Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses

PubMed Central

Cho, Gye-Chun

2018-01-01

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10−5) and mid-strain (10−5 to 10−3) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass. PMID:29596371

David Adler Lectureship Award: n-point Correlation Functions in Heterogeneous Materials.

NASA Astrophysics Data System (ADS)

Torquato, Salvatore

2009-03-01

The determination of the bulk transport, electromagnetic, mechanical, and optical properties of heterogeneous materials has a long and venerable history, attracting the attention of some of the luminaries of science, including Maxwell, Lord Rayleigh, and Einstein. The bulk properties can be shown to depend rigorously upon infinite sets of various n-point correlation functions. Many different types of correlation functions arise, depending on the physics of the problem. A unified approach to characterize the microstructure and bulk properties of a large class of disordered materials is developed [S. Torquato, Random Heterogeneous Materials: Microstructure and Macroscopic Properties (Springer-Verlag, New York, 2002)]. This is accomplished via a canonical n-point function Hn from which one can derive exact analytical expressions for any microstructural function of interest. This microstructural information can then be used to estimate accurately the bulk properties of the material. Unlike homogeneous materials, seemingly different bulk properties (e.g., transport and mechanical properties) of a heterogeneous material can be linked to one another because of the common microstructure that they share. Such cross-property relations can be used to estimate one property given a measurement of another. A recently identified decorrelation principle, roughly speaking, refers to the phenomenon that unconstrained correlations that exist in low-dimensional disordered materials vanish as the space dimension becomes large. Among other results, this implies that in sufficiently high dimensions the densest spheres packings may be disordered (rather than ordered) [S. Torquato and F. H. Stillinger, ``New Conjectural Lower Bounds on the Optimal Density of Sphere Packings," Experimental Mathematics, 15, 307 (2006)].

Self-assembled phase-change nanowire for nonvolatile electronic memory

NASA Astrophysics Data System (ADS)

Jung, Yeonwoong

One of the most important subjects in nanosciences is to identify and exploit the relationship between size and structural/physical properties of materials and to explore novel material properties at a small-length scale. Scale-down of materials is not only advantageous in realizing miniaturized devices but nanometer-sized materials often exhibit intriguing physical/chemical properties that greatly differ from their bulk counterparts. This dissertation studies self-assembled phase-change nanowires for future nonvolatile electronic memories, mainly focusing on their size-dependent memory switching properties. Owing to the one-dimensional, unique geometry coupled with the small and tunable sizes, bottom-designed nanowires offer great opportunities in terms for both fundamental science and practical engineering perspectives, which would be difficult to realize in conventional top-down based approaches. We synthesized chalcogenide phase-change nanowires of different compositions and sizes, and studied their electronic memory switching owing to the structural change between crystalline and amorphous phases. In particular, we investigated nanowire size-dependent memory switching parameters, including writing current, power consumption, and data retention times, as well as studying composition-dependent electronic properties. The observed size and composition-dependent switching and recrystallization kinetics are explained based on the heat transport model and heterogeneous nucleation theories, which help to design phase-change materials with better properties. Moreover, we configured unconventional heterostructured phase-change nanowire memories and studied their multiple memory states in single nanowire devices. Finally, by combining in-situ/ex-situ electron microscopy techniques and electrical measurements, we characterized the structural states involved in electrically-driven phase-change in order to understand the atomistic mechanism that governs the electronic memory switching through phase-change.

Normal and radial impact of composites with embedded penny-shaped cracks

NASA Technical Reports Server (NTRS)

Sih, G. C.

1979-01-01

A method is developed for the dynamic stress analysis of a layered composite containing an embedded penny-shaped crack and subjected to normal and radial impact. The material properties of the layers are chosen such that the crack lies in a layer of matrix material while the surrounding material possesses the average elastic properties of a two-phase medium consisting of a large number of fibers embedded in the matrix. Quantitatively, the time-dependent stresses near the crack border can be described by the dynamic stress intensity factors. Their magnitude depends on time, on the material properties of the composite and on the relative size of the crack compared to the composite local geometry. Results obtained show that, for the same material properties and geometry of the composite, the dynamic stress intensity factors for an embedded (penny-shaped) crack reach their peak values within a shorter period of time and with a lower magnitude than the corresponding dynamic stress intensity factors for a through-crack.

Strain Rate Dependency of Bronze Metal Matrix Composite Mechanical Properties as a Function of Casting Technique

NASA Astrophysics Data System (ADS)

Brown, Lloyd; Joyce, Peter; Radice, Joshua; Gregorian, Dro; Gobble, Michael

2012-07-01

Strain rate dependency of mechanical properties of tungsten carbide (WC)-filled bronze castings fabricated by centrifugal and sedimentation-casting techniques are examined, in this study. Both casting techniques are an attempt to produce a functionally graded material with high wear resistance at a chosen surface. Potential applications of such materials include shaft bushings, electrical contact surfaces, and brake rotors. Knowledge of strain rate-dependent mechanical properties is recommended for predicting component response due to dynamic loading or impact events. A brief overview of the casting techniques for the materials considered in this study is followed by an explanation of the test matrix and testing techniques. Hardness testing, density measurement, and determination of the volume fraction of WC particles are performed throughout the castings using both image analysis and optical microscopy. The effects of particle filling on mechanical properties are first evaluated through a microhardness survey of the castings. The volume fraction of WC particles is validated using a thorough density survey and a rule-of-mixtures model. Split Hopkinson Pressure Bar (SHPB) testing of various volume fraction specimens is conducted to determine strain dependence of mechanical properties and to compare the process-property relationships between the two casting techniques. The baseline performances of C95400 bronze are provided for comparison. The results show that the addition of WC particles improves microhardness significantly for the centrifugally cast specimens, and, to a lesser extent, in the sedimentation-cast specimens, largely because the WC particles are more concentrated as a result of the centrifugal-casting process. Both metal matrix composites (MMCs) demonstrate strain rate dependency, with sedimentation casting having a greater, but variable, effects on material response. This difference is attributed to legacy effects from the casting process, namely, porosity and localized WC particle grouping.

Characterizing the temperature dependence of electronic packaging-material properties

NASA Astrophysics Data System (ADS)

Fu, Chia-Yu; Ume, Charles

1995-06-01

A computer-controlled, temperature-dependent material characterization system has been developed for thermal deformation analysis in electronic packaging applications, especially for printed wiring assembly warpage study. For fiberglass-reinforced epoxy (FR-4 type) material, the Young's moduli decrease to as low as 20-30% of the room-temperature values, while the shear moduli decrease to as low as 60-70% of the room-temperature values. The electrical resistance strain gage technique was used in this research. The test results produced overestimated values in property measurements, and this was shown in a case study. A noncontact strau]n measurement technique (laser extensometer) is now being used to measure these properties. Discrepancies of finite-element warpage predictions using different property values increase as the temperature increases from the stress-free temperature.

Establishment of gel materials with different mechanical properties by 3D gel printer SWIM-ER

NASA Astrophysics Data System (ADS)

Ota, Takafumi; Tase, Taishi; Okada, Koji; Saito, Azusa; Takamatsu, Kyuuichiro; Kawakami, Masaru; Furukawa, Hidemitsu

2016-04-01

A 3D printer is a device which can directly produce objects whose shape is the same as the original 3D digital data. Hydrogels have unique properties such as high water content, low frictional properties, biocompatibility, material permeability and high transparency, which are rare in hard and dry materials. These superior characteristics of gels promise useful medical applications. We have been working on the development of a 3D gel printer, SWIM-ER (Soft and Wet Industrial - Easy Realizer), which can make models of organs and artificial blood vessels with gel material. However, 3D printing has a problem: the mechanical properties of the printed object vary depending on printing conditions, and this matter was investigated with SWIM-ER. In the past, we found that mechanical properties of 3D gel objects depend on the deposition orientation in SWIM-ER. In this study, gels were printed with different laser scanning speeds. The mechanical properties of these gels were investigated by compression tests, water content measurements and SMILS (Scanning Microscopic Light Scattering).

High-Performance Composite Chocolate

ERIC Educational Resources Information Center

Dean, Julian; Thomson, Katrin; Hollands, Lisa; Bates, Joanna; Carter, Melvyn; Freeman, Colin; Kapranos, Plato; Goodall, Russell

2013-01-01

The performance of any engineering component depends on and is limited by the properties of the material from which it is fabricated. It is crucial for engineering students to understand these material properties, interpret them and select the right material for the right application. In this paper we present a new method to engage students with…

Dynamic modulus estimation and structural vibration analysis.

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

Gupta, A.

1998-11-18

Often the dynamic elastic modulus of a material with frequency dependent properties is difficult to estimate. These uncertainties are compounded in any structural vibration analysis using the material properties. Here, different experimental techniques are used to estimate the properties of a particular elastomeric material over a broad frequency range. Once the properties are determined, various structures incorporating the elastomer are analyzed by an interactive finite element method to determine natural frequencies and mode shapes. Then, the finite element results are correlated with results obtained by experimental modal analysis.

Indentation mapping revealed poroelastic, but not viscoelastic, properties spanning native zonal articular cartilage.

PubMed

Wahlquist, Joseph A; DelRio, Frank W; Randolph, Mark A; Aziz, Aaron H; Heveran, Chelsea M; Bryant, Stephanie J; Neu, Corey P; Ferguson, Virginia L

2017-12-01

Osteoarthrosis is a debilitating disease affecting millions, yet engineering materials for cartilage regeneration has proven difficult because of the complex microstructure of this tissue. Articular cartilage, like many biological tissues, produces a time-dependent response to mechanical load that is critical to cell's physiological function in part due to solid and fluid phase interactions and property variations across multiple length scales. Recreating the time-dependent strain and fluid flow may be critical for successfully engineering replacement tissues but thus far has largely been neglected. Here, microindentation is used to accomplish three objectives: (1) quantify a material's time-dependent mechanical response, (2) map material properties at a cellular relevant length scale throughout zonal articular cartilage and (3) elucidate the underlying viscoelastic, poroelastic, and nonlinear poroelastic causes of deformation in articular cartilage. Untreated and trypsin-treated cartilage was sectioned perpendicular to the articular surface and indentation was used to evaluate properties throughout zonal cartilage on the cut surface. The experimental results demonstrated that within all cartilage zones, the mechanical response was well represented by a model assuming nonlinear biphasic behavior and did not follow conventional viscoelastic or linear poroelastic models. Additionally, 10% (w/w) agarose was tested and, as anticipated, behaved as a linear poroelastic material. The approach outlined here provides a method, applicable to many tissues and biomaterials, which reveals and quantifies the underlying causes of time-dependent deformation, elucidates key aspects of material structure and function, and that can be used to provide important inputs for computational models and targets for tissue engineering. Elucidating the time-dependent mechanical behavior of cartilage, and other biological materials, is critical to adequately recapitulate native mechanosensory cues for cells. We used microindentation to map the time-dependent properties of untreated and trypsin treated cartilage throughout each cartilage zone. Unlike conventional approaches that combine viscoelastic and poroelastic behaviors into a single framework, we deconvoluted the mechanical response into separate contributions to time-dependent behavior. Poroelastic effects in all cartilage zones dominated the time-dependent behavior of articular cartilage, and a model that incorporates tension-compression nonlinearity best represented cartilage mechanical behavior. These results can be used to assess the success of regeneration and repair approaches, as design targets for tissue engineering, and for development of accurate computational models. Copyright © 2017 Acta Materialia Inc. All rights reserved.

Anisotropic characterization of magnetorheological materials

NASA Astrophysics Data System (ADS)

Dohmen, E.; Modler, N.; Gude, M.

2017-06-01

For the development of energy efficient lightweight parts novel function integrating materials are needed. Concerning this field of application magnetorheological (MR) fluids, MR elastomers and MR composites are promising materials allowing the adjustment of mechanical properties by an external magnetic field. A key issue for operating such structures in praxis is the magneto-mechanical description. Most rheological properties are gathered at laboratory conditions for high magnetic flux densities and a single field direction, which does not correspond to real praxis conditions. Although anisotropic formation of superstructures can be observed in MR suspensions (Fig. 1) or experimenters intentionally polymerize MR elastomers with anisotropic superstructures these MR materials are usually described in an external magnetic field as uniform, isotropic materials. This is due to missing possibilities for experimentally measuring field angle dependent properties and ways of distinguishing between material properties and frictional effects. Just a few scientific works experimentally investigated the influence of different field angles (Ambacher et al., 1992; Grants et al., 1990; Kuzhir et al., 2003) [1-3] or the influence of surface roughness on the shear behaviour of magnetic fluids (Tang and Conrad, 1996) [4]. The aim of this work is the introduction of a novel field angle cell allowing the determination of anisotropic mechanical properties for various MR materials depending on the applied magnetic field angle.

Temperature dependence of nonlinear optical properties in Li doped nano-carbon bowl material

NASA Astrophysics Data System (ADS)

Li, Wei-qi; Zhou, Xin; Chang, Ying; Quan Tian, Wei; Sun, Xiu-Dong

2013-04-01

The mechanism for change of nonlinear optical (NLO) properties with temperature is proposed for a nonlinear optical material, Li doped curved nano-carbon bowl. Four stable conformations of Li doped corannulene were located and their electronic properties were investigated in detail. The NLO response of those Li doped conformations varies with relative position of doping agent on the curved carbon surface of corannulene. Conversion among those Li doped conformations, which could be controlled by temperature, changes the NLO response of bulk material. Thus, conformation change of alkali metal doped carbon nano-material with temperature rationalizes the variation of NLO properties of those materials.

Strong size-dependent stress relaxation in electrospun polymer nanofibers

NASA Astrophysics Data System (ADS)

Wingert, Matthew C.; Jiang, Zhang; Chen, Renkun; Cai, Shengqiang

2017-01-01

Electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. In most applications, polymers usually exhibit viscoelastic behaviors such as stress relaxation and creep, which are also determined by the motion of polymer chains. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun Nylon-11 nanofibers as well as size-dependent viscosity of the confined amorphous regions. In conjunction with the dramatically increasing stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation.

Strong size-dependent stress relaxation in electrospun polymer nanofibers

DOE PAGES

Wingert, Matthew C.; Jiang, Zhang; Chen, Renkun; ...

2017-01-04

Here, electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. In most applications, polymers usually exhibit viscoelastic behaviors such as stress relaxation and creep, which are also determined by the motion of polymer chains. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun Nylon-11 nanofibers as well as size-dependent viscosity of the confined amorphous regions. In conjunction with themore » dramatically increasing stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation.« less

Evaluation of Student Outcomes in Materials Science and Technology

NASA Technical Reports Server (NTRS)

Piippo, Steven

1996-01-01

This paper specifies 14 benchmarks and exit standards for the introduction of Materials Science and Technology in a secondary school education. Included is the standard that students should be able to name an example of each category of technological materials including metals, glass/ceramics, polymers (plastics) and composites. Students should know that each type of solid material has specific properties that can be measured. Students will learn that all solid materials have either a long range crystalline structure or a short range amorphous structure (i.e., glassy). They should learn the choice of materials for a particular application depends on the properties of the material, and the properties of the material depends on its crystal structure and microstructure. The microstructure may be modified by the methods by which the material is processed; students should explain this by the example of sintering a ceramic body to reduce its porosity and increase its densification and strength. Students will receive exposure to the world of work, post secondary educational opportunities, and in general a learning that will lead to a technologically literate intelligent citizen.

Size-Dependent Materials Properties Toward a Universal Equation

PubMed Central

2010-01-01

Due to the lack of experimental values concerning some material properties at the nanoscale, it is interesting to evaluate this theoretically. Through a “top–down” approach, a universal equation is developed here which is particularly helpful when experiments are difficult to lead on a specific material property. It only requires the knowledge of the surface area to volume ratio of the nanomaterial, its size as well as the statistic (Fermi–Dirac or Bose–Einstein) followed by the particles involved in the considered material property. Comparison between different existing theoretical models and the proposed equation is done. PMID:20596422

Scale-dependent measurements of meteorite strength: Implications for asteroid fragmentation

NASA Astrophysics Data System (ADS)

Cotto-Figueroa, Desireé; Asphaug, Erik; Garvie, Laurence A. J.; Rai, Ashwin; Johnston, Joel; Borkowski, Luke; Datta, Siddhant; Chattopadhyay, Aditi; Morris, Melissa A.

2016-10-01

Measuring the strengths of asteroidal materials is important for developing mitigation strategies for potential Earth impactors and for understanding properties of in situ materials on asteroids during human and robotic exploration. Studies of asteroid disruption and fragmentation have typically used the strengths determined from terrestrial analog materials, although questions have been raised regarding the suitability of these materials. The few published measurements of meteorite strength are typically significantly greater than those estimated from the stratospheric breakup of meter-sized meteoroids. Given the paucity of relevant strength data, the scale-varying strength properties of meteoritic and asteroidal materials are poorly constrained. Based on our uniaxial failure studies of centimeter-sized cubes of a carbonaceous and ordinary chondrite, we develop the first Weibull failure distribution analysis of meteorites. This Weibull distribution projected to meter scales, overlaps the strengths determined from asteroidal airbursts and can be used to predict properties of to the 100 m scale. In addition, our analysis shows that meter-scale boulders on asteroids are significantly weaker than small pieces of meteorites, while large meteorites surviving on Earth are selected by attrition. Further, the common use of terrestrial analog materials to predict scale-dependent strength properties significantly overestimates the strength of meter-sized asteroidal materials and therefore is unlikely well suited for the modeling of asteroid disruption and fragmentation. Given the strength scale-dependence determined for carbonaceous and ordinary chondrite meteorites, our results suggest that boulders of similar composition on asteroids will have compressive strengths significantly less than typical terrestrial rocks.

Thermomechanical Formation–Structure–Property Relationships in Photopolymerized Copper-Catalyzed Azide–Alkyne (CuAAC) Networks

PubMed Central

Baranek, Austin; Song, Han Byul; McBride, Mathew; Finnegan, Patricia; Bowman, Christopher N.

2016-01-01

Bulk photopolymerization of a library of synthesized multifunctional azides and alkynes was carried out toward developing structure–property relationships for CuAAC-based polymer networks. Multifunctional azides and alkynes were formulated with a copper catalyst and a photoinitiator, cured, and analyzed for their mechanical properties. Material properties such as the glass transition temperatures (Tg) show a strong dependence on monomer structure with Tg values ranging from 41 to 90 °C for the series of CuAAC monomers synthesized in this study. Compared to the triazoles, analogous thioether-based polymer networks exhibit a 45–49 °C lower Tg whereas analogous monomers composed of ethers in place of carbamates exhibit a 40 °C lower Tg. Here, the formation of the triazole moiety during the polymerization represents a critical component in dictating the material properties of the ultimate polymer network where material properties such as the rubbery modulus, cross-link density, and Tg all exhibit strong dependence on polymerization conversion, monomer composition, and structure postgelation. PMID:27867223

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

NASA Technical Reports Server (NTRS)

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

1989-01-01

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

Electrically Addressable Optical Devices Using A System Of Composite Layered Flakes Suspended In A Fluid Host To Obtain Angularly Depende

DOEpatents

Kosc, Tanya Z.; Marshall, Kenneth L.; Jacobs, Stephen D.

2004-12-07

Composite or layered flakes having a plurality of layers of different materials, which may be dielectric materials, conductive materials, or liquid crystalline materials suspended in a fluid host and subjected to an electric field, provide optical effects dependent upon the angle or orientation of the flakes in the applied electric field. The optical effects depend upon the composition and thickness of the layers, producing reflectance, interference, additive and/or subtractive color effects. The composition of layered flakes may also be selected to enhance and/or alter the dielectric properties of flakes, whereby flake motion in an electric field is also enhanced and/or altered. The devices are useful as active electro-optical displays, polarizers, filters, light modulators, and wherever controllable polarizing, reflecting and transmissive optical properties are desired.

Thermal stresses in composite tubes using complementary virtual work

NASA Technical Reports Server (NTRS)

Hyer, M. W.; Cooper, D. E.

1988-01-01

This paper addresses the computation of thermally induced stresses in layered, fiber-reinforced composite tubes subjected to a circumferential gradient. The paper focuses on using the principle of complementary virtual work, in conjunction with a Ritz approximation to the stress field, to study the influence on the predicted stresses of including temperature-dependent material properties. Results indicate that the computed values of stress are sensitive to the temperature dependence of the matrix-direction compliance and matrix-direction thermal expansion in the plane of the lamina. There is less sensitivity to the temperature dependence of the other material properties.

Multiple electrical phase transitions in Al substituted barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Kar, Manoranjan

2017-12-01

Barium hexaferrite is known to be a very good ferromagnetic material. However, it shows very good dielectric properties, i.e., the dielectric constant is comparable to that of the ferroelectric material. However, its crystal symmetry does not allow it to be a ferroelectric material. Hence, the electrical properties have revived the considerable research interest on these materials, not only for academic interest, but also for technological applications. There are a few reports on temperature dependent dielectric behavior of these materials. However, the exact cause of dielectric as well as electrical conductivity is yet to be established. Hence, Al (very good conducting material) substituted barium hexaferrite (BaFe12-xAlxO19, x = 0.0-4.0) has been prepared by following the modified sol-gel method to understand the ac and DC electrical properties of these materials. The crystal structure and parameters have been studied by employing the XRD and FTIR techniques. There are two transition temperatures, which have been observed in the temperature dependent ac dielectric and DC resistivity measurement. The response of dielectric behaviors to temperature is similar to that of the ferroelectric material; however, the dielectric polarization is due to the polaron hopping, which is evident from the DC resistivity analysis. Hence, the present observations lead to understand the electrical properties of barium hexaferrite. The frequency dependent dielectric dispersion can be understood by the modified Debye model. More interestingly, the dielectric constant decreases and DC resistivity increases with the increase in the Al concentration, which has the correlation between bond length modifications in the crystal due to substitution.

1D Piezoelectric Material Based Nanogenerators: Methods, Materials and Property Optimization

PubMed Central

Li, Xing; Sun, Mei; Wei, Xianlong; Shan, Chongxin

2018-01-01

Due to the enhanced piezoelectric properties, excellent mechanical properties and tunable electric properties, one-dimensional (1D) piezoelectric materials have shown their promising applications in nanogenerators (NG), sensors, actuators, electronic devices etc. To present a clear view about 1D piezoelectric materials, this review mainly focuses on the characterization and optimization of the piezoelectric properties of 1D nanomaterials, including semiconducting nanowires (NWs) with wurtzite and/or zinc blend phases, perovskite NWs and 1D polymers. Specifically, the piezoelectric coefficients, performance of single NW-based NG and structure-dependent electromechanical properties of 1D nanostructured materials can be respectively investigated through piezoresponse force microscopy, atomic force microscopy and the in-situ scanning/transmission electron microcopy. Along with the introduction of the mechanism and piezoelectric properties of 1D semiconductor, perovskite materials and polymers, their performance improvement strategies are summarized from the view of microstructures, including size-effect, crystal structure, orientation and defects. Finally, the extension of 1D piezoelectric materials in field effect transistors and optoelectronic devices are simply introduced. PMID:29570639

High-performance composite chocolate

NASA Astrophysics Data System (ADS)

Dean, Julian; Thomson, Katrin; Hollands, Lisa; Bates, Joanna; Carter, Melvyn; Freeman, Colin; Kapranos, Plato; Goodall, Russell

2013-07-01

The performance of any engineering component depends on and is limited by the properties of the material from which it is fabricated. It is crucial for engineering students to understand these material properties, interpret them and select the right material for the right application. In this paper we present a new method to engage students with the material selection process. In a competition-based practical, first-year undergraduate students design, cost and cast composite chocolate samples to maximize a particular performance criterion. The same activity could be adapted for any level of education to introduce the subject of materials properties and their effects on the material chosen for specific applications.

Laser diode package with enhanced cooling

DOEpatents

Deri, Robert J; Kotovsky, Jack; Spadaccini, Christopher M

2012-06-26

This invention provides a new method for rapidly analyzing single bioparticles to assess their material condition and state of health. The method is enabled by use of a resonant cavity apparatus to measure an optical property related to the bioparticle size and refractive index. Measuring the refractive index is useful for determining material properties of the bioparticle. The material properties depend on the biomolecular composition of the bioparticle. The biomolecular composition is, in turn, dependent on the state of health of the bioparticle. Thus, measured optical properties can be used to differentiate normal (healthy) and abnormal (diseased) states of bioparticles derived from cells or tissues. The method is illustrated with data obtained from a resonator with a gain medium. The invention also provides new methods for making multiple measurements in a single device and detecting, analyzing, and manipulating bioparticles that are much smaller than the wavelength of light.

Nanolaser spectroscopy and micro-optical resonators for detecting, analyzing, and manipulating bioparticles

DOEpatents

Gourley, Paul L

2012-06-26

This invention provides a new method for rapidly analyzing single bioparticles to assess their material condition and state of health. The method is enabled by use of a resonant cavity apparatus to measure an optical property related to the bioparticle size and refractive index. Measuring the refractive index is useful for determining material properties of the bioparticle. The material properties depend on the biomolecular composition of the bioparticle. The biomolecular composition is, in turn, dependent on the state of health of the bioparticle. Thus, measured optical properties can be used to differentiate normal (healthy) and abnormal (diseased) states of bioparticles derived from cells or tissues. The method is illustrated with data obtained from a resonator with a gain medium. The invention also provides new methods for making multiple measurements in a single device and detecting, analyzing, and manipulating bioparticles that are much smaller than the wavelength of light.

A Statistics-Based Material Property Analysis to Support TPS Characterization

NASA Technical Reports Server (NTRS)

Copeland, Sean R.; Cozmuta, Ioana; Alonso, Juan J.

2012-01-01

Accurate characterization of entry capsule heat shield material properties is a critical component in modeling and simulating Thermal Protection System (TPS) response in a prescribed aerothermal environment. The thermal decomposition of the TPS material during the pyrolysis and charring processes is poorly characterized and typically results in large uncertainties in material properties as inputs for ablation models. These material property uncertainties contribute to large design margins on flight systems and cloud re- construction efforts for data collected during flight and ground testing, making revision to existing models for entry systems more challenging. The analysis presented in this work quantifies how material property uncertainties propagate through an ablation model and guides an experimental test regimen aimed at reducing these uncertainties and characterizing the dependencies between properties in the virgin and charred states for a Phenolic Impregnated Carbon Ablator (PICA) based TPS. A sensitivity analysis identifies how the high-fidelity model behaves in the expected flight environment, while a Monte Carlo based uncertainty propagation strategy is used to quantify the expected spread in the in-depth temperature response of the TPS. An examination of how perturbations to the input probability density functions affect output temperature statistics is accomplished using a Kriging response surface of the high-fidelity model. Simulations are based on capsule configuration and aerothermal environments expected during the Mars Science Laboratory (MSL) entry sequence. We identify and rank primary sources of uncertainty from material properties in a flight-relevant environment, show the dependence on spatial orientation and in-depth location on those uncertainty contributors, and quantify how sensitive the expected results are.

Evaluation of Temperature-Dependent Effective Material Properties and Performance of a Thermoelectric Module

NASA Astrophysics Data System (ADS)

Chien, Heng-Chieh; Chu, En-Ting; Hsieh, Huey-Lin; Huang, Jing-Yi; Wu, Sheng-Tsai; Dai, Ming-Ji; Liu, Chun-Kai; Yao, Da-Jeng

2013-07-01

We devised a novel method to evaluate the temperature-dependent effective properties of a thermoelectric module (TEM): Seebeck coefficient ( S m), internal electrical resistance ( R m), and thermal conductance ( K m). After calculation, the effective properties of the module are converted to the average material properties of a p- n thermoelectric pillar pair inside the module: Seebeck coefficient ( S TE), electrical resistivity ( ρ TE), and thermal conductivity ( k TE). For a commercial thermoelectric module (Altec 1091) chosen to verify the novel method, the measured S TE has a maximum value at bath temperature of 110°C; ρ TE shows a positive linear trend dependent on the bath temperature, and k TE increases slightly with increasing bath temperature. The results show the method to have satisfactory measurement performance in terms of practicability and reliability; the data for tests near 23°C agree with published values.

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

Wingert, Matthew C.; Jiang, Zhang; Chen, Renkun

Here, electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. In most applications, polymers usually exhibit viscoelastic behaviors such as stress relaxation and creep, which are also determined by the motion of polymer chains. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun Nylon-11 nanofibers as well as size-dependent viscosity of the confined amorphous regions. In conjunction with themore » dramatically increasing stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation.« less

A study of the effect of selected material properties on the ablation performance of artificial graphite

NASA Technical Reports Server (NTRS)

Maahs, H. G.

1972-01-01

Eighteen material properties were measured on 45 different, commercially available, artificial graphites. Ablation performance of these same graphites were also measured in a Mach 2 airstream at a stagnation pressure of 5.6 atm. Correlations were developed, where possible, between pairs of the material properties. Multiple regression equations were then formulated relating ablation performance to the various material properties, thus identifying those material properties having the strongest effect on ablation performance. These regression equations reveal that ablation performance in the present test environment depends primarily on maximum grain size, density, ash content, thermal conductivity, and mean pore radius. For optimization of ablation performance, grain size should be small, ash content low, density and thermal conductivity high, and mean pore radius large.

Zonal Articular Cartilage Possesses Complex Mechanical Behavior Spanning Multiple Length Scales: Dependence on Chemical Heterogeneity, Anisotropy, and Microstructure

NASA Astrophysics Data System (ADS)

Wahlquist, Joseph A.

This work focused on characterizing the mechanical behavior of biological material in physiologically relevant conditions and at sub millimeter length scales. Elucidating the time, length scale, and directionally dependent mechanical behavior of cartilage and other biological materials is critical to adequately recapitulate native mechanosensory cues for cells, create computational models that mimic native tissue behavior, and assess disease progression. This work focused on three broad aspects of characterizing the mechanical behavior of articular cartilage. First, we sought to reveal the causes of time-dependent deformation and variation of mechanical properties with distance from the articular surface. Second, we investigated size dependence of mechanical properties. Finally, we examined material anisotropy of both the calcified and uncalcified tissues of the osteochondral interface. This research provides insight into how articular cartilage serves to support physiologic loads and simultaneously sustain chondrocyte viability.

Impact of the interaction of material production and mechanical processing on the magnetic properties of non-oriented electrical steel

NASA Astrophysics Data System (ADS)

Leuning, Nora; Steentjes, Simon; Stöcker, Anett; Kawalla, Rudolf; Wei, Xuefei; Dierdorf, Jens; Hirt, Gerhard; Roggenbuck, Stefan; Korte-Kerzel, Sandra; Weiss, Hannes A.; Volk, Wolfram; Hameyer, Kay

2018-04-01

Thin laminations of non-grain oriented (NO) electrical steels form the magnetic core of rotating electrical machines. The magnetic properties of these laminations are therefore key elements for the efficiency of electric drives and need to be fully utilized. Ideally, high magnetization and low losses are realized over the entire polarization and frequency spectrum at reasonable production and processing costs. However, such an ideal material does not exist and thus, achievable magnetic properties need to be deduced from the respective application requirements. Parameters of the electrical steel such as lamination thickness, microstructure and texture affect the magnetic properties as well as their polarization and frequency dependence. These structural features represent possibilities to actively alter the magnetic properties, e.g., magnetization curve, magnetic loss or frequency dependence. This paper studies the influence of production and processing on the resulting magnetic properties of a 2.4 wt% Si electrical steel. Aim is to close the gap between production influence on the material properties and its resulting effect on the magnetization curves and losses at different frequencies with a strong focus on occurring interdependencies between production and mechanical processing. The material production is realized on an experimental processing route that comprises the steps of hot rolling, cold rolling, annealing and punching.

Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models

NASA Astrophysics Data System (ADS)

Armstrong, Hannah; Boese, Matthew; Carmichael, Cody; Dimich, Hannah; Seay, Dylan; Sheppard, Nathan; Beekman, Matt

2017-01-01

Maximum thermoelectric energy conversion efficiencies are calculated using the conventional "constant property" model and the recently proposed "cumulative/average property" model (Kim et al. in Proc Natl Acad Sci USA 112:8205, 2015) for 18 high-performance thermoelectric materials. We find that the constant property model generally predicts higher energy conversion efficiency for nearly all materials and temperature differences studied. Although significant deviations are observed in some cases, on average the constant property model predicts an efficiency that is a factor of 1.16 larger than that predicted by the average property model, with even lower deviations for temperature differences typical of energy harvesting applications. Based on our analysis, we conclude that the conventional dimensionless figure of merit ZT obtained from the constant property model, while not applicable for some materials with strongly temperature-dependent thermoelectric properties, remains a simple yet useful metric for initial evaluation and/or comparison of thermoelectric materials, provided the ZT at the average temperature of projected operation, not the peak ZT, is used.

Pressure-viscosity coefficient of biobased lubricants

USDA-ARS?s Scientific Manuscript database

Film thickness is an important tribological property that is dependent on the combined effect of lubricant properties, material property of friction surfaces, and the operating conditions of the tribological process. Pressure-viscosity coefficient (PVC) is one of the lubricant properties that influe...

The effects of elevated temperatures on the structural properties of fiber composite materials suitable for use in space shuttle and other space vehicles

NASA Technical Reports Server (NTRS)

Wright, M. A.

1972-01-01

The effects of high temperatures on the structural properties of fiber composite materials for use in spacecraft structures are investigated. Various mechanical properties of boron reinforced aluminum alloys were measured. It was observed that cycling these materials through temperatures that varied from room temperature to 425 C could seriously degrade the properties. The extent of the observed effects depended on alloy type and the maximum cyclic temperature used. Results are discussed in terms of upper and lower strength bonds calculated from the strengths of individual fibers.

Temperature dependent nonlinear metal matrix laminae behavior

NASA Technical Reports Server (NTRS)

Barrett, D. J.; Buesking, K. W.

1986-01-01

An analytical method is described for computing the nonlinear thermal and mechanical response of laminated plates. The material model focuses upon the behavior of metal matrix materials by relating the nonlinear composite response to plasticity effects in the matrix. The foundation of the analysis is the unidirectional material model which is used to compute the instantaneous properties of the lamina based upon the properties of the fibers and matrix. The unidirectional model assumes that the fibers properties are constant with temperature and assumes that the matrix can be modelled as a temperature dependent, bilinear, kinematically hardening material. An incremental approach is used to compute average stresses in the fibers and matrix caused by arbitrary mechanical and thermal loads. The layer model is incorporated in an incremental laminated plate theory to compute the nonlinear response of laminated metal matrix composites of general orientation and stacking sequence. The report includes comparisons of the method with other analytical approaches and compares theoretical calculations with measured experimental material behavior. A section is included which describes the limitations of the material model.

Smart Optical Composite Materials: Dispersions of Metal-Organic Framework@Superparamagnetic Microrods for Switchable Isotropic-Anisotropic Optical Properties.

PubMed

Mandel, Karl; Granath, Tim; Wehner, Tobias; Rey, Marcel; Stracke, Werner; Vogel, Nicolas; Sextl, Gerhard; Müller-Buschbaum, Klaus

2017-01-24

A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF) 3 ∞ [Eu 2 (BDC) 3 ]·2DMF·2H 2 O (BDC 2- = 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.

Molecular dynamics modelling of mechanical properties of polymers for adaptive aerospace structures

NASA Astrophysics Data System (ADS)

Papanikolaou, Michail; Drikakis, Dimitris; Asproulis, Nikolaos

2015-02-01

The features of adaptive structures depend on the properties of the supporting materials. For example, morphing wing structures require wing skin materials, such as rubbers that can withstand the forces imposed by the internal mechanism while maintaining the required aerodynamic properties of the aircraft. In this study, Molecular Dynamics and Minimization simulations are being used to establish well-equilibrated models of Ethylene-Propylene-Diene Monomer (EPDM) elastomer systems and investigate their mechanical properties.

VZLUSAT-1: verification of new materials and technologies for space

NASA Astrophysics Data System (ADS)

Daniel, Vladimir; Urban, Martin; Nentvich, Ondrej; Stehlikova, Veronika

2016-09-01

CubeSats are a good opportunity to test new technologies and materials on orbit. These innovations can be later used for improving of properties and life length of Cubesat or other satellites as well. VZLUSAT-1 is a small satellite from the CubeSat family, which will carry a wide scale of payloads with different purposes. The poster is focused on measuring of degradation and properties measurement of new radiation hardened composite material in orbit due to space environment. Material properties changes can be studied by many methods and in many disciplines. One payload measures mechanical changes in dependence on Young's modulus of elasticity which is got from non-destructive testing by mechanical vibrations. The natural frequencies we get using Fast Fourier Transform. The material is tested also by several thermometers which measure heat distribution through the composite, as well as reflectivity in dependence on different coatings. The satellite also will measure the material radiation shielding properties. There are PIN diodes which measure the relative shielding efficiency of composite and how it will change in time in space environment. Last one of material space testing is measurement of outgassing from tested composite material. It could be very dangerous for other parts of satellite, like detectors, when anything was outgassing, for example water steam. There are several humidity sensors which are sensitive to steam and other gases and measures temperatures as well.

Diffusive, Displacive Deformations and Local Phase Transformation Govern the Mechanics of Layered Crystals: The Case Study of Tobermorite.

PubMed

Tao, Lei; Shahsavari, Rouzbeh

2017-07-19

Understanding the deformation mechanisms underlying the mechanical behavior of materials is the key to fundamental and engineering advances in materials' performance. Herein, we focus on crystalline calcium-silicate-hydrates (C-S-H) as a model system with applications in cementitious materials, bone-tissue engineering, drug delivery and refractory materials, and use molecular dynamics simulation to investigate its loading geometry dependent mechanical properties. By comparing various conventional (e.g. shear, compression and tension) and nano-indentation loading geometries, our findings demonstrate that the former loading leads to size-independent mechanical properties while the latter results in size-dependent mechanical properties at the nanometer scales. We found three key mechanisms govern the deformation and thus mechanics of the layered C-S-H: diffusive-controlled and displacive-controlled deformation mechanisms, and strain gradient with local phase transformations. Together, these elaborately classified mechanisms provide deep fundamental understanding and new insights on the relationship between the macro-scale mechanical properties and underlying molecular deformations, providing new opportunities to control and tune the mechanics of layered crystals and other complex materials such as glassy C-S-H, natural composite structures, and manmade laminated structures.

Method and apparatus for measuring properties of particle beams using thermo-resistive material properties

DOEpatents

Degtiarenko, Pavel V.; Dotson, Danny Wayne

2007-10-09

A beam position detector for measuring the properties of a charged particle beam, including the beam's position, size, shape, and intensity. One or more absorbers are constructed of thermo-resistive material and positioned to intercept and absorb a portion of the incoming beam power, thereby causing local heating of each absorber. The local temperature increase distribution across the absorber, or the distribution between different absorbers, will depend on the intensity, size, and position of the beam. The absorbers are constructed of a material having a strong dependence of electrical resistivity on temperature. The beam position detector has no moving parts in the vicinity of the beam and is especially suited to beam areas having high ionizing radiation dose rates or poor beam quality, including beams dispersed in the transverse direction and in their time radio frequency structure.

PSIDD3: Post-Scan Ultrasonic Data Display System for the Windows-Based PC Including Fuzzy Logic Analysis

NASA Technical Reports Server (NTRS)

Lovelace, Jeffrey J.; Cios, Krzysztof J.; Roth, Don J.; Cao, Wei

2000-01-01

Post-Scan Interactive Data Display (PSIDD) III is a user-oriented Windows-based system that facilitates the display and comparison of ultrasonic contact data. The system is optimized to compare ultrasonic measurements made at different locations within a material or at different stages of material degradation. PSIDD III provides complete analysis of the primary wave forms in the time and frequency domains along with the calculation of several frequency dependent properties including Phase Velocity and Attenuation Coefficient and several frequency independent properties, like the Cross Correlation Velocity. The system allows image generation on all of the frequency dependent properties at any available frequency (limited by the bandwidth used in the scans) and on any of the frequency independent properties. From ultrasonic contact scans, areas of interest on an image can be studied with regard to underlying raw waveforms and derived ultrasonic properties by simply selecting the point on the image. The system offers various modes of in-depth comparison between scan points. Up to five scan points can be selected for comparative analysis at once. The system was developed with Borland Delphi software (Visual Pascal) and is based on a SQL database. It is ideal for classification of material properties, or location of microstructure variations in materials.

Technological parameters influence on the non-autoclaved foam concrete characteristics

NASA Astrophysics Data System (ADS)

Bartenjeva, Ekaterina; Mashkin, Nikolay

2017-01-01

Foam concretes are used as effective heat-insulating materials. The porous structure of foam concrete provides good insulating and strength properties that make them possible to be used as heat-insulating structural materials. Optimal structure of non-autoclaved foam concrete depends on both technological factors and properties of technical foam. In this connection, the possibility to manufacture heat-insulation structural foam concrete on a high-speed cavity plant with the usage of protein and synthetic foamers was estimated. This experiment was carried out using mathematical planning method, and in this case mathematical models were developed that demonstrated the dependence of operating performance of foam concrete on foaming and rotation speed of laboratory plant. The following material properties were selected for the investigation: average density, compressive strength, bending strength and thermal conductivity. The influence of laboratory equipment technological parameters on technical foam strength and foam stability coefficient in the cement paste was investigated, physical and mechanical properties of non-autoclaved foam concrete were defined based on investigated foam. As a result of investigation, foam concrete samples were developed with performance parameters ensuring their use in production. The mathematical data gathered demonstrated the dependence of foam concrete performance on the technological regime.

Microstructure and mechanical properties of horns derived from three domestic bovines.

PubMed

Zhang, Quan-bin; Li, Chun; Pan, Yan-ting; Shan, Guang-hua; Cao, Ping; He, Jia; Lin, Zhong-shi; Ao, Ning-jian; Huang, Yao-xiong

2013-12-01

The microstructure and mechanical properties of horns derived from three domestic bovines (buffalo, cattle and sheep) were examined. The effects of water content, sampling position and orientation of three bovid horns on mechanical properties were systematically investigated by uniaxial tension and micron indentation tests. Meanwhile, the material composition and metal element contents were determined by Raman spectroscopy and elemental analysis respectively, and the microstructures of the horns were measured by scanning electron microscopy (SEM). Results show that the mechanical properties of horns have negative correlation with water contents and depend on sampling position and orientation. The spatial variations of the mechanical properties in horns are attributed to the different keratinization degrees in the proximal, middle and distal parts. And the mechanical properties of horns in the longitudinal direction are better than those in transverse. Among the three kinds of horns, the mechanical properties of buffalo horn are the best, followed by cattle horn, and those in sheep horn are the worst. This is due to the differences in material composition, metal element, and the microstructures of the horns. But the mechanical properties of buffalo horns are not dependent on the source of the buffalo. Therefore, regular engineered buffalo keratinous materials with standard mechanical properties can be obtained from different buffalo horns by using proper preparation methods. © 2013.

Development of a Nondestructive Non-Contact Acousto-Thermal Evaluation Technique for Damage Detection in Materials (Preprint)

DTIC Science & Technology

2011-11-01

horn and the sample to obtain a repeatable excitation for detection of the damage of interest. Varieties of materials, including card stock, leather ...per cycle is, (2). where Tan , is the internal friction in the material, E is the Young’s modulus and σmax is the maximum amplitude of the...of acoustic energy to thermal energy depends on both the elastic properties (E and tan ) and the thermal properties (k, Cp) of the material. It

Measurement and evaluation of the radiative properties of a thin solid fuel

NASA Technical Reports Server (NTRS)

Pettegrew, Richard; Street, Kenneth; Pitch, Nancy; Tien, James; Morrison, Phillip

2003-01-01

Accurate modeling of combustion systems requires knowledge of the radiative properties of the system. Gas phase properties are well known, but detailed knowledge of surface properties is limited. Recent work has provided spectrally resolved data for some solid fuels, but only for the unburned material at room temperature, and for limited sets of previously burned and quenched samples. Due to lack of knowledge of the spectrally resolved properties at elevated temperatures, as well as processing limitations in the modeling effort, graybody values are typically used for the fuels surface radiative properties. However, the spectrally resolved properties for the fuels at room temperature can be used to give a first-order correction for temperature effects on the graybody values. Figure 1 shows a sample of the spectrally resolved emittance/absorptance for a thin solid fuel of the type commonly used in combustion studies, from approximately 2 to 20 microns. This plot clearly shows a strong spectral dependence across the entire range. By definition, the emittance is the ratio of the emitted energy to that of a blackbody at the same temperature. Therefore, to determine a graybody emittance for this material, the spectrally resolved data must be applied to a blackbody curve. The total area under the resulting curve is ratioed to the total area under the blackbody curve to yield the answer. Due to the asymmetry of the spectrally resolved emittance and the changing shape of the blackbody curve as the temperature increases, the relative importance of the emittance value at any given wavelength will change as a function of temperature. Therefore, the graybody emittance value for a given material will change as a function of temperature even if the spectral dependence of the radiative properties remains unchanged. This is demonstrated in Figures 2 and 3, which are plots of the spectrally resolved emittance for KimWipes (shown in Figure 1) multiplied by the blackbody curves for 300 K (Figure 2) and 800 K (Figure 3). Each figure also shows the blackbody curve for that temperature. Ratioing the areas under the curve for each of these figures give a graybody emittance of 0.64 at 300 K, and 0.46 at 800 K. It is recognized that materials undergoing pyrolysis will change in composition as they heat up, and that the radiative properties of the materials may have inherent temperature dependence. Both of these effects will contribute to changes in the radiative characteristics of a given material, and are not accounted for here. However, this paper demonstrates the temperature dependence of graybody radiative properties, and provides a method for a first-order correction (for temperature) to the graybody values if the spectrally resolved properties are known.

Magnesium-Aluminum-Zirconium Oxide Amorphous Ternary Composite: A Dense and Stable Optical Coating

NASA Technical Reports Server (NTRS)

Sahoo, N. K.; Shapiro, A. P.

1998-01-01

In the present work, the process parameter dependent optical and structural properties of MgO-Al(2)O(3)-ZrO(2) ternary mixed-composite material have been investigated. Optical properties were derived from spectrophotometric measurements. The surface morphology, grain size distributions, crystallographic phases and process dependent material composition of films have been investigated through the use of Atomic Force Microscopy (AFM), X-ray diffraction analysis and Energy Dispersive X- ray (EDX) analysis. EDX analysis made evident the correlation between the optical constants and the process dependent compositions in the films. It is possible to achieve environmentally stable amorphous films with high packing density under certain optimized process conditions.

MgO-Al2O3-ZrO2 Amorphous Ternary Composite: A Dense and Stable Optical Coating

NASA Technical Reports Server (NTRS)

Shaoo, Naba K.; Shapiro, Alan P.

1998-01-01

The process-parameter-dependent optical and structural properties of MgO-Al2O3-ZrO2 ternary mixed-composite material were investigated. Optical properties were derived from spectrophotometric measurements. The surface morphology, grain size distributions, crystallographic phases, and process- dependent material composition of films were investigated through the use of atomic force microscopy, x-ray diffraction analysis, and energy-dispersive x-ray analysis. Energy-dispersive x-ray analysis made evident the correlation between the optical constants and the process-dependent compositions in the films. It is possible to achieve environmentally stable amorphous films with high packing density under certain optimized process conditions.

Torsion Tests of Tubes

NASA Technical Reports Server (NTRS)

Stang, Ambrose H; Ramberg, Walter; Back, Goldie

1937-01-01

This report presents the results of tests of 63 chromium-molybdenum steel tubes and 102 17st aluminum-alloy tubes of various sizes and lengths made to study the dependence of the torsional strength on both the dimensions of the tube and the physical properties of the tube material. Three types of failure are found to be important for sizes of tubes frequently used in aircraft construction: (1) failure by plastic shear, in which the tube material reached its yield strength before the critical torque was reached; (2) failure by elastic two-lobe buckling, which depended only on the elastic properties of the tube material and the dimensions of the tube; and (3) failure by a combination of (1) and (2) that is, by buckling taking place after some yielding of the tube material.

Linear analysis using secants for materials with temperature dependent nonlinear elastic modulus and thermal expansion properties

NASA Astrophysics Data System (ADS)

Pepi, John W.

2017-08-01

Thermally induced stress is readily calculated for linear elastic material properties using Hooke's law in which, for situations where expansion is constrained, stress is proportional to the product of the material elastic modulus and its thermal strain. When material behavior is nonlinear, one needs to make use of nonlinear theory. However, we can avoid that complexity in some situations. For situations in which both elastic modulus and coefficient of thermal expansion vary with temperature, solutions can be formulated using secant properties. A theoretical approach is thus presented to calculate stresses for nonlinear, neo-Hookean, materials. This is important for high acuity optical systems undergoing large temperature extremes.

Recent Prospects in the Inline Monitoring of Nanocomposites and Nanocoatings by Optical Technologies.

PubMed

Bugnicourt, Elodie; Kehoe, Timothy; Latorre, Marcos; Serrano, Cristina; Philippe, Séverine; Schmid, Markus

2016-08-19

Nanostructured materials have emerged as a key research field in order to confer materials with unique or enhanced properties. The performance of nanocomposites depends on a number of parameters, but the suitable dispersion of nanoparticles remains the key in order to obtain the full nanocomposites' potential in terms of, e.g., flame retardance, mechanical, barrier, thermal properties, etc. Likewise, the performance of nanocoatings to obtain, for example, tailored surface affinity with selected liquids (e.g., for self-cleaning ability or anti-fog properties), protective effects against flame propagation, ultra violet (UV) radiation or gas permeation, is highly dependent on the nanocoating's thickness and homogeneity. In terms of recent advances in the monitoring of nanocomposites and nanocoatings, this review discusses commonly-used offline characterization approaches, as well as promising inline systems. All in all, having good control over both the dispersion and thickness of these materials would help with reaching optimal and consistent properties to allow nanocomposites to extend their use.

Recent Prospects in the Inline Monitoring of Nanocomposites and Nanocoatings by Optical Technologies

PubMed Central

Bugnicourt, Elodie; Kehoe, Timothy; Latorre, Marcos; Serrano, Cristina; Philippe, Séverine; Schmid, Markus

2016-01-01

Nanostructured materials have emerged as a key research field in order to confer materials with unique or enhanced properties. The performance of nanocomposites depends on a number of parameters, but the suitable dispersion of nanoparticles remains the key in order to obtain the full nanocomposites’ potential in terms of, e.g., flame retardance, mechanical, barrier, thermal properties, etc. Likewise, the performance of nanocoatings to obtain, for example, tailored surface affinity with selected liquids (e.g., for self-cleaning ability or anti-fog properties), protective effects against flame propagation, ultra violet (UV) radiation or gas permeation, is highly dependent on the nanocoating’s thickness and homogeneity. In terms of recent advances in the monitoring of nanocomposites and nanocoatings, this review discusses commonly-used offline characterization approaches, as well as promising inline systems. All in all, having good control over both the dispersion and thickness of these materials would help with reaching optimal and consistent properties to allow nanocomposites to extend their use. PMID:28335278

Digital Materials - Evaluation of the Possibilities of using Selected Hyperelastic Models to Describe Constitutive Relations

NASA Astrophysics Data System (ADS)

Mańkowski, J.; Lipnicki, J.

2017-08-01

The authors tried to identify the parameters of numerical models of digital materials, which are a kind of composite resulting from the manufacture of the product in 3D printers. With the arrangement of several heads of the printer, the new material can result from mixing of materials with radically different properties, during the process of producing single layer of the product. The new material has properties dependent on the base materials properties and their proportions. Digital materials tensile characteristics are often non-linear and qualify to be described by hyperelastic materials models. The identification was conducted based on the results of tensile tests models, its various degrees coefficients of the polynomials to various degrees coefficients of the polynomials. The Drucker's stability criterion was also examined. Fourteen different materials were analyzed.

Exploration of mechanisms underlying the strain-rate-dependent mechanical property of single chondrocytes

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

Nguyen, Trung Dung; Gu, YuanTong, E-mail: yuantong.gu@qut.edu.au

2014-05-05

Based on the characterization by Atomic Force Microscopy, we report that the mechanical property of single chondrocytes has dependency on the strain-rates. By comparing the mechanical deformation responses and the Young's moduli of living and fixed chondrocytes at four different strain-rates, we explore the deformation mechanisms underlying this dependency property. We found that the strain-rate-dependent mechanical property of living cells is governed by both of the cellular cytoskeleton and the intracellular fluid when the fixed chondrocytes are mainly governed by their intracellular fluid, which is called the consolidation-dependent deformation behavior. Finally, we report that the porohyperelastic constitutive material model whichmore » can capture the consolidation-dependent behavior of both living and fixed chondrocytes is a potential candidature to study living cell biomechanics.« less

The Influence of Technological Regimes of Synthesizing a Solar Furnace on the Phase Composition of TiO2-CuO Cermets and the Optical Properties of Coatings on Their Basis

NASA Astrophysics Data System (ADS)

Suleimanov, S. Kh.; Dyskin, V. G.; Dzhanklich, M. U.; Dudko, O. A.; Kulagina, N. A.

2018-01-01

We present the results of studying the effect of technological synthesis regimes of a solar furnace using the method of a partial metal reduction of one of the oxides on the phase formation of cermet composite materials of the TiO2-CuO system. It has been established that the phase composition of the synthesized cermet composite materials depends on the carbon concentration, melting temperature and cooling rate. The dependence of the spectral-optical properties of selectively absorbing coatings on the production technology and properties of synthesized composite materials has been presented. It has been found that the coatings fabricated by melting in air with overheating at a melt cooling rate of about 105-106°C/s have the highest values of the integral absorption coefficient, α s = 91.0-94.5%.

Process-Parameter-Dependent Optical and Structural Properties of ZrO2MgO Mixed-Composite Films Evaporated from the solid Solution

NASA Technical Reports Server (NTRS)

Sahoo, N. K.; Shapiro, A. P.

1998-01-01

The process-parameter-dependent optical and structural properties of ZrO2MgO mixed-composite material have been investigated. Optical properties were derived from spectrophotometric measurements. By use of atomic force microscopy, x-ray diffraction analysis, and energy-dispersive x-ray (EDX) analysis, the surface morphology, grain size distributions, crystallographic phases, and process-dependent material composition of films have been investigated. EDX analysis made evident the correlation between the oxygen enrichment in the films prepared at a high level of oxygen pressure and the very low refractive index. Since oxygen pressure can be dynamically varied during a deposition process, coatings constructed of suitable mixed-composite thin films can benefit from continuous modulation of the index of refraction. A step modulation approach is used to develop various multilayer-equivalent thin-film devices.

Measured iron-gallium alloy tensile properties under magnetic fields

NASA Astrophysics Data System (ADS)

Yoo, Jin-Hyeong; Flatau, Alison B.

2004-07-01

Tension testing is used to identify Galfenol material properties under low level DC magnetic bias fields. Dog bone shaped specimens of single crystal Fe100-xGax, where 17<=x<=33, underwent tensile testing along two crystalographic axis orientations, [110] and [100]. The material properties being investigated and calculated from measured quantities are: Young's modulus and Poisson's ratio. Data are presented that demonstrate the dependence of these material properties on applied magnetic field levels and provide a preliminary assessment of the trends in material properties for performance under varied operating conditions. The elastic properties of Fe-Ga alloys were observed to be increasingly anisotropic with rising Ga content for the stoichiometries examined. The largest elastic anisotropies were manifested in [110] Poisson's ratios of as low as -0.63 in one specimen. This negative Poisson's ratio creates a significant in-plane auxetic behavior that could be exploited in applications that capitalize on unique area effects produced under uniaxial loading.

An inverse method for determining the spatially resolved properties of viscoelastic–viscoplastic three-dimensional printed materials

PubMed Central

Chen, X.; Ashcroft, I. A.; Wildman, R. D.; Tuck, C. J.

2015-01-01

A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic–viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic–viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance. PMID:26730216

An inverse method for determining the spatially resolved properties of viscoelastic-viscoplastic three-dimensional printed materials.

PubMed

Chen, X; Ashcroft, I A; Wildman, R D; Tuck, C J

2015-11-08

A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic-viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic-viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance.

Emission properties of Ce3+ centers in barium borate glasses prepared from different precursor materials

NASA Astrophysics Data System (ADS)

Torimoto, Aya; Masai, Hirokazu; Okada, Go; Kawaguchi, Noriaki; Yanagida, Takayuki; Ohkubo, Takahiro

2017-10-01

The photoluminescence (PL) and X-ray induced luminescence properties of Ce-doped barium borate glasses prepared from different precursor materials have been investigated. Oxidation of Ce3+ takes place during the melting process performed using a pre-vitrified non-doped glass. Residual groups originated from the precursor materials, such as fluorine atoms and OH groups, are found to affect the optical and emission properties of the glasses. Moreover, both the PL and the X-ray induced luminescence properties of the glasses depend on the precursor materials used for their synthesis. Based on a thorough analysis of the emission properties, we conclude that the best synthesis conditions involve melting a batch containing Ce(CH3COO)3·H2O, BaCO3, and B2O3 in Ar atmosphere.

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

NASA Astrophysics Data System (ADS)

Roellig, Mike; Meier, Karsten; Metasch, Rene

2010-11-01

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

The Use of Empirical Methods for Testing Granular Materials in Analogue Modelling

PubMed Central

Montanari, Domenico; Agostini, Andrea; Bonini, Marco; Corti, Giacomo; Del Ventisette, Chiara

2017-01-01

The behaviour of a granular material is mainly dependent on its frictional properties, angle of internal friction, and cohesion, which, together with material density, are the key factors to be considered during the scaling procedure of analogue models. The frictional properties of a granular material are usually investigated by means of technical instruments such as a Hubbert-type apparatus and ring shear testers, which allow for investigating the response of the tested material to a wide range of applied stresses. Here we explore the possibility to determine material properties by means of different empirical methods applied to mixtures of quartz and K-feldspar sand. Empirical methods exhibit the great advantage of measuring the properties of a certain analogue material under the experimental conditions, which are strongly sensitive to the handling techniques. Finally, the results obtained from the empirical methods have been compared with ring shear tests carried out on the same materials, which show a satisfactory agreement with those determined empirically. PMID:28772993

Full space device optimization for solar cells.

PubMed

Baloch, Ahmer A B; Aly, Shahzada P; Hossain, Mohammad I; El-Mellouhi, Fedwa; Tabet, Nouar; Alharbi, Fahhad H

2017-09-20

Advances in computational materials have paved a way to design efficient solar cells by identifying the optimal properties of the device layers. Conventionally, the device optimization has been governed by single or double descriptors for an individual layer; mostly the absorbing layer. However, the performance of the device depends collectively on all the properties of the material and the geometry of each layer in the cell. To address this issue of multi-property optimization and to avoid the paradigm of reoccurring materials in the solar cell field, a full space material-independent optimization approach is developed and presented in this paper. The method is employed to obtain an optimized material data set for maximum efficiency and for targeted functionality for each layer. To ensure the robustness of the method, two cases are studied; namely perovskite solar cells device optimization and cadmium-free CIGS solar cell. The implementation determines the desirable optoelectronic properties of transport mediums and contacts that can maximize the efficiency for both cases. The resulted data sets of material properties can be matched with those in materials databases or by further microscopic material design. Moreover, the presented multi-property optimization framework can be extended to design any solid-state device.

Properties of 5052 Aluminum For Use as Honeycomb Core in Manned Spaceflight

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.

2018-01-01

This work explains that the properties of Al 5052 material used commonly for honeycomb cores in sandwich panels are highly dependent on the tempering condition. It has not been common to specify the temper when ordering HC material nor is it common for the supplier to state what the temper is. For aerospace uses, a temper of H38 or H39 is probably recommended. This temper should be stated in the bill of material and should be verified upon receipt of the core. To this end some properties provided herein can aid as benchmark values.

Plaster-based magnetite composite materials in construction

NASA Astrophysics Data System (ADS)

Klimenko, V. G.; Kashin, G. A.; Prikaznova, T. A.

2018-03-01

Calculation and experimental data demonstrate the possibility of using iron-ore concentrate of Lebedinsky Mining and Processing Plant (Lebedinsky GOK) in the production of plaster concrete. Their physical-mechanical, thermal and radiation protective properties were studied. Structurization mechanisms in plaster magnetite systems depending on the type of plaster binder, textures and the structure of plaster crystals providing for the design of composite materials with predetermined properties are suggested. Composite materials to ensure protection against X-ray radiation are obtained.

Microwave meter for rapid, nondestructive determination of in-shell peanut kernel moisture content from dielectric measurements on cleaned and uncleaned pod samples

USDA-ARS?s Scientific Manuscript database

Microwave Sensing provides a means for nondestructively determining the amount of moisture in materials by sensing the dielectric properties of the material. In this study, dielectric properties of Vidalia onions were analyzed for moisture dependence at 13.36 GHz and 23°C for moisture content betwee...

The Hardness and Strength Properties of WC-Co Composites

PubMed Central

Armstrong, Ronald W.

2011-01-01

The industrially-important WC-Co composite materials provide a useful, albeit complicated materials system for understanding the combined influences on hardness and strength properties of the constituent WC particle strengths, the particle sizes, their contiguities, and of Co binder hardness and mean free paths, and in total, the volume fraction of constituents. A connection is made here between the composite material properties, especially including the material fracture toughness, and the several materials-type considerations of: (1) related hardness stress-strain behaviors; (2) dislocation (viscoplastic) thermal activation characterizations; (3) Hall-Petch type reciprocal square root of particle or grain size dependencies; and (4) indentation and conventional fracture mechanics results. Related behaviors of MgO and Al2O3 crystal and polycrystal materials are also described for the purpose of making comparisons. PMID:28824143

Dielectric properties of biomass and biochar mixtures for bioenergy applications

USDA-ARS?s Scientific Manuscript database

Biomass is an abundant and renewable energy resource, which may be converted into energy-dense products through thermochemical processes such as pyrolysis and gasification. Since microwave heating depends on the dielectric properties of the biomass material, these properties were measured at freque...

Process depending morphology and resulting physical properties of TPU

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

Frick, Achim, E-mail: achim.frick@hs-aalen.de; Spadaro, Marcel, E-mail: marcel.spadaro@hs-aalen.de

2015-12-17

Thermoplastic polyurethane (TPU) is a rubber like material with outstanding properties, e.g. for seal applications. TPU basically provides high strength, low frictional behavior and excellent wear resistance. Though, due to segmented structure of TPU, which is composed of hard segments (HSs) and soft segments (SSs), physical properties depend strongly on the morphological arrangement of the phase separated HSs at a certain ratio of HSs to SSs. It is obvious that the TPU deforms differently depending on its bulk morphology. Basically, the morphology can either consist of HSs segregated into small domains, which are well dispersed in the SS matrix ormore » of few strongly phase separated large size HS domains embedded in the SS matrix. The morphology development is hardly ruled by the melt processing conditions of the TPU. Depending on the morphology, TPU provides quite different physical properties with respect to strength, deformation behavior, thermal stability, creep resistance and tribological performance. The paper deals with the influence of important melt processing parameters, such as temperature, pressure and shear conditions, on the resulting physical properties tested by tensile and relaxation experiments. Furthermore the morphology is studied employing differential scanning calorimeter (DSC), transmission light microscopy (TLM), scanning electron beam microscopy (SEM) and transmission electron beam microscopy (TEM) investigations. Correlations between processing conditions and resulting TPU material properties are elaborated. Flow and shear simulations contribute to the understanding of thermal and flow induced morphology development.« less

Optical method for determining the mechanical properties of a material

DOEpatents

Maris, H.J.; Stoner, R.J.

1998-12-01

Disclosed is a method for characterizing a sample, comprising the steps of: (a) acquiring data from the sample using at least one probe beam wavelength to measure, for times less than a few nanoseconds, a change in the reflectivity of the sample induced by a pump beam; (b) analyzing the data to determine at least one material property by comparing a background signal component of the data with data obtained for a similar delay time range from one or more samples prepared under conditions known to give rise to certain physical and chemical material properties; and (c) analyzing a component of the measured time dependent reflectivity caused by ultrasonic waves generated by the pump beam using the at least one determined material property. The first step of analyzing may include a step of interpolating between reference samples to obtain an intermediate set of material properties. The material properties may include sound velocity, density, and optical constants. In one embodiment, only a correlation is made with the background signal, and at least one of the structural phase, grain orientation, and stoichiometry is determined. 14 figs.

Optical method for determining the mechanical properties of a material

DOEpatents

Maris, Humphrey J.; Stoner, Robert J.

