element solutions than that of ‘free energy’ method. The advantage of the proposed model is that it couples the magnetic field and displacement field, and considers the influence of both particles spatial energy and the relative position on magneto-rheological effect. The stiffer or softer of MREs induced by an applied magnetic field under tensile stress is predicted that is conformed to previous studies.

  9. Micromechanical Behavior of Solid-Solution-Strengthened Mg-1wt.%Al Alloy Investigated by In-Situ Neutron Diffraction

    SciTech Connect

    Lee, Sooyeol; Woo, Wanchuck; Gharghouri, Michael; Yoon, Cheol; An, Ke

    2014-01-01

    In-situ neutron-diffraction experiments were employed to investigate the micromechanical behavior of solid-solution-strengthened Mg-1wt.%Al alloy. Two starting textures were used: 1) as-extruded then solutionized texture, T1, in which the basal poles of most grains are tilted around 70~85 from the extrusion axis, and 2) a reoriented texture, T2, in which the basal poles of most grains are tilted around 10~20 from the extrusion axis. Lattice strains and diffraction peak intensity variations were measured in situ during loading-unloading cycles in uniaxial tension. Twinning activities and stress states for various grain orientations were revealed. The results show that the soft grain orientations, favorably oriented for either extension twinning or basal slip, exhibit the stress relaxation, resulting in the compressive residual strain after unloading. On the other hand, the hard grain orientations, unfavorably oriented for both extension twinning and basal slip, carry more applied load, leading to much higher lattice strains during loading followed by tensile residual strains upon unloading.

  10. EDITORIAL: 16th European Workshop on Micromechanics (MME 2005)

    NASA Astrophysics Data System (ADS)

    Enoksson, Professor Peter

    2006-06-01

    This special issue of Journal of Micromechanics and Microengineering is devoted to the 16th European Workshop on Micromechanics (MME 2005), which was held in Göteborg, Sweden, at the Chalmers Conference Centre on the premises of Chalmers University of Technology, 4-6 September 2005. Göteborg is the second largest city in Sweden and is situated on the beautiful south-west coast. With its relaxed and friendly atmosphere Göteborg proudly lives up to its reputation of having the charm of a small town with all the opportunities of a big city. The MME workshop is a well recognized and established European event for creating microsensors and microactuators in the field of micromachining, microengineering and technology. The very first workshop was held at Twente University, The Netherlands, in 1989. Scientists and people from industry who are interested in the field gather annually for this event. The goals are stimulation and improvement of know-how in the field, as well as establishing cooperation and friendship between delegates. Thus MME is arranged so that people can meet in a friendly and informal atmosphere. That is why the accent is on mutual discussions around poster presentations rather than on formal oral presentations. The contributions, which came from 21 countries, were presented in four sessions and five keynote presentations. I am proud to present 24 high-quality papers from MME 2005 selected for their novelty and relevance to Journal of Micromechanics and Microengineering. Each paper passed a rigorous peer review process. May I take this opportunity to thank those authors who contributed their research to this special issue, which I hope gives an excellent overview of topics discussed at the workshop. I would also like to express my gratitude to Professor Robert Puers for advising on the selection of papers and to Dr Anke Sanz-Velasco for helping to coordinate the special issue with the Institute of Physics Publishing office at the start. I hope you

  11. Micromechanics based simulation of ductile fracture in structural steels

    NASA Astrophysics Data System (ADS)

    Yellavajjala, Ravi Kiran

    The broader aim of this research is to develop fundamental understanding of ductile fracture process in structural steels, propose robust computational models to quantify the associated damage, and provide numerical tools to simplify the implementation of these computational models into general finite element framework. Mechanical testing on different geometries of test specimens made of ASTM A992 steels is conducted to experimentally characterize the ductile fracture at different stress states under monotonic and ultra-low cycle fatigue (ULCF) loading. Scanning electron microscopy studies of the fractured surfaces is conducted to decipher the underlying microscopic damage mechanisms that cause fracture in ASTM A992 steels. Detailed micromechanical analyses for monotonic and cyclic loading are conducted to understand the influence of stress triaxiality and Lode parameter on the void growth phase of ductile fracture. Based on monotonic analyses, an uncoupled micromechanical void growth model is proposed to predict ductile fracture. This model is then incorporated in to finite element program as a weakly coupled model to simulate the loss of load carrying capacity in the post microvoid coalescence regime for high triaxialities. Based on the cyclic analyses, an uncoupled micromechanics based cyclic void growth model is developed to predict the ULCF life of ASTM A992 steels subjected to high stress triaxialities. Furthermore, a computational fracture locus for ASTM A992 steels is developed and incorporated in to finite element program as an uncoupled ductile fracture model. This model can be used to predict the ductile fracture initiation under monotonic loading in a wide range of triaxiality and Lode parameters. Finally, a coupled microvoid elongation and dilation based continuum damage model is proposed, implemented, calibrated and validated. This model is capable of simulating the local softening caused by the various phases of ductile fracture process under

  12. In-Situ Micromechanical Testing in Extreme Environments

    NASA Astrophysics Data System (ADS)

    Lupinacci, Amanda Sofia

    In order to design engineering applications that can withstand extreme environments, we must first understand the underlying deformation mechanisms that can hinder material performance. It is not enough to characterize the mechanical properties alone, we must also characterize the microstructural changes as well so that we can understand the origin of material degradation. This dissertation focuses on two different extreme environments. The first environment is the cryogenic environment, where we focus on the deformation behavior of solder below the ductile to brittle transition temperature (DBTT). The second environment is the irradiated environment, where we focus on the effects that ion beam irradiation has on both the mechanical properties and microstructure of 304 stainless steel. Both classes of materials and testing environments utilize novel in situ micromechanical testing techniques inside a scanning electron microscope which enhances our ability to link the observed deformation behavior with its associated mechanical response. Characterizing plasticity mechanisms below the DBTT is traditionally difficult to accomplish in a systematic fashion. Here, we use a new experimental setup to perform in situ cryogenic mechanical testing of pure Sn micropillars at room temperature and at -142 °C. Subsequent electron microscopy characterization of the micropillars shows a clear difference in the deformation mechanisms at room temperature and at cryogenic temperatures. At room temperature, the Sn micropillars deformed through dislocation plasticity while at -142 °C they exhibited both higher strength and deformation twinning. Two different orientations were tested, a symmetric (100) orientation and a non-symmetric (45¯1) orientation. The deformation mechanisms were found to be the same for both orientations. This approach was also extended to a more complex solder alloy that is commonly used in industry, Sn96. In the case of the solder alloy more complex geometries

  13. Determination of biological and physicochemical parameters of Artemia franciscana strains in hypersaline environments for aquaculture in the Colombian Caribbean

    PubMed Central

    Camargo, William N; Durán, Gabriel C; Rada, Orlando C; Hernández, Licet C; Linero, Juan-Carlos G; Muelle, Igor M; Sorgeloos, Patrick

    2005-01-01

    Background Artemia (Crustacea, Anostraca), also known as brine shrimp, are typical inhabitants of extreme environments. These hypersaline environments vary considerably in their physicochemical composition, and even their climatic conditions and elevation. Several thalassohaline (marine) environments along the Colombian Caribbean coast were surveyed in order to contribute to the knowledge of brine shrimp biotopes in South America by determining some vital biological and physicochemical parameters for Artemia survival. Additionally, cyst quality tests, biometrical and essential fatty acids analysis were performed to evaluate the economic viability of some of these strains for the aquaculture industry. Results In addition to the three locations (Galerazamba, Manaure, and Pozos Colorados) reported in the literature three decades ago in the Colombian Caribbean, six new locations were registered (Salina Cero, Kangaru, Tayrona, Bahía Hondita, Warrego and Pusheo). All habitats sampled showed that chloride was the prevailing anion, as expected, because of their thalassohaline origin. There were significant differences in cyst diameter grouping strains in the following manner according to this parameter: 1) San Francisco Bay (SFB-Control, USA), 2) Galerazamba and Tayrona, 3) Kangarú, 4) Manaure, and 5) Salina Cero and Pozos Colorados. Chorion thickness values were smaller in Tayrona, followed by Salina Cero, Galerazamba, Manaure, SFB, Kangarú and Pozos Colorados. There were significant differences in naupliar size, grouping strains as follows (smallest to largest): 1) Galerazamba, 2) Manaure, 3) SFB, Kangarú, and Salina Cero, 4) Pozos Colorados, and 5) Tayrona. Overall, cyst quality analysis conducted on samples from Manaure, Galerazamba, and Salina Cero revealed that all sites exhibited a relatively high number of cysts.g-1. Essential fatty acids (EFA) analysis performed on nauplii from cyst samples from Manaure, Galerazamba, Salina Cero and Tayrona revealed that cysts

  14. Insights from the Lattice-Strain Evolution on Deformation Mechanisms in Metallic-Glass-Matrix Composites

    DOE PAGESBeta

    Jia, Haoling; Zheng, Lili; Li, Weidong; Li, Nan; Qiao, Junwei; Wang, Gongyao; Ren, Yang; Liaw, Peter K.; Gao, Yanfei

    2015-02-18

    In this paper, in situ high-energy synchrotron X-ray diffraction experiments and micromechanics-based finite element simulations have been conducted to examine the lattice-strain evolution in metallic-glass-matrix composites (MGMCs) with dendritic crystalline phases dispersed in the metallic-glass matrix. Significant plastic deformation can be observed prior to failure from the macroscopic stress–strain curves in these MGMCs. The entire lattice-strain evolution curves can be divided into elastic–elastic (denoting deformation behavior of matrix and inclusion, respectively), elastic–plastic, and plastic–plastic stages. Characteristics of these three stages are governed by the constitutive laws of the two phases (modeled by free-volume theory and crystal plasticity) and geometric informationmore » (crystalline phase morphology and distribution). The load-partitioning mechanisms have been revealed among various crystalline orientations and between the two phases, as determined by slip strain fields in crystalline phase and by strain localizations in matrix. Finally, implications on ductility enhancement of MGMCs are also discussed.« less

  15. Insights from the Lattice-Strain Evolution on Deformation Mechanisms in Metallic-Glass-Matrix Composites

    SciTech Connect

    Jia, Haoling; Zheng, Lili; Li, Weidong; Li, Nan; Qiao, Junwei; Wang, Gongyao; Ren, Yang; Liaw, Peter K.; Gao, Yanfei

    2015-02-18

    In this paper, in situ high-energy synchrotron X-ray diffraction experiments and micromechanics-based finite element simulations have been conducted to examine the lattice-strain evolution in metallic-glass-matrix composites (MGMCs) with dendritic crystalline phases dispersed in the metallic-glass matrix. Significant plastic deformation can be observed prior to failure from the macroscopic stress–strain curves in these MGMCs. The entire lattice-strain evolution curves can be divided into elastic–elastic (denoting deformation behavior of matrix and inclusion, respectively), elastic–plastic, and plastic–plastic stages. Characteristics of these three stages are governed by the constitutive laws of the two phases (modeled by free-volume theory and crystal plasticity) and geometric information (crystalline phase morphology and distribution). The load-partitioning mechanisms have been revealed among various crystalline orientations and between the two phases, as determined by slip strain fields in crystalline phase and by strain localizations in matrix. Finally, implications on ductility enhancement of MGMCs are also discussed.

  16. Micromechanics-Based Continuum Constitutive Modeling of Isotropic Non-Cohesive Particulate Materials, Informed and Validated by the Discrete Element Method

    NASA Astrophysics Data System (ADS)

    Fleischmann, Jonathan A.

    We apply homogenization methods from the field of micromechanics to obtain the macroscale effective elastic moduli and the macroscale effective material friction angle for a statistically isotropic non-cohesive particulate material, such as gravel, sand, or powder, in terms of the microscale properties of the particulate material, such as the inter-particle normal and tangential contact stiffnesses (which can be derived from the mechanical properties of the material constituting the individual particles in the particulate material), the inter-particle static friction coefficient, and the geometric properties of the local particle packing structure. In this way, we obtain macroscale information that can be used in elastoplastic continuum constitutive models for general statistically isotropic non-cohesive particulate materials, based on micromechanics. All of our theoretical results are informed and validated by numerical simulations of quasi-static true triaxial and simple shear tests on multiple randomly packed material specimens of roughly 3,000-30,000 spherical particles, performed using the discrete element method (DEM). Using the discrete element method, and performing simulations with particle rotation either allowed or prohibited, we are able to isolate the effect of particle rotation in a particulate material in both the elastic and plastic ranges. Our theoretical analyses improve previous theoretical analyses in the literature, which are typically based on the principle of minimum potential energy, and are thus unable to capture the effects of mechanisms or zero-energy strains due to particle rotation in a particulate material. In contrast, our direct micromechanics derivations are based on force and moment equilibrium for individual particles, and are thus able to capture the effects of mechanisms or zero-energy strains due to particle rotation in a particulate material. We prove, both analytically and by our discrete element simulations, that mechanisms

  17. Position control system for use with micromechanical actuators

    DOEpatents

    Guckel, Henry; Stiers, Eric W.

    2000-01-01

    A positioning system adapted for use with micromechanical actuators provides feedback control of the position of the movable element of the actuator utilizing a low Q sensing coil. The effective inductance of the sensing coil changes with position of the movable element to change the frequency of oscillation of a variable oscillator. The output of the variable oscillator is compared in a phase detector to a reference oscillator signal. The phase detector provides a pulsed output having a pulse duty cycle related to the phase or frequency difference between the oscillator signals. The output of the phase detector is provided to a drive coil which applies a magnetic force to the movable element which balances the force of a spring. The movable element can be displaced to a new position by changing the frequency of the reference oscillator.

  18. A stochastic framework for the micromechanical analysis of composites

    SciTech Connect

    Williams, T. O.

    2004-01-01

    The formulation of a stochastic micromechanical framework for the history-dependent analysis of composite materials is presented. The theory introduces the statistics of the underlying material microstructure through the incorporation of probability density functions (PDFs) for the different types of concentration tensors. Thus, the theory takes a fundamentally different approach to the analysis of stochastic composites than those theories that follow the current trend of treating stochastic effects by specifying PDFs for the different microstructural arrangements. The general equations governing the behavior of the different types of localization effects within the composite are presented. Based on these governing equations it is shown that in the case of two-phase composites the entire stochastic description for the history-dependent material behavior reduces to the description only of the PDFs for the elastic localization effects in conjunction with any desired set of deterministic constitutive relations for the individual phases.

  19. Micromechanics thermal stress analysis of composites for space structure applications

    NASA Technical Reports Server (NTRS)

    Bowles, David E.

    1991-01-01

    This paper presents results from a finite element micromechanics analysis of thermally induced stresses in composites at cryogenic temperatures typical of spacecraft operating environments. The influence of microstructural geometry, constituent and interphase properties, and laminate orientation were investigated. Stress field results indicated that significant matrix stresses occur in composites exposed to typical spacecraft thermal excursions; these stresses varied with laminate orientation and circumferential position around the fiber. The major difference in the predicted response of unidirectional and multidirectional laminates was the presence of tensile radial stresses, at the fiber/matrix interface, in multidirectional laminates with off-axis ply angles greater than 15 deg. The predicted damage initiation temperatures and modes were in good agreement with experimental data for both low (207 GPa) and high (517 GPa) modulus carbon fiber/epoxy composites.

  20. Porosity estimation of aged mortar using a micromechanical model.

    PubMed

    Hernández, M G; Anaya, J J; Sanchez, T; Segura, I

    2006-12-22

    Degradation of concrete structures located in high humidity atmospheres or under flowing water is a very important problem. In this study, a method for ultrasonic non-destructive characterization in aged mortar is presented. The proposed method makes a prediction of the behaviour of aged mortar accomplished with a three phase micromechanical model using ultrasonic measurements. Aging mortar was accelerated by immersing the probes in ammonium nitrate solution. Both destructive and non-destructive characterization of mortar was performed. Destructive tests of porosity were performed using a vacuum saturation method and non-destructive characterization was carried out using ultrasonic velocities. Aging experiments show that mortar degradation not only involves a porosity increase, but also microstructural changes in the cement matrix. Experimental results show that the estimated porosity using the proposed non-destructive methodology had a comparable performance to classical destructive techniques.

  1. Visualizing intrinsic localized modes with a nonlinear micromechanical array

    NASA Astrophysics Data System (ADS)

    Sato, M.; Sievers, A. J.

    2008-07-01

    Micromechanical cantilever arrays provide the opportunity to visualize the nonlinear excitations of a discrete nonlinear system in real time. Both stationary and moving localized nonlinear excitations can be produced either by driving the system at a frequency outside the plane wave spectrum or by driving the system at a frequency within the small amplitude dispersion curve range. To see these modes the tips of the cantilevers are imaged on a 1D CCD camera. The brightness of the image depends on the oscillation amplitude of the cantilever, so that a distribution of amplitudes in the array can be recorded as a function of position and time. Both the stationary and traveling excitations have been successfully simulated using a nonlinear lumped element lattice model. The former ILM can appear in any size lattice while the latter requires a low density of modes for the formation of smoothly running excitation.

  2. Optical sensors with MEMS, slit masks, and micromechanical devices

    NASA Astrophysics Data System (ADS)

    Riesenberg, Rainer; Wuttig, Andreas

    2001-10-01

    Concepts to increase the performance of optical sensors by combination with optical MEMS are discussed. Architectures of subsystems are reviewed, which modulate or switch the amplitude of the light by scanning, multiplexing and selecting interesting signal components (multi-object-mode). Arrangements with MEMS for optical sensors and instruments can decrease the pixel size and increase their number by creating virtual pixels. A number of signal components can be detected with a smaller number of detectors (detector pixels) by scanning. If the scanning is substituted by multiplexing the best efficiency is achieved. The measurement time can be reduced by selecting interesting objects or signal components to be detected. Architectures which combine single sensors, linear sensor arrays or two dimensional detector arrays with MEMS, slit masks, and micro-mechanical devices are discussed. Such devices are micro-mirrors, micro-shutters, the slit positioning system, the fibre positioning system, and other optical switches.

  3. Dispersive and dissipative coupling in a micromechanical resonator embedded with a nanomechanical resonator.

    PubMed

    Mahboob, I; Perrissin, N; Nishiguchi, K; Hatanaka, D; Okazaki, Y; Fujiwara, A; Yamaguchi, H

    2015-04-01

    A micromechanical resonator embedded with a nanomechanical resonator is developed whose dynamics can be captured by the coupled-Van der Pol-Duffing equations. Activating the nanomechanical resonator can dispersively shift the micromechanical resonance by more than 100 times its bandwidth and concurrently increase its energy dissipation rate to the point where it can even be deactivated. The coupled-Van der Pol-Duffing equations also suggest the possibility of self-oscillations. In the limit of strong excitation for the nanomechanical resonator, the dissipation in the micromechanical resonator can not only be reduced, resulting in a quality factor of >3× 10(6), it can even be eliminated entirely resulting in the micromechanical resonator spontaneously vibrating. PMID:25751406

  4. Methods for detecting formation mechanisms and determining a final strain value for different scales of folded structures

    NASA Astrophysics Data System (ADS)

    Yakovlev, Fedor L.

    2012-03-01

    Linear folding, developing in fold and thrust belts, is treated as a hierarchic system, at each level of which objects are described by special kinematic models. Geometric parameters of natural folded structures are determined by a combination of various mechanisms incorporated in the model, and a value of finite strain. Several case studies demonstrate how such data enables one to solve structural and geodynamic problems for natural objects of different size. Shortening value of two morphological types of folds is determined based on the geometry of competent layers. Application of the method to analyze the folds of the Vorontsov nappe (Greater Caucasus) determines its gravitational origin. Structural cross-sections though several tectonic zones are subdivided into relatively small domains, the geometry of which, particularly in thin-bedded flysch deposits, making it possible to identify the mechanisms of formation of both local and large structures, and also to reconstruct the pre-folded state of each domain and of the entire cross-sections. By aggregation of tectonic domains into large modules and determination of the value of shortening, we have constructed for the first time a 3D model of the present-day structure of the northwestern Caucasus, which is balanced for the whole sedimentary cover. The geometry of large structures makes it possible to validate geodynamic models.

  5. Prion protein detection in serum using micromechanical resonator arrays.

    PubMed

    Varshney, Madhukar; Waggoner, Philip S; Montagna, Richard A; Craighead, Harold G

    2009-12-15

    Prion proteins that have transformed from their normal cellular counterparts (PrP(c)) into infectious form (PrP(res)) are responsible for causing progressive neurodegenerative diseases in numerous species, such as bovine spongiform encephalopathy (BSE) in cattle (also known as mad cow disease), scrapie in sheep, and Creutzfeldt-Jakob disease (CJD) in humans. Due to a possible link between BSE and CJD it is highly desirable to develop non-invasive and ante mortem tests for the detection of prion proteins in bovine samples. Such ante mortem tests of all cows prior to slaughter will help to prevent the introduction of PrP(res) into the human food supply. Furthermore, detection of PrP(res) in donated blood will also help to prevent the transmission of CJD among humans through blood transfusion. In this study, we have continued development of a micromechanical resonator array that is capable of detecting PrP(c) in bovine blood serum. The sensitivity of the resonators for the detection of PrP(c) is further enhanced by the use of secondary mass labels. A pair of antibodies is used in a sandwich immunoassay format to immobilize PrP(c) on the surface of resonators and attach nanoparticles as secondary mass labels to PrP(c). Secondary mass labeling is optimized in terms of incubation time to maximize the frequency shifts that correspond to the presence of PrP(c) on the surface of resonators. Our results show that a minimum of 200 pg mL(-1) of PrP(c) in blood serum can be detected using micromechanical resonator arrays. PMID:19836525

  6. PUBLISHER'S ANNOUNCEMENT: A revised scope for Journal of Micromechanics and Microengineering A revised scope for Journal of Micromechanics and Microengineering

    NASA Astrophysics Data System (ADS)

    Forbes, Ian

    2010-05-01

    Journal of Micromechanics and Microengineering is well known for publishing excellent work in highly competitive timescales. The journal's coverage has consistently evolved to reflect the current state of the field, and from May 2010 it will revisit its scope once again. The aims of the journal remain unchanged, however: to be the first choice of authors and readers in MEMS and micro-scale research. The new scope continues to focus on highlighting the link between fabrication technologies and their capacity to create novel devices. This link will be considered paramount in the journal, and both prospective authors and readers should let it serve as an inspiration to them. The burgeoning fields of NEMS and nano-scale engineering are more explicitly supported in the new scope. Research which ten years ago would have been considered science fiction has, through the tireless efforts of the community, become reality. The Editorial Board feel it is important to reflect the growing significance of this work in the scope. The new scope, drafted by Editor-in-Chief Professor Mark Allen, and approved by the Editorial Board, is as follows: Journal of Micromechanics and Microengineering covers all aspects of microelectromechanical structures, devices, and systems, as well as micromechanics and micromechatronics. The journal focuses on original work in fabrication and integration technologies, on the micro- and nano-scale. The journal aims to highlight the link between new fabrication technologies and their capacity to create novel devices. Original work in microengineering and nanoengineering is also reported. Such work is defined as applications of these fabrication and integration technologies to structures in which key attributes of the devices or systems depend on specific micro- or nano-scale features. Such applications span the physical, chemical, electrical and biological realms. New fabrication and integration techniques for both silicon and non-silicon materials are

  7. Diversity and specificity of Frankia strains in nodules of sympatric Myrica gale, Alnus incana, and Shepherdia canadensis determined by rrs gene polymorphism.

    PubMed

    Huguet, V; Batzli, J M; Zimpfer, J F; Normand, P; Dawson, J O; Fernandez, M P

    2001-05-01

    The identity of Frankia strains from nodules of Myrica gale, Alnus incana subsp. rugosa, and Shepherdia canadensis was determined for a natural stand on a lake shore sand dune in Wisconsin, where the three actinorhizal plant species were growing in close proximity, and from two additional stands with M. gale as the sole actinorhizal component. Unisolated strains were compared by their 16S ribosomal DNA (rDNA) restriction patterns using a direct PCR amplification protocol on nodules. Phylogenetic relationships among nodular Frankia strains were analyzed by comparing complete 16S rDNA sequences of study and reference strains. Where the three actinorhizal species occurred together, each host species was nodulated by a different phylogenetic group of Frankia strains. M. gale strains from all three sites belonged to an Alnus-Casuarina group, closely related to Frankia alni representative strains, and were low in diversity for a host genus considered promiscuous with respect to Frankia microsymbiont genotype. Frankia strains from A. incana nodules were also within the Alnus-Casuarina cluster, distinct from Frankia strains of M. gale nodules at the mixed actinorhizal site but not from Frankia strains from two M. gale nodules at a second site in Wisconsin. Frankia strains from nodules of S. canadensis belonged to a divergent subset of a cluster of Elaeagnaceae-infective strains and exhibited a high degree of diversity. The three closely related local Frankia populations in Myrica nodules could be distinguished from one another using our approach. In addition to geographic separation and host selectivity for Frankia microsymbionts, edaphic factors such as soil moisture and organic matter content, which varied among locales, may account for differences in Frankia populations found in Myrica nodules. PMID:11319089

  8. Micromechanical processes of frictional aging and the affect of shear stress on fault healing: insights from material characterization and ultrasonic velocity measurements

    NASA Astrophysics Data System (ADS)

    Ryan, K. L.; Marone, C.

    2015-12-01

    During the seismic cycle, faults repeatedly fail and regain strength. The gradual strength recovery is often referred to as frictional healing, and existing works suggest that healing can play an important role in determining the mode of fault slip ranging from dynamic rupture to slow earthquakes. Laboratory studies can play an important role in identifying the processes of frictional healing and their evolution with shear strain during the seismic cycle. These studies also provide data for laboratory-derived friction constitutive laws, which can improve dynamic earthquake models. Previous work shows that frictional healing varies with shear stress on a fault during the interseismic period. Unfortunately, the micromechanical processes that cause shear stress dependent frictional healing are not well understood and cannot be incorporated into current earthquake models. In fault gouge, frictional healing involves compaction and particle rearrangement within sheared granular layers. Therefore, to address these issues, we investigate the role grain size reduction plays in frictional re-strengthening processes at different levels of shear stress. Sample material was preserved from biaxial deformation experiments on granular Westerly granite. The normal stress was held constant at 25 MPa and we performed several 100 second slide-hold-slide tests in each experiment. We conducted a series of 5 experiments each with a different value of normalized shear stress (ranging from 0 to 1), defined as the ratio of the pre-hold shear stress to the shear stress during the hold. The particle size distribution for each sample was analyzed. In addition, acoustic measurements were recorded throughout our experiments to investigate variations in ultrasonic velocity and signal amplitude that reflect changes in the elastic moduli of the layer. Acoustic monitoring provides information about healing mechanisms and can provide a link between laboratory studies and tectonic fault zones.

  9. Fluorometric determination of acid proteinase activity in Candida albicans strains from diabetic patients with vulvovaginal candidiasis.

    PubMed

    Yildirim, Zuhal; Kilic, Nedret; Kalkanci, Ayse

    2011-09-01

    Vulvovaginal candidiasis is one of the most frequent disorders in obstetrics and gynaecology. Approximately three-quarters of all adult women experience at least one episode of vulvovaginal candidiasis during their life span. Diabetes mellitus (DM) increases the rate of vaginal colonisation and infection with Candida species. The secreted acid proteinase might be especially relevant in the pathogenesis of vulvovaginal candidiasis. The aim of this study was to determine the acid proteinase activity in the samples of Candida albicans from diabetic patients with vulvovaginal candidiasis by a fluorometric method. Vaginal swabs were taken from 33 women (aged between 22 and 57 years) having symptoms of vaginitis. Patients were divided into three groups: control group, controlled diabetic group and uncontrolled diabetic group. The proteinase activity in the culture supernatants was determined by a modified fluorometric method. Acid proteinase activities were significantly increased in the uncontrolled diabetic group in comparison with both the control group and the controlled diabetic group (P < 0.05). Acid proteinase may play an important role in C. albicans pathogenesis in diabetic patients. Improving glucose control may reduce the risk of Candida colonisation and potentially symptomatic infection, among women with diabetes and hence may be useful even for weaker enzyme activity measurements.

  10. Experimental Characterization and Micromechanical Modeling of Woven Carbon/Copper Composites

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Pauly, Christopher C.; Pindera, Marek-Jerzy

    1997-01-01

    The results of an extensive experimental characterization and a preliminary analytical modeling effort for the elastoplastic mechanical behavior of 8-harness satin weave carbon/copper (C/Cu) composites are presented. Previous experimental and modeling investigations of woven composites are discussed, as is the evolution of, and motivation for, the continuing research on C/Cu composites. Experimental results of monotonic and cyclic tension, compression, and Iosipescu shear tests, and combined tension-compression tests, are presented. With regard to the test results, emphasis is placed on the effect of strain gauge size and placement, the effect of alloying the copper matrix to improve fiber-matrix bonding, yield surface characterization, and failure mechanisms. The analytical methodology used in this investigation consists of an extension of the three-dimensional generalized method of cells (GMC-3D) micromechanics model, developed by Aboudi (1994), to include inhomogeneity and plasticity effects on the subcell level. The extension of the model allows prediction of the elastoplastic mechanical response of woven composites, as represented by a true repeating unit cell for the woven composite. The model is used to examine the effects of refining the representative geometry of the composite, altering the composite overall fiber volume fraction, changing the size and placement of the strain gauge with respect to the composite's reinforcement weave, and including porosity within the infiltrated fiber yarns on the in-plane elastoplastic tensile, compressive, and shear response of 8-harness satin C/Cu. The model predictions are also compared with the appropriate monotonic experimental results.

  11. Superelement methods applications to micromechanics of high temperature metal matrix composites

    NASA Technical Reports Server (NTRS)

    Caruso, J. J.; Chamis, C. C.

    1988-01-01

    Adaptation of the superelement finite-element method for micromechanics of continuous fiber high temperature metal matrix composites (HT-MMC) is described. The method is used to predict the thermomechanical behavior of P100-graphite/copper composites using MSC/NASTRAN and it is also used to validate those predicted by using an in-house computer program designed to perform micromechanics for HT-MMC. Typical results presented in the paper include unidirectional composite thermal properties, mechanical properties, and microstresses.

  12. Apparatus and method for detecting electromagnetic radiation using electron photoemission in a micromechanical sensor

    DOEpatents

    Datskos, Panagiotis G.; Rajic, Slobodan; Datskou, Irene C.; Egert, Charles M.

    2002-01-01

    A micromechanical sensor and method for detecting electromagnetic radiation involve producing photoelectrons from a metal surface in contact with a semiconductor. The photoelectrons are extracted into the semiconductor, which causes photo-induced bending. The resulting bending is measured, and a signal corresponding to the measured bending is generated and processed. A plurality of individual micromechanical sensors can be arranged in a two-dimensional matrix for imaging applications.

  13. Intershell Interaction in a Double Wall Carbon Nanotube with Determined Chiral Indices under a Torsional Strain

    NASA Astrophysics Data System (ADS)

    Lin, Letian; Cui, Taoran; Washburn, Sean; Qin, Lu-Chang

    2011-03-01

    We have used a double wall carbon nanotube to build a torsional pendulum. The nanotube worked as a torsional bearing for a metal block. An external electric field was used to rotate the metal block to cause a fully elastic torsional deformation on the nanotube. Nano-beam electron diffraction patterns were taken before and while the nanotube was twisted. By analysis of the shift of the diffraction patterns, we were able to determine the nanotube chiral indices and measure the inner-shell torisonal responses to the torsional stress applied on the outer-shell. The inter-shell interactions and nanotube shear modulus were also calculated and discussed in connection to the theoretical estimations.

  14. A Micromechanics Finite Element Model for Studying the Mechanical Behavior of Spray-On Foam Insulation (SOFI)

    NASA Technical Reports Server (NTRS)

    Ghosn, Louis J.; Sullivan, Roy M.; Lerch, Bradley A.

    2006-01-01

    A micromechanics model has been constructed to study the mechanical behavior of spray-on foam insulation (SOFI) for the external tank. The model was constructed using finite elements representing the fundamental repeating unit of the SOFI microstructure. The details of the micromechanics model were based on cell observations and measured average cell dimensions discerned from photomicrographs. The unit cell model is an elongated Kelvin model (fourteen-sided polyhedron with 8 hexagonal and six quadrilateral faces), which will pack to a 100% density. The cell faces and cell edges are modeled using three-dimensional 20-node brick elements. Only one-eighth of the cell is modeled due to symmetry. By exercising the model and correlating the results with the macro-mechanical foam behavior obtained through material characterization testing, the intrinsic stiffness and Poisson s Ratio of the polymeric cell walls and edges are determined as a function of temperature. The model is then exercised to study the unique and complex temperature-dependent mechanical behavior as well as the fracture initiation and propagation at the microscopic unit cell level.

  15. Dynamically forced cantilever system: A piezo-polymer characterization tool with possible application for micromechanical HF resonator devices

    NASA Astrophysics Data System (ADS)

    Schwödiauer, Reinhard

    2005-04-01

    A cantilever system, driven to a dynamically forced oscillation by a small piezoelectric specimen is presented as a simple and accurate tool to determine the converse dynamic piezocoefficient up to several kHz. The piezoelectric sample is mounted on top of a reflective cantilever where it is free to oscillate without any mechanical constraint. A Nomarsky-interferometer detects the induced cantilever displacement. The presented technique is especially suited for a precise characterization of small and soft piezoelectric polymer-samples with rough surfaces. The capability of the dynamically forced cantilever principle is demonstrated with a LiNbO3 crystal and with a porous ferroelectretic polypropylene foam. Results from measurements between 400 Hz and 5 kHz were found to be in excellent agreement with published values. Additionally, the dynamically forced cantilever principle may possibly improve the sensitivity of some micromechanical cantilever-sensors and it could also be interesting for the design of enhanced micromechanical high frequency mixer filters. Some ideas about are briefly presented.

