Identifying Structure-Property Relationships Through DREAM.3D Representative Volume Elements and DAMASK Crystal Plasticity Simulations: An Integrated Computational Materials Engineering Approach

NASA Astrophysics Data System (ADS)

Diehl, Martin; Groeber, Michael; Haase, Christian; Molodov, Dmitri A.; Roters, Franz; Raabe, Dierk

2017-05-01

Predicting, understanding, and controlling the mechanical behavior is the most important task when designing structural materials. Modern alloy systems—in which multiple deformation mechanisms, phases, and defects are introduced to overcome the inverse strength-ductility relationship—give raise to multiple possibilities for modifying the deformation behavior, rendering traditional, exclusively experimentally-based alloy development workflows inappropriate. For fast and efficient alloy design, it is therefore desirable to predict the mechanical performance of candidate alloys by simulation studies to replace time- and resource-consuming mechanical tests. Simulation tools suitable for this task need to correctly predict the mechanical behavior in dependence of alloy composition, microstructure, texture, phase fractions, and processing history. Here, an integrated computational materials engineering approach based on the open source software packages DREAM.3D and DAMASK (Düsseldorf Advanced Materials Simulation Kit) that enables such virtual material development is presented. More specific, our approach consists of the following three steps: (1) acquire statistical quantities that describe a microstructure, (2) build a representative volume element based on these quantities employing DREAM.3D, and (3) evaluate the representative volume using a predictive crystal plasticity material model provided by DAMASK. Exemplarily, these steps are here conducted for a high-manganese steel.

The influence of ZrO2/20%Y2O3 and Al2O3 deposited coatings to the behavior of an aluminum alloy subjected to mechanical shock

NASA Astrophysics Data System (ADS)

Pintilei, G. L.; Crismaru, V. I.; Abrudeanu, M.; Munteanu, C.; Luca, D.; Istrate, B.

2015-10-01

Aluminum alloys are used in the aerospace industry due to their good mechanical properties and their low density compared with the density of steels. Usually the parts made of aluminum alloys contribute to the structural frame of aircrafts and they must withstand static and variable mechanical loads and also mechanical loads applied in a very short time which determine different phenomenon's in the material behavior then static or fatigue loads. This paper analysis the resilience of a 2024 aluminum alloy subjected to shock loads and the way how a coating can improve its behavior. For improving the behavior two coatings were considered: Al2O3 with 99.5% purity and ZrO2/20%Y2O3. The coatings were deposited on the base material by plasma spraying. The samples with and without coating were subject to mechanical shock to determine the resilience of the materials and the cracks propagation was investigated using SEM analysis. To highlight the physical phenomenon's that appear in the samples during the mechanical shock, explicit finite element analysis were done using Ansys 14.5 software.

Accelerated aging studies of UHMWPE. I. Effect of resin, processing, and radiation environment on resistance to mechanical degradation.

PubMed

Edidin, A A; Herr, M P; Villarraga, M L; Muth, J; Yau, S S; Kurtz, S M

2002-08-01

The resin and processing route have been identified as potential variables influencing the mechanical behavior, and hence the clinical performance, of ultra-high molecular weight polyethylene (UHMWPE) orthopedic components. Researchers have reported that components fabricated from 1900 resin may oxidize to a lesser extent than components fabricated from GUR resin during shelf aging after gamma sterilization in air. Conflicting reports on the oxidation resistance for 1900 raise the question of whether resin or manufacturing method, or an interaction between resin and manufacturing method, influences the mechanical behavior of UHMWPE. We conducted a series of accelerated aging studies (no aging, aging in oxygen or in nitrogen) to systematically examine the influence of resin (GUR or 1900), manufacturing method (bulk compression molding or extrusion), and sterilization method (none, in air, or in nitrogen) on the mechanical behavior of UHMWPE. The small punch testing technique was used to evaluate the mechanical behavior of the materials, and Fourier transform infrared spectroscopy was used to characterize the oxidation in selected samples. Our study showed that the sterilization environment, aging condition, and specimen location (surface or subsurface) significantly affected the mechanical behavior of UHMWPE. Each of the three polyethylenes evaluated seem to degrade according to a similar pathway after artificial aging in oxygen and gamma irradiation in air. The initial ability of the materials to exhibit post-yield strain hardening was significantly compromised by degradation. In general, there were only minor differences in the aging behavior of molded and extruded GUR 1050, whereas the molded 1900 material seemed to degrade slightly faster than either of the 1050 materials. Copyright 2002 Wiley Periodicals, Inc.

Comparative Analysis of the Biaxial Mechanical Behavior of Carotid Wall Tissue and Biological and Synthetic Materials Used for Carotid Patch Angioplasty

PubMed Central

Kamenskiy, Alexey V.; Pipinos, Iraklis I.; MacTaggart, Jason N.; Jaffar Kazmi, Syed A.; Dzenis, Yuris A.

2011-01-01

Patch angioplasty is the most common technique used for the performance of carotid endarterectomy. A large number of patching materials are available for use while new materials are being continuously developed. Surprisingly little is known about the mechanical properties of these materials and how these properties compare with those of the carotid artery wall. Mismatch of the mechanical properties can produce mechanical and hemodynamic effects that may compromise the long-term patency of the endarterectomized arterial segment. The aim of this paper was to systematically evaluate and compare the biaxial mechanical behavior of the most commonly used patching materials. We compared PTFE (n = 1), Dacron (n = 2), bovine pericardium (n = 10), autogenous greater saphenous vein (n = 10), and autogenous external jugular vein (n = 9) with the wall of the common carotid artery (n = 18). All patching materials were found to be significantly stiffer than the carotid wall in both the longitudinal and circumferential directions. Synthetic patches demonstrated the most mismatch in stiffness values and vein patches the least mismatch in stiffness values compared to those of the native carotid artery. All biological materials, including the carotid artery, demonstrated substantial nonlinearity, anisotropy, and variability; however, the behavior of biological and biologically-derived patches was both qualitatively and quantitatively different from the behavior of the carotid wall. The majority of carotid arteries tested were stiffer in the circumferential direction, while the opposite anisotropy was observed for all types of vein patches and bovine pericardium. The rates of increase in the nonlinear stiffness over the physiological stress range were also different for the carotid and patching materials. Several carotid wall samples exhibited reverse anisotropy compared to the average behavior of the carotid tissue. A similar characteristic was observed for two of 19 vein patches. The obtained results quantify, for the first time, significant mechanical dissimilarity of the currently available patching materials and the carotid artery. The results can be used as guidance for designing more efficient patches with mechanical properties resembling those of the carotid wall. The presented systematic comparative mechanical analysis of the existing patching materials provides valuable information for patch selection in the daily practice of carotid surgery and can be used in future clinical studies comparing the efficacy of different patches in the performance of carotid endarterectomy. PMID:22168740

Self-repairing systems based on ionomers and epoxidized natural rubber blends.

PubMed

Rahman, Md Arifur; Penco, Maurizio; Peroni, Isabella; Ramorino, Giorgio; Grande, Antonio Mattia; Di Landro, Luca

2011-12-01

The development of materials with the ability of intrinsic self-repairing after damage in a fashion resembling that of living tissues has important scientific and technological implications, particularly in relation to cost-effective approaches toward damage management of materials. Natural rubbers with epoxy functional groups in the macromolecular chain (ENR) and ethylene-methacrylic acid ionomers having acid groups partially neutralized with metal ions possess self-repairing behavior following high energy impacts. This research investigates the self-repairing behavior of both ENR and ionomers during ballistic puncture test on the basis of their thermal and mechanical properties. Heterogeneous blending of ionomers and ENR have also been used here as a strategy to tune the thermal and mechanical properties of the materials. Interestingly, blends of sodium ion containing ionomer exhibit complete self-repairing behavior, whereas blends of zinc ion containing ionomer show limited mending. The chemical structure studied by FTIR and thermal analysis shows that both ion content of ionomer and functionality of ENR have significant influence on the self-repairing behavior of blends. The mobility of rubbery phases along with its interaction to ionomer phase in the blends significantly changes the mending capability of materials. The healing behavior of the materials has been discussed on the basis of their thermal, mechanical, and rheological tests for each materials. © 2011 American Chemical Society

INFLUENCE OF HIGH-ENERGY FORMING ON THE BEHAVIOR OF MATERIALS (EINFLUSS DER HOCHENERGIEUMFORMUNG AUF DAS WERKSTOFFVERHALTEN),

DTIC Science & Technology

MATERIAL FORMING, METALS), (*METALS, MECHANICAL PROPERTIES), EXPLOSIVE FORMING, ELECTROFORMING, HYDROFORMING (MECHANICAL), IRON, STEEL, NICKEL, NIOBIUM, TENSILE PROPERTIES, TANTALUM, DEFORMATION, EAST GERMANY.

Passive and active mechanical properties of biotemplated ceramics revisited.

PubMed

Van Opdenbosch, Daniel; Fritz-Popovski, Gerhard; Plank, Johann; Zollfrank, Cordt; Paris, Oskar

2016-10-13

Living nature and human technology apply different principles to create hard, strong and tough materials. In this review, we compare and discuss prominent aspects of these alternative strategies, and demonstrate for selected examples that nanoscale-precision biotemplating is able to produce uncommon mechanical properties as well as actuating behavior, resembling to some extent the properties of the original natural templates. We present and discuss mechanical testing data showing for the first time that nanometer-precision biotemplating can lead to porous ceramic materials with deformation characteristics commonly associated with either biological or highly advanced technical materials. We also review recent findings on the relation between hierarchical structuring and humidity-induced directional motion. Finally, we discuss to which extent the observed behavior is in agreement with previous results and theories on the mechanical properties of multiscale hierarchical materials, as well as studies of highly disperse technical materials, together with an outlook for further lines of investigation.

Experimental validation of 3D printed material behaviors and their influence on the structural topology design

NASA Astrophysics Data System (ADS)

Yang, Kai Ke; Zhu, Ji Hong; Wang, Chuang; Jia, Dong Sheng; Song, Long Long; Zhang, Wei Hong

2018-05-01

The purpose of this paper is to investigate the structures achieved by topology optimization and their fabrications by 3D printing considering the particular features of material microstructures and macro mechanical performances. Combining Digital Image Correlation and Optical Microscope, this paper experimentally explored the anisotropies of stiffness and strength existing in the 3D printed polymer material using Stereolithography (SLA) and titanium material using Selective Laser Melting (SLM). The standard specimens and typical structures obtained by topology optimization were fabricated along different building directions. On the one hand, the experimental results of these SLA produced structures showed stable properties and obviously anisotropic rules in stiffness, ultimate strengths and places of fractures. Further structural designs were performed using topology optimization when the particular mechanical behaviors of SLA printed materials were considered, which resulted in better structural performances compared to the optimized designs using `ideal' isotropic material model. On the other hand, this paper tested the mechanical behaviors of SLM printed multiscale lattice structures which were fabricated using the same metal powder and the same machine. The structural stiffness values are generally similar while the strength behaviors show a difference, which are mainly due to the irregular surface quality of the tiny structural branches of the lattice. The above evidences clearly show that the consideration of the particular behaviors of 3D printed materials is therefore indispensable for structural design and optimization in order to improve the structural performance and strengthen their practical significance.

Experimental validation of 3D printed material behaviors and their influence on the structural topology design

NASA Astrophysics Data System (ADS)

Yang, Kai Ke; Zhu, Ji Hong; Wang, Chuang; Jia, Dong Sheng; Song, Long Long; Zhang, Wei Hong

2018-02-01

The purpose of this paper is to investigate the structures achieved by topology optimization and their fabrications by 3D printing considering the particular features of material microstructures and macro mechanical performances. Combining Digital Image Correlation and Optical Microscope, this paper experimentally explored the anisotropies of stiffness and strength existing in the 3D printed polymer material using Stereolithography (SLA) and titanium material using Selective Laser Melting (SLM). The standard specimens and typical structures obtained by topology optimization were fabricated along different building directions. On the one hand, the experimental results of these SLA produced structures showed stable properties and obviously anisotropic rules in stiffness, ultimate strengths and places of fractures. Further structural designs were performed using topology optimization when the particular mechanical behaviors of SLA printed materials were considered, which resulted in better structural performances compared to the optimized designs using `ideal' isotropic material model. On the other hand, this paper tested the mechanical behaviors of SLM printed multiscale lattice structures which were fabricated using the same metal powder and the same machine. The structural stiffness values are generally similar while the strength behaviors show a difference, which are mainly due to the irregular surface quality of the tiny structural branches of the lattice. The above evidences clearly show that the consideration of the particular behaviors of 3D printed materials is therefore indispensable for structural design and optimization in order to improve the structural performance and strengthen their practical significance.

Application of Video Image Correlation Techniques to the Space Shuttle External Tank Foam Materials

NASA Technical Reports Server (NTRS)

Hilburger, Mark W.; Nemeth, Michael P.

2005-01-01

Results that illustrate the use of a video-image-correlation-based displacement and strain measurement system to assess the effects of material nonuniformities on the behavior of the sprayed-on foam insulation (SOFI) used for the thermal protection system on the Space Shuttle External Tank are presented. Standard structural verification specimens for the SOFI material with and without cracks and subjected to mechanical or thermal loading conditions were tested. Measured full-field displacements and strains are presented for selected loading conditions to illustrate the behavior of the foam and the viability of the measurement technology. The results indicate that significant strain localization can occur in the foam because of material nonuniformities. In particular, elongated cells in the foam can interact with other geometric or material discontinuities in the foam and develop large-magnitude localized strain concentrations that likely initiate failures. Furthermore, some of the results suggest that continuum mechanics and linear elastic fracture mechanics might not adequately represent the physical behavior of the foam, and failure predictions based on homogeneous linear material models are likely to be inadequate.

Application of Video Image Correlation Techniques to the Space Shuttle External Tank Foam Materials

NASA Technical Reports Server (NTRS)

Hilburger, Mark W.; Nemeth, Michael P.

2006-01-01

Results that illustrate the use of a video-image-correlation-based displacement and strain measurement system to assess the effects of material nonuniformities on the behavior of the sprayed-on foam insulation (SOFI) used for the thermal protection system on the Space Shuttle External Tank are presented. Standard structural verification specimens for the SOFI material with and without cracks and subjected to mechanical or thermal loading conditions were tested. Measured full-field displacements and strains are presented for selected loading conditions to illustrate the behavior of the foam and the viability of the measurement technology. The results indicate that significant strain localization can occur in the foam because of material nonuniformities. In particular, elongated cells in the foam can interact with other geometric or material discontinuities in the foam and develop large-magnitude localized strain concentrations that likely initiate failures. Furthermore, some of the results suggest that continuum mechanics and linear elastic fracture mechanics might not adequately represent the physical behavior of the foam, and failure predictions based on homogeneous linear material models are likely to be inadequate.

Material and Mechanical Characterizations for Braided Composite Pressure Vessels

DTIC Science & Technology

1990-05-01

Effects on Mechanical Properties......... 16 2.3 Predictions of Hygrothermal Behavior of Braided Composites ....23 2.4 Summary... Behavior of Braided Composites 0 Predictions of the mechanical response of braided composites have not enjoyed the same plethora of attention given to...specific data for braided composite hygrothermomechanical behavior , broad conclusions developed from other studies may provide some insightful information

Mechanical modeling of self-expandable stent fabricated using braiding technology.

PubMed

Kim, Ju Hyun; Kang, Tae Jin; Yu, Woong-Ryeol

2008-11-14

The mechanical behavior of a stent is one of the important factors involved in ensuring its opening within arterial conduits. This study aimed to develop a mechanical model for designing self-expandable stents fabricated using braiding technology. For this purpose, a finite element model was constructed by developing a preprocessing program for the three-dimensional geometrical modeling of the braiding structure inside stents, and validated for various stents with different braiding structures. The constituent wires (Nitinol) in the braided stents were assumed to be superelastic material and their mechanical behavior was incorporated into the finite element software through a user material subroutine (VUMAT in ABAQUS) employing a one-dimensional superelastic model. For the verification of the model, several braided stents were manufactured using an automated braiding machine and characterized focusing on their compressive behavior. It was observed that the braided stents showed a hysteresis between their loading and unloading behavior when a compressive load was applied to the braided tube. Through the finite element analysis, it was concluded that the current mechanical model can appropriately predict the mechanical behavior of braided stents including such hysteretic behavior, and that the hysteresis was caused by the slippage between the constituent wires and their superelastic property.

Mechanical and Fatigue Properties of Additively Manufactured Metallic Materials

NASA Astrophysics Data System (ADS)

Yadollahi, Aref

This study aims to investigate the mechanical and fatigue behavior of additively manufactured metallic materials. Several challenges associated with different metal additive manufacturing (AM) techniques (i.e. laser-powder bed fusion and direct laser deposition) have been addressed experimentally and numerically. Experiments have been carried out to study the effects of process inter-layer time interval--i.e. either building the samples one-at-a-time or multi-at-a-time (in-parallel)--on the microstructural features and mechanical properties of 316L stainless steel samples, fabricated via a direct laser deposition (DLD). Next, the effect of building orientation--i.e. the orientation in which AM parts are built--on microstructure, tensile, and fatigue behaviors of 17-4 PH stainless steel, fabricated via a laser-powder bed fusion (L-PBF) method was investigated. Afterwards, the effect of surface finishing--here, as-built versus machined--on uniaxial fatigue behavior and failure mechanisms of Inconel 718 fabricated via a laser-powder bed fusion technique was sought. The numerical studies, as part of this dissertation, aimed to model the mechanical behavior of AM materials, under monotonic and cyclic loading, based on the observations and findings from the experiments. Despite significant research efforts for optimizing process parameters, achieving a homogenous, defect-free AM product--immediately after fabrication--has not yet been fully demonstrated. Thus, one solution for ensuring the adoption of AM materials for application should center on predicting the variations in mechanical behavior of AM parts based on their resultant microstructure. In this regard, an internal state variable (ISV) plasticity-damage model was employed to quantify the damage evolution in DLD 316L SS, under tensile loading, using the microstructural features associated with the manufacturing process. Finally, fatigue behavior of AM parts has been modeled based on the crack-growth concept. Using the FASTRAN code, the fatigue-life of L-PBF Inconel 718 was accurately calculated using the size and shape of process-induced voids in the material. In addition, the maximum valley depth of the surface profile was found to be an appropriate representative of the initial surface flaw for fatigue-life prediction of AM materials in an as-built surface condition.

High strain rate behavior of a SiC particulate reinforced Al{sub 2}O{sub 3} ceramic matrix composite

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

Hall, I.W.; Guden, M.

The high strain rate deformation behavior of composite materials is important for several reasons. First, knowledge of the mechanical properties of composites at high strain rates is needed for designing with these materials in applications where sudden changes in loading rates are likely to occur. Second, knowledge of both the dynamic and quasi-static mechanical responses can be used to establish the constitutive equations which are necessary to increase the confidence limits of these materials, particularly if they are to be used in critical structural applications. Moreover, dynamic studies and the knowledge gained form them are essential for the further developmentmore » of new material systems for impact applications. In this study, the high strain rate compressive deformation behavior of a ceramic matrix composite (CMC) consisting of SiC particles and an Al{sub 2}O{sub 3} matrix was studied and compared with its quasi-static behavior. Microscopic observations were conducted to investigate the deformation and fracture mechanism of the composite.« less

Mechanics of Granular Materials (MGM)

NASA Technical Reports Server (NTRS)

Alshibli, Khalid A.; Costes, Nicholas C.; Porter, Ronald F.

1996-01-01

The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extend derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

Nonlinear Inelastic Mechanical Behavior Of Epoxy Resin Polymeric Materials

NASA Astrophysics Data System (ADS)

Yekani Fard, Masoud

Polymer and polymer matrix composites (PMCs) materials are being used extensively in different civil and mechanical engineering applications. The behavior of the epoxy resin polymers under different types of loading conditions has to be understood before the mechanical behavior of Polymer Matrix Composites (PMCs) can be accurately predicted. In many structural applications, PMC structures are subjected to large flexural loadings, examples include repair of structures against earthquake and engine fan cases. Therefore it is important to characterize and model the flexural mechanical behavior of epoxy resin materials. In this thesis, a comprehensive research effort was undertaken combining experiments and theoretical modeling to investigate the mechanical behavior of epoxy resins subject to different loading conditions. Epoxy resin E 863 was tested at different strain rates. Samples with dog-bone geometry were used in the tension tests. Small sized cubic, prismatic, and cylindrical samples were used in compression tests. Flexural tests were conducted on samples with different sizes and loading conditions. Strains were measured using the digital image correlation (DIC) technique, extensometers, strain gauges, and actuators. Effects of triaxiality state of stress were studied. Cubic, prismatic, and cylindrical compression samples undergo stress drop at yield, but it was found that only cubic samples experience strain hardening before failure. Characteristic points of tensile and compressive stress strain relation and load deflection curve in flexure were measured and their variations with strain rate studied. Two different stress strain models were used to investigate the effect of out-of-plane loading on the uniaxial stress strain response of the epoxy resin material. The first model is a strain softening with plastic flow for tension and compression. The influence of softening localization on material behavior was investigated using the DIC system. It was found that compression plastic flow has negligible influence on flexural behavior in epoxy resins, which are stronger in pre-peak and post-peak softening in compression than in tension. The second model was a piecewise-linear stress strain curve simplified in the post-peak response. Beams and plates with different boundary conditions were tested and analytically studied. The flexural over-strength factor for epoxy resin polymeric materials were also evaluated.

Experimental study of thermo-mechanical behavior of a thermosetting shape-memory polymer

NASA Astrophysics Data System (ADS)

Liu, Ruoxuan; Li, Yunxin; Liu, Zishun

2018-01-01

The thermo-mechanical behavior of shape-memory polymers (SMPs) serves for the engineering applications of SMPs. Therefore the understanding of thermo-mechanical behavior of SMPs is of great importance. This paper investigates the influence of loading rate and loading level on the thermo-mechanical behavior of a thermosetting shape-memory polymer through experimental study. A series of cyclic tension tests and shape recovery tests at different loading conditions are performed to study the strain level and strain rate effect. The results of tension tests show that the thermosetting shape-memory polymer will behave as rubber material at temperature lower than the glass transition temperature (Tg) and it can obtain a large shape fix ratio at cyclic loading condition. The shape recovery tests exhibit that loading rate and loading level have little effect on the beginning and ending of shape recovery process of the thermosetting shape-memory polymer. Compared with the material which is deformed at temperature higher than Tg, the material deformed at temperature lower than Tg behaves a bigger recovery speed.

Hyper-elastic modeling and mechanical behavior investigation of porous poly-D-L-lactide/nano-hydroxyapatite scaffold material.

PubMed

Han, Quan Feng; Wang, Ze Wu; Tang, Chak Yin; Chen, Ling; Tsui, Chi Pong; Law, Wing Cheung

2017-07-01

Poly-D-L-lactide/nano-hydroxyapatite (PDLLA/nano-HA) can be used as the biological scaffold material in bone tissue engineering as it can be readily made into a porous composite material with excellent performance. However, constitutive modeling for the mechanical response of porous PDLLA/nano-HA under various stress conditions has been very limited so far. In this work, four types of fundamental compressible hyper-elastic constitutive models were introduced for constitutive modeling and investigation of mechanical behaviors of porous PDLLA/nano-HA. Moreover, the unitary expressions of Cauchy stress tensor have been derived for the PDLLA/nano-HA under uniaxial compression (or stretch), biaxial compression (or stretch), pure shear and simple shear load by using the theory of continuum mechanics. The theoretical results determined from the approach based on the Ogden compressible hyper-elastic constitutive model were in good agreement with the experimental data from the uniaxial compression tests. Furthermore, this approach can also be used to predict the mechanical behaviors of the porous PDLLA/nano-HA material under the biaxial compression (or stretch), pure shear and simple shear. Copyright © 2017 Elsevier Ltd. All rights reserved.

Production, characterization, and mechanical behavior of cementitious materials incorporating carbon nanofibers.

DOT National Transportation Integrated Search

2012-08-01

Carbon nanotubes (CNTs) and carbon nanofirbers (CNFs) have excellent properties : (mechanical, electrical, magnetic, etc.), which can make them effective : nanoreinforcements for improving the properties of materials. The incorporation of : CNT/Fs in...

Mechanical and time-dependent behavior of wood-plastic composites subjected to bending

Treesearch

S. E. Hamel; John Hermanson; S. M. Cramer

2015-01-01

The most popular use of wood–plastic composite (WPC) members in the United States has been as outdoor decking material in residential construction. If the use of these products expands into more structural applications, such as beams and joists, it is imperative that the material’s mechanical behavior be understood. Since most of the potential structural uses of this...

Molecular-Level Computational Investigation of Mechanical Transverse Behavior of p-Phenylene Terephthalamide (PPTA) Fibers

DTIC Science & Technology

2013-01-01

fabricated today are based on polymer matrix composites containing Kevlarw KM2 reinforcements , the present work will deal with generic PPTA fibers . In...Multi-length scale enriched continuum-level material model for Kevlarw- fiber reinforced polymer-matrix composites”, Journal of Materials...mechanical transverse behavior of p-phenylene terephthalamide (PPTA) fibers Purpose – A series of all-atom molecular-level computational analyses is

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.

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.

Characterization of the mechanical behavior of sea ice as a frictional material

NASA Astrophysics Data System (ADS)

Lade, Poul V.

2002-12-01

The mechanical properties of sea ice are determined by the formation process, and the consequent material behavior at the element scale exhibits viscoelastic behavior at the early loading stages, followed by brittle fracture or ductile, irrecoverable deformation that may be captured by hardening/softening plasticity models with nonassociated flow. Failure of sea ice under different loading conditions follows a pattern that demonstrates its highly cross-anisotropic nature as well as its behavior as a frictional material. The interactions between the floes in the pack ice resemble those observed in granular materials. These materials are frictional in nature, they exhibit both contractive and dilative volume changes, the plastic flow is nonassociated, and their stiffnesses and strengths increase with confining pressure, but they do not have any strength when unconfined. The overall behavior of the pack ice may be close to isotropic. Constitutive modeling of this behavior may be achieved by models used in geotechnical engineering. Formation of leads and subsequent freezing of the water results in cementation between the ice floes, and the pack ice becomes stronger. The behavior of the pack ice may now be compared with that observed in cemented soils or concrete. For these materials, increasing amounts of cementation result in increasing rates of dilation when sheared, and this accounts for the largest contribution to the increase in shear strength.

Formulation and validation of a reduced order model of 2D materials exhibiting a two-phase microstructure as applied to graphene oxide

NASA Astrophysics Data System (ADS)

Benedetti, Ivano; Nguyen, Hoang; Soler-Crespo, Rafael A.; Gao, Wei; Mao, Lily; Ghasemi, Arman; Wen, Jianguo; Nguyen, SonBinh; Espinosa, Horacio D.

2018-03-01

Novel 2D materials, e.g., graphene oxide (GO), are attractive building blocks in the design of advanced materials due to their reactive chemistry, which can enhance interfacial interactions while providing good in-plane mechanical properties. Recent studies have hypothesized that the randomly distributed two-phase microstructure of GO, which arises due to its oxidized chemistry, leads to differences in nano- vs meso-scale mechanical responses. However, this effect has not been carefully studied using molecular dynamics due to computational limitations. Herein, a continuum mechanics model, formulated based on density functional based tight binding (DFTB) constitutive results for GO nano-flakes, is establish for capturing the effect of oxidation patterns on the material mechanical properties. GO is idealized as a continuum heterogeneous two-phase material, where the mechanical response of each phase, graphitic and oxidized, is informed from DFTB simulations. A finite element implementation of the model is validated via MD simulations and then used to investigate the existence of GO representative volume elements (RVE). We find that for the studied GO, an RVE behavior arises for monolayer sizes in excess to 40 nm. Moreover, we reveal that the response of monolayers with two main different functional chemistries, epoxide-rich and hydroxyl-rich, present distinct differences in mechanical behavior. In addition, we explored the role of defect density in GO, and validate the applicability of the model to larger length scales by predicting membrane deflection behavior, in close agreement with previous experimental and theoretical observations. As such the work presents a reduced order modeling framework applicable in the study of mechanical properties and deformation mechanisms in 2D multiphase materials.

Flexural behavior of the fibrous cementitious composites (FCC) containing hybrid fibres

NASA Astrophysics Data System (ADS)

Ramli, Mahyuddin; Ban, Cheah Chee; Samsudin, Muhamad Fadli

2018-02-01

In this study, the flexural behavior of the fibrous cementitious composites containing hybrid fibers was investigated. Waste materials or by product materials such as pulverized fuel ash (PFA) and ground granulated blast-furnace slag (GGBS) was used as supplementary cement replacement. In addition, barchip and kenaf fiber will be used as additional materials for enhance the flexural behavior of cementitious composites. A seven mix design of fibrous cementitious composites containing hybrid fiber mortar were fabricated with PFA-GGBS as cement replacement at 50% with hybridization of barchip and kenaf fiber between 0.5% and 2.0% by total volume weight. The FCC with hybrid fibers mortar will be fabricated by using 50 × 50 × 50 mm, 40 × 40 × 160 mm and 350 × 125 × 30 mm steel mold for assessment of mechanical performances and flexural behavior characteristics. The flexural behavior and mechanical performance of the PFA-GGBS with hybrid fiber mortar block was assessed in terms of load deflection response, stress-strain response, crack development, compressive and flexural strength after water curing for 28 days. Moreover, the specimen HBK 1 and HBK 2 was observed equivalent or better in mechanical performance and flexural behavior as compared to control mortar.

Installing Mechanics of Granular Materials (MGM) Experiment Test Cell

NASA Technical Reports Server (NTRS)

1996-01-01

Astronaut Carl Walz installs Mechanics of Granular Materials (MGM) test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/John Space Center

Mechanical Design of Carbon Ion Optics

NASA Technical Reports Server (NTRS)

Haag, Thomas

2005-01-01

Carbon Ion Optics are expected to provide much longer thruster life due to their resistance to sputter erosion. There are a number of different forms of carbon that have been used for fabricating ion thruster optics. The mechanical behavior of carbon is much different than that of most metals, and poses unique design challenges. In order to minimize mission risk, the behavior of carbon must be well understood, and components designed within material limitations. Thermal expansion of the thruster structure must be compatible with thermal expansion of the carbon ion optics. Specially designed interfaces may be needed so that grid gap and aperture alignment are not adversely affected by dissimilar material properties within the thruster. The assembled thruster must be robust and tolerant of launch vibration. The following paper lists some of the characteristics of various carbon materials. Several past ion optics designs are discussed, identifying strengths and weaknesses. Electrostatics and material science are not emphasized so much as the mechanical behavior and integration of grid electrodes into an ion thruster.

Anisotropic mechanical behaviors and their structural dependences of crossed-lamellar structure in a bivalve shell.

PubMed

Jiao, D; Liu, Z Q; Qu, R T; Zhang, Z F

2016-02-01

Crossed-lamellar structure is one of the most common organizations found in mollusk shells and may serve as a natural mimetic model for designing bio-inspired synthetic materials. Nonetheless, the mechanical behaviors and corresponding mechanisms have rarely been investigated for individual macro-layer of such structure. The integrated effects of orientation and hydration also remain unclear. In this study, the mechanical behaviors and their structural dependences of pure crossed-lamellar structure in Saxidomus purpuratus shell were systematically examined by three-point bending and compression tests. Mechanical properties and fracture mechanisms were revealed to depend strongly on the orientation, hydration state and loading condition. Three basic cracking modes of inter-platelet, trans-platelet, and along the interfaces between first-order lamellae were identified, and the interfacial separation was enhanced by hydration. Macroscopic compressive fracture was accomplished through axial splitting during which multiple toughening mechanisms were activated. The competition among different cracking modes was quantitatively evaluated by analyzing their driving stresses and resistances from fundamental mechanics. This study helps to clarify the mechanical behaviors of naturally occurring crossed-lamellar structure, and accordingly, aids in designing new bio-inspired synthetic materials by mimicking it. Copyright © 2015 Elsevier B.V. All rights reserved.

Study on the behavior and mechanism of polycarbonate with hot-water aging

NASA Astrophysics Data System (ADS)

Kong, L. P.; Zhao, Y. X.; Zhou, C. H.; Huang, Y. H.; Tang, M.; Gao, J. G.

2016-07-01

The present work was concerned with hot-water aging behavior and mechanism of Bisphenol A polycarbonate (PC) used as food and packaging materials. It indicated that with the aging time prolonged, PC sample had internal defects and the mechanical properties of PC materials changed not too much, molecular weight decreased, thermal stability declined. Phenolic hydroxyl absorption intensity enhanced in IR spectra and the maximum absorption wavelength red shift of benzene in UV-Vis spectra, the level of BPA increased. The color change of PC sample was not apparent.

High Fidelity Ion Beam Simulation of High Dose Neutron Irradiation

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

Was, Gary; Wirth, Brian; Motta, Athur

The objective of this proposal is to demonstrate the capability to predict the evolution of microstructure and properties of structural materials in-reactor and at high doses, using ion irradiation as a surrogate for reactor irradiations. “Properties” includes both physical properties (irradiated microstructure) and the mechanical properties of the material. Demonstration of the capability to predict properties has two components. One is ion irradiation of a set of alloys to yield an irradiated microstructure and corresponding mechanical behavior that are substantially the same as results from neutron exposure in the appropriate reactor environment. Second is the capability to predict the irradiatedmore » microstructure and corresponding mechanical behavior on the basis of improved models, validated against both ion and reactor irradiations and verified against ion irradiations. Taken together, achievement of these objectives will yield an enhanced capability for simulating the behavior of materials in reactor irradiations.« less

Online monitoring of corrosion behavior in molten metal using laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Zeng, Qiang; Pan, Congyuan; Li, Chaoyang; Fei, Teng; Ding, Xiaokang; Du, Xuewei; Wang, Qiuping

2018-04-01

The corrosion behavior of structure materials in direct contact with molten metals is widespread in metallurgical industry. The corrosion of casting equipment by molten metals is detrimental to the production process, and the corroded materials can also contaminate the metals being produced. Conventional methods for studying the corrosion behavior by molten metal are offline. This work explored the application of laser-induced breakdown spectroscopy (LIBS) for online monitoring of the corrosion behavior of molten metal. The compositional changes of molten aluminum in crucibles made of 304 stainless steel were obtained online at 1000 °C. Several offline techniques were combined to determine the corrosion mechanism, which was highly consistent with previous studies. Results proved that LIBS was an efficient method to study the corrosion mechanism of solid materials in molten metal.

The Usability of Rock-Like Materials for Numerical Studies on Rocks

NASA Astrophysics Data System (ADS)

Zengin, Enes; Abiddin Erguler, Zeynal

2017-04-01

The approaches of synthetic rock material and mass are widely used by many researchers for understanding the failure behavior of different rocks. In order to model the failure behavior of rock material, researchers take advantageous of different techniques and software. But, the majority of all these instruments are based on distinct element method (DEM). For modeling the failure behavior of rocks, and so to create a fundamental synthetic rock material model, it is required to perform related laboratory experiments for providing strength parameters. In modelling studies, model calibration processes are performed by using parameters of intact rocks such as porosity, grain size, modulus of elasticity and Poisson ratio. In some cases, it can be difficult or even impossible to acquire representative rock samples for laboratory experiments from heavily jointed rock masses and vuggy rocks. Considering this limitation, in this study, it was aimed to investigate the applicability of rock-like material (e.g. concrete) to understand and model the failure behavior of rock materials having complex inherent structures. For this purpose, concrete samples having a mixture of %65 cement dust and %35 water were utilized. Accordingly, intact concrete samples representing rocks were prepared in laboratory conditions and their physical properties such as porosity, pore size and density etc. were determined. In addition, to acquire the mechanical parameters of concrete samples, uniaxial compressive strength (UCS) tests were also performed by simultaneously measuring strain during testing. The measured physical and mechanical properties of these extracted concrete samples were used to create synthetic material and then uniaxial compressive tests were modeled and performed by using two dimensional discontinuum program known as Particle Flow Code (PFC2D). After modeling studies in PFC2D, approximately similar failure mechanism and testing results were achieved from both experimental and artificial simulations. The results obtained from these laboratory tests and modelling studies were compared with the other researcher's studies in respect to failure mechanism of different type of rocks. It can be concluded that there is similar failure mechanism between concrete and rock materials. Therefore, the results obtained from concrete samples that would be prepared at different porosity and pore sizes can be used in future studies in selection micro-mechanical and physical properties to constitute synthetic rock materials for understanding failure mechanism of rocks having complex inherent structures such as vuggy rocks or heavily jointed rock masses.

Microstructure and Strengthening Mechanisms in an Ultrafine Grained Al-Mg-Sc Alloy Produced by Powder Metallurgy

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

Tammy J. Harrell; Troy D. Topping; Haiming Wen

2014-12-01

Additions of Sc to an Al-Mg matrix were investigated, paying particular attention to the influence of Al3Sc precipitates and other dispersoids, as well as grain size, on mechanical behavior. Prior studies have shown that Sc significantly increases the strength of coarse-grained Al-Mg alloys. Prompted by these findings, we hypothesized that it would be of fundamental and technological interest to study the behavior of Sc additions to an ultrafine-grained (UFG) microstructure (e.g., 100’s nm). Accordingly, we investigated the microstructural evolution and mechanical behavior of a cryomilled ultrafine grained Al-5Mg-0.4Sc (wt pct) and compared the results to those of an equivalent fine-grainedmore » material (FG) produced by powder metallurgy. Experimental materials were consolidated by hot isostatic pressing (HIP’ing) followed by extrusion or dual mode dynamic forging. Under identical processing conditions, UFG materials generate large Al3Sc precipitates with an average diameter of 154 nm and spaced approximately 1 to 3 µm apart, while precipitates in the FG materials have a diameter of 24 nm and are spaced 50 to 200 nm apart. The strengthening mechanisms are calculated for all materials and it is determined that the greatest strengthening contributions for the UFG and FG materials are Mg-O/N dispersion strengthening and precipitate strengthening, respectively.« less

Mechanism-Based Modeling for Low Cycle Fatigue of Cast Austenitic Steel

NASA Astrophysics Data System (ADS)

Wu, Xijia; Quan, Guangchun; Sloss, Clayton

2017-09-01

A mechanism-based approach—the integrated creep-fatigue theory (ICFT)—is used to model low cycle fatigue behavior of 1.4848 cast austenitic steel over the temperature range from room temperature (RT) to 1173 K (900 °C) and the strain rate range from of 2 × 10-4 to 2 × 10-2 s-1. The ICFT formulates the material's constitutive equation based on the physical strain decomposition into mechanism strains, and the associated damage accumulation consisting of crack nucleation and propagation in coalescence with internally distributed damage. At room temperature, the material behavior is controlled by plasticity, resulting in a rate-independent and cyclically stable behavior. The material exhibits significant cyclic hardening at intermediate temperatures, 673 K to 873 K (400 °C to 600 °C), with negative strain rate sensitivity, due to dynamic strain aging. At high temperatures >1073 K (800 °C), time-dependent deformation is manifested with positive rate sensitivity as commonly seen in metallic materials at high temperature. The ICFT quantitatively delineates the contribution of each mechanism in damage accumulation, and predicts the fatigue life as a result of synergistic interaction of the above identified mechanisms. The model descriptions agree well with the experimental and fractographic observations.

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.

Deformation partitioning provides insight into elastic, plastic, and viscous contributions to bone material behavior.

PubMed

Ferguson, V L

2009-08-01

The relative contributions of elastic, plastic, and viscous material behavior are poorly described by the separate extraction and analysis of the plane strain modulus, E('), the contact hardness, H(c) (a hybrid parameter encompassing both elastic and plastic behavior), and various viscoelastic material constants. A multiple element mechanical model enables the partitioning of a single indentation response into its fundamental elastic, plastic, and viscous deformation components. The objective of this study was to apply deformation partitioning to explore the role of hydration, tissue type, and degree of mineralization in bone and calcified cartilage. Wet, ethanol-dehydrated, and PMMA-embedded equine cortical bone samples and PMMA-embedded human femoral head tissues were analyzed for contributions of elastic, plastic and viscous deformation to the overall nanoindentation response at each site. While the alteration of hydration state had little effect on any measure of deformation, unembedded tissues demonstrated significantly greater measures of resistance to plastic deformation than PMMA-embedded tissues. The PMMA appeared to mechanically stabilize the tissues and prevent extensive permanent deformation within the bone material. Increasing mineral volume fraction correlated with positive changes in E('), H(c), and resistance to plastic deformation, H; however, the partitioned deformation components were generally unaffected by mineralization. The contribution of viscous deformation was minimal and may only play a significant role in poorly mineralized tissues. Deformation partitioning enables a detailed interpretation of the elastic, plastic, and viscous contributions to the nanomechanical behavior of mineralized tissues that is not possible when examining modulus and contact hardness alone. Varying experimental or biological factors, such as hydration or mineralization level, enables the understanding of potential mechanisms for specific mechanical behavior patterns that would otherwise be hidden within a more complex set of material property parameters.

Cubical Mass-Spring Model design based on a tensile deformation test and nonlinear material model.

PubMed

San-Vicente, Gaizka; Aguinaga, Iker; Tomás Celigüeta, Juan

2012-02-01

Mass-Spring Models (MSMs) are used to simulate the mechanical behavior of deformable bodies such as soft tissues in medical applications. Although they are fast to compute, they lack accuracy and their design remains still a great challenge. The major difficulties in building realistic MSMs lie on the spring stiffness estimation and the topology identification. In this work, the mechanical behavior of MSMs under tensile loads is analyzed before studying the spring stiffness estimation. In particular, the performed qualitative and quantitative analysis of the behavior of cubical MSMs shows that they have a nonlinear response similar to hyperelastic material models. According to this behavior, a new method for spring stiffness estimation valid for linear and nonlinear material models is proposed. This method adjusts the stress-strain and compressibility curves to a given reference behavior. The accuracy of the MSMs designed with this method is tested taking as reference some soft-tissue simulations based on nonlinear Finite Element Method (FEM). The obtained results show that MSMs can be designed to realistically model the behavior of hyperelastic materials such as soft tissues and can become an interesting alternative to other approaches such as nonlinear FEM.

EDITORIAL: Adaptive and Active Materials: Selected Papers from the ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 08) (Maryland, USA, 28-30 October 2008) Adaptive and Active Materials: Selected Papers from the ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 08) (Maryland, USA, 28-30 October 2008)

NASA Astrophysics Data System (ADS)

Lynch, Christopher

2009-10-01

The rapid development of the field of Smart Materials, Adaptive Structures, and Materials Systems led the Aerospace Division ASMS TC to launch the new annual SMASIS conference in 2008. The conference focuses on the multi-disciplinary challenges of developing new multifunctional materials and implementing them in advanced systems. The research spans length scales from nano-structured materials to civil, air, and space structures. The first conference consisted of six symposia, each focusing on a different research area. This special issue of Smart Materials and Structures summarizes some of the top research presented at the 2008 SMASIS conference in the materials-focused symposia. These symposia focused on the behavior and mechanics of active materials, on multifunctional materials, and on bio-inspired materials. The behavior and mechanics of active materials is an approach that combines observed material behavior with mechanism-based models that not only give insight into the observed behavior, but guide the development of new materials. This approach has been applied to shape memory metals and polymers, ferroelectrics, ferromagnetics, and recently to multiferroic materials, and has led to considerable improvements in our understanding of multi-field phenomena. Multifunctional materials are the next generation of active materials. These materials include structural, sensing, and actuation components integrated into a material system. A natural extension of multifunctional materials is a new class of bio-inspired materials. Bio-inspired materials range from detailed bio-mimicry of sensing and self healing materials to nano and microstructures that take advantage of features observed in biological systems. The Editors would like to express their sincere thanks to all of the authors for their contributions to this special issue on 'Adaptive and Active Materials' for Smart Materials and Structures. We convey our gratitude to all of the reviewers for their time and dedication. We thank IOP Publishing for their support and encouragement of this special issue and the staff for their special attention and timely response.