1998-01-01

Disclosed is a method for characterizing a sample, comprising the steps of: (a) acquiring data from the sample using at least one probe beam wavelength to measure, for times less than a few nanoseconds, a change in the reflectivity of the sample induced by a pump beam; (b) analyzing the data to determine at least one material property by comparing a background signal component of the data with data obtained for a similar delay time range from one or more samples prepared under conditions known to give rise to certain physical and chemical material properties; and (c) analyzing a component of the measured time dependent reflectivity caused by ultrasonic waves generated by the pump beam using the at least one determined material property. The first step of analyzing may include a step of interpolating between reference samples to obtain an intermediate set of material properties. The material properties may include sound velocity, density, and optical constants. In one embodiment, only a correlation is made with the background signal, and at least one of the structural phase, grain orientation, and stoichiometry is determined.

Development of Nondestructive Non-Contact Acousto-Thermal Evaluation Technique for Damage Detection in Materials (Postprint)

DTIC Science & Technology

2012-09-01

and the sample to obtain a repeatable excitation for detec- tion of the damage of interest. Varieties of materials, includ- ing card stock, leather ...2) where Tan δ is the internal friction in the material, E is the Young’s modulus, and σmax is the maximum amplitude of the acoustic wave. Assuming...interior of a linear elastic material can be seen to depend on both the elastic properties (E and Tan δ) and the thermal properties (k, Cp) of the

Multifunctional, angle dependent antireflection, and hydrophilic properties of SiO2 inspired by nano-scale structures of cicada wings

NASA Astrophysics Data System (ADS)

Zada, Imran; Zhang, Wang; Sun, Peng; Imtiaz, Muhammad; Abbas, Waseem; Zhang, Di

2017-10-01

Inspired by the multifunctional properties of cicada wings, we have precisely replicated biomorphic SiO2 with antireflective structures (ARSs) using a simple, inexpensive, and highly effective sol-gel ultrasonic method. The biomorphic replica of SiO2 was directly achieved from a cicada template at high calcination. The biomorphic SiO2 not only inherited the ARS effectively but also exhibited the excellent angle dependent antireflective properties over a wide range of incident angles (10°-60°). The change in reflectance spectra (visible wavelength) of biomorphic SiO2 was observed from 0.3% to 3.3% with the increasing incident angles. The smooth surface of the SiO2 crystal without nanostructures showed a high reflection of 9.2% compared to the biomorphic SiO2 with ARS. These excellent antireflective properties of biomorphic SiO2 can be attributed to the nanoscale structures which introduce a gradient in the refractive index between air and the material surface via ARS. In the meantime, biomorphic SiO2 demonstrates high hydrophilic properties due to the existence of nanostructures on its surface. These multifunctional properties of biomorphic SiO2, angle dependent antireflective properties, and hydrophilicity with high thermal stability may have potential applications in solar cells and antifogging optical materials.

Thermal Effects Modeling Developed for Smart Structures

NASA Technical Reports Server (NTRS)

Lee, Ho-Jun

1998-01-01

Applying smart materials in aeropropulsion systems may improve the performance of aircraft engines through a variety of vibration, noise, and shape-control applications. To facilitate the experimental characterization of these smart structures, researchers have been focusing on developing analytical models to account for the coupled mechanical, electrical, and thermal response of these materials. One focus of current research efforts has been directed toward incorporating a comprehensive thermal analysis modeling capability. Typically, temperature affects the behavior of smart materials by three distinct mechanisms: Induction of thermal strains because of coefficient of thermal expansion mismatch 1. Pyroelectric effects on the piezoelectric elements; 2. Temperature-dependent changes in material properties; and 3. Previous analytical models only investigated the first two thermal effects mechanisms. However, since the material properties of piezoelectric materials generally vary greatly with temperature (see the graph), incorporating temperature-dependent material properties will significantly affect the structural deflections, sensory voltages, and stresses. Thus, the current analytical model captures thermal effects arising from all three mechanisms through thermopiezoelectric constitutive equations. These constitutive equations were incorporated into a layerwise laminate theory with the inherent capability to model both the active and sensory response of smart structures in thermal environments. Corresponding finite element equations were formulated and implemented for both the beam and plate elements to provide a comprehensive thermal effects modeling capability.

Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

NASA Technical Reports Server (NTRS)

Clancy, Thomas C.; Gates, Thomas S.

2005-01-01

The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

Nondestructive evaluation of nuclear-grade graphite

NASA Astrophysics Data System (ADS)

Kunerth, D. C.; McJunkin, T. R.

2012-05-01

The material of choice for the core of the high-temperature gas-cooled reactors being developed by the U.S. Department of Energy's Next Generation Nuclear Plant Program is graphite. Graphite is a composite material whose properties are highly dependent on the base material and manufacturing methods. In addition to the material variations intrinsic to the manufacturing process, graphite will also undergo changes in material properties resulting from radiation damage and possible oxidation within the reactor. Idaho National Laboratory is presently evaluating the viability of conventional nondestructive evaluation techniques to characterize the material variations inherent to manufacturing and in-service degradation. Approaches of interest include x-ray radiography, eddy currents, and ultrasonics.

Shell-binary nanoparticle materials with variable electrical and electro-mechanical properties.

PubMed

Zhang, P; Bousack, H; Dai, Y; Offenhäusser, A; Mayer, D

2018-01-18

Nanoparticle (NP) materials with the capability to adjust their electrical and electro-mechanical properties facilitate applications in strain sensing technology. Traditional NP materials based on single component NPs lack a systematic and effective means of tuning their electrical and electro-mechanical properties. Here, we report on a new type of shell-binary NP material fabricated by self-assembly with either homogeneous or heterogeneous arrangements of NPs. Variable electrical and electro-mechanical properties were obtained for both materials. We show that the electrical and electro-mechanical properties of these shell-binary NP materials are highly tunable and strongly affected by the NP species as well as their corresponding volume fraction ratio. The conductivity and the gauge factor of these shell-binary NP materials can be altered by about five and two orders of magnitude, respectively. These shell-binary NP materials with different arrangements of NPs also demonstrate different volume fraction dependent electro-mechanical properties. The shell-binary NP materials with a heterogeneous arrangement of NPs exhibit a peaking of the sensitivity at medium mixing ratios, which arises from the aggregation induced local strain enhancement. Studies on the electron transport regimes and micro-morphologies of these shell-binary NP materials revealed the different mechanisms accounting for the variable electrical and electro-mechanical properties. A model based on effective medium theory is used to describe the electrical and electro-mechanical properties of such shell-binary nanomaterials and shows an excellent match with experiment data. These shell-binary NP materials possess great potential applications in high-performance strain sensing technology due to their variable electrical and electro-mechanical properties.

Two-dimensional metal-organic frameworks with high thermoelectric efficiency through metal ion selection.

PubMed

He, Yuping; Spataru, Catalin D; Léonard, Francois; Jones, Reese E; Foster, Michael E; Allendorf, Mark D; Alec Talin, A

2017-07-26

Two-dimensional (2D) materials have attracted much attention due to their novel properties. An exciting new class of 2D materials based on metal-organic frameworks (MOFs) has recently emerged, displaying high electrical conductivity, a rarity among organic nanoporous materials. The emergence of these materials raises intriguing questions about their fundamental electronic, optical, and thermal properties, but few studies exist in this regard. Here we present an atomistic study of the thermoelectric properties of crystalline 2D MOFs X 3 (HITP) 2 with X = Ni, Pd or Pt, and HITP = 2,3,6,7,10,11-hexaiminotriphenylene, using both ab initio transport models and classical molecular dynamics simulations. We find that these materials have a high Seebeck coefficient and low thermal conductivity, making them promising for thermoelectric applications. Furthermore, we explore the dependence of thermoelectric transport properties on the atomic structure by comparing the calculated band structure, band alignment, and electronic density of states of the three 2D MOFs, and find that the thermoelectric transport properties strongly depend on both the interaction between the ligands and the metal ions, and the d orbital splitting of the metal ions induced by the ligands. This demonstrates that selection of the metal ion is a powerful approach to control and enhance the thermoelectric properties. Interestingly we reveal an unexpected effect where, unlike for electrons, the thermal and electrical current may not be equally carried by the holes, leading to a significant deviation from the Wiedemann-Franz law. The results of this work provide fundamental guidance to optimize the existing 2D MOFs, and to design and discover new families of MOF-like materials for thermoelectric applications.

Correlation between strength properties in standard test specimens and molded phenolic parts

NASA Technical Reports Server (NTRS)

Turner, P S; Thomason, R H

1946-01-01

This report describes an investigation of the tensile, flexural, and impact properties of 10 selected types of phenolic molding materials. The materials were studied to see in what ways and to what extent their properties satisfy some assumptions on which the theory of strength of materials is based: namely, (a) isotropy, (b) linear stress-strain relationship for small strains, and (c) homogeneity. The effect of changing the dimensions of tensile and flexural specimens and the span-depth ratio in flexural tests were studied. The strengths of molded boxes and flexural specimens cut from the boxes were compared with results of tests on standard test specimens molded from the respective materials. The nonuniformity of a material, which is indicated by the coefficient of variation, affects the results of tests made with specimens of different sizes and tests with different methods of loading. The strength values were found to depend on the relationship between size and shape of the molded specimen and size and shape of the fillers. The most significant variations observed within a diversified group of materials were found to depend on the orientation of fibrous fillers. Of secondary importance was the dependence of the variability of test results on the pieces of filler incorporated into the molding powder as well as on the size of the piece. Static breaking strength tests on boxes molded from six representative phenolic materials correlated well with falling-ball impact tests on specimens cut from molded flat sheets. Good correlation was obtained with Izod impact tests on standard test specimens prepared from the molding materials. The static breaking strengths of the boxes do not correlate with the results of tensile or flexural tests on standard specimens.

Recent advances in micromechanical characterization of polymer, biomaterial, and cell surfaces with atomic force microscopy

NASA Astrophysics Data System (ADS)

Chyasnavichyus, Marius; Young, Seth L.; Tsukruk, Vladimir V.

2015-08-01

Probing of micro- and nanoscale mechanical properties of soft materials with atomic force microscopy (AFM) gives essential information about the performance of the nanostructured polymer systems, natural nanocomposites, ultrathin coatings, and cell functioning. AFM provides efficient and is some cases the exclusive way to study these properties nondestructively in controlled environment. Precise force control in AFM methods allows its application to variety of soft materials and can be used to go beyond elastic properties and examine temperature and rate dependent materials response. In this review, we discuss experimental AFM methods currently used in the field of soft nanostructured composites and biomaterials. We discuss advantages and disadvantages of common AFM probing techniques, which allow for both qualitative and quantitative mappings of the elastic modulus of soft materials with nanosacle resolution. We also discuss several advanced techniques for more elaborate measurements of viscoelastic properties of soft materials and experiments on single cells.

Elastomer modulus and dielectric strength scaling with sample thickness

NASA Astrophysics Data System (ADS)

Larson, Kent

2015-04-01

Material characteristics such as adhesion and dielectric strength have well recognized dependencies on material thickness. There is disagreement, however, on the scale: the long held dictum that dielectric strength is inversely proportional to the square root of sample thickness has been shown to not always hold true for all materials, nor for all possible thickness regions. In D-EAP applications some studies have postulated a "critical thickness" below which properties show significantly less thickness dependency. While a great deal of data is available for dielectric strength, other properties are not nearly as well documented as samples get thinner. In particular, elastic modulus has been found to increase and elongation to decrease as sample thickness is lowered. This trend can be observed experimentally, but has been rarely reported and certainly does not appear in typical suppliers' product data sheets. Both published and newly generated data were used to study properties such as elastic modulus and dielectric strength vs sample thickness in silicone elastomers. Several theories are examined to explain such behavior, such as the impact of defect size and of common (but not well reported) concentration gradients that occur during elastomer curing that create micron-sized layers at the upper and lower interfaces with divergent properties to the bulk material. As Dielectric Electro-Active Polymer applications strive to lower and lower material thickness, changing mechanical properties must be recognized and taken into consideration for accurate electro-mechanical predictions of performance.

Rate- and Temperature-Dependent Material Behavior of a Multilayer Polymer Battery Separator

NASA Astrophysics Data System (ADS)

Avdeev, Ilya; Martinsen, Michael; Francis, Alex

2014-01-01

Designing battery packs for safety in automotive applications requires multiscale modeling, as macroscopic deformations due to impact cause the mechanical failure of individual cells on a sub-millimeter level. The separator material plays a critical role in this process, as the thinning or perforating of the separator can lead to thermal runaway and catastrophic failure of an entire battery pack. The electrochemical properties of various polymer separators have been extensively investigated; however, the dependency of mechanical properties of these thin films on various factors, such as high temperature and strain rate, has not been sufficiently characterized. In this study, the macroscopic mechanical properties of a multilayer polymer thin film used as a battery separator are studied experimentally at various temperatures, strain rates, and solvent saturations. Due to the anisotropy of the material, material testing was conducted in two perpendicular directions (machine and transverse directions). Material samples were tested in both dry and saturated conditions at several temperatures, and it was found that temperature and strain rate have a nearly linear effect on the stress experienced by the material. Additionally, saturating the separator material in a common lithium-ion solvent had softened it and had a positive effect on its toughness. The experimental results obtained in this study can be used to develop mathematical constitutive models of the multilayer separator material for subsequent numerical simulations and design.

Physical Properties of Granulates Used in Analogue Experiments of Caprock Failure and Sediment Remobilisation

NASA Astrophysics Data System (ADS)

Kukowski, N.; Warsitzka, M.; May, F.

2014-12-01

Geological systems consisting of a porous reservoir and a low-permeable caprock are prone to hydraulic fracturing, if pore pressure rises to the effective stress. Under certain conditions, hydraulic fracturing is associated with sediment remobilisation, e.g. sand injections or pipes, leading to reduced seal capacity of the caprock. In dynamically scaled analogue experiments using granular materials and air pressure, we intent to investigate strain patterns and deformation mechanisms during caprock failure and fluidisation of shallow over-pressured reservoirs. The aim of this study is to improve the understanding of leakage potential of a sealing formation and the fluidisation potential of a reservoir formation depending on rock properties and effective stress. For reliable interpretation of analogue experiments, physical properties of analogue materials, e.g. frictional strength, cohesion, density, permeability etc., have to be correctly scaled according to those of their natural equivalents. The simulation of caprock requires that the analogue material possess a low permeability and is capable to shear failure and tensional failure. In contrast, materials representing the reservoir have to possess high porosity and low shear strength. In order to find suitable analogue materials, we measured the stress-strain behaviour and the permeability of over 25 different types of natural and artificial granular materials, e.g. glass powder, siliceous microspheres, diatomite powder, loess, or plastic granulate. Here, we present data of frictional parameters, compressibility and permeability of these granular materials characterized as a function of sphericity, grain size, and density. The repertoire of different types of granulates facilitates the adjustment of accurate mechanical properties in the analogue experiments. Furthermore, conditions during seal failure and fluidisation can be examined depending on the wide range of varying physical properties.

Elastic Properties and Internal Friction of Two Magnesium Alloys at Elevated Temperatures

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

Freels, M.; Liaw, P. K.; Garlea, E.

2011-06-01

The elastic properties and internal friction of two magnesium alloys were studied from 25 C to 450 C using Resonant Ultrasound Spectroscopy (RUS). The Young's moduli decrease with increasing temperature. At 200 C, a change in the temperature dependence of the elastic constants is observed. The internal friction increases significantly with increasing temperature above 200 C. The observed changes in the temperature dependence of the elastic constants and the internal friction are the result of anelastic relaxation by grain boundary sliding at elevated temperatures. Elastic properties govern the behavior of a materials subjected to stress over a region of strainmore » where the material behaves elastically. The elastic properties, including the Young's modulus (E), shear modulus (G), bulk modulus (B), and Poisson's ratio (?), are of significant interest to many design and engineering applications. The choice of the most appropriate material for a particular application at elevated temperatures therefore requires knowledge of its elastic properties as a function of temperature. In addition, mechanical vibration can cause significant damage in the automotive, aerospace, and architectural industries and thus, the ability of a material to dissipate elastic strain energy in materials, known as damping or internal friction, is also important property. Internal friction can be the result of a wide range of physical mechanisms, and depends on the material, temperature, and frequency of the loading. When utilized effectively in engineering applications, the damping capacity of a material can remove undesirable noise and vibration as heat to the surroundings. The elastic properties of materials can be determined by static or dynamic methods. Resonant Ultrasound Spectroscopy (RUS), used in this study, is a unique and sophisticated non-destructive dynamic technique for determining the complete elastic tensor of a solid by measuring the resonant spectrum of mechanical resonance for a sample of known geometry, dimensions, and mass. In addition, RUS allows determination of internal friction, or damping, at different frequencies and temperatures. Polycrystalline pure magnesium (Mg) exhibits excellent high damping properties. However, the poor mechanical properties limit the applications of pure Mg. Although alloying can improve the mechanical properties of Mg, the damping properties are reduced with additions of alloying elements. Therefore, it becomes necessary to study and develop Mg-alloys with simultaneous high damping capacity and improved mechanical properties. Moreover, studies involving the high temperature dynamic elastic properties of Mg alloys are limited. In this study, the elastic properties and internal friction of two magnesium alloys were studied at elevated temperatures using RUS. The effect of alloy composition and grain size was investigated. The wrought magnesium alloys AZ31 and ZK60 were employed. Table 1 gives the nominal chemical compositions of these two alloys. The ZK60 alloy is a commercial extruded plate with a T5 temper, i.e. solution-treated at 535 C for two hours, quenched in hot water, and aged at 185 C for 24 hours. The AZ31 alloy is a commercial rolled plate with a H24 temper, i.e. strain hardened and partially annealed.« less

Recent advancements in 2D-materials interface based magnetic junctions for spintronics

NASA Astrophysics Data System (ADS)

Iqbal, Muhammad Zahir; Qureshi, Nabeel Anwar; Hussain, Ghulam

2018-07-01

Two-dimensional (2D) materials comprising of graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs) have revealed fascinating properties in various spintronic architectures. Here, we review spin valve effect in lateral and vertical magnetic junctions incorporating 2D materials as non-magnetic layer between ferromagnetic (FM) electrodes. The magnetic field dependent spin transport properties are studied by measuring non-local resistance (RNL) and relative magnetoresistance ratio (MR) for lateral and vertical structures, respectively. The review consists of (i) studying spin lifetimes and spin diffusion length thereby exploring the effect of tunneling and transparent contacts in lateral spin valve structures, temperature dependence, gate tunability and contrasting mechanisms of spin relaxation in single layer graphene (SLG) and bilayer graphene (BLG) devices. (ii) Perpendicular spin valve devices are thoroughly investigated thereby studying the role of different 2D materials in vertical spin dynamics. The dependence of spin valve signal on interface quality, temperature and various other parameters is also investigated. Furthermore, the spin reversal in graphene-hBN hybrid system is examined on the basis of Julliere model.

Design of single piece sabot for a single stage gas gun

NASA Astrophysics Data System (ADS)

Vemparala, Vignesh; Mathew, Arun Tom; Rao Koka, Tirumala

2017-11-01

Single piece sabot is a vital part in single stage gas guns for impact testing in aerospace industries. Depending on the type of projectile used the design of sabot varies to accommodate the testing equipment. The velocity of the projectile exiting the barrel is dependent on the material and shape of the sabot used. The material selected for the design of sabot is rigid polyurethane foam, due to their low elastic modulus and low density. Two samples of rigid PU foam is taken and tests are performed to get their exact material properties. These properties are incorporated in numerical simulation to determine the best fit for practical use. Since the PU foams has a wide range of porosity which plays a prominent role in deciding the exit velocity and accuracy of the projectile coming out of the barrel. By optimisation, to the best suitable material sample can be determined.

The time dependence of rock healing as a universal relaxation process, a tutorial

NASA Astrophysics Data System (ADS)

Snieder, Roel; Sens-Schönfelder, Christoph; Wu, Renjie

2017-01-01

The material properties of earth materials often change after the material has been perturbed (slow dynamics). For example, the seismic velocity of subsurface materials changes after earthquakes, and granular materials compact after being shaken. Such relaxation processes are associated by observables that change logarithmically with time. Since the logarithm diverges for short and long times, the relaxation can, strictly speaking, not have a log-time dependence. We present a self-contained description of a relaxation function that consists of a superposition of decaying exponentials that has log-time behaviour for intermediate times, but converges to zero for long times, and is finite for t = 0. The relaxation function depends on two parameters, the minimum and maximum relaxation time. These parameters can, in principle, be extracted from the observed relaxation. As an example, we present a crude model of a fracture that is closing under an external stress. Although the fracture model violates some of the assumptions on which the relaxation function is based, it follows the relaxation function well. We provide qualitative arguments that the relaxation process, just like the Gutenberg-Richter law, is applicable to a wide range of systems and has universal properties.

A Multiscale Virtual Fabrication and Lattice Modeling Approach for the Fatigue Performance Prediction of Asphalt Concrete

NASA Astrophysics Data System (ADS)

Dehghan Banadaki, Arash

Predicting the ultimate performance of asphalt concrete under realistic loading conditions is the main key to developing better-performing materials, designing long-lasting pavements, and performing reliable lifecycle analysis for pavements. The fatigue performance of asphalt concrete depends on the mechanical properties of the constituent materials, namely asphalt binder and aggregate. This dependent link between performance and mechanical properties is extremely complex, and experimental techniques often are used to try to characterize the performance of hot mix asphalt. However, given the seemingly uncountable number of mixture designs and loading conditions, it is simply not economical to try to understand and characterize the material behavior solely by experimentation. It is well known that analytical and computational modeling methods can be combined with experimental techniques to reduce the costs associated with understanding and characterizing the mechanical behavior of the constituent materials. This study aims to develop a multiscale micromechanical lattice-based model to predict cracking in asphalt concrete using component material properties. The proposed algorithm, while capturing different phenomena for different scales, also minimizes the need for laboratory experiments. The developed methodology builds on a previously developed lattice model and the viscoelastic continuum damage model to link the component material properties to the mixture fatigue performance. The resulting lattice model is applied to predict the dynamic modulus mastercurves for different scales. A framework for capturing the so-called structuralization effects is introduced that significantly improves the accuracy of the modulus prediction. Furthermore, air voids are added to the model to help capture this important micromechanical feature that affects the fatigue performance of asphalt concrete as well as the modulus value. The effects of rate dependency are captured by implementing the viscoelastic fracture criterion. In the end, an efficient cyclic loading framework is developed to evaluate the damage accumulation in the material that is caused by long-sustained cyclic loads.

Metal clusters and nanoparticles in dielectric matrices: Formation and optical properties

NASA Astrophysics Data System (ADS)

Gladskikh, I. A.; Vartanyan, T. A.

2016-12-01

The optical properties of thin dielectric films with metal inclusions and their dependence on thermal and laser annealing are studied experimentally. Metal clusters (Ag, Au, and Cu) in dielectric materials (Al2O3 and SiO2) are obtained by simultaneous vacuum deposition of metal and dielectric on the surface of a corresponding dielectric substrate (sapphire and quartz). It is shown that, depending on the deposited dielectric material, on the weight ratio of deposited metal and dielectric, and on the subsequent thermal treatment, one can obtain different metal structures, from clusters with a small number of atoms to complex dendritic plasmonic structures.

Nanomechanical strength mechanisms of hierarchical biological materials and tissues.

PubMed

Buehler, Markus J; Ackbarow, Theodor

2008-12-01

Biological protein materials (BPMs), intriguing hierarchical structures formed by assembly of chemical building blocks, are crucial for critical functions of life. The structural details of BPMs are fascinating: They represent a combination of universally found motifs such as alpha-helices or beta-sheets with highly adapted protein structures such as cytoskeletal networks or spider silk nanocomposites. BPMs combine properties like strength and robustness, self-healing ability, adaptability, changeability, evolvability and others into multi-functional materials at a level unmatched in synthetic materials. The ability to achieve these properties depends critically on the particular traits of these materials, first and foremost their hierarchical architecture and seamless integration of material and structure, from nano to macro. Here, we provide a brief review of this field and outline new research directions, along with a review of recent research results in the development of structure-property relationships of biological protein materials exemplified in a study of vimentin intermediate filaments.

Effective electromagnetic properties of microheterogeneous materials with surface phenomena

NASA Astrophysics Data System (ADS)

Levin, Valery; Markov, Mikhail; Mousatov, Aleksandr; Kazatchenko, Elena; Pervago, Evgeny

2017-10-01

In this paper, we present an approach to calculate the complex dielectric permittivity of a micro-heterogeneous medium composed of non-conductive solid inclusions embedded into the conductive liquid continuous host. To take into account the surface effects, we approximate the inclusion by a layered ellipsoid consisting of a dielectric core and an infinitesimally thin outer shell corresponding to an electrical double layer (EDL). To predict the effective complex dielectric permittivity of materials with a high concentration of inclusions, we have modified the Effective Field Method (EFM) for the layered ellipsoidal particles with complex electrical properties. We present the results of complex permittivity calculations for the composites with randomly and parallel oriented ellipsoidal inclusions. To analyze the influence of surface polarization, we have accomplished modeling in a wide frequency range for different existing physic-chemical models of double electrical layer. The results obtained show that the tensor of effective complex permittivity of a micro-heterogeneous medium with surface effects has complicate dependences on the component electrical properties, spatial material texture, and the inclusion shape (ellipsoid aspect ratio) and size. The dispersion of dielectric permittivity corresponds to the frequency dependence for individual inclusion of given size, and does not depend on the inclusion concentration.

Non-metal spintronics: study of spin-dependent transport in InSb- and InAs-based nanopatterned heterostructures

NASA Astrophysics Data System (ADS)

Heremans, J. J.; Chen, Hong; Peters, J. A.; Goel, N.; Chung, S. J.; Santos, M. B.; van Roy, W.; Borghs, G.

2006-03-01

Spin-orbit interaction in semiconductor heterostructures can lead to various spin-dependent electronic transport effects without the presence of magnetic materials. Mesoscopic samples were fabricated on InSb/InAlSb and InAs/AlGaSb two-dimensional electron systems, where spin-orbit interaction is strong. In mesoscopic devices, the effects of spin-orbit interaction are not averaged out over the geometry, and lead to observable electronic properties. We experimentally demonstrate spin-split ballistic transport and the creation of fully spin-polarized electron beams using spin-dependent reflection geometries and transverse magnetic focusing geometries. Spin-dependent transport properties in the semiconductor materials are also investigated using antidot lattices. Spin-orbit interaction effects in high-mobility semiconductor devices may be utilized toward the design of novel spintronics implementations. We acknowledge NSF DMR-0094055 (JJH), DMR-0080054, DMR-0209371 (MBS).

Engineering Biomaterial Properties for Central Nervous System Applications

NASA Astrophysics Data System (ADS)

Rivet, Christopher John

Biomaterials offer unique properties that are intrinsic to the chemistry of the material itself or occur as a result of the fabrication process; iron oxide nanoparticles are superparamagnetic, which enables controlled heating in the presence of an alternating magnetic field, and a hydrogel and electrospun fiber hybrid material provides minimally invasive placement of a fibrous, artificial extracellular matrix for tissue regeneration. Utilization of these unique properties towards central nervous system disease and dysfunction requires a thorough definition of the properties in concert with full biological assessment. This enables development of material-specific features to elicit unique cellular responses. Iron oxide nanoparticles are first investigated for material-dependent, cortical neuron cytotoxicity in vitro and subsequently evaluated for alternating magnetic field stimulation induced hyperthermia, emulating the clinical application for enhanced chemotherapy efficacy in glioblastoma treatment. A hydrogel and electrospun fiber hybrid material is first applied to a rat brain to evaluate biomaterial interface astrocyte accumulation as a function of hybrid material composition. The hybrid material is then utilized towards increasing functional engraftment of dopaminergic progenitor neural stem cells in a mouse model of Parkinson's disease. Taken together, these two scenarios display the role of material property characterization in development of biomaterial strategies for central nervous system repair and regeneration.

In-air and pressurized water reactor environment fatigue experiments of 316 stainless steel to study the effect of environment on cyclic hardening

NASA Astrophysics Data System (ADS)

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurindranath; Natesan, Krishnamurti

2016-05-01

Argonne National Laboratory (ANL), under the sponsorship of Department of Energy's Light Water Reactor Sustainability (LWRS) program, is trying to develop a mechanistic approach for more accurate life estimation of LWR components. In this context, ANL has conducted many fatigue experiments under different test and environment conditions on type 316 stainless steel (316 SS) material which is widely used in the US reactors. Contrary to the conventional S ∼ N curve based empirical fatigue life estimation approach, the aim of the present DOE sponsored work is to develop an understanding of the material ageing issues more mechanistically (e.g. time dependent hardening and softening) under different test and environmental conditions. Better mechanistic understanding will help develop computer-based advanced modeling tools to better extrapolate stress-strain evolution of reactor components under multi-axial stress states and hence help predict their fatigue life more accurately. Mechanics-based modeling of fatigue such as by using finite element (FE) tools requires the time/cycle dependent material hardening properties. Presently such time-dependent material hardening properties are hardly available in fatigue modeling literature even under in-air conditions. Getting those material properties under PWR environment, are even harder. Through this work we made preliminary attempt to generate time/cycle dependent stress-strain data both under in-air and PWR water conditions for further study such as for possible development of material models and constitutive relations for FE model implementation. Although, there are open-ended possibility to further improve the discussed test methods and related material estimation techniques we anticipate that the data presented in this paper will help the metal fatigue research community particularly, the researchers who are dealing with mechanistic modeling of metal fatigue such as using FE tools. In this paper the fatigue experiments under different test and environment conditions and related stress-strain results for 316 SS are discussed.

Precise Heat Control: What Every Scientist Needs to Know About Pyrolytic Techniques to Solve Real Problems

NASA Technical Reports Server (NTRS)

Devivar, Rodrigo

2014-01-01

The performance of a material is greatly influenced by its thermal and chemical properties. Analytical pyrolysis, when coupled to a GC-MS system, is a powerful technique that can unlock the thermal and chemical properties of almost any substance and provide vital information. At NASA, we depend on precise thermal analysis instrumentation for understanding aerospace travel. Our analytical techniques allow us to test materials in the laboratory prior to an actual field test; whether the field test is miles up in the sky or miles underground, the properties of any involved material must be fully studied and understood in the laboratory.

Characterization of Viscoelastic Properties of Polymeric Materials Through Nanoindentation

NASA Technical Reports Server (NTRS)

Odegard, G. M.; Bandorawalla, T.; Herring, H. M.; Gates, T. S.

2003-01-01

Nanoindentation is used to determine the dynamic viscoelastic properties of six polymer materials. It is shown that varying the harmonic frequency of the nanoindentation does not have any significant effect on the measured storage and loss moduli of the polymers. Agreement is found between these results and data from DMA testing of the same materials. Varying the harmonic amplitude of the nanoindentation does not have a significant effect on the measured properties of the high performance resins, however, the storage modulus of the polyethylene decreases as the harmonic amplitude increases. Measured storage and loss moduli are also shown to depend on the density of the polyethylene.

Effects of oxidation on the plasmonic properties of aluminum nanoclusters.

PubMed

Douglas-Gallardo, Oscar A; Soldano, Germán J; Mariscal, Marcelo M; Sánchez, Cristián Gabriel

2017-11-16

The scouting of alternative plasmonic materials able to enhance and extend the optical properties of noble metal nanostructures is on the rise. Aluminum is endowed with a set of interesting properties which turn it into an attractive plasmonic material. Here we present the optical and electronic features of different aluminum nanostructures stemming from a multilevel computational study. Molecular Dynamics (MD) simulations using a reactive force field (ReaxFF), carefully validated with Density Functional Theory (DFT), were employed to mimic the oxidation of icosahedral aluminum nanoclusters. Resulting structures with different oxidation degrees were then studied through the Time-Dependent Density Functional Tight Binding (TD-DFTB) method. A similar approach was used in aluminum nanoclusters with a disordered structure to study how the loss of crystallinity affects the optical properties. To the best of our knowledge, this is the first report that addresses this issue from the fully atomistic time-dependent approach by means of two different and powerful simulation tools able to describe quantum and physicochemical properties associated with nanostructured particles.

On the thermoelastic analysis of solar cell arrays and related material properties

NASA Technical Reports Server (NTRS)

Salama, M. A.; Bouquet, F. L.

1976-01-01

Accurate prediction of failure of solar cell arrays requires accuracy in the computation of thermally induced stresses. This was accomplished by using the finite element technique. Improved procedures for stress calculation were introduced together with failure criteria capable of describing a wide range of ductile and brittle material behavior. The stress distribution and associated failure mechanisms in the N-interconnect junction of two solar cell designs were then studied. In such stress and failure analysis, it is essential to know the thermomechanical properties of the materials involved. Measurements were made of properties of materials suitable for the design of lightweight arrays: microsheet-0211 glass material for the solar cell filter, and Kapton-H, Kapton F, Teflon, Tedlar, and Mica Ply PG-402 for lightweight substrates. The temperature-dependence of the thermal coefficient of expansion for these materials was determined together with other properties such as the elastic moduli, Poisson's ratio, and the stress-strain behavior up to failure.

Ultrasonic Data Display and Analysis System Developed (Including Fuzzy Logic Analysis) for the Windows-Based PC

NASA Technical Reports Server (NTRS)

Lovelace, Jeffrey J.; Cios, Kryzsztof J.; Roth, Don J.; cAO, wEI n.

2001-01-01

Post-Scan Interactive Data Display (PSIDD) III is a user-oriented Windows-based system that facilitates the display and comparison of ultrasonic contact measurement data obtained at NASA Glenn Research Center's Ultrasonic Nondestructive Evaluation measurement facility. The system is optimized to compare ultrasonic measurements made at different locations within a material or at different stages of material degradation. PSIDD III provides complete analysis of the primary waveforms in the time and frequency domains along with the calculation of several frequency-dependent properties including phase velocity and attenuation coefficient and several frequency-independent properties, like the cross correlation velocity. The system allows image generation on all the frequency-dependent properties at any available frequency (limited by the bandwidth used in the scans) and on any of the frequency-independent properties. From ultrasonic contact scans, areas of interest on an image can be studied with regard to underlying raw waveforms and derived ultrasonic properties by simply selecting the point on the image. The system offers various modes of indepth comparison between scan points. Up to five scan points can be selected for comparative analysis at once. The system was developed with Borland Delphi software (Visual Pascal) and is based on an SQL data base. It is ideal for the classification of material properties or the location of microstructure variations in materials. Along with the ultrasonic contact measurement software that it is partnered with, this system is technology ready and can be transferred to users worldwide.

Controlling material birefringence in sapphire via self-assembled, sub-wavelength defects

NASA Astrophysics Data System (ADS)

Singh, Astha; Sharma, Geeta; Ranjan, Neeraj; Mittholiya, Kshitij; Bhatnagar, Anuj; Singh, B. P.; Mathur, Deepak; Vasa, Parinda

2018-02-01

Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. Generally, this is an intrinsic optical property of a material and cannot be altered. Here, we report a novel technique—direct laser writing—that enables us to control the natural, material birefringence of sapphire over a broad range of wavelengths. The broadband form birefringence originating from self-assembled, periodic array of sub-wavelength (˜ 50-200 nm) defects created by laser writing, can enhance, suppress or maintain the material birefringence of sapphire without affecting its transparency range in visible or its surface quality.

Holographic sol-gel monoliths: optical properties and application for humidity sensing

NASA Astrophysics Data System (ADS)

Ilatovskii, Daniil A.; Milichko, Valentin; Vinogradov, Alexander V.; Vinogradov, Vladimir V.

2018-05-01

Sol-gel monoliths based on SiO2, TiO2 and ZrO2 with holographic colourful diffraction on their surfaces were obtained via a sol-gel synthesis and soft lithography combined method. The production was carried out without any additional equipment at near room temperature and atmospheric pressure. The accurately replicated wavy structure with nanoscale size of material particles yields holographic effect and its visibility strongly depends on refractive index (RI) of materials. Addition of multi-walled carbon nanotubes (MWCNTs) in systems increases their RI and lends absorbing properties due to extremely high light absorption constant. Further prospective and intriguing applications based on the most successful samples, MWCNTs-doped titania, were investigated as reversible optical humidity sensor. Owing to such property as reversible resuspension of TiO2 nanoparticles while interacting with water, it was proved that holographic xerogels can repeatedly act as humidity sensors. Materials which can be applied as humidity sensors in dependence on holographic response were discovered for the first time.

The interplay of stiffness and force anisotropies drives embryo elongation

PubMed Central

Vuong-Brender, Thanh Thi Kim; Ben Amar, Martine; Pontabry, Julien; Labouesse, Michel

2017-01-01

The morphogenesis of tissues, like the deformation of an object, results from the interplay between their material properties and the mechanical forces exerted on them. The importance of mechanical forces in influencing cell behaviour is widely recognized, whereas the importance of tissue material properties, in particular stiffness, has received much less attention. Using Caenorhabditis elegans as a model, we examine how both aspects contribute to embryonic elongation. Measuring the opening shape of the epidermal actin cortex after laser nano-ablation, we assess the spatiotemporal changes of actomyosin-dependent force and stiffness along the antero-posterior and dorso-ventral axis. Experimental data and analytical modelling show that myosin-II-dependent force anisotropy within the lateral epidermis, and stiffness anisotropy within the fiber-reinforced dorso-ventral epidermis are critical in driving embryonic elongation. Together, our results establish a quantitative link between cortical tension, material properties and morphogenesis of an entire embryo. DOI: http://dx.doi.org/10.7554/eLife.23866.001 PMID:28181905

Bond Strength Mechanism of Fly Ash Based Geopolymer Mortars: A Review

NASA Astrophysics Data System (ADS)

Zailani, W. W. A.; Abdullah, M. M. A. B.; Razak, R. A.; Zainol, M. R. R. M. A.; Tahir, M. F. M.

2017-11-01

Geopolymer possess many excellent properties such as high compressive and bond strength, long term durability, better acid resistance and also known as a “Sustainable Material” due to its low carbon emission and low energy consumption. Thus, it is a good opportunity to develop and explore not only for cement and concrete but also as geopolymeric repair materials. This reviews showed that good bonding properties between geopolymeric repair material and concrete substrate is important in order to acquire an enhanced resistance against penetration of harmful substances and avoiding respalling of the repair material by understanding the bonding behaviour. Bond strength depends to the properties of the repair materials itself and also the surface preparations of concrete substrate.

Thermoelastic analysis of solar cell arrays and their material properties

NASA Technical Reports Server (NTRS)

Salama, M. A.; Rowe, W. M.; Yasui, R. K.

1973-01-01

A thermoelastic stress analysis procedure is reported for predicting the thermally induced stresses and failures in silicon solar cell arrays. A prerequisite for the analysis is the characterization of the temperature-dependent thermal and mechanical properties of the solar cell materials. Extensive material property testing was carried out in the temperature range -200 to +200 C for the filter glass, P- and N-type silicon, interconnector metals, solder, and several candidate silicone rubber adhesives. The analysis procedure is applied to several solar cell array design configurations. Results of the analysis indicate the optimum design configuration, with respect to compatible materials, effect of the solder coating, and effect of the interconnector geometry. Good agreement was found between results of the analysis and the test program.

Mechanics of metal-catecholate complexes: The roles of coordination state and metal types

PubMed Central

Xu, Zhiping

2013-01-01

There have been growing evidences for the critical roles of metal-coordination complexes in defining structural and mechanical properties of unmineralized biological materials, including hardness, toughness, and abrasion resistance. Their dynamic (e.g. pH-responsive, self-healable, reversible) properties inspire promising applications of synthetic materials following this concept. However, mechanics of these coordination crosslinks, which lays the ground for predictive and rational material design, has not yet been well addressed. Here we present a first-principles study of representative coordination complexes between metals and catechols. The results show that these crosslinks offer stiffness and strength near a covalent bond, which strongly depend on the coordination state and type of metals. This dependence is discussed by analyzing the nature of bonding between metals and catechols. The responsive mechanics of metal-coordination is further mapped from the single-molecule level to a networked material. The results presented here provide fundamental understanding and principles for material selection in metal-coordination-based applications. PMID:24107799

Development of a strain rate dependent material model of human cortical bone for computer-aided reconstruction of injury mechanisms.

PubMed

Asgharpour, Zahra; Zioupos, Peter; Graw, Matthias; Peldschus, Steffen

2014-03-01

Computer-aided methods such as finite-element simulation offer a great potential in the forensic reconstruction of injury mechanisms. Numerous studies have been performed on understanding and analysing the mechanical properties of bone and the mechanism of its fracture. Determination of the mechanical properties of bones is made on the same basis used for other structural materials. The mechanical behaviour of bones is affected by the mechanical properties of the bone material, the geometry, the loading direction and mode and of course the loading rate. Strain rate dependency of mechanical properties of cortical bone has been well demonstrated in literature studies, but as many of these were performed on animal bones and at non-physiological strain rates it is questionable how these will apply in the human situations. High strain-rates dominate in a lot of forensic applications in automotive crashes and assault scenarios. There is an overwhelming need to a model which can describe the complex behaviour of bone at lower strain rates as well as higher ones. Some attempts have been made to model the viscoelastic and viscoplastic properties of the bone at high strain rates using constitutive mathematical models with little demonstrated success. The main objective of the present study is to model the rate dependent behaviour of the bones based on experimental data. An isotropic material model of human cortical bone with strain rate dependency effects is implemented using the LS-DYNA material library. We employed a human finite element model called THUMS (Total Human Model for Safety), developed by Toyota R&D Labs and the Wayne State University, USA. The finite element model of the human femur is extracted from the THUMS model. Different methods have been employed to develop a strain rate dependent material model for the femur bone. Results of one the recent experimental studies on human femur have been employed to obtain the numerical model for cortical femur. A forensic application of the model is explained in which impacts to the arm have been reconstructed using the finite element model of THUMS. The advantage of the numerical method is that a wide range of impact conditions can be easily reconstructed. Impact velocity has been changed as a parameter to find the tolerance levels of injuries to the lower arm. The method can be further developed to study the assaults and the injury mechanism which can lead to severe traumatic injuries in forensic cases. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Crash simulation of hybrid structures considering the stress and strain rate dependent material behavior of thermoplastic materials

NASA Astrophysics Data System (ADS)

Hopmann, Ch.; Schöngart, M.; Weber, M.; Klein, J.

2015-05-01

Thermoplastic materials are more and more used as a light weight replacement for metal, especially in the automotive industry. Since these materials do not provide the mechanical properties, which are required to manufacture supporting elements like an auto body or a cross bearer, plastics are combined with metals in so called hybrid structures. Normally, the plastics components are joined to the metal structures using different technologies like welding or screwing. Very often, the hybrid structures are made of flat metal parts, which are stiffened by a reinforcement structure made of thermoplastic materials. The loads on these structures are very often impulsive, for example in the crash situation of an automobile. Due to the large stiffness variation of metal and thermoplastic materials, complex states of stress and very high local strain rates occur in the contact zone under impact conditions. Since the mechanical behavior of thermoplastic materials is highly dependent on these types of load, the crash failure of metal plastic hybrid parts is very complex. The problem is that the normally used strain rate dependent elastic/plastic material models are not capable to simulate the mechanical behavior of thermoplastic materials depended on the state of stress. As part of a research project, a method to simulate the mechanical behavior of hybrid structures under impact conditions is developed at the IKV. For this purpose, a specimen for the measurement of mechanical properties dependet on the state of stress and a method for the strain rate depended characterization of thermoplastic materials were developed. In the second step impact testing is performed. A hybrid structure made from a metal sheet and a reinforcement structure of a Polybutylenterephthalat Polycarbonate blend is tested under impact conditions. The measured stress and strain rate depended material data are used to simulate the mechanical behavior of the hybrid structure under highly dynamic load with impact velocities up to 5 m/s. The mechanical behavior of the plastics structure is simulated using a quadratic yield surface, which takes the state of stress and the strain rate into account. The FE model is made from mid surface elements to reduce the computing time.

Novel tools for accelerated materials discovery in the AFLOWLIB.ORG repository: breakthroughs and challenges in the mapping of the materials genome

NASA Astrophysics Data System (ADS)

Buongiorno Nardelli, Marco

2015-03-01

High-Throughput Quantum-Mechanics computation of materials properties by ab initio methods has become the foundation of an effective approach to materials design, discovery and characterization. This data driven approach to materials science currently presents the most promising path to the development of advanced technological materials that could solve or mitigate important social and economic challenges of the 21st century. In particular, the rapid proliferation of computational data on materials properties presents the possibility to complement and extend materials property databases where the experimental data is lacking and difficult to obtain. Enhanced repositories such as AFLOWLIB, open novel opportunities for structure discovery and optimization, including uncovering of unsuspected compounds, metastable structures and correlations between various properties. The practical realization of these opportunities depends on the the design effcient algorithms for electronic structure simulations of realistic material systems, the systematic compilation and classification of the generated data, and its presentation in easily accessed form to the materials science community, the primary mission of the AFLOW consortium. This work was supported by ONR-MURI under Contract N00014-13-1-0635 and the Duke University Center for Materials Genomics.

Density-functional tight-binding investigation of the structure, stability and material properties of nickel hydroxide nanotubes

NASA Astrophysics Data System (ADS)

Jahangiri, Soran; Mosey, Nicholas J.

2018-01-01

Nickel hydroxide is a material composed of two-dimensional layers that can be rolled up to form cylindrical nanotubes belonging to a class of inorganic metal hydroxide nanotubes that are candidates for applications in catalysis, energy storage, and microelectronics. The stabilities and other properties of this class of inorganic nanotubes have not yet been investigated in detail. The present study uses self-consistent-charge density-functional tight-binding calculations to examine the stabilities, mechanical properties, and electronic properties of nickel hydroxide nanotubes along with the energetics associated with the adsorption of water by these systems. The tight-binding model was parametrized for this system based on the results of first-principles calculations. The stabilities of the nanotubes were examined by calculating strain energies and performing molecular dynamics simulations. The results indicate that single-walled nickel hydroxide nanotubes are stable at room temperature, which is consistent with experimental investigations. The nanotubes possess size-dependent mechanical properties that are similar in magnitude to those of other inorganic nanotubes. The electronic properties of the nanotubes were also found to be size-dependent and small nickel oxyhydroxide nanotubes are predicted to be semiconductors. Despite this size-dependence, both the mechanical and electronic properties were found to be almost independent of the helical structure of the nanotubes. The calculations also show that water molecules have higher adsorption energies when binding to the interior of the nickel hydroxide nanotubes when compared to adsorption in nanotubes formed from other two-dimensional materials such as graphene. The increased adsorption energy is due to the hydrophilic nature of nickel hydroxide. Due to the broad applications of nickel hydroxide, the nanotubes investigated here are also expected to be used in catalysis, electronics, and clean energy production.

Layer-Dependent Ultrafast Carrier and Coherent Phonon Dynamics in Black Phosphorus.

PubMed

Miao, Xianchong; Zhang, Guowei; Wang, Fanjie; Yan, Hugen; Ji, Minbiao

2018-05-09

Black phosphorus is a layered semiconducting material, demonstrating strong layer-dependent optical and electronic properties. Probing the photophysical properties on ultrafast time scales is of central importance in understanding many-body interactions and nonequilibrium quasiparticle dynamics. Here, we applied temporally, spectrally, and spatially resolved pump-probe microscopy to study the transient optical responses of mechanically exfoliated few-layer black phosphorus, with layer numbers ranging from 2 to 9. We have observed layer-dependent resonant transient absorption spectra with both photobleaching and red-shifted photoinduced absorption features, which could be attributed to band gap renormalization of higher subband transitions. Surprisingly, coherent phonon oscillations with unprecedented intensities were observed when the probe photons were in resonance with the optical transitions, which correspond to the low-frequency layer-breathing mode. Our results reveal strong Coulomb interactions and electron-phonon couplings in photoexcited black phosphorus, providing important insights into the ultrafast optical, nanomechanical, and optoelectronic properties of this novel two-dimensional material.

Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties.

PubMed

Stoumpos, Constantinos C; Malliakas, Christos D; Kanatzidis, Mercouri G

2013-08-05

A broad organic-inorganic series of hybrid metal iodide perovskites with the general formulation AMI3, where A is the methylammonium (CH3NH3(+)) or formamidinium (HC(NH2)2(+)) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compounds have been prepared through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. We find that the chemical and physical properties of these materials strongly depend on the preparation method. Single crystal X-ray diffraction analysis of 1-4 classifies the compounds in the perovskite structural family. Structural phase transitions were observed and investigated by temperature-dependent single crystal X-ray diffraction in the 100-400 K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-IR region that display characteristic absorption features. Temperature-dependent studies show a strong dependence of the resistivity as a function of the crystal structure. Optical absorption measurements indicate that 1-4 behave as direct-gap semiconductors with energy band gaps distributed in the range of 1.25-1.75 eV. The compounds exhibit an intense near-IR photoluminescence (PL) emission in the 700-1000 nm range (1.1-1.7 eV) at room temperature. We show that solid solutions between the Sn and Pb compounds are readily accessible throughout the composition range. The optical properties such as energy band gap, emission intensity, and wavelength can be readily controlled as we show for the isostructural series of solid solutions CH3NH3Sn(1-x)Pb(x)I3 (5). The charge transport type in these materials was characterized by Seebeck coefficient and Hall-effect measurements. The compounds behave as p- or n-type semiconductors depending on the preparation method. The samples with the lowest carrier concentration are prepared from solution and are n-type; p-type samples can be obtained through solid state reactions exposed in air in a controllable manner. In the case of Sn compounds, there is a facile tendency toward oxidation which causes the materials to be doped with Sn(4+) and thus behave as p-type semiconductors displaying metal-like conductivity. The compounds appear to possess very high estimated electron and hole mobilities that exceed 2000 cm(2)/(V s) and 300 cm(2)/(V s), respectively, as shown in the case of CH3NH3SnI3 (1). We also compare the properties of the title hybrid materials with those of the "all-inorganic" CsSnI3 and CsPbI3 prepared using identical synthetic methods.

Monte Carlo method for photon heating using temperature-dependent optical properties.

PubMed

Slade, Adam Broadbent; Aguilar, Guillermo

2015-02-01

The Monte Carlo method for photon transport is often used to predict the volumetric heating that an optical source will induce inside a tissue or material. This method relies on constant (with respect to temperature) optical properties, specifically the coefficients of scattering and absorption. In reality, optical coefficients are typically temperature-dependent, leading to error in simulation results. The purpose of this study is to develop a method that can incorporate variable properties and accurately simulate systems where the temperature will greatly vary, such as in the case of laser-thawing of frozen tissues. A numerical simulation was developed that utilizes the Monte Carlo method for photon transport to simulate the thermal response of a system that allows temperature-dependent optical and thermal properties. This was done by combining traditional Monte Carlo photon transport with a heat transfer simulation to provide a feedback loop that selects local properties based on current temperatures, for each moment in time. Additionally, photon steps are segmented to accurately obtain path lengths within a homogenous (but not isothermal) material. Validation of the simulation was done using comparisons to established Monte Carlo simulations using constant properties, and a comparison to the Beer-Lambert law for temperature-variable properties. The simulation is able to accurately predict the thermal response of a system whose properties can vary with temperature. The difference in results between variable-property and constant property methods for the representative system of laser-heated silicon can become larger than 100K. This simulation will return more accurate results of optical irradiation absorption in a material which undergoes a large change in temperature. This increased accuracy in simulated results leads to better thermal predictions in living tissues and can provide enhanced planning and improved experimental and procedural outcomes. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Size-dependent phase transition in methylammonium lead iodide perovskite microplate crystals

PubMed Central

Li, Dehui; Wang, Gongming; Cheng, Hung-Chieh; Chen, Chih-Yen; Wu, Hao; Liu, Yuan; Huang, Yu; Duan, Xiangfeng

2016-01-01

Methylammonium lead iodide perovskite has attracted considerable recent interest for solution processable solar cells and other optoelectronic applications. The orthorhombic-to-tetragonal phase transition in perovskite can significantly alter its optical, electrical properties and impact the corresponding applications. Here, we report a systematic investigation of the size-dependent orthorhombic-to-tetragonal phase transition using a combined temperature-dependent optical, electrical transport and transmission electron microscopy study. Our studies of individual perovskite microplates with variable thicknesses demonstrate that the phase transition temperature decreases with reducing microplate thickness. The sudden decrease of mobility around phase transition temperature and the presence of hysteresis loops in the temperature-dependent mobility confirm that the orthorhombic-to-tetragonal phase transition is a first-order phase transition. Our findings offer significant fundamental insight on the temperature- and size-dependent structural, optical and charge transport properties of perovskite materials, and can greatly impact future exploration of novel electronic and optoelectronic devices from these materials. PMID:27098114

Size-dependent phase transition in methylammonium lead iodide perovskite microplate crystals

DOE PAGES

Li, Dehui; Wang, Gongming; Cheng, Hung -Chieh; ...

2016-04-21

Methylammonium lead iodide perovskite has attracted considerable recent interest for solution processable solar cells and other optoelectronic applications. The orthorhombic-to-tetragonal phase transition in perovskite can significantly alter its optical, electrical properties and impact the corresponding applications. Here, we report a systematic investigation of the size-dependent orthorhombic-to-tetragonal phase transition using a combined temperature-dependent optical, electrical transport and transmission electron microscopy study. Our studies of individual perovskite microplates with variable thicknesses demonstrate that the phase transition temperature decreases with reducing microplate thickness. The sudden decrease of mobility around phase transition temperature and the presence of hysteresis loops in the temperature-dependent mobility confirmmore » that the orthorhombic-to-tetragonal phase transition is a first-order phase transition. Lastly, our findings offer significant fundamental insight on the temperature-and size-dependent structural, optical and charge transport properties of perovskite materials, and can greatly impact future exploration of novel electronic and optoelectronic devices from these materials.« less

Rheological study of clay-kaolin aqueous suspensions

NASA Technical Reports Server (NTRS)

Lapasin, R.; Lucchini, F.

1984-01-01

Rheological characteristics of clay-kaolin aqueous suspensions were studied by a rotational viscometer to correlate their behavior with the properties of ceramic slips for casting containing quartz, feldspars, and other nonplastic materials. In particular, the effects of the different amounts of dry materials and deflocculant (mixture 1:1 of Na2CO3 and Na2SiO3) and of temperatures on the shear-time-dependent properties of suspensions were examined.

Simultaneous measurement of thermal conductivity and heat capacity of bulk and thin film materials using frequency-dependent transient thermoreflectance method.

PubMed

Liu, Jun; Zhu, Jie; Tian, Miao; Gu, Xiaokun; Schmidt, Aaron; Yang, Ronggui

2013-03-01

The increasing interest in the extraordinary thermal properties of nanostructures has led to the development of various measurement techniques. Transient thermoreflectance method has emerged as a reliable measurement technique for thermal conductivity of thin films. In this method, the determination of thermal conductivity usually relies much on the accuracy of heat capacity input. For new nanoscale materials with unknown or less-understood thermal properties, it is either questionable to assume bulk heat capacity for nanostructures or difficult to obtain the bulk form of those materials for a conventional heat capacity measurement. In this paper, we describe a technique for simultaneous measurement of thermal conductivity κ and volumetric heat capacity C of both bulk and thin film materials using frequency-dependent time-domain thermoreflectance (TDTR) signals. The heat transfer model is analyzed first to find how different combinations of κ and C determine the frequency-dependent TDTR signals. Simultaneous measurement of thermal conductivity and volumetric heat capacity is then demonstrated with bulk Si and thin film SiO2 samples using frequency-dependent TDTR measurement. This method is further testified by measuring both thermal conductivity and volumetric heat capacity of novel hybrid organic-inorganic thin films fabricated using the atomic∕molecular layer deposition. Simultaneous measurement of thermal conductivity and heat capacity can significantly shorten the development∕discovery cycle of novel materials.

Algorithmic implementation of particle-particle ladder diagram approximation to study strongly-correlated metals and semiconductors

NASA Astrophysics Data System (ADS)

Prayogi, A.; Majidi, M. A.

2017-07-01

In condensed-matter physics, strongly-correlated systems refer to materials that exhibit variety of fascinating properties and ordered phases, depending on temperature, doping, and other factors. Such unique properties most notably arise due to strong electron-electron interactions, and in some cases due to interactions involving other quasiparticles as well. Electronic correlation effects are non-trivial that one may need a sufficiently accurate approximation technique with quite heavy computation, such as Quantum Monte-Carlo, in order to capture particular material properties arising from such effects. Meanwhile, less accurate techniques may come with lower numerical cost, but the ability to capture particular properties may highly depend on the choice of approximation. Among the many-body techniques derivable from Feynman diagrams, we aim to formulate algorithmic implementation of the Ladder Diagram approximation to capture the effects of electron-electron interactions. We wish to investigate how these correlation effects influence the temperature-dependent properties of strongly-correlated metals and semiconductors. As we are interested to study the temperature-dependent properties of the system, the Ladder diagram method needs to be applied in Matsubara frequency domain to obtain the self-consistent self-energy. However, at the end we would also need to compute the dynamical properties like density of states (DOS) and optical conductivity that are defined in the real frequency domain. For this purpose, we need to perform the analytic continuation procedure. At the end of this study, we will test the technique by observing the occurrence of metal-insulator transition in strongly-correlated metals, and renormalization of the band gap in strongly-correlated semiconductors.

Wood properties affecting finish service life

Treesearch

R. Sam Williams; Charles Jourdain; George I. Daisey; Robert W. Springate

2000-01-01

Wood is a biological material that has widely different properties depending on species, geographic area where the tree grew, the growth conditions, size of the tree at harvest, sawing, and other manufacturing processes. Some of the more important wood properties as they relate to wood finishing are discussed, e.g., growth rate, density, knots, extractives, juvenile...

Finite Element Analysis of Eutectic Structures

DTIC Science & Technology

2014-03-12

Reported are the details of processing conditions, microstructure development, and temperature dependent thermoelectric properties . The material system...Sootsman et al ., Microstructure and Thermoelectric Properties of Mechanically Robust PbTe-Si Eutectic Composites, Chem. Mater. 22 (2010) 869. 7. J...Professor) CASE WESTERN RESERVE UNIVERSTY Thermoelectric Properties of WSi2-SixGe1-x Composites Thermoelectric properties of the W/Si/Ge alloy

Structure and Magnetic Properties of Rare Earth Doped Transparent Alumina

NASA Astrophysics Data System (ADS)

Limmer, Krista; Neupane, Mahesh; Chantawansri, Tanya

Recent experimental studies of rare earth (RE) doped alumina suggest that the RE induced novel phase-dependent structural and magnetic properties. Motivated by these efforts, the effects of RE doping of alpha and theta alumina on the local structure, magnetic properties, and phase stability have been examined in this first principles study. Although a direct correlation between the magnetic field dependent materials properties observed experimentally and calculated from first principles is not feasible because of the applied field and the scale, the internal magnetic properties and other properties of the doped materials are evaluated. The RE dopants are shown to increase the substitutional site volume as well as increasingly distort the site structure as a function of ionic radii. Doping both the alpha (stable) and theta (metastable) phases enhanced the relative stability of the theta phase. The energetic doping cost and internal magnetic moment were shown to be a function of the electronic configuration of the RE-dopant, with magnetic moment directly proportional to the number of unpaired electrons and doping cost being inversely related.

The Effects of Fiber Orientation and Volume Fraction of Fiber on Mechanical Properties of Additively Manufactured Composite Material

NASA Astrophysics Data System (ADS)

Kuchipudi, Suresh Chandra

Additive manufacturing (AM) also known as 3D printing has tremendous advancements in recent days with a vast number of applications in industrial, automotive, architecture, consumer projects, fashion, toys, food, art, etc. Composite materials are widely used in structures with weight as a critical factor especially in aerospace industry. Recently, additive manufacturing technology, a rapidly growing innovative technology, has gained lot of importance in making composite materials. The properties of composite materials depend upon the properties of constituent's matrix and fiber. There is lot of research on effect of fiber orientation on mechanical properties of composite materials made using conventional manufacturing methods. It will be interesting and relevant to study the relationship between the fiber orientation and fiber volume with mechanical properties of additively manufactured composite materials. This thesis work presents experimental investigation of mechanical behavior like tensile strength and fatigue life with variation in fiber orientation and fiber volume fraction of 3D printed composite materials. The aim is to study the best combination of volume fraction of fiber and fiber orientation that has better fatigue strength for additive manufactured composite materials. Using this study, we can decide the type of orientation and volume percent for desired properties. This study also finds the range of fatigue limits of 3d printed composite materials.

Comparison of Predicted Thermoelectric Energy Conversion Efficiency by Cumulative Properties and Reduced Variables Approaches

NASA Astrophysics Data System (ADS)

Linker, Thomas M.; Lee, Glenn S.; Beekman, Matt

2018-06-01

The semi-analytical methods of thermoelectric energy conversion efficiency calculation based on the cumulative properties approach and reduced variables approach are compared for 21 high performance thermoelectric materials. Both approaches account for the temperature dependence of the material properties as well as the Thomson effect, thus the predicted conversion efficiencies are generally lower than that based on the conventional thermoelectric figure of merit ZT for nearly all of the materials evaluated. The two methods also predict material energy conversion efficiencies that are in very good agreement which each other, even for large temperature differences (average percent difference of 4% with maximum observed deviation of 11%). The tradeoff between obtaining a reliable assessment of a material's potential for thermoelectric applications and the complexity of implementation of the three models, as well as the advantages of using more accurate modeling approaches in evaluating new thermoelectric materials, are highlighted.

Superhydrophobic Silicon Nanocrystal-Silica Aerogel Hybrid Materials: Synthesis, Properties, and Sensing Application.

PubMed

Kehrle, Julian; Purkait, Tapas K; Kaiser, Simon; Raftopoulos, Konstantinos N; Winnacker, Malte; Ludwig, Theresa; Aghajamali, Maryam; Hanzlik, Marianne; Rodewald, Katia; Helbich, Tobias; Papadakis, Christine M; Veinot, Jonathan G C; Rieger, Bernhard

2018-04-24

Silicon nanocrystals (SiNCs) are abundant and exhibit exquisitely tailorable optoelectronic properties. The incorporation of SiNCs into highly porous and lightweight substrates such as aerogels leads to hybrid materials possessing the attractive features of both materials. This study describes the covalent deposition of SiNCs on and intercalation into silica aerogels, explores the properties, and demonstrates a prototype sensing application of the composite material. SiNCs of different sizes were functionalized with triethoxyvinylsilane (TEVS) via a radical grafting approach and subsequently used for the synthesis of photoluminescent silica hybrids. The resulting SiNC-containing aerogels possess high porosities, SiNC-based size-dependent photoluminescence, transparency, and a superhydrophobic macroscopic surface. The materials were used to examine the photoluminescence response toward low concentrations of 3-nitrotoluene (270 μM), demonstrating their potential as a sensing platform for high-energy materials.

Hydrophobic Materials Based on Salts of Di(2-ethylhexyl)phosphoric Acid

NASA Astrophysics Data System (ADS)

Kizim, N. F.; Golubina, E. N.

2018-03-01

Interfacial formations of material based on metals di(2-ethylhexyl)phosphates of various metals exhibit hydrophobic properties. The contact angle of the surface, modified by the interfacial formations materials, could reach up to 140° depending on the nature of the solvent, the metal salt, the number of applications.

Polarization dependence of laser interaction with carbon fibers and CFRP.

PubMed

Freitag, Christian; Weber, Rudolf; Graf, Thomas

2014-01-27

A key factor for laser materials processing is the absorptivity of the material at the laser wavelength, which determines the fraction of the laser energy that is coupled into the material. Based on the Fresnel equations, a theoretical model is used to determine the absorptivity for carbon fiber fabrics and carbon fiber reinforced plastics (CFRP). The surface of each carbon fiber is considered as multiple layers of concentric cylinders of graphite. With this the optical properties of carbon fibers and their composites can be estimated from the well-known optical properties of graphite.

Performance and properties of atomic oxygen protective coatings for polymeric materials

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Lamoreaux, Cynthia

1992-01-01

Such large LEO spacecraft as the Space Station Freedom will encounter high atomic oxygen fluences which entail the use of protective coatings for their polymeric structural materials. Such coatings have demonstrated polymer mass losses due to oxidation that are much smaller than those of unprotected materials. Attention is here given to protective and/or electrically conductive coatings of SiO(x), Ge, and indium-tin oxide which have been exposed to atomic oxygen in order to ascertain mass loss, electrical conductivity, and optical property dependence on atomic oxygen exposure.

Development of a Novel Method for Determination of Residual Stresses in a Friction Stir Weld

NASA Technical Reports Server (NTRS)

Reynolds, Anthony P.