  16. Dynamically forced cantilever system: A piezo-polymer characterization tool with possible application for micromechanical HF resonator devices

    SciTech Connect

    Schwoediauer, Reinhard

    2005-04-01

    A cantilever system, driven to a dynamically forced oscillation by a small piezoelectric specimen is presented as a simple and accurate tool to determine the converse dynamic piezocoefficient up to several kHz. The piezoelectric sample is mounted on top of a reflective cantilever where it is free to oscillate without any mechanical constraint. A Nomarsky-interferometer detects the induced cantilever displacement. The presented technique is especially suited for a precise characterization of small and soft piezoelectric polymer-samples with rough surfaces. The capability of the dynamically forced cantilever principle is demonstrated with a LiNbO{sub 3} crystal and with a porous ferroelectretic polypropylene foam. Results from measurements between 400 Hz and 5 kHz were found to be in excellent agreement with published values. Additionally, the dynamically forced cantilever principle may possibly improve the sensitivity of some micromechanical cantilever-sensors and it could also be interesting for the design of enhanced micromechanical high frequency mixer filters. Some ideas about are briefly presented.

  17. [Investigation of pathogenic phenotypes and virulence determinants of food-borne Salmonella enterica strains in Caenorhabditis elegans animal model].

    PubMed

    Aksoy, Deniz; Şen, Ece

    2015-10-01

    Salmonellosis, caused by non-typhoidal Salmonella enterica serovars with the consumption of contaminated food, is one of the leading food-borne disease that makes microbial food safety an important public health issue. This study was performed in order to determine the antibiotic resistance, serotyping, plasmid profiles and pathogenicity potentials of food-borne Salmonella isolates in Caenorhabditis elegans animal model system in Edirne province, located at Thrace region of Turkey. In this study, 32 Salmonella isolates, of which 26 belonged to Infantis, four to Enteritidis, one to Telaviv and one to Kentucky serovars, isolated from chicken carcasses were used. Antibiotic resistance profiles were determined by disc diffusion and broth microdilution methods. A new C.elegans nematode animal model system was used to determine the pathogenicity potential of the isolates. The antibiotic resistance profiles revealed that one (3.1%) isolate was resistant to gentamicin, two (6.2%) to ciprofloxacin, three (9.4%) to ampicillin, 18 (56.3%) to kanamycin, 19 (60.8%) to neomycin, 25 (78.1%) to tetracycline, 25 (78.1%) to trimethoprim, 26 (81.25%) to nalidixic acid, 27 (84.4%) to streptomycin and 32 (100%) to sulfonamide. All of the 32 strains were susceptible to chloramphenicol and ampicillin/sulbactam. High levels of resistance to streptomycin, nalidixic acid, tetracycline, trimethoprim, sulfonamide, kanamycin and neomycin was determined. According to the plasmid analysis, six isolates (18.75%) harboured 1-3 plasmids with sizes between 1.2 and 42.4 kb. In C.elegans nematode animal model system, the time (in days) required to kill 50% (TD50) of nematodes was calculated for each experimental group. TD50 values of the nematode group fed with S.Typhimurium ATCC 14028 that was used as the positive control and another group fed with E.coli OP50 as the negative control were 4.2 ± 0.5 days and 8.0 ± 0.02 days, respectively. TD50 of the groups fed with Salmonella isolates ranged

  18. Determining the Mechanical Constitutive Properties of Metals as Function of Strain Rate and temperature: A Combined Experimental and Modeling Approach

    SciTech Connect

    Ian Robertson

    2007-04-28

    Development and validation of constitutive models for polycrystalline materials subjected to high strain-rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions. To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be integrated fully with precise and targeted experimental measurements that not only verify the predictions of the models, but also provide input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experiment is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models. One aspect of the program involves the direct observation of specific mechanisms of micro-plasticity, as these indicate the boundary value problem that should be addressed. This focus on the pre-yield region in the quasi-static effort (the elasto-plastic transition) is also a tractable one from an

  19. Characterization of the embedded micromechanical device approach to the monolithic integration of MEMS with CMOS

    SciTech Connect

    Smith, J.H.; Montague, S.; Sniegowski, J.J.; Murray, J.R.

    1996-10-01

    Recently, a great deal of interest has developed in manufacturing processes that allow the monolithic integration of MicroElectroMechanical Systems (MEMS) with driving, controlling, and signal processing electronics. This integration promises to improve the performance of micromechanical devices as well as lower the cost of manufacturing, packaging, and instrumenting these devices by combining the micromechanical devices with a electronic devices in the same manufacturing and packaging process. In order to maintain modularity and overcome some of the manufacturing challenges of the CMOS-first approach to integration, we have developed a MEMS-first process. This process places the micromechanical devices in a shallow trench, planarizes the wafer, and seals the micromechanical devices in the trench. Then, a high-temperature anneal is performed after the devices are embedded in the trench prior to microelectronics processing. This anneal stress-relieves the micromechanical polysilicon and ensures that the subsequent thermal processing associated with fabrication of the microelectronic processing does not adversely affect the mechanical properties of the polysilicon structures. These wafers with the completed, planarized micromechanical devices are then used as starting material for conventional CMOS processes. The circuit yield for the process has exceeded 98%. A description of the integration technology, the refinements to the technology, and wafer-scale parametric measurements of device characteristics is presented. Additionally, the performance of integrated sensing devices built using this technology is presented.

  20. Formation of Sr adatom chains on SrTiO3 (1 1 0) surface determined by strain.

    PubMed

    Liang, Yan; Li, Fengmiao; Wang, Weihua; Yang, Hao; Guo, Jiandong

    2016-09-14

    The adsorption behavior of Sr adatoms on the SrTiO3 (1 1 0)-(4  ×  1) reconstructed surface with Ti2O3 vacancies distributed in a superstructure is studied by scanning tunneling microscopy and density functional theory calculations. With the adsorption amount increasing, all the Sr adatoms between adjacent Ti2O3 vacancies are closely packed along the quasi-1D stripes on the surface with a uniform separation from each other. The formation of such adatom chains is determined by the surface strain relief-the local lattice relaxations in response to Sr adatoms and Ti2O3 vacancies are incompatible, leading to the strong repulsive interaction between them. Consequently the distribution of Sr chains follows the long-range order of the growth template with their length tunable in a certain range by evaporation amount. PMID:27390937

  1. Formation of Sr adatom chains on SrTiO3 (1 1 0) surface determined by strain

    NASA Astrophysics Data System (ADS)

    Liang, Yan; Li, Fengmiao; Wang, Weihua; Yang, Hao; Guo, Jiandong

    2016-09-01

    The adsorption behavior of Sr adatoms on the SrTiO3 (1 1 0)-(4  ×  1) reconstructed surface with Ti2O3 vacancies distributed in a superstructure is studied by scanning tunneling microscopy and density functional theory calculations. With the adsorption amount increasing, all the Sr adatoms between adjacent Ti2O3 vacancies are closely packed along the quasi-1D stripes on the surface with a uniform separation from each other. The formation of such adatom chains is determined by the surface strain relief—the local lattice relaxations in response to Sr adatoms and Ti2O3 vacancies are incompatible, leading to the strong repulsive interaction between them. Consequently the distribution of Sr chains follows the long-range order of the growth template with their length tunable in a certain range by evaporation amount.

  2. Micromechanisms of brittle fracture: Acoustic emissions and electron channeling analyses

    SciTech Connect

    Gerberich, W.W.

    1990-06-01

    The objectives of this work are to: (i) Evaluate the initial stages of cleavage nucleation in single and polycrystalline samples; (ii) Determine the controlling event(s) which lead(s) to unstable cleavage (is it an unstable cluster'' of microcracks or a crack-tip opening displacement criterion for an array of ligaments surrounding these microcracks ); (iii) Determine how the process zone, which depends upon microstructure and processing history, affects the controlling event(s); (iv) Use selected area channeling patterns (SACP's) to assist in an independent measure of the cleavage fracture stress of grains cleaved at or just outside the elastic-plastic boundary; also, use it to evaluate static and dynamic strain distributions; and (v) Evaluate the effects of dislocation shielding and overload using combined methods of computational mechanics with discretized dislocation arrays and direct observations of dislocations using channeling, etch pit and birefringence methods. Accomplishments are discussed. 15 refs., 3 figs.

  3. Distributions of energy storage rate and microstructural evolution in the area of plastic strain localization during uniaxial tension of austenitic steel

    NASA Astrophysics Data System (ADS)

    Oliferuk, W.; Maj, M.

    2015-08-01

    The presented work is devoted to an experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using Transmission Electron Microscopy (TEM) and Electron Back Scattered Diffraction (EBSC) were performed. On the basis of microstructural studies it is believed that a 0 value of energy storage rate corresponds to the state in which only two dominant components of the texture appear, creating conditions for crystallographic shear banding.

  4. Determining Recoverable and Irrecoverable Contributions to Accumulated Strain in a NiTiPd High-Temperature Shape Memory Alloy During Thermomechanical Cycling

    NASA Technical Reports Server (NTRS)

    Monroe, J. A.; Karaman, I.; Lagoudas, D. C.; Bigelow, G.; Noebe, R. D.; Padula, S., II

    2011-01-01

    When Ni(29.5)Ti(50.5)Pd30 shape memory alloy is thermally cycled under stress, significant strain can accumulate due to elasticity, remnant oriented martensite and plasticity. The strain due to remnant martensite can be recovered by further thermal cycling under 0 MPa until the original transformation-induced volume change and martensite coefficient of thermal expansion are obtained. Using this technique, it was determined that the 8.15% total accumulated strain after cycling under 200 MPa consisted of 0.38%, 3.97% and 3.87% for elasticity, remnant oriented martensite and creep/plasticity, respectively.

  5. Genome Sequence of Avian Escherichia coli Strain IHIT25637, an Extraintestinal Pathogenic E. coli Strain of ST131 Encoding Colistin Resistance Determinant MCR-1

    PubMed Central

    Göttig, Stephan; Bülte, Maria; Fiedler, Sophie; Tietgen, Manuela; Leidner, Ursula; Heydel, Carsten; Bauerfeind, Rolf; Semmler, Torsten

    2016-01-01

    Sequence type 131 (ST131) is one of the predominant Escherichia coli lineages among extraintestinal pathogenic E. coli (ExPEC) that causes a variety of diseases in humans and animals and frequently shows multidrug resistance. Here, we report the first genome sequence of an ST131-ExPEC strain from poultry carrying the plasmid-encoded colistin resistance gene mcr-1. PMID:27587807

  6. Genome Sequence of Avian Escherichia coli Strain IHIT25637, an Extraintestinal Pathogenic E. coli Strain of ST131 Encoding Colistin Resistance Determinant MCR-1.

    PubMed

    Ewers, Christa; Göttig, Stephan; Bülte, Maria; Fiedler, Sophie; Tietgen, Manuela; Leidner, Ursula; Heydel, Carsten; Bauerfeind, Rolf; Semmler, Torsten

    2016-01-01

    Sequence type 131 (ST131) is one of the predominant Escherichia coli lineages among extraintestinal pathogenic E. coli (ExPEC) that causes a variety of diseases in humans and animals and frequently shows multidrug resistance. Here, we report the first genome sequence of an ST131-ExPEC strain from poultry carrying the plasmid-encoded colistin resistance gene mcr-1. PMID:27587807

  7. Advances in Micromechanics Modeling of Composites Structures for Structural Health Monitoring

    NASA Astrophysics Data System (ADS)

    Moncada, Albert

    Although high performance, light-weight composites are increasingly being used in applications ranging from aircraft, rotorcraft, weapon systems and ground vehicles, the assurance of structural reliability remains a critical issue. In composites, damage is absorbed through various fracture processes, including fiber failure, matrix cracking and delamination. An important element in achieving reliable composite systems is a strong capability of assessing and inspecting physical damage of critical structural components. Installation of a robust Structural Health Monitoring (SHM) system would be very valuable in detecting the onset of composite failure. A number of major issues still require serious attention in connection with the research and development aspects of sensor-integrated reliable SHM systems for composite structures. In particular, the sensitivity of currently available sensor systems does not allow detection of micro level damage; this limits the capability of data driven SHM systems. As a fundamental layer in SHM, modeling can provide in-depth information on material and structural behavior for sensing and detection, as well as data for learning algorithms. This dissertation focuses on the development of a multiscale analysis framework, which is used to detect various forms of damage in complex composite structures. A generalized method of cells based micromechanics analysis, as implemented in NASA's MAC/GMC code, is used for the micro-level analysis. First, a baseline study of MAC/GMC is performed to determine the governing failure theories that best capture the damage progression. The deficiencies associated with various layups and loading conditions are addressed. In most micromechanics analysis, a representative unit cell (RUC) with a common fiber packing arrangement is used. The effect of variation in this arrangement within the RUC has been studied and results indicate this variation influences the macro-scale effective material properties and

  8. An integrated micromechanical large particle in flow sorter (MILPIS)

    NASA Astrophysics Data System (ADS)

    Fuad, Nurul M.; Skommer, Joanna; Friedrich, Timo; Kaslin, Jan; Wlodkowic, Donald

    2015-06-01

    At present, the major hurdle to widespread deployment of zebrafish embryo and larvae in large-scale drug development projects is lack of enabling high-throughput analytical platforms. In order to spearhead drug discovery with the use of zebrafish as a model, platforms need to integrate automated pre-test sorting of organisms (to ensure quality control and standardization) and their in-test positioning (suitable for high-content imaging) with modules for flexible drug delivery. The major obstacle hampering sorting of millimetre sized particles such as zebrafish embryos on chip-based devices is their substantial diameter (above one millimetre), mass (above one milligram), which both lead to rapid gravitational-induced sedimentation and high inertial forces. Manual procedures associated with sorting hundreds of embryos are very monotonous and as such prone to significant analytical errors due to operator's fatigue. In this work, we present an innovative design of a micromechanical large particle in-flow sorter (MILPIS) capable of analysing, sorting and dispensing living zebrafish embryos for drug discovery applications. The system consisted of a microfluidic network, revolving micromechanical receptacle actuated by robotic servomotor and opto-electronic sensing module. The prototypes were fabricated in poly(methyl methacrylate) (PMMA) transparent thermoplastic using infrared laser micromachining. Elements of MILPIS were also fabricated in an optically transparent VisiJet resin using 3D stereolithography (SLA) processes (ProJet 7000HD, 3D Systems). The device operation was based on a rapidly revolving miniaturized mechanical receptacle. The latter function was to hold and position individual fish embryos for (i) interrogation, (ii) sorting decision-making and (iii) physical sorting..The system was designed to separate between fertilized (LIVE) and non-fertilized (DEAD) eggs, based on optical transparency using infrared (IR) emitters and receivers embedded in the system

  9. Analysis of the genetic determinants coding for the S-fimbrial adhesin (sfa) in different Escherichia coli strains causing meningitis or urinary tract infections.

    PubMed

    Ott, M; Hacker, J; Schmoll, T; Jarchau, T; Korhonen, T K; Goebel, W

    1986-12-01

    Recently we have described the molecular cloning of the genetic determinant coding for the S-fimbrial adhesin (Sfa), a sialic acid-recognizing pilus frequently found among extraintestinal Escherichia coli isolates. Fimbriae from the resulting Sfa+ E. coli K-12 clone were isolated, and an Sfa-specific antiserum was prepared. Western blots indicate that S fimbriae isolated from different uropathogenic and meningitis-associated E. coli strains, including O83:K1 isolates, were serologically related. The Sfa-specific antibodies did not cross-react with P fimbriae, but did cross-react with F1C fimbriae. Furthermore the sfa+ recombinant DNAs and some cloned sfa-flanking regions were used as probes in Southern experiments. Chromosomal DNAs isolated from O18:K1 and O83:K1 meningitis strains with and without S fimbriae and from uropathogenic O6:K+ strains were hybridized against these sfa-specific probes. Only one copy of the sfa determinant was identified on the chromosome of these strains. No sfa-specific sequences were observed on the chromosome of E. coli K-12 strains and an O7:K1 isolate. With the exception of small alterations in the sfa-coding region the genetic determinants for S fimbriae were identical in uropathogenic O6:K+ and meningitis O18:K1 and O83:K1 strains. The sfa determinant was also detected on the chromosome of K1 isolates with an Sfa-negative phenotype, and specific cross-hybridization signals were visible after blotting against F1C-specific DNA. In addition homology among the different strains was observed in the sfa-flanking regions.

  10. Effect of material inhomogeneity on the cyclic plastic deformation behavior at the microstructural level: micromechanics-based modeling of dual-phase steel

    NASA Astrophysics Data System (ADS)

    Paul, Surajit Kumar

    2013-07-01

    The microstructure of dual-phase (DP) steels typically consists of a soft ferrite matrix with dispersed islands of hard martensite phase. Due to the composite effect of ferrite and martensite, DP steels exhibit a unique combination of strain hardening, strength and ductility. A microstructure-based micromechanical modeling approach is adopted in this work to capture the tensile and cyclic plastic deformation behavior of DP steel. During tensile straining, strain incompatibility between the softer ferrite matrix and the harder martensite phase arises due to a difference in the flow characteristics of these two phases. Microstructural-level inhomogeneity serves as the initial imperfection, triggering strain incompatibility, strain partitioning and finally shear band localization during tensile straining. The local deformation in the ferrite phase is constrained by adjacent martensite islands, which locally results in stress triaxiality development in the ferrite phase. As the martensite distribution varies within the microstructure, the stress triaxiality also varies in a band within the microstructure. Inhomogeneous stress and strain distribution within the softer ferrite phase arises even during small tensile straining because of material inhomogeneity. The magnitude of cyclic plastic deformation within the softer ferrite phase also varies according to the stress distribution in the first-quarter cycle tensile loading. Accumulation of tensile/compressive plastic strain with number of cycles is noted in different locations within the ferrite phase during both symmetric stress and strain controlled cycling. The basic mode of cyclic plastic deformation in an inhomogeneous material is cyclic strain accumulation, i.e. ratcheting. Microstructural inhomogeneity results in cyclic strain accumulation in the aggregate DP material even in symmetric stress cycling.

  11. On the benefit of aberration-corrected HAADF-STEM for strain determination and its application to tailoring ferroelectric domain patterns.

    PubMed

    Tang, Y L; Zhu, Y L; Ma, X L

    2016-01-01

    Revealing strains on the unit-cell level is essential for understanding the particular performance of materials. Large-scale strain variations with a unit-cell resolution are important for studying ferroelectric materials since the spontaneous polarizations of such materials are strongly coupled with strains. Aberration-corrected high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) is not so sensitive to the sample thickness and therefore thickness gradients. Consequently it is extremely useful for large-scale strain determination, which can be readily extracted by geometrical phase analysis (GPA). Such a combination has various advantages: it is straightforward, accurate on the unit-cell scale, relatively insensitive to crystal orientation and therefore helpful for large-scale. We take a tetragonal ferroelectric PbTiO3 film as an example in which large-scale strains are determined. Furthermore, based on the specific relationship between lattice rotation and spontaneous polarization (Ps) at 180° domain-walls, the Ps directions are identified, which makes the investigation of ferroelectric domain structures accurate and straightforward. This method is proposed to be suitable for investigating strain-related phenomena in other ferroelectric materials.

  12. Data-driven stochastic models for spatial uncertainties in micromechanical systems

    NASA Astrophysics Data System (ADS)

    Alwan, Aravind; Aluru, N. R.

    2015-11-01

    Accurate uncertainty quantification in engineering systems requires the use of proper data-driven stochastic models that bear a good fidelity with respect to experimentally observed variations. This paper looks at a variety of modeling techniques to represent spatially varying uncertainties in a form that can be incorporated into numerical simulations. In the context of microelectromechanical systems, we consider spatial uncertainties at the device level in the form of surface roughness and at the wafer level in the form of non-uniformities that arise as a result of various microfabrication steps. We discuss methods to obtain roughness characterization data ranging from the use of a simple profilometer probe to imaging-based techniques for the extraction of digitized data from images. We model spatial uncertainties as second-order stochastic process and use Bayesian inference to estimate the model parameters from the input data. We apply the data-driven stochastic models generated from this process to micromechanical actuators and sensors in which these spatial uncertainties are likely to cause significant variation. These include an electrostatically-actuated torsion-spring micromirror, an electromechanical comb-drive actuator and a pressure sensor with a piezoresistive strain gauge. We show that the performance of these devices is sensitive to the presence of spatial uncertainties and a proper modeling of these uncertainties helps us make reliable predictions about the variation in device performance. Where data is available, we even show that the predicted variation can be validated against experimental observations, highlighting the significance of proper stochastic modeling in the analysis of such devices.

  13. Neutron diffraction measurements and micromechanical modelling of temperature-dependent variations in TATB lattice parameters

    DOE PAGESBeta

    Yeager, John D.; Luscher, Darby J.; Vogel, Sven C.; Clausen, Bjorn; Brown, Donald W.

    2016-02-02

    Triaminotrinitrobenzene (TATB) is a highly anisotropic molecular crystal used in several plastic-bonded explosive (PBX) formulations. TATB-based explosives exhibit irreversible volume expansion (“ratchet growth”) when thermally cycled. A theoretical understanding of the relationship between anisotropy of the crystal, crystal orientation distribution (texture) of polycrystalline aggregates, and the intergranular interactions leading to this irreversible growth is necessary to accurately develop physics-based predictive models for TATB-based PBXs under various thermal environments. In this work, TATB lattice parameters were measured using neutron diffraction during thermal cycling of loose powder and a pressed pellet. The measured lattice parameters help clarify conflicting reports in the literaturemore » as these new results are more consistent with one set of previous results than another. The lattice parameters of pressed TATB were also measured as a function of temperature, showing some differences from the powder. This data is used along with anisotropic single-crystal stiffness moduli reported in the literature to model the nominal stresses associated with intergranular constraints during thermal expansion. The texture of both specimens were characterized and the pressed pellet exhibits preferential orientation of (001) poles along the pressing direction, whereas no preferred orientation was found for the loose powder. Lastly, thermal strains for single-crystal TATB computed from lattice parameter data for the powder is input to a self-consistent micromechanical model, which predicts the lattice parameters of the constrained TATB crystals within the pellet. The agreement of these model results with the diffraction data obtained from the pellet is discussed along with future directions of research.« less

  14. Micromechanisms of brittle fracture: STM, TEM and electron channeling analysis. Final report

    SciTech Connect

    Gerberich, W.W.

    1997-01-01

    The original thrust of this grant was to apply newly developed techniques in scanning tunneling and transmission electron microscopy to elucidate the mechanism of brittle fracture. This grant spun-off several new directions in that some of the findings on bulk structural materials could be utilized on thin films or intermetallic single crystals. Modeling and material evaluation efforts in this grant are represented in a figure. Out of this grant evolved the field the author has designated as Contact Fracture Mechanics. By appropriate modeling of stress and strain distribution fields around normal indentations or scratch tracks, various measures of thin film fracture or decohesion and brittle fracture of low ductility intermetallics is possible. These measures of fracture resistance in small volumes are still evolving and as such no standard technique or analysis has been uniformly accepted. For brittle ceramics and ceramic films, there are a number of acceptable analyses such as those published by Lawn, Evans and Hutchinson. For more dissipative systems involving metallic or polymeric films and/or substrates, there is still much to be accomplished as can be surmised from some of the findings in the present grant. In Section 2 the author reviews the funding history and accomplishments associated mostly with bulk brittle fracture. This is followed by Section 3 which covers more recent work on using novel techniques to evaluate fracture in low ductility single crystals or thin films using micromechanical probes. Basically Section 3 outlines how the recent work fits in with the goals of defining contact fracture mechanics and gives an overview of how the several examples in Section 4 (the Appendices) fit into this framework.

  15. Horizontal gene transfer in Histophilus somni and its role in the evolution of pathogenic strain 2336, as determined by comparative genomic analyses

    PubMed Central

    2011-01-01

    Background Pneumonia and myocarditis are the most commonly reported diseases due to Histophilus somni, an opportunistic pathogen of the reproductive and respiratory tracts of cattle. Thus far only a few genes involved in metabolic and virulence functions have been identified and characterized in H. somni using traditional methods. Analyses of the genome sequences of several Pasteurellaceae species have provided insights into their biology and evolution. In view of the economic and ecological importance of H. somni, the genome sequence of pneumonia strain 2336 has been determined and compared to that of commensal strain 129Pt and other members of the Pasteurellaceae. Results The chromosome of strain 2336 (2,263,857 bp) contained 1,980 protein coding genes, whereas the chromosome of strain 129Pt (2,007,700 bp) contained only 1,792 protein coding genes. Although the chromosomes of the two strains differ in size, their average GC content, gene density (total number of genes predicted on the chromosome), and percentage of sequence (number of genes) that encodes proteins were similar. The chromosomes of these strains also contained a number of discrete prophage regions and genomic islands. One of the genomic islands in strain 2336 contained genes putatively involved in copper, zinc, and tetracycline resistance. Using the genome sequence data and comparative analyses with other members of the Pasteurellaceae, several H. somni genes that may encode proteins involved in virulence (e.g., filamentous haemaggutinins, adhesins, and polysaccharide biosynthesis/modification enzymes) were identified. The two strains contained a total of 17 ORFs that encode putative glycosyltransferases and some of these ORFs had characteristic simple sequence repeats within them. Most of the genes/loci common to both the strains were located in different regions of the two chromosomes and occurred in opposite orientations, indicating genome rearrangement since their divergence from a common

  16. Biocompatible Optically Transparent MEMS for Micromechanical Stimulation and Multimodal Imaging of Living Cells.

    PubMed

    Fior, Raffaella; Kwok, Jeanie; Malfatti, Francesca; Sbaizero, Orfeo; Lal, Ratnesh

    2015-08-01

    Cells and tissues in our body are continuously subjected to mechanical stress. Mechanical stimuli, such as tensile and contractile forces, and shear stress, elicit cellular responses, including gene and protein alterations that determine key behaviors, including proliferation, differentiation, migration, and adhesion. Several tools and techniques have been developed to study these mechanobiological phenomena, including micro-electro-mechanical systems (MEMS). MEMS provide a platform for nano-to-microscale mechanical stimulation of biological samples and quantitative analysis of their biomechanical responses. However, current devices are limited in their capability to perform single cell micromechanical stimulations as well as correlating their structural phenotype by imaging techniques simultaneously. In this study, a biocompatible and optically transparent MEMS for single cell mechanobiological studies is reported. A silicon nitride microfabricated device is designed to perform uniaxial tensile deformation of single cells and tissue. Optical transparency and open architecture of the device allows coupling of the MEMS to structural and biophysical assays, including optical microscopy techniques and atomic force microscopy (AFM). We demonstrate the design, fabrication, testing, biocompatibility and multimodal imaging with optical and AFM techniques, providing a proof-of-concept for a multimodal MEMS. The integrated multimodal system would allow simultaneous controlled mechanical stimulation of single cells and correlate cellular response.

  17. Micro-mechanics of Post-mortem Retrieved Cement-Bone Interfaces

    PubMed Central

    Miller, Mark A.; Eberhardt, Alan W.; Cleary, Richard J.; Verdonschot, Nico; Mann, Kenneth A.

    2009-01-01

    The cement-bone interface plays an important role in load transfer between cemented implant systems and adjacent bone, but little is known about the micro-mechanical behavior of this interface following in vivo service. Small samples of post-mortem retrieved cement-bone specimens from cemented total hip replacements were prepared and mechanically loaded to determine the mechanical response to tensile and compressive loading. The morphology of the cement-bone interface was quantified using a CT-based stereology approach. Laboratory prepared specimens were used to represent immediate post-operative conditions for comparison. The stiffness and strength of the cement-bone interface from post-mortem retrievals was much lower than that measured from laboratory prepared specimens. The cement-bone interfaces from post-mortem retrievals were very compliant (under tension and compression) and had a very low tensile strength (0.21 ± 0.32 MPa). With a linear regression model, including interface contact fraction and intersection fraction between cement and bone could explain 71% (p<0.0001) of the variability in experimental response. Bony remodeling following an arthroplasty procedure may contribute to reduced contact between cement and bone and this is associated with weaker and more compliant interfaces. PMID:19658167

  18. [Characterization and determination of antibiotic resistance profiles of a single clone Acinetobacter baumannii strains isolated from blood cultures].

    PubMed

    Karagöz, Alper; Baran, Irmak; Aksu, Neriman; Acar, Sümeyra; Durmaz, Rıza

    2014-10-01

    Acinetobacter baumannii which is a significant cause of nosocomial infections, increases the rate of morbidity and mortality in health care settings especially in intensive care units (ICUs). The aim of this study was to determine the antibiotic resistance profiles of A.baumannii strains isolated from blood cultures of inpatients from different ICUs, wards and hospital environment and evaluate their clonal relationships and epidemiologic features. A total of 54 A.baumannii strains (47 from the blood cultures and 7 from the hospital environment), identified between 01 January 2012-28 December 2012 at the Clinical Microbiology Laboratory of Ankara Numune Training and Research Hospital, Turkey, were included in the study. Identification of A.baumannii isolates and their antimicrobial [sulbactam-ampicillin (SAM), piperacillin (PIP), piperacillin-tazobactam (TZP), ceftazidime (CFZ), cefoperazone-sulbactam (SCF), cefepime (CEF), imipenem (IMP), meropenem (MER), amikacin (AMK), gentamicin (GEN), netilmicin (NT), ciprofloxacin (CIP), levofloxacin (LVF), tetracycline (TET), tigecycline (TG), colistin (COL), trimethoprim-sulfamethoxazole (SXT)] susceptibility testing were performed by Vitek 2 (bioMérieux, France) system. The clonal relationship between the A.baumannii isolates was analysed by pulsed-field gel electrophoresis (PFGE). In our study colistin, tigecycline and netilmicin were found to be the most effective agents against A.baumannii isolates. All of the clinical isolates (n= 47) were found susceptible to COL, however all were resistant to SAM, PIP, TZP, CEF, IPM, CFZ, MER and CIP. While 1.85%, 14.8%, 14.8%, 16.6%, 59.2% and 22.2% of the isolates were susceptible to SCF, AMK, NT, GEN, TG and SXT, respectively; 1.85%, 1.85%, 9.2%, 16.6%, 38.8% and 27.7% of the isolates were intermediate to SCF, TET, AMK, NT, LVF and TG, respectively. Similarly, all of the environmental A.baumannii isolates (n= 7) were resistant to SAM, PIP, TZP, CFZ, CEF, IPM, MER and CIP, and all

  19. Micro-mechanical wavelength-selectable switches for photonic networks

    NASA Astrophysics Data System (ADS)

    Mizukami, Masato; Katagiri, Yoshitada

    2005-12-01

    Reconfigurable wideband photonic networks based on dense wavelength division multiplexing (WDM) are promising for versatile ubiquitous services. In such networks, wavelength-selectable optical switches will be needed for WDM-based routing, which is a primary function of the networks. A critical requirement is a wavelength selection time of 20 ms or less; otherwise, data packets will be lost. Various filters, including acousto-optic filters or Fabry-Perot etalon filters, are candidates for such switches, but all are inadequate because of high driving power or low accuracy in selecting wavelengths. We propose and demonstrate a wavelength-selectable switch that consists of micromechanically movable in/out filters. A series of thirty-two in/out elements with highly wavelength-managed dielectric filter units, which have flat-top spectral responses according to ITU-T grids, are densely packaged into a small space of 45 x24 x11 mm using miniaturized voice-coil motors (VCMs). By accurately arranging the filter elements along a collimating optical beam between fibers, we achieve small total insertion losses of less than 2.5 dB for all elements. By optimizing the VCM torque, we also achieve a wavelength-selection time of 10 ms (The minimum is 5 ms). We also achieve good wavelength reproducibility with an error of less than 0.1 nm, which was confirmed by a repetition test. These results show that the proposed switches are suitable for practical use.

  20. Micromechanical study of protein-DNA interactions and chromosomes

    NASA Astrophysics Data System (ADS)

    Marko, John

    I will discuss micromechanics experiments that our group has used to analyze protein-DNA interactions and chromosome organization. In single-DNA experiments we have found that a feature of protein-DNA complexes is that their dissociation rates can depend strikingly on bulk solution concentrations of other proteins and DNA segments; I will describe experiments which demonstrate this effect, which can involve tens-fold changes in off-rates with submicromolar changes in solution concentrations. Second, I will discuss experiments aimed at analyzing large-scale human chromosome structure; we isolate metaphase chromosomes, which in their native form behave as remarkably elastic networks of chromatin. Exposure to DNA-cutting restriction enzymes completely eliminates this elasticity, indicating that there is not a mechanically contiguous protein ''scaffold'' from which the chromosome gains its stability. I will show results of siRNA experiments indicating that depletion of condensin proteins leads to destabilization of chromosome mechanics, indicating condensin's role as the major chromatin ''cross-linker'' in metaphase chromosomes. Finally I will discuss similar experiments on human G1 nuclei, where we use genetic and chemical modifications to separate the contributions of the nuclear lamina and chromatin to the mechanical stiffness of the nucleus as a whole. Supported by the NSF (DMR-1206868, MCB-1022117) and the NIH (GM105847, CA193419).