Fracture behaviors under pure shear loading in bulk metallic glasses

NASA Astrophysics Data System (ADS)

Chen, Cen; Gao, Meng; Wang, Chao; Wang, Wei-Hua; Wang, Tzu-Chiang

2016-12-01

Pure shear fracture test, as a special mechanical means, had been carried out extensively to obtain the critical information for traditional metallic crystalline materials and rocks, such as the intrinsic deformation behavior and fracture mechanism. However, for bulk metallic glasses (BMGs), the pure shear fracture behaviors have not been investigated systematically due to the lack of a suitable test method. Here, we specially introduce a unique antisymmetrical four-point bend shear test method to realize a uniform pure shear stress field and study the pure shear fracture behaviors of two kinds of BMGs, Zr-based and La-based BMGs. All kinds of fracture behaviors, the pure shear fracture strength, fracture angle and fracture surface morphology, are systematically analyzed and compared with those of the conventional compressive and tensile fracture. Our results indicate that both the Zr-based and La-based BMGs follow the same fracture mechanism under pure shear loading, which is significantly different from the situation of some previous research results. Our results might offer new enlightenment on the intrinsic deformation and fracture mechanism of BMGs and other amorphous materials.

Fracture behaviors under pure shear loading in bulk metallic glasses.

PubMed

Chen, Cen; Gao, Meng; Wang, Chao; Wang, Wei-Hua; Wang, Tzu-Chiang

2016-12-23

Pure shear fracture test, as a special mechanical means, had been carried out extensively to obtain the critical information for traditional metallic crystalline materials and rocks, such as the intrinsic deformation behavior and fracture mechanism. However, for bulk metallic glasses (BMGs), the pure shear fracture behaviors have not been investigated systematically due to the lack of a suitable test method. Here, we specially introduce a unique antisymmetrical four-point bend shear test method to realize a uniform pure shear stress field and study the pure shear fracture behaviors of two kinds of BMGs, Zr-based and La-based BMGs. All kinds of fracture behaviors, the pure shear fracture strength, fracture angle and fracture surface morphology, are systematically analyzed and compared with those of the conventional compressive and tensile fracture. Our results indicate that both the Zr-based and La-based BMGs follow the same fracture mechanism under pure shear loading, which is significantly different from the situation of some previous research results. Our results might offer new enlightenment on the intrinsic deformation and fracture mechanism of BMGs and other amorphous materials.

Computer modeling of the mechanical behavior of composites -- Interfacial cracks in fiber-reinforced materials

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

Schmauder, S.; Haake, S.; Mueller, W.H.

Computer modeling of materials and especially modeling the mechanical behavior of composites became increasingly popular in the past few years. Among them are examples of micromechanical modeling of real structures as well as idealized model structures of linear elastic and elasto-plastic material response. In this paper, Erdogan`s Integral Equation Method (IEM) is chosen as an example for a powerful method providing principle insight into elastic fracture mechanical situations. IEM or, alternatively, complex function techniques sometimes even allow for deriving analytical solutions such as in the case of a circumferential crack along a fiber/matrix interface. The analytical formulae of this interfacemore » crack will be analyzed numerically and typical results will be presented graphically.« less

3D Printing of Materials with Tunable Failure via Bioinspired Mechanical Gradients.

PubMed

Kokkinis, Dimitri; Bouville, Florian; Studart, André R

2018-05-01

Mechanical gradients are useful to reduce strain mismatches in heterogeneous materials and thus prevent premature failure of devices in a wide range of applications. While complex graded designs are a hallmark of biological materials, gradients in manmade materials are often limited to 1D profiles due to the lack of adequate fabrication tools. Here, a multimaterial 3D-printing platform is developed to fabricate elastomer gradients spanning three orders of magnitude in elastic modulus and used to investigate the role of various bioinspired gradient designs on the local and global mechanical behavior of synthetic materials. The digital image correlation data and finite element modeling indicate that gradients can be effectively used to manipulate the stress state and thus circumvent the weakening effect of defect-rich interfaces or program the failure behavior of heterogeneous materials. Implementing this concept in materials with bioinspired designs can potentially lead to defect-tolerant structures and to materials whose tunable failure facilitates repair of biomedical implants, stretchable electronics, or soft robotics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Timoshenko beam model for chiral materials

NASA Astrophysics Data System (ADS)

Ma, T. Y.; Wang, Y. N.; Yuan, L.; Wang, J. S.; Qin, Q. H.

2017-12-01

Natural and artificial chiral materials such as deoxyribonucleic acid (DNA), chromatin fibers, flagellar filaments, chiral nanotubes, and chiral lattice materials widely exist. Due to the chirality of intricately helical or twisted microstructures, such materials hold great promise for use in diverse applications in smart sensors and actuators, force probes in biomedical engineering, structural elements for absorption of microwaves and elastic waves, etc. In this paper, a Timoshenko beam model for chiral materials is developed based on noncentrosymmetric micropolar elasticity theory. The governing equations and boundary conditions for a chiral beam problem are derived using the variational method and Hamilton's principle. The static bending and free vibration problem of a chiral beam are investigated using the proposed model. It is found that chirality can significantly affect the mechanical behavior of beams, making materials more flexible compared with nonchiral counterparts, inducing coupled twisting deformation, relatively larger deflection, and lower natural frequency. This study is helpful not only for understanding the mechanical behavior of chiral materials such as DNA and chromatin fibers and characterizing their mechanical properties, but also for the design of hierarchically structured chiral materials.

Timoshenko beam model for chiral materials

NASA Astrophysics Data System (ADS)

Ma, T. Y.; Wang, Y. N.; Yuan, L.; Wang, J. S.; Qin, Q. H.

2018-06-01

Natural and artificial chiral materials such as deoxyribonucleic acid (DNA), chromatin fibers, flagellar filaments, chiral nanotubes, and chiral lattice materials widely exist. Due to the chirality of intricately helical or twisted microstructures, such materials hold great promise for use in diverse applications in smart sensors and actuators, force probes in biomedical engineering, structural elements for absorption of microwaves and elastic waves, etc. In this paper, a Timoshenko beam model for chiral materials is developed based on noncentrosymmetric micropolar elasticity theory. The governing equations and boundary conditions for a chiral beam problem are derived using the variational method and Hamilton's principle. The static bending and free vibration problem of a chiral beam are investigated using the proposed model. It is found that chirality can significantly affect the mechanical behavior of beams, making materials more flexible compared with nonchiral counterparts, inducing coupled twisting deformation, relatively larger deflection, and lower natural frequency. This study is helpful not only for understanding the mechanical behavior of chiral materials such as DNA and chromatin fibers and characterizing their mechanical properties, but also for the design of hierarchically structured chiral materials.

Thermomechanical Fatigue Behavior of a Silicone Carbide Fiber-Reinforced Calcium Aluminosilicate Glass-Ceramic Matrix Composite

DTIC Science & Technology

1991-01-01

Fibers," Journal of Materials Science Letters, Chapman & Hall, Ltd., London, England, 2, [9], 1983, pp. 80-82. Wang, S-W, and Parvizi- Majidi , A...cross-plied [0/9012s material and found behavior similar to that seen by Rousseau, and Wang & Parvizi- Majidi . 17 References - CHAPTER I1: BACKGROUND...eds., American Society for Testing and Materials, Philadelphia, PA, 1990, pp. 136-151. 63 Wang, S-W, and Parvizi- Majidi , A., "Mechanical Behavior of

3D printing of an interpenetrating network hydrogel material with tunable viscoelastic properties.

PubMed

Bootsma, Katherine; Fitzgerald, Martha M; Free, Brandon; Dimbath, Elizabeth; Conjerti, Joe; Reese, Greg; Konkolewicz, Dominik; Berberich, Jason A; Sparks, Jessica L

2017-06-01

Interpenetrating network (IPN) hydrogel materials are recognized for their unique mechanical properties. While IPN elasticity and toughness properties have been explored in previous studies, the factors that impact the time-dependent stress relaxation behavior of IPN materials are not well understood. Time-dependent (i.e. viscoelastic) mechanical behavior is a critical design parameter in the development of materials for a variety of applications, such as medical simulation devices, flexible substrate materials, cellular mechanobiology substrates, or regenerative medicine applications. This study reports a novel technique for 3D printing alginate-polyacrylamide IPN gels with tunable elastic and viscoelastic properties. The viscoelastic stress relaxation behavior of the 3D printed alginate-polyacrylamide IPN hydrogels was influenced most strongly by varying the concentration of the acrylamide cross-linker (MBAA), while the elastic modulus was affected most by varying the concentration of total monomer material. The material properties of our 3D printed IPN constructs were consistent with those reported in the biomechanics literature for soft tissues such as skeletal muscle, cardiac muscle, skin and subcutaneous tissue. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mechanics of Granular Materials (MGM) Test Cell

NASA Technical Reports Server (NTRS)

1998-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is shown approximately 20 and 60 minutes after the start of an experiment on STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Mechanics of Granular Materials Test Cell

NASA Technical Reports Server (NTRS)

1998-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is shown from all three sides by its video camera during STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Mechanical Testing of Common-Use Polymeric Materials with an In-House-Built Apparatus

ERIC Educational Resources Information Center

Pedrosa, Cristiana; Mendes, Joaquim; Magalhaes, Fernao D.

2006-01-01

A low-cost tensile testing machine was built for testing polymeric films. This apparatus also allows for tear-strength and flexural tests. The experimental results, obtained from common-use materials, selected by the students, such as plastic bags, illustrate important aspects of the mechanical behavior of polymeric materials. Some of the tests…

Molecular deformation mechanisms of the wood cell wall material.

PubMed

Jin, Kai; Qin, Zhao; Buehler, Markus J

2015-02-01

Wood is a biological material with outstanding mechanical properties resulting from its hierarchical structure across different scales. Although earlier work has shown that the cellular structure of wood is a key factor that renders it excellent mechanical properties at light weight, the mechanical properties of the wood cell wall material itself still needs to be understood comprehensively. The wood cell wall material features a fiber reinforced composite structure, where cellulose fibrils act as stiff fibers, and hemicellulose and lignin molecules act as soft matrix. The angle between the fiber direction and the loading direction has been found to be the key factor controlling the mechanical properties. However, how the interactions between theses constitutive molecules contribute to the overall properties is still unclear, although the shearing between fibers has been proposed as a primary deformation mechanism. Here we report a molecular model of the wood cell wall material with atomistic resolution, used to assess the mechanical behavior under shear loading in order to understand the deformation mechanisms at the molecular level. The model includes an explicit description of cellulose crystals, hemicellulose, as well as lignin molecules arranged in a layered nanocomposite. The results obtained using this model show that the wood cell wall material under shear loading deforms in an elastic and then plastic manner. The plastic regime can be divided into two parts according to the different deformation mechanisms: yielding of the matrix and sliding of matrix along the cellulose surface. Our molecular dynamics study provides insights of the mechanical behavior of wood cell wall material at the molecular level, and paves a way for the multi-scale understanding of the mechanical properties of wood. Copyright © 2014 Elsevier Ltd. All rights reserved.

Mechanical Behavior of Additive Manufactured Layered Materials, Part 2: Stainless Steels

DTIC Science & Technology

2015-04-30

and/or excellent cyclic fatigue behavior: stainless - steel 316L and 17-4PH. Additive materials were fabricated at a leading-edge facility using their...Tensile deformation Representative engineering stress- strain data from measurements obtained with our stainless steel specimens are shown in... fatigue behavior Cyclic fatigue strengths demonstrated by the DMLS stainless steels fabricated in the horizontal orientation were almost equal to

Electrospun microcrimped fibers with nonlinear mechanical properties enhance ligament fibroblast phenotype.

PubMed

Grace Chao, Pen-hsiu; Hsu, Hsiang-Yi; Tseng, Hsiao-Yun

2014-09-01

Fiber structure and order greatly impact the mechanical behavior of fibrous materials. In biological tissues, the nonlinear mechanics of fibrous scaffolds contribute to the functionality of the material. The nonlinear mechanical properties of the wavy structure (crimp) in collagen allow tissue flexibility while preventing over-extension. A number of approaches have tried to recreate this complex mechanical functionality. We generated microcrimped fibers by briefly heating electrospun parallel fibers over the glass transition temperature or by ethanol treatment. The crimp structure is similar to those of collagen fibers found in native aorta, intestines, or ligaments. Using poly-L-lactic acid fibers, we demonstrated that the bulk materials exhibit changed stress-strain behaviors with a significant increase in the toe region in correlation to the degree of crimp, similar to those observed in collagenous tissues. In addition to mimicking the stress-strain behavior of biological tissues, the microcrimped fibers are instructive in cell morphology and promote ligament phenotypic gene expression. This effect can be further enhanced by dynamic tensile loading, a physiological perturbation in vivo. This rapid and economical approach for microcrimped fiber production provides an accessible platform to study structure-function relationships and a novel functional scaffold for tissue engineering and cell mechanobiology studies.

Bistable Mechanisms for Space Applications

PubMed Central

Zirbel, Shannon A.; Tolman, Kyler A.; Trease, Brian P.

2016-01-01

Compliant bistable mechanisms are monolithic devices with two stable equilibrium positions separated by an unstable equilibrium position. They show promise in space applications as nonexplosive release mechanisms in deployment systems, thereby eliminating friction and improving the reliability and precision of those mechanical devices. This paper presents both analytical and numerical models that are used to predict bistable behavior and can be used to create bistable mechanisms in materials not previously feasible for compliant mechanisms. Materials compatible with space applications are evaluated for use as bistable mechanisms and prototypes are fabricated in three different materials. Pin-puller and cutter release mechanisms are proposed as potential space applications. PMID:28030588

Microstructure, Mechanical and Wear Behaviors of Hot-Pressed Copper-Nickel-Based Materials for Diamond Cutting Tools

NASA Astrophysics Data System (ADS)

Miranda, G.; Ferreira, P.; Buciumeanu, M.; Cabral, A.; Fredel, M.; Silva, F. S.; Henriques, B.

2017-08-01

The current trend to replace cobalt in diamond cutting tools (DCT) for stone cutting has motivated the study of alternative materials for this end. The present study characterizes several copper-nickel-based materials (Cu-Ni; Cu-Ni-10Sn, Cu-Ni-15Sn, Cu-Ni-Sn-2WC and Cu-Ni-Sn-10WC) for using as matrix material for diamond cutting tools for stone. Copper-nickel-based materials were produced by hot pressing, at a temperature of 850 °C during 15 min and under an applied pressure of 50 MPa. The mechanical properties were evaluated though the shear strength and hardness values. The microstructures and fracture surfaces were analyzed by SEM. The wear behavior of all specimens was assessed using a reciprocating ball-on-plate tribometer. The hot pressing produced compacts with good densification. Sn and WC promoted enhanced mechanical properties and wear performance to Cu-Ni alloys. Cu-Ni-10Sn and Cu-Ni-10Sn-2WC displayed the best compromise between mechanical and wear performance.

Mechanical behavior simulation of MEMS-based cantilever beam using COMSOL multiphysics

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

Acheli, A., E-mail: aacheli@cdta.dz; Serhane, R.

This paper presents the studies of mechanical behavior of MEMS cantilever beam made of poly-silicon material, using the coupling of three application modes (plane strain, electrostatics and the moving mesh) of COMSOL Multi-physics software. The cantilevers playing a key role in Micro Electro-Mechanical Systems (MEMS) devices (switches, resonators, etc) working under potential shock. This is why they require actuation under predetermined conditions, such as electrostatic force or inertial force. In this paper, we present mechanical behavior of a cantilever actuated by an electrostatic force. In addition to the simplification of calculations, the weight of the cantilever was not taken intomore » account. Different parameters like beam displacement, electrostatics force and stress over the beam have been calculated by finite element method after having defining the geometry, the material of the cantilever model (fixed at one of ends but is free to move otherwise) and his operational space.« less

Mechanical Behavior of Nanostructured and Ultrafine Grained Materials under Shock Wave Loadings. Experimental Data and Results of Computer Simulation.

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir

2011-06-01

Features of mechanical behavior of nanostructured (NS) and ultrafine grained (UFG) metal and ceramic materials under quasistatic and shock wave loadings are discussed in this report. Multilevel models developed within the approach of computational mechanics of materials were used for simulation mechanical behavior of UFG and NS metals and ceramics. Comparisons of simulation results with experimental data are presented. Models of mechanical behavior of nanostructured metal alloys takes into account a several structural factors influencing on the mechanical behavior of materials (type of a crystal lattice, density of dislocations, a size of dislocation substructures, concentration and size of phase precipitation, and distribution of grains sizes). Results show the strain rate sensitivity of the yield stress of UFG and polycrystalline alloys is various in a range from 103 up to 106 1/s. But the difference of the Hugoniot elastic limits of a UFG and coarse-grained alloys may be not considerable. The spall strength, the yield stress of UFG and NS alloys are depend not only on grains size, but a number of factors such as a distribution of grains sizes, a concentration and sizes of voids and cracks, a concentration and sizes of phase precipitation. Some titanium alloys with grain sizes from 300 to 500 nm have the quasi-static yield strength and the tensile strength twice higher than that of coarse grained counterparts. But the spall strength of the UFG titanium alloys is only 10 percents above than that of coarse grained alloys. At the same time it was found the spall strength of the bulk UFG aluminium and magnesium alloys with precipitation strengthening is essentially higher in comparison of coarse-grained counterparts. The considerable decreasing of the strain before failure of UFG alloys was predicted at high strain rates. The Hugoniot elastic limits of oxide nanoceramics depend not only on the porosity, but also on sizes and volume distribution of voids.

Neural Network Models of Simple Mechanical Systems Illustrating the Feasibility of Accelerated Life Testing

NASA Technical Reports Server (NTRS)

Fusaro, Robert L.; Jones, Steven P.; Jansen, Ralph

1996-01-01

A complete evaluation of the tribological characteristics of a given material/mechanical system is a time-consuming operation since the friction and wear process is extremely systems sensitive. As a result, experimental designs (i.e., Latin Square, Taguchi) have been implemented in an attempt to not only reduce the total number of experimental combinations needed to fully characterize a material/mechanical system, but also to acquire life data for a system without having to perform an actual life test. Unfortunately, these experimental designs still require a great deal of experimental testing and the output does not always produce meaningful information. In order to further reduce the amount of experimental testing required, this study employs a computer neural network model to investigate different material/mechanical systems. The work focuses on the modeling of the wear behavior, while showing the feasibility of using neural networks to predict life data. The model is capable of defining which input variables will influence the tribological behavior of the particular material/mechanical system being studied based on the specifications of the overall system.

Characterization of mechanical properties of pseudoelastic shape memory alloys under harmonic excitation

NASA Astrophysics Data System (ADS)

Böttcher, J.; Jahn, M.; Tatzko, S.

2017-12-01

Pseudoelastic shape memory alloys exhibit a stress-induced phase transformation which leads to high strains during deformation of the material. The stress-strain characteristic during this thermomechanical process is hysteretic and results in the conversion of mechanical energy into thermal energy. This energy conversion allows for the use of shape memory alloys in vibration reduction. For the application of shape memory alloys as vibration damping devices a dynamic modeling of the material behavior is necessary. In this context experimentally determined material parameters which accurately represent the material behavior are essential for a reliable material model. Subject of this publication is the declaration of suitable material parameters for pseudoelastic shape memory alloys and the methodology of their identification from experimental investigations. The used test rig was specifically designed for the characterization of pseudoelastic shape memory alloys.

Thermophysical and mechanical characterization of clay bricks reinforced by alfa or straw fibers

NASA Astrophysics Data System (ADS)

Elhamdouni, Y.; Khabbazi, A.; Benayad, C.; Mounir, S.; Dadi, A.

2017-03-01

This work is part of the valuation of local materials such as clay (earth), alfa fiber and straw fiber. The goal is to use these materials as bricks in rural construction. These materials are abundant, natural, and renewable. The objective of this work is to study the thermal and mechanical behavior of a new material by mixing clay (chosen as the binder) with different mass percentages of alfa fiber (0.5%, 1%, 2%, 3%, 4%), and to compare these results with those of materials often used in the construction of individual houses in rural Morocco (clay + straw). The results obtained prove to us that using straw fibers can reduce the thermal conductivity compared to alfa fiber, which allows to have energy savings of 2% to 7%. By against, alfa fibers can improve the mechanical behavior of clay-based materials when compared to the clay + straw material (an increase of 8% to 17% in the tractive resistance by bending and 6% to 18% for compression resistance). These results also specify the optimal usage conditions of these fibers (alfa and straw) in the clay bricks.

Modeling the rubbing contact in honeycomb seals

NASA Astrophysics Data System (ADS)

Fischer, Tim; Welzenbach, Sarah; Meier, Felix; Werner, Ewald; kyzy, Sonun Ulan; Munz, Oliver

2018-03-01

Metallic honeycomb labyrinth seals are commonly used as sealing systems in gas turbine engines. Because of their capability to withstand high thermo-mechanical loads and oxidation, polycrystalline nickel-based superalloys, such as Hastelloy X and Haynes 214, are used as sealing material. In addition, these materials must exhibit a tolerance against rubbing between the rotating part and the stationary seal component. The tolerance of the sealing material against rubbing preserves the integrity of the rotating part. In this article, the rubbing behavior at the rotor-stator interface is considered numerically. A simulation model is incorporated into the commercial finite element code ABAQUS/explicit and is utilized to simulate a simplified rubbing process. A user-defined interaction routine between the contact surfaces accounts for the thermal and mechanical interfacial behavior. Furthermore, an elasto-plastic constitutive material law captures the extreme temperature conditions and the damage behavior of the alloys. To validate the model, representative quantities of the rubbing process are determined and compared with experimental data from the literature. The simulation results correctly reproduce the observations made on a test rig with a reference stainless steel material (AISI 304). A parametric study using the nickel-based superalloys reveals a clear dependency of the rubbing behavior on the sliding and incursion velocity. Compared to each other, the two superalloys studied exhibit a different rubbing behavior.

Mechanical Behavior of Free-Standing Fuel Cell Electrodes on Water Surface.

PubMed

Kim, Sanwi; Kim, Jae-Han; Oh, Jong-Gil; Jang, Kyung-Lim; Jeong, Byeong-Heon; Hong, Bo Ki; Kim, Taek-Soo

2016-06-22

Fundamental understanding of the mechanical behavior of polymer electrolyte fuel cell electrodes as free-standing materials is essential to develop mechanically robust fuel cells. However, this has been a significant challenge due to critical difficulties, such as separating the pristine electrode from the substrate without damage and precisely measuring the mechanical properties of the very fragile and thin electrodes. We report the mechanical behavior of free-standing fuel cell electrodes on the water surface through adopting an innovative ice-assisted separation method to separate the electrode from decal transfer film. It is found that doubling the ionomer content in electrodes increases not only the tensile stress at the break and the Young's modulus (E) of the electrodes by approximately 2.1-3.5 and 1.7-2.4 times, respectively, but also the elongation at the break by approximately 1.5-1.7 times, which indicates that stronger, stiffer, and tougher electrodes are attained with increasing ionomer content, which have been of significant interest in materials research fields. The scaling law relationship between Young's modulus and density (ρ) has been unveiled as E ∼ ρ(1.6), and it is compared with other materials. These findings can be used to develop mechanically robust electrodes for fuel cell applications.

Characterization of Microporous Insulation, Microsil

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

Thomas, R.

Microsil microporous insulation has been characterized by Lawrence Livermore National Laboratory for possible use in structural and thermal applications in the DPP-1 design. Qualitative test results have provided mechanical behavioral characteristics for DPP-1 design studies and focused on the material behavioral response to being crushed, cyclically loaded, and subjected to vibration for a confined material with an interference fit or a radial gap. Quantitative test results have provided data to support the DPP-1 FEA model analysis and verification and were used to determine mechanical property values for the material under a compression load. The test results are documented within thismore » report.« less

Application of holographic interferometry for analysis of the dynamic and modal characteristics of an advanced exotic metal airfoil structure

NASA Astrophysics Data System (ADS)

Fein, Howard

1999-03-01

Holographic Interferometry has been successfully employed to characterize the materials and behavior of diverse types of structures under stress. Specialized variations of this technology have also been applied to define dynamic and vibration related structural behavior. Such applications of holographic technique offer some of the most effective methods of modal and dynamic analysis available. Real-time dynamic testing of the modal and mechanical behavior of aerodynamic control and airfoil structures for advanced aircraft has always required advanced instrumentation for data collection in either actual flight test or wind-tunnel simulations. Advanced optical holography techniques are alternate methods which result in actual full-field behavioral data on the ground in a noninvasive environment. These methods offer significant insight in both the development and subsequent operational test and modeling of advanced exotic metal control structures and their integration with total vehicle system dynamics. Structures and materials can be analyzed with very low amplitude excitation and the resultant data can be used to adjust the accuracy mathematically derived structural and behavioral models. Holographic Interferometry offers a powerful tool to aid in the developmental engineering of exotic metal structures for high stress applications. Advanced Titanium alloy is a significant example of these sorts of materials which has found continually increased use in advanced aerodynamic, undersea, and other highly mobil platforms. Aircraft applications in particular must consider environments where extremes in vibration and impulsive mechanical stress can affect both operation and structural stability. These considerations present ideal requisites for analysis using advanced holographic methods in the initial design and test of structures made with such advanced materials. Holographic techniques are nondestructive, real- time, and definitive in allowing the identification of vibrational modes, displacements, and motion geometries. Such information can be crucial to the determination of mechanical configurations and designs as well as operational parameters of structural components fabricated from advanced and exotic materials. Anomalous behavioral characteristics can be directly related to hidden structural or mounting anomalies and defects. Deriving such information can be crucial to the determination of mechanical configurations and designs, as well as critical operational parameters of structural components fabricated from advanced and exotic materials.

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Evaluating psychosocial and behavioral mechanisms of change in a tailored communication intervention.

PubMed

Elder, John P; Ayala, Guadalupe X; Slymen, Donald J; Arredondo, Elva M; Campbell, Nadia R

2009-04-01

This study examined the impact of a tailored nutrition intervention at 3 and 6 months postintervention. In all, 357 Latinas were randomly assigned to one of three conditions: (1) a control condition comprised of previously developed Spanish language targeted materials, (2) tailored print materials, or (3) tailored print materials accompanied by personalized dietary counseling via lay heath advisors (promotoras). At 6 months postintervention, significant group by time interactions were observed on the dietary behavioral strategies scales. The promotora condition resulted in significant behavior change initially; however, receipt of tailored and control materials was instrumental in continued behavior change after intervention activities had ceased. Group main effects suggested that the promotora condition was superior at reducing barriers and improving family interactions supporting healthy behaviors. The promotora model is an effective method for changing important dietary behaviors and psychosocial determinants, but longer term behavior change is achievable with less expensive intervention methods.

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.

Mechanical behavior of nanocrystalline NaCl islands on Cu(111).

PubMed

Bombis, Ch; Ample, F; Mielke, J; Mannsberger, M; Villagómez, C J; Roth, Ch; Joachim, C; Grill, L

2010-05-07

The mechanical response of ultrathin NaCl crystallites of nanometer dimensions upon manipulation with the tip of a scanning tunneling microscope (STM) is investigated, expanding STM manipulation to various nanostructuring modes of inorganic materials as cutting, moving, and cracking. In the light of theoretical calculations, our results reveal that atomic-scale NaCl islands can behave elastically and follow a classical Hooke's law. When the elastic limit of the nanocrystallites is reached, the STM tip induces atomic dislocations and consequently the regime of plastic deformation is entered. Our methodology is paving the way to understand the mechanical behavior and properties of other nanoscale materials.

Teaching Methodology of Flexible Pavement Materials and Pavement Systems

ERIC Educational Resources Information Center

Mehta, Yusuf; Najafi, Fazil

2004-01-01

Flexible pavement materials exhibit complex mechanical behavior, in the sense, that they not only show stress and temperature dependency but also are sensitive to moisture conditions. This complex behavior presents a great challenge to the faculty in bringing across the level of complexity and providing the concepts needed to understand them. The…

Characterization of deformable materials in the THOR dummy

DOT National Transportation Integrated Search

2000-01-01

Methodologies used to characterize the mechanical behavior of various materials used in the construction of the crash test dummy called THOR (Test device for Human Occupant Restraint) are described. These materials include polyurethane, neoprene, and...

Aeroelastic flutter enhancement by exploiting the combined use of shape memory alloys and nonlinear piezoelectric circuits

NASA Astrophysics Data System (ADS)

Sousa, Vagner Candido de; Silva, Tarcísio Marinelli Pereira; De Marqui Junior, Carlos

2017-10-01

In this paper, the combined effects of semi-passive control using shunted piezoelectric material and passive pseudoelastic hysteresis of shape memory springs on the aerolastic behavior of a typical section is investigated. An aeroelastic model that accounts for the presence of both smart materials employed as mechanical energy dissipation devices is presented. The Brinson model is used to simulate the shape memory material. New expressions for the modeling of the synchronized switch damping on inductor technique (developed for enhanced piezoelectric damping) are presented, resulting in better agreement with experimental data. The individual effects of each nonlinear mechanism on the aeroelastic behavior of the typical section are first verified. Later, the combined effects of semi-passive piezoelectric control and passive shape memory alloy springs on the post-critical behavior of the system are discussed in details. The range of post-flutter airflow speeds with stable limit cycle oscillations is significantly increased due to the combined effects of both sources of energy dissipation, providing an effective and autonomous way to modify the behavior of aeroelastic systems using smart materials.

Computational Modeling of Interfacial Behaviors in Nanocomposite Materials

PubMed Central

Lin, Liqiang; Wang, Xiaodu; Zeng, Xiaowei

2017-01-01

Towards understanding the bulk material response in nanocomposites, an interfacial zone model was proposed to define a variety of material interface behaviors (e.g. brittle, ductile, rubber-like, elastic-perfectly plastic behavior etc.). It also has the capability to predict bulk material response though independently control of the interface properties (e.g. stiffness, strength, toughness). The mechanical response of granular nanocomposite (i.e. nacre) was investigated through modeling the “relatively soft” organic interface as an interfacial zone among “hard” mineral tablets and simulation results were compared with experimental measurements of stress-strain curves in tension and compression tests. Through modeling varies material interfaces, we found out that the bulk material response of granular nanocomposite was regulated by the interfacial behaviors. This interfacial zone model provides a possible numerical tool for qualitatively understanding of structure-property relationships through material interface design. PMID:28983123

Computational Simulation of the Formation and Material Behavior of Ice

NASA Technical Reports Server (NTRS)

Tong, Michael T.; Singhal, Surendra N.; Chamis, Christos C.

1994-01-01

Computational methods are described for simulating the formation and the material behavior of ice in prevailing transient environments. The methodology developed at the NASA Lewis Research Center was adopted. A three dimensional finite-element heat transfer analyzer was used to predict the thickness of ice formed under prevailing environmental conditions. A multi-factor interaction model for simulating the material behavior of time-variant ice layers is presented. The model, used in conjunction with laminated composite mechanics, updates the material properties of an ice block as its thickness increases with time. A sample case of ice formation in a body of water was used to demonstrate the methodology. The results showed that the formation and the material behavior of ice can be computationally simulated using the available composites technology.

Nonlinear Constitutive Relations for High Temperature Applications

NASA Technical Reports Server (NTRS)

1983-01-01

The topics of discussion addressed were material behavior, design analysis, deformation kinetics, metallurgical characterization, mechanical subelement models, stress analysis, fracture mechanics, viscoplasticity, and thermal loading.

Ferroelectric Phase Transformations for Energy Conversion and Storage Applications

NASA Astrophysics Data System (ADS)

Jo, Hwan Ryul

Ferroelectric materials possess a spontaneous polarization and actively respond to external mechanical, electrical, and thermal loads. Due to their coupled behavior, ferroelectric materials are used in products such as sensors, actuators, detectors, and transducers. However, most current applications rely on low-energy conversion that involves low magnitude fields. They utilize the low-field linear properties of ferroelectric materials (piezoelectric, pyroelectric) and do not take full advantage of the large-field nonlinear behavior (irreversible domain wall motion, phase transformations) that can occur in ferroelectric materials. When external fields exceed a certain critical level, a structural transformation of the crystal can occur. These phase transformations are accompanied by a much larger response than the linear piezoelectric and pyroelectric responses, by as much as a multiple of ten times in the magnitude. This makes the non-linear behavior in ferroelectric materials promising for energy harvesting and energy storage technologies which will benefit from large-energy conversion. Yet, the ferroelectric phase transformation behavior under large external fields have been less studied and only a few studies have been directed at utilizing this large material response in applications. This dissertation addresses the development ferroelectric phase transformation-based applications, with particular focus on the materials. Development of the ferroelectric phase transformation-based applications was approached in several steps. First, the phase transformation behavior was fully characterized and understood by measuring the phase transformation responses under mechanical, electrical, thermal, and combined loads. Once the behavior was well characterized, systems level applications were addressed. This required assessing the effect of the phase transformation behavior on system performance. The performance of ferroelectric devices is strongly dependent on material properties and phase transformation behavior which can be tailored by modifying the chemical composition, processing conditions, and the loading history (poling). This results in optimization of system performance by tailoring material properties and phase transformation behavior. This approach applied to three ferroelectric phase transformation-based applications: 1. Ferroelectric energy generation 2. Ferroelectric high-energy storage capacitor 3. Ferroelectric thermal energy harvesting. This dissertation has addressed tuning the large field properties for phase transformation-based systems.

The Merging of Fatigue and Fracture Mechanics Concepts: A Historical Perspective

NASA Technical Reports Server (NTRS)

Newman, James C., Jr.

1997-01-01

The seventh Jerry L. Swedlow Memorial Lecture presents a review of some of the technical developments, that have occurred during the past 40 years, which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of 'crack propagation.' As methods to observe the 'fatigue' process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by 'crack size.' In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading, conditions. These mechanisms have also provided a rationale for developing, new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified 'fatigue' and 'fracture mechanics' concepts; and has bridged the cap between safe-life and durability/damage-tolerance design concepts.

Stress-strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings

NASA Astrophysics Data System (ADS)

Farrahi, G. H.; Ghodrati, M.; Azadi, M.; Rezvani Rad, M.

2014-08-01

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress-strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson-Cook law were applied to improve the estimation of the stress-strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.

An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Tian, Wen-Ling; Zeng, Wei; Yu, Li-Yuan

2016-06-01

Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young's modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0° to 75°. In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress-time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

Insights to regenerate materials: learning from nature

NASA Astrophysics Data System (ADS)

García-Aznar, J. M.; Valero, C.; Gómez-Benito, M. J.; Javierre, E.

2016-08-01

Self-healing materials, both biological and engineered, integrate the ability to repair themselves and recover their functionality using the resources inherently available to them. Although significant advances have been made, in recent years, for the design of different concepts of self-healing materials, this work aims to provide some insights into how living materials are able to regenerate or heal when a fracture or injury occurs. The main sensors that regulate this adaptive and regenerative behavior are the cells. These are able to sense the mechanical alterations in their surroundings and regulate their activity in order to remove dead tissue and/or create new tissue. Therefore, understanding how cells are able to regenerate tissues under complex and multiphysics conditions can define the biomimetics guidelines to heal through inert or traditional engineering materials. In this work, we present a combination of experiments and different kinds of multiscale and multiphysics models in order to understand how mechanics regulate some mechanisms at cell and tissue level. This combination of results aims to gain insight into the development of novel strategies for self-healing materials, mimicking the behavior induced by cells and biological tissues.

Experimental characterization and microstructure linked modeling of mechanical behavior of ultra-thin aluminum foils used in packaging

NASA Astrophysics Data System (ADS)

Tabourot, Laurent; Charleux, Ludovic; Balland, Pascale; Sène, Ndèye Awa; Andreasson, Eskil

2018-05-01

This paper is based on the hypothesis that introducing distribution of mechanical properties is beneficial for modeling all kinds of mechanical behavior, even of ordinary metallic materials. To bring proof of its admissibility, it has to be first shown that modeling based on this assertion is able to efficiently describe standard mechanical behavior of materials. Searching for typical study case, it has been assessed that at a low scale, yield stresses could be strongly distributed in ultrathin aluminum foils used in packaging industry, offering opportunities to identifying their distribution and showing its role on the mechanical properties. Considering initially reduced modeling allow to establish a valuable connection between the hardening curve and the distribution of local yield stresses. This serves for finding initial value of distribution parameters in a more sophisticated identification procedure. With finally limited number of representative classes of local yield stresses, concretely 3 is enough, it is shown that a 3D finite element simulation involving limited numbers of elements returns realistic behavior of an ultrathin aluminum foil exerted to tensile test, in reference to experimental results. This gives way to large possibilities in modeling in order to give back complex experimental evidence.

An overview on the characterization and mechanical behavior of nanoporous Gold

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

Hodge, A M; Hayes, J R; Caro, J A

2005-09-13

In this paper we present what we believe are the most pressing issues in understanding the mechanical behavior of nanoporous foams. We have postulated that a gold foam presents the best candidate for a systematic study of nanoporous foams since it can be synthesized with a wide range of ligaments sizes and densities. We have also conducted preliminary tests that demonstrate (a) Au foams have a fracture behavior dictated by the ligament size, and (b) nanoporous Au is a high yield strength material. Thus, we have demonstrated the potential in developing nanoporous foams as a new class of high yieldmore » strength/low density materials.« less

Mechanics of Granular Materials (MGM) Test Cell

NASA Technical Reports Server (NTRS)

2000-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the compressed sand column with the protective water jacket removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Mechanics of Granular Materials (MGM) Cell

NASA Technical Reports Server (NTRS)

1996-01-01

One of three Mechanics of Granular Materials (MGM) test cells after flight on STS-79 and before impregnation with resin. Note that the sand column has bulged in the middle, and that the top of the column is several inches lower than the top of the plastic enclosure. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Mechanics of Granular Materials (MGM) Test Cell

NASA Technical Reports Server (NTRS)

2000-01-01

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the top of the sand column with the metal platten removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Biobased, self-healable, high strength rubber with tunicate cellulose nanocrystals.

PubMed

Cao, Liming; Yuan, Daosheng; Xu, Chuanhui; Chen, Yukun

2017-10-19

Cellulose nanocrystals represent a promising and environmentally friendly reinforcing nanofiller for polymers, especially for rubbers and elastomers. Here, a simple approach via latex mixing is used to fabricate biobased, healable rubber with high strength based on epoxidized natural rubber (ENR). Tunicate cellulose nanocrystals (t-CNs) isolated from marine biomass with a high aspect ratio are used to improve both mechanical properties and self-healing behavior of the material. By introducing dynamic hydrogen bond supramolecular networks between oxygenous groups of ENR and hydroxyl groups on the t-CN surface, together with chain interdiffusion in permanently but slightly cross-linked rubber, self-healing and mechanical properties are facilitated significantly in the resulting materials. Macroscopic tensile healing behavior and microscopic morphology analyses are carried out to evaluate the performance of the materials. Both t-CN content and healing time have significant influence on healing behavior. The results indicate that a synergistic effect between molecular interdiffusion and dynamic hydrogen bond supramolecular networks leads to the improved self-healing behavior.

Fracture Characteristics of Two High-Strength, Low-Alloy and Two Stainless Steels

DTIC Science & Technology

1977-01-01

conditions. The effects of hydrogen. and temper. embrittlement on the materials’ behavior when fractured under tensile and fatigue fonditions were... effects of hydrogen- and tomper-embrittlement have a bet, crystal structure, this plane has the type on the materials’ behavior when fractured under...A. Troiano, "The Role of lydrogen and Other Intersiftials high-strength, low-alloy structural steels generally used in the Mechanical Behavior ot

Mechanical Behavior of Dowel-Type Joints Made of Wood Scrimber Composite

PubMed Central

He, Minjuan; Tao, Duo; Li, Zheng; Li, Maolin

2016-01-01

As a renewable building material with low embodied energy characteristics, wood has gained more and more attention in the green and sustainable building industry. In terms of material resource and physical properties, scrimber composite not only makes full use of fast-growing wood species, but also has better mechanical performance and less inherent variability than natural wood material. In this study, the mechanical behavior of bolted beam-to-column joints built with a kind of scrimber composite was investigated both experimentally and numerically. Two groups of specimens were tested under monotonic and low frequency cyclic loading protocols. The experimental results showed that the bolted joints built with scrimber composite performed well in initial stiffness, ductility, and energy dissipation. A three-dimensional (3D) non-linear finite element model (FEM) for the bolted beam-to-column joints was then developed and validated by experimental results. The validated model was further used to investigate the failure mechanism of the bolted joints through stress analysis. This study can contribute to the application of the proposed scrimber composite in structural engineering, and the developed FEM can serve as a useful tool to evaluate the mechanical behavior of such bolted beam-to-column joints with different configurations in future research. PMID:28773703

Mechanical Behavior of Dowel-Type Joints Made of Wood Scrimber Composite.

PubMed

He, Minjuan; Tao, Duo; Li, Zheng; Li, Maolin

2016-07-15

As a renewable building material with low embodied energy characteristics, wood has gained more and more attention in the green and sustainable building industry. In terms of material resource and physical properties, scrimber composite not only makes full use of fast-growing wood species, but also has better mechanical performance and less inherent variability than natural wood material. In this study, the mechanical behavior of bolted beam-to-column joints built with a kind of scrimber composite was investigated both experimentally and numerically. Two groups of specimens were tested under monotonic and low frequency cyclic loading protocols. The experimental results showed that the bolted joints built with scrimber composite performed well in initial stiffness, ductility, and energy dissipation. A three-dimensional (3D) non-linear finite element model (FEM) for the bolted beam-to-column joints was then developed and validated by experimental results. The validated model was further used to investigate the failure mechanism of the bolted joints through stress analysis. This study can contribute to the application of the proposed scrimber composite in structural engineering, and the developed FEM can serve as a useful tool to evaluate the mechanical behavior of such bolted beam-to-column joints with different configurations in future research.

Modeling the dynamic crush of impact mitigating materials

NASA Astrophysics Data System (ADS)

Logan, R. W.; McMichael, L. D.

1995-05-01

Crushable materials are commonly utilized in the design of structural components to absorb energy and mitigate shock during the dynamic impact of a complex structure, such as an automobile chassis or drum-type shipping container. The development and application of several finite-element material models which have been developed at various times at LLNL for DYNA3D are discussed. Between the models, they are able to account for several of the predominant mechanisms which typically influence the dynamic mechanical behavior of crushable materials. One issue we addressed was that no single existing model would account for the entire gambit of constitutive features which are important for crushable materials. Thus, we describe the implementation and use of an additional material model which attempts to provide a more comprehensive model of the mechanics of crushable material behavior. This model combines features of the pre-existing DYNA models and incorporates some new features as well in an invariant large-strain formulation. In addition to examining the behavior of a unit cell in uniaxial compression, two cases were chosen to evaluate the capabilities and accuracy of the various material models in DYNA. In the first case, a model for foam filled box beams was developed and compared to test data from a four-point bend test. The model was subsequently used to study its effectiveness in energy absorption in an aluminum extrusion, spaceframe, vehicle chassis. The second case examined the response of the AT-400A shipping container and the performance of the overpack material during accident environments selected from 10CFR71 and IAEA regulations.

Design of Boiler Welding for Improvement of Lifetime and Cost Control.

PubMed

Thong-On, Atcharawadi; Boonruang, Chatdanai

2016-11-03

Fe-2.25Cr-1Mo a widely used material for headers and steam tubes of boilers. Welding of steam tube to header is required for production of boiler. Heat affected zone of the weld can have poor mechanical properties and poor corrosion behavior leading to weld failure. The cost of material used for steam tube and header of boiler should be controlled. This study propose a new materials design for boiler welding to improve the lifetime and cost control, using tungsten inert gas (TIG) welding of Fe-2.25Cr-1Mo tube to carbon steel pipe with chromium-containing filler. The cost of production could be reduced by the use of low cost material such as carbon steel pipe for boiler header. The effect of chromium content on corrosion behavior of the weld was greater than that of the microstructure. The lifetime of the welded boiler can be increased by improvement of mechanical properties and corrosion behavior of the heat affected zone.