2001-01-01

Material constitutive properties, which describe the mechanical behavior of a material under loading, are vital to the design and implementation of engineering materials. For homogeneous materials, the standard process for determining these properties is the tensile test, which is used to measure the material stress-strain response. However, a majority of the applications for engineering materials involve the use of heterogeneous materials and structures (i.e. alloys, welded components) that exhibit heterogeneity on a global or local level. Regardless of the scale of heterogeneity, the overall response of the material or structure is dependent on the response of each of the constituents. Therefore, in order to produce materials and structures that perform in the best possible manner, the properties of the constituents that make up the heterogeneous material must be thoroughly examined. When materials exhibit heterogeneity on a local level, such as in alloys or particle/matrix composites, they are often treated as statistically homogenous and the resulting 'effective' properties may be determined through homogenization techniques. In the case of globally heterogeneous materials, such as weldments, the standard tensile test provides the global response but no information on what is Occurring locally within the different constituents. This information is necessary to improve the material processing as well as the end product.

Shape-dependent electronic properties of blue phosphorene nano-flakes

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

Bhatia, Pradeep; Swaroop, Ram; Kumar, Ashok, E-mail: ashok@cup.ac.in

In recent year’s considerable attention has been given to the first principles method for modifying and controlling electronic properties of nano-materials. We performed DFT-based calculations on the electronic properties of zigzag-edged nano-flakes of blue phosphorene with three possible shapes namely rectangular, triangular and hexagonal. We observed that HOMO-LUMO gap of zigzag phosphorene nano-flakes with different shapes is ∼2.9 eV with H-passivations and ∼0.7 – 1.2 eV in pristine cases. Electronic properties of blue phosphorene nano-flakes show the strong dependence on their shape. We observed that distributions of molecular orbitals were strongly affected by the different shapes. Zigzag edged considered nanostructuresmore » are non-magnetic and semiconducting in nature. The shape dependent electronic properties may find applications in tunable nano-electronics.« less

Designing for time-dependent material response in spacecraft structures

NASA Technical Reports Server (NTRS)

Hyer, M. W.; Oleksuk, Lynda L. S.; Bowles, D. E.

1992-01-01

To study the influence on overall deformations of the time-dependent constitutive properties of fiber-reinforced polymeric matrix composite materials being considered for use in orbiting precision segmented reflectors, simple sandwich beam models are developed. The beam models include layers representing the face sheets, the core, and the adhesive bonding of the face sheets to the core. A three-layer model lumps the adhesive layers with the face sheets or core, while a five-layer model considers the adhesive layers explicitly. The deformation response of the three-layer and five-layer sandwich beam models to a midspan point load is studied. This elementary loading leads to a simple analysis, and it is easy to create this loading in the laboratory. Using the correspondence principle of viscoelasticity, the models representing the elastic behavior of the two beams are transformed into time-dependent models. Representative cases of time-dependent material behavior for the facesheet material, the core material, and the adhesive are used to evaluate the influence of these constituents being time-dependent on the deformations of the beam. As an example of the results presented, if it assumed that, as a worst case, the polymer-dominated shear properties of the core behave as a Maxwell fluid such that under constant shear stress the shear strain increases by a factor of 10 in 20 years, then it is shown that the beam deflection increases by a factor of 1.4 during that time. In addition to quantitative conclusions, several assumptions are discussed which simplify the analyses for use with more complicated material models. Finally, it is shown that the simpler three-layer model suffices in many situations.

Harman Measurements for Thermoelectric Materials and Modules under Non-Adiabatic Conditions

NASA Astrophysics Data System (ADS)

Roh, Im-Jun; Lee, Yun Goo; Kang, Min-Su; Lee, Jae-Uk; Baek, Seung-Hyub; Kim, Seong Keun; Ju, Byeong-Kwon; Hyun, Dow-Bin; Kim, Jin-Sang; Kwon, Beomjin

2016-12-01

Accuracy of the Harman measurement largely depends on the heat transfer between the sample and its surroundings, so-called parasitic thermal effects (PTEs). Similar to the material evaluations, measuring thermoelectric modules (TEMs) is also affected by the PTEs especially when measuring under atmospheric condition. Here, we study the correction methods for the Harman measurements with systematically varied samples (both bulk materials and TEMs) at various conditions. Among several PTEs, the heat transfer via electric wires is critical. Thus, we estimate the thermal conductance of the electric wires, and correct the measured properties for a certain sample shape and measuring temperature. The PTEs are responsible for the underestimation of the TEM properties especially under atmospheric conditions (10-35%). This study will be useful to accurately characterize the thermoelectric properties of materials and modules.

Properties of three graphite/toughened resin composites

NASA Technical Reports Server (NTRS)

Smith, Donald L.; Dow, Marvin B.

1991-01-01

Results are presented from an experimental evaluation of IM7/977-2, IM7/F655, and T800/F3900. Data presented include ply-level (unidirectional laminate) strength and moduli, unnotched and notched (open hole) tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths. These data are compared with properties of other toughened (IM7/8551-7 and IM6/18081) and brittle (T300/5208) graphite-epoxy materials. The IM7/977-2, IM7/F655, and T800/F3900 materials are substantially stronger and more damage tolerant than widely used first generation composite materials such as T300/5208. The T800/F3900 outperforms IM7/977-2 and IM7/F655 materials in tolerance to projectile impacts. Compression-after-impact strengths were found to be dependent on impactor velocity for a given impact energy. The open hole compression properties of all three materials are degraded by the combination of heat and moisture.

Elucidating Multiscale Periosteal Mechanobiology: A Key to Unlocking the Smart Properties and Regenerative Capacity of the Periosteum?

PubMed Central

Evans, Sarah F.; Chang, Hana

2013-01-01

The periosteum, a thin, fibrous tissue layer covering most bones, resides in a dynamic, mechanically loaded environment. The periosteum also provides a niche for mesenchymal stem cells. The mechanics of periosteum vary greatly between species and anatomical locations, indicating the specialized role of periosteum as bone's bounding membrane. Furthermore, periosteum exhibits stress-state-dependent mechanical and material properties, hallmarks of a smart material. This review discusses what is known about the multiscale mechanical and material properties of the periosteum as well as their potential effect on the mechanosensitive progenitor cells within the tissue. Furthermore, this review addresses open questions and barriers to understanding periosteum's multiscale structure–function relationships. Knowledge of the smart material properties of the periosteum will maximize the translation of periosteum and substitute periosteum to regenerative medicine, facilitate the development of biomimetic tissue-engineered periosteum for use in instances where the native periosteum is lacking or damaged, and provide inspiration for a new class of smart, advanced materials. PMID:23189933

Morphology, stoichiometry, and crystal structure control via post-annealing for Pt-ZnO nanograin Schottky barrier interfaces

NASA Astrophysics Data System (ADS)

Chan, Yuet Ching; Yu, Jerry; Ho, Derek

2018-06-01

Nanointerfaces have attracted intensive research effort for advanced electronics due to their unique and tunable semiconducting properties made possible by metal-contacted oxide structures at the nanoscale. Although much work has been on the adjustment of fabrication parameters to achieve high-quality interfaces, little work has experimentally obtained the various correlations between material parameters and Schottky barrier electronic properties to accurately probe the underlying phenomenon. In this work, we investigate the control of Pt-ZnO nanograin interfaces properties by thermal annealing. Specifically, we quantitatively analyze the correlation between material parameters (such as surface morphology, crystallographic structure, and stoichiometry) and Schottky diode parameters (Schottky barrier height, ideality factor, and contact resistance). Results revealed strong dependencies of Schottky barrier characteristics on oxygen vacancies, surface roughness, grain density, d-spacing, and crystallite size. I-V-T data shows that annealing at 600 °C produces a nanograin based interface with the most rectifying diode characteristics. These dependencies, which have not been previously reported holistically, highlight the close relationship between material properties and Schottky barrier characteristics, and are instrumental for the performance optimization of nanostructured metal-semiconductor interfaces in advanced electronic devices.

Molecular dynamic simulation for nanometric cutting of single-crystal face-centered cubic metals.

PubMed

Huang, Yanhua; Zong, Wenjun

2014-01-01

In this work, molecular dynamics simulations are performed to investigate the influence of material properties on the nanometric cutting of single crystal copper and aluminum with a diamond cutting tool. The atomic interactions in the two metallic materials are modeled by two sets of embedded atom method (EAM) potential parameters. Simulation results show that although the plastic deformation of the two materials is achieved by dislocation activities, the deformation behavior and related physical phenomena, such as the machining forces, machined surface quality, and chip morphology, are significantly different for different materials. Furthermore, the influence of material properties on the nanometric cutting has a strong dependence on the operating temperature.

Photoconductivity in Dirac materials

NASA Astrophysics Data System (ADS)

Shao, J. M.; Yang, G. W.

2015-11-01

Two-dimensional (2D) Dirac materials including graphene and the surface of a three-dimensional (3D) topological insulator, and 3D Dirac materials including 3D Dirac semimetal and Weyl semimetal have attracted great attention due to their linear Dirac nodes and exotic properties. Here, we use the Fermi's golden rule and Boltzmann equation within the relaxation time approximation to study and compare the photoconductivity of Dirac materials under different far- or mid-infrared irradiation. Theoretical results show that the photoconductivity exhibits the anisotropic property under the polarized irradiation, but the anisotropic strength is different between 2D and 3D Dirac materials. The photoconductivity depends strongly on the relaxation time for different scattering mechanism, just like the dark conductivity.

Characterization of viscoelastic response and damping of composite materials used in flywheel rotors

NASA Astrophysics Data System (ADS)

Chen, Jianmin

The long-term goal for spacecraft flywheel systems with higher energy density at the system level requires new and innovative composite material concepts. Multi-Direction Composite (MDC) offers significant advantages over traditional filament-wound and multi-ring press-fit filament-wound wheels in providing higher energy density (i.e., less mass), better crack resistance, and enhanced safety. However there is a lack of systematic characterization for dynamic properties of MDC composite materials. In order to improve the flywheel materials reliability, durability and life time, it is very important to evaluate the time dependent aging effects and damping properties of MDC material, which are significant dynamic parameter for vibration and sound control, fatigue endurance, and impact resistance. The physical aging effects are quantified based on a set of creep curves measured at different aging time or different aging temperature. One parameter (tau) curve fit was proposed to represent the relationship of aging time and aging temperature between different master curves. The long term mechanical behavior was predicted by obtained master curves. The time and temperature shift factors of matrix were obtained from creep curves and the aging time shift rate were calculated. The aging effects on composite are obtained from experiments and compared with prediction. The mechanical quasi-behavior of MDC composite was analyzed. The correspondence principle was used to relate quasi-static elastic properties of composite materials to time-dependent properties of its constituent materials (i.e., fiber and matrix). The Prony series combined with the multi-data fitting method was applied to inverse Laplace transform and to calculate the time dependent stiffness matrix effectively. Accelerated time-dependent deformation of two flywheel rim designs were studied for a period equivalent to 31 years and are compared with hoop reinforcement only composite. Damping of pure resin and T700/epoxy composite lamina and laminate in longitudinal and transverse directions were investigated experimentally and analytically. The effect of aging on damping was also studied by placing samples at 60°C in an oven for extended periods. Damping master curves versus frequency were constructed from individual curves at different temperatures based on the Arrhenius equation. The damping response of the composite lamina was used to predict the response of laminate composites. Analytical results give close numerical values to experimental results from damping of cantilever beam laminated composite samples.

Thermal properties of alkali-activated aluminosilicates with CNT admixture

NASA Astrophysics Data System (ADS)

Zmeskal, Oldrich; Trhlikova, Lucie; Fiala, Lukas; Florian, Pavel; Cerny, Robert

2017-07-01

Material properties of electrically conductive cement-based materials with increased attention paid on electric and thermal properties were often studied in the last years. Both electric and thermal properties play an important role thanks to their possible utilization in various practical applications (e.g. snow-melting systems or building structures monitoring systems without the need of an external monitoring system). The DC/AC characteristics depend significantly on the electrical resistivity and the electrical capacity of bulk materials. With respect to the DC/AC characteristics of cement-based materials, such materials can be basically classified as electric insulators. In order to enhance them, various conductive admixtures such as those based on different forms of carbon, can be used. Typical representatives of carbon-based admixtures are carbon nanotubes (CNT), carbon fibers (CF), graphite powder (GP) and carbon black (CB). With an adequate amount of such admixtures, electric properties significantly change and new materials with higher added value can be prepared. However, other types of materials can be enhanced in the same way. Alkali-activated aluminosilicates (AAA) based on blast furnace slag are materials with high compressive strength comparable with cement-based materials. Moreover, the price of slag is lower than of Portland cement. Therefore, this paper deals with the study of thermal properties of this promising material with different concentrations of CNT. Within the paper a simple method of basic thermal parameters determination based on the thermal transient response to a heat power step is presented.

Influence of Composition on the Thermoelectric Properties of Bi1- x Sb x Thin Films

NASA Astrophysics Data System (ADS)

Rogacheva, E. I.; Nashchekina, O. N.; Orlova, D. S.; Doroshenko, A. N.; Dresselhaus, M. S.

2017-07-01

Bi1- x Sb x solid solutions have attracted much attention as promising thermoelectric (TE) materials for cooling devices at temperatures below ˜200 K and as unique model materials for solid-state science because of a high sensitivity of their band structure to changes in composition, temperature, pressure, etc. Earlier, we revealed a non-monotonic behavior of the concentration dependences of TE properties for polycrystalline Bi1- x Sb x solid solutions and attributed these anomalies to percolation effects in the solid solution, transition to a gapless state, and to a semimetal-semiconductor transition. The goal of the present work is to find out whether the non-monotonic behavior of the concentration dependences of TE properties is observed in the thin film state as well. The objects of the study are Bi1- x Sb x thin films with thicknesses in the range d = 250-300 nm prepared by thermal evaporation of Bi1- x Sb x crystals ( x = 0-0.09) onto mica substrates. It was shown that the anomalies in the dependence of the TE properties on Bi1- x Sb x crystal composition are reproduced in thin films.

Distributional Preferences, Reciprocity-Like Behavior, and Efficiency in Bilateral Exchange

PubMed Central

Benjamin, Daniel J.

2014-01-01

Under what conditions do distributional preferences, such as altruism or a concern for fair outcomes, generate efficient trade? I analyze theoretically a simple bilateral exchange game: each player sequentially takes an action that reduces his own material payoff but increases the other player’s. Each player’s preferences may depend on both his/her own material payoff and the other player’s. I identify two key properties of the second-mover’s preferences: indifference curves kinked around “fair” material-payoff distributions, and materials payoffs entering preferences as “normal goods.” Either property can drive reciprocity-like behavior and generate a Pareto efficient outcome. PMID:25664144

Direct observation of mode-specific phonon-band gap coupling in methylammonium lead halide perovskites.

PubMed

Kim, Heejae; Hunger, Johannes; Cánovas, Enrique; Karakus, Melike; Mics, Zoltán; Grechko, Maksim; Turchinovich, Dmitry; Parekh, Sapun H; Bonn, Mischa

2017-09-25

Methylammonium lead iodide perovskite is an outstanding semiconductor for photovoltaics. One of its intriguing peculiarities is that the band gap of this perovskite increases with increasing lattice temperature. Despite the presence of various thermally accessible phonon modes in this soft material, the understanding of how precisely these phonons affect macroscopic material properties and lead to the peculiar temperature dependence of the band gap has remained elusive. Here, we report a strong coupling of a single phonon mode at the frequency of ~ 1 THz to the optical band gap by monitoring the transient band edge absorption after ultrafast resonant THz phonon excitation. Excitation of the 1 THz phonon causes a blue shift of the band gap over the temperature range of 185 ~ 300 K. Our results uncover the mode-specific coupling between one phonon and the optical properties, which contributes to the temperature dependence of the gap in the tetragonal phase.Methylammonium lead iodide perovskite, a promising material for efficient photovoltaics, shows a unique temperature dependence of its optical properties. Kim et al. quantify the coupling between the optical gap and a lattice phonon at 1 THz, which favorably contributes to the thermal variation of the gap.

Screening and transport in 2D semiconductor systems at low temperatures

PubMed Central

Das Sarma, S.; Hwang, E. H.

2015-01-01

Low temperature carrier transport properties in 2D semiconductor systems can be theoretically well-understood within RPA-Boltzmann theory as being limited by scattering from screened Coulomb disorder arising from random quenched charged impurities in the environment. In this work, we derive a number of analytical formula, supported by realistic numerical calculations, for the relevant density, mobility, and temperature range where 2D transport should manifest strong intrinsic (i.e., arising purely from electronic effects) metallic temperature dependence in different semiconductor materials arising entirely from the 2D screening properties, thus providing an explanation for why the strong temperature dependence of the 2D resistivity can only be observed in high-quality and low-disorder 2D samples and also why some high-quality 2D materials manifest much weaker metallicity than other materials. We also discuss effects of interaction and disorder on the 2D screening properties in this context as well as compare 2D and 3D screening functions to comment why such a strong intrinsic temperature dependence arising from screening cannot occur in 3D metallic carrier transport. Experimentally verifiable predictions are made about the quantitative magnitude of the maximum possible low-temperature metallicity in 2D systems and the scaling behavior of the temperature scale controlling the quantum to classical crossover. PMID:26572738

Prediction of Process-Induced Distortions in L-Shaped Composite Profiles Using Path-Dependent Constitutive Law

NASA Astrophysics Data System (ADS)

Ding, Anxin; Li, Shuxin; Wang, Jihui; Ni, Aiqing; Sun, Liangliang; Chang, Lei

2016-10-01

In this paper, the corner spring-in angles of AS4/8552 L-shaped composite profiles with different thicknesses are predicted using path-dependent constitutive law with the consideration of material properties variation due to phase change during curing. The prediction accuracy mainly depends on the properties in the rubbery and glassy states obtained by homogenization method rather than experimental measurements. Both analytical and finite element (FE) homogenization methods are applied to predict the overall properties of AS4/8552 composite. The effect of fiber volume fraction on the properties is investigated for both rubbery and glassy states using both methods. And the predicted results are compared with experimental measurements for the glassy state. Good agreement is achieved between the predicted results and available experimental data, showing the reliability of the homogenization method. Furthermore, the corner spring-in angles of L-shaped composite profiles are measured experimentally and the reliability of path-dependent constitutive law is validated as well as the properties prediction by FE homogenization method.

Materials Selection for Aerospace Systems

NASA Technical Reports Server (NTRS)

Arnold, Steven M.; Cebon, David; Ashby, Mike

2012-01-01

A systematic design-oriented, five-step approach to material selection is described: 1) establishing design requirements, 2) material screening, 3) ranking, 4) researching specific candidates and 5) applying specific cultural constraints to the selection process. At the core of this approach is the definition performance indices (i.e., particular combinations of material properties that embody the performance of a given component) in conjunction with material property charts. These material selection charts, which plot one property against another, are introduced and shown to provide a powerful graphical environment wherein one can apply and analyze quantitative selection criteria, such as those captured in performance indices, and make trade-offs between conflicting objectives. Finding a material with a high value of these indices maximizes the performance of the component. Two specific examples pertaining to aerospace (engine blades and pressure vessels) are examined, both at room temperature and elevated temperature (where time-dependent effects are important) to demonstrate the methodology. The discussion then turns to engineered/hybrid materials and how these can be effectively tailored to fill in holes in the material property space, so as to enable innovation and increases in performance as compared to monolithic materials. Finally, a brief discussion is presented on managing the data needed for materials selection, including collection, analysis, deployment, and maintenance issues.

Structure and transport properties of dense polycrystalline clathrate-II (K,Ba) 16(Ga,Sn) 136 synthesized by a new approach employing SPS

DOE PAGES

Wei, Kaya; Zeng, Xiaoyu; Tritt, Terry M.; ...

2016-08-26

Tin clathrate-II framework-substituted compositions are of current interest as potential thermoelectric materials for medium-temperature applications. A review of the literature reveals different compositions reported with varying physical properties, which depend strongly on the exact composition as well as the processing conditions. We therefore initiated an approach whereby single crystals of two different (K,Ba) 16(Ga,Sn) 136 compositions were first obtained, followed by grinding of the crystals into fine powder for low temperature spark plasma sintering consolidation into dense polycrystalline solids and subsequent high temperature transport measurements. Powder X-ray refinement results indicate that the hexakaidecahedra are empty, K and Ba occupying onlymore » the decahedra. Their electrical properties depend on composition and have very low thermal conductivities. As a result, the structural and transport properties of these materials are compared to that of other Sn clathrate-II compositions.« less

Optically inactive defects in monolayer and bilayer phosphorene: A first-principles study

NASA Astrophysics Data System (ADS)

Huang, Ling-yi; Zhang, Xu; Zhang, Mingliang; Lu, Gang

2018-05-01

Many-body excitonic effect is crucial in two-dimensional (2D) materials and can significantly impact their optoelectronic properties. Because defects are inevitable in 2D materials, understanding how they influence the optical and excitonic properties of the 2D materials is of significant scientific and technological importance. Here we focus on intrinsic point defects in monolayer and bilayer phosphorene and examine whether and how their optoelectronic properties may be modified by the defects. Based on large-scale first-principles calculations, we have systematically explored the optical and excitonic properties of phosphorene in the presence and absence of the point defects. We find that the optical properties of bilayer phosphorene depend on the stacking order of the layers. More importantly, we reveal that the dominant point defects in few-layer phosphorene are optically inactive, which renders phosphorene particularly attractive in optoelectronic applications.

Better Modeling of Electrostatic Discharge in an Insulator

NASA Technical Reports Server (NTRS)

Pekov, Mihail

2010-01-01

An improved mathematical model has been developed of the time dependence of buildup or decay of electric charge in a high-resistivity (nominally insulating) material. The model is intended primarily for use in extracting the DC electrical resistivity of such a material from voltage -vs.- current measurements performed repeatedly on a sample of the material over a time comparable to the longest characteristic times (typically of the order of months) that govern the evolution of relevant properties of the material. This model is an alternative to a prior simplistic macroscopic model that yields results differing from the results of the time-dependent measurements by two to three orders of magnitude.

Review on factors influencing thermal conductivity of concrete incorporating various type of waste materials

NASA Astrophysics Data System (ADS)

Misri, Z.; Ibrahim, M. H. W.; Awal, A. S. M. A.; Desa, M. S. M.; Ghadzali, N. S.

2018-04-01

Concrete is well-known as a construction material which is widely used in building and infrastructure around the world. However, its widespread use has affected the reduction of natural resources. Hence, many approached have been made by researchers to study the incorporation of waste materials in concrete as a substitution for natural resources besides reducing waste disposal problems. Concrete is basically verified by determining its properties; strengths, permeability, shrinkage, durability, thermal properties etc. In various thermal properties of concrete, thermal conductivity (TC) has received a large amount of attention because it is depend upon the composition of concrete. Thermal conductivity is important in building insulation to measure the ability of a material to transfer heat. The aim of this paper is to discuss the methods and influence factors of TC of concrete containing various type of waste materials.

Extrinsic Contribution and Instability Properties in Lead-Based and Lead-Free Piezoceramics

PubMed Central

García, José Eduardo

2015-01-01

Piezoceramic materials generally exhibit a notable instability of their functional properties when they work under real external conditions. This undesirable effect, known as nonlinear behavior, is mostly associated with the extrinsic contribution to material response. In this article, the role of the ferroelectric domain walls’ motion in the nonlinear response in the most workable lead-based and lead-free piezoceramics is reviewed. Initially, the extrinsic origin of the nonlinear response is discussed in terms of the temperature dependence of material response. The influence of the crystallographic phase and of the phase boundaries on the material response are then reviewed. Subsequently, the impact of the defects created by doping in order to control the extrinsic contribution is discussed as a way of tuning material properties. Finally, some aspects related to the grain-size effect on the nonlinear response of piezoceramics are surveyed. PMID:28793681

Application of Glass Fiber Waste Polypropylene Aggregate in Lightweight Concrete – thermal properties

NASA Astrophysics Data System (ADS)

Citek, D.; Rehacek, S.; Pavlik, Z.; Kolisko, J.; Dobias, D.; Pavlikova, M.

2018-03-01

Actual paper focus on thermal properties of a sustainable lightweight concrete incorporating high volume of waste polypropylene aggregate as partial substitution of natural aggregate. In presented experiments a glass fiber reinforced polypropylene (GFPP) which is a by-product of PP tubes production, partially substituted fine natural silica aggregate in 10, 20, 30, 40 and 50 mass %. Results were compared with a reference concrete mix without plastic waste in order to quantify the effect of GFPP use on concrete properties. Main material physical parameters were studied (bulk density, matrix density without air content, and particle size distribution). Especially a thermal transport and storage properties of GFPP were examined in dependence on compaction time. For the developed lightweight concrete, thermal properties were accessed using transient impulse technique, where the measurement was done in dependence on moisture content (from the fully water saturated state to dry state). It was found that the tested lightweight concrete should be prospective construction material possessing improved thermal insulation function and the reuse of waste plastics in concrete composition was beneficial both from the environmental and financial point of view.

Effect of crystallographic orientations of grains on the global mechanical properties of steel sheets by depth sensing indentation

NASA Astrophysics Data System (ADS)

Burik, P.; Pesek, L.; Kejzlar, P.; Andrsova, Z.; Zubko, P.

2017-01-01

The main idea of this work is using a physical model to prepare a virtual material with required properties. The model is based on the relationship between the microstructure and mechanical properties. The macroscopic (global) mechanical properties of steel are highly dependent upon microstructure, crystallographic orientation of grains, distribution of each phase present, etc... We need to know the local mechanical properties of each phase separately in multiphase materials. The grain size is a scale, where local mechanical properties are responsible for the behavior. Nanomechanical testing using depth sensing indentation (DSI) provides a straightforward solution for quantitatively characterizing each of phases in microstructure because it is very powerful technique for characterization of materials in small volumes. The aim of this experimental investigation is: (i) to prove how the mixing rule works for local mechanical properties (indentation hardness HIT) in microstructure scale using the DSI technique on steel sheets with different microstructure; (ii) to compare measured global properties with properties achieved by mixing rule; (iii) to analyze the effect of crystallographic orientations of grains on the mixing rule.

Predicting the optoelectronic properties of nanowire films based on control of length polydispersity

NASA Astrophysics Data System (ADS)

Large, Matthew J.; Burn, Jake; King, Alice A.; Ogilvie, Sean P.; Jurewicz, Izabela; Dalton, Alan B.

2016-05-01

We demonstrate that the optoelectronic properties of percolating thin films of silver nanowires (AgNWs) are predominantly dependent upon the length distribution of the constituent AgNWs. A generalized expression is derived to describe the dependence of both sheet resistance and optical transmission on this distribution. We experimentally validate the relationship using ultrasonication to controllably vary the length distribution. These results have major implications where nanowire-based films are a desirable material for transparent conductor applications; in particular when application-specific performance criteria must be met. It is of particular interest to have a simple method to generalize the properties of bulk films from an understanding of the base material, as this will speed up the optimisation process. It is anticipated that these results may aid in the adoption of nanowire films in industry, for applications such as touch sensors or photovoltaic electrode structures.

High Volume Fraction Carbon Nanotube Composites for Aerospace Applications

NASA Technical Reports Server (NTRS)

Siochi, E. J.; Kim, J.-W.; Sauti, G.; Cano, R. J.; Wincheski, R. A.; Ratcliffe, J. G.; Czabaj, M.

2016-01-01

Reported mechanical properties of carbon nanotubes (CNTs) at the nanoscale suggest their potential to enable significantly lighter structures of interest for space applications. However, their utility depends on the retention of these properties in bulk material formats that permit practical fabrication of large structures. This presentation summarizes recent progress made to produce carbon nanotube composites with specific tensile properties that begin to rival those of carbon fiber reinforced polymer composites. CNT content in these nanocomposites was greater than 70% by weight. Tested nanocomposite specimens were fabricated from kilometers or tens of square meters of CNT, depending on the starting material format. Processing methods to yield these results, and characterization and testing to evaluate the performance of these composites will be discussed. The final objective is the demonstration of a CNT composite overwrapped pressure vessel to be flight tested in the Fall of 2016.

Nonlinear conductivity in silicon nitride

NASA Astrophysics Data System (ADS)

Tuncer, Enis

2017-08-01

To better comprehend electrical silicon-package interaction in high voltage applications requires full characterization of the electrical properties of dielectric materials employed in wafer and package level design. Not only the packaging but wafer level dielectrics, i.e. passivation layers, would experience high electric fields generated by the voltage applied pads. In addition the interface between the passivation layer and a mold compound might develop space charge because of the mismatch in electrical properties of the materials. In this contribution electrical properties of a thin silicon nitride (Si3N4) dielectric is reported as a function of temperature and electric field. The measured values later analyzed using different temperature dependent exponential expressions and found that the Mott variable range hopping conduction model was successful to express the data. A full temperature/electric field dependency of conductivity is generated. It was found that the conduction in Si3N4 could be expressed like a field ionization or Fowler-Nordheim mechanism.

Dynamic response of a sensor element made of magnetic hybrid elastomer with controllable properties

NASA Astrophysics Data System (ADS)

Becker, T. I.; Zimmermann, K.; Borin, D. Yu.; Stepanov, G. V.; Storozhenko, P. A.

2018-03-01

Smart materials like magnetic hybrid elastomers (MHEs) are based on an elastic composite with a complex hybrid filler of magnetically hard and soft particles. Due to their unique magnetic field depending characteristics, these elastomers offer great potential for designing sensor systems with a complex adaptive behaviour and operating sensitivity. The present paper deals with investigations of the material properties and motion behaviour displayed by synthesised MHE beams in the presence of a uniform magnetic field. The distribution and structure formation of the magnetic components inside the elastic matrix depending on the manufacturing conditions are examined. The specific magnetic features of the MHE material during the magnetising process are revealed. Experimental investigations of the in-plane free vibrational behaviour displayed by the MHE beams with the fixed-free end conditions are performed for various magnitudes of an imposed uniform magnetic field. For the samples pre-magnetised along the length axis, it is demonstrated that the deflection of the beam can be identified unambiguously by magnetic field distortion measurements. It is shown that the material properties of the vibrating MHE element can be specifically adjusted by means of an external magnetic field control. The dependence of the first eigenfrequency of free bending vibrations of the MHE beams on the strength of an imposed uniform magnetic field is obtained. The results are aimed to assess the potential of MHEs to design acceleration sensor systems with an adaptive magnetically controllable sensitivity range.

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

NASA Astrophysics Data System (ADS)

Lippert, Sina; Schneider, Lorenz Maximilian; Renaud, Dylan; Kang, Kyung Nam; Ajayi, Obafunso; Kuhnert, Jan; Halbich, Marc-Uwe; Abdulmunem, Oday M.; Lin, Xing; Hassoon, Khaleel; Edalati-Boostan, Saeideh; Duck Kim, Young; Heimbrodt, Wolfram; Yang, Eui-Hyeok; Hone, James C.; Rahimi-Iman, Arash

2017-06-01

Monolayers of transition-metal dichalcogenides such as WSe2 have become increasingly attractive due to their potential in electrical and optical applications. Because the properties of these 2D systems are known to be affected by their surroundings, we report how the choice of the substrate material affects the optical properties of monolayer WSe2. To accomplish this study, pump-density-dependent micro-photoluminescence measurements are performed with time-integrating and time-resolving acquisition techniques. Spectral information and power-dependent mode intensities are compared at 290 K and 10 K for exfoliated WSe2 on SiO2/Si, sapphire (Al2O3), hBN/Si3N4/Si, and MgF2, indicating substrate-dependent appearance and strength of exciton, trion, and biexciton modes. Additionally, one CVD-grown WSe2 monolayer on sapphire is included in this study for direct comparison with its exfoliated counterpart. Time-resolved micro-photoluminescence shows how radiative decay times strongly differ for different substrate materials. Our data indicates exciton-exciton annihilation as a shortening mechanism at room temperature, and subtle trends in the decay rates in correlation to the dielectric environment at cryogenic temperatures. On the measureable time scales, trends are also related to the extent of the respective 2D-excitonic modes’ appearance. This result highlights the importance of further detailed characterization of exciton features in 2D materials, particularly with respect to the choice of substrate.

Boundary element method for 2D materials and thin films.

PubMed

Hrtoň, M; Křápek, V; Šikola, T

2017-10-02

2D materials emerge as a viable platform for the control of light at the nanoscale. In this context the need has arisen for a fast and reliable tool capable of capturing their strictly 2D nature in 3D light scattering simulations. So far, 2D materials and their patterned structures (ribbons, discs, etc.) have been mostly treated as very thin films of subnanometer thickness with an effective dielectric function derived from their 2D optical conductivity. In this study an extension to the existing framework of the boundary element method (BEM) with 2D materials treated as a conductive interface between two media is presented. The testing of our enhanced method on problems with known analytical solutions reveals that for certain types of tasks the new modification is faster than the original BEM algorithm. Furthermore, the representation of 2D materials as an interface allows us to simulate problems in which their optical properties depend on spatial coordinates. Such spatial dependence can occur naturally or can be tailored artificially to attain new functional properties.

Nanostructured zirconium phosphate as ion exchanger: Synthesis, size dependent property and analytical application in radiochemical separation.

PubMed

Chakraborty, Rajesh; Bhattacharaya, Koustava; Chattopadhyay, Pabitra

2014-02-01

Nanostructured zirconium phosphates (ZPs) of different sizes were synthesized using Tritron X-100 (polyethylene glycol-p-isooctylphenyl ether) surfactant. The materials were characterized by FTIR and powdered X-ray diffraction (XRD). The structural and morphological details of the material were established by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM study was followed by energy dispersive spectroscopic analysis (EDS) for elemental analysis of the sample. The particle sizes were determined by dynamic light scattering (DLS) method. Ion exchange capacity of these nanomaterials towards different metal ions was measured and size-dependent ion exchange property of the materials was investigated thoroughly. The nanomaterial of the smallest size (ca. 21.04nm) was employed to separate carrier-free (137m)Ba from (137)Cs in column chromatographic technique using 1.0M HNO3 as eluting agent at pH=5. © 2013 Elsevier Ltd. All rights reserved.

Estimation of transversely isotropic material properties from magnetic resonance elastography using the optimised virtual fields method.

PubMed

Miller, Renee; Kolipaka, Arunark; Nash, Martyn P; Young, Alistair A

2018-03-12

Magnetic resonance elastography (MRE) has been used to estimate isotropic myocardial stiffness. However, anisotropic stiffness estimates may give insight into structural changes that occur in the myocardium as a result of pathologies such as diastolic heart failure. The virtual fields method (VFM) has been proposed for estimating material stiffness from image data. This study applied the optimised VFM to identify transversely isotropic material properties from both simulated harmonic displacements in a left ventricular (LV) model with a fibre field measured from histology as well as isotropic phantom MRE data. Two material model formulations were implemented, estimating either 3 or 5 material properties. The 3-parameter formulation writes the transversely isotropic constitutive relation in a way that dissociates the bulk modulus from other parameters. Accurate identification of transversely isotropic material properties in the LV model was shown to be dependent on the loading condition applied, amount of Gaussian noise in the signal, and frequency of excitation. Parameter sensitivity values showed that shear moduli are less sensitive to noise than the other parameters. This preliminary investigation showed the feasibility and limitations of using the VFM to identify transversely isotropic material properties from MRE images of a phantom as well as simulated harmonic displacements in an LV geometry. Copyright © 2018 John Wiley & Sons, Ltd.

Influence of nanomechanical crystal properties on the comminution process of particulate solids in spiral jet mills.

PubMed

Zügner, Sascha; Marquardt, Karin; Zimmermann, Ingfried

2006-02-01

Elastic-plastic properties of single crystals are supposed to influence the size reduction process of bulk materials during jet milling. According to Pahl [M.H. Pahl, Zerkleinerungstechnik 2. Auflage. Fachbuchverlag, Leipzig (1993)] and H. Rumpf: [Prinzipien der Prallzerkleinerung und ihre Anwendung bei der Strahlmahlung. Chem. Ing. Tech., 3(1960) 129-135.] fracture toughness, maximum strain or work of fracture for example are strongly dependent on mechanical parameters like hardness (H) and young's modulus of elasticity (E). In addition the dwell time of particles in a spiral jet mill proved to correlate with the hardness of the feed material [F. Rief: Ph. D. Thesis, University of Würzburg (2001)]. Therefore 'near-surface' properties have a direct influence on the effectiveness of the comminution process. The mean particle diameter as well as the size distribution of the ground product may vary significantly with the nanomechanical response of the material. Thus accurate measurement of crystals' hardness and modulus is essential to determine the ideal operational micronisation conditions of the spiral jet mill. The recently developed nanoindentation technique is applied to examine subsurface properties of pharmaceutical bulk materials, namely calcite, sodium ascorbate, lactose and sodium chloride. Pressing a small sized tip into the material while continuously recording load and displacement, characteristic diagrams are derived. The mathematical evaluation of the force-displacement-data allows for calculation of the hardness and the elastic modulus of the investigated material at penetration depths between 50-300 nm. Grinding experiments performed with a modified spiral jet mill (Type Fryma JMRS 80) indicate the strong impact of the elastic-plastic properties of a given substance on its breaking behaviour. The fineness of milled products produced at constant grinding conditions but with different crystalline powders varies significantly as it is dependent on the nanohardness and the elasticity of the feed material. The analysis of this correlation gives new insights into the size reduction process.

Ion-Containing Polymers: Ionomers.

ERIC Educational Resources Information Center

Bazuin, C. G.; Eisenberg, A.

1981-01-01

Demonstrates how the incorporation of relatively low amounts of ionic material into nonionic polymers affects the structure and properties of these polymers. The extent to which properties are altered depends on dielectric constant of the backbone, position and type of ionic group, counterion type, ion concentration, and degree of neutralization.…

Temperature dependence of optically induced cell deformations

NASA Astrophysics Data System (ADS)

Fritsch, Anatol; Kiessling, Tobias R.; Stange, Roland; Kaes, Josef A.

2012-02-01

The mechanical properties of any material change with temperature, hence this must be true for cellular material. In biology many functions are known to undergo modulations with temperature, like myosin motor activity, mechanical properties of actin filament solutions, CO2 uptake of cultured cells or sex determination of several species. As mechanical properties of living cells are considered to play an important role in many cell functions it is surprising that only little is known on how the rheology of single cells is affected by temperature. We report the systematic temperature dependence of single cell deformations in Optical Stretcher (OS) measurements. The temperature is changed on a scale of about 20 minutes up to hours and compared to defined temperature shocks in the range of milliseconds. Thereby, a strong temperature dependence of the mechanics of single suspended cells is revealed. We conclude that the observable differences arise rather from viscosity changes of the cytosol than from structural changes of the cytoskeleton. These findings have implications for the interpretation of many rheological measurements, especially for laser based approaches in biological studies.

Influence of the powder mixture composition on the deposition coefficient and the properties of NI+B4C CGDS coatings

NASA Astrophysics Data System (ADS)

Kosarev, V. F.; Polukhin, A. A.; Ryashin, N. S.; Fomin, V. M.; Shikalov, V. S.

2017-07-01

The cold gas dynamic spray (CGDS) method used to form composite Ni+B4C coatings from mechanical powder mixture with various content of abrasive components is investigated, and the surface and microstructure of these coatings are considered. An experimental dependence of the deposition coefficient on the abrasive content in the mechanical powder mixture is obtained. The coatings are studied by interference profilometry, optical microscopy, and microindentation methods. The dependence of the bulk and mass B4C content in the sprayed material on the abrasive content in the sprayed powder mixture is obtained. The bulk B4C content in the coating c V ≈ 0.27 is attained. The dependence of the microhardness of composite CGDS coatings on the boron carbide content in them is investigated. The results of this paper demonstrate that the powder mixture composition significantly affects the CGDS coating growth and the properties of these coatings and can be used to control the properties of the CGDS cermet materials.

3-D Modeling of Directional Solidification of a Non-Dilute Alloy with Temperature and Concentration Fields Coupling via Materials Properties Dependence and via Double Diffusive Convection

NASA Technical Reports Server (NTRS)

Bune, Andris V.; Gillies, Donald C.; Lehoczky, Sandor L.

1998-01-01

Numerical simulation of the HgCdTe growth by the vertical Bridgman method was performed using FIDAP finite element code. Double-diffusive melt convection is analyzed, as the primary factor at controls inhomogeneity of the solidified material. Temperature and concentration fields in the model are also coupled via material properties, such as thermal and solutal expansion coefficients with the dependence on both temperature and concentration, and melting temperature evaluation from pseudobinary CdTe-HgTe phase diagram. Experimental measurements were used to obtain temperature boundary conditions. Parametric study of the melt convection dependence on the gravity conditions was undertaken. It was found, that the maximum convection velocity in the melt can be reduced under certain conditions. Optimal conditions to obtain a near flat solidified interface are discussed. The predicted interface shape is in agreement with one obtained experimentally by quenching. The results of 3-D calculations are compared with previous 2- D findings. A video film featuring 3-D melt convection will be presented.

Information transport in classical statistical systems

NASA Astrophysics Data System (ADS)

Wetterich, C.

2018-02-01

For "static memory materials" the bulk properties depend on boundary conditions. Such materials can be realized by classical statistical systems which admit no unique equilibrium state. We describe the propagation of information from the boundary to the bulk by classical wave functions. The dependence of wave functions on the location of hypersurfaces in the bulk is governed by a linear evolution equation that can be viewed as a generalized Schrödinger equation. Classical wave functions obey the superposition principle, with local probabilities realized as bilinears of wave functions. For static memory materials the evolution within a subsector is unitary, as characteristic for the time evolution in quantum mechanics. The space-dependence in static memory materials can be used as an analogue representation of the time evolution in quantum mechanics - such materials are "quantum simulators". For example, an asymmetric Ising model on a Euclidean two-dimensional lattice represents the time evolution of free relativistic fermions in two-dimensional Minkowski space.

Microstructure characterization of multi-phase composites and utilization of phase change materials and recycled rubbers in cementitious materials

NASA Astrophysics Data System (ADS)

Meshgin, Pania

2011-12-01

This research focuses on two important subjects: (1) Characterization of heterogeneous microstructure of multi-phase composites and the effect of microstructural features on effective properties of the material. (2) Utilizations of phase change materials and recycled rubber particles from waste tires to improve thermal properties of insulation materials used in building envelopes. Spatial pattern of multi-phase and multidimensional internal structures of most composite materials are highly random. Quantitative description of the spatial distribution should be developed based on proper statistical models, which characterize the morphological features. For a composite material with multi-phases, the volume fraction of the phases as well as the morphological parameters of the phases have very strong influences on the effective property of the composite. These morphological parameters depend on the microstructure of each phase. This study intends to include the effect of higher order morphological details of the microstructure in the composite models. The higher order statistics, called two-point correlation functions characterize various behaviors of the composite at any two points in a stochastic field. Specifically, correlation functions of mosaic patterns are used in the study for characterizing transport properties of composite materials. One of the most effective methods to improve energy efficiency of buildings is to enhance thermal properties of insulation materials. The idea of using phase change materials and recycled rubber particles such as scrap tires in insulation materials for building envelopes has been studied.

Harman Measurements for Thermoelectric Materials and Modules under Non-Adiabatic Conditions

PubMed Central

Roh, Im-Jun; Lee, Yun Goo; Kang, Min-Su; Lee, Jae-Uk; Baek, Seung-Hyub; Kim, Seong Keun; Ju, Byeong-Kwon; Hyun, Dow-Bin; Kim, Jin-Sang; Kwon, Beomjin

2016-01-01

Accuracy of the Harman measurement largely depends on the heat transfer between the sample and its surroundings, so-called parasitic thermal effects (PTEs). Similar to the material evaluations, measuring thermoelectric modules (TEMs) is also affected by the PTEs especially when measuring under atmospheric condition. Here, we study the correction methods for the Harman measurements with systematically varied samples (both bulk materials and TEMs) at various conditions. Among several PTEs, the heat transfer via electric wires is critical. Thus, we estimate the thermal conductance of the electric wires, and correct the measured properties for a certain sample shape and measuring temperature. The PTEs are responsible for the underestimation of the TEM properties especially under atmospheric conditions (10–35%). This study will be useful to accurately characterize the thermoelectric properties of materials and modules. PMID:27966622

Electrospinning of gelatin and SMPU with carbon nanotubes for tissue engineering scaffolds.

PubMed

Mejia, Monica A; Hoyos, Lina M; Zapata, Jenniffer; Restrepo, Luz M; Moneada, Maria E

2016-08-01

The nanofibres created by electrospinning technique are currently used for a variety of applications in tissue engineering; and Gelatin and Polyurethane Shape-Memory (SMPU) have important results in biomedicine. Similarly, carbon nanotubes combined with other biomaterials change important properties, opening new opportunities for biomedical applications. In this work, we constructed scaffold using electrospinning technique based in bovine-hide gelatin, SMPU and both materials hybrid with carbon nanotube. Morphology and cytotoxicity were evaluated and mechanical properties for two materials were obtained in scaffold building. Morphological, mechanical and citotoxic properties of the electrospun fibers were found to be dependent of alteration in materials concentration, electrospinning conditions and MWCNT concentration. According to morphological, cytotoxic and mechanical analysis, SMPU more MWCNT were the best material, with nanofibers of 451 nm, tensile strength of 1.912 MPa, and a high ratio surface volume.

Temperature-Dependent Electrical and Micromechanical Properties of Lanthanum Titanate with Additions of Yttria

NASA Technical Reports Server (NTRS)

Goldsby, Jon C.

2010-01-01

Temperature-dependent elastic properties were determined by establishing continuous flexural vibrations in the material at its lowest resonance frequency of 31tHz. The imaginary part of the complex impedance plotted as a function of frequency and temperature reveals a thermally activated peak, which decreases in magnitude as the temperature increases. Additions of yttria do not degrade the electromechanical in particularly the elastic and anelastic properties of lanthanum titanate. Y2O3/La2Ti2O7 exhibits extremely low internal friction and hence may be more mechanical fatigue-resistant at low strains.

Solvent dependent triphenylamine based D-(pi-A)n type dye molecules and optical properties.

PubMed

Li, Xiaochuan; Son, Young-A; Kim, Young-Sung; Kim, Sung-Hoon; Kun, Jun; Shin, Jong-Il

2012-02-01

D-(pi-A)n type dyes of triphenylamine derivatives were synthesized and their absorption and luminescence in different solvents were examined to investigate solvent dependent properties observed for their emissions in solvents with different dielectric constants. The emission wavelengths showed a dramatic blue shift with increasing solvent polarity. The results of molecular orbital calculations by computer simulation, based on Material Studio suite of programs, were found to reasonably account for the spectral properties. Relative levels of HOMO and LUMO were measured and calculated and all derivatives exhibited strong solid fluorescence with distinctively different FWHMs.

Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites.

PubMed

Bucuta, Stefan; Ilie, Nicoleta

2014-11-01

The aim of this study was to quantify the blue light that passes through different incremental thicknesses of bulk fill in comparison to conventional resin-based composites (RBCs) and to relate it to the induced mechanical properties. Seven bulk fill, five nanohybrid and two flowable RBCs were analysed. Specimens (n = 5) of three incremental thicknesses (2, 4 and 6 mm) were cured from the top for 20 s, while at the bottom, a spectrometer monitored in real time the transmitted irradiance. Micro-mechanical properties (Vickers hardness, HV, and indentation modulus, E) were measured at the top and bottom after 24 h of storage in distilled water at 37 °C. Electron microscope images were taken for assessing the filler distribution and size. Bulk fill RBCs (except SonicFill) were more translucent than conventional RBCs. Low-viscosity bulk fill materials showed the lowest mechanical properties. HV depends highly on the following parameters: material (ηp (2) = 0.952), incremental thickness (0.826), filler volume (0.747), filler weight (0.746) and transmitted irradiance (0.491). The bottom-to-top HV ratio (HVbt) was higher than 80 % in all materials in 2- and 4-mm increments (except for Premise), whereas in 6-mm increments, this is valid only in four bulk fill materials (Venus Bulk Fill, SDR, x-tra fil, Tetric EvoCeram Bulk Fill). The depth of cure is dependent on the RBC's translucency. Low-viscosity bulk fill RBCs have lower mechanical properties than all other types of analysed materials. All bulk fill RBCs (except SonicFill) are more translucent for blue light than conventional RBCs. Although bulk fill RBCs are generally more translucent, the practitioner has to follow the manufacturer's recommendations on curing technique and maximum incremental thickness.

TOPAZ2D heat transfer code users manual and thermal property data base

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

Shapiro, A.B.; Edwards, A.L.

1990-05-01

TOPAZ2D is a two dimensional implicit finite element computer code for heat transfer analysis. This user's manual provides information on the structure of a TOPAZ2D input file. Also included is a material thermal property data base. This manual is supplemented with The TOPAZ2D Theoretical Manual and the TOPAZ2D Verification Manual. TOPAZ2D has been implemented on the CRAY, SUN, and VAX computers. TOPAZ2D can be used to solve for the steady state or transient temperature field on two dimensional planar or axisymmetric geometries. Material properties may be temperature dependent and either isotropic or orthotropic. A variety of time and temperature dependentmore » boundary conditions can be specified including temperature, flux, convection, and radiation. Time or temperature dependent internal heat generation can be defined locally be element or globally by material. TOPAZ2D can solve problems of diffuse and specular band radiation in an enclosure coupled with conduction in material surrounding the enclosure. Additional features include thermally controlled reactive chemical mixtures, thermal contact resistance across an interface, bulk fluid flow, phase change, and energy balances. Thermal stresses can be calculated using the solid mechanics code NIKE2D which reads the temperature state data calculated by TOPAZ2D. A three dimensional version of the code, TOPAZ3D is available. The material thermal property data base, Chapter 4, included in this manual was originally published in 1969 by Art Edwards for use with his TRUMP finite difference heat transfer code. The format of the data has been altered to be compatible with TOPAZ2D. Bob Bailey is responsible for adding the high explosive thermal property data.« less

Investigation of thermal fatigue in fiber composite materials. [(thermal cycling tests)

NASA Technical Reports Server (NTRS)

Fahmy, A. A.; Cunningham, T. G.

1976-01-01

Graphite-epoxy laminates were thermally cycled to determine the effects of thermal cycles on tensile properties and thermal expansion coefficients of the laminates. Three 12-ply laminate configurations were subjected to up to 5,000 thermal cycles. The cumulative effect of the thermal cycles was determined by destructive inspection (electron micrographs and tensile tests) of samples after progressively larger numbers of cycles. After thermal cycling, the materials' tensile strengths, moduli, and thermal expansion coefficients were significantly lower than for the materials as fabricated. Most of the degradation of properties occurred after only a few cycles. The property degradation was attributed primarily to the progressive development of matrix cracks whose locations depended upon the layup orientation of the laminate.

Nanostructured Metal Oxides for Stoichiometric Degradation of Chemical Warfare Agents.

PubMed

Štengl, Václav; Henych, Jiří; Janoš, Pavel; Skoumal, Miroslav

2016-01-01

Metal oxides have very important applications in many areas of chemistry, physics and materials science; their properties are dependent on the method of preparation, the morphology and texture. Nanostructured metal oxides can exhibit unique characteristics unlike those of the bulk form depending on their morphology, with a high density of edges, corners and defect surfaces. In recent years, methods have been developed for the preparation of metal oxide powders with tunable control of the primary particle size as well as of a secondary particle size: the size of agglomerates of crystallites. One of the many ways to take advantage of unique properties of nanostructured oxide materials is stoichiometric degradation of chemical warfare agents (CWAs) and volatile organic compounds (VOC) pollutants on their surfaces.

Elastic and microplastic properties of titanium in different structural states

NASA Astrophysics Data System (ADS)

Kardashev, B. K.; Betekhtin, V. I.; Kadomtsev, A. G.; Narykova, M. V.; Kolobov, Yu. R.

2017-09-01

The behavior of elastic (Young's modulus) and microplastic properties of titanium depending on the initial structure and subsequent severe plastic deformation that transforms the material (concerning the grain size) into the submicrocrystalline structural state has been studied. It has been shown that, to a great extent, different initial structures of the metal predetermine its elastic properties after deformation.

Modeling micromechanical measurements of depth-varying properties with scanning acoustic microscopy

NASA Astrophysics Data System (ADS)

Marangos, Orestes; Misra, Anil

2018-02-01

Scanning acoustic microscopy (SAM) has been applied to measure the near-surface elastic properties of materials. For many substrates, the near-surface property is not constant but varies with depth. In this paper, we aim to interpret the SAM data from such substrates by modeling the interaction of the focused ultrasonic field with a substrate having a near-surface graded layer. The focused ultrasonic field solutions were represented as spherical harmonic expansions while the substrate solutions were represented as plane wave expansions. The bridging of the two solutions was achieved through the decomposition of the ultrasonic pressure fields in their angular spectra. Parametric studies were performed, which showed that near-surface graded layers exhibit distinctive frequency dependence of their reflectance functions. This behavior is characteristic to the material property gradation profile as well as the extent of the property gradation. The developed model was used to explain the frequency-dependent reflection coefficients measured from an acid-etched dentin substrate. Based on the model calculations, the elastic property variations of the acid-etched dentin near-surface indicate that the topmost part of the etched layer is very soft (3-6 GPa) and transitions to the native dentin through a depth of 27 and 36 microns.

High Temperature Properties of an Alumina Enhanced Thermal Barrier

NASA Technical Reports Server (NTRS)

Leiser, Daniel B.; Smith, Marnell; Keating, Elizabeth A.

1987-01-01

The heatshield material requirements for future space vehicles (Aerobraking Orbital Transfer Vehicle & National Aerospace Plane) will depend upon the desired flight capability, configuration and location on the vehicle. These requirements will be more demanding and different from those derived for the materials used in the Shuttle Orbiter thermal protection system. Research was therefore initiated into improving the thermal efficiency of this class of materials by first characterizing their thermal and structural capabilities. Alternate material systems have been developed, tested, and compared with the baseline Shuttle system. This research resulted in the development of several very low density, high porosity (80-90%) materials with enhanced durability and temperature capability. One of the developments was a family of materials referred to as Fibrous Refractory Composite Insulation (FRCI) utilizing a mixture of fibers, each serving a unique purpose. One composition of the FRCI family with two fibers was adopted as a baseline material for use on the third and fourth Orbiters in selected areas due to its strength at a lower density compared to earlier materials. A further improvement in the FRCI family of materials is the Alumina Enhanced Thermal Barrier (AETB), a three-fiber composite. It has a higher temperature capability (composition dependent) than the baseline FRCI as proven by convective heating tests of one composition. AETB was studied to better characterize its performance at high temperature and the mechanisms by which its properties change. In conclusion, the shrinkage of AETB is a factor of six better than baseline FRCI at 1260 C (2300 F) with about a 20% improvement in mechanical properties. This improvement could translate into a 110 C (200 F) higher temperature capability in use as a heat shield material, but further testing in a convective heating environment is required to determine the actual improvement attainable.

Modeling of Abrasion and Crushing of Unbound Granular Materials During Compaction

NASA Astrophysics Data System (ADS)

Ocampo, Manuel S.; Caicedo, Bernardo

2009-06-01

Unbound compacted granular materials are commonly used in engineering structures as layers in road pavements, railroad beds, highway embankments, and foundations. These structures are generally subjected to dynamic loading by construction operations, traffic and wheel loads. These repeated or cyclic loads cause abrasion and crushing of the granular materials. Abrasion changes a particle's shape, and crushing divides the particle into a mixture of many small particles of varying sizes. Particle breakage is important because the mechanical and hydraulic properties of these materials depend upon their grain size distribution. Therefore, it is important to evaluate the evolution of the grain size distribution of these materials. In this paper an analytical model for unbound granular materials is proposed in order to evaluate particle crushing of gravels and soils subjected to cyclic loads. The model is based on a Markov chain which describes the development of grading changes in the material as a function of stress levels. In the model proposed, each particle size is a state in the system, and the evolution of the material is the movement of particles from one state to another in n steps. Each step is a load cycle, and movement between states is possible with a transition probability. The crushing of particles depends on the mechanical properties of each grain and the packing density of the granular material. The transition probability was calculated using both the survival probability defined by Weibull and the compressible packing model developed by De Larrard. Material mechanical properties are considered using the Weibull probability theory. The size and shape of the grains, as well as the method of processing the packing density are considered using De Larrard's model. Results of the proposed analytical model show a good agreement with the experimental tests carried out using the gyratory compaction test.

Determination of temperature dependence of full matrix material constants of PZT-8 piezoceramics using only one sample.

PubMed

Zhang, Yang; Tang, Liguo; Tian, Hua; Wang, Jiyang; Cao, Wenwu; Zhang, Zhongwu

2017-08-15

Resonant ultrasound spectroscopy (RUS) was used to determine the temperature dependence of full matrix material constants of PZT-8 piezoceramics from room temperature to 100 °C. Property variations from sample to samples can be eliminated by using only one sample, so that data self-consistency can be guaranteed. The RUS measurement system error was estimated to be lower than 2.35%. The obtained full matrix material constants at different temperatures all have excellent self-consistency, which can help accurately predict device performance at high temperatures using finite element simulations.

Tunable Bragg filters with a phase transition material defect layer

DOE PAGES

Wang, Xi; Gong, Zilun; Dong, Kaichen; ...

2016-01-01

We propose an all-solid-state tunable Bragg filter with a phase transition material as the defect layer. Bragg filters based on a vanadium dioxide defect layer sandwiched between silicon dioxide/titanium dioxide Bragg gratings are experimentally demonstrated. Temperature dependent reflection spectroscopy shows the dynamic tunability and hysteresis properties of the Bragg filter. Temperature dependent Raman spectroscopy reveals the connection between the tunability and the phase transition of the vanadium dioxide defect layer. This work paves a new avenue in tunable Bragg filter designs and promises more applications by combining phase transition materials and optical cavities.

Tunable Bragg filters with a phase transition material defect layer

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

Wang, Xi; Gong, Zilun; Dong, Kaichen

We propose an all-solid-state tunable Bragg filter with a phase transition material as the defect layer. Bragg filters based on a vanadium dioxide defect layer sandwiched between silicon dioxide/titanium dioxide Bragg gratings are experimentally demonstrated. Temperature dependent reflection spectroscopy shows the dynamic tunability and hysteresis properties of the Bragg filter. Temperature dependent Raman spectroscopy reveals the connection between the tunability and the phase transition of the vanadium dioxide defect layer. This work paves a new avenue in tunable Bragg filter designs and promises more applications by combining phase transition materials and optical cavities.

Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates

NASA Astrophysics Data System (ADS)

Bonilla, Manuel; Kolekar, Sadhu; Ma, Yujing; Diaz, Horacio Coy; Kalappattil, Vijaysankar; Das, Raja; Eggers, Tatiana; Gutierrez, Humberto R.; Phan, Manh-Huong; Batzill, Matthias

2018-04-01

Reduced dimensionality and interlayer coupling in van der Waals materials gives rise to fundamentally different electronic1, optical2 and many-body quantum3-5 properties in monolayers compared with the bulk. This layer-dependence permits the discovery of novel material properties in the monolayer regime. Ferromagnetic order in two-dimensional materials is a coveted property that would allow fundamental studies of spin behaviour in low dimensions and enable new spintronics applications6-8. Recent studies have shown that for the bulk-ferromagnetic layered materials CrI3 (ref. 9) and Cr2Ge2Te6 (ref. 10), ferromagnetic order is maintained down to the ultrathin limit at low temperatures. Contrary to these observations, we report the emergence of strong ferromagnetic ordering for monolayer VSe2, a material that is paramagnetic in the bulk11,12. Importantly, the ferromagnetic ordering with a large magnetic moment persists to above room temperature, making VSe2 an attractive material for van der Waals spintronics applications.

Mechanical biocompatibility of highly deformable biomedical materials.

PubMed

Mazza, Edoardo; Ehret, Alexander E

2015-08-01

Mismatch of mechanical properties between highly deformable biomedical materials and adjacent native tissue might lead to short and long term health impairment. The capability of implants to deform at the right level, i.e. similar to the macroscopic mechanical response of the surrounding biological materials, is often associated with dissimilar microstructural deformation mechanisms. This mismatch on smaller length scales might lead to micro-injuries, cell damage, inflammation, fibrosis or necrosis. Hence, the mechanical biocompatibility of soft implants depends not only on the properties and composition of the implant material, but also on its organization, distribution and motion at one or several length scales. The challenges related to the analysis and attainment of mechanical biocompatibility are illustrated with two examples: prosthetic meshes for hernia and pelvic repair and electrospun scaffolds for tissue engineering. For these material systems we describe existing methods for characterization and analysis of the non-linear response to uniaxial and multiaxial stress states, its time and history dependence, and the changes in deformation behavior associated with tissue in-growth and material resorption. We discuss the multi-scale deformation behavior of biomaterials and adjacent tissue, and indicate major interdisciplinary questions to be addressed in future research. Copyright © 2015 Elsevier Ltd. All rights reserved.

Thermophysical Property Models for Lunar Regolith

NASA Technical Reports Server (NTRS)

Schreiner, Samuel S.; Dominguez, Jesus A.; Sibille, Laurent; Hoffman, Jeffrey A.

2015-01-01

We present a set of models for a wide range of lunar regolith material properties. Data from the literature are t with regression models for the following regolith properties: composition, density, specific heat, thermal conductivity, electrical conductivity, optical absorption length, and latent heat of melting/fusion. These models contain both temperature and composition dependencies so that they can be tailored for a range of applications. These models can enable more consistent, informed analysis and design of lunar regolith processing hardware. Furthermore, these models can be utilized to further inform lunar geological simulations. In addition to regression models for each material property, the raw data is also presented to allow for further interpretation and fitting as necessary.

User-defined Material Model for Thermo-mechanical Progressive Failure Analysis

NASA Technical Reports Server (NTRS)

Knight, Norman F., Jr.

2008-01-01

Previously a user-defined material model for orthotropic bimodulus materials was developed for linear and nonlinear stress analysis of composite structures using either shell or solid finite elements within a nonlinear finite element analysis tool. Extensions of this user-defined material model to thermo-mechanical progressive failure analysis are described, and the required input data are documented. The extensions include providing for temperature-dependent material properties, archival of the elastic strains, and a thermal strain calculation for materials exhibiting a stress-free temperature.

The efficiency of the use of composite materials in electrotechnical equipment

NASA Astrophysics Data System (ADS)

Kim, K.; Ivanov, S.

2018-02-01

The indicators of the efficiency of electrical installations are directly connected with the creating and using of new composite materials with the desired performance properties. The practical application of composite materials is one of the perspective scientific and technical directions, providing the increase of the efficiency of electrical installations due to the sealing of current parts by protecting them from the external medium. The technical characteristics of the composite material match to its structure and depend on the properties of the individual components. The verification of the compliance of material parameters is implemented by the methods of the computer analysis of a model of composite material in the form of the structure in which the individual elements have thermodynamic properties of the corresponding phase state. In the study the topology of individual elements in the material structure is defined by the conditional boundaries of the section within the studied composite. The efficiency of using the composite materials includes the raising of electrical safety, increasing the durability, reducing the costs of maintenance and repair and the extension of the scope of installations.

Use of updated material properties in parametric optimization of spaceborne mirrors

NASA Astrophysics Data System (ADS)

Hull, Tony; Westerhoff, Thomas; Weidmann, Guenter; Kirchhoff, Rule

2016-07-01

Spaceborne sensor mirrors need to be both structurally efficient and to maintain figure through thermal transients. Both properties can be represented in a plot showing structural efficiency on one axis and thermal transient resilience on the other. For material selection, engineers have effectively used such charts. However in some cases thermal attributes have improved considerably. Using contemporary values, this comparison chart looks differently. We will discuss how lines of equal merit may be formulated differently depending on the orbit of the mission.

Strain Rate and Anisotropic Microstructure Dependent Mechanical Behaviors of Silkworm Cocoon Shells

PubMed Central

Xu, Jun; Zhang, Wen; Gao, Xiang; Meng, Wanlin; Guan, Juan

2016-01-01

Silkworm cocoons are multi-layered composite structures comprised of high strength silk fiber and sericin, and their mechanical properties have been naturally selected to protect pupas during metamorphosis from various types of external attacks. The present study attempts to gain a comprehensive understanding of the mechanical properties of cocoon shell materials from wild silkworm species Antheraea pernyi under dynamic loading rates. Five dynamic strain rates from 0.00625 s-1 to 12.5 s-1 are tested to show the strain rate sensitivity of the cocoon shell material. In the meantime, the anisotropy of the cocoon shell is considered and the cocoon shell specimens are cut along 0°, 45° and 90° orientation to the short axis of cocoons. Typical mechanical properties including Young’s modulus, yield strength, ultimate strength and ultimate strain are extracted and analyzed from the stress-strain curves. Furthermore, the fracture morphologies of the cocoon shell specimens are observed under scanning electron microscopy to help understand the relationship between the mechanical properties and the microstructures of the cocoon material. A discussion on the dynamic strain rate effect on the mechanical properties of cocoon shell material is followed by fitting our experimental results to two previous models, and the effect could be well explained. We also compare natural and dried cocoon materials for the dynamic strain rate effect and interestingly the dried cocoon shells show better overall mechanical properties. This study provides a different perspective on the mechanical properties of cocoon material as a composite material, and provides some insight for bio-inspired engineering materials. PMID:26939063

Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances.