  1. Micromechanical Characterization of Polysilicon Films through On-Chip Tests.

    PubMed

    Mirzazadeh, Ramin; Eftekhar Azam, Saeed; Mariani, Stefano

    2016-01-01

    When the dimensions of polycrystalline structures become comparable to the average grain size, some reliability issues can be reported for the moving parts of inertial microelectromechanical systems (MEMS). Not only the overall behavior of the device turns out to be affected by a large scattering, but also the sensitivity to imperfections gets enhanced. In this work, through on-chip tests, we experimentally investigate the behavior of thin polysilicon samples using standard electrostatic actuation/sensing. The discrepancy between the target and actual responses of each sample has then been exploited to identify: (i) the overall stiffness of the film and, according to standard continuum elasticity, a morphology-based value of its Young's modulus; (ii) the relevant over-etch induced by the fabrication process. To properly account for the aforementioned stochastic features at the micro-scale, the identification procedure has been based on particle filtering. A simple analytical reduced-order model of the moving structure has been also developed to account for the nonlinearities in the electrical field, up to pull-in. Results are reported for a set of ten film samples of constant slenderness, and the effects of different actuation mechanisms on the identified micromechanical features are thoroughly discussed. PMID:27483268

  2. Micromechanical Characterization of Polysilicon Films through On-Chip Tests

    PubMed Central

    Mirzazadeh, Ramin; Eftekhar Azam, Saeed; Mariani, Stefano

    2016-01-01

    When the dimensions of polycrystalline structures become comparable to the average grain size, some reliability issues can be reported for the moving parts of inertial microelectromechanical systems (MEMS). Not only the overall behavior of the device turns out to be affected by a large scattering, but also the sensitivity to imperfections gets enhanced. In this work, through on-chip tests, we experimentally investigate the behavior of thin polysilicon samples using standard electrostatic actuation/sensing. The discrepancy between the target and actual responses of each sample has then been exploited to identify: (i) the overall stiffness of the film and, according to standard continuum elasticity, a morphology-based value of its Young’s modulus; (ii) the relevant over-etch induced by the fabrication process. To properly account for the aforementioned stochastic features at the micro-scale, the identification procedure has been based on particle filtering. A simple analytical reduced-order model of the moving structure has been also developed to account for the nonlinearities in the electrical field, up to pull-in. Results are reported for a set of ten film samples of constant slenderness, and the effects of different actuation mechanisms on the identified micromechanical features are thoroughly discussed. PMID:27483268

  3. Micromechanical-biochemical studies of mitotic chromosome elasticity and structure

    NASA Astrophysics Data System (ADS)

    Poirier, Michael Guy

    The structure of mitotic chromosomes was studied by combining micromechanical force measurements with microfluidic biochemical exposures. Our method is to use glass micropipettes attached to either end of a single chromosome to do mechanical experiments in the extracellular buffer. A third pipette can be used to locally 'spray' reactants so as to carry out dynamical mechanical-chemical experiments. The following elastic properties of mitotic chromosomes are found: Young's modulus, Y = 300 Pa; Poisson ratio, sigma = 0.1; Bending rigidity, B = 1 x 10 -22 J·m; Internal viscosity, eta' = 100 kg/m·sec; Volume fraction, ϕ = 0.7; Extensions of less than 3 times the relaxed length are linear and reversible; Extensions beyond 30 fold exhibit a force plateau at 15 nN and convert the chromosome to a disperse ghost-like state with little change in chromatin structure; Mitotic chromosomes are relatively isotropic; dsDNA cuts of at least every 3 kb cause the a mitotic chromosomes to fall apart; dsDNA cuts less frequently than every 50 kb do not affect mitotic chromosome structure. These results lead to the conclusion that mitotic chromosomes are a network crosslinked every 50 kb between which chromatin is fold by chromatin folding proteins, which are likely to be condensins.

  4. Robust design and model validation of nonlinear compliant micromechanisms.

    SciTech Connect

    Howell, Larry L.; Baker, Michael Sean; Wittwer, Jonathan W.

    2005-02-01

    Although the use of compliance or elastic flexibility in microelectromechanical systems (MEMS) helps eliminate friction, wear, and backlash, compliant MEMS are known to be sensitive to variations in material properties and feature geometry, resulting in large uncertainties in performance. This paper proposes an approach for design stage uncertainty analysis, model validation, and robust optimization of nonlinear MEMS to account for critical process uncertainties including residual stress, layer thicknesses, edge bias, and material stiffness. A fully compliant bistable micromechanism (FCBM) is used as an example, demonstrating that the approach can be used to handle complex devices involving nonlinear finite element models. The general shape of the force-displacement curve is validated by comparing the uncertainty predictions to measurements obtained from in situ force gauges. A robust design is presented, where simulations show that the estimated force variation at the point of interest may be reduced from {+-}47 {micro}N to {+-}3 {micro}N. The reduced sensitivity to process variations is experimentally validated by measuring the second stable position at multiple locations on a wafer.

  5. Micromechanical Characterization of Polysilicon Films through On-Chip Tests.

    PubMed

    Mirzazadeh, Ramin; Eftekhar Azam, Saeed; Mariani, Stefano

    2016-07-28

    When the dimensions of polycrystalline structures become comparable to the average grain size, some reliability issues can be reported for the moving parts of inertial microelectromechanical systems (MEMS). Not only the overall behavior of the device turns out to be affected by a large scattering, but also the sensitivity to imperfections gets enhanced. In this work, through on-chip tests, we experimentally investigate the behavior of thin polysilicon samples using standard electrostatic actuation/sensing. The discrepancy between the target and actual responses of each sample has then been exploited to identify: (i) the overall stiffness of the film and, according to standard continuum elasticity, a morphology-based value of its Young's modulus; (ii) the relevant over-etch induced by the fabrication process. To properly account for the aforementioned stochastic features at the micro-scale, the identification procedure has been based on particle filtering. A simple analytical reduced-order model of the moving structure has been also developed to account for the nonlinearities in the electrical field, up to pull-in. Results are reported for a set of ten film samples of constant slenderness, and the effects of different actuation mechanisms on the identified micromechanical features are thoroughly discussed.

  6. Advanced micromechanisms in a multi-level polysilicon technology

    SciTech Connect

    Rodgers, M.S.; Sniegowski, J.J.; Miller, S.L.; Barron, C.C.; McWhorter, P.J.

    1997-08-01

    Quad-level polysilicon surface micromachining technology, comprising three mechanical levels plus an electrical interconnect layer, is giving rise to a new generation of micro-electromechanical devices and assemblies. Enhanced components can not be produced through greater flexibility in fabrication and design. New levels of design complexity that include multi-level gears, single-attempt locks, and optical elements have recently been realized. Extensive utilization of the fourth layer of polysilicon differentiates these latter generation devices from their predecessors. This level of poly enables the fabrication of pin joints, linkage arms, hinges on moveable plates, and multi-level gear assemblies. The mechanical design aspects of these latest micromachines will be discussed with particular emphasis on a number of design aspects of these latest micromachines will be discussed with particular emphasis on a number of design modifications that improve the power, reliability, and smoothness of operation of the microengine. The microengine is the primary actuation mechanism that is being used to drive mirrors out of plane and rotate 1600-{mu}m diameter gears. Also discussed is the authors most advanced micromechanical system to date, a complex proof-of-concept batch-fabricated assembly that, upon transmitting the proper electrical code to a mechanical lock, permits the operation of a micro-optical shutter.

  7. Hybrid circuit cavity quantum electrodynamics with a micromechanical resonator.

    PubMed

    Pirkkalainen, J-M; Cho, S U; Li, Jian; Paraoanu, G S; Hakonen, P J; Sillanpää, M A

    2013-02-14

    Hybrid quantum systems with inherently distinct degrees of freedom have a key role in many physical phenomena. Well-known examples include cavity quantum electrodynamics, trapped ions, and electrons and phonons in the solid state. In those systems, strong coupling makes the constituents lose their individual character and form dressed states, which represent a collective form of dynamics. As well as having fundamental importance, hybrid systems also have practical applications, notably in the emerging field of quantum information control. A promising approach is to combine long-lived atomic states with the accessible electrical degrees of freedom in superconducting cavities and quantum bits (qubits). Here we integrate circuit cavity quantum electrodynamics with phonons. Apart from coupling to a microwave cavity, our superconducting transmon qubit, consisting of tunnel junctions and a capacitor, interacts with a phonon mode in a micromechanical resonator, and thus acts like an atom coupled to two different cavities. We measure the phonon Stark shift, as well as the splitting of the qubit spectral line into motional sidebands, which feature transitions between the dressed electromechanical states. In the time domain, we observe coherent conversion of qubit excitation to phonons as sideband Rabi oscillations. This is a model system with potential for a quantum interface, which may allow for storage of quantum information in long-lived phonon states, coupling to optical photons or for investigations of strongly coupled quantum systems near the classical limit.

  8. Micromechanical model for isolated polymer-colloid clusters under tension

    NASA Astrophysics Data System (ADS)

    Dargazany, Roozbeh; Lin, Jiaqi; Khalili, Leila; Itskov, Mikhail; Chen, Hsieh; Alexander-Katz, Alfredo

    2016-10-01

    Binary polymer-colloid (PC) composites form the majority of biological load-bearing materials. Due to the abundance of the polymer and particles, and their simple aggregation process, PC clusters are used broadly by nature to create biomaterials with a variety of functions. However, our understanding of the mechanical features of the clusters and their load transfer mechanism is limited. Our main focus in this paper is the elastic behavior of close-packed PC clusters formed in the presence of polymer linkers. Therefore, a micromechanical model is proposed to predict the constitutive behavior of isolated polymer-colloid clusters under tension. The mechanical response of a cluster is considered to be governed by a backbone chain, which is the stress path that transfers most of the applied load. The developed model can reproduce the mean behavior of the clusters and is not dependent on their local geometry. The model utilizes four geometrical parameters for defining six shape descriptor functions which can affect the geometrical change of the clusters in the course of deformation. The predictions of the model are benchmarked against an extensive set of simulations by coarse-grained-Brownian dynamics, where clusters with different shapes and sizes were considered. The model exhibits good agreement with these simulations, which, besides its relative simplicity, makes the model an excellent add-on module for implementation into multiscale models of nanocomposites.

  9. Prediction of fracture healing under axial loading, shear loading and bending is possible using distortional and dilatational strains as determining mechanical stimuli

    PubMed Central

    Steiner, Malte; Claes, Lutz; Ignatius, Anita; Niemeyer, Frank; Simon, Ulrich; Wehner, Tim

    2013-01-01

    Numerical models of secondary fracture healing are based on mechanoregulatory algorithms that use distortional strain alone or in combination with either dilatational strain or fluid velocity as determining stimuli for tissue differentiation and development. Comparison of these algorithms has previously suggested that healing processes under torsional rotational loading can only be properly simulated by considering fluid velocity and deviatoric strain as the regulatory stimuli. We hypothesize that sufficient calibration on uncertain input parameters will enhance our existing model, which uses distortional and dilatational strains as determining stimuli, to properly simulate fracture healing under various loading conditions including also torsional rotation. Therefore, we minimized the difference between numerically simulated and experimentally measured courses of interfragmentary movements of two axial compressive cases and two shear load cases (torsional and translational) by varying several input parameter values within their predefined bounds. The calibrated model was then qualitatively evaluated on the ability to predict physiological changes of spatial and temporal tissue distributions, based on respective in vivo data. Finally, we corroborated the model on five additional axial compressive and one asymmetrical bending load case. We conclude that our model, using distortional and dilatational strains as determining stimuli, is able to simulate fracture-healing processes not only under axial compression and torsional rotation but also under translational shear and asymmetrical bending loading conditions. PMID:23825112

  10. Spread and strain determination of Varroa destructor (Acari: Varroidae) in Madagascar since its first report in 2010.

    PubMed

    Rasolofoarivao, Henriette; Clémencet, Johanna; Ravaomanarivo, Lala Harivelo Raveloson; Razafindrazaka, Dimby; Reynaud, Bernard; Delatte, Hélène

    2013-08-01

    Varroa destructor is a major pest in world beekeeping. It was first detected in Madagascar in 2010 on the endemic honeybee Apis mellifera unicolor. To evaluate V. destructor spread dynamics in Madagascar a global survey was conducted in 2011-2012. A total of 695 colonies from 30 districts were inspected for the presence of mites. 2 years after its introduction, nine districts were found infested. Varroa destructor spread was relatively slow compared to other countries with a maximum progression of 40 km per year, the five newly infested districts being located next to the first infested ones. The incidence of mite infestation was also investigated by monitoring 73 colonies from five apiaries during 1 year (2011-2012). Sixty percent of local colony mortality was recorded after 1 year of survey. Varroa destructor strain determination was done by partial sequencing of the cytochrome oxidase I gene of 13 phoretic mites sampled in five districts. A single V. destructor mitochondrial haplotype was detected, the Korean type, also present in the closest African countries. A global pathogen survey was also conducted on the colonies inspected for mite presence. The greater wax moth, Galleria mellonella has been found in all colonies all over the country. Two other pathogens and morphological abnormalities in workers, such as deformed wings, were found associated with only V. destructor presence. A prevention management plan must be implemented to delimit mite spread across the island.

  11. Flow Curve Determination at Large Plastic Strain Levels: Limitations of the Membrane Theory in the Analysis of the Hydraulic Bulge Test

    NASA Astrophysics Data System (ADS)

    Lemoine, X.; Iancu, A.; Ferron, G.

    2011-05-01

    Nowadays, an accurate determination of the true stress-strain curve is a key-element for all finite element (FE) forming predictions. Since the introduction of Advanced High Strength Steels (AHSS) for the automotive market, the standard uniaxial tension test suffers the drawback of relatively low uniform elongations. The extrapolation of the uniaxial stress-strain curve up to large strains is not without consequence in forming predictions—especially formability and springback. One of the means to solve this problem is to use experimental tests where large plastic strain levels can be reached. The hydraulic bulge test is one of these tests. The effective plastic strain levels reached in the bulge test are of about 0.7. From an experimental standpoint, the biaxial flow stress is estimated using measurement of fluid pressure, and calculation of thickness and curvature at the pole, via appropriate measurements and assumptions. The biaxial stress at the pole is determined using the membrane equilibrium equation. The analysis proposed in this paper consists of performing "virtual experiments" where the results obtained by means of FE calculations are used as input data for determining the biaxial stress-strain law in agreement with the experimental procedure. In this way, a critical discussion of the experimental procedure can be made, by comparing the "experimental" stress-strain curve (Membrane theory curve) with the "reference" one introduced in the simulations. In particular, the influences of the "(die diameter)/thickness" ratio and of the plastic anisotropy are studied, and limitations of the hydraulic bulge test analysis are discussed.

  12. Direct Determination of the Effect of Strain on Domain Morphology in Ferroelectric Superlattices with Scanning Probe Microscopy

    SciTech Connect

    Kathan-Galipeau, Kendra; Wu, Pingping; Li, Yulan; Chen, Long-Qing; Soukiassian, A.; Zhu, Ye; Muller, David A.; Xi, X. X.; Schlom, Darrell G.; Bonnell, D. A.

    2012-09-04

    A variant of piezo force microscopy was used to characterize the effect of strain on polarization in [(BaTiO3)n/(SrTiO3)m]p superlattices. The measurements were compared to theoretical predictions based on phase-field calculations. When polarization is constrained to be perpendicular to the substrate, the measured polarization and domain morphology agree quantitatively with the predictions. This case allows the presence of an internal electric field in the thin film to be identified. The measured trend in piezoelectric response with strain state was in qualitative agreement with predictions and the differences were consistent with the presence of internal electrical fields. Clear differences in domain morphology with strain were observed and in some cases the lateral anisotropic strain appeared to influence the domain morphology. The differences in magnitude and morphology were attributed to the internal electric fields and anisotropic strains.

  13. Development of a High-Temperature Tensile Tester for Micromechanical Characterization of Materials Supporting Meso-Scale ICME Models

    NASA Astrophysics Data System (ADS)

    Alam, Zafir; Eastman, David; Jo, Minjea; Hemker, Kevin

    2016-09-01

    A high-temperature tensile tester (HTTT) has been established for the evaluation of micro-mechanical properties of materials at the meso-scale. Metals and ceramics can now be tested at temperatures and strain rates between room temperature and 1200°C and 10-5 s-1 to 10-1 s-1, respectively. The samples are heated in a compact clam shell furnace and strain is measured directly in the sample gage with digital image correlation. The HTTT extracts representative mechanical properties, as evidenced by the similarity in the evaluated micro-tensile properties of a solid solution-strengthened Ni-base superalloy Ni-625 with that of the bulk. The effectiveness of the HTTT has also been demonstrated in evaluating the tensile and stress relaxation/short-term creep properties of a polycrystalline Ni-base superalloy René 88DT. The versatility in carrying out tensile, short-term creep, bend tests, and fracture toughness measurements makes the HTTT a robust experimental tool for small-scale and scale-specific benchmarking of multi-scale ICME models.

  14. Microstructural Analysis and Micromechanical Modeling of Flow Behaviour of Dual Phase Steels Using a Representative Volume Element Method

    NASA Astrophysics Data System (ADS)

    Amirmaleki, Maedeh

    Micromechanical modeling of flow curves of DP500 and DP600 steels in uniaxial tension was carried out using the representative volume element (RVE) method. Digimat and ABAQUS software were coupled and used to provide the required RVE model parameters and to perform simulations. Modeling results were validated using the experimental flow curves of the steels. It was found that the flow curve of DP500 steel was accurately predicted from the onset of plastic deformation up to the onset of necking. In case of DP600 steel, the numerical flow curve accurately predicted the experimental flow curve of steel after 0.07 strain up to necking strain. The RVE size of 12.7x12.7x12.7 mum and 7.9x7.9x7.9 mum containing 26 martensite islands were found as the optimum RVE sizes for DP500 and DP600 steel, respectively. A mesh of C3D4 elements having a size of 0.050 mum was found to be the optimum element type and mesh size.

  15. Micromechanics effects in creep of metal-matrix composites

    NASA Astrophysics Data System (ADS)

    Davis, L. C.; Allison, J. E.

    1995-12-01

    The creep of metal-matrix composites is analyzed by finite element techniques. An axisymmetric unit-cell model with spherical reinforcing particles is used. Parameters appropriate to TiC particles in a precipitation-hardened (2219) Al matrix are chosen. The effects of matrix plasticity and residual stresses on the creep of the composite are calculated. We confirm (1) that the steady-state rate is independent of the particle elastic moduli and the matrix elastic and plastic properties, (2) that the ratio of composite to matrix steady-state rates depends only on the volume fraction and geometry of the reinforcing phase, and (3) that this ratio can be determined from a calculation of the stress-strain relation for the geometrically identical composite (same phase volume and geometry) with rigid particles in the appropriate power-law hardening matrix. The values of steady-state creep are compared to experimental ones (Krajewski et al.). Continuum mechanics predictions give a larger reduction of the composite creep relative to the unreinforced material than measured, suggesting that the effective creep rate of the matrix is larger than in unreinforced precipitation-hardened Al due to changes in microstructure, dislocation density, or creep mechanism. Changes in matrix creep properties are also suggested by the comparison of calculated and measured creep strain rates in the primary creep regime, where significantly different time dependencies are found. It is found that creep calculations performed for a timeindependent matrix creep law can be transformed to obtain the creep for a time-dependent creep law.

  16. Forces loading the tarsal joint in the hind limb of the horse, determined from in vivo strain measurements of the third metatarsal bone.

    PubMed

    Schamhardt, H C; Hartman, W; Lammertink, J L

    1989-05-01

    Strain gauge rosettes were bonded to the dorsal, lateral, medial, and plantar aspects of the third metatarsal bone in the hind limbs of 6 ponies. The maximal compressive principal strain was approximately -600 X 10(-6) m/m, and exceeded the amplitudes of the tensile strains at all aspects of the bone. After transformation, the shear strain and the principal strains parallel and perpendicular to the bone were obtained. The first peak in the bending strain was higher in the dorsal and lateral aspects, and the second peak was higher in the medial and plantar aspects. Young modulus of elasticity was determined in a 4-point bending test at the dorsal and plantar sides; it averaged 19.5 GPa in tension and compression. Applying linear bending theory, the eccentricity of an axial force parallel or a bending force perpendicular to the bone were calculated. The position where the total force penetrated the tarsometatarsal joint surface was largely within the joint surface, indicating that the joint is merely loaded in (eccentric) compression.

  17. A unique set of micromechanics equations for high-temperature metal matrix composites

    NASA Technical Reports Server (NTRS)

    Hopkins, Dale A.; Chamis, Christos C.

    1988-01-01

    A unique set of micromechanic equations is presented for high-temperature metal matrix composites. The set includes expressions to predict mechanical properties, thermal properties and constituent microstresses for the unidirectional fiber reinforced ply. The equations are derived based on a mechanics of materials formulation assuming a square array unit cell model of a single fiber, surrounding matrix and an interphase to account for the chemical reaction which commonly occurs between fiber and matrix. A three-dimensional finite element analysis was used to perform a preliminary validation of the equations. Excellent agreement between properties predicted using the micromechanics equations and properties simulated by the finite element analyses are demonstrated. Implementation of the micromechanics equations as part of an integrated computational capability for nonlinear structural analysis of high temperature multilayered fiber composites is illustrated.

  18. A unique set of micromechanics equations for high temperature metal matrix composites

    NASA Technical Reports Server (NTRS)

    Hopkins, D. A.; Chamis, C. C.

    1985-01-01

    A unique set of micromechanic equations is presented for high temperature metal matrix composites. The set includes expressions to predict mechanical properties, thermal properties and constituent microstresses for the unidirectional fiber reinforced ply. The equations are derived based on a mechanics of materials formulation assuming a square array unit cell model of a single fiber, surrounding matrix and an interphase to account for the chemical reaction which commonly occurs between fiber and matrix. A three-dimensional finite element analysis was used to perform a preliminary validation of the equations. Excellent agreement between properties predicted using the micromechanics equations and properties simulated by the finite element analyses are demonstrated. Implementation of the micromechanics equations as part of an integrated computational capability for nonlinear structural analysis of high temperature multilayered fiber composites is illustrated.

  19. Micromechanical Machining Processes and their Application to Aerospace Structures, Devices and Systems

    NASA Technical Reports Server (NTRS)

    Friedrich, Craig R.; Warrington, Robert O.

    1995-01-01

    Micromechanical machining processes are those micro fabrication techniques which directly remove work piece material by either a physical cutting tool or an energy process. These processes are direct and therefore they can help reduce the cost and time for prototype development of micro mechanical components and systems. This is especially true for aerospace applications where size and weight are critical, and reliability and the operating environment are an integral part of the design and development process. The micromechanical machining processes are rapidly being recognized as a complementary set of tools to traditional lithographic processes (such as LIGA) for the fabrication of micromechanical components. Worldwide efforts in the U.S., Germany, and Japan are leading to results which sometimes rival lithography at a fraction of the time and cost. Efforts to develop processes and systems specific to aerospace applications are well underway.

  20. Population Genetic Structure of Listeria monocytogenes Strains as Determined by Pulsed-Field Gel Electrophoresis and Multilocus Sequence Typing

    PubMed Central

    Henri, Clémentine; Félix, Benjamin; Guillier, Laurent; Leekitcharoenphon, Pimlapas; Michelon, Damien; Mariet, Jean-François; Aarestrup, Frank M.; Mistou, Michel-Yves; Hendriksen, René S.

    2016-01-01

    ABSTRACT Listeria monocytogenes is a ubiquitous bacterium that may cause the foodborne illness listeriosis. Only a small amount of data about the population genetic structure of strains isolated from food is available. This study aimed to provide an accurate view of the L. monocytogenes food strain population in France. From 1999 to 2014, 1,894 L. monocytogenes strains were isolated from food at the French National Reference Laboratory for L. monocytogenes and classified according to the five risk food matrices defined by the European Food Safety Authority (EFSA). A total of 396 strains were selected on the basis of different pulsed-field gel electrophoresis (PFGE) clusters, serotypes, and strain origins and typed by multilocus sequence typing (MLST), and the MLST results were supplemented with MLST data available from Institut Pasteur, representing human and additional food strains from France. The distribution of sequence types (STs) was compared between food and clinical strains on a panel of 675 strains. High congruence between PFGE and MLST was found. Out of 73 PFGE clusters, the two most prevalent corresponded to ST9 and ST121. Using original statistical analysis, we demonstrated that (i) there was not a clear association between ST9 and ST121 and the food matrices, (ii) serotype IIc, ST8, and ST4 were associated with meat products, and (iii) ST13 was associated with dairy products. Of the two major STs, ST121 was the ST that included the fewest clinical strains, which might indicate lower virulence. This observation may be directly relevant for refining risk analysis models for the better management of food safety. IMPORTANCE This study showed a very useful backward compatibility between PFGE and MLST for surveillance. The results enabled better understanding of the population structure of L. monocytogenes strains isolated from food and management of the health risks associated with L. monocytogenes food strains. Moreover, this work provided an accurate view

  1. A macro-micromechanics analysis of a notched metal matrix composite

    NASA Technical Reports Server (NTRS)

    Bigelow, C. A.; Naik, R. A.

    1990-01-01

    A macro-micromechanics analysis was formulated to determine the matrix and fiber behavior near the notch tip in a center-notched metal matrix composite. Results are presented for a boron/aluminum monolayer. The macro-level analysis models the entire notched specimen using a three dimensional finite element program which uses the vanishing-fiber-diameter model to model the elastic-plastic behavior of the matrix and the elastic behavior of the fiber. The micro-behavior is analyzed using a Discrete Fiber-Matrix (DFM) model containing one fabric and the surrounding matrix. The dimensions of the DFM model were determined by the ply thickness and the fiber volume fraction and corresponded to the size of the notch-tip element in the macro-level analysis. The boundary conditions applied to the DFM model were determined from the macro-level analysis. Stress components within the DFM model were calculated and stress distributions are presented along selected planes and surfaces within the DFM model, including the fiber-matrix interface. Yielding in the matrix was examined at the notch tip in both the macro- and micro-level analyses. The DFM model predicted higher stresses (24 percent) in the fiber compared to the global analysis. In the notch-tip element, the interface stresses indicated that a multi-axial criterion may be required to predict interfacial failure. The DFM analysis predicted yielding to initiate in the notch-tip element at a stress level 28 percent lower than predicted by the global analysis.

  2. Phylogeny of 54 representative strains of species in the family Pasteurellaceae as determined by comparison of 16S rRNA sequences.

    PubMed Central

    Dewhirst, F E; Paster, B J; Olsen, I; Fraser, G J

    1992-01-01

    Virtually complete 16S rRNA sequences were determined for 54 representative strains of species in the family Pasteurellaceae. Of these strains, 15 were Pasteurella, 16 were Actinobacillus, and 23 were Haemophilus. A phylogenetic tree was constructed based on sequence similarity, using the Neighbor-Joining method. Fifty-three of the strains fell within four large clusters. The first cluster included the type strains of Haemophilus influenzae, H. aegyptius, H. aphrophilus, H. haemolyticus, H. paraphrophilus, H. segnis, and Actinobacillus actinomycetemcomitans. This cluster also contained A. actinomycetemcomitans FDC Y4, ATCC 29522, ATCC 29523, and ATCC 29524 and H. aphrophilus NCTC 7901. The second cluster included the type strains of A. seminis and Pasteurella aerogenes and H. somnus OVCG 43826. The third cluster was composed of the type strains of Pasteurella multocida, P. anatis, P. avium, P. canis, P. dagmatis, P. gallinarum, P. langaa, P. stomatis, P. volantium, H. haemoglobinophilus, H. parasuis, H. paracuniculus, H. paragallinarum, and A. capsulatus. This cluster also contained Pasteurella species A CCUG 18782, Pasteurella species B CCUG 19974, Haemophilus taxon C CAPM 5111, H. parasuis type 5 Nagasaki, P. volantium (H. parainfluenzae) NCTC 4101, and P. trehalosi NCTC 10624. The fourth cluster included the type strains of Actinobacillus lignieresii, A. equuli, A. pleuropneumoniae, A. suis, A. ureae, H. parahaemolyticus, H. parainfluenzae, H. paraphrohaemolyticus, H. ducreyi, and P. haemolytica. This cluster also contained Actinobacillus species strain CCUG 19799 (Bisgaard taxon 11), A. suis ATCC 15557, H. ducreyi ATCC 27722 and HD 35000, Haemophilus minor group strain 202, and H. parainfluenzae ATCC 29242. The type strain of P. pneumotropica branched alone to form a fifth group. The branching of the Pasteurellaceae family tree was quite complex. The four major clusters contained multiple subclusters. The clusters contained both rapidly and slowly evolving

  3. Species-specific PCR for the Diagnosis and Determination of Antibiotic Susceptibilities of Brucella Strains Isolated from Tehran, Iran

    PubMed Central

    Irajian, Gholam Reza; Masjedian Jazi, Faramarz; Mirnejad, Reza; Piranfar, Vahhab; Zahraei salehi, Taghi; Amir Mozafari, Noor; Ghaznavi-rad, Ehsanollah; Khormali, Mahmoud

    2016-01-01

    Background: Brucellosis is an endemic zoonotic disease in the Middle East. This study intended to design a uniplex PCR assay for the detection and differentiation of Brucella at the species level and determining the antibiotic susceptibility pattern of Brucella in Iran. Methods: Sixty-eight Brucella specimens (38 animal and 30 human specimens) were analyzed using PCR (using one pair of primers). Antibiotic susceptibility patterns were evaluated and compared using the E-Test and disk diffusion susceptibility test. Tigecycline susceptibility pattern was compared with other antibiotics. Results: Thirty six isolates of B. melitensis, 2 isolates of B. abortus and 1 isolate of B. suis from the 38 animal specimens, 24 isolates of B. melitensis and 6 isolates of B. abortus from the 30 human specimens were differentiated. The MIC50 values of doxycycline for human and animal specimens were 125 and 10 μg/ml, respectively, tigecycline 0.064 μg/ml for human specimens and 0.125μg/ml for animal specimens, and trimethoprim/ sulfamethoxazole and ciprofloxacin 0.065 and 0.125μg/ml, respectively, for both human and animal specimens. The highest MIC50 value of streptomycin in the human specimens was 0.5μg/ml and 1μg/ml for the animal specimens. The greatest resistance shown was to tetracycline and gentamicin, respectively. Conclusion: Uniplex PCR for the detection and differentiation of Brucella at the strain level is faster and less expensive than multiplex PCR, and the antibiotics doxycycline, rifampin, trimethoprim-sulfamethoxazole, ciprofloxacin, and ofloxacin are the most effective antibiotics for treating brucellosis. Resistance to tigecycline is increasing, and we recommend that it be used in a combination regimen. PMID:27799972

  4. Micromechanical combined stress analysis: MICSTRAN, a user manual

    NASA Technical Reports Server (NTRS)

    Naik, R. A.

    1992-01-01

    Composite materials are currently being used in aerospace and other applications. The ability to tailor the composite properties by the appropriate selection of its constituents, the fiber and matrix, is a major advantage of composite materials. The Micromechanical Combined Stress Analysis (MICSTRAN) code provides the materials engineer with a user-friendly personal computer (PC) based tool to calculate overall composite properties given the constituent fiber and matrix properties. To assess the ability of the composite to carry structural loads, the materials engineer also needs to calculate the internal stresses in the composite material. MICSTRAN is a simple tool to calculate such internal stresses with a composite ply under combined thermomechanical loading. It assumes that the fibers have a circular cross-section and are arranged either in a repeating square or diamond array pattern within a ply. It uses a classical elasticity solution technique that has been demonstrated to calculate accurate stress results. Input to the program consists of transversely isotropic fiber properties and isotropic matrix properties such as moduli, Poisson's ratios, coefficients of thermal expansion, and volume fraction. Output consists of overall thermoelastic constants and stresses. Stresses can be computed under the combined action of thermal, transverse, longitudinal, transverse shear, and longitudinal shear loadings. Stress output can be requested along the fiber-matrix interface, the model boundaries, circular arcs, or at user-specified points located anywhere in the model. The MICSTRAN program is Windows compatible and takes advantage of the Microsoft Windows graphical user interface which facilitates multitasking and extends memory access far beyond the limits imposed by the DOS operating system.

  5. Development of a high pressure micromechanical force apparatus.

    PubMed

    Lee, Bo Ram; Koh, Carolyn A; Sum, Amadeu K

    2014-09-01

    The formation of gas hydrates and subsequent plugging of pipelines are risks that need to be well understood during the production and transportation of oil and gas in subsea flowlines. These flowlines are typically operating at low temperature and high pressure conditions, which are well within the hydrate formation stability region. One of the key processes for hydrate plugs to develop is the agglomeration of hydrates. To obtain a more comprehensive understanding on this problem, we have developed a high-pressure micromechanical force (MMF) apparatus to directly measure cohesive forces between gas hydrate particles. The MMF system is housed in a stainless steel vessel that can withstand pressures of up to 10 MPa, thereby facilitating studies on a broad spectrum of hydrate formers and conditions. The MMF apparatus comprises of two cantilever fibers: one is stationary and another is manipulated via a nano-manipulator. Water droplets (~500 μm in diameter) are placed at the end of the each cantilever fiber so that they can be converted to hydrate. In order to demonstrate the stability of this apparatus, CH4/C2H6 (74.7 mol. %/25.3 mol. %) mixed hydrates were prepared at 2 MPa and -5 °C and annealed at 0 °C for 15 h. Subsequently, the hydrate particle cohesive force was measured at 2 °C. Compared with the cohesive force of cyclopentane hydrates in cyclopentane liquid (~4.3 mN/m), the average cohesive force of gas hydrates was about 10 times higher, ~43 mN/m. Studies using this new high pressure MMF apparatus will be central to better understand the agglomeration of hydrates in multiphase flowlines. PMID:25273785

  6. Development of a high pressure micromechanical force apparatus

    NASA Astrophysics Data System (ADS)

    Lee, Bo Ram; Koh, Carolyn A.; Sum, Amadeu K.