Design of Boiler Welding for Improvement of Lifetime and Cost Control

PubMed Central

Thong-On, Atcharawadi; Boonruang, Chatdanai

2016-01-01

Fe-2.25Cr-1Mo a widely used material for headers and steam tubes of boilers. Welding of steam tube to header is required for production of boiler. Heat affected zone of the weld can have poor mechanical properties and poor corrosion behavior leading to weld failure. The cost of material used for steam tube and header of boiler should be controlled. This study propose a new materials design for boiler welding to improve the lifetime and cost control, using tungsten inert gas (TIG) welding of Fe-2.25Cr-1Mo tube to carbon steel pipe with chromium-containing filler. The cost of production could be reduced by the use of low cost material such as carbon steel pipe for boiler header. The effect of chromium content on corrosion behavior of the weld was greater than that of the microstructure. The lifetime of the welded boiler can be increased by improvement of mechanical properties and corrosion behavior of the heat affected zone. PMID:28774014

Effect of Sericin on Mechanical Behavior of Composite Material Reinforced by Silk Woven Fabric

NASA Astrophysics Data System (ADS)

Kimura, Teruo; Ino, Haruhiro; Hanada, Koji; Katori, Sigetaka

Recent, attention has been given to shift from glass fibers and carbon fibers to natural fibers for FRP composites for the goal of protecting the environment. This paper concerned with the application of silk fabric for composite materials. Polypropylene (PP) was used for the matrix material and the silk fabric composites were molded using a compression molding method. Especially, the effect of sericin on mechanical behaviors of composite materials was discussed. Good adhesion between silk and PP was obtained by removing the sericin existing around the fibroin. The tensile modulus of composite decreased with decreasing the sericin because of the flexibility of silk fibers without sericin. In particular, the higher Izod impact value was obtained for the composites containing the silk fibers without sericin.

Gradient Plasticity Model and its Implementation into MARMOT

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

Barker, Erin I.; Li, Dongsheng; Zbib, Hussein M.

2013-08-01

The influence of strain gradient on deformation behavior of nuclear structural materials, such as boby centered cubic (bcc) iron alloys has been investigated. We have developed and implemented a dislocation based strain gradient crystal plasticity material model. A mesoscale crystal plasticity model for inelastic deformation of metallic material, bcc steel, has been developed and implemented numerically. Continuum Dislocation Dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals, as well as polycrystalline materials by coupling CDD and crystal plasticity (CP). The dislocation density evolution law in thismore » model is mechanism-based, with parameters measured from experiments or simulated with lower-length scale models, not an empirical law with parameters back-fitted from the flow curves.« less

Impact Compaction of a Granular Material

NASA Astrophysics Data System (ADS)

Fenton, Gregg; Asay, Blaine; Todd, Steve; Grady, Dennis

2017-06-01

The dynamic behavior of granular materials has importance to a variety of engineering applications. Although, the mechanical behavior of granular materials have been studied extensively for several decades, the dynamic behavior of these materials remains poorly understood. High-quality experimental data are needed to improve our general understanding of granular material compaction physics. This paper describes how an instrumented plunger impact system can be used to measure the compaction process for granular materials at high and controlled strain rates and subsequently used for computational modelling. The experimental technique relies on a gas-gun driven plunger system to generate a compaction wave through a volume of granular material. This volume of material has been redundantly instrumented along the bed length to track the progression of the compaction wave, and the piston displacement is measured with Photon Doppler Velocimetry (PDV). Using the gathered experimental data along with the initial material tap density, a granular material equation of state can be determined.

Erosion of iron-chromium alloys by glass particles

NASA Technical Reports Server (NTRS)

Salik, J.; Buckley, D. H.

1984-01-01

The material loss upon erosion was measured for several iron-chromium alloys. Two types of erodent material were used: spherical glass beads and sharp particles of crushed glass. For erosion with glass beads the erosion resistance (defined as the reciprocal of material loss rate) was linearly dependent on hardness. This is in accordance with the erosion behavior of pure metals, but contrary to the erosion behavior of alloys of constant composition that were subjected to different heat treatments. For erosion with crushed glass, however, no correlation existed between hardness and erosion resistance. Instead, the erosion resistance depended on alloy composition rather than on hardness and increased with the chromium content of the alloy. The difference in erosion behavior for the two types of erodent particles suggested that two different material removal mechanisms were involved. This was confirmed by SEM micrographs of the eroded surfaces, which showed that for erosion with glass beads the mechanism of material removal was deformation-induced flaking of surface layers, or peening, whereas for erosion with crushed glass it was cutting or chopping.

Effects of Milling on the Fibrous Structure and Mechanical Behaviors of a Collagen Material--Leather

USDA-ARS?s Scientific Manuscript database

Leather, a fibrous collagen material, is a high value coproduct of the meat industry. Milling is being practiced in the tannery to mechanically tumble and therefore soften leather for adequate stiffness and feel. However, there is no report regarding its effects on the structure change and physica...

Influence of Austenitizing Parameters on Mechanical Behavior of Press Hardened Steels

NASA Astrophysics Data System (ADS)

Golem, Lindsay

Recent increases in the Corporate Average Fuel Economy standard have led to an increased focus on lightweight materials for use in vehicle architectures. In particular, press hardened steels (PHS) have been identified as suitable materials to reduce vehicle mass while maintaining or possibly improving vehicle crash performance. A fundamental understanding of the mechanical behavior of PHS with respect to changes in processing conditions is critical to their proper use. In this work, 22MnB5 Al-Si coated blanks were austenitized at several different times and temperatures to produce a range of prior austenite grain sizes. Mechanical behavior was evaluated using smooth sided tensile testing, double edge notch tensile testing, and free bend testing. Metrics, such as notch tensile strength, notch strength ratio, and notch displacement, which is based on the fracture mechanics parameter crack tip opening displacement, were derived from double edge notch tensile testing to assess material notch sensitivity and toughness as a function of processing conditions. Additionally, bend angle at maximum load, post uniform bending slope, and energy for fracture were measured using free bend testing to provide another means for evaluating mechanical behavior. Increasing the austenitizing temperature and hold time resulted in an increase in the measured prior austenite grain size; however, elevated austenitizing temperatures also increased the thickness of the coating interdiffusion layer. In the coated material, tensile strength decreased with increasing prior austenite grain size for both notched and smooth sided tensile samples, but minimal difference was observed in the strain to failure results. Notch displacement, bend angle at maximum load, and energy for fracture during free bend testing all decreased with increasing prior austenite grain size in the coated PHS and also showed a significant drop in measured behavior for the 1025 °C for 30 minutes austenitizing condition, which was not observed in smooth sided tensile testing. The drop in mechanical behavior for this condition was not observed when the coating was removed, which suggests that the interdiffusion layer may degrade the mechanical behavior of PHS. Bend angle at maximum load and energy for fracture in bend testing also decreased for the smallest prior austenite grain size conditions, which was not observed in any of the other testing methods. Results from the three testing methods indicate that differences in the stress and strain state associated with each test influences their ability to discern differences between microstructure and processing conditions of press hardened steels.

Fracture behavior of reinforced aluminum alloy matrix composites using thermal imaging tools

NASA Astrophysics Data System (ADS)

Avdelidis, N. P.; Exarchos, D.; Vazquez, P.; Ibarra-Castanedo, C.; Sfarra, S.; Maldague, X. P. V.; Matikas, T. E.

2016-05-01

In this work the influence of the microstructure at the vicinity of the interface on the fracture behavior of particulate-reinforced aluminum alloy matrix composites (Al/SiCp composites) is studied by using thermographic tools. In particular, infrared thermography was used to monitor the plane crack propagation behavior of the materials. The deformation of solid materials is almost always accompanied by heat release. When the material becomes deformed or is damaged and fractured, a part of the energy necessary to initiate and propagate the damage is transformed in an irreversible way into heat. The thermal camera detects the heat wave, generated by the thermo-mechanical coupling and the intrinsic dissipated energy during mechanical loading of the sample. By using an adapted detector, thermography records the two dimensional "temperature" field as it results from the infrared radiation emitted by the object. The principal advantage of infrared thermography is its noncontact, non-destructive character. This methodology is being applied to characterise the fracture behavior of the particulate composites. Infrared thermography is being used to monitor the plane crack propagation behavior of such materials. Furthermore, an innovative approach to use microscopic measurements using IR microscopic lenses was attempted, in order to enable smaller features (in the micro scale) to be imaged with accuracy and assurance.

Unit mechanisms of fission gas release: Current understanding and future needs

DOE PAGES

Tonks, Michael; Andersson, David; Devanathan, Ram; ...

2018-03-01

Gaseous fission product transport and release has a large impact on fuel performance, degrading fuel and gap properties. While gaseous fission product behavior has been investigated with bulk reactor experiments and simplified analytical models, recent improvements in experimental and modeling approaches at the atomistic and mesoscales are beginning to reveal new understanding of the unit mechanisms that define fission product behavior. Here, existing research on the basic mechanisms of fission gas release during normal reactor operation are summarized and critical areas where work is needed are identified. Here, this basic understanding of the fission gas behavior mechanisms has the potentialmore » to revolutionize our ability to predict fission product behavior and to design fuels with improved performance. In addition, this work can serve as a model on how a coupled experimental and modeling approach can be applied to understand the unit mechanisms behind other critical behaviors in reactor materials.« less

Unit mechanisms of fission gas release: Current understanding and future needs

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

Tonks, Michael; Andersson, David; Devanathan, Ram

Gaseous fission product transport and release has a large impact on fuel performance, degrading fuel and gap properties. While gaseous fission product behavior has been investigated with bulk reactor experiments and simplified analytical models, recent improvements in experimental and modeling approaches at the atomistic and mesoscales are beginning to reveal new understanding of the unit mechanisms that define fission product behavior. Here, existing research on the basic mechanisms of fission gas release during normal reactor operation are summarized and critical areas where work is needed are identified. Here, this basic understanding of the fission gas behavior mechanisms has the potentialmore » to revolutionize our ability to predict fission product behavior and to design fuels with improved performance. In addition, this work can serve as a model on how a coupled experimental and modeling approach can be applied to understand the unit mechanisms behind other critical behaviors in reactor materials.« less

Unit mechanisms of fission gas release: Current understanding and future needs

NASA Astrophysics Data System (ADS)

Tonks, Michael; Andersson, David; Devanathan, Ram; Dubourg, Roland; El-Azab, Anter; Freyss, Michel; Iglesias, Fernando; Kulacsy, Katalin; Pastore, Giovanni; Phillpot, Simon R.; Welland, Michael

2018-06-01

Gaseous fission product transport and release has a large impact on fuel performance, degrading fuel and gap properties. While gaseous fission product behavior has been investigated with bulk reactor experiments and simplified analytical models, recent improvements in experimental and modeling approaches at the atomistic and mesoscales are beginning to reveal new understanding of the unit mechanisms that define fission product behavior. Here, existing research on the basic mechanisms of fission gas release during normal reactor operation are summarized and critical areas where work is needed are identified. This basic understanding of the fission gas behavior mechanisms has the potential to revolutionize our ability to predict fission product behavior and to design fuels with improved performance. In addition, this work can serve as a model on how a coupled experimental and modeling approach can be applied to understand the unit mechanisms behind other critical behaviors in reactor materials.

Low-Velocity Impact Wear Behavior of Ball-to-Flat Contact Under Constant Kinetic Energy

NASA Astrophysics Data System (ADS)

Wang, Zhang; Cai, Zhen-bing; Chen, Zhi-qiang; Sun, Yang; Zhu, Min-hao

2017-11-01

The impact tests were conducted on metallic materials with different bulk hardness and Young's moduli. Analysis of the dynamics response during the tribological process showed that the tested materials had similar energy absorption, where the peak contact force increased as the tests continued. Moreover, wear volume decreased with the increase in Young's modulus of metals, except for Cr with a relatively low hardness. Wear rate was gradually reduced to a steady stage with increasing cycles, which was attributed to the decrease in contact stress and work-hardening effect. The main wear mechanism of impact was characterized by delamination, and the specific surface degradation mechanisms were depending on the mechanical properties of materials. The absorbed energy was used to the propagation of micro-cracks in the subsurface instead of plastic deformation, when resistance of friction wear and plastic behavior was improved. Hence, both the hardness and Young's modulus played important roles in the impact wear of metallic materials.

Modeling the Mechanical Behavior of Ceramic Matrix Composite Materials

NASA Technical Reports Server (NTRS)

Jordan, William

1998-01-01

Ceramic matrix composites are ceramic materials, such as SiC, that have been reinforced by high strength fibers, such as carbon. Designers are interested in using ceramic matrix composites because they have the capability of withstanding significant loads while at relatively high temperatures (in excess of 1,000 C). Ceramic matrix composites retain the ceramic materials ability to withstand high temperatures, but also possess a much greater ductility and toughness. Their high strength and medium toughness is what makes them of so much interest to the aerospace community. This work concentrated on two different tasks. The first task was to do an extensive literature search into the mechanical behavior of ceramic matrix composite materials. This report contains the results of this task. The second task was to use this understanding to help interpret the ceramic matrix composite mechanical test results that had already been obtained by NASA. Since the specific details of these test results are subject to the International Traffic in Arms Regulations (ITAR), they are reported in a separate document (Jordan, 1997).

Microstructure and Mechanical Behavior of Porous Ti–6Al–4V Processed by Spherical Powder Sintering

PubMed Central

Reig, Lucía; Tojal, Concepción; Busquets, David J.; Amigó, Vicente

2013-01-01

Reducing the stiffness of titanium is an important issue to improve the behavior of this material when working together with bone, which can be achieved by generating a porous structure. The aim of this research was to analyze the porosity and mechanical behavior of Ti–6Al–4V porous samples developed by spherical powder sintering. Four different microsphere sizes were sintered at temperatures ranging from 1300 to 1400 °C for 2, 4 and 8 h. An open, interconnected porosity was obtained, with mean pore sizes ranging from 54.6 to 140 µm. The stiffness of the samples diminished by as much as 40% when compared to that of solid material and the mechanical properties were affected mainly by powder particles size. Bending strengths ranging from 48 to 320 MPa and compressive strengths from 51 to 255 MPa were obtained. PMID:28788365

Microstructure and Mechanical Behavior of Porous Ti-6Al-4V Processed by Spherical Powder Sintering.

PubMed

Reig, Lucía; Tojal, Concepción; Busquets, David J; Amigó, Vicente

2013-10-23

Reducing the stiffness of titanium is an important issue to improve the behavior of this material when working together with bone, which can be achieved by generating a porous structure. The aim of this research was to analyze the porosity and mechanical behavior of Ti-6Al-4V porous samples developed by spherical powder sintering. Four different microsphere sizes were sintered at temperatures ranging from 1300 to 1400 °C for 2, 4 and 8 h. An open, interconnected porosity was obtained, with mean pore sizes ranging from 54.6 to 140 µm. The stiffness of the samples diminished by as much as 40% when compared to that of solid material and the mechanical properties were affected mainly by powder particles size. Bending strengths ranging from 48 to 320 MPa and compressive strengths from 51 to 255 MPa were obtained.

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

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

Montgomery, Robert; Tomé, Carlos; Liu, Wenfeng

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. CASL has endeavored to improve upon this approach by incorporating a microstructurally-based, atomistically-informed, zirconium alloy mechanical deformation analysis capability into the BISON-CASL engineering scale fuel performance code. Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed bymore » Lebensohn and Tome´ [2], has been coupled with BISON-CASL to represent the mechanistic material processes controlling the deformation behavior of the cladding. A critical component of VPSC is the representation of the crystallographic orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON-CASL and provides initial results utilizing the coupled functionality.« less

Extreme mechanical properties of materials under extreme pressure and temperature conditions (Invited)

NASA Astrophysics Data System (ADS)

Kavner, A.; Armentrout, M. M.; Xie, M.; Weinberger, M.; Kaner, R. B.; Tolbert, S. H.

2010-12-01

A strong synergy ties together the high-pressure subfields of mineral physics, solid-state physics, and materials engineering. The catalog of studies measuring the mechanical properties of materials subjected to large differential stresses in the diamond anvil cell demonstrates a significant pressure-enhancement of strength across many classes of materials, including elemental solids, salts, oxides, silicates, and borides and nitrides. High pressure techniques—both radial diffraction and laser heating in the diamond anvil cell—can be used to characterize the behavior of ultrahard materials under extreme conditions, and help test hypotheses about how composition, structure, and bonding work together to govern the mechanical properties of materials. The principles that are elucidated by these studies can then be used to help design engineering materials to encourage desired properties. Understanding Earth and planetary interiors requires measuring equations of state of relevant materials, including oxides, silicates, and metals under extreme conditions. If these minerals in the diamond anvil cell have any ability to support a differential stress, the assumption of quasi-hydrostaticity no longer applies, with a resulting non-salubrious effect on attempts to measure equation of state. We illustrate these applications with the results of variety of studies from our laboratory and others’ that have used high-pressure radial diffraction techniques and also laser heating in the diamond anvil cell to characterize the mechanical properties of a variety of ultrahard materials, especially osmium metal, osmium diboride, rhenium diboride, and tungsten tetraboride. We compare ambient condition strength studies such as hardness testing with high-pressure studies, especially radial diffraction under differential stress. In addition, we outline criteria for evaluating mechanical properties of materials at combination high pressures and temperatures. Finally, we synthesize our understanding of mechanical properties and composite behavior to suggest new approaches to designing high-pressure experiments to target specific measurements of a wide variety of mechanical properties.

The merging of fatigue and fracture mechanics concepts: a historical perspective

NASA Astrophysics Data System (ADS)

Newman, J. C.

1998-07-01

In this review, some of the technical developments that have occurred during the past 40 years are presented which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of “crack propagation”. As methods to observe the “fatigue” process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by “crack size”. In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading conditions. These mechanisms have also provided a rationale for developing new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified “fatigue” and “fracture mechanics” concepts; and has bridged the gap between safe-life and durability/damage-tolerance design concepts.

Sorption/Desorption Behavior and Mechanism of NH4(+) by Biochar as a Nitrogen Fertilizer Sustained-Release Material.

PubMed

Cai, Yanxue; Qi, Hejinyan; Liu, Yujia; He, Xiaowei

2016-06-22

Biochar, the pyrolysis product of biomass material with limited oxygen, has the potential to increase crop production and sustained-release fertilizer, but the understanding of the reason for improving soil fertility is insufficient, especially the behavior and mechanism of ammonium sulfate. In this study, the sorption/desorption effect of NH4(+) by biochar deriving from common agricultural wastes under different preparation temperatures from 200 to 500 °C was studied and its mechanism was discussed. The results showed that biochar displayed excellent retention ability in holding NH4(+) above 90% after 21 days under 200 °C preparation temperature, and it can be deduced that the oxygen functional groups, such as carboxyl and keto group, played the primary role in adsorbing NH4(+) due to hydrogen bonding and electrostatic interaction. The sorption/desorption effect and mechanism were studied for providing an optional way to dispose of agricultural residues into biochar as a nitrogen fertilizer sustained-release material under suitable preparation temperature.

C-Coupon Studies of CMCS: Fracture Behavior and Microstructural Characterization

NASA Technical Reports Server (NTRS)

Hurwitz, Frances I.; Calomino, Anthony M.; McCue, Terry R.; Abdul-Aziz, Ali

2001-01-01

A curved beam 'C-coupon' was used to assess fracture behavior in a Sylramic(tm)/melt infiltration (MI) SiC matrix composite. Failure stresses and fracture mechanisms, as determined by optical and scanning electron microstructural analysis, are compared with finite element stress calculations to analyze failure modes. Material microstructure was found to have a strong influence on mechanical behavior. Fracture occurs in interlaminar tension (ILT), provided that the ratio of ILT to tensile strength for the material is less than the ratio of radial to hoop stresses for the C-coupon geometry. Utilization of 3D architectures to improve interlaminar strength requires significant development efforts to incorporate through thickness fibers in regions with high curvatures while maintaining uniform thickness, radius, and microstructure.

Topological interlocking provides stiffness to stochastically micro-cracked materials beyond the transport percolation limit

NASA Astrophysics Data System (ADS)

Pal, Anirban; Picu, Catalin; Lupulescu, Marian V.

We study the mechanical behavior of two-dimensional, stochastically microcracked continua in the range of crack densities close to, and above the transport percolation threshold. We show that these materials retain stiffness up to crack densities much larger than the transport percolation threshold, due to topological interlocking of sample sub-domains. Even with a linear constitutive law for the continuum, the mechanical behavior becomes non-linear in the range of crack densities bounded by the transport and stiffness percolation thresholds. The effect is due to the fractal nature of the fragmentation process and is not linked to the roughness of individual cracks. We associate this behavior to that of itacolumite, a sandstone that exhibits unusual flexibility.

Mechanical behavior of osteoporotic bone at sub-lamellar length scales

NASA Astrophysics Data System (ADS)

Jimenez-Palomar, Ines; Shipov, Anna; Shahar, Ron; Barber, Asa

2015-02-01

Osteoporosis is a disease known to promote bone fragility but the effect on the mechanical properties of bone material, which is independent of geometric effects, is particularly unclear. To address this problem, micro-beams of osteoporotic bone were prepared using focused ion beam (FIB) microscopy and mechanically tested in compression using an atomic force microscope (AFM) while observing using in situ electron microscopy. This experimental approach was shown to be effective at measuring the subtle changes in the mechanical properties of bone material required to evaluate the effects of osteoporosis. Osteoporotic bone material was found to have lower elastic modulus and increased strain to failure when compared to healthy bone material, while the strength of osteoporotic and healthy bone was similar. A mechanism is suggested based on these results and previous literature that indicates degradation of the organic material in osteoporosis bone is responsible for resultant mechanical properties.

Mechanical behavior of glass and Blackglas{reg_sign} ceramic matrix composite

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

Stawovy, R.H.; Kampe, S.L.; Curtin, W.A.

Room temperature tensile tests are reported on two low-cost ceramic matrix composite materials, comprised of matrices of Blackglas{reg_sign} and a proprietary glass composition each reinforced with Nicalon{reg_sign} SiC-based fibers. The measured mechanical behaviors, supplemented by post-fracture analysis of fiber pullout and fiber fracture mirrors, are compared in detail to the performance predicted theoretically. This allows for an assessment of the roles of the matrix, fiber strength, residual stresses, fiber geometry, and the fiber/matrix interfacial properties in determining mechanical response. The Blackglas{reg_sign} matrix cracks extensively during processing, and so the mechanical response is controlled by the deformation and fracture of themore » fiber bundle. The interfacial sliding resistance, {tau}, is determined to be {approx} 17 MPa and the in-situ (post-processed) fiber characteristic strength, {sigma}{sub c} is found to be {approx} 2.0 GPa, both similar to values reported in the literature for Nicalon{reg_sign}/CAS-glass systems. For the glass matrix, the unidirectional and cross-ply materials show marked differences in mechanical behavior. In the cross-ply composites, {tau} {approx} 14 MPa and {sigma}{sub c} {approx} 2.9 GPa; in the unidirectional variants, these values were 1.7 MPa and 1.6 GPa, respectively. With these data and other derived micromechanical parameters, the stress-strain and failure point of these materials was predicted using existing models, and excellent agreement with the experiments was obtained. These materials thus perform as expected given the in-situ fiber and interface properties. Notably, the cross-ply glass matrix composites exhibit high fiber strength retention and hence show tensile strengths that are better than other Nicalon{reg_sign}-based materials tested to date.« less

Short beam shear tests of polymeric laminates and unidirectional composites

NASA Technical Reports Server (NTRS)

Stinchcomb, W. W.; Henneke, E. G.

1980-01-01

The application of advanced composite materials in aerospace, ground transportation, and sporting industries are discussed. Failure theories for the design and mechanical behavior of composite materials are emphasized. Methods for detecting specific types of flaws are outlined. The effect of detected flaws on mechanical properties such as stiffness, strength, fatigue lifetime, or residual strength is described.

Yield stress materials in soft condensed matter

NASA Astrophysics Data System (ADS)

Bonn, Daniel; Denn, Morton M.; Berthier, Ludovic; Divoux, Thibaut; Manneville, Sébastien

2017-07-01

A comprehensive review is presented of the physical behavior of yield stress materials in soft condensed matter, which encompasses a broad range of materials from colloidal assemblies and gels to emulsions and non-Brownian suspensions. All these disordered materials display a nonlinear flow behavior in response to external mechanical forces due to the existence of a finite force threshold for flow to occur: the yield stress. Both the physical origin and rheological consequences associated with this nonlinear behavior are discussed and an overview is given of experimental techniques available to measure the yield stress. Recent progress is discussed concerning a microscopic theoretical description of the flow dynamics of yield stress materials, emphasizing, in particular, the role played by relaxation time scales, the interplay between shear flow and aging behavior, the existence of inhomogeneous shear flows and shear bands, wall slip, and nonlocal effects in confined geometries.

Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

NASA Astrophysics Data System (ADS)

Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

2018-03-01

Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

NASA Astrophysics Data System (ADS)

Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

2018-02-01

Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

The mechanical behavior of nanoscale metallic multilayers: A survey

NASA Astrophysics Data System (ADS)

Zhou, Q.; Xie, J. Y.; Wang, F.; Huang, P.; Xu, K. W.; Lu, T. J.

2015-06-01

The mechanical behavior of nanoscale metallic multilayers (NMMs) has attracted much attention from both scientific and practical views. Compared with their monolithic counterparts, the large number of interfaces existing in the NMMs dictates the unique behavior of this special class of structural composite materials. While there have been a number of reviews on the mechanical mechanism of microlaminates, the rapid development of nanotechnology brought a pressing need for an overview focusing exclusively on a property-based definition of the NMMs, especially their size-dependent microstructure and mechanical performance. This article attempts to provide a comprehensive and up-to-date review on the microstructure, mechanical property and plastic deformation physics of NMMs. We hope this review could accomplish two purposes: (1) introducing the basic concepts of scaling and dimensional analysis to scientists and engineers working on NMM systems, and (2) providing a better understanding of interface behavior and the exceptional qualities the interfaces in NMMs display at atomic scale.

Differences in Tribological Behaviors upon Switching Fixed and Moving Materials of Tribo-pairs including Metal and Polymer.

PubMed

Xu, Aijie; Tian, Pengyi; Wen, Shizhu; Guo, Fei; Hu, Yueqiang; Jia, Wenpeng; Dong, Conglin; Tian, Yu

2017-10-12

The coefficient of friction (COF) between two materials is usually believed to be an intrinsic property of the materials themselves. In this study, metals of stainless steel (304) and brass (H62), and polymers of polypropylene (PP) and polytetrafluoroethylene (PTFE) were tested on a standard ball-on-three-plates test machine. Significantly different tribological behaviors were observed when fixed and moving materials of tribo-pairs (metal/polymer) were switched. As an example, under the same applied load and rotating speed, the COF (0.49) between a rotating PP ball and three fixed H62 plates was approximately 2.3 times higher than that between switched materials of tribo-pairs. Meanwhile, the COF between H62 and PTFE was relatively stable. The unexpected tribological behaviors were ascribed to the thermal and mechanical properties of tribo-pairs. Theoretical analysis revealed that the differences in the maximum local temperature between switching the fixed and moving materials of tribo-pairs were consistent with the differences in the tested COF. This result indicated the precise prediction of the COF of two materials is complexcity, and that thermal and mechanical properties should be properly considered in designing tribo-pairs, because these properties may significantly affect tribological performance.

Mechanical charactization of sonar window materials

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

DeTeresa, S.J.; Groves, S.E.; Harwood, P.J.

1996-03-25

The three-dimensional mechanical behavior of thick Spectra/epoxy sonar window materials containing various special materials is summarized in this report. Three different materials, which were fabricated by two companies known as `A` and `B` were received from the Naval Warfare Center. The three materials designated `A with microspheres (A micron),` `A without microspheres (A),` and `B` were measured for all properties. The total number of tests was reduced through the assumption that the two orthogonal, in-place directions were identical. Consequently, these materials should have only six independent elastic variables. The measured constants and strengths are given.

From single fiber to macro-level mechanics: A structural finite-element model for elastomeric fibrous biomaterials

PubMed Central

D'Amore, Antonio; Amoroso, Nicholas; Gottardi, Riccardo; Hobson, Christopher; Carruthers, Christopher; Watkins, Simon; Wagner, William R.; Sacks, Michael S.

2014-01-01

In the present work, we demonstrate that the mesoscopic in-plane mechanical behavior of membrane elastomeric scaffolds can be simulated by replication of actual quantified fibrous geometries. Elastomeric electrospun polyurethane (ES-PEUU) scaffolds, with and without particulate inclusions, were utilized. Simulations were developed from experimentally-derived fiber network geometries, based on a range of scaffold isotropic and anisotropic behaviors. These were chosen to evaluate the effects on macro-mechanics based on measurable geometric parameters such as fiber intersections, connectivity, orientation, and diameter. Simulations were conducted with only the fiber material model parameters adjusted to match the macro-level mechanical test data. Fiber model validation was performed at the microscopic level by individual fiber mechanical tests using AFM. Results demonstrated very good agreement to the experimental data, and revealed the formation of extended preferential fiber orientations spanning the entire model space. We speculate that these emergent structures may be responsible for the tissue-like macroscale behaviors observed in electrospun scaffolds. To conclude, the modeling approach has implications for (1) gaining insight on the intricate relationship between fabrication variables, structure, and mechanics to manufacture more functional devices/materials, (2) elucidating the effects of cell or particulate inclusions on global construct mechanics, and (3) fabricating better performing tissue surrogates that could recapitulate native tissue mechanics. PMID:25128869

Coupling of Mechanical Behavior of Lithium Ion Cells to Electrochemical-Thermal (ECT) Models for Battery Crush

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

Zhang, Chao; Santhanagopalan, Shriram; Pesaran, Ahmad

Vehicle crashes can lead to crushing of the battery, damaging lithium ion battery cells and causing local shorts, heat generation, and thermal runaway. Simulating all the physics and geometries at the same time is challenging and takes a lot of effort; thus, simplifications are needed. We developed a material model for simultaneously modeling the mechanical-electrochemical-thermal behavior, which predicted the electrical short, voltage drop, and thermal runaway behaviors followed by a mechanical abuse-induced short. The effect of short resistance on the battery cell performance was studied.

Effect of Interface Structure on Mechanical Properties of Advanced Composite Materials

PubMed Central

Gan, Yong X.

2009-01-01

This paper deals with the effect of interface structures on the mechanical properties of fiber reinforced composite materials. First, the background of research, development and applications on hybrid composite materials is introduced. Second, metal/polymer composite bonded structures are discussed. Then, the rationale is given for nanostructuring the interface in composite materials and structures by introducing nanoscale features such as nanopores and nanofibers. The effects of modifying matrices and nano-architecturing interfaces on the mechanical properties of nanocomposite materials are examined. A nonlinear damage model for characterizing the deformation behavior of polymeric nanocomposites is presented and the application of this model to carbon nanotube-reinforced and reactive graphite nanotube-reinforced epoxy composite materials is shown. PMID:20054466

Understanding deformation mechanisms during powder compaction using principal component analysis of compression data.

PubMed

Roopwani, Rahul; Buckner, Ira S

2011-10-14

Principal component analysis (PCA) was applied to pharmaceutical powder compaction. A solid fraction parameter (SF(c/d)) and a mechanical work parameter (W(c/d)) representing irreversible compression behavior were determined as functions of applied load. Multivariate analysis of the compression data was carried out using PCA. The first principal component (PC1) showed loadings for the solid fraction and work values that agreed with changes in the relative significance of plastic deformation to consolidation at different pressures. The PC1 scores showed the same rank order as the relative plasticity ranking derived from the literature for common pharmaceutical materials. The utility of PC1 in understanding deformation was extended to binary mixtures using a subset of the original materials. Combinations of brittle and plastic materials were characterized using the PCA method. The relationships between PC1 scores and the weight fractions of the mixtures were typically linear showing ideal mixing in their deformation behaviors. The mixture consisting of two plastic materials was the only combination to show a consistent positive deviation from ideality. The application of PCA to solid fraction and mechanical work data appears to be an effective means of predicting deformation behavior during compaction of simple powder mixtures. Copyright © 2011 Elsevier B.V. All rights reserved.

Microstructure and Strain Rate Effects on the Mechanical Behavior of Particle Reinforced Epoxy-Based Reactive Materials

DTIC Science & Technology

2011-12-01

LIST OF TABLES 2.1 Experimentally measured mechanical properties of pure epoxy and Ni+ Al powder -reinforced composites...for the same quantity of Cu , Ni, and Al deposited . Figure taken from [31]. stronger reactivity of Cu with metals also caused clusters to form. In the...Experimentally measured mechanical properties of pure epoxy and Ni+ Al powder -reinforced composites. Table data is from [14] Material Density Measured E

Shock Wave Propagation in Cementitious Materials at Micro/Meso Scales

NASA Astrophysics Data System (ADS)

Rajendran, Arunachalam

2015-06-01

The mechanical and constitutive response of materials like cement, and bio materials like fish scale and abalone shell is very complex due to heterogeneities that are inherently present in the nano and microstructures. The intrinsic constitutive behaviors are driven by the chemical composition and the molecular, micro, and meso structures. Therefore, it becomes important to identify the material genome as the building block for the material. For instance, in cementitious materials, the genome of C-S-H phase (the glue or the paste) that holds the various clinkers, such as the dicalcium silicate, tricalcium silicate, calcium ferroaluminates, and others is extremely complex. Often mechanical behaviors of C-S-H type materials are influenced by the chemistry and the structures at all nano to micro length scales. By explicitly modeling the molecular structures using appropriate potentials, it is then possible to compute the elastic tensor from molecular dynamics simulations using all atom method. The elastic tensors for the C-S-H gel and other clinkers are determined using the software suite ``Accelrys Materials Studio.'' A strain rate dependent, fracture mechanics based tensile damage model has been incorporated into ABAQUS finite element code to model spall evolution in the heterogeneous cementitious material with all constituents explicitly modeled through one micron element resolution. This paper presents results from nano/micro/meso scale analyses of shock wave propagation in a heterogeneous cementitious material using both molecular dynamic and finite element codes.

Assessment of tbe Performance of Ablative Insulators Under Realistic Solid Rocket Motor Operating Conditions (a Doctoral Dissertation)

NASA Technical Reports Server (NTRS)

Martin, Heath Thomas

2013-01-01

Ablative insulators are used in the interior surfaces of solid rocket motors to prevent the mechanical structure of the rocket from failing due to intense heating by the high-temperature solid-propellant combustion products. The complexity of the ablation process underscores the need for ablative material response data procured from a realistic solid rocket motor environment, where all of the potential contributions to material degradation are present and in their appropriate proportions. For this purpose, the present study examines ablative material behavior in a laboratory-scale solid rocket motor. The test apparatus includes a planar, two-dimensional flow channel in which flat ablative material samples are installed downstream of an aluminized solid propellant grain and imaged via real-time X-ray radiography. In this way, the in-situ transient thermal response of an ablator to all of the thermal, chemical, and mechanical erosion mechanisms present in a solid rocket environment can be observed and recorded. The ablative material is instrumented with multiple micro-thermocouples, so that in-depth temperature histories are known. Both total heat flux and thermal radiation flux gauges have been designed, fabricated, and tested to characterize the thermal environment to which the ablative material samples are exposed. These tests not only allow different ablative materials to be compared in a realistic solid rocket motor environment but also improve the understanding of the mechanisms that influence the erosion behavior of a given ablative material.

Investigation of dental alginate and agar impression materials as a brain simulant for ballistic testing.

PubMed

Falland-Cheung, Lisa; Piccione, Neil; Zhao, Tianqi; Lazarjan, Milad Soltanipour; Hanlin, Suzanne; Jermy, Mark; Waddell, J Neil

2016-06-01

Routine forensic research into in vitro skin/skull/brain ballistic blood backspatter behavior has traditionally used gelatin at a 1:10 Water:Powder (W:P) ratio by volume as a brain simulant. A limitation of gelatin is its high elasticity compared to brain tissue. Therefore this study investigated the use of dental alginate and agar impression materials as a brain simulant for ballistic testing. Fresh deer brain, alginate (W:P ratio 91.5:8.5) and agar (W:P ratio 81:19) specimens (n=10) (11×22×33mm) were placed in transparent Perspex boxes of the same internal dimensions prior to shooting with a 0.22inch caliber high velocity air gun. Quantitative analysis to establish kinetic energy loss, vertical displacement elastic behavior and qualitative analysis to establish elasticity behavior was done via high-speed camera footage (SA5, Photron, Japan) using Photron Fastcam Viewer software (Version 3.5.1, Photron, Japan) and visual observation. Damage mechanisms and behavior were qualitatively established by observation of the materials during and after shooting. The qualitative analysis found that of the two simulant materials tested, agar behaved more like brain in terms of damage and showed similar mechanical response to brain during the passage of the projectile, in terms of energy absorption and vertical velocity displacement. In conclusion agar showed a mechanical and subsequent damage response that was similar to brain compared to alginate. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Behavior of stress generated in semiconductor chips with high-temperature joints: Influence of mechanical properties of joint materials

NASA Astrophysics Data System (ADS)

Ito, H.; Kuwahara, M.; Ohta, R.; Usui, M.

2018-04-01

High-temperature joint materials are indispensable to realizing next-generation power modules with high-output performance. However, crack initiation resulting from stress concentration in semiconductor chips joined with high-temperature joint materials remains a critical problem in high-temperature operation. Therefore, clarifying the quantitative influence of joint materials on the stress generated in chips is essential. This study investigates the stress behavior of chips joined by Ni-Sn solid-liquid interdiffusion (SLID), which results in a high-temperature joint material likely to generate cracks after joining or when under thermal cycling. The results are compared with those fabricated using three types of solders, Pb-10%Sn, Sn-0.7%Cu, and Sn-10%Sb (mass %), which are conventional joint materials with different melting points and mechanical properties. Using Ni-Sn SLID results in the generation of high compressive stress (500 MPa) without stress relaxation after the joining process in contrast to the case of solders in which the compressive stresses are low (<300 MPa) and decrease to still lower levels (<250 MPa). In addition, no stress relaxation occurs during thermal cycling when using Ni-Sn SLID, whereas stress relaxation is clearly observed during heating to 200 °C using solders. Different stress behaviors between Ni-Sn SLID and other joint materials are illustrated by their mechanical strength and resistance against plastic and creep deformation. These results suggest that stress relaxation in a chip is key in suppressing crack initiation in highly reliable modules during high-temperature operation.

Development of a Meso-Scale Material Model for Ballistic Fabric and Its Use in Flexible-Armor Protection Systems

NASA Astrophysics Data System (ADS)

Grujicic, M.; Bell, W. C.; Arakere, G.; He, T.; Xie, X.; Cheeseman, B. A.

2010-02-01

A meso-scale ballistic material model for a prototypical plain-woven single-ply flexible armor is developed and implemented in a material user subroutine for the use in commercial explicit finite element programs. The main intent of the model is to attain computational efficiency when calculating the mechanical response of the multi-ply fabric-based flexible-armor material during its impact with various projectiles without significantly sacrificing the key physical aspects of the fabric microstructure, architecture, and behavior. To validate the new model, a comparative finite element method analysis is carried out in which: (a) the plain-woven single-ply fabric is modeled using conventional shell elements and weaving is done in an explicit manner by snaking the yarns through the fabric and (b) the fabric is treated as a planar continuum surface composed of conventional shell elements to which the new meso-scale unit-cell based material model is assigned. The results obtained show that the material model provides a reasonably good description for the fabric deformation and fracture behavior under different combinations of fixed and free boundary conditions. Finally, the model is used in an investigation of the ability of a multi-ply soft-body armor vest to protect the wearer from impact by a 9-mm round nose projectile. The effects of inter-ply friction, projectile/yarn friction, and the far-field boundary conditions are revealed and the results explained using simple wave mechanics principles, high-deformation rate material behavior, and the role of various energy-absorbing mechanisms in the fabric-based armor systems.

Multidisciplinary tailoring of hot composite structures

NASA Technical Reports Server (NTRS)

Singhal, Surendra N.; Chamis, Christos C.

1993-01-01

A computational simulation procedure is described for multidisciplinary analysis and tailoring of layered multi-material hot composite engine structural components subjected to simultaneous multiple discipline-specific thermal, structural, vibration, and acoustic loads. The effect of aggressive environments is also simulated. The simulation is based on a three-dimensional finite element analysis technique in conjunction with structural mechanics codes, thermal/acoustic analysis methods, and tailoring procedures. The integrated multidisciplinary simulation procedure is general-purpose including the coupled effects of nonlinearities in structure geometry, material, loading, and environmental complexities. The composite material behavior is assessed at all composite scales, i.e., laminate/ply/constituents (fiber/matrix), via a nonlinear material characterization hygro-thermo-mechanical model. Sample tailoring cases exhibiting nonlinear material/loading/environmental behavior of aircraft engine fan blades, are presented. The various multidisciplinary loads lead to different tailored designs, even those competing with each other, as in the case of minimum material cost versus minimum structure weight and in the case of minimum vibration frequency versus minimum acoustic noise.

Micro-scale investigation on the quasi-static behavior of granular material

NASA Astrophysics Data System (ADS)

Li, Xia

Granular material exhibits complex responses when subjected to various external loading. Fundamental mechanisms have not been well established so far, including that about the critical state, one of the most important concepts in the modern soil mechanics. With the recognition that granular material is discrete in nature, the basic understanding can only be obtained from the particle scale. The complexity in granular material behavior lies in the fact that the macroscopic behavior of granular material is determined by not only the interactions operating at contacts, but also how the particles become arranged in space to form an internal structure. This research is aimed to microscopically investigate the influence of the internal structure and the fundamental mechanism about the critical state. In view of the extensive laboratory test data already available in the literature, a numerical simulation method, DEM, is employed as the tool to conduct particle-scale investigations. The contact model for two in-contact circular disks is derived theoretically from the elasticity theory, and the result is a linear contact model with constant stiffness and lateral sliding. Based on the contact model, a systematic series of numerical tests has been implemented, and the results can successfully reproduce the main characteristics in the behavior of natural granular material, under various loading conditions. The macro-micro relationship is the link between the investigations at the two worlds. The key point is to describe the internal structure with the two dual cell systems, a particle cell system and a void cell system. Based on these two systems, the stress and strain in a uniform field are equivalently expressed in terms of the contact forces/relative displacements, and the micro-geometrical variables. With the microstructural definition of the stress tensor, the stress state of granular material is studied microscopically. The stress-fabric-force relation is derived, based on the variables describing the statistics of the contact forces and the contact vectors. By studying the evolution of the micro-quantities during shearing, how the internal structure affects the macro stress state under different loading condition is revealed. With the assumption that the influence of the local variance in stress is ignorable, the response of granular material can be investigated based on the void cell system. Starting from the behavior of a single void cell, the evolutions of the internal structure and its influence on the response of granular material are explained. The stress ratio and the dilatancy behavior of granular material are investigated. The influences of the void ratio, the mean normal stress and the drainage condition are discussed. The fundamental mechanism of the critical state is studied in the framework of thermodynamics with properly considering the influence of the internal structure. The normalized stress ratio tensor at critical state is associated with the critical void cell anisotropy, corresponding to the maximal energy dissipation. The (e, p) relationship at critical state is associated with the critical combination of the void cell size and the contact interactions, corresponding to the minimal free energy. The investigation on the influence of the internal structure anisotropy on the granular material behavior and the critical state is carried out. The results show that at small strain levels, the behavior of granular material is mainly affected by the initial fabric. As shearing continuous, the internal structure of granular material is gradually changed. The granular material approaches the critical state, which is irrespective with the initial internal structure. The critical state of granular material is not unique. With different loading modes, the critical state of granular material, including both the critical stress ratio and the critical (e, p) relations, are found to be different. A fabric tensor is defined based on the characteristics of the void cells. The laboratory method to quantify the fabric anisotropy is proposed by deviatoric shearing. 3D numerical simulations have been carried out to investigate the influence of the loading mode, which is found to be an important factor in the large strain behavior of granular material. With the obtained microscopic understanding, the influence of contact model on granular material behavior is investigated. A method to quantify the fabric anisotropy is proposed. And a simple discussion on the state variable used in the elasto-plastic constitutive model is given.