PubMed

Kohda, Naohisa; Iijima, Masahiro; Muguruma, Takeshi; Brantley, William A; Ahluwalia, Karamdeep S; Mizoguchi, Itaru

2013-05-01

To measure the forces delivered by thermoplastic appliances made from three materials and investigate effects of mechanical properties, material thickness, and amount of activation on orthodontic forces. Three thermoplastic materials, Duran (Scheu Dental), Erkodur (Erkodent Erich Kopp GmbH), and Hardcast (Scheu Dental), with two different thicknesses were selected. Values of elastic modulus and hardness were obtained from nanoindentation measurements at 28°C. A custom-fabricated system with a force sensor was employed to obtain measurements of in vitro force delivered by the thermoplastic appliances for 0.5-mm and 1.0-mm activation for bodily tooth movement. Experimental results were subjected to several statistical analyses. Hardcast had significantly lower elastic modulus and hardness than Duran and Erkodur, whose properties were not significantly different. Appliances fabricated from thicker material (0.75 mm or 0.8 mm) always produced significantly greater force than those fabricated from thinner material (0.4 mm or 0.5 mm). Appliances with 1.0-mm activation produced significantly lower force than those with 0.5-mm activation, except for 0.4-mm thick Hardcast appliances. A strong correlation was found between mechanical properties of the thermoplastic materials and force produced by the appliances. Orthodontic forces delivered by thermoplastic appliances depend on the material, thickness, and amount of activation. Mechanical properties of the polymers obtained by nanoindentation testing are predictive of force delivery by these appliances.

Preparation of a Carbon Doped Tissue-Mimicking Material with High Dielectric Properties for Microwave Imaging Application

PubMed Central

Lan, Siang-Wen; Weng, Min-Hang; Yang, Ru-Yuan; Chang, Shoou-Jinn; Chung, Yaoh-Sien; Yu, Tsung-Chih; Wu, Chun-Sen

2016-01-01

In this paper, the oil-in-gelatin based tissue-mimicking materials (TMMs) doped with carbon based materials including carbon nanotube, graphene ink or lignin were prepared. The volume percent for gelatin based mixtures and oil based mixtures were both around 50%, and the doping amounts were 2 wt %, 4 wt %, and 6 wt %. The effect of doping material and amount on the microwave dielectric properties including dielectric constant and conductivity were investigated over an ultra-wide frequency range from 2 GHz to 20 GHz. The coaxial open-ended reflection technology was used to evaluate the microwave dielectric properties. Six measured values in different locations of each sample were averaged and the standard deviations of all the measured dielectric properties, including dielectric constant and conductivity, were less than one, indicating a good uniformity of the prepared samples. Without doping, the dielectric constant was equal to 23 ± 2 approximately. Results showed with doping of carbon based materials that the dielectric constant and conductivity both increased about 5% to 20%, and the increment was dependent on the doping amount. By proper selection of doping amount of the carbon based materials, the prepared material could map the required dielectric properties of special tissues. The proposed materials were suitable for the phantom used in the microwave medical imaging system. PMID:28773678

Impact of Magneto-Electric Materials and Devices on Tactical Radio (and Radar)

DTIC Science & Technology

2007-04-01

and frequency dependent variable permittivity in a single device • Magnetic properties controlled by electric field. The goals of the seedling...such as HoMnO3) and composites (such as PZT- Terfenol-D). Other possible candidate materials are thought to include colossal magnetoresistive oxides

Thermally induced structural transitions in cotton fiber revealed by a finite mixture model of fiber tenacity distribution

USDA-ARS?s Scientific Manuscript database

Much processing of cotton fibrous materials accompanies heat treatments. Despite their critical influence on the properties of the material, the structural responses of cotton fiber to elevated temperatures remain uncertain. This study demonstrated that modeling the temperature dependence of the fib...

Development of constitutive model for composites exhibiting time dependent properties

NASA Astrophysics Data System (ADS)

Pupure, L.; Joffe, R.; Varna, J.; Nyström, B.

2013-12-01

Regenerated cellulose fibres and their composites exhibit highly nonlinear behaviour. The mechanical response of these materials can be successfully described by the model developed by Schapery for time-dependent materials. However, this model requires input parameters that are experimentally determined via large number of time-consuming tests on the studied composite material. If, for example, the volume fraction of fibres is changed we have a different material and new series of experiments on this new material are required. Therefore the ultimate objective of our studies is to develop model which determines the composite behaviour based on behaviour of constituents of the composite. This paper gives an overview of problems and difficulties, associated with development, implementation and verification of such model.

Physical Principles Pertaining to Ultrasonic and Mechanical Properties of Anisotropic Media and Their Application to Nondestructive Evaluation of Fiber-Reinforced Composite Materials

NASA Astrophysics Data System (ADS)

Handley, Scott Michael

The central theme of this thesis is to contribute to the physics underlying the mechanical properties of highly anisotropic materials. Our hypothesis is that a fundamental understanding of the physics involved in the interaction of interrogating ultrasonic waves with anisotropic media will provide useful information applicable to quantitative ultrasonic measurement techniques employed for the determination of material properties. Fiber-reinforced plastics represent a class of advanced composite materials that exhibit substantial anisotropy. The desired characteristics of practical fiber -reinforced composites depend on average mechanical properties achieved by placing fibers at specific angles relative to the external surfaces of the finished part. We examine the physics underlying the use of ultrasound as an interrogation probe for determination of ultrasonic and mechanical properties of anisotropic materials such as fiber-reinforced composites. Fundamental constituent parameters, such as elastic stiffness coefficients (c_{rm IJ}), are experimentally determined from ultrasonic time-of-flight measurements. Mechanical moduli (Poisson's ratio, Young's and shear modulus) descriptive of the anisotropic mechanical properties of unidirectional graphite/epoxy composites are obtained from the ultrasonically determined stiffness coefficients. Three-dimensional visualizations of the anisotropic ultrasonic and mechanical properties of unidirectional graphite/epoxy composites are generated. A related goal of the research is to strengthen the connection-between practical ultrasonic nondestructive evaluation methods and the physics underlying quantitative ultrasonic measurements for the assessment of manufactured fiber-reinforced composites. Production defects such as porosity have proven to be of substantial concern in the manufacturing of composites. We investigate the applicability of ultrasonic interrogation techniques for the detection and characterization of porosity in graphite/epoxy laminates. Complementary ultrasonic parameters based on the frequency dependence of ultrasonic attenuation and integrated polar backscatter are investigated. In summary, the approach taken in this thesis is to examine the physical mechanisms in terms of a continuum mechanics framework and a linear elastic description of ultrasonic wave propagation in anisotropic media with specific application to the nondestructive evaluation of advanced composite materials.

Some functional properties of composite material based on scrap tires

NASA Astrophysics Data System (ADS)

Plesuma, Renate; Malers, Laimonis

2013-09-01

The utilization of scrap tires still obtains a remarkable importance from the aspect of unloading the environment from non-degradable waste [1]. One of the most prospective ways for scrap tires reuse is a production of composite materials [2] This research must be considered as a continuation of previous investigations [3, 4]. It is devoted to the clarification of some functional properties, which are considered important for the view of practical applications, of the composite material. Some functional properties of the material were investigated, for instance, the compressive stress at different extent of deformation of sample (till 67% of initial thickness) (LVS EN 826) [5] and the resistance to UV radiation (modified method based on LVS EN 14836) [6]. Experiments were realized on the purposefully selected samples. The results were evaluated in the correlation with potential changes of Shore C hardness (Shore scale, ISO 7619-1, ISO 868) [7, 8]. The results showed noticeable resistance of the composite material against the mechanical influence and ultraviolet (UV) radiation. The correlation with the composition of the material, activity of binder, definite technological parameters, and the conditions supported during the production, were determined. It was estimated that selected properties and characteristics of the material are strongly dependent from the composition and technological parameters used in production of the composite material, and from the size of rubber crumb. Obtained results show possibility to attain desirable changes in the composite material properties by changing both the composition and technological parameters of examined material.

Low-Temperature Variation of Acoustic Velocity in PDMS for High-Frequency Applications.

PubMed

Streque, Jeremy; Rouxel, Didier; Talbi, Abdelkrim; Thomassey, Matthieu; Vincent, Brice

2018-05-01

Polydimethylsiloxane (PDMS) and other related silicon-based polymers are among the most widely employed elastomeric materials in microsystems, owing to their physical and chemical properties. Meanwhile, surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors and filters have been vastly explored for sensing and wireless applications. Many fields could benefit from the combined use of acoustic wave devices, and polydimethylsiloxane-based soft-substrates, microsystems, or packaging elements. The mechanical constants of PDMS strongly depend on frequency, similar to rubber materials. This brings to the exploration of the specific mechanical properties of PDMS encountered at high frequency, required for its exploitation in SAW or BAW devices. First, low-frequency mechanical behavior is confirmed from stress strain measurements, remaining useful for the exploitation of PDMS as a soft substrate or packaging material. The study, then, proposes a temperature-dependent, high-frequency mechanical study of PDMS based on Brillouin spectroscopy to determine the evolution of the longitudinal acoustic velocity in this material, which constitutes the main mechanical parameter for the design of acoustic wave devices. The PDMS glass transition is then retrieved by differential scanning calorimetry in order to confirm the observations made by Brillouin spectroscopy. This paper validates Brillouin spectroscopy as a very suitable characterization technique for the retrieval of longitudinal mechanical properties at low temperature, as a preliminary investigation for the design of acoustic wave devices coupled with soft materials.

Effects of material properties and object orientation on precision grip kinematics.

PubMed

Paulun, Vivian C; Gegenfurtner, Karl R; Goodale, Melvyn A; Fleming, Roland W

2016-08-01

Successfully picking up and handling objects requires taking into account their physical properties (e.g., material) and position relative to the body. Such features are often inferred by sight, but it remains unclear to what extent observers vary their actions depending on the perceived properties. To investigate this, we asked participants to grasp, lift and carry cylinders to a goal location with a precision grip. The cylinders were made of four different materials (Styrofoam, wood, brass and an additional brass cylinder covered with Vaseline) and were presented at six different orientations with respect to the participant (0°, 30°, 60°, 90°, 120°, 150°). Analysis of their grasping kinematics revealed differences in timing and spatial modulation at all stages of the movement that depended on both material and orientation. Object orientation affected the spatial configuration of index finger and thumb during the grasp, but also the timing of handling and transport duration. Material affected the choice of local grasp points and the duration of the movement from the first visual input until release of the object. We find that conditions that make grasping more difficult (orientation with the base pointing toward the participant, high weight and low surface friction) lead to longer durations of individual movement segments and a more careful placement of the fingers on the object.

Microstructural and Morphological Factors Affecting Uncertainty in Small Scale Mechanical Properties

NASA Astrophysics Data System (ADS)

Maughan, Michael R.

If materials are to be developed from the ground up, the process will be dependent upon accurate and well-defined models of material behavior. These models can be closed-form solutions developed from first principles, simulations, or empirically derived equations, among others. Material behavior at the mesoscale is in general well understood, having had several centuries of study. However, behavior at the micro or nanoscale still requires characterization. Understanding the collective influence of the microstructure on the bulk material, for example with models like the Hall-Petch relation, has advanced our ability to manipulate the material to our advantage. We now have the ability to study not only the structure of the material, but also the material behavior and properties at the nanoscale. Understanding this behavior is critical to developing a framework for interpreting and utilizing these properties in materials design. This research aims to improve the fundamental understanding of the mechanical performance of materials and the subsequent variation in measured properties. The literature reports widely varying material properties such as hardness, elastic modulus, and yield point when measured at the nanoscale. Proposed variation mechanisms in these properties include surface preparation, error in measurement, heterogeneous dislocation density and distribution, crystal orientation, surface oxide film fracture, and others. Among other things, this work shows that these sources of variation can be determined and quantified, and that this information can be utilized as a characterization and/or predictive tool. The main goals of this work are to 1) continue basic research on sources of variation in the nanoscale properties of materials, specifically hardness and modulus in crystalline and glassy solids, 2) study the abrupt transition from elastic to plastic material behavior known as pop-in and resolve the problem of pseudo-elastic behavior prior to plasticity, and 3) integrate the sources of and propagate the variation into materials simulations, 4) study the influence of dislocation processes on indentation size effects, and 5) apply this learning to difficult to measure or interpret materials applications.

Magnetic properties in an ash flow tuff with continuous grain size variation: a natural reference for magnetic particle granulometry

USGS Publications Warehouse

Till, J.L.; Jackson, M.J.; Rosenbaum, J.G.; Solheid, P.

2011-01-01

The Tiva Canyon Tuff contains dispersed nanoscale Fe-Ti-oxide grains with a narrow magnetic grain size distribution, making it an ideal material in which to identify and study grain-size-sensitive magnetic behavior in rocks. A detailed magnetic characterization was performed on samples from the basal 5 m of the tuff. The magnetic materials in this basal section consist primarily of (low-impurity) magnetite in the form of elongated submicron grains exsolved from volcanic glass. Magnetic properties studied include bulk magnetic susceptibility, frequency-dependent and temperature-dependent magnetic susceptibility, anhysteretic remanence acquisition, and hysteresis properties. The combined data constitute a distinct magnetic signature at each stratigraphic level in the section corresponding to different grain size distributions. The inferred magnetic domain state changes progressively upward from superparamagnetic grains near the base to particles with pseudo-single-domain or metastable single-domain characteristics near the top of the sampled section. Direct observations of magnetic grain size confirm that distinct transitions in room temperature magnetic susceptibility and remanence probably denote the limits of stable single-domain behavior in the section. These results provide a unique example of grain-size-dependent magnetic properties in noninteracting particle assemblages over three decades of grain size, including close approximations of ideal Stoner-Wohlfarth assemblages, and may be considered a useful reference for future rock magnetic studies involving grain-size-sensitive properties.

Hygrothermal Effects in Continuous Fibre Reinforced Composites. Part 4. Mechanical Properties 2 - Fatigue and Time-Dependent Properties (Effets Hygrothermiques dans les Composites a Renfort de Fibre Continu. Partie 4. Proprietes Mecaniques 2 - Fatigue et Proprietes Dependant du Temps)

DTIC Science & Technology

1983-09-01

reduction of stress intensity at a crack tip due to Lreep was responsible for increasing the fatigue life during the "slow- fast " L .sts. As creep is clearly...Aeronautical Establishment Structures and Materials Laboratory SPONSORING AGENCY/AGENCE DE SUBVENTION 8 DATE FILE/DOSSIER LAB. ORDER PAGES FIGS/ DIAGRAMMES

Bandgap Engineering of InP QDs Through Shell Thickness and Composition

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

Dennis, Allison M.; Mangum, Benjamin D.; Piryatinski, Andrei

2012-06-21

Fields as diverse as biological imaging and telecommunications utilize the unique photophysical and electronic properties of nanocrystal quantum dots (NQDs). The development of new NQD compositions promises material properties optimized for specific applications, while addressing material toxicity. Indium phosphide (InP) offers a 'green' alternative to the traditional cadmium-based NQDs, but suffers from extreme susceptibility to oxidation. Coating InP cores with more stable shell materials significantly improves nanocrystal resistance to oxidation and photostability. We have investigated several new InP-based core-shell compositions, correlating our results with theoretical predictions of their optical and electronic properties. Specifically, we can tailor the InP core-shell QDsmore » to a type-I, quasi-type-II, or type-II bandgap structure with emission wavelengths ranging from 500-1300 nm depending on the shell material used (ZnS, ZnSe, CdS, or CdSe) and the thickness of the shell. Single molecule microscopy assessments of photobleaching and blinking are used to correlate NQD properties with shell thickness.« less

Materials, critical materials and clean-energy technologies

NASA Astrophysics Data System (ADS)

Eggert, R.

2017-07-01

Modern engineered materials, components and systems depend on raw materials whose properties provide essential functionality to these technologies. Some of these raw materials are subject to supply-chain risks, and such materials are known as critical materials. This paper reviews corporate, national and world perspectives on material criticality. It then narrows its focus to studies that assess "what is critical" to clean-energy technologies. The focus on supply-chain risks is not meant to be alarmist but rather to encourage attention to monitoring these risks and pursuing technological innovation to mitigate the risks.

Are extracted materials truly representative of original samples? Impact of C18 extraction on CDOM optical and chemical properties

NASA Astrophysics Data System (ADS)

Andrew, Andrea; Del Vecchio, Rossana; Zhang, Yi; Subramaniam, Ajit; Blough, Neil

2016-02-01

Some properties of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) can be easily measured directly on whole waters, while others require sample concentration and removal of natural salts. To increase CDOM content and eliminate salts, solid phase extraction is often employed. Biases following extraction and elution are inevitable, thus raising the question of how truly representative the extracted material is of the original. In this context, we investigated the wavelength dependence of extraction efficiency for C18 cartridges with respect to CDOM optical properties using samples obtained from the Middle Atlantic Bight (MAB) and the Equatorial Atlantic Ocean (EAO). Further, we compared the optical changes of C18 extracts and the corresponding whole water following chemical reduction with sodium borohydride (NaBH4). C18 cartridges preferentially extracted long-wavelength absorbing/emitting material for samples impacted by riverine input. Extraction efficiency overall decreased with offshore distance away from riverine input. Spectral slopes of C18-OM samples were also almost always lower than those of their corresponding CDOM samples supporting the preferential extraction of higher molecular weight absorbing material. The wavelength dependence of the optical properties (absorption, fluorescence emission and quantum yield) of the original water samples and their corresponding extracted material were very similar. C18 extracts and corresponding water samples further exhibited comparable optical changes following NaBH4 reduction, thus suggesting a similarity in nature (structure) of the optically active extracted material, independent of geographical locale. Altogether, these data suggested a strong similarity between C18 extracts and corresponding whole waters, thus indicating that extracts are representative of the CDOM content of original waters.

Are Extracted Materials Truly Representative of Original Samples? Impact of C18 Extraction on CDOM Optical and Chemical Properties

PubMed Central

Andrew, Andrea A.; Del Vecchio, Rossana; Zhang, Yi; Subramaniam, Ajit; Blough, Neil V.

2016-01-01

Some properties of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) can be easily measured directly on whole waters, while others require sample concentration and removal of natural salts. To increase CDOM content and eliminate salts, solid phase extraction (SPE) is often employed. Biases following extraction and elution are inevitable, thus raising the question of how truly representative the extracted material is of the original. In this context, we investigated the wavelength dependence of extraction efficiency for C18 cartridges with respect to CDOM optical properties using samples obtained from the Middle Atlantic Bight (MAB) and the Equatorial Atlantic Ocean (EAO). Further, we compared the optical changes of C18 extracts and the corresponding whole water following chemical reduction with sodium borohydride (NaBH4). C18 cartridges preferentially extracted long-wavelength absorbing/emitting material for samples impacted by riverine input. Extraction efficiency overall decreased with offshore distance away from riverine input. Spectral slopes of C18-OM samples were also almost always lower than those of their corresponding CDOM samples supporting the preferential extraction of higher molecular weight absorbing material. The wavelength dependence of the optical properties (absorption, fluorescence emission, and quantum yield) of the original water samples and their corresponding extracted material were very similar. C18 extracts and corresponding water samples further exhibited comparable optical changes following NaBH4 reduction, thus suggesting a similarity in nature (structure) of the optically active extracted material, independent of geographical locale. Altogether, these data suggested a strong similarity between C18 extracts and corresponding whole waters, thus indicating that extracts are representative of the CDOM content of original waters. PMID:26904536

Are Extracted Materials Truly Representative of Original Samples? Impact of C18 Extraction on CDOM Optical and Chemical Properties.

PubMed

Andrew, Andrea A; Del Vecchio, Rossana; Zhang, Yi; Subramaniam, Ajit; Blough, Neil V

2016-01-01

Some properties of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) can be easily measured directly on whole waters, while others require sample concentration and removal of natural salts. To increase CDOM content and eliminate salts, solid phase extraction (SPE) is often employed. Biases following extraction and elution are inevitable, thus raising the question of how truly representative the extracted material is of the original. In this context, we investigated the wavelength dependence of extraction efficiency for C18 cartridges with respect to CDOM optical properties using samples obtained from the Middle Atlantic Bight (MAB) and the Equatorial Atlantic Ocean (EAO). Further, we compared the optical changes of C18 extracts and the corresponding whole water following chemical reduction with sodium borohydride (NaBH4). C18 cartridges preferentially extracted long-wavelength absorbing/emitting material for samples impacted by riverine input. Extraction efficiency overall decreased with offshore distance away from riverine input. Spectral slopes of C18-OM samples were also almost always lower than those of their corresponding CDOM samples supporting the preferential extraction of higher molecular weight absorbing material. The wavelength dependence of the optical properties (absorption, fluorescence emission, and quantum yield) of the original water samples and their corresponding extracted material were very similar. C18 extracts and corresponding water samples further exhibited comparable optical changes following NaBH4 reduction, thus suggesting a similarity in nature (structure) of the optically active extracted material, independent of geographical locale. Altogether, these data suggested a strong similarity between C18 extracts and corresponding whole waters, thus indicating that extracts are representative of the CDOM content of original waters.

Optical Properties of Si, Ge, GaAs, GaSb, InAs, and InP at Elevated Temperatures

DTIC Science & Technology

2010-03-01

transmitted, and an absorbed (or scattered) component. The reflectance can be defined in terms of the index of refraction of the media on either side...of the interface. If the index of refraction of the material is n and the material is surrounded by air (nair ≈ 1), then the reflectance for near...the absorption coefficient and t is the sample thickness. 9 Since R depends on the refractive index and the refractive index depends on the

Graphene - ferroelectric and MoS2 - ferroelectric heterostructures for memory applications

NASA Astrophysics Data System (ADS)

Lipatov, Alexey; Sharma, Pankaj; Gruverman, Alexei; Sinitskii, Alexander

In recent years there has been an unprecedented interest in two-dimensional (2D) materials with unique physical and chemical properties that cannot be found in their three-dimensional (3D) counterparts. One of the important advantages of 2D materials is that they can be easily integrated with other 2D materials and functional films, resulting in multilayered structures with new properties. We fabricated and tested electronic and memory properties of field-effect transistors (FETs) based on a single-layer graphene combined with lead zirconium titanate (PZT) substrate. Previously studied graphene-PZT devices exhibited an unusual electronic behavior such as clockwise hysteresis of electronic transport, in contradiction with counterclockwise polarization dependence of PZT. We investigated how the interplay of polarization and interfacial phenomena affects the electronic behavior and memory characteristics of graphene-PZT FETs, explain the origin of unusual clockwise hysteresis and experimentally demonstrate a reversed polarization-dependent hysteresis of electronic transport. In addition we fabricated and tested properties of MoS2-PZT FETs which exhibit a large hysteresis of electronic transport with high ON/OFF ratios. We demonstrate that MoS2-PZT memories have a number of advantages over commercial FeRAMs, such as nondestructive data readout, low operation voltage, wide memory window and the possibility to write and erase them both electrically and optically.

Dependence of behavioral performance on material category in an object grasping task with monkeys.

PubMed

Yokoi, Isao; Tachibana, Atsumichi; Minamimoto, Takafumi; Goda, Naokazu; Komatsu, Hidehiko

2018-05-02

Material perception is an essential part of our cognitive function that enables us to properly interact with our complex daily environment. One important aspect of material perception is its multimodal nature. When we see an object, we generally recognize its haptic properties as well as its visual properties. Consequently, one must examine behavior using real objects that are perceived both visually and haptically to fully understand the characteristics of material perception. As a first step, we examined whether there is any difference in the behavioral responses to different materials in monkeys trained to perform an object grasping task in which they saw and grasped rod-shaped real objects made of various materials. We found that the monkeys' behavior in the grasping task, measured based on the success rate and the pulling force, differed depending on the material category. Monkeys easily and correctly grasped objects of some materials, such as metal and glass, but failed to grasp objects of other materials. In particular, monkeys avoided grasping fur-covered objects. The differences in the behavioral responses to the material categories cannot be explained solely based on the degree of familiarity with the different materials. These results shed light on the organization of multimodal representation of materials, where their biological significance is an important factor. In addition, a monkey that avoided touching real fur-covered objects readily touched images of the same objects presented on a CRT display. This suggests employing real objects is important when studying behaviors related to material perception.

Understanding the Size-Dependent Sodium Storage Properties of Na2C6O6-Based Organic Electrodes for Sodium-Ion Batteries.

PubMed

Wang, Yaqun; Ding, Yu; Pan, Lijia; Shi, Ye; Yue, Zhuanghao; Shi, Yi; Yu, Guihua

2016-05-11

Organic electroactive materials represent a new generation of sustainable energy storage technology due to their unique features including environmental benignity, material sustainability, and highly tailorable properties. Here a carbonyl-based organic salt Na2C6O6, sodium rhodizonate (SR) dibasic, is systematically investigated for high-performance sodium-ion batteries. A combination of structural control, electrochemical analysis, and computational simulation show that rational morphological control can lead to significantly improved sodium storage performance. A facile antisolvent method was developed to synthesize microbulk, microrod, and nanorod structured SRs, which exhibit strong size-dependent sodium ion storage properties. The SR nanorod exhibited the best performance to deliver a reversible capacity of ∼190 mA h g(-1) at 0.1 C with over 90% retention after 100 cycles. At a high rate of 10 C, 50% of the capacity can be obtained due to enhanced reaction kinetics, and such high electrochemical activity maintains even at 80 °C. These results demonstrate a generic design route toward high-performance organic-based electrode materials for beyond Li-ion batteries. Using such a biomass-derived organic electrode material enables access to sustainable energy storage devices with low cost, high electrochemical performance and thermal stability.

Effect of pH on the electrical properties and conducting mechanism of SnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Periathai, R. Sudha; Abarna, S.; Hirankumar, G.; Jeyakumaran, N.; Prithivikumaran, N.

2017-03-01

Semiconductor nanoparticles have attracted more interests because of their size-dependent optical and electrical properties.SnO2 is an oxygen-deficient n-type semiconductor with a wide band gap of 3.6 eV (300 K). It has many remarkable applications as sensors, catalysts, transparent conducting electrodes, anode material for rechargeable Li- ion batteries and optoelectronic devices. In the present work, the role of pH in determining the electrical and dielectric properties of SnO2 nanoparticles has been studied as a function of temperature ranging from Room temperature (RT) to 114 °C in the frequency range of 7 MHz to 50 mHz using impedance spectroscopic technique. The non linear behavior observed in the thermal dependence of the conductance of SnO2 nanoparticles is explained by means of the surface property of SnO2 nanoparticles where proton hopping mechanism is dealt with. Jonscher's power law has been fitted for the conductance spectra and the frequency exponent ("s" value) gives an insight about the ac conducting mechanism. The temperature dependence of electrical relaxation phenomenon in the material has been observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation.

Transverse crack initiation under combined thermal and mechanical loading of Fibre Metal Laminates and Glass Fibre Reinforced Polymers

NASA Astrophysics Data System (ADS)

van de Camp, W.; Dhallé, M. M. J.; Warnet, L.; Wessel, W. A. J.; Vos, G. S.; Akkerman, R.; ter Brake, H. J. M.

2017-02-01

The paper describes a temperature-dependent extension of the classical laminate theory (CLT) that may be used to predict the mechanical behaviour of Fibre Metal Laminates (FML) at cryogenic conditions, including crack initiation. FML are considered as a possible alternative class of structural materials for the transport and storage of liquified gasses such as LNG. Combining different constituents in a laminate opens up the possibility to enhance its functionality, e.g. offering lower specific weight and increased damage tolerance. To explore this possibility, a test programme is underway at the University of Twente to study transverse crack initiation in different material combinations under combined thermal and mechanical loading. Specifically, the samples are tested in a three-point bending experiment at temperatures ranging from 77 to 293 K. These tests will serve as a validation of the model presented in this paper which, by incorporating temperature-dependent mechanical properties and differential thermal expansion, will allow to select optimal material combinations and laminate layouts. By combining the temperature-dependent mechanical properties and the differential thermal contraction explicitly, the model allows for a more accurate estimate of the resulting thermal stresses which can then be compared to the strength of the constituent materials.

Dielectric Characteristics of Microstructural Changes and Property Evolution in Engineered Materials

NASA Astrophysics Data System (ADS)

Clifford, Jallisa Janet

Heterogeneous materials are increasingly used in a wide range of applications such as aerospace, civil infrastructure, fuel cells and many others. The ability to take properties from two or more materials to create a material with properties engineered to needs is always very attractive. Hence heterogeneous materials are evolving into more complex formulations in multiple disciplines. Design of microstructure at multiple scales control the global functional properties of these materials and their structures. However, local microstructural changes do not directly cause a proportional change to the global properties (such as strength and stiffness). Instead, local changes follow an evolution process including significant interactions. Therefore, in order to understand property evolution of engineered materials, microstructural changes need to be effectively captured. Characterizing these changes and representing them by material variables will enable us to further improve our material level understanding. In this work, we will demonstrate how microstructural features of heterogeneous materials can be described quantitatively using broadband dielectric spectroscopy (BbDS). The frequency dependent dielectric properties can capture the change in material microstructure and represent these changes in terms of material variables, such as complex permittivity. These changes in terms of material properties can then be linked to a number of different conditions, such as increasing damage due to impact or fatigue. Two different broadband dielectric spectroscopy scanning modes are presented: bulk measurements and continuous scanning to measure dielectric property change as a function of position across the specimen. In this study, we will focus on ceramic materials and fiber reinforced polymer matrix composites as test bed material systems. In the first part of the thesis, we will present how different micro-structural design of porous ceramic materials can be captured quantitatively using BbDS. These materials are typically used in solid oxide fuel cells (SOFC). Results show significant effect of microstructural design on material properties at multiple temperatures (up to 800 °C). In the later part of the thesis, we will focus on microstructural changes of fiber reinforced composite materials due to impact and static loading. The changes in dielectric response can then be linked to the bulk mechanical properties of the material and various damage modes. Observing trends in dielectric response enables us to further determine local mechanisms and distribution of properties throughout the damaged specimens. A 3D X-ray microscope and a digital microscope have been used to visualize these changes in material microstructure and validate experimental observations. The increase in damage observed in the material microstructure can then also be linked to the changes in dielectric response. Results show that BbDS is an extremely useful tool for identifying microstructural changes within a heterogeneous material and particularly useful in relating remaining properties. Dielectric material variables can be used directly in property degradation laws and help develop a framework for future predictive modeling methodologies.

Multi-Dimensional, Non-Pyrolyzing Ablation Test Problems

NASA Technical Reports Server (NTRS)

Risch, Tim; Kostyk, Chris

2016-01-01

Non-pyrolyzingcarbonaceous materials represent a class of candidate material for hypersonic vehicle components providing both structural and thermal protection system capabilities. Two problems relevant to this technology are presented. The first considers the one-dimensional ablation of a carbon material subject to convective heating. The second considers two-dimensional conduction in a rectangular block subject to radiative heating. Surface thermochemistry for both problems includes finite-rate surface kinetics at low temperatures, diffusion limited ablation at intermediate temperatures, and vaporization at high temperatures. The first problem requires the solution of both the steady-state thermal profile with respect to the ablating surface and the transient thermal history for a one-dimensional ablating planar slab with temperature-dependent material properties. The slab front face is convectively heated and also reradiates to a room temperature environment. The back face is adiabatic. The steady-state temperature profile and steady-state mass loss rate should be predicted. Time-dependent front and back face temperature, surface recession and recession rate along with the final temperature profile should be predicted for the time-dependent solution. The second problem requires the solution for the transient temperature history for an ablating, two-dimensional rectangular solid with anisotropic, temperature-dependent thermal properties. The front face is radiatively heated, convectively cooled, and also reradiates to a room temperature environment. The back face and sidewalls are adiabatic. The solution should include the following 9 items: final surface recession profile, time-dependent temperature history of both the front face and back face at both the centerline and sidewall, as well as the time-dependent surface recession and recession rate on the front face at both the centerline and sidewall. The results of the problems from all submitters will be collected, summarized, and presented at a later conference.

HEATING 7. 1 user's manual

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

Childs, K.W.

1991-07-01

HEATING is a FORTRAN program designed to solve steady-state and/or transient heat conduction problems in one-, two-, or three- dimensional Cartesian, cylindrical, or spherical coordinates. A model may include multiple materials, and the thermal conductivity, density, and specific heat of each material may be both time- and temperature-dependent. The thermal conductivity may be anisotropic. Materials may undergo change of phase. Thermal properties of materials may be input or may be extracted from a material properties library. Heating generation rates may be dependent on time, temperature, and position, and boundary temperatures may be time- and position-dependent. The boundary conditions, which maymore » be surface-to-boundary or surface-to-surface, may be specified temperatures or any combination of prescribed heat flux, forced convection, natural convection, and radiation. The boundary condition parameters may be time- and/or temperature-dependent. General graybody radiation problems may be modeled with user-defined factors for radiant exchange. The mesh spacing may be variable along each axis. HEATING is variably dimensioned and utilizes free-form input. Three steady-state solution techniques are available: point-successive-overrelaxation iterative method with extrapolation, direct-solution (for one-dimensional or two-dimensional problems), and conjugate gradient. Transient problems may be solved using one of several finite-difference schemes: Crank-Nicolson implicit, Classical Implicit Procedure (CIP), Classical Explicit Procedure (CEP), or Levy explicit method (which for some circumstances allows a time step greater than the CEP stability criterion). The solution of the system of equations arising from the implicit techniques is accomplished by point-successive-overrelaxation iteration and includes procedures to estimate the optimum acceleration parameter.« less

Influence of disorder on transfer characteristics of organic electrochemical transistors

NASA Astrophysics Data System (ADS)

Friedlein, Jacob T.; Rivnay, Jonathan; Dunlap, David H.; McCulloch, Iain; Shaheen, Sean E.; McLeod, Robert R.; Malliaras, George G.

2017-07-01

Organic electrochemical transistors (OECTs) are receiving a great deal of attention as transducers of biological signals due to their high transconductance. A ubiquitous property of these devices is the non-monotonic dependence of transconductance on gate voltage. However, this behavior is not described by existing models. Using OECTs made of materials with different chemical and electrical properties, we show that this behavior arises from the influence of disorder on the electronic transport properties of the organic semiconductor and occurs even in the absence of contact resistance. These results imply that the non-monotonic transconductance is an intrinsic property of OECTs and cannot be eliminated by device design or contact engineering. Finally, we present a model based on the physics of electronic conduction in disordered materials. This model fits experimental transconductance curves and describes strategies for rational material design to improve OECT performance in sensing applications.

Stretchable liquid-crystal blue-phase gels.

PubMed

Castles, F; Morris, S M; Hung, J M C; Qasim, M M; Wright, A D; Nosheen, S; Choi, S S; Outram, B I; Elston, S J; Burgess, C; Hill, L; Wilkinson, T D; Coles, H J

2014-08-01

Liquid-crystalline polymers are materials of considerable scientific interest and technological value. An important subset of these materials exhibit rubber-like elasticity, combining the optical properties of liquid crystals with the mechanical properties of rubber. Moreover, they exhibit behaviour not seen in either type of material independently, and many of their properties depend crucially on the particular mesophase employed. Such stretchable liquid-crystalline polymers have previously been demonstrated in the nematic, chiral-nematic, and smectic mesophases. Here, we report the fabrication of a stretchable gel of blue phase I, which forms a self-assembled, three-dimensional photonic crystal that remains electro-optically switchable under a moderate applied voltage, and whose optical properties can be manipulated by an applied strain. We also find that, unlike its undistorted counterpart, a mechanically deformed blue phase exhibits a Pockels electro-optic effect, which sets out new theoretical challenges and possibilities for low-voltage electro-optic devices.

Review of world experience and properties of materials for encapsulation of terrestrial photovoltaic arrays

NASA Technical Reports Server (NTRS)

Carmichael, D. C.; Gaines, G. B.; Sliemers, F. A.; Kistler, C. W.; Igou, R. D.

1976-01-01

Published and unpublished information relating to encapsulation systems and materials properties was collected by searching the literature and appropriate data bases (over 1,300 documents were selected and reviewed) and by personal contacts including site and company visits. A data tabulation summarizing world experience with terrestrial photovoltaic arrays (50 installations) is presented in the report. Based on criteria of properties, processability, availability, and cost, candidate materials were identified which have potential for use in encapsulation systems for arrays with a lifetime of over 20 years high reliability, an efficiency greater than 10 percent, a total price less than $500/kW, and a production capacity of 500,000 kW/yr. The recommended materials (all commercially available) include, depending upon the device design, various borosilicate and soda-lime glasses and numerous polymerics suitable for specific encapsulation system functions.

Effect of size on bulk and surface cohesion energy of metallic nano-particles

NASA Astrophysics Data System (ADS)

Yaghmaee, M. S.; Shokri, B.

2007-04-01

The knowledge of nano-material properties not only helps us to understand the extreme behaviour of small-scale materials better (expected to be different from what we observe from their bulk value) but also helps us to analyse and design new advanced functionalized materials through different nano technologies. Among these fundamental properties, the cohesion (binding) energy mainly describes most behaviours of materials in different environments. In this work, we discuss this fundamental property through a nano-thermodynamical approach using two algorithms, where in the first approach the size dependence of the inner (bulk) cohesion energy is studied, and in the second approach the surface cohesion energy is considered too. The results, which are presented through a computational demonstration (for four different metals: Al, Ga, W and Ag), can be compared with some experimental values for W metallic nano-particles.

Advances in Porous Biomaterials for Dental and Orthopaedic Applications

PubMed Central

Mour, Meenakshi; Das, Debarun; Winkler, Thomas; Hoenig, Elisa; Mielke, Gabriela; Morlock, Michael M.; Schilling, Arndt F.

2010-01-01

The connective hard tissues bone and teeth are highly porous on a micrometer scale, but show high values of compression strength at a relatively low weight. The fabrication of porous materials has been actively researched and different processes have been developed that vary in preparation complexity and also in the type of porous material that they produce. Methodologies are available for determination of pore properties. The purpose of the paper is to give an overview of these methods, the role of porosity in natural porous materials and the effect of pore properties on the living tissues. The minimum pore size required to allow the ingrowth of mineralized tissue seems to be in the order of 50 µm: larger pore sizes seem to improve speed and depth of penetration of mineralized tissues into the biomaterial, but on the other hand impair the mechanical properties. The optimal pore size is therefore dependent on the application and the used material.

Numerical homogenization of elastic and thermal material properties for metal matrix composites (MMC)

NASA Astrophysics Data System (ADS)

Schindler, Stefan; Mergheim, Julia; Zimmermann, Marco; Aurich, Jan C.; Steinmann, Paul

2017-01-01

A two-scale material modeling approach is adopted in order to determine macroscopic thermal and elastic constitutive laws and the respective parameters for metal matrix composite (MMC). Since the common homogenization framework violates the thermodynamical consistency for non-constant temperature fields, i.e., the dissipation is not conserved through the scale transition, the respective error is calculated numerically in order to prove the applicability of the homogenization method. The thermomechanical homogenization is applied to compute the macroscopic mass density, thermal expansion, elasticity, heat capacity and thermal conductivity for two specific MMCs, i.e., aluminum alloy Al2024 reinforced with 17 or 30 % silicon carbide particles. The temperature dependency of the material properties has been considered in the range from 0 to 500°C, the melting temperature of the alloy. The numerically determined material properties are validated with experimental data from the literature as far as possible.

Metal-Ceramic composites via “in situ” methods

NASA Astrophysics Data System (ADS)

Florea, R. M.

2017-08-01

Several “in situ” methods for obtaining composite materials with ceramic particles were developed in order to overcome some of the inherent problems associated with conventional processes. This paper reviews the obtaining processes of composite materials with a greater emphasis on nitriding and oxidation by directed melting. These obtaining methods provide microstructures with different combinations of metal-ceramic. Metal matrix composites with controlled amounts of dispersed ceramic particles are obtained by “in situ” processes. The composite materials obtained are having different properties by controlling various processing variables such as temperature, time, the reactant phases and the reinforcing material. The properties of the “in situ” obtained materials depend mainly on the matrix and volume fraction of constituent phase. Briefly are reviewed the mechanical properties, hardness mechanisms and possible applications of these composite materials. Nitridation is much more attractive because with the variation of process parameters is obtained a wider range of microstructures and properties. The activation energy for the formation of AlN (A1N ˜ 100 kJ/mole) is smaller than that of oxidation (Al2O3 ˜ 400 kJ/mole) and growth rates (3 × 10-2 gm/cm2/s) are at least three times higher for oxidation.

A review of experimental techniques to produce a nacre-like structure.

PubMed

Corni, I; Harvey, T J; Wharton, J A; Stokes, K R; Walsh, F C; Wood, R J K

2012-09-01

The performance of man-made materials can be improved by exploring new structures inspired by the architecture of biological materials. Natural materials, such as nacre (mother-of-pearl), can have outstanding mechanical properties due to their complicated architecture and hierarchical structure at the nano-, micro- and meso-levels which have evolved over millions of years. This review describes the numerous experimental methods explored to date to produce composites with structures and mechanical properties similar to those of natural nacre. The materials produced have sizes ranging from nanometres to centimetres, processing times varying from a few minutes to several months and a different range of mechanical properties that render them suitable for various applications. For the first time, these techniques have been divided into those producing bulk materials, coatings and free-standing films. This is due to the fact that the material's application strongly depends on its dimensions and different results have been reported by applying the same technique to produce materials with different sizes. The limitations and capabilities of these methodologies have been also described.

The properties of weft knitted fabric medical and preventive treatment action using eco-raw materials

NASA Astrophysics Data System (ADS)

Halavska, L.; Batrak, O.

2016-07-01

A new trend in the world is the clothing production using the new types of ecological raw materials application - milk, pineapple, coconut, hemp, banana, eucalyptus, clams, corn, bamboo, soya, nettle yarn. This makes it possible to create textile materials of new generation with unique antibacterial and antiseptic properties. Such materials have a positive preventive and sometimes therapeutic effect on people, and their health. Eco-raw materials clothing is able to protect the human body from the environment harmful effects: cold, heat, rain, dust, opportunely remove from underclothing layer the steam and gases, sweat; maintain in underclothing layer the necessary microclimate for normal organism functioning. Study of knitwear consumer properties, produced with eco-materials, is an urgent task of the world vector, directed on ecological environmental protection. This paper presents the research results of hygroscopicity and capillarity weft knitted fabrics, what knitted from different types of eco-raw materials: bamboo yarn, yarn containing soybean and nettle yarn. Character of influence of the liquid raising level changes depending on the experiment time and the knitting structure is revealed.

Insight into interfacial effect on effective physical properties of fibrous materials. I. The volume fraction of soft interfaces around anisotropic fibers.

PubMed

Xu, Wenxiang; Wang, Han; Niu, Yanze; Bai, Jingtao

2016-01-07

With advances in interfacial properties characterization technologies, the interfacial volume fraction is a feasible parameter for evaluating effective physical properties of materials. However, there is a need to determine the interfacial volume fraction around anisotropic fibers and a need to assess the influence of such the interfacial property on effective properties of fibrous materials. Either ways, the accurate prediction of interfacial volume fraction is required. Towards this end, we put forward both theoretical and numerical schemes to determine the interfacial volume fraction in fibrous materials, which are considered as a three-phase composite structure consisting of matrix, anisotropic hard spherocylinder fibers, and soft interfacial layers with a constant dimension coated on the surface of each fiber. The interfacial volume fraction actually represents the fraction of space not occupied by all hard fibers and matrix. The theoretical scheme that adopts statistical geometry and stereological theories is essentially an analytic continuation from spherical inclusions. By simulating such three-phase chopped fibrous materials, we numerically derive the interfacial volume fraction. The theoretical and numerical schemes provide a quantitative insight that the interfacial volume fraction depends strongly on the fiber geometries like fiber shape, geometric size factor, and fiber size distribution. As a critical interfacial property, the present contribution can be further drawn into assessing effective physical properties of fibrous materials, which will be demonstrated in another paper (Part II) of this series.

Sequence-Dependent Structure/Function Relationships of Catalytic Peptide-Enabled Gold Nanoparticles Generated under Ambient Synthetic Conditions.

PubMed

Bedford, Nicholas M; Hughes, Zak E; Tang, Zhenghua; Li, Yue; Briggs, Beverly D; Ren, Yang; Swihart, Mark T; Petkov, Valeri G; Naik, Rajesh R; Knecht, Marc R; Walsh, Tiffany R

2016-01-20

Peptide-enabled nanoparticle (NP) synthesis routes can create and/or assemble functional nanomaterials under environmentally friendly conditions, with properties dictated by complex interactions at the biotic/abiotic interface. Manipulation of this interface through sequence modification can provide the capability for material properties to be tailored to create enhanced materials for energy, catalysis, and sensing applications. Fully realizing the potential of these materials requires a comprehensive understanding of sequence-dependent structure/function relationships that is presently lacking. In this work, the atomic-scale structures of a series of peptide-capped Au NPs are determined using a combination of atomic pair distribution function analysis of high-energy X-ray diffraction data and advanced molecular dynamics (MD) simulations. The Au NPs produced with different peptide sequences exhibit varying degrees of catalytic activity for the exemplar reaction 4-nitrophenol reduction. The experimentally derived atomic-scale NP configurations reveal sequence-dependent differences in structural order at the NP surface. Replica exchange with solute-tempering MD simulations are then used to predict the morphology of the peptide overlayer on these Au NPs and identify factors determining the structure/catalytic properties relationship. We show that the amount of exposed Au surface, the underlying surface structural disorder, and the interaction strength of the peptide with the Au surface all influence catalytic performance. A simplified computational prediction of catalytic performance is developed that can potentially serve as a screening tool for future studies. Our approach provides a platform for broadening the analysis of catalytic peptide-enabled metallic NP systems, potentially allowing for the development of rational design rules for property enhancement.

Topological Phase Transitions in the Photonic Spin Hall Effect

DOE PAGES

Kort-Kamp, Wilton Junior de Melo

2017-10-04

The recent synthesis of two-dimensional staggered materials opens up burgeoning opportunities to study optical spin-orbit interactions in semiconducting Dirac-like systems. In this work, we unveil topological phase transitions in the photonic spin Hall effect in the graphene family materials. It is shown that an external static electric field and a high frequency circularly polarized laser allow for active on-demand manipulation of electromagnetic beam shifts. The spin Hall effect of light presents a rich dependence with radiation degrees of freedom, and material properties, and features nontrivial topological properties. Finally, we discover that photonic Hall shifts are sensitive to spin and valleymore » properties of the charge carriers, providing an unprecedented pathway to investigate spintronics and valleytronics in staggered 2D semiconductors.« less

Semiconductor quantum dots: synthesis and water-solubilization for biomedical applications.

PubMed

Yu, William W

2008-10-01

Quantum dots (QDs) are generally nanosized inorganic particles. They have distinctive size-dependent optical properties due to their very small size (mostly < 10 nm). QDs are regarded as promising new fluorescent materials for biological labeling and imaging because of their superior properties compared with traditional organic molecular dyes. These properties include high quantum efficiency, long-term photostability and very narrow emission but broad absorption spectra. Recent developments in synthesizing high quality semiconductor QDs (mainly metal-chalcogenide compounds) and forming biocompatible structures for biomedical applications are discussed in this paper. This information may facilitate the research to create new materials/technologies for future clinical applications.

Modified Continuum Mechanics Modeling on Size-Dependent Properties of Piezoelectric Nanomaterials: A Review

PubMed Central

Yan, Zhi; Jiang, Liying

2017-01-01

Piezoelectric nanomaterials (PNs) are attractive for applications including sensing, actuating, energy harvesting, among others in nano-electro-mechanical-systems (NEMS) because of their excellent electromechanical coupling, mechanical and physical properties. However, the properties of PNs do not coincide with their bulk counterparts and depend on the particular size. A large amount of efforts have been devoted to studying the size-dependent properties of PNs by using experimental characterization, atomistic simulation and continuum mechanics modeling with the consideration of the scale features of the nanomaterials. This paper reviews the recent progresses and achievements in the research on the continuum mechanics modeling of the size-dependent mechanical and physical properties of PNs. We start from the fundamentals of the modified continuum mechanics models for PNs, including the theories of surface piezoelectricity, flexoelectricity and non-local piezoelectricity, with the introduction of the modified piezoelectric beam and plate models particularly for nanostructured piezoelectric materials with certain configurations. Then, we give a review on the investigation of the size-dependent properties of PNs by using the modified continuum mechanics models, such as the electromechanical coupling, bending, vibration, buckling, wave propagation and dynamic characteristics. Finally, analytical modeling and analysis of nanoscale actuators and energy harvesters based on piezoelectric nanostructures are presented. PMID:28336861

Modified Continuum Mechanics Modeling on Size-Dependent Properties of Piezoelectric Nanomaterials: A Review.

PubMed

Yan, Zhi; Jiang, Liying

2017-01-26

Piezoelectric nanomaterials (PNs) are attractive for applications including sensing, actuating, energy harvesting, among others in nano-electro-mechanical-systems (NEMS) because of their excellent electromechanical coupling, mechanical and physical properties. However, the properties of PNs do not coincide with their bulk counterparts and depend on the particular size. A large amount of efforts have been devoted to studying the size-dependent properties of PNs by using experimental characterization, atomistic simulation and continuum mechanics modeling with the consideration of the scale features of the nanomaterials. This paper reviews the recent progresses and achievements in the research on the continuum mechanics modeling of the size-dependent mechanical and physical properties of PNs. We start from the fundamentals of the modified continuum mechanics models for PNs, including the theories of surface piezoelectricity, flexoelectricity and non-local piezoelectricity, with the introduction of the modified piezoelectric beam and plate models particularly for nanostructured piezoelectric materials with certain configurations. Then, we give a review on the investigation of the size-dependent properties of PNs by using the modified continuum mechanics models, such as the electromechanical coupling, bending, vibration, buckling, wave propagation and dynamic characteristics. Finally, analytical modeling and analysis of nanoscale actuators and energy harvesters based on piezoelectric nanostructures are presented.

Polymer composites and porous materials prepared by thermally induced phase separation and polymer-metal hybrid methods

NASA Astrophysics Data System (ADS)

Yoon, Joonsung

The primary objective of this research is to investigate the morphological and mechanical properties of composite materials and porous materials prepared by thermally induced phase separation. High melting crystallizable diluents were mixed with polymers so that the phase separation would be induced by the solidification of the diluents upon cooling. Theoretical phase diagrams were calculated using Flory-Huggins solution thermodynamics which show good agreement with the experimental results. Porous materials were prepared by the extraction of the crystallized diluents after cooling the mixtures (hexamethylbenzene/polyethylene and pyrene/polyethylene). Anisotropic structures show strong dependence on the identity of the diluents and the composition of the mixtures. Anisotropic crystal growth of the diluents was studied in terms of thermodynamics and kinetics using DSC, optical microscopy and SEM. Microstructures of the porous materials were explained in terms of supercooling and dendritic solidification. Dual functionality of the crystallizable diluents for composite materials was evaluated using isotactic polypropylene (iPP) and compatible diluents that crystallize upon cooling. The selected diluents form homogeneous mixtures with iPP at high temperature and lower the viscosity (improved processability), which undergo phase separation upon cooling to form solid particles that function as a toughening agent at room temperature. Tensile properties and morphology of the composites showed that organic crystalline particles have the similar effect as rigid particles to increase toughness; de-wetting between the particle and iPP matrix occurs at the early stage of deformation, followed by unhindered plastic flow that consumes significant amount of fracture energy. The effect of the diluents, however, strongly depends on the identity of the diluents that interact with the iPP during solidification step, which was demonstrated by comparing tetrabromobisphenol-A and phthalic anhydride. A simple method to prepare composite surfaces that can change the wettability in response to the temperature change was proposed and evaluated. Composite surfaces prepared by nanoporous alumina templates filled with polymers showed surface morphology and wettability that depend on temperature. This effect is attributed to the significant difference in thermal conductivity and the thermal expansion coefficient between the alumina and the polymers. The reversibility in thermal response depends on the properties of the polymers.

Size and density avalanche scaling near jamming.

PubMed

Arévalo, Roberto; Ciamarra, Massimo Pica

2014-04-28

The current microscopic picture of plasticity in amorphous materials assumes local failure events to produce displacement fields complying with linear elasticity. Indeed, the flow properties of nonaffine systems, such as foams, emulsions and granular materials close to jamming, that produce a fluctuating displacement field when failing, are still controversial. Here we show, via a thorough numerical investigation of jammed materials, that nonaffinity induces a critical scaling of the flow properties dictated by the distance to the jamming point. We rationalize this critical behavior by introducing a new universal jamming exponent and hyperscaling relationships, and we use these results to describe the volume fraction dependence of the friction coefficient.

Complexity in modeling of residual stresses and strains during polymerization of bone cement: effects of conversion, constraint, heat transfer, and viscoelastic property changes.

PubMed

Gilbert, Jeremy L

2006-12-15

Aseptic loosening of cemented joint prostheses remains a significant concern in orthopedic biomaterials. One possible contributor to cement loosening is the development of porosity, residual stresses, and local fracture of the cement that may arise from the in-situ polymerization of the cement. In-situ polymerization of acrylic bone cement is a complex set of interacting processes that involve polymerization reactions, heat generation and transfer, full or partial mechanical constraint, evolution of conversion- and temperature-dependent viscoelastic material properties, and thermal and conversion-driven changes in the density of the cement. Interactions between heat transfer and polymerization can lead to polymerization fronts moving through the material. Density changes during polymerization can, in the presence of mechanical constraint, lead to the development of locally high residual strain energy and residual stresses. This study models the interactions during bone cement polymerization and determines how residual stresses develop in cement and incorporates temperature and conversion-dependent viscoelastic behavior. The results show that the presence of polymerization fronts in bone cement result in locally high residual strain energies. A novel heredity integral approach is presented to track residual stresses incorporating conversion and temperature dependent material property changes. Finally, the relative contribution of thermal- and conversion-dependent strains to residual stresses is evaluated and it is found that the conversion-based strains are the major contributor to the overall behavior. This framework provides the basis for understanding the complex development of residual stresses and can be used as the basis for developing more complex models of cement behavior.

Mechanical Properties of Mass Concrete at Early Ages

DTIC Science & Technology

1991-08-01

I.............. 15 WES UMAT Time-Dependent Material Properties Model.........15: CHAPTER IV: EXPERIMENTAL PROGRAM.................................. 17...Equationi.......................................41 WES UMAT Creep, Eqtation .................................. 42 Bazant Sinh-Double Power Law...and All ......... 42 7 UMAT Creep Equation Coefficients for Mixtures A2 and All .... 43 8 SDPL Creep Constants for Mixtures A2 and All

First-principles investigation of structural, elastic, lattice dynamical and thermodynamic properties of lithium sulfur under pressure

NASA Astrophysics Data System (ADS)

Saib, S.; Bouarissa, N.

2017-10-01

In this study we report on the influence of hydrostatic pressure on structural, elastic, lattice dynamical and thermal properties of Li2S in the anti-fluorite structure using ab initio pseudopotential approach based on the density functional perturbation theory. Our results are found to be in good agreement with those existing in the literature. The present phonon dispersion spectra, dielectric constants and Born effective charges may be seen as the first investigation for the material under load. The pressure dependence of all features of interest has been examined and discussed. Besides, the temperature dependence of the lattice parameter and bulk modulus is predicted. The generalized elastic stability criteria showed that the material of interest is mechanically unstable for pressures beyond 55 GPa.

Metasurface Mirrors for External Control of Mie Resonances.

PubMed

van de Groep, Jorik; Brongersma, Mark L

2018-06-13

The ability to control and structurally tune the optical resonances of semiconductor nanostructures has far-reaching implications for a wide range of optical applications, including photodetectors, (bio)sensors, and photovoltaics. Such control is commonly obtained by tailoring the nanostructure's geometry, material, or dielectric environment. Here, we combine insights from the field of coherent optics and metasurface mirrors to effectively turn Mie resonances on and off with high spatial control and in a polarization-dependent fashion. We illustrate this in an integrated device by manipulating the photocurrent spectra of a single-nanowire photodetector placed on a metasurface mirror. This approach can be generalized to control spectral, angle-dependent, absorption, and scattering properties of semiconductor nanostructures with an engineered metasurface and without a need to alter their geometric or materials properties.

Axisymmetric elastodynamic response from normal and radial impact of layered composites with embedded penny-shaped cracks

NASA Technical Reports Server (NTRS)

Sih, G. C.; Chen, E. P.

1980-01-01

A method is developed for the dynamic stress analysis of a layered composite containing an embedded penny-shaped crack and subjected to normal and radial impact. Quantitatively, the time-dependent stresses near the crack border can be described by the dynamic stress intensity factors. Their magnitude depends on time, on the material properties of the composite and on the relative size of the crack compared to the composite local geometry. Results obtained show that, for the same material properties and geometry of the composite, the dynamic stress intensity factors for an embedded (penny-shaped) crack reach their peak values within a shorter period of time and with a lower magnitude than the corresponding dynamic stress factors for a through-crack.

Experimental and theoretical study of the absorption properties of thiolated diamondoids

NASA Astrophysics Data System (ADS)

Landt, Lasse; Bostedt, Christoph; Wolter, David; Möller, Thomas; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Tkachenko, Boryslav A.; Fokin, Andrey A.; Schreiner, Peter R.; Kulesza, Alexander; Mitrić, Roland; Bonačić-Koutecký, Vlasta

2010-04-01

Nanoscale hybrid systems are a new class of molecular aggregates that offer numerous new possibilities in materials design. Diamondoid thiols are promising nanoscale building blocks for such hybrid systems. They allow the incorporation of functional groups and the investigation of their effects on the unique materials' properties of diamondoids. Here we combine experimental data with ab initio theory to explore the optical properties of diamondoid thiols and their dependence on size and shape. Agreement between theoretically and experimentally obtained absorption spectra allows the identification of the nature of the optical transitions that are responsible for some photophysical and photochemical processes. We show that the optical properties of diamondoid thiols in the deep UV regime depend on the functionalization site but are largely size independent. Our findings provide an explanation for the disappearance of diamondoid UV photoluminescence upon thiolation for smaller diamondoids. However, our theoretical results indicate that for larger diamondoid thiols beyond the critical size of six diamondoid cages the lowest energy transitions are characterized by diamondoidlike states suggesting that UV luminescence may be regained.

Optimization of BI test parameters to investigate mechanical properties of Grade 92 steel

NASA Astrophysics Data System (ADS)

Barbadikar, Dipika R.; Vincent, S.; Ballal, Atul R.; Peshwe, Dilip R.; Mathew, M. D.

2018-04-01

The ball indentation (BI) testing is used to evaluate the tensile properties of materials namely yield strength, strength coefficient, ultimate tensile strength, and strain hardening exponent. The properties evaluated depend on a number of BI test parameters. These parameters include the material constants like yield slope (YS), constraint factor (CF), yield offset parameter (YOP). Number of loading/unloading cycles, preload, indenter size and depth of penetration of indenter also affects the properties. In present investigation the effect of these parameters on the stress-strain curve of normalized and tempered Grade 92 steel is evaluated. Grade 92 is a candidate material for power plant application over austenitic stainless steel and derives its strength from M23C6, MX precipitates and high dislocation density. CF, YS and YOP changed the strength properties considerably. Indenter size effect resulted in higher strength for smaller indenter. It is suggested to use larger indenter diameter and higher number of loading cycles for GRADE 92 steel to get best results using BI technique.

Procedure for implementation of temperature-dependent mechanical property capability in the Engineering Analysis Language (EAL) system

NASA Technical Reports Server (NTRS)

Glass, David E.; Robinson, James C.

1990-01-01

A procedure is presented to allow the use of temperature dependent mechanical properties in the Engineering Analysis Language (EAL) System for solid structural elements. This is accomplished by including a modular runstream in the main EAL runstream. The procedure is applicable for models with multiple materials and with anisotropic properties, and can easily be incorporated into an existing EAL runstream. The procedure (which is applicable for EAL elastic solid elements) is described in detail, followed by a description of the validation of the routine. A listing of the EAL runstream used to validate the procedure is included in the Appendix.

Plasma assisted surface treatments of biomaterials.

PubMed

Minati, L; Migliaresi, C; Lunelli, L; Viero, G; Dalla Serra, M; Speranza, G

2017-10-01

The biocompatibility of an implant depends upon the material it is composed of, in addition to the prosthetic device's morphology, mechanical and surface properties. Properties as porosity and pore size should allow, when required, cells penetration and proliferation. Stiffness and strength, that depend on the bulk characteristics of the material, should match the mechanical requirements of the prosthetic applications. Surface properties should allow integration in the surrounding tissues by activating proper communication pathways with the surrounding cells. Bulk and surface properties are not interconnected, and for instance a bone prosthesis could possess the necessary stiffness and strength for the application omitting out prerequisite surface properties essential for the osteointegration. In this case, surface treatment is mandatory and can be accomplished using various techniques such as applying coatings to the prosthesis, ion beams, chemical grafting or modification, low temperature plasma, or a combination of the aforementioned. Low temperature plasma-based techniques have gained increasing consensus for the surface modification of biomaterials for being effective and competitive compared to other ways to introduce surface functionalities. In this paper we review plasma processing techniques and describe potentialities and applications of plasma to tailor the interface of biomaterials. Copyright © 2017 Elsevier B.V. All rights reserved.

Changes Coming to the International System of Units

ERIC Educational Resources Information Center

Aubrecht, Gordon J., II

2012-01-01

The International System of Units (SI) is a coherent system based originally on measurements of properties of material objects. In more recent times, the adopted definitions depend on setting values of universal constants wherever possible. The last remaining human-made material object on which a standard is based is a platinum-iridium kilogram…

Colloidal Inorganic Nanocrystal Based Nanocomposites: Functional Materials for Micro and Nanofabrication

PubMed Central

Ingrosso, Chiara; Panniello, AnnaMaria; Comparelli, Roberto; Curri, Maria Lucia; Striccoli, Marinella

2010-01-01

The unique size- and shape-dependent electronic properties of nanocrystals (NCs) make them extremely attractive as novel structural building blocks for constructing a new generation of innovative materials and solid-state devices. Recent advances in material chemistry has allowed the synthesis of colloidal NCs with a wide range of compositions, with a precise control on size, shape and uniformity as well as specific surface chemistry. By incorporating such nanostructures in polymers, mesoscopic materials can be achieved and their properties engineered by choosing NCs differing in size and/or composition, properly tuning the interaction between NCs and surrounding environment. In this contribution, different approaches will be presented as effective opportunities for conveying colloidal NC properties to nanocomposite materials for micro and nanofabrication. Patterning of such nanocomposites either by conventional lithographic techniques and emerging patterning tools, such as ink jet printing and nanoimprint lithography, will be illustrated, pointing out their technological impact on developing new optoelectronic and sensing devices.

Silk/nano-material hybrid: properties and functions

NASA Astrophysics Data System (ADS)

Steven, Eden; Lebedev, Victor; Laukhina, Elena; Laukhin, Vladimir; Alamo, Rufina G.; Rovira, Concepcio; Veciana, Jaume; Brooks, James S.

2014-03-01

Silk continues to emerge as a material of interest in electronics. In this work, the interaction between silk and conducting nano-materials are investigated. Simple fabrication methods, physical, electronic, thermal, and actuation properties are reported for spider silk / carbon nanotube (CNT-SS) and Bombyx mori / (BEDT-TTF)-based organic molecular conductor hybrids (ET-S). The CNT-SS fibers are produced via water and shear assisted method, resulting in fibers that are tough, custom-shapeable, flexible, and electrically conducting. For ET-S bilayer films, a layer transfer technique is developed to deposit linked crystallites of (BEDT-TTF)2I3 molecular conductor onto silk films, generating highly piezoresistive semi-transparent films. In both cases, the hybridization allows us to gain additional functions by harnessing the water-dependent properties of silk materials, for example, as humidity sensor and electrical current- or water-driven actuators. SEM, TEM, FT-IR, and resistance measurements under varying temperature, strain, and relative humidity reveal the synergistic interactions between the bio- and nano-materials. E.S. is supported by NSF-DMR 1005293.

Temperature dependence of thermal boundary resistances between multiwalled carbon nanotubes and some typical counterpart materials.

