Redistribution of Welding Residual Stresses of Crack Tip Opening Displacement Specimen by Local Compression.

PubMed

Kim, Young-Gon; Song, Kuk-Hyun; Lee, Dong-Hoon; Joo, Sung-Min

2018-03-01

The demand of crack tip opening displacement (CTOD) test which evaluates fracture toughness of a cracked material is very important to ensure the stability of structure under severe service environment. The validity of the CTOD test result is judged using several criterions of the specification standards. One of them is the artificially generated fatigue pre-crack length inside the specimen. For acceptable CTOD test results, fatigue pre-crack must have a reasonable sharp crack front. The propagation of fatigue crack started from the tip of the machined notch, which might have propagated irregularly due to residual stress field. To overcome this problem, test codes suggest local compression method, reversed bending method and stepwise high-R ratio method to reduce the disparity of residual stress distribution inside the specimen. In this paper, the relation between the degree of local compression and distribution of welding residual stress has been analyzed by finite element analyses in order to determine the amount of effective local compression of the test piece. Analysis results show that initial welding residual stress is dramatically varied three-dimensionally while cutting, notch machining and local compressing due to the change of internal restraint force. From the simulation result, the authors find that there is an optimum amount of local compression to modify regularly for generating fatigue pre-crack propagation. In the case of 0.5% compressions of the model width is the most effective for uniforming residual stress distribution.

Computational analysis of forebody tangential slot blowing

NASA Technical Reports Server (NTRS)

Gee, Ken; Agosta-Greenman, Roxana M.; Rizk, Yehia M.; Schiff, Lewis B.; Cummings, Russell M.

1994-01-01

An overview of the computational effort to analyze forebody tangential slot blowing is presented. Tangential slot blowing generates side force and yawing moment which may be used to control an aircraft flying at high-angle-of-attack. Two different geometries are used in the analysis: (1) The High Alpha Research Vehicle; and (2) a generic chined forebody. Computations using the isolated F/A-18 forebody are obtained at full-scale wind tunnel test conditions for direct comparison with available experimental data. The effects of over- and under-blowing on force and moment production are analyzed. Time-accurate solutions using the isolated forebody are obtained to study the force onset timelag of tangential slot blowing. Computations using the generic chined forebody are obtained at experimental wind tunnel conditions, and the results compared with available experimental data. This computational analysis compliments the experimental results and provides a detailed understanding of the effects of tangential slot blowing on the flow field about simple and complex geometries.

Obliquity dependence of the tangential YORP

NASA Astrophysics Data System (ADS)

Ševeček, P.; Golubov, O.; Scheeres, D. J.; Krugly, Yu. N.

2016-08-01

Context. The tangential Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is a thermophysical effect that can alter the rotation rate of asteroids and is distinct from the so-called normal YORP effect, but to date has only been studied for asteroids with zero obliquity. Aims: We aim to study the tangential YORP force produced by spherical boulders on the surface of an asteroid with an arbitrary obliquity. Methods: A finite element method is used to simulate heat conductivity inside a boulder, to find the recoil force experienced by it. Then an ellipsoidal asteroid uniformly covered by these types of boulders is considered and the torque is numerically integrated over its surface. Results: Tangential YORP is found to operate on non-zero obliquities and decreases by a factor of two for increasing obliquity.

Turbulent shear stresses in compressible boundary layers

NASA Technical Reports Server (NTRS)

Laderman, A. J.; Demetriades, A.

1979-01-01

Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.

Development of a defect stream function, law of the wall/wake method for compressible turbulent boundary layers. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Wahls, Richard A.

1990-01-01

The method presented is designed to improve the accuracy and computational efficiency of existing numerical methods for the solution of flows with compressible turbulent boundary layers. A compressible defect stream function formulation of the governing equations assuming an arbitrary turbulence model is derived. This formulation is advantageous because it has a constrained zero-order approximation with respect to the wall shear stress and the tangential momentum equation has a first integral. Previous problems with this type of formulation near the wall are eliminated by using empirically based analytic expressions to define the flow near the wall. The van Driest law of the wall for velocity and the modified Crocco temperature-velocity relationship are used. The associated compressible law of the wake is determined and it extends the valid range of the analytical expressions beyond the logarithmic region of the boundary layer. The need for an inner-region eddy viscosity model is completely avoided. The near-wall analytic expressions are patched to numerically computed outer region solutions at a point determined during the computation. A new boundary condition on the normal derivative of the tangential velocity at the surface is presented; this condition replaces the no-slip condition and enables numerical integration to the surface with a relatively coarse grid using only an outer region turbulence model. The method was evaluated for incompressible and compressible equilibrium flows and was implemented into an existing Navier-Stokes code using the assumption of local equilibrium flow with respect to the patching. The method has proven to be accurate and efficient.

Development, characterization, and modeling of ballistic impact on composite laminates under compressive pre-stress

NASA Astrophysics Data System (ADS)

Kerr-Anderson, Eric

Structural composite laminates were ballistically impacted while under in-plane compressive pre-stress. Residual properties, damage characterization, and energy absorption were compared to determine synergistic effects of in-plane compressive pre-stress and impact velocity. A fixture was developed to apply in-plane compressive loads up to 30 tons to structural composites during an impact event using a single-stage light-gas gun. Observed failure modes included typical conical delamination, the development of an impact initiated shear crack (IISC), and the shear failure of a pre-stressed composite due to impact. It was observed that the compressive failure threshold quadratically decreased in relation to the impact velocity up to velocities that caused partial penetration. For all laminates impacted at velocities causing partial or full penetration up to 350 ms-1, the failure threshold was consistent and used as an experimental normalization. Samples impacted below 65% of the failure threshold witnessed no significant change in damage morphology or residual properties when compared to typical conical delamination. Samples impacted above 65% of the failure threshold witnessed additional damage in the form of a shear crack extending perpendicular to the applied load from the point of impact. The presence of an IISC reduced the residual properties and even caused failure upon impact at extreme combinations. Four failure envelopes have been established as: transient failure, steady state failure, impact initiated shear crack, and conical damage. Boundaries and empirically based equations for residual compressive strength have been developed for each envelope with relation to two E-glass/vinyl ester laminate systems. Many aspects of pre-stressed impact have been individually examined, but there have been no comprehensive examinations of pre-stressed impact. This research has resulted in the exploration and characterization of compressively pre-stressed damage for impact

Application of a Reynolds stress turbulence model to the compressible shear layer

NASA Technical Reports Server (NTRS)

Sarkar, S.; Balakrishnan, L.

1990-01-01

Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

Bi-tangential hybrid IMRT for sparing the shoulder in whole breast irradiation.

PubMed

Farace, P; Deidda, M A; Iamundo de Cumis, I; Iamundo de Curtis, I; Deiana, E; Farigu, R; Lay, G; Porru, S

2013-11-01

A bi-tangential technique is proposed to reduce undesired doses to the shoulder produced by standard tangential irradiation. A total of 6 patients affected by shoulder pain and reduced functional capacity after whole-breast irradiation were retrospectively analysed. The standard tangential plan used for treatment was compared with (1) a single bi-tangential plan where, to spare the shoulder, the lateral open tangent was split into two half-beams at isocentre, with the superior portion rotated by 10-20° medially with respect to the standard lateral beam; (2) a double bi-tangential plan, where both the tangential open beams were split. The planning target volume (PTV) coverage and the dose to the portion of muscles and axilla included in the standard tangential beams were compared. PTV95 % of standard plan (91.9 ± 3.8) was not significantly different from single bi-tangential plan (91.8 ± 3.4); a small but significant (p < 0.01) decrease was observed with the double bi-tangential plan (90.1 ± 3.7). A marked dose reduction to the muscle was produced by the single bi-tangential plan around 30-40 Gy. The application of the double bi-tangential technique further reduced the volume receiving around 20 Gy, but did not markedly affect the higher doses. The dose to the axilla was reduced both in the single and the double bi-tangential plans. The single bi-tangential technique would have been able to reduce the dose to shoulder and axilla, without compromising target coverage. This simple technique is valuable for irradiation after axillary lymph node dissection or in patients without dissection due to negative or low-volume sentinel lymph node disease.

Numerical simulation and experiment on split tungsten carbide cylinder of high pressure apparatus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Yunfei; Li, Mingzhe, E-mail: limz@jlu.edu.cn; Wang, Bolong

2015-12-15

A new high pressure device with a split cylinder was investigated on the basis of the belt-type apparatus. The belt-type die is subjected to excessive tangential tensile stress and the tungsten carbide cylinder is easily damaged in the running process. Taking into account the operating conditions and material properties of the tungsten carbide cylinder, it is divided into 6 blocks to eliminate the tangential tensile stress. We studied two forms of the split type: radial split and tangential split. Simulation results indicate that the split cylinder has more uniform stress distribution and smaller equivalent stress compared with the belt-type cylinder.more » The inner wall of the tangential split cylinder is in the situation that compressive stress is distributed in the axial, radial, and tangential directions. It is similar to the condition of hydrostatic pressure, and it is the best condition for tungsten carbide materials. The experimental results also verify that the tangential split die can bear the highest chamber pressure. Therefore, the tangential split structure can increase the pressure bearing capacity significantly.« less

An alternative to FASTSIM for tangential solution of the wheel-rail contact

NASA Astrophysics Data System (ADS)

Sichani, Matin Sh.; Enblom, Roger; Berg, Mats

2016-06-01

In most rail vehicle dynamics simulation packages, tangential solution of the wheel-rail contact is gained by means of Kalker's FASTSIM algorithm. While 5-25% error is expected for creep force estimation, the errors of shear stress distribution, needed for wheel-rail damage analysis, may rise above 30% due to the parabolic traction bound. Therefore, a novel algorithm named FaStrip is proposed as an alternative to FASTSIM. It is based on the strip theory which extends the two-dimensional rolling contact solution to three-dimensional contacts. To form FaStrip, the original strip theory is amended to obtain accurate estimations for any contact ellipse size and it is combined by a numerical algorithm to handle spin. The comparison between the two algorithms shows that using FaStrip improves the accuracy of the estimated shear stress distribution and the creep force estimation in all studied cases. In combined lateral creepage and spin cases, for instance, the error in force estimation reduces from 18% to less than 2%. The estimation of the slip velocities in the slip zone, needed for wear analysis, is also studied. Since FaStrip is as fast as FASTSIM, it can be an alternative for tangential solution of the wheel-rail contact in simulation packages.

Modeling of coupled thermodynamic and geomechanical performance of underground compressed air energy storage in lined rock caverns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rutqvist, Jonny; Kim, Hyung-Mok; Ryu, Dong-Woo

We applied coupled nonisothermal, multiphase fluid flow and geomechanical numerical modeling to study the coupled thermodynamic and geomechanical performance of underground compressed air energy storage (CAES) in concrete-lined rock caverns. The paper focuses on CAES in lined caverns at relatively shallow depth (e.g., 100 m depth) in which a typical CAES operational pressure of 5 to 8 MPa is significantly higher than both ambient fluid pressure and in situ stress. We simulated a storage operation that included cyclic compression and decompression of air in the cavern, and investigated how pressure, temperature and stress evolve over several months of operation. Wemore » analyzed two different lining options, both with a 50 cm thick low permeability concrete lining, but in one case with an internal synthetic seal such as steel or rubber. For our simulated CAES system, the thermodynamic analysis showed that 96.7% of the energy injected during compression could be recovered during subsequent decompression, while 3.3% of the energy was lost by heat conduction to the surrounding media. Our geomechanical analysis showed that tensile effective stresses as high as 8 MPa could develop in the lining as a result of the air pressure exerted on the inner surface of the lining, whereas thermal stresses were relatively smaller and compressive. With the option of an internal synthetic seal, the maximum effective tensile stress was reduced from 8 to 5 MPa, but was still in substantial tension. We performed one simulation in which the tensile tangential stresses resulted in radial cracks and air leakage though the lining. This air leakage, however, was minor (about 0.16% of the air mass loss from one daily compression) in terms of CAES operational efficiency, and did not significantly impact the overall energy balance of the system. However, despite being minor in terms of energy balance, the air leakage resulted in a distinct pressure increase in the surrounding rock that could

Properties of Tangential and Cyclic Polygons: An Application of Circulant Matrices

ERIC Educational Resources Information Center

Leung, Allen; Lopez-Real, Francis

2003-01-01

In this paper, the properties of tangential and cyclic polygons proposed by Lopez-Real are proved rigorously using the theory of circulant matrices. In particular, the concepts of slippable tangential polygons and conformable cyclic polygons are defined. It is shown that an n-sided tangential (or cyclic) polygon P[subscript n] with n even is…

Determination of stresses in RC eccentrically compressed members using optimization methods

NASA Astrophysics Data System (ADS)

Lechman, Marek; Stachurski, Andrzej

2018-01-01

The paper presents an optimization method for determining the strains and stresses in reinforced concrete (RC) members subjected to the eccentric compression. The governing equations for strains in the rectangular cross-sections are derived by integrating the equilibrium equations of cross-sections, taking account of the effect of concrete softening in plastic range and the mean compressive strength of concrete. The stress-strain relationship for concrete in compression for short term uniaxial loading is assumed according to Eurocode 2 for nonlinear analysis. For reinforcing steel linear-elastic model with hardening in plastic range is applied. The task consists in the solving the set of the derived equations s.t. box constraints. The resulting problem was solved by means of fmincon function implemented from the Matlab's Optimization Toolbox. Numerical experiments have shown the existence of many points verifying the equations with a very good accuracy. Therefore, some operations from the global optimization were included: start of fmincon from many points and clusterization. The model is verified on the set of data encountered in the engineering practice.

Tensile and compressive stress-strain behavior of heat treated boron-aluminum

NASA Technical Reports Server (NTRS)

Kennedy, J. M.; Tenney, D. R.; Herakovich, C. T.

1978-01-01

An experimental study was conducted to assess the effects of heat treatment and cyclic mechanical loading on the tensile and compressive stress-strain behavior of six boron-aluminum composites having different laminate orientations and being subjected to different heat treatments. The heat treatments were as-fabricated, T6, and T6N consisting of T6 treatment followed by cryogenic quench in liquid nitrogen prior to testing. All laminates were tested in monotonic and cyclic compression, while the tensile-test data are taken from the literature for comparison purposes. It is shown that the linear elastic range of the T6- and T6N-condition specimens is larger than that of the as-fabricated specimens, and that cyclic loading in tension or compression strain hardens the specimens and extends the linear elastic range. For laminates containing 0-deg plies, the stress-strain behavior upon unloading is found to be nonlinear, whereas the other laminates exhibit a linear behavior upon unloading. Specimens in the T6 and T6N conditions show higher strain hardening than the as-fabricated specimens.

Simulation of a tangential soft x-ray imaging system.

PubMed

Battaglia, D J; Shafer, M W; Unterberg, E A; Bell, R E; Hillis, D L; LeBlanc, B P; Maingi, R; Sabbagh, S; Stratton, B C

2010-10-01

Tangentially viewing soft x-ray (SXR) cameras are capable of detecting nonaxisymmetric plasma structures in magnetically confined plasmas. They are particularly useful for studying stationary perturbations or phenomenon that occur on a timescale faster than the plasma rotation period. Tangential SXR camera diagnostics are planned for the DIII-D and NSTX tokamaks to elucidate the static edge magnetic structure during the application of 3D perturbations. To support the design of the proposed diagnostics, a synthetic diagnostic model was developed using the CHIANTI database to estimate the SXR emission. The model is shown to be in good agreement with the measurements from an existing tangential SXR camera diagnostic on NSTX.

Measurements of the stress supported by the crush zone in open hole composite laminates loaded in compression

NASA Technical Reports Server (NTRS)

Guynn, E. Gail; Bradley, Walter L.

1989-01-01

Measurements of the stress supported by the crush zone in open hole specimens loaded in compression were carried out on two composite laminates, AS4/PEEK and IM6/HST-7, containing circular holes of three different diameters. Compression tests were conducted in a specially designed high-axial-alignment material test system machine. Results indicated that the local stress supported in the crush zone is much less than the stress required to initiate the crush, providing the reason for the finding of Guynn et al. (1987) that the Dugdale model does not accurately predict the load-damage size relationship of open hole composite specimens loaded in compression.

Tangential synthetic jets for separation control

NASA Astrophysics Data System (ADS)

Esmaeili Monir, H.; Tadjfar, M.; Bakhtian, A.

2014-02-01

A numerical study of separation control has been made to investigate aerodynamic characteristics of a NACA23012 airfoil with a tangential synthetic jet. Simulations are carried out at the chord Reynolds number of Re=2.19×106. The present approach relies on solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. The turbulence model used in the present computation is the Spalart-Allmaras one-equation model. All computations are performed with a finite volume based code. Stall characteristics are significantly improved by controlling the formation of separation vortices in the flow. We placed the synthetic jet at the 12% chord, xj=0.12c, where we expected the separation to occur. Two distinct jet oscillating frequencies: Fj+=0.159 and Fj+=1 were considered. We studied the effect of blowing ratio, Vj/U∞, where it was varied from 0 to 5. The inclined angle of the synthetic jet was varied from αj=0° up to αj=83°. For the non-zero inclined angles, the local maximum in the aerodynamic performance, Cl/Cd, of 6.89 was found for the inclined angle of about 43°. In the present method, by means of creating a dent on the airfoil, linear momentum is transferred to the flow system in tangential direction to the airfoil surface. Thus the absolute maximum of 11.19 was found for the tangential synthetic jet at the inclined angle of the jet of 0°. The mechanisms involved for a tangential jet appear to behave linearly, as by multiplying the activation frequency of the jet by a factor produces the same multiplication factor in the resulting frequency in the flow. However, the mechanisms involved in the non-zero inclined angle cases behave nonlinearly when the activation frequency is multiplied.

Compressible Analysis of Bénard Convection of Magneto Rotatory Couple-Stress Fluid

NASA Astrophysics Data System (ADS)

Mehta, C. B.; Singh, M.

2018-02-01

Thermal Instability (Benard's Convection) in the presence of uniform rotation and uniform magnetic field (separately) is studied. Using the linearized stability theory and normal mode analyses the dispersion relation is obtained in each case. In the case of rotatory Benard's stationary convection compressibility and rotation postpone the onset of convection whereas the couple-stress have duel character onset of convection depending on rotation parameter. While in the absence of rotation couple-stress always postpones the onset of convection. On the other hand, magnetic field on thermal instability problem on couple-stress fluid for stationary convection couple-stress parameter and magnetic field postpones the onset of convection. The effect of compressibility also postpones the onset of convection in both cases as rotation and magnetic field. Graphs have been plotted by giving numerical values to the parameters to depict the stationary characteristics. Further, the magnetic field and rotation are found to introduce oscillatory modes which were non-existent in their absence and then the principle of exchange of stability is valid. The sufficient conditions for non-existence of overstability are also obtained.

Microstructure Evolution and Flow Stress Model of a 20Mn5 Hollow Steel Ingot during Hot Compression.

PubMed

Liu, Min; Ma, Qing-Xian; Luo, Jian-Bin

2018-03-21

20Mn5 steel is widely used in the manufacture of heavy hydro-generator shaft due to its good performance of strength, toughness and wear resistance. However, the hot deformation and recrystallization behaviors of 20Mn5 steel compressed under high temperature were not studied. In this study, the hot compression experiments under temperatures of 850-1200 °C and strain rates of 0.01/s-1/s are conducted using Gleeble thermal and mechanical simulation machine. And the flow stress curves and microstructure after hot compression are obtained. Effects of temperature and strain rate on microstructure are analyzed. Based on the classical stress-dislocation relation and the kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of 20Mn5 steel. Comparisons between experimental flow stress and predicted flow stress show that the predicted flow stress values are in good agreement with the experimental flow stress values, which indicates that the proposed constitutive model is reliable and can be used for numerical simulation of hot forging of 20Mn5 hollow steel ingot.

A compressible Navier-Stokes solver with two-equation and Reynolds stress turbulence closure models

NASA Technical Reports Server (NTRS)

Morrison, Joseph H.

1992-01-01

This report outlines the development of a general purpose aerodynamic solver for compressible turbulent flows. Turbulent closure is achieved using either two equation or Reynolds stress transportation equations. The applicable equation set consists of Favre-averaged conservation equations for the mass, momentum and total energy, and transport equations for the turbulent stresses and turbulent dissipation rate. In order to develop a scheme with good shock capturing capabilities, good accuracy and general geometric capabilities, a multi-block cell centered finite volume approach is used. Viscous fluxes are discretized using a finite volume representation of a central difference operator and the source terms are treated as an integral over the control volume. The methodology is validated by testing the algorithm on both two and three dimensional flows. Both the two equation and Reynolds stress models are used on a two dimensional 10 degree compression ramp at Mach 3, and the two equation model is used on the three dimensional flow over a cone at angle of attack at Mach 3.5. With the development of this algorithm, it is now possible to compute complex, compressible high speed flow fields using both two equation and Reynolds stress turbulent closure models, with the capability of eventually evaluating their predictive performance.

Microstructure Evolution and Flow Stress Model of a 20Mn5 Hollow Steel Ingot during Hot Compression

PubMed Central

Liu, Min; Ma, Qing-Xian; Luo, Jian-Bin

2018-01-01

20Mn5 steel is widely used in the manufacture of heavy hydro-generator shaft due to its good performance of strength, toughness and wear resistance. However, the hot deformation and recrystallization behaviors of 20Mn5 steel compressed under high temperature were not studied. In this study, the hot compression experiments under temperatures of 850–1200 °C and strain rates of 0.01/s–1/s are conducted using Gleeble thermal and mechanical simulation machine. And the flow stress curves and microstructure after hot compression are obtained. Effects of temperature and strain rate on microstructure are analyzed. Based on the classical stress-dislocation relation and the kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of 20Mn5 steel. Comparisons between experimental flow stress and predicted flow stress show that the predicted flow stress values are in good agreement with the experimental flow stress values, which indicates that the proposed constitutive model is reliable and can be used for numerical simulation of hot forging of 20Mn5 hollow steel ingot. PMID:29561826

High Temperature Uniaxial Compression and Stress-Relaxation Behavior of India-Specific RAFM Steel

NASA Astrophysics Data System (ADS)

Shah, Naimish S.; Sunil, Saurav; Sarkar, Apu

2018-07-01

India-specific reduced activity ferritic martensitic steel (INRAFM), a modified 9Cr-1Mo grade, has been developed by India as its own structural material for fabrication of the Indian Test Blanket Module (TBM) to be installed in the International Thermonuclear Energy Reactor (ITER). The extensive study on mechanical and physical properties of this material has been currently going on for appraisal of this material before being put to use in the ITER. High temperature compression, stress-relaxation, and strain-rate change behavior of the INRAFM steel have been investigated. The optical microscopic and scanning electron microscopic characterizations were carried out to observe the microstructural changes that occur during uniaxial compressive deformation test. Comparable true plastic stress values at 300 °C and 500 °C and a high drop in true plastic stress at 600 °C were observed during the compression test. Stress-relaxation behaviors were investigated at 500 °C, 550 °C, and 600 °C at a strain rate of 10-3 s-1. The creep properties of the steel at different temperatures were predicted from the stress-relaxation test. The Norton's stress exponent ( n) was found to decrease with the increasing temperature. Using Bird-Mukherjee-Dorn relationship, the temperature-compensated normalized strain rate vs stress was plotted. The stress exponent ( n) value of 10.05 was obtained from the normalized plot. The increasing nature of the strain rate sensitivity ( m) with the test temperature was found from strain-rate change test. The low plastic stability with m 0.06 was observed at 600 °C. The activation volume ( V *) values were obtained in the range of 100 to 300 b3. By comparing the experimental values with the literature, the rate-controlling mechanisms at the thermally activated region of high temperature were found to be the nonconservative movement of jogged screw dislocations and thermal breaking of attractive junctions.

High Temperature Uniaxial Compression and Stress-Relaxation Behavior of India-Specific RAFM Steel

NASA Astrophysics Data System (ADS)

Shah, Naimish S.; Sunil, Saurav; Sarkar, Apu

2018-05-01

India-specific reduced activity ferritic martensitic steel (INRAFM), a modified 9Cr-1Mo grade, has been developed by India as its own structural material for fabrication of the Indian Test Blanket Module (TBM) to be installed in the International Thermonuclear Energy Reactor (ITER). The extensive study on mechanical and physical properties of this material has been currently going on for appraisal of this material before being put to use in the ITER. High temperature compression, stress-relaxation, and strain-rate change behavior of the INRAFM steel have been investigated. The optical microscopic and scanning electron microscopic characterizations were carried out to observe the microstructural changes that occur during uniaxial compressive deformation test. Comparable true plastic stress values at 300 °C and 500 °C and a high drop in true plastic stress at 600 °C were observed during the compression test. Stress-relaxation behaviors were investigated at 500 °C, 550 °C, and 600 °C at a strain rate of 10-3 s-1. The creep properties of the steel at different temperatures were predicted from the stress-relaxation test. The Norton's stress exponent (n) was found to decrease with the increasing temperature. Using Bird-Mukherjee-Dorn relationship, the temperature-compensated normalized strain rate vs stress was plotted. The stress exponent (n) value of 10.05 was obtained from the normalized plot. The increasing nature of the strain rate sensitivity (m) with the test temperature was found from strain-rate change test. The low plastic stability with m 0.06 was observed at 600 °C. The activation volume (V *) values were obtained in the range of 100 to 300 b3. By comparing the experimental values with the literature, the rate-controlling mechanisms at the thermally activated region of high temperature were found to be the nonconservative movement of jogged screw dislocations and thermal breaking of attractive junctions.

Influence of residual welding stresses, overload and specimen preparation on fatigue crack growth under axial compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greasley, A.

1995-02-01

Double edge notched axial compression specimens taken from thick welded steel joints have been used to grow fatigue cracks under pulsating compressive loads at mean stresses up to 55% of that needed for general yielding. The redistribution of residual stresses during specimen preparation and during crack growth influences the nucleation, growth rate and extent of fatigue cracks. Crack growth rates which are comparable to the equivalent tensile situation have been observed in as-welded, welded plus overloaded and stress relieved plus overloaded joints. Multiple nucleation and curved crack profiles have been observed in all cases. 5 refs.

Fatigue life of additively manufactured Ti6Al4V scaffolds under tension-tension, tension-compression and compression-compression fatigue load.

PubMed

Lietaert, Karel; Cutolo, Antonio; Boey, Dries; Van Hooreweder, Brecht

2018-03-21

Mechanical performance of additively manufactured (AM) Ti6Al4V scaffolds has mostly been studied in uniaxial compression. However, in real-life applications, more complex load conditions occur. To address this, a novel sample geometry was designed, tested and analyzed in this work. The new scaffold geometry, with porosity gradient between the solid ends and scaffold middle, was successfully used for quasi-static tension, tension-tension (R = 0.1), tension-compression (R = -1) and compression-compression (R = 10) fatigue tests. Results show that global loading in tension-tension leads to a decreased fatigue performance compared to global loading in compression-compression. This difference in fatigue life can be understood fairly well by approximating the local tensile stress amplitudes in the struts near the nodes. Local stress based Haigh diagrams were constructed to provide more insight in the fatigue behavior. When fatigue life is interpreted in terms of local stresses, the behavior of single struts is shown to be qualitatively the same as bulk Ti6Al4V. Compression-compression and tension-tension fatigue regimes lead to a shorter fatigue life than fully reversed loading due to the presence of a mean local tensile stress. Fractographic analysis showed that most fracture sites were located close to the nodes, where the highest tensile stresses are located.

A primary study on the performance of piezoceramic based smart aggregate under various compressive stresses

NASA Astrophysics Data System (ADS)

Zou, Dujian; Liu, Tiejun; Yang, Antai; Zhao, Yanru; Du, Chengcheng

2017-10-01

The reliability of piezoceramic based smart aggregate (SA) used for damage detection of concrete structures has already been validated by laboratory tests. However, the in situ concrete members are generally under a big range of stress levels, and the performance of SA under various compressive stresses is still unclear. In this study, an electronic universal testing machine was employed to apply different stresses on the SAs. The received signals of SA sensor accompanying with different drive signals were recorded. The experimental results show that the amplitude of received signals increases firstly, and then tends to be stable with stress. This enhancement is mainly induced by the decrease in thickness of epoxy resin layer caused by compressive stress. It indicates that the change of load applied on monitored concrete members embedded with SAs may lead to a change in monitoring signal amplitude even in elastic range, but it does not stand for the change of health state of monitored concrete member.

In vitro degradation kinetics of pure PLA and Mg/PLA composite: Effects of immersion temperature and compression stress.

PubMed

Li, Xuan; Chu, Chenglin; Wei, Yalin; Qi, Chenxi; Bai, Jing; Guo, Chao; Xue, Feng; Lin, Pinghua; Chu, Paul K

2017-01-15

The effects of the immersion temperature and compression stress on the in vitro degradation behavior of pure poly-lactic acid (pure-PLA) and PLA-based composite unidirectionally reinforced with micro-arc oxidized magnesium alloy wires (Mg/PLA or MAO-MAWs/PLA) are investigated. The degradation kinetics of pure-PLA and the PLA matrix in MAO-MAWs/PLA exhibit an Arrhenius-type behavior. For the composite, the synergic degradation of MAO-MAWs maintains a steady pH and mitigates the degradation of PLA matrix during immersion. However, the external compression stress decreases the activation energy (E a ) and pre-exponential factor (k 0 ) consequently increasing the degradation rate of PLA. Under a compression stress of 1MPa, E a and k 0 of pure PLA are 57.54kJ/mol and 9.74×10 7 day -1 , respectively, but 65.5kJ/mol and 9.81×10 8 day -1 for the PLA matrix in the composite. Accelerated tests are conducted in rising immersion temperature in order to shorten the experimental time. Our analysis indicates there are well-defined relationships between the bending strength of the specimens and the PLA molecular weight during immersion, which are independent of the degradation temperature and external compression stress. Finally, a numerical model is established to elucidate the relationship of bending strength, the PLA molecular weight, activation energy, immersion time and temperature. We systematically evaluate the effects of compression stress and temperature on the degradation properties of two materials: (pure-PLA) and MAO-MAWs/PLA (or Mg/PLA). The initial in vitro degradation kinetics of the unstressed or stressed pure-PLA and MAO-MAWs/PLA composite is confirmed to be Arrhenius-like. MAO-MAWs and external compression stress would influence the degradation activation energy (E a ) and pre-exponential factor (k 0 ) of PLA, and we noticed there is a linear relationship between E a and ln k 0 . Thereafter, we noticed that Mg 2+ , not H + , plays a significant role on the

Tangential gunshot wound with MagSafe ammunition.

PubMed

Rapkiewicz, Amy V; Tamburri, Robert; Basoa, Mark E; Catanese, Charles A

2005-09-01

MagSafe ammunition is a type of unconventional prefragmented ammunition. A fatal tangential gunshot wound involving MagSafe ammunition is presented. The ammunition and wound characteristics are discussed.

In-situ investigation of stress conditions during expansion of bare metal stents and PLLA-coated stents using the XRD sin(2)ψ-technique.

PubMed

Kowalski, Wolfgang; Dammer, Markus; Bakczewitz, Frank; Schmitz, Klaus-Peter; Grabow, Niels; Kessler, Olaf

2015-09-01

Drug eluting stents (DES) consist of platform, coating and drug. The platform often is a balloon-expandable bare metal stent made of the CoCr alloy L-605 or stainless steel 316 L. The function of the coating, typically a permanent polymer, is to hold and release the drug, which should improve therapeutic outcome. Before implantation, DES are compressed (crimped) to allow implantation in the human body. During implantation, DES are expanded by balloon inflation. Crimping, as well as expansion, causes high stresses and high strains locally in the DES struts, as well as in the polymer coating. These stresses and strains are important design criteria of DES. Usually, they are calculated numerically by finite element analysis (FEA), but experimental results for validation are hardly available. In this work, the X-ray diffraction (XRD) sin(2)ψ-technique is applied to in-situ determination of stress conditions of bare metal L-605 stents, and Poly-(L-lactide) (PLLA) coated stents. This provides a realistic characterization of the near-surface stress state and a validation option of the numerical FEA. XRD-results from terminal stent struts of the bare metal stent show an increasing compressive load stress in tangential direction with increasing stent expansion. These findings correlate with numerical FEA results. The PLLA-coating also bears increasing compressive load stress during expansion. Copyright © 2015 Elsevier Ltd. All rights reserved.

Analysis of Tangential Slot Blowing on F/A-18 Isolated Forebody

NASA Technical Reports Server (NTRS)

Gee, Ken; Rizk, Yehia M.; Schiff, Lewis B.

1995-01-01

The generation of significant side forces and yawing moments on an F/A-18 fuselage through tangential slot blowing is analyzed using computational fluid dynamics. The effects of freestream Mach number, jet exit conditions, jet length, and jet location are studied. The effects of over- and underblowing on force and moment production are analyzed. Non-time-accurate solutions are obtained to determine the steady-state side forces, yawing moments, and surface pressure distributions generated by tangential slot blowing. Time-accurate solutions are obtained to study the force onset time lag of tangential slot blowing. Comparison with available experimental data from full-scale wind-tunnel and subscale wind-tunnel tests are made. This computational analysis complements the experimental results and provides a detailed understanding of the effects of tangential slot blowing on the flowfield about the isolated F/A-18 forebody. Additionally, it extends the slot-blowing database to transonic maneuvering Mach numbers.

Experimental Study on Properties of Methane Diffusion of Coal Block under Triaxial Compressive Stress

PubMed Central

Zhao, Hong-Bao

2014-01-01

Taking the standard size coal block samples defined by ISRM as research objects, both properties of methane diffusion of coal block under triaxial compressive stress and characteristic influences caused by methane pressure were systematically studied with thermo-fluid-solid coupling with triaxial servocontrolled seepage equipment of methane-containing coal. The result shows the methane diffusion property of coal block under triaxial compressive stress was shown in four-stage as follow, first is sharply reduce stage, second is hyperbolic reduce stage, third is close to a fixed value stage, fourth stage is 0. There is a special point making the reduced rate of characteristic curve of methane diffusion speed become sharply small; the influences of shape of methane diffusion speed characteristic curve caused by methane pressure are not obvious, which only is shown in numerical size of methane diffusion speed. Test time was extended required by appear of the special point makes the reduce rate of methane diffusion speed become sharply small. The fitting four-phase relation of methane diffusion of coal block under triaxial compressive stress was obtained, and the idea is proposed that influences of the fitting four-phase relation caused by methane pressure were only shown in value of fitting parameters. PMID:25531000

Effects of oxidative stress-induced changes in the actin cytoskeletal structure on myoblast damage under compressive stress: confocal-based cell-specific finite element analysis.

PubMed

Yao, Yifei; Lacroix, Damien; Mak, Arthur F T

2016-12-01

Muscle cells are frequently subjected to both mechanical and oxidative stresses in various physiological and pathological situations. To explore the mechanical mechanism of muscle cell damage under loading and oxidative stresses, we experimentally studied the effects of extrinsic hydrogen peroxides on the actin cytoskeletal structure in C2C12 myoblasts and presented a finite element (FE) analysis of how such changes in the actin cytoskeletal structure affected a myoblast's capability to resist damage under compression. A confocal-based cell-specific FE model was built to parametrically study the effects of stress fiber density, fiber cross-sectional area, fiber tensile prestrain, as well as the elastic moduli of the stress fibers, actin cortex, nucleus and cytoplasm. The results showed that a decrease in the elastic moduli of both the stress fibers and actin cortex could increase the average tensile strain on the actin cortex-membrane structure and reduce the apparent cell elastic modulus. Assuming the cell would die when a certain percentage of membrane elements were strained beyond a threshold, a lower elastic modulus of actin cytoskeleton would compromise the compressive resistance of a myoblast and lead to cell death more readily. This model was used with a Weibull distribution function to successfully describe the extent of myoblasts damaged in a monolayer under compression.

Vibrotactile Compliance Feedback for Tangential Force Interaction.

PubMed

Heo, Seongkook; Lee, Geehyuk

2017-01-01

This paper presents a method to generate a haptic illusion of compliance using a vibrotactile actuator when a tangential force is applied to a rigid surface. The novel method builds on a conceptual compliance model where a physical object moves on a textured surface in response to a tangential force. The method plays vibration patterns simulating friction-induced vibrations as an applied tangential force changes. We built a prototype consisting of a two-dimensional tangential force sensor and a surface transducer to test the effectiveness of the model. Participants in user experiments with the prototype perceived the rigid surface of the prototype as a moving, rubber-like plate. The main findings of the experiments are: 1) the perceived stiffness of a simulated material can be controlled by controlling the force-playback transfer function, 2) its perceptual properties such as softness and pleasantness can be controlled by changing friction grain parameters, and 3) the use of the vibrotactile compliance feedback reduces participants' workload including physical demand and frustration while performing a force repetition task.

Numerical Prediction of Residual Stresses in an Autofrettaged Tube of Compressible Material

DTIC Science & Technology

1981-05-01

2 LEVEL TECHNICAL REPORT ARLCB-TR- 81019 NUMERICAL PREDICTION OF RESIDUAL STRESSES IN AN AUTOFRETTAGED TUBE OF COMPRESSIBLE MATERIAL 7 P. C. T. Chen...DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM I. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT’S CATALOG NUMBER ARLCB-TR- 81019 At

Effect of Compressive Stresses on Leakage Currents in Microchip Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2012-01-01

Microchip tantalum capacitors are manufactured using new technologies that allow for production of small size capacitors (down to EIA case size 0402) with volumetric efficiency much greater than for regular chip capacitors. Due to a small size of the parts and leadless design they might be more sensitive to mechanical stresses that develop after soldering onto printed wiring boards (PWB) compared to standard chip capacitors. In this work, the effect of compressive stresses on leakage currents in capacitors has been investigated in the range of stresses up to 200 MPa. Significant, up to three orders of magnitude, variations of currents were observed after the stress exceeds a certain critical level that varied from 10 MPa to 180 MPa for capacitors used in this study. A stress-induced generation of electron traps in tantalum pentoxide dielectric is suggested to explain reversible variations of leakage currents in tantalum capacitors. Thermo-mechanical characteristics of microchip capacitors have been studied to estimate the level of stresses caused by assembly onto PWB and assess the risk of stress-related degradation and failures. Keywords: tantalum capacitors, leakage current, soldering, reliability, mechanical stress.

The Origin of Compressible Magnetic Turbulence in the Very Local Interstellar Medium

NASA Astrophysics Data System (ADS)

Zank, G. P.; Du, S.; Hunana, P.

2017-06-01

Voyager 1 observed compressible magnetic turbulence in the very local interstellar medium (VLISM). We show that inner heliosheath (IHS) fast- and slow-mode waves incident on the heliopause (HP) generate VLISM fast-mode waves only that propagate into the VLISM. We suggest that this is the origin of compressible turbulence in the VLISM. We show that fast- and slow-mode waves transmitted across a tangential discontinuity such as the HP are strongly refracted on crossing the HP and subsequently propagate at highly oblique angles to the VLISM magnetic field. Thus, fast-mode waves in the VLISM contribute primarily to the compressible and not the transverse components of the VLISM fluctuating magnetic field variance < δ {\\hat{B}}2> since < δ {\\hat{B}}{fz}2> \

Gas turbine power plant with supersonic shock compression ramps

DOEpatents

Lawlor, Shawn P [Bellevue, WA; Novaresi, Mark A [San Diego, CA; Cornelius, Charles C [Kirkland, WA

2008-10-14

A gas turbine engine. The engine is based on the use of a gas turbine driven rotor having a compression ramp traveling at a local supersonic inlet velocity (based on the combination of inlet gas velocity and tangential speed of the ramp) which compresses inlet gas against a stationary sidewall. The supersonic compressor efficiently achieves high compression ratios while utilizing a compact, stabilized gasdynamic flow path. Operated at supersonic speeds, the inlet stabilizes an oblique/normal shock system in the gasdynamic flow path formed between the rim of the rotor, the strakes, and a stationary external housing. Part load efficiency is enhanced by use of a lean pre-mix system, a pre-swirl compressor, and a bypass stream to bleed a portion of the gas after passing through the pre-swirl compressor to the combustion gas outlet. Use of a stationary low NOx combustor provides excellent emissions results.

Stress-dislocation interaction mechanism in low-temperature thermo-compression sintering of Ag NPs

NASA Astrophysics Data System (ADS)

Wang, Fuliang; Tang, Zikai; He, Hu

2018-04-01

The sintering of metal nanoparticles (NPs) has been widely studied in the field of nanotechnology, and low-temperature sintering has become the industry standard. In this study, a molecular dynamics (MD) model was established to study the sintering behaviour of silver NPs during low-temperature thermo-compression. Primarily, we studied the sintering process, in which the ratio of neck radius to particle radius (x/r) changes. Under a uniaxial pressure, the maximum ratio in the temperature range 420-425 K was 1. According to the change of x/r, the process can be broken down into three stages: the neck-formation stage, neck-growth stage, and neck-stability stage. In addition, the relationship between potential energy, internal stress, and dislocation density during sintering is discussed. The results showed that cycling internal stress played an important role in sintering. Under the uniaxial pressure, the stress-dislocation interaction was found to be the major mechanism for thermo-compression sintering because the plastic deformation product dislocation intensified the diffusion of atoms. Also, the displacement vector, the mean square displacement, and the changing crystal structure during sintering were studied.

Evolution of network architecture in a granular material under compression

NASA Astrophysics Data System (ADS)

Papadopoulos, Lia; Puckett, James G.; Daniels, Karen E.; Bassett, Danielle S.

2016-09-01

As a granular material is compressed, the particles and forces within the system arrange to form complex and heterogeneous collective structures. Force chains are a prime example of such structures, and are thought to constrain bulk properties such as mechanical stability and acoustic transmission. However, capturing and characterizing the evolving nature of the intrinsic inhomogeneity and mesoscale architecture of granular systems can be challenging. A growing body of work has shown that graph theoretic approaches may provide a useful foundation for tackling these problems. Here, we extend the current approaches by utilizing multilayer networks as a framework for directly quantifying the progression of mesoscale architecture in a compressed granular system. We examine a quasi-two-dimensional aggregate of photoelastic disks, subject to biaxial compressions through a series of small, quasistatic steps. Treating particles as network nodes and interparticle forces as network edges, we construct a multilayer network for the system by linking together the series of static force networks that exist at each strain step. We then extract the inherent mesoscale structure from the system by using a generalization of community detection methods to multilayer networks, and we define quantitative measures to characterize the changes in this structure throughout the compression process. We separately consider the network of normal and tangential forces, and find that they display a different progression throughout compression. To test the sensitivity of the network model to particle properties, we examine whether the method can distinguish a subsystem of low-friction particles within a bath of higher-friction particles. We find that this can be achieved by considering the network of tangential forces, and that the community structure is better able to separate the subsystem than a purely local measure of interparticle forces alone. The results discussed throughout this study

Forebody tangential blowing for control at high angles of attack

NASA Technical Reports Server (NTRS)

Kroo, I.; Rock, S.; Roberts, L.

1991-01-01

A feasibility study to determine if the use of tangential leading edge blowing over the forebody could produce effective and practical control of the F-18 HARV aircraft at high angles of attack was conducted. A simplified model of the F-18 configuration using a vortex-lattice model was developed to obtain a better understanding of basic aerodynamic coupling effects and the influence of forebody circulation on lifting surface behavior. The effect of tangential blowing was estimated using existing wind tunnel data on normal forebody blowing and analytical studies of tangential blowing over conical forebodies. Incorporation of forebody blowing into the flight control system was investigated by adding this additional yaw control and sideforce generating actuator into the existing F-18 HARV simulation model. A control law was synthesized using LQG design methods that would schedule blowing rates as a function of vehicle sideslip, angle of attack, and roll and yaw rates.

Critical contribution of RIPK1 mediated mitochondrial dysfunction and oxidative stress to compression-induced rat nucleus pulposus cells necroptosis and apoptosis.

PubMed

Chen, Songfeng; Lv, Xiao; Hu, Binwu; Zhao, Lei; Li, Shuai; Li, Zhiliang; Qing, Xiangcheng; Liu, Hongjian; Xu, Jianzhong; Shao, Zengwu

2018-04-28

The aim of this study was to investigate whether RIPK1 mediated mitochondrial dysfunction and oxidative stress contributed to compression-induced nucleus pulposus (NP) cells necroptosis and apoptosis, together with the interplay relationship between necroptosis and apoptosis in vitro. Rat NP cells underwent various periods of 1.0 MPa compression. To determine whether compression affected mitochondrial function, we evaluated the mitochondrial membrane potential, mitochondrial permeability transition pore (mPTP), mitochondrial ultrastructure and ATP content. Oxidative stress-related indicators reactive oxygen species, superoxide dismutase and malondialdehyde were also assessed. To verify the relevance between oxidative stress and necroptosis together with apoptosis, RIPK1 inhibitor necrostatin-1(Nec-1), mPTP inhibitor cyclosporine A (CsA), antioxidants and small interfering RNA technology were utilized. The results established that compression elicited a time-dependent mitochondrial dysfunction and elevated oxidative stress. Nec-1 and CsA restored mitochondrial function and reduced oxidative stress, which corresponded to decreased necroptosis and apoptosis. CsA down-regulated mitochondrial cyclophilin D expression, but had little effects on RIPK1 expression and pRIPK1 activation. Additionally, we found that Nec-1 largely blocked apoptosis; whereas, the apoptosis inhibitor Z-VAD-FMK increased RIPK1 expression and pRIPK1 activation, and coordinated regulation of necroptosis and apoptosis enabled NP cells survival more efficiently. In contrast to Nec-1, SiRIPK1 exacerbated mitochondrial dysfunction and oxidative stress. In summary, RIPK1-mediated mitochondrial dysfunction and oxidative stress play a crucial role in NP cells necroptosis and apoptosis during compression injury. The synergistic regulation of necroptosis and apoptosis may exert more beneficial effects on NP cells survival, and ultimately delaying or even retarding intervertebral disc degeneration.

Variable Thermal-Force Bending of a Three-Layer Bar with a Compressible Filler

NASA Astrophysics Data System (ADS)

Starovoitov, E. I.; Leonenko, D. V.

2017-11-01

Deformation of a three-layer elastoplastic bar with a compressible filler in a temperature field is considered. To describe the kinematics of a pack asymmetric across its thickness, the hypothesis of broken line is accepted, according to which the Bernoulli hypothesis is true in thin bearing layers, and the Timoshenko hypothesis is valid for a filler compressible across the its thickness, with a linear approximation of displacements across the layer thickness. The work of filler in the tangential direction is taken into account. The physical stress-strain relations correspond to the theory of small elastoplastic deformations. Temperature variations are calculated from a formula obtained by averaging the thermophysical properties of layer materials across the bar thickness. Using the variational method, a system of differential equilibrium equations is derived. On the boundary, the kinematic conditions of simply supported ends of the bar are assumed. The solution of the boundary problem is reduced to the search for four functions, namely, deflections and longitudinal displacements of median surfaces of the bearing layers. An analytical solution is derived by the method of elastic solutions with the use of the Moskvitin theorem on variable loadings. Its numerical analysis is performed for the cases of continuous and local loads.

Algebraic Reynolds stress modeling of turbulence subject to rapid homogeneous and non-homogeneous compression or expansion

NASA Astrophysics Data System (ADS)

Grigoriev, I. A.; Wallin, S.; Brethouwer, G.; Grundestam, O.; Johansson, A. V.

2016-02-01

A recently developed explicit algebraic Reynolds stress model (EARSM) by Grigoriev et al. ["A realizable explicit algebraic Reynolds stress model for compressible turbulent flow with significant mean dilatation," Phys. Fluids 25(10), 105112 (2013)] and the related differential Reynolds stress model (DRSM) are used to investigate the influence of homogeneous shear and compression on the evolution of turbulence in the limit of rapid distortion theory (RDT). The DRSM predictions of the turbulence kinetic energy evolution are in reasonable agreement with RDT while the evolution of diagonal components of anisotropy correctly captures the essential features, which is not the case for standard compressible extensions of DRSMs. The EARSM is shown to give a realizable anisotropy tensor and a correct trend of the growth of turbulence kinetic energy K, which saturates at a power law growth versus compression ratio, as well as retaining a normalized strain in the RDT regime. In contrast, an eddy-viscosity model results in a rapid exponential growth of K and excludes both realizability and high magnitude of the strain rate. We illustrate the importance of using a proper algebraic treatment of EARSM in systems with high values of dilatation and vorticity but low shear. A homogeneously compressed and rotating gas cloud with cylindrical symmetry, related to astrophysical flows and swirling supercritical flows, was investigated too. We also outline the extension of DRSM and EARSM to include the effect of non-homogeneous density coupled with "local mean acceleration" which can be important for, e.g., stratified flows or flows with heat release. A fixed-point analysis of direct numerical simulation data of combustion in a wall-jet flow demonstrates that our model gives quantitatively correct predictions of both streamwise and cross-stream components of turbulent density flux as well as their influence on the anisotropies. In summary, we believe that our approach, based on a proper

Compressive yield stress of depletion gels from stationary centrifugation profiles

NASA Astrophysics Data System (ADS)

Lattuada, Enrico; Buzzaccaro, Stefano; Piazza, Roberto

2018-01-01

We have investigated the stationary sedimentation profiles of colloidal gels obtained by an arrested phase-separation process driven by depletion forces, which have been compressed either by natural gravity or by a centrifugal acceleration ranging between 6g and 2300g. Our measurements show that the gel rheological properties display a drastic change when the gel particle volume fraction exceeds a value φc , which barely depends on the strength of the interparticle attractive forces that consolidate the network. In particular, the gel compressive yield stress \\Pi(φ) , which increases as \\Pi(φ) ∼ φ4.2 for φ ≲ φc , displays a diverging behaviour for φ>φc , with an asymptotic value that is close to the random close packing value for hard spheres. The evidence we obtained suggests that φc basically coincides with the liquid (colloid-rich) branch of the metastable coexistence curve, rather than with the lower (and ϕ-dependent) values expected for an attractive glass line penetrating inside the coexistence region.

Tracking mechanical Dauphiné twin evolution with applied stress in axial compression experiments on a low-grade metamorphic quartzite

NASA Astrophysics Data System (ADS)

Minor, Alexander; Rybacki, Erik; Sintubin, Manuel; Vogel, Sven; Wenk, Hans-Rudolf

2018-07-01

The stress-dependent evolution of mechanical Dauphiné twinning has been investigated in axial compression experiments on a low-grade metamorphic quartzite, applying both time-of-flight neutron diffraction and electron backscatter diffraction. The data of the experimentally stressed quartzite samples were compared with those of the naturally deformed starting material to monitor Dauphiné twinning in relation to different experimental stress states. This comparison shows that in the experimental conditions of 500 °C temperature and 300 MPa confining pressure, Dauphiné twinning initiates below 145 MPa differential stress and saturates between 250 MPa and 460 MPa differential stress. A single grain orientation analysis (SGOA) has been developed based on the distinction of quartz grains free of Dauphiné twin boundaries (DTBs) and containing Dauphiné twin boundaries. Comparing pole figures and inverse pole figures of DTB-free grains of the starting material with those of the experimentally stressed samples shows a significantly different orientation distribution of the positive {10 1 bar 1} (r) and the negative {01 1 bar 1} (z) rhombs. In DTB-containing grains, the SGOA allows to distinguish between host and twin domains. Using DTB-free grains, the SGOA furthermore reveals a particular pattern, with one of the r rhomb maxima parallel to the axial compressive stress direction and a girdle with two r rhomb submaxima perpendicular to it. We believe that this relationship between the axial compressive stress direction and the rhomb orientation distribution shows the potential of the SGOA in the reconstruction of the paleostress state in naturally stressed quartz-bearing rocks.

Dynamics of fingertip contact during the onset of tangential slip

PubMed Central

Delhaye, Benoit; Lefèvre, Philippe; Thonnard, Jean-Louis

2014-01-01

Through highly precise perceptual and sensorimotor activities, the human tactile system continuously acquires information about the environment. Mechanical interactions between the skin at the point of contact and a touched surface serve as the source of this tactile information. Using a dedicated custom robotic platform, we imaged skin deformation at the contact area between the finger and a flat surface during the onset of tangential sliding movements in four different directions (proximal, distal, radial and ulnar) and with varying normal force and tangential speeds. This simple tactile event evidenced complex mechanics. We observed a reduction of the contact area while increasing the tangential force and proposed to explain this phenomenon by nonlinear stiffening of the skin. The deformation's shape and amplitude were highly dependent on stimulation direction. We conclude that the complex, but highly patterned and reproducible, deformations measured in this study are a potential source of information for the central nervous system and that further mechanical measurement are needed to better understand tactile perceptual and motor performances. PMID:25253033

Numerical analysis of tangential slot blowing on a generic chined forebody

NASA Technical Reports Server (NTRS)

Agosta, Roxana M.

1994-01-01

A numerical study is performed to investigate the effects of tangential slot blowing on a generic chined forebody. The Reynolds-averaged, thin-layer, Navier-Stokes equations are solved to obtain the high-angle-of-attack viscous flow field about a generic chined forebody. Tangential slot blowing is investigated as a means of forebody flow control to generate side force and yawing moment on the forebody. The effects of jet mass flow ratios, angle of attack, and blowing slot location in the axial and circumferential directions are studied. The computed results are compared with available wind tunnel experimental data. The solutions with and without blowing are also analyzed using helicity density contours, surface flow patterns, and off-surface instantaneous streamlines. The results of this analysis provide details of the flow field about the generic chined forebody, as well as show that tangential slot blowing can be used as a means of forebody flow control to generate side force and yawing moment.

Design and fabrication of a large area freestanding compressive stress SiO2 optical window

NASA Astrophysics Data System (ADS)

Van Toan, Nguyen; Sangu, Suguru; Ono, Takahito

2016-07-01

This paper reports the design and fabrication of a 7.2 mm  ×  9.6 mm freestanding compressive stress SiO2 optical window without buckling. An application of the SiO2 optical window with and without liquid penetration has been demonstrated for an optical modulator and its optical characteristic is evaluated by using an image sensor. Two methods for SiO2 optical window fabrication have been presented. The first method is a combination of silicon etching and a thermal oxidation process. Silicon capillaries fabricated by deep reactive ion etching (deep RIE) are completely oxidized to form the SiO2 capillaries. The large compressive stress of the oxide causes buckling of the optical window, which is reduced by optimizing the design of the device structure. A magnetron-type RIE, which is investigated for deep SiO2 etching, is the second method. This method achieves deep SiO2 etching together with smooth surfaces, vertical shapes and a high aspect ratio. Additionally, in order to avoid a wrinkling optical window, the idea of a Peano curve structure has been proposed to achieve a freestanding compressive stress SiO2 optical window. A 7.2 mm  ×  9.6 mm optical window area without buckling integrated with an image sensor for an optical modulator has been successfully fabricated. The qualitative and quantitative evaluations have been performed in cases with and without liquid penetration.

Stability of retained austenite in high carbon steel under compressive stress: an investigation from macro to nano scale

PubMed Central

Hossain, R.; Pahlevani, F.; Quadir, M. Z.; Sahajwalla, V.

2016-01-01

Although high carbon martensitic steels are well known for their industrial utility in high abrasion and extreme operating environments, due to their hardness and strength, the compressive stability of their retained austenite, and the implications for the steels’ performance and potential uses, is not well understood. This article describes the first investigation at both the macro and nano scale of the compressive stability of retained austenite in high carbon martensitic steel. Using a combination of standard compression testing, X-ray diffraction, optical microstructure, electron backscattering diffraction imaging, electron probe micro-analysis, nano-indentation and micro-indentation measurements, we determined the mechanical stability of retained austenite and martensite in high carbon steel under compressive stress and identified the phase transformation mechanism, from the macro to the nano level. We found at the early stage of plastic deformation hexagonal close-packed (HCP) martensite formation dominates, while higher compression loads trigger body-centred tetragonal (BCT) martensite formation. The combination of this phase transformation and strain hardening led to an increase in the hardness of high carbon steel of around 30%. This comprehensive characterisation of stress induced phase transformation could enable the precise control of the microstructures of high carbon martensitic steels, and hence their properties. PMID:27725722

Tangential Flow Ultrafiltration Allows Purification and Concentration of Lauric Acid-/Albumin-Coated Particles for Improved Magnetic Treatment.