A Tensile Specimen of Tailor Rolled Blanks with Equal Probability in Yield and Its Mechanical Behavior Analysis

PubMed Central

Zhang, Sijia; Liu, Xianghua; Liu, Lizhong

2018-01-01

In this paper, the microstructure and mechanical properties that distribute regulation along the rolling direction of tailor rolled blanks (TRB) were investigated. A tensile specimen with equal probability in yield (EYS) was first designed considering variation both in thickness and in material strength. The uniaxial tension test was carried out with a digital image correlation method to analyze the mechanical behaviors. The results showed that the strain distribution of EYS was homogeneous. From the results, it can be known that a new design philosophy for a TRB tensile specimen is reasonable and EYS is suitable to characterize the mechanical behavior of TRB. The true stress-strain curves of metal in different cross sections of TRB were calculated. On the basis of the true stress-strain curves, a material model of TRB was constructed and then implemented into finite element simulations of TRB uniaxial tensile tests. The strain distribution of numerical and experimental results was similar and the error between the elongation of the specimen after fracture obtained by experiment and FE ranged from 9.51% to 13.06%. Therefore, the simulation results match well with the experimental results and the material model has high accuracy and as well as practicability. PMID:29710772

Modeling the viscoplastic behavior of Inconel 718 at 1200 F

NASA Technical Reports Server (NTRS)

Abdel-Kader, M. S.; Eftis, J.; Jones, D. L.

1988-01-01

A large number of tests, including tensile, creep, fatigue, and creep-fatigue were performed to characterize the mechanical properties of Inconel 718 (a nickel based superalloy) at 1200 F, the operating temperature for turbine blades. In addition, a few attempts were made to model the behavior of Inconel 718 at 1200 F using viscoplastic theories. The Chaboche theory of viscoplasticity can model a wide variety of mechanical behavior, including monotonic, sustained, and cyclic responses of homogeneous, initially-isotropic, strain hardening (or softening) materials. It is shown how the Chaboche theory can be used to model the viscoplastic behavior of Inconel 718 at 1200 F. First, an algorithm was developed to systematically determine the material parameters of the Chaboche theory from uniaxial tensile, creep, and cyclic data. The algorithm is general and can be used in conjunction with similar high temperature materials. A sensitivity study was then performed and an optimal set of Chaboche's parameters were obtained. This study has also indicated the role of each parameter in modeling the response to different loading conditions.

A representative-sandwich model for simultaneously coupled mechanical-electrical-thermal simulation of a lithium-ion cell under quasi-static indentation tests

DOE PAGES

Zhang, Chao; Santhanagopalan, Shriram; Sprague, Michael A.; ...

2015-08-29

The safety behavior of lithium-ion batteries under external mechanical crush is a critical concern, especially during large scale deployment. We previously presented a sequentially coupled mechanical-electrical-thermal modeling approach for studying mechanical abuse induced short circuit. Here in this work, we study different mechanical test conditions and examine the interaction between mechanical failure and electrical-thermal responses, by developing a simultaneous coupled mechanical-electrical-thermal model. The present work utilizes a single representative-sandwich (RS) to model the full pouch cell with explicit representations for each individual component such as the active material, current collector, separator, etc. Anisotropic constitutive material models are presented to describemore » the mechanical properties of active materials and separator. The model predicts accurately the force-strain response and fracture of battery structure, simulates the local failure of separator layer, and captures the onset of short circuit for lithium-ion battery cell under sphere indentation tests with three different diameters. Electrical-thermal responses to the three different indentation tests are elaborated and discussed. Lastly, numerical studies are presented to show the potential impact of test conditions on the electrical-thermal behavior of the cell after the occurrence of short circuit.« less

A representative-sandwich model for simultaneously coupled mechanical-electrical-thermal simulation of a lithium-ion cell under quasi-static indentation tests

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

Zhang, Chao; Santhanagopalan, Shriram; Sprague, Michael A.

The safety behavior of lithium-ion batteries under external mechanical crush is a critical concern, especially during large scale deployment. We previously presented a sequentially coupled mechanical-electrical-thermal modeling approach for studying mechanical abuse induced short circuit. Here in this work, we study different mechanical test conditions and examine the interaction between mechanical failure and electrical-thermal responses, by developing a simultaneous coupled mechanical-electrical-thermal model. The present work utilizes a single representative-sandwich (RS) to model the full pouch cell with explicit representations for each individual component such as the active material, current collector, separator, etc. Anisotropic constitutive material models are presented to describemore » the mechanical properties of active materials and separator. The model predicts accurately the force-strain response and fracture of battery structure, simulates the local failure of separator layer, and captures the onset of short circuit for lithium-ion battery cell under sphere indentation tests with three different diameters. Electrical-thermal responses to the three different indentation tests are elaborated and discussed. Lastly, numerical studies are presented to show the potential impact of test conditions on the electrical-thermal behavior of the cell after the occurrence of short circuit.« less

Mechanical Properties and Failure of Biopolymers: Atomistic Reactions to Macroscale Response

PubMed Central

Jung, GangSeob; Qin, Zhao

2017-01-01

The behavior of chemical bonding under various mechanical loadings is an intriguing mechanochemical property of biological materials, and the property plays a critical role in determining their deformation and failure mechanisms. Because of their astonishing mechanical properties and roles in constituting the basis of a variety of physiologically relevant materials, biological protein materials have been intensively studied. Understanding the relation between chemical bond networks (structures) and their mechanical properties offers great possibilities to enable new materials design in nanotechnology and new medical treatments for human diseases. Here we focus on how the chemical bonds in biological systems affect mechanical properties and how they change during mechanical deformation and failure. Three representative cases of biomaterials related to the human diseases are discussed in case studies, including: amyloids, intermediate filaments, and collagen, each describing mechanochemical features and how they relate to the pathological conditions at multiple scales. PMID:26108895

Thermal - Hydraulic Behavior of Unsaturated Bentonite and Sand-Bentonite Material as Seal for Nuclear Waste Repository: Numerical Simulation of Column Experiments

NASA Astrophysics Data System (ADS)

Ballarini, E.; Graupner, B.; Bauer, S.

2015-12-01

For deep geological repositories of high-level radioactive waste (HLRW), bentonite and sand bentonite mixtures are investigated as buffer materials to form a a sealing layer. This sealing layer surrounds the canisters and experiences an initial drying due to the heat produced by HLRW and a successive re-saturation with fluid from the host rock. These complex thermal, hydraulic and mechanical processes interact and were investigated in laboratory column experiments using MX-80 clay pellets as well as a mixture of 35% sand and 65% bentonite. The aim of this study is to both understand the individual processes taking place in the buffer materials and to identify the key physical parameters that determine the material behavior under heating and hydrating conditions. For this end, detailed and process-oriented numerical modelling was applied to the experiments, simulating heat transport, multiphase flow and mechanical effects from swelling. For both columns, the same set of parameters was assigned to the experimental set-up (i.e. insulation, heater and hydration system), while the parameters of the buffer material were adapted during model calibration. A good fit between model results and data was achieved for temperature, relative humidity, water intake and swelling pressure, thus explaining the material behavior. The key variables identified by the model are the permeability and relative permeability, the water retention curve and the thermal conductivity of the buffer material. The different hydraulic and thermal behavior of the two buffer materials observed in the laboratory observations was well reproduced by the numerical model.

Mechanics: Statics; A Syllabus.

ERIC Educational Resources Information Center

Compo, Louis

The instructor's guide presents material for structuring an engineering fundamentals course covering the basic laws of statistics as part of a mechanical technology program. Detailed behavioral objectives are described for the following five areas of course content: principles of mechanics, two-dimensional equilibrium, equilibrium of internal…

Investigation on mechanical properties of basalt composite fabrics (experiment study)

NASA Astrophysics Data System (ADS)

Talebi Mazraehshahi, H.; Zamani, H.

2010-06-01

To fully appreciate the role and application of composite materials to structures, correct understanding of mechanical behaviors required for selection of optimum material. Fabric reinforced composites are composed of a matrix that is reinforced with pliable fabric, glass fabric is most popular reinforcement for different application specially in aircraft structure, although other fabric material are also used. At this study new fabric material called basalt with epoxy resin introduced and mechanical behaviors of this material investigated from view point of testing. For this study two type of fabric with different thickness used. Comparison between this composite reinforcement with popular reinforcement as carbon, glass, kevlar performed. To determine mechanical properties of epoxy based basalt fabric following test procedure performed : 1). Tensile testing according to ASTM D3039 in 0° and 90° direction to find ultimate strength in tension and shear, modulus of elasticity, elangation and ultimate strain. 2). Compression testing according to EN 2850 ultimate compression strength and maximum deformation under compression loading. 3). Shear testing according to ASTM D3518-94 to find in plane shear response of polymer matrix composites materials. 4). Predict flexural properties of sandwich construction which manufactured from basalt facing with PVC foam core according to ASTM C393-94. Material strength properties must be based on enough tests of material to meet the test procedure specifications [1]. For this reason six specimens were manufactured for testing and the tests were performed on them using an INSTRON machine model 5582. In the study, the effect of percent of resin in basalt reinforced composite was investigated. Also the weights of the ballast based composites with different percent of resin were measured with conventional composites. As the weight is an important parameter in aerospace industry when the designer wants to replace one material with another, the effect of weight must be considered. Weight measurement showed that the replacement of glass fabric reinforcement with basalt fabric has little effect on weight. Investigation also shows that mechanical behavior of basalt fabric is higher than glass fabric. This is due to the excellent mechanical properties of the ballast fabric such as Young modulus and strength in compare with the glass fabric. Figure1 shows the samples which used for tensile testing in warp direction.

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.

Fatigue behavior of a cross-ply ceramic matrix composite at elevated temperature under tension-tension loading. Master`s thesis

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

Steiner, C.D.

This study investigated the fatigue behavior and damage mechanisms of a (0/90)4s SiC/MAS ceramic matrix composite under tension-tension loading at two elevated temperatures and two frequencies. Stress and strain hystereses, maximum and minimum strain, and modulus of elasticity were evaluated to characterize the material behavior. Microscopy and fractography were used to evaluate damage progression and mechanisms. Fatigue life was independent of frequency at both temperatures.

Magnetic Field-Induced Phase Transformation in Magnetic Shape Memory Alloys with High Actuation Stress and Work Output

DTIC Science & Technology

2010-05-03

Mechanisms for Advanced Properties in Phase Transforming Materials , Materials Science & Technology 2009 Conference, October 25-29, 2009, Pittsburgh, PA...Advanced Properties in Phase Transforming Materials , Materials Science & Technology 2009 Conference, October 25-29, 2009, Pittsburgh, PA, 2009. 11...observed materials behavior. Indeed, measured materials properties were found not to be the exact indication of the materials real response

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.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

PubMed Central

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; Peng, Haowei; Deml, Ann M.; Matthews, Bethany E.; Schelhas, Laura T.; Toney, Michael F.; Gordon, Roy G.; Tumas, William; Perkins, John D.; Ginley, David S.; Gorman, Brian P.; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-01-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region. PMID:28630928

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

PubMed

Holder, Aaron M; Siol, Sebastian; Ndione, Paul F; Peng, Haowei; Deml, Ann M; Matthews, Bethany E; Schelhas, Laura T; Toney, Michael F; Gordon, Roy G; Tumas, William; Perkins, John D; Ginley, David S; Gorman, Brian P; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-06-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

DOE PAGES

Holder, Aaron M.; Siol, Sebastian; Ndione, Paul F.; ...

2017-06-07

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the criticalmore » composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.« less

The Influence of Pore Size on the Indentation Behavior of Metallic Nanoporous Materials: A Molecular Dynamics Study

PubMed Central

Esqué-de los Ojos, Daniel; Pellicer, Eva; Sort, Jordi

2016-01-01

In general, the influence of pore size is not considered when determining the Young’s modulus of nanoporous materials. Here, we demonstrate that the pore size needs to be taken into account to properly assess the mechanical properties of these materials. Molecular dynamics simulations of spherical indentation experiments on single crystalline nanoporous Cu have been undertaken in systems with: (i) a constant degree of porosity and variable pore diameter; and (ii) a constant pore diameter and variable porosity degree. The classical Gibson and Ashby expression relating Young’s modulus with the relative density of the nanoporous metal is modified to include the influence of the pore size. The simulations reveal that, for a fixed porosity degree, the mechanical behavior of materials with smaller pores differs more significantly from the behavior of the bulk, fully dense counterpart. This effect is ascribed to the increase of the overall surface area as the pore size is reduced, together with the reduced coordination number of the atoms located at the pores edges. PMID:28773476

Determination of the axial and circumferential mechanical properties of the skin tissue using experimental testing and constitutive modeling.

PubMed

Karimi, Alireza; Navidbakhsh, Mahdi; Haghighatnama, Maedeh; Haghi, Afsaneh Motevalli

2015-01-01

The skin, being a multi-layered material, is responsible for protecting the human body from the mechanical, bacterial, and viral insults. The skin tissue may display different mechanical properties according to the anatomical locations of a body. However, these mechanical properties in different anatomical regions and at different loading directions (axial and circumferential) of the mice body to date have not been determined. In this study, the axial and circumferential loads were imposed on the mice skin samples. The elastic modulus and maximum stress of the skin tissues were measured before the failure occurred. The nonlinear mechanical behavior of the skin tissues was also computationally investigated through a suitable constitutive equation. Hyperelastic material model was calibrated using the experimental data. Regardless of the anatomic locations of the mice body, the results revealed significantly different mechanical properties in the axial and circumferential directions and, consequently, the mice skin tissue behaves like a pure anisotropic material. The highest elastic modulus was observed in the back skin under the circumferential direction (6.67 MPa), while the lowest one was seen in the abdomen skin under circumferential loading (0.80 MPa). The Ogden material model was narrowly captured the nonlinear mechanical response of the skin at different loading directions. The results help to understand the isotropic/anisotropic mechanical behavior of the skin tissue at different anatomical locations. They also have implications for a diversity of disciplines, i.e., dermatology, cosmetics industry, clinical decision making, and clinical intervention.

Mechanical behaviors of multi-filament twist superconducting strand under tensile and cyclic loading

NASA Astrophysics Data System (ADS)

Wang, Xu; Li, Yingxu; Gao, Yuanwen

2016-01-01

The superconducting strand, serving as the basic unit cell of the cable-in-conduit-conductors (CICCs), is a typical multi-filament twist composite which is always subjected to a cyclic loading under the operating condition. Meanwhile, the superconducting material Nb3Sn in the strand is sensitive to strain frequently relating to the performance degradation of the superconductivity. Therefore, a comprehensive study on the mechanical behavior of the strand helps understanding the superconducting performance of the strained Nb3Sn strands. To address this issue, taking the LMI (internal tin) strand as an example, a three-dimensional structural finite element model, named as the Multi-filament twist model, of the strand with the real configuration of the LMI strand is built to study the influences of the plasticity of the component materials, the twist of the filament bundle, the initial thermal residual stress and the breakage and its evolution of the filaments on the mechanical behaviors of the strand. The effective properties of superconducting filament bundle with random filament breakage and its evolution versus strain are obtained based on the damage theory of fiber-reinforced composite materials proposed by Curtin and Zhou. From the calculation results of this model, we find that the occurrence of the hysteresis loop in the cyclic loading curve is determined by the reverse yielding of the elastic-plastic materials in the strand. Both the initial thermal residual stress in the strand and the pitch length of the filaments have significant impacts on the axial and hysteretic behaviors of the strand. The damage of the filaments also affects the axial mechanical behavior of the strand remarkably at large axial strain. The critical current of the strand is calculated by the scaling law with the results of the Multi-filament twist model. The predicted results of the Multi-filament twist model show an acceptable agreement with the experiment.

Design of electro-active polymer gels as actuator materials

NASA Astrophysics Data System (ADS)

Popovic, Suzana

Smart materials, alternatively called active or adaptive, differ from passive materials in their sensing and activation capability. These materials can sense changes in environment such as: electric field, magnetic field, UV light, pH, temperature. They are capable of responding in numerous ways. Some change their stiffness properties (electro-rheological fluids), other deform (piezos, shape memory alloys, electrostrictive materials) or change optic properties (electrochromic polymers). Polymer gels are one of such materials which can change the shape, volume and even optical properties upon different applied stimuli. Due to their low stiffness property they are capable of having up to 100% of strain in a short time, order of seconds. Their motion resembles the one of biosystems, and they are often seen as possible artificial muscle materials. Despite their delicate nature, appropriate design can make them being used as actuator materials which can form controllable surfaces and mechanical switches. In this study several different groups of polymer gel material were investigated: (a) acrylamide based gels are sensitive to pH and electric field and respond in volume change, (b) polyacrylonitrile (PAN) gel is sensitive to pH and electric field and responds in axial strain and bending, (c) polyvinylalcohol (PVA) gel is sensitive to electric field and responds in axial strain and bending and (d) perfluorinated sulfonic acid membrane, Nafion RTM, is sensitive to electric field and responds in bending. Electro-mechanical and chemo-mechanical behavior of these materials is a function of a variety of phenomena: polymer structure, affinity of polymer to the solvent, charge distribution within material, type of solvent, elasticity of polymer matrix, etc. Modeling of this behavior is a task aimed to identify what is driving mechanism for activation and express it in a quantitative way in terms of deformation of material. In this work behavior of the most promising material as an actuator material, Nafion 117, was simulated. It was suggested that dominant phenomenon causing the material deformation is non-uniform water distribution within a material, that causes it to expand on one side and shrink on the other, macroscopically inducing bending of membrane. Uneven distribution of water is believed to be under the influence of two processes, electroosmosis and self-diffusion of free water.

(International seminar on the inelastic behavior of solids: Models and utilization)

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

Ruggles, M.B.

The traveler attended the International Seminar on the Inelastic Behavior of Solids: Models and Utilization, and presented an invited paper. Development and validation of constitutive models for complex loading and environmental conditions was the principal subject of the seminar. Session 1. Constitutive Models: Theoretical Development, Analysis and Comparison, and Session 2. Constitutive Models: Experimental Identification and Use, were of particular interest to the ORNL constitutive equations development effort. The traveler also visited the Applied Mechanics Laboratory at the University of Franche-Comte in Besancon and the Laboratory of Mechanics and Technology at the ENSET/Paris University 6 in Cachan. In both laboratoriesmore » the traveler held discussions regarding inelastic material behavior at room and elevated temperatures, exploratory testing and modeling, and materials testing equipment and techniques.« less

Materials science. Dynamic mechanical behavior of multilayer graphene via supersonic projectile penetration.

PubMed

Lee, Jae-Hwang; Loya, Phillip E; Lou, Jun; Thomas, Edwin L

2014-11-28

Multilayer graphene is an exceptional anisotropic material due to its layered structure composed of two-dimensional carbon lattices. Although the intrinsic mechanical properties of graphene have been investigated at quasi-static conditions, its behavior under extreme dynamic conditions has not yet been studied. We report the high-strain-rate behavior of multilayer graphene over a range of thicknesses from 10 to 100 nanometers by using miniaturized ballistic tests. Tensile stretching of the membrane into a cone shape is followed by initiation of radial cracks that approximately follow crystallographic directions and extend outward well beyond the impact area. The specific penetration energy for multilayer graphene is ~10 times more than literature values for macroscopic steel sheets at 600 meters per second. Copyright © 2014, American Association for the Advancement of Science.

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

NASA Astrophysics Data System (ADS)

Montgomery, Robert; Tomé, Carlos; Liu, Wenfeng; Alankar, Alankar; Subramanian, Gopinath; Stanek, Christopher

2017-01-01

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical constitutive models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. To improve upon this approach, a microstructurally-based zirconium alloy mechanical deformation analysis capability is being developed within the United States Department of Energy Consortium for Advanced Simulation of Light Water Reactors (CASL). Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed by Lebensohn and Tomé [1], has been coupled with the BISON engineering scale fuel performance code to represent the mechanistic material processes controlling the deformation behavior of light water reactor (LWR) cladding. A critical component of VPSC is the representation of the crystallographic nature (defect and dislocation movement) and orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. A future goal is for VPSC to obtain information on reaction rate kinetics from atomistic calculations to inform the defect and dislocation behavior models described in VPSC. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON and provides initial results utilizing the coupled functionality.

The mechanical and electrochemical properties of bulk metallic glasses

NASA Astrophysics Data System (ADS)

Morrison, Mark Lee

The objectives of this study were to define and model the electrochemical and mechanical behaviors of BMGs, in addition to the interactions between these. The electrochemical behaviors of Zr-, Ti-, and Ca-based BMGs have been studied in various environments. Moreover, the electrochemical behaviors of several common, crystalline materials have also been characterized in the same environments to facilitate comparisons. Mechanical characterization of the Vitreloy 105 alloy was conducted through four-point bend fatigue testing, as well as tensile testing with in situ thermography. After the electrochemical and mechanical behaviors of the Vit 105 BMG alloy were defined separately, the corrosion-fatigue behavior of this alloy was studied. Corrosion-fatigue tests were conducted in a 0.6 M NaCl electrolyte, identical to one of the environments in which the electrochemical behavior was previously defined. The environmental effect was found to be significant at most stress levels, with decreasing effects at higher stress levels due to decreasing time in the detrimental environment, and severely depressed the corrosion-fatigue endurance limit. Cyclic-anodic-polarization tests were conducted during cyclic loading to elucidate the effect of cyclic stresses on the electrochemical behavior. It was found that a stress range of 900 MPa resulted in active pitting at the open-circuit potentials. The degradation mechanism was determined to be stress-assisted dissolution, not hydrogen embrittlement. Finally, tensile tests were conducted with the Vit 105 BMG alloy with in situ infrared (IR) thermography to observe the evolution of shear bands during deformation. More importantly, the length, location, sequence, temperature evolution, and velocity of individual shear bands have been quantified through the use of IR thermography. Based upon all of these studies on a variety of BMG alloy systems, the most important factor in the mechanical and electrochemical behavior was found to be material quality and homogeneity. Therefore, future research on the improvement of BMG alloys should be focused on this area.

ICCM/2; Proceedings of the Second International Conference on Composite Materials, Toronto, Canada, April 16-20, 1978

NASA Technical Reports Server (NTRS)

Noton, B. R. (Editor); Signorelli, R. A.; Street, K. N.; Phillips, L. N.

1978-01-01

Composite materials are discussed with reference to their mechanical and physical properties, fatigue and fracture testing and analysis, nondestructive evaluation, fabrication, and commercial applications. Particular papers are presented on such topics as analysis of mechanical strength data from hybrid laminates of glass and graphite fibers, graphite-aluminum composites, the mechanical behavior of molybdenum-reinforced metal composites, and composite laminate application in magnetic fusion energy superconducting magnet systems.

An Overview of the State of the Art in Atomistic and Multiscale Simulation of Fracture

NASA Technical Reports Server (NTRS)

Saether, Erik; Yamakov, Vesselin; Phillips, Dawn R.; Glaessgen, Edward H.

2009-01-01

The emerging field of nanomechanics is providing a new focus in the study of the mechanics of materials, particularly in simulating fundamental atomic mechanisms involved in the initiation and evolution of damage. Simulating fundamental material processes using first principles in physics strongly motivates the formulation of computational multiscale methods to link macroscopic failure to the underlying atomic processes from which all material behavior originates. This report gives an overview of the state of the art in applying concurrent and sequential multiscale methods to analyze damage and failure mechanisms across length scales.

Effect of Copper Oxide, Titanium Dioxide, and Lithium Fluoride on the Thermal Behavior and Decomposition Kinetics of Ammonium Nitrate

NASA Astrophysics Data System (ADS)

Vargeese, Anuj A.; Mija, S. J.; Muralidharan, Krishnamurthi

2014-07-01

Ammonium nitrate (AN) is crystallized along with copper oxide, titanium dioxide, and lithium fluoride. Thermal kinetic constants for the decomposition reaction of the samples were calculated by model-free (Friedman's differential and Vyzovkins nonlinear integral) and model-fitting (Coats-Redfern) methods. To determine the decomposition mechanisms, 12 solid-state mechanisms were tested using the Coats-Redfern method. The results of the Coats-Redfern method show that the decomposition mechanism for all samples is the contracting cylinder mechanism. The phase behavior of the obtained samples was evaluated by differential scanning calorimetry (DSC), and structural properties were determined by X-ray powder diffraction (XRPD). The results indicate that copper oxide modifies the phase transition behavior and can catalyze AN decomposition, whereas LiF inhibits AN decomposition, and TiO2 shows no influence on the rate of decomposition. Possible explanations for these results are discussed. Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Energetic Materials to view the free supplemental file.

Interlocking-induced stiffness in stochastically microcracked materials beyond the transport percolation threshold

NASA Astrophysics Data System (ADS)

Picu, R. C.; Pal, A.; Lupulescu, M. V.

2016-04-01

We study the mechanical behavior of two-dimensional, stochastically microcracked continua in the range of crack densities close to, and above, the transport percolation threshold. We show that these materials retain stiffness up to crack densities much larger than the transport percolation threshold due to topological interlocking of sample subdomains. Even with a linear constitutive law for the continuum, the mechanical behavior becomes nonlinear in the range of crack densities bounded by the transport and stiffness percolation thresholds. The effect is due to the fractal nature of the fragmentation process and is not linked to the roughness of individual cracks.

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

Lin, J.S.; Miyamoto, Y.

The fracture behavior of graded Al{sub 2}O{sub 3}/TiC/Ni materials with a symmetric structure was investigated using single-edge notch-bend (SENB) specimens with surface compression. The fracture toughness of the graded materials was determined according to ASTM Standard E399. The results show that the effective fracture toughness increases with an increase in notch depth in the compressive stress zone, and reaches the maximum of 39.2 MPa m{sup 1/2} at the interface of compressive/tensile stress zones. Finite elements analysis reveals that the surface compression will be intensified at the notch root once the specimen is edge-notched because of the stress concentration, and themore » digress of the compressive stress intensification increases with an increase in notch depth. The dependence of the effective fracture toughness of the graded materials on the notch depth shows a behavior similar to the R-curve that is usually associated with microstructural toughening mechanisms. This toughening behavior is caused by the intensification of the compressive stress concentration with the increase of the notch depth. A theoretical analysis based on fracture mechanics verifies that the mechanical reliability of brittle ceramics can be improved effectively by tailoring and controlling the internal stresses.« less

Microgravity

NASA Image and Video Library

1998-01-25

Astronaut James Reilly uses a laptop computer monitor the Mechanics of Granular Materials (MGM) experiment during STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Microgravity

NASA Image and Video Library

1996-09-18

Astronaut Carl Walz installs Mechanics of Granular Materials (MGM) test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/John Space Center

Installing Mechanics of Granular Materials (MGM) experiment Test Cell

NASA Technical Reports Server (NTRS)

1996-01-01

Astronaut Jay Apt installs Mechanics of Granular Materials (MGM0 test cell on STS-79. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/John Space Center).

Mechanics of Granular Materials labeled hardware

NASA Technical Reports Server (NTRS)

2000-01-01

Mechanics of Granular Materials (MGM) flight hardware takes two twin double locker assemblies in the Space Shuttle middeck or the Spacehab module. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: NASA/MSFC).

Constitutive Modeling of Crosslinked Nanotube Materials

NASA Technical Reports Server (NTRS)

Odegard, G. M.; Frankland, S. J. V.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

2004-01-01

A non-linear, continuum-based constitutive model is developed for carbon nanotube materials in which bundles of aligned carbon nanotubes have varying amounts of crosslinks between the nanotubes. The model accounts for the non-linear elastic constitutive behavior of the material in terms of strain, and is developed using a thermodynamic energy approach. The model is used to examine the effect of the crosslinking on the overall mechanical properties of variations of the crosslinked carbon nanotube material with varying degrees of crosslinking. It is shown that the presence of the crosslinks has significant effects on the mechanical properties of the carbon nanotube materials. An increase in the transverse shear properties is observed when the nanotubes are crosslinked. However, this increase is accompanied by a decrease in axial mechanical properties of the nanotube material upon crosslinking.

Identification Damage Model for Thermomechanical Degradation of Ductile Heterogeneous Materials

NASA Astrophysics Data System (ADS)

Amri, A. El; Yakhloufi, M. H. El; Khamlichi, A.

2017-05-01

The failure of ductile materials subject to high thermal and mechanical loading rates is notably affected by material inertia. The mechanisms of fatigue-crack propagation are examined with particular emphasis on the similarities and differences between cyclic crack growth in ductile materials, such as metals, and corresponding behavior in brittle materials, such as intermetallic and ceramics. Numerical simulations of crack propagation in a cylindrical specimen demonstrate that the proposed method provides an effective means to simulate ductile fracture in large scale cylindrical structures with engineering accuracy. The influence of damage on the intensity of the destruction of materials is studied as well.

Characterization of fatigue behavior of 2-D woven fabric reinforced ceramic matrix composite at elevated temperature. Final report

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

Groner, D.J.

This study investigated the fatigue behavior and associated damage mechanisms in notched and unnotched enhanced SiC/SiC ceramic matrix composite specimens at 1100 deg C. Stiffness degradation, strain variation, and hysteresis were evaluated to characterize material behavior. Microscopic examination was performed to characterize damage mechanisms. During high cycle/low stress fatigue tests, far less fiber/matrix interface debond was evident than in low cycle/high stress fatigue tests. Notched specimens exhibited minimal stress concentration during monotonic tensile testing and minimal notch sensitivity during fatigue testing. Damage mechanisms were also similar to unnotched.

Parameter estimation of a nonlinear Burger's model using nanoindentation and finite element-based inverse analysis

NASA Astrophysics Data System (ADS)

Hamim, Salah Uddin Ahmed

Nanoindentation involves probing a hard diamond tip into a material, where the load and the displacement experienced by the tip is recorded continuously. This load-displacement data is a direct function of material's innate stress-strain behavior. Thus, theoretically it is possible to extract mechanical properties of a material through nanoindentation. However, due to various nonlinearities associated with nanoindentation the process of interpreting load-displacement data into material properties is difficult. Although, simple elastic behavior can be characterized easily, a method to characterize complicated material behavior such as nonlinear viscoelasticity is still lacking. In this study, a nanoindentation-based material characterization technique is developed to characterize soft materials exhibiting nonlinear viscoelasticity. Nanoindentation experiment was modeled in finite element analysis software (ABAQUS), where a nonlinear viscoelastic behavior was incorporated using user-defined subroutine (UMAT). The model parameters were calibrated using a process called inverse analysis. In this study, a surrogate model-based approach was used for the inverse analysis. The different factors affecting the surrogate model performance are analyzed in order to optimize the performance with respect to the computational cost.

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.

Nb-Base FS-85 Alloy as a Candidate Structural Material for Space Reactor Applications: Effects of Thermal Aging

NASA Astrophysics Data System (ADS)

Leonard, Keith J.; Busby, Jeremy T.; Hoelzer, David T.; Zinkle, Steven J.

2009-04-01

The proposed uses of fission reactors for manned or deep space missions have typically relied on the potential use of refractory metal alloys as structural materials. Throughout the history of these programs, a leading candidate has been Nb-1Zr, due to its good fabrication and welding characteristics. However, the less-than-optimal creep resistance of this alloy has encouraged interest in the more complex FS-85 (Nb-28Ta-10W-1Zr) alloy. Despite this interest, only a relatively small database exists for the properties of FS-85. Database gaps include the potential microstructural instabilities that can lead to mechanical property degradation. In this work, changes in the microstructure and mechanical properties of FS-85 were investigated following 1100 hours of thermal aging at 1098, 1248, and 1398 K. The changes in electrical resistivity, hardness, and tensile properties between the as-annealed and aged materials are compared. Evaluation of the microstructural changes was performed through optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The development of intragranular and grain-boundary precipitation of Zr-rich compounds as a function of aging temperature was followed. Brittle tensile behavior was measured in the material aged at 1248 K, while ductile behavior occurred in samples aged above and below this temperature. The effect of temperature on the under- and overaging of the grain-boundary particles is believed to have contributed to the mechanical property behavior of the aged materials.

Thermal Shock Behavior of Single Crystal Oxide Refractive Concentrators for High Temperatures Solar Thermal Propulsion

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Jacobson, Nathan S.; Miller, Robert A.

1999-01-01

Single crystal oxides such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium-aluminum-garnet (Y3Al5O12, or YAG), magnesium oxide (MgO) and sapphire (Al2O3) have been considered as refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermal mechanical reliability of the oxide components in severe thermal environments during space mission sun/shade transitions is of great concern. In this paper, critical mechanical properties of these oxide crystals are determined by the indentation technique. Thermal shock resistance of the oxides is evaluated using a high power CO, laser under high temperature-high thermal gradients. Thermal stress fracture behavior and failure mechanisms of these oxide materials are investigated under various temperature and heating conditions.

How does tissue regeneration influence the mechanical behavior of additively manufactured porous biomaterials?

PubMed

Hedayati, R; Janbaz, S; Sadighi, M; Mohammadi-Aghdam, M; Zadpoor, A A

2017-01-01

Although the initial mechanical properties of additively manufactured porous biomaterials are intensively studied during the last few years, almost no information is available regarding the evolution of the mechanical properties of implant-bone complex as the tissue regeneration progresses. In this paper, we studied the effects of tissue regeneration on the static and fatigue behavior of selective laser melted porous titanium structures with three different porosities (i.e. 77, 81, and 85%). The porous structures were filled with four different polymeric materials with mechanical properties in the range of those observed for de novo bone (0.7GPa

Mechanics of responsive polymers via conformationally switchable molecules

NASA Astrophysics Data System (ADS)

Brighenti, Roberto; Artoni, Federico; Vernerey, Franck; Torelli, Martina; Pedrini, Alessandro; Domenichelli, Ilaria; Dalcanale, Enrico

2018-04-01

Active materials are those capable of giving some physical reaction under external stimuli coming from the environment such as temperature, pH, light, mechanical stress, etc. Reactive polymeric materials can be obtained through the introduction of switchable molecules in their network, i.e. molecules having two distinct stable conformations: if properly linked to the hosting polymer chains, the switching from one state to the other can promote a mechanical reaction of the material, detectable at the macroscale, and thus enables us to tune the response according to a desired functionality. In the present paper, the main aspects of the mechanical behavior of polymeric materials with embedded switchable molecules-properly linked to the polymer's chains-are presented and discussed. Starting from the micro mechanisms occurring in such active material, a continuum model is developed, providing a straightforward implementation in computational approaches. Finally, some experimental outcomes related to a switchable molecules (known as quinoxaline cavitands) added to an elastomeric PDMS under chemical stimuli, are presented and quantitatively discussed through the use of the developed mechanical framework.

Long-life physical property preservation and postendodontic rehabilitation with the Composipost.

PubMed

Duret, B; Duret, F; Reynaud, M

1996-01-01

Most coronal radicular reconstructions are made of cast inlay core metals or prefabricated posts covered in composite. The differences in the mechanical properties of these elements create a heterogeneous mass with inconsistent mechanical behavior. Studies using the Finite Element Method have shown the biomechanical disturbances caused by the inclusion of materials with a modulus of elasticity that is superior to that of dentine (i.e., nickel, chrome, zircon, etc). The use of materials with a modulus of elasticity close to that of dentine does not disturb the flow of stress inside the root. To our knowledge, only a composite material structured with programmable mechanical properties would be capable of producing both high mechanical performance and a modulus of elasticity adapted to dentine values. The C-POST, made of carbon epoxy, accommodates the demands of the dentine, as well as the in vitro stress linked to the prosthesis. The internal structure, consisting of long high-performance carbon fibers, unidirectionally and equally stretched, confers a totally original behavior that is adapted to clinical objectives. In addition, the C-POST has a fracture resistance superior to most metals.

Modeling of AA5083 Material-Microstructure Evolution During Butt Friction-Stir Welding

NASA Astrophysics Data System (ADS)

Grujicic, M.; Arakere, G.; Yalavarthy, H. V.; He, T.; Yen, C.-F.; Cheeseman, B. A.

2010-07-01

A concise yet a fairly comprehensive overview of the friction stir welding (FSW) process is provided. This is followed by a computational investigation in which FSW behavior of a prototypical solution-strengthened and strain-hardened aluminum alloy, AA5083-H131, is modeled using a fully coupled thermo-mechanical finite-element procedure developed in our prior study. Particular attention is given to proper modeling of the welding work-piece material behavior during the FSW process. Specifically, competition and interactions between plastic-deformation and dynamic-recrystallization processes are considered to properly account for the material-microstructure evolution in the weld nugget zone. The results showed that with proper modeling of the material behavior under high-temperature/severe-plastic-deformation conditions, significantly improved agreement can be attained between the computed and measured post-FSW residual-stress and material-strength distribution results.

Thickness-dependent resistance switching in Cr-doped SrTiO3

NASA Astrophysics Data System (ADS)

Kim, TaeKwang; Du, Hyewon; Kim, Minchang; Seo, Sunae; Hwang, Inrok; Kim, Yeonsoo; Jeon, Jihoon; Lee, Sangik; Park, Baeho

2012-09-01

The thickness-dependent bipolar resistance-switching behavior was investigated for epitaxiallygrown Cr-doped SrTiO3 (Cr-STO). All the pristine devices of different thickness showed polarity-independent symmetric current-voltage characteristic and the same space-charge-limited conduction mechanism. However, after a forming process, the resultant conduction and switching phenomena were significantly different depending on the thickness of Cr-STO. The forming process itself was highly influenced by resistance value of each pristine device. Based on our results, we suggest that the resistance-switching mechanism in Cr-STO depends not only on the insulating material's composition or the contact metal as previously reported but also on the initial resistance level determined by the geometry and the quality of the insulating material. The bipolar resistance-switching behaviors in oxide materials of different thicknesses exhibit mixed bulk and interface switching. This indicates that efforts in resistance-based memory research should be focused on scalability or process method to control a given oxide material in addition to material type and device structure.

Coupled multi-disciplinary simulation of composite engine structures in propulsion environment

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Singhal, Surendra N.

1992-01-01

A computational simulation procedure is described for the coupled response of multi-layered multi-material composite engine structural components which are subjected to simultaneous multi-disciplinary thermal, structural, vibration, and acoustic loadings including the effect of hostile environments. The simulation is based on a three dimensional finite element analysis technique in conjunction with structural mechanics codes and with acoustic analysis methods. The composite material behavior is assessed at the various composite scales, i.e., the laminate/ply/constituents (fiber/matrix), via a nonlinear material characterization model. Sample cases exhibiting nonlinear geometrical, material, loading, and environmental behavior of aircraft engine fan blades, are presented. Results for deformed shape, vibration frequency, mode shapes, and acoustic noise emitted from the fan blade, are discussed for their coupled effect in hot and humid environments. Results such as acoustic noise for coupled composite-mechanics/heat transfer/structural/vibration/acoustic analyses demonstrate the effectiveness of coupled multi-disciplinary computational simulation and the various advantages of composite materials compared to metals.

Engineering three-dimensional cell mechanical microenvironment with hydrogels.

PubMed

Huang, Guoyou; Wang, Lin; Wang, Shuqi; Han, Yulong; Wu, Jinhui; Zhang, Qiancheng; Xu, Feng; Lu, Tian Jian

2012-12-01

Cell mechanical microenvironment (CMM) significantly affects cell behaviors such as spreading, migration, proliferation and differentiation. However, most studies on cell response to mechanical stimulation are based on two-dimensional (2D) planar substrates, which cannot mimic native three-dimensional (3D) CMM. Accumulating evidence has shown that there is a significant difference in cell behavior in 2D and 3D microenvironments. Among the materials used for engineering 3D CMM, hydrogels have gained increasing attention due to their tunable properties (e.g. chemical and mechanical properties). In this paper, we provide an overview of recent advances in engineering hydrogel-based 3D CMM. Effects of mechanical cues (e.g. hydrogel stiffness and externally induced stress/strain in hydrogels) on cell behaviors are described. A variety of approaches to load mechanical stimuli in 3D hydrogel-based constructs are also discussed.

Human skeletal muscle behavior in vivo: Finite element implementation, experiment, and passive mechanical characterization.

PubMed

Clemen, Christof B; Benderoth, Günther E K; Schmidt, Andreas; Hübner, Frank; Vogl, Thomas J; Silber, Gerhard

2017-01-01

In this study, useful methods for active human skeletal muscle material parameter determination are provided. First, a straightforward approach to the implementation of a transversely isotropic hyperelastic continuum mechanical material model in an invariant formulation is presented. This procedure is found to be feasible even if the strain energy is formulated in terms of invariants other than those predetermined by the software's requirements. Next, an appropriate experimental setup for the observation of activation-dependent material behavior, corresponding data acquisition, and evaluation is given. Geometry reconstruction based on magnetic resonance imaging of different deformation states is used to generate realistic, subject-specific finite element models of the upper arm. Using the deterministic SIMPLEX optimization strategy, a convenient quasi-static passive-elastic material characterization is pursued; the results of this approach used to characterize the behavior of human biceps in vivo indicate the feasibility of the illustrated methods to identify active material parameters comprising multiple loading modes. A comparison of a contact simulation incorporating the optimized parameters to a reconstructed deformed geometry of an indented upper arm shows the validity of the obtained results regarding deformation scenarios perpendicular to the effective direction of the nonactivated biceps. However, for a valid, activatable, general-purpose material characterization, the material model needs some modifications as well as a multicriteria optimization of the force-displacement data for different loading modes. Copyright © 2016 Elsevier Ltd. All rights reserved.

From single fiber to macro-level mechanics: A structural finite-element model for elastomeric fibrous biomaterials.

PubMed

D'Amore, Antonio; Amoroso, Nicholas; Gottardi, Riccardo; Hobson, Christopher; Carruthers, Christopher; Watkins, Simon; Wagner, William R; Sacks, Michael S

2014-11-01

In the present work, we demonstrate that the mesoscopic in-plane mechanical behavior of membrane elastomeric scaffolds can be simulated by replication of actual quantified fibrous geometries. Elastomeric electrospun polyurethane (ES-PEUU) scaffolds, with and without particulate inclusions, were utilized. Simulations were developed from experimentally-derived fiber network geometries, based on a range of scaffold isotropic and anisotropic behaviors. These were chosen to evaluate the effects on macro-mechanics based on measurable geometric parameters such as fiber intersections, connectivity, orientation, and diameter. Simulations were conducted with only the fiber material model parameters adjusted to match the macro-level mechanical test data. Fiber model validation was performed at the microscopic level by individual fiber mechanical tests using AFM. Results demonstrated very good agreement to the experimental data, and revealed the formation of extended preferential fiber orientations spanning the entire model space. We speculate that these emergent structures may be responsible for the tissue-like macroscale behaviors observed in electrospun scaffolds. To conclude, the modeling approach has implications for (1) gaining insight on the intricate relationship between fabrication variables, structure, and mechanics to manufacture more functional devices/materials, (2) elucidating the effects of cell or particulate inclusions on global construct mechanics, and (3) fabricating better performing tissue surrogates that could recapitulate native tissue mechanics. Copyright © 2014 Elsevier Ltd. All rights reserved.

An Introduction to the Mechanical Properties of Ceramics

NASA Astrophysics Data System (ADS)

Green, David J.

1998-09-01

Over the past twenty-five years ceramics have become key materials in the development of many new technologies as scientists have been able to design these materials with new structures and properties. An understanding of the factors that influence their mechanical behavior and reliability is essential. This book will introduce the reader to current concepts in the field. It contains problems and exercises to help readers develop their skills. This is a comprehensive introduction to the mechanical properties of ceramics, and is designed primarily as a textbook for advanced undergraduates in materials science and engineering. It will also be of value as a supplementary text for more general courses and to industrial scientists and engineers involved in the development of ceramic-based products, materials selection and mechanical design.

The behavior of a macroscopic granular material in vortex flow

NASA Astrophysics Data System (ADS)

Nishikawa, Asami

A granular material is defined as a collection of discrete particles such as powder and grain. Granular materials display a large number of complex behaviors. In this project, the behavior of macroscopic granular materials under tornado-like vortex airflow, with varying airflow velocity, was observed and studied. The experimental system was composed of a 9.20-cm inner diameter acrylic pipe with a metal mesh bottom holding the particles, a PVC duct, and an airflow source controlled by a variable auto-transformer, and a power-meter. A fixed fan blade was attached to the duct's inner wall to create a tornado-like vortex airflow from straight flow. As the airflow velocity was increased gradually, the behavior of a set of same-diameter granular materials was observed. The observed behaviors were classified into six phases based on the macroscopic mechanical dynamics. Through this project, we gained insights on the significant parameters for a computer simulation of a similar system by Heath Rice [5]. Comparing computationally and experimentally observed phase diagrams, we can see similar structure. The experimental observations showed the effect of initial arrangement of particles on the phase transitions.