PubMed

Zhang, Guang; Liu, Changhong; Fan, Shoushan

2012-04-24

We directly measured the temperature dependence of thermal boundary resistances (TBRs) between multiwalled carbon nanotubes (MWCNTs) and different materials at elevated temperatures. Using the steady-state heat flow and the noncontacted measurement method, we could conveniently obtain the TBR-temperature relations. Our results indicate that the TBR-temperature relations vary distinctively with different contact materials when heating temperatures change from about 300 to 450 K; that is, the CNT-metal TBRs increase with increasing temperatures, whereas the CNT-insulator TBRs decrease. As a comparison, the TBRs between superaligned MWCNTs were measured and we found that the CNT-CNT TBRs remain basically unchanged as temperatures increase. We also found that the magnitude of TBRs between MWCNTs and different materials could differ from each other significantly. These results suggest that the choice of the right electrode may have an obvious influence on the thermal properties and other properties of the CNT-based devices. From another perspective, in view of some existing theoretical models about TBRs, our results support the validity of the molecular dynamics (MD) simulations in the calculation of CNT-solid TBRs at elevated temperatures.

Non-Newtonian behavior observed via dynamic rheology for various particle types in energetic materials and simulant composites

NASA Astrophysics Data System (ADS)

Choi, Jong Han; Lee, Sangmook; Lee, Jae Wook

2017-02-01

The rheological properties of polymer composites highly filled with different filler materials were examined using a stress-controlled rheometer with a parallel-plate configuration, for particle characterization of the filler materials in plastic (polymer) bonded explosive (PBX). Ethylene vinyl acetate (EVA) with dioctyl adipate (DOA) was used as the matrix phase, which was shown to exhibit Newtonian-like behavior. The dispersed phase consisted of one of two energetic materials, i.e., explosive cyclotrimethylene trinitramine (RDX) or cyclotetramethylene tetranitramine (HMX), or a simulant (Dechlorane) in a bimodal size distribution. Before the test, preshearing was conducted to identify the initial condition of each sample. All examined filled polymer specimens exhibited yield stress and shear-thinning behavior over the investigated frequency range. The complex viscosity dependence on the dynamic oscillation frequency was also fitted using an appropriate rheological model, suggesting the model parameters. Furthermore, the temperature dependency of the different filler particle types was determined for different filler volume fractions. These comparative studies revealed the influence of the particle characteristics on the rheological properties of the filled polymer.

Natural ageing of EPDM composite insulators

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

Vlastos, A.E.; Sherif, E.

1990-01-01

Long-rod composite insulators, with weather sheds (sheds) made of ethylene propylene rubbers (EPDM), were exposed for many years to HVAC and HVDC under realistic conditions and natural pollution. The change of their properties with time and their aging was studied. The results show that the insulator shed material undergoes a slow degradation process and loses successively its water repelling properties which initially make the EPDM composite insulators superior to inorganic glass and porcelain insulator. The outdoor degradation of the shed material depends on the electric stress, in the environmental factors (such as pollution, rain, salt-laden fog, and UV-radiation from sun)more » and on the materials and fillers used in the construction of the composite insulators. A thorough macro- and microscopic study of the EPDM composite insulator sheds illustrates the differences of the surface state of EPDM insulators of different makes in which different basic material compositions and fillers are used. The poor performance of aged EPDM composite insulators compared to inorganic insulators depends on the design and on environmental factors.« less

Effects of a power and photon energy of incident light on near-field etching properties

NASA Astrophysics Data System (ADS)

Yatsui, T.; Saito, H.; Nishioka, K.; Leuschel, B.; Soppera, O.; Nobusada, K.

2017-12-01

We developed a near-field etching technique for realizing an ultra-flat surfaces of various materials and structures. To elucidate the near-field etching properties, we have investigated the effects of power and the photon energy of the incident light. First, we established theoretically that an optical near-field with photon energy lower than the absorption edge of the molecules can induce molecular vibrations. We used nanodiamonds to study the power dependence of the near-field etching properties. From the topological changes of the nanodiamonds, we confirmed the linear-dependence of the etching volume with the incident power. Furthermore, we studied the photon energy dependence using TiO2 nanostriped structures, which revealed that a lower photon energy results in a lower etching rate.

Revisit to three-dimensional percolation theory: Accurate analysis for highly stretchable conductive composite materials

PubMed Central

Kim, Sangwoo; Choi, Seongdae; Oh, Eunho; Byun, Junghwan; Kim, Hyunjong; Lee, Byeongmoon; Lee, Seunghwan; Hong, Yongtaek

2016-01-01

A percolation theory based on variation of conductive filler fraction has been widely used to explain the behavior of conductive composite materials under both small and large deformation conditions. However, it typically fails in properly analyzing the materials under the large deformation since the assumption may not be valid in such a case. Therefore, we proposed a new three-dimensional percolation theory by considering three key factors: nonlinear elasticity, precisely measured strain-dependent Poisson’s ratio, and strain-dependent percolation threshold. Digital image correlation (DIC) method was used to determine actual Poisson’s ratios at various strain levels, which were used to accurately estimate variation of conductive filler volume fraction under deformation. We also adopted strain-dependent percolation threshold caused by the filler re-location with deformation. When three key factors were considered, electrical performance change was accurately analyzed for composite materials with both isotropic and anisotropic mechanical properties. PMID:27694856

3D Viscoelastic Traction Force Microscopy

PubMed Central

Toyjanova, Jennet; Hannen, Erin; Bar-Kochba, Eyal; Darling, Eric M.; Henann, David L.; Franck, Christian

2014-01-01

Native cell-material interactions occur on materials differing in their structural composition, chemistry, and physical compliance. While the last two decades have shown the importance of traction forces during cell-material interactions, they have been almost exclusively presented on purely elastic in-vitro materials. Yet, most bodily tissue materials exhibit some level of viscoelasticity, which could play an important role in how cells sense and transduce tractions. To expand the realm of cell traction measurements and to encompass all materials from elastic to viscoelastic, this paper presents a general, and comprehensive approach for quantifying 3D cell tractions in viscoelastic materials. This methodology includes the experimental characterization of the time-dependent material properties for any viscoelastic material with the subsequent mathematical implementation of the determined material model into a 3D traction force microscopy (3D TFM) framework. Utilizing this new 3D viscoelastic TFM (3D VTFM) approach, we quantify the influence of viscosity on the overall material traction calculations and quantify the error associated with omitting time-dependent material effects, as is the case for all other TFM formulations. We anticipate that the 3D VTFM technique will open up new avenues of cell-material investigations on even more physiologically relevant time-dependent materials including collagen and fibrin gels. PMID:25170569

A continuum deformation theory for metal-matrix composites at high temperature

NASA Technical Reports Server (NTRS)

Robinson, D. N.

1987-01-01

A continuum theory is presented for representing the high temperature, time dependent, hereditary deformation behavior of metallic composites that can be idealized as pseudohomogeneous continua with locally definable directional characteristics. Homogenization of textured materials (molecular, granular, fibrous) and applicability of continuum mechanics in structural applications depends on characteristic body dimensions, the severity of gradients (stress, temperature, etc.) in the structure and the relative size of the internal structure (cell size) of the material. The point of view taken here is that the composite is a material in its own right, with its own properties that can be measured and specified for the composite as a whole.

Experimental and Analytical Studies for a Computational Materials Program

NASA Technical Reports Server (NTRS)

Knauss, W. G.

1999-01-01

The studies supported by Grant NAG1-1780 were directed at providing physical data on polymer behavior that would form the basis for computationally modeling these types of materials. Because of ongoing work in polymer characterization this grant supported part of a larger picture in this regard. Efforts went into two combined areas of their time dependent mechanical response characteristics: Creep properties on the one hand, subject to different volumetric changes (nonlinearly viscoelastic behavior) and time or frequency dependence of dilatational material behavior. The details of these endeavors are outlined sufficiently in the two appended publications, so that no further description of the effort is necessary.

Laboratory experiments from the toy store

NASA Technical Reports Server (NTRS)

Mcclelland, H. T.

1992-01-01

The following is a laboratory experiment designed to further understanding of materials science. This material could be taught to a typical student of materials science or manufacturing at the high school level or above. The objectives of this experiment are as follows: (1) to qualitatively demonstrate the concepts of elasticity, plasticity, and the strain rate and temperature dependence of the mechanical properties of engineering materials; (2) to qualitatively demonstrate the basics of extrusion including material flow, strain rate dependence of defects, lubrication effects, and the making of hollow shapes by extrusion (the two parts may be two separate experiments done at different times when the respective subjects are covered); and (3) to demonstrate the importance of qualitative observations and the amount of information which can be gathered without quantitative measurements.

The effect of winding and core support material on the thermal gain dependence of a fluxgate magnetometer sensor

NASA Astrophysics Data System (ADS)

Miles, David M.; Mann, Ian R.; Kale, Andy; Milling, David K.; Narod, Barry B.; Bennest, John R.; Barona, David; Unsworth, Martyn J.

2017-10-01

Fluxgate magnetometers are an important tool in geophysics and space physics but are typically sensitive to variations in sensor temperature. Changes in instrumental gain with temperature, thermal gain dependence, are thought to be predominantly due to changes in the geometry of the wire coils that sense the magnetic field and/or provide magnetic feedback. Scientific fluxgate magnetometers typically employ some form of temperature compensation and support and constrain wire sense coils with bobbins constructed from materials such as MACOR machinable ceramic (Corning Inc.) which are selected for their ultra-low thermal deformation rather than for robustness, cost, or ease of manufacturing. We present laboratory results comparing the performance of six geometrically and electrically matched fluxgate sensors in which the material used to support the windings and for the base of the sensor is varied. We use a novel, low-cost thermal calibration procedure based on a controlled sinusoidal magnetic source and quantitative spectral analysis to measure the thermal gain dependence of fluxgate magnetometer sensors at the ppm°C-1 level in a typical magnetically noisy university laboratory environment. We compare the thermal gain dependence of sensors built from MACOR, polyetheretherketone (PEEK) engineering plastic (virgin, 30 % glass filled and 30 % carbon filled), and acetal to examine the trade between the thermal properties of the material, the impact on the thermal gain dependence of the fluxgate, and the cost and ease of manufacture. We find that thermal gain dependence of the sensor varies as one half of the material properties of the bobbin supporting the wire sense coils rather than being directly related as has been historically thought. An experimental sensor constructed from 30 % glass-filled PEEK (21.6 ppm°C-1) had a thermal gain dependence within 5 ppm°C-1 of a traditional sensor constructed from MACOR ceramic (8.1 ppm°C-1). If a modest increase in thermal dependence can be tolerated or compensated, then 30 % glass-filled PEEK is a good candidate for future fluxgate sensors as it is more economical, easier to machine, lighter, and more robust than MACOR.

Properties of Extruded PS-212 Type Self-Lubricating Materials

NASA Technical Reports Server (NTRS)

Waters, W. J.; Sliney, H. E.; Soltis, R. F.

1993-01-01

Research has been underway at the NASA Lewis Research Center since the 1960's to develop high temperature, self-lubricating materials. The bulk of the research has been done in-house by a team of researchers from the Materials Division. A series of self-lubricating solid material systems has been developed over the years. One of the most promising is the composite material system referred to as PS-212 or PM-212. This material is a powder metallurgy product composed of metal bonded chromium carbide and two solid lubricating materials known to be self-lubricating over a wide temperature range. NASA feels this material has a wide potential in industrial applications. Simplified processing of this material would enhance its commercial potential. Processing changes have the potential to reduce processing costs, but tribological and physical properties must not be adversely affected. Extrusion processing has been employed in this investigation as a consolidation process for PM-212/PS-212. It has been successful in that high density bars of EX-212 (extruded PM-212) can readily be fabricated. Friction and strength data indicate these properties have been maintained or improved over the P.M. version. A range of extrusion temperatures have been investigated and tensile, friction, wear, and microstructural data have been obtained. Results indicate extrusion temperatures are not critical from a densification standpoint, but other properties are temperature dependent.

Towards a definition of inorganic nanoparticles from an environmental, health and safety perspective.

PubMed

Auffan, Mélanie; Rose, Jérôme; Bottero, Jean-Yves; Lowry, Gregory V; Jolivet, Jean-Pierre; Wiesner, Mark R

2009-10-01

The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.

Mechanical characterization and modeling for anodes and cathodes in lithium-ion batteries

NASA Astrophysics Data System (ADS)

Wang, Lubing; Yin, Sha; Zhang, Chao; Huan, Yong; Xu, Jun

2018-07-01

Mechanical properties of electrode materials have significant influence over electrochemical properties as well as mechanical integrity of lithium-ion battery cells. Here, anode and cathode in a commercially available 18650 NCA (Nickel Cobalt Aluminum Oxide)/graphite cell were comprehensively studied by tensile tests considering material anisotropy, SOC (state of charge), strain rate and electrolyte content. Results showed that the mechanical properties of both electrodes were highly dependent on strain rate and electrolyte content; however, anode was SOC dependent while cathode was not. Besides, coupled effects of strain rate and SOC of anodes were also discussed. SEM (scanning electron microscope) images of surfaces and cross-sections of electrodes showed the fracture morphology. In addition, mechanical behavior of Cu foil separated from anode with different SOC values were studied and compared. Finally, constitutive models of electrodes considering both strain rate and anisotropy effects were established. This study reveals the relationship between electrochemical dependent mechanical behavior of the electrodes. The established mechanical models of electrodes can be applied to the numerical computation of battery cells. Results are essential to predict the mechanical responses as well as the deformation of battery cell under various loading conditions, facilitating safer battery design and manufacturing.

Seeding materials: Health and safety considerations

NASA Technical Reports Server (NTRS)

Brown, R. D.

1985-01-01

The choice of a proper seeding material for laser velocimeters must include health and safety considerations. Failure to do so can lead to catastrophic results. All materials are toxic, and laser velocimeter seeding materials are no exception. Toxicity may be considered an inherent property of a given material. The manifestation of that property or the physiological response to the material is dependent on dose and exposure conditions. An approximate physiological classification of toxicity is given in tablular form. Toxicity in some situations is not necessarily the most restrictive factor in selection of materials. It is also very important to consider how the material is used so that actual exposure to the material in a damaging form can result. For example, nickel and cadmium are both extremely toxic as systemic poisons and in the case of nickel as a carcinogen. Seeding materials are dispersed in air under conditions that favor personnel exposure. Dispersal equipment is frequently if not normally manned, and personnel are often required to make frequent adjustments to assure proper operations.

General Nonlinear Ferroelectric Model v. Beta

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

Dong, Wen; Robbins, Josh

2017-03-14

The purpose of this software is to function as a generalized ferroelectric material model. The material model is designed to work with existing finite element packages by providing updated information on material properties that are nonlinear and dependent on loading history. The two major nonlinear phenomena this model captures are domain-switching and phase transformation. The software itself does not contain potentially sensitive material information and instead provides a framework for different physical phenomena observed within ferroelectric materials. The model is calibrated to a specific ferroelectric material through input parameters provided by the user.

Polarization and Thickness Dependent Absorption Properties of Black Phosphorus: New Saturable Absorber for Ultrafast Pulse Generation

PubMed Central

Li, Diao; Jussila, Henri; Karvonen, Lasse; Ye, Guojun; Lipsanen, Harri; Chen, Xianhui; Sun, Zhipei

2015-01-01

Black phosphorus (BP) has recently been rediscovered as a new and interesting two-dimensional material due to its unique electronic and optical properties. Here, we study the linear and nonlinear optical properties of BP flakes. We observe that both the linear and nonlinear optical properties are anisotropic and can be tuned by the film thickness in BP, completely different from other typical two-dimensional layered materials (e.g., graphene and the most studied transition metal dichalcogenides). We then use the nonlinear optical properties of BP for ultrafast (pulse duration down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in Q-switching) pulse generation in fiber lasers at the near-infrared telecommunication band ~1.5 μm. We observe that the output of our BP based pulsed lasers is linearly polarized (with a degree-of-polarization ~98% in mode-locking, >99% in Q-switching, respectively) due to the anisotropic optical property of BP. Our results underscore the relatively large optical nonlinearity of BP with unique polarization and thickness dependence, and its potential for polarized optical pulse generation, paving the way to BP based nonlinear and ultrafast photonic applications (e.g., ultrafast all-optical polarization switches/modulators, frequency converters etc.). PMID:26514090

Fabrication and material properties of fibrous PHBV scaffolds depending on the cross-ply angle for tissue engineering.

PubMed

Kim, Yang-Hee; Min, Young-Ki; Lee, Byong-Taek

2012-11-01

Fibrous PHBV cross-ply scaffolds were fabricated using the electrospinning technique. The electrospun fibers were arranged depending on angles of alignment, which were 180°, 90°, 60°, and 45°. The stress and strain values of the fibrous PHBV cross-ply scaffolds increased as the cross-ply angle increased. At 180°, the strength and strain values of the fibers depended on tensile loading directions. At an alignment of 90°, the PHBV scaffolds had a stress value of 3.5 MPa, which was more than two times higher than the random structure. The cell morphology and proliferation of L-929 cells was strongly dependant on the fiber alignment and the best results were observed when the angle alignment was high. The results of this study showed that the cross-ply structure of the PHBV scaffold affected not only the cell adhesion and spreading properties but also dictated the mechanical properties, which were dependent on the angles of alignment.

Layer-dependent quantum cooperation of electron and hole states in the anomalous semimetal WTe 2

DOE PAGES

Das, Pranab Kumar; Di Sante, D.; Vobornik, I.; ...

2016-02-29

The behaviour of electrons and holes in a crystal lattice is a fundamental quantum phenomenon, accounting for a rich variety of material properties. Boosted by the remarkable electronic and physical properties of two-dimensional materials such as graphene and topological insulators, transition metal dichalcogenides have recently received renewed attention. In this context, the anomalous bulk properties of semimetallic WTe 2 have attracted considerable interest. We report angle- and spin-resolved photoemission spectroscopy of WTe 2 single crystals, through which we disentangle the role of W and Te atoms in the formation of the band structure and identify the interplay of charge, spinmore » and orbital degrees of freedom. Supported by first-principles calculations and high-resolution surface topography, we also reveal the existence of a layer-dependent behaviour. The balance of electron and hole states is found only when considering at least three Te–W–Te layers, showing that the behaviour of WTe 2 is not strictly two dimensional.« less

Hemispherical Reflectance and Emittance Properties of Carbon Nanotubes Coatings at Far-Infrared Wavelengths

NASA Technical Reports Server (NTRS)

Quijada, Manuel A.; Hagopian, John G.; Getty, Stephanie; Kinzer, Raymond (Robin) E., Jr.; Wollack, Edward

2011-01-01

Recent visible wavelength observations of Multiwalled Carbon Nanotubes (MWCNT) coatings have revealed that they represent the blackest materials known in nature with a Total Hemispherical Reflectance (THR) less than .25%. This makes them as exceptionally good absorbers, with the potential to provide order-of-magnitude improvement in stray-light suppression over current black surface treatments when used in an optical system. Here we extend the characterization of this class of materials into the infrared spectral region to further evaluate their potential for use on instrument baffles for stray-light suppression and to manage spacecraft thermal properties to dissipate heat through radiant heat transfer process. These characterizations will include the wavelength-dependent Total Hemispherical Reflectance properties in the mid-IR and far-infrared spectral regions (2-100 micrometers). Determination of the temperature-dependent emittance will be investigated in the temperature range of 20 to 300 K. These results will be compared against other more conventional black coatings such as Acktar Fractal Black or Z-306 coatings among others.

Thermoplastic Elastomer Part Color as Function of Temperature Histories and Oxygen Atmosphere During Selective Laser Sintering

NASA Astrophysics Data System (ADS)

Kummert, C.; Josupeit, S.; Schmid, H.-J.

2018-03-01

The influence of selective laser sintering (SLS) parameters on PA12 part properties is well known, but research on other materials is rare. One alternative material is a thermoplastic elastomer (TPE) called PrimePart ST that is more elastic and shows a distinct SLS processing behavior. It undergoes a three-dimensional temperature distribution during the SLS process within the TPE part cake. To examine this further, a temperature measurement system that allows temperature measurements inside the part cake is applied to TPE in the present work. Position-dependent temperature histories are directly correlated with the color and mechanical properties of built parts and are in very good agreement with artificial heat treatment in a furnace. Furthermore, it is clearly shown that the yellowish discoloration of parts in different intensities is not only temperature dependent but also influenced by the residual oxygen content in the process atmosphere. Nevertheless, the discoloration has no influence on the mechanical part properties.

Moiré-pattern interlayer potentials in van der Waals materials in the random-phase approximation

NASA Astrophysics Data System (ADS)

Leconte, Nicolas; Jung, Jeil; Lebègue, Sébastien; Gould, Tim

2017-11-01

Stacking-dependent interlayer interactions are important for understanding the structural and electronic properties in incommensurable two-dimensional material assemblies where long-range moiré patterns arise due to small lattice constant mismatch or twist angles. Here we study the stacking-dependent interlayer coupling energies between graphene (G) and hexagonal boron nitride (BN) homo- and heterostructures using high-level random-phase approximation (RPA) ab initio calculations. Our results show that although total binding energies within LDA and RPA differ substantially by a factor of 200%-400%, the energy differences as a function of stacking configuration yield nearly constant values with variations smaller than 20%, meaning that LDA estimates are quite reliable. We produce phenomenological fits to these energy differences, which allows us to calculate various properties of interest including interlayer spacing, sliding energetics, pressure gradients, and elastic coefficients to high accuracy. The importance of long-range interactions (captured by RPA but not LDA) on various properties is also discussed. Parametrizations for all fits are provided.

Controlled surface functionality of magnetic nanoparticles by layer-by-layer assembled nano-films

NASA Astrophysics Data System (ADS)

Choi, Daheui; Son, Boram; Park, Tai Hyun; Hong, Jinkee

2015-04-01

Over the past several years, the preparation of functionalized nanoparticles has been aggressively pursued in order to develop desired structures, compositions, and structural order. Among the various nanoparticles, iron oxide magnetic nanoparticles (MNPs) have shown great promise because the material generated using these MNPs can be used in a variety of biomedical applications and possible bioactive functionalities. In this study, we report the development of various functionalized MNPs (F-MNPs) generated using the layer-by-layer (LbL) self-assembly method. To provide broad functional opportunities, we fabricated F-MNP bio-toolbox by using three different materials: synthetic polymers, natural polymers, and carbon materials. Each of these F-MNPs displays distinct properties, such as enhanced thickness or unique morphologies. In an effort to explore their biomedical applications, we generated basic fibroblast growth factor (bFGF)-loaded F-MNPs. The bFGF-loaded F-MNPs exhibited different release mechanisms and loading amounts, depending on the film material and composition order. Moreover, bFGF-loaded F-MNPs displayed higher biocompatibility and possessed superior proliferation properties than the bare MNPs and pure bFGF, respectively. We conclude that by simply optimizing the building materials and the nanoparticle's film composition, MNPs exhibiting various bioactive properties can be generated.Over the past several years, the preparation of functionalized nanoparticles has been aggressively pursued in order to develop desired structures, compositions, and structural order. Among the various nanoparticles, iron oxide magnetic nanoparticles (MNPs) have shown great promise because the material generated using these MNPs can be used in a variety of biomedical applications and possible bioactive functionalities. In this study, we report the development of various functionalized MNPs (F-MNPs) generated using the layer-by-layer (LbL) self-assembly method. To provide broad functional opportunities, we fabricated F-MNP bio-toolbox by using three different materials: synthetic polymers, natural polymers, and carbon materials. Each of these F-MNPs displays distinct properties, such as enhanced thickness or unique morphologies. In an effort to explore their biomedical applications, we generated basic fibroblast growth factor (bFGF)-loaded F-MNPs. The bFGF-loaded F-MNPs exhibited different release mechanisms and loading amounts, depending on the film material and composition order. Moreover, bFGF-loaded F-MNPs displayed higher biocompatibility and possessed superior proliferation properties than the bare MNPs and pure bFGF, respectively. We conclude that by simply optimizing the building materials and the nanoparticle's film composition, MNPs exhibiting various bioactive properties can be generated. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07373h

Temperature-dependent microindentation data of an epoxy composition in the glassy region

NASA Astrophysics Data System (ADS)

Minster, Jiří; Králík, Vlastimil

2015-02-01

The short-term instrumented microindentation technique was applied for assessing the influence of temperature in the glassy region on the time-dependent mechanical properties of an average epoxy resin mix near to its native state. Linear viscoelasticity theory with the assumption of time-independent Poisson ratio value forms the basis for processing the experimental results. The sharp standard Berkovich indenter was used to measure the local mechanical properties at temperatures 20, 24, 28, and 35 °C. The short-term viscoelastic compliance histories were defined by the Kohlrausch-Williams-Watts double exponential function. The findings suggest that depth-sensing indentation data of thermorheologically simple materials influenced by different temperatures in the glassy region can also be used, through the time-temperature superposition, to extract viscoelastic response functions accurately. This statement is supported by the comparison of the viscoelastic compliance master curve of the tested material with data derived from standard macro creep measurements under pressure on the material in a conformable state.

Combined Mechanical and Electrical Study of Polymers of Biological Origin

NASA Astrophysics Data System (ADS)

Zsoldos, G.; Szoda, K.; Marossy, K.

2017-02-01

Thermally Simulated Depolarization Current measurement is an excellent but not widely used method for identifying relaxation processes in polymers. The DMA method is used here to analyze the mechanical changes depend on temperature in biopolymers. The two techniques take advantage of the energy changes involved in the various phase transitions of certain polymer molecules. This allows for several properties of the material to be ascertained; melting points, enthalpies of melting, crystallization temperatures, glass transition temperatures and degradation temperatures. The examined biopolymer films are made from biological materials such as proteins and polysaccharides. These materials have gained wide usage in pharmaceutical, medical and food areas. The uses of biopolymer films depend on their structure and mechanical properties. This work is based on pectin and gelatin films. The films were prepared by casting. The casting technique used aqueous solutions in each case of sample preparation. The manufacturing process of the pectin and gelatin films was a single stage solving process.

Length-Scale Effects and Material Models at Numerical Simulations of Nanoindentation of A Metallic Alloy

NASA Astrophysics Data System (ADS)

Nikolov, N.; Avdjieva, T.; Altaparmakov, I.

2014-06-01

Some specially designed metallic alloys crystallize during process of rapid quenching which aims their amorphization. Nevertheless, change in their mechanical properties could be seen compared to these obtained during conventional technological regimes of cooling. That attracts the attention in this elaboration. Full 3-D numerical simulations of nanoindentation process of two material models are performed. The models reflect equivalent elastic and different plastic material properties. The plastic behaviour of the first one is subjected to yield criterion of Dracker-Prager and this of the second one to yield criterion of Mises. The reported numerical results depending on the nanoindentation scale length of 1000 nanometers, suggest different adequacy of the two yield criteria to the data obtained experimentally with a Zr-Al-Cu-Ni-Mo alloy. It could be speculated that the different effects developed depending on the indenter travel of 1000 nanometers and taken into account in the two yield criteria stand behind this fact and determinate three structural levels of plastic deformation.

Effect of nanoscale size and medium on metal work function in oleylamine-capped gold nanocrystals

NASA Astrophysics Data System (ADS)

Abdellatif, M. H.; Ghosh, S.; Liakos, I.; Scarpellini, A.; Marras, S.; Diaspro, A.; Salerno, M.

2016-02-01

The work function is an important material property with several applications in photonics and optoelectronics. We aimed to characterize the work function of clusters resulting from gold nanocrystals capped with oleylamine surfactant and drop-casted onto gold substrate. We used scanning Kelvin probe microscopy to investigate the work function, and complemented our study mainly with X-ray diffraction and X-ray photoelectron spectroscopy. The oleylamine works as an electron blocking layer through which the electrical conduction takes place by tunneling effect. The surface potential appears to depend on the size of the clusters, which can be ascribed to their difference in effective work function with the substrate. The charge state of gold clusters is discussed in comparison with theory, and their capacitance is calculated from a semi-analytical equation. The results suggest that at the nanoscale the work function is not an intrinsic property of a material but rather depends on the size and morphology of the clusters, including also effects of the surrounding materials.

Temperature dependence of thermal pressure for NaCl

NASA Astrophysics Data System (ADS)

Singh, Chandra K.; Pande, Brijesh K.; Pandey, Anjani K.

2018-05-01

Engineering applications of the materials can be explored upto the desired limit of accuracy with the better knowledge of its mechanical and thermal properties such as ductility, brittleness and Thermal Pressure. For the resistance to fracture (K) and plastic deformation (G) the ratio K/G is treated as an indication of ductile or brittle character of solids. In the present work we have tested the condition of ductility and brittleness with the calculated values of K/G for the NaCl. It is concluded that the nature of NaCl can be predicted upto high temperature simply with the knowledge of its elastic stiffness constant only. Thermoelastic properties of materials at high temperature is directly related to thermal pressure and volume expansion of the materials. An expression for the temperature dependence of thermal pressure is formulated using basic thermodynamic identities. It is observed that thermal pressure ΔPth calculated for NaCl by using Kushwah formulation is in good agreement with the experimental values also the thermal pressure increases with the increase in temperature.

Influence of Surrounding Dielectrics on the Data Retention Time of Doped Sb2Te Phase Change Material

NASA Astrophysics Data System (ADS)

Jedema, Friso; in `t Zandt, Micha; Wolters, Rob; Gravesteijn, Dirk

2011-02-01

The crystallization properties of as-deposited and laser written amorphous marks of doped Sb2Te phase change material are found to be only dependent on the top dielectric layer. A ZnS:SiO2 top dielectric layer yields a higher crystallization temperature and a larger crystal growth activation energy as compared to a SiO2 top dielectric layer, leading to superior data retention times at ambient temperatures. The observed correlation between the larger crystallization temperatures and larger crystal growth activation energies indicates that the viscosity of the phase change material in the amorphous state is dependent on the interfacial energy between the phase change material and the top dielectric layer.

Fatigue strength degradation of metals in corrosive environments

NASA Astrophysics Data System (ADS)

Adasooriya, N. D.; Hemmingsen, T.; Pavlou, D.

2017-12-01

Structures exposed to aggressive environmental conditions are often subjected to time-dependent loss of coating and loss of material due to corrosion; this causes reduction in the cross-sectional properties of the members, increased surface roughness, surface irregularities and corrosion pits, and degradation of material strengths. These effects have been identified and simulated in different research studies. However, time and corrosive media dependent fatigue strength curves for materials have not been discussed in the design or assessment guidelines for structures. This paper attempts to review the corrosion degradation process and available approaches/models used to determine the fatigue strength of corroded materials and to interpolate corrosion deterioration data. High cycle fatigue and full range fatigue life formulae for fatigue strength of corroded materials are proposed. The above formulae depend on the endurance limit of corroded material, in addition to the stress-life fatigue curve parameters of the uncorroded material. The endurance limit of corroded material can either be determined by a limited number of tests in the very high-cycle fatigue region or predicted by an analytical approach. Comparison with experimentally measured corrosion fatigue behavior of several materials is provided and discussed.

Method for deriving information regarding stress from a stressed ferromagnetic material

DOEpatents

Jiles, David C.

1991-04-30

A non-destructive evaluation technique for deriving stress in ferromagnetic materials including deriving anhysteretic and hysteresis magnetization curves for the material in both unstressed and stressed states. The anhysteretic curve is expressed as a Langevin function. The stress is expressed as an equivalent magnetic field dependent on stress and change of magnetostriction with magnetization. By measurement of these bulk magnetic properties, stress can be derived.

Method for deriving information regarding stress from a stressed ferromagnetic material

DOEpatents

Jiles, D.C.

1991-04-30

A nondestructive evaluation technique is disclosed for deriving stress in ferromagnetic materials including deriving anhysteretic and hysteresis magnetization curves for the material in both unstressed and stressed states. The anhysteretic curve is expressed as a Langevin function. The stress is expressed as an equivalent magnetic field dependent on stress and change of magnetostriction with magnetization. By measurement of these bulk magnetic properties, stress can be derived.

Food structure: Its formation and relationships with other properties.

PubMed

Joardder, Mohammad U H; Kumar, Chandan; Karim, M A

2017-04-13

Food materials are complex in nature as it has heterogeneous, amorphous, hygroscopic and porous properties. During processing, microstructure of food materials changes which significantly affects other properties of food. An appropriate understanding of the microstructure of the raw food material and its evolution during processing is critical in order to understand and accurately describe dehydration processes and quality anticipation. This review critically assesses the factors that influence the modification of microstructure in the course of drying of fruits and vegetables. The effect of simultaneous heat and mass transfer on microstructure in various drying methods is investigated. Effects of changes in microstructure on other functional properties of dried foods are discussed. After an extensive review of the literature, it is found that development of food structure significantly depends on fresh food properties and process parameters. Also, modification of microstructure influences the other properties of final product. An enhanced understanding of the relationships between food microstructure, drying process parameters and final product quality will facilitate the energy efficient optimum design of the food processor in order to achieve high-quality food.

Graphene-Reinforced Metal and Polymer Matrix Composites

NASA Astrophysics Data System (ADS)

Kasar, Ashish K.; Xiong, Guoping; Menezes, Pradeep L.

2018-03-01

Composites have tremendous applicability due to their excellent capabilities. The performance of composites mainly depends on the reinforcing material applied. Graphene is successful as an efficient reinforcing material due to its versatile as well as superior properties. Even at very low content, graphene can dramatically improve the properties of polymer and metal matrix composites. This article reviews the fabrication followed by mechanical and tribological properties of metal and polymer matrix composites filled with different kinds of graphene, including single-layer, multilayer, and functionalized graphene. Results reported to date in literature indicate that functionalized graphene or graphene oxide-polymer composites are promising materials offering significantly improved strength and frictional properties. A similar trend of improved properties has been observed in case of graphene-metal matrix composites. However, achieving higher graphene loading with uniform dispersion in metal matrix composites remains a challenge. Although graphene-reinforced composites face some challenges, such as understanding the graphene-matrix interaction or fabrication techniques, graphene-reinforced polymer and metal matrix composites have great potential for application in various fields due to their outstanding properties.

Graphene-Reinforced Metal and Polymer Matrix Composites

NASA Astrophysics Data System (ADS)

Kasar, Ashish K.; Xiong, Guoping; Menezes, Pradeep L.

2018-06-01

Composites have tremendous applicability due to their excellent capabilities. The performance of composites mainly depends on the reinforcing material applied. Graphene is successful as an efficient reinforcing material due to its versatile as well as superior properties. Even at very low content, graphene can dramatically improve the properties of polymer and metal matrix composites. This article reviews the fabrication followed by mechanical and tribological properties of metal and polymer matrix composites filled with different kinds of graphene, including single-layer, multilayer, and functionalized graphene. Results reported to date in literature indicate that functionalized graphene or graphene oxide-polymer composites are promising materials offering significantly improved strength and frictional properties. A similar trend of improved properties has been observed in case of graphene-metal matrix composites. However, achieving higher graphene loading with uniform dispersion in metal matrix composites remains a challenge. Although graphene-reinforced composites face some challenges, such as understanding the graphene-matrix interaction or fabrication techniques, graphene-reinforced polymer and metal matrix composites have great potential for application in various fields due to their outstanding properties.

Nonequilibrium material effects on the behavior of polymeric composite matrices and their related composites

NASA Technical Reports Server (NTRS)

Wilkes, G. L.

1982-01-01

The effects of physical aging on the material properties of some linear and network macromolecular glasses are discussed. The free volume concept is used to describe this behavior. The effect of physical aging on properties of some uniaxial graphite/fiber epoxy resin composites is investigated using stress relaxation in both tensile and flexural modes. The matrix polymers used were resins both of which are based on a 4,4-methylenedianiline derivative of epichlorohydrin with diamino diphenyl sulfone (DDS) as the curing agent. The matrix resin, as used in the practical application in composites, not fully cured and the glass transition of the network was dependent on the curing schedule. The physical aging of the bulk crosslinked epoxy was found to depend on the annealing temperature, and the T sub g of the resin. The physical aging of the composite, monitored by the stress relaxation method, was found to be dependent on the testing direction.

Experimental Injury Biomechanics of the Pediatric Head and Brain

NASA Astrophysics Data System (ADS)

Margulies, Susan; Coats, Brittany

Traumatic brain injury (TBI) is a leading cause of death and disability among children and young adults in the United States and results in over 2,500 childhood deaths, 37,000 hospitalizations, and 435,000 emergency department visits each year (Langlois et al. 2004). Computational models of the head have proven to be powerful tools to help us understand mechanisms of adult TBI and to determine load thresholds for injuries specific to adult TBI. Similar models need to be developed for children and young adults to identify age-specific mechanisms and injury tolerances appropriate for children and young adults. The reliability of these tools, however, depends heavily on the availability of pediatric tissue material property data. To date the majority of material and structural properties used in pediatric computer models have been scaled from adult human data. Studies have shown significant age-related differences in brain and skull properties (Prange and Margulies 2002; Coats and Margulies 2006a, b), indicating that the pediatric head cannot be modeled as a miniature adult head, and pediatric computer models incorporating age-specific data are necessary to accurately mimic the pediatric head response to impact or rotation. This chapter details the developmental changes of the pediatric head and summarizes human pediatric properties currently available in the literature. Because there is a paucity of human pediatric data, material properties derived from animal tissue are also presented to demonstrate possible age-related differences in the heterogeneity and rate dependence of tissue properties. The chapter is divided into three main sections: (1) brain, meninges, and cerebral spinal fluid (CSF); (2) skull; and (3) scalp.

On the continuum mechanics approach for the analysis of single walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Chaudhry, M. S.; Czekanski, A.

2016-04-01

Today carbon nanotubes have found various applications in structural, thermal and almost every field of engineering. Carbon nanotubes provide great strength, stiffness resilience properties. Evaluating the structural behavior of nanoscale materials is an important task. In order to understand the materialistic behavior of nanotubes, atomistic models provide a basis for continuum mechanics modelling. Although the properties of bulk materials are consistent with the size and depends mainly on the material but the properties when we are in Nano-range, continuously change with the size. Such models start from the modelling of interatomic interaction. Modelling and simulation has advantage of cost saving when compared with the experiments. So in this project our aim is to use a continuum mechanics model of carbon nanotubes from atomistic perspective and analyses some structural behaviors of nanotubes. It is generally recognized that mechanical properties of nanotubes are dependent upon their structural details. The properties of nanotubes vary with the varying with the interatomic distance, angular orientation, radius of the tube and many such parameters. Based on such models one can analyses the variation of young's modulus, strength, deformation behavior, vibration behavior and thermal behavior. In this study some of the structural behaviors of the nanotubes are analyzed with the help of continuum mechanics models. Using the properties derived from the molecular mechanics model a Finite Element Analysis of carbon nanotubes is performed and results are verified. This study provides the insight on continuum mechanics modelling of nanotubes and hence the scope to study the effect of various parameters on some structural behavior of nanotubes.

Aerosol Route Synthesis and Applications of Doped Nanostructured Materials

NASA Astrophysics Data System (ADS)

Sahu, Manoranjan

Nanotechnology presents an attractive opportunity to address various challenges in air and water purification, energy, and other environment issues. Thus, the development of new nanoscale materials in low-cost scalable synthesis processes is important. Furthermore, the ability to independently manipulate the material properties as well as characterize the material at different steps along the synthesis route will aide in product optimization. In addition, to ensure safe and sustainable development of nanotechnology applications, potential impacts need to be evaluated. In this study, nanomaterial synthesis in a single-step gas phase reactor to continuously produce doped metal oxides was demonstrated. Copper-doped TiO2 nanomaterial properties (composition, size, and crystal phase) were independently controlled based on nanoparticle formation and growth mechanisms dictated by process control parameters. Copper dopant found to significantly affect TiO2 properties such as particle size, crystal phase, stability in the suspension, and absorption spectrum (shift from UV to visible light absorption). The in-situ charge distribution characterization of the synthesized nanomaterials was carried out by integrating a tandem differential mobility analyzer (TDMA) set up with the flame reactor synthesis system. Both singly- and doubly- charged nanoparticles were measured, with the charged fractions dependent on particle mobility and dopant concentration. A theoretical calculation was conducted to evaluate the relative importance of the two charging mechanisms, diffusion and thermo-ionization, in the flame. Nanoparticle exposure characterization was conducted during synthesis as a function of operating condition, product recovery and handling technique, and during maintenance of the reactors. Strategies were then indentified to minimize the exposure risk. The nanoparticle exposure potential varied depending on the operating conditions such as precursor feed rate, working conditions of the fume hood, ventilation system, and distance from the reactors. Nanoparticle exposure varied during product recovery and handling depending on the quantity of nanomaterial handled. Most nanomaterial applications require nanomaterials to be in solution. Thus, the role of nanomaterial physio-chemical properties (size, crystal phase, dopant types and concentrations) on dispersion properties was investigated based on hydrodynamic size and surface charge. Dopant type and concentration were found to significantly affect iso-electric point (IEP)-shifting the IEP to a high or lower pH value compared to pristine TiO2 based on the oxidation state of the dopant. The microbial inactivation effectiveness of as-synthesized nanomaterials was investigated under different light irradiation conditions. Microbial inactivation was found to strongly depend on the light irradiation condition as well as on material properties such chemical composition, crystal phase, and particle size. The potential interaction mechanisms of copper-doped TiO2 nanomaterial with microbes were also explored. The studies conducted as part of this dissertation addressed issues in nanomaterial synthesis, characterization and their potential environmental applications.

Mechanical properties in crumple-formed paper derived materials subjected to compression.

PubMed

Hanaor, D A H; Flores Johnson, E A; Wang, S; Quach, S; Dela-Torre, K N; Gan, Y; Shen, L

2017-06-01

The crumpling of precursor materials to form dense three dimensional geometries offers an attractive route towards the utilisation of minor-value waste materials. Crumple-forming results in a mesostructured system in which mechanical properties of the material are governed by complex cross-scale deformation mechanisms. Here we investigate the physical and mechanical properties of dense compacted structures fabricated by the confined uniaxial compression of a cellulose tissue to yield crumpled mesostructuring. A total of 25 specimens of various densities were tested under compression. Crumple formed specimens exhibited densities in the range 0.8-1.3 g cm -3 , and showed high strength to weight characteristics, achieving ultimate compressive strength values of up to 200 MPa under both quasi-static and high strain rate loading conditions and deformation energy that compares well to engineering materials of similar density. The materials fabricated in this work and their mechanical attributes demonstrate the potential of crumple-forming approaches in the fabrication of novel energy-absorbing materials from low-cost precursors such as recycled paper. Stiffness and toughness of the materials exhibit density dependence suggesting this forming technique further allows controllable impact energy dissipation rates in dynamic applications.

Thermophysical properties of hydrophobised lime plasters - The influence of ageing

NASA Astrophysics Data System (ADS)

Pavlíková, Milena; Zemanová, Lucie; Pavlík, Zbyšek

2017-07-01

The building envelope is a principal responsible for buildings energy loses. Lime plasters as the most popular finishing materials of historical buildings and culture monuments influence the thermal behaviour as well as construction material of masonry. On this account, the effect of ageing on the thermophysical properties of a newly designed lime plasters containing hydrophobic admixture is analysed in the paper. For the comparative purposes, the reference lime plaster is tested. The ageing is accelerated with controlled carbonation process to simulate the final plasters properties. Basic characterization of the tested materials is done using bulk density, matrix density, and porosity measurements. Thermal conductivity and volumetric heat capacity are experimentally assessed using a transient impulse method. The obtained data revealed the significant changes of the both studied thermal parameters in the dependence on plasters composition and age. The assessed material parameters will be stored in a material database, where will find use as an input data for computational modelling of heat transport in this type of porous building materials and evaluation of energy-savings and sustainability issues.

On the relationships between hardness and the elastic and plastic properties of isotropic power-law hardening materials

NASA Astrophysics Data System (ADS)

Lan, Hongzhi; Venkatesh, T. A.

2014-01-01

A comprehensive understanding of the relationship between the hardness and the elastic and plastic properties for a wide range of materials is obtained by analysing the hardness characteristics (that are predicted by experimentally verified indentation analyses) of over 9000 distinct combinations of material properties that represent isotropic, homogeneous, power-law hardening metallic materials. Finite element analysis has been used to develop the indentation algorithms that provide the relationships between the elastic and plastic properties of the indented material and its indentation hardness. Based on computational analysis and virtual testing, the following observations are made. The hardness (H) of a material tends to increase with an increase in the elastic modulus (E), yield strength (σy) and the strain-hardening exponent (n). Several materials with different combinations of elastic and plastic properties can exhibit identical true hardness (for a particular indenter geometry/apex angle). In general, combinations of materials that exhibit relatively low elastic modulus and high yield strength or strain-hardening exponents and those that exhibit relatively high elastic modulus and low yield strength or strain-hardening exponents exhibit similar hardness properties. Depending on the strain-hardening characteristics of the indented material, (i.e. n = 0 or ?), the ratio H/σy ranges, respectively, from 2.2 to 2.6 or 2 to 20 (for indentations with a cone angle of 70.3°). The materials that have lower σy/E and higher n exhibit higher H/σy ratios. The commonly invoked relationship between hardness and the yield strength, i.e. H ≈ 3σy, is not generally valid or applicable for all power-law hardening materials. The indentation hardness of a power law hardening material can be taken as following the relationship H ≈ (2.1-2.8)σr where σr is the representative stress based on Tabor's representative strain for a wide range of materials.

Optical response of semiconductors in a dc-electric field

NASA Astrophysics Data System (ADS)

Prussel, Lucie; Veniard, Valerie

A deep understanding of the optical properties of solids is crucial for the improvement of nonlinear materials and devices. It offers the opportunity to search for new materials with specific properties. One way to tune some of those properties is to apply an electrostatic field. This gives rise to electro-optic effects. The most known among those is the Pockel or linear electro-optic effect (LEO), which is a second order response property described by the susceptibility χ (2) (- ω ω , 0) . An important nonlinear process is the second harmonic generation (SHG), where two photons are absorbed by the material. While this process is sensitive to the symmetry of the material, adding a static field would enable a nonlinear response from every material, including centrosymmetric ones. This happens through a third order process, named EFISH (Electric Field Induced Second Harmonic) for which the susceptibility of interest is χ (3) (- 2 ω ω , ω , 0) . We have developed a theoretical approach and a numerical tool to study these two nonlinear properties (LEO and EFISH) in the context of Time-dependent Density Functional Theory (TDDFT), and we have applied it to the case of bulk SiC and GaAs as well as layered systems such as Ge/SiGe.

Do encapsulated heat storage materials really retain their original thermal properties?

PubMed

Chaiyasat, Preeyaporn; Noppalit, Sayrung; Okubo, Masayoshi; Chaiyasat, Amorn

2015-01-14

The encapsulation of Rubitherm®27 (RT27), which is one of the most common commercially supplied heat storage materials, by polystyrene (PS), polydivinyl benzene (PDVB) and polymethyl methacrylate (PMMA) was carried out using conventional radical microsuspension polymerization. The products were purified to remove free RT27 and free polymer particles without RT27. In the cases of PS and PDVB microcapsules, the latent heats of melting and crystallization for RT27 ( and , J/g-RT27) were clearly decreased by the encapsulation. On the other hand, those of the PMMA microcapsules were the same as pure RT27. A supercooling phenomenon was observed not only for PS and PDVB but also for the PMMA microcapsules. These results indicate that the thermal properties of the heat storage materials encapsulated depend on the type of polymer shells, i.e., encapsulation by polymer shell changes the thermal properties of RT27. This is quite different from the idea of other groups in the world, in which they discussed the thermal properties based on the ΔHm and ΔHc values expressed in J/g-capsule, assuming that the thermal properties of the heat storage materials are not changed by the encapsulation. Hereafter, this report should raise an alarm concerning the "wrong" common knowledge behind developing the encapsulation technology of heat storage materials.

Relationship between Surface Modifications of Nanoparticle and Invasion into Suspension Cells

NASA Astrophysics Data System (ADS)

Matsui, Y.; Sakai, N.; Tsuda, A.; Yoneda, M.

2011-07-01

Nanomaterials have a variety of properties for each material. There is little information available on which kinds of material properties have effects on toxicity and kinetics. This paper presents that a relationship between material properties and hazard data by undertaking a bibliographical survey at first. With respect to cytotoxicity, it probably depends mainly on the particle volume dose and to a certain degree on particle solubility. It can be concluded from these results that there is a relationship between material properties and hazard data. Many activities involving nano risk are occurring all over the world. Secondly, we assayed actually for cellular uptake of three kinds of Quantum dots (15 nm, 5.5×1012 particles/ml) to demonstrate our result of bibliographical survey. Three different surface modification quantum dots (non-modification, -COOH, -NH3) were mixed with floating Jurkat cells in each. After thirty minute, we washed these cells three times and detected fluorescence by flow cytometer. Almost all the carboxylate particles invaded a cell, about 60% aminated them also invaded and few non-modification particles were taken up. Nanomaterials are often very broadly categorized and named based upon their basic material composition or product shape. Our results confirm that we have to examine which physical-chemical properties affect some adverse effects for each nanomaterial.

Finite element analysis and simulation of rheological properties of bulk molding compound (BMC)

NASA Astrophysics Data System (ADS)

Ergin, M. Fatih; Aydin, Ismail

2013-12-01

Bulk molding compound (BMC) is one of the important composite materials with various engineering applications. BMC is a thermoset plastic resin blend of various inert fillers, fiber reinforcements, catalysts, stabilizers and pigments that form a viscous, molding compound. Depending on the end-use application, bulk molding compounds are formulated to achieve close dimensional control, flame and scratch resistance, electrical insulation, corrosion and stain resistance, superior mechanical properties, low shrink and color stability. Its excellent flow characteristics, dielectric properties, and flame resistance make this thermoset material well-suited to a wide variety of applications requiring precision in detail and dimensions as well as high performance. When a BMC is used for these purposes, the rheological behavior and properties of the BMC is the main concern. In this paper, finite element analysis of rheological properties of bulk molding composite material was studied. For this purpose, standard samples of composite material were obtained by means of uniaxial hot pressing. 3 point flexural tests were then carried out by using a universal testing machine. Finite element analyses were then performed with defined material properties within a specific constitutive material behavior. Experimental and numerical results were then compared. Good correlation between the numerical simulation and the experimental results was obtained. It was expected with this study that effects of various process parameters and boundary conditions on the rheological behavior of bulk molding compounds could be determined by means of numerical analysis without detailed experimental work.

Dynamic dielectric properties of a wood liquefaction system using polyethylene glycol and glycerol

Treesearch

Mengchao Zhou; Thomas L. Eberhardt; Bo Cai; Chung-Yun Hse; Hui Pan

2017-01-01

Microwave-assisted liquefaction has shown potential for rapid thermal processing of lignocellulosic biomass. The efficiency of microwave heating depends largely on the dielectric properties of the materials being heated. The objective of this study was to investigate the dynamic interactions between microwave energy and the reaction system during the liquefaction of a...

Evaluation of reactive force fields for prediction of the thermo-mechanical properties of cellulose Iâ

Treesearch

Fernando L. Dri; Xiawa Wu; Robert J. Moon; Ashlie Martini; Pablo D. Zavattieri

2015-01-01

Molecular dynamics simulation is commonly used to study the properties of nanocellulose-based materials at the atomic scale. It is well known that the accuracy of these simulations strongly depends on the force field that describes energetic interactions. However, since there is no force field developed specifically for cellulose, researchers utilize models...

Calculation of single chain cellulose elasticity using fully atomistic modeling

Treesearch

Xiawa Wu; Robert J. Moon; Ashlie Martini

2011-01-01

Cellulose nanocrystals, a potential base material for green nanocomposites, are ordered bundles of cellulose chains. The properties of these chains have been studied for many years using atomic-scale modeling. However, model predictions are difficult to interpret because of the significant dependence of predicted properties on model details. The goal of this study is...

Moisture relations and physical properties of wood

Treesearch

Samuel V. Glass; Samuel L. Zelinka

2010-01-01

Wood, like many natural materials, is hygroscopic; it takes on moisture from the surrounding environment. Moisture exchange between wood and air depends on the relative humidity and temperature of the air and the current amount of water in the wood. This moisture relationship has an important influence on wood properties and performance. Many of the challenges of using...

Rheological and thermal properties of suspensions of microcapsules containing phase change materials.

PubMed

Cao, Vinh Duy; Salas-Bringas, Carlos; Schüller, Reidar Barfod; Szczotok, Anna M; Hiorth, Marianne; Carmona, Manuel; Rodriguez, Juan F; Kjøniksen, Anna-Lena

2018-01-01

The thermal and rheological properties of suspensions of microencapsulated phase change materials (MPCM) in glycerol were investigated. When the microcapsule concentration is raised, the heat storage capacity of the suspensions becomes higher and a slight decline in the thermal conductivity of the suspensions is observed. The temperature-dependent shear-thinning behaviour of the suspensions was found to be strongly affected by non-encapsulated phase change materials (PCM). Accordingly, the rheological properties of the MPCM suspensions could be described by the Cross model below the PCM melting point while a power law model best described the data above the PCM melting point. The MPCM suspensions are interesting for energy storage and heat transfer applications. However, the non-encapsulated PCM contributes to the agglomeration of the microcapsules, which can lead to higher pumping consumption and clogging of piping systems.

Peculiarities of hydration of Portland cement with synthetic nano-silica

NASA Astrophysics Data System (ADS)

Kotsay, Galyna

2017-12-01

Application of nano-materials in cement products significantly, improves their properties. Of course, the effectiveness of the materials depends on their quantity and the way they are introduced into the system. So far, amongst nano-materials used in construction, the most preferred was nano-silica. This research investigated the effect of synthetic precipitated nano-silica on the cement hydration as well as, on the physical and mechanical properties of pastes and mortars. Obtained results showed that admixture of nano-silica enhanced flexural and compressive strength of cement after 2 and 28 days, however, only when admixture made up 0.5% and 1.0%. On the other hand, the use of nano-silica in the amount 2% had some limitations, due to its ability to agglomerate, which resulted in deterioration of the rheological and mechanical properties.

Dynamic characterization of high damping viscoelastic materials from vibration test data

NASA Astrophysics Data System (ADS)

Martinez-Agirre, Manex; Elejabarrieta, María Jesús

2011-08-01

The numerical analysis and design of structural systems involving viscoelastic damping materials require knowledge of material properties and proper mathematical models. A new inverse method for the dynamic characterization of high damping and strong frequency-dependent viscoelastic materials from vibration test data measured by forced vibration tests with resonance is presented. Classical material parameter extraction methods are reviewed; their accuracy for characterizing high damping materials is discussed; and the bases of the new analysis method are detailed. The proposed inverse method minimizes the residue between the experimental and theoretical dynamic response at certain discrete frequencies selected by the user in order to identify the parameters of the material constitutive model. Thus, the material properties are identified in the whole bandwidth under study and not just at resonances. Moreover, the use of control frequencies makes the method insensitive to experimental noise and the efficiency is notably enhanced. Therefore, the number of tests required is drastically reduced and the overall process is carried out faster and more accurately. The effectiveness of the proposed method is demonstrated with the characterization of a CLD (constrained layer damping) cantilever beam. First, the elastic properties of the constraining layers are identified from the dynamic response of a metallic cantilever beam. Then, the viscoelastic properties of the core, represented by a four-parameter fractional derivative model, are identified from the dynamic response of a CLD cantilever beam.

Measurements of Acoustic Properties of Porous and Granular Materials and Application to Vibration Control

NASA Technical Reports Server (NTRS)

Park, Junhong; Palumbo, Daniel L.

2004-01-01

For application of porous and granular materials to vibro-acoustic controls, a finite dynamic strength of the solid component (frame) is an important design factor. The primary goal of this study was to investigate structural vibration damping through this frame wave propagation for various poroelastic materials. A measurement method to investigate the vibration characteristics of the frame was proposed. The measured properties were found to follow closely the characteristics of the viscoelastic materials - the dynamic modulus increased with frequency and the degree of the frequency dependence was determined by its loss factor. The dynamic stiffness of hollow cylindrical beams containing porous and granular materials as damping treatment was measured also. The data were used to extract the damping materials characteristics using the Rayleigh-Ritz method. The results suggested that the acoustic structure interaction between the frame and the structure enhances the dissipation of the vibration energy significantly.

Modeling Non-Linear Material Properties in Composite Materials

DTIC Science & Technology

2016-06-28

2 Figure 2: Implementation of multiscale enrichment into FEA ...corresponding to the mth degree of freedom, and is the associated degree of freedom. For FEA , the standard shape function, NI, which can be...varies depending on the governing method. In this presentation we will focus in the FEA approach. Reference [4] gives complete details on the

First principles calculation of two dimensional antimony and antimony arsenide

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

Pillai, Sharad Babu, E-mail: sbpillai001@gmail.com; Narayan, Som; Jha, Prafulla K.

2016-05-23

This work focuses on the strain dependence of the electronic properties of two dimensional antimony (Sb) material and its alloy with As (SbAs) using density functional theory based first principles calculations. Both systems show indirect bandgap semiconducting character which can be transformed into a direct bandgap material with the application of relatively small strain.

Biostable scaffolds of polyacrylate polymers implanted in the articular cartilage induce hyaline-like cartilage regeneration in rabbits.

PubMed

Sancho-Tello, María; Forriol, Francisco; Martín de Llano, José J; Antolinos-Turpin, Carmen; Gómez-Tejedor, José A; Gómez Ribelles, José L; Carda, Carmen

2017-07-05

To study the influence of scaffold properties on the organization of in vivo cartilage regeneration. Our hypothesis was that stress transmission to the cells seeded inside the pores of the scaffold or surrounding it, which is highly dependent on the scaffold properties, determines the differentiation of both mesenchymal cells and dedifferentiated autologous chondrocytes. 4 series of porous scaffolds made of different polyacrylate polymers, previously seeded with cultured rabbit chondrocytes or without cells, were implanted in cartilage defects in rabbits. Subchondral bone was injured during the surgery to allow blood to reach the implantation site and fill the scaffold pores. At 3 months after implantation, excellent tissue regeneration was obtained, with a well-organized layer of hyaline-like cartilage at the condylar surface in most cases of the hydrophobic or slightly hydrophilic series. The most hydrophilic material induced the poorest regeneration. However, no statistically significant difference was observed between preseeded and non-preseeded scaffolds. All of the materials used were biocompatible, biostable polymers, so, in contrast to some other studies, our results were not perturbed by possible effects attributable to material degradation products or to the loss of scaffold mechanical properties over time due to degradation. Cartilage regeneration depends mainly on the properties of the scaffold, such as stiffness and hydrophilicity, whereas little difference was observed between preseeded and non-preseeded scaffolds.

On the Size Dependence of Molar and Specific Properties of Independent Nano-phases and Those in Contact with Other Phases

NASA Astrophysics Data System (ADS)

Kaptay, George

2018-05-01

Nano-materials are materials with at least one nano-phase. A nano-phase is a phase with at least one of its dimensions below 100 nm. It is shown here that nano-phases have at least 1% of their atoms along their surface layer. The ratio of surface atoms is proportional to the specific surface area of the phase, defined as the ratio of its surface area to its volume. Each specific/molar property has its bulk value and its surface value for the given phase, being always different, as the energetic states of the atoms in the bulk and in the surface layer of a phase are different. The average specific/molar property of a nano-phase is modeled here as a linear combination of the bulk and surface values of the same property, scaled with the ratio of the surface atoms. That makes the performance of all nano-phases proportional to their specific surface area. As the characteristic size of the nano-phase is inversely proportional to its specific surface area, all specific/molar properties of nano-phases are inversely proportional to the characteristic size of the phase. This is applied to the size dependence of the molar Gibbs energy of the nano-phase, which appears to be in agreement with the thermodynamics of Gibbs. This agreement proves the general validity of the present model on the size dependence of the specific/molar properties of independent nano-phases. It is shown that the properties of nano-phases are different for independent nano-phases (surrounded only by their equilibrium vapor phase) and for nano-phases in multi-phase situations, such as a liquid nano-droplet in the sessile drop configuration.

Development of Highly Fluorescent Materials Based on Thiophenylimidazole Dyes

NASA Technical Reports Server (NTRS)

Santos, Javier; Bu, Xiu R.; Mintz, Eric A.; Meador, Michael A. (Technical Monitor)

2000-01-01

Organic fluorescent materials are expected to find many potential applications in optical devices and photo-functionalized materials. Although many investigations have been focused on heterocyclic compounds such as coumarins, bipyridines, rhodamines, and pyrrole derivatives, little is known for fluorescent imidazole materials. We discovered that one particular class of imidazole derivatives is highly fluorescent. A series of monomeric and polymeric based fluorescent dyes were prepared containing a thiophene unit at the second position of the imidazole ring. Dependence of fluorescence efficiency on parameters such as solvent polarity and substituent groups has been investigated. It was found that a formyl group at the 2-position of the thiophene ring dramatically enhance fluorescence properties. Ion recognition probes indicated their potential as sensor materials. These fluorophores have flexibility for introduction of versatile substituent groups that could improve the fluorescence efficiency and sensor properties.

Effect of Moisture Content on Thermal Properties of Porous Building Materials

NASA Astrophysics Data System (ADS)

Kočí, Václav; Vejmelková, Eva; Čáchová, Monika; Koňáková, Dana; Keppert, Martin; Maděra, Jiří; Černý, Robert

2017-02-01

The thermal conductivity and specific heat capacity of characteristic types of porous building materials are determined in the whole range of moisture content from dry to fully water-saturated state. A transient pulse technique is used in the experiments, in order to avoid the influence of moisture transport on measured data. The investigated specimens include cement composites, ceramics, plasters, and thermal insulation boards. The effect of moisture-induced changes in thermal conductivity and specific heat capacity on the energy performance of selected building envelopes containing the studied materials is then analyzed using computational modeling of coupled heat and moisture transport. The results show an increased moisture content as a substantial negative factor affecting both thermal properties of materials and energy balance of envelopes, which underlines the necessity to use moisture-dependent thermal parameters of building materials in energy-related calculations.

Heating 7.2 user`s manual

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

Childs, K.W.

1993-02-01

HEATING is a general-purpose conduction heat transfer program written in Fortran 77. HEATING can solve steady-state and/or transient heat conduction problems in one-, two-, or three-dimensional Cartesian, cylindrical, or spherical coordinates. A model may include multiple materials, and the thermal conductivity, density, and specific heat of each material may be both time- and temperature-dependent. The thermal conductivity may also be anisotropic. Materials may undergo change of phase. Thermal properties of materials may be input or may be extracted from a material properties library. Heat-generation rates may be dependent on time, temperature, and position, and boundary temperatures may be time- andmore » position-dependent. The boundary conditions, which may be surface-to-environment or surface-to-surface, may be specified temperatures or any combination of prescribed heat flux, forced convection, natural convection, and radiation. The boundary condition parameters may be time- and/or temperature-dependent. General gray-body radiation problems may be modeled with user-defined factors for radiant exchange. The mesh spacing may be variable along each axis. HEATING uses a runtime memory allocation scheme to avoid having to recompile to match memory requirements for each specific problem. HEATING utilizes free-form input. Three steady-state solution techniques are available: point-successive-overrelaxation iterative method with extrapolation, direct-solution, and conjugate gradient. Transient problems may be solved using any one of several finite-difference schemes: Crank-Nicolson implicit, Classical Implicit Procedure (CIP), Classical Explicit Procedure (CEP), or Levy explicit method. The solution of the system of equations arising from the implicit techniques is accomplished by point-successive-overrelaxation iteration and includes procedures to estimate the optimum acceleration parameter.« less

Heating 7. 2 user's manual

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

Childs, K.W.