PubMed

Zaloga, Jan; Stapf, Marcus; Nowak, Johannes; Pöttler, Marina; Friedrich, Ralf P; Tietze, Rainer; Lyer, Stefan; Lee, Geoffrey; Odenbach, Stefan; Hilger, Ingrid; Alexiou, Christoph

2015-08-14

Superparamagnetic iron oxide nanoparticles (SPIONs) are frequently used for drug targeting, hyperthermia and other biomedical purposes. Recently, we have reported the synthesis of lauric acid-/albumin-coated iron oxide nanoparticles SEON(LA-BSA), which were synthesized using excess albumin. For optimization of magnetic treatment applications, SPION suspensions need to be purified of excess surfactant and concentrated. Conventional methods for the purification and concentration of such ferrofluids often involve high shear stress and low purification rates for macromolecules, like albumin. In this work, removal of albumin by low shear stress tangential ultrafiltration and its influence on SEON(LA-BSA) particles was studied. Hydrodynamic size, surface properties and, consequently, colloidal stability of the nanoparticles remained unchanged by filtration or concentration up to four-fold (v/v). Thereby, the saturation magnetization of the suspension can be increased from 446.5 A/m up to 1667.9 A/m. In vitro analysis revealed that cellular uptake of SEON(LA-BSA) changed only marginally. The specific absorption rate (SAR) was not greatly affected by concentration. In contrast, the maximum temperature Tmax in magnetic hyperthermia is greatly enhanced from 44.4 °C up to 64.9 °C by the concentration of the particles up to 16.9 mg/mL total iron. Taken together, tangential ultrafiltration is feasible for purifying and concentrating complex hybrid coated SPION suspensions without negatively influencing specific particle characteristics. This enhances their potential for magnetic treatment.

Ascl1 promotes tangential migration and confines migratory routes by induction of Ephb2 in the telencephalon

PubMed Central

Liu, Yuan-Hsuan; Tsai, Jin-Wu; Chen, Jia-Long; Yang, Wan-Shan; Chang, Pei-Ching; Cheng, Pei-Lin; Turner, David L.; Yanagawa, Yuchio; Wang, Tsu-Wei; Yu, Jenn-Yah

2017-01-01

During development, cortical interneurons generated from the ventral telencephalon migrate tangentially into the dorsal telencephalon. Although Achaete-scute family bHLH transcription factor 1 (Ascl1) plays important roles in the developing telencephalon, whether Ascl1 regulates tangential migration remains unclear. Here, we found that Ascl1 promoted tangential migration along the ventricular zone/subventricular zone (VZ/SVZ) and intermediate zone (IZ) of the dorsal telencephalon. Distal-less homeobox 2 (Dlx2) acted downstream of Ascl1 in promoting tangential migration along the VZ/SVZ but not IZ. We further identified Eph receptor B2 (Ephb2) as a direct target of Ascl1. Knockdown of EphB2 disrupted the separation of the VZ/SVZ and IZ migratory routes. Ephrin-A5, a ligand of EphB2, was sufficient to repel both Ascl1-expressing cells in vitro and tangentially migrating cortical interneurons in vivo. Together, our results demonstrate that Ascl1 induces expression of Dlx2 and Ephb2 to maintain distinct tangential migratory routes in the dorsal telencephalon. PMID:28276447

Design and analysis of a toroidal tester for the measurement of core losses under axial compressive stress

NASA Astrophysics Data System (ADS)

Alatawneh, Natheer; Rahman, Tanvir; Lowther, David A.; Chromik, Richard

2017-06-01

Electric machine cores are subjected to mechanical stresses due to manufacturing processes. These stresses include radial, circumferential and axial components that may have significant influences on the magnetic properties of the electrical steel and hence, on the output and efficiencies of electrical machines. Previously, most studies of iron losses due to mechanical stress have considered only radial and circumferential components. In this work, an improved toroidal tester has been designed and developed to measure the core losses and the magnetic properties of electrical steel under a compressive axial stress. The shape of the toroidal ring has been verified using 3D stress analysis. Also, 3D electromagnetic simulations show a uniform flux density distribution in the specimen with a variation of 0.03 T and a maximum average induction level of 1.5 T. The developed design has been prototyped, and measurements were carried out using a steel sample of grade 35WW300. Measurements show that applying small mechanical stresses normal to the sample thickness rises the delivered core losses, then the losses decrease continuously as the stress increases. However, the drop in core losses at high stresses does not go lower than the free-stress condition. Physical explanations for the observed trend of core losses as a function of stress are provided based on core loss separation to the hysteresis and eddy current loss components. The experimental results show that the effect of axial compressive stress on magnetic properties of electrical steel at high level of inductions becomes less pronounced.

Structure and Orientation Behavior of Highly Oriented Polymers Under Tensile and Compressive Stresses

NASA Astrophysics Data System (ADS)

Garcia-Ramirez, Rafael

The birefringence of Kevlar 49^ circler fibers has been shown to decrease with compressive strain, suggesting that structure changes under compression involve decreasing crystallite orientation. This mechanism appears to be the inverse of that occurring under tension, for which increasing crystallite orientation has been reported to occur, leading to non-linear elasticity. A contrast between the effects of both stress modes on structure (orientation) response is presented. While birefringence presents itself as a technically convenient and economically attractive technique for this type of study, caution must be exercised when interpreting results from measurements under stress. For highly crystalline fibers, experiments have led to the attribution of the observed changes in birefringence almost entirely to crystallite orientation. This study presents an analysis of the different contributions to birefringence under stress. X-ray diffraction experiments have been performed for Kevlar 49^ circler fibers under tensile stress. Results from crystal orientation cannot account for changes observed in birefringence. Moreover, they appear to account only for a small fraction of the total change. These observations suggest significant contributions from other sources. Theoretical calculations have been carried out under simulated stress conditions to quantify the effect of molecular deformation on the observed birefringence of Kevlar 49^circler fibers. The results have been obtained using semi-empirical molecular orbital calculations with the AM1 Hamiltonian in MOPAC. This analysis has been applied to poly(p^' -phenylene terephthalamide) (PPTA) and polyethylene (PE) chains. For PE, stress-free computations were performed on segments of up to 50 -(CH_2-CH _2)- units. Strains up to 1% were applied on segments of up to 40 units. For PPTA, segments of up to 5 PTA units were analyzed. Strain-free results indicate a linear dependence of molecular polarizability on chain length

Retention of Compressive Residual Stresses Introduced by Shot Peening in a Powder Metal Disk Superalloy

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Danetti, Andrew; Draper, Susan L.; Locci, Ivan E.; Telesman, Jack

2016-01-01

The fatigue lives of disk superalloys can be increased by shot peening their surfaces, to induce compressive residual stresses near the surface that impede cracking there. As disk application temperatures increase for improved efficiency, the persistence of these beneficial stresses could be impaired, especially with continued fatigue cycling. The objective of this work was to study the retention of residual stresses introduced by shot peening, when subjected to fatigue and high temperatures. Fatigue specimens of powder metallurgy processed nickel-base disk superalloy ME3 were prepared with consistent processing and heat treatment. They were then shot peened using varied conditions. Strain-controlled fatigue cycles were run at room temperature and 704 C, to allow re-assessment of residual stresses.

Cell-like pressure sensors reveal increase of mechanical stress towards the core of multicellular spheroids under compression.

PubMed

Dolega, M E; Delarue, M; Ingremeau, F; Prost, J; Delon, A; Cappello, G

2017-01-27

The surrounding microenvironment limits tumour expansion, imposing a compressive stress on the tumour, but little is known how pressure propagates inside the tumour. Here we present non-destructive cell-like microsensors to locally quantify mechanical stress distribution in three-dimensional tissue. Our sensors are polyacrylamide microbeads of well-defined elasticity, size and surface coating to enable internalization within the cellular environment. By isotropically compressing multicellular spheroids (MCS), which are spherical aggregates of cells mimicking a tumour, we show that the pressure is transmitted in a non-trivial manner inside the MCS, with a pressure rise towards the core. This observed pressure profile is explained by the anisotropic arrangement of cells and our results suggest that such anisotropy alone is sufficient to explain the pressure rise inside MCS composed of a single cell type. Furthermore, such pressure distribution suggests a direct link between increased mechanical stress and previously observed lack of proliferation within the spheroids core.

A representation for the turbulent mass flux contribution to Reynolds-stress and two-equation closures for compressible turbulence

NASA Technical Reports Server (NTRS)

Ristorcelli, J. R.

1993-01-01

The turbulent mass flux, or equivalently the fluctuating Favre velocity mean, appears in the first and second moment equations of compressible kappa-epsilon and Reynolds stress closures. Mathematically it is the difference between the unweighted and density-weighted averages of the velocity field and is therefore a measure of the effects of compressibility through variations in density. It appears to be fundamental to an inhomogeneous compressible turbulence, in which it characterizes the effects of the mean density gradients, in the same way the anisotropy tensor characterizes the effects of the mean velocity gradients. An evolution equation for the turbulent mass flux is derived. A truncation of this equation produces an algebraic expression for the mass flux. The mass flux is found to be proportional to the mean density gradients with a tensor eddy-viscosity that depends on both the mean deformation and the Reynolds stresses. The model is tested in a wall bounded DNS at Mach 4.5 with notable results.

Design of tangential viewing phase contrast imaging for turbulence measurements in JT-60SA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, K., E-mail: ktanaka@nifs.ac.jp; Department of Advanced Energy Engineering, Kyushu University, Kasuga, Fukuoka 816-8580; Coda, S.

2016-11-15

A tangential viewing phase contrast imaging system is being designed for the JT-60SA tokamak to investigate microturbulence. In order to obtain localized information on the turbulence, a spatial-filtering technique is applied, based on magnetic shearing. The tangential viewing geometry enhances the radial localization. The probing laser beam is injected tangentially and traverses the entire plasma region including both low and high field sides. The spatial resolution for an Internal Transport Barrier discharge is estimated at 30%–70% of the minor radius at k = 5 cm{sup −1}, which is the typical expected wave number of ion scale turbulence such as ionmore » temperature gradient/trapped electron mode.« less

Band-Moment Compression of AVIRIS Hyperspectral Data and its Use in the Detection of Vegetation Stress

NASA Technical Reports Server (NTRS)

Estep, L.; Davis, B.

2001-01-01

A remote sensing campaign was conducted over a U.S. Department of Agriculture test farm at Shelton, Nebraska. An experimental field was set off in plots that were differentially treated with anhydrous ammonia. Four replicates of 0-kg/ha to 200-kg/ha plots, in 50-kg/ha increments, were set out in a random block design. Low-altitude (GSD of 3 m) Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) hyperspectral data were collected over the site in 224 bands. Simultaneously, ground data were collected to support the airborne imagery. In an effort to reduce data load while maintaining or enhancing algorithm performance for vegetation stress detection, band-moment compression and analysis was applied to the AVIRIS image cube. The results indicated that band-moment techniques compress the AVIRIS dataset significantly while retaining the capability of detecting environmentally induced vegetation stress.

Lithospheric flexure under the Hawaiian volcanic load: Internal stresses and a broken plate revealed by earthquakes

NASA Astrophysics Data System (ADS)

Klein, Fred W.

2016-04-01

Several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of Hawai`i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress-free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P axes below the neutral plane display a striking radial pattern pointing to the stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns; T axes tend to be radial. The M6.2 Honomu and M6.7 Kiholo main shocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilauea's deep conduit is seismically active because it is in the ring of maximum bending. A simplified two-dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks.

Normal and Tangential Momentum Accommodation for Earth Satellite Conditions

NASA Technical Reports Server (NTRS)

Knechtel, Earl D.; Pitts, William C.

1973-01-01

Momentum accommodation was determined experimentally for gas-surface interactions simulating in a practical way those of near-earth satellites. Throughout the ranges of gas energies and incidence angles of interest for earth-conditions, two components of force were measured by means of a vacuum microbalance to determine the normal and tangential momentum-accommodation coefficients for nitrogen ions on technical-quality aluminum surfaces. For these experimental conditions, the electrodynamics of ion neutralization near the surface indicate that results for nitrogen ions should differ relatively little from those for nitrogen molecules, which comprise the largest component of momentum flux for near-earth satellites. The experimental results indicated that both normal and tangential momentum-accommodation coefficients varied widely with energy, tending to be relatively well accommodated at the higher energies, but becoming progressively less accommodated as the energy was reduced to and below that for earth-satellite speeds. Both coefficients also varied greatly with incidence angle, the normal momentum becoming less accommodated as the incidence angle became more glancing, whereas the tangential momentum generally became more fully accommodated. For each momentum coefficient, an empirical correlation function was obtained which closely approximated the experimental results over the ranges of energy and incidence angle. Most of the observed variations of momentum accommodation with energy and incidence angle were qualitatively indicated by a calculation using a three-dimensional model that simulated the target surface by a one-dimensional attractive potential and hard sphere reflectors.

Tangential System of Thomson Scattering for Tokamak T-15

NASA Astrophysics Data System (ADS)

Asadulin, G. M.; Bel'bas, I. S.; Gorshkov, A. V.

2017-12-01

Two systems of Thomson scattering diagnostics, with vertical and tangential probing, are used in the D-shaped plasma cross section in tokamak T-15. The tangential system allows measuring plasma temperature and density profiles along the major radius of the tokamak. This paper presents the tangential system project. The system is based on a Nd:YAG laser with wavelength of 1064 nm, pulse energy of 3 J, pulse duration of 10 ns, and repetition rate of 100 Hz. The chosen geometry allows collecting light from ten uniformly spaced points. Optimization of the registration system has been accomplished. The collected light will be transmitted through an optical fiber bundle with diameter of 3 mm and quartz fibers (numerical aperture is 0.22). Six-channel polychromators based on high-contrast interference filters have been chosen as spectral equipment. The radiation will be registered by avalanche photodiodes. The technique of electron temperature and density measurement is described, and estimation of its accuracy is carried out. The proposed system allows measuring the electron temperature with accuracy not worse than 10% within the range of 50 eV to 10 keV on the pinch edge over the internal contour, from 20 eV to 9 keV in the plasma central region, and from 2 eV to 400 eV on the pinch edge over the outer contour. The estimation is made for electron density of not less than 2.6 × 1013 cm-3.

Charts relating the compressive buckling stress of longitudinally supported plates to the effective deflectional and rotational stiffness of the supports

NASA Technical Reports Server (NTRS)

Anderson, Roger A; Semonian, Joseph W

1954-01-01

A stability analysis is made of a long flat rectangular plate subjected to a uniform longitudinal compressive stress and supported along its longitudinal edges and along one or more longitudinal lines by elastic line supports. The elastic supports possess deflectional and rotational stiffness. Such configuration is an idealization of the compression cover skin and internal structure of a wing and tail surfaces. The results of the analysis are presented in the form of charts in which the buckling-stress coefficient is plotted against the buckle length of the plate for a wide range of support stiffnesses. The charts make possible the determination of the compressive buckling stress of plates supported by members whose stiffness may or may not be defined by elementary beam bending and twisting theory but yet whose effective restraint is amenable to evaluation. The deflectional and rotational stiffness provided by longitudinal stiffeners and full-depth webs is discussed and numerical examples are given to illustrate the application of the charts to the design of wing structures.

Optimization of Tangential Mass Injection for Minimizing Flow Separation in a Scramjet Inlet

DTIC Science & Technology

1991-12-01

34 Aerospace EnQineering, Vol. 11. No. 8, August 1991, p.23. 26. Heppenheimer , Thomas A . Lecture notes from Hypersonic Technologies seminar. University...AFIT/GAE/ENY,/9 lD-2 ( /~ AD-A243 868 "DTIC OPTIMIZATION OF TANGENTIAL MASS INJECTION FOR MINIMIZING FLOW SEPARATION IN A SC.R-.MJET INLET THESIS...OF TANGENTIAL MASS INJECTION FOR MINIMIZING FLOW SEPARATION IN A SCRAMJET INLEr THESIS Presented to the Faculty of the School of E.ngineering of the

Tangential migratory pathways of subpallial origin in the embryonic telencephalon of sharks: evolutionary implications.

PubMed

Quintana-Urzainqui, Idoia; Rodríguez-Moldes, Isabel; Mazan, Sylvie; Candal, Eva

2015-09-01

Tangential neuronal migration occurs along different axes from the axis demarcated by radial glia and it is thought to have evolved as a mechanism to increase the diversity of cell types in brain areas, which in turn resulted in increased complexity of functional networks. In the telencephalon of amniotes, different embryonic tangential pathways have been characterized. However, little is known about the exact routes of migrations in basal vertebrates. Cartilaginous fishes occupy a key phylogenetic position to assess the ancestral condition of vertebrate brain organization. In order to identify putative subpallial-derived tangential migratory pathways in the telencephalon of sharks, we performed a detailed analysis of the distribution pattern of GAD and Dlx2, two reliable markers of tangentially migrating interneurons of subpallial origin in the developing forebrain. We propose the existence of five tangential routes directed toward different telencephalic regions. We conclude that four of the five routes might have emerged in the common ancestor of jawed vertebrates. We have paid special attention to the characterization of the proposed migratory pathway directed towards the olfactory bulbs. Our results suggest that it may be equivalent to the "rostral migratory stream" of mammals and led us to propose a hypothesis about its evolution. The analysis of the final destinations of two other streams allowed us to identify the putative dorsal and medial pallium of sharks, the regions from which the neocortex and hippocampus might have, respectively, evolved. Derived features were also reported and served to explain some distinctive traits in the morphology of the telencephalon of cartilaginous fishes.

Tangential Bicortical Locked Fixation Improves Stability in Vancouver B1 Periprosthetic Femur Fractures: A Biomechanical Study.

PubMed

Lewis, Gregory S; Caroom, Cyrus T; Wee, Hwabok; Jurgensmeier, Darin; Rothermel, Shane D; Bramer, Michelle A; Reid, John Spence

2015-10-01

The biomechanical difficulty in fixation of a Vancouver B1 periprosthetic fracture is purchase of the proximal femoral segment in the presence of the hip stem. Several newer technologies provide the ability to place bicortical locking screws tangential to the hip stem with much longer lengths of screw purchase compared with unicortical screws. This biomechanical study compares the stability of 2 of these newer constructs to previous methods. Thirty composite synthetic femurs were prepared with cemented hip stems. The distal femur segment was osteotomized, and plates were fixed proximally with either (1) cerclage cables, (2) locked unicortical screws, (3) a composite of locked screws and cables, or tangentially directed bicortical locking screws using either (4) a stainless steel locking compression plate system with a Locking Attachment Plate (Synthes) or (5) a titanium alloy Non-Contact Bridging system (Zimmer). Specimens were tested to failure in either axial or torsional quasistatic loading modes (n = 3) after 20 moderate load preconditioning cycles. Stiffness, maximum force, and failure mechanism were determined. Bicortical constructs resisted higher (by an average of at least 27%) maximum forces than the other 3 constructs in torsional loading (P < 0.05). Cables constructs exhibited lower maximum force than all other constructs, in both axial and torsional loading. The bicortical titanium construct was stiffer than the bicortical stainless steel construct in axial loading. Proximal fixation stability is likely improved with the use of bicortical locking screws as compared with traditional unicortical screws and cable techniques. In this study with a limited sample size, we found the addition of cerclage cables to unicortical screws may not offer much improvement in biomechanical stability of unstable B1 fractures.

Effects of increasing the allowable compressive stress at release on the shear strength of prestressed concrete girders.

DOT National Transportation Integrated Search

2008-09-01

In recent years, several research projects have been conducted to study the feasibility of increasing the allowable : compressive stress in concrete at prestress transfer, currently defined as 0.60f'ci in the AASHTO LRFD Bridge : Design Specification...

Dissipative processes under the shock compression of glass

NASA Astrophysics Data System (ADS)

Savinykh, A. S.; Kanel, G. I.; Cherepanov, I. A.; Razorenov, S. V.

2016-03-01

New experimental data on the behavior of the K8 and TF1 glasses under shock-wave loading conditions are obtained. It is found that the propagation of shock waves is close to the self-similar one in the maximum compression stress range 4-12 GPa. Deviations from a general deformation diagram, which are related to viscous dissipation, take place when the final state of compression is approached. The parameter region in which failure waves form in glass is found not to be limited to the elastic compression stress range, as was thought earlier. The failure front velocity increases with the shock compression stress. Outside the region covered by a failure wave, the glasses demonstrate a high tensile dynamic strength (6-7 GPa) in the case of elastic compression, and this strength is still very high after transition through the elastic limit in a compression wave.

Tangential migration of glutamatergic neurons and cortical patterning during development: Lessons from Cajal-Retzius cells.

PubMed

Barber, Melissa; Pierani, Alessandra

2016-08-01

Tangential migration is a mode of cell movement, which in the developing cerebral cortex, is defined by displacement parallel to the ventricular surface and orthogonal to the radial glial fibers. This mode of long-range migration is a strategy by which distinct neuronal classes generated from spatially and molecularly distinct origins can integrate to form appropriate neural circuits within the cortical plate. While it was previously believed that only GABAergic cortical interneurons migrate tangentially from their origins in the subpallial ganglionic eminences to integrate in the cortical plate, it is now known that transient populations of glutamatergic neurons also adopt this mode of migration. These include Cajal-Retzius cells (CRs), subplate neurons (SPs), and cortical plate transient neurons (CPTs), which have crucial roles in orchestrating the radial and tangential development of the embryonic cerebral cortex in a noncell-autonomous manner. While CRs have been extensively studied, it is only in the last decade that the molecular mechanisms governing their tangential migration have begun to be elucidated. To date, the mechanisms of SPs and CPTs tangential migration remain unknown. We therefore review the known signaling pathways, which regulate parameters of CRs migration including their motility, contact-redistribution and adhesion to the pial surface, and discuss this in the context of how CR migration may regulate their signaling activity in a spatial and temporal manner. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 847-881, 2016. © 2015 Wiley Periodicals, Inc.

Axisymmetric deformations and stresses of unsymmetrically laminated composite cylinders in axial compression with thermally-induced preloading effects

NASA Technical Reports Server (NTRS)

Paraska, Peter J.

1993-01-01

This report documents an analytical study of the response of unsymmetrically laminated cylinders subjected to thermally-induced preloading effects and compressive axial load. Closed-form solutions are obtained for the displacements and intralaminar stresses and recursive relations for the interlaminar shear stress were obtained using the closed-form intralaminar stress solutions. For the cylinder geometries and stacking sequence examples analyzed, several important and as yet undocumented effects of including thermally-induced preloading in the analysis are observed. It should be noted that this work is easily extended to include uniform internal and/or external pressure loadings and the application of strain and stress failure theories.

Kalker's algorithm Fastsim solves tangential contact problems with slip-dependent friction and friction anisotropy

NASA Astrophysics Data System (ADS)

Piotrowski, J.

2010-07-01

This paper presents two extensions of Kalker's algorithm Fastsim of the simplified theory of rolling contact. The first extension is for solving tangential contact problems with the coefficient of friction depending on slip velocity. Two friction laws have been considered: with and without recuperation of the static friction. According to the tribological hypothesis for metallic bodies shear failure, the friction law without recuperation of static friction is more suitable for wheel and rail than the other one. Sample results present local quantities inside the contact area (division to slip and adhesion, traction) as well as global ones (creep forces as functions of creepages and rolling velocity). For the coefficient of friction diminishing with slip, the creep forces decay after reaching the maximum and they depend on the rolling velocity. The second extension is for solving tangential contact problems with friction anisotropy characterised by a convex set of the permissible tangential tractions. The effect of the anisotropy has been shown on examples of rolling without spin and in the presence of pure spin for the elliptical set. The friction anisotropy influences tangential tractions and creep forces. Sample results present local and global quantities. Both extensions have been described with the same language of formulation and they may be merged into one, joint algorithm.

The quality assessment of radial and tangential neutron radiography beamlines of TRR

NASA Astrophysics Data System (ADS)

Choopan Dastjerdi, M. H.; Movafeghi, A.; Khalafi, H.; Kasesaz, Y.

2017-07-01

To achieve a quality neutron radiographic image in a relatively short exposure time, the neutron radiography beam must be of good quality and relatively high neutron flux. Characterization of a neutron radiography beam, such as determination of the image quality and the neutron flux, is vital for producing quality radiographic images and also provides a means to compare the quality of different neutron radiography facilities. This paper provides a characterization of the radial and tangential neutron radiography beamlines at the Tehran research reactor. This work includes determination of the facilities category according to the American Society for Testing and Materials (ASTM) standards, and also uses the gold foils to determine the neutron beam flux. The radial neutron beam is a Category I neutron radiography facility, the highest possible quality level according to the ASTM. The tangential beam is a Category IV neutron radiography facility. Gold foil activation experiments show that the measured neutron flux for radial beamline with length-to-diameter ratio (L/D) =150 is 6.1× 106 n cm-2 s-1 and for tangential beamline with (L/D)=115 is 2.4× 104 n cm-2 s-1.

Forbidden tangential orbit transfers between intersecting Keplerian orbits

NASA Technical Reports Server (NTRS)

Burns, Rowland E.

1990-01-01

The classical problem of tangential impulse transfer between coplanar Keplerian orbits is addressed. A completely analytic solution which does not rely on sequential calculation is obtained and this solution is used to demonstrate that certain initially chosen angles can produce singularities in the parameters of the transfer orbit. A necessary and sufficient condition for such singularities is that the initial and final orbits intersect.

Effects of Single-Bundle and Double-Bundle ACL Reconstruction on Tibiofemoral Compressive Stresses and Joint Kinematics During Simulated Squatting

PubMed Central

Mulcahey, Mary K.; Monchik, Keith O.; Yongpravat, Charlie; Badger, Gary J.; Fadale, Paul D.; Hulstyn, Michael J.; Fleming, Braden C.

2011-01-01

The purpose of this study was to compare tibiofemoral (TF) kinematics and TF compressive stresses between single bundle- (SB-) and double bundle-ACL reconstruction (DB-ACLR) during simulated squatting. Twelve matched pairs of fresh frozen cadaver knees were utilized. A simulated squat through 100° of knee flexion was performed in the ACL-intact joint. The ACL was transected and SB- and DB-ACLR procedures were performed in one knee of each pair. The squat was repeated. Knee kinematics were measured using a motion tracking system and the TF compressive forces were measured using thin film pressure sensors. The posterior shifts of the tibia for SB- and DB-ACLR knees were significantly greater than the ACL-intact condition for knee flexion angles 0° to 40° (p<.05). However, there was no difference between the SB- and DB-ACLR knees at any flexion angle (0° to 100°; p=.37). SB- and DB-ACLR knees had greater IE rotation than intact knees from 90° through 50° of flexion (p<.05), but not between 40° and full extension. There was no difference between SB- and DB-ACLR knees (p=.68). The TF compressive stresses of the DB-ACLR were significantly lower than intact for all angles except 10° (p=.06), whereas SB-ACLR knees did not differ from intact at flexion angles between 30° and 50° (p>.32). There were no significant differences between the two reconstruction conditions (p=.74). This study showed that there was no difference in the TF kinematics or compressive stresses between SB- and DB-ACLR, and only minor differences when compared to the intact state. PMID:21696962

Long-term prediction of creep strains of mineral wool slabs under constant compressive stress

NASA Astrophysics Data System (ADS)

Gnip, Ivan; Vaitkus, Saulius; Keršulis, Vladislovas; Vėjelis, Sigitas

2012-02-01

The results obtained in determining the creep strain of mineral wool slabs under compressive stress, used for insulating flat roofs and facades, cast-in-place floors, curtain and external basement walls, as well as for sound insulation of floors, are presented. The creep strain tests were conducted under a compressive stress of σ c =0.35 σ 10%. Interval forecasting of creep strain was made by extrapolating the creep behaviour and approximated in accordance with EN 1606 by a power equation and reduced to a linear form using logarithms. This was performed for a lead time of 10 years. The extension of the range of the confidence interval due to discount of the prediction data, i.e. a decrease in their informativity was allowed for by an additional coefficient. Analysis of the experimental data obtained from the tests having 65 and 122 days duration showed that the prediction of creep strains for 10 years can be made based on data obtained in experiments with durations shorter than the 122 days as specified by EN 13162. Interval prediction of creep strains (with a confidence probability of 90%) was based on using the mean square deviation of the actual direct observations of creep strains in logarithmic form to have the linear trend in a retrospective area.

Exact solution for the layered convection of a viscous incompressible fluid at specified temperature gradients and tangential forces on the free boundary

NASA Astrophysics Data System (ADS)

Burmasheva, N. V.; Prosviryakov, E. Yu.

2017-12-01

A new exact analytical solution of a system of thermal convection equations in the Boussinesq approximation describing layered flows in an incompressible viscous fluid is obtained. A fluid flow in an infinite layer is considered. Convection in the fluid is induced by tangential stresses specified on the upper non-deformable boundary. At the fixed lower boundary, the no-slip condition is satisfied. Temperature corrections are given on the both boundaries of the fluid layer. The possibility of physical field stratification is investigated.

Comparison of histologic margin status in low-grade cutaneous and subcutaneous canine mast cell tumours examined by radial and tangential sections.

PubMed

Dores, C B; Milovancev, M; Russell, D S

2018-03-01

Radial sections are widely used to estimate adequacy of excision in canine cutaneous mast cell tumours (MCTs); however, this sectioning technique estimates only a small fraction of total margin circumference. This study aimed to compare histologic margin status in grade II/low grade MCTs sectioned using both radial and tangential sectioning techniques. A total of 43 circumferential margins were evaluated from 21 different tumours. Margins were first sectioned radially, followed by tangential sections. Tissues were examined by routine histopathology. Tangential margin status differed in 10 of 43 (23.3%) margins compared with their initial status on radial section. Of 39 margins, 9 (23.1%) categorized as histologic tumour-free margin (HTFM) >0 mm were positive on tangential sectioning. Tangential sections detected a significantly higher proportion of positive margins relative to radial sections (exact 2-tailed P-value = .0215). The HTFM was significantly longer in negative tangential margins than positive tangential margins (mean 10.1 vs 3.2 mm; P = .0008). A receiver operating characteristic curve comparing HTFM and tangentially negative margins found an area under the curve of 0.83 (95% confidence interval: 0.71-0.96). Although correct classification peaked at the sixth cut-point of HTFM ≥1 mm, radial sections still incorrectly classified 50% of margins as lacking tumour cells. Radial sections had 100% specificity for predicting negative tangential margins at a cut-point of 10.9 mm. These data indicate that for low grade MCTs, HTFMs >0 mm should not be considered completely excised, particularly when HTFM is <10.9 mm. This will inform future studies that use HTFM and overall excisional status as dependent variables in multivariable prognostic models. © 2017 John Wiley & Sons Ltd.

A role for intermediate radial glia in the tangential expansion of the mammalian cerebral cortex.

PubMed

Reillo, Isabel; de Juan Romero, Camino; García-Cabezas, Miguel Ángel; Borrell, Víctor

2011-07-01

The cerebral cortex of large mammals undergoes massive surface area expansion and folding during development. Specific mechanisms to orchestrate the growth of the cortex in surface area rather than in thickness are likely to exist, but they have not been identified. Analyzing multiple species, we have identified a specialized type of progenitor cell that is exclusive to mammals with a folded cerebral cortex, which we named intermediate radial glia cell (IRGC). IRGCs express Pax6 but not Tbr2, have a radial fiber contacting the pial surface but not the ventricular surface, and are found in both the inner subventricular zone and outer subventricular zone (OSVZ). We find that IRGCs are massively generated in the OSVZ, thus augmenting the numbers of radial fibers. Fanning out of this expanding radial fiber scaffold promotes the tangential dispersion of radially migrating neurons, allowing for the growth in surface area of the cortical sheet. Accordingly, the tangential expansion of particular cortical regions was preceded by high proliferation in the underlying OSVZ, whereas the experimental reduction of IRGCs impaired the tangential dispersion of neurons and resulted in a smaller cortical surface. Thus, the generation of IRGCs plays a key role in the tangential expansion of the mammalian cerebral cortex.

Predicting guar seed splitting by compression between two plates using Hertz theory of contact stresses.

PubMed

Vishwakarma, R K; Shivhare, U S; Nanda, S K

2012-09-01

Hertz's theory of contact stresses was applied to predict the splitting of guar seeds during uni-axial compressive loading between 2 rigid parallel plates. The apparent modulus of elasticity of guar seeds varied between 296.18 and 116.19 MPa when force was applied normal to hilum joint (horizontal position), whereas it varied between 171.86 and 54.18 MPa when force was applied in the direction of hilum joint (vertical position) with in moisture content range of 5.16% to 15.28% (d.b.). At higher moisture contents, the seeds yielded after considerable deformation, thus showing ductile nature. Distribution of stresses below the point of contact were plotted to predict the location of critical point, which was found at 0.44 to 0.64 mm and 0.37 to 0.53 mm below the contact point in vertical and horizontal loading, respectively, depending upon moisture content. The separation of cotyledons from each other initiated before yielding of cotyledons and thus splitting of seed took place. The relationships between apparent modulus of elasticity, principal stresses with moisture content were described using second-order polynomial equations and validated experimentally. Manufacture of guar gum powder requires dehulling and splitting of guar seeds. This article describes splitting behavior of guar seeds under compressive loading. Results of this study may be used for design of dehulling and splitting systems of guar seeds. © 2012 Institute of Food Technologists®

Lithospheric flexure under the Hawaiian volcanic load: Internal stresses and a broken plate revealed by earthquakes

USGS Publications Warehouse

Klein, Fred W.

2016-01-01

Several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of Hawai`i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress-free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P axes below the neutral plane display a striking radial pattern pointing to the stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns; T axes tend to be radial. The M6.2 Honomu and M6.7 Kiholo main shocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilauea's deep conduit is seismically active because it is in the ring of maximum bending. A simplified two-dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks.

Further studies on cortical tangential migration in wild type and Pax-6 mutant mice.

PubMed

Jiménez, D; López-Mascaraque, L; de Carlos, J A; Valverde, F

2002-01-01

In this study we present new data concerning the tangential migration from the medial and lateral ganglionic eminences (MGE and LGE) to the cerebral cortex during development. We have used Calbindin as a useful marker to follow the itinerary of tangential migratory cells during early developmental stages in wild-type and Pax-6 homozygous mutant mice. In the wild-type mice, at early developmental stages, migrating cells advance through the intermediate zone (IZ) and preplate (PP). At more advanced stages, migrating cells were present in the subplate (SP) and cortical plate (CP) to reach the entire developing cerebral cortex. We found that, in the homozygous mutant mice (Pax-6(Sey-Neu)/Pax-6(Sey-Neu)), this tangential migration is severely affected at early developmental stages: migrating cells were absent in the IZ, which were only found some days later, suggesting that in the mutant mice, there is a temporal delay in tangential migration. We have also defined some possible mechanisms to explain certain migratory routes from the basal telencephalon to the cerebral cortex. We describe the existence of two factors, which we consider to be essential for the normal migration; the first one is the cell adhesion molecule PSA-NCAM, whose role in other migratory systems is well known. The second factor is Robo-2, whose expression delimits a channel for the passage of migratory cells from the basal telencephalon to the cerebral cortex.

β-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp

NASA Astrophysics Data System (ADS)

Hu, YanChao; Bi, WeiTao; Li, ShiYao; She, ZhenSu

2017-12-01

A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after sep-aration and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.

Electrochemical behavior of single-walled carbon nanotube supercapacitors under compressive stress.

PubMed

Li, Xin; Rong, Jiepeng; Wei, Bingqing

2010-10-26

The effect of compressive stress on the electrochemical behavior of flexible supercapacitors assembled with single-walled carbon nanotube (SWNT) film electrodes and 1 M aqueous electrolytes with different anions and cations were thoroughly investigated. The under-pressed capacitive and resistive features of the supercapacitors were studied by means of cyclic voltammetry measurements and electrochemical impedance analysis. The results demonstrated that the specific capacitance increased first and saturated in corresponding decreases of the series resistance, the charge-transfer resistance, and the Warburg diffusion resistance under an increased pressure from 0 to 1723.96 kPa. Wettability as well as ion-size effect of different aqueous electrolytes played important roles to determine the pressure dependence behavior of the suerpcapacitors under an applied pressure. An improved high-frequency capacitive response with 1172 Hz knee frequency, which is significantly higher compared to reported values, was observed under the compressive pressure of 1723.96 kPa, indicating an improving and excellent high-power capability of the supercapacitors under the pressure. The experimental results and the thorough analysis described in this work not only provide fundamental insight of pressure effects on supercapacitors but also give an important guideline for future design of next generation flexible/stretchable supercapacitors for industrial and consumer applications.

Assessment and application of Reynolds stress closure models to high-speed compressible flows

NASA Technical Reports Server (NTRS)

Gatski, T. B.; Sarkar, S.; Speziale, C. G.; Balakrishnan, L.; Abid, R.; Anderson, E. C.

1990-01-01

The paper presents results from the development of higher order closure models for the phenomological modeling of high-speed compressible flows. The work presented includes the introduction of an improved pressure-strain correlationi model applicable in both the low- and high-speed regime as well as modifications to the isotropic dissipation rate to account for dilatational effects. Finally, the question of stiffness commonly associated with the solution of two-equation and Reynolds stress transport equations in wall-bounded flows is examined and ways of relaxing these restrictions are discussed.

Development of the apparatus for measuring magnetic properties of electrical steel sheets in arbitrary directions under compressive stress normal to their surface

NASA Astrophysics Data System (ADS)

Maeda, Yoshitaka; Urata, Shinya; Nakai, Hideo; Takeuchi, Yuuya; Yun, Kyyoul; Yanase, Shunji; Okazaki, Yasuo

2017-05-01

In designing motors, one must grasp the magnetic properties of electrical steel sheets considering actual conditions in motors. Especially important is grasping the stress dependence of magnetic power loss. This paper describes a newly developed apparatus to measure two-dimensional (2-D) magnetic properties (properties under the arbitrary alternating and the rotating flux conditions) of electrical steel sheets under compressive stress normal to the sheet surface. The apparatus has a 2-D magnetic excitation circuit to generate magnetic fields in arbitrary directions in the evaluation area. It also has a pressing unit to apply compressive stress normal to the sheet surface. During measurement, it is important to apply uniform stress throughout the evaluation area. Therefore, we have developed a new flux density sensor using needle probe method. It is composed of thin copper foils sputtered on electrical steel sheets. By using this sensor, the stress can be applied to the surface of the specimen without influence of this sensor. This paper described the details of newly developed apparatus with this sensor, and measurement results of iron loss by using are shown.

Shear wave transducer for stress measurements in boreholes

DOEpatents

Mao, Nai-Hsien

1987-01-01

A technique and apparatus for estimating in situ stresses by measuring stress-induced velocity anisotropy around a borehole. Two sets each of radially and tangentially polarized transducers are placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times are measured by both a pulsed phase-locked loop technique and a cross correlation of digitized waveforms. The biaxial velocity data is used to back-calculate the applied stress.

Numerical Stress Analysis during Cooldown and Compressive Loading in an Imperfect Nb 3Sn Wire

DOE Office of Scientific and Technical Information (OSTI.GOV)

d’Hauthuille, Luc; Zhai, Yuhu

In this paper, high field superconductors are critical to the success of next step magnetic fusion confinement devices such as ITER and DEMO. The low-temperature superconducting material that is currently favored for these applications, Nb 3Sn, is susceptible to performance due to its brittleness and high strain-sensitivity. Under extreme loads, an irreversible degradation in the maximum critical current density has been shown to occur and believed to be strongly influenced by two factors: plasticity and cracked filaments. Cracks in filaments are induced when sufficiently high stress concentrations occur in the wire. In this paper, we explore using finite element analysismore » the impact that voids have on the stress distributions and peak stresses under two loading conditions: transverse compressive loading in a 2D model, and a full cool down phase in a 3D model.« less

Numerical Stress Analysis during Cooldown and Compressive Loading in an Imperfect Nb 3Sn Wire

DOE PAGES

d’Hauthuille, Luc; Zhai, Yuhu

2017-07-11

In this paper, high field superconductors are critical to the success of next step magnetic fusion confinement devices such as ITER and DEMO. The low-temperature superconducting material that is currently favored for these applications, Nb 3Sn, is susceptible to performance due to its brittleness and high strain-sensitivity. Under extreme loads, an irreversible degradation in the maximum critical current density has been shown to occur and believed to be strongly influenced by two factors: plasticity and cracked filaments. Cracks in filaments are induced when sufficiently high stress concentrations occur in the wire. In this paper, we explore using finite element analysismore » the impact that voids have on the stress distributions and peak stresses under two loading conditions: transverse compressive loading in a 2D model, and a full cool down phase in a 3D model.« less

Effects of applied stress ratio on the fatigue behavior of additively manufactured porous biomaterials under compressive loading.

PubMed

de Krijger, Joep; Rans, Calvin; Van Hooreweder, Brecht; Lietaert, Karel; Pouran, Behdad; Zadpoor, Amir A

2017-06-01

Additively manufactured (AM) porous metallic biomaterials are considered promising candidates for bone substitution. In particular, AM porous titanium can be designed to exhibit mechanical properties similar to bone. There is some experimental data available in the literature regarding the fatigue behavior of AM porous titanium, but the effect of stress ratio on the fatigue behavior of those materials has not been studied before. In this paper, we study the effect of applied stress ratio on the compression-compression fatigue behavior of selective laser melted porous titanium (Ti-6Al-4V) based on the diamond unit cell. The porous titanium biomaterial is treated as a meta-material in the context of this work, meaning that R-ratios are calculated based on the applied stresses acting on a homogenized volume. After morphological characterization using micro computed tomography and quasi-static mechanical testing, the porous structures were tested under cyclic loading using five different stress ratios, i.e. R = 0.1, 0.3, 0.5, 0.7 and 0.8, to determine their S-N curves. Feature tracking algorithms were used for full-field deformation measurements during the fatigue tests. It was observed that the S-N curves of the porous structures shift upwards as the stress ratio increases. The stress amplitude was the most important factor determining the fatigue life. Constant fatigue life diagrams were constructed and compared with similar diagrams for bulk Ti-6Al-4V. Contrary to the bulk material, there was limited dependency of the constant life diagrams to mean stress. The notches present in the AM biomaterials were the sites of crack initiation. This observation and other evidence suggest that the notches created by the AM process cause the insensitivity of the fatigue life diagrams to mean stress. Feature tracking algorithms visualized the deformation during fatigue tests and demonstrated the root cause of inclined (45°) planes of specimen failure. In conclusion, the R

Elastic stress transmission and transformation (ESTT) by confined liquid: A new mechanics for fracture in elastic lithosphere of the earth

USGS Publications Warehouse

Xu, Xing-Wang; Peters, Stephen; Liang, Guang-He; Zhang, Bao-Lin

2016-01-01

Tectonic stress alters local stress fields in the surrounding country rocks and therefore synchronously varies the local effective tensile tangential stress and the nature and geometry of the liquid-driven fractures.

Uncertainties in estimating heart doses from 2D-tangential breast cancer radiotherapy.

PubMed

Lorenzen, Ebbe L; Brink, Carsten; Taylor, Carolyn W; Darby, Sarah C; Ewertz, Marianne

2016-04-01

We evaluated the accuracy of three methods of estimating radiation dose to the heart from two-dimensional tangential radiotherapy for breast cancer, as used in Denmark during 1982-2002. Three tangential radiotherapy regimens were reconstructed using CT-based planning scans for 40 patients with left-sided and 10 with right-sided breast cancer. Setup errors and organ motion were simulated using estimated uncertainties. For left-sided patients, mean heart dose was related to maximum heart distance in the medial field. For left-sided breast cancer, mean heart dose estimated from individual CT-scans varied from <1Gy to >8Gy, and maximum dose from 5 to 50Gy for all three regimens, so that estimates based only on regimen had substantial uncertainty. When maximum heart distance was taken into account, the uncertainty was reduced and was comparable to the uncertainty of estimates based on individual CT-scans. For right-sided breast cancer patients, mean heart dose based on individual CT-scans was always <1Gy and maximum dose always <5Gy for all three regimens. The use of stored individual simulator films provides a method for estimating heart doses in left-tangential radiotherapy for breast cancer that is almost as accurate as estimates based on individual CT-scans. Copyright © 2016. Published by Elsevier Ireland Ltd.

Correlation of compressive stress with spalling of plasma sprayed ceramic materials

NASA Technical Reports Server (NTRS)

Mullen, R. L.; Mcdonald, G.; Hendricks, R. C.; Hofle, M. M.

1983-01-01

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic.

Volcanism on Mercury (dikes, lava flows, pyroclastics): Crust/mantle density contrasts, the evolution of compressive stress and the presence of mantle volatiles

NASA Astrophysics Data System (ADS)

Wilson, L.; Head, J. W., III

2008-09-01

Background. There is great uncertainty about the internal structure of Mercury and the composition of the mantle [e.g., 1, 2]. The high mean density of the body suggests that it may have lost parts of its crust and mantle in a giant impact at some stage after most of its initial accretion was sufficiently complete that at least partial separation of a core had occurred. It is the uncertainty about the timing of the giant impact, and hence the physico-chemical state of proto-Mercury at the time that it occurred, that leads to difficulties in predicting the interior structure and mantle composition. However, it seems reasonable to assume that the Mercury we see today has some combination of a relatively low-density crust and a relatively highdensity mantle; uncertainty remains about the presence and types of volatiles [2]. The second uncertainty is the nature of the surface plains units, specifically, are these lava flows and pyroclastics erupted from the interior, or impact-reworked earlier crust [3-5] (Figs. 1-2)? The detection of candidate pyroclastic deposits [4] has very important implications for mantle volatiles. Furthermore, whatever the surface composition, the presence of planet-wide systems of wrinkle ridges and thrust faults implies that a compressive crustal stress regime became dominant at some stage in the planet's history [3, 6]. If the plains units are indeed lava flows, then the fact that the products of the compressive regime deform many plains units suggests that the development of the compressive stresses may have played a vital role in determining when and if surface eruptions of mantle-derived magmas could occur. This would be analogous to the way in which the change with time from extensional to compressive global stresses in the lithosphere of the Moon influenced the viability of erupting magmas from deep mantle sources [7-9]. Analysis: To investigate the relationship between lithospheric stresses and magma eruption conditions [e.g., 9-11] we

Effect of load introduction on graphite epoxy compression specimens

NASA Technical Reports Server (NTRS)

Reiss, R.; Yao, T. M.

1981-01-01

Compression testing of modern composite materials is affected by the manner in which the compressive load is introduced. Two such effects are investigated: (1) the constrained edge effect which prevents transverse expansion and is common to all compression testing in which the specimen is gripped in the fixture; and (2) nonuniform gripping which induces bending into the specimen. An analytical model capable of quantifying these foregoing effects was developed which is based upon the principle of minimum complementary energy. For pure compression, the stresses are approximated by Fourier series. For pure bending, the stresses are approximated by Legendre polynomials.

Stress concentration in the vicinity of a hole defect under conditions of Hertzian contact

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Eguchi, M.; Murayama, K.

1981-01-01

Two dimensional photoelastic stress analyses were conducted for epoxy resin models containing a hole defect under the conditions of Hertzian contact. Stress concentrations around the defect were determined as a function of several parameters. The effect of tangential traction on the stress concentration was also determined. Sharp stress concentrations occur in the vicinity of both the left and the right side of the hole. The stress concentration becomes more distinct the larger the hole diameter and the smaller distance between the hole and the contact surface. The stress concentration is greatest when the disk imposing a normal load is located at the contact surface directly over the hole. The magnitude and the location of stress concentration varies with the distance between the Hertzian contact area and the hole. The area involved in a process of rolling contact fatigue is confined to a shallow region at both sides of the hole. It was found that the effect of tangential traction is comparatively small on the stress concentration around the hole.

On Compression of a Heavy Compressible Layer of an Elastoplastic or Elastoviscoplastic Medium

NASA Astrophysics Data System (ADS)

Kovtanyuk, L. V.; Panchenko, G. L.

2017-11-01

The problem of deformation of a horizontal plane layer of a compressible material is solved in the framework of the theory of small strains. The upper boundary of the layer is under the action of shear and compressing loads, and the no-slip condition is satisfied on the lower boundary of the layer. The loads increase in absolute value with time, then become constant, and then decrease to zero.Various plasticity conditions are consideredwith regard to the material compressibility, namely, the Coulomb-Mohr plasticity condition, the von Mises-Schleicher plasticity condition, and the same conditions with the viscous properties of the material taken into account. To solve the system of partial differential equations for the components of irreversible strains, a finite-difference scheme is developed for a spatial domain increasing with time. The laws of motion of elastoplastic boundaries are presented, the stresses, strains, rates of strain, and displacements are calculated, and the residual stresses and strains are found.

Model Estimates of Non-Hydrostatic Stresses in the Martian Crust and Mantle: 1—Two-Level Model

NASA Astrophysics Data System (ADS)

Gudkova, T. V.; Batov, A. V.; Zharkov, V. N.

2017-11-01

Regions of maximum shear and tension-compression stresses in the Martian interior have been revealed using two types of models: the elastic model and the model with an elastic lithosphere of varied thickness (150-500 km) positioned on a weak layer that has partially lost its elastic properties. The weakening is simulated by a ten-fold lower value of the shear modulus down to the core boundary. The numerical simulation applies Green's functions (load number method) with the step of 1 × 1 grade along latitude and longitude down to a depth of 1000 km. The boundary condition is the expansion of the latest data on Martian topography and the gravitational field (model MRO120D) in spherical harmonics up to the degree and order of 90 in relation to the reference surface that is assumed an equilibrium spheroid. The considered two-level compensation model assumes nonequilibrium relief and density anomalies at the crust-mantle boundary to be the sources of the anomalous gravitational field. Calculations are performed for two test models of Martian internal structure with the crust mean thicknesses of 50 to 100 km and mean density of 2900 kg/m3. Considerable tangential and simultaneously compressive stresses occur under the Tharsis region. The main regions of high shear and simultaneously extentional stresses are located in the Hellas region crust and in the lithosphere of the following regions: Argyre Planitia, Mare Acidalium, Arcadia Planitia and Valles Marineris. The zone of high maximum shear and extentional stresses has been found at the base of the lithosphere under the Olympus volcano and that under the Elysium rise.

Experimental investigation of magnetically actuated separation using tangential microfluidic channels and magnetic nanoparticles.

PubMed

Munir, Ahsan; Zhu, Zanzan; Wang, Jianlong; Zhou, Hong Susan

2014-06-01

A novel continuous switching/separation scheme of magnetic nanoparticles (MNPs) in a sub-microlitre fluid volume surrounded by neodymium permanent magnet is studied in this work using tangential microfluidic channels. Polydimethylsiloxane tangential microchannels are fabricated using a novel micromoulding technique that can be done without a clean room and at much lower cost and time. Negligible switching of MNPs is seen in the absence of magnetic field, whereas 90% of switching is observed in the presence of magnetic field. The flow rate of MNPs solution had dramatic impact on separation performance. An optimum value of the flow rate is found that resulted in providing effective MNP separation at much faster rate. Separation performance is also investigated for a mixture containing non-magnetic polystyrene particles and MNPs. It is found that MNPs preferentially moved from lower microchannel to upper microchannel resulting in efficient separation. The proof-of-concept experiments performed in this work demonstrates that microfluidic bioseparation can be efficiently achieved using functionalised MNPs, together with tangential microchannels, appropriate magnetic field strength and optimum flow rates. This work verifies that a simple low-cost magnetic switching scheme can be potentially of great utility for the separation and detection of biomolecules in microfluidic lab-on-a-chip systems.

Near-wall modelling of compressible turbulent flows

NASA Technical Reports Server (NTRS)

So, Ronald M. C.

1990-01-01

Work was carried out to formulate near-wall models for the equations governing the transport of the temperature-variance and its dissipation rate. With these equations properly modeled, a foundation is laid for their extension together with the heat-flux equations to compressible flows. This extension is carried out in a manner similar to that used to extend the incompressible near-wall Reynolds-stress models to compressible flows. The methodology used to accomplish the extension of the near-wall Reynolds-stress models is examined and the actual extension of the models for the Reynolds-stress equations and the near-wall dissipation-rate equation to compressible flows is given. Then the formulation of the near-wall models for the equations governing the transport of the temperature variance and its dissipation rate is discussed. Finally, a sample calculation of a flat plate compressible turbulent boundary-layer flow with adiabatic wall boundary condition and a free-stream Mach number of 2.5 using a two-equation near-wall closure is presented. The results show that the near-wall two-equation closure formulated for compressible flows is quite valid and the calculated properties are in good agreement with measurements. Furthermore, the near-wall behavior of the turbulence statistics and structure parameters is consistent with that found in incompressible flows.

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

DOE PAGES

Song, Bo; Sanborn, Brett

2018-05-07

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Relationship of compressive stress-strain response of engineering materials obtained at constant engineering and true strain rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Bo; Sanborn, Brett

In this paper, a Johnson–Cook model was used as an example to analyze the relationship of compressive stress-strain response of engineering materials experimentally obtained at constant engineering and true strain rates. There was a minimal deviation between the stress-strain curves obtained at the same constant engineering and true strain rates. The stress-strain curves obtained at either constant engineering or true strain rates could be converted from one to the other, which both represented the intrinsic material response. There is no need to specify the testing requirement of constant engineering or true strain rates for material property characterization, provided that eithermore » constant engineering or constant true strain rate is attained during the experiment.« less

Nonlinear interaction of a fast magnetogasdynamic shock with a tangential discontinuity

NASA Technical Reports Server (NTRS)

Neubauer, F. M.

1973-01-01

A basic problem, which is of considerable interest in geoastrophysical applications of magnetogasdynamics, is the nonlinear interaction of a fast shock (S sub f) with a tangential discontinuity (T). The problem is treated for an arbitrary S sub f interacting with an arbitrary T under the assumption that in the frame of reference in which S sub f and T are at rest, the flow is superfast on both sides of T, and that a steady flow develops. As a result of the nonlinear analysis a flow pattern is obtained consisting of the incident discontinuities S sub f 1 and T2 and a transmitted fast shock S sub f 3, the modified tangential discontinuity T4 and a reflected fast shock S sub f 5 or fast rarefaction wave R sub f 5. The results are discussed in terms of seven significant similarity parameters. In addition special cases like changes in magnetic field direction only, changes in desnity or velocity shear only etc. are discussed.

Tectonic stress in the plates

NASA Technical Reports Server (NTRS)

Richardson, R. M.; Solomon, S. C.; Sleep, N. H.

1979-01-01

In the present paper, the basic set of global intraplate stress orientation data is plotted and tabulated. Although the global intraplate stress field is complicated, several large-scale patterns can be seen. Much of stable North America is characterized by an E-W to NE-SW trend for the maximum compressive stress. South American lithosphere beneath the Andes, and perhaps farther east in the stable interior, has horizontal compressive stresses trending E-W to NW-SE. Western Europe north of the Alps is characterized by a NW-SE trending maximum horizontal compression, while Asia has the maximum horizontal compressive stress trending more nearly N-S, especially near the Himalayan front.

Numerical investigation of contact stresses for fretting fatigue damage initiation

NASA Astrophysics Data System (ADS)

Bhatti, N. A.; Abdel Wahab, M.

2017-05-01

Fretting fatigue phenomena occurs due to interaction between contacting bodies under application of cyclic and normal loads. In addition to environmental conditions and material properties, the response at the contact interface highly depends on the combination of applied loads. High stress concentration is present at the contact interface, which can start the damage nucleation process. At the culmination of nucleation process several micro cracks are initiated, ultimately leading to the structural failure. In this study, effect of ratio of tangential to normal load on contact stresses, slip amplitude and damage initiation is studied using finite element analysis. The results are evaluated for Ruiz parameter as it involves the slip amplitude which in an important factor in fretting fatigue conditions. It is observed that tangential to normal load ratio influences the stick zone size and damage initiation life. Furthermore, it is observed that tensile stress is the most important factor that drives the damage initiation to failure for the cases where failure occurs predominantly in mode I manner.