Designing a new three-dimensional periodic cellular auxetic material

NASA Astrophysics Data System (ADS)

Zhou, Yiyi; Chen, Lianmen

2017-07-01

Auxetics are materials showing a negative Poisson’s ratio. Early research found several categories of auxetic materials in the chemical field. Later research identified the fundamental mechanism generating this behavior is rotation; a variety of two-dimensional auxetic material have been generated accordingly. Nevertheless, the successful example of three-dimensional auxetic material is still rare. This paper introduces a new design of three-dimensional periodic cellular auxetic material based on geometrical and mechanical methodology. The projections of the optimized periodic modules in two horizontal directions are geometrically same with auxetic hexahedral poem, so that the optimized periodic material can perform auxetic in both two horizontal directions under vertical compression. Parametric model is simulated to prove the design.

Mechanical and thermal behavior of ionic polymer metal composites: effects of electroded metals

NASA Astrophysics Data System (ADS)

Park, Il-Seok; Kim, Sang-Mun; Kim, Kwang J.

2007-08-01

In this study, we investigated the mechanical properties of various types of ionic polymer-metal composites (IPMCs) and Pt, Au, Pd, and Pt electroded ionic liquid (IL-Pt) IPMCs, by testing tensile modulus and dynamic mechanical behavior. The SEM was utilized to investigate the characteristics of the doped electroding layer, and the DSC was probed in order to look into the thermal behavior of various types of IPMCs. Au IPMCs, having a 5-7 µm-doped layer and nanosized Au particles (ca. 10 nm), showed the highest tensile strength (56 MPa) and modulus (602 MPa) in dried conditions. With regards to thermal behavior, Au IPMC had the highest Tg (153 °C) and Tm (263 °C) in both the DMA and DSC results. The fracture behavior of various types of IPMCs followed the behavior of the base material, Nafion™, which is represented as the semicrystalline polymer characteristic.

PDMS Network Structure-Property Relationships: Influence of Molecular Architecture on Mechanical and Wetting Properties

NASA Astrophysics Data System (ADS)

Melillo, Matthew Joseph

Poly(dimethylsiloxane) (PDMS) is one of the most common elastomers, with applications ranging from sealants and marine-antifouling coatings to medical devices and absorbents for water treatment. Fundamental understanding of how liquids spread on the surface of and absorb into and leach out of PDMS networks is of critical importance for the design and use in another application - microfluidic devices. The growing use of PDMS in microfluidic devices raises the concern that some researchers may use this material without fully understanding all of its advantages, drawbacks, and intricacies. The primary goal of this Ph.D. dissertation is to elucidate PDMS network molecular structure to macroscopic property relationships and to demonstrate how molecular architecture can alter dynamic mechanical and wetting characteristics. We prepare PDMS materials by using vinyl/ tetrakis(dimethylsiloxy)silane (TDSS) and silanol/ tetraethylorthosilicate (TEOS) combinations of PDMS end-groups and crosslinkers as two model systems. Under constant curing conditions, we systematically study the effects of polymer molecular weight, loading of crosslinker, and end-group chemical functionality on the extent of gelation and the dynamic mechanical and water wetting properties of end-linked PDMS networks. The extent of the gelation reaction is determined using the Soxhlet extraction to quantify the amount of material that did and did not participate in the crosslinking reactions, termed the gel and sol fractions, respectively. We use the Miller-Macosko model in conjunction with the gel fraction and precise chemical composition (i.e., stoichiometric ratio and molecular weight) to determine the fractions of elastic and pendant material, the molecular weight between chemical crosslinks, and the average effective functionality of the crosslinker molecule. Based on dynamic mechanical testing, we find that the maximum storage moduli are achieved at optimal stoichiometric conditions in the vinyl/TDSS and commercial PDMS-based Sylgard 184 composite, but only keep improving with additional crosslinker in the silanol/TEOS systems due to in situ TEOS aggregation. We relate molecular network topology to mechanical properties using outputs from the Miller-Macosko model in the vinyl/TDSS system. The elastic fraction and storage modulus correlate well, as do the pendant fraction and the loss tangent, demonstrating the importance of each fraction in bulk mechanical properties. By studying the dynamic behavior of water droplets wetting PDMS substrates, we observe non-linear wetting behaviors that are markedly different from linear behaviors seen on glassy polymer substrates. The non-linear behavior is only observed prior to extraction, while after extraction, both systems demonstrate behavior similar to glassy polymers. This reveals the dramatic role small amounts of uncrosslinked materials present in the sol fraction play in the surface wetting dynamics of PDMS materials. We further demonstrate the role of uncrosslinked material by adding silicone oils into otherwise fully crosslinked PDMS networks and study their wetting properties. Through careful formulation and preparation of PDMS materials, compared to simply mixing two formulations present in Sylgard 184, one can apply polymer network models to glean useful information about network topology. The benefits of doing so outweigh the costs. We stress the importance of performing Soxhlet extraction to remove unreacted components from PDMS materials, even when using optimal stoichiometry. These mobile molecules that remain after crosslinking can alter significantly wetting behavior and readily leach into liquid environments. However, it is equally important to stress that Soxhlet extraction will not remove all unreacted material. Some will always remain in PDMS, which is often the practice in preparing microfluidic devices. While Sylgard 184 is very well suited for some applications, the results presented in this dissertation demonstrate to researchers that the material does have its limitations and that other options are available. These findings will aid in the design and implementation of reliable microfluidic devices and other PDMS-based materials that encounter liquid interfaces.

Influence of Strain Rate, Microstructure and Chemical and Phase Composition on Mechanical Behavior of Different Titanium Alloys

NASA Astrophysics Data System (ADS)

Markovsky, P. E.; Bondarchuk, V. I.

2017-07-01

Taking three titanium commercial alloys: commercial purity titanium (c.p.Ti), Ti-6-4 (Ti-6(wt.%)Al-4V) and TIMETAL-LCB (Ti-1.5Al-4.5Fe-6.8Mo) as program materials, the influence of phase composition, microstructure and strain rate (varied from 8 × 10-4 to 1.81 × 10-1) on the mechanical behavior was studied. The size of the matrix phase ( α- or β-grains) and size of α + β intragranular mixture were varied. Such parameter such as tensile toughness (TT) was used for analysis of the mechanical behavior of the materials on tension with different rates. It was found that the TT values monotonically decreased with strain rate, except Ti-6-4 alloy with a globular type of microstructure. In single-phase α-material (c.p.Ti), tensile deformation led to the formation of voids at the intragranular cell substructure, and merging of these voids caused the formation of main crack. In two-phase α + β materials, the deformation defects were localized upon tension predominantly near the α/ β interphase boundaries, and subsequent fracture had different characters: In Ti-6-4 globular condition fracture started by formation of voids at the α/ β interphase boundaries, whereas in all other conditions the voids nucleated at the tips of α-lamellae/needles.

Mechanics of Granular Materials (MGM) Flight Hardware

NASA Technical Reports Server (NTRS)

1997-01-01

A test cell for the Mechanics of Granular Materials (MGM) experiment is shown in its on-orbit configuration in Spacehab during preparations for STS-89. The twin locker to the left contains the hydraulic system to operate the experiment. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Note: Because the image on the screen was muted in the original image, its brightness and contrast are boosted in this rendering to make the test cell more visible. Credit: NASA/Marshall Space Flight Center (MSFC)

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.

Micromechanical model for protein materials: From macromolecules to macroscopic fibers

NASA Astrophysics Data System (ADS)

Puglisi, G.; De Tommasi, D.; Pantano, M. F.; Pugno, N. M.; Saccomandi, G.

2017-10-01

We propose a model for the mechanical behavior of protein materials. Based on a limited number of experimental macromolecular parameters (persistence and contour length) we obtain the macroscopic behavior of keratin fibers (human, cow, and rabbit hair), taking into account the damage and residual stretches effects that are fundamental in many functions of life. We also show the capability of our approach to describe the main dissipation and permanent strain effects observed in the more complex spider silk fibers. The comparison between our results and the data obtained experimentally from cyclic tests demonstrates that our model is robust and is able to reproduce with a remarkable accuracy the experimental behavior of all protein materials we tested.

Use of photostress to characterize the mechanical behavior of weldments

NASA Technical Reports Server (NTRS)

Gambrell, S. C., Jr.

1992-01-01

Welded aluminum is an important part of many space structures. Knowledge of the properties and behavior of weld material and the material surrounding the weld is important for modeling and design of the structures. Photoelastic coatings (Photostress) and strain gages were used to determine behavior of heat treated and as welded joints made from 2219T87 parent material and 2319 weld material subjected to tensile loads. TIG welds of 1/8, 1/2, and 1.4 inches thickness were investigated. Discontinuous yielding was observed in all tests and highly non-uniform behavior through the weld thickness was observed in joints having welds 1.4 inches thick. Joints having welds 1/8 and 1/2 inches thick had only small differences in behavior through the thickness of the weld. Joints in the 1/2 inch thick material contained distinct zones of constant strain within the normal strain gradient extending outward from the weld centerline. These zones had different thickness and locations. Points at the weld centerline, and for a distance of nearly one inch from the centerline, exhibited very nonlinear behavior during the first loading but exhibited near perfect strain hardening during the second loading.

Auto-Mechanics Course. Bilingual Vocational Instructional Materials.

ERIC Educational Resources Information Center

Lopez-Cox, Guadalupe

This auto-mechanics course, one of a series of bilingual English-Spanish vocational education courses, is designed to introduce the basic skills that an automotive mechanics student should know. It is geared to teach the student basic manipulative skills, safety judgments, proper work habits, desirable attitudes, and proper behavior for initial…

Factors affecting the mechanical behavior of collagen hydrogels for skin tissue engineering.

PubMed

Pensalfini, Marco; Ehret, Alexander E; Stüdeli, Silvia; Marino, Daniela; Kaech, Andres; Reichmann, Ernst; Mazza, Edoardo

2017-05-01

The effect of the production factors yielding a functional dermal substitute was investigated by means of monotonic and cyclic uniaxial tensile tests, as well as electron microscopy visualizations. The role of (i) plastic compression, (ii) product incubation, and (iii) cell permanence in the collagenous matrix in order to achieve a skin-like behavior were characterized in terms of material and structural stiffness, in-plane kinematics, and cyclic response, as well as pore size and network density. The plastic compression resulted in a denser and stiffer material, while no corresponding change was observed in the behavior of the entire structure. This was related to the progressive reduction in product thickness and amount of excess water, rather than to formation of new crosslinks between fibers. Contrary, irrespective of the presence of human fibroblasts, the product incubation induced both material and structural stiffening, indicating the formation of a denser network. These results were confirmed by similar evolutions in the construct in-plane kinematics and cyclic stress reduction. Finally, comparison of constructs incubated in different culture media indicated a determinant contribution of the biochemical environment, rather than of the seeded cells, to the achieved mechanical properties. The observed features are relevant in terms of mechanical biocompatibility of the implant and might direct future optimizations of the production process in order to rapidly attain the desired mechanical properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

On the dynamic behavior of mineralized tissues

NASA Astrophysics Data System (ADS)

Kulin, Robb Michael

Mineralized tissues, such as bone and antler, are complex hierarchical materials that have adapted over millennia to optimize strength and fracture resistance for their in vivo applications. As a structural support, skeletal bone primarily acts as a rigid framework that is resistant to fracture, and able to repair damage and adapt to sustained loads during its lifetime. Antler is typically deciduous and subjected to large bending moments and violent impacts during its annual cycle. To date, extensive characterization of the quasi-static mechanical properties of these materials has been performed. However, very little has been done to characterize their dynamic properties, despite the fact that the majority of failures in these materials occur under impact loads. Here, an in depth analysis of the dynamic mechanical behavior of these two materials is presented, using equine bone obtained post-mortem from donors ranging in age from 6 months to 28 years, and antler from the North American Elk. Specimens were tested under compressive strain rates of 10-3, 100, and 103 sec-1 in order to investigate their strain rate dependent compressive response. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack propagation between dynamic (˜2x105 MPa˙m1/2/s) and quasi-static (˜0.25 MPa˙m1/2/s) loading rates. After testing, specimens were analyzed using a combination of optical, electron and confocal microscopy. Results indicated that the mechanical response of these materials is highly dependent on loading rate. Decreasing quasi-static fracture toughness is observed with age in bone specimens, while dynamic specimens show no age trends, yet universally decreased fracture toughness compared to those tested quasi-statically. For the first time, rising R-curve behavior in bone was also shown to exist under both quasi-static and dynamic loading. Antler demonstrated itself to be extremely resistant to impact loading, often requiring multiple impacts to fracture a specimen. Microscopy observations of deformation and crack propagation mechanisms indicate that differences in mechanical behavior between bone and antler, and at varying strain rates, are the result of subtle differences in bulk composition and active microstructural toughening mechanisms.

Elucidating the atomistic mechanisms underpinning plasticity in Li-Si nanostructures

NASA Astrophysics Data System (ADS)

Yan, Xin; Gouissem, Afif; Guduru, Pradeep R.; Sharma, Pradeep

2017-10-01

Amorphous lithium-silicon (a-Li-Si), especially in nanostructure form, is an attractive high-capacity anode material for next-generation Li-ion batteries. During cycles of charging and discharging, a-Li-Si undergoes substantive inelastic deformation and exhibits microcracking. The mechanical response to repeated lithiation-delithiation eventually results in the loss of electrical contact and consequent decrease of capacity, thus underscoring the importance of studying the plasticity of a-Li-Si nanostructures. In recent years, a variety of phenomenological continuum theories have been introduced that purport to model plasticity and the electro-chemo-mechanical behavior of a-Li-Si. Unfortunately, the micromechanisms and atomistic considerations underlying plasticity in Li-Si material are not yet fully understood and this impedes the development of physics-based constitutive models. Conventional molecular dynamics, although extensively used to study this material, is grossly inadequate to resolve this matter. As is well known, conventional molecular dynamics simulations can only address phenomena with characteristic time scales of (at most) a microsecond. Accordingly, in such simulations, the mechanical behavior is deduced under conditions of very high strain rates (usually, 108s-1 or even higher). This limitation severely impacts a realistic assessment of rate-dependent effects. In this work, we attempt to circumvent the time-scale bottleneck of conventional molecular dynamics and provide novel insights into the mechanisms underpinning plastic deformation of Li-Si nanostructures. We utilize an approach that allows imposition of slow strain rates and involves the employment of a new and recently developed potential energy surface sampling method—the so-called autonomous basin climbing—to identify the local minima in the potential energy surface. Combined with other techniques, such as nudged elastic band, kinetic Monte Carlo and transition state theory, we assess the behavior of a-Li-Si nanostructures under tensile strain rates ranging from 103 to 108s-1 . We find significant differences in the deformation behavior across the strain rates and discover that the well-known shear transformation zones (widely discussed in the context of amorphous materials) are formed by a "diffusionlike" process. We identify the rotation of the shear transformation zone as a key dissipation mechanism.

Frictional forces in material removal for glasses and ceramics using magnetorheological finishing

NASA Astrophysics Data System (ADS)

Miao, Chunlin

Magnetorheological finishing (MRF) spotting experiments on stationary parts are conducted in this work to understand the material removal mechanism in MRF. Drag force and normal force are measured in situ, simultaneously for the first time for a variety of optical materials in MRF. We study material removal process in MRF as a function of material mechanical properties. We experimentally demonstrate that material removal in MRF is strongly related to shear stress. Shear stress is predominantly determined by material mechanical properties. A modified Preston's equation is proposed to estimate the material removal in MRF by combining shear stress and material mechanical properties. We investigate extensively the effect of various MRF process parameters, including abrasive concentration, magnetic field strength, penetration depth and wheel speed, on material removal efficiency. Material removal rate model is expanded to include these parameters. We develop a nonaqueous magnetorheological (MR) fluid for examining the mechanical contribution in MRF material removal. This fluid is based on a combination of two CI particles and a combination of two organic liquids. Material removal with this nonaqueous MR fluid is discussed. We formulate a new corrosion resistant MR fluid which is based on metal oxide coated carbonyl iron (CI) particles. The rheological behavior, stability and corrosion resistance are examined.

Evaluating Psychosocial and Behavioral Mechanisms of Change in a Tailored Communication Intervention

ERIC Educational Resources Information Center

Elder, John P.; Ayala, Guadalupe X.; Slymen, Donald J.; Arredondo, Elva M.; Campbell, Nadia R.

2009-01-01

This study examined the impact of a tailored nutrition intervention at 3 and 6 months postintervention. In all, 357 Latinas were randomly assigned to one of three conditions: (1) a control condition comprised of previously developed Spanish language targeted materials, (2) tailored print materials, or (3) tailored print materials accompanied by…

An investigation of the compressive strength of PRD-49-3/Epoxy composites

NASA Technical Reports Server (NTRS)

Kulkarni, S. V.; Rice, J. S.; Rosen, B. W.

1973-01-01

The development of unidirectional fiber composite materials is discussed. The mechanical and physical properties of the materials are described. Emphasis is placed in analyzing the compressive behavior of composite materials and developing methods for increasing compressive strength. The test program for evaluating the various procedures for improving compressive strength are reported.

Study of erosion characterization of carbon fiber reinforced composite material

NASA Astrophysics Data System (ADS)

Debnath, Uttam Kumar; Chowdhury, Mohammad Asaduzzaman; Kowser, Md. Arefin; Mia, Md. Shahin

2017-06-01

Carbon fiber composite materials are widely used at different engineering and industrial applications there are good physical, mechanical, chemical properties and light weight. Erosion behavior of materials depends on various factors such as impact angle, particle velocity, particle size, particle shape, particle type, particle flux, temperature of the tested materials. Among these factors impact angle and particle velocity have been recognized as two parameters that noticeably influence the erosion rates of all tested materials. Irregular shaped sand (SiO2) particles of various sizes (200-300 µm, 400-500 µm, and 500-600 µm) were selected erosive element. Tested conditions such as impingement angles between 15 degree to 90 degree, impact velocities between 30-50 m/sec, and stand-off distances 15-25 mm at surrounding room temperature were maintained. The highest level of erosion of the tested composite is obtained at 60° impact angle, which signifies the semi-ductile behavior of this material. Erosion showed increasing trend with impact velocity and decreasing nature in relation to stand-off distance. Surface damage was analyzed using SEM to examine the nature of the erosive wear mechanism.

Mechanics of Granular Materials (MGM0 Flight Hardware in Bench Test

NASA Technical Reports Server (NTRS)

2000-01-01

Engineering bench system hardware for the Mechanics of Granular Materials (MGM) experiment is tested on a lab bench at the University of Colorado in Boulder. This is done in a horizontal arrangement to reduce pressure differences so the tests more closely resemble behavior in the microgravity of space. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

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

Montgomery, Robert, E-mail: robert.montgomery@pnnl.gov; Tomé, Carlos, E-mail: tome@lanl.gov; Liu, Wenfeng, E-mail: wenfeng.liu@anatech.com

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical constitutive models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. To improve upon this approach, a microstructurally-based zirconium alloy mechanical deformation analysis capability is being developed within the United States Department of Energy Consortium for Advanced Simulation of Light Water Reactors (CASL). Specifically, the viscoplastic self-consistent (VPSC)more » polycrystal plasticity modeling approach, developed by Lebensohn and Tomé [1], has been coupled with the BISON engineering scale fuel performance code to represent the mechanistic material processes controlling the deformation behavior of light water reactor (LWR) cladding. A critical component of VPSC is the representation of the crystallographic nature (defect and dislocation movement) and orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. A future goal is for VPSC to obtain information on reaction rate kinetics from atomistic calculations to inform the defect and dislocation behavior models described in VPSC. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON and provides initial results utilizing the coupled functionality.« less

Predictive characterization of aging and degradation of reactor materials in extreme environments. Final report, December 20, 2013 - September 20, 2017

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

Qu, Jianmin

Understanding of reactor material behavior in extreme environments is vital not only to the development of new materials for the next generation nuclear reactors, but also to the extension of the operating lifetimes of the current fleet of nuclear reactors. To this end, this project conducted a suite of unique experimental techniques, augmented by a mesoscale computational framework, to understand and predict the long-term effects of irradiation, temperature, and stress on material microstructures and their macroscopic behavior. The experimental techniques and computational tools were demonstrated on two distinctive types of reactor materials, namely, Zr alloys and high-Cr martensitic steels. Thesemore » materials are chosen as the test beds because they are the archetypes of high-performance reactor materials (cladding, wrappers, ducts, pressure vessel, piping, etc.). To fill the knowledge gaps, and to meet the technology needs, a suite of innovative in situ transmission electron microscopy (TEM) characterization techniques (heating, heavy ion irradiation, He implantation, quantitative small-scale mechanical testing, and various combinations thereof) were developed and used to elucidate and map the fundamental mechanisms of microstructure evolution in both Zr and Cr alloys for a wide range environmental boundary conditions in the thermal-mechanical-irradiation input space. Knowledge gained from the experimental observations of the active mechanisms and the role of local microstructural defects on the response of the material has been incorporated into a mathematically rigorous and comprehensive three-dimensional mesoscale framework capable of accounting for the compositional variation, microstructural evolution and localized deformation (radiation damage) to predict aging and degradation of key reactor materials operating in extreme environments. Predictions from this mesoscale framework were compared with the in situ TEM observations to validate the model.« less

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

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

Estrada Rodas, Ernesto A.; Neu, Richard W.

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformationmore » on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.« less

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

DOE PAGES

Estrada Rodas, Ernesto A.; Neu, Richard W.

2017-09-11

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformationmore » on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.« less

Programming function into mechanical forms by directed assembly of silk bulk materials

PubMed Central

Patel, Nereus; Duggan, Thomas; Perotto, Giovanni; Shirman, Elijah; Li, Chunmei; Kaplan, David L.; Omenetto, Fiorenzo G.

2017-01-01

We report simple, water-based fabrication methods based on protein self-assembly to generate 3D silk fibroin bulk materials that can be easily hybridized with water-soluble molecules to obtain multiple solid formats with predesigned functions. Controlling self-assembly leads to robust, machinable formats that exhibit thermoplastic behavior consenting material reshaping at the nanoscale, microscale, and macroscale. We illustrate the versatility of the approach by realizing demonstrator devices where large silk monoliths can be generated, polished, and reshaped into functional mechanical components that can be nanopatterned, embed optical function, heated on demand in response to infrared light, or can visualize mechanical failure through colorimetric chemistries embedded in the assembled (bulk) protein matrix. Finally, we show an enzyme-loaded solid mechanical part, illustrating the ability to incorporate biological function within the bulk material with possible utility for sustained release in robust, programmably shapeable mechanical formats. PMID:28028213

Using ABAQUS Scripting Interface for Materials Evaluation and Life Prediction

NASA Technical Reports Server (NTRS)

Powers, Lynn M.; Arnold, Steven M.; Baranski, Andrzej

2006-01-01

An ABAQUS script has been written to aid in the evaluation of the mechanical behavior of viscoplastic materials. The purposes of the script are to: handle complex load histories; control load/displacement with alternate stopping criteria; predict failure and life; and verify constitutive models. Material models from the ABAQUS library may be used or the UMAT routine may specify mechanical behavior. User subroutines implemented include: UMAT for the constitutive model; UEXTERNALDB for file manipulation; DISP for boundary conditions; and URDFIL for results processing. Examples presented include load, strain and displacement control tests on a single element model. The tests are creep with a life limiting strain criterion, strain control with a stress limiting cycle and a complex interrupted cyclic relaxation test. The techniques implemented in this paper enable complex load conditions to be solved efficiently with ABAQUS.

Discrete Model for the Structure and Strength of Cementitious Materials

NASA Astrophysics Data System (ADS)

Balopoulos, Victor D.; Archontas, Nikolaos; Pantazopoulou, Stavroula J.

2017-12-01

Cementitious materials are characterized by brittle behavior in direct tension and by transverse dilatation (due to microcracking) under compression. Microcracking causes increasingly larger transverse strains and a phenomenological Poisson's ratio that gradually increases to about ν =0.5 and beyond, at the limit point in compression. This behavior is due to the underlying structure of cementitious pastes which is simulated here with a discrete physical model. The computational model is generic, assembled from a statistically generated, continuous network of flaky dendrites consisting of cement hydrates that emanate from partially hydrated cement grains. In the actual amorphous material, the dendrites constitute the solid phase of the cement gel and interconnect to provide the strength and stiffness against load. The idealized dendrite solid is loaded in compression and tension to compute values for strength and Poisson's effects. Parametric studies are conducted, to calibrate the statistical parameters of the discrete model with the physical and mechanical characteristics of the material, so that the familiar experimental trends may be reproduced. The model provides a framework for the study of the mechanical behavior of the material under various states of stress and strain and can be used to model the effects of additives (e.g., fibers) that may be explicitly simulated in the discrete structure.

Correlating particle hardness with powder compaction performance.

PubMed

Cao, Xiaoping; Morganti, Mikayla; Hancock, Bruno C; Masterson, Victoria M

2010-10-01

Assessing particle mechanical properties of pharmaceutical materials quickly and with little material can be very important to early stages of pharmaceutical research. In this study, a wide range of pharmaceutical materials were studied using atomic force microscopy (AFM) nanoindentation. A significant amount of particle hardness and elastic modulus data were provided. Moreover, powder compact mechanical properties of these materials were investigated in order to build correlation between the particle hardness and powder compaction performance. It was found that the materials with very low or high particle hardness most likely exhibit poor compaction performance while the materials with medium particle hardness usually have good compaction behavior. Additionally, the results from this study enriched Hiestand's special case concept on particle hardness and powder compaction performance. This study suggests that the use of AFM nanoindentation can help to screen mechanical properties of pharmaceutical materials at early development stages of pharmaceutical research.

Porous Media Approach for Modeling Closed Cell Foam

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Sullivan, Roy M.

2006-01-01

In order to minimize boil off of the liquid oxygen and liquid hydrogen and to prevent the formation of ice on its exterior surface, the Space Shuttle External Tank (ET) is insulated using various low-density, closed-cell polymeric foams. Improved analysis methods for these foam materials are needed to predict the foam structural response and to help identify the foam fracture behavior in order to help minimize foam shedding occurrences. This presentation describes a continuum based approach to modeling the foam thermo-mechanical behavior that accounts for the cellular nature of the material and explicitly addresses the effect of the internal cell gas pressure. A porous media approach is implemented in a finite element frame work to model the mechanical behavior of the closed cell foam. The ABAQUS general purpose finite element program is used to simulate the continuum behavior of the foam. The soil mechanics element is implemented to account for the cell internal pressure and its effect on the stress and strain fields. The pressure variation inside the closed cells is calculated using the ideal gas laws. The soil mechanics element is compatible with an orthotropic materials model to capture the different behavior between the rise and in-plane directions of the foam. The porous media approach is applied to model the foam thermal strain and calculate the foam effective coefficient of thermal expansion. The calculated foam coefficients of thermal expansion were able to simulate the measured thermal strain during heat up from cryogenic temperature to room temperature in vacuum. The porous media approach was applied to an insulated substrate with one inch foam and compared to a simple elastic solution without pore pressure. The porous media approach is also applied to model the foam mechanical behavior during subscale laboratory experiments. In this test, a foam layer sprayed on a metal substrate is subjected to a temperature variation while the metal substrate is stretched to simulate the structural response of the tank during operation. The thermal expansion mismatch between the foam and the metal substrate and the thermal gradient in the foam layer causes high tensile stresses near the metal/foam interface that can lead to delamination.

Constitutive Models Based on Compressible Plastic Flows

NASA Technical Reports Server (NTRS)

Rajendran, A. M.

1983-01-01

The need for describing materials under time or cycle dependent loading conditions has been emphasized in recent years by several investigators. In response to the need, various constitutive models describing the nonlinear behavior of materials under creep, fatigue, or other complex loading conditions were developed. The developed models for describing the fully dense (non-porous) materials were mostly based on uncoupled plasticity theory. The improved characterization of materials provides a better understanding of the structual response under complex loading conditions. The pesent studies demonstrate that the rate or time dependency of the response of a porous aggregate can be incorporated into the nonlinear constitutive behavior of a porous solid by appropriately modeling the incompressible matrix behavior. It is also sown that the yield function which wads determined by a continuum mechanics approach must be verified by appropriate experiments on void containing sintered materials in order to obtain meaningful numbers for the constants that appear in the yield function.

Analytical, numerical, and experimental investigations on effective mechanical properties and performances of carbon nanotubes and nanotube based nanocomposites with novel three dimensional nanostructures

NASA Astrophysics Data System (ADS)

Askari, Davood

The theoretical objectives and accomplishment of this work are the analytical and numerical investigation of material properties and mechanical behavior of carbon nanotubes (CNTs) and nanotube nanocomposites when they are subjected to various loading conditions. First, the finite element method is employed to investigate numerically the effective Young's modulus and Poisson's ratio of a single-walled CNT. Next, the effects of chirality on the effective Young's modulus and Poisson's ratio are investigated and then variations of their effective coefficient of thermal expansions and effective thermal conductivities are studied for CNTs with different structural configurations. To study the influence of small vacancy defects on mechanical properties of CNTs, finite element analyses are performed and the behavior of CNTs with various structural configurations having different types of vacancy defects is studied. It is frequently reported that nano-materials are excellent candidates as reinforcements in nanocomposites to change or enhance material properties of polymers and their nanocomposites. Second, the inclusion of nano-materials can considerably improve electrical, thermal, and mechanical properties of the bonding agent, i.e., resin. Note that, materials atomic and molecular level do not usually show isotropic behaviour, rather they have orthotropic properties. Therefore, two-phase and three-phase cylindrically orthotropic composite models consisting of different constituents with orthotropic properties are developed and introduced in this work to analytically predict the effective mechanical properties and mechanical behavior of such structures when they are subjected to various external loading conditions. To verify the analytically obtained exact solutions, finite element analyses of identical cylindrical structures are also performed and then results are compared with those obtained analytically, and excellent agreement is achieved. The third part of this dissertation investigates the growth of vertically aligned, long, and high density arrays of CNTs and novel 3-D carbon nanotube nano-forests. A Chemical vapor deposition technique is used to grow radially aligned CNTs on various types of fibrous materials such as silicon carbide, carbon, Kevlar, and glass fibers and clothes that can be used for the fabrication of multifunctional high performing laminated nanocomposite structures. Using the CNTs nano-forest clothes, nanocomposite samples are prepared and tested giving promising results for the improvement of mechanical properties and performance of composites structures.

Study of the toughening mechanisms in bone and biomimetic hydroxyapatite materials using Raman microprobe spectroscopy.

PubMed

Pezzotti, Giuseppe; Sakakura, Seiji

2003-05-01

A Raman microprobe spectroscopy characterization of microscopic fracture mechanisms is presented for a natural hydroxyapatite material (cortical bovine femur) and two synthetic hydroxyapatite-based materials with biomimetic structures-a hydroxyapatite skeleton interpenetrated with a metallic (silver) or a polymeric (nylon-6) phase. In both the natural and synthetic materials, a conspicuous amount of toughening arose from a microscopic crack-bridging mechanism operated by elasto-plastic stretching of unbroken second-phase ligaments along the crack wake. This mechanism led to a rising R-curve behavior. An additional micromechanism, responsible for stress relaxation at the crack tip, was recognized in the natural bone material and was partly mimicked in the hydroxyapatite/silver composite. This crack-tip mechanism conspicuously enhanced the cortical bone material resistance to fracture initiation. A piezo-spectroscopic technique, based on a microprobe measurement of 980 cm(-1) Raman line of hydroxyapatite, enabled us to quantitatively assess in situ the microscopic stress fields developed during fracture both at the crack tip and along the crack wake. Using the Raman piezo-spectroscopy technique, toughening mechanisms were assessed quantitatively and rationally related to the macroscopic fracture characteristics of hydroxyapatite-based materials. Copyright 2003 Wiley Periodicals, Inc.

Mechanical Behavior Optimization of Chitosan Extracted from Shrimp Shells as a Sustainable Material for Shopping Bags.

PubMed

D'Angelo, Giacomo; Elhussieny, Amal; Faisal, Marwa; Fahim, I S; Everitt, Nicola M

2018-05-22

The use of biodegradable materials for shopping bag production, and other products made from plastics, has recently been an object of intense research-with the aim of reducing the environmental burdens given by conventional materials. Chitosan is a potential material because of its biocompatibility, degradability, and non-toxicity. It is a semi-natural biopolymeric material produced by the deacetylation of chitin, which is the second most abundant natural biopolymer (after cellulose). Chitin is found in the exoskeleton of insects, marine crustaceans, and the cell walls of certain fungi and algae. The raw materials most abundantly available are the shells of crab, shrimp, and prawn. Hence, in this study chitosan was selected as one of the main components of biodegradable materials used for shopping bag production. Firstly, chitin was extracted from shrimp shell waste and then converted to chitosan. The chitosan was next ground to a powder. Although, currently, polyethylene bags are prepared by blown extrusion, in this preliminary research the chitosan powder was dissolved in a solvent and the films were cast. Composite films with several fillers were used as a reinforcement at different dosages to optimize mechanical properties, which have been assessed using tensile tests. These results were compared with those of conventional polyethylene bags used in Egypt. Overall, the chitosan films were found to have a lower ductility but appeared to be strong enough to fulfill shopping bag functions. The addition of fillers, such as chitin whiskers and rice straw, enhanced the mechanical properties of chitosan films, while the addition of chitin worsened overall mechanical behavior.

Linking nanoscale mechanical behavior to bulk physical properties and phenomena of energetic materials

NASA Astrophysics Data System (ADS)

Taw, Matthew R.

The hardness and reduced modulus of aspirin, RDX, HMX, TATB, FOX-7, ADAAF, and TNT/CL-20 were experimentally measured with nanoindentation. These values are reported for the first time using as-received micron sized crystals of energetic materials with no additional mechanical processing. The results for TATB, ADAAF, and TNT/CL-20 are the first of their kind, while comparisons to previous nanoindentation studies on large, carefully grown single crystals of the other energetic materials show that mechanical properties of the larger crystals are comparable to crystals in the condition they are practically used. Measurements on aspirin demonstrate the variation that can occur between nanoindentation indents based on the orientation of a Berkovich tip relative to the surface of the sample. The Hertzian elastic contact model was used to analyze the materials initial yield, or pop-in, behavior. The length, energy, indentation load, and shear stress at initial yielding were used to characterize each material. For the energetic materials the length and energy of the yield excursions were compared to the drop weight sensitivity. This comparison revealed a general trend that more impact sensitive materials have longer, more severe pop-in excursions. Hot spot initiation mechanisms involving crystal defects such as void collapses and dislocation pile-up followed by avalanche are supported by these trends. While this only takes one aspect of impact sensitivity into consideration, if this trend is observed in a larger range of energetics these methods could possibly be used to great advantage in the early stages of new explosives synthesis to obtain an estimation of drop weight sensitivity.

Discovering mechanisms relevant for radiation damage evolution

DOE PAGES

Uberuaga, Blas Pedro; Martinez, Enrique Saez; Perez, Danny; ...

2018-02-22

he response of a material to irradiation is a consequence of the kinetic evolution of defects produced during energetic damage events. Thus, accurate predictions of radiation damage evolution require knowing the atomic scale mechanisms associated with those defects. Atomistic simulations are a key tool in providing insight into the types of mechanisms possible. Further, by extending the time scale beyond what is achievable with conventional molecular dynamics, even greater insight can be obtained. Here, we provide examples in which such simulations have revealed new kinetic mechanisms that were not obvious before performing the simulations. We also demonstrate, through the couplingmore » with higher level models, how those mechanisms impact experimental observables in irradiated materials. Lastly, we discuss the importance of these types of simulations in the context of predicting material behavior.« less

Discovering mechanisms relevant for radiation damage evolution

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

Uberuaga, Blas Pedro; Martinez, Enrique Saez; Perez, Danny

he response of a material to irradiation is a consequence of the kinetic evolution of defects produced during energetic damage events. Thus, accurate predictions of radiation damage evolution require knowing the atomic scale mechanisms associated with those defects. Atomistic simulations are a key tool in providing insight into the types of mechanisms possible. Further, by extending the time scale beyond what is achievable with conventional molecular dynamics, even greater insight can be obtained. Here, we provide examples in which such simulations have revealed new kinetic mechanisms that were not obvious before performing the simulations. We also demonstrate, through the couplingmore » with higher level models, how those mechanisms impact experimental observables in irradiated materials. Lastly, we discuss the importance of these types of simulations in the context of predicting material behavior.« less

Direct Associations or Internal Transformations? Exploring the Mechanisms Underlying Sequential Learning Behavior

PubMed Central

Gureckis, Todd M.; Love, Bradley C.

2009-01-01

We evaluate two broad classes of cognitive mechanisms that might support the learning of sequential patterns. According to the first, learning is based on the gradual accumulation of direct associations between events based on simple conditioning principles. The other view describes learning as the process of inducing the transformational structure that defines the material. Each of these learning mechanisms predict differences in the rate of acquisition for differently organized sequences. Across a set of empirical studies, we compare the predictions of each class of model with the behavior of human subjects. We find that learning mechanisms based on transformations of an internal state, such as recurrent network architectures (e.g., Elman, 1990), have difficulty accounting for the pattern of human results relative to a simpler (but more limited) learning mechanism based on learning direct associations. Our results suggest new constraints on the cognitive mechanisms supporting sequential learning behavior. PMID:20396653

Aging and loading rate effects on the mechanical behavior of equine bone

NASA Astrophysics Data System (ADS)

Kulin, Robb M.; Jiang, Fengchun; Vecchio, Kenneth S.

2008-06-01

Whether due to a sporting accident, high-speed impact, fall, or other catastrophic event, the majority of clinical bone fractures occur under dynamic loading conditions. However, although extensive research has been performed on the quasi-static fracture and mechanical behavior of bone to date, few high-quality studies on the fracture behavior of bone at high strain rates have been performed. Therefore, many questions remain regarding the material behavior, including not only the loading-rate-dependent response of bone, but also how this response varies with age. In this study, tests were performed on equine femoral bone taken post-mortem from donors 6 months to 28 years of age. Quasi-static and dynamic tests were performed to determine the fracture toughness and compressive mechanical behavior as a function of age at varying loading rates. Fracture paths were then analyzed using scanning confocal and scanning-electron microscopy techniques to assess the role of various microstructural features on toughening mechanisms.

Free body analysis, beam mechanics, and finite element modeling of the mandible of Alligator mississippiensis.

PubMed

Porro, Laura B; Holliday, Casey M; Anapol, Fred; Ontiveros, Lupita C; Ontiveros, Lolita T; Ross, Callum F

2011-08-01

The mechanical behavior of mammalian mandibles is well-studied, but a comprehensive biomechanical analysis (incorporating detailed muscle architecture, accurate material properties, and three-dimensional mechanical behavior) of an extant archosaur mandible has never been carried out. This makes it unclear how closely models of extant and extinct archosaur mandibles reflect reality and prevents comparisons of structure-function relationships in mammalian and archosaur mandibles. We tested hypotheses regarding the mechanical behavior of the mandible of Alligator mississippiensis by analyzing reaction forces and bending, shear, and torsional stress regimes in six models of varying complexity. Models included free body analysis using basic lever arm mechanics, 2D and 3D beam models, and three high-resolution finite element models of the Alligator mandible, incorporating, respectively, isotropic bone without sutures, anisotropic bone with sutures, and anisotropic bone with sutures and contact between the mandible and the pterygoid flange. Compared with the beam models, the Alligator finite element models exhibited less spatial variability in dorsoventral bending and sagittal shear stress, as well as lower peak values for these stresses, suggesting that Alligator mandibular morphology is in part designed to reduce these stresses during biting. However, the Alligator models exhibited greater variability in the distribution of mediolateral and torsional stresses than the beam models. Incorporating anisotropic bone material properties and sutures into the model reduced dorsoventral and torsional stresses within the mandible, but led to elevated mediolateral stresses. These mediolateral stresses were mitigated by the addition of a pterygoid-mandibular contact, suggesting important contributions from, and trade-offs between, material properties and external constraints in Alligator mandible design. Our results suggest that beam modeling does not accurately represent the mechanical behavior of the Alligator mandible, including important performance metrics such as magnitude and orientation of reaction forces, and mediolateral bending and torsional stress distributions. J.Morphol. 2011. © 2011 Wiley-Liss, Inc. Copyright © 2011 Wiley-Liss, Inc.

Prediction of high temperature metal matrix composite ply properties

NASA Technical Reports Server (NTRS)

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

1988-01-01

The application of the finite element method (superelement technique) in conjunction with basic concepts from mechanics of materials theory is demonstrated to predict the thermomechanical behavior of high temperature metal matrix composites (HTMMC). The simulated behavior is used as a basis to establish characteristic properties of a unidirectional composite idealized an as equivalent homogeneous material. The ply properties predicted include: thermal properties (thermal conductivities and thermal expansion coefficients) and mechanical properties (moduli and Poisson's ratio). These properties are compared with those predicted by a simplified, analytical composite micromechanics model. The predictive capabilities of the finite element method and the simplified model are illustrated through the simulation of the thermomechanical behavior of a P100-graphite/copper unidirectional composite at room temperature and near matrix melting temperature. The advantage of the finite element analysis approach is its ability to more precisely represent the composite local geometry and hence capture the subtle effects that are dependent on this. The closed form micromechanics model does a good job at representing the average behavior of the constituents to predict composite behavior.

Dynamic mechanical control of local vacancies in NiO thin films

NASA Astrophysics Data System (ADS)

Seol, Daehee; Yang, Sang Mo; Jesse, Stephen; Choi, Minseok; Hwang, Inrok; Choi, Taekjib; Park, Bae Ho; Kalinin, Sergei V.; Kim, Yunseok

2018-07-01

The manipulation of local ionic behavior via external stimuli in oxide systems is of great interest because it can help in directly tuning material properties. Among external stimuli, mechanical force has attracted intriguing attention as novel stimulus for ionic modulation. Even though effectiveness of mechanical force on local ionic modulation has been validated in terms of static effect, its real-time i.e., dynamic, behavior under an application of the force is barely investigated in spite of its crucial impact on device performance such as force or pressure sensors. In this study, we explore dynamic ionic behavior modulated by mechanical force in NiO thin films using electrochemical strain microscopy (ESM). Ionically mediated ESM hysteresis loops were significantly varied under an application of mechanical force. Based on these results, we were able to investigate relative relationship between the force and voltage effects on ionic motion and, further, control effectively ionic behavior through combination of mechanical and electrical stimuli. Our results can provide comprehensive information on the effect of mechanical forces on ionic dynamics in ionic systems.

Dynamic mechanical control of local vacancies in NiO thin films.

PubMed

Seol, Daehee; Yang, Sang Mo; Jesse, Stephen; Choi, Minseok; Hwang, Inrok; Choi, Taekjib; Park, Bae Ho; Kalinin, Sergei V; Kim, Yunseok

2018-07-06

The manipulation of local ionic behavior via external stimuli in oxide systems is of great interest because it can help in directly tuning material properties. Among external stimuli, mechanical force has attracted intriguing attention as novel stimulus for ionic modulation. Even though effectiveness of mechanical force on local ionic modulation has been validated in terms of static effect, its real-time i.e., dynamic, behavior under an application of the force is barely investigated in spite of its crucial impact on device performance such as force or pressure sensors. In this study, we explore dynamic ionic behavior modulated by mechanical force in NiO thin films using electrochemical strain microscopy (ESM). Ionically mediated ESM hysteresis loops were significantly varied under an application of mechanical force. Based on these results, we were able to investigate relative relationship between the force and voltage effects on ionic motion and, further, control effectively ionic behavior through combination of mechanical and electrical stimuli. Our results can provide comprehensive information on the effect of mechanical forces on ionic dynamics in ionic systems.