1993-02-01

HEATING is a general-purpose conduction heat transfer program written in Fortran 77. HEATING can solve steady-state and/or transient heat conduction problems in one-, two-, or three-dimensional Cartesian, cylindrical, or spherical coordinates. A model may include multiple materials, and the thermal conductivity, density, and specific heat of each material may be both time- and temperature-dependent. The thermal conductivity may also be anisotropic. Materials may undergo change of phase. Thermal properties of materials may be input or may be extracted from a material properties library. Heat-generation rates may be dependent on time, temperature, and position, and boundary temperatures may be time- andmore » position-dependent. The boundary conditions, which may be surface-to-environment or surface-to-surface, may be specified temperatures or any combination of prescribed heat flux, forced convection, natural convection, and radiation. The boundary condition parameters may be time- and/or temperature-dependent. General gray-body radiation problems may be modeled with user-defined factors for radiant exchange. The mesh spacing may be variable along each axis. HEATING uses a runtime memory allocation scheme to avoid having to recompile to match memory requirements for each specific problem. HEATING utilizes free-form input. Three steady-state solution techniques are available: point-successive-overrelaxation iterative method with extrapolation, direct-solution, and conjugate gradient. Transient problems may be solved using any one of several finite-difference schemes: Crank-Nicolson implicit, Classical Implicit Procedure (CIP), Classical Explicit Procedure (CEP), or Levy explicit method. The solution of the system of equations arising from the implicit techniques is accomplished by point-successive-overrelaxation iteration and includes procedures to estimate the optimum acceleration parameter.« less

DFT Studies of Semiconductor and Scintillator Detection Materials

NASA Astrophysics Data System (ADS)

Biswas, Koushik

2013-03-01

Efficient radiation detection technology is dependent upon the development of new semiconductor and scintillator materials with advanced capabilities. First-principles based approaches can provide vital information about the structural, electrical, optical and defect properties that will help develop new materials. In addition to the predictive power of modern density functional methods, these techniques can be used to establish trends in properties that may lead to identifying new materials with optimum properties. We will discuss the properties of materials that are of current interest both in the field of scintillators and room temperature semiconductor detectors. In case of semiconductors, binary compounds such as TlBr, InI, CdTe and recently developed ternary chalcohalide Tl6SeI4 will be discussed. Tl6SeI4 mixes a halide (TlI) with a chalcogenide (Tl2Se), which results in an intermediate band gap (1.86 eV) between that of TlI (2.75 eV) and Tl2Se (0.6 eV). For scintillators, we will discuss the case of the elpasolite compounds whose rich chemical compositions should enable the fine-tuning of the band gap and band edges to achieve high light yield and fast scintillation response.

Mechanical Properties and Microstructure of Biomorphic Silicon Carbide Ceramics Fabricated from Wood Precursors

NASA Technical Reports Server (NTRS)

Singh, Mrityunjay; Salem, J. A.; Gray, Hugh R. (Technical Monitor)

2002-01-01

Silicon carbide based, environment friendly, biomorphic ceramics have been fabricated by the pyrolysis and infiltration of natural wood (maple and mahogany) precursors. This technology provides an eco-friendly route to advanced ceramic materials. These biomorphic silicon carbide ceramics have tailorable properties and behave like silicon carbide based materials manufactured by conventional approaches. The elastic moduli and fracture toughness of biomorphic ceramics strongly depend on the properties of starting wood preforms and the degree of molten silicon infiltration. Mechanical properties of silicon carbide ceramics fabricated from maple wood precursors indicate the flexural strengths of 3441+/-58 MPa at room temperature and 230136 MPa at 1350C. Room temperature fracture toughness of the maple based material is 2.6 +/- 0.2 MPa(square root of)m while the mahogany precursor derived ceramics show a fracture toughness of 2.0 +/- 0.2 Mpa(square root of)m. The fracture toughness and the strength increase as the density of final material increases. Fractographic characterization indicates the failure origins to be pores and chipped pockets of silicon.

Study of the thermal properties of filaments for 3D printing

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

Trhlíková, Lucie, E-mail: xctrhlikova@fch.vutbr.cz; Zmeskal, Oldrich, E-mail: zmeskal@fch.vutbr.cz; Florian, Pavel, E-mail: xcflorianp@fch.vutbr.cz

Various materials are used for 3D printing, most commonly Acrylonitrile butadiene styrene (ABS), Polylactic acid (PLA), Polyethylene (PET) and Polypropylene (PP). These materials differ mainly in their melting point, which significantly influences the properties of the final products. Filaments are melted in the print head during the printing process. The temperature range is from 150 °C to 250 °C depending on the technology used. The optimum temperature for the cooling substrate on which printing is carried out is chosen so as to ensure uniform cooling and deformation. It generally varies between (40 – 100) °C. From the above it ismore » clear that both temperatures can significantly affect the properties of the printed 3D object. It is therefore important to determine the thermal parameters (thermal conductivity, specific heat and thermal diffusivity) of the materials used across the entire range of temperatures. For evaluating the properties of different types of PLA materials, the step transient method was used, which allows determination of all required parameters using a fractal heat transfer model.« less

Direct Numerical Simulations of Microstructure Effects During High-Rate Loading of Additively Manufactured Metals

NASA Astrophysics Data System (ADS)

Battaile, Corbett; Owen, Steven; Moore, Nathan

2017-06-01

The properties of most engineering materials depend on the characteristics of internal microstructures and defects. In additively manufactured (AM) metals, these can include polycrystalline grains, impurities, phases, and significant porosity that qualitatively differ from conventional engineering materials. The microscopic details of the interactions between these internal defects, and the propagation of applied loads through the body, act in concert to dictate macro-observable properties like strength and compressibility. In this work, we used Sandia's ALEGRA finite element software to simulate the high-strain-rate loading of AM metals from laser engineered net shaping (LENS) and thermal spraying. The microstructural details of the material were represented explicitly, such that internal features like second phases and pores are captured and meshed as individual entities in the computational domain. We will discuss the dependence of the high-strain-rate mechanical properties on microstructural characteristics such as the shapes, sizes, and volume fractions of second phases and pores. In addition, we will examine how the details of the microstructural representation affect the microscopic material response to dynamic loads, and the effects of using ``stair-step'' versus conformal interfaces smoothed via the SCULPT tool in Sandia's CUBIT software. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE NNSA under contract DE-AC04-94AL85000.

Amorphous carbon for photovoltaics

NASA Astrophysics Data System (ADS)

Risplendi, Francesca; Grossman, Jeffrey C.

2015-03-01

All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

Simulation based estimation of dynamic mechanical properties for viscoelastic materials used for vocal fold models

NASA Astrophysics Data System (ADS)

Rupitsch, Stefan J.; Ilg, Jürgen; Sutor, Alexander; Lerch, Reinhard; Döllinger, Michael

2011-08-01

In order to obtain a deeper understanding of the human phonation process and the mechanisms generating sound, realistic setups are built up containing artificial vocal folds. Usually, these vocal folds consist of viscoelastic materials (e.g., polyurethane mixtures). Reliable simulation based studies on the setups require the mechanical properties of the utilized viscoelastic materials. The aim of this work is the identification of mechanical material parameters (Young's modulus, Poisson's ratio, and loss factor) for those materials. Therefore, we suggest a low-cost measurement setup, the so-called vibration transmission analyzer (VTA) enabling to analyze the transfer behavior of viscoelastic materials for propagating mechanical waves. With the aid of a mathematical Inverse Method, the material parameters are adjusted in a convenient way so that the simulation results coincide with the measurement results for the transfer behavior. Contrary to other works, we determine frequency dependent functions for the mechanical properties characterizing the viscoelastic material in the frequency range of human speech (100-250 Hz). The results for three different materials clearly show that the Poisson's ratio is close to 0.5 and that the Young's modulus increases with higher frequencies. For a frequency of 400 Hz, the Young's modulus of the investigated viscoelastic materials is approximately 80% higher than for the static case (0 Hz). We verify the identified mechanical properties with experiments on fabricated vocal fold models. Thereby, only small deviations between measurements and simulations occur.

Recent advances in 2D materials for photocatalysis.

PubMed

Luo, Bin; Liu, Gang; Wang, Lianzhou

2016-04-07

Two-dimensional (2D) materials have attracted increasing attention for photocatalytic applications because of their unique thickness dependent physical and chemical properties. This review gives a brief overview of the recent developments concerning the chemical synthesis and structural design of 2D materials at the nanoscale and their applications in photocatalytic areas. In particular, recent progress on the emerging strategies for tailoring 2D material-based photocatalysts to improve their photo-activity including elemental doping, heterostructure design and functional architecture assembly is discussed.

Three-dimensional solutions for the thermal buckling and sensitivity derivatives of temperature-sensitive multilayered angle-ply plates

NASA Technical Reports Server (NTRS)

Noor, A. K.; Burton, W. S.

1992-01-01

Analytic three-dimensional thermoelasticity solutions are presented for the thermal buckling of multilayered angle-ply composite plates with temperature-dependent thermoelastic properties. Both the critical temperatures and the sensitivity derivatives are computed. The sensitivity derivatives measure the sensitivity of the buckling response to variations in the different lamination and material parameters of the plate. The plates are assumed to have rectangular geometry and an antisymmetric lamination with respect to the middle plane. The temperature is assumed to be independent of the surface coordinates, but has an arbitrary symmetric variation through the thickness of the plate. The prebuckling deformations are accounted for. Numerical results are presented, for plates subjected to uniform temperature increase, showing the effects of temperature-dependent material properties on the prebuckling stresses, critical temperatures, and their sensitivity derivatives.

Damage monitoring of aircraft structures made of composite materials using wavelet transforms

NASA Astrophysics Data System (ADS)

Molchanov, D.; Safin, A.; Luhyna, N.

2016-10-01

The present article is dedicated to the study of the acoustic properties of composite materials and the application of non-destructive testing methods to aircraft components. A mathematical model of a wavelet transformed signal is presented. The main acoustic (vibration) properties of different composite material structures were researched. Multiple vibration parameter dependencies on the noise reduction factor were derived. The main steps of a research procedure and new method algorithm are presented. The data obtained was compared with the data from a three dimensional laser-Doppler scanning vibrometer, to validate the results. The new technique was tested in the laboratory and on civil aircraft at a training airfield.

Sequence-Dependent Structure/Function Relationships of Catalytic Peptide-Enabled Gold Nanoparticles Generated under Ambient Synthetic Conditions

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

Bedford, Nicholas M.; Hughes, Zak E.; Tang, Zhenghua

Peptide-enabled nanoparticle (NP) synthesis routes can create and/or assemble functional nanomaterials under environmentally friendly conditions, with properties dictated by complex interactions at the biotic/abiotic interface. Manipulation of this interface through sequence modification can provide the capability for material properties to be tailored to create enhanced materials for energy, catalysis, and sensing applications. Fully realizing the potential of these materials requires a comprehensive understanding of sequence-dependent structure/function relationships that is presently lacking. In this work, the atomic-scale structures of a series of peptide-capped Au NPs are determined using a combination of atomic pair distribution function analysis of high-energy X-ray diffraction datamore » and advanced molecular dynamics (MD) simulations. The Au NPs produced with different peptide sequences exhibit varying degrees of catalytic activity for the exemplar reaction 4-nitrophenol reduction. The experimentally derived atomic-scale NP configurations reveal sequence-dependent differences in structural order at the NP surface. Replica exchange with solute-tempering MD simulations are then used to predict the morphology of the peptide overlayer on these Au NPs and identify factors determining the structure/catalytic properties relationship. We show that the amount of exposed Au surface, the underlying surface structural disorder, and the interaction strength of the peptide with the Au surface all influence catalytic performance. A simplified computational prediction of catalytic performance is developed that can potentially serve as a screening tool for future studies. Our approach provides a platform for broadening the analysis of catalytic peptide-enabled metallic NP systems, potentially allowing for the development of rational design rules for property enhancement.« less

On the Relative Relevance of Subject-Specific Geometries and Degeneration-Specific Mechanical Properties for the Study of Cell Death in Human Intervertebral Disk Models

PubMed Central

Malandrino, Andrea; Pozo, José M.; Castro-Mateos, Isaac; Frangi, Alejandro F.; van Rijsbergen, Marc M.; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme

2015-01-01

Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration. PMID:25717471

Temperature-dependent mechanical properties of single-layer molybdenum disulphide: Molecular dynamics nanoindentation simulations

NASA Astrophysics Data System (ADS)

Zhao, Junhua; Jiang, Jin-Wu; Rabczuk, Timon

2013-12-01

The temperature-dependent mechanical properties of single-layer molybdenum disulphide (MoS2) are obtained using molecular dynamics (MD) nanoindentation simulations. The Young's moduli, maximum load stress, and maximum loading strain decrease with increasing temperature from 4.2 K to 500 K. The obtained Young's moduli are in good agreement with those using our MD uniaxial tension simulations and the available experimental results. The tendency of maximum loading strain with different temperature is opposite with that of metal materials due to the short range Stillinger-Weber potentials in MoS2. Furthermore, the indenter tip radius and fitting strain effect on the mechanical properties are also discussed.

Suppression and enhancement of deep level emission of ZnO on Si4+ & V5+ substitution

NASA Astrophysics Data System (ADS)

Srivastava, T.; Bajpai, G.; Sen, S.

2018-03-01

ZnO possess a wide range of tunable properties depending on the type and concentration of dopant. Defects in ZnO due to doped aliovalent ions can generate certain functionalities. Such defects in the lattice do not deteriorate the material properties but actually modifies the material towards infinite number of possibilities. Defects like oxygen vacancies play a significant role in photocatalytic and sensing applications. Depending upon the functionality, defect state of ZnO can be modified by suitable doping. Amount and nature of different dopant has different effect on defect state of ZnO. It depends upon the ionic radii, valence state, chemical stability etc. of the ion doped. Two samples with two different dopants i.e., silicon and vanadium, Zn1-xSixO and Zn1-xVxO, for x=0 & 0.020, were synthesized using solgel method (a citric acid-glycerol route) followed by solid state sintering. A comparison of their optical properties, photoluminescence and UV-Vis spectroscopy, with pure ZnO was studied at room temperature. Silicon doping drastically reduces whereas vanadium doping enhances the green emission as compared with pure ZnO. Suppression and enhancement of defect levels (DLE) is rationalized by the effects of extra charge present on Si4+ & V5+ (in comparison to Zn2+) and formation of new hybrid state (V3d O2p) within bandgap. Reduction of defects in Zn1-xSixO makes it suitable material for opto-electronics application whereas enhancement in defects in Zn1-xVxO makes it suitable material for photocatalytic as well as gas sensing application.

Predicting Young’s Modulus of Glass/Ceramic Sealant for Solid Oxide Fuel Cell Considering the Combined Effects of Aging, Micro-Voids and Self-Healing

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

Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

We study the temperature dependent Young’s modulus for the glass/ceramic seal material used in Solid Oxide Fuel Cells (SOFCs). With longer heat treatment or aging time during operation, further devitrification may reduce the residual glass content in the seal material while boosting the ceramic crystalline content. In the meantime, micro-voids induced by the cooling process from the high operating temperature to room temperature can potentially degrade the mechanical properties of the glass/ceramic sealant. Upon reheating to the SOFC operating temperature, possible self-healing phenomenon may occur in the glass/ceramic sealant which can potentially restore some of its mechanical properties. A phenomenologicalmore » model is developed to model the temperature dependent Young’s modulus of glass/ceramic seal considering the combined effects of aging, micro-voids, and possible self-healing. An aging-time-dependent crystalline content model is first developed to describe the increase of the crystalline content due to the continuing devitrification under high operating temperature. A continuum damage mechanics (CDM) model is then adapted to model the effects of both cooling induced micro-voids and reheating induced self-healing. This model is applied to model the glass-ceramic G18, a candidate SOFC seal material previously developed at PNNL. Experimentally determined temperature dependent Young’s modulus is used to validate the model predictions« less

Large linear magnetoresistance in a new Dirac material BaMnBi2

NASA Astrophysics Data System (ADS)

Wang, Yi-Yan; Yu, Qiao-He; Xia, Tian-Long

2016-10-01

Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles. Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials. In this paper, we report the synthesis of high quality single crystals of BaMnBi2 and investigate the transport properties of the samples. BaMnBi2 is a metal with an antiferromagnetic transition at T N = 288 K. The temperature dependence of magnetization displays different behavior from CaMnBi2 and SrMnBi2, which suggests the possible different magnetic structure of BaMnBi2. The Hall data reveals electron-type carriers and a mobility μ(5 K) = 1500 cm2/V·s. Angle-dependent magnetoresistance reveals the quasi-two-dimensional (2D) Fermi surface in BaMnBi2. A crossover from semiclassical MR ˜ H 2 dependence in low field to MR ˜ H dependence in high field, which is attributed to the quantum limit of Dirac fermions, has been observed in magnetoresistance. Our results indicate the existence of Dirac fermions in BaMnBi2. Project supported by the National Natural Science Foundation of China (Grant No. 11574391), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant No. 14XNLQ07).

Polymeric materials science in the microgravity environment

NASA Technical Reports Server (NTRS)

Coulter, Daniel R.

1989-01-01

The microgravity environment presents some interesting possibilities for the study of polymer science. Properties of polymeric materials depend heavily on their processing history and environment. Thus, there seem to be some potentially interesting and useful new materials that could be developed. The requirements for studying polymeric materials are in general much less rigorous than those developed for studying metals, for example. Many of the techniques developed for working with other materials, including heat sources, thermal control hardware and noncontact temperature measurement schemes should meet the needs of the polymer scientist.

From the molecular structure to spectroscopic and material properties: computational investigation of a bent-core nematic liquid crystal.

PubMed

Greco, Cristina; Marini, Alberto; Frezza, Elisa; Ferrarini, Alberta

2014-05-19

We present a computational investigation of the nematic phase of the bent-core liquid crystal A131. We use an integrated approach that bridges density functional theory calculations of molecular geometry and torsional potentials to elastic properties through the molecular conformational and orientational distribution function. This unique capability to simultaneously access different length scales enables us to consistently describe molecular and material properties. We can reassign (13)C NMR chemical shifts and analyze the dependence of phase properties on molecular shape. Focusing on the elastic constants we can draw some general conclusions on the unconventional behavior of bent-core nematics and highlight the crucial role of a properly-bent shape. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural Ceramic Nanocomposites: A Review of Properties and Powders’ Synthesis Methods

PubMed Central

Palmero, Paola

2015-01-01

Ceramic nanocomposites are attracting growing interest, thanks to new processing methods enabling these materials to go from the research laboratory scale to the commercial level. Today, many different types of nanocomposite structures are proposed in the literature; however, to fully exploit their exceptional properties, a deep understanding of the materials’ behavior across length scales is necessary. In fact, knowing how the nanoscale structure influences the bulk properties enables the design of increasingly performing composite materials. A further key point is the ability of tailoring the desired nanostructured features in the sintered composites, a challenging issue requiring a careful control of all stages of manufacturing, from powder synthesis to sintering. This review is divided into four parts. In the first, classification and general issues of nanostructured ceramics are reported. The second provides basic structure–property relations, highlighting the grain-size dependence of the materials properties. The third describes the role of nanocrystalline second-phases on the mechanical properties of ordinary grain sized ceramics. Finally, the fourth part revises the mainly used synthesis routes to produce nanocomposite ceramic powders, underlining when possible the critical role of the synthesis method on the control of microstructure and properties of the sintered ceramics. PMID:28347029

Effects of stress ratio on the temperature-dependent high-cycle fatigue properties of alloy steels

NASA Astrophysics Data System (ADS)

Lü, Zhi-yang; Wan, Ao-shuang; Xiong, Jun-jiang; Li, Kuang; Liu, Jian-zhong

2016-12-01

This paper addresses the effects of stress ratio on the temperature-dependent high-cycle fatigue (HCF) properties of alloy steels 2CrMo and 9CrCo, which suffer from substantial vibrational loading at small stress amplitude, high stress ratio, and high frequency in the high-temperature environments in which they function as blade and rotor spindle materials in advanced gas or steam turbine engines. Fatigue tests were performed on alloy steels 2CrMo and 9CrCo subjected to constant-amplitude loading at four stress ratios and at four and three temperatures, respectively, to determine their temperature-dependent HCF properties. The interaction mechanisms between high temperature and stress ratio were deduced and compared with each other on the basis of the results of fractographic analysis. A phenomenological model was developed to evaluate the effects of stress ratio on the temperature-dependent HCF properties of alloy steels 2CrMo and 9CrCo. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed method.

Structure and magnetic properties of mechanically alloyed Co and Co-Ni

NASA Astrophysics Data System (ADS)

Guessasma, S.; Fenineche, N.

The influence of milling process on magnetic properties of Co and Co-Ni materials is studied. Coercivity, squareness ratio and crystallite size of mechanically alloyed Co-Ni material were related to milling time. For Co material, coercivity, cubic phase ratio and crystallite size were related to milling energy considering the vial and plateau rotation velocities. An artificial neural network (ANN) combining the parameters for both materials is used to predict magnetic and structure results versus milling conditions. Predicted results showed that milling energy is mostly dependent on the ratio vial to plateau rotation velocities and that milling times larger than 40 h do not add significant change to both structure and magnetic responses. Magnetic parameters were correlated to crystallite size and the D 6 law was only valid for small sizes.

Properties of five toughened matrix composite materials

NASA Technical Reports Server (NTRS)

Cano, Roberto J.; Dow, Marvin B.

1992-01-01

The use of toughened matrix composite materials offers an attractive solution to the problem of poor damage tolerance associated with advanced composite materials. In this study, the unidirectional laminate strengths and moduli, notched (open-hole) and unnotched tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths of five carbon fiber/toughened matrix composites, IM7/E7T1-2, IM7/X1845, G40-800X/5255-3, IM7/5255-3, and IM7/5260 have been evaluated. The compression-after-impact (CAI) strengths were determined primarily by impacting quasi-isotropic laminates with the NASA Langley air gun. A few CAI tests were also made with a drop-weight impactor. For a given impact energy, compression after impact strengths were determined to be dependent on impactor velocity. Properties and strengths for the five materials tested are compared with NASA data on other toughened matrix materials (IM7/8551-7, IM6/1808I, IM7/F655, and T800/F3900). This investigation found that all five materials were stronger and more impact damage tolerant than more brittle carbon/epoxy composite materials currently used in aircraft structures.

Strain-tuned optoelectronic properties of hollow gallium sulphide microspheres

NASA Astrophysics Data System (ADS)

Zhang, Yin; Chen, Chen; Liang, C. Y.; Liu, Z. W.; Li, Y. S.; Che, Renchao

2015-10-01

Sulfide semiconductors have attracted considerable attention. The main challenge is to prepare materials with a designable morphology, a controllable band structure and optoelectronic properties. Herein, we report a facile chemical transportation reaction for the synthesis of Ga2S3 microspheres with novel hollow morphologies and partially filled volumes. Even without any extrinsic dopant, photoluminescence (PL) emission wavelength could be facilely tuned from 635 to 665 nm, depending on its intrinsic inhomogeneous strain distribution. Geometric phase analysis (GPA) based on high-resolution transmission electron microscopy (HRTEM) imaging reveals that the strain distribution and the associated PL properties can be accurately controlled by changing the growth temperature gradient, which depends on the distance between the boats used for raw material evaporation and microsphere deposition. The stacking-fault density, lattice distortion degree and strain distribution at the shell interfacial region of the Ga2S3 microspheres could be readily adjusted. Ab initio first-principles calculations confirm that the lowest conductive band (LCB) is dominated by S-3s and Ga-4p states, which shift to the low-energy band as a result of the introduction of tensile strain, well in accordance with the observed PL evolution. Therefore, based on our strain driving strategy, novel guidelines toward the reasonable design of sulfide semiconductors with tunable photoluminescence properties are proposed.Sulfide semiconductors have attracted considerable attention. The main challenge is to prepare materials with a designable morphology, a controllable band structure and optoelectronic properties. Herein, we report a facile chemical transportation reaction for the synthesis of Ga2S3 microspheres with novel hollow morphologies and partially filled volumes. Even without any extrinsic dopant, photoluminescence (PL) emission wavelength could be facilely tuned from 635 to 665 nm, depending on its intrinsic inhomogeneous strain distribution. Geometric phase analysis (GPA) based on high-resolution transmission electron microscopy (HRTEM) imaging reveals that the strain distribution and the associated PL properties can be accurately controlled by changing the growth temperature gradient, which depends on the distance between the boats used for raw material evaporation and microsphere deposition. The stacking-fault density, lattice distortion degree and strain distribution at the shell interfacial region of the Ga2S3 microspheres could be readily adjusted. Ab initio first-principles calculations confirm that the lowest conductive band (LCB) is dominated by S-3s and Ga-4p states, which shift to the low-energy band as a result of the introduction of tensile strain, well in accordance with the observed PL evolution. Therefore, based on our strain driving strategy, novel guidelines toward the reasonable design of sulfide semiconductors with tunable photoluminescence properties are proposed. Electronic supplementary information (ESI) available: Crystal structure pattern; calculated DOS diagram. See DOI: 10.1039/c5nr05528h

Synthesis, crystal structure, photophysical properties and theoretical studies of a novel bis(phenylisoxazolyl) benzene derivative

NASA Astrophysics Data System (ADS)

de Brito, A. C. F.; Correa, R. S.; Pinto, A. A.; Matos, M. J. S.; Tenorio, J. C.; Taylor, J. G.; Cazati, T.

2018-07-01

Isoxazoles have well established biological activities but, have been underexplored as synthetic intermediates for applications in materials science. The aims of this work are to synthesis a novel isoxazole and analyze its structural and photophysical properties for application in electronic organic materials. The novel bis (phenylisoxazolyl) benzene compound was synthesized in four steps and characterized by NMR, high resolution mass spectrometry, differential thermal analysis, infrared spectroscopy, cyclic voltammetry, ultraviolet-visible spectroscopy, fluorescence spectroscopy, DFT and TDDFT calculations. The molecule presented optical absorption in the ultraviolet region (from 290 nm to 330 nm), with maximum absorption length centered at 306 nm. The molar extinction coefficients (ε), fluorescence emission spectra and quantum efficiencies in chloroform and dimethylformamide solution were determined. Cyclic voltammetry analysis was carried out for estimating the HOMO energy level and these properties make it desirable material for photovoltaic device applications. Finally, the excited-state properties of present compound were calculated by time-dependent density functional theory (TDDFT).

Inverse estimation of the elastic and anelastic properties of the porous frame of anisotropic open-cell foams.

PubMed

Cuenca, Jacques; Göransson, Peter

2012-08-01

This paper presents a method for simultaneously identifying both the elastic and anelastic properties of the porous frame of anisotropic open-cell foams. The approach is based on an inverse estimation procedure of the complex stiffness matrix of the frame by performing a model fit of a set of transfer functions of a sample of material subjected to compression excitation in vacuo. The material elastic properties are assumed to have orthotropic symmetry and the anelastic properties are described using a fractional-derivative model within the framework of an augmented Hooke's law. The inverse estimation problem is formulated as a numerical optimization procedure and solved using the globally convergent method of moving asymptotes. To show the feasibility of the approach a numerically generated target material is used here as a benchmark. It is shown that the method provides the full frequency-dependent orthotropic complex stiffness matrix within a reasonable degree of accuracy.

Materials design principles of ancient fish armour

NASA Astrophysics Data System (ADS)

Bruet, Benjamin J. F.; Song, Juha; Boyce, Mary C.; Ortiz, Christine

2008-09-01

Knowledge of the structure-property-function relationships of dermal scales of armoured fish could enable pathways to improved bioinspired human body armour, and may provide clues to the evolutionary origins of mineralized tissues. Here, we present a multiscale experimental and computational approach that reveals the materials design principles present within individual ganoid scales from the `living fossil' Polypterus senegalus. This fish belongs to the ancient family Polypteridae, which first appeared 96 million years ago during the Cretaceous period and still retains many of their characteristics. The mechanistic origins of penetration resistance (approximating a biting attack) were investigated and found to include the juxtaposition of multiple distinct reinforcing composite layers that each undergo their own unique deformation mechanisms, a unique spatial functional form of mechanical properties with regions of differing levels of gradation within and between material layers, and layers with an undetectable gradation, load-dependent effective material properties, circumferential surface cracking, orthogonal microcracking in laminated sublayers and geometrically corrugated junctions between layers.

Materials design principles of ancient fish armour.

PubMed

Bruet, Benjamin J F; Song, Juha; Boyce, Mary C; Ortiz, Christine

2008-09-01

Knowledge of the structure-property-function relationships of dermal scales of armoured fish could enable pathways to improved bioinspired human body armour, and may provide clues to the evolutionary origins of mineralized tissues. Here, we present a multiscale experimental and computational approach that reveals the materials design principles present within individual ganoid scales from the 'living fossil' Polypterus senegalus. This fish belongs to the ancient family Polypteridae, which first appeared 96 million years ago during the Cretaceous period and still retains many of their characteristics. The mechanistic origins of penetration resistance (approximating a biting attack) were investigated and found to include the juxtaposition of multiple distinct reinforcing composite layers that each undergo their own unique deformation mechanisms, a unique spatial functional form of mechanical properties with regions of differing levels of gradation within and between material layers, and layers with an undetectable gradation, load-dependent effective material properties, circumferential surface cracking, orthogonal microcracking in laminated sublayers and geometrically corrugated junctions between layers.

Nanoarchitectured materials composed of fullerene-like spheroids and disordered graphene layers with tunable mechanical properties.

PubMed

Zhao, Zhisheng; Wang, Erik F; Yan, Hongping; Kono, Yoshio; Wen, Bin; Bai, Ligang; Shi, Feng; Zhang, Junfeng; Kenney-Benson, Curtis; Park, Changyong; Wang, Yanbin; Shen, Guoyin

2015-02-04

Type-II glass-like carbon is a widely used material with a unique combination of properties including low density, high strength, extreme impermeability to gas and liquid and resistance to chemical corrosion. It can be considered as a carbon-based nanoarchitectured material, consisting of a disordered multilayer graphene matrix encasing numerous randomly distributed nanosized fullerene-like spheroids. Here we show that under both hydrostatic compression and triaxial deformation, this high-strength material is highly compressible and exhibits a superelastic ability to recover from large strains. Under hydrostatic compression, bulk, shear and Young's moduli decrease anomalously with pressure, reaching minima around 1-2 GPa, where Poisson's ratio approaches zero, and then revert to normal behaviour with positive pressure dependences. Controlling the concentration, size and shape of fullerene-like spheroids with tailored topological connectivity to graphene layers is expected to yield exceptional and tunable mechanical properties, similar to mechanical metamaterials, with potentially wide applications.

Nanoarchitectured materials composed of fullerene-like spheroids and disordered graphene layers with tunable mechanical properties

NASA Astrophysics Data System (ADS)

Zhao, Zhisheng; Wang, Erik F.; Yan, Hongping; Kono, Yoshio; Wen, Bin; Bai, Ligang; Shi, Feng; Zhang, Junfeng; Kenney-Benson, Curtis; Park, Changyong; Wang, Yanbin; Shen, Guoyin

2015-02-01

Type-II glass-like carbon is a widely used material with a unique combination of properties including low density, high strength, extreme impermeability to gas and liquid and resistance to chemical corrosion. It can be considered as a carbon-based nanoarchitectured material, consisting of a disordered multilayer graphene matrix encasing numerous randomly distributed nanosized fullerene-like spheroids. Here we show that under both hydrostatic compression and triaxial deformation, this high-strength material is highly compressible and exhibits a superelastic ability to recover from large strains. Under hydrostatic compression, bulk, shear and Young’s moduli decrease anomalously with pressure, reaching minima around 1-2 GPa, where Poisson’s ratio approaches zero, and then revert to normal behaviour with positive pressure dependences. Controlling the concentration, size and shape of fullerene-like spheroids with tailored topological connectivity to graphene layers is expected to yield exceptional and tunable mechanical properties, similar to mechanical metamaterials, with potentially wide applications.

Oxide Thermoelectric Materials: A Structure-Property Relationship

NASA Astrophysics Data System (ADS)

Nag, Abanti; Shubha, V.

2014-04-01

Recent demand for thermoelectric materials for power harvesting from automobile and industrial waste heat requires oxide materials because of their potential advantages over intermetallic alloys in terms of chemical and thermal stability at high temperatures. Achievement of thermoelectric figure of merit equivalent to unity ( ZT ≈ 1) for transition-metal oxides necessitates a second look at the fundamental theory on the basis of the structure-property relationship giving rise to electron correlation accompanied by spin fluctuation. Promising transition-metal oxides based on wide-bandgap semiconductors, perovskite and layered oxides have been studied as potential candidate n- and p-type materials. This paper reviews the correlation between the crystal structure and thermoelectric properties of transition-metal oxides. The crystal-site-dependent electronic configuration and spin degeneracy to control the thermopower and electron-phonon interaction leading to polaron hopping to control electrical conductivity is discussed. Crystal structure tailoring leading to phonon scattering at interfaces and nanograin domains to achieve low thermal conductivity is also highlighted.

Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation

PubMed Central

Gayle, Andrew J.; Cook, Robert F.

2016-01-01

An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes. PMID:27563168

Effect of artificial toothbrushing and water storage on the surface roughness and micromechanical properties of tooth-colored CAD-CAM materials.

PubMed

Flury, Simon; Diebold, Elisabeth; Peutzfeldt, Anne; Lussi, Adrian

2017-06-01

Because of the different composition of resin-ceramic computer-aided design and computer-aided manufacturing (CAD-CAM) materials, their polishability and their micromechanical properties vary. Moreover, depending on the composition of the materials, their surface roughness and micromechanical properties are likely to change with time. The purpose of this in vitro study was to investigate the effect of artificial toothbrushing and water storage on the surface roughness (Ra and Rz) and the micromechanical properties, surface hardness (Vickers [VHN]) and indentation modulus (E IT ), of 5 different tooth-colored CAD-CAM materials when polished with 2 different polishing systems. Specimens (n=40 per material) were cut from a composite resin (Paradigm MZ100; 3M ESPE), a feldspathic ceramic (Vitablocs Mark II; Vita Zahnfabrik), a resin nanoceramic (Lava Ultimate; 3M ESPE), a hybrid dental ceramic (Vita Enamic; Vita Zahnfabrik), and a nanocomposite resin (Ambarino High-Class; Creamed). All specimens were roughened in a standardized manner and polished either with Sof-Lex XT discs or the Vita Polishing Set Clinical. Surface roughness, VHN, and E IT were measured after polishing and after storage for 6 months (tap water, 37°C) with periodic, artificial toothbrushing. The surface roughness, VHN, and E IT results were analyzed with a nonparametric ANOVA followed by Kruskal-Wallis and exact Wilcoxon rank sum tests (α=.05). Irrespective of polishing system and of artificial toothbrushing and storage, Lava Ultimate generally showed the lowest surface roughness and Vitablocs Mark II the highest. As regards micromechanical properties, the following ranking of the CAD-CAM materials was found (from highest VHN/E IT to lowest VHN/E IT ): Vitablocs Mark II > Vita Enamic > Paradigm MZ100 > Lava Ultimate > Ambarino High-Class. Irrespective of material and of artificial toothbrushing and storage, polishing with Sof-Lex XT discs resulted in lower surface roughness than the Vita Polishing Set Clinical (P≤.016). However, the polishing system generally had no influence on the micromechanical properties (P>.05). The effect of artificial toothbrushing and storage on surface roughness depended on the material and the polishing system: Ambarino High-Class was most sensitive to storage, Lava Ultimate and Vita Enamic were least sensitive. Artificial toothbrushing and storage generally resulted in a decrease in VHN and E IT for Paradigm MZ100, Lava Ultimate, and Ambarino High-Class but not for Vita Enamic and Vitablocs Mark II. Tooth-colored CAD-CAM materials with lower VHN and E IT generally showed better polishability. However, these materials were more prone to degradation by artificial toothbrushing and water storage than materials with higher VHN and E IT . Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Analytical Ultrasonics in Materials Research and Testing

NASA Technical Reports Server (NTRS)

Vary, A.

1986-01-01

Research results in analytical ultrasonics for characterizing structural materials from metals and ceramics to composites are presented. General topics covered by the conference included: status and advances in analytical ultrasonics for characterizing material microstructures and mechanical properties; status and prospects for ultrasonic measurements of microdamage, degradation, and underlying morphological factors; status and problems in precision measurements of frequency-dependent velocity and attenuation for materials analysis; procedures and requirements for automated, digital signal acquisition, processing, analysis, and interpretation; incentives for analytical ultrasonics in materials research and materials processing, testing, and inspection; and examples of progress in ultrasonics for interrelating microstructure, mechanical properites, and dynamic response.

Characteristics of aluminum alloy microplastic deformation in different structural states

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

Seregin, G.V.; Efimenko, L.L.; Leonov, M.V.

The solution to the problem of improving the mechanical properties (including cyclic strength) of structural materials is largely dependent on our knowledge of the laws governing the development of microplastic deformations in them. The effect of heat and mechanical treatment on the elastoplastic properties and fatigue resistance of the commercial aluminum alloys AK4-1 and D16 is analyzed.

Effect of cellulose fiber reinforcement on the temperature dependent mechanical performance of nylon 6

Treesearch

Mehdi Tajvidi; Mokhtar Feizmand; Robert H. Falk; Colin Felton

2009-01-01

In order to quantify the effect of temperature on the mechanical properties of pure nylon 6 and its composite with cellulose fibers (containing 25 wt% cellulose fibers), the materials were sampled and tested at three representative temperatures of 256, 296, and 336 K. Flexural and tensile tests were performed and the reductions in mechanical properties were evaluated....

Proposed test program and data base for LDEF polymer matrix composites

NASA Technical Reports Server (NTRS)

Tennyson, R. C.; George, Pete; Steckel, Gary L.; Zimcik, D. G.

1992-01-01

A survey of the polymer matrix composite materials that were flown on Long Duration Exposure Facility (LDEF) is presented with particular attention to the effect of circumferential location (alpha) on the measured degradation and property changes. Specifically, it is known that atomic oxygen fluence (AO), VUV radiation dose, and number of impacts by micrometeoroids/debris vary with alpha. Thus, it is possible to assess material degradation and property damage changes with alpha for those materials that are common to three or more locations. Once the alpha-dependence functions were defined, other material samples will provide data that can readily be used to predict damage and property changes as a function of alpha as well. What data can be realistically obtained from these materials, how this data can be obtained, and the scientific/design value of the data to the user community is summarized. Finally, a proposed test plan is presented with recommended characterization methodologies that should be employed by all investigators to ensure consistency in the data base that will result from this exercise.

The development and characterization of degradable poly(vinyl ester) and poly(vinyl ester)/PEO block copolymers

NASA Astrophysics Data System (ADS)

Lipscomb, Corinne Elizabeth

The development of biodegradable materials is a challenging and important problem in polymer science. A review of the state of the art in degradable materials is presented, which reveals that current biodegradable materials do not exhibit the thermal or mechanical properties necessary for widespread applications. One strategy for toughening polymeric materials, which has previously been applied to non-degradable thermoplastics and thermoplastic elastomers, is the formation of block copolymers. Poly(vinyl esters) (PVE) homopolymers are known to have a wide range of properties, but PVE block copolymers comprise a class of inexpensive and (bio)degradable materials that were previously unknown. Therefore, the synthesis and properties of these block copolymers were explored in an effort to develop robust degradable materials. This thesis research probes the reaction conditions necessary for the reversible-addition fragmentation chain transfer (RAFT) polymerization and chain extension reactions of vinyl ester monomers. PVE di- and triblock copolymers are synthesized and studied, and the triblock copolymers display extremely poor toughness due to their relatively low molecular weights in light of the high entanglement molecular weight of the poly(vinyl acetate) center block. Attempts to improve the mechanical properties of these materials focus on the incorporation of poly(ethylene oxide) (PEO) as a low entanglement molecular weight and biocompatible center block in PVE-containing triblock copolymers. Depending on the choice of PVE endblocks and the overall polymer composition, crystallization of the PEO block can be controlled, confined, or inhibited. Polymers in which PEO crystallization is completely inhibited exhibit enhanced mechanical properties and behave as weak thermoplastics. In order to understand the relationship between the inhibition of PEO crystallization and the mechanical properties of PVE/PEO materials, these polymers were studied using dynamic mechanical spectroscopy, wide angle X-ray scattering, small angle X-ray scattering, differential scanning calorimetry, and uniaxial tensile tests. By combining insights gained from these techniques, a complex picture emerges that explains the enhanced mechanical properties of these materials based on the type and location of thermal transitions, amorphous PEO entanglements, and the strain-induced crystallization of PEO. This work represents an important step toward developing robust materials with tunable properties containing (bio)degradable components.

Determination of Temperature- Dependent Mechanical Properties of Carbon Composites Under Tensile and Flexural Loading

NASA Astrophysics Data System (ADS)

Chripunow, Andre; Kubisch, Aline; Ruder, Matthias; Forster, Andreas; Korber, Hannes

2014-06-01

The presented test setup utilises a custom-built furnace realising test temperatures of up to 500°C. In order to ensure always optimal test conditions the temperature cell can be exchanged depending on the mechanical tests and specimen sizes. Cells for tensile and flexural loadings had been developed. With the latter one it is possible to perform three-point-bending tests, interlaminar-shear-strength tests as well as tests to determine the interlaminar fracture toughness. In this work the effect of fibre orientation on the mechanical properties of CFRP prepreg material under tensile and flexural loads at elevated temperatures was studied. Especially the matrix dominated layups showed a rather early decay of the mechanical properties even at temperatures quite lower than Tg. An analytical model has been used to describe the temperature-dependent properties. The model shows good agreement concerning the strength whereas the proper prediction of the moduli was only possible for the matrix dominated layups.

Unified theory for inhomogeneous thermoelectric generators and coolers including multistage devices.

PubMed

Gerstenmaier, York Christian; Wachutka, Gerhard

2012-11-01

A novel generalized Lagrange multiplier method for functional optimization with inclusion of subsidiary conditions is presented and applied to the optimization of material distributions in thermoelectric converters. Multistaged devices are considered within the same formalism by inclusion of position-dependent electric current in the legs leading to a modified thermoelectric equation. Previous analytical solutions for maximized efficiencies for generators and coolers obtained by Sherman [J. Appl. Phys. 31, 1 (1960)], Snyder [Phys. Rev. B 86, 045202 (2012)], and Seifert et al. [Phys. Status Solidi A 207, 760 (2010)] by a method of local optimization of reduced efficiencies are recovered by independent proof. The outstanding maximization problems for generated electric power and cooling power can be solved swiftly numerically by solution of a differential equation-system obtained within the new formalism. As far as suitable materials are available, the inhomogeneous TE converters can have increased performance by use of purely temperature-dependent material properties in the thermoelectric legs or by use of purely spatial variation of material properties or by a combination of both. It turns out that the optimization domain is larger for the second kind of device which can, thus, outperform the first kind of device.

Cooperative enhancement of the nonlinear optical response in conjugated energetic materials: A TD-DFT study

DOE PAGES

Sifain, Andrew E.; Tadesse, Loza F.; Bjorgaard, Josiah August; ...

2017-03-21

Conjugated energetic molecules (CEMs) are a class of explosives with high nitrogen content that posses both enhanced safety and energetic performance properties and are ideal for direct optical initiation. As isolated molecules, they absorb within the range of conventional lasers. Crystalline CEMs are used in practice, however, and their properties can differ due to intermolecular interaction. Herein, time-dependent density functional theory was used to investigate one-photon absorption (OPA) and two-photon absorption (TPA) of monomers and dimers obtained from experimentally determined crystal structures of CEMs. OPA scales linearly with the number of chromophore units, while TPA scales nonlinearly, where a moremore » than 3-fold enhancement in peak intensity, per chromophore unit, is calculated. Cooperative enhancement depends on electronic delocalization spanning both chromophore units. An increase in sensitivity to nonlinear laser initiation makes these materials suitable for practical use. This is the first study predicting a cooperative enhancement of the nonlinear optical response in energetic materials composed of relatively small molecules. Finally, the proposed model quantum chemistry is validated by comparison to crystal structure geometries and the optical absorption of these materials dissolved in solution.« less

Advances in first-principles calculations of thermodynamic properties of planetary materials (Invited)

NASA Astrophysics Data System (ADS)

Wilson, H. F.

2013-12-01

First-principles atomistic simulation is a vital tool for understanding the properties of materials at the high-pressure high-temperature conditions prevalent in giant planet interiors, but properties such as solubility and phase boundaries are dependent on entropy, a quantity not directly accessible in simulation. Determining entropic properties from atomistic simulations is a difficult problem typically requiring a time-consuming integration over molecular dynamics trajectories. Here I will describe recent advances in first-principles thermodynamic calculations which substantially increase the simplicity and efficiency of thermodynamic integration and make entropic properties more readily accessible. I will also describe the use of first-principles thermodynamic calculations for understanding problems including core solubility in gas giants and superionic phase changes in ice giants, as well as future prospects for combining first-principles thermodynamics with planetary-scale models to help us understand the origin and consequences of compositional inhomogeneity in giant planet interiors.

Concrete Model Descriptions and Summary of Benchmark Studies for Blast Effects Simulations

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

Noble, C; Kokko, E; Darnell, I

2005-07-21

Concrete is perhaps one of the most widely used construction materials in the world. Engineers use it to build massive concrete dams, concrete waterways, highways, bridges, and even nuclear reactors. The advantages of using concrete is that it can be cast into any desired shape, it is durable, and very economical compared to structural steel. The disadvantages are its low tensile strength, low ductility, and low strength-to-weight ratio. Concrete is a composite material that consists of a coarse granular material, or aggregate, embedded in a hard matrix of material, or cement, which fills the gaps between the aggregates and bindsmore » them together. Concrete properties, however, vary widely. The properties depend on the choice of materials used and the proportions for a particular application, as well as differences in fabrication techniques. Table 1 provides a listing of typical engineering properties for structural concrete. Properties also depend on the level of concrete confinement, or hydrostatic pressure, the material is being subjected to. In general, concrete is rarely subjected to a single axial stress. The material may experience a combination of stresses all acting simultaneously. The behavior of concrete under these combined stresses are, however, extremely difficult to characterize. In addition to the type of loading, one must also consider the stress history of the material. Failure is determined not only by the ultimate stresses, but also by the rate of loading and the order in which these stresses were applied. The concrete model described herein accounts for this complex behavior of concrete. It was developed by Javier Malvar, Jim Wesevich, and John Crawford of Karagozian and Case, and Don Simon of Logicon RDA in support of the Defense Threat Reduction Agency's programs. The model is an enhanced version of the Concrete/Geological Material Model 16 in the Lagrangian finite element code DYNA3D. The modifications that were made to the original model ensured that the material response followed experimental observations for standard uniaxial, biaxial, and triaxial tests for both tension and compression type loading. A disadvantage of using this material model, however, is the overwhelming amount of input that is required from the user. Therefore, the goal of this report is to provide future users with the tools necessary for successfully using this model.« less

Mechanical properties of shape memory polymers for morphing aircraft applications

NASA Astrophysics Data System (ADS)

Keihl, Michelle M.; Bortolin, Robert S.; Sanders, Brian; Joshi, Shiv; Tidwell, Zeb

2005-05-01

This investigation addresses basic characterization of a shape memory polymer (SMP) as a suitable structural material for morphing aircraft applications. Tests were performed for monotonic loading in high shear at constant temperature, well below, or just above the glass transition temperature. The SMP properties were time-and temperature-dependent. Recovery by the SMP to its original shape needed to be unfettered. Based on the testing SMPs appear to be an attractive and promising component in the solution for a skin material of a morphing aircraft. Their multiple state abilities allow them to easily change shape and, once cooled, resist large loads.

Thermomechanical response of metal-ceramic graded composites for high-temperature aerospace applications

NASA Astrophysics Data System (ADS)

Deierling, Phillip Eugene

Airframes operating in the hypersonic regime are subjected to complex structural and thermal loads. Structural loads are a result of aggressive high G maneuvers, rapid vehicle acceleration and deceleration, and dynamic pressure, while thermal loads are a result of aerodynamic heating. For such airframes, structural members are typically constructed from steel, titanium and nickel alloys. However, with most materials, rapid elevations in temperature lead to undesirable changes in material properties. In particular, reductions in strength and stiffness are observed, along with an increase in thermal conductivity, specific heat and thermal expansion. Thus, hypersonic airframes are typically designed with external insulation, active cooling or a thermal protection system (TPS) added to the structure to protect the underling material from the effects of temperature. Such thermal protection may consist of adhesively bonded, pinned, and bolted thermal protection layers over exterior panels. These types of attachments create abrupt changes in thermal expansion and stiffness that make the structure susceptible to cracking and debonding as well as adding mass to the airframe. One of the promising materials concepts for extreme environments that was introduced in the past is the so-called Spatially Tailored Advanced Thermal Structures (STATS). The concept of STATS is rooted in functionally graded materials (FGMs), in which a directional variation of material properties exists. These materials are essentially composites and consist of two or more phases of distinct materials in which the volume fractions of each phase continuously change in space. Here, the graded material will serve a dual-purpose role as both the structural/skin member and thermal management with the goal of reducing the weight of the structure while maintaining structural soundness. This is achieved through the ability to tailor material properties to create a desired or enhanced thermomechanical response through spatial variation (e.g. grading). The objective of this study is to present a computational framework for modeling and evaluating the thermomechanical response of STATS and FGMs for highly maneuverable hypersonic (Mach > 5) airframes. To meet the objective of this study, four key steps have been defined to study the thermomechanical response of such materials in extreme environments. They involve: (1) modeling of graded microstructures; (2) validation of analytical and numerical modeling techniques for graded microstructures; (3) determination of effective properties of variable composition composites; (4) parametric studies to evaluate the performance of FGMs for use in the hypersonic operating environment; (5) optimization of the material spatial grading in hypersonic panels aiming to improve the thermomechanical performance. Modeling of graded microstructures, representing particulate reinforced FGMs, has been accomplished using power law distribution functions to specify the spatial variation of the constituents. Artificial microstructures consisting of disks and spheres have been generated using developed algorithms. These algorithms allow for the creation of dense packing fractions up to 0.61 and 0.91 for 2D and 3D geometry, respectively. Effective properties of FGMs are obtained using micromechanics models and finite element analysis of representative volume elements (RVEs). Two approaches have been adopted and compared to determine the proper RVE for materials with graded microstructures. In the first approach, RVEs are generated by considering regions that have a uniform to slow variation in material composition (i.e., constant volume fraction), resulting in statistically homogenous piecewise RVEs of the graded microstructure neglecting interactions from neighboring cells. In the second approach, continuous RVEs are generated by considering the entire FGM. Here it is presumed that modeling of the complete variation in a microstructure may influence the surrounding layers due to the interactions of varying material composition, particularly when there is a steep variation in material composition along the grading direction. To determine these effects of interlayer interactions, FGM microstructures were generated using three different types of material grading functions, linear, quadratic and square root, providing uniform, gradual and steep variations, respectively. Two- and three-dimensional finite element analysis was performed to determine the effective temperature-dependent material properties of the composite over a wide temperature range. The outcome of the computational analysis show that the similar effective properties are obtained by each of the modeling approaches. Furthermore, the obtained computational results for effective elastic, thermal, and thermal expansion properties are consistent with the known analytical bounds. Resulting effective temperature-dependent material properties were used to evaluate the time-dependent thermostructural response and effectiveness of FGM structural panels. Structural panels are subjected to time- and spatial-dependent thermal and mechanical loads resulting from hypersonic flight over a representative trajectory. Mechanical loads are the by-product of aggressive maneuvering at high air speeds and angles of attack. Thermal loads as a result of aerodynamic heating are applied to the material systems as laminar, turbulent and transitional heat flux on the outer surface. Laminar and turbulent uniform heat fluxes are used to evaluate the effectiveness of FGM panels graded in the through-thickness direction only. Transitional heat fluxes are used to evaluate the effectiveness of FGMs graded in two principal directions, e.g., through-thickness and the surface parallel to flow. The computational results indicate that when subjected to uniform surface heat flux, the graded material system can eliminate through-thickness temperature gradients that are otherwise present in traditional thermal protection systems. Furthermore, two-dimensional graded material systems can also eliminate through-thickness temperature gradients and significantly reduce in-plane surface temperature gradients when subjected to non-uniform surface aerodynamic heating.

Effect of the quality of powder materials on the properties of the wear-resistant coatings on the rotor blades in an aviation gas-turbine engine compressor

NASA Astrophysics Data System (ADS)

Abraimov, N. V.; Ryabenko, B. V.; Kryukov, M. A.

2015-06-01

The physicomechanical properties, the structures of a wear-resistant WC-Co coating on a VT3-1 titanium alloy and the powder materials used for their deposition by gas-detonation method are studied. The VK-25M coatings are found to inherit the chemical and phase compositions of the powders. The properties of the coating are substantially dependent on the shape, the sizes, and the ratio of carbide WC granules in commercial powder materials. A high content of coarse lamellar WC fractions is accompanied by an increase in the hardness and a decrease in the ductility and the fracture toughness of the coatings. The tensile stresses in the VK-25M coating on the VT3-1 titanium alloy and the fracture toughness decrease as the coating thickness increases or annealing is applied.

Thermal expansion and magnetostriction measurements at cryogenic temperature using the strain gage method

NASA Astrophysics Data System (ADS)

Wang, Wei; Liu, Huiming; Huang, Rongjin; Zhao, Yuqiang; Huang, Chuangjun; Guo, Shibin; Shan, Yi; Li, Laifeng

2018-03-01

Thermal expansion and magnetostriction, the strain responses of a material to temperature and a magnetic field, especially properties at low temperature, are extremely useful to study electronic and phononic properties, phase transitions, quantum criticality, and other interesting phenomena in cryogenic engineering and materials science. However, traditional dilatometers cannot provide magnetic field and ultra low temperature (＜77 K) environment easily. This paper describes the design and test results of thermal expansion and magnetostriction at cryogenic temperature using the strain gage method based on a Physical Properties Measurements System (PPMS). The interfacing software and automation were developed using LabVIEW. The sample temperature range can be tuned continuously between 1.8 K and 400 K. With this PPMS-aided measuring system, we can observe temperature and magnetic field dependence of the linear thermal expansion of different solid materials easily and accurately.

Dependence of equivalent thermal conductivity coefficients of single-wall carbon nanotubes on their chirality

NASA Astrophysics Data System (ADS)

Zarubin, V. S.; Sergeeva, E. S.

2018-04-01

Composite materials (composites) composed of a matrix and reinforcing components are currently widely used as structural materials for various engineering devices designed to operate under extreme thermal and mechanical loads. By modifying a composite with structure-sensitive inclusions such as single-wall carbon nanotubes, one can significantly improve the thermomechanical properties of the resulting material. The paper presents relationships obtained for the equivalent thermal conductivity coefficients of single-wall carbon nanotubes versus their chirality using a simulation model developed to simulate the heat transfer process through thermal conductivity in a transversely isotropic environment. With these coefficients, one can conventionally substitute a single-wall carbon nanotube with a continuous anisotropic fiber, thus allowing one to estimate the thermal properties of composites reinforced with objects of this sort by using the well-known models developed for fibered composites. The results presented here can be used to estimate the thermal properties of carbon nanotube-reinforced composites.

Experimental Evaluation of Equivalent-Fluid Models for Melamine Foam

NASA Technical Reports Server (NTRS)

Allen, Albert R.; Schiller, Noah H.

2016-01-01

Melamine foam is a soft porous material commonly used in noise control applications. Many models exist to represent porous materials at various levels of fidelity. This work focuses on rigid frame equivalent fluid models, which represent the foam as a fluid with a complex speed of sound and density. There are several empirical models available to determine these frequency dependent parameters based on an estimate of the material flow resistivity. Alternatively, these properties can be experimentally educed using an impedance tube setup. Since vibroacoustic models are generally sensitive to these properties, this paper assesses the accuracy of several empirical models relative to impedance tube measurements collected with melamine foam samples. Diffuse field sound absorption measurements collected using large test articles in a laboratory are also compared with absorption predictions determined using model-based and measured foam properties. Melamine foam slabs of various thicknesses are considered.

Unified interatomic potential and energy barrier distributions for amorphous oxides.

PubMed

Trinastic, J P; Hamdan, R; Wu, Y; Zhang, L; Cheng, Hai-Ping

2013-10-21

Amorphous tantala, titania, and hafnia are important oxides for biomedical implants, optics, and gate insulators. Understanding the effects of oxide doping is crucial to optimize performance in these applications. However, no molecular dynamics potentials have been created to date that combine these and other oxides that would allow computational analyses of doping-dependent structural and mechanical properties. We report a novel set of computationally efficient, two-body potentials modeling van der Waals and covalent interactions that reproduce the structural and elastic properties of both pure and doped amorphous oxides. In addition, we demonstrate that the potential accurately produces energy barrier distributions for pure and doped samples. The distributions can be directly compared to experiment and used to calculate physical quantities such as internal friction to understand how doping affects material properties. Future analyses using these potentials will be of great value to determine optimal doping concentrations and material combinations for myriad material science applications.

Thinking Like a Chemist: Intuition in Thermoelectric Materials.

PubMed

Zeier, Wolfgang G; Zevalkink, Alex; Gibbs, Zachary M; Hautier, Geoffroy; Kanatzidis, Mercouri G; Snyder, G Jeffrey

2016-06-06

The coupled transport properties required to create an efficient thermoelectric material necessitates a thorough understanding of the relationship between the chemistry and physics in a solid. We approach thermoelectric material design using the chemical intuition provided by molecular orbital diagrams, tight binding theory, and a classic understanding of bond strength. Concepts such as electronegativity, band width, orbital overlap, bond energy, and bond length are used to explain trends in electronic properties such as the magnitude and temperature dependence of band gap, carrier effective mass, and band degeneracy and convergence. The lattice thermal conductivity is discussed in relation to the crystal structure and bond strength, with emphasis on the importance of bond length. We provide an overview of how symmetry and bonding strength affect electron and phonon transport in solids, and how altering these properties may be used in strategies to improve thermoelectric performance. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Benefits of on-wafer calibration standards fabricated in membrane technology

NASA Astrophysics Data System (ADS)

Rohland, M.; Arz, U.; Büttgenbach, S.

2011-07-01

In this work we compare on-wafer calibration standards fabricated in membrane technology with standards built in conventional thin-film technology. We perform this comparison by investigating the propagation of uncertainties in the geometry and material properties to the broadband electrical properties of the standards. For coplanar waveguides used as line standards the analysis based on Monte Carlo simulations demonstrates an up to tenfold reduction in uncertainty depending on the electromagnetic waveguide property we look at.

Dielectric properties of metallic alloy FeCoZr-dielectric ceramic PZT nanostructures prepared by ion sputtering in vacuum conditions

NASA Astrophysics Data System (ADS)

Boiko, O.

2018-05-01

The main objective of the research was investigation of dielectric properties of (FeCoZr)x(PZT)(100-x) granular nanocomposites and determination the influence of isochronous annealing in temperatures of 398 K-573 K on them. The impedance spectroscopy methodology was used. The measurements of electrical parameters, such as: phase shift angle φ, dielectric loss factor tgδ, capacity C and conductivity σ of (FeCoZr)x(PZT)(100-x) nanocomposites have been performed. Frequency dependencies of these parameters were obtained for the ambient temperature range 98 K-373 K for the frequencies ranging from 50 Hz to 105 Hz. It was established, that the conductivity σ of the tested materials before the percolation threshold demonstrates non-linear dependence on frequency. Furthermore, it increases when the ambient temperature is increasing, which indicates a dielectric type of the material. The two types of electrical conduction: capacitive (phase shift angle φ takes negative values) and inductive (φ takes positive values) have been observed. It was concluded that the hopping conductivity dominated in the nanocomposites. Voltage and current resonances phenomena are observed in the materials. The isochronous annealing intensifies the dielectric properties of (FeCoZr)x(PZT)(100-x) nanocomposites.

Comparative thermometric properties of bi-functional Er3+-Yb3+ doped rare earth (RE = Y, Gd and La) molybdates

NASA Astrophysics Data System (ADS)

Sinha, Shriya; Mahata, Manoj Kumar; Kumar, Kaushal

2018-02-01

The molybdate compounds as luminescent medium have received great attention of recent research due to their excellent intrinsic optical properties. Therefore, the investigation on the optical thermometry and nanoheating effect in Er3+-Yb3+ doped molybdates of yttrium (EYYMO), gadolinium (EYGMO) and lanthanum (EYLMO) nanophosphors is reported herein. The temperature dependent fluorescence intensity ratio of green (525 and 548 nm) emission bands of Er3+ ions were analyzed within 300-500 K temperature range to determine the thermal behavior. The comparative temperature sensitivity of the materials has been found to depend on the phonon energy of their own. The thermal sensitivity is higher in the materials with low phonon energy. The intensity ratio of the green emission bands has been found to alter with the laser excitation density, which can be used to estimate the induced temperature in the materials. Furthermore, the photothermal conversion efficiency is calculated in the water dispersed samples and the maximum photothermal conversion efficiency of 49.6% is achieved for EYGMO nanophosphor. Comparative experimental results explore unequal thermal sensing and induced optical heating in the three rare earth molybdates. The optical properties of the green emitting molybdates are interesting for temperature sensing and optical heating applications.

Directed assembly of bio-inspired hierarchical materials with controlled nanofibrillar architectures

NASA Astrophysics Data System (ADS)

Tseng, Peter; Napier, Bradley; Zhao, Siwei; Mitropoulos, Alexander N.; Applegate, Matthew B.; Marelli, Benedetto; Kaplan, David L.; Omenetto, Fiorenzo G.

2017-05-01

In natural systems, directed self-assembly of structural proteins produces complex, hierarchical materials that exhibit a unique combination of mechanical, chemical and transport properties. This controlled process covers dimensions ranging from the nano- to the macroscale. Such materials are desirable to synthesize integrated and adaptive materials and systems. We describe a bio-inspired process to generate hierarchically defined structures with multiscale morphology by using regenerated silk fibroin. The combination of protein self-assembly and microscale mechanical constraints is used to form oriented, porous nanofibrillar networks within predesigned macroscopic structures. This approach allows us to predefine the mechanical and physical properties of these materials, achieved by the definition of gradients in nano- to macroscale order. We fabricate centimetre-scale material geometries including anchors, cables, lattices and webs, as well as functional materials with structure-dependent strength and anisotropic thermal transport. Finally, multiple three-dimensional geometries and doped nanofibrillar constructs are presented to illustrate the facile integration of synthetic and natural additives to form functional, interactive, hierarchical networks.

Borophene as a prototype for synthetic 2D materials development.

PubMed

Mannix, Andrew J; Zhang, Zhuhua; Guisinger, Nathan P; Yakobson, Boris I; Hersam, Mark C

2018-06-01

The synthesis of 2D materials with no analogous bulk layered allotropes promises a substantial breadth of physical and chemical properties through the diverse structural options afforded by substrate-dependent epitaxy. However, despite the joint theoretical and experimental efforts to guide materials discovery, successful demonstrations of synthetic 2D materials have been rare. The recent synthesis of 2D boron polymorphs (that is, borophene) provides a notable example of such success. In this Perspective, we discuss recent progress and future opportunities for borophene research. Borophene combines unique mechanical properties with anisotropic metallicity, which complements the canon of conventional 2D materials. The multi-centre characteristics of boron-boron bonding lead to the formation of configurationally varied, vacancy-mediated structural motifs, providing unprecedented diversity in a mono-elemental 2D system with potential for electronic applications, chemical functionalization, materials synthesis and complex heterostructures. With its foundations in computationally guided synthesis, borophene can serve as a prototype for ongoing efforts to discover and exploit synthetic 2D materials.

Borophene as a prototype for synthetic 2D materials development

NASA Astrophysics Data System (ADS)

Mannix, Andrew J.; Zhang, Zhuhua; Guisinger, Nathan P.; Yakobson, Boris I.; Hersam, Mark C.

2018-06-01

The synthesis of 2D materials with no analogous bulk layered allotropes promises a substantial breadth of physical and chemical properties through the diverse structural options afforded by substrate-dependent epitaxy. However, despite the joint theoretical and experimental efforts to guide materials discovery, successful demonstrations of synthetic 2D materials have been rare. The recent synthesis of 2D boron polymorphs (that is, borophene) provides a notable example of such success. In this Perspective, we discuss recent progress and future opportunities for borophene research. Borophene combines unique mechanical properties with anisotropic metallicity, which complements the canon of conventional 2D materials. The multi-centre characteristics of boron-boron bonding lead to the formation of configurationally varied, vacancy-mediated structural motifs, providing unprecedented diversity in a mono-elemental 2D system with potential for electronic applications, chemical functionalization, materials synthesis and complex heterostructures. With its foundations in computationally guided synthesis, borophene can serve as a prototype for ongoing efforts to discover and exploit synthetic 2D materials.

Optical contrast for identifying the thickness of two-dimensional materials

NASA Astrophysics Data System (ADS)

Bing, Dan; Wang, Yingying; Bai, Jing; Du, Ruxia; Wu, Guoqing; Liu, Liyan

2018-01-01

One of the most intriguing properties of two-dimensional (2D) materials is their thickness dependent properties. A quick and precise technique to identify the layer number of 2D materials is therefore highly desirable. In this review, we will introduce the basic principle of using optical contrast to determine the thickness of 2D material and also its advantage as compared to other modern techniques. Different 2D materials, including graphene, graphene oxide, transitional metal dichalcogenides, black phosphorus, boron nitride, have been used as examples to demonstrate the capability of optical contrast methods. A simple and more efficient optical contrast image technique is also emphasized, which is suitable for quick and large-scale thickness identification. We have also discussed the factors that could affect the experimental results of optical contrast, including incident light angle, anisotropic nature of materials, and also the twisted angle between 2D layers. Finally, we give perspectives on future development of optical contrast methods for the study and application of 2D materials.