Droplet condensation on superhydrophobic surfaces with enhanced dewetting under a tangential AC electric field

NASA Astrophysics Data System (ADS)

Yan, Xinzhu; Li, Jian; Li, Licheng; Huang, Zhengyong; Wang, Feipeng; Wei, Yuan

2016-10-01

In this Letter, the dewetting behavior of superhydrophobic condensing surfaces under a tangential AC electric field is reported. The surface coverage of condensed droplets only exhibits a negligible increase with time. The jumping frequency of droplets is enhanced. The AC electric field motivates the dynamic transition of droplets from stretch to recoil, resulting in the counterforce propelling droplet jumping. The considerable horizontal component of jumping velocity facilitates droplet departure from superhydrophobic surfaces. Both the amplitude and frequency of AC voltage are important factors for droplet departure and dewetting effect. Thereby, the tangential electric field provides a unique and easily implementable approach to enhance droplet removal from superhydrophobic condensing surfaces.

Pneumatic microfluidic cell compression device for high-throughput study of chondrocyte mechanobiology.

PubMed

Lee, Donghee; Erickson, Alek; You, Taesun; Dudley, Andrew T; Ryu, Sangjin

2018-06-13

Hyaline cartilage is a specialized type of connective tissue that lines many moveable joints (articular cartilage) and contributes to bone growth (growth plate cartilage). Hyaline cartilage is composed of a single cell type, the chondrocyte, which produces a unique hydrated matrix to resist compressive stress. Although compressive stress has profound effects on transcriptional networks and matrix biosynthesis in chondrocytes, mechanistic relationships between strain, signal transduction, cell metabolism, and matrix production remain superficial. Here, we describe development and validation of a polydimethylsiloxane (PDMS)-based pneumatic microfluidic cell compression device which generates multiple compression conditions in a single platform. The device contained an array of PDMS balloons of different sizes which were actuated by pressurized air, and the balloons compressed chondrocytes cells in alginate hydrogel constructs. Our characterization and testing of the device showed that the developed platform could compress chondrocytes with various magnitudes simultaneously with negligible effect on cell viability. Also, the device is compatible with live cell imaging to probe early effects of compressive stress, and it can be rapidly dismantled to facilitate molecular studies of compressive stress on transcriptional networks. Therefore, the proposed device will enhance the productivity of chondrocyte mechanobiology studies, and it can be applied to study mechanobiology of other cell types.

Compressive behavior of fine sand.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, Bradley E.; Kabir, Md. E.; Song, Bo

2010-04-01

The compressive mechanical response of fine sand is experimentally investigated. The strain rate, initial density, stress state, and moisture level are systematically varied. A Kolsky bar was modified to obtain uniaxial and triaxial compressive response at high strain rates. A controlled loading pulse allows the specimen to acquire stress equilibrium and constant strain-rates. The results show that the compressive response of the fine sand is not sensitive to strain rate under the loading conditions in this study, but significantly dependent on the moisture content, initial density and lateral confinement. Partially saturated sand is more compliant than dry sand. Similar trendsmore » were reported in the quasi-static regime for experiments conducted at comparable specimen conditions. The sand becomes stiffer as initial density and/or confinement pressure increases. The sand particle size become smaller after hydrostatic pressure and further smaller after dynamic axial loading.« less

Complex large-scale convection of a viscous incompressible fluid with heat exchange according to Newton's law

NASA Astrophysics Data System (ADS)

Gorshkov, A. V.; Prosviryakov, E. Yu.

2017-12-01

The paper considers the construction of analytical solutions to the Oberbeck-Boussinesq system. This system describes layered Bénard-Marangoni convective flows of an incompressible viscous fluid. The third-kind boundary condition, i. e. Newton's heat transfer law, is used on the boundaries of a fluid layer. The obtained solution is analyzed. It is demonstrated that there is a fluid layer thickness with tangential stresses vanishing simultaneously, this being equivalent to the existence of tensile and compressive stresses.

Meninges control tangential migration of hem-derived Cajal-Retzius cells via CXCL12/CXCR4 signaling.

PubMed

Borrell, Víctor; Marín, Oscar

2006-10-01

Cajal-Retzius cells are critical in the development of the cerebral cortex, but little is known about the mechanisms controlling their development. Three focal sources of Cajal-Retzius cells have been identified in mice-the cortical hem, the ventral pallium and the septum-from where they migrate tangentially to populate the cortical surface. Using a variety of tissue culture assays and in vivo manipulations, we demonstrate that the tangential migration of cortical hem-derived Cajal-Retzius cells is controlled by the meninges. We show that the meningeal membranes are a necessary and sufficient substrate for the tangential migration of Cajal-Retzius cells. We also show that the chemokine CXCL12 secreted by the meninges enhances the dispersion of Cajal-Retzius cells along the cortical surface, while retaining them within the marginal zone in a CXCR4-dependent manner. Thus, the meningeal membranes are fundamental in the development of Cajal-Retzius cells and, hence, in the normal development of the cerebral cortex.

CHRONIC PERIPHERAL NERVE COMPRESSION DISRUPTS PARANODAL AXOGLIAL JUNCTIONS

PubMed Central

Otani, Yoshinori; Yermakov, Leonid M.; Dupree, Jeffrey L.; Susuki, Keiichiro

2016-01-01

Introduction Peripheral nerves are often exposed to mechanical stress leading to compression neuropathies. The pathophysiology underlying nerve dysfunction by chronic compression is largely unknown. Methods We analyzed molecular organization and fine structures at and near nodes of Ranvier in a compression neuropathy model in which a silastic tube was placed around the mouse sciatic nerve. Results Immunofluorescence study showed that clusters of cell adhesion complex forming paranodal axoglial junctions were dispersed with frequent overlap with juxtaparanodal components. These paranodal changes occurred without internodal myelin damage. The distribution and pattern of paranodal disruption suggests that these changes are the direct result of mechanical stress. Electron microscopy confirmed loss of paranodal axoglial junctions. Discussion Our data show that chronic nerve compression disrupts paranodal junctions and axonal domains required for proper peripheral nerve function. These results provide important clues toward better understanding of the pathophysiology underlying nerve dysfunction in compression neuropathies. PMID:27463510

A realizable explicit algebraic Reynolds stress model for compressible turbulent flow with significant mean dilatation

NASA Astrophysics Data System (ADS)

Grigoriev, I. A.; Wallin, S.; Brethouwer, G.; Johansson, A. V.

2013-10-01

The explicit algebraic Reynolds stress model of Wallin and Johansson [J. Fluid Mech. 403, 89 (2000)] is extended to compressible and variable-density turbulent flows. This is achieved by correctly taking into account the influence of the mean dilatation on the rapid pressure-strain correlation. The resulting model is formally identical to the original model in the limit of constant density. For two-dimensional mean flows the model is analyzed and the physical root of the resulting quartic equation is identified. Using a fixed-point analysis of homogeneously sheared and strained compressible flows, we show that the new model is realizable, unlike the previous model. Application of the model together with a K - ω model to quasi one-dimensional plane nozzle flow, transcending from subsonic to supersonic regime, also demonstrates realizability. Negative "dilatational" production of turbulence kinetic energy competes with positive "incompressible" production, eventually making the total production negative during the spatial evolution of the nozzle flow. Finally, an approach to include the baroclinic effect into the dissipation equation is proposed and an algebraic model for density-velocity correlations is outlined to estimate the corrections associated with density fluctuations. All in all, the new model can become a significant tool for CFD (computational fluid dynamics) of compressible flows.

Involvement of upper torso stress amplification, tissue compression and distortion in the pathogenesis of keloids.

PubMed

Bux, Shamin; Madaree, Anil

2012-03-01

Keloids are benign tumours composed of fibrous tissue produced during excessive tissue repair triggered by minor injury, trauma or surgical incision. Although it is recognized that keloids have a propensity to form in the upper torso of the body, the predisposing factors responsible for this have not been investigated. It is crucial that the aetiopathoical factors implicated in keloid formation be established to provide guidelines for well-informed more successful treatment. We compared keloid-prone and keloid-protected skin, identified pertinent morphological differences and explored how inherent structural characteristics and intrinsic factors may promote keloid formation. It was determined that keloid prone areas were covered with high tension skin that had low stretch and a low elastic modulus when compared with skin in keloid protected areas where the skin was lax with a high elastic modulus and low pre-stress level. Factors contributing to elevated internal stress in keloid susceptible skin were the protrusion of hard connective tissue such as bony prominences or cartilage into the dermis of skin as well as inherent skin characteristics such as the bundled arrangement of collagen in the reticular dermis, the existent high tension, the low elastic modulus, low stretch ability, contractile forces exerted by wound healing fibroblastic cells and external forces. Stress promotes keloid formation by causing dermal distortion and compression which subsequently stimulate proliferation and enhanced protein synthesis in wound healing fibroblastic cells. The strain caused by stress also compresses and occludes microvessels causing ischaemic effects and reperfusion injury which stimulate growth when blood rich in growth factors returns to the tissue. The growth promoting effects of increased internal stress, primarily, and growth factors released by reperfusing blood, manifest in keloid formation. Other inherent skin characteristics promoting keloid growth during the

Stress-Shielding Effect of Nitinol Swan-Like Memory Compressive Connector on Fracture Healing of Upper Limb

NASA Astrophysics Data System (ADS)

Fu, Q. G.; Liu, X. W.; Xu, S. G.; Li, M.; Zhang, C. C.

2009-08-01

In this article, the stress-shielding effect of a Nitinol swan-like memory compressive connector (SMC) is evaluated. Patients with fracture healing of an upper limb after SMC internal fixation or stainless steel plate fixation were randomly selected and observed comparatively. With the informed consent of the SMC group, minimal cortical bone under the swan-body and swan-neck was harvested; and in the steel plate fixation group, minimal cortical bone under the steel plate and opposite side to the steel plate was also harvested for observation. Main outcome measurements were taken such as osteocyte morphology, Harversian canal histological observation under light microscope; radiographic observation of fracture healing, and computed tomography quantitative scanning of cortical bone. As a conclusion, SMC has a lesser stress-shielding effect to fixed bone than steel plate. Finally, the mechanism of the lesser stress-shielding effect of SMC is discussed.

The fracture characteristic of three collinear cracks under true triaxial compression.

PubMed

Liu, Jianjun; Zhu, Zheming; Wang, Bo

2014-01-01

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses.

The Fracture Characteristic of Three Collinear Cracks under True Triaxial Compression

PubMed Central

Liu, Jianjun; Zhu, Zheming; Wang, Bo

2014-01-01

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses. PMID:24790569

Shape Optimisation of Holes in Loaded Plates by Minimisation of Multiple Stress Peaks

DTIC Science & Technology

2015-04-01

UNCLASSIFIED UNCLASSIFIED Shape Optimisation of Holes in Loaded Plates by Minimisation of Multiple Stress Peaks Witold Waldman and Manfred...minimising the peak tangential stresses on multiple segments around the boundary of a hole in a uniaxially-loaded or biaxially-loaded plate . It is based...RELEASE UNCLASSIFIED UNCLASSIFIED Shape Optimisation of Holes in Loaded Plates by Minimisation of Multiple Stress Peaks Executive Summary Aerospace

Comparison of Open-Hole Compression Strength and Compression After Impact Strength on Carbon Fiber/Epoxy Laminates for the Ares I Composite Interstage

NASA Technical Reports Server (NTRS)

Hodge, Andrew J.; Nettles, Alan T.; Jackson, Justin R.

2011-01-01

Notched (open hole) composite laminates were tested in compression. The effect on strength of various sizes of through holes was examined. Results were compared to the average stress criterion model. Additionally, laminated sandwich structures were damaged from low-velocity impact with various impact energy levels and different impactor geometries. The compression strength relative to damage size was compared to the notched compression result strength. Open-hole compression strength was found to provide a reasonable bound on compression after impact.

Tensile and compressive behavior of Borsic/aluminum

NASA Technical Reports Server (NTRS)

Herakovich, C. T.; Davis, J. G., Jr.; Viswanathan, C. N.

1977-01-01

The results of an experimental investigation of the mechanical behavior of Borsic/aluminum are presented. Composite laminates were tested in tension and compression for monotonically increasing load and also for variable loading cycles in which the maximum load was increased in each successive cycle. It is shown that significant strain-hardening, and corresponding increase in yield stress, is exhibited by the metal matrix laminates. For matrix dominated laminates, the current yield stress is essentially identical to the previous maximum stress, and unloading is essentially linear with large permanent strains after unloading. For laminates with fiber dominated behavior, the yield stress increases with increase in the previous maximum stress, but the increase in yield stress does not keep pace with the previous maximum stress. These fiber dominated laminates exhibit smaller nonlinear strains, reversed nonlinear behavior during unloading, and smaller permanent strains after unloading. Compression results from sandwich beams and flat coupons are shown to differ considerably. Results from beam specimens tend to exhibit higher values for modulus, yield stress, and strength.

Modeling for stress-strain curve of a porous NiTi under compressive loading

NASA Astrophysics Data System (ADS)

Zhao, Ying; Taya, Minoru

2005-05-01

Two models for predicting the stress-strain curve of porous NiTi under compressive loading are presented in this paper. Porous NiTi shape memory alloy is investigated as a composite composed of solid NiTi as matrix and pores as inclusions. Eshelby"s equivalent inclusion method and Mori-Tanaka"s mean-field theory are employed in both models. In the first model, the geometry of the pores is assumed as sphere. The composite is with close-cells. While in the second model, two geometries of the pores, sphere and ellipsoid, are investigated. The pores are interconnected to each other forming an open-cell microstructure. The two adjacent pores connected along equator ring are investigated as a unit. Two pores interact with each other as they are connected. The average eigenstrain of each unit is obtained by taking the average of each pore"s eigenstrain. The stress-strain curves of porous shape memory alloy with spherical pores and ellipsoidal pores are compared, it is found that the shape of the pores has a nonignorable influence on the mechanical property of the porous NiTi. Comparison of the stress-strain curves of the two models shows that introducing of the average eigenstrains in the second model makes the predictions more agreeable to the experimental results.

Automated planning of tangential breast intensity-modulated radiotherapy using heuristic optimization.

PubMed

Purdie, Thomas G; Dinniwell, Robert E; Letourneau, Daniel; Hill, Christine; Sharpe, Michael B

2011-10-01

To present an automated technique for two-field tangential breast intensity-modulated radiotherapy (IMRT) treatment planning. A total of 158 planned patients with Stage 0, I, and II breast cancer treated using whole-breast IMRT were retrospectively replanned using automated treatment planning tools. The tools developed are integrated into the existing clinical treatment planning system (Pinnacle(3)) and are designed to perform the manual volume delineation, beam placement, and IMRT treatment planning steps carried out by the treatment planning radiation therapist. The automated algorithm, using only the radio-opaque markers placed at CT simulation as inputs, optimizes the tangential beam parameters to geometrically minimize the amount of lung and heart treated while covering the whole-breast volume. The IMRT parameters are optimized according to the automatically delineated whole-breast volume. The mean time to generate a complete treatment plan was 6 min, 50 s ± 1 min 12 s. For the automated plans, 157 of 158 plans (99%) were deemed clinically acceptable, and 138 of 158 plans (87%) were deemed clinically improved or equal to the corresponding clinical plan when reviewed in a randomized, double-blinded study by one experienced breast radiation oncologist. In addition, overall the automated plans were dosimetrically equivalent to the clinical plans when scored for target coverage and lung and heart doses. We have developed robust and efficient automated tools for fully inversed planned tangential breast IMRT planning that can be readily integrated into clinical practice. The tools produce clinically acceptable plans using only the common anatomic landmarks from the CT simulation process as an input. We anticipate the tools will improve patient access to high-quality IMRT treatment by simplifying the planning process and will reduce the effort and cost of incorporating more advanced planning into clinical practice. Crown Copyright © 2011. Published by Elsevier Inc

Spiral Galaxy Central Bulge Tangential Speed of Revolution Curves

NASA Astrophysics Data System (ADS)

Taff, Laurence

2013-03-01

The objective was to, for the first time in a century, scientifically analyze the ``rotation curves'' (sic) of the central bulges of scores of spiral galaxies. I commenced with a methodological, rational, geometrical, arithmetic, and statistical examination--none of them carried through before--of the radial velocity data. The requirement for such a thorough treatment is the paucity of data typically available for the central bulge: fewer than 10 observations and frequently only five. The most must be made of these. A consequence of this logical handling is the discovery of a unique model for the central bulge volume mass density resting on the positive slope, linear, rise of its tangential speed of revolution curve and hence--for the first time--a reliable mass estimate. The deduction comes from a known physics-based, mathematically valid, derivation (not assertion). It rests on the full (not partial) equations of motion plus Poisson's equation. Following that is a prediction for the gravitational potential energy and thence the gravitational force. From this comes a forecast for the tangential speed of revolution curve. It was analyzed in a fashion identical to that of the data thereby closing the circle and demonstrating internal self-consistency. This is a hallmark of a scientific method-informed approach to an experimental problem. Multiple plots of the relevant quantities and measures of goodness of fit will be shown. Astronomy related

Magnetic properties of Fe-Si steel depending on compressive and tensile stresses under sinusoidal and distorted excitations

NASA Astrophysics Data System (ADS)

Permiakov, V.; Pulnikov, A.; Dupré, L.; De Wulf, M.; Melkebeek, J.

2003-05-01

In this article, the magnetic properties of nonoriented electrical steel under sinusoidal and distorted excitations are investigated for the whole range of unidirectional mechanical stresses. The distorted flux obtained from the tooth tip of 3 kW induction machine at no-load test was put into the measurement system. The total losses increase for compressive stress both under sinusoidal and distorted excitations. For tensile elastic stresses, the total losses first decrease and then increase in a very similar way for both excitations. In contrast, the difference between total losses under sinusoidal and distorted magnetic fluxes becomes smaller with increase of the plastic strain. This work is a serious step toward complete characterization of the magnetic properties of electrical steel in the teeth area of induction machines. A deeper insight of that problem can improve the design of induction machines and other electromagnetic devices.

Computational analysis of forebody tangential slot blowing on the high alpha research vehicle

NASA Technical Reports Server (NTRS)

Gee, Ken

1994-01-01

Current and future fighter aircraft can maneuver in the high-angle-of-attack flight regime while flying at low subsonic and transonic freestream Mach numbers. However, at any flight speed, the ability of the vertical tails to generate yawing moment is limited in high-angle-of-attack flight. Thus, any system designed to provide the pilot with additional side force and yawing moment must work in both low subsonic and transonic flight. However, previous investigations of the effectiveness of forebody tangential slot blowing in generating the desired control forces and moments have been limited to the low subsonic freestream flow regime. In order to investigate the effectiveness of tangential slot blowing in transonic flight, a computational fluid dynamics analysis was carried out during the grant period. Computational solutions were obtained at three different freestream Mach numbers and at various jet mass flow ratios. All results were obtained using the isolated F/A-18 forebody grid geometry at 30.3 degrees angle of attack. One goal of the research was to determine the effect of freestream Mach number on the effectiveness of forebody tangential slot blowing in generating yawing moment. The second part of the research studied the force onset time lag associated with blowing. The time required for the yawing moment to reach a steady-state value from the onset of blowing may have an impact on the implementation of a pneumatic system on a flight vehicle.

Compression-compression fatigue of selective electron beam melted cellular titanium (Ti-6Al-4V).

PubMed

Hrabe, Nikolas W; Heinl, Peter; Flinn, Brian; Körner, Carolin; Bordia, Rajendra K

2011-11-01

Regular 3D periodic porous Ti-6Al-4V structures intended to reduce the effects of stress shielding in load-bearing bone replacement implants (e.g., hip stems) were fabricated over a range of relative densities (0.17-0.40) and pore sizes (approximately 500-1500 μm) using selective electron beam melting (EBM). Compression-compression fatigue testing (15 Hz, R = 0.1) resulted in normalized fatigue strengths at 10(6) cycles ranging from 0.15 to 0.25, which is lower than the expected value of 0.4 for solid material of the same acicular α microstructure. The three possible reasons for this reduced fatigue lifetime are stress concentrations from closed porosity observed within struts, stress concentrations from observed strut surface features (sintered particles and texture lines), and microstructure (either acicular α or martensite) with less than optimal high-cycle fatigue resistance. 2011 Wiley Periodicals, Inc.

A Numerical Experiment on the Role of Surface Shear Stress in the Generation of Sound

NASA Technical Reports Server (NTRS)

Shariff, Karim; Wang, Meng; Merriam, Marshal (Technical Monitor)

1996-01-01

The sound generated due to a localized flow over an infinite flat surface is considered. It is known that the unsteady surface pressure, while appearing in a formal solution to the Lighthill equation, does not constitute a source of sound but rather represents the effect of image quadrupoles. The question of whether a similar surface shear stress term constitutes a true source of dipole sound is less settled. Some have boldly assumed it is a true source while others have argued that, like the surface pressure, it depends on the sound field (via an acoustic boundary layer) and is therefore not a true source. A numerical experiment based on the viscous, compressible Navier-Stokes equations was undertaken to investigate the issue. A small region of a wall was oscillated tangentially. The directly computed sound field was found to to agree with an acoustic analogy based calculation which regards the surface shear as an acoustically compact dipole source of sound.

Stress concentration in the vicinity of a hole defect under conditions of Hertzian contact

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Eguchi, M.; Murayama, K.

1981-01-01

Two-dimensional photoelastic stress analyses were conducted for epoxy resin models containing a hole defect under the conditions of Hertzian contact. Stress concentrations around the defect were determined as a function of several parameters. These were hole diameter, its vertical distance from the contact surface, and the horizontal distance from the Hertzian contact area. Also determined was the effect of tangential traction (generated by a friction coefficient of 0.1) on the stress concentration. Sharp stress concentrations occur in the vicinity of both the left and the right side of the hole. The stress concentration becomes more distinct the larger the hole diameter and the smaller the distance between the hole and the contact surface. The stress concentration is greatest when the disk imposing a normal load is located at the contact surface directly over the hole. The magnitude and the location of stress concentration varies with the distance between the Hertzian contact area and the hole. Taking into account the stress amplitude, the area which can be involved in a process of rolling contact fatigue seems to be confined to a shallow region at both sides of the hole. The effect of tangential traction is comparatively small on the stress concentration around the hole.

Experimental investigations of the time and flow-direction responses of shear-stress-sensitive liquid crystal coatings

NASA Technical Reports Server (NTRS)

Reda, Daniel C.; Muratore, Joseph J., Jr.; Heineck, James T.

1993-01-01

Time and flow-direction responses of shearstress-sensitive liquid crystal coatings were explored experimentally. For the time-response experiments, coatings were exposed to transient, compressible flows created during the startup and off-design operation of an injector-driven supersonic wind tunnel. Flow transients were visualized with a focusing Schlieren system and recorded with a 1000 frame/sec color video camera. Liquid crystal responses to these changing-shear environments were then recorded with the same video system, documenting color-play response times equal to, or faster than, the time interval between sequential frames (i.e., 1 millisecond). For the flow-direction experiments, a planar test surface was exposed to equal-magnitude and known-direction surface shear stresses generated by both normal and tangential subsonic jet-impingement flows. Under shear, the sense of the angular displacement of the liquid crystal dispersed (reflected) spectrum was found to be a function of the instantaneous direction of the applied shear. This technique thus renders dynamic flow reversals or flow divergences visible over entire test surfaces at image recording rates up to 1 KHz. Extensions of the technique to visualize relatively small changes in surface shear stress direction appear feasible.

Method of analysis for compressible flow through mixed-flow centrifugal impellers of arbitrary design

NASA Technical Reports Server (NTRS)

Hamrick, Joseph T; Ginsburg, Ambrose; Osborn, Walter M

1952-01-01

A method is presented for analysis of the compressible flow between the hub and the shroud of mixed-flow impellers of arbitrary design. Axial symmetry was assumed, but the forces in the meridional (hub to shroud) plane, which are derived from tangential pressure gradients, were taken into account. The method was applied to an experimental mixed-flow impeller. The analysis of the flow in the meridional plane of the impeller showed that the rotational forces, the blade curvature, and the hub-shroud profile can introduce severe velocity gradients along the hub and the shroud surfaces. Choked flow at the impeller inlet as determined by the analysis was verified by experimental results.

Rationale and Application of Tangential Scanning to Industrial Inspection of Hardwood Logs

Treesearch

Nand K. Gupta; Daniel L. Schmoldt; Bruce Isaacson

1998-01-01

Industrial computed tomography (CT) inspection of hardwood logs has some unique requirements not found in other CT applications. Sawmill operations demand that large volumes of wood be scanned quickly at high spatial resolution for extended duty cycles. Current CT scanning geometries and commercial systems have both technical and economic [imitations. Tangential...

Injector Element which Maintains a Constant Mean Spray Angle and Optimum Pressure Drop During Throttling by Varying the Geometry of Tangential Inlets

NASA Technical Reports Server (NTRS)

Trinh, Huu P. (Inventor); Myers, William Neill (Inventor)

2014-01-01

A method for determining the optimum inlet geometry of a liquid rocket engine swirl injector includes obtaining a throttleable level phase value, volume flow rate, chamber pressure, liquid propellant density, inlet injector pressure, desired target spray angle and desired target optimum delta pressure value between an inlet and a chamber for a plurality of engine stages. The tangential inlet area for each throttleable stage is calculated. The correlation between the tangential inlet areas and delta pressure values is used to calculate the spring displacement and variable inlet geometry. An injector designed using the method includes a plurality of geometrically calculated tangential inlets in an injection tube; an injection tube cap with a plurality of inlet slots slidably engages the injection tube. A pressure differential across the injector element causes the cap to slide along the injection tube and variably align the inlet slots with the tangential inlets.

Radial and tangential gravity rates from GRACE in areas of glacial isostatic adjustment

NASA Astrophysics Data System (ADS)

van der Wal, Wouter; Kurtenbach, Enrico; Kusche, Jürgen; Vermeersen, Bert

2011-11-01

In areas dominated by Glacial Isostatic Adjustment (GIA), the free-air gravity anomaly rate can be converted to uplift rate to good approximation by using a simple spectral relation. We provide quantitative comparisons between gravity rates derived from monthly gravity field solutions (GFZ Potsdam, CSR Texas, IGG Bonn) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission with uplift rates measured by GPS in these areas. The band-limited gravity data from the GRACE satellite mission can be brought to very good agreement with the point data from GPS by using scaling factors derived from a GIA model (the root-mean-square of differences is 0.55 mm yr-1 for a maximum uplift rate signal of 10 mm yr-1). The root-mean-square of the differences between GRACE derived uplift rates and GPS derived uplift rates decreases with increasing GRACE time period to a level below the uncertainty that is expected from GRACE observations, GPS measurements and the conversion from gravity rate to uplift rate. With the current length of time-series (more than 8 yr) applying filters and a hydrology correction to the GRACE data does not reduce the root-mean-square of differences significantly. The smallest root-mean-square was obtained with the GFZ solution in Fennoscandia and with the CSR solution in North America. With radial gravity rates in excellent agreement with GPS uplift rates, more information on the GIA process can be extracted from GRACE gravity field solutions in the form of tangential gravity rates, which are equivalent to a rate of change in the deflection of the vertical scaled by the magnitude of gravity rate vector. Tangential gravity rates derived from GRACE point towards the centre of the previously glaciated area, and are largest in a location close to the centre of the former ice sheet. Forward modelling showed that present day tangential gravity rates have maximum sensitivity between the centre and edge of the former ice sheet, while radial gravity

Measurement of the through thickness compression of a battery separator

NASA Astrophysics Data System (ADS)

Yan, Shutian; Huang, Xiaosong; Xiao, Xinran

2018-04-01

The mechanical integrity of the separator is critical to the reliable operation of a battery. Due to its minimal thickness, compression experiments with a single/a few layers of separator are difficult to perform. In this work, a capacitance based displacement set-up has been developed for the measurement of the through thickness direction (TTD) compression stress-strain behavior of the separator and the investigation of its interaction with the electrode. The experiments were performed for a stack of two layers of Celgard 2400 separator, NMC cathode, and separator/NMC cathode/separator stack in both dry and wet (i.e. submersed in dimethyl carbonate DMC) conditions. The experimental results reveal that the separator compression modulus can be significantly affected by the presence of DMC. The iso-stress based rule of mixtures was used to compute the compressive stress-strain curve for the stack from that of the separator and NMC layer. The computed curve agreed with the experimental curve reasonably well up to about 0.16 strain but deviated significantly to a softer response at higher strains. The results suggest that, in the stack, the TTD compressive deformation of the separator is influenced by the NMC cathode.

Effect of Applied Stress and Temperature on Residual Stresses Induced by Peening Surface Treatments in Alloy 600

NASA Astrophysics Data System (ADS)

Telang, A.; Gnäupel-Herold, T.; Gill, A.; Vasudevan, V. K.

2018-04-01

In this study, the effects of applied tensile stress and temperature on laser shock peening (LSP) and cavitation shotless peening (CSP)-induced compressive residual stresses were investigated using neutron and x-ray diffraction. Residual stresses on the surface, measured in situ, were lower than the applied stress in LSP- and CSP-treated Alloy 600 samples (2 mm thick). The residual stress averaged over the volume was similar to the applied stress. Compressive residual stresses on the surface and balancing tensile stresses in the interior relax differently due to hardening induced by LSP. Ex situ residual stress measurements, using XRD, show that residual stresses relaxed as the applied stress exceeded the yield strength of the LSP- and CSP-treated Alloy 600. Compressive residual stresses induced by CSP and LSP decreased by 15-25% in magnitude, respectively, on exposure to 250-450 °C for more than 500 h with 10-11% of relaxation occurring in the first few hours. Further, 80% of the compressive residual stresses induced by LSP and CSP treatments in Alloy 600 were retained even after long-term aging at 350 °C for 2400 h.

Theoretical predicting of permeability evolution in damaged rock under compressive stress

NASA Astrophysics Data System (ADS)

Vu, M. N.; Nguyen, S. T.; To, Q. D.; Dao, N. H.

2017-05-01

This paper outlines an analytical model of crack growth induced permeability changes. A theoretical solution of effective permeability of cracked porous media is derived. The fluid flow obeys Poisseuille's law along the crack and Darcy's law in the porous matrix. This solution exhibits a percolation threshold for any type of crack distribution apart from a parallel crack distribution. The physical behaviour of fluid flow through a cracked porous material is well reproduced by the proposed model. The presence of this effective permeability coupling to analytical expression of crack growth under compression enables the modelling of the permeability variation due to stress-induced cracking in a porous rock. This incorporation allows the prediction of the permeability change of a porous rock embedding an anisotropic crack distribution from any initial crack density, that is, lower, around or upper to percolation threshold. The interaction between cracks is not explicitly taken into account. The model is well applicable both to micro- and macrocracks.

Antecedent Avian Immunity Limits Tangential Transmission of West Nile Virus to Humans

PubMed Central

Kwan, Jennifer L.; Kluh, Susanne; Reisen, William K.

2012-01-01

Background West Nile virus (WNV) is a mosquito-borne flavivirus maintained and amplified among birds and tangentially transmitted to humans and horses which may develop terminal neuroinvasive disease. Outbreaks typically have a three-year pattern of silent introduction, rapid amplification and subsidence, followed by intermittent recrudescence. Our hypothesis that amplification to outbreak levels is contingent upon antecedent seroprevalence within maintenance host populations was tested by tracking WNV transmission in Los Angeles, California from 2003 through 2011. Methods Prevalence of antibodies against WNV was monitored weekly in House Finches and House Sparrows. Tangential or spillover transmission was measured by seroconversions in sentinel chickens and by the number of West Nile neuroinvasive disease (WNND) cases reported to the Los Angeles County Department of Public Health. Results Elevated seroprevalence in these avian populations was associated with the subsidence of outbreaks and in the antecedent dampening of amplification during succeeding years. Dilution of seroprevalence by recruitment resulted in the progressive loss of herd immunity following the 2004 outbreak, leading to recrudescence during 2008 and 2011. WNV appeared to be a significant cause of death in these avian species, because the survivorship of antibody positive birds significantly exceeded that of antibody negative birds. Cross-correlation analysis showed that seroprevalence was negatively correlated prior to the onset of human cases and then positively correlated, peaking at 4–6 weeks after the onset of tangential transmission. Antecedent seroprevalence during winter (Jan – Mar) was negatively correlated with the number of WNND cases during the succeeding summer (Jul–Sep). Conclusions Herd immunity levels within after hatching year avian maintenance host populations <10% during the antecedent late winter and spring period were followed on three occasions by outbreaks of WNND

Evolution of network architecture in a granular material under compression

NASA Astrophysics Data System (ADS)

Bassett, Danielle

As a granular material is compressed, the particles and forces within the system arrange to form complex and heterogeneous collective structures. However, capturing and characterizing the dynamic nature of the intrinsic inhomogeneity and mesoscale architecture of granular systems can be challenging. Here, we utilize multilayer networks as a framework for directly quantifying the evolution of mesoscale architecture in a compressed granular system. We examine a quasi-two-dimensional aggregate of photoelastic disks, subject to biaxial compressions through a series of small, quasistatic steps. Treating particles as network nodes and inter-particle forces as network edges, we construct a multilayer network for the system by linking together the series of static force networks that exist at each strain step. We then extract the inherent mesoscale structure from the system by using a generalization of community detection methods to multilayer networks, and we define quantitative measures to characterize the reconfiguration and evolution of this structure throughout the compression process. To test the sensitivity of the network model to particle properties, we examine whether the method can distinguish a subsystem of low-friction particles within a bath of higher-friction particles. We find that this can be done by considering the network of tangential forces, and that the community structure is better able to separate the subsystem than consideration of the local inter-particle forces alone. The results discussed throughout this study suggest that these novel network science techniques may provide a direct way to compare and classify data from systems under different external conditions or with different physical makeup. National Science Foundation (BCS-1441502, PHY-1554488, and BCS-1631550).

Enhanced dielectric properties of Pb0.92La0.08 Zr0.52Ti0.48O3 films with compressive stress

NASA Astrophysics Data System (ADS)

Ma, Beihai; Liu, Shanshan; Tong, Sheng; Narayanan, Manoj; (Balu) Balachandran, U.

2012-12-01

We deposited ferroelectric (Pb0.92La0.08)(Zr0.52Ti0.48)O3 (PLZT 8/52/48) films on nickel foils and platinized silicon (PtSi) substrates by chemical solution deposition. Prior to the deposition of PLZT, a conductive oxide buffer layer of LaNiO3 (LNO) was deposited on the nickel foil. Residual stresses of the films were determined by x-ray diffraction. Compressive stress of ≈-370 MPa and tensile stress of ≈250 MPa were measured in ≈2-μm-thick PLZT grown on LNO-buffered Ni foil and PtSi substrate, respectively. We also measured the following electrical properties for the PLZT films grown on LNO-buffered Ni and PtSi substrates, respectively: remanent polarization, ≈23.5 μC/cm2 and ≈10.1 μC/cm2; coercive electric field, ≈23.8 kV/cm and ≈27.9 kV/cm; dielectric constant at room temperature, ≈1300 and ≈1350; and dielectric loss at room temperature, ≈0.06 and ≈0.05. Weibull analysis determined the mean breakdown strength to be 2.6 MV/cm and 1.5 MV/cm for PLZT films grown on LNO-buffered Ni and PtSi substrates, respectively. The difference in dielectric properties and breakdown strength can be attributed to the residual stress in the PLZT films. Our results suggest that compressive stress enhances the dielectric breakdown strength of the PLZT films.

Can the starpatch on Xi Bootis A be explained by using tangential flows?

NASA Technical Reports Server (NTRS)

Toner, Clifford G.; Labonte, Barry J.

1991-01-01

It is demonstrated that a modification of the starpatch model of Toner and Gray (1988), using tangential flows instead of an enhanced granulation velocity dispersion within the patch, is very successful at reproducing both the observed line asymmetry and the line broadening variations observed in the G8 dwarf Xi Boo A. Areal coverage of 10 percent + or - 3 percent of the visible disk, latitude 30 deg + or - 4 deg, mean brightness 0.85 + or - 0.05 relative to the 'quiet' photosphere, mean tangential flow velocities of 8.0 + or - 1.5 km/s, and dispersions about the mean of 8/0 + or - 2.0 km/s are inferred for the patch. A feature at a latitude of about 30 deg is inferred which covers about 10 percent of the visible disk and is 10-20 percent fainter than the rest of the photosphere. It is inferred that 70-80 percent of the patch is penumbra.

Compressible homogeneous shear: Simulation and modeling

NASA Technical Reports Server (NTRS)

Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.

1992-01-01

Compressibility effects were studied on turbulence by direct numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent kinetic energy decreases with increasing turbulent Mach number. The sinks provided by compressible dissipation and the pressure dilatation, along with reduced Reynolds shear stress, are shown to contribute to the reduced growth of kinetic energy. Models are proposed for these dilatational terms and verified by direct comparison with the simulations. The differences between the incompressible and compressible fields are brought out by the examination of spectra, statistical moments, and structure of the rate of strain tensor.

Compressible homogeneous shear - Simulation and modeling

NASA Technical Reports Server (NTRS)

Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.

1991-01-01

Compressibility effects were studied on turbulence by direct numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent kinetic energy decreases with increasing turbulent Mach number. The sinks provided by compressible dissipation and the pressure dilatation, along with reduced Reynolds shear stress, are shown to contribute to the reduced growth of kinetic energy. Models are proposed for these dilatational terms and verified by direct comparison with the simulations. The differences between the incompressible and compressible fields are brought out by the examination of spectra, statistical moments, and structure of the rate of strain tensor.

Tangential velocity measurement using interferometric MTI radar

DOEpatents

Doerry, Armin W.; Mileshosky, Brian P.; Bickel, Douglas L.

2006-01-03

Radar systems use time delay measurements between a transmitted signal and its echo to calculate range to a target. Ranges that change with time cause a Doppler offset in phase and frequency of the echo. Consequently, the closing velocity between target and radar can be measured by measuring the Doppler offset of the echo. The closing velocity is also known as radial velocity, or line-of-sight velocity. Doppler frequency is measured in a pulse-Doppler radar as a linear phase shift over a set of radar pulses during some Coherent Processing Interval (CPI). An Interferometric Moving Target Indicator (MTI) radar can be used to measure the tangential velocity component of a moving target. Multiple baselines, along with the conventional radial velocity measurement, allow estimating the true 3-D velocity of a target.

Tangential Field Changes in the Great Flare of 1990 May 24.

PubMed

Cameron; Sammis

1999-11-01

We examine the great (solar) flare of 1990 May 24 that occurred in active region NOAA 6063. The Big Bear Solar Observatory videomagnetograph Stokes V and I images show a change in the longitudinal field before and after the flare. Since the flare occurred near the limb, the change reflects a rearrangement of the tangential components of the magnetic field. These observations lack the 180 degrees ambiguity that characterizes vector magnetograms.

Effect of Combustion-chamber Shape on the Performance of a Prechamber Compression-ignition Engine

NASA Technical Reports Server (NTRS)

Moore, C S; Collins, J H , Jr

1934-01-01

The effect on engine performance of variations in the shape of the prechamber, the shape and direction of the connecting passage, the chamber volume using a tangential passage, the injection system, and the direction od the fuel spray in the chamber was investigated using a 5 by 7 inch single-cylinder compression-ignition engine. The results show that the performance of this engine can be considerably improved by selecting the best combination of variables and incorporating them in a single design. The best combination as determined from these tests consisted of a disk-shaped chamber connected to the cylinder by means of a flared tangential passage. The fuel was injected through a single-orifice nozzle directed normal to the air swirl and in the same plane. At an engine speed of 1,500 r.p.m. and with the theoretical fuel quantity for no excess air, the engine developed a brake mean effective pressure of 115 pounds per square inch with a fuel consumption of 0.49 pound per brake horsepower-hour and an explosion pressure of 820 pounds per square inch. A brake mean effective pressure of 100 pounds per square inch with a brake-fuel consumption of 0.44 pound per horsepower-hour at 1,500 r.p.m. was obtained.

Preliminary Investigation of Workplace-Provided Compressed Mindfulness-Based Stress Reduction with Pediatric Medical Social Workers.

PubMed

Trowbridge, Kelly; Mische Lawson, Lisa; Andrews, Stephanie; Pecora, Jodi; Boyd, Sabra

2017-11-01

Mindfulness practices, including mindfulness meditation, show promise for decreasing stress among health care providers. This exploratory study investigates the feasibility of a two-day compressed mindfulness-based stress reduction (cMBSR) course provided in the hospital workplace with pediatric health care social workers. The standard course of Jon Kabat-Zinn's MBSR requires a participant commitment to eight weeks of instruction consisting of one 2.5-hour-per-week class, a single day retreat, and 45 minutes of practice for six of seven days each week. Commitments to family, work, caregiving, education, and so on, as well as limitations such as distance, may prevent health care providers from participating in a standard MBSR course. Using t tests, researchers measured the effect of cMBSR on (a) positive and negative experiences in pediatric social work, (b) perceived stress, (c) mindfulness, and (d) caring self-efficacy (as a component of patient- and family-centered care). Results included significant differences between the pre- and post-intervention outcome variables on the Professional Quality of Life Secondary Traumatic Stress subscale, the Mindful Attention and Awareness Scale, and the Caring Efficacy Scale. Findings found adequate evidence for the feasibility of cMBSR design and for a need of a more rigorous study of the effects of the cMBSR intervention. © 2017 National Association of Social Workers.

Evaluation of shear-compressive strength properties for laminated GFRP composites in electromagnet system

NASA Astrophysics Data System (ADS)

Song, Jun Hee; Kim, Hak Kun; Kim, Sam Yeon

2014-07-01

Laminated fiber-reinforced composites can be applied to an insulating structure of a nuclear fusion device. It is necessary to investigate the interlaminar fracture characteristics of the laminated composites for the assurance of design and structural integrity. The three methods used to prepare the glass fiber reinforced plastic composites tested in this study were vacuum pressure impregnation, high pressure laminate (HPL), and prepreg laminate. We discuss the design criteria for safe application of composites and the shear-compressive test methods for evaluating mechanical properties of the material. Shear-compressive tests could be performed successfully using series-type test jigs that were inclined 0°, 30°, 45°, 60°, and 75° to the normal axis. Shear strength depends strongly on the applied compressive stress. The design range of allowable shear stress was extended by use of the appropriate composite fabrication method. HPL had the largest design range, and the allowable interlaminar shear stress was 0.254 times the compressive stress.

Performance characteristics of an excimer laser (XeCl) with single-stage magnetic pulse compression

NASA Astrophysics Data System (ADS)

Varshnay, N. K.; Singh, A.; Benerji, N. S.

2017-02-01

Performance characteristics of an excimer laser (XeCl) with single-stage magnetic pulse compression suitable for material processing applications are presented here. The laser incorporates in-built compact gas circulation and gas cooling to ensure fresh gas mixture between the electrodes for repetitive operation. A magnetically coupled tangential blower is used for gas circulation inside the laser chamber for repetitive operation. The exciter consists of C-C energy transfer circuit and thyratron is used as a high-voltage main switch with single-stage magnetic pulse compression (MPC) between thyratron and the laser electrodes. Low inductance of the laser head and uniform and intense pre-ionization are the main features of the electric circuit used in the laser. A 250 ns rise time voltage pulse was compressed to 100 ns duration with a single-stage magnetic pulse compressor using Ni-Zn ferrite cores. The laser can generate about 150 mJ at ˜100 Hz rep-rate reliably from a discharge volume of 100 cm 3. 2D spatial laser beam profile generated is presented here. The profile shows that the laser beam is completely filled with flat-top which is suitable for material processing applications. The SEM image of the microhole generated on copper target is presented here.

Asymmetry of Radial and Symmetry of Tangential Neuronal Migration Pathways in Developing Human Fetal Brains

PubMed Central

Miyazaki, Yuta; Song, Jae W.; Takahashi, Emi

2016-01-01

The radial and tangential neural migration pathways are two major neuronal migration streams in humans that are critical during corticogenesis. Corticogenesis is a complex process of neuronal proliferation that is followed by neuronal migration and the formation of axonal connections. Existing histological assessments of these two neuronal migration pathways have limitations inherent to microscopic studies and are confined to small anatomic regions of interest (ROIs). Thus, little evidence is available about their three-dimensional (3-D) fiber pathways and development throughout the entire brain. In this study, we imaged and analyzed radial and tangential migration pathways in the whole human brain using high-angular resolution diffusion MR imaging (HARDI) tractography. We imaged ten fixed, postmortem fetal (17 gestational weeks (GW), 18 GW, 19 GW, three 20 GW, three 21 GW and 22 GW) and eight in vivo newborn (two 30 GW, 34 GW, 35 GW and four 40 GW) brains with no neurological/pathological conditions. We statistically compared the volume of the left and right radial and tangential migration pathways, and the volume of the radial migration pathways of the anterior and posterior regions of the brain. In specimens 22 GW or younger, the volume of radial migration pathways of the left hemisphere was significantly larger than that of the right hemisphere. The volume of posterior radial migration pathways was also larger when compared to the anterior pathways in specimens 22 GW or younger. In contrast, no significant differences were observed in the radial migration pathways of brains older than 22 GW. Moreover, our study did not identify any significant differences in volumetric laterality in the tangential migration pathways. These results suggest that these two neuronal migration pathways develop and regress differently, and radial neuronal migration varies regionally based on hemispheric and anterior-posterior laterality, potentially explaining regional differences in

Correlation of compressive and shear stress with spalling of plasma-sprayed ceramic materials

NASA Technical Reports Server (NTRS)

Mullen, R. L.; Mcdonald, G.; Hendricks, R. C.; Hofle, M. M.

1983-01-01

Ceramics on metal substrates for potential use as high temperature seals or other applications are exposed to forces originating from differences in thermal expansion between the ceramic and the metal substrate. This report develops a relationship between the difference in expansion of the ceramic and the substrate, defines conditions under which shear between the ceramic and the substrate occurs, and those under which bending forces are produced in the ceramic. The off-axis effect of compression forces resulting from high temperature plastic flow of the ceramic producing buckling of the ceramic is developed. Shear is associated with the edge or boundary stresses on the component while bending is associated with the distortion of an interior region. Both modes are significant in predicting life of the ceramic. Previously announced in STAR as N83-27016

Effect of compressive stress on stability of N-doped p-type ZnO

NASA Astrophysics Data System (ADS)

Chen, Xingyou; Zhang, Zhenzhong; Yao, Bin; Jiang, Mingming; Wang, Shuangpeng; Li, Binghui; Shan, Chongxin; Liu, Lei; Zhao, Dongxu; Shen, Dezhen

2011-08-01

Nitrogen-doped p-type zinc oxide (p-ZnO:N) thin films were fabricated on a-/c-plane sapphire (a-/c-Al2O3) by plasma-assisted molecular beam epitaxy. Hall-effect measurements show that the p-type ZnO:N on c-Al2O3 degenerated into n-type after a preservation time; however, the one grown on a-Al2O3 showed good stability. The conversion of conductivity in the one grown on c-Al2O3 ascribed to the faster disappearance of NO and the growing N2(O), which is demonstrated by x-ray photoelectron spectroscopy (XPS). Compressive stress, caused by lattice misfit, was revealed by Raman spectra and optical absorption spectra, and it was regarded as the root of the instability in ZnO:N.

Compressive strength evolution of thermally-stressed Saint Maximin limestone.

NASA Astrophysics Data System (ADS)

Farquharson, J.; Griffiths, L.; Baud, P.; Wadsworth, F. B.; Heap, M. J.

2017-12-01

The Saint Maximin quarry (Oise, France) opened in the early 1600s, and its limestone has been used extensively as masonry stone, particularly during the classical era of Parisian architecture from the 17th century onwards. Its widespread use has been due to a combination of its regional availability, its high workability, and its aesthetic appeal. Notable buildings completed using this material include sections of the Place de la Concorde and the Louvre in Paris. More recently, however, it has seen increasing use in the construction of large private residences throughout the United States as well as extensions to private institutions such as Stanford University. For any large building, fire hazard can be a substantial concern, especially in tectonically active areas where catastrophic fires may arise following large-magnitude earthquakes. Typically, house fires burn at temperatures of around 600 °C ( 1000 F). Given the ubiquity of this geomaterial as a building stone, it is important to ascertain the influence of heating on the strength of Saint Maximin limestone (SML), and in turn the structural stability of the buildings it is used in. We performed a series of compressive tests and permeability measurements on samples of SML to determine its strength evolution in response to heating to incrementally higher temperatures. We observe that the uniaxial compressive strength of SML decreases from >12 MPa at room temperature to <7 MPa at 600 °C. The rate of strength reduction increases at elevated temperature (>400 °C). We anticipate that this substantial weakening is in part a result of thermal microcracking, whereby changes in temperature induce thermal stresses due to a mismatch in thermal expansion between the constituent grains. This mechanism is compounded by the volumetric increase of quartz through its alpha - beta transition at 573 °C, and by the thermal decomposition of calcite. To track the formation of thermal microcracks, we monitor acoustic emissions

Critical Compressive Stress for Flat Rectangular Plates Supported Along All Edges and Elastically Restrained Against Rotation along the Unloaded Edges

NASA Technical Reports Server (NTRS)

Lundquist, Eugene E; Stowell, Elbridge Z

1942-01-01

A chart is presented for the values of the coefficient in the formula for the critical compressive stress at which buckling may be expected to occur in flat rectangular plates supported along all edges and, in addition, elastically restrained against rotation along the unloaded edges. The mathematical derivations of the formulas required in the construction of the chart are given.

Drag reduction and thrust generation by tangential surface motion in flow past a cylinder

NASA Astrophysics Data System (ADS)

Mao, Xuerui; Pearson, Emily

2018-03-01

Sensitivity of drag to tangential surface motion is calculated in flow past a circular cylinder in both two- and three-dimensional conditions at Reynolds number Re ≤ 1000 . The magnitude of the sensitivity maximises in the region slightly upstream of the separation points where the contour lines of spanwise vorticity are normal to the cylinder surface. A control to reduce drag can be obtained by (negatively) scaling the sensitivity. The high correlation of sensitivities of controlled and uncontrolled flow indicates that the scaled sensitivity is a good approximation of the nonlinear optimal control. It is validated through direct numerical simulations that the linear range of the steady control is much higher than the unsteady control, which synchronises the vortex shedding and induces lock-in effects. The steady control injects angular momentum into the separating boundary layer, stabilises the flow and increases the base pressure significantly. At Re=100 , when the maximum tangential motion reaches 50% of the free-stream velocity, the vortex shedding, boundary-layer separation and recirculation bubbles are eliminated and 32% of the drag is reduced. When the maximum tangential motion reaches 2.5 times of the free-stream velocity, thrust is generated and the power savings ratio, defined as the ratio of the reduced drag power to the control input power, reaches 19.6. The mechanism of drag reduction is attributed to the change of the radial gradient of spanwise vorticity (partial r \\hat{ζ } ) and the subsequent accelerated pressure recovery from the uncontrolled separation points to the rear stagnation point.

Near-wall modelling of compressible turbulent flows

NASA Technical Reports Server (NTRS)

So, Ronald M. C.

1990-01-01

Work was carried out to extend the near-wall models formulated for the incompressible Reynolds stress equations to compressible flows. The idea of splitting the compressible dissipation function into a solenoidal part that is not sensitive to changes of compressibility indicators and a compressible part that is directly affected by these changes is adopted. This means that all models involving the dissipation rate could be expressed in terms of the solenoidal dissipation rate and an equation governing its transport could be formulated to close the set of compressible Reynolds stress equations. The near-wall modelling of the dissipation rate equation is investigated and its behavior near a wall is studied in detail using k-epsilon closure. It is found that all existing modelled equations give the wrong behavior for the dissipation rate near a wall. Improvements are suggested and the resultant behavior is found to be in good agreement with near-wall data. Furthermore, the present modified k-epsilon closure is used too calculate a flat plate boundary layer and the results are compared with four existing k-epsilon closures. These comparisons show that all closures tested give essentially the same flow properties, except in a region very close to the wall. In this region, the present k-epsilon closure calculations are in better agreement with measurements and direct simulation data; in particular, the behavior of the dissipation rate.

Compressive Failure of Fiber Composites under Multi-Axial Loading

NASA Technical Reports Server (NTRS)

Basu, Shiladitya; Waas, Anthony M.; Ambur, Damodar R.

2006-01-01

This paper examines the compressive strength of a fiber reinforced lamina under multi-axial stress states. An equilibrium analysis is carried out in which a kinked band of rotated fibers, described by two angles, is sandwiched between two regions in which the fibers are nominally straight. Proportional multi-axial stress states are examined. The analysis includes the possibility of bifurcation from the current equilibrium state. The compressive strength of the lamina is contingent upon either attaining a load maximum in the equilibrium response or satisfaction of a bifurcation condition, whichever occurs first. The results show that for uniaxial loading a non-zero kink band angle beta produces the minimum limit load. For multi-axial loading, different proportional loading paths show regimes of bifurcation dominated and limit load dominated behavior. The present results are able to capture the beneficial effect of transverse compression in raising the composite compressive strength as observed in experiments.

Compressibility of 304 Stainless Steel Powder Metallurgy Materials Reinforced with 304 Short Stainless Steel Fibers

PubMed Central

Yao, Bibo; Zhou, Zhaoyao; Duan, Liuyang; Xiao, Zhiyu

2016-01-01

Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders and 304 short stainless steel fibers, which were alternately laid in layers according to mass ratio. In this paper, the compressive properties of the P/M materials were characterized by a series of uniaxial compression tests. The effects of fiber content, compaction pressure and high temperature nitriding on compressive properties were investigated. The results indicated that, without nitriding, the samples changed from cuboid to cydariform without damage in the process of compression. The compressive stress was enhanced with increasing fiber content ranging from 0 to 8 wt.%. For compaction pressure from 55 to 75 MPa, greater compaction pressure improved compressive stress. Moreover, high temperature nitriding was able to significantly improve the yield stress, but collapse failure eventually occurred. PMID:28773285

Compressibility of 304 Stainless Steel Powder Metallurgy Materials Reinforced with 304 Short Stainless Steel Fibers.

PubMed

Yao, Bibo; Zhou, Zhaoyao; Duan, Liuyang; Xiao, Zhiyu

2016-03-04

Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders and 304 short stainless steel fibers, which were alternately laid in layers according to mass ratio. In this paper, the compressive properties of the P/M materials were characterized by a series of uniaxial compression tests. The effects of fiber content, compaction pressure and high temperature nitriding on compressive properties were investigated. The results indicated that, without nitriding, the samples changed from cuboid to cydariform without damage in the process of compression. The compressive stress was enhanced with increasing fiber content ranging from 0 to 8 wt.%. For compaction pressure from 55 to 75 MPa, greater compaction pressure improved compressive stress. Moreover, high temperature nitriding was able to significantly improve the yield stress, but collapse failure eventually occurred.

Quasi-static and ratcheting properties of trabecular bone under uniaxial and cyclic compression.

PubMed

Gao, Li-Lan; Wei, Chao-Lei; Zhang, Chun-Qiu; Gao, Hong; Yang, Nan; Dong, Li-Min

2017-08-01

The quasi-static and ratcheting properties of trabecular bone were investigated by experiments and theoretical predictions. The creep tests with different stress levels were completed and it is found that both the creep strain and creep compliance increase rapidly at first and then increase slowly as the creep time goes by. With increase of compressive stress the creep strain increases and the creep compliance decreases. The uniaxial compressive tests show that the applied stress rate makes remarkable influence on the compressive behaviors of trabecular bone. The Young's modulus of trabecular bone increases with increase of stress rate. The stress-strain hysteresis loops of trabecular bone under cyclic load change from sparse to dense with increase of number of cycles, which agrees with the change trend of ratcheting strain. The ratcheting strain rate rapidly decreases at first, and then exhibits a relatively stable and small value after 50cycles. Both the ratcheting strain and ratcheting strain rate increase with increase of stress amplitude or with decrease of stress rate. The creep model and the nonlinear viscoelastic constitutive model of trabecular bone were proposed and used to predict its creep property and rate-dependent compressive property. The results show that there are good agreements between the experimental data and predictions. Copyright © 2017 Elsevier B.V. All rights reserved.