    2014-09-01

    The formation of gas hydrates and subsequent plugging of pipelines are risks that need to be well understood during the production and transportation of oil and gas in subsea flowlines. These flowlines are typically operating at low temperature and high pressure conditions, which are well within the hydrate formation stability region. One of the key processes for hydrate plugs to develop is the agglomeration of hydrates. To obtain a more comprehensive understanding on this problem, we have developed a high-pressure micromechanical force (MMF) apparatus to directly measure cohesive forces between gas hydrate particles. The MMF system is housed in a stainless steel vessel that can withstand pressures of up to 10 MPa, thereby facilitating studies on a broad spectrum of hydrate formers and conditions. The MMF apparatus comprises of two cantilever fibers: one is stationary and another is manipulated via a nano-manipulator. Water droplets (˜500 μm in diameter) are placed at the end of the each cantilever fiber so that they can be converted to hydrate. In order to demonstrate the stability of this apparatus, CH4/C2H6 (74.7 mol. %/25.3 mol. %) mixed hydrates were prepared at 2 MPa and -5 °C and annealed at 0 °C for 15 h. Subsequently, the hydrate particle cohesive force was measured at 2 °C. Compared with the cohesive force of cyclopentane hydrates in cyclopentane liquid (˜4.3 mN/m), the average cohesive force of gas hydrates was about 10 times higher, ˜43 mN/m. Studies using this new high pressure MMF apparatus will be central to better understand the agglomeration of hydrates in multiphase flowlines.

  7. Micromechanical design of hierarchical composites using global load sharing theory

    NASA Astrophysics Data System (ADS)

    Rajan, V. P.; Curtin, W. A.

    2016-05-01

    Hierarchical composites, embodied by natural materials ranging from bone to bamboo, may offer combinations of material properties inaccessible to conventional composites. Using global load sharing (GLS) theory, a well-established micromechanics model for composites, we develop accurate numerical and analytical predictions for the strength and toughness of hierarchical composites with arbitrary fiber geometries, fiber strengths, interface properties, and number of hierarchical levels, N. The model demonstrates that two key material properties at each hierarchical level-a characteristic strength and a characteristic fiber length-control the scalings of composite properties. One crucial finding is that short- and long-fiber composites behave radically differently. Long-fiber composites are significantly stronger than short-fiber composites, by a factor of 2N or more; they are also significantly tougher because their fiber breaks are bridged by smaller-scale fibers that dissipate additional energy. Indeed, an "infinite" fiber length appears to be optimal in hierarchical composites. However, at the highest level of the composite, long fibers localize on planes of pre-existing damage, and thus short fibers must be employed instead to achieve notch sensitivity and damage tolerance. We conclude by providing simple guidelines for microstructural design of hierarchical composites, including the selection of N, the fiber lengths, the ratio of length scales at successive hierarchical levels, the fiber volume fractions, and the desired properties of the smallest-scale reinforcement. Our model enables superior hierarchical composites to be designed in a rational way, without resorting either to numerical simulation or trial-and-error-based experimentation.

  8. Micromechanical modeling of dynamic fracture in heterogeneous materials

    NASA Astrophysics Data System (ADS)

    Zhai, Jun

    Fracture is the principal mode of failure for a variety of materials under dynamic conditions. The mathematical complexity precludes analytical solution to be obtained. The difficulty is especially pronounced when material inhomogeneities and anisotropy need to be considered. Recently, alumina/titanium diboride (Al2O3/TiB 2) composites with a wide range of micro and nano phase sizes and phase morphologies have been developed in the School of Materials Science and Engineering at Georgia Tech. In order to understand failure mechanisms in this material system and the influence of phase morphologies and phase size on fracture resistance, a numerical framework is needed to explicitly account for arbitrary microstructures and fracture patterns. Micromechanical modeling and simulation provide an important approach for analyzing the effects of material inhomogeneity and anisotropy over a range of microscopic length scales. A framework is proposed in this research for explicit modeling and simulation of microscopic damage/fracture/failure processes. The model and approach account for the real arbitrary microstructural morphologies. A cohesive finite element method (CFEM) based on cohesive surface theory is used. A fully dynamic kinetic framework and finite deformation kinematic formulation are used. Mesh independence of solution is studied and verified. Idealized microstructures containing circular and elliptical particles and real microstructures with arbitrary morphologies are used to investigate the effects of phase morphologies, phase size and phase anisotropy on fracture of this ceramic composite system. Numerical results show that rnicrostructural variations give rise to a range of fracture resistance. Higher fracture resistance is obtained from microstructures with fine evenly distributed microstructural reinforcement entities. The failure mode is found to be significantly influenced by the interfacial bonding strength between the phases. Two distinct failure modes

  9. Extent of systemic spread determines CD8+ T cell immunodominance for laboratory strains, smallpox vaccines and zoonotic isolates of vaccinia virus1

    PubMed Central

    Flesch, Inge E.A.; Hollett, Natasha A.; Wong, Yik Chun; Quinan, Bárbara Resende; Howard, Debbie; da Fonseca, Flávio G.; Tscharke, David C.

    2015-01-01

    CD8+ T cells that recognize virus-derived peptides presented on MHC class I (pMHC) are vital anti-viral effectors. The pMHC presented by any given virus vary greatly in immunogenicity allowing them to be ranked in an immunodominance hierarchy. However, the full range of parameters that determine immunodominance and the underlying mechanisms remain unknown. Here we show across a range of vaccinia virus (VACV) strains, including the current clonal smallpox vaccine, that the ability of a strain to spread systemically correlated with reduced immunodominance. Reduction in immunodominance was observed both in the lymphoid system and at the primary site of infection. Mechanistically, reduced immunodominance was associated with more robust priming and especially priming in the spleen. Finally, we show this is not just a property of vaccine and laboratory strains of virus, because an association between virulence and immunodominance was also observed in isolates from an outbreak of zoonotic VACV that occurred in Brazil. PMID:26195812

  10. Extent of Systemic Spread Determines CD8+ T Cell Immunodominance for Laboratory Strains, Smallpox Vaccines, and Zoonotic Isolates of Vaccinia Virus.

    PubMed

    Flesch, Inge E A; Hollett, Natasha A; Wong, Yik Chun; Quinan, Bárbara Resende; Howard, Debbie; da Fonseca, Flávio G; Tscharke, David C

    2015-09-01

    CD8(+) T cells that recognize virus-derived peptides presented on MHC class I are vital antiviral effectors. Such peptides presented by any given virus vary greatly in immunogenicity, allowing them to be ranked in an immunodominance hierarchy. However, the full range of parameters that determine immunodominance and the underlying mechanisms remain unknown. In this study, we show across a range of vaccinia virus strains, including the current clonal smallpox vaccine, that the ability of a strain to spread systemically correlated with reduced immunodominance. Reduction in immunodominance was observed both in the lymphoid system and at the primary site of infection. Mechanistically, reduced immunodominance was associated with more robust priming and especially priming in the spleen. Finally, we show this is not just a property of vaccine and laboratory strains of virus, because an association between virulence and immunodominance was also observed in isolates from an outbreak of zoonotic vaccinia virus that occurred in Brazil.

  11. Superlattice strain gage

    DOEpatents

    Noel, B.W.; Smith, D.L.; Sinha, D.N.

    1988-06-28

    A strain gage comprising a strained-layer superlattice crystal exhibiting piezoelectric properties is described. A substrate upon which such a strained-layer superlattice crystal has been deposited is attached to an element to be monitored for strain. A light source is focused on the superlattice crystal and the light reflected from, passed through, or emitted from the crystal is gathered and compared with previously obtained optical property data to determine the strain in the element. 8 figs.

  12. Superlattice strain gage

    DOEpatents

    Noel, Bruce W.; Smith, Darryl L.; Sinha, Dipen N.

    1990-01-01

    A strain gage comprising a strained-layer superlattice crystal exhibiting piezoelectric properties is described. A substrate upon which such a strained-layer superlattice crystal has been deposited is attached to an element to be monitored for strain. A light source is focused on the superlattice crystal and the light reflected from, passed through, or emitted from the crystal is gathered and compared with previously obtained optical property data to determine the strain in the element.

  13. Influence of alloy inhomogeneities on the determination by Raman scattering of composition and strain in Si1-xGex/Si(001) layers

    NASA Astrophysics Data System (ADS)

    Reparaz, J. S.; Marcus, I. C.; Goñi, A. R.; Garriga, M.; Alonso, M. I.

    2012-07-01

    In this work, we investigate the influence of alloy composition inhomogeneities on the vibrational properties of strained Si1-xGex/Si layers with x ranging from 0 to 0.5. We show that the frequencies of the principal alloy vibrational modes (Ge-Ge, Si-Ge, and Si-Si) are strongly influenced by the distribution of Ge atoms within the alloy layers, which becomes gradually random following a series of sequential annealing steps. Our measurements suggest that the composition dependence of the optical phonon frequencies in fully random and unstrained alloys is well described by the results previously published by Alonso and Winer [Phys. Rev. B 39, 10056 (1989)]. In the general case of an alloy layer with unknown degree of compositional inhomogeneity and/or strain relaxation, though the analysis of the Raman spectra is not straightforward. Therefore, we propose an analytical/graphical method to accurately estimate the Ge content and residual strain of SiGe layers exhibiting any level of compositional disorder or strain status, by performing a single Raman measurement. This would be extremely useful in situations where x-ray measurements cannot be conducted. We show that our procedure to treat the Raman data holds for the whole compositional range but with different accuracy depending upon the case: (i) For annealed SiGe layers (mostly strain relaxed) the Ge content x can be directly determined with high accuracy of ±0.01. (ii) For strained samples (usually as-grown samples) an extra criterion must be adopted seeking for a graphical solution, accounting for the degree of compositional inhomogeneity. In this case, the error in the determination of Ge content depends on alloy composition, being the upper bound ±0.02 for x <0.3 and ±0.03 for x >0.3.

  14. Salicylic acid determines differential senescence produced by two Turnip mosaic virus strains involving reactive oxygen species and early transcriptomic changes.

    PubMed

    Manacorda, Carlos Augusto; Mansilla, Carmen; Debat, Humberto Julio; Zavallo, Diego; Sánchez, Flora; Ponz, Fernando; Asurmendi, Sebastián

    2013-12-01

    Losses produced by virus diseases depend mostly on symptom severity. Turnip mosaic virus (TuMV) is one of the most damaging and widespread potyvirus infecting members of the family Brassicaceae, including Arabidopsis thaliana. We used JPN1 and UK1 TuMV strains to characterize viral infections regarding symptom development, senescence progression, antioxidant response, reactive oxygen species (ROS) accumulation, and transcriptional profiling. Both isolates, despite accumulating similar viral titers, induced different symptomatology and strong differences in oxidative status. Early differences in several senescence-associated genes linked to the ORE1 and ORS1 regulatory networks as well as persistent divergence in key ROS production and scavenging systems of the plant were detected. However, at a later stage, both strains induced nutrient competition, indicating that senescence rates are influenced by different mechanisms upon viral infections. Analyses of ORE1 and ORS1 levels in infected Brassica juncea plants showed a similar pattern, suggesting a conserved differential response to both strains in Brassicaceae spp. Transcriptional analysis of the ORE1 and ORS1 regulons showed similarities between salicylic acid (SA) response and the early induction triggered by UK1, the most severe strain. By means of SA-defective NahG transgenic plants, we found that differential senescence progression and ROS accumulation between strains rely on an intact SA pathway. PMID:23945002

  15. Serum Neutralization Assay for the Determination of Antibody Levels Against Non-Polio Enterovirus Strains in Central and Western Greece.

    PubMed

    Fikatas, Antonis; Dimitriou, Tilemachos G; Kyriakopoulou, Zaharoula; Tsachouridou, Ourania; Gartzonika, Constantina; Levidiotou-Stefanou, Stamatina; Amoutzias, Grigoris D; Markoulatos, Panayotis

    2016-09-01

    Mutations and recombination events have been identified in enteroviruses. Point mutations accumulate with a frequency of 6.3 × 10(-4) per base pair per replication cycle affecting the fitness, the circulation, and the infectivity of enteroviral strains. In the present report, the serological status of the Central and Western Greek population (Larissa and Ioannina, respectively) in the 1-10-year, 11-20-year, 21-30-year, and 31-40-year age groups against six non-polio enterovirus strains, their respective echovirus prototypes, and Sabin 1, 2, and 3 vaccine strains was evaluated, through serum-neutralization assay. In the Western Greek population, antibody levels were detected only for clinical isolates of E30 serotype in all age groups, and for environmental isolate LR61G3 (E6 serotype) only in the 31-40 age group, whereas an immunity level was observed in the Central Greek population, against all strains, except for EIS6B (E3 serotype). Amino acid substitutions were encountered across the structural region of the capsid, between the prototypes and the respective isolates. These substitutions may alter the antigenicity of each strain and may explain the variations observed in the neutralization titers of the different strains. As a consequence, these substitutions severely affect antibody binding and increase the ability of the virus to escape the immune response. It is tempting to assume that changes in the antigenic properties observed in circulating echoviruses represent a selection of viral variants that are less prone to be neutralized by human antibodies. These facts argue for the need of immunological studies to the population to avoid epidemics due to the circulation of highly evolved derivatives. PMID:27410516

  16. Sequence of Colonization Determines the Composition of Mixed Biofilms by Escherichia coli O157:H7 and O111:H8 Strains.

    PubMed

    Wang, Rong; Kalchayanand, Norasak; Bono, James L

    2015-08-01

    Bacterial biofilms are one of the potential sources of cross-contamination in food processing environments. Shiga toxin-producing Escherichia coli (STEC) O157:H7 and O111:H8 are important foodborne pathogens capable of forming biofilms, and the coexistence of these two STEC serotypes has been detected in various food samples and in multiple commercial meat plants throughout the United States. Here, we investigated how the coexistence of these two STEC serotypes and their sequence of colonization could affect bacterial growth competition and mixed biofilm development. Our data showed that E. coli O157:H7 strains were able to maintain a higher cell percentage in mixed biofilms with the co-inoculated O111:H8 companion strains, even though the results of planktonic growth competition were strain dependent. On solid surfaces with preexisting biofilms, the sequence of colonization played a critical role in determining the composition of the mixed biofilms because early stage precolonization significantly affected the competition results between the E. coli O157:H7 and O111:H8 strains. The precolonizer of either serotype was able to outgrow the other serotype in both planktonic and biofilm phases. The competitive interactions among the various STEC serotypes would determine the composition and structure of the mixed biofilms as well as their potential risks to food safety and public health, which is largely influenced by the dominant strains in the mixtures. Thus, the analysis of mixed biofilms under various conditions would be of importance to determine the nature of mixed biofilms composed of multiple microorganisms and to help implement the most effective disinfection operations accordingly.

  17. Determination of microcystins in natural blooms and cyanobacterial strain cultures by matrix solid-phase dispersion and liquid chromatography-mass spectrometry.

    PubMed

    Cameán, Ana; Moreno, Isabel M; Ruiz, María J; Picó, Yolanda

    2004-10-01

    An analytical procedure based on matrix solid-phase dispersion (MSPD) and liquid chromatography-mass spectrometry (LC-MS) was developed for determining three microcystins (MCs) in natural water blooms and cyanobacteria strain cultures. The procedure involves sample homogenization with C(18), washed with dichloromethane to eliminate interfering compounds, and elution with acidic methanol. Results were compared to those achieved by using an organic solvent standard method. Mean recoveries of MCs with MSPD were 85-92% with intra-day relative standard deviation (RSDs) of 9-19%, whereas organic solvent extraction resulted in recovery rates of 92-105% with intra-day RSDs ranging from 8 to 18%. Limits of quantification (LOQs) were 1 microg g(-1) dry weight for the MCs either by MSPD or organic solvent extraction. The two analytical methods tested were specific and sensitive to the extraction of MCs and were applied to the detection of MCs in water blooms and culture strains. The concentration of MCs varied from 7 to 3,330 microg g(-1) of lyophilized cells with MC-LR always showing the highest concentration. MCs levels were higher in culture strains than in water blooms, except for MC-LR, whose concentration in blooms was slightly superior to that determined in culture strains.

  18. Strain rate hardening: a hidden but critical mechanism for biological composites?

    PubMed

    Chintapalli, Ravi Kiran; Breton, Stephanie; Dastjerdi, Ahmad Khayer; Barthelat, Francois

    2014-12-01

    Natural materials such as nacre, bone, collagen and spider silk boast unusual combinations of stiffness, strength and toughness. Behind this performance is a staggered microstructure, which consists of stiff and elongated inclusions embedded in a softer and more deformable matrix. The micromechanics of deformation and failure associated with this microstructure are now well understood at the "unit cell" level, the smallest representative volume for this type of material. However, these mechanisms only translate to high performance if they propagate throughout large volumes, an important condition which is often overlooked. Here we present, for the first time, a model which captures the conditions for either spreading of deformations or localization, which determines whether a staggered composite is brittle or deformable at the macroscale. The macroscopic failure strain for the material was calculated as function of the viscoplastic properties of the interfaces and the severity of the defect. As expected, larger strains at failure can be achieved when smaller defects are present within the material, or with more strain hardening at the interface. The model also shows that strain rate hardening is a powerful source of large deformations for the material as well, a result we confirmed and validated with tensile experiments on glass-polydimethylsiloxane (PDMS) nacre-like staggered composites. An important implication is that natural materials, largely made of rate-dependent materials, could rely on strain rate hardening to tolerate initial defects and damage to maintain their functionality. Strain rate hardening could also be harnessed and optimized in bio-inspired composites in order to maximize their overall performance. PMID:25174668

  19. Strain rate hardening: a hidden but critical mechanism for biological composites?

    PubMed

    Chintapalli, Ravi Kiran; Breton, Stephanie; Dastjerdi, Ahmad Khayer; Barthelat, Francois

    2014-12-01

    Natural materials such as nacre, bone, collagen and spider silk boast unusual combinations of stiffness, strength and toughness. Behind this performance is a staggered microstructure, which consists of stiff and elongated inclusions embedded in a softer and more deformable matrix. The micromechanics of deformation and failure associated with this microstructure are now well understood at the "unit cell" level, the smallest representative volume for this type of material. However, these mechanisms only translate to high performance if they propagate throughout large volumes, an important condition which is often overlooked. Here we present, for the first time, a model which captures the conditions for either spreading of deformations or localization, which determines whether a staggered composite is brittle or deformable at the macroscale. The macroscopic failure strain for the material was calculated as function of the viscoplastic properties of the interfaces and the severity of the defect. As expected, larger strains at failure can be achieved when smaller defects are present within the material, or with more strain hardening at the interface. The model also shows that strain rate hardening is a powerful source of large deformations for the material as well, a result we confirmed and validated with tensile experiments on glass-polydimethylsiloxane (PDMS) nacre-like staggered composites. An important implication is that natural materials, largely made of rate-dependent materials, could rely on strain rate hardening to tolerate initial defects and damage to maintain their functionality. Strain rate hardening could also be harnessed and optimized in bio-inspired composites in order to maximize their overall performance.

  20. Micromechanical characterization of the interphase zone in adhesive joints

    NASA Astrophysics Data System (ADS)

    Safavi-Ardebili, Vahid

    The interphase in an epoxy-aluminum adhesive system has been characterized using acoustic microscopy, scanning electron microscopy, ion etching, energy-dispersive x-ray analysis, and nano-indentation, with particular attention to micromechanical characterization. A systematic search method was proposed for locating an acoustic coupling fluid which had a sufficiently low velocity of sound and attenuation factor for the acoustic microscopy of polymers. A new acoustic microscope system was developed, which operated at a frequency of 250 MHz, and utilized an ultrasonic probe designed specifically for the characteristics of the new couplant. This acoustic microscope system is the first one being able to induce Rayleigh waves on the surface of plastics. A new angular spectrum formulation was introduced for a type-II acoustic microscope probe. No prior assumption, regarding the field on the aperture plane of the transducer, is needed in this new formulation. The angular spectrum model was extended to the case of a type-I probe in the presence of deviations of the lens shape from the ideal sphere as long as it remains axisymmetric. A multiple curve fitting procedure was used to infer the interphase property profiles by simultaneously fitting a large number of calculated V (z) curves to the experimental ones. The interphase was between 2 and 6 mum thick, and corresponded to a region of greater resistance to ion etching and a marked absence of the silica particles used in the epoxy adhesive. The acoustic microscope V(z) scans showed that the interphase had, on average, 20% larger values of tensile and shear moduli than the bulk, and smaller values of the shear attenuation factor and density than the bulk adhesive. Nano-indentation tests, traversing various sections of the interphase from the aluminum to the bulk adhesive, showed that the interphase region had, on average, a reduced elastic modulus (E/(1 - nu2)) that was 13% greater than that of the bulk adhesive. The

  1. Towards the development of micromechanics equations for ceramic matrix composites via fiber substructuring

    NASA Technical Reports Server (NTRS)

    Murthy, P. L. N.; Chamis, C. C.

    1992-01-01

    A generic unit cell model which includes a unique fiber substructuring concept is proposed for the development of micromechanics equations for continuous fiber reinforcement ceramic composites. The unit cell consists of three constituents: fiber, matrix, and an interphase. In the present approach, the unit cell is further subdivided into several slices and the equations of micromechanics are derived for each slice. These are subsequently integrated to obtain ply level properties. A stand alone computer code containing the micromechanics model as a module is currently being developed specifically for the analysis of ceramic matrix composites. Towards this development, equivalent ply property results for a SiC/Ti-15-3 composite with 0.5 fiber volume ratio are presented and compared with those obtained from customary micromechanics models to illustrate the concept. Also, comparisons with limited experimental data for the ceramic matrix composite, SiC/RBSN (Reaction Bonded Silicon Nitride) with a 0.3 fiber volume ratio are given to validate the concepts.

  2. A micromechanics model for the acoustic nonlinearity parameter in solids with distributed microcracks

    NASA Astrophysics Data System (ADS)

    Zhao, Youxuan; Qiu, Yanjun; Jacobs, Laurence J.; Qu, Jianmin

    2016-02-01

    As a longitudinal wave propagates through a linearly elastic solid with distributed cracks, the solid is subjected to cyclic tension and compression. During the tensile cycles, a crack might be open and its faces are traction-free. During the compressive cycles, a crack might be closed and its faces are in contact. Such contact may also be frictional because of crack face roughness. Such tension and compression asymmetry causes acoustic nonlinearity. This paper develops a micromechanics model that relates the crack density to the acoustic nonlinearity parameter. The model is based on a micromechanics homogenization of the cracked solid under dynamic loading. It is shown that the acoustic nonlinearity parameter is proportional to the crack density. Furthermore, the acoustic nonlinearity parameter also depends on the frequency of the wave motion, and the coefficient of friction of the crack faces. Unlike the second harmonic generated by dislocations, the amplitude of the second harmonic due to crack face contact is proportional to the amplitude of the fundamental frequency. To validate the micromechanics model, the finite element method is used to simulate wave propagation in solid with randomly distributed microcracks. The micromechanics model predictions agree well with the finite element simulation results.

  3. Micromechanical Prediction of the Effective Behavior of Fully Coupled Electro-Magneto-Thermo-Elastic Multiphase Composites

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob

    2000-01-01

    The micromechanical generalized method of cells model is employed for the prediction of the effective moduli of electro-magneto-thermo-elastic composites. These include the effective elastic, piezoelectric, piezomagnetic, dielectric, magnetic permeability, electromagnetic coupling moduli, as well as the effective thermal expansion coefficients and the associated pyroelectric and pyromagnetic constants. Results are given for fibrous and periodically bilaminated composites.

  4. Polyols, not sugars, determine the structural diversity of anti-streptococcal liamocins produced by Aureobasidium pullulans strain NRRL 50380

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Liamocins are polyol-lipids produced by the fungus Aureobasidium pullulans, and have selective antibacterial activity against Streptococcus species. Liamocins produced by A. pullulans strain NRRL 50380 on sucrose medium have a D-mannitol head-group ester linked to 3,5-dihydroxydecanoate acyl chains,...

  5. Identification of putative plant pathogenic determinants from a draft genome sequence of an opportunistic klebsiella pneumoniae strain

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Klebsiella pneumoniae has been known historically as a causal agent of bacterial pneumonia. More recently, K. pneumoniaerepresentatives have been shown to have a broad ecological distribution and are recognized nitrogen-fixers. Previously, we demonstrated the capacity of K. pneumoniae strain Kp 5-1R...

  6. Isolation of culturable mycobiota from agricultural soils and determination of tolerance to glyphosate of nontoxigenic Aspergillus section Flavi strains.

    PubMed

    Carranza, Cecilia S; Barberis, Carla L; Chiacchiera, Stella M; Dalcero, Ana María; Magnoli, Carina E

    2016-01-01

    Glyphosate-based herbicides are extensively used in Argentina's agricultural system to control undesirable weeds. This study was conducted to evaluate the culturable mycobiota [colony forming units (CFU) g(-1) and frequency of fungal genera or species] from an agricultural field exposed to pesticides. In addition, we evaluated the tolerance of A. oryzae and nontoxigenic A. flavus strains to high concentrations (100 to 500 mM - 17,000 to 84,500 ppm) of a glyphosate commercial formulation. The analysis of the mycobiota showed that the frequency of the main fungal genera varied according to the analyzed sampling period. Aspergillus spp. or Aspergillus section Flavi strains were isolated from 20 to 100% of the soil samples. Sterilia spp. were also observed throughout the sampling (50 to 100%). Aspergillus section Flavi tolerance assays showed that all of the tested strains were able to develop at the highest glyphosate concentration tested regardless of the water availability conditions. In general, significant reductions in growth rates were observed with increasing concentrations of the herbicide. However, a complete inhibition of fungal growth was not observed with the concentrations assayed. This study contributes to the knowledge of culturable mycobiota from agricultural soils exposed to pesticides and provides evidence on the effective growth ability of A. oryzae and nontoxigenic A. flavus strains exposed to high glyphosate concentrations in vitro. PMID:26549415

  7. Isolation of culturable mycobiota from agricultural soils and determination of tolerance to glyphosate of nontoxigenic Aspergillus section Flavi strains.

    PubMed

    Carranza, Cecilia S; Barberis, Carla L; Chiacchiera, Stella M; Dalcero, Ana María; Magnoli, Carina E

    2016-01-01

    Glyphosate-based herbicides are extensively used in Argentina's agricultural system to control undesirable weeds. This study was conducted to evaluate the culturable mycobiota [colony forming units (CFU) g(-1) and frequency of fungal genera or species] from an agricultural field exposed to pesticides. In addition, we evaluated the tolerance of A. oryzae and nontoxigenic A. flavus strains to high concentrations (100 to 500 mM - 17,000 to 84,500 ppm) of a glyphosate commercial formulation. The analysis of the mycobiota showed that the frequency of the main fungal genera varied according to the analyzed sampling period. Aspergillus spp. or Aspergillus section Flavi strains were isolated from 20 to 100% of the soil samples. Sterilia spp. were also observed throughout the sampling (50 to 100%). Aspergillus section Flavi tolerance assays showed that all of the tested strains were able to develop at the highest glyphosate concentration tested regardless of the water availability conditions. In general, significant reductions in growth rates were observed with increasing concentrations of the herbicide. However, a complete inhibition of fungal growth was not observed with the concentrations assayed. This study contributes to the knowledge of culturable mycobiota from agricultural soils exposed to pesticides and provides evidence on the effective growth ability of A. oryzae and nontoxigenic A. flavus strains exposed to high glyphosate concentrations in vitro.

  8. Expression of factor H binding protein in meningococcal strains can vary at least 15-fold and is genetically determined.

    PubMed

    Biagini, Massimiliano; Spinsanti, Marco; De Angelis, Gabriella; Tomei, Sara; Ferlenghi, Ilaria; Scarselli, Maria; Rigat, Fabio; Messuti, Nicola; Biolchi, Alessia; Muzzi, Alessandro; Anderloni, Giulia; Brunelli, Brunella; Cartocci, Elena; Buricchi, Francesca; Tani, Chiara; Stella, Maria; Moschioni, Monica; Del Tordello, Elena; Colaprico, Annalisa; Savino, Silvana; Giuliani, Marzia M; Delany, Isabel; Pizza, Mariagrazia; Costantino, Paolo; Norais, Nathalie; Rappuoli, Rino; Masignani, Vega

    2016-03-01

    Factor H binding protein (fHbp) is a lipoprotein of Neisseria meningitidis important for the survival of the bacterium in human blood and a component of two recently licensed vaccines against serogroup B meningococcus (MenB). Based on 866 different amino acid sequences this protein is divided into three variants or two families. Quantification of the protein is done by immunoassays such as ELISA or FACS that are susceptible to the sequence variation and expression level of the protein. Here, selected reaction monitoring mass spectrometry was used for the absolute quantification of fHbp in a large panel of strains representative of the population diversity of MenB. The analysis revealed that the level of fHbp expression can vary at least 15-fold and that variant 1 strains express significantly more protein than variant 2 or variant 3 strains. The susceptibility to complement-mediated killing correlated with the amount of protein expressed by the different meningococcal strains and this could be predicted from the nucleotide sequence of the promoter region. Finally, the absolute quantification allowed the calculation of the number of fHbp molecules per cell and to propose a mechanistic model of the engagement of C1q, the recognition component of the complement cascade.

  9. Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties.

    PubMed

    Brown, Erika P; Koh, Carolyn A

    2016-01-01

    Investigating the effect of surfactants on clathrate hydrate growth and morphology, especially particle shell strength and cohesion force, is critical to advancing new strategies to mitigate hydrate plug formation. In this study, dodecylbenzenesulfonic acid and polysorbate 80 surfactants were included during the growth of cyclopentane hydrates at several concentrations above and below the critical micelle concentration. A novel micromechanical method was applied to determine the force required to puncture the hydrate shell using a glass cantilever (with and without surfactants), with annealing times ranging from immediately after the hydrate nucleated to 90 minutes after formation. It was shown that the puncture force was decreased by the addition of both surfactants up to a maximum of 79%. Over the entire range of annealing times (0-90 minutes), the thickness of the hydrate shell was also measured. However, there was no clear change in shell thickness with the addition of surfactants. The growth rate of the hydrate shell was found to vary less than 15% with the addition of surfactants. The cohesive force between two hydrate particles was measured for each surfactant and found to be reduced by 28% to 78%. Interfacial tension measurements were also performed. Based on these results, microscopic changes to the hydrate shell morphology (due to the presence of surfactants) were proposed to cause the decrease in the force required to break the hydrate shell, since no macroscopic morphology changes were observed. Understanding the hydrate shell strength can be critical to reducing the capillary bridge interaction between hydrate particles or controlling the release of unconverted water from the interior of the hydrate particle, which can cause rapid hydrate conversion.

  10. Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties.

    PubMed

    Brown, Erika P; Koh, Carolyn A

    2016-01-01

    Investigating the effect of surfactants on clathrate hydrate growth and morphology, especially particle shell strength and cohesion force, is critical to advancing new strategies to mitigate hydrate plug formation. In this study, dodecylbenzenesulfonic acid and polysorbate 80 surfactants were included during the growth of cyclopentane hydrates at several concentrations above and below the critical micelle concentration. A novel micromechanical method was applied to determine the force required to puncture the hydrate shell using a glass cantilever (with and without surfactants), with annealing times ranging from immediately after the hydrate nucleated to 90 minutes after formation. It was shown that the puncture force was decreased by the addition of both surfactants up to a maximum of 79%. Over the entire range of annealing times (0-90 minutes), the thickness of the hydrate shell was also measured. However, there was no clear change in shell thickness with the addition of surfactants. The growth rate of the hydrate shell was found to vary less than 15% with the addition of surfactants. The cohesive force between two hydrate particles was measured for each surfactant and found to be reduced by 28% to 78%. Interfacial tension measurements were also performed. Based on these results, microscopic changes to the hydrate shell morphology (due to the presence of surfactants) were proposed to cause the decrease in the force required to break the hydrate shell, since no macroscopic morphology changes were observed. Understanding the hydrate shell strength can be critical to reducing the capillary bridge interaction between hydrate particles or controlling the release of unconverted water from the interior of the hydrate particle, which can cause rapid hydrate conversion. PMID:26618773

  11. Radiation effects and micromechanics of SiC/SiC composites

    SciTech Connect

    Ghoniem, N.M.

    1992-01-01

    The basic displacement damage process in SiC has been fully explored, and the mechanisms identified. Major modifications have been made to the theory of damage dosimetry in Fusion, Fission and Ion Simulation studies of Sic. For the first time, calculations of displacements per atoms in SiC can be made in any irradiation environment. Applications to irradiations in fusion first wall neutron spectra (ARIES and PROMETHEUS) as well as in fission spectra (HIFIR and FFTF) are given. Nucleation of helium-filled cavities in SiC was studied, using concepts of stability theory to determine the size of the critical nucleus under continuous generation of helium and displacement damage. It is predicted that a bimodal distribution of cavity sizes is likely to occur in heavily irradiated SiC. A study of the chemical compatibility of SiC composite structures with fusion reactor coolants at high-temperatures was undertaken. It was shown that SiC itself is chemically very stable in helium coolants in the temperature range 500--1000[degree]C. However, current fiber/matrix interfaces, such as C and BN are not. The fracture mechanics of high-temperature matrix cracks with bridging fibers is now in progress. A fundamentally unique approach to study the propagation and interaction of cracks in a composite was initiated. The main focus of our research during the following period will be : (1) Theory and experiments for the micro-mechanics of high-temperature failure; and (2) Analysis of radiation damage and microstructure evolution.