An unusual type of polymorphism in a liquid crystal

DOE PAGES

Li, Lin; Salamonczyk, Miroslaw; Shadpour, Sasan; ...

2018-02-19

Polymorphism is a remarkable concept in chemistry, materials science, computer science, and biology. Whether it is the ability of a material to exist in two or more crystal structures, a single interface connecting to two different entities, or alternative phenotypes of an organism, polymorphism determines function and properties. In materials science, polymorphism can be found in an impressively wide range of materials, including crystalline materials, minerals, metals, alloys, and polymers. Here in this paper we report on polymorphism in a liquid crystal. A bent-core liquid crystal with a single chiral side chain forms two structurally and morphologically significantly different liquidmore » crystal phases solely depending on the cooling rate from the isotropic liquid state. On slow cooling, the thermodynamically more stable oblique columnar phase forms, and on rapid cooling, a not heretofore reported helical microfilament phase. Since structure determines function and properties, the structural color for these phases also differs.« less

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

Fu, Fang; Yao, Yuze; Wang, Haiyan

Rational and precise control of the structure and dimension of electrode materials is an efficient way to improve their electrochemical performance. In this work, solvothermal or co-precipitation method is used to synthesize lithium-rich layered oxide materials of Li1.2Mn0.56Co0.12Ni0.12O2 (LLO) with various morphologies and structures, including microspheres, microrods, nanoplates, and irregular nanoparticles. These materials exhibit strong structure- dependent electrochemical properties. The porous hierarchical structured LLO microrods exhibit the best performance, delivering a discharge capacity of 264.6 mAh g(-1) at 0.5 C with over 91% retention after 100 cycles. At a high rate of 5 C, a high discharge capacity of 173.6more » mAh g(-1) can be achieved. This work reveals the relationship between the morphologies and electrochemical properties of LLO cathode materials, and provides a feasible approach to fabricating robust and high-performance electrode materials for lithium-ion batteries.« less

Steady State Structural Analysis of High Pressure Gas Turbine Blade using Finite Element Analysis

NASA Astrophysics Data System (ADS)

Mazarbhuiya, Hussain Mahamed Sahed Mostafa; Murari Pandey, Krishna

2017-08-01

In gas turbines the major portion of performance dependency lies upon turbine blade design. Turbine blades experience very high centrifugal, axial and tangential force during power generation. While withstanding these forces blades undergo elongation. Different methods have proposed for better enhancement of the mechanical properties of blade to withstand in extreme condition. Present paper describes the stress and elongation for blades having properties of different materials. Steady state structural analysis have performed in the present work for different materials (In 625, In 718, In 738, In 738 LC, MAR M246, Ni-Cr, Ti-alloy, Ti-Al, Ti-T6, U500). Remarkable finding is that the root of the blade is subjected to maximum stress for all blade materials and the blade made of MAR M246 has less stress and deformation among all other blade materials which can be selected as a suitable material for gas turbine blade.

An unusual type of polymorphism in a liquid crystal

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

Li, Lin; Salamonczyk, Miroslaw; Shadpour, Sasan

Polymorphism is a remarkable concept in chemistry, materials science, computer science, and biology. Whether it is the ability of a material to exist in two or more crystal structures, a single interface connecting to two different entities, or alternative phenotypes of an organism, polymorphism determines function and properties. In materials science, polymorphism can be found in an impressively wide range of materials, including crystalline materials, minerals, metals, alloys, and polymers. Here in this paper we report on polymorphism in a liquid crystal. A bent-core liquid crystal with a single chiral side chain forms two structurally and morphologically significantly different liquidmore » crystal phases solely depending on the cooling rate from the isotropic liquid state. On slow cooling, the thermodynamically more stable oblique columnar phase forms, and on rapid cooling, a not heretofore reported helical microfilament phase. Since structure determines function and properties, the structural color for these phases also differs.« less

Nonlinear absorption properties of AlGaAs/GaAs multiple quantum wells grown by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Lee, Hsing-Chung; Kost, A.; Kawase, M.; Hariz, A.; Dapkus, P. Daniel

1988-01-01

The nonlinear absorption properties of the excitonic resonances associated with multiple quantum wells (MQWs) in AlGaAs/GaAs grown by metalorganic chemical vapor deposition are reported. The dependence of the saturation properties on growth parameters, especially growth temperature, and the well width are described. The minimum measured saturation intensity for these materials is 250 W/sq cm, the lowest reported value to date. The low saturation intensities are the result of excellent minority carrier properties. A systematic study of minority carrier lifetimes in quantum wells are reported. Lifetimes range from 50-350 ns depending on growth temperature and well width. When corrected for lateral diffusion effects and the measured minority carrier lifetime, the saturation data suggest that saturation intensities as low as 2.3 W/sq cm can be achieved in this system. The first measurements of the dependence of the exciton area and the magnitude of the excitonic absorption on well width are prsented. The growth of MQW structures on transparent GaP substrates is demonstrated and the electroabsorption properties of these structures are reviewed.

Thickness dependent properties of CMR Manganite thin films on lattice mismatched substrates: Distinguishing Strain and Interface Effects

NASA Astrophysics Data System (ADS)

Davidson, Anthony, III; Kolagani, Rajeswari; Bacharova, Ellisaveta; Yong, Grace; Smolyaninova, Vera; Schaefer, David; Mundle, Rajeh

2007-03-01

Epitaxial thin films of CMR manganite materials have been known to show thickness dependent electrical and magnetic properties on lattice mismatched substrates. Below a critical thickness, insulator-metal transition is suppressed. These effects have been largely attributed to the role of bi-axial lattice mismatch strain. Our recent results of epitaxial thin films of La0.67Ca0.33MnO3 (LCMO) on two substrates with varying degrees of compressive lattice mismatch indicate that, in addition to the effect of lattice mismatch strain, the thickness dependence of the properties are influenced by other factors possibly related to the nature of the film substrate interface and defects such as twin boundaries. We have compared the properties of LCMO films on (100) oriented LaAlO3 and (001) oriented NdCaAlO4 both of which induce compressive bi-axial strain. Interestingly, the suppression of the insulator-metal transition is less in films on NCAO which has a larger lattice mismatch. We will present results correlating the electrical and magneto transport properties with the structure and morphology of the films.

Correlations Between Optical, Chemical and Physical Properties of Biomass Burn Aerosols

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

Hopkins, Rebecca J.; Lewis, Keith M.; Dessiaterik, Yury

2007-09-20

Single scattering albedo (ω) and Angstrom absorption coefficient (αap) values are measured at 405, 532 and 870 nm for aerosols generated during controlled laboratory combustion of twelve wildland fuels. Considerable fuel dependent variation in these optical properties is observed at these wavelengths. Complementary microspectroscopy techniques are used to elucidate spatially resolved local chemical bonding, carbon-to-oxygen atomic ratios, percent of sp2 hybridization (graphitic nature), elemental composition, particle size and morphology. These parameters are compared directly with the corresponding optical properties for each combustion product, facilitating an understanding of the fuel dependent variability observed. Results indicate that combustion products can be dividedmore » into three categories based on chemical, physical and optical properties. Only materials displaying a high degree of sp2 hybridization, with chemical and physical properties characteristic of ‘soot’ or black carbon, exhibit ω and αap values that indicate a high light absorbing capacity.« less

Combinatorial techniques to efficiently investigate and optimize organic thin film processing and properties.

PubMed

Wieberger, Florian; Kolb, Tristan; Neuber, Christian; Ober, Christopher K; Schmidt, Hans-Werner

2013-04-08

In this article we present several developed and improved combinatorial techniques to optimize processing conditions and material properties of organic thin films. The combinatorial approach allows investigations of multi-variable dependencies and is the perfect tool to investigate organic thin films regarding their high performance purposes. In this context we develop and establish the reliable preparation of gradients of material composition, temperature, exposure, and immersion time. Furthermore we demonstrate the smart application of combinations of composition and processing gradients to create combinatorial libraries. First a binary combinatorial library is created by applying two gradients perpendicular to each other. A third gradient is carried out in very small areas and arranged matrix-like over the entire binary combinatorial library resulting in a ternary combinatorial library. Ternary combinatorial libraries allow identifying precise trends for the optimization of multi-variable dependent processes which is demonstrated on the lithographic patterning process. Here we verify conclusively the strong interaction and thus the interdependency of variables in the preparation and properties of complex organic thin film systems. The established gradient preparation techniques are not limited to lithographic patterning. It is possible to utilize and transfer the reported combinatorial techniques to other multi-variable dependent processes and to investigate and optimize thin film layers and devices for optical, electro-optical, and electronic applications.

Effect of surface moisture on dielectric behavior of ultrafine BaTiO3 particulates.

NASA Technical Reports Server (NTRS)

Mountvala, A. J.

1971-01-01

The effects of adsorbed H2O on the dielectric properties of ultrafine BaTiO3 particulates of varying particle size and environmental history were determined. The dielectric behavior depends strongly on surface hydration. No particle size dependence of dielectric constant was found for dehydroxylated surfaces in ultrafine particulate (unsintered) BaTiO3 materials. For equivalent particle sizes, the ac conductivity is sensitive to surface morphology. Reactions with H2O vapor appear to account for the variations in dielectric properties. Surface dehydration was effectively accomplished by washing as-received powders in isopropanol.

Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders

NASA Astrophysics Data System (ADS)

Airey, G. D.; Grenfell, J. R. A.; Apeagyei, A.; Subhy, A.; Lo Presti, D.

2016-08-01

Bitumen is a viscoelastic material that exhibits both elastic and viscous components of response and displays both a temperature and time dependent relationship between applied stresses and resultant strains. In addition, as bitumen is responsible for the viscoelastic behaviour of all bituminous materials, it plays a dominant role in defining many of the aspects of asphalt road performance, such as strength and stiffness, permanent deformation and cracking. Although conventional bituminous materials perform satisfactorily in most highway pavement applications, there are situations that require the modification of the binder to enhance the properties of existing asphalt material. The best known form of modification is by means of polymer modification, traditionally used to improve the temperature and time susceptibility of bitumen. Tyre rubber modification is another form using recycled crumb tyre rubber to alter the properties of conventional bitumen. In addition, alternative binders (synthetic polymeric binders as well as renewable, environmental-friendly bio-binders) have entered the bitumen market over the last few years due to concerns over the continued availability of bitumen from current crudes and refinery processes. This paper provides a detailed rheological assessment, under both temperature and time regimes, of a range of conventional, modified and alternative binders in terms of the materials dynamic (oscillatory) viscoelastic response. The rheological results show the improved viscoelastic properties of polymer- and rubber-modified binders in terms of increased complex shear modulus and elastic response, particularly at high temperatures and low frequencies. The synthetic binders were found to demonstrate complex rheological behaviour relative to that seen for conventional bituminous binders.

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

PubMed Central

Tang, Liguo; Cao, Wenwu

2016-01-01

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 °C. Measured free dielectric constants and  were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS. PMID:27168336

a Study on the Effect of Annealing Process on Sound Velocity and Internal Friction Using the Vibrating Reed Technique

NASA Astrophysics Data System (ADS)

Mukhopadhyay, P. K.; Kumar, Uday; Badawi, Emad

Al has unique intrinsic characteristics, which are of interest to scientists as well as engineers. Al and its alloys are slightly paramagnetic materials. Al has very low cross section for thermal neutrons of 0.23 barn, hence Al can be used in nuclear fields as a structural material which is virtually transparent to neutrons. We report VRT as a new technique to study material problems. We also discuss, the results of sound velocity and internal friction, and resonance frequency as a function of temperature range for a pure aluminum sample under investigation. By using VRT, we found that the annealing temperature (450°C) is sufficient to remove the type of defects introduced in the materials under study. The activation energy to remove point defect for Al samples was calculated and found to be about 0.0624 eV. Also, we could easily observe that Q-1 is a function of annealing time. From these measurements of sound velocity and internal friction we can conclude that VRT is a powerful tool for detecting and probing the physical properties of the material under study. Internal friction is a microscopic property for the indication of the purity of the sample. Sound velocity depends on the state of the materials (which depends on the process of treatment).

Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles

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

Mangeri, John; Espinal, Yomery; Jokisaari, Andrea M.

Here, composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO 3 or BaTiO 3 nanoparticles embedded in a dielectric medium, including air. The equilibrium polarization topology is strongly affected by particlemore » diameter, as well as the choice of inclusion and matrix materials, with monodomain, vortex-like and multidomain patterns emerging for various combinations of size and materials parameters. This leads to radically different polarization vs electric field responses, resulting in highly tunable size-dependent dielectric properties that should be possible to observe experimentally. Our calculations show that there is a critical particle size below which ferroelectricity vanishes. For the PbTiO 3 particle, this size is 2 and 3.4 nm, respectively, for high- and low-permittivity media. For the BaTiO 3 particle, it is ~3.6 nm regardless of the medium dielectric strength.« less

Multiferroic properties of Indian natural ilmenite

NASA Astrophysics Data System (ADS)

Acharya, Truptimayee; Choudhary, R. N. P.

2017-03-01

In this communication, the main results and analysis of extensive studies of electric and magnetic characteristics (relative dielectric constant, tangent loss, electric polarization, electric transport, impedance, magnetic polarization and magneto-electric coupling coefficient) of Indian natural ilmenite (NI) have been presented. Preliminary structural analysis was studied by Rietveld refinement of room temperature XRD data, which suggests the rhombohedral crystal system of NI. Maxwell-Wagner mechanism was used to explain the nature of the frequency dependence of the relative dielectric constant. The impedance analysis reveals that below 270 °C, only the bulk contributes, whereas at higher temperature, both grain boundary and the bulk contribute to the resistive characteristics of the material. The magnitude of the depression angles of the semicircles in the Nyquist plot has been estimated. The correlated barrier hopping model has been used to explain the frequency dependence of ac conductivity of the material. The activation energy of the compound has been estimated using the temperature dependence of dc conductivity plot. The obtained polarization hysteresis loops manifest improper ferroelectric behavior of NI. The existence M-H hysteresis loop supports anti-ferromagnetism in the studied material. The magneto-electric voltage coupling coefficient is found to be 0.7 mV/cm Oe. Hence, other than dielectric constant, electric polarization, magnetization and magneto-electric studies support the existence of multiferroic properties in NI.

Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles

DOE PAGES

Mangeri, John; Espinal, Yomery; Jokisaari, Andrea M.; ...

2017-01-06

Here, composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO 3 or BaTiO 3 nanoparticles embedded in a dielectric medium, including air. The equilibrium polarization topology is strongly affected by particlemore » diameter, as well as the choice of inclusion and matrix materials, with monodomain, vortex-like and multidomain patterns emerging for various combinations of size and materials parameters. This leads to radically different polarization vs electric field responses, resulting in highly tunable size-dependent dielectric properties that should be possible to observe experimentally. Our calculations show that there is a critical particle size below which ferroelectricity vanishes. For the PbTiO 3 particle, this size is 2 and 3.4 nm, respectively, for high- and low-permittivity media. For the BaTiO 3 particle, it is ~3.6 nm regardless of the medium dielectric strength.« less

Method for modeling the gradual physical degradation of a porous material

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

Flach, Greg

Cementitious and other engineered porous materials encountered in waste disposals may degrade over time due to one or more mechanisms. Physical degradation may take the form of cracking (fracturing) and/or altered (e.g. increased) porosity, depending on the material and underlying degradation mechanism. In most cases, the hydraulic properties of degrading materials are expected to evolve due to physical changes occurring over roughly the pore to decimeter scale, which is conducive to calculating equivalent or effective material properties. The exact morphology of a degrading material in its end-state may or may not be known. In the latter case, the fully-degraded conditionmore » can be assumed to be similar to a more-permeable material in the surrounding environment, such as backfill soil. Then the fully-degraded waste form or barrier material is hydraulically neutral with respect to its surroundings, constituting neither a barrier to nor conduit for moisture flow and solute transport. Unless the degradation mechanism is abrupt, a gradual transition between the intact initial and fully-degraded final states is desired. Linear interpolation through time is one method for smoothly blending hydraulic properties between those of an intact matrix and those of a soil or other surrogate for the end-state.« less

High-throughput materials discovery and development: breakthroughs and challenges in the mapping of the materials genome

NASA Astrophysics Data System (ADS)

Buongiorno Nardelli, Marco

High-Throughput Quantum-Mechanics computation of materials properties by ab initio methods has become the foundation of an effective approach to materials design, discovery and characterization. This data driven approach to materials science currently presents the most promising path to the development of advanced technological materials that could solve or mitigate important social and economic challenges of the 21st century. In particular, the rapid proliferation of computational data on materials properties presents the possibility to complement and extend materials property databases where the experimental data is lacking and difficult to obtain. Enhanced repositories such as AFLOWLIB open novel opportunities for structure discovery and optimization, including uncovering of unsuspected compounds, metastable structures and correlations between various properties. The practical realization of these opportunities depends almost exclusively on the the design of efficient algorithms for electronic structure simulations of realistic material systems beyond the limitations of the current standard theories. In this talk, I will review recent progress in theoretical and computational tools, and in particular, discuss the development and validation of novel functionals within Density Functional Theory and of local basis representations for effective ab-initio tight-binding schemes. Marco Buongiorno Nardelli is a pioneer in the development of computational platforms for theory/data/applications integration rooted in his profound and extensive expertise in the design of electronic structure codes and in his vision for sustainable and innovative software development for high-performance materials simulations. His research activities range from the design and discovery of novel materials for 21st century applications in renewable energy, environment, nano-electronics and devices, the development of advanced electronic structure theories and high-throughput techniques in materials genomics and computational materials design, to an active role as community scientific software developer (QUANTUM ESPRESSO, WanT, AFLOWpi)

A model for acoustic vaporization dynamics of a bubble/droplet system encapsulated within a hyperelastic shell.

PubMed

Lacour, Thomas; Guédra, Matthieu; Valier-Brasier, Tony; Coulouvrat, François

2018-01-01

Nanodroplets have great, promising medical applications such as contrast imaging, embolotherapy, or targeted drug delivery. Their functions can be mechanically activated by means of focused ultrasound inducing a phase change of the inner liquid known as the acoustic droplet vaporization (ADV) process. In this context, a four-phases (vapor + liquid + shell + surrounding environment) model of ADV is proposed. Attention is especially devoted to the mechanical properties of the encapsulating shell, incorporating the well-known strain-softening behavior of Mooney-Rivlin material adapted to very large deformations of soft, nearly incompressible materials. Various responses to ultrasound excitation are illustrated, depending on linear and nonlinear mechanical shell properties and acoustical excitation parameters. Different classes of ADV outcomes are exhibited, and a relevant threshold ensuring complete vaporization of the inner liquid layer is defined. The dependence of this threshold with acoustical, geometrical, and mechanical parameters is also provided.

Spin Hall Effects in Metallic Antiferromagnets

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2014-11-04

In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spinmore » Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.« less

Aggregate linear properties of ferroelectric ceramics and polycrystalline thin films: Calculation by the method of effective piezoelectric medium

NASA Astrophysics Data System (ADS)

Pertsev, N. A.; Zembilgotov, A. G.; Waser, R.

1998-08-01

The effective dielectric, piezoelectric, and elastic constants of polycrystalline ferroelectric materials are calculated from single-crystal data by an advanced method of effective medium, which takes into account the piezoelectric interactions between grains in full measure. For bulk BaTiO3 and PbTiO3 polarized ceramics, the dependences of material constants on the remanent polarization are reported. Dielectric and elastic constants are computed also for unpolarized c- and a-textured ferroelectric thin films deposited on cubic or amorphous substrates. It is found that the dielectric properties of BaTiO3 and PbTiO3 polycrystalline thin films strongly depend on the type of crystal texture. The influence of two-dimensional clamping by the substrate on the dielectric and piezoelectric responses of polarized films is described quantitatively and shown to be especially important for the piezoelectric charge coefficient of BaTiO3 films.

An investigation of the optical constants and band gap of chromium disilicide

NASA Technical Reports Server (NTRS)

Bost, M. C.; Mahan, John E.

1988-01-01

Optical properties of polycrystalline thin films of CrSi2 grown by the diffusion couple method on silicon substrates were investigated. An analysis of the energy dependence of the absorption coefficient indicates that the material is an indirect forbidden gap semiconductor with a band-gap value of slightly less than 0.35 eV. This result was confirmed by measurements of the temperature dependence of the intrinsic conductivity. The value of the bandgap corresponds well to an important window of transparency in the earth's atmosphere (3-5 microns), which makes the material of potential interest for IR detector applications.

Paradigm Shift in Data Content and Informatics Infrastructure Required for Generalized Constitutive Modeling of Materials Behavior

NASA Technical Reports Server (NTRS)

Arnold, S. M.

2006-01-01

Materials property information such as composition and thermophysical/mechanical properties abound in the literature. Oftentimes, however, the corresponding response curves from which these data are determined are missing or at the very least difficult to retrieve. Further, the paradigm for collecting materials property information has historically centered on (1) properties for materials comparison/selection purposes and (2) input requirements for conventional design/analysis methods. However, just as not all materials are alike or equal, neither are all constitutive models (and thus design/ analysis methods) equal; each model typically has its own specific and often unique required materials parameters, some directly measurable and others indirectly measurable. Therefore, the type and extent of materials information routinely collected is not always sufficient to meet the current, much less future, needs of the materials modeling community. Informatics has been defined as the science concerned with gathering, manipulating, storing, retrieving, and classifying recorded information. A key aspect of informatics is its focus on understanding problems and applying information technology as needed to address those problems. The primary objective of this article is to highlight the need for a paradigm shift in materials data collection, analysis, and dissemination so as to maximize the impact on both practitioners and researchers. Our hope is to identify and articulate what constitutes "sufficient" data content (i.e., quality and quantity) for developing, characterizing, and validating sophisticated nonlinear time- and history-dependent (hereditary) constitutive models. Likewise, the informatics infrastructure required for handling the potentially massive amounts of materials data will be discussed.

Concentration state dependence of the rheological and structural properties of reconstituted silk.

PubMed

Mo, Chunli; Holland, Chris; Porter, David; Shao, Zhengzhong; Vollrath, Fritz

2009-10-12

The ability to control the processing of artificial silk is key to the successful application of this important and high performance biopolymer. Understanding where our current reconstitution process can be improved will not only aid us in the creation of better materials, but will also provide insight into the natural material along the way. This study aims to understand what proportion of reconstituted silk contributes to its rheological properties and what conformational state the silk proteins are in. It shows, for the first time, that a change in rheological properties can be related to a change in silk structures present in solution and reveals a low concentration gel state for silk that may have important implications for future successful artificial processing of silk.

Dynamics of a DNA Gel

NASA Astrophysics Data System (ADS)

Adhikari, Ramesh; Bhattacharya, Aniket; Dogariu, Aristide

We study in silico the properties of a gel consisting of DNA strands (modeled as semi-flexible chains) and linkers of varying flexibility, length, and topology. These linkers are envisioned and modeled as active components with additional attributes so as to mimic properties of a synthetic DNA gel containing motor proteins. We use Brownian dynamics to directly obtain frequency dependent complex shear moduli of the gel. We further carry out force spectroscopy on these computer generated gels and study the relaxation properties as a function of the important parameters of the model, e.g., densities and relative ratios of the DNAs and the linkers, the average life time of a link, etc. Our studies are relevant for designing synthetic bio-materials for both materials and medical applications.

Measurements of Thermophysical Properties of Molten Silicon and Geranium

NASA Technical Reports Server (NTRS)

Rhim, Won-Kyu

2001-01-01

The objective of this ground base program is to measure thermophysical properties of molten/ undercooled silicon, germanium, and Si-Ge alloys using a high temperature electrostatic levitator and in clearly assessing the need of the microgravity environment to achieve the objective with higher degrees of accuracy. Silicon and germanium are two of the most important semiconductors for industrial applications: silicon is unsurpassed as a microelectronics material, occupying more than 95% of the electronics market. Si-Ge alloy is attracting keen interest for advanced electronic and optoelectronic applications in view of its variable band gap and lattice parameter depending upon its composition. Accurate thermophysical properties of these materials are very much needed in the semiconductor industry for the growth of large high quality crystals.

Modeling Diffusion Induced Stresses for Lithium-Ion Battery Materials

NASA Astrophysics Data System (ADS)

Chiu Huang, Cheng-Kai

Advancing lithium-ion battery technology is of paramount importance for satisfying the energy storage needs in the U.S., especially for the application in the electric vehicle industry. To provide a better acceleration for electric vehicles, a fast and repeatable discharging rate is required. However, particle fractures and capacity loss have been reported under high current rate (C-rate) during charging/discharging and after a period of cycling. During charging and discharging, lithium ions extract from and intercalate into electrode materials accompanied with the volume change and phase transition between Li-rich phase and Li-poor phase. It is suggested that the diffusion-induced-stress is one of the main reasons causing capacity loss due to the mechanical degradation of electrode particles. Therefore, there is a fundamental need to provide a mechanistic understanding by considering the structure-mechanics-property interactions in lithium-ion battery materials. Among many cathode materials, the olivine-based lithium-iron-phosphate (LiFePO4) with an orthorhombic crystal structure is one of the promising cathode materials for the application in electric vehicles. In this research we first use a multiphysic approach to investigate the stress evolution, especially on the phase boundary during lithiation in single LiFePO4 particles. A diffusion-controlled finite element model accompanied with the experimentally observed phase boundary propagation is developed via a finite element package, ANSYS, in which lithium ion concentration-dependent anisotropic material properties and volume misfits are incorporated. The stress components on the phase boundary are used to explain the Mode I, Mode II, and Mode III fracture propensities in LiFePO4 particles. The elastic strain energy evolution is also discussed to explain why a layer-by-layer lithium insertion mechanism (i.e. first-order phase transformation) is energetically preferred. Another importation issue is how current rate (C-rate) during charging/discharging affects diffusion induced stresses inside electrode materials. For the experimental part we first conduct charging/discharging under different C-rates to observe the voltage responses for commercial LiFePO4 batteries. Then Time-of-Flight Secondary Ion Mass Spectrometry technique is applied to measure the lithium ion intensities in different C-rate charged/discharged samples. These experimental results could be used to support that a more significant voltage fluctuation under high C-rates is due to different lithium insertion mechanisms, rather than the amount of lithium ions intercalated into electrode materials. Thus the investigation of C-rate-dependent stress evolution is required for the development of a more durable lithium ion battery. In this dissertation, we extend the single particle finite element model to investigate the C-rate-dependent diffusion induced stresses in a multi-particle system. Concentration dependent anisotropic material properties, C-rate-dependent volume misfits and concentration dependent Li-ion diffusivity are incorporated in the model. The concentration gradients, diffusion induced stresses, and strain energies under different C-rates are discussed in this study. Particle fractures have been observed in many experimental results, in this study we further discuss the effect of the crack surface orientation on the lithium concentration profile and stress level in cathode materials. The results of this dissertation provide a better understanding of diffusion induced stresses in electrode materials and contribute to our fundamental knowledge of interplay between lithium intercalations, stress evolutions, particle fractures and the capacity fade in lithium-ion batteries.

The Optical Janus Effect: Asymmetric Structural Color Reflection Materials.

PubMed

England, Grant T; Russell, Calvin; Shirman, Elijah; Kay, Theresa; Vogel, Nicolas; Aizenberg, Joanna

2017-08-01

Structurally colored materials are often used for their resistance to photobleaching and their complex viewing-direction-dependent optical properties. Frequently, absorption has been added to these types of materials in order to improve the color saturation by mitigating the effects of nonspecific scattering that is present in most samples due to imperfect manufacturing procedures. The combination of absorbing elements and structural coloration often yields emergent optical properties. Here, a new hybrid architecture is introduced that leads to an interesting, highly directional optical effect. By localizing absorption in a thin layer within a transparent, structurally colored multilayer material, an optical Janus effect is created, wherein the observed reflected color is different on one side of the sample than on the other. A systematic characterization of the optical properties of these structures as a function of their geometry and composition is performed. The experimental studies are coupled with a theoretical analysis that enables a precise, rational design of various optical Janus structures with highly controlled color, pattern, and fabrication approaches. These asymmetrically colored materials will open applications in art, architecture, semitransparent solar cells, and security features in anticounterfeiting materials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unraveling metamaterial properties in zigzag-base folded sheets.

PubMed

Eidini, Maryam; Paulino, Glaucio H

2015-09-01

Creating complex spatial objects from a flat sheet of material using origami folding techniques has attracted attention in science and engineering. In the present work, we use the geometric properties of partially folded zigzag strips to better describe the kinematics of known zigzag/herringbone-base folded sheet metamaterials such as Miura-ori. Inspired by the kinematics of a one-degree of freedom zigzag strip, we introduce a class of cellular folded mechanical metamaterials comprising different scales of zigzag strips. This class of patterns combines origami folding techniques with kirigami. Using analytical and numerical models, we study the key mechanical properties of the folded materials. We show that our class of patterns, by expanding on the design space of Miura-ori, is appropriate for a wide range of applications from mechanical metamaterials to deployable structures at small and large scales. We further show that, depending on the geometry, these materials exhibit either negative or positive in-plane Poisson's ratios. By introducing a class of zigzag-base materials in the current study, we unify the concept of in-plane Poisson's ratio for similar materials in the literature and extend it to the class of zigzag-base folded sheet materials.

Unleashing elastic energy: dynamics of energy release in rubber bands and impulsive biological systems

NASA Astrophysics Data System (ADS)

Ilton, Mark; Cox, Suzanne; Egelmeers, Thijs; Patek, S. N.; Crosby, Alfred J.

Impulsive biological systems - which include mantis shrimp, trap-jaw ants, and venus fly traps - can reach high speeds by using elastic elements to store and rapidly release energy. The material behavior and shape changes critical to achieving rapid energy release in these systems are largely unknown due to limitations of materials testing instruments operating at high speed and large displacement. In this work, we perform fundamental, proof-of-concept measurements on the tensile retraction of elastomers. Using high speed imaging, the kinematics of retraction are measured for elastomers with varying mechanical properties and geometry. Based on the kinematics, the rate of energy dissipation in the material is determined as a function of strain and strain-rate, along with a scaling relation which describes the dependence of maximum velocity on material properties. Understanding this scaling relation along with the material failure limits of the elastomer allows the prediction of material properties required for optimal performance. We demonstrate this concept experimentally by optimizing for maximum velocity in our synthetic model system, and achieve retraction velocities that exceed those in biological impulsive systems. This model system provides a foundation for future work connecting continuum performance to molecular architecture in impulsive systems.

The study about the use of the natural fibres in composite materials

NASA Astrophysics Data System (ADS)

Hristian, L.; Ostafe, M. M.; Manea, L. R.; Leon, A. L.

2016-08-01

The current technological development, the crises of raw materials and energy, the increased aggression towards the environment have led to the development of the new materials and unconventional technologies. The composite materials have both many important advantages compared to the traditional materials and provide many functional advantages: low weight, mechanical resistance, low maintenance costs. The main advantage of the composites lies in their ability to combine the physical properties of components to achieve new structural functionalities, so the modulation of the properties and finally, to obtain a wide variety of materials which may be used in all areas of activities. Some biodegradable fibers, flax, hemp, may provide the specific mechanical properties compared to those of the glass fiber, due to their high strength and low density of their volume. To make the right choice, even if the natural fibers have very low power consumption compared with the synthetic fibers, such as glass or carbon, it should be considered a careful assessment of the environmental impact. The present study shows that the validity of the replacement of the synthetic fibers with natural fibers, depends on the reinforcement type and the complexity of the problems due to the processing of natural fibers.

Two-magnon bound state causes ultrafast thermally induced magnetisation switching

PubMed Central

Barker, J.; Atxitia, U.; Ostler, T. A.; Hovorka, O.; Chubykalo-Fesenko, O.; Chantrell, R. W.

2013-01-01

There has been much interest recently in the discovery of thermally induced magnetisation switching using femtosecond laser excitation, where a ferrimagnetic system can be switched deterministically without an applied magnetic field. Experimental results suggest that the reversal occurs due to intrinsic material properties, but so far the microscopic mechanism responsible for reversal has not been identified. Using computational and analytic methods we show that the switching is caused by the excitation of two-magnon bound states, the properties of which are dependent on material factors. This discovery allows us to accurately predict the onset of switching and the identification of this mechanism will allow new classes of materials to be identified or designed for memory devices in the THz regime. PMID:24253110

Bayesian methods for characterizing unknown parameters of material models

DOE PAGES

Emery, J. M.; Grigoriu, M. D.; Field Jr., R. V.

2016-02-04

A Bayesian framework is developed for characterizing the unknown parameters of probabilistic models for material properties. In this framework, the unknown parameters are viewed as random and described by their posterior distributions obtained from prior information and measurements of quantities of interest that are observable and depend on the unknown parameters. The proposed Bayesian method is applied to characterize an unknown spatial correlation of the conductivity field in the definition of a stochastic transport equation and to solve this equation by Monte Carlo simulation and stochastic reduced order models (SROMs). As a result, the Bayesian method is also employed tomore » characterize unknown parameters of material properties for laser welds from measurements of peak forces sustained by these welds.« less

Antibacterial effect of bioactive glasses on clinically important anaerobic bacteria in vitro.

PubMed

Leppäranta, Outi; Vaahtio, Minna; Peltola, Timo; Zhang, Di; Hupa, Leena; Hupa, Mikko; Ylänen, Heimo; Salonen, Jukka I; Viljanen, Matti K; Eerola, Erkki

2008-02-01

Bioactive glasses (BAGs) of different compositions have been studied for decades for clinical use and they have found many dental and orthopaedic applications. Particulate BAGs have also been shown to have antibacterial properties. This large-scale study shows that two bioactive glass powders (S53P4 and 13-93) and a sol-gel derived material (CaPSiO II) have an antibacterial effect on 17 clinically important anaerobic bacterial species. All the materials tested demonstrated growth inhibition, although the concentration and time needed for the effect varied depending on the BAG. Glass S53P4 had a strong growth-inhibitory effect on all pathogens tested. Glass 13-93 and sol-gel derived material CaPSiO II showed moderate antibacterial properties.

Bayesian methods for characterizing unknown parameters of material models

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

Emery, J. M.; Grigoriu, M. D.; Field Jr., R. V.

A Bayesian framework is developed for characterizing the unknown parameters of probabilistic models for material properties. In this framework, the unknown parameters are viewed as random and described by their posterior distributions obtained from prior information and measurements of quantities of interest that are observable and depend on the unknown parameters. The proposed Bayesian method is applied to characterize an unknown spatial correlation of the conductivity field in the definition of a stochastic transport equation and to solve this equation by Monte Carlo simulation and stochastic reduced order models (SROMs). As a result, the Bayesian method is also employed tomore » characterize unknown parameters of material properties for laser welds from measurements of peak forces sustained by these welds.« less

Influence of porosity on thermophysical properties of a composite

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

Grishaeva, N. Yu., E-mail: anohina@mail2000.ru; Ljukshin, B. A., E-mail: lba2008@yandex.ru; Bochkareva, S. A., E-mail: svetlanab7@yandex.ru

2015-10-27

In many modern information systems, the heat generated during the operation of electronic devices is usually dissipated by heat-conductive pads between the casing of the respective equipment and a massive base (platform). For newly developed pads, the promising materials are composites on the basis of various types of silicone rubber. At the same time, during the production of the pads without a vacuum setup, the material can contain air bubbles, which causes the porosity potentially negative for the thermal properties of the material. This work studies the thermal conductivity depending on the degree of silicone matrix filling by copper particles,more » introduced to improve thermal conductivity, and by air bubbles that are considered as reinforcing inclusions.« less

Lamb Wave Assessment of Fiber Volume Fraction in Composites

NASA Technical Reports Server (NTRS)

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.; Zalameda, Joseph N.

1998-01-01

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of examining composite materials. Since the Lamb wave velocity depends on the elastic properties of a material, an effective tool exists to evaluate composites by measuring the velocity of these waves. Lamb waves can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper discusses a study in which Lamb waves were used to examine fiber volume fraction variations of approximately 0.40-0.70 in composites. The Lamb wave measurements were compared to fiber volume fractions obtained from acid digestion tests. Additionally, a model to predict the fiber volume fraction from Lamb wave velocity values was evaluated.

Finite Element Estimation of Meteorite Structural Properties

NASA Technical Reports Server (NTRS)

Hart, Kenneth Arthur

2015-01-01

The goal of the project titled Asteroid Threat Assessment at NASA Ames Research Center is to develop risk assessment tools. The expertise in atmospheric entry in the Entry Systems and Technology Division is being used to describe the complex physics of meteor breakup in the atmosphere. The breakup of a meteor is dependent on its structural properties, including homogeneity of the material. The present work describes an 11-week effort in which a literature survey was carried for structural properties of meteoritic material. In addition, the effect of scale on homogeneity isotropy was studied using a Monte Carlo approach in Nastran. The properties were then in a static structural response simulation of an irregularly-shape meteor (138-scale version of Asteroid Itokawa). Finally, an early plan was developed for doctoral research work at Georgia Tech. in the structural failure fragmentation of meteors.

Interpenetrating polymer networks from acetylene terminated materials

NASA Technical Reports Server (NTRS)

Connell, J. W.; Hergenrother, P. M.

1989-01-01

As part of a program to develop high temperature/high performance structural resins for aerospace applications, the chemistry and properties of a novel class of interpenetrating polymer networks (IPNs) were investigated. These IPNs consist of a simple diacetylenic compound (aspartimide) blended with an acetylene terminated arylene ether oligomer. Various compositional blends were prepared and thermally cured to evaluate the effect of crosslink density on resin properties. The cured IPNs exhibited glass transition temperatures ranging from 197 to 254 C depending upon the composition and cure temperature. The solvent resistance, fracture toughness and coefficient of thermal expansion of the cured blends were related to the crosslink density. Isothermal aging of neat resin moldings, adhesive and composite specimens showed a postcure effect which resulted in improved elevated temperature properties. The chemistry, physical and mechanical properties of these materials will be discussed.

Skeletal muscle tensile strain dependence: hyperviscoelastic nonlinearity

PubMed Central

Wheatley, Benjamin B; Morrow, Duane A; Odegard, Gregory M; Kaufman, Kenton R; Donahue, Tammy L Haut

2015-01-01

Introduction Computational modeling of skeletal muscle requires characterization at the tissue level. While most skeletal muscle studies focus on hyperelasticity, the goal of this study was to examine and model the nonlinear behavior of both time-independent and time-dependent properties of skeletal muscle as a function of strain. Materials and Methods Nine tibialis anterior muscles from New Zealand White rabbits were subject to five consecutive stress relaxation cycles of roughly 3% strain. Individual relaxation steps were fit with a three-term linear Prony series. Prony series coefficients and relaxation ratio were assessed for strain dependence using a general linear statistical model. A fully nonlinear constitutive model was employed to capture the strain dependence of both the viscoelastic and instantaneous components. Results Instantaneous modulus (p<0.0005) and mid-range relaxation (p<0.0005) increased significantly with strain level, while relaxation at longer time periods decreased with strain (p<0.0005). Time constants and overall relaxation ratio did not change with strain level (p>0.1). Additionally, the fully nonlinear hyperviscoelastic constitutive model provided an excellent fit to experimental data, while other models which included linear components failed to capture muscle function as accurately. Conclusions Material properties of skeletal muscle are strain-dependent at the tissue level. This strain dependence can be included in computational models of skeletal muscle performance with a fully nonlinear hyperviscoelastic model. PMID:26409235

A One-Dimensional Organic Lead Chloride Hybrid with Excitation-Dependent Broadband Emissions

DOE PAGES

Wu, Guanhong; Zhou, Chenkun; Ming, Wenmei; ...

2018-05-23

Organic–inorganic metal halide hybrids have emerged as a new class of materials with fascinating optical and electronic properties. The exceptional structure tunability has enabled the development of materials with various dimensionalities at the molecular level, from three-dimensional (3D) to 2D, 1D, and 0D. Here, we report a new 1D lead chloride hybrid, C 4N 2H 14PbCl 4, which exhibits unusual inverse excitation-dependent broadband emission from bluish-green to yellow. Density functional theory calculations were performed to better understand the mechanism of this excitation-dependent broadband emission. This 1D hybrid material is found to have two emission centers, corresponding to the self-trapped excitonsmore » (STEs) and vacancy-bound excitons. The excitation-dependent emission is due to different populations of these two types of excitons generated at different excitation wavelengths. Furthermore, this work shows the rich chemistry and physics of organic–inorganic metal halide hybrids and paves the way to achieving novel light emitters with excitation-dependent broadband emissions at room temperature.« less

A One-Dimensional Organic Lead Chloride Hybrid with Excitation-Dependent Broadband Emissions

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

Wu, Guanhong; Zhou, Chenkun; Ming, Wenmei

Organic–inorganic metal halide hybrids have emerged as a new class of materials with fascinating optical and electronic properties. The exceptional structure tunability has enabled the development of materials with various dimensionalities at the molecular level, from three-dimensional (3D) to 2D, 1D, and 0D. Here, we report a new 1D lead chloride hybrid, C 4N 2H 14PbCl 4, which exhibits unusual inverse excitation-dependent broadband emission from bluish-green to yellow. Density functional theory calculations were performed to better understand the mechanism of this excitation-dependent broadband emission. This 1D hybrid material is found to have two emission centers, corresponding to the self-trapped excitonsmore » (STEs) and vacancy-bound excitons. The excitation-dependent emission is due to different populations of these two types of excitons generated at different excitation wavelengths. Furthermore, this work shows the rich chemistry and physics of organic–inorganic metal halide hybrids and paves the way to achieving novel light emitters with excitation-dependent broadband emissions at room temperature.« less

Reconstructing Space- and Energy-Dependent Exciton Generation in Solution-Processed Inverted Organic Solar Cells.

PubMed

Wang, Yuheng; Zhang, Yajie; Lu, Guanghao; Feng, Xiaoshan; Xiao, Tong; Xie, Jing; Liu, Xiaoyan; Ji, Jiahui; Wei, Zhixiang; Bu, Laju

2018-04-25

Photon absorption-induced exciton generation plays an important role in determining the photovoltaic properties of donor/acceptor organic solar cells with an inverted architecture. However, the reconstruction of light harvesting and thus exciton generation at different locations within organic inverted device are still not well resolved. Here, we investigate the film depth-dependent light absorption spectra in a small molecule donor/acceptor film. Including depth-dependent spectra into an optical transfer matrix method allows us to reconstruct both film depth- and energy-dependent exciton generation profiles, using which short-circuit current and external quantum efficiency of the inverted device are simulated and compared with the experimental measurements. The film depth-dependent spectroscopy, from which we are able to simultaneously reconstruct light harvesting profile, depth-dependent composition distribution, and vertical energy level variations, provides insights into photovoltaic process. In combination with appropriate material processing methods and device architecture, the method proposed in this work will help optimizing film depth-dependent optical/electronic properties for high-performance solar cells.

Analysis of the statistic al properties of pulses in atmospheric corona discharge

NASA Astrophysics Data System (ADS)

Aubrecht, L.; Koller, J.; Plocek, J.; Stanék, Z.

2000-03-01

The properties of the negative corona current pulses in a single point-to-plane configuration have been extensively studied by many investigators. The amplitude and the interval of these pulses are not generally constant and depend on many variables. The repetition rate and the amplitude of the pulses fluctuate in time. Since these fluctuations are subject to a certain probability distribution, the statistical processing was used for the analysis of the pulse fluctuations. The behavior of the pulses has been also investigated in a multipoint geometry configuration. The dependence of the behavior of the corona pulses on the gap lengths, the material, the shape of the point electrode, the number and separation of electrodes (in the multiple-point mode) has been investigated, too. No detailed study has been carried out up to now for this case. The attention has been devoted also to the study of the pulses on the points of live materials (needles of coniferous trees). This contribution describes recent studies of the statistical properties of the pulses for various conditions.

Composite materials research and education program: The NASA-Virginia Tech composites program

NASA Technical Reports Server (NTRS)

Herakovich, C. T.

1980-01-01

Major areas of study include: (1) edge effects in finite width laminated composites subjected to mechanical, thermal and hygroscopic loading with temperature dependent material properties and the influence of edge effects on the initiation of failure; (2) shear and compression testing of composite materials at room and elevated temperatures; (3) optical techniques for precise measurement of coefficients of thermal expansion of composites; (4) models for the nonlinear behavior of composites including material nonlinearity and damage accumulation and verification of the models under biaxial loading; (5) compressive failure of graphite/epoxy plates with circular holes and the buckling of composite cylinders under combined compression and torsion; (6) nonlinear mechanical properties of borsic/aluminum, graphite/polyimide and boron/aluminum; (7) the strength characteristics of spliced sandwich panels; and (8) curved graphite/epoxy panels subjected to internal pressure.

Study of Effects on Mechanical Properties of PLA Filament which is blended with Recycled PLA Materials

NASA Astrophysics Data System (ADS)

Babagowda; Kadadevara Math, R. S.; Goutham, R.; Srinivas Prasad, K. R.

2018-02-01

Fused deposition modeling is a rapidly growing additive manufacturing technology due to its ability to build functional parts having complex geometry. The mechanical properties of the build part is depends on several process parameters and build material of the printed specimen. The aim of this study is to characterize and optimize the parameters such as layer thickness and PLA build material which is mixed with recycled PLA material. Tensile and flexural or bending test are carried out to determine the mechanical response characteristics of the printed specimen. Taguchi method is used for number of experiments and Taguchi S/N ratio is used to identify the set of parameters which give good results for respective response characteristics, effectiveness of each parameters is investigated by using analysis of variance (ANOVA).

Determination of acoustic properties of thin polymer films utilizing the frequency dependence of the reflection coefficient of ultrasound.

PubMed

Tohmyoh, Hironori; Sakamoto, Yuhei

2015-11-01

This paper reports on a technique to measure the acoustic properties of a thin polymer film utilizing the frequency dependence of the reflection coefficient of ultrasound reflected back from a system comprising a reflection plate, the film, and a material that covers the film. The frequency components of the echo reflected from the back of the plate, where the film is attached, take their minimum values at the resonant frequency, and from these frequency characteristics, the acoustic impedance, sound velocity, and the density of the film can be determined. We applied this technique to characterize an ion exchange membrane, which has high water absorbability, and successfully determined the acoustic properties of the membrane without getting it wet.

Influence of Thermal Cycling on Flexural Properties and Simulated Wear of Computer-aided Design/Computer-aided Manufacturing Resin Composites.

PubMed

Tsujimoto, A; Barkmeier, W W; Takamizawa, T; Latta, M A; Miyazaki, M

The purpose of this study was to evaluate the influence of thermal cycling on the flexural properties and simulated wear of computer-aided design/computer-aided manufacturing (CAD/CAM) resin composites. The six CAD/CAM resin composites used in this study were 1) Lava Ultimate CAD/CAM Restorative (LU); 2) Paradigm MZ100 (PM); 3) CERASMART (CS); 4) Shofu Block HC (SB); 5) KATANA AVENCIA Block (KA); and 6) VITA ENAMIC (VE). Specimens were divided randomly into two groups, one of which was stored in distilled water for 24 hours, and the other of which was subjected to 10,000 thermal cycles. For each material, 15 specimens from each group were used to determine the flexural strength and modulus according to ISO 6872, and 20 specimens from each group were used to examine wear using a localized wear simulation model. The test materials were subjected to a wear challenge of 400,000 cycles in a Leinfelder-Suzuki device (Alabama machine). The materials were placed in custom-cylinder stainless steel fixtures, and simulated localized wear was generated using a stainless steel ball bearing (r=2.387 mm) antagonist in a water slurry of polymethyl methacrylate beads. Simulated wear was determined using a noncontact profilometer (Proscan 2100) with Proscan and AnSur 3D software. The two-way analysis of variance of flexural properties and simulated wear of CAD/CAM resin composites revealed that material type and thermal cycling had a significant influence (p<0.05), but there was no significant interaction (p>0.05) between the two factors. The flexural properties and maximum depth of wear facets of CAD/CAM resin composite were different (p<0.05) depending on the material, and their values were influenced (p>0.05) by thermal cycling, except in the case of VE. The volume losses in wear facets on LU, PM, and SB after 10,000 thermal cycles were significantly higher (p<0.05) than those after 24 hours of water storage, unlike CS, KA, and VE. The results of this study indicate that the flexural properties and simulated wear of CAD/CAM resin composites are different depending on the material. In addition, the flexural properties and simulated wear of CAD/CAM resin composites are influenced by thermal cycling.

Comparative study of the swabbing properties of seven commercially available swab materials for cleaning verification.

PubMed

Corrigan, Damion K; Piletsky, Sergey; McCrossen, Sean

2009-01-01

This article compares the technical performances of several different commercially available swabbing materials for the purpose of cleaning verification. A steel surface was soiled with solutions of acetaminophen, nicotinic acid, diclofenac, and benzamidine and wiped with each swabbing material. The compounds were extracted with water or ethanol (depending on polarity of analyte) and their concentration in extract was quantified spectrophotometrically. The study also investigated swab debris on the wiped surface. The swab performances were compared and the best swab material was identified.

Thermomechanical Properties and Glass Dynamics of Polymer-Tethered Colloidal Particles and Films.

PubMed

Cang, Yu; Reuss, Anna N; Lee, Jaejun; Yan, Jiajun; Zhang, Jianan; Alonso-Redondo, Elena; Sainidou, Rebecca; Rembert, Pascal; Matyjaszewski, Krzysztof; Bockstaller, Michael R; Fytas, George

2017-11-14

Polymer-tethered colloidal particles (aka "particle brush materials") have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush-brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems.

Morphology-dependent optical absorption and conduction properties of photoelectrochemical photocatalysts for H2 production: A case study

NASA Astrophysics Data System (ADS)

Huda, Muhammad N.; Turner, John A.

2010-06-01

Efficient photoelectrochemical H2 production by solar irradiation depends not only on the photocatalyst's band gap and its band-edge positions but also on the detailed electronic nature of the bands, such as the localization or delocalization of the band edges and their orbital characteristics. These determine the carrier transport properties, reactivity, light absorption strength, etc. and significantly impact the material's efficiency as a photoconverter. The localization or delocalization of the band edges may arise either due to the orbital nature of the bands or the structural morphology of the material. A recent experimental report on a photocatalyst based on s /p orbitals showed very poor performance for H2 production despite the delocalized nature of the s /p bands as compared to the d-bands of transition metal oxides. It is then important to examine whether this poor performance is inherent to these materials or rather arises from some experimental limitations. A theoretical analysis by first-principle methods is well suited to shed light on this question.

The effect of collagen crosslinking on the biphasic poroviscoelastic cartilage properties determined from a semi-automated microindentation protocol for stress relaxation.

PubMed

McGann, Megan E; Bonitsky, Craig M; Ovaert, Timothy C; Wagner, Diane R

2014-06-01

Given the important role of the collagenous structure in cartilage mechanics, there is considerable interest in the relationship between collagen crosslinking and the mechanical behavior of the cartilage matrix. While crosslink-induced alterations to the elastic modulus of cartilage have been described, changes to time-dependent behavior have not yet been determined. The objective of the study was to quantify changes to cartilage material properties, including viscoelastic coefficients, with crosslinking via indentation. To accomplish this, a semi-autonomous microindentation stress relaxation protocol was first developed, validated and then applied to cartilage specimens before and after crosslinking. The change in mechanical properties with crosslinking was analyzed both in the unloading portions of the test via the Oliver-Pharr method and in the holding portion with an inverse iterative finite element model that represented cartilage as a biphasic poroviscoelastic material. Although both techniques suggested a similar increase in equilibrium modulus in the crosslinked specimens as compared to the controls, distinct differences in the control specimens were apparent, suggesting that the two different techniques may be capturing different aspects of the material behavior. No differences in time-dependent properties were observed between the crosslinked and the control specimens. These results give further insight into the effects of crosslinking in cartilage mechanical behavior. Additionally, the microindentation stress relaxation protocol may enable increased automation for high-throughput testing. Copyright © 2014 Elsevier Ltd. All rights reserved.

Thermal mirror spectrometry: An experimental investigation of optical glasses

NASA Astrophysics Data System (ADS)

Zanuto, V. S.; Herculano, L. S.; Baesso, M. L.; Lukasievicz, G. V. B.; Jacinto, C.; Malacarne, L. C.; Astrath, N. G. C.

2013-03-01

The Thermal mirror technique relies on measuring laser-induced nanoscale surface deformation of a solid sample. The amplitude of the effect is directly dependent on the optical absorption and linear thermal expansion coefficients, and the time evolution depends on the heat diffusion properties of the sample. Measurement of transient signals provide direct access to thermal, optical and mechanical properties of the material. The theoretical models describing this effect can be formulated for very low optical absorbing and for absorbing materials. In addition, the theories describing the effect apply for semi-infinite and finite samples. In this work, we apply the Thermal mirror technique to measure physical properties of optical glasses. The semi-infinite and finite models are used to investigate very low optical absorbing glasses. The thickness limit for which the semi-infinite model retrieves the correct values of the thermal diffusivity and amplitude of the transient is obtained using the finite description. This procedure is also employed on absorbing glasses, and the semi-infinite Beer-Lambert law model is used to analyze the experimental data. The experimental data show the need to use the finite model for samples with very low bulk absorption coefficients and thicknesses L < 1.5 mm. This analysis helped to establish limit values of thickness for which the semi-infinite model for absorbing materials could be used, L > 1.0 mm in this case. In addition, the physical properties of the samples were calculated and absolute values derived.

Ab initio theory of point defects in oxide materials: structure, properties, chemical reactivity

NASA Astrophysics Data System (ADS)

Pacchioni, Gianfranco

2000-05-01

Point defects play a fundamental role in determining the physical and chemical properties of inorganic materials. This holds not only for the bulk properties but also for the surface of oxides where several kinds of point defects exist and exhibit a rich and complex chemistry. A particularly important defect in oxides is the oxygen vacancy. Depending on the electronic structure of the material the nature of oxygen vacancies changes dramatically. In this article we provide a rationalization of the very different electronic structure of neutral and charged oxygen vacancies in SiO 2 and MgO, two oxide materials with completely different electronic structure (from very ionic, MgO, to largely covalent, SiO 2). We used methods of ab initio quantum chemistry, from density functional theory (DFT) to configuration interaction (CI), to determine the ground and excited state properties of these defects. The theoretical results are combined with recent spectroscopic measurements. A series of observable properties has been determined in this way: defect formation energies, hyperfine interactions in electron paramagnetic resonance (EPR) spectra of paramagnetic centers, optical spectra, surface chemical reactivity. The interplay between experimental and theoretical information allows one to unambiguously identify the structure of oxygen vacancies in these binary oxides and on their surfaces.

Electronic structure, mechanical and thermodynamic properties of BaPaO3 under pressure.

PubMed

Khandy, Shakeel Ahmad; Islam, Ishtihadah; Gupta, Dinesh C; Laref, Amel

2018-05-07

Density functional theory (DFT)-based investigations have been put forward on the elastic, mechanical, and thermo-dynamical properties of BaPaO 3 . The pressure dependence of electronic band structure and other physical properties has been carefully analyzed. The increase in Bulk modulus and decrease in lattice constant is seen on going from 0 to 30 GPa. The predicted lattice constants describe this material as anisotropic and ductile in nature at ambient conditions. Post-DFT calculations using quasi-harmonic Debye model are employed to envisage the pressure-dependent thermodynamic properties like Debye temperature, specific heat capacity, Grüneisen parameter, thermal expansion, etc. Also, the computed Debye temperature and melting temperature of BaPaO 3 at 0 K are 523 K and 1764.75 K, respectively.

Magnetic Property Measurements on Single Wall Carbon Nanotube-Polyimide Composites

NASA Technical Reports Server (NTRS)

Sun, Keun J.; Wincheski, Russell A.; Park, Cheol

2008-01-01

Temperature and magnetic field dependent magnetization measurements were performed on polyimide nanocomposite samples, synthesized with various weight percentages of single wall carbon nanotubes. It was found that the magnetization of the composite, normalized to the mass of nanotube material in the sample, decreased with increasing weight percentage of nanotubes. It is possible that the interfacial coupling between the carbon nanotube (CNT) fillers and the polyimide matrix promotes the diamagnetic response from CNTs and reduces the total magnetization of the composite. The coercivity of the samples, believed to originate from the residual magnetic catalyst particles, was enhanced and had a stronger temperature dependence as a result of the composite synthesis. These changes in magnetic properties can form the basis of a new approach to investigate the interfacial properties in the CNT nanocomposites through magnetic property measurements.

Asphalt pavement aging and temperature dependent properties using functionally graded viscoelastic model

NASA Astrophysics Data System (ADS)

Dave, Eshan V.

Asphalt concrete pavements are inherently graded viscoelastic structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions being the major cause of non-homogeneity. Current pavement analysis and simulation procedures dwell on the use of layered approach to account for these non-homogeneities. The conventional finite-element modeling (FEM) technique discretizes the problem domain into smaller elements, each with a unique constitutive property. However the assignment of unique material property description to an element in the FEM approach makes it an unattractive choice for simulation of problems with material non-homogeneities. Specialized elements such as "graded elements" allow for non-homogenous material property definitions within an element. This dissertation describes the development of graded viscoelastic finite element analysis method and its application for analysis of asphalt concrete pavements. Results show that the present research improves efficiency and accuracy of simulations for asphalt pavement systems. Some of the practical implications of this work include the new technique's capability for accurate analysis and design of asphalt pavements and overlay systems and for the determination of pavement performance with varying climatic conditions and amount of in-service age. Other application areas include simulation of functionally graded fiber-reinforced concrete, geotechnical materials, metal and metal composites at high temperatures, polymers, and several other naturally existing and engineered materials.

Advanced Materials From Fungal Mycelium: Fabrication and Tuning of Physical Properties

NASA Astrophysics Data System (ADS)

Haneef, Muhammad; Ceseracciu, Luca; Canale, Claudio; Bayer, Ilker S.; Heredia-Guerrero, José A.; Athanassiou, Athanassia

2017-01-01

In this work is presented a new category of self-growing, fibrous, natural composite materials with controlled physical properties that can be produced in large quantities and over wide areas, based on mycelium, the main body of fungi. Mycelia from two types of edible, medicinal fungi, Ganoderma lucidum and Pleurotus ostreatus, have been carefully cultivated, being fed by two bio-substrates: cellulose and cellulose/potato-dextrose, the second being easier to digest by mycelium due to presence of simple sugars in its composition. After specific growing times the mycelia have been processed in order to cease their growth. Depending on their feeding substrate, the final fibrous structures showed different relative concentrations in polysaccharides, lipids, proteins and chitin. Such differences are reflected as alterations in morphology and mechanical properties. The materials grown on cellulose contained more chitin and showed higher Young’s modulus and lower elongation than those grown on dextrose-containing substrates, indicating that the mycelium materials get stiffer when their feeding substrate is harder to digest. All the developed fibrous materials were hydrophobic with water contact angles higher than 120°. The possibility of tailoring mycelium materials’ properties by properly choosing their nutrient substrates paves the way for their use in various scale applications.

Dependence of Capillary Properties of Contemporary Clinker Bricks on Their Microstructure

NASA Astrophysics Data System (ADS)

Wesołowska, Maria; Kaczmarek, Anna

2017-10-01

Contemporary clinker bricks are applied for outer layers of walls built from other materials and walls which should have high durability and aesthetic qualities. The intended effect depends not only on the mortar applied but also on clinker properties. Traditional macroscopic tests do not allow to predict clinker behaviour in contact with mortars and external environment. The basic information for this issue is open porosity of material. It defines the material ability to absorb liquids: rain water (through the face wall surface) and grout from mortar (through base surface). The main capillary flow goes on in pores with diameters from 300 to 3000nm. It is possible to define pore distribution and their size using the Mercury Intrusion Porosimetry method. The aim of these research is evaluation of clinker brick capillary properties (initial water absorption and capillary rate) and analysis of differences in microstructure of the face and base wall of a product. Detailed results allowed to show pore distribution in function of their diameters and definition of pore amount responsible for capillary flow. Based on relation between volume function differential and pore diameter, a differential distribution curve was obtained which helped to determine the dominant diameters. The results obtained let us state that face wall of bricks was characterized with the lowest material density and open porosity. In this layer (most burnt) part of pores could be closed by locally appearing liquid phase during brick burning. Thus density is lower comparing to other part of the product.

A simple and effective method for making multipotent/multilineage scaffolds with hydrophilic nature without any postmodification/treatment.

PubMed

Vaikkath, Dhanesh; Anitha, Rakhi; Sumathy, Babitha; Nair, Prabha D

2016-05-01

A number of biodegradable and bioresorbable materials, as well as scaffold designs, have been experimentally and/or clinically studied for tissue engineering of diverse tissue types. Cell-material responses are strongly dependent on the properties of the scaffold material. In this study, scaffolds based on polycaprolactone (PCL) and PCL blended with a triblock copolymer, Polycaprolactone-polytetrahydrofuran-polycaprolactone (PCL-PTHF-PCL) at different ratios were fabricated by electrospinning. Blending and electrospinning of the triblock copolymer with PCL generated a super hydrophilic scaffold, the mechanical and biological properties of which varied with the concentration of the triblock copolymer. The hydrophilicity of the electrospun scaffolds was determined by measurement of water-air contact angle. Cellular response to the electrospun scaffolds was studied by seeding two types of cells, L929 fibroblast cell line and rat mesenchymal stem cells (RMSC). We observed that the super hydrophilicity of the material did not prevent cell adhesion, while the cell proliferation was low or negligible for scaffolds containing higher amount of PCL-PTHF-PCL. Chondrogenic differentiation of RMSC was found to be better on the PCL blend containing 10% (w/v) of PCL-PTHF-PCL than the bare PCL. Our studies indicate that the cellular response is dependent on the biomaterial composition and highlight the importance of tailoring the scaffold properties for applications in tissue engineering and regenerative medicine. Copyright © 2015 Elsevier B.V. All rights reserved.

Time-dependent deformation of titanium metal matrix composites

NASA Technical Reports Server (NTRS)

Bigelow, C. A.; Bahei-El-din, Y. A.; Mirdamadi, M.

1995-01-01

A three-dimensional finite element program called VISCOPAC was developed and used to conduct a micromechanics analysis of titanium metal matrix composites. The VISCOPAC program uses a modified Eisenberg-Yen thermo-viscoplastic constitutive model to predict matrix behavior under thermomechanical fatigue loading. The analysis incorporated temperature-dependent elastic properties in the fiber and temperature-dependent viscoplastic properties in the matrix. The material model was described and the necessary material constants were determined experimentally. Fiber-matrix interfacial behavior was analyzed using a discrete fiber-matrix model. The thermal residual stresses due to the fabrication cycle were predicted with a failed interface, The failed interface resulted in lower thermal residual stresses in the matrix and fiber. Stresses due to a uniform transverse load were calculated at two temperatures, room temperature and an elevated temperature of 650 C. At both temperatures, a large stress concentration was calculated when the interface had failed. The results indicate the importance of accuracy accounting for fiber-matrix interface failure and the need for a micromechanics-based analytical technique to understand and predict the behavior of titanium metal matrix composites.

Tunable Assembly of Gold Nanorods in Polymer Solutions To Generate Controlled Nanostructured Materials

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

Poling-Skutvik, Ryan; Lee, Jonghun; Narayanan, Suresh

In this study, gold nanorods grafted with short chain polymers are assembled into controlled open structures using polymer-induced depletion interactions and structurally characterized using small angle x-ray scattering. When the nanorod diameter is smaller than the radius of gyration of the depletant polymer, the depletion interaction depends solely on the correlation length of the polymer solution and not directly on the polymer molecular weight. As the polymer concentration increases, the stronger depletion interactions increasingly compress the grafted chains and push the gold nanorods closer together. By contrast, other structural characteristics such as the number of nearest neighbors and fractal dimensionmore » exhibit a non-monotonic dependence on polymer concentration. These parameters are maximal at intermediate concentrations, which are attributed to a crossover from reaction-limited to diffusion-limited aggregation. Finally, the control over structural properties of anisotropic nanoscale building blocks demonstrated here will be beneficial to designing and producing materials in situ with specific direction-dependent nanoscale properties and provides a crucial route for advances in additive manufacturing.« less

Tunable Assembly of Gold Nanorods in Polymer Solutions To Generate Controlled Nanostructured Materials

DOE PAGES

Poling-Skutvik, Ryan; Lee, Jonghun; Narayanan, Suresh; ...