Improved compression molding process

NASA Technical Reports Server (NTRS)

Heier, W. C.

1967-01-01

Modified compression molding process produces plastic molding compounds that are strong, homogeneous, free of residual stresses, and have improved ablative characteristics. The conventional method is modified by applying a vacuum to the mold during the molding cycle, using a volatile sink, and exercising precise control of the mold closure limits.

Fracture in compression of brittle solids

NASA Technical Reports Server (NTRS)

1983-01-01

The fracture of brittle solids in monotonic compression is reviewed from both the mechanistic and phenomenological points of view. The fundamental theoretical developments based on the extension of pre-existing cracks in general multiaxial stress fields are recognized as explaining extrinsic behavior where a single crack is responsible for the final failure. In contrast, shear faulting in compression is recognized to be the result of an evolutionary localization process involving en echelon action of cracks and is termed intrinsic.

Compressive buckling of black phosphorene nanotubes: an atomistic study

NASA Astrophysics Data System (ADS)

Nguyen, Van-Trang; Le, Minh-Quy

2018-04-01

We investigate through molecular dynamics finite element method with Stillinger-Weber potential the uniaxial compression of armchair and zigzag black phosphorene nanotubes. We focus especially on the effects of the tube’s diameter with fixed length-diameter ratio, effects of the tube’s length for a pair of armchair and zigzag tubes of equal diameters, and effects of the tube’s diameter with fixed lengths. Their Young’s modulus, critical compressive stress and critical compressive strain are studied and discussed for these 3 case studies. Compressive buckling was clearly observed in the armchair nanotubes. Local bond breaking near the boundary occurred in the zigzag ones under compression.

Flow Stress and Processing Map of a PM 8009Al/SiC Particle Reinforced Composite During Hot Compression

NASA Astrophysics Data System (ADS)

Luo, Haibo; Teng, Jie; Chen, Shuang; Wang, Yu; Zhang, Hui

2017-10-01

Hot compression tests of 8009Al alloy reinforced with 15% SiC particles (8009Al/15%SiCp composites) prepared by powder metallurgy (direct hot extrusion methods) were performed on Gleeble-3500 system in the temperature range of 400-550 °C and strain rate range of 0.001-1 s-1. The processing map based on the dynamic material model was established to evaluate the flow instability regime and optimize processing parameters; the associated microstructural changes were studied by the observations of optical metallographic and scanning electron microscopy. The results showed that the flow stress increased initially and reached a plateau after peak stress value with increasing strain. The peak stress increased as the strain rate increased and deformation temperature decreased. The optimum parameters were identified to be deformation temperature range of 500-550 °C and strain rate range of 0.001-0.02 s-1 by combining the processing map with microstructural observation.

Longitudinal residual stresses in boron fibers

NASA Technical Reports Server (NTRS)

Behrendt, D. R.

1976-01-01

A method of measuring the longitudinal residual stress distribution in boron fibers is presented. The residual stresses in commercial CVD boron on tungsten fibers of 102, 142, and 203 microns (4, 5.6, and 8 mil) diameters were determined. Results for the three sizes show a compressive stress at the surface 800 to -1400 MN/sq m 120 to -200 ksi), changing monotonically to a region of tensile stress within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile 600 to 1000 MN/sq m(90 to 150 ksi) and then decreases to compressive near the tungsten boride core. The core itself is under a compressive stress of approximately -1300 MN/sq m (-190 ksi). The effects of surface removal on core residual stress and core-initiated fracture are discussed.

Electromechanical Apparatus Measures Residual Stress

NASA Technical Reports Server (NTRS)

Chern, Engmin J.; Flom, Yury

1993-01-01

Nondestructive test exploits relationship between stress and eddy-current-probe resistance. Yields data on residual stress or strain in metal tension/compression specimen (stress or strain remaining in specimen when no stress applied from without). Apparatus is assembly of commercial equipment: tension-or-compression testing machine, eddy-current probe, impedance gain-and-phase analyzer measuring impedance of probe coil, and desktop computer, which controls other equipment and processes data received from impedance gain-and-phase analyzer.

Effect of Impact Compression on the Age-Hardening of Rapidly Solidified Al-Zn-Mg Base Alloys

NASA Astrophysics Data System (ADS)

Horikawa, Keitaro; Kobayashi, Hidetoshi

Effect of impact compression on the age-hardening behavior and the mechanical properties of Mesoalite aluminum alloy was examined by means of the high-velocity plane collision between a projectile and Mesoalite by using a single powder gun. By imposing the impact compression to the Meso10 and Meso20 alloys in the state of quenching after the solution heat treatment, the following age-hardening at 110 °C was highly increased, comparing with the Mesoalite without the impact compression. XRD results revealed that high plastic strain was introduced on the specimen inside after the impact compression. Compression test results also clarified that both Meso10 and Meso20 alloy specimens imposed the impact compressive stresses more than 5 GPa after the peak-aging at 110°C showed higher yield stresses, comparing with the alloys without the impact compression. It was also shown that the Meso10 and Meso20 specimens after the solution heat treatment, followed by the high-velocity impact compression (12 GPa) and the peak-aging treatment indicated the highest compressive yield stresses such as 994 GPa in Meso10 and 1091 GPa in Meso20.

Tensile and Compressive Constitutive Response of 316 Stainless Steel at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Manson, S. S.; Muralidharan, U.; Halford, G. R.

1983-01-01

Creep rate in compression is lower by factors of 2 to 10 than in tension if the microstructure of the two specimens is the same and are tested at equal temperatures and equal but opposite stresses. Such behavior is characteristic for monotonic creep and conditions involving cyclic creep. In the latter case creep rate in both tension and compression progressively increases from cycle to cycle, rendering questionable the possibility of expressing a time stabilized constitutive relationship. The difference in creep rates in tension and compression is considerably reduced if the tension specimen is first subjected to cycles of tensile creep (reversed by compressive plasticity), while the compression specimen is first subjected to cycles of compressive creep (reversed by tensile plasticity). In both cases, the test temperature is the same and the stresses are equal and opposite. Such reduction is a reflection of differences in microstructure of the specimens resulting from different prior mechanical history.

Tensile and compressive constitutive response of 316 stainless steel at elevated temperatures

NASA Technical Reports Server (NTRS)

Manson, S. S.; Muralidharan, U.; Halford, G. R.

1982-01-01

It is demonstrated that creep rate of 316 SS is lower by factors of 2 to 10 in compression than in tension if the microstructure is the same and tests are conducted at identical temperatures and equal but opposite stresses. Such behavior was observed for both monotonic creep and conditions involving cyclic creep. In the latter case creep rate in both tension and compression progressively increases from cycle to cycle, rendering questionable the possibility of expressing a time-stabilized constitutive relationship. The difference in creep rates in tension and compression is considerably reduced if the tension specimen is first subjected to cycles of tensile creep (reversed by compressive plasticity), while the compression specimen is first subjected to cycles of compressive creep (reversed by tensile plasticity). In both cases, the test temperature is the same and the stresses are equal and opposite. Such reduction is a reflection of differences in microstructure of the specimens resulting from different prior mechanical history.

Tensile and pack compressive tests of some sheets of aluminum alloy, 1025 carbon steel, and chromium-nickel steel

NASA Technical Reports Server (NTRS)

Atchison, C S; Miller, James A

1942-01-01

Tensile and compressive stress-strain curves, stress-deviation curves, and secant modulus-stress curves are given for longitudinal and transverse specimens of 17S-T, 24S-T, and 24S-RT aluminum-alloy sheet in thicknesses from 0.032 to 0.081 inch, 1025 carbon steel sheet in thicknesses of 0.054 and 0.120 inch, and chromium-nickel steel sheet in thicknesses form 0.020 to 0.0275 inch. Significant differences were found between the tensile and the compressive stress-strain curves, and also the corresponding corollary curves; similarly, differences were found between the curves for the longitudinal and transverse directions. These differences are of particular importance in considering the compressive strength of aircraft structures made of thin sheet. They are explored further for the case of compression by giving tangent modulus-stress curves in longitudinal and transverse compression and dimensionless curves of the ratio of tangent modulus to Young's modulus and of the ratio of reduced modulus for a rectangular section to Young's modulus, both plotted against the ratio of stress to secant yield strength.

Exploratory Investigation into the Durability of Beneficial Cold Worked Fastener Hole in Aluminum

NASA Technical Reports Server (NTRS)

Johnson, W. S.; Clark, David A.

1999-01-01

Cold working fastener holes in aluminum alloys is a widely used technique in the aerospace industry for improving the fatigue performance of structures. A compressive tangential stress introduced in the material during the cold working of the hole reduces the natural tendency of the material to crack at the holes under cyclic tensile loading. It is a lucrative technique for the aerospace industry in that it provides an increase in performance without any weight cost.

DEMONSTRATION OF SORBENT INJECTION TECHNOLOGY ON A TANGENTIALLY COAL-FIRED UTILITY BOILER (YORKTOWN LIMB DEMONSTRATION)

EPA Science Inventory

The report summarizes activities conducted and results achieved in an EPA-sponsored program to demonstrate Limestone Injection Multistage Burner (LIMB) technology on a tangentially fired coal-burning utility boiler, Virginia Power's 180-MWe Yorktown Unit No. 2. his successfully d...

Ramp compression of magnesium oxide to 234 GPa

DOE PAGES

Wang, Jue; Smith, R. F.; Coppari, F.; ...

2014-05-07

Single-crystal magnesium oxide (MgO) samples were ramp compressed to above 200 GPa pressure at the Omega laser facility. Multi-stepped MgO targets were prepared using lithography and wet etching techniques. Free surface velocities of ramp-compressed MgO were measured with a VISAR. The sound velocity and stress-density response were determined using an iterative Lagrangian analysis. The measured equation of state is consistent with expectations from previous shock and static data as well as with a recent X-ray diffraction measurement under ramp loading. The peak elastic stresses observed in our samples had amplitudes of 3-5.5 GPa, decreasing with propagation distance.

Morphological changes in polycrystalline Fe after compression and release

NASA Astrophysics Data System (ADS)

Gunkelmann, Nina; Tramontina, Diego R.; Bringa, Eduardo M.; Urbassek, Herbert M.

2015-02-01

Despite a number of large-scale molecular dynamics simulations of shock compressed iron, the morphological properties of simulated recovered samples are still unexplored. Key questions remain open in this area, including the role of dislocation motion and deformation twinning in shear stress release. In this study, we present simulations of homogeneous uniaxial compression and recovery of large polycrystalline iron samples. Our results reveal significant recovery of the body-centered cubic grains with some deformation twinning driven by shear stress, in agreement with experimental results by Wang et al. [Sci. Rep. 3, 1086 (2013)]. The twin fraction agrees reasonably well with a semi-analytical model which assumes a critical shear stress for twinning. On reloading, twins disappear and the material reaches a very low strength value.

Proceedings of the Scientific Data Compression Workshop

NASA Technical Reports Server (NTRS)

Ramapriyan, H. K. (Editor)

1989-01-01

Continuing advances in space and Earth science requires increasing amounts of data to be gathered from spaceborne sensors. NASA expects to launch sensors during the next two decades which will be capable of producing an aggregate of 1500 Megabits per second if operated simultaneously. Such high data rates cause stresses in all aspects of end-to-end data systems. Technologies and techniques are needed to relieve such stresses. Potential solutions to the massive data rate problems are: data editing, greater transmission bandwidths, higher density and faster media, and data compression. Through four subpanels on Science Payload Operations, Multispectral Imaging, Microwave Remote Sensing and Science Data Management, recommendations were made for research in data compression and scientific data applications to space platforms.

The start-up of a gas turbine engine using compressed air tangentially fed onto the blades of the basic turbine

NASA Technical Reports Server (NTRS)

Slobodyanyuk, L. K.; Dayneko, V. I.

1983-01-01

The use of compressed air was suggested to increase the reliability and motor lifetime of a gas turbine engine. Experiments were carried out and the results are shown in the form of the variation in circumferential force as a function of the entry angle of the working jet onto the turbine blade. The described start-up method is recommended for use with massive rotors.

Strength of inserts in titanium alloy machining

NASA Astrophysics Data System (ADS)

Kozlov, V.; Huang, Z.; Zhang, J.

2016-04-01

In this paper, a stressed state of a non-worn cutting wedge in a machined titanium alloy (Ti6Al2Mo2Cr) is analyzed. The distribution of contact loads on the face of a cutting tool was obtained experimentally with the use of a ‘split cutting tool’. Calculation of internal stresses in the indexable insert made from cemented carbide (WC8Co) was carried out with the help of ANSYS 14.0 software. Investigations showed that a small thickness of the cutting insert leads to extremely high compressive stresses near the cutting edge, stresses that exceed the ultimate compressive strength of cemented carbide. The face and the base of the insert experience high tensile stresses, which approach the ultimate tensile strength of cemented carbide and increase a probability of cutting insert destruction. If the thickness of the cutting insert is bigger than 5 mm, compressive stresses near the cutting edge decrease, and tensile stresses on the face and base decrease to zero. The dependences of the greatest normal and tangential stresses on thickness of the cutting insert were found. Abbreviation and symbols: m/s - meter per second (cutting speed v); mm/r - millimeter per revolution (feed rate f); MPa - mega Pascal (dimension of specific contact loads and stresses); γ - rake angle of the cutting tool [°] α - clearance angle of the sharp cutting tool [°].

Measurement of seismometer orientation using the tangential P-wave receiver function based on harmonic decomposition

NASA Astrophysics Data System (ADS)

Lim, Hobin; Kim, YoungHee; Song, Teh-Ru Alex; Shen, Xuzhang

2018-03-01

Accurate determination of the seismometer orientation is a prerequisite for seismic studies including, but not limited to seismic anisotropy. While borehole seismometers on land produce seismic waveform data somewhat free of human-induced noise, they might have a drawback of an uncertain orientation. This study calculates a harmonic decomposition of teleseismic receiver functions from the P and PP phases and determines the orientation of a seismometer by minimizing a constant term in a harmonic expansion of tangential receiver functions in backazimuth near and at 0 s. This method normalizes the effect of seismic sources and determines the orientation of a seismometer without having to assume for an isotropic medium. Compared to the method of minimizing the amplitudes of a mean of the tangential receiver functions near and at 0 s, the method yields more accurate orientations in cases where the backazimuthal coverage of earthquake sources (even in the case of ocean bottom seismometers) is uneven and incomplete. We apply this method to data from the Korean seismic network (52 broad-band velocity seismometers, 30 of which are borehole sensors) to estimate the sensor orientation in the period of 2005-2016. We also track temporal changes in the sensor orientation through the change in the polarity and the amplitude of the tangential receiver function. Six borehole stations are confirmed to experience a significant orientation change (10°-180°) over the period of 10 yr. We demonstrate the usefulness of our method by estimating the orientation of ocean bottom sensors, which are known to have high noise level during the relatively short deployment period.

Roll-Yaw control at high angle of attack by forebody tangential blowing

NASA Technical Reports Server (NTRS)

Pedreiro, N.; Rock, S. M.; Celik, Z. Z.; Roberts, L.

1995-01-01

The feasibility of using forebody tangential blowing to control the roll-yaw motion of a wind tunnel model is experimentally demonstrated. An unsteady model of the aerodynamics is developed based on the fundamental physics of the flow. Data from dynamic experiments is used to validate the aerodynamic model. A unique apparatus is designed and built that allows the wind tunnel model two degrees of freedom, roll and yaw. Dynamic experiments conducted at 45 degrees angle of attack reveal the system to be unstable. The natural motion is divergent. The aerodynamic model is incorporated into the equations of motion of the system and used for the design of closed loop control laws that make the system stable. These laws are proven through dynamic experiments in the wind tunnel using blowing as the only actuator. It is shown that asymmetric blowing is a highly non-linear effector that can be linearized by superimposing symmetric blowing. The effects of forebody tangential blowing and roll and yaw angles on the flow structure are determined through flow visualization experiments. The transient response of roll and yaw moments to a step input blowing are determined. Differences on the roll and yaw moment dependence on blowing are explained based on the physics of the phenomena.

Roll-yaw control at high angle of attack by forebody tangential blowing

NASA Technical Reports Server (NTRS)

Pedreiro, N.; Rock, S. M.; Celik, Z. Z.; Roberts, L.

1995-01-01

The feasibility of using forebody tangential blowing to control the roll-yaw motion of a wind tunnel model is experimentally demonstrated. An unsteady model of the aerodynamics is developed based on the fundamental physics of the flow. Data from dynamic experiments is used to validate the aerodynamic model. A unique apparatus is designed and built that allows the wind tunnel model two degrees of freedom, roll and yaw. Dynamic experiments conducted at 45 degrees angle of attack reveal the system to be unstable. The natural motion is divergent. The aerodynamic model is incorporated into the equations of motion of the system and used for the design of closed loop control laws that make the system stable. These laws are proven through dynamic experiments in the wind tunnel using blowing as the only actuator. It is shown that asymmetric blowing is a highly non-linear effector that can be linearized by superimposing symmetric blowing. The effects of forebody tangential blowing and roll and yaw angles on the flow structure are determined through flow visualization experiments. The transient response of roll and yaw moments to a step input blowing are determined. Differences on the roll and yaw moment dependence on blowing are explained based on the physics of the phenomena.

DNABIT Compress - Genome compression algorithm.

PubMed

Rajarajeswari, Pothuraju; Apparao, Allam

2011-01-22

Data compression is concerned with how information is organized in data. Efficient storage means removal of redundancy from the data being stored in the DNA molecule. Data compression algorithms remove redundancy and are used to understand biologically important molecules. We present a compression algorithm, "DNABIT Compress" for DNA sequences based on a novel algorithm of assigning binary bits for smaller segments of DNA bases to compress both repetitive and non repetitive DNA sequence. Our proposed algorithm achieves the best compression ratio for DNA sequences for larger genome. Significantly better compression results show that "DNABIT Compress" algorithm is the best among the remaining compression algorithms. While achieving the best compression ratios for DNA sequences (Genomes),our new DNABIT Compress algorithm significantly improves the running time of all previous DNA compression programs. Assigning binary bits (Unique BIT CODE) for (Exact Repeats, Reverse Repeats) fragments of DNA sequence is also a unique concept introduced in this algorithm for the first time in DNA compression. This proposed new algorithm could achieve the best compression ratio as much as 1.58 bits/bases where the existing best methods could not achieve a ratio less than 1.72 bits/bases.

Thermoelastic Stress Analysis: An NDE Tool for the Residual Stress Assessment of Metallic Alloys

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.; Baaklini, George Y.

2000-01-01

During manufacturing, certain propulsion components that will be used in a cyclic fatigue environment are fabricated to contain compressive residual stresses on their surfaces because these stresses inhibit the nucleation of cracks. Overloads and elevated temperature excursions cause the induced residual stresses to dissipate while the component is still in service, lowering its resistance to crack initiation. Research at the NASA Glenn Research Center at Lewis Field has focused on employing the Thermoelastic Stress Analysis technique (TSA, also recognized as SPATE: Stress Pattern Analysis by Thermal Emission) as a tool for monitoring the residual stress state of propulsion components. TSA is based on the fact that materials experience small temperature changes when they are compressed or expanded. When a structure is cyclically loaded (i.e., cyclically compressed and expanded), the resulting surface-temperature profile correlates to the stress state of the structure s surface. The surface-temperature variations resulting from a cyclic load are measured with an infrared camera. Traditionally, the temperature amplitude of a TSA signal has been theoretically defined to be linearly dependent on the cyclic stress amplitude. As a result, the temperature amplitude resulting from an applied cyclic stress was assumed to be independent of the cyclic mean stress.

Jamming by compressing a system of granular crosses

NASA Astrophysics Data System (ADS)

Zheng, Hu; Wang, Dong; Barés, Jonathan; Behringer, Robert

2017-06-01

A disordered stress-free granular packing can be jammed, transformed into a mechanically rigid structure, by increasing the density of particles or by applying shear deformation. The jamming behavior of systems made of 2D circular discs has been investigated in detail, but very little is known about jamming for non-spherical particles, and particularly, non-convex particles. Here, we perform an experimental study on jamming by compression of a system of quasi-2D granular crosses made of photo-elastic crosses. We measure the pressure evolution during cyclic compression and decompression. The Jamming packing fraction of these quasi-2D granular crosses is ϕJ ≃ 0.475, which is much smaller than the value ϕJ ≃ 0.84 for-2D granular disks. The packing fraction shifts systematically to higher values under compressive cycling, corresponding to systematic shifts in the stress-strain response curves. Associated with these shifts are rotations of the crosses, with minimal changes in their centers of mass.

INTRINSIC CURVATURE: A MARKER OF MILLIMETER-SCALE TANGENTIAL CORTICO-CORTICAL CONNECTIVITY?

PubMed Central

RONAN, LISA; PIENAAR, RUDOLPH; WILLIAMS, GUY; BULLMORE, ED; CROW, TIM J.; ROBERTS, NEIL; JONES, PETER B.; SUCKLING, JOHN; FLETCHER, PAUL C.

2012-01-01

In this paper, we draw a link between cortical intrinsic curvature and the distributions of tangential connection lengths. We suggest that differential rates of surface expansion not only lead to intrinsic curvature of the cortical sheet, but also to differential inter-neuronal spacing. We propose that there follows a consequential change in the profile of neuronal connections: specifically an enhancement of the tendency towards proportionately more short connections. Thus, the degree of cortical intrinsic curvature may have implications for short-range connectivity. PMID:21956929

Buckling vs. particle desorption in a particle-covered drop subject to compressive surface stresses: a simulation study.

PubMed

Gu, Chuan; Botto, Lorenzo

2018-01-31

Predicting the behaviour of particle-covered fluid interfaces under compression has implications in several fields. The surface-tension driven adhesion of particles to drops and bubbles is exploited for example to enhance the stability of foams and emulsion and develop new generation materials. When a particle-covered fluid interface is compressed, one can observe either smooth buckling or particle desorption from the interface. The microscopic mechanisms leading to the buckling-to-desorption transition are not fully understood. In this paper we simulate a spherical drop covered by a monolayer of spherical particles. The particle-covered interface is subject to time-dependent compressive surface stresses that mimic the slow deflation of the drop. The buckling-to-desorption transition depends in a non-trivial way on three non-dimensional parameters: the ratio Π s /γ of particle-induced surface pressure and bare surface tension, the ratio a/R of particle and drop radii, and the parameter f characterising the strength of adhesion of each particle to the interface. Based on the insights from the simulations, we propose a configuration diagram describing the effect of these controlling parameters. We find that particle desorption is highly correlated with a mechanical instability that produces small-scale undulations of the monolayer of the order of the particle size that grow when the surface pressure is sufficiently large. We argue that the large local curvature associated with these small undulations can produce large normal forces, enhancing the probability of desorption.

Experimental Characteristics of Dry Stack Masonry under Compression and Shear Loading

PubMed Central

Lin, Kun; Totoev, Yuri Zarevich; Liu, Hongjun; Wei, Chunli

2015-01-01

The behavior of dry stack masonry (DSM) is influenced by the interaction of the infill with the frame (especially the joints between bricks), which requires further research. This study investigates the compression and shear behaviors of DSM. First, a series of compression tests were carried out on both masonry prism with mortar (MP_m) and DSM prism (MP_ds). The failure mode of each prism was determined. Different from the MP_m, the stress-strain relationship of the MP_ds was characterized by an upward concavity at the initial stage. The compression strength of the MP_ds was slightly reduced by 15%, while the elastic modulus was reduced by over 62%. In addition, 36 shear-compression tests were carried out under cyclic loads to emphasize the influence of various loads on the shear-compression behavior of DSM. The results showed that the Mohr-Coulomb friction law adequately represents the failure of dry joints at moderate stress levels, and the varying friction coefficients under different load amplitudes cannot be neglected. The experimental setup and results are valuable for further research. PMID:28793741

Experimental Characteristics of Dry Stack Masonry under Compression and Shear Loading.

PubMed

Lin, Kun; Totoev, Yuri Zarevich; Liu, Hongjun; Wei, Chunli

2015-12-12

The behavior of dry stack masonry (DSM) is influenced by the interaction of the infill with the frame (especially the joints between bricks), which requires further research. This study investigates the compression and shear behaviors of DSM. First, a series of compression tests were carried out on both masonry prism with mortar (MP_m) and DSM prism (MP_ds). The failure mode of each prism was determined. Different from the MP_m, the stress-strain relationship of the MP_ds was characterized by an upward concavity at the initial stage. The compression strength of the MP_ds was slightly reduced by 15%, while the elastic modulus was reduced by over 62%. In addition, 36 shear-compression tests were carried out under cyclic loads to emphasize the influence of various loads on the shear-compression behavior of DSM. The results showed that the Mohr-Coulomb friction law adequately represents the failure of dry joints at moderate stress levels, and the varying friction coefficients under different load amplitudes cannot be neglected. The experimental setup and results are valuable for further research.

Multilayer compressive seal for sealing in high temperature devices

DOEpatents

Chou, Yeong-Shyung [Richland, WA; Stevenson, Jeffry W [Richland, WA

2007-08-21

A mica based compressive seal has been developed exhibiting superior thermal cycle stability when compared to other compressive seals known in the art. The seal is composed of compliant glass or metal interlayers and a sealing (gasket) member layer composed of mica that is infiltrated with a glass forming material, which effectively reduces leaks within the seal. The compressive seal shows approximately a 100-fold reduction in leak rates compared with previously developed hybrid seals after from 10 to about 40 thermal cycles under a compressive stress of from 50 psi to 100 psi at temperatures in the range from 600.degree. C. to about 850.degree. C.

Predicting the compressibility behaviour of tire shred samples for landfill applications.

PubMed

Warith, M A; Rao, Sudhakar M

2006-01-01

Tire shreds have been used as an alternative to crushed stones (gravel) as drainage media in landfill leachate collection systems. The highly compressible nature of tire shreds (25-47% axial strain on vertical stress applications of 20-700 kPa) may reduce the thickness of the tire shred drainage layer to less than 300 mm (minimum design requirement) during the life of the municipal solid waste landfill. There hence exists a need to predict axial strains of tire shred samples in response to vertical stress applications so that the initial thickness of the tire shred drainage layer can be corrected for compression. The present study performs one-dimensional compressibility tests on four tire shred samples and compares the results with stress/strain curves from other studies. The stress/strain curves are developed into charts for choosing the correct initial thickness of tire shred layers that maintain the minimum thickness of 300 mm throughout the life of the landfill. The charts are developed for a range of vertical stresses based on the design height of municipal waste cell and bulk unit weight of municipal waste. Experimental results also showed that despite experiencing large axial strains, the average permeability of the tire shred sample consistently remained two to three orders of magnitude higher than the design performance criterion of 0.01cm/s for landfill drainage layers. Laboratory experiments, however, need to verify whether long-term chemical and bio-chemical reactions between landfill leachate and the tire shred layer will deteriorate their mechanical functions (hydraulic conductivity, compressibility, strength) beyond permissible limits for geotechnical applications.

Refraction of the principal stress trajectories and the stress jumps on faults and contact surfaces: Part 1. Non-constrained regular trajectories

NASA Astrophysics Data System (ADS)

Mukhamediev, Sh. A.

2014-09-01

Rock masses contain ubiquitous multiscale heterogeneities, which (or whose boundaries) serve as the surfaces of discontinuity for some characteristics of the stress state, e.g., for the orientation of principal stress axes. Revealing the regularities that control these discontinuities is a key to understanding the processes taking place at the boundaries of the heterogeneities and for designing the correct procedures for reconstructing and theoretical modeling of tectonic stresses. In the present study, the local laws describing the refraction of the axes of extreme principal stresses T 1 (maximal tension in the deviatoric sense) and T 3 (maximal compression) of the Cauchy stress tensor at the transition over the elementary area n of discontinuity whose orientation is specified by the unit normal n are derived. It is assumed that on the area n of discontinuity, frictional contact takes place. No hypotheses are made on the constitutive equations, and a priori constraints are not posed on the orientation on the stress axes. Two domains, which adjoin area n on the opposite sides and are conventionally marked + and -, are distinguished. In the case of the two-dimensional (2D) stress state, any principal stress axis on passing from domain - to domain + remains in the same quadrant of the plane as the continuation of this axis in domain +. The sign and size of the refraction angle depend on the sign and amplitude of the jump of the normal stress, which is tangential to the surface of discontinuity. In the three-dimensional (3D) case, the refraction of axes T 1 and T 3 should be analyzed simultaneously. For each side, + and -, the projections of the T 1 and T 3 axes on the generally oriented plane n form the shear sectors S + and S -, which are determined unambiguously and to whose angular domains the possible directions p + and p - of the shear stress vectors belong. In order for the extreme stress axes T {1/+}, T {3/+} and T {1/-}, T {3/-} to be statically compatible on

Dimensional Changes of Tracheids during Drying of Radiata Pine (Pinus radiata D. Don) Compression Woods: A Study Using Variable-Pressure Scanning Electron Microscopy (VP-SEM)

PubMed Central

Zhang, Miao; Smith, Bronwen G.; McArdle, Brian H.; Chavan, Ramesh R.; James, Bryony J.

2018-01-01

Variable-pressure scanning electron microscopy was used to investigate the dimensional changes in longitudinal, tangential and radial directions, on wetting and drying, of tracheids of opposite wood (OW) and three grades of compression woods (CWs), including severe CW (SCW) and two grades of mild compression wood (MCW) (MCW1 and MCW2) in corewood of radiata pine (Pinus radiata) saplings. The CW was formed on the underside and OW on the upper side of slightly tilted stems. In the longitudinal direction, the shrinkage of SCW tracheids was ~300% greater than that of OW tracheids, with the shrinkage of the MCW1 and MCW2 tracheids being intermediate. Longitudinal swelling was also investigated and hysteresis was demonstrated for the tracheids of all corewood types, with the extent of hysteresis increasing with CW severity. A statistical association was found between longitudinal shrinkage and the content of lignin and galactosyl residues in the cell-wall matrix. The galactosyl residues are present mostly as (1→4)-β-galactans, which are known to have a high capacity for binding water and swell on hydration. The small proportions of (1→3)-β-glucans in the CWs have similar properties. These polysaccharides may play a functional role in the longitudinal shrinking and swelling of CW tracheids. Tangential shrinkage of tracheids was greater than radial shrinkage but both were greatest for OW and least for SCW, with the MCW1 and MCW2 being intermediate. PMID:29495536

Effect of pressure on tangential-injection film cooling in a combustor exhaust stream

NASA Technical Reports Server (NTRS)

Marek, C. J.

1973-01-01

A tangential-injection film cooled test section was placed in the exhaust stream of a high pressure combustor. Film cooling data were taken at pressure of 1, 10, and 20 atmospheres. The film cooling effectiveness was found to be independent of pressure. The data were correlated adequately by a turbulent-mixing film cooling correlation with a turbulent-mixing coefficient of 0.05 + or - 0.02.

Compression failure of angle-ply laminates

NASA Technical Reports Server (NTRS)

Peel, Larry D.; Hyer, Michael W.; Shuart, Mark J.

1991-01-01

The present work deals with modes and mechanisms of failure in compression of angle-ply laminates. Experimental results were obtained from 42 angle-ply IM7/8551-7a specimens with a lay-up of ((plus or minus theta)/(plus or minus theta)) sub 6s where theta, the off-axis angle, ranged from 0 degrees to 90 degrees. The results showed four failure modes, these modes being a function of off-axis angle. Failure modes include fiber compression, inplane transverse tension, inplane shear, and inplane transverse compression. Excessive interlaminar shear strain was also considered as an important mode of failure. At low off-axis angles, experimentally observed values were considerably lower than published strengths. It was determined that laminate imperfections in the form of layer waviness could be a major factor in reducing compression strength. Previously developed linear buckling and geometrically nonlinear theories were used, with modifications and enhancements, to examine the influence of layer waviness on compression response. The wavy layer is described by a wave amplitude and a wave length. Linear elastic stress-strain response is assumed. The geometrically nonlinear theory, in conjunction with the maximum stress failure criterion, was used to predict compression failure and failure modes for the angle-ply laminates. A range of wave length and amplitudes were used. It was found that for 0 less than or equal to theta less than or equal to 15 degrees failure was most likely due to fiber compression. For 15 degrees less than theta less than or equal to 35 degrees, failure was most likely due to inplane transverse tension. For 35 degrees less than theta less than or equal to 70 degrees, failure was most likely due to inplane shear. For theta less than 70 degrees, failure was most likely due to inplane transverse compression. The fiber compression and transverse tension failure modes depended more heavily on wave length than on wave amplitude. Thus using a single

Predicting the shock compression response of heterogeneous powder mixtures

NASA Astrophysics Data System (ADS)

Fredenburg, D. A.; Thadhani, N. N.

2013-06-01

A model framework for predicting the dynamic shock-compression response of heterogeneous powder mixtures using readily obtained measurements from quasi-static tests is presented. Low-strain-rate compression data are first analyzed to determine the region of the bulk response over which particle rearrangement does not contribute to compaction. This region is then fit to determine the densification modulus of the mixture, σD, an newly defined parameter describing the resistance of the mixture to yielding. The measured densification modulus, reflective of the diverse yielding phenomena that occur at the meso-scale, is implemented into a rate-independent formulation of the P-α model, which is combined with an isobaric equation of state to predict the low and high stress dynamic compression response of heterogeneous powder mixtures. The framework is applied to two metal + metal-oxide (thermite) powder mixtures, and good agreement between the model and experiment is obtained for all mixtures at stresses near and above those required to reach full density. At lower stresses, rate-dependencies of the constituents, and specifically those of the matrix constituent, determine the ability of the model to predict the measured response in the incomplete compaction regime.

Semiconductor Film Grown on a Circular Substrate: Predictive Modeling of Lattice-Misfit Stresses

NASA Astrophysics Data System (ADS)

Suhir, E.; Nicolics, J.; Khatibi, G.; Lederer, M.

2016-03-01

An effective and physically meaningful analytical predictive model is developed for the evaluation the lattice-misfit stresses (LMS) in a semiconductor film grown on a circular substrate (wafer). The two-dimensional (plane-stress) theory-of-elasticity approximation (TEA) is employed in the analysis. The addressed stresses include the interfacial shearing stress, responsible for the occurrence and growth of dislocations, as well as for possible delaminations and the cohesive strength of a buffering material, if any. Normal radial and circumferential (tangential) stresses acting in the film cross-sections and responsible for its short- and long-term strength (fracture toughness) are also addressed. The analysis is geared to the GaN technology.

Tension and compression fatigue response of unnotched 3D braided composites

NASA Technical Reports Server (NTRS)

Portanova, M. A.

1992-01-01

The unnotched compression and tension fatigue response of a 3-D braided composite was measured. Both gross compressive stress and tensile stress were plotted against cycles to failure to evaluate the fatigue life of these materials. Damage initiation and growth was monitored visually and by tracking compliance change during cycle loading. The intent was to establish by what means the strength of a 3-D architecture will start to degrade, at what point will it degrade beyond an acceptable level, and how this material will typically fail.

Characterization of the constitutive behavior of municipal solid waste considering particle compressibility.

PubMed

Lü, Xilin; Zhai, Xinle; Huang, Maosong

2017-11-01

This paper presents a characterization of the mechanical behavior of municipal solid waste (MSW) under consolidated drained and undrained triaxial conditions. The constitutive model was established based on a deviatoric hardening plasticity model. A power form function and incremental hyperbolic form function were proposed to describe the shear strength and the hardening role of MSW. The stress ratio that corresponds to the zero dilatancy was not fixed but depended on mean stress, making the Rowe's rule be able to describe the stress-dilatancy of MSW. A pore water pressure reduction coefficient, which attributed to the compressibility of a particle and the solid matrix, was introduced to the effective stress formulation to modify the Terzaghi's principle. The effects of particle compressibility and solid matrix compressibility on the undrained behavior of MSW were analyzed by parametric analysis, and the changing characteristic of stress-path, stress-strain, and pore-water pressure were obtained. The applicability of the proposed model on MSW under drained and undrained conditions was verified by model predictions of three triaxial tests. The comparison between model simulations and experiments indicated that the proposed model can capture the observed different characteristics of MSW response from normal soil, such as nonlinear shear strength, pressure dependent stress dilatancy, and the reduced value of pore water pressure. Copyright © 2017 Elsevier Ltd. All rights reserved.

Large tangential electric fields in plasmas close to temperature screening

NASA Astrophysics Data System (ADS)

Velasco, J. L.; Calvo, I.; García-Regaña, J. M.; Parra, F. I.; Satake, S.; Alonso, J. A.; the LHD team

2018-07-01

Low collisionality stellarator plasmas usually display a large negative radial electric field that has been expected to cause accumulation of impurities due to their high charge number. In this paper, two combined effects that can potentially modify this scenario are discussed. First, it is shown that, in low collisionality plasmas, the kinetic contribution of the electrons to the radial electric field can make it negative but small, bringing the plasma close to impurity temperature screening (i.e., to a situation in which the ion temperature gradient is the main drive of impurity transport and causes outward flux); in plasmas of very low collisionality, such as those of the large helical device displaying impurity hole (Ida et al (The LHD Experimental Group) 2009 Phys. Plasmas 16 056111; Yoshinuma et al (The LHD Experimental Group) 2009 Nucl. Fusion 49 062002), screening may actually occur. Second, the component of the electric field that is tangent to the flux surface (in other words, the variation of the electrostatic potential on the flux surface), although smaller than the radial component, has recently been suggested to be an additional relevant drive for radial impurity transport. Here, it is explained that, especially when the radial electric field is small, the tangential magnetic drift has to be kept in order to correctly compute the tangential electric field, that can be larger than previously expected. This can have a strong impact on impurity transport, as we illustrate by means of simulations using the newly developed code kinetic orbit-averaging-solver for stellarators, although it is not enough to explain by itself the behavior of the fluxes in situations like the impurity hole.

Stress in Lumbar Intervertebral Discs during Distraction

PubMed Central

Gay, Ralph E.; Ilharreborde, Brice; Zhao, Kristin D.; Berglund, Lawrence J.; Bronfort, Gert; An, Kai-Nan

2008-01-01

BACKGROUND CONTEXT The intervertebral disc is a common source of low back pain. Prospective studies suggest that treatments that intermittently distract the disc might be beneficial for chronic low back pain. Although the potential exists for distraction therapies to affect the disc biomechanically their effect on intradiscal stress is debated. PURPOSE To determine if distraction alone, distraction combined with flexion or distraction combined with extension can reduce nucleus pulposus pressure and posterior anulus compressive stress in cadaveric lumbar discs compared to simulated standing or lying. STUDY DESIGN Laboratory study using single cadaveric motion segments. OUTCOME MEASURES Strain gauge measures of nucleus pulposus pressure and compressive stress in the anterior and posterior annulus fibrosus METHODS Intradiscal stress profilometry was performed on 15 motion segments during 5 simulated conditions: standing, lying, and 3 distracted conditions. Disc degeneration was graded by inspection from 1 (normal) to 4 (severe degeneration). RESULTS All distraction conditions markedly reduced nucleus pressure compared to either simulated standing or lying. There was no difference between distraction with flexion and distraction with extension in regard to posterior annulus compressive stress. Discs with little or no degeneration appeared to distributed compressive stress differently than those with moderate or severe degeneration. CONCLUSIONS Distraction appears to predictably reduce nucleus pulposus pressure. The effect of distraction therapy on the distribution of compressive stress may be dependent in part on the health of the disc. PMID:17981092

Fracture Property of Y-Shaped Cracks of Brittle Materials under Compression

PubMed Central

Zhang, Xiaoyan; Zhu, Zheming; Liu, Hongjie

2014-01-01

In order to investigate the properties of Y-shaped cracks of brittle materials under compression, compression tests by using square cement mortar specimens with Y-shaped crack were conducted. A true triaxial loading device was applied in the tests, and the major principle stresses or the critical stresses were measured. The results show that as the branch angle θ between the branch crack and the stem crack is 75°, the cracked specimen has the lowest strength. In order to explain the test results, numerical models of Y-shaped cracks by using ABAQUS code were established, and the J-integral method was applied in calculating crack tip stress intensity factor (SIF). The results show that when the branch angle θ increases, the SIF K I of the branch crack increases from negative to positive and the absolute value K II of the branch crack first increases, and as θ is 50°, it is the maximum, and then it decreases. Finally, in order to further investigate the stress distribution around Y-shaped cracks, photoelastic tests were conducted, and the test results generally agree with the compressive test results. PMID:25013846

A priori evaluation of the Pantano and Sarkar model in compressible homogeneous shear flows

NASA Astrophysics Data System (ADS)

Khlifi, Hechmi; Abdallah, J.; Aïcha, H.; Taïeb, L.

2011-01-01

In this study, a Reynolds stress closure, including the Pantano and Sarkar model of the mean part of the pressure-strain correlation is used for the computation of compressible homogeneous at high-speed shear flow. Several studies concerning the compressible homogeneous shear flow show that the changes of the turbulence structures are principally due to the structural compressibility effects which significantly affect the pressure field and then the pressure-strain correlation. Eventually, this term appears as the main term responsible for the changes in the magnitude of the Reynolds stress anisotropies. The structure of the gradient Mach number is similar to that of turbulence, therefore this parameter may be appropriate to study the changes in turbulence structures that arise from structural compressibility effects. Thus, the incompressible model of the pressure strain correlation and its corrected form by using the turbulent Mach turbulent only, fail to correctly evaluate the compressibility effects at high shear flow. An extension of the widely used incompressible Launder, Reece and Rodi model on compressible homogeneous shear flow is the major aim of the present work. From this extension, the standard coefficients C become a function of the extra compressibility parameters (the turbulent Mach number M and the gradient Mach number M) through the Pantano and Sarkar model. Application of the model on compressible homogeneous shear flow by considering various initial conditions shows reasonable agreement with the DNS results of Simone et al. and Sarkar. The observed trend of the dramatic increase in the normal Reynolds stress anisotropies, the significant decrease in the Reynolds shear stress anisotropy and the increase of the turbulent kinetic energy amplification rate with increasing the gradient Mach number are well predicted by the model. The ability of the model to predict the equilibrium states for the flow in cases A to A from DNS results of Sarkar is

Accumulation of p62 in degenerated spinal cord under chronic mechanical compression

PubMed Central

Tanabe, Fumito; Yone, Kazunori; Kawabata, Naoya; Sakakima, Harutoshi; Matsuda, Fumiyo; Ishidou, Yasuhiro; Maeda, Shingo; Abematsu, Masahiko; Komiya, Setsuro

2011-01-01

Intracellular accumulation of altered proteins, including p62 and ubiquitinated proteins, is the basis of most neurodegenerative disorders. The relationship among the accumulation of altered proteins, autophagy, and spinal cord dysfunction by cervical spondylotic myelopathy has not been clarified. We examined the expression of p62 and autophagy markers in the chronically compressed spinal cord of tiptoe-walking Yoshimura mice. In addition, we examined the expression and roles of p62 and autophagy in hypoxic neuronal cells. Western blot analysis showed the accumulation of p62, ubiquitinated proteins, and microtubule-associated protein 1 light chain 3 (LC3), an autophagic marker, in the compressed spinal cord. Immunohistochemical examinations showed that p62 accumulated in neurons, axons, astrocytes, and oligodendrocytes. Electron microscopy showed the expression of autophagy markers, including autolysosomes and autophagic vesicles, in the compressed spinal cord. These findings suggest the presence of p62 and autophagy in the degenerated compressed spinal cord. Hypoxic stress increased the expression of p62, ubiquitinated proteins, and LC3-II in neuronal cells. In addition, LC3 turnover assay and GFP-LC3 cleavage assay showed that hypoxic stress increased autophagy flux in neuronal cells. These findings suggest that hypoxic stress induces accumulation of p62 and autophagy in neuronal cells. The forced expression of p62 decreased the number of neuronal cells under hypoxic stress. These findings suggest that p62 accumulation under hypoxic stress promotes neuronal cell death. Treatment with 3-methyladenine, an autophagy inhibitor decreased the number of neuronal cells, whereas lithium chloride, an autophagy inducer increased the number of cells under hypoxic stress. These findings suggest that autophagy promotes neuronal cell survival under hypoxic stress. Our findings suggest that pharmacological inducers of autophagy may be useful for treating cervical spondylotic

Flow-through compression cell for small-angle and ultra-small-angle neutron scattering measurements

NASA Astrophysics Data System (ADS)

Hjelm, Rex P.; Taylor, Mark A.; Frash, Luke P.; Hawley, Marilyn E.; Ding, Mei; Xu, Hongwu; Barker, John; Olds, Daniel; Heath, Jason; Dewers, Thomas

2018-05-01

In situ measurements of geological materials under compression and with hydrostatic fluid pressure are important in understanding their behavior under field conditions, which in turn provides critical information for application-driven research. In particular, understanding the role of nano- to micro-scale porosity in the subsurface liquid and gas flow is critical for the high-fidelity characterization of the transport and more efficient extraction of the associated energy resources. In other applications, where parts are produced by the consolidation of powders by compression, the resulting porosity and crystallite orientation (texture) may affect its in-use characteristics. Small-angle neutron scattering (SANS) and ultra SANS are ideal probes for characterization of these porous structures over the nano to micro length scales. Here we show the design, realization, and performance of a novel neutron scattering sample environment, a specially designed compression cell, which provides compressive stress and hydrostatic pressures with effective stress up to 60 MPa, using the neutron beam to probe the effects of stress vectors parallel to the neutron beam. We demonstrate that the neutron optics is suitable for the experimental objectives and that the system is highly stable to the stress and pressure conditions of the measurements.

Cross-ply laminates with holes in compression - Straight free-edge stresses determined by two- to three-dimensional global/local finite element analysis

NASA Technical Reports Server (NTRS)

Thompson, Danniella Muheim; Griffin, O. Hayden, Jr.; Vidussoni, Marco A.

1990-01-01

A practical example of applying two- to three-dimensional (2- to 3-D) global/local finite element analysis to laminated composites is presented. Cross-ply graphite/epoxy laminates of 0.1-in. (0.254-cm) thickness with central circular holes ranging from 1 to 6 in. (2.54 to 15.2 cm) in diameter, subjected to in-plane compression were analyzed. Guidelines for full three-dimensional finite element analysis and two- to three-dimensional global/local analysis of interlaminar stresses at straight free edges of laminated composites are included. The larger holes were found to reduce substantially the interlaminar stresses at the straight free-edge in proximity to the hole. Three-dimensional stress results were obtained for thin laminates which require prohibitive computer resources for full three-dimensional analyses of comparative accuracy.

Wearing graduated compression stockings augments cutaneous vasodilation in heat-stressed resting humans.

PubMed

Fujii, Naoto; Nikawa, Toshiya; Tsuji, Bun; Kondo, Narihiko; Kenny, Glen P; Nishiyasu, Takeshi

2017-05-01

We investigated whether graduated compression induced by stockings enhances cutaneous vasodilation in passively heated resting humans. Nine habitually active young men were heated at rest using water-perfusable suits, resulting in a 1.0 °C increase in body core temperature. Heating was repeated twice on separate occasions while wearing either (1) stockings that cause graduated compression (pressures of 26.4 ± 5.3, 17.5 ± 4.4, and 6.1 ± 2.0 mmHg at the ankle, calf, and thigh, respectively), or (2) loose-fitting stockings without causing compression (Control). Forearm vascular conductance during heating was evaluated by forearm blood flow (venous occlusion plethysmography) divided by mean arterial pressure to estimate heat-induced cutaneous vasodilation. Body core (esophageal), skin, and mean body temperatures were measured continuously. Compared to the Control, forearm vascular conductance during heating was higher with graduated compression stockings (e.g., 23.2 ± 5.5 vs. 28.6 ± 5.8 units at 45 min into heating, P = 0.001). In line with this, graduated compression stockings resulted in a greater sensitivity (27.5 ± 8.3 vs. 34.0 ± 9.4 units °C -1 , P = 0.02) and peak level (25.5 ± 5.8 vs. 29.7 ± 5.8 units, P = 0.004) of cutaneous vasodilation as evaluated from the relationship between forearm vascular conductance with mean body temperature. In contrast, the mean body temperature threshold for increases in forearm vascular conductance did not differ between the Control and graduated compression stockings (36.5 ± 0.1 vs. 36.5 ± 0.2 °C, P = 0.85). Our results show that graduated compression associated with the use of stockings augments cutaneous vasodilation by modulating sensitivity and peak level of cutaneous vasodilation in relation to mean body temperature. However, the effect of these changes on whole-body heat loss remains unclear.

Tangential Flow Filtration of Colloidal Silver Nanoparticles: A "Green" Laboratory Experiment for Chemistry and Engineering Students

ERIC Educational Resources Information Center

Dorney, Kevin M.; Baker, Joshua D.; Edwards, Michelle L.; Kanel, Sushil R.; O'Malley, Matthew; Pavel Sizemore, Ioana E.

2014-01-01

Numerous nanoparticle (NP) fabrication methodologies employ "bottom-up" syntheses, which may result in heterogeneous mixtures of NPs or may require toxic capping agents to reduce NP polydispersity. Tangential flow filtration (TFF) is an alternative "green" technique for the purification, concentration, and size-selection of…

Elastic-Plastic Behaviour of Ultrasonic Assisted Compression of Polyvinyl Chloride (PVC) Foam

NASA Astrophysics Data System (ADS)

Muhalim, N. A. D.; Hassan, M. Z.; Daud, Y.

2018-04-01

The present study aims to investigate the elastic-plastic behaviour of ultrasonic assisted compression of PVC closed-cell foam. A series of static and ultrasonic compression test of PVC closed-cell foam were conducted at a constant cross head speed of 30 mm/min on dry surface condition. For quasi-static test, specimen was compressed between two rigid platens using universal testing machine. In order to evaluate the specimen behavior under ultrasonic condition, specimen was placed between a specifically design double-slotted block horn and rigid platen. The horn was designed and fabricated prior to the test as a medium to transmit the ultrasonic vibration from the ultrasonic transducer to the working specimen. It was tuned to a frequency of 19.89 kHz in longitudinal mode and provided an average oscillation amplitude at 6 µm on the uppermost surface. Following, the characteristics of stress-strain curves for quasi-static and ultrasonic compression tests were analyzed. It was found that the compressive stress was significantly reduced at the onset of superimposed ultrasonic vibration during plastic deformation.

Mathematical Model Relating Uniaxial Compressive Behavior of Manufactured Sand Mortar to MIP-Derived Pore Structure Parameters

PubMed Central

Tian, Zhenghong; Bu, Jingwu

2014-01-01

The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed. PMID:25133257

Mathematical model relating uniaxial compressive behavior of manufactured sand mortar to MIP-derived pore structure parameters.

PubMed

Tian, Zhenghong; Bu, Jingwu

2014-01-01

The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed.

Pre-stressed/pre-compressed gas turbine nozzle

DOEpatents

Jang, Hoyle; Itzel, Gary Michael; Yu, Yufeng Phillip

2002-01-01

A method of increasing low cycle fatigue life of a turbine nozzle comprising a plurality of stationary airfoils extending between radially inner and outer ring segments comprising a) providing at least one radial passage in each of the plurality of airfoils; b) installing a rod in the radial passage extending between the radially inner and outer ring segments and fixing one end of the rod to one of the inner and outer rings; and c) pre-loading the rod to compress the airfoil between the inner and outer ring segments.

Slipping and tangential discontinuity instabilities in quasi-one-dimensional planar and cylindrical flows

NASA Astrophysics Data System (ADS)

Kuzelev, M. V.

2017-09-01

An analytical linear theory of instability of an electron beam with a nonuniform directional velocity (slipping instability) against perturbations with wavelengths exceeding the transverse beam size is offered. An analogy with hydrodynamic instabilities of tangential discontinuity of an incompressible liquid flow is drawn. The instability growth rates are calculated for particular cases and in a general form in planar and cylindrical geometries. The stabilizing effect of the external magnetic field is analyzed.

Quantitative micro-elastography: imaging of tissue elasticity using compression optical coherence elastography

PubMed Central

Kennedy, Kelsey M.; Chin, Lixin; McLaughlin, Robert A.; Latham, Bruce; Saunders, Christobel M.; Sampson, David D.; Kennedy, Brendan F.

2015-01-01

Probing the mechanical properties of tissue on the microscale could aid in the identification of diseased tissues that are inadequately detected using palpation or current clinical imaging modalities, with potential to guide medical procedures such as the excision of breast tumours. Compression optical coherence elastography (OCE) maps tissue strain with microscale spatial resolution and can delineate microstructural features within breast tissues. However, without a measure of the locally applied stress, strain provides only a qualitative indication of mechanical properties. To overcome this limitation, we present quantitative micro-elastography, which combines compression OCE with a compliant stress sensor to image tissue elasticity. The sensor consists of a layer of translucent silicone with well-characterized stress-strain behaviour. The measured strain in the sensor is used to estimate the two-dimensional stress distribution applied to the sample surface. Elasticity is determined by dividing the stress by the strain in the sample. We show that quantification of elasticity can improve the ability of compression OCE to distinguish between tissues, thereby extending the potential for inter-sample comparison and longitudinal studies of tissue elasticity. We validate the technique using tissue-mimicking phantoms and demonstrate the ability to map elasticity of freshly excised malignant and benign human breast tissues. PMID:26503225

Compression selective solid-state chemistry

NASA Astrophysics Data System (ADS)

Hu, Anguang

Compression selective solid-state chemistry refers to mechanically induced selective reactions of solids under thermomechanical extreme conditions. Advanced quantum solid-state chemistry simulations, based on density functional theory with localized basis functions, were performed to provide a remarkable insight into bonding pathways of high-pressure chemical reactions in all agreement with experiments. These pathways clearly demonstrate reaction mechanisms in unprecedented structural details, showing not only the chemical identity of reactive intermediates but also how atoms move along the reaction coordinate associated with a specific vibrational mode, directed by induced chemical stress occurred during bond breaking and forming. It indicates that chemical bonds in solids can break and form precisely under compression as we wish. This can be realized through strongly coupling of mechanical work to an initiation vibrational mode when all other modes can be suppressed under compression, resulting in ultrafast reactions to take place isothermally in a few femtoseconds. Thermodynamically, such reactions correspond to an entropy minimum process on an isotherm where the compression can force thermal expansion coefficient equal to zero. Combining a significantly brief reaction process with specific mode selectivity, both statistical laws and quantum uncertainty principle can be bypassed to precisely break chemical bonds, establishing fundamental principles of compression selective solid-state chemistry. Naturally this leads to understand the ''alchemy'' to purify, grow, and perfect certain materials such as emerging novel disruptive energetics.

An experimental study of the effects of bodyside compression on forward swept sidewall compression inlets ingesting a turbulent boundary layer

NASA Technical Reports Server (NTRS)

Rodi, Patrick E.

1993-01-01

Forward swept sidewall compression inlets have been tested in the Mach 4 Blowdown Facility at the NASA Langley Research Center to study the effects of bodyside compression surfaces on inlet performance in the presence of an incoming turbulent boundary layer. The measurements include mass flow capture and mean surface pressure distributions obtained during simulated combustion pressure increases downstream of the inlet. The kerosene-lampblack surface tracer technique has been used to obtain patterns of the local wall shear stress direction. Inlet performance is evaluated using starting and unstarting characteristics, mass capture, mean surface pressure distributions and permissible back pressure limits. The results indicate that inlet performance can be improved with selected bodyside compression surfaces placed between the inlet sidewalls.

Effect of initial tangential velocity distribution on the mean evolution of a swirling turbulent free jet

NASA Technical Reports Server (NTRS)

Farokhi, S.; Taghavi, R.; Rice, E. J.