  12. Passive micromechanical tags. An investigation into writing information at nanometer resolution on micrometer size objects

    SciTech Connect

    Schmieder, R.W.; Bastasz, R.J.

    1995-01-01

    The authors have completed a 3-year study of the technology related to the development of micron-sized passive micromechanical tags. The project was motivated by the discovery in 1990 by the present authors that low energy, high charge state ions (e.g., Xe{sup +44}) can produce nanometer-size damage sites on solid surfaces, and the realization that a pattern of these sites represents information. It was envisioned that extremely small, chemically inert, mechanical tags carrying a large label could be fabricated for a variety of applications, including tracking of controlled substances, document verification, process control, research, and engineering. Potential applications exist in the data storage, chemical, food, security, and other industries. The goals of this project were fully accomplished, and they are fully documented here. The work was both experimental and developmental. Most of the experimental effort was a search for appropriate tag materials. Several good materials were found, and the upper limits of information density were determined (ca. 10{sup 12} bit/cm{sup 2}). Most of the developmental work involved inventing systems and strategies for using these tags, and compiling available technologies for implementing them. The technology provided herein is application-specific: first, the application must be specified, then the tag can be developed for it. The project was not intended to develop a single tag for a single application or for all possible applications. Rather, it was meant to provide the enabling technology for fabricating tags for a range of applications. The results of this project provide sufficient information to proceed directly with such development.

  13. Structure determination of the clean (001) surface of strained Si on Si{sub 1−x}Ge{sub x}

    SciTech Connect

    Shirasawa, Tetsuroh; Takeda, Sakura Nishino; Takahashi, Toshio

    2015-02-09

    The surface structure of the strained Si(001) (thickness of 20 nm) on Si{sub 1−x}Ge{sub x} (x = 0.1, 0.2, and 0.3) was studied by low-energy electron diffraction (LEED). LEED intensity-energy spectra of the 2 × 1 reconstructed clean surfaces showed a systematic change that indicates the lattice contraction along the [001] direction remains even at the surfaces. The atomic structures were quantitatively determined, and they were compared with the unstrained pristine Si. The differences in the atomic position almost follow the difference in the bulk lattice constant determined by X-ray diffraction measurements. The results indicate that the strain produced at the Si/Si{sub 1−x}Ge{sub x} interface remains unchanged up to the surface layer.

  14. A combined molecular dynamics/micromechanics/finite element approach for multiscale constitutive modeling of nanocomposites with interface effects

    NASA Astrophysics Data System (ADS)

    Yang, B. J.; Shin, H.; Lee, H. K.; Kim, H.

    2013-12-01

    We introduce a multiscale framework based on molecular dynamic (MD) simulation, micromechanics, and finite element method (FEM). A micromechanical model, which considers influences of the interface properties, nanoparticle (NP) size, and microcracks, is developed. Then, we perform MD simulations to characterize the mechanical properties of the nanocomposite system (silica/nylon 6) with varying volume fraction and size of NPs. By comparing the MD with micromechanics results, intrinsic physical properties at interfacial region are derived. Finally, we implement the developed model in the FEM code with the derived interfacial parameters, and predict the mechanical behavior of the nanocomposite at the macroscopic scale.

  15. The effect of hydration on the micromechanics of regenerated cellulose fibres from ionic liquid solutions of varying draw ratios.

    PubMed

    Bulota, M; Michud, A; Hummel, M; Hughes, M; Sixta, H

    2016-10-20

    Regenerated cellulose fibres - Ioncell-F, have been prepared with different draw ratios from cellulose solution in 1,5-diazabicyclo[4.3.0]non-5-ene-1-ium acetate ([DBNH]OAc) ionic liquid. Properties of the fibres were investigated in dry and wet conditions. The stiffness of fibres decreased on average 5 times upon the hydration while the tensile strength remained at around 70% of the initial value. The effect of hydration on the deformation mechanisms and mechanical properties was addressed using Raman spectroscopy. Bands located at 1095cm(-1) and 1414cm(-1) corresponding to the glucosidic linkage C-O-C and side groups C-O-H were followed upon straining. Raman band shifts were observed indicating molecular deformations. Moreover, the hydration of fibres altered the shifting rates implying changes in the molecular micromechanics. It is suggested that hydration affects inter-chain hydrogen bonds thus resulting in the slippage of the chains and lower stiffness of fibres. Some discrepancies from the series aggregate model have been observed which is indicative of changes in the deformation mechanisms upon hydration of the fibres. PMID:27474661

  16. Reproducibility and feasibility of right ventricular strain and strain rate (SR) as determined by myocardial speckle tracking during high-intensity upright exercise: a comparison with tissue Doppler-derived strain and SR in healthy human hearts

    PubMed Central

    Lord, Rachel N; George, Keith; Jones, Helen; Somauroo, John

    2014-01-01

    This study aimed to establish feasibility for myocardial speckle tracking (MST) and intra-observer reliability of both MST and tissue velocity imaging (TVI)-derived right ventricular (RV) strain (ϵ) and strain rate (SR) at rest and during upright incremental exercise. RV ϵ and SR were derived using both techniques in 19 healthy male participants. MST-derived ϵ and SR were feasible at rest (85% of segments tracked appropriately). Feasibility reduced significantly with progressive exercise intensity (3% of segments tracking appropriately at 90% maximum heart rate (HRmax)). Coefficient of variations (CoVs) of global ϵ values at rest was acceptable for both TVI and MST (7–12%), with low bias and narrow limits of agreement. Global SR data were less reliable for MST compared with TVI as demonstrated with CoV data (systolic SR=15 and 61%, early diastolic SR=16 and 17% and late diastolic SR=26 and 31% respectively). CoVs of global RV ϵ and SR obtained at 50% HRmax were acceptable using both techniques. As exercise intensity increased to 70 and 90% HRmax, reliability of ϵ and SR values reduced with larger variability in MST. We conclude that RV global and regional ϵ and SR data are feasible, comparable and reliable at rest and at 50% HRmax using both MST and TVI. Reliability was reduced during higher exercise intensities with only TVI acceptable for clinical and scientific use. PMID:26693290

  17. High strain-rate model for fiber-reinforced composites

    SciTech Connect

    Aidun, J.B.; Addessio, F.L.

    1995-07-01

    Numerical simulations of dynamic uniaxial strain loading of fiber-reinforced composites are presented that illustrate the wide range of deformation mechanisms that can be captured using a micromechanics-based homogenization technique as the material model in existing continuum mechanics computer programs. Enhancements to the material model incorporate high strain-rate plastic response, elastic nonlinearity, and rate-dependent strength degradation due to material damage, fiber debonding, and delamination. These make the model relevant to designing composite structural components for crash safety, armor, and munitions applications.

  18. Epithelial entry rather than the ensuing systemic immune response determines the pathogenicity of two Salmonella enterica serovar Typhimurium strains in a mouse model.

    PubMed

    Brandt, Rikke; Petersen, Anne; Brix, Susanne; Licht, Tine Rask; Frøkiær, Hanne

    2013-11-01

    Most studies of Salmonella enterica serovar Typhimurium infection focus only on the pathogenicity of one strain. We investigated whether differences in pathogenicity of two wild-type S. Typhimurium strains; DT120 and SL1344, were related to gut invasion or the resulting immune response. Oral administration of a ten-fold lower number of SL1344 (10(6) CFU) as compared to DT120 (10(7) CFU) resulted in higher bacterial counts in liver and lymph nodes, and led to massive neutrophil infiltration of the spleen, while DT120 administration did not. In contrast, administration of the same dose (10(3) CFU) of the two strains intravenously resulted in the same levels of bacteria and neutrophils in spleen and bone marrow. Oral administration of SL1344 led to an increase in neutrophil apoptosis in both spleen and the bone marrow and four out of five mice died before Day 8, while in DT120 mice, no increase in neutrophil apoptosis was observed and all mice survived until Day 8. This study reveals that two wild-type S. Typhimurium strains, despite evoking highly comparable immune responses upon intravenous injection, exhibit diverse pathogenicity in mice and thus suggests that differences in their invasiveness and survival during gut passage determines the success of the ensuing immune response.

  19. Genomic survey of pathogenicity determinants and VNTR markers in the cassava bacterial pathogen Xanthomonas axonopodis pv. Manihotis strain CIO151.

    PubMed

    Arrieta-Ortiz, Mario L; Rodríguez-R, Luis M; Pérez-Quintero, Álvaro L; Poulin, Lucie; Díaz, Ana C; Arias Rojas, Nathalia; Trujillo, Cesar; Restrepo Benavides, Mariana; Bart, Rebecca; Boch, Jens; Boureau, Tristan; Darrasse, Armelle; David, Perrine; Dugé de Bernonville, Thomas; Fontanilla, Paula; Gagnevin, Lionel; Guérin, Fabien; Jacques, Marie-Agnès; Lauber, Emmanuelle; Lefeuvre, Pierre; Medina, Cesar; Medina, Edgar; Montenegro, Nathaly; Muñoz Bodnar, Alejandra; Noël, Laurent D; Ortiz Quiñones, Juan F; Osorio, Daniela; Pardo, Carolina; Patil, Prabhu B; Poussier, Stéphane; Pruvost, Olivier; Robène-Soustrade, Isabelle; Ryan, Robert P; Tabima, Javier; Urrego Morales, Oscar G; Vernière, Christian; Carrere, Sébastien; Verdier, Valérie; Szurek, Boris; Restrepo, Silvia; López, Camilo; Koebnik, Ralf; Bernal, Adriana

    2013-01-01

    Xanthomonas axonopodis pv. manihotis (Xam) is the causal agent of bacterial blight of cassava, which is among the main components of human diet in Africa and South America. Current information about the molecular pathogenicity factors involved in the infection process of this organism is limited. Previous studies in other bacteria in this genus suggest that advanced draft genome sequences are valuable resources for molecular studies on their interaction with plants and could provide valuable tools for diagnostics and detection. Here we have generated the first manually annotated high-quality draft genome sequence of Xam strain CIO151. Its genomic structure is similar to that of other xanthomonads, especially Xanthomonas euvesicatoria and Xanthomonas citri pv. citri species. Several putative pathogenicity factors were identified, including type III effectors, cell wall-degrading enzymes and clusters encoding protein secretion systems. Specific characteristics in this genome include changes in the xanthomonadin cluster that could explain the lack of typical yellow color in all strains of this pathovar and the presence of 50 regions in the genome with atypical nucleotide composition. The genome sequence was used to predict and evaluate 22 variable number of tandem repeat (VNTR) loci that were subsequently demonstrated as polymorphic in representative Xam strains. Our results demonstrate that Xanthomonas axonopodis pv. manihotis strain CIO151 possesses ten clusters of pathogenicity factors conserved within the genus Xanthomonas. We report 126 genes that are potentially unique to Xam, as well as potential horizontal transfer events in the history of the genome. The relation of these regions with virulence and pathogenicity could explain several aspects of the biology of this pathogen, including its ability to colonize both vascular and non-vascular tissues of cassava plants. A set of 16 robust, polymorphic VNTR loci will be useful to develop a multi-locus VNTR analysis

  20. Genotypic Diversity and Population Structure of Vibrio vulnificus Strains Isolated in Taiwan and Korea as Determined by Multilocus Sequence Typing

    PubMed Central

    Kim, Hye-Jin; Cho, Jae-Chang

    2015-01-01

    The genetic diversity and population structure of Vibrio vulnificus isolates from Korea and Taiwan were investigated using PCR-based assays targeting putative virulence-related genes and multilocus sequence typing (MLST). BOX-PCR genomic fingerprinting identified 52 unique genotypes in 84 environmental and clinical V. vulnificus isolates. The majority (> 50%) of strains had pathogenic genotypes for all loci tested; moreover, many environmental strains had pathogenic genotypes. Although significant (p < 0.05) inter-relationships among the genotypes were observed, the association between genotype and strain source (environmental or clinical) was not significant, indicating that genotypic characteristics alone are not sufficient to predict the isolation source or the virulence of a given V. vulnificus strain and vice versa. MLST revealed 23–35 allelic types per locus analyzed, resulting in a total of 44 unique sequence types (STs). Two major monophyletic groups (lineages A and B) corresponding to the two known lineages of V. vulnificus were observed; lineage A had six STs that were exclusively environmental, whereas lineage B had STs from both environmental and clinical sources. Pathogenic and nonpathogenic genotypes predominated in MLST lineages B and A, respectively. In addition, V. vulnificus was shown to be in linkage disequilibrium (p < 0.05), although two different recombination tests (PHI and Sawyer’s tests) detected significant evidence of recombination. Tajima’s D test also indicated that V. vulnificus might be comprised of recently sub-divided lineages. These results suggested that the two lineages revealed by MLST correspond to two distinct ecotypes of V. vulnificus. PMID:26599487

  1. Genotypic Diversity and Population Structure of Vibrio vulnificus Strains Isolated in Taiwan and Korea as Determined by Multilocus Sequence Typing.

    PubMed

    Kim, Hye-Jin; Cho, Jae-Chang

    2015-01-01

    The genetic diversity and population structure of Vibrio vulnificus isolates from Korea and Taiwan were investigated using PCR-based assays targeting putative virulence-related genes and multilocus sequence typing (MLST). BOX-PCR genomic fingerprinting identified 52 unique genotypes in 84 environmental and clinical V. vulnificus isolates. The majority (> 50%) of strains had pathogenic genotypes for all loci tested; moreover, many environmental strains had pathogenic genotypes. Although significant (p < 0.05) inter-relationships among the genotypes were observed, the association between genotype and strain source (environmental or clinical) was not significant, indicating that genotypic characteristics alone are not sufficient to predict the isolation source or the virulence of a given V. vulnificus strain and vice versa. MLST revealed 23-35 allelic types per locus analyzed, resulting in a total of 44 unique sequence types (STs). Two major monophyletic groups (lineages A and B) corresponding to the two known lineages of V. vulnificus were observed; lineage A had six STs that were exclusively environmental, whereas lineage B had STs from both environmental and clinical sources. Pathogenic and nonpathogenic genotypes predominated in MLST lineages B and A, respectively. In addition, V. vulnificus was shown to be in linkage disequilibrium (p < 0.05), although two different recombination tests (PHI and Sawyer's tests) detected significant evidence of recombination. Tajima's D test also indicated that V. vulnificus might be comprised of recently sub-divided lineages. These results suggested that the two lineages revealed by MLST correspond to two distinct ecotypes of V. vulnificus. PMID:26599487

  2. Assessment of Hip Fracture Risk Using Cross-Section Strain Energy Determined by QCT-Based Finite Element Modeling

    PubMed Central

    Kheirollahi, Hossein; Luo, Yunhua

    2015-01-01

    Accurate assessment of hip fracture risk is very important to prevent hip fracture and to monitor the effect of a treatment. A subject-specific QCT-based finite element model was constructed to assess hip fracture risk at the critical locations of femur during the single-leg stance and the sideways fall. The aim of this study was to improve the prediction of hip fracture risk by introducing a novel failure criterion to more accurately describe bone failure mechanism. Hip fracture risk index was defined using cross-section strain energy, which is able to integrate information of stresses, strains, and material properties affecting bone failure. It was found that the femoral neck and the intertrochanteric region have higher fracture risk than other parts of the femur, probably owing to the larger content of cancellous bone in these regions. The study results also suggested that women are more prone to hip fracture than men. The findings in this study have a good agreement with those clinical observations reported in the literature. The proposed hip fracture risk index based on strain energy has the potential of more accurate assessment of hip fracture risk. However, experimental validation should be conducted before its clinical applications. PMID:26601105

  3. [Obtaining of bacterial bioluminescent strain Protobacterium phosphoreum B7071 (lux+) for the determination of zinc ion concentration].

    PubMed

    Gruzina, T G; Dybkova, S N; Chekhovskaia, T P; Vember, V V; Zadorozhniaia, A M; Ul'berg, Z R

    2006-01-01

    The transconjugate containing hybrid plasmid (Te(R)Zn(R)lux+) was obtained using the conjugation method on Pseudomonasfragi T2(5) (Te(R)ZnR) strain and bioluminescent strain Protobacterium phosphoreum B7071 (lux+). The expression regulation of lux-genes on the obtained plasmid is carried out by promotor-operational area conjointly with zinc resistance genes. The cells of the obtained genetically modified bacteria have the ability to specific induced luminescence, which is a respond to zinc ions' presence in the measuring medium. It was shown that the cells' bioluminescence intensity of trans-conjugate is linearly dependent on zinc ions' concentration within the range of 1-100 microM, that provides the opportunity of using biosensor as a strain for qualitative and quantitative detection of the metal. The low sensitivity limit of this method is 0.5 microM for the metal. Besides having high sensitivity, the developed lux-biosensor is highly specified. PMID:17147278

  4. A point mutation in AgrC determines cytotoxic or colonizing properties associated with phenotypic variants of ST22 MRSA strains

    PubMed Central

    Mairpady Shambat, Srikanth; Siemens, Nikolai; Monk, Ian R.; Mohan, Disha B.; Mukundan, Santhosh; Krishnan, Karthickeyan Chella; Prabhakara, Sushma; Snäll, Johanna; Kearns, Angela; Vandenesch, Francois; Svensson, Mattias; Kotb, Malak; Gopal, Balasubramanian; Arakere, Gayathri; Norrby-Teglund, Anna

    2016-01-01

    Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of skin and soft tissue infections. One of the highly successful and rapidly disseminating clones is MRSA ST22 commonly associated with skin tropism. Here we show that a naturally occurring single amino acid substitution (tyrosine to cysteine) at position 223 of AgrC determines starkly different ST22 S. aureus virulence phenotypes, e.g. cytotoxic or colonizing, as evident in both in vitro and in vivo skin infections. Y223C amino acid substitution destabilizes AgrC-AgrA interaction leading to a colonizing phenotype characterized by upregulation of bacterial surface proteins. The colonizing phenotype strains cause less severe skin tissue damage, show decreased susceptibility towards the antimicrobial LL-37 and induce autophagy. In contrast, cytotoxic strains with tyrosine at position 223 of AgrC cause infections characterized by inflammasome activation and severe skin tissue pathology. Taken together, the study demonstrates how a single amino acid substitution in the histidine kinase receptor AgrC of ST22 strains determines virulence properties and infection outcome. PMID:27511873

  5. A point mutation in AgrC determines cytotoxic or colonizing properties associated with phenotypic variants of ST22 MRSA strains.

    PubMed

    Mairpady Shambat, Srikanth; Siemens, Nikolai; Monk, Ian R; Mohan, Disha B; Mukundan, Santhosh; Krishnan, Karthickeyan Chella; Prabhakara, Sushma; Snäll, Johanna; Kearns, Angela; Vandenesch, Francois; Svensson, Mattias; Kotb, Malak; Gopal, Balasubramanian; Arakere, Gayathri; Norrby-Teglund, Anna

    2016-01-01

    Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of skin and soft tissue infections. One of the highly successful and rapidly disseminating clones is MRSA ST22 commonly associated with skin tropism. Here we show that a naturally occurring single amino acid substitution (tyrosine to cysteine) at position 223 of AgrC determines starkly different ST22 S. aureus virulence phenotypes, e.g. cytotoxic or colonizing, as evident in both in vitro and in vivo skin infections. Y223C amino acid substitution destabilizes AgrC-AgrA interaction leading to a colonizing phenotype characterized by upregulation of bacterial surface proteins. The colonizing phenotype strains cause less severe skin tissue damage, show decreased susceptibility towards the antimicrobial LL-37 and induce autophagy. In contrast, cytotoxic strains with tyrosine at position 223 of AgrC cause infections characterized by inflammasome activation and severe skin tissue pathology. Taken together, the study demonstrates how a single amino acid substitution in the histidine kinase receptor AgrC of ST22 strains determines virulence properties and infection outcome. PMID:27511873

  6. Identification of Pseudomonas syringae pv. actinidiae strains causing bacterial canker of kiwifruit in the Anhui Province of China, and determination of their streptomycin sensitivities.

    PubMed

    Yang, X; Yi, X-K; Chen, Y; Zhang, A-F; Zhang, J-Y; Gao, Z-H; Qi, Y-J; Xu, Y-L

    2015-01-01

    Bacterial canker, caused by Pseudomonas syringae pv. actinidiae, is one of the most severe diseases of kiwifruit. It has become an international pandemic and threatens the sustainable development of kiwifruit production in all main kiwi-growing regions worldwide. Streptomycin has been the major bactericide for the control of kiwifruit canker, especially in Anhui Province, one of the main kiwifruit production regions in China. However, until now, no studies on the baseline sensitivity to streptomycin of field isolates of P. syringae pv. actinidiae from China have been available. During 2012-2013, a total of 102 single-colony P. syringae pv. actinidiae strains were isolated: 36, 12, 13, 26, and 15 strains from Yuexi, Jinzhai, Huoshan, Qianshan, and Taihu counties, respectively. All strains were confirmed by production of a 280-bp fragment using the specific primers PsaF1/R2 upon polymerase chain reaction amplification, followed by an assay for confirmation of pathogenicity to fulfill Koch's postulates. In this study, the streptomycin sensitivity of the 102 isolated strains was determined. The half-maximal effective concentration values for inhibition of growth by streptomycin were 0.03-0.42 μg/mL (average 0.12 ± 0.06 μg/mL). The baseline sensitivity curve was unimodal, representing range-of-variation factors of 14.0. No resistant subpopulation was identified among the strains used in the study. Thus, these sensitivity data could be used as a baseline for monitoring the shift in sensitivity of P. syringae pv. actinidiae populations to streptomycin in Anhui Province. Continuous resistance monitoring should be carried out, as streptomycin is an at-risk bactericide agent.

  7. Identification of Pseudomonas syringae pv. actinidiae strains causing bacterial canker of kiwifruit in the Anhui Province of China, and determination of their streptomycin sensitivities.

    PubMed

    Yang, X; Yi, X-K; Chen, Y; Zhang, A-F; Zhang, J-Y; Gao, Z-H; Qi, Y-J; Xu, Y-L

    2015-01-01

    Bacterial canker, caused by Pseudomonas syringae pv. actinidiae, is one of the most severe diseases of kiwifruit. It has become an international pandemic and threatens the sustainable development of kiwifruit production in all main kiwi-growing regions worldwide. Streptomycin has been the major bactericide for the control of kiwifruit canker, especially in Anhui Province, one of the main kiwifruit production regions in China. However, until now, no studies on the baseline sensitivity to streptomycin of field isolates of P. syringae pv. actinidiae from China have been available. During 2012-2013, a total of 102 single-colony P. syringae pv. actinidiae strains were isolated: 36, 12, 13, 26, and 15 strains from Yuexi, Jinzhai, Huoshan, Qianshan, and Taihu counties, respectively. All strains were confirmed by production of a 280-bp fragment using the specific primers PsaF1/R2 upon polymerase chain reaction amplification, followed by an assay for confirmation of pathogenicity to fulfill Koch's postulates. In this study, the streptomycin sensitivity of the 102 isolated strains was determined. The half-maximal effective concentration values for inhibition of growth by streptomycin were 0.03-0.42 μg/mL (average 0.12 ± 0.06 μg/mL). The baseline sensitivity curve was unimodal, representing range-of-variation factors of 14.0. No resistant subpopulation was identified among the strains used in the study. Thus, these sensitivity data could be used as a baseline for monitoring the shift in sensitivity of P. syringae pv. actinidiae populations to streptomycin in Anhui Province. Continuous resistance monitoring should be carried out, as streptomycin is an at-risk bactericide agent. PMID:26345745

  8. Determination of microbial diversity of Aeromonas strains on the basis of multilocus sequence typing, phenotype, and presence of putative virulence genes.

    PubMed

    Martino, Maria Elena; Fasolato, Luca; Montemurro, Filomena; Rosteghin, Marina; Manfrin, Amedeo; Patarnello, Tomaso; Novelli, Enrico; Cardazzo, Barbara

    2011-07-01

    The genus Aeromonas has been described as comprising several species associated with the aquatic environment, which represents their principal reservoir. Aeromonas spp. are commonly isolated from diseased and healthy fish, but the involvement of such bacteria in human infection and gastroenteritis has frequently been reported. The primary challenge in establishing an unequivocal link between the Aeromonas genus and pathogenesis in humans is the extremely complicated taxonomy. With the aim of clarifying taxonomic relationships among the strains and phenotypes, a multilocus sequencing approach was developed and applied to characterize 23 type and reference strains of Aeromonas spp. and a collection of 77 field strains isolated from fish, crustaceans, and mollusks. All strains were also screened for putative determinants of virulence by PCR (ast, ahh1, act, asa1, eno, ascV, and aexT) and the production of acylated homoserine lactones (AHLs). In addition, the phenotypic fingerprinting obtained from 29 biochemical tests was submitted to the nonparametric combination (NPC) test methodology to define the statistical differences among the identified genetic clusters. Multilocus sequence typing (MLST) achieved precise strain genotyping, and the phylogenetic analysis of concatenated sequences delineated the relationship among the taxa belonging to the genus Aeromonas, providing a powerful tool for outbreak traceability, host range diffusion, and ecological studies. The NPC test showed the feasibility of phenotypic differentiation among the majority of the MLST clusters by using a selection of tests or the entire biochemical fingerprinting. A Web-based MLST sequence database (http://pubmlst.org/aeromonas) specific for the Aeromonas genus was developed and implemented with all the results.

  9. Strain distribution in extents of lysozyme resistance and O-acetylation of gonococcal peptidoglycan determined by high-performance liquid chromatography.

    PubMed Central

    Swim, S C; Gfell, M A; Wilde, C E; Rosenthal, R S

    1983-01-01

    The extent of lysozyme resistance and O-acetylation of purified peptidoglycan (PG) from 20 strains of Neisseria gonorrhoeae was examined to determine how widespread these properties are among various subsets of gonococcal isolates. To determine digestibility by lysozyme, we treated [3H]- or [14C]glucosamine-labeled PG with hen egg white lysozyme (HEW-LZ) and determined the size distribution of HEW-LZ soluble PG at the completion of the reaction by molecular-sieve high-performance liquid chromatography, using a Varian TSK SW2000 column, a method that proved considerably more efficient than traditional chromatography for fractionating low-molecular-weight PG fragments solely on the basis of size. The extent of HEW-LZ resistance was expressed as the percentage of PG that was larger in size than disaccharide peptide tetramers (including insoluble PG removed by centrifugation). The percent O-acetylation was determined by converting insoluble PG totally to uncross-linked monomers by the combined action of Chalaropsis B muramidase followed by Escherichia coli endopeptidase and then quantitating radioactivity in O-acetylated and non-O-acetylated monomers after paper chromatography. The PG of the vast majority (19 of 20) of gonococcal strains examined was extensively HEW-LZ resistant (range, 40 to 60% larger than tetramers) and extensively O-acetylated (range, 34 to 52%). Only the PG of strain RD5 (highest rate of PG turnover among gonococci so far examined and the prototype of gonococci having O-acetyl-deficient PG) had greatly reduced O-acetylation (15%) and exhibited virtually no HEW-LZ resistance (2% larger than tetramers). Extensive HEW-LZ resistance and O-acetylation were apparently not associated specifically with (i) a given type of colonial variant (piliated versus nonpiliated or opaque versus transparent), (ii) a given type of clinical isolate (local versus disseminated), (iii) the extent of laboratory passage, or (iv) (with the possible exception of penicillin

  10. An Overview of Micromechanics-Based Techniques for the Analysis of Microstructural Randomness in Functionally Graded Materials

    SciTech Connect

    Ferrante, Fernando J.; Brady, Lori L. Graham; Acton, Katherine; Arwade, Sanjay R.

    2008-02-15

    A review of current research efforts to develop micromechanics-based techniques for the study of microstructural randomness of functionally graded materials is presented, along with a framework developed by the authors of this paper that includes stochastic simulation of statistically inhomogeneous samples and a windowing technique coupled with a micromechanical homogenization technique. The methodology is illustrated through the analysis of one sample coupled with finite element modeling.

  11. In Situ Neutron Diffraction Studies of Increasing Tension Strains of Superelastic Nitinol

    NASA Astrophysics Data System (ADS)

    Pelton, Alan R.; Clausen, Bjørn; Stebner, Aaron P.

    2015-09-01

    A micromechanical study of the effect of varying amounts of tensile strains on the microstructures and subsequent mechanical behaviors of superelastic Nitinol rods is presented. It is found that strains up to ~8-9 % develop microstructures that assist both forward and reverse transformation relative to un-strained material. This superelastic phenomenon is explained to be analogous to two-way shape memory effect in Nitinol actuation materials. These results provide understanding as to why such "pre-strains" may lead to improvements in subsequent superelastic fatigue life. Beyond 9 %, a drastic change is observed, as large amounts of martensite (75 % and more) are retained in unloaded samples. Thus, a competition between transformation, plasticity, and reorientation is found to give rise to microstructures that inhibit complete transformation. Furthermore, even though similar inelastic strain magnitudes are observed in loading and unloading plateaus, micromechanical mechanisms differ substantially from samples with less pre-strain. For example, in highly pre-strained samples at least half of the plateau strains are due to martensite reorientation, whereas, in low and moderately pre-strained samples nearly the entirety of the plateau strain is due to transformation. We also find that latent heat of plastic flow is larger than latent heat of transformation.

  12. Driving- stress waveform and the determination of rock internal friction by the stress-strain curve method.

    USGS Publications Warehouse

    Hsi-Ping, Liu

    1980-01-01

    Harmonic distortion in the stress-time function applied to rock specimens affects the measurement of rock internal friction in the seismic wave periods by the stress-strain hysteresis loop method. If neglected, the harmonic distortion can cause measurements of rock internal friction to be in error by 3O% in the linear range. The stress-time function therefore must be recorded and Fourier analysed for correct interpretation of the experimental data. Such a procedure would also yield a value for internal friction at the higher harmonic frequencies.-Author

  13. EDITORIAL: The 19th MicroMechanics Europe Workshop (MME 2008) The 19th MicroMechanics Europe Workshop (MME 2008)

    NASA Astrophysics Data System (ADS)

    Schnakenberg, Uwe

    2009-07-01

    This special issue of Journal of Micromechanics and Microengineering is devoted to the 19th MicroMechanics Europe Workshop (MME 08), which took place at the RWTH Aachen University, Aachen, Germany, from 28-30 September, 2008. The workshop is a well recognized and established European event in the field of micro system technology using thin-film technologies for creating micro components, micro sensors, micro actuators, and micro systems. The first MME Workshop was held 1989 in Enschede (The Netherlands) and continued 1990 in Berlin (Germany), 1992 in Leuven (Belgium), and then was held annually in Neuchâtel (Switzerland), Pisa (Italy), Copenhagen (Denmark), Barcelona (Spain), Southampton (UK), Ulvik in Hardanger (Norway), Gif-sur-Yvette (France), Uppsala (Sweden), Cork (Ireland), Sinaia (Romania), Delft (The Netherlands), Leuven (Belgium), Göteborg (Sweden), Southampton (UK), and in Guimarães (Portugal). The two day workshop was attended by 180 delegates from 26 countries all over Europe and from Armenia, Austria, Bulgaria, Canada, China, Cuba, Iran, Japan, Korea, Malaysia, Taiwan, Turkey, and the United States of America. A total of 97 papers were accepted for presentation and there were a further five keynote presentations. I am proud to present 22 high-quality papers from MME 2008 selected for their novelty and relevance to Journal of Micromechanics and Microengineering. All the papers went through the regular reviewing procedure of IOP Publishing. I am eternally grateful to all the referees for their excellent work. I would also like to extend my thanks to the members of the Programme Committee of MME 2008, Dr Reinoud Wolffenbuttel, Professor José Higino Correia, and Dr Patrick Pons for pre-selection of the papers as well as to Professor Robert Puers for advice on the final selection of papers. My thanks also go to Dr Ian Forbes of IOP Publishing for managing the entire process and to the editorial staff of Journal of Micromechanics and Microengineering. I

  14. Controlled carbon nanotube synthesis for quantification of polymer-nanotube composite micromechanics

    NASA Astrophysics Data System (ADS)

    Bult, Justin Bernard

    Conventional experimental approaches to the understanding of nanotube-polymer micro-mechanics have struggled to produce reproducible data due to the inherent difficulty in physically manipulating the nanotube in-situ. To avoid the problems scale represents in nanotube-polymer composites a novel approach of using Polarized Raman spectroscopy was developed. The Raman spectroscopic technique has the advantage of using non-invasive analysis to compute the composite micro mechanical properties of interfacial shear stress and critical length. Composites with nanotubes of defined length were needed in order to use the Raman technique. To satisfy this requirement a new thermal Chemical Vapor Deposition (CVD) tool capable of reproducibly growing aligned length uniformity with large mass yield was designed and built. The course of developing these furnace capabilities led to the investigation of nanotube growth mechanics. It is shown herein that a stable passivation barrier is required for nanotube growth. Using X-Ray Photoelectron Spectroscopy (XPS) depth profiling of metal substrate growth conclusively shows the presence of a stable catalyst layer on the outer surface of stable oxides of greater than 100 nm. By analyzing the diffusion profile represented in the XPS data it is shown that a critical thickness for the passivation oxide can be calculated as a function of time and temperature. For the growth parameters used in this study the critical thickness was found to be between 10 nm and 30 nm depending on the diffusivity value used for iron in chromia. This value agrees well with experimental observation. Uniformly grown carbon nanotubes with lengths of 4, 14, 17, 22, 43, 74, and 116 mum were incorporated into a polycarbonate matrix polymer via solvent-antisolvent processing. The nanotube composites of varied length were tested in tensile strain while Raman spectra were taken concurrently to deduce the load transfer to the nanotube due to composite strain. It is found

  15. Micromechanical and Electrical Properties of Monolithic Aluminum Nitride at High Temperatures

    NASA Technical Reports Server (NTRS)

    Goldsby, Jon C.