Effects of environment and frequency on the fatigue behavior of the spallation neutron source (SNS) target container material - 316 LN stainless steel

NASA Astrophysics Data System (ADS)

Tian, Hongbo

As the candidate target container material of the new Spallation Neutron Source (SNS) being designed and constructed at the Oak Ridge National Laboratory (ORNL), Type 316 low-carbon nitrogen-added (LN) stainless steel (SS) will operate in an aggressive environment, subjected to intense fluxes of high-energy protons and neutrons while exposed to liquid mercury. The current project is oriented toward materials studies regarding the effects of test environment and frequency on the fatigue behavior of 316 LN SS. In order to study the structural applications of this material and improve the fundamental understanding of the fatigue damage mechanisms, fatigue tests were performed in air and mercury environments at various frequencies and R ratios (R = sigma min/sigmamax, sigmamin and sigmamax are the applied minimum and maximum stresses, respectively). Fatigue data were developed for the structural design and engineering applications of this material. Specifically, high-cycle fatigue tests, fatigue crack-propagation tests, and ultrahigh cycle fatigue tests up to 10 9 cycles were conducted in air and mercury with test frequencies from 10 Hz to 700 Hz. Microstructure characterizations were performed using optical microscopy (OM), scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM). It was found that mercury doesn't seem to have a large impact on the crack-initiation behavior of 316 LN SS. However, the crack-propagation mechanisms in air and mercury are different in some test conditions. Transgranular cracks seem to be the main mechanism in air, and intergranular in mercury. A significant specimen self-heating effect was found during high-cycle faituge. Theoretical calculation was performed to predict temperature responses of the material subjected to cyclic deformation. The predicted cyclic temperature evolution seems to be in good agreement with the experimental results.

Low carbon steel: Metallurgical structure vs. mechanical properties

NASA Technical Reports Server (NTRS)

Shull, Robert D.

1990-01-01

The objective is to provide a low cost, simple experiment for either demonstration purposes or as a laboratory experiment that will teach the student the importance of the thermal-mechanical history of a metallic alloy in determining that material's mechanical behavior. Hairpins are subjected to various treatments. The experimental equipment and procedures are discussed.

Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior

NASA Astrophysics Data System (ADS)

Rahmat, Meysam

2018-05-01

A significant number of materials show different mechanical behavior under dynamic loads compared to quasi-static (Salvado et al. in Prog. Mater. Sci. 88:186-231, 2017). Therefore, a comprehensive study of material dynamic behavior is essential for applications in which dynamic loads are dominant (Li et al. in J. Mater. Process. Technol. 255:373-386, 2018). In this work, aluminum 6061-T6, as an example of ductile alloys with numerous applications including in the aerospace industry, has been studied under quasi-static and dynamic tensile tests with strain rates of up to 156 s^{-1}. Dogbone specimens were designed, instrumented and tested with a high speed servo-hydraulic load frame, and the results were validated with the literature. It was observed that at a strain rate of 156 s^{-1} the yield and ultimate strength increased by 31% and 33% from their quasi-static values, respectively. Moreover, the failure elongation and fracture energy per unit volume also increased by 18% and 52%, respectively. A Johnson-Cook model was used to capture the behavior of the material at different strain rates, and a modified version of this model was presented to enhance the capabilities of the original model, especially in predicting material properties close to the failure point. Finally, the fracture surfaces of specimens tested under quasi-static and dynamic loads were compared and conclusions about the differences were drawn.

Enhanced mechanical properties of self-polymerized polydopamine-coated recycled PLA filament used in 3D printing

NASA Astrophysics Data System (ADS)

Zhao, Xing Guan; Hwang, Kyung-Jun; Lee, Dongoh; Kim, Taemin; Kim, Namsu

2018-05-01

Dopamine readily adsorbs onto almost all kinds of surfaces and develops cohesive strength through self-polymerization; hence, aqueous solutions of dopamine can be used as adhesives. These properties were used to prevent the degradation in the mechanical properties of recycled PLA fabricated by 3D printer. The mechanical properties of 3D printed PLA play a critical role in determining its applications. To reduce the manufacturing cost as well as environmental pollutants, recycling of 3D printed materials has attracted many attentions. However, recycling of polymeric materials causes the degradation of the mechanical properties. Our study is aimed at advancing the current knowledge on the adhesion behavior of polydopamine coatings on PLA pellets used in 3D printing process. Polydopamine was synthesized by oxidative polymerization and used to coat PLA specimens. The adhesion behavior and mechanical properties of the 3D printed specimens were evaluated by tensile tests. It was found that the mechanical properties of recycled specimen with polydopamine coating have been improved. Microstructural and chemical characterization of the coated specimens was carried out using FE-SEM, FTIR, and XPS analyses.

Carbon nanotubes reinforced chitosan films: mechanical properties and cell response of a novel biomaterial for cardiovascular tissue engineering.

PubMed

Kroustalli, A; Zisimopoulou, A E; Koch, S; Rongen, L; Deligianni, D; Diamantouros, S; Athanassiou, G; Kokozidou, M; Mavrilas, D; Jockenhoevel, S

2013-12-01

Carbon nanotubes have been proposed as fillers to reinforce polymeric biomaterials for the strengthening of their structural integrity to achieve better biomechanical properties. In this study, a new polymeric composite material was introduced by incorporating various low concentrations of multiwalled carbon nanotubes (MWCNTs) into chitosan (CS), aiming at achieving a novel composite biomaterial with superior mechanical and biological properties compared to neat CS, in order to be used in cardiovascular tissue engineering applications. Both mechanical and biological characteristics in contact with the two relevant cell types (endothelial cells and vascular myofibroblasts) were studied. Regarding the mechanical behavior of MWCNT reinforced CS (MWCNT/CS), 5 and 10 % concentrations of MWCNTs enhanced the mechanical behavior of CS, with that of 5 % exhibiting a superior mechanical strength compared to 10 % concentration and neat CS. Regarding biological properties, MWCNT/CS best supported proliferation of endothelial and myofibroblast cells, MWCNTs and MWCNT/CS caused no apoptosis and were not toxic of the examined cell types. Conclusively, the new material could be suitable for tissue engineering (TE) and particularly for cardiovascular TE applications.

Mechanical Behavior of Glidcop Al-15 at High Temperature and Strain Rate

NASA Astrophysics Data System (ADS)

Scapin, M.; Peroni, L.; Fichera, C.

2014-05-01

Strain rate and temperature are variables of fundamental importance for the definition of the mechanical behavior of materials. In some elastic-plastic models, the effects, coming from these two quantities, are considered to act independently. This approach should, in some cases, allow to greatly simplify the experimental phase correlated to the parameter identification of the material model. Nevertheless, in several applications, the material is subjected to dynamic load at very high temperature, as, for example, in case of machining operation or high energy deposition on metals. In these cases, to consider the effect of strain rate and temperature decoupled could not be acceptable. In this perspective, in this work, a methodology for testing materials varying both strain rate and temperature was described and applied for the mechanical characterization of Glidcop Al-15, a copper-based composite reinforced with alumina dispersion, often used in nuclear applications. The tests at high strain rate were performed using the Hopkinson Bar setup for the direct tensile tests. The heating of the specimen was performed using an induction coil system and the temperature was controlled on the basis of signals from thermocouples directly welded on the specimen surface. Varying the strain rate, Glidcop Al-15 shows a moderate strain-rate sensitivity at room temperature, while it considerably increases at high temperature: material thermal softening and strain-rate hardening are strongly coupled. The experimental data were fitted using a modified formulation of the Zerilli-Armstrong model able to reproduce this kind of behavior with a good level of accuracy.

Mechanical behavior of nanostructured and ultrafine-grained materials under shock wave loadings. experimental data and results of computer simulation

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir

2012-03-01

Features of mechanical behavior of nanostructured and ultrafine-grained metals under quasistatic and shock wave loadings are discussed. Features of mechanical behavior of nanostructured and ultrafine grained metals over a wide range of strain rates are discussed. A constitutive model for mechanical behavior of metal alloys under shock wave loading including a grain size distribution, a precipitate hardening, and physical mechanisms of shear stress relaxation is presented. Strain rate sensitivity of the yield stress of face-centered-cubic, hexagonal close-packed metal alloys depends on grain size, whereas the Hugoniot elastic limits of ultrafine-grained copper, aluminum, and titanium alloys are close to values of coarse-grained counterparts. At quasi-static loading the yield strength and the tensile strength of titanium alloys with grain size from 300 to 500 nm are twice higher than at coarse-grained counterparts. But the spall strength of the UFG titanium alloys exceeds the value of coarse-grained counterparts only for 10 percents.

Mechanical behavior of nanotwinned materials – experimental and computational approaches

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

Yavas, Hakan

2016-12-17

Nanotwinned materials exhibit high strength combined with excellent thermal stability, making them potentially attractive for numerous applications. When deposited on cold substrates at high rates, for example, silver films can be prepared with a high-density of growth twins with an average twin boundary spacing of less than 10 nm. These films show a very strong {111} texture, with the twin boundaries being perpendicular to the growth direction. The origins of superior mechanical and thermal properties of nanotwinned materials, however, are not yet fully understood and need further improvements.

A Model of Thermal Aging of Hyper-Elastic Materials with an Application to Natural Rubber

NASA Astrophysics Data System (ADS)

Korba, Ahmed G.

Understanding the degradation of material properties and stress-strain behavior of rubber-like materials that has been exposed to elevated temperature is essential for rubber among components design and lifetime prediction. The complexity of the relationship between hyper-elastic materials, crosslinking density, and chemical composition present a difficult problem for the accurate prediction of mechanical properties under thermal aging. In the first part of the current research, a new and relatively simple mathematical formulation is presented to expresses the change in material properties of natural rubber subjected to various elevated temperatures and aging times. The aging temperatures ranged from 76.7 °C to 115.0 °C, and the aging times ranged from 0 to 600 hours. Based on the experimental data, the natural rubber mechanical properties under thermal aging showed a similar behavior to the rate of change of the crosslinking density (CLD) with aging time and temperature as determined as of the research. Three mechanical properties have been chosen to be studied: the ultimate tensile strength, the fracture stretch value, and the secant modulus at 11.0% strain. The proposed phenomenological model relates the mechanical properties with the rate of change of the CLD based on a form of Arrhenius equation. The proposed equations showed promising results compared to the experimental data with an acceptable error margin of less than 10% in most of the cases studied. In the second part of the current research, a closed form set of equations that was based on basic continuum mechanics assumptions has been proposed to define the material stress-strain behavior of natural rubber as an application of hyper-elastic materials. The proposed formulas include the influence of aging time and temperature. The newly proposed "Wight Function Based" (WFB) method has been verified against the historic Treloar's test data for uni-axial, bi-axial and pure shear loadings of Treloar's vulcanized rubber material, showing a promising level of confidence compared to the Ogden and the Yeoh methods. Tensile testing was performed on strip specimens that were thermally aged then subjected uni-axial tension and hardness tests. A non-linear least square optimization tool in Matlab (Lscurvefitt) was used for all fitting purposes.

The mechanical properties of ionic polymer-metal composites

NASA Astrophysics Data System (ADS)

Park, Il-Seok; Kim, Sang-Mun; Kim, Doyeon; Kim, Kwang J.

2007-04-01

In this study, we investigated the mechanical properties of various type ionic polymer-metal composites (IPMCs) and Pt, Au, Pd, and Pt electroded ionic liquid (IL-Pt) IPMCs, by testing tensile modulus and dynamic mechanical behavior. The SEM was utilized to investigate the characteristics of the doped electroding layer, and the DSC was probed in order to look into the thermal behavior of various types of IPMCs. Au IPMCs, having a 5~7 μm doped layer and nano-sized Au particles (ca. 10 nm), showed the highest tensile strength (56 MPa) and modulus (602 MPa) in a dried condition. In a thermal behavior, Au IPMC has the highest T g (153°C) and T m (263°C) in both the DMA and DSC results. The fracture behavior of various types IPMCs followed base material's behavior, Nafion TM, which is represented as the semicrystalline polymer characteristic.

Metallic materials for mechanical damping capacity applications

NASA Astrophysics Data System (ADS)

Crăciun, R. C.; Stanciu, S.; Cimpoeșu, R.; (Dragoș Ursanu, A. I.; Manole, V.; Paraschiv, P.; Chicet, D. L.

2016-08-01

Some metallic materials exhibit good damping capacity of mechanical energy into thermal energy. This property along with the others metallic characteristics make this materials interesting for a big number of applications. These materials can be used as bumpers in different applications including automotive field. Beside grey cast iron and shape memory alloys few new metallic materials are presented for the supposition of high damping capacity. We analyze the causes that increase the internal friction of some metallic materials and possibilities to enhance this property through different mechanical, physical or chemical methods. Shape memory alloys, especially those based on copper, present a different damping capacity on martensite, austenite or transition state. In the transformation range M ↔A, which in case of copper base shape memory alloys is quite large, the metallic intelligent materials present a high internal friction, almost comparable with natural rubber behavior that can transform mechanical energy into thermal energy till a certain value of the external solicitation. These materials can be used as noise or small vibrations bumpers or even as shock absorbers in automotive industry.

Microstructure-fatigue crack propagation relationship in TiB{sub 2} particulate reinforced Zn (ZA-8) alloy

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

Hua, W.; Zhang, J.; Wang, Z.

1995-10-01

The relationship between microstructure and propagation behavior of fatigue crack in TiB{sub 2} particulate reinforced ZA-8 Zn alloy and in the corresponding constituent matrix material was studied in three point bending fatigue tests with well-polished and pre-etched specimens. Special attention was paid to the observation of microstructure along the crack path as well as on the fracture surface. Mechanism for the difference in fatigue crack growth behavior of the two materials was investigated. The present results indicate that the addition of reinforcement modified the solidification process of the matrix material leading to a considerable change in the matrix microstructure. Thismore » change in the matrix microstructure and the presence of reinforcing particles considerably affected the fatigue crack propagation behavior in the material.« less

Microstructure and mechanical behavior of direct metal laser sintered Inconel alloy 718

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

Smith, Derek H.; Bicknell, Jonathan; Jorgensen, Luke

2016-03-15

In this paper, we investigate microstructure and quasi-static mechanical behavior of the direct metal laser sintered Inconel 718 superalloy as a function of build direction (BD). The printed material was further processed by annealing and double-aging, hot isostatic pressing (HIP), and machining. We characterize porosity fraction and distribution using micro X-ray computed tomography (μXCT), grain structure and crystallographic texture using electron backscattered diffraction (EBSD), and mechanical response in quasi-static tension and compression using standard mechanical testing at room temperature. Analysis of the μXCT imaging shows that majority of porosity develops in the outer layer of the printed material. However, porositymore » inside the material is also present. The EBSD measurements reveal formation of columnar grains, which favor < 001 > fiber texture components along the BD. These measurements also show evidence of coarse-grained microstructure present in the samples treated by HIP. Finally, analysis of grain boundaries reveal that HIP results in a large number of annealing twins compared to that in samples that underwent annealing and double-aging. The yield strength varies with the testing direction by approximately 7%, which is governed by a combination of grain morphology and crystallographic texture. In particular, we determine tension–compression asymmetry in the yield stress as well as anisotropy of the material flow during compression. We find that HIP lowers yield stress but improves ductility relative to the annealed and aged material. These results are discussed and critically compared with the data reported for wrought material in the same condition. - Highlights: • Microstructure and mechanical properties of DMLS Inconel 718 are studied in function of build direction. • Inhomogeneity of microstructure in the material in several conditions is quantified by μXCT and EBSD. • Anisotropy and asymmetry in the mechanical response are determined by tension and compression testing.« less

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.

Scale effects in crystal plasticity

NASA Astrophysics Data System (ADS)

Padubidri Janardhanachar, Guruprasad

The goal of this research work is to further the understanding of crystal plasticity, particularly at reduced structural and material length scales. Fundamental understanding of plasticity is central to various challenges facing design and manufacturing of materials for structural and electronic device applications. The development of microstructurally tailored advanced metallic materials with enhanced mechanical properties that can withstand extremes in stress, strain, and temperature, will aid in increasing the efficiency of power generating systems by allowing them to work at higher temperatures and pressures. High specific strength materials can lead to low fuel consumption in transport vehicles. Experiments have shown that enhanced mechanical properties can be obtained in materials by constraining their size, microstructure (e.g. grain size), or both for various applications. For the successful design of these materials, it is necessary to have a thorough understanding of the influence of different length scales and evolving microstructure on the overall behavior. In this study, distinction is made between the effect of structural and material length scale on the mechanical behavior of materials. A length scale associated with an underlying physical mechanism influencing the mechanical behavior can overlap with either structural length scales or material length scales. If it overlaps with structural length scales, then the material is said to be dimensionally constrained. On the other hand, if it overlaps with material length scales, for example grain size, then the material is said to be microstructurally constrained. The objectives of this research work are: (1) to investigate scale and size effects due to dimensional constraints; (2) to investigate size effects due to microstructural constraints; and (3) to develop a size dependent hardening model through coarse graining of dislocation dynamics. A discrete dislocation dynamics (DDD) framework where the scale of analysis is intermediate between a fully discretized (e.g. atomistic) and fully continuum is used for this study. This mesoscale tool allows to address all the stated objectives of this study within a single framework. Within this framework, the effect of structural and the material length scales are naturally accounted for in the simulations and need not be specified in an ad hoc manner, as in some continuum models. It holds the promise of connecting the evolution of the defect microstructure to the effective response of the crystal. Further, it provides useful information to develop physically motivated continuum models to model size effects in materials. The contributions of this study are: (a) provides a new interpretation of mechanical size effect due to only dimensional constraint using DDD; (b) a development of an experimentally validated DDD simulation methodology to model Cu micropillars; (c) a coarse graining technique using DDD to develop a phenomenological model to capture size effect on strain hardening; and (d) a development of a DDD framework for polycrystals to investigate grain size effect on yield strength and strain hardening.

Thermal behavior of silicone rubber-based ceramizable composites characterized by Fourier transform infrared (FT-IR) spectroscopy and microcalorimetry.

PubMed

Anyszka, Rafał; Bieliński, Dariusz M; Jędrzejczyk, Marcin

2013-12-01

Ceramizable (ceramifiable) silicone rubber-based composites are commonly used for cable insulation. These materials are able to create a protective ceramic layer during fire due to the ceramization process, which occurs at high temperature. When the temperature is increased, the polymer matrix is degraded and filler particles stick together by the fluxing agent, producing a solid, continuous ceramic phase that protects the copper wire from heat and mechanical stress. Despite increasing interest in these materials that has resulted in growing applications in the cable industry, their thermal behavior and ceramization process are still insufficiently described in the literature. In this paper, the thermal behavior of ceramizable silicone rubber-based composites is studied using microcalorimetry and Fourier transform infrared spectroscopy. The analysis of the experimental data made it possible to develop complete information on the mechanism of composite ceramization.

Evaluating the effects of hydroxyapatite coating on the corrosion behavior of severely deformed 316Ti SS for surgical implants.

PubMed

Mhaede, Mansour; Ahmed, Aymen; Wollmann, Manfred; Wagner, Lothar

2015-05-01

The present work investigates the effects of severe plastic deformation by cold rolling on the microstructure, the mechanical properties and the corrosion behavior of austenitic stainless steel (SS) 316Ti. Hydroxyapatite coating (HA) was applied on the deformed material to improve their corrosion resistance. The martensitic transformation due to cold rolling was recorded by X-ray diffraction spectra. The effects of cold rolling on the corrosion behavior were studied using potentiodynamic polarization. The electrochemical tests were carried out in Ringer's solution at 37±1 °C. Cold rolling markedly enhanced the mechanical properties while the electrochemical tests referred to a lower corrosion resistance of the deformed material. The best combination of both high strength and good corrosion resistance was achieved after applying hydroxyapatite coating. Copyright © 2015 Elsevier B.V. All rights reserved.

Multiscale Homogenization Theory: An Analysis Tool for Revealing Mechanical Design Principles in Bone and Bone Replacement Materials

NASA Astrophysics Data System (ADS)

Hellmich, Christian; Fritsch, Andreas; Dormieux, Luc

Biomimetics deals with the application of nature-made "design solutions" to the realm of engineering. In the quest to understand mechanical implications of structural hierarchies found in biological materials, multiscale mechanics may hold the key to understand "building plans" inherent to entire material classes, here bone and bone replacement materials. Analyzing a multitude of biophysical hierarchical and biomechanical experiments through homogenization theories for upscaling stiffness and strength properties reveals the following design principles: The elementary component "collagen" induces, right at the nanolevel, the mechanical anisotropy of bone materials, which is amplified by fibrillar collagen-based structures at the 100-nm scale, and by pores in the micrometer-to-millimeter regime. Hydroxyapatite minerals are poorly organized, and provide stiffness and strength in a quasi-brittle manner. Water layers between hydroxyapatite crystals govern the inelastic behavior of the nanocomposite, unless the "collagen reinforcement" breaks. Bone replacement materials should mimic these "microstructural mechanics" features as closely as possible if an imitation of the natural form of bone is desired (Gebeshuber et al., Adv Mater Res 74:265-268, 2009).

Rayleigh wave behavior in functionally graded magneto-electro-elastic material

NASA Astrophysics Data System (ADS)

Ezzin, Hamdi; Mkaoir, Mohamed; Amor, Morched Ben

2017-12-01

Piezoelectric-piezomagnetic functionally graded materials, with a gradual change of the mechanical and electromagnetic properties have greatly applying promises. Based on the ordinary differential equation and stiffness matrix methods, a dynamic solution is presented for the propagation of the wave on a semi-infinite piezomagnetic substrate covered with a functionally graded piezoelectric material (FGPM) layer. The materials properties are assumed to vary in the direction of the thickness according to a known variation law. The phase and group velocity of the Rayleigh wave is numerically calculated for the magneto-electrically open and short cases, respectively. The effect of gradient coefficients on the phase velocity, group velocity, coupled magneto-electromechanical factor, on the stress fields, the magnetic potential and the mechanical displacement are discussed, respectively. Illustration is achieved on the hetero-structure PZT-5A/CoFe2O4; the obtained results are especially useful in the design of high-performance acoustic surface devices and accurately prediction of the Rayleigh wave propagation behavior.

Microgravity

NASA Image and Video Library

2000-05-05

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the top of the sand column with the metal platten removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Microgravity

NASA Image and Video Library

2000-05-05

A test cell for Mechanics of Granular Materials (MGM) experiment is tested for long-term storage with water in the system as plarned for STS-107. This view shows the compressed sand column with the protective water jacket removed. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Microgravity

NASA Image and Video Library

1998-01-25

A test cell for Mechanics of Granular Materials (MGM) experiment is shown approximately 20 and 60 minutes after the start of an experiment on STS-89. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Mechanics of Granular Materials (MGM) Investigators

NASA Technical Reports Server (NTRS)

2000-01-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment at the University of Colorado at Boulder include Tawnya Ferbiak (software engineer), Susan Batiste (research assistant), and Christina Winkler (graduate research assistant). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Mechanic of Granular Materials (MGM) Investigator

NASA Technical Reports Server (NTRS)

2000-01-01

Key persornel in the Mechanics of Granular Materials (MGM) experiment are Mark Lankton (Program Manager at University Colorado at Boulder), Susan Batiste (research assistance, UCB), and Stein Sture (principal investigator). Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditions that cannot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. (Credit: University of Colorado at Boulder).

Toward broadband mechanical spectroscopy.

PubMed

Hecksher, Tina; Torchinsky, Darius H; Klieber, Christoph; Johnson, Jeremy A; Dyre, Jeppe C; Nelson, Keith A

2017-08-15

Diverse material classes exhibit qualitatively similar behavior when made viscous upon cooling toward the glass transition, suggesting a common theoretical basis. We used seven different measurement methods to determine the mechanical relaxation kinetics of a prototype molecular glass former over a temporal range of 13 decades and over a temperature range spanning liquid to glassy states. The data conform to time-temperature superposition for the main (alpha) process and to a scaling relation of schematic mode-coupling theory. The broadband mechanical measurements demonstrated have fundamental and practical applications in polymer science, geophysics, multifunctional materials, and other areas.

Electrode characteristics of nanocrystalline AB{sub 5} compounds prepared by mechanical alloying

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

Chen, Z.; Chen, Z.; Zhou, D.

1998-10-01

Nanocrystalline LaNi{sub 5} and LaNi{sub 4.5}Si{sub 0.5} synthesized by mechanical alloying were used as negative materials for Ni-MH batteries. It was found that the electrodes prepared with the nanocrystalline powders had similar discharge capacities, better activation behaviors, and longer cycle lifetimes, compared with the negative electrode prepared with polycrystalline coarse-grained LaNi{sub 5} alloy. The properties of the electrodes prepared with these nanocrystalline materials were attributed to the structural characteristics of the compounds caused by mechanical alloying.

Parametric Study Of A Ceramic-Fiber/Metal-Matrix Composite

NASA Technical Reports Server (NTRS)

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

1992-01-01

Report describes computer-model parametric study of effects of degradation of constituent materials upon mechanical properties of ceramic-fiber/metal-matrix composite material. Contributes to understanding of weakening effects of large changes in temperature and mechanical stresses in fabrication and use. Concerned mainly with influences of in situ fiber and matrix properties upon behavior of composite. Particular attention given to influence of in situ matrix strength and influence of interphase degradation.

Time-dependent chemo-electro-mechanical behavior of hydrogel-based structures

NASA Astrophysics Data System (ADS)

Leichsenring, Peter; Wallmersperger, Thomas

2018-03-01

Charged hydrogels are ionic polymer gels and belong to the class of smart materials. These gels are multiphasic materials which consist of a solid phase, a fluid phase and an ionic phase. Due to the presence of bound charges these materials are stimuli-responsive to electrical or chemical loads. The application of electrical or chemical stimuli as well as mechanical loads lead to a viscoelastic response. On the macroscopic scale, the response is governed by a local reversible release or absorption of water which, in turn, leads to a local decrease or increase of mass and a respective volume change. Furthermore, the chemo-electro-mechanical equilibrium of a hydrogel depends on the chemical composition of the gel and the surrounding solution bath. Due to the presence of bound charges in the hydrogel, this system can be understood as an osmotic cell where differences in the concentration of mobile ions in the gel and solution domain lead to an osmotic pressure difference. In the present work, a continuum-based numerical model is presented in order to describe the time-dependent swelling behavior of hydrogels. The numerical model is based on the Theory of Porous Media and captures the fluid-solid, fluid-ion and ion-ion interactions. As a direct consequence of the chemo-electro-mechanical equilibrium, the corresponding boundary conditions are defined following the equilibrium conditions. For the interaction of the hydrogel with surrounding mechanical structures, also respective jump condtions are formulated. Finaly, numerical results of the time-dependent behavior of a hydrogel-based chemo-sensor will be presented.

Thermodynamics and mechanics of photochemcially reacting polymers

NASA Astrophysics Data System (ADS)

Long, Rong; Qi, H. Jerry; Dunn, Martin L.

2013-11-01

We develop a thermodynamics and mechanics theory for polymers that when irradiated with light, undergo photochemical reactions that alter their macromolecular structure, e.g., by bond breaking and/or reformation, and in turn affect their mechanical and physical behavior. This emerging class of highly-engineered active materials shows great promise for myriad applications and is a subset of a broader class of polymers with covalent bonds that can be dynamically tuned with various environmental stimuli. We formulate a general thermodynamic and kinetic framework to model the complex photochemical-thermal-mechanical coupling in these materials. Our theory considers the behavior of a polymer that is subjected to the combination of mechanical and thermal loading while simultaneously irradiated by light with multiple frequency components and directions. We introduce an approach to model the photochemical reactions that can change the network topology, resulting chemical species transport, heat conduction and finite deformation. We describe the interaction of the material with light via a radiometric description and show how it can be linked to a full electromagnetic treatment when appropriate and if desired. Our approach is sufficiently general to permit the modeling of various materials that operate via different photochemical reaction mechanisms. After formulating the general theory, we specialize it to a polymer that when irradiated with light undergoes a series of photochemical reactions that cause chain scission and reformation which continuously rearrange the polymer network into a stress-free configuration. Based on the operant physical mechanisms we develop a constitutive model using a polymer chain decomposition and evolution approach to track the molecular structure changes during simultaneous irradiation and mechanical loading. In the special case of isothermal conditions with monochromatic and unidirectional irradiation, we recover a previous model based on intuitive ad-hoc assumptions and thus put it on strong thermodynamic footing. Finally we use our model to simulate the behavior of a polymer that is biaxially stretched and then irradiated with light from one side. We simulate the process and emphasize the spontaneous bending that occurs due to inhomogeneous photoinduced stress relaxation. From our theory, we obtain an analytical expression of a characteristic time for photo-induced stress relaxation in terms of the dominating system parameters.

Multiscale mechanics of graphene oxide and graphene based composite films

NASA Astrophysics Data System (ADS)

Cao, Changhong

The mechanical behavior of graphene oxide is length scale dependent: orders of magnitude different between the bulk forms and monolayer counterparts. Understanding the underlying mechanisms plays a significant role in their versatile application. A systematic multiscale mechanical study from monolayer to multilayer, including the interactions between layers of GO, can provide fundamental support for material engineering. In this thesis, an experimental coupled with simulation approach was used to study the multiscale mechanics of graphene oxide (GO) and the methods developed for GO study are proved to be applicable also to mechanical study of graphene based composites. GO is a layered nanomaterial comprised of hierarchical units whose characteristic dimension lies between monolayer GO (0.7 nm - 1.2 nm) and bulk GO papers (≥ 1 mum). Mechanical behaviors of monolayer GO and GO nanosheets (10 nm- 100 nm) were comprehensively studied this work. Monolayer GO was measured to have an average strength of 24.7 GPa,, orders of magnitude higher than previously reported values for GO paper and approximately 50% of the 2D intrinsic strength of pristine graphene. The huge discrepancy between the strength of monolayer GO and that of bulk GO paper motivated the study of GO at the intermediate length scale (GO nanosheets). Experimental results showed that GO nanosheets possess high strength in the gigapascal range. Molecular Dynamic simulations showed that the transition in the failure behavior from interplanar fracture to intraplanar fracture was responsible for the huge strength discrepancy between nanometer scale GO and bulk GO papers. Additionally, the interfacial shear strength between GO layers was found to be a key contributing factor to the distinct mechanical behavior among hierarchical units of GO. The understanding of the multiscale mechanics of GO is transferrable in heterogeneous layered nanomaterials, such as graphene-metal oxide based anode materials in Li-ion batteries. The novel methods developed in this work to study GO multilayered structures were also applied to study the mechanics of graphene-TiO 2 composites. It was found that a critical thickness range of TiO2 deposition on graphene is required for the observed stiffness enhancement effect of graphene to influence the mechanical behavior of the composite.

A comprehensive Reputation mechanism for ubiquitous healthcare environment exploiting cloud model.

PubMed

Athanasiou, Georgia; Lymberopoulos, Dimitrios

2016-08-01

Absence of trust foundations may outweigh benefits of ubiquitous and personalized mental healthcare supervision provided within a Ubiquitous Healthcare environment (UH). Trust is composed by patient's Personal Interaction Experience (PIE) and social entourage accumulated PIE, i.e. Reputation (R). In this paper, a cloud-based Reputation mechanism is proposed. Since PIE is the elementary trust information source, also an Updating mechanism of PIE, is introduced, in this paper. Cloud materialization of combined mechanisms provides adaptability to UH Providers' dynamic behavior, facilitates detection of milking behaviors and complex malicious attacks while meets the challenge of limited accuracy in case of data sparseness. The effectiveness of the proposed mechanisms is verified via simulation in MATLAB.

Two phase modeling of the influence of plastic strain on the magnetic and magnetostrictive behaviors of ferromagnetic materials

NASA Astrophysics Data System (ADS)

Hubert, Olivier; Lazreg, Said

2017-02-01

A growing interest of automotive industry in the use of high performance steels is observed. These materials are obtained thanks to complex manufacturing processes whose parameters fluctuations lead to strong variations of microstructure and mechanical properties. The on-line magnetic non-destructive monitoring is a relevant response to this problem but it requires fast models sensitive to different parameters of the forming process. The plastic deformation is one of these important parameters. Indeed, ferromagnetic materials are known to be sensitive to stress application and especially to plastic strains. In this paper, a macroscopic approach using the kinematic hardening is proposed to model this behavior, considering a plastic strained material as a two phase system. Relationship between kinematic hardening and residual stress is defined in this framework. Since stress fields are multiaxial, an uniaxial equivalent stress is calculated and introduced inside the so-called magneto-mechanical multidomain modeling to represent the effect of plastic strain. The modeling approach is complemented by many experiments involving magnetic and magnetostrictive measurements. They are carried out with or without applied stress, using a dual-phase steel deformed at different levels. The main interest of this material is that the mechanically hard phase, soft phase and the kinematic hardening can be clearly identified thanks to simple experiments. It is shown how this model can be extended to single phase materials.

Animal Hairs as Water-stimulated Shape Memory Materials: Mechanism and Structural Networks in Molecular Assemblies

NASA Astrophysics Data System (ADS)

Xiao, Xueliang; Hu, Jinlian

2016-05-01

Animal hairs consisting of α-keratin biopolymers existing broadly in nature may be responsive to water for recovery to the innate shape from their fixed deformation, thus possess smart behavior, namely shape memory effect (SME). In this article, three typical animal hair fibers were first time investigated for their water-stimulated SME, and therefrom to identify the corresponding net-points and switches in their molecular and morphological structures. Experimentally, the SME manifested a good stability of high shape fixation ratio and reasonable recovery rate after many cycles of deformation programming under water stimulation. The effects of hydration on hair lateral size, recovery kinetics, dynamic mechanical behaviors and structural components (crystal, disulfide and hydrogen bonds) were then systematically studied. SME mechanisms were explored based on the variations of structural components in molecular assemblies of such smart fibers. A hybrid structural network model with single-switch and twin-net-points was thereafter proposed to interpret the water-stimulated shape memory mechanism of animal hairs. This original work is expected to provide inspiration for exploring other natural materials to reveal their smart functions and natural laws in animals including human as well as making more remarkable synthetic smart materials.

Wsbnd Cu functionally graded material: Low temperature fabrication and mechanical characterization

NASA Astrophysics Data System (ADS)

Yusefi, Ali; Parvin, Nader; Mohammadi, Hossein

2018-04-01

In this study, we fabricated and characterized a Wsbnd Cu functionally graded material (FGM) with 11 layers, including a pure copper layer. Samples were prepared by mixing a mechanically alloyed Nisbnd Mnsbnd Cu powder with W and Cu powders, stacking the powders, pressing the stacked layers, and finally sintering at 1000 °C. The utilization of a Nisbnd Mnsbnd Cu system may reduce the cost but without losing the good sintering behavior and physical and mechanical properties. The composition of the material was analyzed based on scanning electron microscopy images and by energy dispersive X-ray spectroscopy mapping, which indicated that in the presence of Ni and Mn, the Cu atoms could diffuse into the W particles. All of the layers had a very high relative density, thereby indicating their densification and excellent sintering behavior. We also found that the porosity values in the Cu phase remained unchanged at approximately 2.39% across the FGM. Mechanical measurements showed that the hardness (72%), modulus of elasticity (61%), and ultimate tensile strength (58%) increased with the W content across the Wsbnd Cu FGM, whereas the fracture toughness (KIC) varied in the opposite manner (minimum of 4.52 MPa/m0.5).

Animal Hairs as Water-stimulated Shape Memory Materials: Mechanism and Structural Networks in Molecular Assemblies

PubMed Central

Xiao, Xueliang; Hu, Jinlian

2016-01-01

Animal hairs consisting of α-keratin biopolymers existing broadly in nature may be responsive to water for recovery to the innate shape from their fixed deformation, thus possess smart behavior, namely shape memory effect (SME). In this article, three typical animal hair fibers were first time investigated for their water-stimulated SME, and therefrom to identify the corresponding net-points and switches in their molecular and morphological structures. Experimentally, the SME manifested a good stability of high shape fixation ratio and reasonable recovery rate after many cycles of deformation programming under water stimulation. The effects of hydration on hair lateral size, recovery kinetics, dynamic mechanical behaviors and structural components (crystal, disulfide and hydrogen bonds) were then systematically studied. SME mechanisms were explored based on the variations of structural components in molecular assemblies of such smart fibers. A hybrid structural network model with single-switch and twin-net-points was thereafter proposed to interpret the water-stimulated shape memory mechanism of animal hairs. This original work is expected to provide inspiration for exploring other natural materials to reveal their smart functions and natural laws in animals including human as well as making more remarkable synthetic smart materials. PMID:27230823

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nutt, S. R.; Widener, C. A.; Champagne, V. K.; Hrabe, R. H.

2017-08-01

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

A finite element framework for multiscale/multiphysics analysis of structures with complex microstructures

NASA Astrophysics Data System (ADS)

Varghese, Julian

This research work has contributed in various ways to help develop a better understanding of textile composites and materials with complex microstructures in general. An instrumental part of this work was the development of an object-oriented framework that made it convenient to perform multiscale/multiphysics analyses of advanced materials with complex microstructures such as textile composites. In addition to the studies conducted in this work, this framework lays the groundwork for continued research of these materials. This framework enabled a detailed multiscale stress analysis of a woven DCB specimen that revealed the effect of the complex microstructure on the stress and strain energy release rate distribution along the crack front. In addition to implementing an oxidation model, the framework was also used to implement strategies that expedited the simulation of oxidation in textile composites so that it would take only a few hours. The simulation showed that the tow architecture played a significant role in the oxidation behavior in textile composites. Finally, a coupled diffusion/oxidation and damage progression analysis was implemented that was used to study the mechanical behavior of textile composites under mechanical loading as well as oxidation. A parametric study was performed to determine the effect of material properties and the number of plies in the laminate on its mechanical behavior. The analyses indicated a significant effect of the tow architecture and other parameters on the damage progression in the laminates.

On the Mechanical Behavior of Advanced Composite Material Structures

NASA Astrophysics Data System (ADS)

Vinson, Jack

During the period between 1993 and 2004, the author, as well as some colleagues and graduate students, had the honor to be supported by the Office of Naval Research to conduct research in several aspects of the behavior of structures composed of composite materials. The topics involved in this research program were numerous, but all contributed to increasing the understanding of how various structures that are useful for marine applications behaved. More specifically, the research topics focused on the reaction of structures that were made of fiber reinforced polymer matrix composites when subjected to various loads and environmental conditions. This included the behavior of beam, plate/panel and shell structures. It involved studies that are applicable to fiberglass, graphite/carbon and Kevlar fibers imbedded in epoxy, polyester and other polymeric matrices. Unidirectional, cross-ply, angle ply, and woven composites were involved, both in laminated, monocoque as well as in sandwich constructions. Mid-plane symmetric as well as asymmetric laminates were studied, the latter involving bending-stretching coupling and other couplings that only can be achieved with advanced composite materials. The composite structures studied involved static loads, dynamic loading, shock loading as well as thermal and hygrothermal environments. One major consideration was determining the mechanical properties of composite materials subjected to high strain rates because the mechanical properties vary so significantly as the strain rate increases. A considerable number of references are cited for further reading and study for those interested.

Mechanical Behavior of Fabric-Film Laminates

NASA Technical Reports Server (NTRS)

Said, Magdi S.

1999-01-01

Inflatable structures are gaining wide support in planetary scientific missions as well as commercial applications. For such applications a new class of materials made of laminating thin homogenous films to lightweight fabrics are being considered us structura1 gas envelops. The emerging composite materials are a result of recent advances in the manufacturing cf 1ightweight, high strength fibers, fabrics and scrims. The lamination of these load-carrying members with the proper gas barrier film results in wide range of materials suitable for various loading and environmental conditions. Polyester - based woven fabrics laminated to thin homogeneus film of polyester (Maylar) is an example of this class. This fabric/ film laminate is being considered for the development a material suitable for building large gas envelopes for use in the NASA Ultra Long Duration Balloon Program (ULDB). Compared to commercial homogeneus films, the material provides relatively high strength to weight ratio as well as better resistance to crack and tear propagation. The purpose of this papers is to introduce the mechanical behavior of this class of multi-layers composite and to highlight some of the concerns observed during the characterization of these laminate composites.

Mechanical properties of heat-treated organic foams

NASA Astrophysics Data System (ADS)

Amaral-Labat, G.; Sahimi, Muhammad; Pizzi, A.; Fierro, V.; Celzard, Alain

2013-03-01

The mechanical properties of a class of cellular material were measured. The composition of the material was progressively modified, while its pore structure was kept unchanged. Rigid foam, prepared from a thermoset resin, was gradually converted into reticulated vitreous carbon foam by pyrolysis at increasingly higher heat-treatment temperatures (HHT). The corresponding changes in the Young's modulus Y and the compressive strength σ of the materials were measured over a wide range of porosities. The materials exhibit a percolation behavior with a zero percolation threshold. At very low densities the Young's modulus and the compressive strength appear to follow the power laws predicted by percolation theory near the percolation threshold. But, whereas the exponent τ associated with the power-law behavior of Y appears to vary significantly with the material's density and the HHT, the exponent associated with σ does not change much. The possible cause of the apparent and surprising nonuniversality of τ is discussed in detail, in the light of the fact that only the materials’ composition varies, not the structure of their pore space that could have caused the nonuniversality.

Experimental Study on the Anisotropic Stress-Strain Behavior of Polycrystalline Ni-Mn-Ga in Directional Solidification

NASA Astrophysics Data System (ADS)

Teng, Yao; Shi, Tao; Zhu, Yuping; Li, Zongbin; Deng, Tao; Bai, Guonan

2016-03-01

A polycrystalline Ni-Mn-Ga ferromagnetic shape memory alloy produced by directional solidification is the subject of this research paper. The compressive stress-strain curves of the material for different cutting angles to the solidification direction are tested. The martensite Young's modulus, macroscopic reorientation strain, and phase transition critical stress are analyzed experimentally. The results show that mechanical behaviors in the loading-unloading cycle of the material present nonlinear and anisotropic characteristics, which are all closely related to the material's orientation to the solidification direction. The martensite Young's modulus, macroscopic reorientation strain, and phase transition critical stress achieve maximum values in the solidification direction. A 50° orientation to the solidification direction is the cut-off direction of the mechanical properties, where the martensite Young's modulus and reorientation start critical stress reach minimum values. The present study is expected to provide sound guidance for practical applications.

Encoding Hydrogel Mechanics via Network Cross-Linking Structure.

PubMed

Schweller, Ryan M; West, Jennifer L

2015-05-11

The effects of mechanical cues on cell behaviors in 3D remain difficult to characterize as the ability to tune hydrogel mechanics often requires changes in the polymer density, potentially altering the material's biochemical and physical characteristics. Additionally, with most PEG diacrylate (PEGDA) hydrogels, forming materials with compressive moduli less than ∼10 kPa has been virtually impossible. Here, we present a new method of controlling the mechanical properties of PEGDA hydrogels independent of polymer chain density through the incorporation of additional vinyl group moieties that interfere with the cross-linking of the network. This modification can tune hydrogel mechanics in a concentration dependent manner from <1 to 17 kPa, a more physiologically relevant range than previously possible with PEG-based hydrogels, without altering the hydrogel's degradation and permeability. Across this range of mechanical properties, endothelial cells (ECs) encapsulated within MMP-2/MMP-9 degradable hydrogels with RGDS adhesive peptides revealed increased cell spreading as hydrogel stiffness decreased in contrast to behavior typically observed for cells on 2D surfaces. EC-pericyte cocultures exhibited vessel-like networks within 3 days in highly compliant hydrogels as compared to a week in stiffer hydrogels. These vessel networks persisted for at least 4 weeks and deposited laminin and collagen IV perivascularly. These results indicate that EC morphogenesis can be regulated using mechanical cues in 3D. Furthermore, controlling hydrogel compliance independent of density allows for the attainment of highly compliant mechanical regimes in materials that can act as customizable cell microenvironments.

Dynamic Deformation Behavior of Soft Material Using Shpb Technique and Pulse Shaper

NASA Astrophysics Data System (ADS)

Lee, Ouk Sub; Cho, Kyu Sang; Kim, Sung Hyun; Han, Yong Hwan

This paper presents a modified Split Hopkinson Pressure Bar (SHPB) technique to obtain compressive stress strain data for NBR rubber materials. An experimental technique with a modified the conventional SHPB has been developed for measuring the compressive stress strain responses of materials with low mechanical impedance and low compressive strengths, such as the rubber and the polymeric material. This paper uses an aluminum pressure bar to achieve a closer impedance match between the pressure bar and the specimen materials. In addition, a pulse shaper is utilized to lengthen the rising time of the incident pulse to ensure dynamic stress equilibrium and homogeneous deformation of NBR rubber materials. It is found that the modified technique can determine the dynamic deformation behavior of rubbers more accurately.