1988-01-01

An existing cold jet facility at NASA-Lewis was modified to produce swirling flows with controllable initial tangential velocity distribution. Distinctly different swirl velocity profiles were produced, and their effects on jet mixing characteristics were measured downstream of an 11.43 cm diameter convergent nozzle. It was experimentally shown that in the near field of a swirling turbulent jet, the mean velocity field strongly depends on the initial swirl profile. Two extreme tangential velocity distributions were produced. The two jets shared approximately the same initial mass flow rate of 5.9 kg/s, mass averaged axial Mach number and swirl number. Mean centerline velocity decay characteristics of the solid body rotation jet flow exhibited classical decay features of a swirling jet with S = 0.48 reported in the literature. It is concluded that the integrated swirl effect, reflected in the swirl number, is inadequate in describing the mean swirling jet behavior in the near field.

Radial Features around Irnini Mons, Venus: Implications for Timing of Regional Compression

NASA Astrophysics Data System (ADS)

Buczkowski, D. L.; McGill, G. E.; Cooke, M. L.

2003-12-01

Flows and other deposits from Irnini Mons are superimposed on an older, regional plains material. Wrinkle ridges are generally abundant on this regional plains material and are present in at least two sets: one trending east-west and another concentric to Irnini Mons. Radial features on top of the Irnini flows are mapped as lineations or grabens, as resolution allows. High resolution mapping at 75 m/pixel also reveals ridges radial to Irnini Mons on top of the Irnini flows. These radial ridges are located from approximately N60E to N75E. Radial grabens around a volcano have been explained mathematically, with the magma chamber of a volcano simplistically described as a pressurized hole in an elastic plate. However, magma pressure alone can not explain the presence of radial ridges. The regional east-west trending wrinkle ridges imply a regional north-south compression affecting the Irnini Mons area. The regional stress field around an empty hole in an elastic plate is perturbed close to the hole, although it remains unperturbed at infinity; the change in material properties from the surrounding rock to a magma-filled chamber allows us to consider the chamber as "soft" and thus effectively empty. The perturbation of a uniaxial regional compressive stress around a pressurized hole is such that at angles of 90 and 270 degrees (east-west) the maximum principal stresses close to the hole are compressive, while at angles 0 and 180 degrees (north-south) the maximum principal stresses are tensile. The angle at which maximum principal stresses change from tension to compression depends upon the distance from the hole and the relative magnitudes of magma pressure and the regional compression. While in the simple model resultant stresses would be symmetric around the hole, structural complexities to the south and west of Irnini Mons restrict the predicted pattern of radial ridges as well as grabens to the region northeast of the volcano. Thus, the existence of radial ridges

DNABIT Compress – Genome compression algorithm

PubMed Central

Rajarajeswari, Pothuraju; Apparao, Allam

2011-01-01

Data compression is concerned with how information is organized in data. Efficient storage means removal of redundancy from the data being stored in the DNA molecule. Data compression algorithms remove redundancy and are used to understand biologically important molecules. We present a compression algorithm, “DNABIT Compress” for DNA sequences based on a novel algorithm of assigning binary bits for smaller segments of DNA bases to compress both repetitive and non repetitive DNA sequence. Our proposed algorithm achieves the best compression ratio for DNA sequences for larger genome. Significantly better compression results show that “DNABIT Compress” algorithm is the best among the remaining compression algorithms. While achieving the best compression ratios for DNA sequences (Genomes),our new DNABIT Compress algorithm significantly improves the running time of all previous DNA compression programs. Assigning binary bits (Unique BIT CODE) for (Exact Repeats, Reverse Repeats) fragments of DNA sequence is also a unique concept introduced in this algorithm for the first time in DNA compression. This proposed new algorithm could achieve the best compression ratio as much as 1.58 bits/bases where the existing best methods could not achieve a ratio less than 1.72 bits/bases. PMID:21383923

Dynamic compressive properties of bovine knee layered tissue

NASA Astrophysics Data System (ADS)

Nishida, Masahiro; Hino, Yuki; Todo, Mitsugu

2015-09-01

In Japan, the most common articular disease is knee osteoarthritis. Among many treatment methodologies, tissue engineering and regenerative medicine have recently received a lot of attention. In this field, cells and scaffolds are important, both ex vivo and in vivo. From the viewpoint of effective treatment, in addition to histological features, the compatibility of mechanical properties is also important. In this study, the dynamic and static compressive properties of bovine articular cartilage-cancellous bone layered tissue were measured using a universal testing machine and a split Hopkinson pressure bar method. The compressive behaviors of bovine articular cartilage-cancellous bone layered tissue were examined. The effects of strain rate on the maximum stress and the slope of stress-strain curves of the bovine articular cartilage-cancellous bone layered tissue were discussed.

Initial boundary-value problem for the spherically symmetric Einstein equations with fluids with tangential pressure.

PubMed

Brito, Irene; Mena, Filipe C

2017-08-01

We prove that, for a given spherically symmetric fluid distribution with tangential pressure on an initial space-like hypersurface with a time-like boundary, there exists a unique, local in time solution to the Einstein equations in a neighbourhood of the boundary. As an application, we consider a particular elastic fluid interior matched to a vacuum exterior.

Stress relaxation in quasi-two-dimensional self-assembled nanoparticle monolayers

NASA Astrophysics Data System (ADS)

Boucheron, Leandra S.; Stanley, Jacob T.; Dai, Yeling; You, Siheng Sean; Parzyck, Christopher T.; Narayanan, Suresh; Sandy, Alec R.; Jiang, Zhang; Meron, Mati; Lin, Binhua; Shpyrko, Oleg G.

2018-05-01

We experimentally probed the stress relaxation of a monolayer of iron oxide nanoparticles at the water-air interface. Upon drop-casting onto a water surface, the nanoparticles self-assembled into islands of two-dimensional hexagonally close packed crystalline domains surrounded by large voids. When compressed laterally, the voids gradually disappeared as the surface pressure increased. After the compression was stopped, the surface pressure (as measured by a Wilhelmy plate) evolved as a function of the film aging time with three distinct timescales. These aging dynamics were intrinsic to the stressed state built up during the non-equilibrium compression of the film. Utilizing x-ray photon correlation spectroscopy, we measured the characteristic relaxation time (τ ) of in-plane nanoparticle motion as a function of the aging time through both second-order and two-time autocorrelation analysis. Compressed and stretched exponential fitting of the intermediate scattering function yielded exponents (β ) indicating different relaxation mechanisms of the films under different compression stresses. For a monolayer compressed to a lower surface pressure (between 20 mN/m and 30 mN/m), the relaxation time (τ ) decreased continuously as a function of the aging time, as did the fitted exponent, which transitioned from being compressed (>1 ) to stretched (<1 ), indicating that the monolayer underwent a stress release through crystalline domain reorganization. However, for a monolayer compressed to a higher surface pressure (around 40 mN/m), the relaxation time increased continuously and the compressed exponent varied very little from a value of 1.6, suggesting that the system may have been highly stressed and jammed. Despite the interesting stress relaxation signatures seen in these samples, the structural ordering of the monolayer remained the same over the sample lifetime, as revealed by grazing incidence x-ray diffraction.

Mechanics of the Compression Wood Response: II. On the Location, Action, and Distribution of Compression Wood Formation.

PubMed

Archer, R R; Wilson, B F

1973-04-01

A new method for simulation of cross-sectional growth provided detailed information on the location of normal wood and compression wood increments in two tilted white pine (Pinus strobus L.) leaders. These data were combined with data on stiffness, slope, and curvature changes over a 16-week period to make the mechanical analysis. The location of compression wood changed from the under side to a flank side and then to the upper side of the leader as the geotropic stimulus decreased, owing to compression wood action. Its location shifted back to a flank side when the direction of movement of the leader reversed. A model for this action, based on elongation strains, was developed and predicted the observed curvature changes with elongation strains of 0.3 to 0.5%, or a maximal compressive stress of 60 to 300 kilograms per square centimeter. After tilting, new wood formation was distributed so as to maintain consistent strain levels along the leaders in bending under gravitational loads. The computed effective elastic moduli were about the same for the two leaders throughout the season.

Stress distribution during cold compression of a quartz aggregate using synchrotron X-ray diffraction: Observed yielding, damage, and grain crushing: STRESS DISTRIBUTION OF QUARTZ AGGREGATE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheung, C. S. N.; Weidner, D. J.; Li, L.

We report new experimental results that quantify the stress distribution within a quartz aggregate during pore collapse and grain crushing. The samples were probed with synchrotron X-ray diffraction as they were compressed in a multianvil deformation apparatus at room temperature from low pressure (tens of megapascal) to pressures of a few gigapascal. In such a material, stress is likely to concentrate at grain-to-grain contacts and vanish where grains are bounded by open porosity. Therefore, internal stress is likely to vary significantly from point to point in such an aggregate, and hence, it is important to understand both the heterogeneity andmore » anisotropy of such variation with respect to the externally applied stress. In our quartz aggregate (grain size of ~4 μm), the measured diffraction peaks broaden asymmetrically at low pressure (tens of megapascal), suggesting that open pores are still a dominant characteristic of grain boundaries. In contrast, a reference sample of novaculite (a highly dense quartz polycrystal, grain size of ~6–9 μm) showed virtually no peak broadening with increasing pressure. In the quartz aggregate, we observed significant deviation in the pressure-volume curves in the range of P = 400–600 MPa. We suggest that this marks the onset of grain crushing (generally denoted as P* in the rock mechanic literature), which is commonly reported to occur in sandstones at pressures of this order, in general agreement with a Hertzian analysis of fracturing at grain contacts.« less

Study on the Aging Behaviors of Rubber Materials in Tension and Compression Loads

NASA Astrophysics Data System (ADS)

Jiang, Can; Wang, Hongyu; Ma, Xiaobing

Rubber materials are widely used in aviation, aerospace, shipbuilding, automobile and other military field. However, rubber materials are easy to aging, which largely restricts its using life. In working environment, due to the combined effect of heat and oxygen, vulcanized rubber will undergo degradation and crosslinking reaction which will cause elasticity decease and permanent deformation, so mostly rubber products are used under stress state. Due to the asymmetric structure and asymmetric stress distribution, mechanical stress may cause serious damage to molecular structure; therefore, this paper is aimed to analyze the aging behavior of rubber materials under tensile and compressive loadings, through analyzing experiment data, and adopting Gauss function to describe stress relaxation coefficient, to build an aging equation containing compression ratio parameter and aging time.

On the compressibility and temperature boundary of warm frozen soils

NASA Astrophysics Data System (ADS)

Qi, Jilin; Dang, Boxiang; Guo, Xueluan; Sun, Xiaoyu; Yan, Xu

2017-04-01

A silty-clay obtained along the Qinghai-Tibetan railway and a standard Chinese sand were taken as study objects. Saturated frozen soil samples were prepared for testing. Step-load was used and confined compression was carried out on the soils under different temperatures. Compression index and pseudo-preconsolidation pressure (PPC) were obtained. Unlike unfrozen soils, PPC is not associated with stress history. However, it is still the boundary of elastic and plastic deformations. Different compression indexes can be obtained from an individual compression curve under pressures before and after PPC. The parameters at different thermal and stress conditions were analyzed. It is found that temperature plays a critical role in mechanical behaviours of frozen soils. Efforts were then made on the silty-clay in order to suggest a convincing temperature boundary in defining warm frozen soil. Three groups of ice-rich samples with different ice contents were prepared and tested under confined compression. The samples were compressed under a constant load and with 5 stepped temperatures. Strain rates at different temperatures were examined. It was found that the strain rate at around -0.6°C increased abruptly. Analysis of compression index was performed on the data both from our own testing program and from the literature, which showed that at about -1°C was a turning point in the curves for compression index against temperature. Based on both our work and taking into account the unfrozen water content vs. temperature, the range of -1°C to -0.5°C seems to be the temperature where the mechanical properties change greatly. For convenience, -1.0°C can be defined as the boundary for warm frozen soils.

Verification of conventional equations of state for tantalum under quasi-isentropic compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binqiang, Luo; Guiji, Wang; Jianjun, Mo

2014-11-21

Shock Hugoniot data have been widely used to calibrate analytic equations of state (EOSs) of condensed matter at high pressures. However, the suitability of particular analytic EOSs under off-Hugoniot states has not been sufficiently verified using experimental data. We have conducted quasi-isentropic compression experiments (ICEs) of tantalum using the compact pulsed power generator CQ-4, and explored the relation of longitudinal stress versus volume of tantalum under quasi-isentropic compression using backward integration and characteristic inverse methods. By subtracting the deviatoric stress and additional pressure caused by irreversible plastic dissipation, the isentropic pressure can be extracted from the longitudinal stress. Several theoreticalmore » isentropes are deduced from analytic EOSs and compared with ICE results to validate the suitability of these analytic EOSs in isentropic compression states. The comparisons show that the Gruneisen EOS with Gruneisen Gamma proportional to volume is accurate, regardless whether the Hugoniot or isentrope is used as the reference line. The Vinet EOS yields better accuracy in isentropic compression states. Theoretical isentropes derived from Tillotson, PUFF, and Birch-Murnaghan EOSs well agree with the experimental isentrope in the range of 0–100 GPa, but deviate gradually with pressure increasing further.« less

Compressibility effects in the shear layer over a rectangular cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beresh, Steven J.; Wagner, Justin L.; Casper, Katya M.

2016-10-26

we studied the influence of compressibility on the shear layer over a rectangular cavity of variable width in a free stream Mach number range of 0.6–2.5 using particle image velocimetry data in the streamwise centre plane. As the Mach number increases, the vertical component of the turbulence intensity diminishes modestly in the widest cavity, but the two narrower cavities show a more substantial drop in all three components as well as the turbulent shear stress. Furthermore, this contrasts with canonical free shear layers, which show significant reductions in only the vertical component and the turbulent shear stress due to compressibility.more » The vorticity thickness of the cavity shear layer grows rapidly as it initially develops, then transitions to a slower growth rate once its instability saturates. When normalized by their estimated incompressible values, the growth rates prior to saturation display the classic compressibility effect of suppression as the convective Mach number rises, in excellent agreement with comparable free shear layer data. The specific trend of the reduction in growth rate due to compressibility is modified by the cavity width.« less

Effect of angle-ply orientation on compression strength of composite laminates

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeTeresa, S J; Hoppel, C P

1999-03-01

An experimental program was initiated to investigate the effect of angle-ply orientations on the compressive strength (X{sub 1C}) of 0{degree} plies in fiber reinforced composite laminates. Graphite fiber-reinforced epoxy test coupons with the generic architecture [0{sub 2}/{+-}{theta}] (where {theta} varied between 0{degree} and 90{degree}) and for the quasi-isotropic architecture were evaluated. The effective compressive strength of the 0{degree} plies varied considerably. The results were related to the Poisson's ratios of the laminates with high Poisson's ratios leading to high transverse tensile strains in the test coupons and lower than expected strengths. Specimens with the [O{sub 2}/{+-}30] architecture had both themore » highest Poisson's ratio and the lowest calculated ply-level compression strength for the 0{degree} plies. This work has implications in the selection of composite failure criterion for compression performance, design of test coupons for acceptance testing, and the selection of laminate architectures for optimum combinations of compressive and shear behavior. Two commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict significantly different laminate strengths depending on the Poisson's ratio of the laminate. This implies that the biaxial stress state in the laminate needs to be carefully considered before backing out unidirectional properties.« less

Fibrocartilage in tendons and ligaments — an adaptation to compressive load

PubMed Central

BENJAMIN, M.; RALPHS, J. R.

1998-01-01

Where tendons and ligaments are subject to compression, they are frequently fibrocartilaginous. This occurs at 2 principal sites: where tendons (and sometimes ligaments) wrap around bony or fibrous pulleys, and in the region where they attach to bone, i.e. at their entheses. Wrap-around tendons are most characteristic of the limbs and are commonly wider at their point of bony contact so that the pressure is reduced. The most fibrocartilaginous tendons are heavily loaded and permanently bent around their pulleys. There is often pronounced interweaving of collagen fibres that prevents the tendons from splaying apart under compression. The fibrocartilage can be located within fascicles, or in endo- or epitenon (where it may protect blood vessels from compression or allow fascicles to slide). Fibrocartilage cells are commonly packed with intermediate filaments which could be involved in transducing mechanical load. The ECM often contains aggrecan which allows the tendon to imbibe water and withstand compression. Type II collagen may also be present, particularly in tendons that are heavily loaded. Fibrocartilage is a dynamic tissue that disappears when the tendons are rerouted surgically and can be maintained in vitro when discs of tendon are compressed. Finite element analyses provide a good correlation between its distribution and levels of compressive stress, but at some locations fibrocartilage is a sign of pathology. Enthesis fibrocartilage is most typical of tendons or ligaments that attach to the epiphyses of long bones where it may also be accompanied by sesamoid and periosteal fibrocartilages. It is characteristic of sites where the angle of attachment changes throughout the range of joint movement and it reduces wear and tear by dissipating stress concentration at the bony interface. There is a good correlation between the distribution of fibrocartilage within an enthesis and the levels of compressive stress. The complex interlocking between calcified

The estimation of tissue loss during tangential hydrosurgical debridement.

PubMed

Matsumura, Hajime; Nozaki, Motohiro; Watanabe, Katsueki; Sakurai, Hiroyuki; Kawakami, Shigehiko; Nakazawa, Hiroaki; Matsumura, Izumi; Katahira, Jiro; Inokuchi, Sadaki; Ichioka, Shigeru; Ikeda, Hiroto; Mole, Trevor; Smith, Jennifer; Martin, Robin; Aikawa, Naoki

2012-11-01

The preservation of healthy tissue during surgical debridement is desirable as this may improve clinical outcomes. This study has estimated for the first time the amount of tissue lost during debridement using the VERSAJET system of tangential hydrosurgery. A multicenter, prospective case series was carried out on 47 patients with mixed wound types: 21 (45%) burns, 13 (28%) chronic wounds, and 13 (28%) acute wounds. Overall, 44 (94%) of 47 patients achieved appropriate debridement after a single debridement procedure as verified by an independent photographic assessment. The percentage of necrotic tissue reduced from a median of 50% to 0% (P < 0.001). Median wound area and depth increased by only 0.3 cm (6.8%) and 0.5 mm (25%), respectively. Notably, 43 (91%) of 47 wounds did not progress into a deeper compartment, indicating a high degree of tissue preservation.

Micromechanics of compression failures in open hole composite laminates

NASA Technical Reports Server (NTRS)

Guynn, E. Gail; Bradley, Walter L.

1987-01-01

The high strength-to-weight ratio of composite materials is ideally suited for aerospace applications where they already are used in commercial and military aircraft secondary structures and will soon be used for heavily loaded primary structures. One area impeding the widespread application of composites is their inherent weakness in compressive strength when compared to the tensile properties of the same material. Furthermore, these airframe designs typically contain many bolted or riveted joints, as well as electrical and hydraulic control lines. These applications produce areas of stress concentration, and thus, further complicate the compression failure problem. Open hole compression failures which represent a typical failure mode for composite materials are addressed.

Far-infrared tangential interferometer/polarimeter design and installation for NSTX-U

DOE PAGES

Scott, E. R.; Barchfeld, R.; Riemenschneider, P.; ...

2016-08-09

Here, the Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system has been refurbished and is being reinstalled on the National Spherical Torus Experiment—Upgrade (NSTX-U) to supply real-time line-integrated core electron density measurements for use in the NSTX-U plasma control system (PCS) to facilitate real-time density feedback control of the NSTX-U plasma. Inclusion of a visible light heterodyne interferometer in the FIReTIP system allows for real-time vibration compensation due to movement of an internally mounted retroreflector and the FIReTIP front-end optics. Real-time signal correction is achieved through use of a National Instruments CompactRIO field-programmable gate array.

Anisotropy of demineralized bone matrix under compressive load.

PubMed

Trębacz, Hanna; Zdunek, Artur

2011-01-01

Two groups of cubic specimens from diaphysis of bovine femur, intact and completely demineralized, were axially compressed. One half of the samples from each group were loaded along the axis of the femur (L) and the other - perpendicularly (T). Intact samples were characterized in terms of elastic modulus; for demineralized samples secant modulus of elasticity was calculated. During compression an acoustic emission (AE) signal was recorded and AE events and energy were analyzed. Samples of intact bone did not reveal any anisotropy under compression at the stress of 80 MPa. However, AE signal indicated an initiation of failure in samples loaded in T direction. Demineralized samples were anisotropic under compression. Both secant modulus of elasticity and AE parameters were significantly higher in T direction than in L direction, which is attributed to shifting and separation of lamellae of collagen fibrils and lamellae in bone matrix.

INVESTIGATION OF CONVENTIONAL MEMBRANE AND TANGENTIAL FLOW ULTRAFILTRATION ARTIFACTS AND THEIR APPLICATION TO THE CHARACTERIZATION OF FRESHWATER COLLOIDS

EPA Science Inventory

Artifacts associated with the fractionation of colloids in a freshwater sample were investigated for conventional membrane filtration (0.45 micron cutoff), and two tangential flow ultrafiltration cartridges (0.1 micron cutoff and 3000 MW cutoff). Membrane clogging during conventi...

Three-dimensional numerical simulation for plastic injection-compression molding

NASA Astrophysics Data System (ADS)

Zhang, Yun; Yu, Wenjie; Liang, Junjie; Lang, Jianlin; Li, Dequn

2018-03-01

Compared with conventional injection molding, injection-compression molding can mold optical parts with higher precision and lower flow residual stress. However, the melt flow process in a closed cavity becomes more complex because of the moving cavity boundary during compression and the nonlinear problems caused by non-Newtonian polymer melt. In this study, a 3D simulation method was developed for injection-compression molding. In this method, arbitrary Lagrangian- Eulerian was introduced to model the moving-boundary flow problem in the compression stage. The non-Newtonian characteristics and compressibility of the polymer melt were considered. The melt flow and pressure distribution in the cavity were investigated by using the proposed simulation method and compared with those of injection molding. Results reveal that the fountain flow effect becomes significant when the cavity thickness increases during compression. The back flow also plays an important role in the flow pattern and redistribution of cavity pressure. The discrepancy in pressures at different points along the flow path is complicated rather than monotonically decreased in injection molding.

A computer program for performance prediction of tripropellant rocket engines with tangential slot injection

NASA Technical Reports Server (NTRS)

Dang, Anthony; Nickerson, Gary R.

1987-01-01

For the development of a Heavy Lift Launch Vehicle (HLLV) several engines with different operating cycles and using LOX/Hydrocarbon propellants are presently being examined. Some concepts utilize hydrogen for thrust chamber wall cooling followed by a gas generator turbine drive cycle with subsequent dumping of H2/O2 combustion products into the nozzle downstream of the throat. In the Space Transportation Booster Engine (STBE) selection process the specific impulse will be one of the optimization criteria; however, the current performance prediction programs do not have the capability to include a third propellant in this process, nor to account for the effect of dumping the gas-generator product tangentially inside the nozzle. The purpose is to describe a computer program for accurately predicting the performance of such an engine. The code consists of two modules; one for the inviscid performance, and the other for the viscous loss. For the first module, the two-dimensional kinetics program (TDK) was modified to account for tripropellant chemistry, and for the effect of tangential slot injection. For the viscous loss, the Mass Addition Boundary Layer program (MABL) was modified to include the effects of the boundary layer-shear layer interaction, and tripropellant chemistry. Calculations were made for a real engine and compared with available data.

Experimental and Theoretical Research on the Compression Performance of CFRP Sheet Confined GFRP Short Pipe

PubMed Central

Zhao, Qilin; Chen, Li; Shao, Guojian

2014-01-01

The axial compressive strength of unidirectional FRP made by pultrusion is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. A theoretical iterative calculation approach was suggested to predict the ultimate axial compressive stress of the combined structure and analyze the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure. In this paper, the experimental and theoretical research on the CFRP sheet confined GFRP short pole was extended to the CFRP sheet confined GFRP short pipe, namely, a hollow section pole. Experiment shows that the bearing capacity of the GFRP short pipe can also be heightened obviously by confining CFRP sheet. The theoretical iterative calculation approach in the previous paper is amended to predict the ultimate axial compressive stress of the CFRP sheet confined GFRP short pipe, of which the results agree with the experiment. Lastly the influences of geometrical parameters on the new combined structure are analyzed. PMID:24672288

A three-dimensional model of Tangential YORP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golubov, O.; Scheeres, D. J.; Krugly, Yu. N., E-mail: golubov@astron.kharkov.ua

2014-10-10

Tangential YORP, or TYORP, has recently been demonstrated to be an important factor in the evolution of an asteroid's rotation state. It is complementary to normal YORP, or NYORP, which used to be considered previously. While NYORP is produced by non-symmetry in the large-scale geometry of an asteroid, TYORP is due to heat conductivity in stones on the surface of the asteroid. To date, TYORP has been studied only in a simplified one-dimensional model, substituting stones with high long walls. This article for the first time considers TYORP in a realistic three-dimensional model, also including shadowing and self-illumination effects viamore » ray tracing. TYORP is simulated for spherical stones lying on regolith. The model includes only five free parameters and the dependence of the TYORP on each of them is studied. The TYORP torque appears to be smaller than previous estimates from the one-dimensional model, but is still comparable to the NYORP torques. These results can be used to estimate TYORP of different asteroids and also as a basis for more sophisticated models of TYORP.« less

A reassessment of the compressive strength properties of southern yellow pine bark

Treesearch

Thomas L. Eberhardt

2007-01-01

Samples of southern yellow pine outer bark and wood were tested in compression to determine values for modulus of elasticity, stress at proportional limit, and maximum crushing strength. Results reported here resolve inconsistencies in the compressive strength data previously reported by others for pine bark. Testing of solvent-treated bark blocks suggests that...

A theoretical approach to quantify the effect of random cracks on rock deformation in uniaxial compression

NASA Astrophysics Data System (ADS)

Zhou, Shuwei; Xia, Caichu; Zhou, Yu

2018-06-01

Cracks have a significant effect on the uniaxial compression of rocks. Thus, a theoretically analytical approach was proposed to assess the effects of randomly distributed cracks on the effective Young’s modulus during the uniaxial compression of rocks. Each stage of the rock failure during uniaxial compression was analyzed and classified. The analytical approach for the effective Young’s modulus of a rock with only a single crack was derived while considering the three crack states under stress, namely, opening, closure-sliding, and closure-nonsliding. The rock was then assumed to have many cracks with randomly distributed direction, and the effect of crack shape and number during each stage of the uniaxial compression on the effective Young’s modulus was considered. Thus, the approach for the effective Young’s modulus was used to obtain the whole stress-strain process of uniaxial compression. Afterward, the proposed approach was employed to analyze the effects of related parameters on the whole stress-stain curve. The proposed approach was eventually compared with some existing rock tests to validate its applicability and feasibility. The proposed approach has clear physical meaning and shows favorable agreement with the rock test results.

Thermophysical property and pore structure evolution in stressed and non-stressed neutron irradiated IG-110 nuclear graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snead, Lance; Contescu, Christian I.; Byun, Thak Sang

2016-08-01

The nuclear graphite, IG-110, was irradiated with and without a compressive load of 5 MPa at ~400 *C up to 9.3E25 n/m2 (E > 0.1 MeV). Following irradiation physical properties were studied to compare the effect of graphite irradiation on microstructure developed under compression and in stress-free conditions. Properties included: dimensional change, thermal conductivity, dynamic modulus, and CTE. The effect of stress on open internal porosity was determined through nitrogen adsorption. The IG-110 graphite experienced irradiation-induced creep that is differentiated from irradiation-induced swelling. Irradiation under stress resulted in somewhat greater thermal conductivity and coefficient of thermal expansion. While a significantmore » increase in dynamic modulus occurs, no differentiation between materials irradiated with and without compressive stress was observed. Nitrogen adsorption analysis suggests a difference in pore evolution in the 0.3e40 nm range for graphite irradiated with and without stress, but this evolution is seen to be a small contributor to the overall dimensional change.« less

Thermophysical property and pore structure evolution in stressed and non-stressed neutron irradiated IG-110 nuclear graphite

DOE PAGES

Snead, Lance L.; Contescu, C. I.; Byun, T. S.; ...

2016-04-23

The nuclear graphite, IG-110, was irradiated with and without a compressive load of 5 MPa at ~400 C up to 9.3x10 25 n/m 2 (E>0.1 MeV.) Following irradiation physical properties were studied to compare the effect of graphite irradiation on microstructure developed under compression and in stress-free condition. Properties included: dimensional change, thermal conductivity, dynamic modulus, and CTE. The effect of stress on open internal porosity was determined through nitrogen adsorption. The IG-110 graphite experienced irradiation-induced creep that is differentiated from irradiation-induced swelling. Irradiation under stress resulted in somewhat greater thermal conductivity and coefficient of thermal expansion. While a significantmore » increase in dynamic modulus occurs, no differentiation between materials irradiated with and without compressive stress was observed. Nitrogen adsorption analysis suggests a difference in pore evolution in the 0.3-40 nm range for graphite irradiated with and without stress, but this evolution is seen to be a small contributor to the overall dimensional change.« less

A model for compression-weakening materials and the elastic fields due to contractile cells

NASA Astrophysics Data System (ADS)

Rosakis, Phoebus; Notbohm, Jacob; Ravichandran, Guruswami

2015-12-01

We construct a homogeneous, nonlinear elastic constitutive law that models aspects of the mechanical behavior of inhomogeneous fibrin networks. Fibers in such networks buckle when in compression. We model this as a loss of stiffness in compression in the stress-strain relations of the homogeneous constitutive model. Problems that model a contracting biological cell in a finite matrix are solved. It is found that matrix displacements and stresses induced by cell contraction decay slower (with distance from the cell) in a compression weakening material than linear elasticity would predict. This points toward a mechanism for long-range cell mechanosensing. In contrast, an expanding cell would induce displacements that decay faster than in a linear elastic matrix.

SU-E-T-373: Evaluation and Reduction of Contralateral Skin /subcutaneous Dose for Tangential Breast Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butson, M; Carroll, S; Whitaker, M

2015-06-15

Purpose: Tangential breast irradiation is a standard treatment technique for breast cancer therapy. One aspect of dose delivery includes dose delivered to the skin caused by electron contamination. This effect is especially important for highly oblique beams used on the medical tangent where the electron contamination deposits dose on the contralateral breast side. This work aims to investigate and predict as well as define a method to reduce this dose during tangential breast radiotherapy. Methods: Analysis and calculation of breast skin and subcutaneous dose is performed using a Varian Eclipse planning system, AAA algorithm for 6MV x-ray treatments. Measurements weremore » made using EBT3 Gafchromic film to verify the accuracy of planning data. Various materials were tested to assess their ability to remove electron contamination on the contralateral breast. Results: Results showed that the Varian Eclipse AAA algorithm could accurately estimate contralateral breast dose in the build-up region at depths of 2mm or deeper. Surface dose was underestimated by the AAA algorithm. Doses up to 12% of applied dose were seen on the contralateral breast surface and up to 9 % at 2mm depth. Due to the nature of this radiation, being mainly low energy electron contamination, a bolus material could be used to reduce this dose to less than 3%. This is accomplished by 10 mm of superflab bolus or by 1 mm of lead. Conclusion: Contralateral breast skin and subcutaneous dose is present for tangential breast treatment and has been measured to be up to 12% of applied dose from the medial tangent beam. This dose is deposited at shallow depths and is accurately calculated by the Eclipse AAA algorithm at depths of 2mm or greater. Bolus material placed over the contralateral can be used to effectively reduce this skin dose.« less

Study of factors influencing the mechanical properties of polyurethane foams under dynamic compression

NASA Astrophysics Data System (ADS)

Linul, E.; Marsavina, L.; Voiconi, T.; Sadowski, T.

2013-07-01

Effect of density, loading rate, material orientation and temperature on dynamic compression behavior of rigid polyurethane foams are investigated in this paper. These parameters have a very important role, taking into account that foams are used as packing materials or dampers which require high energy impact absorption. The experimental study was carried out on closed-cell rigid polyurethane (PUR) foam specimens of different densities (100, 160 respectively 300 kg/m3), having a cubic shape. The specimens were subjected to uniaxial dynamic compression with loading rate in range of 1.37-3.25 m/s, using four different temperatures (20, 60, 90, 110°C) and two loading planes (direction (3) - rise direction and direction (2) - in plane). Experimental results show that Young's modulus, yield stress and plateau stress values increases with increasing density. One of the most significant effects of mechanical properties in dynamic compression of rigid PUR foams is the density, but also the loading speed, material orientation and temperature influences the behavior in compression

Estimation of Power Consumption in the Circular Sawing of Stone Based on Tangential Force Distribution

NASA Astrophysics Data System (ADS)

Huang, Guoqin; Zhang, Meiqin; Huang, Hui; Guo, Hua; Xu, Xipeng

2018-04-01

Circular sawing is an important method for the processing of natural stone. The ability to predict sawing power is important in the optimisation, monitoring and control of the sawing process. In this paper, a predictive model (PFD) of sawing power, which is based on the tangential force distribution at the sawing contact zone, was proposed, experimentally validated and modified. With regard to the influence of sawing speed on tangential force distribution, the modified PFD (MPFD) performed with high predictive accuracy across a wide range of sawing parameters, including sawing speed. The mean maximum absolute error rate was within 6.78%, and the maximum absolute error rate was within 11.7%. The practicability of predicting sawing power by the MPFD with few initial experimental samples was proved in case studies. On the premise of high sample measurement accuracy, only two samples are required for a fixed sawing speed. The feasibility of applying the MPFD to optimise sawing parameters while lowering the energy consumption of the sawing system was validated. The case study shows that energy use was reduced 28% by optimising the sawing parameters. The MPFD model can be used to predict sawing power, optimise sawing parameters and control energy.

Pore-water extraction from unsaturated tuff by triaxial and one-dimensional compression methods, Nevada Test Site, Nevada

USGS Publications Warehouse

Mower, Timothy E.; Higgins, Jerry D.; Yang, In C.; Peters, Charles A.

1994-01-01

Study of the hydrologic system at Yucca Mountain, Nevada, requires the extraction of pore-water samples from welded and nonwelded, unsaturated tuffs. Two compression methods (triaxial compression and one-dimensional compression) were examined to develop a repeatable extraction technique and to investigate the effects of the extraction method on the original pore-fluid composition. A commercially available triaxial cell was modified to collect pore water expelled from tuff cores. The triaxial cell applied a maximum axial stress of 193 MPa and a maximum confining stress of 68 MPa. Results obtained from triaxial compression testing indicated that pore-water samples could be obtained from nonwelded tuff cores that had initial moisture contents as small as 13 percent (by weight of dry soil). Injection of nitrogen gas while the test core was held at the maximum axial stress caused expulsion of additional pore water and reduced the required initial moisture content from 13 to 11 percent. Experimental calculations, together with experience gained from testing moderately welded tuff cores, indicated that the triaxial cell used in this study could not apply adequate axial or confining stress to expel pore water from cores of densely welded tuffs. This concern led to the design, fabrication, and testing of a one-dimensional compression cell. The one-dimensional compression cell used in this study was constructed from hardened 4340-alloy and nickel-alloy steels and could apply a maximum axial stress of 552 MPa. The major components of the device include a corpus ring and sample sleeve to confine the sample, a piston and base platen to apply axial load, and drainage plates to transmit expelled water from the test core out of the cell. One-dimensional compression extracted pore water from nonwelded tuff cores that had initial moisture contents as small as 7.6 percent; pore water was expelled from densely welded tuff cores that had initial moisture contents as small as 7

Universal behavior of the osmotically compressed cell and its analogy to the colloidal glass transition

PubMed Central

Zhou, E. H.; Trepat, X.; Park, C. Y.; Lenormand, G.; Oliver, M. N.; Mijailovich, S. M.; Hardin, C.; Weitz, D. A.; Butler, J. P.; Fredberg, J. J.

2009-01-01

Mechanical robustness of the cell under different modes of stress and deformation is essential to its survival and function. Under tension, mechanical rigidity is provided by the cytoskeletal network; with increasing stress, this network stiffens, providing increased resistance to deformation. However, a cell must also resist compression, which will inevitably occur whenever cell volume is decreased during such biologically important processes as anhydrobiosis and apoptosis. Under compression, individual filaments can buckle, thereby reducing the stiffness and weakening the cytoskeletal network. However, the intracellular space is crowded with macromolecules and organelles that can resist compression. A simple picture describing their behavior is that of colloidal particles; colloids exhibit a sharp increase in viscosity with increasing volume fraction, ultimately undergoing a glass transition and becoming a solid. We investigate the consequences of these 2 competing effects and show that as a cell is compressed by hyperosmotic stress it becomes progressively more rigid. Although this stiffening behavior depends somewhat on cell type, starting conditions, molecular motors, and cytoskeletal contributions, its dependence on solid volume fraction is exponential in every instance. This universal behavior suggests that compression-induced weakening of the network is overwhelmed by crowding-induced stiffening of the cytoplasm. We also show that compression dramatically slows intracellular relaxation processes. The increase in stiffness, combined with the slowing of relaxation processes, is reminiscent of a glass transition of colloidal suspensions, but only when comprised of deformable particles. Our work provides a means to probe the physical nature of the cytoplasm under compression, and leads to results that are universal across cell type. PMID:19520830

Correlation between swift effects and tension-compression asymmetry in various polycrystalline materials

NASA Astrophysics Data System (ADS)

Revil-Baudard, Benoit; Chandola, Nitin; Cazacu, Oana; Barlat, Frédéric

2014-10-01

The Swift phenomenon, which refers to the occurrence of permanent axial deformation during monotonic free-end torsion, has been known for a very long time. While plastic anisotropy is considered to be its main cause, there is no explanation as to why in certain materials irreversible elongation occurs while in others permanent shortening is observed. In this paper, a correlation between Swift effects and the stress-strain behavior in uniaxial tension and compression is established. It is based on an elastic-plastic model that accounts for the combined influence of anisotropy and tension-compression asymmetry. It is shown that, if for a given orientation the uniaxial yield stress in tension is larger than that in compression, the specimen will shorten when twisted about that direction; however, if the yield stress in uniaxial compression is larger than that in uniaxial tension, axial elongation will occur. Furthermore, it is shown that on the basis of a few simple mechanical tests it is possible to predict the particularities of the plastic response in torsion for both isotropic and initially anisotropic materials. Unlike other previous interpretations of the Swift effects, which were mainly based on crystal plasticity and/or texture evolution, it is explained the occurrence of Swift effects at small to moderate plastic strains. In particular, the very good quantitative agreement between model and data for a strongly anisotropic AZ31-Mg alloy confirm the correlation established in this work between tension-compression asymmetry and Swift effects. Furthermore, it is explained why the sign of the axial plastic strains that develop depends on the twisting direction.

Closed-form solution of the Ogden-Hill's compressible hyperelastic model for ramp loading

NASA Astrophysics Data System (ADS)

Berezvai, Szabolcs; Kossa, Attila

2017-05-01

This article deals with the visco-hyperelastic modelling approach for compressible polymer foam materials. Polymer foams can exhibit large elastic strains and displacements in case of volumetric compression. In addition, they often show significant rate-dependent properties. This material behaviour can be accurately modelled using the visco-hyperelastic approach, in which the large strain viscoelastic description is combined with the rate-independent hyperelastic material model. In case of polymer foams, the most widely used compressible hyperelastic material model, the so-called Ogden-Hill's model, was applied, which is implemented in the commercial finite element (FE) software Abaqus. The visco-hyperelastic model is defined in hereditary integral form, therefore, obtaining a closed-form solution for the stress is not a trivial task. However, the parameter-fitting procedure could be much faster and accurate if closed-form solution exists. In this contribution, exact stress solutions are derived in case of uniaxial, biaxial and volumetric compression loading cases using ramp-loading history. The analytical stress solutions are compared with the stress results in Abaqus using FE analysis. In order to highlight the benefits of the analytical closed-form solution during the parameter-fitting process experimental work has been carried out on a particular open-cell memory foam material. The results of the material identification process shows significant accuracy improvement in the fitting procedure by applying the derived analytical solutions compared to the so-called separated approach applied in the engineering practice.

A compressibility correction of the pressure strain correlation model in turbulent flow

NASA Astrophysics Data System (ADS)

Klifi, Hechmi; Lili, Taieb

2013-07-01

This paper is devoted to the second-order closure for compressible turbulent flows with special attention paid to modeling the pressure-strain correlation appearing in the Reynolds stress equation. This term appears as the main one responsible for the changes of the turbulence structures that arise from structural compressibility effects. From the analysis and DNS results of Simone et al. and Sarkar, the compressibility effects on the homogeneous turbulence shear flow are parameterized by the gradient Mach number. Several experiment and DNS results suggest that the convective Mach number is appropriate to study the compressibility effects on the mixing layers. The extension of the LRR model recently proposed by Marzougui, Khlifi and Lili for the pressure-strain correlation gives results that are in disagreement with the DNS results of Sarkar for high-speed shear flows. This extension is revised to derive a turbulence model for the pressure-strain correlation in which the compressibility is included in the turbulent Mach number, the gradient Mach number and then the convective Mach number. The behavior of the proposed model is compared to the compressible model of Adumitroiae et al. for the pressure-strain correlation in two turbulent compressible flows: homogeneous shear flow and mixing layers. In compressible homogeneous shear flows, the predicted results are compared with the DNS data of Simone et al. and those of Sarkar. For low compressibility, the two compressible models are similar, but they become substantially different at high compressibilities. The proposed model shows good agreement with all cases of DNS results. Those of Adumitroiae et al. do not reflect any effect of a change in the initial value of the gradient Mach number on the Reynolds stress anisotropy. The models are used to simulate compressible mixing layers. Comparison of our predictions with those of Adumitroiae et al. and with the experimental results of Goebel et al. shows good qualitative

Laser quench hardening of steel: Effects of superimposed elastic pre-stress on the hardness and residual stress distribution

NASA Astrophysics Data System (ADS)

Meserve, Justin

Cold drawn AISI 4140 beams were LASER surface hardened with a 2 kW CO2 LASER. Specimens were treated in the free state and while restrained in a bending fixture inducing surface tensile stresses of 94 and 230 MPa. Knoop hardness indentation was used to evaluate the through thickness hardness distribution, and a layer removal methodology was used to evaluate the residual stress distribution. Results showed the maximum surface hardness attained was not affected by pre-stress during hardening, and ranged from 513 to 676 kg/mm2. The depth of effective hardening varied at different magnitudes of pre-stress, but did not vary proportionately to the pre-stress. The surface residual stress, coinciding with the maximum compressive residual stress, increased as pre-stress was increased, from 1040 MPa for the nominally treated specimens to 1270 MPa for specimens pre-stressed to 230 MPa. The maximum tensile residual stress observed in the specimens decreased from 1060 MPa in the nominally treated specimens to 760 MPa for specimens pre-stressed to 230 MPa. Similarly, thickness of the compressive residual stress region increased and the depth at which maximum tensile residual stress occurred increased as the pre-stress during treatment was increased Overall, application of tensile elastic pre-stress during LASER hardening is beneficial to the development of compressive residual stress in AISI 4140, with minimal impact to the hardness attained from the treatment. The newly developed approach for LASER hardening may support efforts to increase both the wear and fatigue resistance of parts made from hardenable steels.

Miniature stress transducer has directional capability

NASA Technical Reports Server (NTRS)

San Miguel, A.; Silver, R. H.

1965-01-01

Miniature stress transducer uses a semiconductive piezoresistive element to detect stress only on specific axes. Measurement of internal mass stress is based on the compressive deformation of the transducer. The device is applicable to constant stress monitoring in building and dam structural parts.

Stress path dependent hydromechanical behaviour of heterogeneous carbonate rock

NASA Astrophysics Data System (ADS)

Gland, N.; Dautriat, J.; Dimanov, A.; Raphanel, J.

2010-06-01

The influence of stress paths, representative of reservoir conditions, on the hydromechanical behavior of a moderately heterogeneous carbonate has been investigated. Multiscale structural heterogeneities, common for instance in carbonate rocks, can strongly alter the mechanical response and significantly influence the evolution of flow properties with stress. Using a triaxial cell, the permeability evolutions during compression and the effects of brittle (fracture) and plastic (pore collapse) deformations at yield, were measured. A strong scattering was observed on the mechanical response both in term of compressibility and failure threshold. Using the porosity scaling predicted by an adapted effective medium theory (based on crack growth under Hertzian contact), we have rescaled the critical pressures by the normalized porosity deviation. This procedure reduces efficiently the scattering, revealing in the framework of proportional stress path loading, a linear relation between the critical pressures and the stress path parameter through all the deformation regimes. It leads to a new formulation for the critical state envelope in the 'mean stress, deviatoric stress' diagram. The attractive feature of this new yield envelope formulation relies on the fact that only the two most common different mechanical tests 'Uniaxial Compression' and 'Hydrostatic Compression', are needed to define entirely the yield envelope. Volumic strains and normalized permeabilities are finally mapped in the stresses diagram and correlated.

Compression-induced texture change in NiMnGa-polymer composites observed by synchrotron radiation

NASA Astrophysics Data System (ADS)

Scheerbaum, Nils; Hinz, Dietrich; Gutfleisch, Oliver; Skrotzki, Werner; Schultz, Ludwig

2007-05-01

Composites consisting of magnetic shape memory (MSM) particles embedded in a polyester matrix were prepared. Single-crystalline MSM particles were obtained by mortar grinding of melt-extracted and subsequently annealed Ni50.9Mn27.1Ga22.0 (at. %) fibers. The crystal structure of the martensite is tetragonal (5M) with c stress induced twin boundary motion in the MSM particles, as the compressed composite is easy to magnetize in the direction of compression and more difficult to magnetize in the perpendicular directions. The texture of all the embedded MSM particles is investigated before and after compression by means of synchrotron radiation. In the initial state, the MSM particles in the composite have a random texture, i.e., there is no preferred orientation of the c axis. After a 30% compression (height reduction), the MSM particles have a (004)-fiber texture in the direction of compression. This is unambiguous evidence for stress induced twin boundary motion within the MSM particles.

Individualized Selection of Beam Angles and Treatment Isocenter in Tangential Breast Intensity Modulated Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penninkhof, Joan, E-mail: j.penninkhof@erasmusmc.nl; Spadola, Sara; Department of Physics and Astronomy, Alma Mater Studiorum, University of Bologna, Bologna

Purpose and Objective: Propose a novel method for individualized selection of beam angles and treatment isocenter in tangential breast intensity modulated radiation therapy (IMRT). Methods and Materials: For each patient, beam and isocenter selection starts with the fully automatic generation of a large database of IMRT plans (up to 847 in this study); each of these plans belongs to a unique combination of isocenter position, lateral beam angle, and medial beam angle. The imposed hard planning constraint on patient maximum dose may result in plans with unacceptable target dose delivery. Such plans are excluded from further analyses. Owing to differencesmore » in beam setup, database plans differ in mean doses to organs at risk (OARs). These mean doses are used to construct 2-dimensional graphs, showing relationships between: (1) contralateral breast dose and ipsilateral lung dose; and (2) contralateral breast dose and heart dose (analyzed only for left-sided). The graphs can be used for selection of the isocenter and beam angles with the optimal, patient-specific tradeoffs between the mean OAR doses. For 30 previously treated patients (15 left-sided and 15 right-sided tumors), graphs were generated considering only the clinically applied isocenter with 121 tangential beam angle pairs. For 20 of the 30 patients, 6 alternative isocenters were also investigated. Results: Computation time for automatic generation of 121 IMRT plans took on average 30 minutes. The generated graphs demonstrated large variations in tradeoffs between conflicting OAR objectives, depending on beam angles and patient anatomy. For patients with isocenter optimization, 847 IMRT plans were considered. Adding isocenter position optimization next to beam angle optimization had a small impact on the final plan quality. Conclusion: A method is proposed for individualized selection of beam angles in tangential breast IMRT. This may be especially important for patients with cardiac risk factors or

Deformation behavior of open-cell dry natural rubber foam: Effect of different concentration of blowing agent and compression strain rate

NASA Astrophysics Data System (ADS)

Samsudin, M. S. F.; Ariff, Z. M.; Ariffin, A.

2017-04-01

Compression and deformation behavior of partially open cell natural rubber (NR) foam produced from dry natural rubber (DNR), were investigated by performing compressive deformation at different strains and strain rates. Different concentrations of sodium bicarbonate as a blowing agent (BA) were utilized, from 4 to 16 phr in order to produce foams with range of cell size and morphology. Overall, increasing of blowing agent concentration had significantly changed relative foam density. Compression stress-strain curves of the foams exhibited that the compression behavior was directly correlated to the foam cells morphology and physical density. Pronounced changes were noticed for foams with bigger cells particularly at 4 phr concentration of BA where the compression stress at plateau region was greater compared to those with higher concentration of BA. Cell deformation progressive images confirmed that the foams demonstrated small degree of struts bending at 15% of strain and followed by continuous severe struts bending and elastic buckling up to 50% of strain. Compression test at different strain rates revealed that the strain rate factor only affected the foams with 4 phr of BA by causing immediate increment in the compression stress value when higher strain rate was applied.

Long-Term Stability of Residual Stress Improvement by Water Jet Peening Considering Working Processes.

PubMed

Hashimoto, Tadafumi; Osawa, Yusuke; Itoh, Shinsuke; Mochizuki, Masahito; Nishimoto, Kazutoshi

2013-06-01

To prevent primary water stress corrosion cracking (PWSCC), water jet peening (WJP) has been used on the welds of Ni-based alloys in pressurized water reactors (PWRs). Before WJP, the welds are machined and buffed in order to conduct a penetrant test (PT) to verify the weld qualities to access, and microstructure evolution takes place in the target area due to the severe plastic deformation. The compressive residual stresses induced by WJP might be unstable under elevated temperatures because of the high dislocation density in the compressive stress layer. Therefore, the stability of the compressive residual stresses caused by WJP was investigated during long-term operation by considering the microstructure evolution due to the working processes. The following conclusions were made: The compressive residual stresses were slightly relaxed in the surface layers of the thermally aged specimens. There were no differences in the magnitude of the relaxation based on temperature or time. The compressive residual stresses induced by WJP were confirmed to remain stable under elevated temperatures. The stress relaxation at the surface followed the Johnson-Mehl equation, which states that stress relaxation can occur due to the recovery of severe plastic strain, since the estimated activation energy agrees very well with the self-diffusion energy for Ni. By utilizing the additivity rule, it was indicated that stress relaxation due to recovery is completed during the startup process. It was proposed that the long-term stability of WJP under elevated temperatures must be assessed based on compressive stresses with respect to the yield stress. Thermal elastic-plastic creep analysis was performed to predict the effect of creep strain. After 100 yr of simulated continuous operation at 80% capacity, there was little change in the WJP compressive stresses under an actual operating temperature of 623 K. Therefore, the long-term stability of WJP during actual operation was

Stability of a horizontal well and hydraulic fracture initiation in rocks of the bazhenov formation

NASA Astrophysics Data System (ADS)

Stefanov, Yu. P.; Bakeev, R. A.; Myasnikov, A. V.; Akhtyamova, A. I.; Romanov, A. S.

2017-12-01

Three-dimensional numerical modeling of the formation of the stress-strain state in the vicinity of a horizontal well in weakened rocks of the Bazhenov formation is carried out. The influence of the well orientation and plastic deformation on the stress-strain state and the possibility of hydraulic fracturing are considered. It is shown that the deviation of the well from the direction of maximum compression leads to an increase in plastic deformation and a discrepancy between tangential stresses around the well bore and principle stresses in the surrounding medium. In an elastoplastic medium, an increase in the pressure in the well can lead to a large-scale development of plastic deformation, at which no tensile stresses necessary for hydraulic fracturing according to the classical scheme arise. In this case, there occur plastic expansion and fracture of the well.

Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser

NASA Astrophysics Data System (ADS)

Sano, Yuji; Kimura, Motohiko; Mukai, Naruhiko; Yoda, Masaki; Obata, Minoru; Ogisu, Tatsuki

2000-02-01

The authors have developed a new process of laser-induced shock compression to introduce a residual compressive stress on material surface, which is effective for prevention of stress corrosion cracking (SCC) and enhancement of fatigue strength of metal materials. The process developed is unique and beneficial. It requires no pre-conditioning for the surface, whereas the conventional process requires that the so-called sacrificial layer is made to protect the surface from damage. The new process can be freely applied to water- immersed components, since it uses water-penetrable green light of a frequency-doubled Nd:YAG laser. The process developed has the potential to open up new high-power laser applications in manufacturing and maintenance technologies. The laser-induced shock compression process (LSP) can be used to improve a residual stress field from tensile to compressive. In order to understand the physics and optimize the process, the propagation of a shock wave generated by the impulse of laser irradiation and the dynamic response of the material were analyzed by time-dependent elasto-plastic calculations with a finite element program using laser-induced plasma pressure as an external load. The analysis shows that a permanent strain and a residual compressive stress remain after the passage of the shock wave with amplitude exceeding the yield strength of the material. A practical system materializing the LSP was designed, manufactured, and tested to confirm the applicability to core components of light water reactors (LWRs). The system accesses the target component and remotely irradiates laser pulses to the heat affected zone (HAZ) along weld lines. Various functional tests were conducted using a full-scale mockup facility, in which remote maintenance work in a reactor vessel could be simulated. The results showed that the system remotely accessed the target weld lines and successfully introduced a residual compressive stress. After sufficient training

Radial force distribution changes associated with tangential force production in cylindrical grasping, and the importance of anatomical registration.

PubMed

Pataky, Todd C; Slota, Gregory P; Latash, Mark L; Zatsiorsky, Vladimir M

2012-01-10

Radial force (F(r)) distributions describe grip force coordination about a cylindrical object. Recent studies have employed only explicit F(r) tasks, and have not normalized for anatomical variance when considering F(r) distributions. The goals of the present study were (i) to explore F(r) during tangential force production tasks, and (ii) to examine the extent to which anatomical registration (i.e. spatial normalization of anatomically analogous structures) could improve signal detectability in F(r) data. Twelve subjects grasped a vertically oriented cylindrical handle (diameter=6 cm) and matched target upward tangential forces of 10, 20, and 30 N. F(r) data were measured using a flexible pressure mat with an angular resolution of 4.8°, and were registered using piecewise-linear interpolation between five manually identified points-of-interest. Results indicate that F(r) was primarily limited to three contact regions: the distal thumb, the distal fingers, and the fingers' metatacarpal heads, and that, while increases in tangential force caused significant increases in F(r) for these regions, they did not significantly affect the F(r) distribution across the hand. Registration was found to substantially reduce between-subject variability, as indicated by both accentuated F(r) trends, and amplification of the test statistic. These results imply that, while subjects focus F(r) primarily on three anatomical regions during cylindrical grasp, inter-subject anatomical differences introduce a variability that, if not corrected for via registration, may compromise one's ability to draw anatomically relevant conclusions from grasping force data. Copyright © 2011 Elsevier Ltd. All rights reserved.

Flight trajectories with maximum tangential thrust in a central Newtonian field

NASA Astrophysics Data System (ADS)

Azizov, A. G.; Korshunova, N. A.

1983-07-01

The paper examines the two-dimensional problem of determining the optimal trajectories of a point moving with a limited per-second mass consumption in a central Newtonian field. It is shown that one of the cases in which the variational equations in the Meier formulation can be integrated in quadratures is motion with maximum tangential thrust. Trajectories corresponding to this motion are determined. By way of application, attention is given to the problem of determining the thrust which assures maximum kinetic energy for the point at the moment t = t1, corresponding to the mass consumption M0 - M1, where M0 and M1 are, respectively, the initial and final mass.