    2001-01-01

    Micromechanical spectroscopy of aluminum nitride reveals it to possess extremely low background internal friction at less than 1 x 10 (exp -4) logarithmic decrement (log dec.) from 20 to 1200 C. Two mechanical loss peaks were observed, the first at 350 C approximating a single Debye peak with a peak height of 60 x 10 (exp -4) log dec. The second peak was seen at 950 C with a peak height of 20 x 10 (exp -4) log dec. and extended from 200 to over 1200 C. These micromechanical observations manifested themselves in the electrical behavior of these materials. Electrical conduction processes were predominately intrinsic. Both mechanical and electrical relaxations appear to be thermally activated processes, with activation energies of 0.78 and 1.32 eV respectively.

  16. Micromechanical and Electrical Properties of Monolithic Aluminum Nitride at High Temperatures

    NASA Technical Reports Server (NTRS)

    Goldsby, Jon C.

    2000-01-01

    Micromechanical spectroscopy of aluminum nitride reveals it to possess extremely low background internal friction at less than 1x10(exp-4) logarithmic decrement (log dec) from 20 to 1200 T. Two mechanical loss peaks were observed, the first at 350 C approximating a single Debye peak with a peak height of 60x10(exp-4) log dec. The second peak was seen at 950 'C with a peak height of 20x 10' log dec and extended from 200 to over 1200 C. These micromechanical observations manifested themselves in the electrical behavior of these materials. Electrical conduction processes were predominately intrinsic. Both mechanical and electrical relaxations appear to be thermally activated processes, with activation energies of 0.78 and 1.32 eV respectively.

  17. An Energy Approach to a Micromechanics Model Accounting for Nonlinear Interface Debonding.

    SciTech Connect

    Tan, H.; Huang, Y.; Geubelle, P. H.; Liu, C.; Breitenfeld, M. S.

    2005-01-01

    We developed a micromechanics model to study the effect of nonlinear interface debonding on the constitutive behavior of composite materials. While implementing this micromechanics model into a large simulation code on solid rockets, we are challenged by problems such as tension/shear coupling and the nonuniform distribution of displacement jump at the particle/matrix interfaces. We therefore propose an energy approach to solve these problems. This energy approach calculates the potential energy of the representative volume element, including the contribution from the interface debonding. By minimizing the potential energy with respect to the variation of the interface displacement jump, the traction balanced interface debonding can be found and the macroscopic constitutive relations established. This energy approach has the ability to treat different load conditions in a unified way, and the interface cohesive law can be in any arbitrary forms. In this paper, the energy approach is verified to give the same constitutive behaviors as reported before.

  18. Reducing support loss in micromechanical ring resonators using phononic band-gap structures

    NASA Astrophysics Data System (ADS)

    Hsu, Feng-Chia; Hsu, Jin-Chen; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin

    2011-09-01

    In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

  19. Micromechanical exfoliation of two-dimensional materials by a polymeric stamp

    NASA Astrophysics Data System (ADS)

    Ferraz da Costa, M. C.; Ribeiro, H. B.; Kessler, F.; de Souza, E. A. T.; Fechine, G. J. M.

    2016-02-01

    In this work, an alternative technique to the traditional micromechanical exfoliation of two-dimensional materials is proposed, consisting of isolated flakes of graphite and molybdenum disulphide onto polymeric surfaces films. The set made up of polymer and flakes is fabricated by using a hot-press machine called polymeric stamp. The polymeric stamp was used to allocate flakes and also to allow the exfoliation process to take place just in one face of isolated flake. Optical microscopy, Raman spectroscopy and photoluminescence spectroscopy results showed that multilayers, bilayers and single layers of graphene and MoS2 were obtained by using a polymeric stamp as tool for micromechanical exfoliation. These crystals were more easily found because the exfoliation process concentrates them in well-defined locations. The results prove the effectiveness of the method by embedding two-dimensional materials into polymers to fabricate fewer layers crystals in a fast, economic and clean way.

  20. Micromechanical modeling of the multiphysical behavior of smart materials using the variational asymptotic method

    NASA Astrophysics Data System (ADS)

    Tang, Tian; Yu, Wenbin

    2009-12-01

    A multiphysics micromechanics model is developed to predict the effective properties as well as the local fields of periodic smart materials responsive to fully coupled electric, magnetic, thermal and mechanical fields. This work is based on the framework of the variational asymptotic method for unit cell homogenization (VAMUCH), a recently developed micromechanics modeling scheme. To treat the general microstructure of smart materials, we implemented this model using the finite element technique. Several examples of smart materials are used to demonstrate the application of the proposed model for prediction of multiphysical behavior. A preliminary version of this paper was presented at the 2008 ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Ellicott City, MD, USA.

  1. An extended micromechanics method for probing interphase properties in polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Liu, Zeliang; Moore, John A.; Liu, Wing Kam

    2016-10-01

    Inclusions comprised on filler particles and interphase regions commonly form complex morphologies in polymer nanocomposites. Addressing these morphologies as systems of overlapping simple shapes allows for the study of dilute particles, clustered particles, and interacting interphases all in one general modeling framework. To account for the material properties in these overlapping geometries, weighted-mean and additive overlapping conditions are introduced and the corresponding inclusion-wise integral equations are formulated. An extended micromechanics method based on these overlapping conditions for linear elastic and viscoelastic heterogeneous material is then developed. An important feature of the proposed approach is that the effect of both the geometric overlapping (clustered particles) and physical overlapping (interacting interphases) on the effective properties can be distinguished. We apply the extended micromechanics method to a viscoelastic polymer nanocomposite with interphase regions, and estimate the properties and thickness of the interphase region based on experimental data for carbon-black filled styrene butadiene rubbers.

  2. Interlayer micromechanics of the aortic heart valve leaflet.

    PubMed

    Buchanan, Rachel M; Sacks, Michael S

    2014-08-01

    While the mechanical behaviors of the fibrosa and ventricularis layers of the aortic valve (AV) leaflet are understood, little information exists on their mechanical interactions mediated by the GAG-rich central spongiosa layer. Parametric simulations of the interlayer interactions of the AV leaflets in flexure utilized a tri-layered finite element (FE) model of circumferentially oriented tissue sections to investigate inter-layer sliding hypothesized to occur. Simulation results indicated that the leaflet tissue functions as a tightly bonded structure when the spongiosa effective modulus was at least 25 % that of the fibrosa and ventricularis layers. Novel studies that directly measured transmural strain in flexure of AV leaflet tissue specimens validated these findings. Interestingly, a smooth transmural strain distribution indicated that the layers of the leaflet indeed act as a bonded unit, consistent with our previous observations (Stella and Sacks in J Biomech Eng 129:757-766, 2007) of a large number of transverse collagen fibers interconnecting the fibrosa and ventricularis layers. Additionally, when the tri-layered FE model was refined to match the transmural deformations, a layer-specific bimodular material model (resulting in four total moduli) accurately matched the transmural strain and moment-curvature relations simultaneously. Collectively, these results provide evidence, contrary to previous assumptions, that the valve layers function as a bonded structure in the low-strain flexure deformation mode. Most likely, this results directly from the transverse collagen fibers that bind the layers together to disable physical sliding and maintain layer residual stresses. Further, the spongiosa may function as a general dampening layer while the AV leaflets deforms as a homogenous structure despite its heterogeneous architecture.

  3. MICROMECHANICS IN CONTINOUS GRAPHITE FIBER/EPOXY COMPOSITES DURING CREEP

    SciTech Connect

    C. ZHOU; ET AL

    2001-02-01

    Micro Raman spectroscopy and classic composite shear-lag models were used to analyze the evolution with time of fiber and matrix strain/stress around fiber breaks in planar model graphite fiber-epoxy matrix composites. Impressive agreements were found between the model predictions and the experimental results. The local matrix creep leads to an increase in the load transfer length around the break under a constant load. This increases the chance of fiber breakage in the neighboring intact fibers.

  4. PhyloFlu, a DNA microarray for determining the phylogenetic origin of influenza A virus gene segments and the genomic fingerprint of viral strains.

    PubMed

    Paulin, Luis F; de los D Soto-Del Río, María; Sánchez, Iván; Hernández, Jesús; Gutiérrez-Ríos, Rosa M; López-Martínez, Irma; Wong-Chew, Rosa M; Parissi-Crivelli, Aurora; Isa, P; López, Susana; Arias, Carlos F

    2014-03-01

    Recent evidence suggests that most influenza A virus gene segments can contribute to the pathogenicity of the virus. In this regard, the hemagglutinin (HA) subtype of the circulating strains has been closely surveyed, but the reassortment of internal gene segments is usually not monitored as a potential source of an increased pathogenicity. In this work, an oligonucleotide DNA microarray (PhyloFlu) designed to determine the phylogenetic origins of the eight segments of the influenza virus genome was constructed and validated. Clades were defined for each segment and also for the 16 HA and 9 neuraminidase (NA) subtypes. Viral genetic material was amplified by reverse transcription-PCR (RT-PCR) with primers specific to the conserved 5' and 3' ends of the influenza A virus genes, followed by PCR amplification with random primers and Cy3 labeling. The microarray unambiguously determined the clades for all eight influenza virus genes in 74% (28/38) of the samples. The microarray was validated with reference strains from different animal origins, as well as from human, swine, and avian viruses from field or clinical samples. In most cases, the phylogenetic clade of each segment defined its animal host of origin. The genomic fingerprint deduced by the combined information of the individual clades allowed for the determination of the time and place that strains with the same genomic pattern were previously reported. PhyloFlu is useful for characterizing and surveying the genetic diversity and variation of animal viruses circulating in different environmental niches and for obtaining a more detailed surveillance and follow up of reassortant events that can potentially modify virus pathogenicity.

  5. Supercritical carbon dioxide solvent extraction from surface-micromachined micromechanical structures

    SciTech Connect

    Dyck, C.W.; Smith, J.H.; Miller, S.L.; Russick, E.M.; Adkins, C.L.J.

    1996-10-01

    Results are presented supporting the use of supercritical carbon dioxide (SCCO{sub 2}) drying to enhance the yield of surface-micromachined micromechanical devices following the final release etch. The equipment and extraction process of the SCCO{sub 2} system are described, and results of successfully released cantilevered beams and microengines are presented. A new system capable of drying 6 inch wafers is also described.

  6. Micromechanics of metal matrix composites using the Generalized Method of Cells model (GMC) user's guide

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob; Pindera, Marek-Jerzy

    1992-01-01

    A user's guide for the program gmc.f is presented. The program is based on the generalized method of cells model (GMC) which is capable via a micromechanical analysis, of predicting the overall, inelastic behavior of unidirectional, multi-phase composites from the knowledge of the properties of the viscoplastic constituents. In particular, the program is sufficiently general to predict the response of unidirectional composites having variable fiber shapes and arrays.

  7. Modeling of fiber-optic sensors based on micromechanical vibrations in liquid.

    PubMed

    Prokhorov, A M; Claus, R O; Popov, A L; Tulaikova, T V

    1997-08-01

    Fiber-optic chemical sensors based on optical power absorption or wavelength changes are well known. A new type of sensing element is considered. A micromechanical vibrated fiber-optic tip changes its resonance frequency during its operation. Sensors of this type are simple and convenient and do not require adjustment while in use. They are useful in industry and in medical applications. The action of this sensitive element in a liquid is considered.

  8. Activation barrier scaling and crossover for noise-induced switching in micromechanical parametric oscillators.

    PubMed

    Chan, H B; Stambaugh, C

    2007-08-10

    We explore fluctuation-induced switching in parametrically driven micromechanical torsional oscillators. The oscillators possess one, two, or three stable attractors depending on the modulation frequency. Noise induces transitions between the coexisting attractors. Near the bifurcation points, the activation barriers are found to have a power law dependence on frequency detuning with critical exponents that are in agreement with predicted universal scaling relationships. At large detuning, we observe a crossover to a different power law dependence with an exponent that is device specific.

  9. Micromechanical modeling of laminated composites with interfaces and woven composites using the boundary element method

    SciTech Connect

    Goldberg, R.K.; Hopkins, D.A.

    1993-10-01

    The boundary element method is utilized to analyze the effects of fiber/matrix interfaces on the micromechanical behavior of laminated composites as well as the elastic behavior of woven composites. Effective composite properties are computed for laminated SiC/RBSN and SiC/Ti-15-3 composites, as well as a woven SiC/SiC composite. The properties calculated using the computerized tool BEST-CMS match the experimental results well.

  10. Micromechanical modeling of laminated composites with interfaces and woven composites using the boundary element method

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Hopkins, Dale A.

    1993-01-01

    The boundary element method is utilized to analyze the effects of fiber/matrix interfaces on the micromechanical behavior of laminated composites as well as the elastic behavior of woven composites. Effective composite properties are computed for laminated SiC/RBSN and SiC/Ti-15-3 composites, as well as a woven SiC/SiC composite. The properties calculated using the computerized tool BEST-CMS match the experimental results well.

  11. Complete Genome Sequences of Eight Helicobacter pylori Strains with Different Virulence Factor Genotypes and Methylation Profiles, Isolated from Patients with Diverse Gastrointestinal Diseases on Okinawa Island, Japan, Determined Using PacBio Single-Molecule Real-Time Technology.

    PubMed

    Satou, Kazuhito; Shiroma, Akino; Teruya, Kuniko; Shimoji, Makiko; Nakano, Kazuma; Juan, Ayaka; Tamotsu, Hinako; Terabayashi, Yasunobu; Aoyama, Misako; Teruya, Morimi; Suzuki, Rumiko; Matsuda, Miyuki; Sekine, Akihiro; Kinjo, Nagisa; Kinjo, Fukunori; Yamaoka, Yoshio; Hirano, Takashi

    2014-04-17

    We report the complete genome sequences of eight Helicobacter pylori strains isolated from patients with gastrointestinal diseases in Okinawa, Japan. Whole-genome sequencing and DNA methylation detection were performed using the PacBio platform. De novo assembly determined a single, complete contig for each strain. Furthermore, methylation analysis identified virulence factor genotype-dependent motifs.

  12. Evaluation of effective thermal diffusivity and conductivity of fibrous materials through computational micromechanics

    NASA Astrophysics Data System (ADS)

    Ahmadi, Isa

    2016-04-01

    The aim of present study is to investigate the effective thermal properties of composite material via micromechanical modeling of the composite material as a heterogeneous material. These properties mainly include the thermal diffusivity and the thermal conductivity of composites. For this purpose, a definition is presented for effective thermal diffusivity for heterogeneous materials based on heat diffusion rate into the material in a transient heat transfer. A micromechanical model based on the Representative Volume Element (RVE) is presented for modeling the heat conduction in the fibrous composite materials. An appropriate heat transfer problem for the RVE is defined so that by the analogy of the numerical results the effective properties of the RVE can be estimated. A numerical method is employed to analyze the steady-state and transient heat flux and temperature in the RVE. To validate the model, the predictions of present model are compared with results of analytical method, FEM and some available experimental data in the open literature. The effective thermal conductivity and thermal diffusivity are then obtained for fibrous composites via the present micromechanical model. The SiC/Ti, SiC/Ti6%Al4%V and Glass/Epoxy composites with various fiber volume fractions are considered in this study.

  13. Micromechanics-Based Structural Analysis (FEAMAC) and Multiscale Visualization within Abaqus/CAE Environment

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Bednarcyk, Brett A.; Hussain, Aquila; Katiyar, Vivek

    2010-01-01

    A unified framework is presented that enables coupled multiscale analysis of composite structures and associated graphical pre- and postprocessing within the Abaqus/CAE environment. The recently developed, free, Finite Element Analysis--Micromechanics Analysis Code (FEAMAC) software couples NASA's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) with Abaqus/Standard and Abaqus/Explicit to perform micromechanics based FEA such that the nonlinear composite material response at each integration point is modeled at each increment by MAC/GMC. The Graphical User Interfaces (FEAMAC-Pre and FEAMAC-Post), developed through collaboration between SIMULIA Erie and the NASA Glenn Research Center, enable users to employ a new FEAMAC module within Abaqus/CAE that provides access to the composite microscale. FEA IAC-Pre is used to define and store constituent material properties, set-up and store composite repeating unit cells, and assign composite materials as sections with all data being stored within the CAE database. Likewise FEAMAC-Post enables multiscale field quantity visualization (contour plots, X-Y plots), with point and click access to the microscale i.e., fiber and matrix fields).

  14. A micromechanical study of drying and carbonation effects in cement-based materials

    NASA Astrophysics Data System (ADS)

    Shen, W. Q.; Shao, J. F.; Kondo, D.

    2015-01-01

    This paper is devoted to a micromechanical study of mechanical properties of cement-based materials by taking into account effects of water saturation degree and carbonation process. To this end, the cement-based materials are considered as a composite material constituted with a cement matrix and aggregates (inclusions). Further, the cement matrix is seen as a porous medium with a solid phase (CSH) and pores. Using a two-step homogenization procedure, a closed-form micromechanical model is first formulated to describe the basic mechanical behavior of materials. This model is then extended to partially saturated materials in order to account for the effects of water saturation degree on the mechanical properties. Finally, considering the solid phase change and porosity variation related to the carbonation process, the micromechanical model is coupled with the chemical reaction and is able to describe the consequences of carbonation on the macroscopic mechanical properties of material. Some comparisons between numerical results and experimental data are presented.

  15. Micromechanics for Fiber Volume Percent With a Photocure Vinyl Ester Composite

    PubMed Central

    Petersen, Richard C.; Lemons, Jack E.; McCracken, Michael S.

    2014-01-01

    Micromechanics for fiber volume percent (Vf) from 0.0Vf to 54.0 Vf were conducted using (3 mm long × 9 µm diameter) high-purity quartz fibers in a visible-light vinyl ester particulate-filled photocure resin. MTS fully articulated four-point bend fixtures were used with a 40 mm test span and 50 × 2 × 2 mm3 sample dimensions. Specimens were tested following the combined modified ASTM standards for advanced ceramics ASTM-C-1161–94 and polymers ASTM-D-6272–00 for modulus, flexural strength, and yield strength. Experimental data provided reliable statistical support for the dominant fiber contribution expressed through the rule-of-mixtures theory as a valid representation of micromechanical physics. The rule-of-mixtures micromechanics described by Vf could explain 92, 85, and 78% of the variability related to modulus, flexural strength, and yield strength respectively. Statistically significant improvements with fiber addition began at 10.3Vf for modulus, 5.4Vf for flexural strength, and 10.3Vf for yield strength, p < 0.05. In addition, correlation matrix analysis was performed for all mechanical test data. An increase in Vf correlated significantly with increases in modulus, flexural strength, and yield strength as measured by the four-point bending test, p < 10−10. All mechanical properties in turn correlated highly significantly with one another, p < 10−9. PMID:25382895

  16. Application of finite element substructuring to composite micromechanics. M.S. Thesis - Akron Univ., May 1984

    NASA Technical Reports Server (NTRS)

    Caruso, J. J.

    1984-01-01

    Finite element substructuring is used to predict unidirectional fiber composite hygral (moisture), thermal, and mechanical properties. COSMIC NASTRAN and MSC/NASTRAN are used to perform the finite element analysis. The results obtained from the finite element model are compared with those obtained from the simplified composite micromechanics equations. A unidirectional composite structure made of boron/HM-epoxy, S-glass/IMHS-epoxy and AS/IMHS-epoxy are studied. The finite element analysis is performed using three dimensional isoparametric brick elements and two distinct models. The first model consists of a single cell (one fiber surrounded by matrix) to form a square. The second model uses the single cell and substructuring to form a nine cell square array. To compare computer time and results with the nine cell superelement model, another nine cell model is constructed using conventional mesh generation techniques. An independent computer program consisting of the simplified micromechanics equation is developed to predict the hygral, thermal, and mechanical properties for this comparison. The results indicate that advanced techniques can be used advantageously for fiber composite micromechanics.

  17. Heterogeneous micromechanical properties of the extracellular matrix in healthy and infarcted hearts.

    PubMed

    Andreu, Ion; Luque, Tomás; Sancho, Ana; Pelacho, Beatriz; Iglesias-García, Olalla; Melo, Esther; Farré, Ramon; Prósper, Felipe; Elizalde, M Reyes; Navajas, Daniel

    2014-07-01

    Infarcted hearts are macroscopically stiffer than healthy organs. Nevertheless, although cell behavior is mediated by the physical features of the cell niche, the intrinsic micromechanical properties of healthy and infarcted heart extracellular matrix (ECM) remain poorly characterized. Using atomic force microscopy, we studied ECM micromechanics of different histological regions of the left ventricle wall of healthy and infarcted mice. Hearts excised from healthy (n=8) and infarcted mice (n=8) were decellularized with sodium dodecyl sulfate and cut into 12 μm thick slices. Healthy ventricular ECM revealed marked mechanical heterogeneity across histological regions of the ventricular wall with the effective Young's modulus ranging from 30.2 ± 2.8 to 74.5 ± 8.7 kPa in collagen- and elastin-rich regions of the myocardium, respectively. Infarcted ECM showed a predominant collagen composition and was 3-fold stiffer than collagen-rich regions of the healthy myocardium. ECM of both healthy and infarcted hearts exhibited a solid-like viscoelastic behavior that conforms to two power-law rheology. Knowledge of intrinsic micromechanical properties of the ECM at the length scale at which cells sense their environment will provide further insight into the cell-scaffold interplay in healthy and infarcted hearts. PMID:24717359

  18. Mechanical Characterization and Micromechanical Modeling of Woven Carbon/Copper Composites

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Pindera, Marek-Jerzy; Ellis, David L.; Miner, Robert V.

    1997-01-01

    The present investigation examines the in-plane mechanical behavior of a particular woven metal matrix composite (MMC); 8-harness (8H) satin carbon/copper (C/Cu). This is accomplished via mechanical testing as well as micromechanical modeling. While the literature is replete with experimental and modeling efforts for woven and braided polymer matrix composites, little work has been done on woven and braided MMC's. Thus, the development and understanding of woven MMC's is at an early stage. 8H satin C/Cu owes its existence to the high thermal conductivity of copper and low density and thermal expansion of carbon fibers. It is a candidate material for high heat flux applications, such as space power radiator panels. The experimental portion of this investigation consists of monotonic and cyclic tension, compression, and Iosipescu shear tests, as well as combined tension-compression tests. Tests were performed on composite specimens with three copper matrix alloy types: pure Cu, Cu-0.5 weight percent Ti (Cu-Ti), and Cu-0.7 weight percent Cr (Cu-Cr). The small alloying additions are present to promote fiber/matrix interfacial bonding. The analytical modeling effort utilizes an approach in which a local micromechanical model is embedded in a global micromechanical model. This approach differs from previously developed analytical models for woven composites in that a true repeating unit cell is analyzed. However, unlike finite element modeling of woven composites, the geometry is sufficiently idealized to allow efficient geometric discretization and efficient execution.

  19. Design and Analysis of High Quality Factor Chemical Vapor Deposition (CVD) Diamond Micromechanical Resonators

    NASA Astrophysics Data System (ADS)

    Motieian Najar, Mohammad Hadi

    Diamond is an excellent material for Microelectromechanical Systems (MEMS) due to its superlative material properties compared to commonly used materials such as silicon. In its single crystalline form, diamond offers properties such as very high Young's modulus, low thermal coefficient of expansion, and very high thermal conductivity as well as being chemically inert. Specifically, diamond's high thermal conductivity offers the potential for very low thermoelastic damping (TED) in micromechanical resonators. Polycrystalline (Poly-C) diamond films deposited by Hot Filament Chemical Vapor Deposition (HFCVD) have been explored in this research. HFCVD Poly-C diamond films are easy and inexpensive to deposit at wafer-scale, and retain many material properties that single crystalline diamond possesses. The first part of the study focuses on fabrication and testing of high quality factor micro-resonators such as double-ended tuning forks (DETF) and micro-cantilevers fabricated from microcrystalline and nanocrystalline diamond films with grain sizes ranging from 20 nm (nanocrystalline films) to 2.5 microm (microcrystalline films). The aim of this first study was to determine whether the quality factor of HFCVD diamond resonators could reach the limits imposed by intrinsic dissipation mechanisms such as thermoelastic damping (TED). Previous studies showed large differences between measured Q-factors and the TED limit, in part because these studies assumed thermal conductivity similar to that of single crystalline diamond. Here the thermal conductivity of NCD and MCD films was measured using time-domain thermoreflectance (TDTR), and the resulting Q-factor measurements were shown to agree well with the theoretical TED limit. The second part of this research focuses on identifying the causes of dissipation in diamond resonators and suggesting approaches to improve the mechanical Q-factor. It is shown that, besides variations in deposition conditions such as decreasing the CH4

  20. Finite element based micro-mechanics modeling of textile composites

    NASA Technical Reports Server (NTRS)

    Glaessgen, E. H.; Griffin, O. H., Jr.

    1995-01-01

    Textile composites have the advantage over laminated composites of a significantly greater damage tolerance and resistance to delamination. Currently, a disadvantage of textile composites is the inability to examine the details of the internal response of these materials under load. Traditional approaches to the study fo textile based composite materials neglect many of the geometric details that affect the performance of the material. The present three dimensional analysis, based on the representative volume element (RVE) of a plain weave, allows prediction of the internal details of displacement, strain, stress, and failure quantities. Through this analysis, the effect of geometric and material parameters on the aforementioned quantities are studied.

  1. Relating micromechanical properties and mineral densities in severely suppressed bone turnover patients, osteoporotic patients, and normal subjects.

    PubMed

    Tjhia, Crystal K; Stover, Susan M; Rao, D Sudhaker; Odvina, Clarita V; Fyhrie, David P

    2012-07-01

    Mineralization of bone, from the tissue level to whole bones, is associated with mechanical properties. The relationship between bone tissue mineralization and micromechanical properties may be affected by age, disease, and drug treatment. Patients with severely suppressed bone turnover (SSBT) suffered atypical fractures while on bisphosphonate treatment. The role of tissue level mineralization in predicting material level properties of SSBT bone may be different from that of other osteoporotic patients and of normal subjects. The aim of this study was to compare the relationships between mineralization and micromechanical properties of bone biopsies from patients with SSBT, bisphosphonate-naive osteoporotic patients with typical vertebral fracture, and normal young and age-matched subjects. We used nanoindentation and quantitative backscattered electron microscopy to characterize the elastic modulus, contact hardness, plastic deformation resistance, and tissue mineralization of the biopsies at site-matched locations within each biopsy. The linear mineralization-mechanical property relationships were different among the groups with respect to the intercepts for only cortical bone tissue but not the slopes for cortical and trabecular bone tissues. For a given mineral density, there was a trend of greater plastic deformation resistance in SSBT cortical bone compared to young normal bone. Similarly, there was a trend of greater plastic deformation resistance in osteoporotic trabecular bone compared to young normal bone for a given mineral density. The age-matched normal group had higher elastic modulus and a trend of higher contact hardness compared to the young normal group for a given mineral density. However, the mechanical property-mineralization relationships within an individual were weak, and only 21 of 53 biopsies that were analyzed had at least one significant association between mineralization and a mechanical property measurement for either cortical or

  2. New method of determination of spot welding-adhesive joint fatigue life using full field strain evolution

    NASA Astrophysics Data System (ADS)

    Sadowski, T.; Kneć, M.

    2016-04-01

    Fatigue tests were conducted since more than two hundred years ago. Despite this long period, as fatigue phenomena are very complex, assessment of fatigue response of standard materials or composites still requires a long time. Quite precise way to estimate fatigue parameters is to test at least 30 standardized specimens for the analysed material and further statistical post processing is required. In case of structural elements analysis like hybrid joints (Figure 1), the situation is much more complex as more factors influence the fatigue load capacity due to much more complicated structure of the joint in comparison to standard materials specimen, i.e. occurrence of: welded hot spots or rivets, adhesive layers, local notches creating the stress concentrations, etc. In order to shorten testing time some rapid methods are known: Locati's method [1] - step by step load increments up to failure, Prot's method [2] - constant increase of the load amplitude up to failure; Lehr's method [2] - seeking for the point during regular fatigue loading when an increase of temperature or strains become non-linear. The present article proposes new method of the fatigue response assessment - combination of the Locati's and Lehr's method.

  3. Analytic and computational micromechanics of clustering and interphase effects in carbon nanotube composites.

    SciTech Connect

    Seidel, Gary D.; Hammerand, Daniel Carl; Lagoudas, Dimitris C.

    2006-01-01

    Effective elastic properties for carbon nanotube reinforced composites are obtained through a variety of micromechanics techniques. Using the in-plane elastic properties of graphene, the effective properties of carbon nanotubes are calculated utilizing a composite cylinders micromechanics technique as a first step in a two-step process. These effective properties are then used in the self-consistent and Mori-Tanaka methods to obtain effective elastic properties of composites consisting of aligned single or multi-walled carbon nanotubes embedded in a polymer matrix. Effective composite properties from these averaging methods are compared to a direct composite cylinders approach extended from the work of Hashin and Rosen (1964) and Christensen and Lo (1979). Comparisons with finite element simulations are also performed. The effects of an interphase layer between the nanotubes and the polymer matrix as result of functionalization is also investigated using a multi-layer composite cylinders approach. Finally, the modeling of the clustering of nanotubes into bundles due to interatomic forces is accomplished herein using a tessellation method in conjunction with a multi-phase Mori-Tanaka technique. In addition to aligned nanotube composites, modeling of the effective elastic properties of randomly dispersed nanotubes into a matrix is performed using the Mori-Tanaka method, and comparisons with experimental data are made. Computational micromechanical analysis of high-stiffness hollow fiber nanocomposites is performed using the finite element method. The high-stiffness hollow fibers are modeled either directly as isotropic hollow tubes or equivalent transversely isotropic effective solid cylinders with properties computed using a micromechanics based composite cylinders method. Using a representative volume element for clustered high-stiffness hollow fibers embedded in a compliant matrix with the appropriate periodic boundary conditions, the effective elastic properties

  4. Sediment micromechanics in sheet flows induced by asymmetric waves: A CFD-DEM study

    NASA Astrophysics Data System (ADS)

    Sun, Rui; Xiao, Heng

    2016-11-01

    Understanding the sediment transport in oscillatory flows is essential to the investigation of the overall sediment budget for coastal regions. This overall budget is crucial for the prediction of the morphological change of the coastline in engineering applications. Since the sediment transport in oscillatory flows is dense particle-laden flow, appropriate modeling the particle interaction is critical. Although traditional two-fluid approaches have been applied to the study of sediment transport in oscillatory flows, the approaches do not capture the interaction of the particles. The study of the motion of individual sediment particles and their micromechanics (e.g., packing and contact force) in oscillatory flows is still lacking. In this work, a parallel CFD-DEM solver SediFoam that can model the inter-particle collision is applied to study the granular micromechanics of sediment particles in oscillatory flows. The results obtained from the CFD-DEM solver are validated by using the experimental data of coarse and medium sands. The comparison with experimental results suggests that the flow velocity, the sediment flux and the net sediment transport rate predicted by SediFoam are satisfactory. Moreover, the micromechanic quantities of the sediment bed are presented in detail, including the Voronoi concentration, the coordination number, and the particle interaction force. It is demonstrated that the variation of these micromechanic quantities at different phases in the oscillatory cycle is significant, which is due to different responses of the sediment bed. To investigate the structural properties of the sediment bed, the correlation of the Voronoi volume fraction and coordination number is compared to the results from the fluidized bed simulations. The consistency in the comparison indicates the structural micromechanics of sediment transport and fluidized bed are similar despite the differences in flow patterns. From the prediction of the CFD-DEM model, we

  5. Deformation micromechanisms of collagen fibrils under uniaxial tension

    PubMed Central

    Tang, Yuye; Ballarini, Roberto; Buehler, Markus J.; Eppell, Steven J.