2018-01-17

In this study, gold nanorods grafted with short chain polymers are assembled into controlled open structures using polymer-induced depletion interactions and structurally characterized using small angle x-ray scattering. When the nanorod diameter is smaller than the radius of gyration of the depletant polymer, the depletion interaction depends solely on the correlation length of the polymer solution and not directly on the polymer molecular weight. As the polymer concentration increases, the stronger depletion interactions increasingly compress the grafted chains and push the gold nanorods closer together. By contrast, other structural characteristics such as the number of nearest neighbors and fractal dimensionmore » exhibit a non-monotonic dependence on polymer concentration. These parameters are maximal at intermediate concentrations, which are attributed to a crossover from reaction-limited to diffusion-limited aggregation. Finally, the control over structural properties of anisotropic nanoscale building blocks demonstrated here will be beneficial to designing and producing materials in situ with specific direction-dependent nanoscale properties and provides a crucial route for advances in additive manufacturing.« less

Anomalous solute transport in saturated porous media: Relating transport model parameters to electrical and nuclear magnetic resonance properties

USGS Publications Warehouse

Swanson, Ryan D; Binley, Andrew; Keating, Kristina; France, Samantha; Osterman, Gordon; Day-Lewis, Frederick D.; Singha, Kamini

2015-01-01

The advection-dispersion equation (ADE) fails to describe commonly observed non-Fickian solute transport in saturated porous media, necessitating the use of other models such as the dual-domain mass-transfer (DDMT) model. DDMT model parameters are commonly calibrated via curve fitting, providing little insight into the relation between effective parameters and physical properties of the medium. There is a clear need for material characterization techniques that can provide insight into the geometry and connectedness of pore spaces related to transport model parameters. Here, we consider proton nuclear magnetic resonance (NMR), direct-current (DC) resistivity, and complex conductivity (CC) measurements for this purpose, and assess these methods using glass beads as a control and two different samples of the zeolite clinoptilolite, a material that demonstrates non-Fickian transport due to intragranular porosity. We estimate DDMT parameters via calibration of a transport model to column-scale solute tracer tests, and compare NMR, DC resistivity, CC results, which reveal that grain size alone does not control transport properties and measured geophysical parameters; rather, volume and arrangement of the pore space play important roles. NMR cannot provide estimates of more-mobile and less-mobile pore volumes in the absence of tracer tests because these estimates depend critically on the selection of a material-dependent and flow-dependent cutoff time. Increased electrical connectedness from DC resistivity measurements are associated with greater mobile pore space determined from transport model calibration. CC was hypothesized to be related to length scales of mass transfer, but the CC response is unrelated to DDMT.

Simulating Damage Due to a Lightning Strike Event: Effects of Temperature Dependent Properties on Interlaminar Damage

NASA Technical Reports Server (NTRS)

Ghezeljeh, Paria Naghipour; Pineda, Evan Jorge

2014-01-01

A multidirectional, carbon fiber-epoxy, composite panel is subjected to a simulated lightning strike, within a finite element method framework, and the effect of material properties on the failure (delamination) response is investigated through a detailed numerical study. The numerical model of the composite panel consists of individual homogenized plies with user-defined, cohesive interface elements between them. Lightning strikes are simulated as an assumed combination of excessive heat and high pressure loadings. It is observed that the initiation and propagation of lightning-induced delamination is a significant function of the temperature dependency of interfacial fracture toughness. This dependency must be defined properly in order to achieve reliable predictions of the present lightning-induced delamination in the composite panel.

Advanced manufacturing of microdisk vaccines for uniform control of material properties and immune cell function.

PubMed

Zeng, Qin; Zhang, Peipei; Zeng, Xiangbin; Tostanoski, Lisa H; Jewell, Christopher M

2017-12-19

The continued challenges facing vaccines in infectious disease and cancer highlight a need for better control over the features of vaccines and the responses they generate. Biomaterials offer unique advantages to achieve this goal through features such as controlled release and co-delivery of antigens and adjuvants. However, many synthesis strategies lead to particles with heterogeneity in diameter, shape, loading level, or other properties. In contrast, advanced manufacturing techniques allow precision control of material properties at the micro- and nano-scale. These capabilities in vaccines and immunotherapies could allow more rational design to speed efficient design and clinical translation. Here we employed soft lithography to generate polymer microdisk vaccines with uniform structures and tunable compositions of vaccine antigens and toll like receptor agonists (TLRas) that serve as molecular adjuvants. Compared to conventional PLGA particles formed by emulsion, microdisks provided a dramatic improvement in the consistency of properties such as diameter. During culture with primary dendritic cells (DCs) from mice, microdisks were internalized by the cells without toxicity, while promoting co-delivery of antigen and TLRa to the same cell. Analysis of DC surface activation markers by flow cytometry revealed microdisk vaccines activated dendritic cells in a manner that depended on the level of TLRa, while antigen processing and presentation depended on the amount of antigen in the microdisks. Together, this work demonstrates the use of advanced manufacturing techniques to produce uniform vaccines that direct DC function depending on the composition in the disks.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Dependence of the photoluminescence density on surface preparation and properties of n-type InP

NASA Astrophysics Data System (ADS)

Knauer, A.; Gramlich, S.; Staske, R.

1988-11-01

Comprehensive studies were made of the relationship between the photoluminescence intensity and the effective carrier lifetime, on the one hand, and the quality of the surface treatment of wafers (damage, oxide layer thickness) and the initial properties of a material (surface and bulk defects, inhomogeneity of the dopant concentration), on the other.

Resonance of electromagnetic absorption in a dielectric composite based on a high temperature superconductor

NASA Astrophysics Data System (ADS)

Grishin, A. M.; D'Iakonov, V. P.; Mezin, N. I.; Shapovalov, V. A.; Starostiuk, N. Iu.; Iarosh, G. S.

1992-10-01

A dielectric composite has been produced which is characterized by a sufficiently strong dependence of its microwave properties on weak magnetic fields. The composite is based on highly dispersed YBa2Cu3O(7-x) superconducting powder, with paraffin used as the matrix material. Results of a study of the magnetic and microwave properties of the composite are presented.

Structural, Transport and Electrochemical Properties of LiFePO4 Substituted in Lithium and Iron Sublattices (Al, Zr, W, Mn, Co and Ni)

PubMed Central

Molenda, Janina; Kulka, Andrzej; Milewska, Anna; Zając, Wojciech; Świerczek, Konrad

2013-01-01

LiFePO4 is considered to be one of the most promising cathode materials for lithium ion batteries for electric vehicle (EV) application. However, there are still a number of unsolved issues regarding the influence of Li and Fe-site substitution on the physicochemical properties of LiFePO4. This is a review-type article, presenting results of our group, related to the possibility of the chemical modification of phosphoolivine by introduction of cation dopants in Li and Fe sublattices. Along with a synthetic review of previous papers, a large number of new results are included. The possibility of substitution of Li+ by Al3+, Zr4+, W6+ and its influence on the physicochemical properties of LiFePO4 was investigated by means of XRD, SEM/EDS, electrical conductivity and Seebeck coefficient measurements. The range of solid solution formation in Li1−3xAlxFePO4, Li1−4xZrxFePO4 and Li1−6xWxFePO4 materials was found to be very narrow. Transport properties of the synthesized materials were found to be rather weakly dependent on the chemical composition. The battery performance of selected olivines was tested by cyclic voltammetry (CV). In the case of LiFe1−yMyPO4 (M = Mn, Co and Ni), solid solution formation was observed over a large range of y (0 < y ≤ 1). An increase of electrical conductivity for the substitution level y = 0.25 was observed. Electrons of 3d metals other than iron do not contribute to the electrical properties of LiFe1−yMyPO4, and substitution level y > 0.25 leads to considerably lower values of σ. The activated character of electrical conductivity with a rather weak temperature dependence of the Seebeck coefficient suggests a small polaron-type conduction mechanism. The electrochemical properties of LiFe1−yMyPO4 strongly depend on the Fe substitution level. PMID:28809235

Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces

NASA Astrophysics Data System (ADS)

McBriarty, Martin E.

Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.

Meniscal material properties are minimally affected by matrix stabilization using glutaraldehyde and glycation with ribose.

PubMed

Hunter, Shawn A; Noyes, Frank R; Haridas, Balakrishna; Levy, Martin S; Butler, David L

2005-05-01

Knee meniscus replacement holds promise, but current allografts are susceptible to biodegradation. Matrix stabilization with glutaraldehyde, a crosslinking agent used clinically to fabricate cardiovascular bioprostheses, or with glycation, a process of crosslinking collagen with sugars such as ribose, is a potential means of rendering tissue resistant to such degradation. However, stabilization should not significantly alter meniscal material properties, which could disturb normal function in the knee. Our objective was to evaluate the effects of glutaraldehyde- and glycation-induced matrix stabilization on the material properties of porcine meniscus. Normal untreated meniscus specimens were tested in confined compression at one of three applied stresses (0.069, 0.208, 0.347 MPa), subjected to either a glutaraldehyde or glycation stabilization treatment, and then re-tested to measure changes in tissue aggregate modulus, permeability, and compressive strain at equilibrium. Changes in these properties significantly increased with glutaraldehyde concentration and exposure time to ribose. One glutaraldehyde and three glycation treatments did not alter aggregate modulus or compressive strain at equilibrium compared to controls (p > 0.10). However, all treatments increased permeability by at least 108% compared to controls (p < 0.001). This study reveals a dose-dependent relationship between meniscal material properties and certain stabilization conditions and identifies treatments that minimally affect these properties. Further research is necessary to determine whether these treatments prevent enzymatic degradation before and after surgical implantation in the knee.

Choosing the function of mechanical properties of grounds and rock formations due to their heterogeneity

NASA Astrophysics Data System (ADS)

Frolova, Irina; Agakhanov, Murad

2018-03-01

The development of computing techniques to analyze underground structures, buildings in high-rise construction that would fully take account of the conditions of their design and operation, as well as the real material properties, is one of the important trends in structural mechanics. For the territory in high-rise construction it is necessary to monitor the deformations of the soil surface. When high-rise construction is recommended to take into account the rheological properties and temperature deformations of the soil, the effect of temperature on the mechanical characteristics of the surrounding massif. Similar tasks also arise in the creation and operation of underground parts of high-rise construction, which are used for various purposes. These parts of the structures are surrounded by rock massifs of various materials. The actual mechanical characteristics of such materials must be taken into account. The objective property of nearly all materials is their non-homogeneity, both natural and technological. The work addresses the matters of building nonhomogeneous media initial models based on the experimental evidence. This made it possible to approximate real dependencies and obtain the appropriate functions in a simple and convenient way.

Dimethacrylate network formation and polymer property evolution as determined by the selection of monomers and curing conditions

PubMed Central

Stansbury, Jeffrey W.

2011-01-01

Objectives This overview is intended to highlight connections between monomer structure and the development of highly crosslinked photopolymer networks including the conversion dependent properties of shrinkage, modulus and stress. Methods A review is provided that combines the polymer science and dental materials literature along with examples of relevant experimental results, which include measurements of reaction kinetics, photorheology as well as polymerization shrinkage and stress. Results While new monomers are continually under development for dental materials applications, mixtures of dimethacrylate monomers persist as the most common form of dental resins used on composite restorative materials. Monomer viscosity and reaction potential is derived from molecular structure and by employing real-time near-infrared spectroscopic techniques, the development of macromolecular networks is linked to the evolution of polymerization shrinkage (measured by linometer), modulus (measured by photorheometer), and stress (measured by tensometer). Relationships between the respective polymer properties are examined. Significance Through a better understanding of the polymer network formation and property development processes using conventional dimethacrylate monomer formulations, the rational design of improved materials is facilitated with the ultimate goal of achieving dental polymers that deliver enhanced clinical outcomes. PMID:22192248

A review: applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials

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

Li, Yulan; Hu, Shenyang; Sun, Xin

Here, complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature. This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical, thermal, and magnetic properties. The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials. Then, the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiatedmore » nuclear materials are reviewed. The review shows that (1) Phase field models can correctly describe important phenomena such as spatial-dependent generation, migration, and recombination of defects, radiation-induced dissolution, the Soret effect, strong interfacial energy anisotropy, and elastic interaction; (2) The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution, including radiation-induced segregation, second phase nucleation, void migration, void and gas bubble superlattice formation, interstitial loop evolution, hydrate formation, and grain growth, and (3) The Phase field method correctly predicts the relationships between microstructures and properties. The final section is dedicated to a discussion of the strengths and limitations of the phase field method, as applied to irradiation effects in nuclear materials.« less

A review: applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials

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

Li, Yulan; Hu, Shenyang; Sun, Xin

Complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature. This paper evaluates the role of the phase field (PF) method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical, thermal, and magnetic properties. The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials. Then, the PF method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiated nuclearmore » materials are reviewed. The review shows that 1) FP models can correctly describe important phenomena such as spatial dependent generation, migration, and recombination of defects, radiation-induced dissolution, the Soret effect, strong interfacial energy anisotropy, and elastic interaction; 2) The PF method can qualitatively and quantitatively simulate 2-D and 3-D microstructure evolution, including radiation-induced segregation, second phase nucleation, void migration, void and gas bubble superlattice formation, interstitial loop evolution, hydrate formation, and grain growth, and 3) The FP method correctly predicts the relationships between microstructures and properties. The final section is dedicated to a discussion of the strengths and limitations of the PF method, as applied to irradiation effects in nuclear materials.« less

A review: applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials

DOE PAGES

Li, Yulan; Hu, Shenyang; Sun, Xin; ...

2017-04-14

Here, complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature. This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical, thermal, and magnetic properties. The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials. Then, the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiatedmore » nuclear materials are reviewed. The review shows that (1) Phase field models can correctly describe important phenomena such as spatial-dependent generation, migration, and recombination of defects, radiation-induced dissolution, the Soret effect, strong interfacial energy anisotropy, and elastic interaction; (2) The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution, including radiation-induced segregation, second phase nucleation, void migration, void and gas bubble superlattice formation, interstitial loop evolution, hydrate formation, and grain growth, and (3) The Phase field method correctly predicts the relationships between microstructures and properties. The final section is dedicated to a discussion of the strengths and limitations of the phase field method, as applied to irradiation effects in nuclear materials.« less

The novel solution for negative impact of out-of-band and outgassing by top coat materials in EUVL

NASA Astrophysics Data System (ADS)

Fujitani, Noriaki; Sakamoto, Rikimaru; Endo, Takafumi; Onishi, Ryuji; Nishita, Tokio; Yaguchi, Hiroaki; Ho, Bang-Ching

2013-03-01

EUV lithography (EUVL) is the most promising candidate of next generation technology for hp20nm node device manufacturing and beyond. However, the power of light source, masks and photo resists are the most critical issues for driving the EUVL. Especially, concerning about deterioration of the patterning performance by Out-of-Band (OoB) light existing in the EUV light, and contamination problem of exposure tool due to the resist outgassing are the key issues which have to be resolved in the material view point toward the high volume manufacturing by EUVL. This paper proposes the solution for these critical issues by applying the top coat material. The key characteristics for top coat material are the protection of the OoB effect, the prevention of the outgassing from resist as a barrier layer and enhancement of photo resist performance, like resist profile and process window. This paper describes the material design and performance. The optical property needs having the high absorbance of DUV light in OoB range and high transmittance for 13.5nm wavelength. Outgassing barrier property needs high broking property against non contamination chemical species from photo resist outgassing. The study of TOF-SIMS analysis indicates how much the polymer chemistry can impact for outgassing barrier property. The dependency of material design and lithography performance is also discussed.

Quantifying the risks of solid aerosol geoengineering: the role of fundamental material properties

NASA Astrophysics Data System (ADS)

Dykema, J. A.; Keutsch, F. N.; Keith, D.

2017-12-01

Solid aerosols have been considered as an alternative to sulfate aerosols for solar geoengineering due to their optical and chemical properties, which lead to different and possibly more attractive risk profiles. Solid aerosols can achieve higher solar scattering efficiency due to their higher refractive index, and in some cases may also be less effective absorbers of thermal infrared radiation. The optical properties of solid aerosols are however sensitive functions of the detailed physical properties of solid materials in question. The relevant details include the exact crystalline structure of the aerosols, the physical size of the particles, and interactions with background stratospheric molecular and particulate constituents. In this work, we examine the impact of these detailed physical properties on the radiative properties of calcite (CaCO3) solid aerosols. We examine how crystal morphology, size, chemical reactions, and interaction with background stratospheric aerosol may alter the scattering and absorption properties of calcite aerosols for solar and thermal infrared radiation. For example, in small particles, crystal lattice vibrations associated with the particle surface may lead to substantially different infrared absorption properties than bulk materials. We examine the wavelength dependence of absorption by the particles, which may lead to altered patterns of stratospheric radiative heating and equilibrium temperatures. Such temperature changes can lead to dynamical changes, with consequences for both stratospheric composition and tropospheric climate. We identify important uncertainties in the current state of understanding, investigate risks associated with these uncertainties, and survey potential approaches to quantitatively improving our knowledge of the relevant material properties.

Fatigue properties of JIS H3300 C1220 copper for strain life prediction

NASA Astrophysics Data System (ADS)

Harun, Muhammad Faiz; Mohammad, Roslina

2018-05-01

The existing methods for estimating strain life parameters are dependent on the material's monotonic tensile properties. However, a few of these methods yield quite complicated expressions for calculating fatigue parameters, and are specific to certain groups of materials only. The Universal Slopes method, Modified Universal Slopes method, Uniform Material Law, the Hardness method, and Medians method are a few existing methods for predicting strain-life fatigue based on monotonic tensile material properties and hardness of material. In the present study, nine methods for estimating fatigue life and properties are applied on JIS H3300 C1220 copper to determine the best methods for strain life estimation of this ductile material. Experimental strain-life curves are compared to estimations obtained using each method. Muralidharan-Manson's Modified Universal Slopes method and Bäumel-Seeger's method for unalloyed and low-alloy steels are found to yield batter accuracy in estimating fatigue life with a deviation of less than 25%. However, the prediction of both methods only yield much better accuracy for a cycle of less than 1000 or for strain amplitudes of more than 1% and less than 6%. Manson's Original Universal Slopes method and Ong's Modified Four-Point Correlation method are found to predict the strain-life fatigue of copper with better accuracy for a high number of cycles of strain amplitudes of less than 1%. The differences between mechanical behavior during monotonic and cyclic loading and the complexity in deciding the coefficient in an equation are probably the reason for the lack of a reliable method for estimating fatigue behavior using the monotonic properties of a group of materials. It is therefore suggested that a differential approach and new expressions be developed to estimate the strain-life fatigue parameters for ductile materials such as copper.

Role of segregation and precipitates on interfacial strengthening mechanisms in metal matrix composites when subjected to thermo-mechanical processing

NASA Astrophysics Data System (ADS)

Myriounis, Dimitrios

Metal Matrix ceramic-reinforced composites are rapidly becoming strong candidates as structural materials for many high temperatures and aerospace applications. Metal matrix composites combine the ductile properties of the matrix with a brittle phase of the reinforcement, leading to high stiffness and strength with a reduction in structural weight. The main objective of using a metal matrix composite system is to increase service temperature or improve specific mechanical properties of structural components by replacing existing superalloys.The satisfactory performance of metal matrix composites depends critically on their integrity, the heart of which is the quality of the matrix-reinforcement interface. The nature of the interface depends on the processing of the metal matrix composite component. At the micro-level the development of local stress concentration gradients around the ceramic reinforcement, as the metal matrix attempts to deform during processing, can be very different to the nominal conditions and play a crucial role in important microstructural events such as segregation and precipitation at the matrix-reinforcement interface. These events dominate the cohesive strength and subsequent mechanical properties of the interface.At present the relationship between the strength properties of metal matrix composites and the details of the thermo-mechanical forming processes is not well understood.The purpose of the study is to investigate several strengthening mechanisms and the effect of thermo-mechanical processing of SiCp reinforced A359 aluminium alloy composites on the particle-matrix interface and the overall mechanical properties of the material. From experiments performed on composite materials subjected to various thermo-mechanical conditions and by observation using SEM microanalysis and mechanical testing, data were obtained, summarised and mathematically/statistically analysed upon their significance.The Al/SiCp composites studied, processed in specific thermo-mechanical conditions in order to attain higher values of interfacial fracture strength, due to precipitation hardening and segregation mechanisms, also exhibited enhanced bulk mechanical and fracture resistant properties.An analytical model to predict the interfacial fracture strength in the presence of material segregation was also developed during this research effort. Its validity was determined based on the data gathered from the experiments.The tailoring of the properties due to the microstructural modification of the composites was examined in relation to the experimental measurements obtained, which define the macroscopical behaviour of the material.

Rubber-like materials derived from biosourced phenolic resins

NASA Astrophysics Data System (ADS)

Amaral-Labat, G.; Grishechko, L. I.; Silva, G. F. B. Lenz e.; Kuznetsov, B. N.; Fierro, V.; Pizzi, A.; Celzard, A.

2017-07-01

The present work describes new gels derived from cheap, abundant and non-toxic wood bark extracts of phenolic nature, behaving like elastomers. Especially, we show that these materials might be used as rubber springs. Such amazing properties were obtained by a quite simple synthesis based on the autocondensation of flavonoid tannins in water at low pH in the presence of a plasticizer. After gelation and drying, the materials presented elastic properties that could be tuned from hard and brittle to quite soft and deformable, depending on the amount of plasticizer in the starting formulation. Not only the materials containing the relevant amount of plasticizer had stress-strain characteristics in quasi-static and cyclic compression similar to most commercial rubber springs, but they presented outstanding fire retardance, surviving 5 min in a flame at 1000°C in air. Neither flame propagation nor drips were noticed during the fire test, and the materials were auto-extinguishable. These excellent features make these materials potential substitutes to usual organic elastomers.

Proceedings of the 13th Army Symposium on Solid Mechanics, 17-19 August 1993, Plymouth, Massachusetts.

DTIC Science & Technology

1993-01-01

the material relating the average stresses Ux(= Uz) to the eigenstrains e * is (Mallick and Krajcinovic, 1992a,b) 21 (yt)+ (p), 2 d-x(y, s) +R3 (y, s... eigenstrain in the material due to chemical shrinkage and thermal dilatation. During the chemical reaction of bonding two reacting monomers must reduce their...reaction (3) and connectivity dependent material properties and eigenstrains (4). However, the most prominent source of complexity is the fact that the

Thermal insulation materials for inside applications: Hygric and thermal properties

NASA Astrophysics Data System (ADS)

Jerman, Miloš; Černý, Robert

2017-11-01

Two thermal insulation materials suitable for the application on the interior side of historical building envelopes, namely calcium silicate and polyurethane-based foam are studied. Moisture diffusivity and thermal conductivity of both materials, as fundamental moisture and heat transport parameters, are measured in a dependence on moisture content. The measured data will be used as input parameters in computer simulation studies which will provide moisture and temperature fields necessary for an appropriate design of interior thermal insulation systems.

Microplasma device architectures with various diamond nanostructures

NASA Astrophysics Data System (ADS)

Kunuku, Srinivasu; Jothiramalingam Sankaran, Kamatchi; Leou, Keh-Chyang; Lin, I.-Nan

2017-02-01

Diamond nanostructures (DNSs) were fabricated from three different morphological diamonds, microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films, using a reactive ion etching method. The plasma illumination (PI) behavior of microplasma devices using the DNSs and the diamond films as cathode were investigated. The Paschen curve approach revealed that the secondary electron emission coefficient (γ value) of diamond materials is similar irrespective of the microstructure (MCD, NCD, and UNCD) and geometry of the materials (DNSs and diamond films). The diamond materials show markedly larger γ-coefficient than conventional metallic cathode materials such as Mo that resulted in markedly better PI behavior for the corresponding microplasma devices. Moreover, the PI behavior, i.e. the voltage dependence of plasma current density (J pl-V), plasma density (n e-V), and the robustness of the devices, varied markedly with the microstructure and geometry of the cathode materials that was closely correlated to the electron field emission (EFE) properties of the cathode materials. The UNCD nanopillars, possessing good EFE properties, resulted in superior PI behavior, whereas the MCD diamond films with insufficient EFE properties led to inferior PI behavior. Consequently, enhancement of plasma characteristics is the collective effects of EFE behavior and secondary electron emission characteristics of diamond-based cathode materials.

Bias Voltage-Dependent Impedance Spectroscopy Analysis of Hydrothermally Synthesized ZnS Nanoparticles

NASA Astrophysics Data System (ADS)

Dey, Arka; Dhar, Joydeep; Sil, Sayantan; Jana, Rajkumar; Ray, Partha Pratim

2018-04-01

In this report, bias voltage-dependent dielectric and electron transport properties of ZnS nanoparticles were discussed. ZnS nanoparticles were synthesized by introducing a modified hydrothermal process. The powder XRD pattern indicates the phase purity, and field emission scanning electron microscope image demonstrates the morphology of the synthesized sample. The optical band gap energy (E g = 4.2 eV) from UV measurement explores semiconductor behavior of the synthesized material. The electrical properties were performed at room temperature using complex impedance spectroscopy (CIS) technique as a function of frequency (40 Hz-10 MHz) under different forward dc bias voltages (0-1 V). The CIS analysis demonstrates the contribution of bulk resistance in conduction mechanism and its dependency on forward dc bias voltages. The imaginary part of the impedance versus frequency curve exhibits the existence of relaxation peak which shifts with increasing dc forward bias voltages. The dc bias voltage-dependent ac and dc conductivity of the synthesized ZnS was studied on thin film structure. A possible hopping mechanism for electrical transport processes in the system was investigated. Finally, it is worth to mention that this analysis of bias voltage-dependent dielectric and transport properties of as-synthesized ZnS showed excellent properties for emerging energy applications.

The influence of time dependent flight and maneuver velocities and elastic or viscoelastic flexibilities on aerodynamic and stability derivatives

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

Cochrane, Alexander P.; Merrett, Craig G.; Hilton, Harry H.

2014-12-10

The advent of new structural concepts employing composites in primary load carrying aerospace structures in UAVs, MAVs, Boeing 787s, Airbus A380s, etc., necessitates the inclusion of flexibility as well as viscoelasticity in static structural and aero-viscoelastic analyses. Differences and similarities between aeroelasticity and aero-viscoelasticity have been investigated in [2]. An investigation is undertaken as to the dependence and sensitivity of aerodynamic and stability derivatives to elastic and viscoelastic structural flexibility and as to time dependent flight and maneuver velocities. Longitudinal, lateral and directional stabilities are investigated. It has been a well established fact that elastic lifting surfaces are subject tomore » loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings one of the critical static parameters is the velocity at which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. The influence of the twin effects of viscoelastic and elastic materials and of variable flight velocities on longitudinal, lateral, directional and spin stabilities are also investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are here extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings the critical parameter is the velocity at which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. This paper reports on analytical analyses and simulations of the effects of flexibility and time dependent material properties (viscoelasticity) on aerodynamic derivatives and on lateral, longitudinal, directional and spin stability derivatives. Cases of both constant and variable flight and maneuver velocities are considered. Analytical results for maneuvers involving constant and time dependent rolling velocities are analyzed, discussed and evaluated. The relationships between rolling velocity p and aileron angular displacement β as well as control effectiveness are analyzed and discussed in detail for elastic and viscoelastic wings. Such analyses establish the roll effectiveness derivatives (∂[p(t)])/(V{sub ∞}∂β(t)) . Similar studies involving other stability and aerodynamic derivatives are also undertaken. The influence of the twin effects of viscoelastic and elastic materials and of variable flight, rolling, pitching and yawing velocities on longitudinal, lateral and directional are also investigated. Variable flight velocities, encountered during maneuvers, render the usually linear problem at constant velocities into a nonlinear one.« less

A decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping).

PubMed

Arts, Josje H E; Hadi, Mackenzie; Irfan, Muhammad-Adeel; Keene, Athena M; Kreiling, Reinhard; Lyon, Delina; Maier, Monika; Michel, Karin; Petry, Thomas; Sauer, Ursula G; Warheit, David; Wiench, Karin; Wohlleben, Wendel; Landsiedel, Robert

2015-03-15

The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) 'Nano Task Force' proposes a Decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping) that consists of 3 tiers to assign nanomaterials to 4 main groups, to perform sub-grouping within the main groups and to determine and refine specific information needs. The DF4nanoGrouping covers all relevant aspects of a nanomaterial's life cycle and biological pathways, i.e. intrinsic material and system-dependent properties, biopersistence, uptake and biodistribution, cellular and apical toxic effects. Use (including manufacture), release and route of exposure are applied as 'qualifiers' within the DF4nanoGrouping to determine if, e.g. nanomaterials cannot be released from a product matrix, which may justify the waiving of testing. The four main groups encompass (1) soluble nanomaterials, (2) biopersistent high aspect ratio nanomaterials, (3) passive nanomaterials, and (4) active nanomaterials. The DF4nanoGrouping aims to group nanomaterials by their specific mode-of-action that results in an apical toxic effect. This is eventually directed by a nanomaterial's intrinsic properties. However, since the exact correlation of intrinsic material properties and apical toxic effect is not yet established, the DF4nanoGrouping uses the 'functionality' of nanomaterials for grouping rather than relying on intrinsic material properties alone. Such functionalities include system-dependent material properties (such as dissolution rate in biologically relevant media), bio-physical interactions, in vitro effects and release and exposure. The DF4nanoGrouping is a hazard and risk assessment tool that applies modern toxicology and contributes to the sustainable development of nanotechnological products. It ensures that no studies are performed that do not provide crucial data and therefore saves animals and resources. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

The stability of new transparent polymeric materials: The epoxy trimethoxyboroxine system. Part 1: The preparation, characterization and curing of epoxy resins and their copolymers

NASA Technical Reports Server (NTRS)

Pearce, E.; Lin, S. C.

1981-01-01

The effects of resin composition, curing conditions fillers, and flame retardant additives on the flammability of diglycidyl ether of bisphenol-A (DGEBA) as measured by the oxygen index is examined. The oxygen index of DGEBA cured with various curing agents was between 0.198 to 0.238. Fillers and flame retardant additives can increase the oxygen index dependent on the material and the amount used. Changes in the basic cured resin properties can be anticipated with the addition of noncompatible additives. High flame resistant epoxy resins with good stability and mechanical properties are investigated.

Beyond the Periodic Table of Elements: The Role of Superatoms.

PubMed

Jena, Puru

2013-05-02

Atomic clusters composed of homo or heteroatomic species constitute an intermediate phase of matter where every atom counts and whose properties depend on their size, shape, composition, and charge. If specific clusters mimicking the chemistry of atoms can be produced, they can be thought of as man-made superatoms forming the building blocks of a new three-dimensional periodic table. Novel materials with tailored properties can then be synthesized by assembling these superatoms. This invited Perspective presents a brief summary of the pioneering works that led to this concept, and highlights the recent breakthroughs that hold promise for a new era in materials science.

Investigation of the properties of Sb doping on tin oxide SNO2 materials for technological applications

NASA Astrophysics Data System (ADS)

Hachoun, Z.; Ouerdane, A.; Bouslama, M.; Ghaffour, M.; Abdellaoui, A.; Caudano, Y.; benamara, A. Ali

2016-04-01

The conductivities of the oxide SnO2 is dependent on the nature of the surrounding gas. This property stems from the adsorption or desorption on the surface of oxide grains. These phenomena are usually accompanied by electronic transfer between the adsorbed molecule and the semiconductor material, changing its conductivity. Tin oxidation and Sb doping were realized without and with heating process. The XPS technique and the TEM microscopy showed the synthesized nanocrystals. Simulated Monte Carlo program Casino is used for a scanning its profile. The surface characteristics are highlighted in the aim to be used as spatial gas sensors.

Spatially resolved quantitative mapping of thermomechanical properties and phase transition temperatures using scanning probe microscopy

DOEpatents

Jesse, Stephen; Kalinin, Sergei V; Nikiforov, Maxim P

2013-07-09

An approach for the thermomechanical characterization of phase transitions in polymeric materials (polyethyleneterephthalate) by band excitation acoustic force microscopy is developed. This methodology allows the independent measurement of resonance frequency, Q factor, and oscillation amplitude of a tip-surface contact area as a function of tip temperature, from which the thermal evolution of tip-surface spring constant and mechanical dissipation can be extracted. A heating protocol maintained a constant tip-surface contact area and constant contact force, thereby allowing for reproducible measurements and quantitative extraction of material properties including temperature dependence of indentation-based elastic and loss moduli.

Group-identity completion and the symbolic value of property.

PubMed

Ledgerwood, Alison; Liviatan, Ido; Carnevale, Peter J

2007-10-01

Building on symbolic self-completion theory, we conceptualize group identity as a goal toward which group members strive, using material symbols of that identity. We report four studies showing that the value placed on such material symbols (e.g., a building) depends on commitment to group identity, the extent to which a symbol can be used to represent in-group identity, and situational variability in goal strength induced through group-identity affirmation or threat. Our results suggest that property derives value from its capacity to serve as an effective means in the pursuit of group-identity goals. Implications for intergroup conflict are discussed.

Fatigue performance of additively manufactured meta-biomaterials: The effects of topology and material type.

PubMed

Ahmadi, S M; Hedayati, R; Li, Y; Lietaert, K; Tümer, N; Fatemi, A; Rans, C D; Pouran, B; Weinans, H; Zadpoor, A A

2018-01-01

Additive manufacturing (AM) techniques enable fabrication of bone-mimicking meta-biomaterials with unprecedented combinations of topological, mechanical, and mass transport properties. The mechanical performance of AM meta-biomaterials is a direct function of their topological design. It is, however, not clear to what extent the material type is important in determining the fatigue behavior of such biomaterials. We therefore aimed to determine the isolated and modulated effects of topological design and material type on the fatigue response of metallic meta-biomaterials fabricated with selective laser melting. Towards that end, we designed and additively manufactured Co-Cr meta-biomaterials with three types of repeating unit cells and three to four porosities per type of repeating unit cell. The AM meta-biomaterials were then mechanically tested to obtain their normalized S-N curves. The obtained S-N curves of Co-Cr meta-biomaterials were compared to those of meta-biomaterials with same topological designs but made from other materials, i.e. Ti-6Al-4V, tantalum, and pure titanium, available from our previous studies. We found the material type to be far more important than the topological design in determining the normalized fatigue strength of our AM metallic meta-biomaterials. This is the opposite of what we have found for the quasi-static mechanical properties of the same meta-biomaterials. The effects of material type, manufacturing imperfections, and topological design were different in the high and low cycle fatigue regions. That is likely because the cyclic response of meta-biomaterials depends not only on the static and fatigue strengths of the bulk material but also on other factors that may include strut roughness, distribution of the micro-pores created inside the struts during the AM process, and plasticity. Meta-biomaterials are a special class of metamaterials with unusual or unprecedented combinations of mechanical, physical (e.g. mass transport), and biological properties. Topologically complex and additively manufactured meta-biomaterials have been shown to improve bone regeneration and osseointegration. The mechanical properties of such biomaterials are directly related to their topological design and material type. However, previous studies of such biomaterials have largely neglected the effects of material type, instead focusing on topological design. We show here that neglecting the effects of material type is unjustified. We studied the isolated and combined effects of topological design and material type on the normalized S-N curves of metallic bone-mimicking biomaterials and found them to be more strongly dependent on the material type than topological design. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Preparation and characterization of functionalized single walled carbon nanotubes (fSWCNT)/ Hydroxyapatite (HAp)-Nylon hybridized composite biomaterial to study the mechanical properties

NASA Astrophysics Data System (ADS)

Khanal, Suraj; Leventouri, Theodora; Mahfuz, Hassan; Rondinone, Adam

2014-03-01

Synthetic hydroxyapatite (HAp) bears poor mechanical properties that limit its applicability in orthopedics. We study the possibility of overcoming such limitations by incorporating functionalized single walled carbon nanotubes (fSWCNT) in a biocompatible/bioactive nano-composite. We present results from synthesis and characterization of samples prepared under different processing parameters. Ultra sonication method was to disperse functionalized single walled carbon nanotubes (fSWCNT) in HAp followed by a simple hot assorting method to incorporate with polymerized ɛ-caprolactam. The fracture toughness of the composite materials was tested in compliance with the ASTM D-5045 standard. We have found that while the fracture toughness strongly depends on the processing parameters, a value comparable to the one for cortical bone is achieved. Mechanical properties, electron microscopy and crystal structure properties of the composite materials will be discussed.

Data supporting the prediction of the properties of eutectic organic phase change materials.

PubMed

Kahwaji, Samer; White, Mary Anne

2018-04-01

The data presented in this article include the molar masses, melting temperatures, latent heats of fusion and temperature-dependent heat capacities of fifteen fatty acid phase change materials (PCMs). The data are used in conjunction with the thermodynamic models discussed in Kahwaji and White (2018) [1] to develop a computational tool that calculates the eutectic compositions and thermal properties of eutectic mixtures of PCMs. The computational tool is part of this article and consists of a Microsoft Excel® file available in Mendeley Data repository [2]. A description of the computational tool along with the properties of nearly 100 binary mixtures of fatty acid PCMs calculated using this tool are also included in the present article. The Excel® file is designed such that it can be easily modified or expanded by users to calculate the properties of eutectic mixtures of other classes of PCMs.

Using surfaces, ligands, and dimensionality to obtain desired nanostructure properties

NASA Astrophysics Data System (ADS)

Nagpal, Prashant; Singh, Vivek; Ding, Yuchen

2014-03-01

Nanostructured materials are intensively investigated to obtain material properties different from their bulk counterparts. It has been demonstrated that nanoscaled semiconductor can have interesting size, shape and morphology dependent optoelectronic properties. But the effect of surfaces, ligands and dimensionality (0D quantum dots to 2D nanosheets) has been largely unexplored. Here, we will show how tuning the surface and dimensionality can affect the electronic states of the semiconductor, and how these states can play an important role in their fundamental photophysical properties or thermal transport. Using the specific case for silicon, we will show how ``new'' surface states in small uniform can lead to light absorption/emission without phonon assistance, while hindering the phonon-drag of charge carriers leading to low Seebeck coefficient for thermoelectric applications. These measurements will shed light on designing appropriate surface, size, and dimensionality for desired applications of nanostructured films.

Developing a New Thermophysical Model for Lunar Regolith Soil at Low Temperatures

NASA Astrophysics Data System (ADS)

Woods-Robinson, R.; Siegler, M. A.; Paige, D. A.

2016-12-01

The thermophysical properties of the lunar regolith soil have been thoroughly investigated within the temperature range of 100 - 400 K. Extensive laboratory measurements of temperature-dependent thermal conductivity and specific heat have been performed on lunar samples collected from the Apollo and Luna missions. However, recent thermal emission measurements from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment have revealed temperatures near the poles as low 20 K, far below where existing thermophysical models begin to break down. In the absence of comprehensive laboratory measurements of lunar soil thermal properties at these low temperatures (20 - 100 K), we investigate solid state theory and lunar simulant materials to derive a physically-based theoretical model of specific heat and thermal conductivity in lunar soils in the full range 20 - 400 K. The primary distinctions between this model and its predecessors are: The focus on soil bulk density as a master variable The temperature dependence of the solid conduction component of thermal conductivity at low temperatures, and The concept that the composition and modal petrology of grains - both amorphous and crystalline components - could significantly influence thermal properties of the bulk soil. The simplest version of this model, which assumes that the soil behaves predominantly as a homogeneous particulate material composed of amorphous grains, shows that at low temperatures (20 - 100 K), specific heat is likely higher than expected from current models ( 0.027 J/gK at 20 K) and that thermal conductivity is almost an order of magnitude lower than has generally been assumed in the literature.Any higher-order approximation is difficult at this stage; the thermal conductivity at low temperature could vary drastically depending on the constituent grain materials, their degree of crystallinity, and contributions from phonon scattering modes, among other factors. We use a one-dimensional thermal model to illustrate the effects of our model on diurnal surface temperature variations in permanently shadowed regions on the moon. We aim to lay the theoretical foundation for a new approach to model thermal properties of regolith materials, and to justify the importance of new laboratory measurements of lunar soil below 100 K.

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

Fernando, Amendra; Weerawardene, K. L. Dimuthu M.; Karimova, Natalia V.

Here, metal, metal oxide, and metal chalcogenide materials have a wide variety of applications. For example, many metal clusters and nanoparticles are used as catalysts for reactions varying from the oxidation of carbon monoxide to the reduction of protons to hydrogen gas. Noble metal nanoparticles have unique optical properties such as a surface plasmon resonance for large nanoparticles that yield applications in sensing and photonics. In addition, a number of transition metal clusters are magnetic. Metal oxide clusters and surfaces are commonly used as catalysts for reactions such as water splitting. Both metal oxide and metal chalcogenide materials can bemore » semiconducting, which leads to applications in sensors, electronics, and solar cells. Many researchers have been interested in studying nanoparticles and/or small clusters of these materials. Some of the system sizes under investigation have been experimentally synthesized, which enables direct theory–experiment comparison. Other clusters that have been examined theoretically are of interest as models of larger systems or surfaces. Often, the size-dependence of their properties such as their HOMO–LUMO gap, magnetic properties, optical properties, etc., is of interest.« less

Numerical Estimation of the Elastic Properties of Thin-Walled Structures Manufactured from Short-Fiber-Reinforced Thermoplastics

NASA Astrophysics Data System (ADS)

Altenbach, H.; Naumenko, K.; L'vov, G. I.; Pilipenko, S. N.

2003-05-01

A model which allows us to estimate the elastic properties of thin-walled structures manufactured by injection molding is presented. The starting step is the numerical prediction of the microstructure of a short-fiber-reinforced composite developed during the filling stage of the manufacturing process. For this purpose, the Moldflow Plastic Insight® commercial program is used. As a result of simulating the filling process, a second-rank orientation tensor characterizing the microstructure of the material is obtained. The elastic properties of the prepared material locally depend on the orientational distribution of fibers. The constitutive equation is formulated by means of orientational averaging for a given orientation tensor. The tensor of elastic material properties is computed and translated into the format for a stress-strain analysis based on the ANSYSÒ finite-element code. The numerical procedure and the convergence of results are discussed for a thin strip, a rectangular plate, and a shell of revolution. The influence of manufacturing conditions on the stress-strain state of statically loaded thin-walled elements is illustrated.

Additives for cement compositions based on modified peat

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

Kopanitsa, Natalya, E-mail: kopanitsa@mail.ru; Sarkisov, Yurij, E-mail: sarkisov@tsuab.ru; Gorshkova, Aleksandra, E-mail: kasatkina.alexandra@gmail.com

High quality competitive dry building mixes require modifying additives for various purposes to be included in their composition. There is insufficient amount of quality additives having stable properties for controlling the properties of cement compositions produced in Russia. Using of foreign modifying additives leads to significant increasing of the final cost of the product. The cost of imported modifiers in the composition of the dry building mixes can be up to 90% of the material cost, depending on the composition complexity. Thus, the problem of import substitution becomes relevant, especially in recent years, due to difficult economic situation. The articlemore » discusses the possibility of using local raw materials as a basis for obtaining dry building mixtures components. The properties of organo-mineral additives for cement compositions based on thermally modified peat raw materials are studied. Studies of the structure and composition of the additives are carried out by physicochemical research methods: electron microscopy and X-ray analysis. Results of experimental research showed that the peat additives contribute to improving of cement-sand mortar strength and hydrophysical properties.« less

Bilayered graphene/h-BN with folded holes as new nanoelectronic materials: modeling of structures and electronic properties

PubMed Central

Chernozatonskii, Leonid A.; Demin, Viсtor A.; Bellucci, Stefano

2016-01-01

The latest achievements in 2-dimensional (2D) material research have shown the perspective use of sandwich structures in nanodevices. We demonstrate the following generation of bilayer materials for electronics and optoelectronics. The atomic structures, the stability and electronic properties of Moiré graphene (G)/h-BN bilayers with folded nanoholes have been investigated theoretically by ab-initio DFT method. These perforated bilayers with folded hole edges may present electronic properties different from the properties of both graphene and monolayer nanomesh structures. The closing of the edges is realized by C-B(N) bonds that form after folding the borders of the holes. Stable ≪round≫ and ≪triangle≫ holes organization are studied and compared with similar hole forms in single layer graphene. The electronic band structures of the considered G/BN nanomeshes reveal semiconducting or metallic characteristics depending on the sizes and edge terminations of the created holes. This investigation of the new types of G/BN nanostructures with folded edges might provide a directional guide for the future of this emerging area. PMID:27897237

General introduction: Liquid and solid (materials, main properties and applications …)

NASA Astrophysics Data System (ADS)

Zabler, Simon

2014-10-01

A general introduction about the diversity of foam structures is given with focus onto the structural, mechanical and dynamical properties at hand. Two classes of materials are addressed: liquid and semi-solid foams, on the one hand, solid foams, on the other hand. The latter can be subdivided into metallic, ceramic and organic foams, depending on the nature of the solid skeleton that supports the overall cell structure. Solid foams generally stem from the concept of mechanical light-weight structures, but they can just as well be employed for their large surface area as well as for their acoustic and thermal properties. Modern biomaterials use tailored ceramic or organo-ceramic foams as bone scaffolds, whereas hierarchically micro- and nanoporous structures are being used by chemistry to control catalytic reactions. Future materials design and development is going to rely increasingly on natural and synthetic foam structures and properties, be it food, thermal insulators or car frames, thus giving a promising outlook onto the foam research and development that is about to come. xml:lang="fr"

Synthesis and properties of the compound: LiNi 3/5Cu 2/5VO 4

NASA Astrophysics Data System (ADS)

Ram, Moti

2009-12-01

The LiNi 3/5Cu 2/5VO 4 is synthesized by solution-based chemical method and its formation has been checked by X-ray diffraction (XRD) study. XRD study shows a tetragonal unit cell structure with lattice parameters of a = 11.6475 (18) Å, c = 2.4855 (18) Å and c/ a = 0.2134 Å. Electrical properties are verified using complex impedance spectroscopy (CIS) technique. Complex impedance analysis reveals following points: (i) the bulk contribution to electrical properties up to 200 °C, (ii) the bulk and grain boundary contribution at T ≥ 225 °C, (iii) the presence of temperature dependent electrical relaxation phenomena in the material. D.c. conductivity study indicates that electrical conduction in the material is a thermally activated process.

How Water’s Properties Are Encoded in Its Molecular Structure and Energies

PubMed Central

2017-01-01

How are water’s material properties encoded within the structure of the water molecule? This is pertinent to understanding Earth’s living systems, its materials, its geochemistry and geophysics, and a broad spectrum of its industrial chemistry. Water has distinctive liquid and solid properties: It is highly cohesive. It has volumetric anomalies—water’s solid (ice) floats on its liquid; pressure can melt the solid rather than freezing the liquid; heating can shrink the liquid. It has more solid phases than other materials. Its supercooled liquid has divergent thermodynamic response functions. Its glassy state is neither fragile nor strong. Its component ions—hydroxide and protons—diffuse much faster than other ions. Aqueous solvation of ions or oils entails large entropies and heat capacities. We review how these properties are encoded within water’s molecular structure and energies, as understood from theories, simulations, and experiments. Like simpler liquids, water molecules are nearly spherical and interact with each other through van der Waals forces. Unlike simpler liquids, water’s orientation-dependent hydrogen bonding leads to open tetrahedral cage-like structuring that contributes to its remarkable volumetric and thermal properties. PMID:28949513

Modifying the Interface Edge to Control the Electrical Transport Properties of Nanocontacts to Nanowires.

PubMed

Lord, Alex M; Ramasse, Quentin M; Kepaptsoglou, Despoina M; Evans, Jonathan E; Davies, Philip R; Ward, Michael B; Wilks, Steve P

2017-02-08

Selecting the electrical properties of nanomaterials is essential if their potential as manufacturable devices is to be reached. Here, we show that the addition or removal of native semiconductor material at the edge of a nanocontact can be used to determine the electrical transport properties of metal-nanowire interfaces. While the transport properties of as-grown Au nanocatalyst contacts to semiconductor nanowires are well-studied, there are few techniques that have been explored to modify the electrical behavior. In this work, we use an iterative analytical process that directly correlates multiprobe transport measurements with subsequent aberration-corrected scanning transmission electron microscopy to study the effects of chemical processes that create structural changes at the contact interface edge. A strong metal-support interaction that encapsulates the Au nanocontacts over time, adding ZnO material to the edge region, gives rise to ohmic transport behavior due to the enhanced quantum-mechanical tunneling path. Removal of the extraneous material at the Au-nanowire interface eliminates the edge-tunneling path, producing a range of transport behavior that is dependent on the final interface quality. These results demonstrate chemically driven processes that can be factored into nanowire-device design to select the final properties.

Novel laser induced photoacoustic spectroscopy for instantaneous trace detection of explosive materials.

PubMed

El-Sharkawy, Yasser H; Elbasuney, Sherif

2017-08-01

Laser photoacoustic spectroscopy (LPAS) is an attractive technology in terms of simplicity, ruggedness, and overall sensitivity; it detects the time dependent heat generated (thermo-elastic effect) in the target via interaction with pulsed optical radiation. This study reports on novel LPAS technique that offers instant and standoff detection capabilities of trace explosives. Over the current study, light is generated using pulsed Q-switched Nd:YAG laser; the generated photoacoustic response in stimulated explosive material offers signature values that depend on the optical, thermal, and acoustical properties. The generated acoustic waves were captured using piezoelectric transducer as well as novel customized optical sensor with remotely laser interferometer probe. A digital signal processing algorithm was employed to identify explosive material signatures via calculation of characteristic optical properties (absorption coefficient), sound velocity, and frequency response of the generated photoacoustic signal. Customized LPAS technique was employed for instantaneous trace detection of three main different high explosive materials including TNT, RDX, and HMX. The main outcome of this study is that the novel customized optical sensor signals were validated with traditional piezoelectric transducer. Furthermore, the customized optical sensor offered standoff detection capabilities (10cm), fast response, high sensitivity, and enhanced signal to noise ratio. This manuscript shaded the light on the instant detection of trace explosive materials from significant standoffs using novel customized LPAS technique. Copyright © 2017 Elsevier B.V. All rights reserved.

Sulfate reduction in sulfuric material after re-flooding: Effectiveness of organic carbon addition and pH increase depends on soil properties.

PubMed

Yuan, Chaolei; Fitzpatrick, Rob; Mosley, Luke M; Marschner, Petra

2015-11-15

Sulfuric material is formed upon oxidation of sulfidic material; it is extremely acidic, and therefore, an environmental hazard. One option for increasing pH of sulfuric material may be stimulation of bacterial sulfate reduction. We investigated the effects of organic carbon addition and pH increase on sulfate reduction after re-flooding in ten sulfuric materials with four treatments: control, pH increase to 5.5 (+pH), organic carbon addition with 2% w/w finely ground wheat straw (+C), and organic carbon addition and pH increase (+C+pH). After 36 weeks, in five of the ten soils, only treatment +C+pH significantly increased the concentration of reduced inorganic sulfur (RIS) compared to the control and increased the soil pore water pH compared to treatment+pH. In four other soils, pH increase or/and organic carbon addition had no significant effect on RIS concentration compared to the control. The RIS concentration in treatment +C+pH as percentage of the control was negatively correlated with soil clay content and initial nitrate concentration. The results suggest that organic carbon addition and pH increase can stimulate sulfate reduction after re-flooding, but the effectiveness of this treatment depends on soil properties. Copyright © 2015 Elsevier B.V. All rights reserved.

Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing.

PubMed

Luecke, William E; Slotwinski, John A

2014-01-01

Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands.

Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing

PubMed Central

Luecke, William E; Slotwinski, John A

2014-01-01

Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands. PMID:26601037

Interface failure modes explain non-monotonic size-dependent mechanical properties in bioinspired nanolaminates.

PubMed

Song, Z Q; Ni, Y; Peng, L M; Liang, H Y; He, L H

2016-03-31

Bioinspired discontinuous nanolaminate design becomes an efficient way to mitigate the strength-ductility tradeoff in brittle materials via arresting the crack at the interface followed by controllable interface failure. The analytical solution and numerical simulation based on the nonlinear shear-lag model indicates that propagation of the interface failure can be unstable or stable when the interfacial shear stress between laminae is uniform or highly localized, respectively. A dimensionless key parameter defined by the ratio of two characteristic lengths governs the transition between the two interface-failure modes, which can explain the non-monotonic size-dependent mechanical properties observed in various laminate composites.

Non-linear properties of metallic cellular materials with a negative Poisson's ratio

NASA Technical Reports Server (NTRS)

Choi, J. B.; Lakes, R. S.

1992-01-01

Negative Poisson's ratio copper foam was prepared and characterized experimentally. The transformation into re-entrant foam was accomplished by applying sequential permanent compressions above the yield point to achieve a triaxial compression. The Poisson's ratio of the re-entrant foam depended on strain and attained a relative minimum at strains near zero. Poisson's ratio as small as -0.8 was achieved. The strain dependence of properties occurred over a narrower range of strain than in the polymer foams studied earlier. Annealing of the foam resulted in a slightly greater magnitude of negative Poisson's ratio and greater toughness at the expense of a decrease in the Young's modulus.

Temperature Dependent Electrical and Micromechanical Properties of Lanthanum Titanate with Additions of Yttria

NASA Technical Reports Server (NTRS)

Goldsby, Jon C.

2003-01-01

Lanthanum titanate (La2Ti2O7) a layered distorted perovskite (1) with space group Pna2(sub 1) has been shown to have potential as a high temperature piezoelectric (2). However this highly refractory oxide compound must be consolidated at relatively high temperatures approximately 1400 C. Commercial La2Ti207 powders were mechanically alloyed with additions of Y2O3 to lower the consolidation temperature by 300 C and to provide post processing mechanical stability. Temperature dependent electrical, elastic and anelastic behavior were selected as nondestructive means of evaluating the effects of yttria on the properties of this ferroceramic material.

Physically based reflectance model utilizing polarization measurement.

PubMed

Nakano, Takayuki; Tamagawa, Yasuhisa

2005-05-20

A surface bidirectional reflectance distribution function (BRDF) depends on both the optical properties of the material and the microstructure of the surface and appears as combination of these factors. We propose a method for modeling the BRDF based on a separate optical-property (refractive-index) estimation by polarization measurement. Because the BRDF and the refractive index for precisely the same place can be determined, errors cased by individual difference or spatial dependence can be eliminated. Our BRDF model treats the surface as an aggregation of microfacets, and the diffractive effect is negligible because of randomness. An example model of a painted aluminum plate is presented.

Frequency dependence of electrical properties of polyvinylidene fluoride/graphite electrode waste/natural carbon black composite

NASA Astrophysics Data System (ADS)

Insiyanda, D. R.; Indayaningsih, N.; Prihandoko, B.; Subhan, A.; Khaerudini, D. S.; Widodo, H.; Destyorini, F.; Chaer, A.

2018-03-01

Polyvinylidene fluoride (PVdF) is a semi-crystalline thermoplastic material with remarkably high piezoelectric coefficient and an attractive polymer matrix for micro-composite with superior mechanical and electrical properties. The conductive filler is obtained from Graphite Electrode Waste (GEW) and Natural Carbon Black (NCB). The variation of composite content (%) of PVdF/NCB/GEW were 100/0/0, 95/5/0, 95/0/5, 95/2.5/2.5. This experiment employed dry dispersion method for material mixing. The materials were then moulded using hot press machine with compression parameters of P = 5.5 MPa, T = 150 °C, t = 60 minutes, A = 5×5×(0.2 - 0.4) cm3. The electrical conductivity properties of pure PVdF, as well as PVdF/GEW, PVdF/NCB, and PVdF/NCB/GEW composites were investigated in a frequency range of 100 to 100000 Hz. The PVdF/GEW sample obtained the highest electrical conductivity. It is concluded that GEW and NCB can be incorporated into PVdF as a conductive filler to increase the conductivity of conductive material composite without solvent.

Expanded experimental parameter space of semiflexible polymer assemblies through programmable nanomaterials

NASA Astrophysics Data System (ADS)

Smith, David; Schuldt, Carsten; Lorenz, Jessica; Tschirner, Teresa; Moebius-Winkler, Maximilian; Kaes, Josef; Glaser, Martin; Haendler, Tina; Schnauss, Joerg

2015-03-01

Biologically evolved materials are often used as inspiration in the development of new materials as well as examinations into the underlying physical principles governing their behavior. For instance, the biopolymer constituents of the highly dynamic cellular cytoskeleton such as actin have inspired a deep understanding of soft polymer-based materials. However, the molecular toolbox provided by biological systems has been evolutionarily optimized to carry out the necessary functions of cells, and the inability modify basic properties such as biopolymer stiffness hinders a meticulous examination of parameter space. Using actin as inspiration, we circumvent these limitations using model systems assembled from programmable materials such as DNA. Nanorods with comparable, but controllable dimensions and mechanical properties as actin can be constructed from small sets of specially designed DNA strands. In entangled gels, these allow us to systematically determine the dependence of network mechanical properties on parameters such as persistence length and crosslink strength. At higher concentrations in the presence of local attractive forces, we see a transition to highly-ordered bundled and ``aster'' phases similar to those previously characterized in systems of actin or microtubules.

Depth-Dependent Defect Studies Using Coherent Acoustic Phonons

DTIC Science & Technology

2014-09-29

using CAP waves as an active moving interface to induce local changes in electric, acoustic , and optical properties. This is able to generate ultrafast...the elastic strain component [6]. b) Modification of the crystal lattice due to transient strain caused by the coherent acoustic phonon wave . The...opto-electronic properties of materials. We are also using CAP waves as an active moving interface to induce local changes in electric, acoustic , and

Modeling of Microstructure Evolution During the Thermomechanical Processing of Titanium Alloys (Preprint)

DTIC Science & Technology

2008-07-01

Tailoring the Properties of Aluminum and Titanium Alloys", Deformation, Processing, and Structure , G. Krauss, ed., ASM International, Materials Park, OH...1984, pp. 279-354. 51. G.W. Kuhlman, "A Critical Appraisal of Thermomechanical Processing of Structural Titanium Alloys", Microstructure/ Property ... titanium alloys is heavily dependent on the allotropic transformation from a hexagonal-close-packed crystal structure (denoted as alpha phase) found at

Determination of orthotropic mechanical properties of 3D printed parts for structural health monitoring

NASA Astrophysics Data System (ADS)

Poissenot-Arrigoni, Bastien; Scheyer, Austin; Anton, Steven R.

2017-04-01

The evolution of additive manufacturing has allowed engineers to use 3D printing for many purposes. As a natural consequence of the 3D printing process, the printed object is anisotropic. As part of an ongoing project to embed piezoelectric devices in 3D printed structures for structural health monitoring (SHM), this study aims to find the mechanical properties of the 3D printed material and the influence of different external factors on those properties. The orthotropic mechanical properties of a 3D printed structure are dependent on the printing parameters used to create the structure. In order to develop an orthotropic material model, mechanical properties will be found experimentally from additively manufactured samples created from polylactic acid (PLA) using a consumer-level fused deposition modeling (FDM) printer; the Lulzbot TAZ 6. Nine mechanical constants including three Young's moduli, three Poisson's ratios, and three shear moduli are needed to fully describe the 3D elastic behavior of the material. Printed specimens with different raster orientations and print orientations allow calculation of the different material constants. In this work, seven of the nine mechanical constants were found. Two shear moduli were unable to be measured due to difficulties in printing two of the sample orientations. These mechanical properties are needed in order to develop orthotropic material models of systems employing 3D printed PLA. The results from this paper will be used to create a model of a piezoelectric transducer embedded in a 3D printed structure for structural health monitoring.

Strain-tuned optoelectronic properties of hollow gallium sulphide microspheres.

PubMed

Zhang, Yin; Chen, Chen; Liang, C Y; Liu, Z W; Li, Y S; Che, Renchao

2015-11-07

Sulfide semiconductors have attracted considerable attention. The main challenge is to prepare materials with a designable morphology, a controllable band structure and optoelectronic properties. Herein, we report a facile chemical transportation reaction for the synthesis of Ga2S3 microspheres with novel hollow morphologies and partially filled volumes. Even without any extrinsic dopant, photoluminescence (PL) emission wavelength could be facilely tuned from 635 to 665 nm, depending on its intrinsic inhomogeneous strain distribution. Geometric phase analysis (GPA) based on high-resolution transmission electron microscopy (HRTEM) imaging reveals that the strain distribution and the associated PL properties can be accurately controlled by changing the growth temperature gradient, which depends on the distance between the boats used for raw material evaporation and microsphere deposition. The stacking-fault density, lattice distortion degree and strain distribution at the shell interfacial region of the Ga2S3 microspheres could be readily adjusted. Ab initio first-principles calculations confirm that the lowest conductive band (LCB) is dominated by S-3s and Ga-4p states, which shift to the low-energy band as a result of the introduction of tensile strain, well in accordance with the observed PL evolution. Therefore, based on our strain driving strategy, novel guidelines toward the reasonable design of sulfide semiconductors with tunable photoluminescence properties are proposed.

3D printing of photocurable poly(glycerol sebacate) elastomers.

PubMed

Yeh, Yi-Cheun; Highley, Christopher B; Ouyang, Liliang; Burdick, Jason A

2016-10-07

Three-dimensional (3D) printed scaffolds have great potential in biomedicine; however, it is important that we are able to design such scaffolds with a range of diverse properties towards specific applications. Here, we report the extrusion-based 3D printing of biodegradable and photocurable acrylated polyglycerol sebacate (Acr-PGS) to fabricate scaffolds with elastic properties. Two Acr-PGS macromers were synthesized with varied molecular weights and viscosity, which were then blended to obtain photocurable macromer inks with a range of viscosities. The quality of extruded and photocured scaffolds was dependent on the initial ink viscosity, with flow of printed material resulting in a loss of structural resolution or sample breaking observed with too low or too high viscosity inks, respectively. However, scaffolds with high print resolution and up to ten layers were fabricated with an optimal ink viscosity. The mechanical properties of printed scaffolds were dependent on printing density, where the scaffolds with lower printing density possessed lower moduli and failure properties than higher density scaffolds. The 3D printed scaffolds supported the culture of 3T3 fibroblasts and both spreading and proliferation were observed, indicating that 3D printed Acr-PGS scaffolds are cytocompatible. These results demonstrate that Acr-PGS is a promising material for the fabrication of elastomeric scaffolds for biomedical applications.

Remote Determination of Time-Dependent Stiffness of Surface-Degrading-Polymer Scaffolds Via Synchrotron-Based Imaging.

PubMed

Bawolin, N K; Chen, X B

2017-04-01

Surface-degrading polymers have been widely used to fabricate scaffolds with the mechanical properties appropriate for tissue regeneration/repair. During their surface degradation, the material properties of polymers remain approximately unchanged, but the scaffold geometry and thus mechanical properties vary with time. This paper presents a novel method to determine the time-dependent mechanical properties, particularly stiffness, of scaffolds from the geometric changes captured by synchrotron-based imaging, with the help of finite element analysis (FEA). Three-dimensional (3D) tissue scaffolds were fabricated from surface-degrading polymers, and during their degradation, the tissue scaffolds were imaged via the synchrotron-based imaging to characterize their changing geometry. On this basis, the stiffness behavior of scaffolds was estimated from the FEA, and the results obtained were compared to the direct measurements of scaffold stiffness from the load-displacement material testing. The comparison illustrates that the Young's moduli estimated from the FEA and characterized geometry are in agreement with the ones of direct measurements. The developed method of estimating the mechanical behavior was also demonstrated effective with a nondegrading scaffold that displays the nonlinear stress-strain behavior. The in vivo monitoring of Young's modulus by morphology characterization also suggests the feasibility of characterizing experimentally the difference between in vivo and in vitro surface degradation of tissue engineering constructs.

Controlled nanostructrures formation by ultra fast laser pulses for color marking.

PubMed

Dusser, B; Sagan, Z; Soder, H; Faure, N; Colombier, J P; Jourlin, M; Audouard, E

2010-02-01

Precise nanostructuration of surface and the subsequent upgrades in material properties is a strong outcome of ultra fast laser irradiations. Material characteristics can be designed on mesoscopic scales, carrying new optical properties. We demonstrate in this work, the possibility of achieving material modifications using ultra short pulses, via polarization dependent structures generation, that can generate specific color patterns. These oriented nanostructures created on the metal surface, called ripples, are typically smaller than the laser wavelength and in the range of visible spectrum. In this way, a complex colorization process of the material, involving imprinting, calibration and reading, has been performed to associate a priori defined colors. This new method based on the control of the laser-driven nanostructure orientation allows cumulating high quantity of information in a minimal surface, proposing new applications for laser marking and new types of identifying codes.