Experimental and Numerical Study on the Deformation Mechanism in AZ31B Mg Alloy Sheets Under Pulsed Electric-Assisted Tensile and Compressive Tests

NASA Astrophysics Data System (ADS)

Lee, Jinwoo; Kim, Se-Jong; Lee, Myoung-Gyu; Song, Jung Han; Choi, Seogou; Han, Heung Nam; Kim, Daeyong

2016-06-01

The uniaxial tensile and compressive stress-strain responses of AZ31B magnesium alloy sheet under pulsed electric current are reported. Tension and compression tests with pulsed electric current showed that flow stresses dropped instantaneously when the electric pulses were applied. Thermo-mechanical-electrical finite element analyses were also performed to investigate the effects of Joule heating and electro-plasticity on the flow responses of AZ31B sheets under electric-pulsed tension and compression tests. The proposed finite element simulations could reproduce the measured uniaxial tensile and compressive stress-strain curves under pulsed electric currents, when the temperature-dependent flow stress hardening model and thermal properties of AZ31B sheet were properly described in the simulations. In particular, the simulation results that fit best with experimental results showed that almost 100 pct of the electric current was subject to transform into Joule heating during electrically assisted tensile and compressive tests.

A tangentially viewing fast ion D-alpha diagnostic for NSTX.

PubMed

Bortolon, A; Heidbrink, W W; Podestà, M

2010-10-01

A second fast ion D-alpha (FIDA) installation is planned at NSTX to complement the present perpendicular viewing FIDA diagnostics. Following the present diagnostic scheme, the new diagnostic will consist of two instruments: a spectroscopic diagnostic that measures fast ion spectra and profiles at 16 radial points with 5-10 ms resolution and a system that uses a band pass filter and photomultiplier to measure changes in FIDA light with 50 kHz sampling rate. The new pair of FIDA instruments will view the heating beams tangentially. The viewing geometry minimizes spectral contamination by beam emission or edge sources of background emission. The improved velocity-space resolution will provide detailed information about neutral-beam current drive and about fast ion acceleration and transport by injected radio frequency waves and plasma instabilities.

Improved design of a tangential entry cyclone separator for separation of particles from exhaust gas of diesel engine.

PubMed

Mukhopadhyay, N

2011-01-01

An effective design of cyclone separator with tangential inlet is developed applying an equation derived from the correlation of collection efficiency with maximum pressure drop components of the cyclone, which can efficiently remove the particles around 1microm of the exhaust gas of diesel engine.

Modelling the effect of shear strength on isentropic compression experiments

NASA Astrophysics Data System (ADS)

Thomson, Stuart; Howell, Peter; Ockendon, John; Ockendon, Hilary

2017-01-01

Isentropic compression experiments (ICE) are a way of obtaining equation of state information for metals undergoing violent plastic deformation. In a typical experiment, millimetre thick metal samples are subjected to pressures on the order of 10 - 102 GPa, while the yield strength of the material can be as low as 10-2 GPa. The analysis of such experiments has so far neglected the effect of shear strength, instead treating the highly plasticised metal as an inviscid compressible fluid. However making this approximation belies the basic elastic nature of a solid object. A more accurate method should strive to incorporate the small but measurable effects of shear strength. Here we present a one-dimensional mathematical model for elastoplasticity at high stress which allows for both compressibility and the shear strength of the material. In the limit of zero yield stress this model reproduces the hydrodynamic models currently used to analyse ICEs. Numerical solutions of the governing equations will then be presented for problems relevant to ICEs in order to investigate the effects of shear strength compared with a model based purely on hydrodynamics.

Wave Augmented Diffusers for Centrifugal Compressors

NASA Technical Reports Server (NTRS)

Paxson, Daniel E.; Skoch, Gary J.

1998-01-01

A conceptual device is introduced which would utilize unsteady wave motion to slow and turn flows in the diffuser section of a centrifugal compressor. The envisioned device would substantially reduce the size of conventional centrifugal diffusers by eliminating the relatively large ninety degree bend needed to turn the flow from the radial/tangential to the axial direction. The bend would be replaced by a wall and the flow would instead exit through a series of rotating ports located on a disk, adjacent to the diffuser hub, and fixed to the impeller shaft. The ports would generate both expansion and compression waves which would rapidly transition from the hub/shroud (axial) direction to the radial/tangential direction. The waves would in turn induce radial/tangential and axial flow. This paper presents a detailed description of the device. Simplified cycle analysis and performance results are presented which were obtained using a time accurate, quasi-one-dimensional CFD code with models for turning, port flow conditions, and losses due to wall shear stress. The results indicate that a periodic wave system can be established which yields diffuser performance comparable to a conventional diffuser. Discussion concerning feasibility, accuracy, and integration follow.

Effects of gas sorption-induced swelling/shrinkage on the cleat compressibility of coal under different bedding directions.

PubMed

Peng, Shoujian; Fang, Zhiming; Shen, Jian; Xu, Jiang; Wang, Geoff

2017-10-30

The cleat compressibility of coal is a key parameter that is extensively used in modeling the coal reservoir permeability for Coal Bed Methane (CBM) recovery. Cleat compressibility is often determined from the permeability measurement made at different confining pressures but with a constant pore pressure. Hence, this parameter ignores the sorption strain effects on the cleat compressibility. By using the transient pulse decay (TPD) technique, this study presents the results from a laboratory characterization program using coal core drilled from different bedding directions to estimate gas permeability and coal cleat compressibility under different pore pressures while maintaining effective stress constant. Cleat compressibility was determined from permeability and sorption strain measurements that are made at different pore pressures under an effective stress constant. Results show that the cleat compressibility of coal increases slightly with the increase of pore pressure. Moreover, the cleat compressibility of Sample P (representing the face cleats in coal) is larger than that of Sample C (representing the butt cleats in coal). This result suggests that cleat compressibility should not be regarded as constant in the modeling of the CBM recovery. Furthermore, the compressibility of face cleats is considerably sensitive to the sorption-induced swelling/shrinkage and offers significant effects on the coal permeability.

Analysis of stresses at the bore of a drilled ball operating in a high-speed bearing. [with stiffening web

NASA Technical Reports Server (NTRS)

Coe, H. H.; Lynch, J. E.

1973-01-01

Three-dimensional stress distributions were calculated for both a regular drilled ball with a stiffening web. The balls were 20.6 mm (0.8125 in.) in diameter and had a 12.6 mm (0.496 in.) diameter concentric hole. The stiffening web was 1.5 mm (0.06 in.) thick. The calculations showed that a large reversing tangential stress at the hole bore was reduced by one-half by the addition of the web.

Effective Size Analysis of the Diametral Compression (Brazil) Test Specimen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadaan, Osama M.; Wereszczak, Andrew A

2009-04-01

This study considers the finite element analysis (FEA) simulation and Weibull effective size analysis for the diametral compression (DC) or Brazil specimen loaded with three different push-rod geometries. Those geometries are a flat push-rod, a push-rod whose radius of curvature is larger than that for the DC specimen, and a push-rod whose radius of curvature matches that of the DC specimen. Such established effective size analysis recognizes that the tensile strength of structural ceramics is typically one to two orders of magnitude less than its compressive strength. Therefore, because fracture is much more apt to result from a tensile stressmore » than a compressive one, this traditional analysis only considers the first principal tensile stress field in the mechanically loaded ceramic component for the effective size analysis. The effective areas and effective volumes were computed as function of Weibull modulus using the CARES/Life code. Particular attention was devoted to the effect of mesh sensitivity and localized stress concentration. The effect of specimen width on the stress state was also investigated. The effects of push-rod geometry, the use of steel versus WC push-rods, and considering a frictionless versus no-slip interface between push-rod and specimen on the maximum stresses, where those stresses are located, and the effective area and effective volume results are described. Of the three push-rod geometries, it is concluded that the push-rod (made from WC rather than steel) whose radius of curvature matches that of the DC specimen is the most apt to cause fracture initiation within the specimen's bulk rather than at the loading interface. Therefore, its geometry is the most likely to produce a valid diametral compression strength test. However, the DC specimen remains inefficient in terms of its area and volume efficiencies; namely, the tensile strength of only a few percent of the specimen's entire area or volume is sampled. Given the high

Evaluation on Compressive Characteristics of Medical Stents Applied by Mesh Structures

NASA Astrophysics Data System (ADS)

Hirayama, Kazuki; He, Jianmei

2017-11-01

There are concerns about strength reduction and fatigue fracture due to stress concentration in currently used medical stents. To address these problems, meshed stents applied by mesh structures were interested for achieving long life and high strength perfromance of medical stents. The purpose of this study is to design basic mesh shapes to obatin three dimensional (3D) meshed stent models for mechanical property evaluation. The influence of introduced design variables on compressive characteristics of meshed stent models are evaluated through finite element analysis using ANSYS Workbench code. From the analytical results, the compressive stiffness are changed periodically with compressive directions, average results need to be introduced as the mean value of compressive stiffness of meshed stents. Secondly, compressive flexibility of meshed stents can be improved by increasing the angle proportional to the arm length of the mesh basic shape. By increasing the number of basic mesh shapes arranged in stent’s circumferential direction, compressive rigidity of meshed stent tends to be increased. Finaly reducing the mesh line width is found effective to improve compressive flexibility of meshed stents.

Compressive Behavior of Fiber-Reinforced Concrete with End-Hooked Steel Fibers.

PubMed

Lee, Seong-Cheol; Oh, Joung-Hwan; Cho, Jae-Yeol

2015-03-27

In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize the effect of specimen size on fiber distribution, 48 cylinder specimens 150 mm in diameter and 300 mm in height were prepared and then subjected to uniaxial compression. From the test results, it was shown that steel fiber-reinforced concrete (SFRC) specimens exhibited ductile behavior after reaching their compressive strength. It was also shown that the strain at the compressive strength generally increased along with an increase in the fiber volumetric ratio and fiber aspect ratio, while the elastic modulus decreased. With consideration for the effect of steel fibers, a model for the stress-strain relationship of SFRC under compression is proposed here. Simple formulae to predict the strain at the compressive strength and the elastic modulus of SFRC were developed as well. The proposed model and formulae will be useful for realistic predictions of the structural behavior of SFRC members or structures.

Compressive strength of marine material mixed concrete

NASA Astrophysics Data System (ADS)

Adnan; Parung, H.; Tjaronge, M. W.; Djamaluddin, R.

2017-11-01

Many cement factories have been incorporated fly ash with clinker cement to produce blended cement. PCC is a type of blended cement incorporated fly ash that produced in Indonesia cement factories. To promote the sustainable development in the remote islands this present paper attempted to study the suitability of sea water, marine sand that available abundantly surround the remote island with Portland Composite Cement (PCC) and crushed river stone to produce concrete. Slump test was conducted to evaluate the workability of fresh concrete and also compressive strength with stress-strain relationship was carried out to evaluate the hardened concrete that cured with two curing condition (e.g. sea water curing, and tap water-wet burlap curing). Test result indicated that fresh concrete had proper workability and all hardened specimens appeared a good compaction result. Compressive strength of specimens cured which sea water was higher than the specimens which cured by tap water-wet burlap where stress-strain behavior of specimens made with sea water, marine sand, and PCC had similar behavior with specimens which made with PCC and tap water.

Tangential Flow Filtration of Hemoglobin

PubMed Central

Sun, Guoyong; Harris, David R.

2009-01-01

Bovine and human hemoglobin (bHb and hHb, respectively) was purified from bovine and human red blood cells (bRBCs and hRBCs, respectively) via tangential flow filtration (TFF) in four successive stages. TFF is a fast and simple method to purify Hb from RBCs using filtration through hollow fiber (HF) membranes. Most of the Hb was retained in stage III (100 kDa HF membrane) and displayed methemoglobin levels less than 1%, yielding final concentrations of 318 and 300 mg/mL for bHb and hHb, respectively. Purified Hb exhibited much lower endotoxin levels than their respective RBCs. The purity of Hb was initially assessed via SDS-PAGE, and showed tiny impurity bands for the stage III retentate. The oxygen affinity (P50), and cooperativity coefficient (n) were regressed from the measured oxygen-RBC/Hb equilibrium curves of RBCs and purified Hb. These results suggest that TFF yielded oxygen affinities of bHb and hHb that are comparable to values in the literature. LC-MS was used to measure the molecular weight of the alpha (α) and beta (β) globin chains of purified Hb. No impurity peaks were present in the HPLC chromatograms of purified Hb. The mass of the molecular ions corresponding to the α and β globin chains agreed well with the calculated theoretical mass of the α-and β-globin chains. Taken together, our results demonstrate that HPLC grade Hb can be generated via TFF. In general, this method can be more broadly applied to purify Hb from any source of RBCs. This work is significant, since it outlines a simple method for generating Hb for synthesis and/or formulation of Hb-based oxygen carriers (HBOCs). PMID:19224583

Effect of stress nonhomogeneity on the shear melting of a thin boundary lubrication layer.

PubMed

Lyashenko, Iakov A; Filippov, Alexander E; Popov, Mikhail; Popov, Valentin L

2016-11-01

We consider the dynamical properties of boundary lubrication in contact between two atomically smooth solid surfaces separated by an ultrathin layer of lubricant. In contrast to previous works on this topic, we explicitly consider the heterogeneity of tangential stresses, which arises in a contact of elastic bodies that are moved tangentially relative to each other. To describe phase transitions between structural states of the lubricant we use an approach based on the field theory of phase transitions. It is assumed that the lubricant layer, when stressed, can undergo a shear-melting transition of first or second order. While solutions for the homogeneous system can be easily obtained analytically, the kinetics of the phase transitions in the spatially heterogeneous system can only be studied numerically. In our numerical experiments melting of the lubricant layer starts from the outer boundary of contact and propagates to its center. The melting wave is followed by a wave of solidification. This process repeats itself periodically, following the stick-slip pattern that is characteristic of such systems. Depending on the thermodynamic and kinetic parameters of the model, different modes of sliding with almost complete or only partial intermediate solidification are possible.

Safety for Compressed Gas and Air Equipment. Module SH-26. Safety and Health.

ERIC Educational Resources Information Center

Center for Occupational Research and Development, Inc., Waco, TX.

This student module on safety for compressed gas and air equipment is one of 50 modules concerned with job safety and health. This module presents technical data about commonly used gases and stresses the procedures necessary for safe handling of compressed gases. Following the introduction, 14 objectives (each keyed to a page in the text) the…

Axial residual stresses in boron fibers

NASA Technical Reports Server (NTRS)

Behrendt, D. R.

1978-01-01

The axial residual stress distribution as a function of radius was determined from the fiber surface to the core including the average residual stress in the core. Such measurements on boron on tungsten (B/W) fibers show that the residual stresses for 102, 142, 203, and 366 micron diameter fibers were similar, being compressive at the surface and changing monotonically to a region of tensile within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile stress of about 860 mn/sq.m and then decreases to a compressive stress near the tungsten boride core. Data were presented for 203 micron diameter B/W fibers that show annealing above 900 C reduces the residual stresses. A comparison between 102 micron diameter B/W and boron on carbon (b/C) shows that the residual stresses were similar in the outer regions of the fibers, but that large differences near and in the core were observed. The effects of these residual stresses on the fracture of boron fibers were discussed.

Failure analysis of composite laminates including biaxial compression

NASA Technical Reports Server (NTRS)

Tennyson, R. C.; Elliott, W. G.

1983-01-01

This report describes a continued effort on the development and application of the tensor polynomial failure criterion for composite laminate analysis. In particular, emphasis is given to the design, construction and testing of a cross-beam laminate configuration to obtain "pure' biaxial compression failure. The purpose of this test case was to provide to permit "closure' of the cubic form of the failure surface in the 1-2 compression-compression quadrant. This resulted in a revised set of interaction strength parameters and the construction of a failure surface which can be used with confidence for strength predictions, assuming a plane stress state exists. Furthermore, the problem of complex conjugate roots which can occur in some failure regions is addressed and an "engineering' interpretation is provided. Results are presented illustrating this behavior and the methodology for overcoming this problem is discussed.

A critical state model for mudrock behavior at high stress levels

NASA Astrophysics Data System (ADS)

Heidari, M.; Nikolinakou, M. A.; Flemings, P. B.

2016-12-01

Recent experimental work has documented that the compression behavior, friction angle, and lateral stress ratio (k0) of mudrocks vary over the stress range of 1 to 100 MPa. We integrate these observations into a critical state model. The internal friction angle and the slope of the compression curve are key parameters in a mudrock critical state model. Published models assume that these parameters do not depend on the stress level, and hence predict lateral stress and normalized strength ratios that do not change with the stress level. However, recent experimental data on resedimented mudrock samples from Eugene Island, Gulf of Mexico, demonstrate that all these parameters vary considerably with the stress level (Casey and Germaine, 2013; Casey et al., 2015). To represent these variations, we develop an enhanced critical state model that uses a stress-level-dependent friction angle and a curvilinear compression curve. We show that this enhanced model predicts the observed variations of the lateral stress and strength ratios. The successful performance of our model indicates that the critical state theory developed for soil can predict mudrock nonlinear behavior at high stress levels and thus can be used in modeling geologic systems. Casey, B., Germaine, J., 2013. Stress Dependence of Shear Strength in Fine-Grained Soils and Correlations with Liquid Limit. J. Geotech. Geoenviron. Eng. 139, 1709-1717. Casey, B., Germaine, J., Flemings, P.B., Fahy, B.P., 2015. Estimating horizontal stresses for mudrocks under one-dimensional compression. Mar. Pet. Geol. 65, 178-186.

Investigation of the ellipsoidal-statistical Bhatnagar-Gross-Krook kinetic model applied to gas-phase transport of heat and tangential momentum between parallel walls

NASA Astrophysics Data System (ADS)

Gallis, M. A.; Torczynski, J. R.

2011-03-01

The ellipsoidal-statistical Bhatnagar-Gross-Krook (ES-BGK) kinetic model is investigated for steady gas-phase transport of heat, tangential momentum, and mass between parallel walls (i.e., Fourier, Couette, and Fickian flows). This investigation extends the original study of Cercignani and Tironi, who first applied the ES-BGK model to heat transport (i.e., Fourier flow) shortly after this model was proposed by Holway. The ES-BGK model is implemented in a molecular-gas-dynamics code so that results from this model can be compared directly to results from the full Boltzmann collision term, as computed by the same code with the direct simulation Monte Carlo (DSMC) algorithm of Bird. A gas of monatomic molecules is considered. These molecules collide in a pairwise fashion according to either the Maxwell or the hard-sphere interaction and reflect from the walls according to the Cercignani-Lampis-Lord model with unity accommodation coefficients. Simulations are performed at pressures from near-free-molecular to near-continuum. Unlike the BGK model, the ES-BGK model produces heat-flux and shear-stress values that both agree closely with the DSMC values at all pressures. However, for both interactions, the ES-BGK model produces molecular-velocity-distribution functions that are qualitatively similar to those determined for the Maxwell interaction from Chapman-Enskog theory for small wall temperature differences and moment-hierarchy theory for large wall temperature differences. Moreover, the ES-BGK model does not produce accurate values of the mass self-diffusion coefficient for either interaction. Nevertheless, given its reasonable accuracy for heat and tangential-momentum transport, its sound theoretical foundation (it obeys the H-theorem), and its available extension to polyatomic molecules, the ES-BGK model may be a useful method for simulating certain classes of single-species noncontinuum gas flows, as Cercignani suggested.

Hot Deformation Behavior and a Two-Stage Constitutive Model of 20Mn5 Solid Steel Ingot during Hot Compression

PubMed Central

Liu, Min; Ma, Qing-Xian; Luo, Jian-Bin

2018-01-01

20Mn5 steel is widely used in the manufacture of heavy hydro-generator shaft forging due to its strength, toughness, and wear resistance. However, the hot deformation and recrystallization behaviors of 20Mn5 steel compressed under a high temperature were not studied. For this article, hot compression experiments under temperatures of 850–1200 °C and strain rates of 0.01 s−1–1 s−1 were conducted using a Gleeble-1500D thermo-mechanical simulator. Flow stress-strain curves and microstructure after hot compression were obtained. Effects of temperature and strain rate on microstructure are analyzed. Based on the classical stress-dislocation relationship and the kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of 20Mn5 steel. Comparisons between experimental flow stress and predicted flow stress show that the predicted flow stress values are in good agreement with the experimental flow stress values, which indicates that the proposed constitutive model is reliable and can be used for numerical simulation of hot forging of 20Mn5 solid steel ingot. PMID:29547570

Experiments in Aircraft Roll-Yaw Control using Forebody Tangential Blowing

NASA Technical Reports Server (NTRS)

Pedreiro, Nelson

1997-01-01

Advantages of flight at high angles of attack include increased maneuverability and lift capabilities. These are beneficial not only for fighter aircraft, but also for future supersonic and hypersonic transport aircraft during take-off and landing. At high angles of attack the aerodynamics of the vehicle are dominated by separation, vortex shedding and possibly vortex breakdown. These phenomena severely compromise the effectiveness of conventional control surfaces. As a result, controlled flight at high angles of attack is not feasible for current aircraft configurations. Alternate means to augment the control of the vehicle at these flight regimes are therefore necessary. The present work investigates the augmentation of an aircraft flight control system by the injection of a thin sheet of air tangentially to the forebody of the vehicle. This method, known as Forebody Tangential Blowing (FTB), has been proposed as an effective means of increasing the controllability of aircraft at high angles of attack. The idea is based on the fact that a small amount of air is sufficient to change the separation lines on the forebody. As a consequence, the strength and position of the vortices are altered causing a change on the aerodynamic loads. Although a very effective actuator, forebody tangential blowing is also highly non-linear which makes its use for aircraft control very difficult. In this work, the feasibility of using FTB to control the roll-yaw motion of a wind tunnel model was demonstrated both through simulations and experimentally. The wind tunnel model used in the experiments consists of a wing-body configuration incorporating a delta wing with 70-degree sweep angle and a cone-cylinder fuselage. The model is equipped with forebody slots through which blowing is applied. There are no movable control surfaces, therefore blowing is the only form of actuation. Experiments were conducted at a nominal angle of attack of 45 degrees. A unique apparatus that constrains

Exact solutions for layered thermocapillary convection of a viscous incompressible fluid with specified stresses on the bottom

NASA Astrophysics Data System (ADS)

Prosviryakov, E. Yu.; Spevak, L. F.

2017-12-01

A new exact solution of the Oberbeck-Boussinesq system is found. The Marangoni thermocapillary convection in an infinite fluid layer is described. It is demonstrated that the specification of tangential stresses at both boundaries of the layered velocity field is nonstationary. Velocities describe a superposition of unidirectional flows with an intermediate time interval when there are counterflows.

Stress perturbation associated with the Amazonas and other ancient continental rifts

USGS Publications Warehouse

Zoback, M.L.; Richardson, R.M.

1996-01-01

The state of stress in the vicinity of old continental rifts is examined to investigate the possibility that crustal structure associated with ancient rifts (specifically a dense rift pillow in the lower crust) may modify substantially the regional stress field. Both shallow (2.0-2.6 km depth) breakout data and deep (20-45 km depth) crustal earthquake focal mechanisms indicate a N to NNE maximum horizontal compression in the vicinity of the Paleozoic Amazonas rift in central Brazil. This compressive stress direction is nearly perpendicular to the rift structure and represents a ???75?? rotation relative to a regional E-W compressive stress direction in the South American plate. Elastic two-dimensional finite element models of the density structure associated with the Amazonas rift (as inferred from independent gravity modeling) indicate that elastic support of this dense feature would generate horizontal rift-normal compressional stresses between 60 and 120 MPa, with values of 80-100 MPa probably most representative of the overall structure. The observed ???75?? stress rotation constrains the ratio of the regional horizontal stress difference to the rift-normal compressive stress to be between 0.25 and 1.0, suggesting that this rift-normal stress may be from 1 to 4 times larger than the regional horizontal stress difference. A general expression for the modification of the normalized local horizontal shear stress (relative to the regional horizontal shear stress) shows that the same ratio of the rift-normal compression relative to the regional horizontal stress difference, which controls the amount of stress rotation, also determines whether the superposed stress increases or decreases the local maximum horizontal shear stress. The potential for fault reactivation of ancient continental rifts in general is analyzed considering both the local stress rotation and modification of horizontal shear stress for both thrust and strike-slip stress regimes. In the Amazonas

The fatigue behavior of composite laminates under various mean stresses

NASA Technical Reports Server (NTRS)

Rotem, A.

1991-01-01

A method is developed for predicting the S-N curve of a composite laminate which is subjected to an arbitrary stress ratio, R (minimum stress/maximum stress). The method is based on the measuring of the S-N behavior of two distinct cases, tension-tension and compression-compression fatigue loadings. Using these parameters, expressions are formulated that estimate the fatigue behavior under any stress ratio loading. Experimental results from the testing of graphite/epoxy laminates, with various structures, are compared with the predictions and show good agreement.

Stress distribution in two-dimensional silos

NASA Astrophysics Data System (ADS)

Blanco-Rodríguez, Rodolfo; Pérez-Ángel, Gabriel

2018-01-01

Simulations of a polydispersed two-dimensional silo were performed using molecular dynamics, with different numbers of grains reaching up to 64 000, verifying numerically the model derived by Janssen and also the main assumption that the walls carry part of the weight due to the static friction between grains with themselves and those with the silo's walls. We vary the friction coefficient, the radii dispersity, the silo width, and the size of grains. We find that the Janssen's model becomes less relevant as the the silo width increases since the behavior of the stresses becomes more hydrostatic. Likewise, we get the normal and tangential stress distribution on the walls evidencing the existence of points of maximum stress. We also obtained the stress matrix with which we observe zones of concentration of load, located always at a height around two thirds of the granular columns. Finally, we observe that the size of the grains affects the distribution of stresses, increasing the weight on the bottom and reducing the normal stress on the walls, as the grains are made smaller (for the same total mass of the granulate), giving again a more hydrostatic and therefore less Janssen-type behavior for the weight of the column.

The problem of a finite strip compressed between two rough rigid stamps

NASA Technical Reports Server (NTRS)

Gupta, G. D.

1975-01-01

A finite strip compressed between two rough rigid stamps is considered. The elastostatic problem is formulated in terms of a singular integral equation from which the proper stress singularities at the corners are determined. The singular integral equation is solved numerically to determine the stresses along the fixed ends of the strip. The effect of material properties and strip geometry on the stress-intensity factor is presented graphically.

Compressive Deformation Behavior of Closed-Cell Micro-Pore Magnesium Composite Foam.

PubMed

Wang, Jing; Wang, Nannan; Liu, Xin; Ding, Jian; Xia, Xingchuan; Chen, Xueguang; Zhao, Weimin

2018-05-04

The closed-cell micro-pore magnesium composite foam with hollow ceramic microspheres (CMs) was fabricated by a modified melt foaming method. The effect of CMs on the compressive deformation behavior of CM-containing magnesium composite foam was investigated. Optical microscopy and scanning electron microscopy were used for observation of the microstructure. Finite element modeling of the magnesium composite foam was established to predict localized stress, fracture of CMs, and the compressive deformation behavior of the foam. The results showed that CMs and pores directly affected the compressive deformation behavior of the magnesium composite foam by sharing a part of load applied on the foam. Meanwhile, the presence of Mg₂Si phase influenced the mechanical properties of the foam by acting as the crack source during the compression process.

Compressive Deformation Behavior of Closed-Cell Micro-Pore Magnesium Composite Foam

PubMed Central

Wang, Jing; Wang, Nannan; Liu, Xin; Ding, Jian; Xia, Xingchuan; Chen, Xueguang; Zhao, Weimin

2018-01-01

The closed-cell micro-pore magnesium composite foam with hollow ceramic microspheres (CMs) was fabricated by a modified melt foaming method. The effect of CMs on the compressive deformation behavior of CM-containing magnesium composite foam was investigated. Optical microscopy and scanning electron microscopy were used for observation of the microstructure. Finite element modeling of the magnesium composite foam was established to predict localized stress, fracture of CMs, and the compressive deformation behavior of the foam. The results showed that CMs and pores directly affected the compressive deformation behavior of the magnesium composite foam by sharing a part of load applied on the foam. Meanwhile, the presence of Mg2Si phase influenced the mechanical properties of the foam by acting as the crack source during the compression process. PMID:29734700

The influence of the compression interface on the failure behavior and size effect of concrete

NASA Astrophysics Data System (ADS)

Kampmann, Raphael

The failure behavior of concrete materials is not completely understood because conventional test methods fail to assess the material response independent of the sample size and shape. To study the influence of strength and strain affecting test conditions, four typical concrete sample types were experimentally evaluated in uniaxial compression and analyzed for strength, deformational behavior, crack initiation/propagation, and fracture patterns under varying boundary conditions. Both low friction and conventional compression interfaces were assessed. High-speed video technology was used to monitor macrocracking. Inferential data analysis proved reliably lower strength results for reduced surface friction at the compression interfaces, regardless of sample shape. Reciprocal comparisons revealed statistically significant strength differences between most sample shapes. Crack initiation and propagation was found to differ for dissimilar compression interfaces. The principal stress and strain distributions were analyzed, and the strain domain was found to resemble the experimental results, whereas the stress analysis failed to explain failure for reduced end confinement. Neither stresses nor strains indicated strength reductions due to reduced friction, and therefore, buckling effects were considered. The high-speed video analysis revealed localize buckling phenomena, regardless of end confinement. Slender elements were the result of low friction, and stocky fragments developed under conventional confinement. The critical buckling load increased accordingly. The research showed that current test methods do not reflect the "true'' compressive strength and that concrete failure is strain driven. Ultimate collapse results from buckling preceded by unstable cracking.

The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

PubMed Central

Amjad, Khurram; Asquith, David; Sebastian, Christopher M.; Wang, Wei-Chung

2017-01-01

This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life. PMID:29291095

The stress relaxation of cement clinkers under high temperature

NASA Astrophysics Data System (ADS)

Wang, Xiufang; Bao, Yiwang; Liu, Xiaogen; Qiu, Yan

2015-12-01

The energy consumption of crushing is directly affected by the mechanical properties of cement materials. This research provides a theoretical proof for the mechanism of the stress relaxation of cement clinkers under high temperature. Compression stress relaxation under various high temperatures is discussed using a specially developed load cell, which can measure stress and displacement under high temperatures inside an autoclave. The cell shows that stress relaxation dramatically increases and that the remaining stress rapidly decreases with an increase in temperature. Mechanical experiments are conducted under various temperatures during the cooling process to study the changes in the grinding resistance of the cement clinker with temperature. The effects of high temperature on the load-displacement curve, compressive strength, and elastic modulus of cement clinkers are systematically studied. Results show that the hardening phenomenon of the clinker becomes apparent with a decrease in temperature and that post-peak behaviors manifest characteristics of the transformation from plasticity to brittleness. The elastic modulus and compressive strength of cement clinkers increase with a decrease in temperature. The elastic modulus increases greatly when the temperature is lower than 1000 °C. The compressive strength of clinkers increases by 73.4% when the temperature drops from 1100 to 800 °C.

Compression wave studies in Blair dolomite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grady, D.E.; Hollenbach, R.E.; Schuler, K.W.

Dynamic compression wave studies have been conducted on Blair dolomite in the stress range of 0-7.0 GPa. Impact techniques were used to generate stress impulse input functions, and diffuse surface laser interferometry provided the dynamic instrumentation. Experimental particle velocity profiles obtained by this method were coupled with the conservation laws of mass and momentum to determine the stress-strain and stress-modulus constitutive properties of the material. Comparison between dynamic and quasistatic uniaxial stress-strain curves uncovered significant differences. Energy dissipated in a complete load and unload cycle differed by almost an order of magnitude and the longitudinal moduli differed by as muchmore » as a factor of two. Blair dolomite was observed to yield under dynamic loading at 2.5 GPa. Below 2.5 GPa the loading waves had a finite risetime and exhibited steady propagation. A finite linear viscoelastic constitutive model satisfactorily predicted the observed wave propagation. We speculate that dynamic properties of preexisting cracks provides a physical mechanism for both the rate dependent steady wave behavior and the difference between dynamic and quasistatic response.« less

The effect of shear strength on isentropic compression experiments

NASA Astrophysics Data System (ADS)

Thomson, Stuart; Howell, Peter; Ockendon, John; Ockendon, Hilary

2015-06-01

Isentropic compression experiments (ICE) are a novel way of obtaining equation of state information for metals undergoing violent plastic deformation. In a typical experiment, millimetre thick metal samples are subjected to pressures on the order of 10 -102 GPa, while the yield strength of the material can be as low as 10-1GPa. The analysis of such experiments has so far neglected the effect of shear strength, instead treating the highly plasticised metal as an inviscid compressible fluid. However making this approximation belies the basic elastic nature of a solid object. A more accurate method should strive to incorporate the small but measurable effects of shear strength. Here we present a one-dimensional mathematical model for elastoplasticity at high stress which allows for both compressibility and the shear strength of the material. In the limit of zero yield stress this model reproduces the hydrodynamic models currently used to analyse ICEs. We will also show using a systematic asymptotic analysis that entropy changes are universally negligible in the absence of shocks. Numerical solutions of the governing equations will then be presented for problems relevant to ICEs in order to investigate the effects of shear strength over a model based purely on hydrodynamics.

Design Issues of the Pre-Compression Rings of Iter

NASA Astrophysics Data System (ADS)

Knaster, J.; Baker, W.; Bettinali, L.; Jong, C.; Mallick, K.; Nardi, C.; Rajainmaki, H.; Rossi, P.; Semeraro, L.

2010-04-01

The pre-compression system is the keystone of ITER. A centripetal force of ˜30 MN will be applied at cryogenic conditions on top and bottom of each TF coil. It will prevent the `breathing effect' caused by the bursting forces occurring during plasma operation that would affect the machine design life of 30000 cycles. Different alternatives have been studied throughout the years. There are two major design requirements limiting the engineering possibilities: 1) the limited available space and 2) the need to hamper eddy currents flowing in the structures. Six unidirectionally wound glass-fibre composite rings (˜5 m diameter and ˜300 mm cross section) are the final design choice. The rings will withstand the maximum hoop stresses <500 MPa at room temperature conditions. Although retightening or replacing the pre-compression rings in case of malfunctioning is possible, they have to sustain the load during the entire 20 years of machine operation. The present paper summarizes the pre-compression ring R&D carried out during several years. In particular, we will address the composite choice and mechanical characterization, assessment of creep or stress relaxation phenomena, sub-sized rings testing and the optimal ring fabrication processes that have led to the present final design.

Application of PDF methods to compressible turbulent flows

NASA Astrophysics Data System (ADS)

Delarue, B. J.; Pope, S. B.

1997-09-01

A particle method applying the probability density function (PDF) approach to turbulent compressible flows is presented. The method is applied to several turbulent flows, including the compressible mixing layer, and good agreement is obtained with experimental data. The PDF equation is solved using a Lagrangian/Monte Carlo method. To accurately account for the effects of compressibility on the flow, the velocity PDF formulation is extended to include thermodynamic variables such as the pressure and the internal energy. The mean pressure, the determination of which has been the object of active research over the last few years, is obtained directly from the particle properties. It is therefore not necessary to link the PDF solver with a finite-volume type solver. The stochastic differential equations (SDE) which model the evolution of particle properties are based on existing second-order closures for compressible turbulence, limited in application to low turbulent Mach number flows. Tests are conducted in decaying isotropic turbulence to compare the performances of the PDF method with the Reynolds-stress closures from which it is derived, and in homogeneous shear flows, at which stage comparison with direct numerical simulation (DNS) data is conducted. The model is then applied to the plane compressible mixing layer, reproducing the well-known decrease in the spreading rate with increasing compressibility. It must be emphasized that the goal of this paper is not as much to assess the performance of models of compressibility effects, as it is to present an innovative and consistent PDF formulation designed for turbulent inhomogeneous compressible flows, with the aim of extending it further to deal with supersonic reacting flows.

Measured Biaxial Residual Stress Maps in a Stainless Steel Weld

DOE PAGES

Olson, Mitchell D.; Hill, Michael R.; Patel, Vipul I.; ...

2015-09-16

Here, this paper describes a sequence of residual stress measurements made to determine a two-dimensional map of biaxial residual stress in a stainless steel weld. A long stainless steel (316L) plate with an eight-pass groove weld (308L filler) was used. The biaxial stress measurements follow a recently developed approach, comprising a combination of contour method and slitting measurements, with a computation to determine the effects of out-of-plane stress on a thin slice. The measured longitudinal stress is highly tensile in the weld- and heat-affected zone, with a maximum around 450 MPa, and compressive stress toward the transverse edges around ₋250more » MPa. The total transverse stress has a banded profile in the weld with highly tensile stress at the bottom of the plate (y = 0) of 400 MPa, rapidly changing to compressive stress (at y = 5 mm) of ₋200 MPa, then tensile stress at the weld root (y = 17 mm) and in the weld around 200 MPa, followed by compressive stress at the top of the weld at around ₋150 MPa. Finally, the results of the biaxial map compare well with the results of neutron diffraction measurements and output from a computational weld simulation.« less

The Role of Microfossils in the Compression of Marine Sediments: Implications for Submarine Slope Failure

NASA Astrophysics Data System (ADS)

Reece, J. S.; Shackleton, T.

2016-12-01

The influence of microfossils on engineering properties has long been recognized. However, most experimental studies have been conducted on diatomites, which are almost exclusively composed of diatom fossils. Here, instead, we analyze the impact of varying amounts of microfossils in natural marine sediments on the macro-scale mechanical behavior. We use foraminifera as an example for microfossils, which, in contrast to diatoms, have been understudied. We uniformly mix foraminifera with natural mudstone from Site C0011 in the Nankai Trough, offshore Japan, obtained during Integrated Ocean Drilling Program (IODP) Expedition 322, at three different microfossil concentrations: 0 wt%, 5 wt%, and 10 wt%. The foraminifera, extracted by washing and sieving, originated from IODP Site U1338 in the Equatorial Pacific. We use resedimentation to prepare the homogeneous microfossil-rich mudstone samples and uniaxially compress them to 100 kPa. Additionally, we use scanning electron microscopy to investigate microstructural changes during compression as a function of microfossil content. Microfossil-rich sediments are known to initially not consolidate to as low porosities as other marine clays owing to microfossil shells acting as structural components. But they show a delayed compressibility when the yield stress is overcome and microfossil shells collapse resulting in an increase in porosity and compressibility. Here, we investigate the 1) threshold microfossil content at which the microfabric significantly changes during compression and 2) stress at which foraminifera chambers start to break. We anticipate to observe an increase in compressibility and microstructural changes in the vicinity of the yield stress with increasing microfossil content attributed to the crushing of foraminifera and particle rearrangement. But the total axial stress of 100 kPa at the end of the resedimentation experiments may not be large enough to have a significant effect on the macroscopic

Compressible Turbulence

NASA Astrophysics Data System (ADS)

Canuto, V. M.

1997-06-01

We present a model to treat fully compressible, nonlocal, time-dependent turbulent convection in the presence of large-scale flows and arbitrary density stratification. The problem is of interest, for example, in stellar pulsation problems, especially since accurate helioseismological data are now available, as well as in accretion disks. Owing to the difficulties in formulating an analytical model, it is not surprising that most of the work has gone into numerical simulations. At present, there are three analytical models: one by the author, which leads to a rather complicated set of equations; one by Yoshizawa; and one by Xiong. The latter two use a Reynolds stress model together with phenomenological relations with adjustable parameters whose determination on the basis of terrestrial flows does not guarantee that they may be extrapolated to astrophysical flows. Moreover, all third-order moments representing nonlocality are taken to be of the down gradient form (which in the case of the planetary boundary layer yields incorrect results). In addition, correlations among pressure, temperature, and velocities are often neglected or treated as in the incompressible case. To avoid phenomenological relations, we derive the full set of dynamic, time-dependent, nonlocal equations to describe all mean variables, second- and third-order moments. Closures are carried out at the fourth order following standard procedures in turbulence modeling. The equations are collected in an Appendix. Some of the novelties of the treatment are (1) new flux conservation law that includes the large-scale flow, (2) increase of the rate of dissipation of turbulent kinetic energy owing to compressibility and thus (3) a smaller overshooting, and (4) a new source of mean temperature due to compressibility; moreover, contrary to some phenomenological suggestions, the adiabatic temperature gradient depends only on the thermal pressure, while in the equation for the large-scale flow, the physical

Predicting failure: acoustic emission of berlinite under compression.

PubMed

Nataf, Guillaume F; Castillo-Villa, Pedro O; Sellappan, Pathikumar; Kriven, Waltraud M; Vives, Eduard; Planes, Antoni; Salje, Ekhard K H

2014-07-09

Acoustic emission has been measured and statistical characteristics analyzed during the stress-induced collapse of porous berlinite, AlPO4, containing up to 50 vol% porosity. Stress collapse occurs in a series of individual events (avalanches), and each avalanche leads to a jerk in sample compression with corresponding acoustic emission (AE) signals. The distribution of AE avalanche energies can be approximately described by a power law p(E)dE = E(-ε)dE (ε ~ 1.8) over a large stress interval. We observed several collapse mechanisms whereby less porous minerals show the superposition of independent jerks, which were not related to the major collapse at the failure stress. In highly porous berlinite (40% and 50%) an increase of energy emission occurred near the failure point. In contrast, the less porous samples did not show such an increase in energy emission. Instead, in the near vicinity of the main failure point they showed a reduction in the energy exponent to ~ 1.4, which is consistent with the value reported for compressed porous systems displaying critical behavior. This suggests that a critical avalanche regime with a lack of precursor events occurs. In this case, all preceding large events were 'false alarms' and unrelated to the main failure event. Our results identify a method to use pico-seismicity detection of foreshocks to warn of mine collapse before the main failure (the collapse) occurs, which can be applied to highly porous materials only.

Permeability of Concrete with Recycled Concrete Aggregate and Pozzolanic Materials under Stress

PubMed Central

Wang, Hailong; Sun, Xiaoyan; Wang, Junjie; Monteiro, Paulo J.M.

2016-01-01

The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the permeability of RAC is much lower than that of the reference concrete due to the on-going hydration and the pozzolanic reaction provided by the PHS and GGBS additives in the RAC mixture. The permeability of chloride under flexural load is much more sensitive than that under compressive load due to the differences in porosity and cracking pattern. At low compressive stress levels, the permeability of chloride decreased by the closing of pores and microcracks within RAC specimens. However, in a relatively short time the chloride diffusion coefficient and the chloride content increased rapidly with the increase of compressive stress when it exceeded a threshold stress level of approximate 35% of the ultimate compressive strength. Under flexural stress, the chloride transport capability increased with the increase of stress level and time. At high compressive and flexural stress levels, creep had a significant effect on the permeability of chloride in the RAC specimens due to the damage from the nucleation and propagation of microcracks over time. It is apparent that mortar cracking has more of a significant effect on the chloride transport in concrete than cracking in the interfacial transition zone (ITZ). PMID:28773376

Permeability of Concrete with Recycled Concrete Aggregate and Pozzolanic Materials under Stress.

PubMed

Wang, Hailong; Sun, Xiaoyan; Wang, Junjie; Monteiro, Paulo J M

2016-03-30

The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the permeability of RAC is much lower than that of the reference concrete due to the on-going hydration and the pozzolanic reaction provided by the PHS and GGBS additives in the RAC mixture. The permeability of chloride under flexural load is much more sensitive than that under compressive load due to the differences in porosity and cracking pattern. At low compressive stress levels, the permeability of chloride decreased by the closing of pores and microcracks within RAC specimens. However, in a relatively short time the chloride diffusion coefficient and the chloride content increased rapidly with the increase of compressive stress when it exceeded a threshold stress level of approximate 35% of the ultimate compressive strength. Under flexural stress, the chloride transport capability increased with the increase of stress level and time. At high compressive and flexural stress levels, creep had a significant effect on the permeability of chloride in the RAC specimens due to the damage from the nucleation and propagation of microcracks over time. It is apparent that mortar cracking has more of a significant effect on the chloride transport in concrete than cracking in the interfacial transition zone (ITZ).

The Pack Method for Compressive Tests of Thin Specimens of Materials Used in Thin-Wall Structures

NASA Technical Reports Server (NTRS)

Aitchison, C S; Tuckerman, L B

1939-01-01

The strength of modern lightweight thin-wall structures is generally limited by the strength of the compression members. An adequate design of these members requires a knowledge of the compressive stress-strain graph of the thin-wall material. The "pack" method was developed at the National Bureau of Standards with the support of the National Advisory Committee for Aeronautics to make possible a determination of compressive stress-strain graphs for such material. In the pack test an odd number of specimens are assembled into a relatively stable pack, like a "pack of cards." Additional lateral stability is obtained from lateral supports between the external sheet faces of the pack and outside reactions. The tests seems adequate for many problems in structural research.

In situ stress evolution during magnetron sputtering of transition metal nitride thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abadias, G.; Guerin, Ph.

2008-09-15

Stress evolution during reactive magnetron sputtering of TiN, ZrN, and TiZrN layers was studied using real-time wafer curvature measurements. The presence of stress gradients is revealed, as the result of two kinetically competing stress generation mechanisms: atomic peening effect, inducing compressive stress, and void formation, leading to a tensile stress regime predominant at higher film thickness. No stress relaxation is detected during growth interrupt in both regimes. A change from compressive to tensile stress is evidenced with increasing film thickness, Ti content, sputtering pressure, and decreasing bias voltage.

The Combined Effects of Stress Concentration and Tensile Stresses from Autofrettage on the Life of Pressure Vessels

DTIC Science & Technology

2017-02-01

Technical Report ARWSB-TR-17011 THE COMBINED EFFECTS OF STRESS CONCENTRATION AND TENSILE STRESSES FROM AUTOFRETTAGE ON THE LIFE OF...SUBTITLE THE COMBINED EFFECTS OF STRESS CONCENTRATION AND TENSILE STRESSES FROM AUTOFRETTAGE ON THE LIFE OF PRESSURE VESSELS 5a. CONTRACT NUMBER...hydraulically or mechanically overstrained in order to impart favorable near bore residual compressive hoop stresses in an attempt to enhance fatigue life. As a

THE COMBINED EFFECTS OF STRESS CONCENTRATION AND TENSILE STRESSES FROM AUTOFRETTAGE ON THE LIFE OF PRESSURE VESSELS

DTIC Science & Technology

2017-02-22

Technical Report ARWSB-TR-17011 THE COMBINED EFFECTS OF STRESS CONCENTRATION AND TENSILE STRESSES FROM AUTOFRETTAGE ON THE LIFE OF...SUBTITLE THE COMBINED EFFECTS OF STRESS CONCENTRATION AND TENSILE STRESSES FROM AUTOFRETTAGE ON THE LIFE OF PRESSURE VESSELS 5a. CONTRACT NUMBER...hydraulically or mechanically overstrained in order to impart favorable near bore residual compressive hoop stresses in an attempt to enhance fatigue life. As a

Tangential symbols: using visual symbolization to teach pharmacological principles of drug addiction to international audiences.

PubMed

Giannini, A J

1993-12-01

Visual art was used to teach the biopsychiatric model of addiction to audiences in the Caribbean, Europe and Mideast. Art slides were tangentially linked to slides of pharmacological data. Stylistically dense art was processed by the intuitive right brain while spare notational pharmacological data was processed by the intellectual (rationalistic) left brain. Simultaneous presentation of these data enhanced attention and retention. This teaching paradigm was based on the nonliterate methods developed by Medieval architects and refined by Italian Renaissance philosopher, Marsilio Ficino.

Computational analysis of forebody tangential slot blowing on the high alpha research vehicle

NASA Technical Reports Server (NTRS)

Gee, Ken

1995-01-01

A numerical analysis of forebody tangential slot blowing as a means of generating side force and yawing moment is conducted using an aircraft geometry. The Reynolds-averaged, thin-layer, Navier-Stokes equations are solved using a partially flux-split, approximately-factored algorithm. An algebraic turbulence model is used to determine the turbulent eddy viscosity values. Solutions are obtained using both patched and overset grid systems. In the patched grid model, and actuator plane is used to introduce jet variables into the flow field. The overset grid model is used to model the physical slot geometry and facilitate modeling of the full aircraft configuration. A slot optimization study indicates that a short slot located close to the nose of the aircraft provided the most side force and yawing moment per unit blowing coefficient. Comparison of computed surface pressure with that obtained in full-scale wind tunnel tests produce good agreement, indicating the numerical method and grid system used in the study are valid. Full aircraft computations resolve the changes in vortex burst point due to blowing. A time-accurate full-aircraft solution shows the effect of blowing on the changes in the frequency of the aerodynamic loads over the vertical tails. A study of the effects of freestream Mach number and various jet parameters indicates blowing remains effective through the transonic Mach range. An investigation of the force onset time lag associated with forebody blowing shows the lag to be minimal. The knowledge obtained in this study may be applied to the design of a forebody tangential slot blowing system for use on flight aircraft.

Compression embedding

DOEpatents

Sandford, M.T. II; Handel, T.G.; Bradley, J.N.

1998-07-07

A method and apparatus for embedding auxiliary information into the digital representation of host data created by a lossy compression technique and a method and apparatus for constructing auxiliary data from the correspondence between values in a digital key-pair table with integer index values existing in a representation of host data created by a lossy compression technique are disclosed. The methods apply to data compressed with algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as ordered sequences of blocks containing integer indices having redundancy and uncertainty of value by one unit, allowing indices which are adjacent in value to be manipulated to encode auxiliary data. Also included is a method to improve the efficiency of lossy compression algorithms by embedding white noise into the integer indices. Lossy compression methods use loss-less compression to reduce to the final size the intermediate representation as indices. The efficiency of the loss-less compression, known also as entropy coding compression, is increased by manipulating the indices at the intermediate stage. Manipulation of the intermediate representation improves lossy compression performance by 1 to 10%. 21 figs.

Compression embedding

DOEpatents

Sandford, II, Maxwell T.; Handel, Theodore G.; Bradley, Jonathan N.

1998-01-01

A method and apparatus for embedding auxiliary information into the digital representation of host data created by a lossy compression technique and a method and apparatus for constructing auxiliary data from the correspondence between values in a digital key-pair table with integer index values existing in a representation of host data created by a lossy compression technique. The methods apply to data compressed with algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as ordered sequences of blocks containing integer indices having redundancy and uncertainty of value by one unit, allowing indices which are adjacent in value to be manipulated to encode auxiliary data. Also included is a method to improve the efficiency of lossy compression algorithms by embedding white noise into the integer indices. Lossy compression methods use loss-less compression to reduce to the final size the intermediate representation as indices. The efficiency of the loss-less compression, known also as entropy coding compression, is increased by manipulating the indices at the intermediate stage. Manipulation of the intermediate representation improves lossy compression performance by 1 to 10%.

Comparative data compression techniques and multi-compression results

NASA Astrophysics Data System (ADS)

Hasan, M. R.; Ibrahimy, M. I.; Motakabber, S. M. A.; Ferdaus, M. M.; Khan, M. N. H.

2013-12-01

Data compression is very necessary in business data processing, because of the cost savings that it offers and the large volume of data manipulated in many business applications. It is a method or system for transmitting a digital image (i.e., an array of pixels) from a digital data source to a digital data receiver. More the size of the data be smaller, it provides better transmission speed and saves time. In this communication, we always want to transmit data efficiently and noise freely. This paper will provide some compression techniques for lossless text type data compression and comparative result of multiple and single compression, that will help to find out better compression output and to develop compression algorithms.

Stress Analysis of B-52B and B-52H Air-Launching Systems Failure-Critical Structural Components

NASA Technical Reports Server (NTRS)

Ko, William L.

2005-01-01

The operational life analysis of any airborne failure-critical structural component requires the stress-load equation, which relates the applied load to the maximum tangential tensile stress at the critical stress point. The failure-critical structural components identified are the B-52B Pegasus pylon adapter shackles, B-52B Pegasus pylon hooks, B-52H airplane pylon hooks, B-52H airplane front fittings, B-52H airplane rear pylon fitting, and the B-52H airplane pylon lower sway brace. Finite-element stress analysis was performed on the said structural components, and the critical stress point was located and the stress-load equation was established for each failure-critical structural component. The ultimate load, yield load, and proof load needed for operational life analysis were established for each failure-critical structural component.

Neurofilaments Function as Shock Absorbers: Compression Response Arising from Disordered Proteins.

PubMed

Kornreich, Micha; Malka-Gibor, Eti; Zuker, Ben; Laser-Azogui, Adi; Beck, Roy

2016-09-30

What can cells gain by using disordered, rather than folded, proteins in the architecture of their skeleton? Disordered proteins take multiple coexisting conformations, and often contain segments which act as random-walk-shaped polymers. Using x-ray scattering we measure the compression response of disordered protein hydrogels, which are the main stress-responsive component of neuron cells. We find that at high compression their mechanics are dominated by gaslike steric and ionic repulsions. At low compression, specific attractive interactions dominate. This is demonstrated by the considerable hydrogel expansion induced by the truncation of critical short protein segments. Accordingly, the floppy disordered proteins form a weakly cross-bridged hydrogel, and act as shock absorbers that sustain large deformations without failure.

Neurofilaments Function as Shock Absorbers: Compression Response Arising from Disordered Proteins

NASA Astrophysics Data System (ADS)

Kornreich, Micha; Malka-Gibor, Eti; Zuker, Ben; Laser-Azogui, Adi; Beck, Roy

2016-09-01

What can cells gain by using disordered, rather than folded, proteins in the architecture of their skeleton? Disordered proteins take multiple coexisting conformations, and often contain segments which act as random-walk-shaped polymers. Using x-ray scattering we measure the compression response of disordered protein hydrogels, which are the main stress-responsive component of neuron cells. We find that at high compression their mechanics are dominated by gaslike steric and ionic repulsions. At low compression, specific attractive interactions dominate. This is demonstrated by the considerable hydrogel expansion induced by the truncation of critical short protein segments. Accordingly, the floppy disordered proteins form a weakly cross-bridged hydrogel, and act as shock absorbers that sustain large deformations without failure.

Phase transitions during compression and decompression of clots from platelet-poor plasma, platelet-rich plasma and whole blood.

PubMed

Liang, Xiaojun; Chernysh, Irina; Purohit, Prashant K; Weisel, John W

2017-09-15

Blood clots are required to stem bleeding and are subject to a variety of stresses, but they can also block blood vessels and cause heart attacks and ischemic strokes. We measured the compressive response of human platelet-poor plasma (PPP) clots, platelet-rich plasma (PRP) clots and whole blood clots and correlated these measurements with confocal and scanning electron microscopy to track changes in clot structure. Stress-strain curves revealed four characteristic regions, for compression-decompression: (1) linear elastic region; (2) upper plateau or softening region; (3) non-linear elastic region or re-stretching of the network; (4) lower plateau in which dissociation of some newly made connections occurs. Our experiments revealed that compression proceeds by the passage of a phase boundary through the clot separating rarefied and densified phases. This observation motivates a model of fibrin mechanics based on the continuum theory of phase transitions, which accounts for the pre-stress caused by platelets, the adhesion of fibrin fibers in the densified phase, the compression of red blood cells (RBCs), and the pumping of liquids through the clot during compression/decompression. Our experiments and theory provide insights into the mechanical behavior of blood clots that could have implications clinically and in the design of fibrin-based biomaterials. The objective of this paper is to measure and mathematically model the compression behavior of various human blood clots. We show by a combination of confocal and scanning electron microscopy that compression proceeds by the passage of a front through the sample that separates a densified region of the clot from a rarefied region, and that the compression/decompression response is reversible with hysteresis. These observations form the basis of a model for the compression response of clots based on the continuum theory of phase transitions. Our studies may reveal how clot rheology under large compression in vivo due

Compression of electromyographic signals using image compression techniques.

PubMed

Costa, Marcus Vinícius Chaffim; Berger, Pedro de Azevedo; da Rocha, Adson Ferreira; de Carvalho, João Luiz Azevedo; Nascimento, Francisco Assis de Oliveira

2008-01-01

Despite the growing interest in the transmission and storage of electromyographic signals for long periods of time, few studies have addressed the compression of such signals. In this article we present an algorithm for compression of electromyographic signals based on the JPEG2000 coding system. Although the JPEG2000 codec was originally designed for compression of still images, we show that it can also be used to compress EMG signals for both isotonic and isometric contractions. For EMG signals acquired during isometric contractions, the proposed algorithm provided compression factors ranging from 75 to 90%, with an average PRD ranging from 3.75% to 13.7%. For isotonic EMG signals, the algorithm provided compression factors ranging from 75 to 90%, with an average PRD ranging from 3.4% to 7%. The compression results using the JPEG2000 algorithm were compared to those using other algorithms based on the wavelet transform.