    2010-01-01

    Collagen, an essential building block of connective tissues, possesses useful mechanical properties due to its hierarchical structure. However, little is known about the mechanical properties of collagen fibril, an intermediate structure between the collagen molecule and connective tissue. Here, we report the results of systematic molecular dynamics simulations to probe the mechanical response of initially unflawed finite size collagen fibrils subjected to uniaxial tension. The observed deformation mechanisms, associated with rupture and sliding of tropocollagen molecules, are strongly influenced by fibril length, width and cross-linking density. Fibrils containing more than approximately 10 molecules along their length and across their width behave as representative volume elements and exhibit brittle fracture. Shorter fibrils experience a more graceful ductile-like failure. An analytical model is constructed and the results of the molecular modelling are used to find curve-fitted expressions for yield stress, yield strain and fracture strain as functions of fibril structural parameters. Our results for the first time elucidate the size dependence of mechanical failure properties of collagen fibrils. The associated molecular deformation mechanisms allow the full power of traditional material and structural engineering theory to be applied to our understanding of the normal and pathological mechanical behaviours of collagenous tissues under load. PMID:19897533

  6. Cyclic Plastic Deformation, Fatigue, and the Associated Micro-Mechanisms in Magnesium: From Single Crystal to Polycrystal

    NASA Astrophysics Data System (ADS)

    Yu, Qin

    Magnesium and its alloys have received substantial interests as the government initiatives on energy saving and environment protection demand an increasing use of lightweight materials in structural parts, especially in transportation industries. A good understanding of fatigue behavior in magnesium is critical to ensure the reliability and durability of the magnesium components. Unlike the body centered cubic and face centered cubic metals, fundamental knowledge concerning the cyclic deformation and fatigue in hexagonal close packed magnesium is limited. The current research aims at a better understanding of the micro-mechanisms associated with the cyclic deformation and fatigue of magnesium. Magnesium single crystal was chosen to study the fundamental twinning/detwinning process while extruded polycrystalline pure magnesium was studied for the fatigue damage mechanisms. Cyclic deformation and the corresponding morphology evolution of {1 0 1¯ 2} twinning-detwinning-retwinning are, for the first time, characterized in magnesium single crystal under fully reserved strain-controlled tension-compression utilizing in situ optical microscopy. As loading cycles are increased, the activity of twinning-detwinning-retwinning gradually decreases. Microscopy after fatigue shows that the matrix region having experienced repeated twinning-detwinning cannot be completely detwinned to its original crystal orientation. Fragmented secondary tension twins are found to result from twin-twin interactions. Various twin-twin interaction structures exist in fatigued magnesium single crystal: quilted-looking twin structure, "apparent crossing" twin structure, and double tension twin structure. According to the crystallography of magnesium, twin-twin interactions are classified into Type I for two twin variants sharing the same zone axis and Type II for two twins with different zone axes. For Type I twin-twin interactions, one twin does not transmit across the twin boundary and into the

  7. Determinants of General Health, Work-Related Strain, and Burnout in Public Versus Private Emergency Medical Technicians in Istanbul.

    PubMed

    Tunaligil, Verda; Dokucu, Ali Ihsan; Erdogan, Mehmet Sarper

    2016-07-01

    This study investigated the impact of working for public versus private ambulance services in Turkey and elaborated on predictors of mental, physical, and emotional well-being in emergency medical technicians (EMT-Bs). In this observational cross-sectional study, an 81-question self-report survey was used to gather data about employee demographics, socioeconomic status, educational background, working conditions, and occupational health and workplace safety (OHS), followed by the 12-item General Health Questionnaire (GHQ-12), the Work-Related Strain Inventory (WRSI), and the Maslach Burnout Inventory (MBI) with three subscales: Emotional Exhaustion (MBI-EE), Depersonalization (MBI-DP), and Diminished Personal Accomplishment (MBI-PA). In 2011, 1,038 EMT-Bs worked for publicly operated and 483 EMT-Bs worked for privately owned ambulance services in Istanbul, Turkey, of which 606 (58.4%) and 236 (48.9%) participated in the study (overall participation rate = 55.4%), respectively. On all scales, differences between total mean scores in both sectors were statistically insignificant (p > .05). In the public sector, work locations, false accusations, occupational injuries and diseases, work-related permanent disabilities, and organizational support were found to significantly influence self-reported perceptions of well-being (p < .05). In the private sector, commute time to and from work (p < .05), false accusations (p < .05), vocational training and education (p < .05), informed career choices (p < .05), and work-related permanent disabilities (p < .05) were found to significantly influence self-reported perceptions of well-being. EMT-Bs were asked about aspects of their working lives that need improvement; priority expectations in the public and private sectors were higher earnings (17.5%; 16.7%) and better social opportunities (17.4%; 16.8%). Working conditions, vocational training, and OHS emerged as topics that merit priority attention.

  8. Determinants of General Health, Work-Related Strain, and Burnout in Public Versus Private Emergency Medical Technicians in Istanbul.

    PubMed

    Tunaligil, Verda; Dokucu, Ali Ihsan; Erdogan, Mehmet Sarper

    2016-07-01

    This study investigated the impact of working for public versus private ambulance services in Turkey and elaborated on predictors of mental, physical, and emotional well-being in emergency medical technicians (EMT-Bs). In this observational cross-sectional study, an 81-question self-report survey was used to gather data about employee demographics, socioeconomic status, educational background, working conditions, and occupational health and workplace safety (OHS), followed by the 12-item General Health Questionnaire (GHQ-12), the Work-Related Strain Inventory (WRSI), and the Maslach Burnout Inventory (MBI) with three subscales: Emotional Exhaustion (MBI-EE), Depersonalization (MBI-DP), and Diminished Personal Accomplishment (MBI-PA). In 2011, 1,038 EMT-Bs worked for publicly operated and 483 EMT-Bs worked for privately owned ambulance services in Istanbul, Turkey, of which 606 (58.4%) and 236 (48.9%) participated in the study (overall participation rate = 55.4%), respectively. On all scales, differences between total mean scores in both sectors were statistically insignificant (p > .05). In the public sector, work locations, false accusations, occupational injuries and diseases, work-related permanent disabilities, and organizational support were found to significantly influence self-reported perceptions of well-being (p < .05). In the private sector, commute time to and from work (p < .05), false accusations (p < .05), vocational training and education (p < .05), informed career choices (p < .05), and work-related permanent disabilities (p < .05) were found to significantly influence self-reported perceptions of well-being. EMT-Bs were asked about aspects of their working lives that need improvement; priority expectations in the public and private sectors were higher earnings (17.5%; 16.7%) and better social opportunities (17.4%; 16.8%). Working conditions, vocational training, and OHS emerged as topics that merit priority attention. PMID:27034407

  9. VHF-band biconvex AlN-on-silicon micromechanical resonators with enhanced quality factor and suppressed spurious modes

    NASA Astrophysics Data System (ADS)

    Tu, Cheng; E-Y Lee, Joshua

    2016-06-01

    This paper reports experimental results demonstrating the use of biconvex-edge designs to enhance the quality factor (Q) in aluminum nitride (AlN)-on-silicon micromechanical resonators. The proposed biconvex design serves to confine the acoustic energy to the center of the resonators, thus reducing out-of-plane bending on the supporting tethers that contribute to acoustic energy leakage, thereby enhancing Q. We here demonstrate that the biconvex design concept can be scaled and applied across a range of operating frequencies from 70 to 141 MHz with the notable effect of boosting Q relative to conventional flat-edge designs. Our measurements of several resonators have shown that the biconvex designs result in an increase in Q by 4–10 times compared to conventional flat-edge designs. In addition, we have also investigated the effect of using different lengths of supporting tethers on Q for both biconvex and flat-edge designs. From the measurement results of devices under test, we have found that the variation in Q as a function of tether length was insignificant compared to the increase in Q going from a flat-edge to biconvex design. As such, the level of enhancement for Q using the biconvex design is much more significant compared to varying the geometry of the support structures. Interestingly, the biconvex shape causes a modal split that gives rise to an additional anti-symmetric mode not found in the flat-edge design. We show experimentally that this spurious anti-symmetric mode can be suppressed by over 54 dB by applying a novel center-loaded electrode design that matches the strain field pattern of the desired symmetric mode. Close agreements between the 3D coupled-domain finite element simulations and the measured results of fabricated devices have been obtained for the resonant frequencies and motional capacitances.

  10. VHF-band biconvex AlN-on-silicon micromechanical resonators with enhanced quality factor and suppressed spurious modes

    NASA Astrophysics Data System (ADS)

    Tu, Cheng; E-Y Lee, Joshua

    2016-06-01

    This paper reports experimental results demonstrating the use of biconvex-edge designs to enhance the quality factor (Q) in aluminum nitride (AlN)-on-silicon micromechanical resonators. The proposed biconvex design serves to confine the acoustic energy to the center of the resonators, thus reducing out-of-plane bending on the supporting tethers that contribute to acoustic energy leakage, thereby enhancing Q. We here demonstrate that the biconvex design concept can be scaled and applied across a range of operating frequencies from 70 to 141 MHz with the notable effect of boosting Q relative to conventional flat-edge designs. Our measurements of several resonators have shown that the biconvex designs result in an increase in Q by 4-10 times compared to conventional flat-edge designs. In addition, we have also investigated the effect of using different lengths of supporting tethers on Q for both biconvex and flat-edge designs. From the measurement results of devices under test, we have found that the variation in Q as a function of tether length was insignificant compared to the increase in Q going from a flat-edge to biconvex design. As such, the level of enhancement for Q using the biconvex design is much more significant compared to varying the geometry of the support structures. Interestingly, the biconvex shape causes a modal split that gives rise to an additional anti-symmetric mode not found in the flat-edge design. We show experimentally that this spurious anti-symmetric mode can be suppressed by over 54 dB by applying a novel center-loaded electrode design that matches the strain field pattern of the desired symmetric mode. Close agreements between the 3D coupled-domain finite element simulations and the measured results of fabricated devices have been obtained for the resonant frequencies and motional capacitances.

  11. A micromechanical model for the deformation behavior of titanium polycrystals

    NASA Astrophysics Data System (ADS)

    Romanova, V.; Balokhonov, R.; Shakhidjanov, V.; Zinovieva, O.

    2015-10-01

    A microstructure-based constitutive model for a polycrystalline titanium alloy is constructed on the basis of anisotropic elasticity and crystal plasticity theory, with allowance made for the prismatic and basal slip systems. A three-dimensional polycrystalline structure consisting of 1600 grains is designed by a step-by-step packing method and introduced explicitly into finite-element calculations. Numerical modeling of uniaxial tension is performed using Abaqus/Explicit. Grains unfavorably oriented to the loading axis are shown to remain elastic, while slip occurs in the neighboring grains. As this takes place, rotational modes of deformation are activated in addition to shear strain (translational) modes, and surface grains with a low ability to yield demonstrate a tendency towards extrusion.

  12. The use of RT-PCR for determination of separate end-points for the strains IB H120 and IB D274 in titration of the combination vaccine Poulvac IB® primer.

    PubMed

    Geerligs, H J; Meinders, C A M; Snel, J; Duyves, W

    2013-11-01

    Poulvac IB® Primer is a lyophilized vaccine containing two attenuated infectious bronchitis strains in one vial, IB H120 and IB D274. For quantification of the viral content of the vaccine, dilution series of the final product are inoculated in embryonated chicken eggs. After the incubation period of seven days standard practice is for the embryos to be taken from each egg and examined visually for IB specific lesions; these readings are used to determine an end-point in viral titrations. The result is a titre value to which both strains contribute. However, it is not clear what the live virus titre is for strain IB H120 and for strain IB D274. In order to determine end-points in the titration for each of the two strains, we collected the allantoic fluids from each egg after the incubation period and tested these for the presence of IB H120 and IB D274 by a strain specific reverse phase PCR. Based on the data obtained by PCR we were able to determine an end-point for each of the two strains. For a given commercial batch of Poulvac IB primer we determined titres of 10(6.31) EID50 per vial for IB H120 and 10(6.59) EID50 for IB D274 using PCR for end-point determination. These end-points matched well with the end-point determined for both strains cumulatively after visual examination, i.e. 10(6.67) EID50 per vial. It is concluded that PCR is a suitable means to determine end-points in titrations of live viruses.

  13. A method for the on-site determination of prestressing forces using long-gauge fiber optic strain sensors

    NASA Astrophysics Data System (ADS)

    Abdel-Jaber, H.; Glisic, B.

    2014-07-01

    Structural health monitoring (SHM) consists of the continuous or periodic measurement of structural parameters and their analysis with the aim of deducing information about the performance and health condition of a structure. The significant increase in the construction of prestressed concrete bridges motivated this research on an SHM method for the on-site determination of the distribution of prestressing forces along prestressed concrete beam structures. The estimation of the distribution of forces is important as it can give information regarding the overall performance and structural integrity of the bridge. An inadequate transfer of the designed prestressing forces to the concrete cross-section can lead to a reduced capacity of the bridge and consequently malfunction or failure at lower loads than predicted by design. This paper researches a universal method for the determination of the distribution of prestressing forces along concrete beam structures at the time of transfer of the prestressing force (e.g., at the time of prestressing or post-tensioning). The method is based on the use of long-gauge fiber optic sensors, and the sensor network is similar (practically identical) to the one used for damage identification. The method encompasses the determination of prestressing forces at both healthy and cracked cross-sections, and for the latter it can yield information about the condition of the cracks. The method is validated on-site by comparison to design forces through the application to two structures: (1) a deck-stiffened arch and (2) a curved continuous girder. The uncertainty in the determination of prestressing forces was calculated and the comparison with the design forces has shown very good agreement in most of the structures’ cross-sections, but also helped identify some unusual behaviors. The method and its validation are presented in this paper.

  14. Experimental and computational micromechanics at the tibial cement-trabeculae interface.

    PubMed

    Srinivasan, Priyanka; Miller, Mark A; Verdonschot, Nico; Mann, Kenneth A; Janssen, Dennis

    2016-06-14

    Aseptic loosening of the tibial component in cemented total knee arthroplasty remains a major concern. We hypothesize that micromotion between the cement and trabeculae leads to increased circulation of interstitial fluid which in turn causes fluid-induced resorption of the trabeculae. Another mechanism for implant loosening is trabecular strain shielding. Using a newly developed experimental setup and digital image correlation (DIC) methods we were able to measure micromotion and strains in lab-prepared cement-trabeculae interface specimens (n=4). Finite element (FE) models of these specimens were developed to determine whether differences in micromotion and strain in morphologically varying specimens could be simulated accurately. Results showed that the measured micromotion and strains correlated well with FE model predictions (r(2)=0.59-0.85; r(2)=0.66-0.90). Global specimen strains measured axially matched well with the FE model strains (r(2)=0.87). FE model cement strains showed an increasing trend with distance from the cement border. The influence of loss of trabecular connectivity at the specimen edges was studied using our FE model results. Micromotion values at the outer edge of the specimens were higher than the specimen interior when considering a very thin outer edge (0.1mm). When the outer edge thickness was increased to about one trabecular length (0.8mm), there was a drop in the median and peak values. Using the experimental and modelling approach outlined in this study, we can further study the mechanisms that lead to loss of interlock between cement and trabeculae at the tibial interface.

  15. Determinants of antimicrobial resistance in Escherichia coli strains isolated from faeces and urine of women with recurrent urinary tract infections.

    PubMed

    den Heijer, Casper D J; Beerepoot, Mariëlle A J; Prins, Jan M; Geerlings, Suzanne E; Stobberingh, Ellen E

    2012-01-01

    For women with recurrent urinary tract infections (rUTI), the contribution of antibiotic use versus patient-related factors in determining the presence of antimicrobial resistance in faecal and urinary Escherichia coli, obtained from the same patient population, has not been assessed yet. Within the context of the 'Non-antibiotic prophylaxis for recurrent urinary tract infections' (NAPRUTI) study, the present study assessed determinants of antimicrobial resistance in E. coli isolated from urinary and faecal samples of women with rUTIs collected at baseline. Potential determinants of resistance were retrieved from self-administered questionnaires. From 434 asymptomatic women, 433 urinary and 424 faecal samples were obtained. E. coli was isolated from 146 (34%) urinary samples and from 336 (79%) faecal samples, and subsequently tested for antimicrobial susceptibility. Multivariable analysis showed trimethoprim/sulfamethoxazole (SXT) use three months prior to inclusion to be associated with urine E. coli resistance to amoxicillin (OR 3.6, 95% confidence interval: 1.3-9.9), amoxicillin-clavulanic acid (OR 4.4, 1.5-13.3), trimethoprim (OR 3.9, 1.4-10.5) and SXT (OR 3.2, 1.2-8.5), and with faecal E. coli resistance to trimethoprim (OR 2.0, 1.0-3.7). The number of UTIs in the preceding year was correlated with urine E. coli resistance to amoxicillin-clavulanic acid (OR 1.11, 1.01-1.22), trimethoprim (OR 1.13, 1.03-1.23) and SXT (OR 1.10, 1.01-1.19). Age was predictive for faecal E. coli resistance to amoxicillin (OR 1.02, 1.00-1.03), norfloxacin and ciprofloxacin (both OR 1.03, 1.01-1.06). In conclusion, in women with rUTI different determinants were found for urinary and faecal E. coli resistance. Previous antibiotic use and UTI history were associated with urine E. coli resistance and age was a predictor of faecal E. coli resistance. These associations could best be explained by cumulative antibiotic use. PMID:23166796

  16. Nanoscale strain distributions in embedded SiGe semiconductor devices revealed by precession electron diffraction and dual lens dark field electron holography

    SciTech Connect

    Wang, Y. Y.; Cooper, D.; Bernier, N.; Rouviere, J.; Murray, C. E.; Bruley, J.

    2015-01-26

    The detailed strain distributions produced by embedded SiGe stressor structures are measured at high spatial resolution with high precision, with dual lens dark field electron holography and precession electron diffraction. Shear strain and lattice rotation within the crystalline lattice are observed at the boundaries between the SiGe and Si regions. The experimental results are compared to micromechanical modeling simulations to understand the mechanisms of elastic relaxation on all the modes of deformation at a sub-micron length scale.

  17. The Sakaguchi reaction product quenches phycobilisome fluorescence, allowing determination of the arginine concentration in cells of Anabaena strain PCC 7120.

    PubMed

    Ke, Shan; Haselkorn, Robert

    2013-01-01

    The filamentous cyanobacterium Anabaena fixes nitrogen in specialized cells called heterocysts. The immediate product of fixation, ammonia, is known to be assimilated by addition to glutamate to make glutamine. How fixed nitrogen is transported along the filament to the 10 to 20 vegetative cells that separate heterocysts is unknown. N-fixing heterocysts accumulate an insoluble polymer containing aspartate and arginine at the cell poles. Lockau's group has proposed that the polymer is degraded at the poles to provide a mobile carrier, arginine, to the vegetative cells (R. Richter, M. Hejazi, R. Kraft, K. Ziegler, and W. Lockau, Eur. J. Biochem. 263:163-169, 1999). We wished to use the Sakaguchi reaction for arginine to determine the relative cellular concentration of arginine along the filament. At present, the methods for measuring absorption of the Sakaguchi reaction product at 520 nm are insufficiently sensitive for that purpose. However, that product quenches the fluorescence of phycobiliproteins, which we have adapted to a determination of arginine. Our results are consistent with the proposal that arginine is a principal nitrogen carrier from heterocysts to vegetative cells in Anabaena.

  18. Micromechanical models of delamination in aluminum-lithium alloys

    NASA Astrophysics Data System (ADS)

    Messner, Mark Christian

    Aluminum lithium (Al-Li) alloys are lighter, stiffer, and tougher than conventional aerospace aluminum alloys. Replacing conventional aluminums with Al-Li could substantially decrease the weight and cost of aerospace structures. However, Al-Li alloys often fracture intergranularly via a mechanism called delamination cracking. While secondary delamination cracks can improve the effective toughness of a component, no current model accurately predicts the initiation and growth of intergranular cracks. Since simulations cannot incorporate delamination into a structural model, designers cannot quantify the effect of delamination cracking on a particular component. This uncertainty limits the application of Al-Li alloys. Previous experiments identify microstructural features linked to delamination. Fractography of failed surfaces indicates plastic void growth triggers intergranular failure. Furthermore, certain types of soft/stiff grain boundaries tend to localize void growth and nucleate delamination cracks. This dissertation develops a mechanism for the initiation of delamination on the microscale that accounts for these experimental observations. Microscale simulations of grain boundaries near a long primary crack explore the delamination mechanism on the mesoscale. In these simulations, a physically-based crystal plasticity (CP) model represents the constitutive response of individual grains. This CP model incorporates plastic voriticity correction terms into a standard objective stress rate integration, to accurately account for the kinematics of lattice deformation. The CP model implements slip system hardening with a modular approach to facilitate quick testing and calibration of different theories of hardening. The microscale models reveal soft/stiff grain boundaries develop elevated mean stress and plastic strain as a consequence of the mechanics of the interface. These elevated stresses and strain drive plastic void growth. The results indicate plastic void

  19. Consensus sequence determination and elucidation of the evolutionary history of a rotavirus Wa variant reveal a close relationship to various Wa variants derived from the original Wa strain.

    PubMed

    Wentzel, Johannes F; Yuan, Lijuan; Rao, Shujing; van Dijk, Alberdina A; O'Neill, Hester G

    2013-12-01

    The consensus nucleotide sequence of a human rotavirus Wa strain, with only a partially known passage history, was determined with sequence-independent amplification and next generation 454® pyrosequencing. This rotavirus Wa strain had the expected genome constellation of G1-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1 and was designated RVA/Human-tc/USA/WaCS/1974/G1P[8]. Phylogenetic analyses revealed a close relationship to four human rotavirus Wa variants (Wag5re, Wag7/8re, ParWa and VirWa) derived from the original 1974 human isolate. There were rearrangements in the Wag5re- and Wag7/8re variants in genome segments 5 (Wag5re) and 7 and 8 (Wag7/8re), which were not present in WaCS. Pairwise comparisons and a combined molecular clock for the Wa rotavirus genome indicated a close relationship between WaCS and ParWa and VirWa. These results suggest that WaCS is most probably an early cell culture adapted variant from the initial gnotobiotic pig passaged Wa isolate. Evolutionary pressure analysis identified a possible negative selected amino acid site in VP1 (genome segment 1) and a likely positive selected site in VP4 (genome segment 4). The WaCS may be more appropriate as a rotavirus Wa reference sequence than the current composite Wa reference genome.

  20. Natural Strain

    NASA Technical Reports Server (NTRS)

    Freed, Alan D.

    1997-01-01

    Logarithmic strain is the preferred measure of strain used by materials scientists, who typically refer to it as the "true strain." It was Nadai who gave it the name "natural strain," which seems more appropriate. This strain measure was proposed by Ludwik for the one-dimensional extension of a rod with length l. It was defined via the integral of dl/l to which Ludwik gave the name "effective specific strain." Today, it is after Hencky, who extended Ludwik's measure to three-dimensional analysis by defining logarithmic strains for the three principal directions.

  1. Determining the mechanical constitutive properties of metals as a function of strain rate and temperature: A combined experimental and modeling approach

    SciTech Connect

    I. M. Robertson; A. Beaudoin; J. Lambros

    2004-01-05

    OAK-135 Development and validation of constitutive models for polycrystalline materials subjected to high strain rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions (foreign object damage, high-strain rate forging, high-speed sheet forming, deformation behavior during forming, response to extreme conditions, etc.). To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be closely coupled with precise and targeted experimental measurements that not only verify the predictions of the models, but also provide input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experimentation is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models, which will include dislocation-grain boundary interactions for polycrystalline systems. One aspect of the program will involve the dire ct

  2. Micromechanical behavior of single-fiber type and hybrid microcomposites

    SciTech Connect

    Qiu Yiping.

    1992-01-01

    Single-fiber type and hybrid microcomposites were fabricated using Kevlar {reg sign} 149 as the low elongation (LE) fiber and S-glass fibers as the high elongation fiber using a DER 331/DER 732 epoxy mixture (70/30, w/w). In tensile tests, it was found that Kevlar{reg sign} 149 fiber was significantly stronger in the microcomposite than as a single filament. For the hybrid microcomposite, Kevlar{reg sign} 149 fibers usually broke one by one. A positive hybrid effect for the failure strain but a negative hybrid effect for the strength of the hybrid were observed. The tensile modulus of the hybrid microcomposite followed the rule of mixtures well. The fiber/matrix interface properties were investigated using the single-fiber pull-out from a microcomposite (SFPOM) test and the microbond test. SFPOM test reflected the feeling of the fibers in a real composite, showing the decrease of interfacial shear strength (IFSS) with fiber volume fraction increase. To predict the stress-rupture lifetime of a hybrid composite, a stochastic model was proposed assuming that the failure of LE fibers in a hybrid follows a continuous time Markov chain.

  3. Comparison of the slow strain rate technique and the NACE TM0177/sup (1)/ tensile test for determining sulfide stress cracking resistance

    SciTech Connect

    Hoey, G.R.; Revie, R.W.; Ramsingh, R.R.

    1987-10-01

    Samples of a commercial sour service API C-90 (modified AISI 4130 steel) oil country seamless casing in the asquenched state were tempered at six temperatures in the range of 610 to 780 C. The sulfide stress cracking (SSC) resistance of the tempered steels was investigated by the NACE Standard TMO177 tensile bar test and the slow strain rate technique (SSRT). By the NACE TMO177 test, a maximum SSC threshold stress of 662 MPa (96 ksi) was obtained for a steel with a yield strength of 690 MPa (100 ksi), which has been tempered at 715 C. Data on time to failure, percent reduction of area, and percent elongation by the SSRT correlated well with the threshold stresses of the six tempered steels. Compared with the NACE TMO177 test, the SSRT saved considerable time in determining SSC resistance.

  4. Oscillating optical tweezer-based 3-D confocal microrheometer for investigating the intracellular micromechanics and structures

    NASA Astrophysics Data System (ADS)

    Ou-Yang, H. D.; Rickter, E. A.; Pu, C.; Latinovic, O.; Kumar, A.; Mengistu, M.; Lowe-Krentz, L.; Chien, S.

    2005-08-01

    Mechanical properties of living biological cells are important for cells to maintain their shapes, support mechanical stresses and move through tissue matrix. The use of optical tweezers to measure micromechanical properties of cells has recently made significant progresses. This paper presents a new approach, the oscillating optical tweezer cytorheometer (OOTC), which takes advantage of the coherent detection of harmonically modulated particle motions by a lock-in amplifier to increase sensitivity, temporal resolution and simplicity. We demonstrate that OOTC can measure the dynamic mechanical modulus in the frequency range of 0.1-6,000 Hz at a rate as fast as 1 data point per second with submicron spatial resolution. More importantly, OOTC is capable of distinguishing the intrinsic non-random temporal variations from random fluctuations due to Brownian motion; this capability, not achievable by conventional approaches, is particular useful because living systems are highly dynamic and often exhibit non-thermal, rhythmic behavior in a broad time scale from a fraction of a second to hours or days. Although OOTC is effective in measuring the intracellular micromechanical properties, unless we can visualize the cytoskeleton in situ, the mechanical property data would only be as informative as that of "Blind men and the Elephant". To solve this problem, we take two steps, the first, to use of fluorescent imaging to identify the granular structures trapped by optical tweezers, and second, to integrate OOTC with 3-D confocal microscopy so we can take simultaneous, in situ measurements of the micromechanics and intracellular structure in living cells. In this paper, we discuss examples of applying the oscillating tweezer-based cytorheometer for investigating cultured bovine endothelial cells, the identification of caveolae as some of the granular structures in the cell as well as our approach to integrate optical tweezers with a spinning disk confocal microscope.

  5. Development, Implementation and Application of Micromechanical Analysis Tools for Advanced High Temperature Composites

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This document contains the final report to the NASA Glenn Research Center (GRC) for the research project entitled Development, Implementation, and Application of Micromechanical Analysis Tools for Advanced High-Temperature Composites. The research supporting this initiative has been conducted by Dr. Brett A. Bednarcyk, a Senior Scientist at OM in Brookpark, Ohio from the period of August 1998 to March 2005. Most of the work summarized herein involved development, implementation, and application of enhancements and new capabilities for NASA GRC's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) software package. When the project began, this software was at a low TRL (3-4) and at release version 2.0. Due to this project, the TRL of MAC/GMC has been raised to 7 and two new versions (3.0 and 4.0) have been released. The most important accomplishments with respect to MAC/GMC are: (1) A multi-scale framework has been built around the software, enabling coupled design and analysis from the global structure scale down to the micro fiber-matrix scale; (2) The software has been expanded to analyze smart materials; (3) State-of-the-art micromechanics theories have been implemented and validated within the code; (4) The damage, failure, and lifing capabilities of the code have been expanded from a very limited state to a vast degree of functionality and utility; and (5) The user flexibility of the code has been significantly enhanced. MAC/GMC is now the premier code for design and analysis of advanced composite and smart materials. It is a candidate for the 2005 NASA Software of the Year Award. The work completed over the course of the project is summarized below on a year by year basis. All publications resulting from the project are listed at the end of this report.

  6. Discrete Element Models of the Micromechanics of Sedimentary Rock: The Role of Organization vs. Friction

    NASA Astrophysics Data System (ADS)

    Boutt, D. F.; McPherson, B. J.

    2001-12-01

    The micromechanics of sedimentary rock deformation are a fundamental aspect of many research fields, ranging from geotechnical engineering to petroleum recovery and hazardous waste disposal. Laboratory triaxial tests yield information concerning macroscopic behaviors but are not capable of quantifying micromechanical processes such as microcracking and localization. Thus, to quantify micromechanical processes we employed the discrete element method (DEM) of rock deformation, calibrated with triaxial test results. This DEM simulates rock using rigid disc shaped particles bonded at contacts between particles. Previous studies demonstrated that this type of DEM can qualitatively and quantitatively mimic macroscopic behaviors of triaxial tests. An important conclusion of these studies is that a number of particles must be bonded together with higher bond strengths than the surrounding particles to achieve a steeper strength envelope of rocks. This process, termed clustering, is the focus of this study. We hypothesize that since clusters posses a more complicated geometry, they may increase failure strength at elevated confining pressures by interlocking and creating a higher apparent friction. An alternative hypothesis is that the clusters change force chain development by allowing chains to persist longer in specimens. This ultimately causes failure to occur at higher strengths compared to unclustered material. A systematic study comparing effects of cluster shape, particle friction, and force chain development was undertaken. Several model simulations with various cluster shapes and sizes were compared with each other as well as single particle models with high friction coefficients (>1). Preliminary results suggest that the organization of the particle clusters play a key role in increasing the strength envelope. Particle friction coefficients needed to increase slopes of the strength envelopes are well beyond those of geological materials measured in the laboratory

  7. Micromechanics Modeling of Functionally Graded Interphase Regions in Carbon Nanotube-Polymer Composites

    NASA Technical Reports Server (NTRS)

    Seidel, Gary D.; Lagoudas, Dimitris C.; Frankland, Sarah Jane V.; Gates, Thomas S.

    2006-01-01

    The effective elastic properties of a unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes are modeled herein through the use of a multi-scale method involving the molecular dynamics/equivalent continuum and micromechanics methods. The specific lamina representative volume element studied consists of a carbon fiber surrounded by a region of epoxy containing a radially varying concentration of carbon nanotubes which is then embedded in the pure epoxy matrix. The variable concentration of carbon nanotubes surrounding the carbon fiber results in a functionally graded interphase region as the properties of the interphase region vary according to the carbon nanotube volume fraction. Molecular dynamics and equivalent continuum methods are used to assess the local effective properties of the carbon nanotube/epoxy comprising the interphase region. Micromechanics in the form of the Mori-Tanaka method are then applied to obtain the global effective properties of the graded interphase region wherein the carbon nanotubes are randomly oriented. Finally, the multi-layer composite cylinders micromechanics approach is used to obtain the effective lamina properties from the lamina representative volume element. It was found that even very small quantities of carbon nanotubes (0.36% of lamina by volume) coating the surface of the carbon fibers in the lamina can have a significant effect (8% increase) on the transverse properties of the lamina (E22, k23, G23 and G12) with almost no affect on the lamina properties in the fiber direction (E11 and v12).

  8. Occurrence of S and F1C/S-related fimbrial determinants and their expression in Escherichia coli strains isolated from extraintestinal infections.

    PubMed

    Sokolowska-Köhler, W; Schönian, G; Bollmann, R; Schubert, A; Parschau, J; Seeberg, A; Presber, W

    1997-05-01

    The presence of S and F1C/S-related fimbrial determinants was determined in 462 E. coli strains obtained from different extraintestinal infections and in 162 control isolates of E. coli by using two different DNA probes: an oligonucleotide probe consisting of three oligonucleotides that bind specifically to the S adhesin gene and a polynucleotide probe which is not able to distinguish between S, F1C, and S-related sequences. The expression of S and F1C phenotypes was tested by dot enzyme immunoassay with the corresponding monoclonal antibodies. S fimbriae genotypes were observed more frequently in septic (25%) and urinary (12%) isolates of E. coli than in faecal and water isolates (1%) and often occurred together with O2, O6, O18 and O83 antigens. F1C/S-related fimbrial DNA was detected with a higher frequency in UTI isolates (26%) than in septic (16%) and faecal (10%) isolates and was most frequently associated with O4, O6, and O75 serotypes. Since the production of S and F1C fimbriae was comparatively rare in all clinical and control isolates of E. coli, DNA hybridization assays which allow the sensitive and specific detection of fimbrial determinants even in the absence of their expression are preferable to phenotypic assays.

  9. A Micromechanics-Based Damage Model for [+/- Theta/90n]s Composite Laminates

    NASA Technical Reports Server (NTRS)

    Mayugo, Joan-Andreu; Camanho, Pedro P.; Maimi, Pere; Davila, Carlos G.

    2006-01-01

    A new damage model based on a micromechanical analysis of cracked [+/- Theta/90n]s laminates subjected to multiaxial loads is proposed. The model predicts the onset and accumulation of transverse matrix cracks in uniformly stressed laminates, the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate. The model also accounts for the effect of the ply thickness on the ply strength. Predictions relating the elastic properties of several laminates and multiaxial loads are presented.

  10. High-Fidelity Micromechanics Model Developed for the Response of Multiphase Materials

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob; Pindera, Marek-Jerzy; Arnold, Steven M.

    2002-01-01

    A new high-fidelity micromechanics model has been developed under funding from the NASA Glenn Research Center for predicting the response of multiphase materials with arbitrary periodic microstructures. The model's analytical framework is based on the homogenization technique, but the method of solution for the local displacement and stress fields borrows concepts previously employed in constructing the higher order theory for functionally graded materials. The resulting closed-form macroscopic and microscopic constitutive equations, valid for both uniaxial and multiaxial loading of periodic materials with elastic and inelastic constitutive phases, can be incorporated into a structural analysis computer code. Consequently, this model now provides an alternative, accurate method.