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

Modeling the Coupled Chemo-Thermo-Mechanical Behavior of Amorphous Polymer Networks.

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

Zimmerman, Jonathan A.; Nguyen, Thao D.; Xiao, Rui

2015-02-01

Amorphous polymers exhibit a rich landscape of time-dependent behavior including viscoelasticity, structural relaxation, and viscoplasticity. These time-dependent mechanisms can be exploited to achieve shape-memory behavior, which allows the material to store a programmed deformed shape indefinitely and to recover entirely the undeformed shape in response to specific environmental stimulus. The shape-memory performance of amorphous polymers depends on the coordination of multiple physical mechanisms, and considerable opportunities exist to tailor the polymer structure and shape-memory programming procedure to achieve the desired performance. The goal of this project was to use a combination of theoretical, numerical and experimental methods to investigate themore » effect of shape memory programming, thermo-mechanical properties, and physical and environmental aging on the shape memory performance. Physical and environmental aging occurs during storage and through exposure to solvents, such as water, and can significantly alter the viscoelastic behavior and shape memory behavior of amorphous polymers. This project – executed primarily by Professor Thao Nguyen and Graduate Student Rui Xiao at Johns Hopkins University in support of a DOE/NNSA Presidential Early Career Award in Science and Engineering (PECASE) – developed a theoretical framework for chemothermo- mechanical behavior of amorphous polymers to model the effects of physical aging and solvent-induced environmental factors on their thermoviscoelastic behavior.« less

High-Temperature Deformation Behavior of HCP Alloys -- An Internal Variable Approach

DTIC Science & Technology

2006-05-31

successfully to characterize the high temperature deformation behavior of various metallic materials such as Al alloys, Pb-Sn hyper- eutectic alloy, and...implying dynamic recrystallization (DRX) and GBS as the major deformation mechanisms at 523 K and 10-4 /s. Large cavities are observed at the

Capturing the Complexity of Additively Manufactured Microstructures

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

Livescu, Veronica; Bronkhorst, Curt Allan; Vander Wiel, Scott Alan

2016-05-12

The underlying mechanisms and kinetics controlling damage nucleation and growth as a function of material microstructure and loading paths are discussed. These experiments indicate that structural features such as grain boundaries, grain size distribution, grain morphology crystallographic texture are all factors that influence mechanical behavior.

Effect of microstructure on the coupled electromagnetic-thermo-mechanical response of cyclotrimethylenetrinitramine-estane energetic aggregates to infrared laser radiation

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

Brown, Judith A.; Zikry, M. A., E-mail: zikry@ncsu.edu

2015-09-28

The coupled electromagnetic (EM)-thermo-mechanical response of cyclotrimethylenetrinitramine-estane energetic aggregates under laser irradiation and high strain rate loads has been investigated for various aggregate sizes and binder volume fractions. The cyclotrimethylenetrinitramine (RDX) crystals are modeled with a dislocation density-based crystalline plasticity formulation and the estane binder is modeled with finite viscoelasticity through a nonlinear finite element approach that couples EM wave propagation with laser heat absorption, thermal conduction, and inelastic deformation. Material property and local behavior mismatch at the crystal-binder interfaces resulted in geometric scattering of the EM wave, electric field and laser heating localization, high stress gradients, dislocation density, andmore » crystalline shear slip accumulation. Viscous sliding in the binder was another energy dissipation mechanism that reduced stresses in aggregates with thicker binder ligaments and larger binder volume fractions. This investigation indicates the complex interactions between EM waves and mechanical behavior, for accurate predictions of laser irradiation of heterogeneous materials.« less

Micro- and nano-mechanics in China: A brief review of recent progress and perspectives

NASA Astrophysics Data System (ADS)

Xu, ZhiPing; Zheng, QuanShui

2018-07-01

The past three decades have witnessed the explosion of nanoscience and technology, where notable research efforts have been made in synthesizing nanomaterials and controlling nanostructures of bulk materials. The uncovered mechanical behaviors of structures and materials with reduced sizes and dimensions pose open questions to the community of mechanicians, which expand the framework of continuum mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in China have been actively involved into this exciting area, making remarkable contributions to the understanding of nanoscale mechanical processes, the development of multi-scale, multi-field modeling and experimental techniques to resolve the processing-microstructures-properties relationship of materials, and the interdisciplinary studies that broaden the subjects of mechanics. This article reviews selected progress made by this community, with the aim to clarify the key concepts, methods and applications of micro- and nano-mechanics, and to outline the perspectives in this fast-evolving field.

Direct comparison of nanoindentation and tensile test results on reactor-irradiated materials

NASA Astrophysics Data System (ADS)

Krumwiede, D. L.; Yamamoto, T.; Saleh, T. A.; Maloy, S. A.; Odette, G. R.; Hosemann, P.

2018-06-01

Nanoindentation testing has been used for decades to assess materials on a local scale and to obtain fundamental mechanical property parameters. Nuclear materials research often faces the challenge of testing rather small samples due to the hazardous nature, limited space in reactors, and shallow ion-irradiated zones, fostering the need for small-scale mechanical testing (SSMT). As such, correlating the results from SSMT to bulk properties is particularly of interest. This study compares macroscopic tensile test data (yield and flow stresses) to nanoindentation data (hardness) obtained on a number of different neutron-irradiated materials in order to understand the scaling behavior on radiation-damaged samples.

Observation of creep behavior of cellulose electro-active paper (EAPap) actuator

NASA Astrophysics Data System (ADS)

Kim, Joo-Hyung; Lee, Sang-Woo; Yun, Gyu-Young; Yang, Chulho; Kim, Heung Soo; Kim, Jaehwan

2009-03-01

Understanding of creep effects on actuating mechanisms is important to precisely figure out the behavior of material. Creep behaviors of cellulose based Electro-Active Paper (EAPap) were studied under different constant loading conditions. We found the structural modification of microfibrils in EAPap after creep test. Structural differences of as-prepared and after creep tested samples were compared by SEM measurements. From the measured creep behaviors by different loading conditions, two different regions of induced strain and current were clearly observed as the measurement time increased. It is consider that local defects may occur and becomes micro-dimple or micro-crack formations in lower load cases as localized deformation proceeds, while the shrinkage of diameter of elongated fibers was observed only at the high level of loading. Therefore, cellulose nanofibers may play a role to be against the creep load and prevent the localized structural deformations. The results provide useful creep behavior and mechanism to understand the mechanical behavior of thin visco-elastic EAPap actuator.

Multilevel model of polycrystalline materials: grain boundary sliding description

NASA Astrophysics Data System (ADS)

Sharifullina, E.; Shveykin, A.; Trusov, P.

2017-12-01

Material behavior description in a wide range of thermomechanical effects is one of the topical areas in mathematical modeling. Inclusion of grain boundary sliding as an important mechanism of polycrystalline material deformation at elevated temperatures and predominant deformation mechanism of metals and alloys in structural superplasticity allows to simulate various deformation regimes and their transitions (including superplasticity regime with switch-on and switch-off regimes). The paper is devoted to description of grain boundary sliding in structure of two-level model, based on crystal plasticity, and relations for determination the contribution of this mechanism to inelastic deformation. Some results are presented concerning computational experiments of polycrystalline representative volume deformation using developed model.

The effects of Nitinol phases on corrosion and fatigue behavior

NASA Astrophysics Data System (ADS)

Denton, Melissa

The purpose of these studies was to provide a detailed understanding of Nitinol phases and their effects on corrosion and fatigue life. The two primary phases, austenite and martensite, were carefully evaluated with respect to material geometry, corrosion behavior, wear, and fatigue life. Material characterization was performed using several techniques that include metallography, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray photoelectron spectrum (XPS), and Auger electron spectroscopy (AES). Uniaxial tensile tests were conducted to determine the mechanical properties such as elongation, ultimate tensile strength, modulus, transformation strain, and plateau stress. In addition, accelerated wear testing and four point bend fatigue testing were completed to study the fatigue life and durability of the material. The corrosion of Nitinol was found to be dependent on various surface conditions. Electrochemical corrosion behavior of each phase was investigated using cyclic potentiodyamic polarization testing. The corrosion response of electropolished Nitinol was found to be acceptable, even after durability testing. Stress-induced martensite had a lower breakdown potential due to a rougher surface morphology, while thermally induced martensite and austenite performed similarly well. The surface conditioning also had a significant effect on Nitinol mechanical properties. Electropolishing provided a smooth mirror finish that reduced localized texture and enhanced the ductility of the material. Quasi-static mechanical properties can be good indicators of fatigue life, but further fatigue testing revealed that phase transformations had an important role as well. The governing mechanisms for the fatigue life of Nitinol were determined to be both martesitic phase transformations and surface defects. A new ultimate dislocation strain model was proposed based on specific accelerated step-strain testing.

Softening due to Grain Boundary Cavity Formation and its Competition with Hardening in Helium Implanted Nanocrystalline Tungsten

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

Cunningham, W. Streit; Gentile, Jonathan M.; El-Atwani, Osman

The unique ability of grain boundaries to act as effective sinks for radiation damage plays a significant role in nanocrystalline materials due to their large interfacial area per unit volume. Leveraging this mechanism in the design of tungsten as a plasma-facing material provides a potential pathway for enhancing its radiation tolerance under fusion-relevant conditions. In this study, we explore the impact of defect microstructures on the mechanical behavior of helium ion implanted nanocrystalline tungsten through nanoindentation. Softening was apparent across all implantation temperatures and attributed to bubble/cavity loaded grain boundaries suppressing the activation barrier for the onset of plasticity viamore » grain boundary mediated dislocation nucleation. An increase in fluence placed cavity induced grain boundary softening in competition with hardening from intragranular defect loop damage, thus signaling a new transition in the mechanical behavior of helium implanted nanocrystalline tungsten.« less

Softening due to Grain Boundary Cavity Formation and its Competition with Hardening in Helium Implanted Nanocrystalline Tungsten

DOE PAGES

Cunningham, W. Streit; Gentile, Jonathan M.; El-Atwani, Osman; ...

2018-02-13

The unique ability of grain boundaries to act as effective sinks for radiation damage plays a significant role in nanocrystalline materials due to their large interfacial area per unit volume. Leveraging this mechanism in the design of tungsten as a plasma-facing material provides a potential pathway for enhancing its radiation tolerance under fusion-relevant conditions. In this study, we explore the impact of defect microstructures on the mechanical behavior of helium ion implanted nanocrystalline tungsten through nanoindentation. Softening was apparent across all implantation temperatures and attributed to bubble/cavity loaded grain boundaries suppressing the activation barrier for the onset of plasticity viamore » grain boundary mediated dislocation nucleation. An increase in fluence placed cavity induced grain boundary softening in competition with hardening from intragranular defect loop damage, thus signaling a new transition in the mechanical behavior of helium implanted nanocrystalline tungsten.« less

Mechanical analysis of non-uniform bi-directional functionally graded intelligent micro-beams using modified couple stress theory

NASA Astrophysics Data System (ADS)

Bakhshi Khaniki, Hossein; Rajasekaran, Sundaramoorthy

2018-05-01

This study develops a comprehensive investigation on mechanical behavior of non-uniform bi-directional functionally graded beam sensors in the framework of modified couple stress theory. Material variation is modelled through both length and thickness directions using power-law, sigmoid and exponential functions. Moreover, beam is assumed with linear, exponential and parabolic cross-section variation through the length using power-law and sigmoid varying functions. Using these assumptions, a general model for microbeams is presented and formulated by employing Hamilton’s principle. Governing equations are solved using a mixed finite element method with Lagrangian interpolation technique, Gaussian quadrature method and Wilson’s Lagrangian multiplier method. It is shown that by using bi-directional functionally graded materials in nonuniform microbeams, mechanical behavior of such structures could be affected noticeably and scale parameter has a significant effect in changing the rigidity of nonuniform bi-directional functionally graded beams.

Thermo-mechanically coupled fracture analysis of shape memory alloys using the extended finite element method

NASA Astrophysics Data System (ADS)

Hatefi Ardakani, S.; Ahmadian, H.; Mohammadi, S.

2015-04-01

In this paper, the extended finite element method is used for fracture analysis of shape memory alloys for both cases of super elastic and shape memory effects. Heat generation during the forward and reverse phase transformations can lead to temperature variation in the material because of strong thermo-mechanical coupling, which significantly influences the SMA mechanical behavior. First, the stationary crack mode is studied and the effects of loading rate on material behavior in the crack tip are examined. Then, the crack propagation analysis is performed in the presence of an initial crack by adopting a weighted averaging criterion, where the direction of crack propagation is determined by weighted averaging of effective stresses at all the integration points in the vicinity of the crack tip. Finally, several numerical examples are analyzed and the obtained results are compared with the available reference results.

Effect of Heat Index on Microstructure and Mechanical Behavior of Friction Stir Processed AZ31

NASA Astrophysics Data System (ADS)

Yuan, Wei; Mishra, Rajiv S.

Friction stir processing modifies the micro structure and properties of metals through intense plastic deformation. The frictional heat input affects the microstructure evolution and resulting mechanical properties. 2 mm thick commercial AZ31B-H24 Mg alloy was friction stir processed under various process parameter combinations to investigate the effect of heat index on micro structure and properties. Recrystallized grain structure in the nugget region was observed for all processing conditions with decrease in hardness. Results indicate a reduced tensile yield strength and ultimate tensile strength compared to the as-received material in H-temper, but with an improved hardening capacity. The strain hardening behavior of friction stir processed material is discussed.

Micromechanics of Amorphous Metal/Polymer Hybrid Structures with 3D Cellular Architectures: Size Effects, Buckling Behavior, and Energy Absorption Capability.

PubMed

Mieszala, Maxime; Hasegawa, Madoka; Guillonneau, Gaylord; Bauer, Jens; Raghavan, Rejin; Frantz, Cédric; Kraft, Oliver; Mischler, Stefano; Michler, Johann; Philippe, Laetitia

2017-02-01

By designing advantageous cellular geometries and combining the material size effects at the nanometer scale, lightweight hybrid microarchitectured materials with tailored structural properties are achieved. Prior studies reported the mechanical properties of high strength cellular ceramic composites, obtained by atomic layer deposition. However, few studies have examined the properties of similar structures with metal coatings. To determine the mechanical performance of polymer cellular structures reinforced with a metal coating, 3D laser lithography and electroless deposition of an amorphous layer of nickel-boron (NiB) is used for the first time to produce metal/polymer hybrid structures. In this work, the mechanical response of microarchitectured structures is investigated with an emphasis on the effects of the architecture and the amorphous NiB thickness on their deformation mechanisms and energy absorption capability. Microcompression experiments show an enhancement of the mechanical properties with the NiB thickness, suggesting that the deformation mechanism and the buckling behavior are controlled by the brittle-to-ductile transition in the NiB layer. In addition, the energy absorption properties demonstrate the possibility of tuning the energy absorption efficiency with adequate designs. These findings suggest that microarchitectured metal/polymer hybrid structures are effective in producing materials with unique property combinations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microfabrication of hierarchical structures for engineered mechanical materials

NASA Astrophysics Data System (ADS)

Vera Canudas, Marc

Materials found in nature present, in some cases, unique properties from their constituents that are of great interest in engineered materials for applications ranging from structural materials for the construction of bridges, canals and buildings to the fabrication of new lightweight composites for airplane and automotive bodies, to protective thin film coatings, amongst other fields. Research in the growing field of biomimetic materials indicates that the micro-architectures present in natural materials are critical to their macroscopic mechanical properties. A better understanding of the effect that structure and hierarchy across scales have on the material properties will enable engineered materials with enhanced properties. At the moment, very few theoretical models predict mechanical properties of simple materials based on their microstructures. Moreover these models are based on observations from complex biological systems. One way to overcome this challenge is through the use of microfabrication techniques to design and fabricate simple materials, more appropriate for the study of hierarchical organizations and microstructured materials. Arrays of structures with controlled geometry and dimension can be designed and fabricated at different length scales, ranging from a few hundred nanometers to centimeters, in order to mimic similar systems found in nature. In this thesis, materials have been fabricated in order to gain fundamental insight into the complex hierarchical materials found in nature and to engineer novel materials with enhanced mechanical properties. The materials fabricated here were mechanically characterized and compared to simple mechanics models to describe their behavior with the goal of applying the knowledge acquired to the design and synthesis of future engineered materials with novel properties.

How Deformation Behavior Controls Product Performance After Twin Screw Granulation With High Drug Loads and Crospovidone as Disintegrant.

PubMed

Meier, Robin; Moll, Klaus-Peter; Krumme, Markus; Kleinebudde, Peter

2017-01-01

This study addresses the quantitative influence of 12 different materials (active pharmaceutical ingredients and excipients as surrogate active pharmaceutical ingredients) on the critical quality attributes of twin screw granulated products and subsequently produced tablets. Prestudies demonstrated the significant influence of the chosen model materials (in combination with crospovidone) on the disintegration behavior of the resulting tablets, despite comparable tablet porosities. This study elucidates possible reasons for the varying disintegration behavior by investigating raw material, granule, and tablet properties. An answer could be found in the mechanical properties of the raw materials and the produced granules. Through compressibility studies, the materials could be classified into materials with high compressibility, which deform rather plastically under compression stress, and low compressibility, which display breakages under compression stress. In general, and apart from (pseudo)-polymorphic transformations, brittle materials featured excellent disintegration performance, even at low resulting tablet porosities <8%, whereas plastically deformable materials mostly did not reveal any disintegration. These findings must be considered in the development of simplified formulations with high drug loads, in which the active pharmaceutical ingredient predominantly defines the deformation behavior of the granule. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

FY17 Status Report on the Micromechanical Finite Element Modeling of Creep Fracture of Grade 91 Steel

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

Messner, M. C.; Truster, T. J.; Cochran, K. B.

Advanced reactors designed to operate at higher temperatures than current light water reactors require structural materials with high creep strength and creep-fatigue resistance to achieve long design lives. Grade 91 is a ferritic/martensitic steel designed for long creep life at elevated temperatures. It has been selected as a candidate material for sodium fast reactor intermediate heat exchangers and other advanced reactor structural components. This report focuses on the creep deformation and rupture life of Grade 91 steel. The time required to complete an experiment limits the availability of long-life creep data for Grade 91 and other structural materials. Design methodsmore » often extrapolate the available shorter-term experimental data to longer design lives. However, extrapolation methods tacitly assume the underlying material mechanisms causing creep for long-life/low-stress conditions are the same as the mechanisms controlling creep in the short-life/high-stress experiments. A change in mechanism for long-term creep could cause design methods based on extrapolation to be non-conservative. The goal for physically-based microstructural models is to accurately predict material response in experimentally-inaccessible regions of design space. An accurate physically-based model for creep represents all the material mechanisms that contribute to creep deformation and damage and predicts the relative influence of each mechanism, which changes with loading conditions. Ideally, the individual mechanism models adhere to the material physics and not an empirical calibration to experimental data and so the model remains predictive for a wider range of loading conditions. This report describes such a physically-based microstructural model for Grade 91 at 600° C. The model explicitly represents competing dislocation and diffusional mechanisms in both the grain bulk and grain boundaries. The model accurately recovers the available experimental creep curves at higher stresses and the limited experimental data at lower stresses, predominately primary creep rates. The current model considers only one temperature. However, because the model parameters are, for the most part, directly related to the physics of fundamental material processes, the temperature dependence of the properties are known. Therefore, temperature dependence can be included in the model with limited additional effort. The model predicts a mechanism shift for 600° C at approximately 100 MPa from a dislocation- dominated regime at higher stress to a diffusion-dominated regime at lower stress. This mechanism shift impacts the creep life, notch-sensitivity, and, likely, creep ductility of Grade 91. In particular, the model predicts existing extrapolation methods for creep life may be non-conservative when attempting to extrapolate data for higher stress creep tests to low stress, long-life conditions. Furthermore, the model predicts a transition from notchstrengthening behavior at high stress to notch-weakening behavior at lower stresses. Both behaviors may affect the conservatism of existing design methods.« less

The application of continuum damage mechanics to solve problems in geodynamics

NASA Astrophysics Data System (ADS)

Manaker, David Martin

Deformation within the Earth's lithosphere is largely controlled by the rheology of the rock. Ductile behavior in rocks is often associated with plasticity due to dislocation motion or diffusion under high pressures and temperatures. However, ductile behavior can also occur in brittle materials. An example would be cataclastic flow associated with folding at shallow crustal levels, steep subduction zones, and large-scale deformation at plate boundaries. Engineers utilize damage mechanics to model the continuum deformation of brittle materials. We utilize a modified form of damage mechanics where damage represents a reduction in frictional strength and includes a yield stress. We use this empirical approach to simulate the bending of the lithosphere. We use numerical simulations to obtain elastostatic solutions for plate bending and where the stress exceeds a yield stress, we apply damage to reduce the elastic moduli. Damage is calculated at each time step by a power-law relationship of the ratio of the yield stress to stress and the yield strain to the strain. To test our method, we apply our damage rheology to a plate deforming under applied shear, a constant bending moment, and a constant load. We simulate a wide range of behaviors from slow relaxation to instantaneous failure, over timescales that span six orders of magnitude. Stress relaxation produces elastic-perfectly plastic behavior in cases where failure does not occur. For cases of failure, we observe a rapid increase in damage leading to failure. The changes in the rate of damage accumulation in failure cases are similar to the changes in b-values of acoustic emissions observed in triaxial compression tests of fractured rock and b-value changes prior to some large earthquakes. Thus continuum damage mechanics can simulate ductile behavior due to brittle mechanisms as well as observations of laboratory experiments and seismicity.

Mechanical properties, morphology, and hydrolytic degradation behavior of polylactic acid / natural rubber blends

NASA Astrophysics Data System (ADS)

Buys, Y. F.; Aznan, A. N. A.; Anuar, H.

2018-01-01

Due to its biodegradability and renewability, polylactic acid (PLA) has been receiving enormous attention as a potential candidate to replace petroleum based polymers. However, PLA has limitation due to its inherent brittleness. In order to overcome this limitation, blending PLA with elastomeric materials such as natural rubber (NR) are commonly reported. In previous, several researches on PLA/NR blend had been reported, with most of them evaluated the mechanical properties. On the other hand, study of degradation behavior is significance of importance, as controlling materials degradation is required in some applications. This research studied the effect of blend composition on mechanical properties, morphology development, and hydrolytic degradation behavior of PLA/NR blends. Various compositions of PLA/NR blends were prepared by melt blending technique. Tensile test and impact test of the blends were performed to evaluate the mechanical properties. Addition of NR improved the elongation at break and impact strength of the blends, but reduced the tensile strength and stiffness of the specimens. Dynamic Mechanical Analysis (DMA) measurements of the blends displayed two peaks at temperature -70˚C which corresponded to T g of NR and 65˚C which corresponded to T g of PLA. Field Emission Scanning Electron Microscopy (FE-SEM) micrograph of 70/30 PLA/NR specimen also showed two distinct phases, which lead to indication that PLA/NR blends are immiscible. Hydrolytic degradation behavior was evaluated by measuring the remaining weight of the samples immersed in sodium hydroxide solution for a predetermined times. It was shown that the degradation behavior of PLA/NR blends is affected by composition of the blends, with 100 PLA and 70/30 PLA/NR blend showed the fastest degradation rate and 100 NR displayed the slowest one.

Fracture mechanics of cellular glass

NASA Technical Reports Server (NTRS)

Zwissler, J. G.; Adams, M. A.

1981-01-01

The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses.

Analysis of the mechanical behavior of single wall carbon nanotubes by a modified molecular structural mechanics model incorporating an advanced chemical force field

NASA Astrophysics Data System (ADS)

Eberhardt, Oliver; Wallmersperger, Thomas

2018-03-01

The outstanding properties of carbon nanotubes (CNTs) keep attracting the attention of researchers from different fields. CNTs are promising candidates for applications e.g. in lightweight construction but also in electronics, medicine and many more. The basis for the realization of the manifold applications is a detailed knowledge of the material properties of the carbon nanotubes. In particular for applications in lightweight constructions or in composites, the knowledge of the mechanical behavior of the CNTs is of vital interest. Hence, a lot of effort is put into the experimental and theoretical determination of the mechanical material properties of CNTs. Due to their small size, special techniques have to be applied. In this research, a modified molecular structural mechanics model for the numerical determination of the mechanical behavior of carbon nanotubes is presented. It uses an advanced approach for the geometrical representation of the CNT structure while the covalent bonds in the CNTs are represented by beam elements. Furthermore, the model is specifically designed to overcome major drawbacks in existing molecular structural mechanics models. This includes energetic consistency with the underlying chemical force field. The model is developed further to enable the application of a more advanced chemical force field representation. The developed model is able to predict, inter alia, the lateral and radial stiffness properties of the CNTs. The results for the lateral stiffness are given and discussed in order to emphasize the progress made with the presented approach.

The effect of various deformation processes on the corrosion behavior of casing and tubing carbon steels in sweet environment

NASA Astrophysics Data System (ADS)

Elramady, Alyaa Gamal

The aim of this research project is to correlate the plastic deformation and mechanical instability of casing steel materials with corrosion behavior and surface change, in order to identify a tolerable degree of deformation for casing steel materials. While the corrosion of pipeline and casing steels has been investigated extensively, corrosion of these steels in sweet environments with respect to plastic deformation due to bending, rolling, autofrettage, or handling needs more investigation. Downhole tubular expansion of pipes (casings) is becoming standard practice in the petroleum industry to repair damaged casings, shutdown perforations, and ultimately achieve mono-diameter wells. Tubular expansion is a cold-drawing metal forming process, which consists of running conical mandrels through casings either mechanically using a piston or hydraulically by applying a back pressure. This mechanism subjects the pipes to large radial plastic deformations of up to 30 pct. of the inner diameter. It is known that cold-working is a way of strengthening materials such as low carbon steel, but given that this material will be subjected to corrosive environments, susceptibility to stress corrosion cracking (SCC) should be investigated. This research studies the effect of cold-work, in the form of cold-rolling and cold-expansion, on the surface behavior of API 5CT steels when it is exposed to a CO2-containing environment. Cold-work has a pronounced influence on the corrosion behavior of both API 5CT K55 and P110 grade steels. The lowest strength grade steel, API 5CT K55, performed poorly in a corrosive environment in the slow strain rate test. The ductile material exhibited the highest loss in strength and highest susceptibility to stress corrosion cracking in a CO 2-containing environment. The loss in strength declined with cold-rolling, which can be ascribed to the surface compressive stresses induced by cold-work. On the other hand, API 5CT P110 grade steels showed higher susceptibility to SCC when they were cold-rolled and cold-expanded. The research found that surface compressive stresses have an effect on the SCC behavior of casing and tubing steels. The CO2 corrosion behavior and atomic processes at the corroding interface were investigated at laboratory temperature using electrochemical techniques. Cold-work was found to have an influence on the corrosion behavior of both API 5CT K55 and P110 grade steels. These behaviors were found to be material and process dependent. Surface evaluation techniques such as field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) analysis did not detect formation of a protective scale. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) analysis both detected the appearance of a scale that was traced back to magnetite.

Fatigue characteristics of carbon nanotube blocks under compression

NASA Astrophysics Data System (ADS)

Suhr, J.; Ci, L.; Victor, P.; Ajayan, P. M.

2008-03-01

In this paper we investigate the mechanical response from repeated high compressive strains on freestanding, long, vertically aligned multiwalled carbon nanotube membranes and show that the arrays of nanotubes under compression behave very similar to soft tissue and exhibit viscoelastic behavior. Under compressive cyclic loading, the mechanical response of nanotube blocks shows initial preconditioning and hysteresis characteristic of viscoeleastic materials. Furthermore, no fatigue failure is observed even at high strain amplitudes up to half million cycles. The outstanding fatigue life and extraordinary soft tissue-like mechanical behavior suggest that properly engineered carbon nanotube structures could mimic artificial muscles.

Apollo soil mechanics experiment S-200

NASA Technical Reports Server (NTRS)

Mitchell, J. K.; Houston, W. N.; Carrier, W. D., III; Costes, N. C.

1974-01-01

The physical and mechanical properties of the unconsolidated lunar surface material samples that were obtained during the Apollo missions were studied. Sources of data useful for deduction of soil information, and methods used to obtained the data are indicated. A model for lunar soil behavior is described which considers soil characteristics, density and porosity, strength, compressibility, and trafficability parameters. Lunar history and processes are considered, and a comparison is made of lunar and terrestrial soil behavior. The impact of the findings on future exploration and development of the moon are discussed, and publications resulting from lunar research by the soil mechanics team members are listed.

Fracture mechanics and corrosion fatigue.

NASA Technical Reports Server (NTRS)

Mcevily, A. J.; Wei, R. P.

1972-01-01

Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

High Density Polyetherurethane Foam as a Fragmentation and Radiographic Surrogate for Cortical Bone

PubMed Central

Beardsley, Christina L; Heiner, Anneliese D; Brandser, Eric A; Marsh, J Lawrence; Brown, Thomas D

2000-01-01

Background Although one of the most important factors in predicting outcome of articular fracture, the comminution of the fracture is only subjectively assessed. To facilitate development of objective, quantitative measures of comminution phenomena, there is need for a bone fragmentation surrogate. Methods Laboratory investigation was undertaken to develop and characterize a novel synthetic material capable of emulating the fragmentation and radiographic behavior of human cortical bone. Result Screening tests performed with a drop tower apparatus identified high-density polyetherurethane foam as having suitable fragmentation properties. The material's impact behavior and its quasi-static mechanical properties are here described. Dispersal of barium sulfate (BaSO4) in the resin achieved radio-density closely resembling that of bone, without detectably altering mechanical behavior. The surrogate material's ultimate strength, elastic modulus, and quasi-static toughness are within an order of magnitude of those of mammalian cortical bone. The spectrum of comminution patterns produced by this material when impacted with varying amounts of energy is very comparable to the spectrum of bone fragment comminution seen clinically. Conclusions A novel high-density polyetherurethane foam, when subjected to impact loading, sustains comminuted fracture in a manner strikingly similar to cortical bone. Moreover, since the material also can be doped with radio-opacifier so as to closely emulate bone's radiographic signature, it opens many new possibilities for CT-based systematic study of comminution phenomena. PMID:10934621

Internal strain analysis of ceramics using scanning laser acoustic microscopy

NASA Technical Reports Server (NTRS)

Kent, Renee M.

1993-01-01

Quantitative studies of material behavior characteristics are essential for predicting the functionality of a material under its operating conditions. A nonintrusive methodology for measuring the in situ strain of small dimeter (to 11 microns) ceramic fibers under uniaxial tensile loading and the local internal strains of ceramics and ceramic composites under flexural loading is introduced. The strain measurements and experimentally observed mechanical behavior are analyzed in terms of the microstructural development and fracture behavior of each test specimen evaluated. Measurement and analysis of Nicalon silicon carbide (SiC) fiber (15 microns diameter) indicate that the mean elastic modulus of the individual fiber is 185.3 GPa. Deviations observed in the experimentally determined elastic modulus values between specimens were attributed to microstructural variations which occur during processing. Corresponding variations in the fracture surface morphology were also observed. The observed local mechanical behavior of a lithium alumino-silicate (LAS) glass ceramic, a LAS/SiC monofilament composite, and a calcium alumino-silicate (CAS)/SiC fully reinforced composite exhibits nonlinearities and apparent hysteresis due to the subcritical mechanical loading. Local hysteresis in the LAS matrices coincided with the occurrence of multiple fracture initiation sites, localized microcracking, and secondary cracking. The observed microcracking phenomenon was attributed to stress relaxation of residual stresses developed during processing, and local interaction of the crack front with the microstructure. The relaxation strain and stress predicted on apparent mechanical hysteresis effects were defined and correlated with the magnitude of the measured fracture stress for each specimen studied. This quantitative correlation indicated a repeatable measure of the stress at which matrix microcracking occurred for stress relief of each material system. Stress relaxation occurred prior to the onset of steady state cracking conditions. The relaxation stress occurred at 18.5 percent of the fracture stress in LAS and 11.0 percent of the yield stress in CAS/SiC. The relaxation stress ratio was dependent upon the dominant fracture mode of the LAS/SiC specimens. Relaxation stress ratios greater than 0.30 were observed for specimens which fractured due to shear at the fiber matrix interface; specimens which fracture due to tensile cracking had relaxation stress ratios less than 0.30. The stress relaxation ratio appeared to be a specific characteristic of the glass ceramic material. The measured stress relaxation for LAS indicated a measure of the inherent residual stresses in the material due to processing and suggested localized toughening mechanisms for brittle material structures.

Understanding the bond-energy, hardness, and adhesive force from the phase diagram via the electron work function

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

Lu, Hao; Huang, Xiaochen; Li, Dongyang, E-mail: dongyang.li@ualberta.ca

2014-11-07

Properties of metallic materials are intrinsically determined by their electron behavior. However, relevant theoretical treatment involving quantum mechanics is complicated and difficult to be applied in materials design. Electron work function (EWF) has been demonstrated to be a simple but fundamental parameter which well correlates properties of materials with their electron behavior and could thus be used to predict material properties from the aspect of electron activities in a relatively easy manner. In this article, we propose a method to extract the electron work functions of binary solid solutions or alloys from their phase diagrams and use this simple approachmore » to predict their mechanical strength and surface properties, such as adhesion. Two alloys, Fe-Ni and Cu-Zn, are used as samples for the study. EWFs extracted from phase diagrams show same trends as experimentally observed ones, based on which hardness and surface adhesive force of the alloys are predicted. This new methodology provides an alternative approach to predict material properties based on the work function, which is extractable from the phase diagram. This work may also help maximize the power of phase diagram for materials design and development.« less

Non-linear Mechanics of Three-dimensional Architected Materials; Design of Soft and Functional Systems and Structures

NASA Astrophysics Data System (ADS)

Babaee, Sahab

In the search for materials with new properties, there have been significant advances in recent years aimed at the construction of architected materials whose behavior is governed by structure, rather than composition. Through careful design of the material's architecture, new mechanical properties have been demonstrated, including negative Poisson's ratio, high stiffness to weight ratio and mechanical cloaking. However, most of the proposed architected materials (also known as mechanical metamaterials) have a unique structure that cannot be recon figured after fabrication, making them suitable only for a specific task. This thesis focuses on the design of architected materials that take advantage of the applied large deformation to enhance their functionality. Mechanical instabilities, which have been traditionally viewed as a failure mode with research focusing on how to avoid them, are exploited to achieve novel and tunable functionalities. In particular I demonstrate the design of mechanical metamaterials with tunable negative Poisson ratio, adaptive phononic band gaps, acoustic switches, and reconfigurable origami-inspired waveguides. Remarkably, due to large deformation capability and full reversibility of soft materials, the responses of the proposed designs are reversible, repeatable, and scale independent. The results presented here pave the way for the design of a new class of soft, active, adaptive, programmable and tunable structures and systems with unprecedented performance and improved functionalities.

Research Update: Mechanical properties of metal-organic frameworks - Influence of structure and chemical bonding

NASA Astrophysics Data System (ADS)

Li, Wei; Henke, Sebastian; Cheetham, Anthony K.

2014-12-01

Metal-organic frameworks (MOFs), a young family of functional materials, have been attracting considerable attention from the chemistry, materials science, and physics communities. In the light of their potential applications in industry and technology, the fundamental mechanical properties of MOFs, which are of critical importance for manufacturing, processing, and performance, need to be addressed and understood. It has been widely accepted that the framework topology, which describes the overall connectivity pattern of the MOF building units, is of vital importance for the mechanical properties. However, recent advances in the area of MOF mechanics reveal that chemistry plays a major role as well. From the viewpoint of materials science, a deep understanding of the influence of chemical effects on MOF mechanics is not only highly desirable for the development of novel functional materials with targeted mechanical response, but also for a better understanding of important properties such as structural flexibility and framework breathing. The present work discusses the intrinsic connection between chemical effects and the mechanical behavior of MOFs through a number of prototypical examples.

The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1983-01-01

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

Mechanical Signal Filtering by Viscoelastic Properties of Cuticle in a Wandering Spider

NASA Astrophysics Data System (ADS)

McConney, Michael E.; Schaber, Clemens; Julian, Michael; Humphrey, Joseph A. C.; Barth, Friedrich; Tsukruk, Vladimir V.

2009-03-01

As recently found, in mechano-sensors of wandering spiders (Cupiennius salei) viscoelastic materials are important in signal filtering. We used atomic force microscopy to probe the time dependent mechanical behavior of these materials in live animals. We measured Young's modulus of a rubbery material located between a vibration receptor and the stimulus source. Earlier electrophysiological studies had demonstrated that the strain needed to elicit a sensory response (action potential) increased drastically as stimulus frequencies went below 10 Hz. Our surface force spectroscopy data similarly indicated a significant decrease in stiffness of the cuticular material and therefore less efficient energy transmission due to viscoelastic effects, as the frequency dropped to around 10 Hz. The stimulus transmitting cuticular material is acting as a high-pass filter for the mechanical stimulus on its way to the strain receptors. Again our results indicate that viscoelastic mechanical signal filtering is an important tool for arthropods to specifically respond to biologically relevant stimulus patterns.

Study of the time varying properties of flax fiber reinforced composites

NASA Astrophysics Data System (ADS)

Stochioiu, Constantin; Chettah, Ameur; Piezel, Benoit; Fontaine, Stéphane; Gheorghiu, Horia-Miron

2018-02-01

Bio materials have seen an increase of interest from the scientific community and the industry as a possible future generation of mass produced materials, some of the main arguments being their renewability, low production costs and recyclability. The current work is focused on the experimental data required for the viscoelastic characterization of a composite material. Similar work has been conducted on different types of composite materials by Tuttle and Brinson [1] who verified for a carbon epoxy laminate the possibility of long term predicament of creep. Nordin et al [2] studied paper impregnated with phenol-formaldehyde under compression. Muliana [3] conducted experiments on E-glass/vinyl ester materials. Behavior characterization was based on a model presented by Schapery [4]. The main objective of this work is to understand the mechanical behaviors of bio-laminates structures subjected to long and severe operating conditions. The studied material is a bio composite laminate consisting in long flax fibers embedded in an epoxy resin system. The laminates were obtained from pre-impregnated unidirectional fibers, which were cured though a thermo-compression cycle followed by a post curing cycle. Test specimens were cut down to sizes, with the help of an electric saw. The concerned fiber direction was 0° with sample dimensions of 250x25x2 mm. First, testing consisted in quasi static mechanical tests. Second, to characterize linear viscoelastic behavior of the bio-laminates, creep - recovery tests with multiple load levels have been performed for the chosen fiber direction.

Learning by Seeing: The TEMAS Multimedia Learning Objects for Civil Engineers

ERIC Educational Resources Information Center

Cadoni, Ezio; Botturi, Luca; Forni, Daniele

2008-01-01

A goal of engineering and architecture bachelor and master's programs is to provide students with practical and technical preparation in the mechanical characterization of materials and structures: future architects and civil engineers should be able to recognize and describe different construction materials and their behavior when used for…

Application of the endochronic theory of viscoplasticity to solid propellants and sandasphalt concrete

NASA Technical Reports Server (NTRS)

Peng, S. T. J.; Valanis, K. C.

1977-01-01

Solid propellants, sand-asphalt concrete and hard plastics showed rate sensitive mechanical behavior which, in addition, indicated that these materials have a permanent memory of the strain (or loading) path by which their present state was attained. A constitutive equation was formulated in general three dimensional tensorial form by means of irreversible thermodynamics. By using a very simple analytical form, it was shown that the mechanical behavior of solid propellants and sand-asphalt concrete can be readily described.

Ottawa Sand for Mechanics of Granular Materials (MGM) Experiment

NASA Technical Reports Server (NTRS)

2000-01-01

What appear to be boulders fresh from a tumble down a mountain are really grains of Ottawa sand, a standard material used in civil engineering tests and also used in the Mechanics of Granular Materials (MGM) experiment. The craggy surface shows how sand grans have faces that can cause friction as they roll and slide against each other, or even causing sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. MGM uses the microgravity of space to simulate this behavior under conditions that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. These images are from an Electron Spectroscopy for Chemical Analysis (ESCA) study conducted by Dr. Binayak Panda of IITRI for Marshall Space Flight Center (MSFC). (Credit: NASA/MSFC)

Influence of muscle-tendon complex geometrical parameters on modeling passive stretch behavior with the Discrete Element Method.

PubMed

Roux, A; Laporte, S; Lecompte, J; Gras, L-L; Iordanoff, I

2016-01-25

The muscle-tendon complex (MTC) is a multi-scale, anisotropic, non-homogeneous structure. It is composed of fascicles, gathered together in a conjunctive aponeurosis. Fibers are oriented into the MTC with a pennation angle. Many MTC models use the Finite Element Method (FEM) to simulate the behavior of the MTC as a hyper-viscoelastic material. The Discrete Element Method (DEM) could be adapted to model fibrous materials, such as the MTC. DEM could capture the complex behavior of a material with a simple discretization scheme and help in understanding the influence of the orientation of fibers on the MTC׳s behavior. The aims of this study were to model the MTC in DEM at the macroscopic scale and to obtain the force/displacement curve during a non-destructive passive tensile test. Another aim was to highlight the influence of the geometrical parameters of the MTC on the global mechanical behavior. A geometrical construction of the MTC was done using discrete element linked by springs. Young׳s modulus values of the MTC׳s components were retrieved from the literature to model the microscopic stiffness of each spring. Alignment and re-orientation of all of the muscle׳s fibers with the tensile axis were observed numerically. The hyper-elastic behavior of the MTC was pointed out. The structure׳s effects, added to the geometrical parameters, highlight the MTC׳s mechanical behavior. It is also highlighted by the heterogeneity of the strain of the MTC׳s components. DEM seems to be a promising method to model the hyper-elastic macroscopic behavior of the MTC with simple elastic microscopic elements. Copyright © 2015 Elsevier Ltd. All rights reserved.

Multi-physics modeling of multifunctional composite materials for damage detection

NASA Astrophysics Data System (ADS)

Sujidkul, Thanyawalai

This study presents a modeling of multifunction composite materials for damage detection with its verification and validation to mechanical behavior predictions of Carbon Fibre Reinforced Polymer composites (CFRPs), CFRPs laminated composites, and woven SiC/SiC matrix composites that are subjected to fracture damage. Advantages of those materials are low cost, low density, high strength-to-weight ratio, and comparable specific tensile properties, the special of SiC/SiC is good environmental stability at high temperature. Resulting in, the composite has been used for many important structures such as helicopter rotors, aerojet engines, gas turbines, hot control surfaces, sporting goods, and windmill blades. Damage or material defect detection in a mechanical component can provide vital information for the prediction of remaining useful life, which will result in the prevention of catastrophic failures. Thus the understanding of the mechanical behavior have been challenge to the prevent damage and failure of composites in different scales. The damage detection methods in composites have been investigated widely in recent years. Non-destructive techniques are the traditional methods to detect the damage such as X-ray, acoustic emission and thermography. However, due to the invisible damage in composite can be occurred, to prevent the failure in composites. The developments of damage detection methods have been considered. Due to carbon fibers are conductive materials, in resulting CFRPs can be self-sensing to detect damage. As is well known, the electrical resistance has been shown to be a sensitive measure of internal damage, and also this work study in thermal resistance can detect damage in composites. However, there is a few number of different micromechanical modeling schemes has been proposed in the published literature for various types of composites. This works will provide with a numerical, analytical, and theoretical failure models in different damages to predict the mechanical damage behavior with electrical properties and thermal properties.