Failure Mechanisms of Brittle Rocks under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Liu, Taoying; Cao, Ping

2017-09-01

The behaviour of a rock mass is determined not only by the properties of the rock matrix, but mostly by the presence and properties of discontinuities or fractures within the mass. The compression test on rock-like specimens with two prefabricated transfixion fissures, made by pulling out the embedded metal inserts in the pre-cured period was carried out on the servo control uniaxial loading tester. The influence of the geometry of pre-existing cracks on the cracking processes was analysed with reference to the experimental observation of crack initiation and propagation from pre-existing flaws. Based on the rock fracture mechanics and the stress-strain curves, the evolution failure mechanism of the fissure body was also analyzed on the basis of exploring the law of the compression-shear crack initiation, wing crack growth and rock bridge connection. Meanwhile, damage fracture mechanical models of a compression-shear rock mass are established when the rock bridge axial transfixion failure, tension-shear combined failure, or wing crack shear connection failure occurs on the specimen under axial compression. This research was of significance in studying the failure mechanism of fractured rock mass.

Relation Between Residual and Hoop Stresses and Rolling Bearing Fatigue Life

NASA Technical Reports Server (NTRS)

Oswald, Fred B.; Zaretsky, Erwin V.; Poplawski, Joseph V.

2015-01-01

Rolling-element bearings operated at high speed or high vibration may require a tight interference fit between the bore of the bearing and shaft to prevent rotation of the bearing bore around the shaft and fretting damage at the interfaces. Previous work showed that the hoop stresses resulting from tight interference fits can reduce bearing lives by as much as 65 percent. Where tight interference fits are required, case-carburized steel such as AISI 9310 or M50 NiL is often used because the compressive residual stresses inhibit subsurface crack formation and the ductile core inhibits inner-ring fracture. The presence of compressive residual stress and its combination with hoop stress also modifies the Hertz stress-life relation. This paper analyzes the beneficial effect of residual stresses on rolling-element bearing fatigue life in the presence of high hoop stresses for three bearing steels. These additional stresses were superimposed on Hertzian principal stresses to calculate the inner-race maximum shearing stress and the resulting fatigue life of the bearing. The load-life exponent p and Hertz stress-life exponent n increase in the presence of compressive residual stress, which yields increased life, particularly at lower stress levels. The Zaretsky life equation is described and is shown to predict longer bearing lives and greater load- and stress-life exponents, which better predicts observed life of bearings made from vacuum-processed steel.

The tangential velocity of M31: CLUES from constrained simulations

NASA Astrophysics Data System (ADS)

Carlesi, Edoardo; Hoffman, Yehuda; Sorce, Jenny G.; Gottlöber, Stefan; Yepes, Gustavo; Courtois, Hélène; Tully, R. Brent

2016-07-01

Determining the precise value of the tangential component of the velocity of M31 is a non-trivial astrophysical issue that relies on complicated modelling. This has recently lead to conflicting estimates, obtained by several groups that used different methodologies and assumptions. This Letter addresses the issue by computing a Bayesian posterior distribution function of this quantity, in order to measure the compatibility of those estimates with Λ cold dark matter (ΛCDM). This is achieved using an ensemble of Local Group (LG) look-alikes collected from a set of constrained simulations (CSs) of the local Universe, and a standard unconstrained ΛCDM. The latter allows us to build a control sample of LG-like pairs and to single out the influence of the environment in our results. We find that neither estimate is at odds with ΛCDM; however, whereas CSs favour higher values of vtan, the reverse is true for estimates based on LG samples gathered from unconstrained simulations, overlooking the environmental element.

Tangential migration of corridor guidepost neurons contributes to anxiety circuits.

PubMed

Tinterri, Andrea; Deck, Marie; Keita, Maryama; Mailhes, Caroline; Rubin, Anna Noren; Kessaris, Nicoletta; Lokmane, Ludmilla; Bielle, Franck; Garel, Sonia

2018-02-15

In mammals, thalamic axons are guided internally toward their neocortical target by corridor (Co) neurons that act as axonal guideposts. The existence of Co-like neurons in non-mammalian species, in which thalamic axons do not grow internally, raised the possibility that Co cells might have an ancestral role. Here, we investigated the contribution of corridor (Co) cells to mature brain circuits using a combination of genetic fate-mapping and assays in mice. We unexpectedly found that Co neurons contribute to striatal-like projection neurons in the central extended amygdala. In particular, Co-like neurons participate in specific nuclei of the bed nucleus of the stria terminalis, which plays essential roles in anxiety circuits. Our study shows that Co neurons possess an evolutionary conserved role in anxiety circuits independently from an acquired guidepost function. It furthermore highlights that neurons can have multiple sequential functions during brain wiring and supports a general role of tangential migration in the building of subpallial circuits. © 2017 Wiley Periodicals, Inc.

Very High Density of Chinese Hamster Ovary Cells in Perfusion by Alternating Tangential Flow or Tangential Flow Filtration in WAVE Bioreactor™—Part II: Applications for Antibody Production and Cryopreservation

PubMed Central

Clincke, Marie-Françoise; Mölleryd, Carin; Samani, Puneeth K; Lindskog, Eva; Fäldt, Eric; Walsh, Kieron; Chotteau, Véronique

2013-01-01

A high cell density perfusion process of monoclonal antibody (MAb) producing Chinese hamster ovary (CHO) cells was developed in disposable WAVE Bioreactor™ using external hollow fiber (HF) filter as cell separation device. Tangential flow filtration (TFF) and alternating tangential flow (ATF) systems were compared and process applications of high cell density perfusion were studied here: MAb production and cryopreservation. Operations by perfusion using microfiltration (MF) or ultrafiltration (UF) with ATF or TFF and by fed-batch were compared. Cell densities higher than 108 cells/mL were obtained using UF TFF or UF ATF. The cells produced comparable amounts of MAb in perfusion by ATF or TFF, MF or UF. MAbs were partially retained by the MF using ATF or TFF but more severely using TFF. Consequently, MAbs were lost when cell broth was discarded from the bioreactor in the daily bleeds. The MAb cell-specific productivity was comparable at cell densities up to 1.3 × 108 cells/mL in perfusion and was comparable or lower in fed-batch. After 12 days, six times more MAbs were harvested using perfusion by ATF or TFF with MF or UF, compared to fed-batch and 28× more in a 1-month perfusion at 108 cells/mL density. Pumping at a recirculation rate up to 2.75 L/min did not damage the cells with the present TFF settings with HF short circuited. Cell cryopreservation at 0.5 × 108 and 108 cells/mL was performed using cells from a perfusion run at 108 cells/mL density. Cell resuscitation was very successful, showing that this system was a reliable process for cell bank manufacturing. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:768–777, 2013 PMID:23436783

Finite element analysis of maxillary bone stress caused by Aramany Class IV obturator prostheses.

PubMed

Miyashita, Elcio Ricardo; Mattos, Beatriz Silva Câmara; Noritomi, Pedro Yoshito; Navarro, Hamilton

2012-05-01

The retention of an Aramany Class IV removable partial dental prosthesis can be compromised by a lack of support. The biomechanics of this obturator prosthesis result in an unusual stress distribution on the residual maxillary bone. This study evaluated the biomechanics of an Aramany Class IV obturator prosthesis with finite element analysis and a digital 3-dimensional (3-D) model developed from a computed tomography scan; bone stress was evaluated according to the load placed on the prosthesis. A 3-D model of an Aramany Class IV maxillary resection and prosthesis was constructed. This model was used to develop a finite element mesh. A 120 N load was applied to the occlusal and incisal platforms corresponding to the prosthetic teeth. Qualitative analysis was based on the scale of maximum principal stress; values obtained through quantitative analysis were expressed in MPa. Under posterior load, tensile and compressive stresses were observed; the tensile stress was greater than the compressive stress, regardless of the bone region, and the greatest compressive stress was observed on the anterior palate near the midline. Under an anterior load, tensile stress was observed in all of the evaluated bone regions; the tensile stress was greater than the compressive stress, regardless of the bone region. The Aramany Class IV obturator prosthesis tended to rotate toward the surgical resection when subjected to posterior or anterior loads. The amount of tensile and compressive stress caused by the Aramany Class IV obturator prosthesis did not exceed the physiological limits of the maxillary bone tissue. (J Prosthet Dent 2012;107:336-342). Copyright © 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Direct method of design and stress analysis of rotating disks with temperature gradient

NASA Technical Reports Server (NTRS)

Manson, S S

1950-01-01

A method is presented for the determination of the contour of disks, typified by those of aircraft gas turbines, to incorporate arbitrary elastic-stress distributions resulting from either centrifugal or combined centrifugal and thermal effects. The specified stress may be radial, tangential, or any combination of the two. Use is made of the finite-difference approach in solving the stress equations, the amount of computation necessary in the evolution of a design being greatly reduced by the judicious selection of point stations by the aid of a design chart. Use of the charts and of a preselected schedule of point stations is also applied to the direct problem of finding the elastic and plastic stress distribution in disks of a given design, thereby effecting a great reduction in the amount of calculation. Illustrative examples are presented to show computational procedures in the determination of a new design and in analyzing an existing design for elastic stress and for stresses resulting from plastic flow.

Buckling Behavior of Compression-Loaded Composite Cylindrical Shells With Reinforced Cutouts

NASA Technical Reports Server (NTRS)

Hilburger, Mark W.; Sarnes, James H., Jr.

2004-01-01

Results from a numerical study of the response of thin-walled compression-loaded quasi-isotropic laminated composite cylindrical shells with unreinforced and reinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the nonlinear response of the shells are described. A nonlinear analysis procedure has been used to predict the nonlinear response of the shells. The results indicate that a local buckling response occurs in the shell near the cutout when subjected to load and is caused by a nonlinear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, reinforcement around a cutout in a compression-loaded shell is shown to retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell. However, some results show that certain reinforcement configurations can cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved buckling response characteristics.

[Contact characteristics research of acetabular weight-bearing area with different internal fixation methods after compression fracture of acetabular dome].

PubMed

Xu, Bowen; Zhang, Qingsong; An, Siqi; Pei, Baorui; Wu, Xiaobo

2017-08-01

To establish the model of compression fracture of acetabular dome, and to measure the contact characteristics of acetabular weight-bearing area of acetabulum after 3 kinds of internal fixation. Sixteen fresh adult half pelvis specimens were randomly divided into 4 groups, 4 specimens each group. Group D was the complete acetabulum (control group), and the remaining 3 groups were prepared acetabular dome compression fracture model. The fractures were fixed with reconstruction plate in group A, antegrade raft screws in group B, and retrograde raft screws in group C. The pressure sensitive films were attached to the femoral head, and the axial compression test was carried out on the inverted single leg standing position. The weight-bearing area, average stress, and peak stress were measured in each group. Under the loading of 500 N, the acetabular weight-bearing area was significantly higher in group D than in other 3 groups ( P <0.05), and the average stress and peak stress were significantly lower than in other 3 groups ( P <0.05). The acetabular weight-bearing area were significantly higher in group B and group C than in group A, and the average stress and peak stress were significantly lower than in group A ( P <0.05). There was no significant difference in the above indexes between group B and group C ( P >0.05). For the compression fracture of the acetabular dome, the contact characteristics of the weight-bearing area can not restore to the normal level, even if the anatomical reduction and rigid internal fixation were performed; compared with the reconstruction plate fixation, antegrade and retrograde raft screws fixations can increase the weight-bearing area, reduce the average stress and peak stress, and reduce the incidence of traumatic arthritis.

Computational Investigation of Tangential Slot Blowing on a Generic Chined Forebody

NASA Technical Reports Server (NTRS)

Agosta-Greenman, Roxana M.; Gee, Ken; Cummings, Russell M.; Schiff, Lewis B.

1995-01-01

The effect of tangential slot blowing on the flowfield about a generic chined forebody at high angles of attack is investigated numerically using solutions of the thin-layer, Reynolds-averaged, Navier-Stokes equations. The effects of jet mass now ratios, angle of attack, and blowing slot location in the axial and circumferential directions are studied. The computed results compare well with available wind-tunnel experimental data. Computational results show that for a given mass now rate, the yawing moments generated by slot blowing increase as the body angle of attack increases. It is observed that greater changes in the yawing moments are produced by a slot located closest to the lip of the nose. Also, computational solutions show that inboard blowing across the top surface is more effective at generating yawing moments than blowing outboard from the bottom surface.

Tangential acceleration feedback control of friction induced vibration

NASA Astrophysics Data System (ADS)

Nath, Jyayasi; Chatterjee, S.

2016-09-01

Tangential control action is studied on a phenomenological mass-on-belt model exhibiting friction-induced self-excited vibration attributed to the low-velocity drooping characteristics of friction which is also known as Stribeck effect. The friction phenomenon is modelled by the exponential model. Linear stability analysis is carried out near the equilibrium point and local stability boundary is delineated in the plane of control parameters. The system is observed to undergo a Hopf bifurcation as the eigenvalues determined from the linear stability analysis are found to cross the imaginary axis transversally from RHS s-plane to LHS s-plane or vice-versa as one varies the control parameters, namely non-dimensional belt velocity and the control gain. A nonlinear stability analysis by the method of Averaging reveals the subcritical nature of the Hopf bifurcation. Thus, a global stability boundary is constructed so that any choice of control parameters from the globally stable region leads to a stable equilibrium. Numerical simulations in a MATLAB SIMULINK model and bifurcation diagrams obtained in AUTO validate these analytically obtained results. Pole crossover design is implemented to optimize the filter parameters with an independent choice of belt velocity and control gain. The efficacy of this optimization (based on numerical results) in the delicate low velocity region is also enclosed.

Flow Curve Analysis of 17-4 PH Stainless Steel under Hot Compression Test

NASA Astrophysics Data System (ADS)

Mirzadeh, Hamed; Najafizadeh, Abbas; Moazeny, Mohammad

2009-12-01

The hot compression behavior of a 17-4 PH stainless steel (AISI 630) has been investigated at temperatures of 950 °C to 1150 °C and strain rates of 10-3 to 10 s-1. Glass powder in the Rastegaev reservoirs of the specimen was used as a lubricant material. A step-by-step procedure for data analysis in the hot compression test was given. The work hardening rate analysis was performed to reveal if dynamic recrystallization (DRX) occurred. Many samples exhibited typical DRX stress-strain curves with a single peak stress followed by a gradual fall toward the steady-state stress. At low Zener-Hollomon ( Z) parameter, this material showed a new DRX flow behavior, which was called multiple transient steady state (MTSS). At high Z, as a result of adiabatic deformation heating, a drop in flow stress was observed. The general constitutive equations were used to determine the hot working constants of this material. Moreover, after a critical discussion, the deformation activation energy of 17-4 PH stainless steel was determined as 337 kJ/mol.

Investigation of tension-compression fatigue behavior of a cross-ply metal matrix composite at room and elevated temperatures. Master's thesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyum, E.A.

1993-12-01

This research, the first load-controlled tension-compression fatigue testing to be performed on a MMC, extends the existing knowledge of MMC fatigue damage mechanisms to include the tension compression loading condition. To accomplish this, a (0/90)2, SCS-6/Ti-15-3 laminate was subjected to tension-tension fatigue at room temperature, and tension-compression fatigue at both room temperature and 427 deg C. Stress and strain data was taken to evaluate the macro-mechanic behavior of the material. Microscopy and fractography were performed to characterize the damage on a micro-mechanic level. On a maximum applied stress basis, the room temperature tension-tension specimens had longer fatigue lives than themore » room temperature tension-compression specimens. The room and high temperature tension-compression fatigue lives were nearly identical in the fiber-dominated high stress region of the SN curve. However, the increased ductility and diffused plasticity of the titanium matrix at 427 deg C delayed the onset and severity of matrix cracking, and thus increased the elevated temperature fatigue lives in the matrix dominated region of the SN curve. In all cases, matrix damage initiated at reaction zone cracks which nucleated both matrix plasticity and matrix cracking. Metal matrix composite, Elevated temperature, Fatigue testing, Compression, Fully-reversed, Titanium, Silicon carbide.« less

Finite element analysis of residual stress in cold expanded plate with different thickness and expansion ratio

NASA Astrophysics Data System (ADS)

Arifin Shariffudin, Kamarul; Karuppanan, Saravanan; Patil, Santosh S.

2017-10-01

Cold expansion of fastener/rivet holes is a common way to generate beneficial compressive residual stress around the fastener hole. In this study, cold expansion process was simulated by finite-element method in order to determine the residual stress field around two cold expanded holes by varying the plate thickness and expansion ratio of the hole. The model was developed in ANSYS and assigned to aluminium alloy 7475-T61 material model. The results showed that the residual stress become more compressive as the plate thickness is increased up to t/d = 2.6 and decreased for further level of thickness. In addition, the residual stress at the edge of the hole become more compressive as the expansion ratio is increased up to 4.5% and decreased for further level of expansion. This study also found that the residual stresses near the entrance and the exit face of the plate are less compressive than the residual stresses on the mid-thickness of the plate.

The joint use of the tangential electric field and surface Laplacian in EEG classification.

PubMed

Carvalhaes, C G; de Barros, J Acacio; Perreau-Guimaraes, M; Suppes, P

2014-01-01

We investigate the joint use of the tangential electric field (EF) and the surface Laplacian (SL) derivation as a method to improve the classification of EEG signals. We considered five classification tasks to test the validity of such approach. In all five tasks, the joint use of the components of the EF and the SL outperformed the scalar potential. The smallest effect occurred in the classification of a mental task, wherein the average classification rate was improved by 0.5 standard deviations. The largest effect was obtained in the classification of visual stimuli and corresponded to an improvement of 2.1 standard deviations.

30 CFR 75.1730 - Compressed air; general; compressed air systems.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Compressed air; general; compressed air systems... Compressed air; general; compressed air systems. (a) All pressure vessels shall be constructed, installed... Safety and Health district office. (b) Compressors and compressed-air receivers shall be equipped with...

30 CFR 75.1730 - Compressed air; general; compressed air systems.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Compressed air; general; compressed air systems... Compressed air; general; compressed air systems. (a) All pressure vessels shall be constructed, installed... Safety and Health district office. (b) Compressors and compressed-air receivers shall be equipped with...

30 CFR 75.1730 - Compressed air; general; compressed air systems.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Compressed air; general; compressed air systems... Compressed air; general; compressed air systems. (a) All pressure vessels shall be constructed, installed... Safety and Health district office. (b) Compressors and compressed-air receivers shall be equipped with...

30 CFR 75.1730 - Compressed air; general; compressed air systems.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Compressed air; general; compressed air systems... Compressed air; general; compressed air systems. (a) All pressure vessels shall be constructed, installed... Safety and Health district office. (b) Compressors and compressed-air receivers shall be equipped with...

Rheological State Diagrams for Rough Colloids in Shear Flow.

PubMed

Hsiao, Lilian C; Jamali, Safa; Glynos, Emmanouil; Green, Peter F; Larson, Ronald G; Solomon, Michael J

2017-10-13

To assess the role of particle roughness in the rheological phenomena of concentrated colloidal suspensions, we develop model colloids with varying surface roughness length scales up to 10% of the particle radius. Increasing surface roughness shifts the onset of both shear thickening and dilatancy towards lower volume fractions and critical stresses. Experimental data are supported by computer simulations of spherical colloids with adjustable friction coefficients, demonstrating that a reduction in the onset stress of thickening and a sign change in the first normal stresses occur when friction competes with lubrication. In the quasi-Newtonian flow regime, roughness increases the effective packing fraction of colloids. As the shear stress increases and suspensions of rough colloids approach jamming, the first normal stresses switch signs and the critical force required to generate contacts is drastically reduced. This is likely a signature of the lubrication films giving way to roughness-induced tangential interactions that bring about load-bearing contacts in the compression axis of flow.

Rheological State Diagrams for Rough Colloids in Shear Flow

NASA Astrophysics Data System (ADS)

Hsiao, Lilian C.; Jamali, Safa; Glynos, Emmanouil; Green, Peter F.; Larson, Ronald G.; Solomon, Michael J.

2017-10-01

To assess the role of particle roughness in the rheological phenomena of concentrated colloidal suspensions, we develop model colloids with varying surface roughness length scales up to 10% of the particle radius. Increasing surface roughness shifts the onset of both shear thickening and dilatancy towards lower volume fractions and critical stresses. Experimental data are supported by computer simulations of spherical colloids with adjustable friction coefficients, demonstrating that a reduction in the onset stress of thickening and a sign change in the first normal stresses occur when friction competes with lubrication. In the quasi-Newtonian flow regime, roughness increases the effective packing fraction of colloids. As the shear stress increases and suspensions of rough colloids approach jamming, the first normal stresses switch signs and the critical force required to generate contacts is drastically reduced. This is likely a signature of the lubrication films giving way to roughness-induced tangential interactions that bring about load-bearing contacts in the compression axis of flow.

Strain-dependent dynamic compressive properties of magnetorheological elastomeric foams

NASA Astrophysics Data System (ADS)

Wereley, Norman M.; Perez, Colette; Choi, Young T.

2018-05-01

This paper addresses the strain-dependent dynamic compressive properties (i.e., so-called Payne effect) of magnetorheological elastomeric foams (MREFs). Isotropic MREF samples (i.e., no oriented particle chain structures), fabricated in flat square shapes (nominal size of 26.5 mm x 26.5 mm x 9.5 mm) were synthesized by randomly dispersing micron-sized iron oxide particles (Fe3O4) into a liquid silicone foam in the absence of magnetic field. Five different Fe3O4 particle concentrations of 0, 2.5, 5.0, 7.5, and 10 percent by volume fraction (hereinafter denoted as vol%) were used to investigate the effect of particle concentration on the dynamic compressive properties of the MREFs. The MREFs were sandwiched between two multi-pole flexible plate magnets in order to activate the magnetorheological (MR) strengthening effect. Under two different pre-compression conditions (i.e., 35% and 50%), the dynamic compressive stresses of the MREFs with respect to dynamic strain amplitudes (i.e., 1%-10%) were measured by using a servo-hydraulic testing machine. The complex modulus (i.e., storage modulus and loss modulus) and loss factors of the MREFs with respect to dynamic strain amplitudes were presented as performance indices to evaluate their strain-dependent dynamic compressive behavior.

Effects of low-modulus coatings on pin-bone contact stresses in external fixation.

PubMed

Manley, M T; Hurst, L; Hindes, R; Dee, R; Chiang, F P

1984-01-01

The intent of this study was to investigate the stress distribution in cortical bone around fracture fixation pins and around pins coated with various polymeric and elastomeric materials. Since these interface stresses cannot be measured directly, a photoelastic technique was employed and stresses were measured in two-dimensional bone models fabricated from sheets of epoxy resin. Our results showed that when a fixation pin was loaded in compression, the compressive stress measured in the model was greatest at the pin-model interface. The magnitude of the compressive stress was found to diminish steeply away from the hole in a log decrement distribution which was asymptotic to the value of the average stress in the model. When polymeric and elastomeric materials were applied as pin coatings and the performance of the coated pins was compared to that of uncoated pins of the same overall diameter, a reduction of the maximum stress in the bone model was demonstrated. Among the coatings tested, we found that of the polymeric materials ultrahigh molecular weight polyethylene (UHMWPE) was most effective at reducing the peak cortical stress magnitude. The most effective coating material overall was found to be silicon elastomer. Computation of stress values in models loaded through stainless-steel pins and through pins coated with 1-mm silicon elastomer showed that the presence of the elastomer layer caused a reduction of about 50% in the maximum compressive stress in the model.

Thermal stresses in the laser disc from a tetragonal c-cut crystal

NASA Astrophysics Data System (ADS)

Yumashev, K. V.; Loiko, P. A.

2014-12-01

Analytical expressions for thermal stresses and strains, as well as displacements, are obtained for the laser disc from a tetragonal crystal cut along the [0 0 1] axis under plane stress approximation, for the first time, to our knowledge. This study illustrates that, in polar coordinates, the normal stresses, σr and σθ, are angular independent, while the shear one τrθ is zero. The thermal strains, εr and εθ, and displacements, u and υ, depend on both radial and tangential coordinates; this dependence has the shape of a four-leaf rose. For considered crystal cutting with isotropic in-plane thermal expansion, the displacements are not pure radial (υ≠0). The values of stresses, strains and displacements are calculated for the disc from a c-cut yttrium vanadate laser crystal, Nd:YVO4. The thermal fracture issues are analyzed for this crystal.

Evaluation of Full Reynolds Stress Turbulence Models in FUN3D

NASA Technical Reports Server (NTRS)

Dudek, Julianne C.; Carlson, Jan-Renee

2017-01-01

Full seven-equation Reynolds stress turbulence models are a relatively new and promising tool for todays aerospace technology challenges. This paper uses two stress-omega full Reynolds stress models to evaluate challenging flows including shock-wave boundary layer interactions, separation and mixing layers. The Wilcox and the SSGLRR full second-moment Reynolds stress models are evaluated for four problems: a transonic two-dimensional diffuser, a supersonic axisymmetric compression corner, a compressible planar shear layer, and a subsonic axisymmetric jet. Simulation results are compared with experimental data and results using the more commonly used Spalart-Allmaras (SA) one-equation and the Menter Shear Stress Transport (SST) two-equation models.

Stresses in Circular Plates with Rigid Elements

NASA Astrophysics Data System (ADS)

Velikanov, N. L.; Koryagin, S. I.; Sharkov, O. V.

2018-05-01

Calculations of residual stress fields are carried out by numerical and static methods, using the flat cross-section hypothesis. The failure of metal when exposed to residual stresses is, in most cases, brittle. The presence in the engineering structures of rigid elements often leads to the crack initiation and structure failure. This is due to the fact that rigid elements under the influence of external stresses are stress concentrators. In addition, if these elements are fixed by welding, the residual welding stresses can lead to an increase in stress concentration and, ultimately, to failure. The development of design schemes for such structures is a very urgent task for complex technical systems. To determine the stresses in a circular plate with a welded circular rigid insert under the influence of an external load, one can use the solution of the plane stress problem for annular plates in polar coordinates. The polar coordinates of the points are the polar radius and the polar angle, and the stress state is determined by normal radial stresses, tangential and shearing stresses. The use of the above mentioned design schemes, formulas, will allow more accurate determination of residual stresses in annular welded structures. This will help to establish the most likely directions of failure and take measures at the stages of designing, manufacturing and repairing engineering structures to prevent these failures. However, it must be taken into account that the external load, the presence of insulation can lead to a change in the residual stress field.

Buckling Behavior of Compression-Loaded Composite Cylindrical Shells with Reinforced Cutouts

NASA Technical Reports Server (NTRS)

Hilburger, Mark W.; Starnes, James H., Jr.

2002-01-01

Results from a numerical study of the response of thin-wall compression-loaded quasi-isotropic laminated composite cylindrical shells with reinforced and unreinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the nonlinear response of the shells are described. A high-fidelity nonlinear analysis procedure has been used to predict the nonlinear response of the shells. The analysis procedure includes a nonlinear static analysis that predicts stable response characteristics of the shells and a nonlinear transient analysis that predicts unstable dynamic buckling response characteristics. The results illustrate how a compression-loaded shell with an unreinforced cutout can exhibit a complex nonlinear response. In particular, a local buckling response occurs in the shell near the cutout and is caused by a complex nonlinear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, the addition of reinforcement around a cutout in a compression-loaded shell can retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell, as expected. However, results are presented that show how certain reinforcement configurations can actually cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved response characteristics.

Sources of stress gradients in electrodeposited Ni MEMS.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hearne, Sean Joseph; Floro, Jerrold Anthony; Dyck, Christopher William

2004-06-01

The ability of future integrated metal-semiconductor micro-systems such as RF MEMS to perform highly complex functions will depend on developing freestanding metal structures that offer improved conductivity and reflectivity over polysilicon structures. For example, metal-based RF MEMS technology could replace the bulky RF system presently used in communications, navigation, and avionics systems. However, stress gradients that induce warpage of active components have prevented the implementation of this technology. Figure 1, is an interference micrograph image of a series of cantilever beams fabricated from electrodeposited Ni. The curvature in the beams was the result of stress gradients intrinsic to the electrodepositionmore » process. To study the sources of the stress in electrodeposition of Ni we have incorporated a wafer curvature based stress sensor, the multibeam optical stress sensor, into an electrodeposition cell. We have determined that there are two regions of stress induced by electrodepositing Ni from a sulfamate-based bath (Fig 2). The stress evolution during the first region, 0-1000{angstrom}, was determined to be dependent only on the substrate material (Au vs. Cu), whereas the stress evolution during the second region, >1000{angstrom}, was highly dependent on the deposition conditions. In this region, the stress varied from +0.5 GPa to -0.5GPa, depending solely on the deposition rate. We examined four likely sources for the compressive intrinsic stress, i.e. reduction in tensile stress, and determined that only the adatom diffusion into grain boundaries model of Sheldon, et al. could account for the observed compressive stress. In the presentation, we shall discuss the compressive stress generation mechanisms considered and the ramifications of these results on fabrication of electrodeposited Ni for MEMS applications.« less

Multi-scale analysis and characterization of the ITER pre-compression rings

NASA Astrophysics Data System (ADS)

Foussat, A.; Park, B.; Rajainmaki, H.

2014-01-01

The toroidal field (TF) system of ITER Tokamak composed of 18 "D" shaped Toroidal Field (TF) coils during an operating scenario experiences out-of-plane forces caused by the interaction between the 68kA operating TF current and the poloidal magnetic fields. In order to keep the induced static and cyclic stress range in the intercoil shear keys between coils cases within the ITER allowable limits [1], centripetal preload is introduced by means of S2 fiber-glass/epoxy composite pre-compression rings (PCRs). Those PCRs consist in two sets of three rings, each 5 m in diameter and 337 × 288 mm in cross-section, and are installed at the top and bottom regions to apply a total resultant preload of 70 MN per TF coil equivalent to about 400 MPa hoop stress. Recent developments of composites in the aerospace industry have accelerated the use of advanced composites as primary structural materials. The PCRs represent one of the most challenging composite applications of large dimensions and highly stressed structures operating at 4 K over a long term life. Efficient design of those pre-compression composite structures requires a detailed understanding of both the failure behavior of the structure and the fracture behavior of the material. Due to the inherent difficulties to carry out real scale testing campaign, there is a need to develop simulation tools to predict the multiple complex failure mechanisms in pre-compression rings. A framework contract was placed by ITER Organization with SENER Ingenieria y Sistemas SA to develop multi-scale models representative of the composite structure of the Pre-compression rings based on experimental material data. The predictive modeling based on ABAQUS FEM provides the opportunity both to understand better how PCR composites behave in operating conditions and to support the development of materials by the supplier with enhanced performance to withstand the machine design lifetime of 30,000 cycles. The multi-scale stress analysis has

The Evolution of Stress Intensity Factors and the Propagation of Cracks in Elastic Media

NASA Astrophysics Data System (ADS)

Friedman, Avner; Hu, Bei; Velazquez, Juan J. L.

When a crack Γs propagates in an elastic medium the stress intensity factors evolve with the tip x(s) of Γs. In this paper we derive formulae which describe the evolution of these stress intensity factors for a homogeneous isotropic elastic medium under plane strain conditions. Denoting by ψ=ψ(x,s) the stress potential (ψ is biharmonic and has zero traction along the crack Γs) and by κ(s) the curvature of the crack at the tip x(s), we prove that the stress intensity factors A1(s), A2(s), as functions of s, satisfy: where , are stress intensity factors of the tangential derivative of in the polar coordinate system at x(s) with θ=0 in the direction of the crack at x(s). The case of antiplane shearing is also briefly considered; in this case ψ is harmonic.

Is Seasonal Stress a Career Choice of Professional Accountants?

ERIC Educational Resources Information Center

Cluskey, G. R., Jr.; Vaux, Alan C.

1997-01-01

Examines stressors on tax professionals during periods of relatively high stress and periods of low stress. Results indicate that the strongest stressor-strain relationship was for the group surveyed in January (high stress), indicating that workload compression contributes to seasonal occupational stress. Looks at implications for employee…

A coupled creep plasticity model for residual stress relaxation of a shot-peened nickel-based superalloy

NASA Astrophysics Data System (ADS)

Buchanan, Dennis J.; John, Reji; Brockman, Robert A.; Rosenberger, Andrew H.

2010-01-01

Shot peening is a commonly used surface treatment process that imparts compressive residual stresses into the surface of metal components. Compressive residual stresses retard initiation and growth of fatigue cracks. During component loading history, shot-peened residual stresses may change due to thermal exposure, creep, and cyclic loading. In these instances, taking full credit for compressive residual stresses would result in a nonconservative life prediction. This article describes a methodical approach for characterizing and modeling residual stress relaxation under elevated temperature loading, near and above the monotonic yield strength of INI 00. The model incorporates the dominant creep deformation mechanism, coupling between the creep and plasticity models, and effects of prior plastic strain to simulate surface treatment deformation.

1000 to 1300 K slow plastic compression properties of Al-deficient NiAl

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.; Kumar, K. S.; Mannan, S. K.

1991-01-01

Nickel aluminides containing 37, 38.5 and 40 at. pct Al have been fabricated by XD synthesis and hot pressing. Such materials were compression tested in air under constant velocity conditions between 1000 and 1300 K. Examination of the microstructures of hot pressed and compression tested aluminides indicated that the structure consisted of two phases, gamma-prime and NiAl, for essentially all conditions, where gamma-prime was usually found on the NiAl grain boundaries. The stress-strain behavior of all three intermetallics was similar where flow at a nominally constant stress occurred after about two-percent plastic deformation. Furthermore, the 1000 to 1300 K flow stress-strain rate properties are nearly identical for these materials, and they are much lower than those for XD processed Ni-50Al. The overall deformation of the two phase nickel aluminides appears to be controlled by dislocation climb in NiAl rather than processes in gamma-prime.

Compression failure of angle-ply laminates

NASA Technical Reports Server (NTRS)

Peel, L. D.; Hyer, M. W.; Shuart, M. J.

1992-01-01

Test results from the compression loading of (+ or - Theta/ - or + Theta)(sub 6s) angle-ply IM7-8551-7a specimens, 0 less than or = Theta less than or = 90 degs, are presented. The observed failure strengths and modes are discussed, and typical stress-strain relations shown. Using classical lamination theory and the maximum stress criterion, an attempt is made to predict failure stress as a function of Theta. This attempt results in poor correlation with test results and thus a more advanced model is used. The model, which is based on a geometrically nonlinear theory, and which was taken from previous work, includes the influence of observed layer waviness. The waviness is described by the wave length and the wave amplitude. The theory is briefly described and results from the theory are correlated with test results. It is shown that by using levels of waviness observed in the specimens, the correlation between predictions and observations is good.

Purification of Hemoglobin by Tangential Flow Filtration with Diafiltration

PubMed Central

Elmer, Jacob; Harris, David R.; Sun, Guoyong; Palmer, Andre F.

2009-01-01

A recent study by Palmer et al. (2009) demonstrated that tangential flow filtration (TFF) can be used to produce HPLC-grade bovine and human hemoglobin (Hb). In this current study, we assessed the quality of bovine Hb (bHb) purified by introducing a 10 L batch-mode diafiltration step to the previously mentioned TFF Hb purification process. bHb was purified from bovine red blood cells (RBCs) by filtering clarified RBC lysate through 50 nm (stage I) & 500 kDa (stage II) hollow fiber (HF) membranes. The filtrate was then passed through a 100 kDa (stage III) HF membrane with or without an additional 10 L diafiltration step to potentially remove additional small molecular weight impurities. Protein assays, SDS-PAGE, and LC-MS of the purified bHb (stage III retentate) reveal that addition of a diafiltration step has no effect on bHb purity or yield; however, it does increase the methemoglobin level and oxygen affinity of purified bHb. Therefore, we conclude that no additional benefit is gained from diafiltration at stage III and a three-stage TFF process is sufficient to produce HPLC-grade bHb. PMID:19621471

Tension and Compression Creep Apparatus for wood-Plastic Composites

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2011-01-01

Design of structural members made of wood-plastic composites (WPC) is not possible without accurate test data for tension and compression. The viscoelastic behavior of these materials means that these data are required for both the quasi-static stress-strain response, and the long-term creep response. Their relative incompressibility causes inherent difficulties in...

The role of stress waves in thoracic visceral injury from blast loading: modification of stress transmission by foams and high-density materials.

PubMed

Cooper, G J; Townend, D J; Cater, S R; Pearce, B P

1991-01-01

Materials have been applied to the thoracic wall of anaesthetised experimental animals exposed to blast overpressure to investigate the coupling of direct stress waves into the thorax and the relative contribution of compressive stress waves and gross thoracic compression to lung injury. The ultimate purpose of the work is to develop effective personal protection from the primary effects of blast overpressure--efficient protection can only be achieved if the injury mechanism is identified and characterized. Foam materials acted as acoustic couplers and resulted in a significant augmentation of the visceral injury; decoupling and elimination of injury were achieved by application of a high acoustic impedance layer on top of the foam. In vitro experiments studying stress wave transmission from air through various layers into an anechoic water chamber showed a significant increase in power transmitted by the foams, principally at high frequencies. Material such as copper or resin bonded Kevlar incorporated as a facing upon the foam achieved substantial decoupling at high frequencies--low frequency transmission was largely unaffected. An acoustic transmission model replicated the coupling of the blast waves into the anechoic water chamber. The studies suggest that direct transmission of stress waves plays a dominant role in lung parenchymal injury from blast loading and that gross thoracic compression is not the primary injury mechanism. Acoustic decoupling principles may therefore be employed to reduce the direct stress coupled into the body and thus reduce the severity of lung injury--the most simple decoupler is a high acoustic impedance material as a facing upon a foam, but decoupling layers may be optimized using acoustic transmission models. Conventional impacts producing high body wall velocities will also lead to stress wave generation and transmission--stress wave effects may dominate the visceral response to the impact with direct compression and shear

Extra-fibrillar matrix mechanics of annulus fibrosus in tension and compression.

PubMed

Cortes, Daniel H; Elliott, Dawn M

2012-07-01

The annulus fibrosus (AF) of the disk is a highly nonlinear and anisotropic material that undergoes a complex combination of loads in multiple orientations. The tensile mechanical behavior of AF in the lamellar plane is dominated by collagen fibers and has been accurately modeled using exponential functions. On the other hand, AF mechanics perpendicular to the lamella, in the radial direction, depend on the properties of the ground matrix with little to no fiber contribution. The ground matrix is mainly composed of proteoglycans (PG), which are negatively charged macromolecules that maintain the tissue hydration via osmotic pressure. The mechanical response of the ground matrix can be divided in the contribution of osmotic pressure and an elastic solid part known as extra-fibrillar matrix (EFM). Mechanical properties of the ground matrix have been measured using tensile and confined compression tests. However, EFM mechanics have not been measured directly. The objective of this study was to measure AF nonlinear mechanics of the EFM in tension and compression. To accomplish this, a combination of osmotic swelling and confined compression in disk radial direction, perpendicular to the lamella, was used. For this type of analysis, it was necessary to define a stress-free reference configuration. Thus, a brief analysis on residual stress in the disk and a procedure to estimate the reference configuration are presented. The proposed method was able to predict similar swelling deformations when using different loading protocols and models for the EFM, demonstrating its robustness. The stress-stretch curve of the EFM was linear in the range 0.9 < λ₃ < 1.3 with an aggregate modulus of 10.18±3.32 kPa; however, a significant nonlinearity was observed for compression below 0.8. The contribution of the EFM to the total aggregate modulus of the AF decreased from 70 to 30% for an applied compression of 50% of the initial thickness. The properties obtained in this study are

Sinusoidal current and stress evolutions in lithium-ion batteries

NASA Astrophysics Data System (ADS)

Yang, Xiao-Guang; Bauer, Christoph; Wang, Chao-Yang

2016-09-01

Mechanical breakdown of graphite materials due to diffusion-induced stress (DIS) is a key aging mechanism of lithium-ion batteries. In this work, electrochemical-thermal coupled model along with a DIS model is developed to study the DIS distribution across the anode thickness. Special attention is paid to the evolution behavior of surface tangential stress (STS) in the discharge process for graphite at different locations of the anode. For the first time, we report that the evolution of STS, as well as local current, at all locations of the anode, evolve like sinusoidal waves in the discharge process with several crests and troughs. The staging behavior of graphite active material, in particular the sharp change of open-circuit potential (OCP) of graphite in the region between two plateaus, is found to be the root cause for the sinusoidal patterns of current and stress evolution. Furthermore, the effects of various parameters, such as starting state of charge, discharge C-rate and electrode thickness on the current and stress evolutions are investigated.

Preliminary design of a tangentially viewing imaging bolometer for NSTX-U

DOE PAGES

Peterson, B. J.; Sano, R.; Reinke, M. L.; ...

2016-08-03

The InfraRed imaging Video Bolometer measures plasma radiated power images using a thin metal foil. Two different designs with a tangential view of NSTX-U are made assuming a 640 x 480 (1280 x 1024) pixel, 30 (105) fps, 50 (20) mK, IR camera imaging the 9 cm x 9 cm x 2 μm Pt foil. The foil is divided into 40 x 40 (64 x 64) IRVB channels. This gives a spatial resolution of 3.4 (2.2) cm on the machine mid-plane. The noise equivalent power density of the IRVB is given as 113 (46) μW/cm 2 for a time resolutionmore » of 33 (20) ms. Synthetic images derived from SOLPS data using the IRVB geometry show peak signal levels ranging from ~0.8 - ~80 (~0.36 - ~26) mW/cm 2.« less

SeqCompress: an algorithm for biological sequence compression.

PubMed

Sardaraz, Muhammad; Tahir, Muhammad; Ikram, Ataul Aziz; Bajwa, Hassan

2014-10-01

The growth of Next Generation Sequencing technologies presents significant research challenges, specifically to design bioinformatics tools that handle massive amount of data efficiently. Biological sequence data storage cost has become a noticeable proportion of total cost in the generation and analysis. Particularly increase in DNA sequencing rate is significantly outstripping the rate of increase in disk storage capacity, which may go beyond the limit of storage capacity. It is essential to develop algorithms that handle large data sets via better memory management. This article presents a DNA sequence compression algorithm SeqCompress that copes with the space complexity of biological sequences. The algorithm is based on lossless data compression and uses statistical model as well as arithmetic coding to compress DNA sequences. The proposed algorithm is compared with recent specialized compression tools for biological sequences. Experimental results show that proposed algorithm has better compression gain as compared to other existing algorithms. Copyright © 2014 Elsevier Inc. All rights reserved.

A Modified EPA Method 1623 that Uses Tangential Flow Hollow-Fiber Ultrafiltration and Heat Dissociation Steps to Detect Waterborne Cryptosporidum and Giardia spp.

EPA Science Inventory

This protocol describes the use of a tangential flow hollow-fiber ultrafiltration sample concentration system and a heat dissociation as alternative steps for the detection of waterborne Cryptosporidium and Giardia species using EPA Method 1623.

Stress Distribution, Friction and Listeria Propulsion

NASA Astrophysics Data System (ADS)

Prost, Jacques

2003-03-01

I will review our work on the physics of listeria propulsion based on an unavoidable elastic analysis of the stress distribution in the actin gel and dynamical boundary conditions (both normal and tangential). I will show in particular that it provides a natural explanation for the symmetry breaking transition occurring with beads (work with K. Sekimoto and F. Julicher), of the saltatory behavior of beads reported by A Bernheim et al (Nature 2002) and of the shape of soft beads (with O. Campas and J.F Joanny). This last analysis proves that, as announced in an earlier paper (F; Gerbal et al Biophys Journal 2000) the rear part of the gel contributes negatively to the motion.

Explosion-induced stress changes estimated from vibrating-wire stressmeter measurements near the Mighty Epic event, Nevada Test Site

USGS Publications Warehouse

Ellis, William L.; Kibler, J.D.

1983-01-01

Explosion-induced compressive stress increases near an underground nuclear explosion are believed to contribute significantly to the containment of high-pressure gases within the explosion-produced cavity. These induced compressive stresses are predicted by computer calculations, but have never been adequately confirmed by field measurements, owing primarily to the unique difficulties of obtaining such field data. Vibrating-wire stressmeter measurements made near the Mighty Epic nuclear detonation, however, qualitatively indicate that within 150 meters of the working point, permanent compressive stress increases of several megapascals were present 15 weeks after the event. Additionally, stress-change magnitudes interpreted from the stressmeter data between the 75- and 260-meter range from the working point compare favorably with calculational predictions of the stress changes believed to be present shortly after detonation of the event. The measurements and calculations differ, however, with regard to the pattern of stress change radial and transverse to the explosion source. For the range of the field measurements from the working point, computer models predict the largest compressive-stress increase to be radial to the explosion source, while the field data indicate the transverse component of. stress change to be the most compressive. The significance of time-dependent modification of the initial explosion-induced stress distribution is, however, uncertain with regard to the comparison of the field measurements and theoretical predictions.

Failure modes for compression loaded angle-ply plates with holes

NASA Technical Reports Server (NTRS)

Burns, S. W.; Herakovich, C. T.; Williams, J. G.

1987-01-01

A combined theoretical-experimental investigation of failure in notched, graphite-epoxy, angle-ply laminates subjected to far-field compression loading indicates that failure generally initiates on the hole boundary and propagates along a line parallel to the fiber orientation of the laminate. The strength of notched laminates with specimen width-to-hole diameter ratios of 5 and 10 are compared to the strength of unnotched laminates. The experimental results are complemented by a three-dimensional finite element stress analysis that includes interlaminar stresses around holes in (+/- theta)s laminates. The finite element predictions indicate that failure is initiated by shear stresses at the hole boundary.

Compression embedding

DOEpatents

Sandford, II, Maxwell T.; Handel, Theodore G.; Bradley, Jonathan N.

1998-01-01

A method of embedding auxiliary information into the digital representation of host data created by a lossy compression technique. The method applies to data compressed with lossy algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as integer indices having redundancy and uncertainty in value by one unit. Indices which are adjacent in value are manipulated to encode auxiliary data. By a substantially reverse process, the embedded auxiliary data can be retrieved easily by an authorized user. Lossy compression methods use loss-less compressions known also as entropy coding, to reduce to the final size the intermediate representation as indices. The efficiency of the compression entropy coding, known also as entropy coding is increased by manipulating the indices at the intermediate stage in the manner taught by the method.

An equivalent-time-lines model for municipal solid waste based on its compression characteristics.

PubMed

Gao, Wu; Bian, Xuecheng; Xu, Wenjie; Chen, Yunmin

2017-10-01

Municipal solid waste (MSW) demonstrates a noticeable time-dependent stress-strain behavior, which contributes greatly to the settlement of landfills and therefore influences both the storage capacity of landfills and the integrity of internal structures. The long-term compression tests for MSW under different biodegradation conditions were analyzed. It showed that the primary compression can affect the secondary compression due to the biodegradation and mechanical creep. Based on the time-lines model for clays and the compression characteristics of MSW, relationships between MSW's viscous strain rate and equivalent time were established, and then the viscous strain functions of MSW under different biodegradation conditions were deduced, and an equivalent-time-lines model for MSW settlement for two biodegradation conditions was developed, including the Type I model for the enhanced biodegradation condition and the Type II model for the normal biodegradation condition. The simulated compression results of laboratory and field compression tests under different biodegradation conditions were consistent with the measured data, which showed the reliability of both types of the equivalent-time-lines model for MSW. In addition, investigations of the long-term settlement of landfills from the literature indicated that the Type I model is suitable for predicting settlement in MSW landfills with a distinct biodegradation progress of MSW, a high content of organics in MSW, a short fill age or under an enhanced biodegradation environment; while the Type II model is good at predicting settlement in MSW landfills with a distinct progress of mechanical creep compression, a low content of organics in MSW, a long fill age or under a normal biodegradation condition. Furthermore, relationships between model parameters and the fill age of landfills were summarized. Finally, the similarities and differences between the equivalent-time-lines model for MSW and the stress

Concrete Behavior under Dynamic Tensile-Compressive Load.

DTIC Science & Technology

1984-01-01

be reviewed as well. Although structural concrete does not possess the thermal cracking problems during curing to the extent that mass concrete does...reasonable bounds for these unknown properties were assumed, suggests that the extent of cracking induced by seismic ground motion can be very...space. But an understanding of biaxial tension-compression be- havior is the foremost concern, since the stress state of a dam’s cracked regions occur in

Strength and texture of Pt compressed to 63 GPa

NASA Astrophysics Data System (ADS)

Dorfman, Susannah M.; Shieh, Sean R.; Duffy, Thomas S.

2015-02-01

Angle- and energy-dispersive X-ray diffraction experiments in a radial geometry were performed in the diamond anvil cell on polycrystalline platinum samples at pressures up to 63 GPa. Observed yield strength and texture depend on grain size. For samples with 70-300-nm particle size, the yield strength is 5-6 GPa at ˜60 GPa. Coarse-grained (˜2-μm particles) Pt has a much lower yield strength of 1-1.5 GPa at ˜60 GPa. Face-centered cubic metals Pt and Au have lower strength to shear modulus ratio than body-centered cubic or hexagonal close-packed metals. While a 300-nm particle sample exhibits the <110> texture expected of face-centered-cubic metals under compression, smaller and larger particles show a weak mixed <110> and <100> texture under compression. Differences in texture development may also occur due to deviations from uniaxial stress under compression in the diamond anvil cell.

Development of high-temperature Kolsky compression bar techniques for recrystallization investigation

NASA Astrophysics Data System (ADS)

Song, B.; Antoun, B. R.; Boston, M.

2012-05-01

We modified the design originally developed by Kuokkala's group to develop an automated high-temperature Kolsky compression bar for characterizing high-rate properties of 304L stainless steel at elevated temperatures. Additional features have been implemented to this high-temperature Kolsky compression bar for recrystallization investigation. The new features ensure a single loading on the specimen and precise time and temperature control for quenching to the specimen after dynamic loading. Dynamic compressive stress-strain curves of 304L stainless steel were obtained at 21, 204, 427, 649, and 871 °C (or 70, 400, 800, 1200, and 1600 °F) at the same constant strain rate of 332 s-1. The specimen subjected to specific time and temperature control for quenching after a single dynamic loading was preserved for investigating microstructure recrystallization.

Compression embedding

DOEpatents

Sandford, M.T. II; Handel, T.G.; Bradley, J.N.

1998-03-10

A method of embedding auxiliary information into the digital representation of host data created by a lossy compression technique is disclosed. The method applies to data compressed with lossy algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as integer indices having redundancy and uncertainty in value by one unit. Indices which are adjacent in value are manipulated to encode auxiliary data. By a substantially reverse process, the embedded auxiliary data can be retrieved easily by an authorized user. Lossy compression methods use loss-less compressions known also as entropy coding, to reduce to the final size the intermediate representation as indices. The efficiency of the compression entropy coding, known also as entropy coding is increased by manipulating the indices at the intermediate stage in the manner taught by the method. 11 figs.

Failure of flight feathers under uniaxial compression.

PubMed

Schelestow, Kristina; Troncoso, Omar P; Torres, Fernando G

2017-09-01

Flight feathers are light weight engineering structures. They have a central shaft divided in two parts: the calamus and the rachis. The rachis is a thinly walled conical shell filled with foam, while the calamus is a hollow tube-like structure. Due to the fact that bending loads are produced during birds' flight, the resistance to bending of feathers has been reported in different studies. However, the analysis of bent feathers has shown that compression could induce failure by buckling. Here, we have studied the compression of feathers in order to assess the failure mechanisms involved. Axial compression tests were carried out on the rachis and the calamus of dove and pelican feathers. The failure mechanisms and folding structures that resulted from the compression tests were observed from images obtained by scanning electron microscopy (SEM). The rachis and calamus fail due to structural instability. In the case of the calamus, this instability leads to a progressive folding process. In contrast, the rachis undergoes a typical Euler column-type buckling failure. The study of failed specimens showed that delamination buckling, cell collapse and cell densification are the primary failure mechanisms of the rachis structure. The role of the foam is also discussed with regard to the mechanical response of the samples and the energy dissipated during the compression tests. Critical stress values were calculated using delamination buckling models and were found to be in very good agreement with the experimental values measured. Failure analysis and mechanical testing have confirmed that flight feathers are complex thin walled structures with mechanical adaptations that allow them to fulfil their functions. Copyright © 2017 Elsevier B.V. All rights reserved.

Dynamic compression of copper to over 450 GPa: A high-pressure standard

DOE PAGES

Kraus, R. G.; Davis, J. -P.; Seagle, C. T.; ...

2016-04-12

We obtained an absolute stress-density path for shocklessly compressed copper to over 450 GPa. A magnetic pressure drive is temporally tailored to generate shockless compression waves through over 2.5-mm-thick copper samples. Furthermore, the free-surface velocity data is analyzed for Lagrangian sound velocity using the iterative Lagrangian analysis (ILA) technique, which relies upon the method of characteristics. We correct for the effects of strength and plastic work heating to determine an isentropic compression path. By assuming a Debye model for the heat capacity, we can further correct the isentrope to an isotherm. Finally, our determination of the isentrope and isotherm ofmore » copper represents a highly accurate pressure standard for copper to over 450 GPa.« less

Intermittent vibration protects aged muscle from mechanical and oxidative damage under prolonged compression.

PubMed

Wong, Sing Wan; Cheung, Brian Chun Ho; Pang, Bruce Tak Keung; Kwong, Ateline; Chung, Anna; Lee, Kenneth Ka Ho; Mak, Arthur Fut Tak

2017-04-11

Deep tissue pressure ulcers, a serious clinical challenge originating in the muscle layer, are hardly detectable at the beginning. The challenge apparently occurs in aged subjects more frequently. As the ulcer propagates to the skin surface, it becomes very difficult to manage and can lead to fatal complications. Preventive measures are thus highly desirable. Although the complex pathological mechanisms have not been fully understood, prolonged and excessive physical challenges and oxidative stress are believed to be involved in the ulcer development. Previous reports have demonstrated that oxidative stress could compromise the mechanical properties of muscle cells, making them easier to be damaged when physical challenges are introduced. In this study, we used senescence accelerated (SAMP8) mice and its control breed (SAMR1) to examine the protective effects of intermittent vibration on aged and control muscle tissues during prolonged epidermal compression under 100mmHg for 6h. Results showed that an application of 35Hz, 0.25g intermittent vibration during compression decreased the compression-induced muscle breakdown in SAMP8 mice, as indicated histologically in terms of number of interstitial nuclei. The fact that no significant difference in muscle damage could be established in the corresponding groups in SAMR1 mice suggests that SAMR1 mice could better accommodate the compression insult than SAMP8 mice. Compression-induced oxidative damage was successfully curbed using intermittent vibration in SAMP8 mice, as indicated by 8-OHdG. A possible explanation is that the anti-oxidative defense could be maintained with intermittent vibration during compression. This was supported by the expression level of PGC-1-alpha, catalase, Gpx-1 and SOD1. Our data suggested intermittent vibration could serve as a preventive measure for deep tissue ulcer, particularly in aged subjects. Copyright © 2017 Elsevier Ltd. All rights reserved.

Compressed domain indexing of losslessly compressed images

NASA Astrophysics Data System (ADS)

Schaefer, Gerald

2001-12-01

Image retrieval and image compression have been pursued separately in the past. Only little research has been done on a synthesis of the two by allowing image retrieval to be performed directly in the compressed domain of images without the need to uncompress them first. In this paper methods for image retrieval in the compressed domain of losslessly compressed images are introduced. While most image compression techniques are lossy, i.e. discard visually less significant information, lossless techniques are still required in fields like medical imaging or in situations where images must not be changed due to legal reasons. The algorithms in this paper are based on predictive coding methods where a pixel is encoded based on the pixel values of its (already encoded) neighborhood. The first method is based on an understanding that predictively coded data is itself indexable and represents a textural description of the image. The second method operates directly on the entropy encoded data by comparing codebooks of images. Experiments show good image retrieval results for both approaches.