  11. Resonant Coupling of a Bose-Einstein Condensate to a Micromechanical Oscillator

    SciTech Connect

    Hunger, David; Camerer, Stephan; Haensch, Theodor W.; Treutlein, Philipp; Koenig, Daniel; Kotthaus, Joerg P.; Reichel, Jakob

    2010-04-09

    We report experiments in which the vibrations of a micromechanical oscillator are coupled to the motion of Bose-condensed atoms in a trap. The interaction relies on surface forces experienced by the atoms at about 1 {mu}m distance from the mechanical structure. We observe resonant coupling to several well-resolved mechanical modes of the condensate. Coupling via surface forces does not require magnets, electrodes, or mirrors on the oscillator and could thus be employed to couple atoms to molecular-scale oscillators such as carbon nanotubes.

  12. Micromechanical analysis of thermo-inelastic multiphase short-fiber composites

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob

    1994-01-01

    A micromechanical formulation is presented for the prediction of the overall thermo-inelastic behavior of multiphase composites which consist of short fibers. The analysis is an extension of the generalized method of cells that was previously derived for inelastic composites with continuous fibers, and the reliability of which was critically examined in several situations. The resulting three dimensional formulation is extremely general, wherein the analysis of thermo-inelastic composites with continuous fibers as well as particulate and porous inelastic materials are merely special cases.

  13. A micromechanical proof-of-principle experiment for measuring the gravitational force of milligram masses

    NASA Astrophysics Data System (ADS)

    Schmöle, Jonas; Dragosits, Mathias; Hepach, Hans; Aspelmeyer, Markus

    2016-06-01

    This paper addresses a simple question: how small can one make a gravitational source mass and still detect its gravitational coupling to a nearby test mass? We describe an experimental scheme based on micromechanical sensing to observe gravity between milligram-scale source masses, thereby improving the current smallest source mass values by three orders of magnitude and possibly even more. We also discuss the implications of such measurements both for improved precision measurements of Newton’s constant and for a new generation of experiments at the interface between quantum physics and gravity.

  14. COMGEN-BEM: Boundary element model generation for composite materials micromechanical analysis

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    1992-01-01

    Composite Model Generation-Boundary Element Method (COMGEN-BEM) is a program developed in PATRAN command language (PCL) which generates boundary element models of continuous fiber composites at the micromechanical (constituent) scale. Based on the entry of a few simple parameters such as fiber volume fraction and fiber diameter, the model geometry and boundary element model are generated. In addition, various mesh densities, material properties, fiber orientation angles, loads, and boundary conditions can be specified. The generated model can then be translated to a format consistent with a boundary element analysis code such as BEST-CMS.

  15. Cooling of a micro-mechanical resonator by the back-action of Lorentz force

    NASA Astrophysics Data System (ADS)

    Wang, Ying-Dan; Semba, K.; Yamaguchi, H.

    2008-04-01

    Using a semi-classical approach, we describe an on-chip cooling protocol for a micro-mechanical resonator by employing a superconducting flux qubit. A Lorentz force, generated by the passive back-action of the resonator's displacement, can cool down the thermal motion of the mechanical resonator by applying an appropriate microwave drive to the qubit. We show that this on-chip cooling protocol, with well-controlled cooling power and a tunable response time of passive back-action, can be highly efficient. With feasible experimental parameters, the effective mode temperature of a resonator could be cooled down by several orders of magnitude.

  16. Detection of micromechanical deformation under rigid body displacement using twin-pulsed 3D digital holography

    NASA Astrophysics Data System (ADS)

    Perez-Lopez, Carlos; Hernandez-Montes, Maria del Socorro; Mendoza-Santoyo, Fernando

    2005-02-01

    Twin-pulsed digital holography in its 3D set up is used to recover exclusively the micro-mechanical deformation of an object. The test object is allowed to have rigid body movements such as rotation and translation, with the result that the fringe patterns contain information of the latter and the object deformation, a feature that may significantly modify the interpretation of the results. Experimental results from a flat metal plate subject to micro stress and a displacement in the x-z plane are presented to demonstrate that using this optical method it is possible to recover exclusively the contribution of the micro stress.

  17. Natural Strain

    NASA Technical Reports Server (NTRS)

    Freed, Alan D.

    1995-01-01

    The purpose of this paper is to present a consistent and thorough development of the strain and strain-rate measures affiliated with Hencky. Natural measures for strain and strain-rate, as I refer to them, are first expressed in terms of of the fundamental body-metric tensors of Lodge. These strain and strain-rate measures are mixed tensor fields. They are mapped from the body to space in both the Eulerian and Lagrangian configurations, and then transformed from general to Cartesian fields. There they are compared with the various strain and strain-rate measures found in the literature. A simple Cartesian description for Hencky strain-rate in the Lagrangian state is obtained.

  18. The influence on predicted harmonic and distortion product generation of the position of the nonlinearity within cochlear micromechanical models.

    PubMed

    How, Jacqueline A; Elliott, Stephen J; Lineton, Ben

    2010-02-01

    Numerical techniques are used to explore the influence on the predicted basilar membrane (BM) response of the position of the nonlinearity within the micromechanical feedback loop of an active nonlinear cochlear model. This position is found to influence both the harmonic and distortion product spectra of the predicted BM response. The BM motion at the fundamental or primary frequencies is not significantly altered by the position of the nonlinearity, however, provided that the gain is appropriately adjusted. The observed effects are explained in terms of the frequency responses of the elements within the micromechanical feedback loop.

  19. CovRS-Regulated Transcriptome Analysis of a Hypervirulent M23 Strain of Group A Streptococcus pyogenes Provides New Insights into Virulence Determinants

    PubMed Central

    Bao, Yun-Juan; Liang, Zhong; Mayfield, Jeffrey A.; Lee, Shaun W.; Ploplis, Victoria A.

    2015-01-01

    ABSTRACT The two-component control of virulence (Cov) regulator (R)-sensor (S) (CovRS) regulates the virulence of Streptococcus pyogenes (group A Streptococcus [GAS]). Inactivation of CovS during infection switches the pathogenicity of GAS to a more invasive form by regulating transcription of diverse virulence genes via CovR. However, the manner in which CovRS controls virulence through expression of extended gene families has not been fully determined. In the current study, the CovS-regulated gene expression profiles of a hypervirulent emm23 GAS strain (M23ND/CovS negative [M23ND/CovS−]) and a noninvasive isogenic strain (M23ND/CovS+), under different growth conditions, were investigated. RNA sequencing identified altered expression of ∼349 genes (18% of the chromosome). The data demonstrated that M23ND/CovS− achieved hypervirulence by allowing enhanced expression of genes responsible for antiphagocytosis (e.g., hasABC), by abrogating expression of toxin genes (e.g., speB), and by compromising gene products with dispensable functions (e.g., sfb1). Among these genes, several (e.g., parE and parC) were not previously reported to be regulated by CovRS. Furthermore, the study revealed that CovS also modulated the expression of a broad spectrum of metabolic genes that maximized nutrient utilization and energy metabolism during growth and dissemination, where the bacteria encounter large variations in available nutrients, thus restructuring metabolism of GAS for adaption to diverse growth environments. From constructing a genome-scale metabolic model, we identified 16 nonredundant metabolic gene modules that constitute unique nutrient sources. These genes were proposed to be essential for pathogen growth and are likely associated with GAS virulence. The genome-wide prediction of genes associated with virulence identifies new candidate genes that potentially contribute to GAS virulence. IMPORTANCE The CovRS system modulates transcription of ∼18% of the genes in

  20. Klebsiella pneumoniae Asparagine tDNAs Are Integration Hotspots for Different Genomic Islands Encoding Microcin E492 Production Determinants and Other Putative Virulence Factors Present in Hypervirulent Strains

    PubMed Central

    Marcoleta, Andrés E.; Berríos-Pastén, Camilo; Nuñez, Gonzalo; Monasterio, Octavio; Lagos, Rosalba

    2016-01-01

    Due to the developing of multi-resistant and invasive hypervirulent strains, Klebsiella pneumoniae has become one of the most urgent bacterial pathogen threats in the last years. Genomic comparison of a growing number of sequenced isolates has allowed the identification of putative virulence factors, proposed to be acquirable mainly through horizontal gene transfer. In particular, those related with synthesizing the antibacterial peptide microcin E492 (MccE492) and salmochelin siderophores were found to be highly prevalent among hypervirulent strains. The determinants for the production of both molecules were first reported as part of a 13-kbp segment of K. pneumoniae RYC492 chromosome, and were cloned and characterized in E. coli. However, the genomic context of this segment in K. pneumoniae remained uncharacterized. In this work, we provided experimental and bioinformatics evidence indicating that the MccE492 cluster is part of a highly conserved 23-kbp genomic island (GI) named GIE492, that was integrated in a specific asparagine-tRNA gene (asn-tDNA) and was found in a high proportion of isolates from liver abscesses sampled around the world. This element resulted to be unstable and its excision frequency increased after treating bacteria with mitomycin C and upon the overexpression of the island-encoded integrase. Besides the MccE492 genetic cluster, it invariably included an integrase-coding gene, at least seven protein-coding genes of unknown function, and a putative transfer origin that possibly allows this GI to be mobilized through conjugation. In addition, we analyzed the asn-tDNA loci of all the available K. pneumoniae assembled chromosomes to evaluate them as GI-integration sites. Remarkably, 73% of the strains harbored at least one GI integrated in one of the four asn-tDNA present in this species, confirming them as integration hotspots. Each of these tDNAs was occupied with different frequencies, although they were 100% identical. Also, we identified

  1. Complete genome sequence of hypervirulent and outbreak-associated Acinetobacter baumannii strain LAC-4: epidemiology, resistance genetic determinants and potential virulence factors

    PubMed Central

    Ou, Hong-Yu; Kuang, Shan N.; He, Xinyi; Molgora, Brenda M.; Ewing, Peter J.; Deng, Zixin; Osby, Melanie; Chen, Wangxue; Xu, H. Howard

    2015-01-01

    Acinetobacter baumannii is an important human pathogen due to its multi-drug resistance. In this study, the genome of an ST10 outbreak A. baumannii isolate LAC-4 was completely sequenced to better understand its epidemiology, antibiotic resistance genetic determinants and potential virulence factors. Compared with 20 other complete genomes of A. baumannii, LAC-4 genome harbors at least 12 copies of five distinct insertion sequences. It contains 12 and 14 copies of two novel IS elements, ISAba25 and ISAba26, respectively. Additionally, three novel composite transposons were identified: Tn6250, Tn6251 and Tn6252, two of which contain resistance genes. The antibiotic resistance genetic determinants on the LAC-4 genome correlate well with observed antimicrobial susceptibility patterns. Moreover, twelve genomic islands (GI) were identified in LAC-4 genome. Among them, the 33.4-kb GI12 contains a large number of genes which constitute the K (capsule) locus. LAC-4 harbors several unique putative virulence factor loci. Furthermore, LAC-4 and all 19 other outbreak isolates were found to harbor a heme oxygenase gene (hemO)-containing gene cluster. The sequencing of the first complete genome of an ST10 A. baumannii clinical strain should accelerate our understanding of the epidemiology, mechanisms of resistance and virulence of A. baumannii. PMID:25728466

  2. A multilayer micromechanical model of the cuticle of Curculio longinasus Chittenden, 1927 (Coleoptera: Curculionidae).

    PubMed

    Andrew Jansen, M; Singh, Sudhanshu S; Chawla, Nikhilesh; Franz, Nico M

    2016-08-01

    Curculio longinasus Chittenden, 1927 (Coleoptera: Curculionidae), is a weevil species common throughout the southwestern United States that uses its rostrum - a very slender, curved, beak-like projection of the head - to excavate tunnels in plant organs (such as acorns) for egg laying (oviposition). Once the apical portion of the rostrum has been inserted into the preferred substrate for oviposition, the female begins rotating around the perimeter of the hole, elevating her head by extending the fore-legs, and rotating the head in place in a drilling motion. This action causes significant elastic deformation of the rostrum, which will bend until it becomes completely straight. To better understand the mechanical behavior of the cuticle as it undergoes deformation during the preparation of oviposition sites, we develop a comprehensive micro/macro model of the micromechanical structure and properties of the cuticle, spanning across all cuticular regions, and reliably mirroring the resultant macroscale properties of the cuticle. Our modeling approach relies on the use of multi-scale, hierarchical biomaterial representation, and employs various micromechanical schemata - e.g., Mori-Tanaka, effective field, and Maxwell - to calculate the homogenized properties of representative volume elements at each level in the hierarchy. We describe the configuration and behavior of this model in detail, and discuss the theoretical implications and limitations of this approach with emphasis on future biomechanical and comparative evolutionary research. Our detailed account of this approach can thereby serve as a methodological template for exploring the biomechanical behavior of new insect structures. PMID:27189867

  3. Mechanical design and force calibration of dual-axis micromechanical probe for friction force microscopy

    SciTech Connect

    Fukuzawa, Kenji; Terada, Satoshi; Shikida, Mitsuhiro; Amakawa, Hiroaki; Zhang, Hedong; Mitsuya, Yasunaga

    2007-02-01

    A dual-axis micromechanical probe that combines a double cantilever and torsion beams is presented. This probe can reduce the mechanical cross-talk between the lateral and vertical force detections. In addition, dual-axis forces can be detected by measuring the dual-axis displacement of the probe end using the optical lever-based method used in conventional friction force microscopes (FFMs). In this paper, the mechanical design of the probe, the details of the fabrication method, FFM performance, and calibration of the friction force are discussed. The mechanical design and the microfabrication method for probes that can provide a force resolution of the order of 1 nN without mechanical cross-talk are presented. Calibration of the lateral force signal is possible by using the relationship between the lateral force and the piezodisplacement at the onset of the probe scanning. The micromechanical probe enables simultaneous and independent detection of atomic and friction forces. This leads to accurate investigation of nanotribological phenomena and visualization of the distribution of the friction properties, which helps the identification of the material properties.

  4. Biological thermal detection: micromechanical and microthermal properties of biological infrared receptors.

    PubMed

    Gorbunov, V; Fuchigami, N; Stone, M; Grace, M; Tsukruk, V V

    2002-01-01

    Bioinspired design of biomimetic sensors relies upon the complete understanding of properties and functioning of biological analogues in conjunction with an understanding of their microstructural organization at various length scales. In the spirit of this approach, the microscopic properties of infrared (IR) receptors of snakes with "infrared vision" were studied with scanning thermal microscopy and micromechanical analysis. Low surface thermal conductivity of 0.11 W/(m K) was measured for the IR receptor surfaces as compared to the nonspecific skin areas. This difference in surface thermal conductivity should result in a significant local temperature gradient around the receptor areas. Micromechanical analysis showed that pit organs were more compliant than surrounding skin areas with an elastic modulus close to 40 MPa. In addition, the maximum elastic modulus was detected for the outermost layer with gradually reduced elastic resistance for the interior. The porous microstructure of the underlying tissue combined with the highly branched microfibrillar network (Biomacromolecules 2001, 2, 757) is thought to be responsible for such a combination of biomaterial properties. Considering these biomaterials features, we postulated a possible design of an artificial photothermal detector inspired by the microstructure of natural receptors. This bioinspired design would include a microfabricated cavity filled with an ordered lattice of microspheres with a gradient periodicity from the surface to the interior. Such a "photonic cavity" could provide an opportunity for multiple scattering at wavelength tuned to 8-12 microm as a range of highest sensitivity.

  5. Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Xue, D.; Shi, Y.

    2013-01-01

    A micromechanics analysis modeling method was developed to analyze the damage progression and fatigue failure of fabric reinforced composite structures, especially for the brittle ceramic matrix material composites. A repeating unit cell concept of fabric reinforced composites was used to represent the global composite structure. The thermal and mechanical properties of the repeating unit cell were considered as the same as those of the global composite structure. The three-phase micromechanics, the shear-lag, and the continuum fracture mechanics models were integrated with a statistical model in the repeating unit cell to predict the progressive damages and fatigue life of the composite structures. The global structure failure was defined as the loss of loading capability of the repeating unit cell, which depends on the stiffness reduction due to material slice failures and nonlinear material properties in the repeating unit cell. The present methodology is demonstrated with the analysis results evaluated through the experimental test performed with carbon fiber reinforced silicon carbide matrix plain weave composite specimens.

  6. Analysis of Fiber Clustering in Composite Materials Using High-Fidelity Multiscale Micromechanics

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Arnold, Steven M.

    2015-01-01

    A new multiscale micromechanical approach is developed for the prediction of the behavior of fiber reinforced composites in presence of fiber clustering. The developed method is based on a coupled two-scale implementation of the High-Fidelity Generalized Method of Cells theory, wherein both the local and global scales are represented using this micromechanical method. Concentration tensors and effective constitutive equations are established on both scales and linked to establish the required coupling, thus providing the local fields throughout the composite as well as the global properties and effective nonlinear response. Two nondimensional parameters, in conjunction with actual composite micrographs, are used to characterize the clustering of fibers in the composite. Based on the predicted local fields, initial yield and damage envelopes are generated for various clustering parameters for a polymer matrix composite with both carbon and glass fibers. Nonlinear epoxy matrix behavior is also considered, with results in the form of effective nonlinear response curves, with varying fiber clustering and for two sets of nonlinear matrix parameters.

  7. Micro-mechanical modelling of cellulose aerogels from molten salt hydrates.

    PubMed

    Rege, Ameya; Schestakow, Maria; Karadagli, Ilknur; Ratke, Lorenz; Itskov, Mikhail

    2016-09-14

    In this paper, a generalised micro-mechanical model capable of capturing the mechanical behaviour of polysaccharidic aerogels, in particular cellulose aerogels, is proposed. To this end, first the mechanical structure and properties of these highly nanoporous cellulose aerogels prepared from aqueous salt hydrate melts (calcium thiocyanate, Ca(SCN)2·6H2O and zinc chloride, ZnCl2·4H2O) are studied. The cellulose content within these aerogels is found to have a direct relation to the microstructural quantities such as the fibril length and diameter. This, along with porosity, appears to influence the resulting mechanical properties. Furthermore, experimental characterisation of cellulose aerogels was done using scanning electron microscopy (SEM), pore-size data analysis, and compression tests. Cellulose aerogels are of a characteristic cellular microstructures and accordingly a network formed by square shaped cells is considered in the micro-mechanical model proposed in this paper. This model is based on the non-linear bending and collapse of such cells of varying pore sizes. The extended Euler-Bernoulli beam theory for large deflections is used to describe the bending in the cell walls. The proposed model is physically motivated and demonstrates a good agreement with our experimental data of both ZnCl2 and Ca(SCN)2 based cellulose aerogels with different cellulose contents.

  8. Linearity enhancement of scale factor in an optical interrogated micromechanical accelerometer.

    PubMed

    Zhang, Yu; Feng, Lishuang; Wang, Xiao; Wang, Yang

    2016-08-01

    A method to reduce the residual stress of support arms in an optical interrogated micromechanical accelerometer is proposed in order to enhance the linearity of the scale factor of the accelerometer. First, the behavior of residual stress in support arms is analyzed in detail, and the simulation of shape curvature caused by residual stress in aluminum-made support arms is completed using finite element analysis. Then, by comparing two different materials of support arms (aluminum-made and silicon-made support arms), a modified fabrication is introduced in order to reduce the unexpected residual stress in support arms. Finally, based on contrast experiments, the linearity of the scale factor of accelerometers with aluminum-made and silicon-made support arms is measured using the force feedback test system, respectively. Results show that the linearity of the scale factor of the accelerometer with silicon-made support arms is 0.85%, which is reduced about an order of magnitude compared to that of the accelerometer with aluminum-made support arms with the linearity of scale factor of 7.48%; linearity enhancement of the scale factor is validated. This allows accuracy improvement of the optical interrogated micromechanical accelerometer in the application of inertial navigation and positioning. PMID:27505396

  9. A Micromechanical Constitutive Model of Progressive Crushing in Random Carbon Fiber Polymer Matrix Composites

    SciTech Connect

    Lee, H.K.; Simunovic, S.

    1999-09-01

    A micromechanical damage constitutive model is presented to predict the overall elastoplastic behavior and damage evolution in random carbon fiber polymer matrix composites (RFPCs).To estimate the overall elastoplastic damage responses,an effective yield criterion is derived based on the ensemble-volume averaging process and first-order effects of eigenstrains due to the existence of spheroidal (prolate) fibers.The proposed effective yield criterion,to ether with the assumed overall associative plastic flow rule and hardening law, constitutes the analytical foundation for the estimation of effective elastoplastic behavior of ductile matrix composites.First,an effective elastoplastic constitutive dama e model for aligned fiber-reinforced composites is proposed.A micromechanical damage constitutive model for RFPCs is then developed.The average process over all orientations upon overning constitutive field equations and overall yield function for aligned fiber-reinforced composites i s performed to obtain the constitutive relations and effective yield function of RFPCs.The discrete numerical integration algorithms and the continuum tan ent operator are also presented to implement the proposed dama e constitutive model.The dama e constitutive model forms the basis for the pro ressive crushing in composite structures under impact loading.

  10. Micromechanics Analysis Code Post-Processing (MACPOST) User Guide. 1.0

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Comiskey, Michele D.; Bednarcyk, Brett A.

    1999-01-01

    As advanced composite materials have gained wider usage. the need for analytical models and computer codes to predict the thermomechanical deformation response of these materials has increased significantly. Recently, a micromechanics technique called the generalized method of cells (GMC) has been developed, which has the capability to fulfill this -oal. Tc provide a framework for GMC, the Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) has been developed. As MAC/GMC has been updated, significant improvements have been made to the post-processing capabilities of the code. Through the MACPOST program, which operates directly within the MSC/PATRAN graphical pre- and post-processing package, a direct link between the analysis capabilities of MAC/GMC and the post-processing capabilities of MSC/PATRAN has been established. MACPOST has simplified the production, printing. and exportation of results for unit cells analyzed by MAC/GMC. MACPOST allows different micro-level quantities to be plotted quickly and easily in contour plots. In addition, meaningful data for X-Y plots can be examined. MACPOST thus serves as an important analysis and visualization tool for the macro- and micro-level data generated by MAC/GMC. This report serves as the user's manual for the MACPOST program.

  11. Micro-mechanical modelling of cellulose aerogels from molten salt hydrates.

    PubMed

    Rege, Ameya; Schestakow, Maria; Karadagli, Ilknur; Ratke, Lorenz; Itskov, Mikhail

    2016-09-14

    In this paper, a generalised micro-mechanical model capable of capturing the mechanical behaviour of polysaccharidic aerogels, in particular cellulose aerogels, is proposed. To this end, first the mechanical structure and properties of these highly nanoporous cellulose aerogels prepared from aqueous salt hydrate melts (calcium thiocyanate, Ca(SCN)2·6H2O and zinc chloride, ZnCl2·4H2O) are studied. The cellulose content within these aerogels is found to have a direct relation to the microstructural quantities such as the fibril length and diameter. This, along with porosity, appears to influence the resulting mechanical properties. Furthermore, experimental characterisation of cellulose aerogels was done using scanning electron microscopy (SEM), pore-size data analysis, and compression tests. Cellulose aerogels are of a characteristic cellular microstructures and accordingly a network formed by square shaped cells is considered in the micro-mechanical model proposed in this paper. This model is based on the non-linear bending and collapse of such cells of varying pore sizes. The extended Euler-Bernoulli beam theory for large deflections is used to describe the bending in the cell walls. The proposed model is physically motivated and demonstrates a good agreement with our experimental data of both ZnCl2 and Ca(SCN)2 based cellulose aerogels with different cellulose contents. PMID:27487115

  12. Relations between a micro-mechanical model and a damage model for ductile failure in shear

    NASA Astrophysics Data System (ADS)

    Tvergaard, Viggo; Nielsen, Kim Lau

    2010-09-01

    Gurson type constitutive models that account for void growth to coalescence are not able to describe ductile fracture in simple shear, where there is no hydrostatic tension in the material. But recent micro-mechanical studies have shown that in shear the voids are flattened out to micro-cracks, which rotate and elongate until interaction with neighbouring micro-cracks gives coalescence. Thus, the failure mechanism is very different from that under tensile loading. Also, the Gurson model has recently been extended to describe failure in shear, by adding a damage term to the expression for the growth of the void volume fraction, and it has been shown that this extended model can represent experimental observations. Here, numerical studies are carried out to compare predictions of the shear-extended Gurson model with the shear failures predicted by the micro-mechanical cell model. Both models show a strong dependence on the level of hydrostatic tension. Even though the reason for this pressure dependence is different in the two models, as the shear-extended Gurson model does not describe voids flattening out and the associated failure mechanism by micro-cracks interacting with neighbouring micro-cracks, it is shown that the trends of the predictions are in good agreement.

  13. Micromechanical IR thermal detector using torsional oscillation: Improvement of resonator profile for high sensitivity

    NASA Astrophysics Data System (ADS)

    Jeong, Jonghyeon; Kumagai, Shinya; Yamashita, Ichiro; Uraoka, Yukiharu; Sasaki, Minoru

    2015-04-01

    An infrared (IR) thermal detector, which used the torsional oscillation of a micromechanical resonator, was developed to achieve a high sensitivity. The detector has a bimaterial structure consisting of a tense Si film (oscillating body) and a metal film (IR absorber). Owing to the difference in thermal expansion between the two materials, the resonator is bent by light incidence. Because the axis of torsion is bent from the initial flat state, the spring for torsional oscillation hardens and resonant frequency shifts. To enhance bending, an Al film with a large coefficient of thermal expansion was used. In addition, the tension in the polycrystalline Si film was enhanced by metal-induced lateral crystallization using biomineralized Ni nanoparticles. The fabricated detector was flat under initial conditions and showed a bending response to the light incidence and heating. The present IR detector achieved a thermal coefficient of frequency of 1000 ppm/K, which was one order larger than that of the conventional micromechanical IR sensors.

  14. Monitoring the formation of self-assembled monolayers of alkanedithiols using a micromechanical cantilever sensor.

    PubMed

    Kohale, Swapnil; Molina, Sara M; Weeks, Brandon L; Khare, Rajesh; Hope-Weeks, Louisa J

    2007-01-30

    Using a micromechanical cantilever device, the surface stress induced during the growth of alkanedithiol (HS(CH2)nSH) monolayers on gold in solution is continuously monitored and reported. Adsorption of alkanedithiols of varying chain lengths is observed and compared to each other, as well as to the adsorption of hydroxyalkanethiols (HS(CH2)nOH) and alkanethiols (HS(CH2)nCH3). The results have revealed a significant change in surface stress on the basis of the chain length of the alkanedithiol. The long-chain (n > 10) alkanedithiol adsorption imposes a tensile stress on the gold-coated surface of the cantilever rather than the compressive stress exhibited by both alkanethiols and short-chain dithiols. Our results suggest a phenomenon in which the two thiols of the alkanedithiol adsorb onto the gold surface forming a loop inducing a tensile stress on the cantilever for long chain lengths. This study shows that micromechanical cantilever sensors can be very valuable tools in the exploration and characterization of self-assembled monolayers.

  15. Micromechanics of brittle faulting and cataclastic flow in Mount Etna basalt

    NASA Astrophysics Data System (ADS)

    Zhu, Wei; Baud, Patrick; Vinciguerra, Sergio; Wong, Teng-fong

    2016-06-01

    Understanding how the strength of volcanic rocks varies with stress state, pressure, and microstructural attributes is fundamental to understanding the dynamics and tectonics of a volcanic system and also very important in applications such as geothermics or reservoir management in volcanic environments. In this study we investigated the micromechanics of deformation and failure in basalt, focusing on samples from Mount Etna. We performed 65 uniaxial and triaxial compression experiments on nominally dry and water-saturated samples covering a porosity range between 5 and 16%, at effective pressures up to 200 MPa. Dilatancy and brittle faulting were observed in all samples with porosity of 5%. Water-saturated samples were found to be significantly weaker than comparable dry samples. Shear-enhanced compaction was observed at effective pressures as low as 80 MPa in samples of 8% porosity. Microstructural data revealed the complex interplay of microcracks, pores, and phenocrysts on dilatant failure and inelastic compaction in basalt. The micromechanics of brittle failure is controlled by wing crack propagation under triaxial compression and by pore-emanated cracking under uniaxial compression especially in the more porous samples. The mechanism of inelastic compaction in basalt is cataclastic pore-collapse in agreement with a recent dual-porosity model.

  16. Self-Sustained Micromechanical Oscillator with Linear Feedback.

    PubMed

    Chen, Changyao; Zanette, Damián H; Guest, Jeffrey R; Czaplewski, David A; López, Daniel

    2016-07-01

    Autonomous oscillators, such as clocks and lasers, produce periodic signals without any external frequency reference. In order to sustain stable periodic motion, there needs to be an external energy supply as well as nonlinearity built into the oscillator to regulate the amplitude. Usually, nonlinearity is provided by the sustaining feedback mechanism, which also supplies energy, whereas the constituent resonator that determines the output frequency stays linear. Here, we propose a new self-sustaining scheme that relies on the nonlinearity originating from the resonator itself to limit the oscillation amplitude, while the feedback remains linear. We introduce a model for describing the working principle of the self-sustained oscillations and validate it with experiments performed on a nonlinear microelectromechanical oscillator.

  17. Fluid Dynamics Prize Lecture: The Micromechanics of Colloidal Dispersions

    NASA Astrophysics Data System (ADS)

    Brady, John F.

    2012-11-01

    What do corn starch, swimming spermatozoa, DNA and self-assembling nanoparticles have in common? They are all (or can be modeled as) ``particles'' dispersed in a continuum suspending fluid where hydrodynamic interactions compete with thermal (Brownian) and interparticle forces to set structure and determine properties. These systems are ``soft'' as compared to molecular systems largely because their number density is much less and their time scales much longer than atomic or molecular systems. In this talk I will describe the common framework for modeling these diverse systems and the essential features that any hydrodynamic modeling must incorporate in order to capture the correct behavior. Actually computing the hydrodynamics in an accurate and efficient manner is the real challenge, and I will illustrate past successes and current efforts with examples drawn from the diffusion and rheology of colloids to the ``swimming'' of catalytic nanomotors.

  18. Self-Sustained Micromechanical Oscillator with Linear Feedback

    NASA Astrophysics Data System (ADS)

    Chen, Changyao; Zanette, Damián H.; Guest, Jeffrey R.; Czaplewski, David A.; López, Daniel

    2016-07-01

    Autonomous oscillators, such as clocks and lasers, produce periodic signals without any external frequency reference. In order to sustain stable periodic motion, there needs to be an external energy supply as well as nonlinearity built into the oscillator to regulate the amplitude. Usually, nonlinearity is provided by the sustaining feedback mechanism, which also supplies energy, whereas the constituent resonator that determines the output frequency stays linear. Here, we propose a new self-sustaining scheme that relies on the nonlinearity originating from the resonator itself to limit the oscillation amplitude, while the feedback remains linear. We introduce a model for describing the working principle of the self-sustained oscillations and validate it with experiments performed on a nonlinear microelectromechanical oscillator.

  19. Micromechanics of fatigue in woven and stitched composites

    NASA Technical Reports Server (NTRS)

    Cox, B. N.; Dadkhah, M. S.; Inman, R. V.; Mitchell, M. R.; Morris, W. L.; Schroeder, S.

    1991-01-01

    The goal is to determine how microstructural factors, especially the architecture of microstructural factors, control fatigue damage in 3D reinforced polymer composites. Test materials were fabricated from various preforms, including stitched quasi-isotropic laminates, and through-the-thickness angle interlock, layer-to-layer angle interlock, and through-the-thickness stitching effect weaves. Preforms were impregnated with a tough resin by a special vacuum infiltration method. Most tests are being performed in uniaxial compression/compression loading. In all cases to date, failure has occurred not by delamination, but by shear failure, which occurs suddenly rather than by gradual macroscopic crack growth. Some theoretical aspects of bridging are also examined.

  20. Cement lines and interlamellar areas in compact bone as strain amplifiers - contributors to elasticity, fracture toughness and mechanotransduction.

    PubMed

    Nobakhti, Sabah; Limbert, Georges; Thurner, Philipp J

    2014-01-01

    Bone is multi-scale hierarchical composite material making the prediction of fragility, as well as pinning it to a certain cause, complicated. For proper mechanical simulation and reflection of bone properties in models, microscopic structural features of bone tissue need to be included. This study sets out to gain a mechanistic insight into the role of various microstructural features of bone tissue in particular cement lines and interlamellar areas. Further the hypothesis that compliant interlamellar areas and cement lines within osteonal bone act as strain amplifiers was explored. To this end, a series of experimentally-based micromechanical finite element models of bovine osteonal bone were developed. Different levels of detail for the bone microstructure were considered and combined with the results of physical three-point bending tests and an analytical composite model of a single osteon. The objective was to examine local and global effects of interface structures. The geometrical and microstructural characteristics of the bone samples were derived from microscopy imaging. Parametric finite element studies were conducted to determine optimal values of the elastic modulus of interstitial bone and interlamellar areas. The average isotropic elastic modulus of interfaces suggested in this study is 88.5MPa. Based on the modelling results, it is shown that interfaces are areas of accumulated strain in bone and are likely to act as potential paths for crack propagation. The strain amplification capability of interface structures in the order of 10 predicted by the models suggests a new explanation for the levels of strain required in bone homoeostasis for maintenance and adaptation.