Compressive properties of passive skeletal muscle-the impact of precise sample geometry on parameter identification in inverse finite element analysis.

PubMed

Böl, Markus; Kruse, Roland; Ehret, Alexander E; Leichsenring, Kay; Siebert, Tobias

2012-10-11

Due to the increasing developments in modelling of biological material, adequate parameter identification techniques are urgently needed. The majority of recent contributions on passive muscle tissue identify material parameters solely by comparing characteristic, compressive stress-stretch curves from experiments and simulation. In doing so, different assumptions concerning e.g. the sample geometry or the degree of friction between the sample and the platens are required. In most cases these assumptions are grossly simplified leading to incorrect material parameters. In order to overcome such oversimplifications, in this paper a more reliable parameter identification technique is presented: we use the inverse finite element method (iFEM) to identify the optimal parameter set by comparison of the compressive stress-stretch response including the realistic geometries of the samples and the presence of friction at the compressed sample faces. Moreover, we judge the quality of the parameter identification by comparing the simulated and experimental deformed shapes of the samples. Besides this, the study includes a comprehensive set of compressive stress-stretch data on rabbit soleus muscle and the determination of static friction coefficients between muscle and PTFE. Copyright © 2012 Elsevier Ltd. All rights reserved.

Radiological Image Compression

NASA Astrophysics Data System (ADS)

Lo, Shih-Chung Benedict

The movement toward digital images in radiology presents the problem of how to conveniently and economically store, retrieve, and transmit the volume of digital images. Basic research into image data compression is necessary in order to move from a film-based department to an efficient digital -based department. Digital data compression technology consists of two types of compression technique: error-free and irreversible. Error -free image compression is desired; however, present techniques can only achieve compression ratio of from 1.5:1 to 3:1, depending upon the image characteristics. Irreversible image compression can achieve a much higher compression ratio; however, the image reconstructed from the compressed data shows some difference from the original image. This dissertation studies both error-free and irreversible image compression techniques. In particular, some modified error-free techniques have been tested and the recommended strategies for various radiological images are discussed. A full-frame bit-allocation irreversible compression technique has been derived. A total of 76 images which include CT head and body, and radiographs digitized to 2048 x 2048, 1024 x 1024, and 512 x 512 have been used to test this algorithm. The normalized mean -square-error (NMSE) on the difference image, defined as the difference between the original and the reconstructed image from a given compression ratio, is used as a global measurement on the quality of the reconstructed image. The NMSE's of total of 380 reconstructed and 380 difference images are measured and the results tabulated. Three complex compression methods are also suggested to compress images with special characteristics. Finally, various parameters which would effect the quality of the reconstructed images are discussed. A proposed hardware compression module is given in the last chapter.

Curvature and tangential deflection of discrete arcs: a theory based on the commutator of scatter matrix pairs and its application to vertex detection in planar shape data.

PubMed

Anderson, I M; Bezdek, J C

1984-01-01

This paper introduces a new theory for the tangential deflection and curvature of plane discrete curves. Our theory applies to discrete data in either rectangular boundary coordinate or chain coded formats: its rationale is drawn from the statistical and geometric properties associated with the eigenvalue-eigenvector structure of sample covariance matrices. Specifically, we prove that the nonzero entry of the commutator of a piar of scatter matrices constructed from discrete arcs is related to the angle between their eigenspaces. And further, we show that this entry is-in certain limiting cases-also proportional to the analytical curvature of the plane curve from which the discrete data are drawn. These results lend a sound theoretical basis to the notions of discrete curvature and tangential deflection; and moreover, they provide a means for computationally efficient implementation of algorithms which use these ideas in various image processing contexts. As a concrete example, we develop the commutator vertex detection (CVD) algorithm, which identifies the location of vertices in shape data based on excessive cummulative tangential deflection; and we compare its performance to several well established corner detectors that utilize the alternative strategy of finding (approximate) curvature extrema.

Stress Measurements in Railroad Wheels Via the Barkhausen Effect

DOT National Transportation Integrated Search

1977-02-01

The feasibility of utilizing the Barkhausen Effect in ferromagnetic steels as a nondestructive means for ascertaining residual stresses in railroad wheels was investigated. Railroad wheels are generally manufactured with compressive stress distributi...

Simultaneous Optical Measurements of Axial and Tangential Steady-State Blade Deflections

NASA Technical Reports Server (NTRS)

Kurkov, Anatole P.; Dhadwal, Harbans S.

1999-01-01

Currently, the majority of fiber-optic blade instrumentation is being designed and manufactured by aircraft-engine companies for their own use. The most commonly employed probe for optical blade deflection measurements is the spot probe. One of its characteristics is that the incident spot on a blade is not fixed relative to the blade, but changes depending on the blade deformation associated with centrifugal and aerodynamic loading. While there are geometrically more complicated optical probe designs in use by different engine companies, this paper offers an alternate solution derived from a probe-mount design feature that allows one to change the probe axial position until the incident spot contacts either a leading or a trailing edge. By tracing the axial position of either blade edge one is essentially extending the deflection measurement to two dimensions, axial and tangential. The blade deflection measurements were obtained during a wind tunnel test of a fan prototype.

Integrated axial and tangential serpentine cooling circuit in a turbine airfoil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ching-Pang; Jiang, Nan; Marra, John J

2015-05-05

A continuous serpentine cooling circuit forming a progression of radial passages (44, 45, 46, 47A, 48A) between pressure and suction side walls (52, 54) in a MID region of a turbine airfoil (24). The circuit progresses first axially, then tangentially, ending in a last radial passage (48A) adjacent to the suction side (54) and not adjacent to the pressure side (52). The passages of the axial progression (44, 45, 46) may be adjacent to both the pressure and suction side walls of the airfoil. The next to last radial passage (47A) may be adjacent to the pressure side wall andmore » not adjacent to the suction side wall. The last two radial passages (47A, 48A) may be longer along the pressure and suction side walls respectively than they are in a width direction, providing increased direct cooling surface area on the interiors of these hot walls.« less

Preliminary design of a tangentially viewing imaging bolometer for NSTX-U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peterson, B. J., E-mail: peterson@LHD.nifs.ac.jp; Mukai, K.; SOKENDAI

2016-11-15

The infrared imaging video bolometer (IRVB) measures plasma radiated power images using a thin metal foil. Two different designs with a tangential view of NSTX-U are made assuming a 640 × 480 (1280 × 1024) pixel, 30 (105) fps, 50 (20) mK, IR camera imaging the 9 cm × 9 cm × 2 μm Pt foil. The foil is divided into 40 × 40 (64 × 64) IRVB channels. This gives a spatial resolution of 3.4 (2.2) cm on the machine mid-plane. The noise equivalent power density of the IRVB is given as 113 (46) μW/cm{sup 2} for a timemore » resolution of 33 (20) ms. Synthetic images derived from Scrape Off Layer Plasma Simulation data using the IRVB geometry show peak signal levels ranging from ∼0.8 to ∼80 (∼0.36 to ∼26) mW/cm{sup 2}.« less

Impact compressive and bending behaviour of rocks accompanied by electromagnetic phenomena.

PubMed

Kobayashi, Hidetoshi; Horikawa, Keitaro; Ogawa, Kinya; Watanabe, Keiko

2014-08-28

It is well known that electromagnetic phenomena are often observed preceding earthquakes. However, the mechanism by which these electromagnetic waves are generated during the fracture and deformation of rocks has not been fully identified. Therefore, in order to examine the relationship between the electromagnetic phenomena and the mechanical properties of rocks, uniaxial compression and three-point bending tests for two kinds of rocks with different quartz content, granite and gabbro, have been carried out at quasi-static and dynamic rates. Especially, in the bending tests, pre-cracked specimens of granite were also tested. Using a split Hopkinson pressure bar and a ferrite-core antenna in close proximity to the specimens, both the stress-strain (load-displacement) curve and simultaneous electromagnetic wave magnitude were measured. It was found that the dynamic compressive and bending strengths and the stress increase slope of both rocks were higher than those observed in static tests; therefore, there is a strain-rate dependence in their strength and stress increase rate. It was found from the tests using the pre-cracked bending specimens that the intensity of electromagnetic waves measured during crack extension increased almost proportionally to the increase of the maximum stress intensity factor of specimens. This tendency was observed in both the dynamic and quasi-static three-point bending tests for granite. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Compression etiology in tendinopathy.

PubMed

Almekinders, Louis C; Weinhold, Paul S; Maffulli, Nicola

2003-10-01

Recent studies have emphasized that the etiology of tendinopathy is not as simple as was once thought. The etiology is likely to be multifactorial. Etiologic factors may include some of the traditional factors such as overuse, inflexibility, and equipment problems; however, other factors need to be considered as well, such as age-related tendon degeneration and biomechanical considerations as outlined in this article. More research is needed to determine the significance of stress-shielding and compression in tendinopathy. If they are confirmed to play a role, this finding may significantly alter our approach in both prevention and in treatment through exercise therapy. The current biomechanical studies indicate that certain joint positions are more likely to place tensile stress on the area of the tendon commonly affected by tendinopathy. These joint positions seem to be different than the traditional positions for stretching exercises used for prevention and rehabilitation of tendinopathic conditions. Incorporation of different joint positions during stretching exercises may exert more uniform, controlled tensile stress on these affected areas of the tendon and avoid stresshielding. These exercises may be able to better maintain the mechanical strength of that region of the tendon and thereby avoid injury. Alternatively, they could more uniformly stress a healing area of the tendon in a controlled manner, and thereby stimulate healing once an injury has occurred. Additional work will have to prove if a change in rehabilitation exercises is more efficacious that current techniques.

Purification of monoclonal antibodies from clarified cell culture fluid using Protein A capture continuous countercurrent tangential chromatography

PubMed Central

Dutta, Amit K.; Tran, Travis; Napadensky, Boris; Teella, Achyuta; Brookhart, Gary; Ropp, Philip A.; Zhang, Ada W.; Tustian, Andrew D.; Zydney, Andrew L.; Shinkazh, Oleg

2015-01-01

Recent studies using simple model systems have demonstrated that Continuous Countercurrent Tangential Chromatography (CCTC) has the potential to overcome many of the limitations of conventional Protein A chromatography using packed columns. The objective of this work was to optimize and implement a CCTC system for monoclonal antibody purification from clarified Chinese Hamster Ovary (CHO) cell culture fluid using a commercial Protein A resin. Several improvements were introduced to the previous CCTC system including the use of retentate pumps to maintain stable resin concentrations in the flowing slurry, the elimination of a slurry holding tank to improve productivity, and the introduction of an “after binder” to the binding step to increase antibody recovery. A kinetic binding model was developed to estimate the required residence times in the multi-stage binding step to optimize yield and productivity. Data were obtained by purifying two commercial antibodies from two different manufactures, one with low titer (~0.67 g/L) and one with high titer (~6.9 g/L), demonstrating the versatility of the CCTC system. Host cell protein removal, antibody yields and purities were similar to that obtained with conventional column chromatography; however, the CCTC system showed much higher productivity. These results clearly demonstrate the capabilities of continuous countercurrent tangential chromatography for the commercial purification of monoclonal antibody products. PMID:25747172

Purification of monoclonal antibodies from clarified cell culture fluid using Protein A capture continuous countercurrent tangential chromatography.

PubMed

Dutta, Amit K; Tran, Travis; Napadensky, Boris; Teella, Achyuta; Brookhart, Gary; Ropp, Philip A; Zhang, Ada W; Tustian, Andrew D; Zydney, Andrew L; Shinkazh, Oleg

2015-11-10

Recent studies using simple model systems have demonstrated that continuous countercurrent tangential chromatography (CCTC) has the potential to overcome many of the limitations of conventional Protein A chromatography using packed columns. The objective of this work was to optimize and implement a CCTC system for monoclonal antibody purification from clarified Chinese Hamster Ovary (CHO) cell culture fluid using a commercial Protein A resin. Several improvements were introduced to the previous CCTC system including the use of retentate pumps to maintain stable resin concentrations in the flowing slurry, the elimination of a slurry holding tank to improve productivity, and the introduction of an "after binder" to the binding step to increase antibody recovery. A kinetic binding model was developed to estimate the required residence times in the multi-stage binding step to optimize yield and productivity. Data were obtained by purifying two commercial antibodies from two different manufactures, one with low titer (∼ 0.67 g/L) and one with high titer (∼ 6.9 g/L), demonstrating the versatility of the CCTC system. Host cell protein removal, antibody yields and purities were similar to those obtained with conventional column chromatography; however, the CCTC system showed much higher productivity. These results clearly demonstrate the capabilities of continuous countercurrent tangential chromatography for the commercial purification of monoclonal antibody products. Copyright © 2015 Elsevier B.V. All rights reserved.

Relationship between linear velocity and tangential push force while turning to change the direction of the manual wheelchair.

PubMed

Hwang, Seonhong; Lin, Yen-Sheng; Hogaboom, Nathan S; Wang, Lin-Hwa; Koontz, Alicia M

2017-08-28

Wheelchair propulsion is a major cause of upper limb pain and injuries for manual wheelchair users with spinal cord injuries (SCIs). Few studies have investigated wheelchair turning biomechanics on natural ground surfaces. The purpose of this study was to investigate the relationship between tangential push force and linear velocity of the wheelchair during the turning portions of propulsion. Using an instrumented handrim, velocity and push force data were recorded for 25 subjects while they propel their own wheelchairs on a concrete floor along a figure-eight-shaped course at a maximum velocity. The braking force (1.03 N) of the inside wheel while turning was the largest of all other push forces (p<0.05). Larger changes in squared velocity while turning were significantly correlated with higher propulsive and braking forces used at the pre-turning, turning, and post-turning phases (p<0.05). Subjects with less change of velocity while turning needed less braking force to maneuver themselves successfully and safely around the turns. Considering the magnitude and direction of tangential force applied to the wheel, it seems that there are higher risks of injury and instability for upper limb joints when braking the inside wheel to turn. The results provide insight into wheelchair setup and mobility skills training for wheelchair users.

Experimental investigation of dynamic compression and spallation of Cerium at pressures up to 6 GPa

NASA Astrophysics Data System (ADS)

Zubareva, A. N.; Kolesnikov, S. A.; Utkin, A. V.

2014-05-01

In this study the experiments on one-dimensional dynamic compression of Cerium (Ce) samples to pressures of 0.5 to 6 GPa using various types of explosively driven generators were conducted. VISAR laser velocimeter was used to obtain Ce free surface velocity profiles. The isentropic compression wave was registered for γ-phase of Ce at pressures lower than 0.76 GPa that corresponds to γ-α phase transition pressure in Ce. Shock rarefaction waves were also registered in several experiments. Both observations were the result of the anomalous compressibility of γ-phase of Ce. On the basis of our experimental results the compression isentrope of Ce γ-phase was constructed. Its comparison with volumetric compression curves allowed to estimate the magnitude of shear stress at dynamic compression conditions for Ce. Spall strength measurements were also conducted for several samples. They showed a strong dependence of the spall strength of Ce on the strain rate.

Enhanced densification under shock compression in porous silicon

NASA Astrophysics Data System (ADS)

Lane, J. Matthew D.; Thompson, Aidan P.; Vogler, Tracy J.

2014-10-01

Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. We demonstrate a molecular mechanism that drives this behavior. We also present evidence from atomistic simulation that silicon belongs to this anomalous class of materials. Atomistic simulations indicate that local shear strain in the neighborhood of collapsing pores nucleates a local solid-solid phase transformation even when bulk pressures are below the thermodynamic phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials.

Influence of Radial Stress Gradient on Strainbursts: An Experimental Study

NASA Astrophysics Data System (ADS)

Su, Guoshao; Zhai, Shaobin; Jiang, Jianqing; Zhang, Gangliang; Yan, Liubin

2017-10-01

Strainbursts, which are violent disasters that are accompanied by the ejection failure of rocks, usually occur in hard brittle rocks around highly stressed underground openings. The release of the radial stress at excavation boundaries is one of the major inducing factors for strainbursts in tunnels. After excavation, the radial stress usually exhibits different but apparent gradient variations along the radial direction near the boundary within a certain depth under different in situ stress conditions. In this study, the influence of the radial stress gradient on strainbursts of granite was investigated using an improved true-triaxial rockburst testing system, which was equipped with an acoustic emission monitoring system. The stress state and boundary conditions (i.e., one face free, other faces loaded and increasing tangential stress) of the representative rock element in the vicinity of the excavation boundary were simulated. High-speed cameras were used to capture the ejection failure processes during strainbursts, and the kinetic energy of ejected fragments was quantitatively estimated by analyzing the recorded videos. The experimental results indicate that with an increasing radial stress gradient, the strength increases, the apparent yield platform prior to the peak stress on the stress-strain curves decreases, the failure mode changes from strainburst characterized by tensile splitting to strainburst characterized by shear rupture, and the kinetic energy of ejected fragments during strainbursts significantly increases.

Bolus-dependent dosimetric effect of positioning errors for tangential scalp radiotherapy with helical tomotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lobb, Eric, E-mail: eclobb2@gmail.com

2014-04-01

The dosimetric effect of errors in patient position is studied on-phantom as a function of simulated bolus thickness to assess the need for bolus utilization in scalp radiotherapy with tomotherapy. A treatment plan is generated on a cylindrical phantom, mimicking a radiotherapy technique for the scalp utilizing primarily tangential beamlets. A planning target volume with embedded scalplike clinical target volumes (CTVs) is planned to a uniform dose of 200 cGy. Translational errors in phantom position are introduced in 1-mm increments and dose is recomputed from the original sinogram. For each error the maximum dose, minimum dose, clinical target dose homogeneitymore » index (HI), and dose-volume histogram (DVH) are presented for simulated bolus thicknesses from 0 to 10 mm. Baseline HI values for all bolus thicknesses were in the 5.5 to 7.0 range, increasing to a maximum of 18.0 to 30.5 for the largest positioning errors when 0 to 2 mm of bolus is used. Utilizing 5 mm of bolus resulted in a maximum HI value of 9.5 for the largest positioning errors. Using 0 to 2 mm of bolus resulted in minimum and maximum dose values of 85% to 94% and 118% to 125% of the prescription dose, respectively. When using 5 mm of bolus these values were 98.5% and 109.5%. DVHs showed minimal changes in CTV dose coverage when using 5 mm of bolus, even for the largest positioning errors. CTV dose homogeneity becomes increasingly sensitive to errors in patient position as bolus thickness decreases when treating the scalp with primarily tangential beamlets. Performing a radial expansion of the scalp CTV into 5 mm of bolus material minimizes dosimetric sensitivity to errors in patient position as large as 5 mm and is therefore recommended.« less

Tensile and compressive creep behavior of extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, H.; The State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240; Wang, Q.D., E-mail: wangqudong@sjtu.edu.cn

2015-01-15

The tensile and compressive creep behavior of an extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy was investigated at temperatures ranging from 200 °C to 300 °C and under stresses ranging from 30 MPa to 120 MPa. There existed an asymmetry in the tensile and compressive creep properties. The minimum creep rate of the alloy was slightly greater in tension than in compression. The measured values of the transient strain and initial creep rate in compression were greater than those in tension. The creep stress exponent was approximately 2.5 at low temperatures (T < 250 °C) and 3.4 at higher temperatures both in tensionmore » and in compression. The compression creep activation energy at low temperatures and high temperatures was 83.4 and 184.3 kJ/mol respectively, while one activation energy (184 kJ/mol) represented the tensile–creep behavior over the temperature range examined. Dislocation creep was suggested to be the main mechanism in tensile creep and in the high-temperature regime in compressive creep, while grain boundary sliding was suggested to dominate in the low-temperature regime in compressive creep. Precipitate free zones were observed near grain boundaries perpendicular to the loading direction in tension and parallel to the loading direction in compression. Electron backscattered diffraction analysis revealed that the texture changed slightly during creep. Non-basal slip was suggested to contribute to the deformation after basal slip was introduced. In the tensile–creep ruptured specimens, intergranular cracks were mainly observed at general high-angle boundaries. - Highlights: • Creep behavior of an extruded Mg–RE alloy was characterized by EBSD. • T5 aging treatment enhanced the tension–compression creep asymmetry. • The grains grew slightly during tensile creep, but not for compressive creep. • Precipitate free zones (PFZs) were observed at specific grain boundaries. • Intergranular fracture was dominant and cracks mainly originated

Biomechanical Property of a Newly Designed Assembly Locking Compression Plate: Three-Dimensional Finite Element Analysis

PubMed Central

Liu, Da

2017-01-01

In this study, we developed and validated a refined three-dimensional finite element model of middle femoral comminuted fracture to compare the biomechanical stability after two kinds of plate fixation: a newly designed assembly locking compression plate (NALCP) and a locking compression plate (LCP). CT data of a male volunteer was converted to middle femoral comminuted fracture finite element analysis model. The fracture was fixated by NALCP and LCP. Stress distributions were observed. Under slow walking load and torsion load, the stress distribution tendency of the two plates was roughly uniform. The anterolateral femur was the tension stress area, and the bone block shifted toward the anterolateral femur. Maximum stress was found on the lateral border of the number 5 countersink of the plate. Under a slow walking load, the NALCP maximum stress was 2.160e+03 MPa and the LCP was 8.561e+02 MPa. Under torsion load, the NALCP maximum stress was 2.260e+03 MPa and the LCP was 6.813e+02 MPa. Based on those results of finite element analysis, the NALCP can provide adequate mechanical stability for comminuted fractures, which would help fixate the bone block and promote bone healing. PMID:29065654

Development and comparison of processing maps of Mg-3Sn-1Ca alloy from data obtained in tension versus compression

NASA Astrophysics Data System (ADS)

Rao, K. P.; Suresh, K.; Prasad, Y. V. R. K.; Hort, N.

2018-01-01

The hot workability of extruded Mg-3Sn-1Ca alloy has been evaluated by developing processing maps with flow stress data from compression and tensile tests with a view to find the effect of the applied state-of-stress. The processing maps developed at a strain of 0.2 are essentially similar irrespective of the mode of deformation - compression or tension, and exhibit three domains in the temperature ranges: (1) 350 - 425 °C, and (2) 450 - 550 °C and (3) 400 - 500 °C, the first two occurring at lower strain rates and the third occurring at higher strain rates. In all the three domains, dynamic recrystallization occurs and is caused by non-basal slip and controlled by lattice self-diffusion in the first and second domains and grain boundary self-diffusion in the third domain. The state-of-stress imposed on the specimen (compression or tension) does not have any significant effect on the processing maps.

Performance of a Compression-ignition Engine with a Precombustion Chamber Having High-Velocity Air Flow

NASA Technical Reports Server (NTRS)

Spanogle, J A; Moore, C S

1931-01-01

Presented here are the results of performance tests made with a single-cylinder, four stroke cycle, compression-ignition engine. These tests were made on a precombustion chamber type of cylinder head designed to have air velocity and tangential air flow in both the chamber and cylinder. The performance was investigated for variable load and engine speed, type of fuel spray, valve opening pressure, injection period and, for the spherical chamber, position of the injection spray relative to the air flow. The pressure variations between the pear-shaped precombustion chamber and the cylinder for motoring and full load conditions were determined with a Farnboro electric indicator. The combustion chamber designs tested gave good mixing of a single compact fuel spray with the air, but did not control the ensuing combustion sufficiently. Relative to each other, the velocity of air flow was too high, the spray dispersion by injection too great, and the metering effect of the cylinder head passage insufficient. The correct relation of these factors is of the utmost importance for engine performance.

Strain-rate/temperature behavior of high density polyethylene in compression

NASA Technical Reports Server (NTRS)

Clements, L. L.; Sherby, O. D.

1978-01-01

The compressive strain rate/temperature behavior of highly linear, high density polyethylene was analyzed in terms of the predictive relations developed for metals and other crystalline materials. For strains of 5 percent and above, the relationship between applied strain rate, dotted epsilon, and resulting flow stress, sigma, was found to be: dotted epsilon exp times (Q sub f/RT) = k'(sigma/sigma sub c) to the nth power; the left-hand side is the activation-energy-compensated strain rate, where Q sub f is activation energy for flow, R is gas constant, and T is temperature; k is a constant, n is temperature-independent stress exponent, and sigma/sigma sub c is structure-compensated stress. A master curve resulted from a logarithmic plot of activation-energy-compensated strain rate versus structure-compensated stress.

Compressed NMR: Combining compressive sampling and pure shift NMR techniques.

PubMed

Aguilar, Juan A; Kenwright, Alan M

2017-12-26

Historically, the resolution of multidimensional nuclear magnetic resonance (NMR) has been orders of magnitude lower than the intrinsic resolution that NMR spectrometers are capable of producing. The slowness of Nyquist sampling as well as the existence of signals as multiplets instead of singlets have been two of the main reasons for this underperformance. Fortunately, two compressive techniques have appeared that can overcome these limitations. Compressive sensing, also known as compressed sampling (CS), avoids the first limitation by exploiting the compressibility of typical NMR spectra, thus allowing sampling at sub-Nyquist rates, and pure shift techniques eliminate the second issue "compressing" multiplets into singlets. This paper explores the possibilities and challenges presented by this combination (compressed NMR). First, a description of the CS framework is given, followed by a description of the importance of combining it with the right pure shift experiment. Second, examples of compressed NMR spectra and how they can be combined with covariance methods will be shown. Copyright © 2017 John Wiley & Sons, Ltd.

Mechanism for amorphization of boron carbide under complex stress conditions

NASA Astrophysics Data System (ADS)

Li, Jun; Xu, Shuang; Liu, Lisheng; Wang, Zhen; Zhang, Jinyong; Liu, Qiwen

2018-05-01

As an excellent material, the application of boron carbide (B4C) is limited by pressure-induced amorphization. To understand the mechanism for amorphization in B4C, first-principles methods based on density functional theory were employed to investigate the mechanical behaviors and the deformation process in B4C under complex stress conditions with six different biaxial perpendicular compression directions. The angle (θ) between one of the loading directions and the [0 0 0 1] c-axis ranged from 0° to 75° with every 15° interval. We found that the maximum stress at θ = 30° is 124.5 GPa, which is the lowest among six biaxial compressions. Simulation results show that the mechanism for amorphization in B4C under complex stress conditions is complicated. We take the θ = 30° biaxial compression as an example to explain the complicated deformation process. In the elastic deformation region, sudden bending of three-atom chains occurs and results in a stress fluctuation. Then the formation of new B–B bonds between the three-atom chains and the icosahedra leads to the first stress drop. After that, the B–C bonds in the chains are broken, resulting in the second stress drop. In this process, the icosahedra are partially destroyed. The stress increases continuously and then drops at the critical failure strain. Finally, the fully destruction of icosahedra leads to amorphization in B4C. However, under other five biaxial compressions, the B–C bonds in three-atom chains are not fractured before structural failure. Understanding the deformation mechanism for amorphization of B4C in real applications is prime important for proposing how to resist amorphization and enhance the toughness of B4C.

Finite Element Analysis of Aluminum Honeycombs Subjected to Dynamic Indentation and Compression Loads

PubMed Central

Ashab, A.S.M. Ayman; Ruan, Dong; Lu, Guoxing; Bhuiyan, Arafat A.

2016-01-01

The mechanical behavior of aluminum hexagonal honeycombs subjected to out-of-plane dynamic indentation and compression loads has been investigated numerically using ANSYS/LS-DYNA in this paper. The finite element (FE) models have been verified by previous experimental results in terms of deformation pattern, stress-strain curve, and energy dissipation. The verified FE models have then been used in comprehensive numerical analysis of different aluminum honeycombs. Plateau stress, σpl, and dissipated energy (EI for indentation and EC for compression) have been calculated at different strain rates ranging from 102 to 104 s−1. The effects of strain rate and t/l ratio on the plateau stress, dissipated energy, and tearing energy have been discussed. An empirical formula is proposed to describe the relationship between the tearing energy per unit fracture area, relative density, and strain rate for honeycombs. Moreover, it has been found that a generic formula can be used to describe the relationship between tearing energy per unit fracture area and relative density for both aluminum honeycombs and foams. PMID:28773288

Mesoscale Phase Field Modeling of Glass Strengthening Under Triaxial Compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yulan; Sun, Xin

2015-09-28

Recent hydraulic bomb and confined sleeve tests on transparent armor glass materials such as borosilicate glass and soda-lime glass showed that the glass strength was a function of confinement pressure. The measured stress-strain relation is not a straight line as most brittle materials behave under little or no confinement. Moreover, borosilicate glass exhibited a stronger compressive strength when compared to soda-lime glass, even though soda-lime has higher bulk and shear moduli as well as apparent yield strength. To better understand these experimental findings, a mesoscale phase field model is developed to simulate the nonlinear stress versus strain behaviors under confinementmore » by considering heterogeneity formation under triaxial compression and the energy barrier of a micro shear banding event (referred to as pseudo-slip hereafter) in the amorphous glass. With calibrated modeling parameters, the simulation results demonstrate that the developed phase field model can quantitatively predict the pressure-dependent strength, and it can also explain the difference between the two types of glasses from the perspective of energy barrier associated with a pseudo-slip event.« less

The present state and future direction of second order closure models for compressible flows

NASA Technical Reports Server (NTRS)

Gatski, Thomas B.; Sarkar, Sutanu; Speziale, Charles G.

1992-01-01

The topics are presented in viewgraph form and include: (1) Reynolds stress closure models; (2) Favre averages and governing equations; (3) the model for the deviatoric part of the pressure-strain rate correlation; (4) the SSG pressure-strain correlation model; (5) a compressible turbulent dissipation rate model; (6) variable viscosity effects; (7) near-wall stiffness problems; (8) models of the Reynolds mass and heat flux; and (9) a numerical solution of the compressible turbulent transport equation.

Fibrocartilage tissue engineering: the role of the stress environment on cell morphology and matrix expression.

PubMed

Thomopoulos, Stavros; Das, Rosalina; Birman, Victor; Smith, Lester; Ku, Katherine; Elson, Elliott L; Pryse, Kenneth M; Marquez, Juan Pablo; Genin, Guy M

2011-04-01

Although much is known about the effects of uniaxial mechanical loading on fibrocartilage development, the stress fields to which fibrocartilaginous regions are subjected to during development are mutiaxial. That fibrocartilage develops at tendon-to-bone attachments and in compressive regions of tendons is well established. However, the three-dimensional (3D) nature of the stresses needed for the development of fibrocartilage is not known. Here, we developed and applied an in vitro system to determine whether fibrocartilage can develop under a state of periodic hydrostatic tension in which only a single principal component of stress is compressive. This question is vital to efforts to mechanically guide morphogenesis and matrix expression in engineered tissue replacements. Mesenchymal stromal cells in a 3D culture were exposed to compressive and tensile stresses as a result of an external tensile hydrostatic stress field. The stress field was characterized through mechanical modeling. Tensile cyclic stresses promoted spindle-shaped cells, upregulation of scleraxis and type one collagen, and cell alignment with the direction of tension. Cells experiencing a single compressive stress component exhibited rounded cell morphology and random cell orientation. No difference in mRNA expression of the genes Sox9 and aggrecan was observed when comparing tensile and compressive regions unless the medium was supplemented with the chondrogenic factor transforming growth factor beta3. In that case, Sox9 was upregulated under static loading conditions and aggrecan was upregulated under cyclic loading conditions. In conclusion, the fibrous component of fibrocartilage could be generated using only mechanical cues, but generation of the cartilaginous component of fibrocartilage required biologic factors in addition to mechanical cues. These studies support the hypothesis that the 3D stress environment influences cell activity and gene expression in fibrocartilage development.

Fibrocartilage Tissue Engineering: The Role of the Stress Environment on Cell Morphology and Matrix Expression

PubMed Central

Das, Rosalina; Birman, Victor; Smith, Lester; Ku, Katherine; Elson, Elliott L.; Pryse, Kenneth M.; Marquez, Juan Pablo; Genin, Guy M.

2011-01-01

Although much is known about the effects of uniaxial mechanical loading on fibrocartilage development, the stress fields to which fibrocartilaginous regions are subjected to during development are mutiaxial. That fibrocartilage develops at tendon-to-bone attachments and in compressive regions of tendons is well established. However, the three-dimensional (3D) nature of the stresses needed for the development of fibrocartilage is not known. Here, we developed and applied an in vitro system to determine whether fibrocartilage can develop under a state of periodic hydrostatic tension in which only a single principal component of stress is compressive. This question is vital to efforts to mechanically guide morphogenesis and matrix expression in engineered tissue replacements. Mesenchymal stromal cells in a 3D culture were exposed to compressive and tensile stresses as a result of an external tensile hydrostatic stress field. The stress field was characterized through mechanical modeling. Tensile cyclic stresses promoted spindle-shaped cells, upregulation of scleraxis and type one collagen, and cell alignment with the direction of tension. Cells experiencing a single compressive stress component exhibited rounded cell morphology and random cell orientation. No difference in mRNA expression of the genes Sox9 and aggrecan was observed when comparing tensile and compressive regions unless the medium was supplemented with the chondrogenic factor transforming growth factor beta3. In that case, Sox9 was upregulated under static loading conditions and aggrecan was upregulated under cyclic loading conditions. In conclusion, the fibrous component of fibrocartilage could be generated using only mechanical cues, but generation of the cartilaginous component of fibrocartilage required biologic factors in addition to mechanical cues. These studies support the hypothesis that the 3D stress environment influences cell activity and gene expression in fibrocartilage development. PMID

Residual stresses and their effects on deformation

NASA Astrophysics Data System (ADS)

Davis, L. C.; Allison, J. E.

1993-11-01

Residual stresses induced by thermal expansion mismatch in metal-matrix composites are studied by three-dimensional (3-D) elastic-plastic finite element analyses. Typically, the stress-free state is 150 to 300 K above room temperature. The coefficient of thermal expansion of the matrix is 3 to 5 times larger than that of the ceramic inclusion, resulting in compressive stresses of order 200 MPa in the inclusions. Both compressive and tensile stresses can be found in the matrix. Since the stress may exceed the matrix yield strength near the particles, plastic flow occurs. The authors find a significant influence of this flow on the elastic and plastic properties of the composite. The calculated residual strains in TiC particles due to thermal expansion mismatch and external loads compare well with recent neutron diffraction experiments (Bourke et al.) The present work is the first reported three-dimensional analysis of spherical inclusions in different arrays (simple cubic (sc) and face-centered cubic (fcc)) that permit a study of particle interactions.

Direct numerical simulations of premixed autoignition in compressible uniformly-sheared turbulence

NASA Astrophysics Data System (ADS)

Towery, Colin; Darragh, Ryan; Poludnenko, Alexei; Hamlington, Peter

2017-11-01

High-speed combustion systems, such as scramjet engines, operate at high temperatures and pressures, extremely short combustor residence times, very high rates of shear stress, and intense turbulent mixing. As a result, the reacting flow can be premixed and have highly-compressible turbulence fluctuations. We investigate the effects of compressible turbulence on the ignition delay time, heat-release-rate (HRR) intermittency, and mode of autoignition of premixed Hydrogen-air fuel in uniformly-sheared turbulence using new three-dimensional direct numerical simulations with a multi-step chemistry mechanism. We analyze autoignition in both the Eulerian and Lagrangian reference frames at eight different turbulence Mach numbers, Mat , spanning the quasi-isentropic, linear thermodynamic, and nonlinear compressibility regimes, with eddy shocklets appearing in the nonlinear regime. Results are compared to our previous study of premixed autoignition in isotropic turbulence at the same Mat and with a single-step reaction mechanism. This previous study found large decreases in delay times and large increases in HRR intermittency between the linear and nonlinear compressibility regimes and that detonation waves could form in both regimes.

In situ micropillar compression reveals superior strength and ductility but an absence of damage in lamellar bone

NASA Astrophysics Data System (ADS)

Schwiedrzik, Jakob; Raghavan, Rejin; Bürki, Alexander; Lenader, Victor; Wolfram, Uwe; Michler, Johann; Zysset, Philippe

2014-07-01

Ageing societies suffer from an increasing incidence of bone fractures. Bone strength depends on the amount of mineral measured by clinical densitometry, but also on the micromechanical properties of the hierarchical organization of bone. Here, we investigate the mechanical response under monotonic and cyclic compression of both single osteonal lamellae and macroscopic samples containing numerous osteons. Micropillar compression tests in a scanning electron microscope, microindentation and macroscopic compression tests were performed on dry ovine bone to identify the elastic modulus, yield stress, plastic deformation, damage accumulation and failure mechanisms. We found that isolated lamellae exhibit a plastic behaviour, with higher yield stress and ductility but no damage. In agreement with a proposed rheological model, these experiments illustrate a transition from a ductile mechanical behaviour of bone at the microscale to a quasi-brittle response driven by the growth of cracks along interfaces or in the vicinity of pores at the macroscale.

Investigation of the Radial Compression of Carbon Nanotubes with a Scanning Probe Microscope

NASA Astrophysics Data System (ADS)

Shen, Weidian; Jiang, Bin; Han, Bao Shan; Xie, Si-Shen

2001-03-01

Carbon nanotubes have attracted great interest since they were first synthesized. The tubes have substantial promise in a variety of applications due to their unique properties. Efforts have been made to characterize the mechanical properties of the tubes. However, previous work has concentrated on the tubes’ longitudinal properties, and studies of their radial properties lag behind. We have operated a scanning probe microscope, NanoScopeTM IIIa, in the indentation/scratching mode to carry out a nanoindentation test on the top of multiwalled carbon nanotubes. We measured the correlation between the radial stress and the tube compression, and thereby determined the radial compressive elastic modulus at different compressive forces. The measurements also allowed us to estimate the radial compressive strength of the tubes. Support of this work by an Eastern Michigan University Faculty Research Fellowship and by the K. C. Wong Education Foundation, Hong Kong is gratefully acknowledged.

Compressive Behaviour and Energy Absorption of Aluminium Foam Sandwich

NASA Astrophysics Data System (ADS)

Endut, N. A.; Hazza, M. H. F. Al; Sidek, A. A.; Adesta, E. T. Y.; Ibrahim, N. A.

2018-01-01

Development of materials in automotive industries plays an important role in order to retain the safety, performance and cost. Metal foams are one of the idea to evolve new material in automotive industries since it can absorb energy when it deformed and good for crash management. Recently, new technology had been introduced to replace metallic foam by using aluminium foam sandwich (AFS) due to lightweight and high energy absorption behaviour. Therefore, this paper provides reliable data that can be used to analyze the energy absorption behaviour of aluminium foam sandwich by conducting experimental work which is compression test. Six experiments of the compression test were carried out to analyze the stress-strain relationship in terms of energy absorption behavior. The effects of input variables include varying the thickness of aluminium foam core and aluminium sheets on energy absorption behavior were evaluated comprehensively. Stress-strain relationship curves was used for energy absorption of aluminium foam sandwich calculation. The result highlights that the energy absorption of aluminium foam sandwich increases from 12.74 J to 64.42 J respectively with increasing the foam and skin thickness.

Strength properties and structure of a submicrocrystalline Al-Mg-Mn alloy under shock compression

NASA Astrophysics Data System (ADS)

Petrova, A. N.; Brodova, I. G.; Razorenov, S. V.

2017-06-01

The results of studying the strength of a submicrocrystalline aluminum A5083 alloy (chemical composition was 4.4Mg-0.6Mn-0.11Si-0.23Fe-0.03Cr-0.02Cu-0.06Ti wt % and Al base) under shockwave compression are presented. The submicrocrystalline structure of the alloy was produced in the process of dynamic channel-angular pressing at a strain rate of 104 s-1. The average size of crystallites in the alloy was 180-460 nm. Hugoniot elastic limit σHEL, dynamic yield stress σy, and the spall strength σSP of the submicrocrystalline alloy were determined based on the free-surface velocity profiles of samples during shock compression. It has been established that upon shock compression, the σHEL and σy of the submicrocrystalline alloy are higher than those of the coarse-grained alloy and σsp does not depend on the grain size. The maximum value of σHEL reached for the submicrocrystalline alloy is 0.66 GPa, which is greater than that in the coarse-crystalline alloy by 78%. The dynamic yield stress is σy = 0.31 GPa, which is higher than that of the coarse-crystalline alloy by 63%. The spall strength is σsp = 1.49 GPa. The evolution of the submicrocrystalline structure of the alloy during shock compression was studied. It has been established that a mixed nonequilibrium grain-subgrain structure with a fragment size of about 400 nm is retained after shock compression, and the dislocation density and the hardness of the alloy are increased.

Structural changes in shock compressed silicon observed using time-resolved x-ray diffraction at the Dynamic Compression Sector

NASA Astrophysics Data System (ADS)

Turneaure, Stefan; Zdanowicz, E.; Sinclair, N.; Graber, T.; Gupta, Y. M.

2015-06-01

Structural changes in shock compressed silicon were observed directly using time-resolved x-ray diffraction (XRD) measurements at the Dynamic Compression Sector at the Advanced Photon Source. The silicon samples were impacted by polycarbonate impactors accelerated to velocities greater than 5 km/s using a two-stage light gas gun resulting in impact stresses of about 25 GPa. The 23.5 keV synchrotron x-ray beam passed through the polycarbonate impactor, the silicon sample, and an x-ray window (polycarbonate or LiF) at an angle of 30 degrees relative to the impact plane. Four XRD frames (~ 100 ps snapshots) were obtained with 153.4 ns between frames near the time of impact. The XRD measurements indicate that in the peak shocked state, the silicon samples completely transformed to a high-pressure phase. XRD results for both shocked polycrystalline silicon and single crystal silicon will be presented and compared. Work supported by DOE/NNSA.

Scramjet fuel injector design parameters and considerations: Development of a two-dimensional tangential fuel injector with constant pressure at the flame

NASA Technical Reports Server (NTRS)

Agnone, A. M.

1972-01-01

The factors affecting a tangential fuel injector design for scramjet operation are reviewed and their effect on the efficiency of the supersonic combustion process is evaluated using both experimental data and theoretical predictions. A description of the physical problem of supersonic combustion and method of analysis is followed by a presentation and evaluation of some standard and exotic types of fuel injectors. Engineering fuel injector design criteria and hydrogen ignition schemes are presented along with a cursory review of available experimental data. A two-dimensional tangential fuel injector design is developed using analyses as a guide in evaluating the effects on the combustion process of various initial and boundary conditions including splitter plate thickness, injector wall temperature, pressure gradients, etc. The fuel injector wall geometry is shaped so as to maintain approximately constant pressure at the flame as required by a cycle analysis. A viscous characteristics program which accounts for lateral as well as axial pressure variations due to the mixing and combustion process is used in determining the wall geometry.

A uniaxial cyclic compression method for characterizing the rheological and textural behaviors of mechanically dewatered sewage sludge.

PubMed

Liang, Fenglin; Sauceau, Martial; Dusserre, Gilles; Arlabosse, Patricia

2017-04-15

The mechanically dewatered sewage sludge with total solid content around 20% on a weight basis is very similar to yield stress fluid, its complex transition between solid and fluid states is not perfectly reversible and especially challenging in terms of pumping, land spreading and drying. To characterize the rheological and textural properties of highly concentrated sludge, a specific methodology based on uniaxial single and cyclic compression tests is developed. Three types of sludge samples (fresh original, fresh premixed and aged original ones) are extruded into cylinders and pressed between two parallel plates using a material testing machine. In single compression, the bioyield point beyond which the sludge fractures is around 7.3 kPa with true strain equal to 0.21. The cyclic compression tests reveal that the sludge behaves as a viscoelastic body when the true strain is smaller than 0.05 and as a visco-elasto-plastic once exceeding the yield stress. The elastic module is around 78 kPa; the viscosity is deduced, in the order of magnitude 10 4 -10 5  Pa·s and the yield stress is estimated about 4 kPa. In the unloading phase, the sludge behaves again as a viscoelastic body with clear hysteresis. With the increase of compression speed, the viscosity declines, which confirms that the sludge is a shear-thinning material. The yield stress and the bioyield increase with compression speed, but it does not induce extra internal damage in the samples since the resilience and the cohesiveness are unaltered. The reliability and sensitivity of the method is justified by highlighting the changes of sludge behavior due to aging and premixing effects: both decrease the strain energy density, but do aggravate the adhesiveness of the sludge; the aging makes the sludge less cohesive, while the premixing does not modify its cohesiveness. In spite of changes in test conditions, the elastic module of sludge samples remains unchanged. Copyright © 2017 Elsevier Ltd. All rights

Study on Relationships between Internal Stress and Photodecomposition Properties of Thin Film Titanium Dioxide Photocatalyst

NASA Astrophysics Data System (ADS)

Miyamura, Amica; Kaneda, Kenji; Sato, Yasushi; Shigesato, Yuzo

Photocatalytic activities of titanium dioxide (TiO2) films deposited by rf sputtering were investigated from view points of their internal stress. TiO2 films were deposited on fused quartz glass or 100 μm thick micro-sheet glass substrates at room temperature, 200 or 400°C under various total gas pressures (Ptot) of 0.3~5.0 Pa with oxygen flow ratio [O2/(O2+Ar)] of 60% using a Ti metal target. Photocatalytic activity was evaluated by photodecomposition of acetaldehyde (CH3CHO) under UV illumination (black light lamp, 0.4 mW/cm2). Compressive internal stress was estimated by cantilever method using the micro-sheet glass, which clearly decreased from -2.1 to -0.1 GPa with the increase in the Ptot from 0.3 to 3.0 Pa. The films with the compressive stress less than -0.5 GPa performed the photocatalytic activity. Furthermore, compressive or tensile stress was applied by external force on the TiO2 films deposited on the curved micro sheet glasses by flattening these substrates after the deposition. The photodecomposition activity of the films with the slight compressive stress improved clearly, whereas the one of the films with the tensile stress degraded.

Rapid-Rate Compression Testing of Sheet Materials at High Temperatures

NASA Technical Reports Server (NTRS)

Bernett, E. C.; Gerberich, W. W.

1961-01-01

This Report describes the test equipment that was developed and the procedures that were used to evaluate structural sheet-material compression properties at preselected constant strain rates and/or loads. Electrical self-resistance was used to achieve a rapid heating rate of 200 F/sec. Four materials were tested at maximum temperatures which ranged from 600 F for the aluminum alloy to 2000 F for the Ni-Cr-Co iron-base alloy. Tests at 0.1, 0.001, and 0.00001 in./in./sec showed that strain rate has a major effect on the measured strength, especially at the high temperatures. The tests, under conditions of constant temperature and constant compression stress, showed that creep deformation can be a critical factor even when the time involved is on the order of a few seconds or less. The theoretical and practical aspects of rapid-rate compression testing are presented, and suggestions are made regarding possible modifications of the equipment which would improve the over-all capabilities.

Parallel momentum input by tangential neutral beam injections in stellarator and heliotron plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishimura, S., E-mail: nishimura.shin@lhd.nifs.ac.jp; Nakamura, Y.; Nishioka, K.

The configuration dependence of parallel momentum inputs to target plasma particle species by tangentially injected neutral beams is investigated in non-axisymmetric stellarator/heliotron model magnetic fields by assuming the existence of magnetic flux-surfaces. In parallel friction integrals of the full Rosenbluth-MacDonald-Judd collision operator in thermal particles' kinetic equations, numerically obtained eigenfunctions are used for excluding trapped fast ions that cannot contribute to the friction integrals. It is found that the momentum inputs to thermal ions strongly depend on magnetic field strength modulations on the flux-surfaces, while the input to electrons is insensitive to the modulation. In future plasma flow studies requiringmore » flow calculations of all particle species in more general non-symmetric toroidal configurations, the eigenfunction method investigated here will be useful.« less

Recent tectonic stress field, active faults and geothermal fields (hot-water type) in China

NASA Astrophysics Data System (ADS)

Wan, Tianfeng

1984-10-01

It is quite probable that geothermal fields of the hot-water type in China do not develop in the absence of recently active faults. Such active faults are all controlled by tectonic stress fields. Using the data of earthquake fault-plane solutions, active faults, and surface thermal manifestations, a map showing the recent tectonic stress field, and the location of active faults and geothermal fields in China is presented. Data collected from 89 investigated prospects with geothermal manifestations indicate that the locations of geothermal fields are controlled by active faults and the recent tectonic stress field. About 68% of the prospects are controlled by tensional or tensional-shear faults. The angle between these faults and the direction of maximum compressive stress is less than 45°, and both tend to be parallel. About 15% of the prospects are controlled by conjugate faults. Another 14% are controlled by compressive-shear faults where the angle between these faults and the direction maximum compressive stress is greater than 45°.

Influence of temper condition on the nonlinear stress-strain behavior of boron-aluminum

NASA Technical Reports Server (NTRS)

Kennedy, J. M.; Herakovich, E. T.; Tenney, D. R.

1977-01-01

The influence of temper condition on the tensile and compressive stress-strain behavior for six boron-aluminum laminates was investigated. In addition to monotonic tension and compression tests, tension-tension, compression-compression, and tension--compression tests were conducted to study the effects of cyclic loading. Tensile strength results are a function of the laminate configuration; unidirectional laminates were affected considerably more than other laminates with some strength values increasing and others decreasing.

Mechanic stress generated by a time-varying electromagnetic field on bone surface.

PubMed

Ye, Hui

2018-03-19

Bone cells sense mechanical load, which is essential for bone growth and remodeling. In a fracture, this mechanism is compromised. Electromagnetic stimulation has been widely used to assist in bone healing, but the underlying mechanisms are largely unknown. A recent hypothesis suggests that electromagnetic stimulation could influence tissue biomechanics; however, a detailed quantitative understanding of EM-induced biomechanical changes in the bone is unavailable. This paper used a muscle/bone model to study the biomechanics of the bone under EM exposure. Due to the dielectric properties of the muscle/bone interface, a time-varying magnetic field can generate both compressing and shear stresses on the bone surface, where many mechanical sensing cells are available for cellular mechanotransduction. I calculated these stresses and found that the shear stress is significantly greater than the compressing stress. Detailed parametric analysis suggests that both the compressing and shear stresses are dependent on the geometrical and electrical properties of the muscle and the bone. These stresses are also functions of the orientation of the coil and the frequency of the magnetic field. It is speculated that the EM field could apply biomechanical influence to fractured bone, through the fine-tuning of the controllable field parameters. Graphical abstract Mechanic stress on bone surface in a time-varying magnetic field.

Creep-induced residual stress strengthening in a Nicalon-fiber-reinforced BMAS-glass-ceramic-matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Widjaja, S.; Jakus, K.; Ritter, J.E.

The feasibility of inducing a compressive residual stress in the matrix of a Nicalon-fiber-reinforced BMAS-glass-ceramic-matrix composite through a creep-load transfer treatment was studied. Specimens were crept at 1100 C under constant tensile load to cause load transfer from the matrix to the fibers, then cooled under load. Upon removal of the load at room temperature, the matrix was put into compression by the elastic recovery of the fibers. This compressive residual stress in the matrix increased the room-temperature proportional limit stress of the composite. The increase in the proportional limit stress was found to be dependent upon the applied creepmore » stress, with an increase in creep stress resulting in an increase in the proportional limit stress. Acoustic emission results showed that the onset of significant matrix cracking correlated closely to the proportional limit stress. Changes in the state of residual stress in the matrix were supported by X-ray diffraction results. Fracture surfaces of all specimens exhibited fiber pullout behavior, indicating that the creep-load transfer process did not embrittle the fiber/matrix interface.« less

Microalgae fractionation using steam explosion, dynamic and tangential cross-flow membrane filtration.

PubMed

Lorente, E; Hapońska, M; Clavero, E; Torras, C; Salvadó, J

2017-08-01

In this study, the microalga Nannochloropsis gaditana was subjected to acid catalysed steam explosion treatment and the resulting exploded material was subsequently fractionated to separate the different fractions (lipids, sugars and solids). Conventional and vibrational membrane setups were used with several polymeric commercial membranes. Two different routes were followed: 1) filtration+lipid solvent extraction and 2) lipid solvent extraction+filtration. Route 1 revealed to be much better since the used membrane for filtration was able to permeate the sugar aqueous phase and retained the fraction containing lipids; after this, an extraction required a much lower amount of solvent and a better recovering yield. Filtration allowed complete lipid rejection. Dynamic filtration improved permeability compared to the tangential cross-flow filtration. Best membrane performance was achieved using a 5000Da membrane with the dynamic system, obtaining a permeability of 6L/h/m 2 /bar. Copyright © 2017 Elsevier Ltd. All rights reserved.

Comparison of mechanical compressive properties of commercial and autologous fibrin glues for tissue engineering applications.

PubMed

Cravens, Matthew G; Behn, Anthony W; Dragoo, Jason L

2017-11-01

Fibrin glues are widely used in orthopedic surgery as adhesives and hemostatic agents. We evaluated the compressive properties of selected fibrin glues in order to identify which are appropriate for tissue regeneration applications subject to compression. Uniaxial unconfined compression tests were performed on fibrin gels prepared from commercial and autologous products: (1) Evicel (Ethicon), (2) Tisseel (Baxter), (3) Angel (Arthrex), and (4) ProPlaz (Biorich). Cyclic loads were applied from 0 to 30% strain for 100cycles at 0.5Hz. Following cyclic testing, specimens were subjected to ramp displacement of 1% strain per second to 80% strain. Throughout cyclic loading, Evicel and Tisseel deformed (shortened) less than Angel at all but one time point, and deformed less than ProPlaz at cycles 10 and 20. The dynamic moduli, peak stress, and strain energy were significantly greater in Tisseel than all other groups. Evicel displayed significantly greater dynamic moduli, peak stress, and strain energy than Angel and ProPlaz. Following cyclic testing, Tisseel and Evicel were significantly less deformed than Angel. No specimens exhibited gross failure during ramp loading to 80% strain. Ramp loading trends mirrored those of cyclic loading. The tested commercial glues were significantly more resistant to compression than the autologous products. The compressive properties of Tisseel were approximately twice those of Evicel. All preparations displayed moduli multiple orders of magnitude less than that of native articular cartilage. We conclude that in knee surgeries requiring fibrin glue to undergo compression of daily activity, commercial products are preferable to autologous preparations from platelet-poor plasma, though both will deform significantly. Copyright © 2017 Elsevier Ltd. All rights reserved.

Compression-triggered instabilities of multi-layer systems: From thin elastic membranes to lipid bilayers on flexible substrates

NASA Astrophysics Data System (ADS)

Stone, Howard A.

2013-03-01

Instabilities are triggered when elastic materials are subjected to compression. We explore new features of two distinct systems of this type. First, we describe a two-layer polymeric system under biaxial compressive stress, which exhibits a repetitive wrinkle-to-fold transition that subsequently generates a hierarchical network of folds during reorganization of the stress field. The folds delineate individual domains, and each domain subdivides into smaller ones over multiple generations. By modifying the boundary conditions and geometry, we demonstrate control over the final network morphology. Some analogies to the venation pattern of leaves are indicated. Second, motivated by the confined configurations common to cells, which are wrapped in lipid bilayer membranes, we study a lipid bilayer, coupled to an elastic sheet, and demonstrate that, upon straining, the confined lipid membrane is able to passively regulate its area. In particular, by stretching the elastic support, the bilayer laterally expands without rupture by fusing adhered lipid vesicles; upon compression, lipid tubes grow out of the membrane plane, thus reducing its area. These transformations are reversible, as we show using cycles of expansion and compression, and closely reproduce membrane processes found in cells during area regulation. The two distinct systems illustrate the influence of the substrate on finite amplitude shape changes, for which we describe the time-dependent shape evolution as the stress relaxes. This talk describes joint research with Manouk Abkarian, Marino Arroyo, Pilnam Kim, Mohammad Rahimi and Margarita Staykova.

Effects of hot compression deformation temperature on the microstructure and properties of Al-Zr-La alloys

NASA Astrophysics Data System (ADS)

Yue, Xian-hua; Liu, Chun-fang; Liu, Hui-hua; Xiao, Su-fen; Tang, Zheng-hua; Tang, Tian

2018-02-01

The main goal of this study is to investigate the microstructure and electrical properties of Al-Zr-La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al3Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.