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

Zimmerman, Jonathan A.; Jones, Reese E.; Templeton, Jeremy Alan

Materials with characteristic structures at nanoscale sizes exhibit significantly different mechani-cal responses from those predicted by conventional, macroscopic continuum theory. For example,nanocrystalline metals display an inverse Hall-Petch effect whereby the strength of the materialdecreases with decreasing grain size. The origin of this effect is believed to be a change in defor-mation mechanisms from dislocation motion across grains and pileup at grain boundaries at mi-croscopic grain sizes to rotation of grains and deformation within grain boundary interface regionsfor nanostructured materials. These rotational defects are represented by the mathematical conceptof disclinations. The ability to capture these effects within continuum theory, thereby connectingnanoscalemore » materials phenomena and macroscale behavior, has eluded the research community.The goal of our project was to develop a consistent theory to model both the evolution ofdisclinations and their kinetics. Additionally, we sought to develop approaches to extract contin-uum mechanical information from nanoscale structure to verify any developed continuum theorythat includes dislocation and disclination behavior. These approaches yield engineering-scale ex-pressions to quantify elastic and inelastic deformation in all varieties of materials, even those thatpossess highly directional bonding within their molecular structures such as liquid crystals, cova-lent ceramics, polymers and biological materials. This level of accuracy is critical for engineeringdesign and thermo-mechanical analysis is performed in micro- and nanosystems. The researchproposed here innovates on how these nanoscale deformation mechanisms should be incorporatedinto a continuum mechanical formulation, and provides the foundation upon which to develop ameans for predicting the performance of advanced engineering materials.4 AcknowledgmentThe authors acknowledge helpful discussions with Farid F. Abraham, Youping Chen, Terry J.Delph, Remi Dingreville, James W. Foulk III, Robert J. Hardy, Richard Lehoucq, Alejandro Mota,Gregory J. Wagner, Edmund B. Webb III and Xiaowang Zhou. Support for this project was pro-vided by the Enabling Predictive Simulation Investment Area of Sandia's Laboratory DirectedResearch and Development (LDRD) program.5« less

Overview of the US Fusion Materials Sciences Program

NASA Astrophysics Data System (ADS)

Zinkle, Steven

2004-11-01

The challenging fusion reactor environment (radiation, heat flux, chemical compatibility, thermo-mechanical stresses) requires utilization of advanced materials to fulfill the promise of fusion to provide safe, economical, and environmentally acceptable energy. This presentation reviews recent experimental and modeling highlights on structural materials for fusion energy. The materials requirements for fusion will be compared with other demanding technologies, including high temperature turbine components, proposed Generation IV fission reactors, and the current NASA space fission reactor project to explore the icy moons of Jupiter. A series of high-performance structural materials have been developed by fusion scientists over the past ten years with significantly improved properties compared to earlier materials. Recent advances in the development of high-performance ferritic/martensitic and bainitic steels, nanocomposited oxide dispersion strengthened ferritic steels, high-strength V alloys, improved-ductility Mo alloys, and radiation-resistant SiC composites will be reviewed. Multiscale modeling is providing important insight on radiation damage and plastic deformation mechanisms and fracture mechanics behavior. Electron microscope in-situ straining experiments are uncovering fundamental physical processes controlling deformation in irradiated metals. Fundamental modeling and experimental studies are determining the behavior of transmutant helium in metals, enabling design of materials with improved resistance to void swelling and helium embrittlement. Recent chemical compatibility tests have identified promising new candidates for magnetohydrodynamic insulators in lithium-cooled systems, and have established the basic compatibility of SiC with Pb-Li up to high temperature. Research on advanced joining techniques such as friction stir welding will be described. ITER materials research will be briefly summarized.

Bioinspired self-healing materials: lessons from nature

PubMed Central

Cremaldi, Joseph C

2018-01-01

Healing is an intrinsic ability in the incredibly biodiverse populations of the plant and animal kingdoms created through evolution. Plants and animals approach healing in similar ways but with unique pathways, such as damage containment in plants or clotting in animals. After analyzing the examples of healing and defense mechanisms found in living nature, eight prevalent mechanisms were identified: reversible muscle control, clotting, cellular response, layering, protective surfaces, vascular networks or capsules, exposure, and replenishable functional coatings. Then the relationship between these mechanisms, nature’s best (evolutionary) methods of mitigating and healing damage, and existing technology in self-healing materials are described. The goals of this top-level overview are to provide a framework for relating the behavior seen in living nature to bioinspired materials, act as a resource to addressing the limitations/problems with existing materials, and open up new avenues of insight and research into self-healing materials. PMID:29600152

Enhanced densification under shock compression in porous silicon

DOE PAGES

Lane, J. Matthew; Thompson, Aidan Patrick; Vogler, Tracy

2014-10-27

Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. The mechanism driving this behavior was not completely determined. We present evidence from atomistic simulation that pure silicon belongs to this anomalous class of materials and demonstrate the associated mechanisms responsible for the effect in porous silicon. Atomistic response indicates that local shear strain in the neighborhood of collapsing pores catalyzes a local solid-solid phase transformation even when bulk pressures are below the thermodynamicmore » phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials.« less

Ductile Fracture Behaviour of Hot Isostatically Pressed Inconel 690 Superalloy

NASA Astrophysics Data System (ADS)

Cooper, A. J.; Brayshaw, W. J.; Sherry, A. H.

2018-04-01

Herein we assess the differences in Charpy impact behavior between Hot Isostatically Pressed and forged Inconel 690 alloy over the temperature range of 300 °C to - 196 °C. The impact toughness of forged 690 exhibited a relatively small temperature dependence, with a maximum difference of ca. 40 J measured between 300 °C and - 196 °C, whereas the HIP'd alloy exhibited a difference of approximately double that of the forged alloy over the same temperature range. We have conducted Charpy impact testing, tensile testing, and metallographic analyses on the as-received materials as well as fractography of the failed Charpy specimens in order to understand the mechanisms that cause the observed differences in material fracture properties. The work supports a recent series of studies which assess differences in fundamental fracture behavior between Hot Isostatically Pressed and forged austenitic stainless steel materials of equivalent grades, and the results obtained in this study are compared to those of the previous stainless steel investigations to paint a more general picture of the comparisons between HIP vs forged material fracture behavior. Inconel 690 was selected in this study since previous studies were unable to completely omit the effects of strain-induced martensitic transformation at the tip of the Chary V-notch from the fracture mechanism; Inconel 690 is unable to undergo strain-induced martensitic transformation due to the alloy's high nickel content, thereby providing a sister study with the omission of any martensitic transformation effects on ductile fracture behavior.

The effect of various metallurgical parameters on the flow and fracture behavior of polycrystalline NiAl near the brittle-to-ductile transition

NASA Technical Reports Server (NTRS)

Noebe, Ronald D.

1994-01-01

An investigation of the effect of various metallurgical parameters such as interfaces, allowing additions, test temperature, and strain rate on the flow and fracture behavior of polycrystalline NiAl is summarized. From this study, a more complete understanding of the deformation and fracture behavior of polycrystalline NiAl near the brittle-to-ductile transition temperature has been developed. A mechanism for the BDTT is proposed that is based on the operation of localized dislocation climb processes that operate within the vicinity of the grain boundaries and provide the additional deformation mechanisms necessary for grain-to-grain compatibility during plastic deformation. Finally, methods for improving the low temperature mechanical behavior of NiAl were considered and reviewed within the context of the present knowledge of NiAl-based materials and the operative deformation and fracture mechanisms determined in this study. Special emphasis was placed on the use of second phases for improving low temperature properties.

A Viscoplastic Constitutive Theory for Monolithic Ceramic Materials. Series 1

NASA Technical Reports Server (NTRS)

Janosik, Lesley A.; Duffy, Stephen F.

1997-01-01

With increasing use of ceramic materials in high temperature structural applications such as advanced heat engine components, the need arises to accurately predict thermomechanical behavior. This paper, which is the first of two in a series, will focus on inelastic deformation behavior associated with these service conditions by providing an overview of a viscoplastic constitutive model that accounts for time-dependent hereditary material deformation (e.g., creep, stress relaxation, etc.) in monolithic structural ceramics. Early work in the field of metal plasticity indicated that inelastic deformations are essentially unaffected by hydrostatic stress. This is not the case, however, for ceramic-based material systems, unless the ceramic is fully dense. The theory presented here allows for fully dense material behavior as a limiting case. In addition, ceramic materials exhibit different time-dependent behavior in tension and compression. Thus, inelastic deformation models for ceramics must be constructed in a fashion that admits both sensitivity to hydrostatic stress and differing behavior in tension and compression. A number of constitutive theories for materials that exhibit sensitivity to the hydrostatic component of stress have been proposed that characterize deformation using time-independent classical plasticity as a foundation. However, none of these theories allow different behavior in tension and compression. In addition, these theories are somewhat lacking in that they are unable to capture creep, relaxation, and rate-sensitive phenomena exhibited by ceramic materials at high temperature. When subjected to elevated service temperatures, ceramic materials exhibit complex thermomechanical behavior that is inherently time-dependent, and hereditary in the sense that current behavior depends not only on current conditions, but also on thermo-mechanical history. The objective of this work is to present the formulation of a macroscopic continuum theory that captures these time-dependent phenomena. Specifically, the overview contained in this paper focuses on the multiaxial derivation of the constitutive model, and examines the scalar threshold function and its attending geometrical implications.

Unit mechanisms of fission gas release: Current understanding and future needs

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

Tonks, Michael; Andersson, David; Devanathan, Ram

Gaseous fission product transport and release has a large impact on fuel performance, degrading fuel properties and, once the gas is released into the gap between the fuel and cladding, lowering gap thermal conductivity and increasing gap pressure. While gaseous fission product behavior has been investigated with bulk reactor experiments and simplified analytical models, recent improvements in experimental and modeling approaches at the atomistic and mesoscales are being applied to provide unprecedented understanding of the unit mechanisms that define the fission product behavior. In this article, existing research on the basic mechanisms behind the various stages of fission gas releasemore » during normal reactor operation are summarized and critical areas where experimental and simulation work is needed are identified. This basic understanding of the fission gas behavior mechanisms has the potential to revolutionize our ability to predict fission product behavior during reactor operation and to design fuels that have improved fission product retention. In addition, this work can serve as a model on how a coupled experimental and modeling approach can be applied to understand the unit mechanisms behind other critical behaviors in reactor materials.« less

Control of Polymer Glass Formation Behaviour Using Molecular Diluents and Dynamic Interfaces

NASA Astrophysics Data System (ADS)

Mangalara, Jayachandra Hari

The end use application of polymeric materials is mainly determined by their viscosity, thermal stability and processability. These properties are primarily determined by the segmental relaxation time (taualpha) of the polymer and its glass state modulus, which determines its glassy mechanical response. Developing design principles to obtain rational control over these properties would enable fabrication of new polymers or polymer blends with improved thermal stability, enhanced processability and better mechanical robustness of the material. Introduction of diluents and nanostructuring of the material serve as invaluable tools for altering polymers' glass transition and associated dynamic and mechanical properties. Besides providing guidelines for technologically important improvements in processability, glassy mechanical properties, and transport behavior, diluent effects and behavior of nanostructured materials can provide insights into the fundamental physics of the glass transition, for example, by elucidating the interrelation between high- and low-frequency structural relaxation processes. It has been previously suggested that there exists a similarity between how diluents and interfaces impact the glass formation behavior of the polymer, raising the possibility that the effects of these two polymer modifications may be separate manifestations of a common set of physics in glass forming polymers. Here we address several interrelated questions in the understanding of glass formation in polymer/diluent blends and nanostructured polymers. First, what is the relationship between a diluent's molecular structure and its impact on a polymer's glass formation behavior? How does this compare to the effect of interfaces? Second, how does the introduction of diluents impact the role of interfaces in modifying polymer glass formation? Third, how does the introduction of interfaces impact metrology of the polymer glass transition? Finally, we address a major open question regarding the role of interfaces in the formation of a new class of 'ultrastable' glassy materials. The major conclusions of this work are as follows. We show how the effect of diluent on polymer glass formation depends on its molecular properties like structure, backbone stiffness, interaction strength with the host polymer etc. These effects are shown to be predicted by a functional form analogous to the one shown in the literature for predicting Tg shits in nanostructure materials. We further show that these diluents when introduced in nanostructured materials, bring about Tg shifts in a manner which does not correlate completely with the bulk fragility of the material, as previously suggested. We also show that there are confounding variables other than bulk fragility of the material - such as composition gradients, variability in measurement of Tg using different experimental techniques, etc. - that need to be considered when identifying the Tg nanoconfinement effects of the material. We also address this issue of having metrological differences in measuring Tg, by establishing appropriate weighting factors to be used while using different experimental techniques to measure Tg of confined materials. Finally, we propose a three layer model of the interface in which a facilitated layer intermediate between the surface and bulk exhibits enhanced bulk like liquid density which leads to the emergence of exceptional mechanical properties in "ultrastable" glasses.

Mechanical characterization of hybrid and functionally-graded aluminum open-cell foams with nanocrystalline-copper coatings

NASA Astrophysics Data System (ADS)

Sun, Yi

Cellular/foam materials found in nature such as bone, wood, and bamboo are usually functionally graded by having a non-uniform density distribution and inhomogenous composition that optimizes their global mechanical performance. Inspired by such naturally engineered products, the current study was conducted towards the development of functionally graded hybrid metal foams (FGHMF) with electrodeposited (ED) nanocrystalline coatings. First, the deformation and failure mechanisms of aluminum/copper (Al/Cu) hybrid foams were investigated using finite element analyses at different scales. The micro-scale behavior was studied based on single ligament models discretized using continuum elements and the macro-scale behavior was investigated using beam-element based finite element models of representative unit volumes consisting of multiple foam cells. With a detailed constitutive material behavior and material failure considered for both the aluminum ligament and the nano-copper coating, the numerical models were able to capture the unique behavior of Al/Cu hybrid foams, such as the typically observed sudden load drop after yielding. The numerical models indicate that such load drop is caused by the fracture of foam ligaments initiated from the rupture of the ED nano-copper coating due to its low ductility. This failure mode jeopardizes the global energy absorption capacity of hybrid foams, especially when a thick coating is applied. With the purpose of enhancing the performance of Al/Cu hybrid foams, an annealing process, which increased the ductility of the nanocrystalline copper coating by causing recovery, recrystallination and grain growth, was introduced in the manufacturing of Al/Cu hybrid foams. Quasi-static experimental results indicate that when a proper amount of annealing is applied, the ductility of the ED copper can be effectively improved and the compressive and tensile behavior of Al/Cu hybrid foams can be significantly enhanced, including better energy absorption capacity. The behavior of Al/Cu hybrid foams under high-strain-rate condition was then investigated using experiments on a split Hopkinson pressure bar. It was found that the ED nano-copper coating can also effectively enhance the energy absorption capacities of aluminum open-cell foams under high strain rate. Similar to the quasi-static behavior, a large stress drop was observed in the compressive response of Al/Cu hybrid foams under high strain rate, which was accompanied by dramatic shattering of material. It is shown that a more ductile behavior and better energy absorption performance under high strain rate condition can be also obtained by introducing an annealing process. Finally, the manufacturing process of Al/Cu hybrid foams was customized to fabricate FGHMF systems with two dimensional property gradients. The performance of these FGHMFs at both quasi-static and dynamic conditions was evaluated. Under quasi-static condition, two flexural type loading conditions were considered, namely, a three point bending condition and a cantilever beam condition. The dynamic behavior of FGHMFs was investigated by conducting drop weight tower tests on a three point bending setup. It was found that the failure mechanism of hybrid metal foams can be modified and the mechanical properties, such as stiffness and strength, and energy absorption capacities of hybrid metal foams can be optimized under both quasi-static and dynamic conditions by introducing strategically designed coating patterns. The presented novel approach and findings in this study provide valuable information on the development of high performance hybrid and functionally-graded cellular materials.

High Temperature Mechanical Behavior of Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Hemann, John

1996-01-01

The research accomplishments under this grant were very extensive in the areas of the high temperature behavior of ceramics, ceramic composites and testing standards for these materials. Rather than try to summarize all this research I have enclosed research papers and reports which were completed with the funding provided by the grant.

Tensile Fracture Behavior of 316L Austenitic Stainless Steel Manufactured by Hot Isostatic Pressing

NASA Astrophysics Data System (ADS)

Cooper, A. J.; Brayshaw, W. J.; Sherry, A. H.

2018-02-01

Herein we investigate how the oxygen content in hot isostatically pressed (HIP'd) 316L stainless steel affects the mechanical properties and tensile fracture behavior. This work follows on from previous studies, which aimed to understand the effect of oxygen content on the Charpy impact toughness of HIP'd steel. We expand on the work by performing room-temperature tensile testing on different heats of 316L stainless steel, which contain different levels of interstitial elements (carbon and nitrogen) as well as oxygen in the bulk material. Throughout the work we repeat the experiments on conventionally forged 316L steel as a reference material. The analysis of the work indicates that oxygen does not contribute to a measureable solution strengthening mechanism, as is the case with carbon and nitrogen in austenitic stainless steels (Werner in Mater Sci Eng A 101:93-98, 1988). Neither does oxygen, in the form of oxide inclusions, contribute to precipitation hardening due to the size and spacing of particles. However, the oxide particles do influence fracture behavior; fractography of the failed tension test specimens indicates that the average ductile dimple size is related to the oxygen content in the bulk material, the results of which support an on-going hypothesis relating oxygen content in HIP'd steels to their fracture mechanisms by providing additional sites for the initiation of ductile damage in the form of voids.

Advances and trends in computational structural mechanics

NASA Technical Reports Server (NTRS)

Noor, A. K.

1986-01-01

Recent developments in computational structural mechanics are reviewed with reference to computational needs for future structures technology, advances in computational models for material behavior, discrete element technology, assessment and control of numerical simulations of structural response, hybrid analysis, and techniques for large-scale optimization. Research areas in computational structural mechanics which have high potential for meeting future technological needs are identified. These include prediction and analysis of the failure of structural components made of new materials, development of computational strategies and solution methodologies for large-scale structural calculations, and assessment of reliability and adaptive improvement of response predictions.

Mechanical response of collagen molecule under hydrostatic compression.

PubMed

Saini, Karanvir; Kumar, Navin

2015-04-01

Proteins like collagen are the basic building blocks of various body tissues (soft and hard). Collagen molecules find their presence in the skeletal system of the body where they bear mechanical loads from different directions, either individually or along with hydroxy-apatite crystals. Therefore, it is very important to understand the mechanical behavior of the collagen molecule which is subjected to multi-axial state of loading. The estimation of strains of collagen molecule along different directions resulting from the changes in hydrostatic pressure magnitude, can provide us new insights into its mechanical behavior. In the present work, full atomistic simulations have been used to study global (volumetric) as well as local (along different directions) mechanical properties of the hydrated collagen molecule which is subjected to different hydrostatic pressure magnitudes. To estimate the local mechanical properties, the strains of collagen molecule along its longitudinal and transverse directions have been acquired at different hydrostatic pressure magnitudes. In spite of non-homogeneous distribution of atoms within the collagen molecule, the calculated values of local mechanical properties have been found to carry the same order of magnitude along the longitudinal and transverse directions. It has been demonstrated that the values of global mechanical properties like compressibility, bulk modulus, etc. as well as local mechanical properties like linear compressibility, linear elastic modulus, etc. are functions of magnitudes of applied hydrostatic pressures. The mechanical characteristics of collagen molecule based on the atomistic model have also been compared with that of the continuum model in the present work. The comparison showed up orthotropic material behavior for the collagen molecule. The information on collagen molecule provided in the present study can be very helpful in designing the future bio-materials. Copyright © 2015 Elsevier B.V. All rights reserved.

NASA-UVA Light Aerospace Alloy and Structures Technology Program (LA2ST)

NASA Technical Reports Server (NTRS)

Scully, John R.; Shiflet, Gary J.; Stoner, Glenn E.; Wert, John A.

1996-01-01

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA2ST) Program was initiated in 1986 and continues with a high level of activity. The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light-weight aerospace alloys, composites and thermal gradient structures in collaboration with NASA-Langley researchers. Specific technical objectives are presented for each research project. We generally aim to produce relevant data and basic understanding of material mechanical response, environmental/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and a pool of educated graduate students for aerospace technologies. Three research areas are being actively investigated, including: (1) Mechanical and environmental degradation mechanisms in advanced light metals, (2) Aerospace materials science, and (3) Mechanics of materials for light aerospace structures.

Mechanical exfoliation of two-dimensional materials

NASA Astrophysics Data System (ADS)

Gao, Enlai; Lin, Shao-Zhen; Qin, Zhao; Buehler, Markus J.; Feng, Xi-Qiao; Xu, Zhiping

2018-06-01

Two-dimensional materials such as graphene and transition metal dichalcogenides have been identified and drawn much attention over the last few years for their unique structural and electronic properties. However, their rise begins only after these materials are successfully isolated from their layered assemblies or adhesive substrates into individual monolayers. Mechanical exfoliation and transfer are the most successful techniques to obtain high-quality single- or few-layer nanocrystals from their native multi-layer structures or their substrate for growth, which involves interfacial peeling and intralayer tearing processes that are controlled by material properties, geometry and the kinetics of exfoliation. This procedure is rationalized in this work through theoretical analysis and atomistic simulations. We propose a criterion to assess the feasibility for the exfoliation of two-dimensional sheets from an adhesive substrate without fracturing itself, and explore the effects of material and interface properties, as well as the geometrical, kinetic factors on the peeling behaviors and the torn morphology. This multi-scale approach elucidates the microscopic mechanism of the mechanical processes, offering predictive models and tools for the design of experimental procedures to obtain single- or few-layer two-dimensional materials and structures.

Technical features and criteria in designing fiber-reinforced composite materials: from the aerospace and aeronautical field to biomedical applications.

PubMed

Gloria, Antonio; Ronca, Dante; Russo, Teresa; D'Amora, Ugo; Chierchia, Marianna; De Santis, Roberto; Nicolais, Luigi; Ambrosio, Luigi

2011-01-01

Polymer-based composite materials are ideal for applications where high stiffness-to-weight and strength-to-weight ratios are required. From aerospace and aeronautical field to biomedical applications, fiber-reinforced polymers have replaced metals, thus emerging as an interesting alternative. As widely reported, the mechanical behavior of the composite materials involves investigation on micro- and macro-scale, taking into consideration micromechanics, macromechanics and lamination theory. Clinical situations often require repairing connective tissues and the use of composite materials may be suitable for these applications because of the possibility to design tissue substitutes or implants with the required mechanical properties. Accordingly, this review aims at stressing the importance of fiber-reinforced composite materials to make advanced and biomimetic prostheses with tailored mechanical properties, starting from the basic principle design, technologies, and a brief overview of composites applications in several fields. Fiber-reinforced composite materials for artificial tendons, ligaments, and intervertebral discs, as well as for hip stems and mandible models will be reviewed, highlighting the possibility to mimic the mechanical properties of the soft and hard tissues that they replace.

Comparison of electron beam and laser beam powder bed fusion additive manufacturing process for high temperature turbine component materials

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

Dryepondt, Sebastien N; Pint, Bruce A; Ryan, Daniel

2016-04-01

The evolving 3D printer technology is now at the point where some turbine components could be additive manufactured (AM) for both development and production purposes. However, this will require a significant evaluation program to qualify the process and components to meet current design and quality standards. The goal of the project was to begin characterization of the microstructure and mechanical properties of Nickel Alloy X (Ni-22Cr-18Fe-9Mo) test bars fabricated by powder bed fusion (PBF) AM processes that use either an electron beam (EB) or laser beam (LB) power source. The AM materials produced with the EB and LB processes displayedmore » significant differences in microstructure and resultant mechanical properties. Accordingly, during the design analysis of AM turbine components, the specific mechanical behavior of the material produced with the selected AM process should be considered. Comparison of the mechanical properties of both the EB and LB materials to those of conventionally processed Nickel Alloy X materials indicates the subject AM materials are viable alternatives for manufacture of some turbine components.« less

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.

Hybrid networks based on epoxidized camelina oil

PubMed Central

Balanuca, Brindusa; Stan, Raluca; Lungu, Adriana; Vasile, Eugeniu; Iovu, Horia

2017-01-01

Abstract Lately, renewable resources received great attention in the macromolecular compounds area, regarding the design of the monomers and polymers with different applications. In this study the capacity of several modified vegetable oil-based monomers to build competitive hybrid networks was investigate, taking into account thermal and mechanical behavior of the designed materials. In order to synthesize such competitive nanocomposites, the selected renewable raw material, camelina oil, was employed due to the non-toxicity and biodegradability behavior. General properties of epoxidized camelina oil-based materials were improved by loading of different types of organic-inorganic hybrid compounds – polyhedral oligomeric silsesquioxane (POSS) bearing one (POSS1Ep) or eight (POSS8Ep) epoxy rings on the cages. In order to identify the chemical changes occurring after the thermal curing reactions, FT-IR spectrometry was employed. The new synthesized nanocomposites based on epoxidized camelina oil (ECO) were characterized by dynamic mechanical analyze and thermogravimetric analyze. The morphology of the ECO-based materials was investigate by scanning electron microscopy and supplementary information regarding the presence of the POSS compounds were establish by energy dispersive X-ray analysis and X-ray photoelectron spectroscopy. The smooth materials without any separation phase indicates a well dispersion of the Si–O–Si cages within the organic matrix and the incorporation of this hybrid compounds into the ECO network demonstrates to be a well strategy to improve the thermal and mechanical properties, simultaneously. PMID:29491775

Plastics as structural materials for aircraft

NASA Technical Reports Server (NTRS)

Kline, G M

1937-01-01

The purpose here is to consider the mechanical characteristics of reinforced phenol-formaldehyde resin as related to its use as structural material for aircraft. Data and graphs that have appeared in the literature are reproduced to illustrate the comparative behavior of plastics and materials commonly used in aircraft construction. Materials are characterized as to density, static strength, modulus of elasticity, resistance to long-time loading, strength under repeated impact, energy absorption, corrosion resistance, and ease of fabrication.

Impact Ignition and Combustion Behavior of Amorphous Metal-Based Reactive Composites

NASA Astrophysics Data System (ADS)

Mason, Benjamin; Groven, Lori; Son, Steven

2013-06-01

Recently published molecular dynamic simulations have shown that metal-based reactive powder composites consisting of at least one amorphous component could lead to improved reaction performance due to amorphous materials having a zero heat of fusion, in addition to having high energy densities and potential uses such as structural energetic materials and enhanced blast materials. In order to investigate the feasibility of these systems, thermochemical equilibrium calculations were performed on various amorphous metal/metalloid based reactive systems with an emphasis on commercially available or easily manufactured amorphous metals, such as Zr and Ti based amorphous alloys in combination with carbon, boron, and aluminum. Based on the calculations and material availability material combinations were chosen. Initial materials were either mixed via a Resodyn mixer or mechanically activated using high energy ball milling where the microstructure of the milled material was characterized using x-ray diffraction, optical microscopy and scanning electron microscopy. The mechanical impact response and combustion behavior of select reactive systems was characterized using the Asay shear impact experiment where impact ignition thresholds, ignition delays, combustion velocities, and temperatures were quantified, and reported. Funding from the Defense Threat Reduction Agency (DTRA), Grant Number HDTRA1-10-1-0119. Counter-WMD basic research program, Dr. Suhithi M. Peiris, program director is gratefully acknowledged.

Structural Behavior of Concrete Beams Reinforced with Basalt Fiber Reinforced Polymer (BFRP) Bars

NASA Astrophysics Data System (ADS)

Ovitigala, Thilan

The main challenge for civil engineers is to provide sustainable, environmentally friendly and financially feasible structures to the society. Finding new materials such as fiber reinforced polymer (FRP) material that can fulfill the above requirements is a must. FRP material was expensive and it was limited to niche markets such as space shuttles and air industry in the 1960s. Over the time, it became cheaper and spread to other industries such as sporting goods in the 1980-1990, and then towards the infrastructure industry. Design and construction guidelines are available for carbon fiber reinforced polymer (CFRP), aramid fiber reinforced polymer (AFRP) and glass fiber reinforced polymer (GFRP) and they are currently used in structural applications. Since FRP is linear elastic brittle material, design guidelines for the steel reinforcement are not valid for FRP materials. Corrosion of steel reinforcement affects the durability of the concrete structures. FRP reinforcement is identified as an alternative to steel reinforcement in corrosive environments. Although basalt fiber reinforced polymer (BFRP) has many advantages over other FRP materials, but limited studies have been done. These studies didn't include larger BFRP bar diameters that are mostly used in practice. Therefore, larger beam sizes with larger BFRP reinforcement bar diameters are needed to investigate the flexural and shear behavior of BFRP reinforced concrete beams. Also, shear behavior of BFRP reinforced concrete beams was not yet studied. Experimental testing of mechanical properties and bond strength of BFRP bars and flexural and shear behavior of BFRP reinforced concrete beams are needed to include BFRP reinforcement bars in the design codes. This study mainly focuses on the use of BFRP bars as internal reinforcement. The test results of the mechanical properties of BFRP reinforcement bars, the bond strength of BFRP reinforcement bars, and the flexural and shear behavior of concrete beams reinforced with BFRP reinforcement bars are presented and verified with other research studies, existing design codes and guidelines provided for other FRP bars. Based on the experimental testing results, analytical equations were developed and existing equations were modified to predict the actual structural behavior of FRP bar reinforced concrete beams with reasonable accuracy.

Development and characterization of amorphous acrylate networks for use as switchable adhesives inspired from shapememory behavior

NASA Astrophysics Data System (ADS)

Lakhera, Nishant

Several types of insects and animals such as spiders and geckos are inherently able to climb along vertical walls and ceilings. This remarkable switchable adhesive behavior has been attributed to the fibrillar structures on their feet, with size ranging from few nanometers to a few micrometers depending on the species. Several studies have attempted to create synthetic micro-patterned surfaces trying to imitate this adhesive behavior seen in nature. The experimental procedures are scattered, with sole purpose of trying to increase adhesion, thereby making direct comparison between studies very difficult. There is a lack of fundamental understanding on adhesion of patterned surfaces. The influence of critical parameters like material modulus, glass transition temperature, viscoelastic effects, temperature and water absorption on adhesion is not fully explored and characterized. These parameters are expected to have a decisive influence on adhesion behavior of the polymer. Previous studies have utilized conventional "off-the-shelf" materials like epoxy, polyurethanes etc. It is however, impossible to change the material modulus, glass transition temperature etc. of these polymer systems without changing the base constituents itself, thereby explaining the gaps in the current research landscape. The purpose of this study was to use acrylate shape-memory polymers (SMPs) for their ability to be tailored to specific mechanical properties by control of polymer chemistry, without changing the base constituents. Polymer networks with tailorable glass transition, material modulus, water absorption etc. were developed and adhesion studies were performed to investigate the influence of temperature, viscoelastic effects, material modulus on the adhesion behavior of flat acrylate polymer surfaces. The knowledge base gained from these studies was utilized to better understand the fundamental mechanisms associated with adhesion behavior of patterned acrylate surfaces. Thermally induced switchable adhesion and water induced switchable adhesion of patterned acrylate surfaces was investigated. The viscoelastic energy dissipation occurring during the detachment phase was shown to dramatically increase adhesion under both thermally induced and water induced conditions. This effect was most pre-dominant at the glass transition temperature of the material. Increase in pre-load force and unloading velocity were also shown to increase the adhesive capability of the patterned acrylate SMPs.

Uncovering the Physical Basis Connecting Environment and Tribological Performance of Ultrananocrystalline Diamond

DTIC Science & Technology

2012-10-05

Anisotropic Nanotribological Properties,” Journal of the Mechanical Behavior of Biomedical Materials, Vol. 4, Issue 4, pp. 515-522 (SCI) Kuo -Cheng Chen...Nanodiamond With the Polymer Used as an Additive in Lubricant Oil,” Journal of Materials Chemistry, Vol. 21, pp. 13213-13222 (SCI) Chih- Jung Chen, Ray...Deep Submicron to Nano-Scale,” Journal of Mechanics, Vol. 28, Issue 3, pp. 507-511 (SCI) Yeau-Ren Jeng, Yi-Min Wang, Hua-Chiang Wen, Shih -Ming Huang

Nonlinear mechanical behavior of thermoplastic matrix materials for advanced composites

NASA Technical Reports Server (NTRS)

Arenz, R. J.; Landel, R. F.

1989-01-01

Two recent theories of nonlinear mechanical response are quantitatively compared and related to experimental data. Computer techniques are formulated to handle the numerical integration and iterative procedures needed to solve the associated sets of coupled nonlinear differential equations. Problems encountered during these formulations are discussed and some open questions described. Bearing in mind these cautions, the consequences of changing parameters that appear in the formulations on the resulting engineering properties are discussed. Hence, engineering approaches to the analysis of thermoplastic matrix material can be suggested.

Ultralow-intensity magneto-optical and mechanical effects in metal nanocolloids.

PubMed

Moocarme, M; Domínguez-Juárez, J L; Vuong, L T

2014-03-12

Magneto-plasmonics is a designation generally associated with ferromagnetic-plasmonic materials because such optical responses from nonmagnetic materials alone are considered weak. Here, we show that there exists a switching transition between linear and nonlinear magneto-optical behaviors in noble-metal nanocolloids that is observable at ultralow illumination intensities and direct current magnetic fields. The response is attributed to polarization-dependent nonzero-time-averaged plasmonic loops, vortex power flows, and nanoparticle magnetization. This work identifies significant mechanical effects that subsequently exist via magnetic-dipole interactions.

Critical Behavior of Transport and Mechanical Properties in Particulate Dispersions and Granular Media

DTIC Science & Technology

1988-07-29

ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION University of Southern 1 (i aplicable ) It California I J R 6c. ADDRESS (City, State...Materials Based on the Theory of "Compound Mobilized Planes" (CMP) and "Spatial Mobilized Planes" (SMP), in Vol. II of Advances in the Mechanics and the Flow...of Disordered and Reinforced Materials", M. S. Thesis , M. D. Stephens, Department of Chemical Engineering, May 1988, , 13 UNIVERSITY OF SOUTHERN

Rigid Biological Systems as Models for Synthetic Composites

NASA Astrophysics Data System (ADS)

Mayer, George

2005-11-01

Advances that have been made in understanding the mechanisms underlying the mechanical behavior of a number of biological materials (namely mollusk shells and sponge spicules) are discussed here. Attempts at biomimicry of the structure of a nacreous layer of a mollusk shell have shown reasonable success. However, they have revealed additional issues that must be addressed if new synthetic composite materials that are based on natural systems are to be constructed. Some of the important advantages and limitations of copying from nature are also described here.

Statistical distribution of mechanical properties for three graphite-epoxy material systems

NASA Technical Reports Server (NTRS)

Reese, C.; Sorem, J., Jr.

1981-01-01

Graphite-epoxy composites are playing an increasing role as viable alternative materials in structural applications necessitating thorough investigation into the predictability and reproducibility of their material strength properties. This investigation was concerned with tension, compression, and short beam shear coupon testing of large samples from three different material suppliers to determine their statistical strength behavior. Statistical results indicate that a two Parameter Weibull distribution model provides better overall characterization of material behavior for the graphite-epoxy systems tested than does the standard Normal distribution model that is employed for most design work. While either a Weibull or Normal distribution model provides adequate predictions for average strength values, the Weibull model provides better characterization in the lower tail region where the predictions are of maximum design interest. The two sets of the same material were found to have essentially the same material properties, and indicate that repeatability can be achieved.

Stability of faults with heterogeneous friction properties and effective normal stress

NASA Astrophysics Data System (ADS)

Luo, Yingdi; Ampuero, Jean-Paul

2018-05-01

Abundant geological, seismological and experimental evidence of the heterogeneous structure of natural faults motivates the theoretical and computational study of the mechanical behavior of heterogeneous frictional fault interfaces. Fault zones are composed of a mixture of materials with contrasting strength, which may affect the spatial variability of seismic coupling, the location of high-frequency radiation and the diversity of slip behavior observed in natural faults. To develop a quantitative understanding of the effect of strength heterogeneity on the mechanical behavior of faults, here we investigate a fault model with spatially variable frictional properties and pore pressure. Conceptually, this model may correspond to two rough surfaces in contact along discrete asperities, the space in between being filled by compressed gouge. The asperities have different permeability than the gouge matrix and may be hydraulically sealed, resulting in different pore pressure. We consider faults governed by rate-and-state friction, with mixtures of velocity-weakening and velocity-strengthening materials and contrasts of effective normal stress. We systematically study the diversity of slip behaviors generated by this model through multi-cycle simulations and linear stability analysis. The fault can be either stable without spontaneous slip transients, or unstable with spontaneous rupture. When the fault is unstable, slip can rupture either part or the entire fault. In some cases the fault alternates between these behaviors throughout multiple cycles. We determine how the fault behavior is controlled by the proportion of velocity-weakening and velocity-strengthening materials, their relative strength and other frictional properties. We also develop, through heuristic approximations, closed-form equations to predict the stability of slip on heterogeneous faults. Our study shows that a fault model with heterogeneous materials and pore pressure contrasts is a viable framework to reproduce the full spectrum of fault behaviors observed in natural faults: from fast earthquakes, to slow transients, to stable sliding. In particular, this model constitutes a building block for models of episodic tremor and slow slip events.

Comparison of mechanical behavior between implant-simulated bone tissue and implant-jaw bone tissue interfaces based on Pull Out testing

NASA Astrophysics Data System (ADS)

Lopez, C.; Muñoz, J. C.; Pinillos, J. C.

2013-11-01

The main purpose of this research was to achieve a better understanding of the relationship within the mechanical properties of human cadaver jaw bone with kind D2 density regarding a substitute polymer to simulate bone tissue, proposed by the ASTM, to evaluate orthopedic implants. However, despite the existence of several densities of foams and his mechanical characterization has been classified into different degrees of tissue densities to simulate cancellous and cortical bone, the value of the densities are different contrasted with the densities of bone tissue, making difficult to establish direct relationship about mechanical behavior between the polymer and the bone material, and therefore no clear criteria known for choosing the polymeric foam which describes the mechanical behavior of tissue for a specific or particular study. To understand such behavior from bone tissue regarding the polymer samples, on this research was a dental implant inserted into the samples, and subjected to destructive Pull Out test according to ASTM F543The Pull Out strength was compared between implant-jawbone and implant-rigid polyurethane foam interfaces. Thus, the test pieces with mechanical behavior similar to bone tissue, enabling an approximation to choose degree appropriate of polymer to replace the bone tissue in future trials biomechanical.

Tribomaterial factors in space mechanism brake performance

NASA Technical Reports Server (NTRS)

Hawthorne, H. M.

1990-01-01

The asbestos/phenolic pads of Shuttle Remote Manipulator System (SRMS) brakes are unsuitable for use in long life space mechanisms because their friction decreases on extended sliding in high vacuum. Dehydration of the material and accumulation of wear debris in the conforming interface of this tribosystem induces the permanent friction changes. Other polymer and some ceramic based materials exhibit similar frictional torque behavior due to the development of minimal contact patches by the interfacial debris. In contrast, high friction occurs when other ceramics form many small contacts throughout fine debris beds. Generating this latter interfacial structure during run-in ensures that the in-vacuo friction remains stable thereafter. Such materials with low wear rates are potential candidates for friction elements in SSRMS and similar mechanisms.

Effects of anisotropy and irradiation on the deformation behavior of Zircaloy 2. Final report

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

Pelloux, R.M.; Ballinger, R.; Lucas, G.

1979-01-01

An experimental program investigated the effects of texture anisotropy and irradiation on the mechanical behavior of Zircaloy-2. Short time and time dependent mechanical behavior were considered. Irradiation effects were simulated through the use of 4.75 MeV protons. The temperature ranges investigated were 298/sup 0/K and 573 to 673/sup 0/K. Both cold worked-stress relieved and annealed material were used in this experimental program. Short time yield behavior of different crystallographic textures was determined by uniaxial and plane strain tests in the temperature range 298/sup 0/K and 573 to 673/sup 0/K. Monotonic flow loci were constructed for each texture. Yield behavior ismore » a strong function of the crystallographic texture number f at all temperatures investigated. The rotation of texture with increasing plastic strain was investigated as a function of initial texture at 298/sup 0/K and 623/sup 0/K. The rate of texture rotation df/epsilon/sub p/ was found to be a unique function of the initial texture for plastic strains less than 0.08. Time dependent mechanical behavior was investigated in the range 573 to 673/sup 0/K using constant load creep and stress relaxation tests. The tensile creep strength is proportional to the resolved fraction of basal poles in the test direction. In variable stress and temperature tests, the time-hardening rule was found to be inapplicable. The strain-hardening rule was applied with success to data obtained at temperatures less than or equal to 648/sup 0/K. Irradiation creep tests were conducted in vacuum at 598/sup 0/K and 102 to 241 MPa on 80..mu..m thick Zircaloy-2 foil specimens in both the recrystallized and cold worked-stress relieved condition. In the irradiation creep tests irradiation hardening and enhanced irradiation creep were observed. Radiation hardening effects were significant in annealed material but were attenuated in cold worked-stress relieved material.« less

An application of holographic interferometry for dynamic vibration analysis of a jet engine turbine compressor rotor

NASA Astrophysics Data System (ADS)

Fein, Howard

2003-09-01

Holographic Interferometry has been successfully employed to characterize the materials and behavior of diverse types of structures under dynamic stress. Specialized variations of this technology have also been applied to define dynamic and vibration related structural behavior. Such applications of holographic technique offer some of the most effective methods of modal and dynamic analysis available. Real-time dynamic testing of the modal and mechanical behavior of jet engine turbine, rotor, vane, and compressor structures has always required advanced instrumentation for data collection in either simulated flight operation test or computer-based modeling and simulations. Advanced optical holography techniques are alternate methods which result in actual full-field behavioral data in a noninvasive, noncontact environment. These methods offer significant insight in both the development and subsequent operational test and modeling of advanced jet engine turbine and compressor rotor structures and their integration with total vehicle system dynamics. Structures and materials can be analyzed with very low amplitude excitation and the resultant data can be used to adjust the accuracy of mathematically derived structural and behavioral models. Holographic Interferometry offers a powerful tool to aid in the developmental engineering of turbine rotor and compressor structures for high stress applications. Aircraft engine applications in particular most consider operational environments where extremes in vibration and impulsive as well as continuous mechanical stress can affect both operation and structural stability. These considerations present ideal requisites for analysis using advanced holographic methods in the initial design and test of turbine rotor components. Holographic techniques are nondestructive, real-time, and definitive in allowing the identification of vibrational modes, displacements, and motion geometries. Such information can be crucial to the determination of mechanical configurations and designs as well as critical operational parameters of turbine structural components or unit turbine components fabricated from advanced and exotic new materials or using new fabrication methods. Anomalous behavioral characteristics can be directly related to hidden structural or mounting anomalies and defects.

Revival of pure titanium for dynamically loaded porous implants using additive manufacturing.

PubMed

Wauthle, Ruben; Ahmadi, Seyed Mohammad; Amin Yavari, Saber; Mulier, Michiel; Zadpoor, Amir Abbas; Weinans, Harrie; Van Humbeeck, Jan; Kruth, Jean-Pierre; Schrooten, Jan

2015-09-01

Additive manufacturing techniques are getting more and more established as reliable methods for producing porous metal implants thanks to the almost full geometrical and mechanical control of the designed porous biomaterial. Today, Ti6Al4V ELI is still the most widely used material for porous implants, and none or little interest goes to pure titanium for use in orthopedic or load-bearing implants. Given the special mechanical behavior of cellular structures and the material properties inherent to the additive manufacturing of metals, the aim of this study is to investigate the properties of selective laser melted pure unalloyed titanium porous structures. Therefore, the static and dynamic compressive properties of pure titanium structures are determined and compared to previously reported results for identical structures made from Ti6Al4V ELI and tantalum. The results show that porous Ti6Al4V ELI still remains the strongest material for statically loaded applications, whereas pure titanium has a mechanical behavior similar to tantalum and is the material of choice for cyclically loaded porous implants. These findings are considered to be important for future implant developments since it announces a potential revival of the use of pure titanium for additively manufactured porous implants. Copyright © 2015 Elsevier B.V. All rights reserved.

Thermo-mechanical Fatigue Failure of Thermal Barrier Coated Superalloy Specimen

NASA Astrophysics Data System (ADS)

Subramanian, Rajivgandhi; Mori, Yuzuru; Yamagishi, Satoshi; Okazaki, Masakazu

2015-09-01

Failure behavior of thermal barrier coated (TBC) Ni-based superalloy specimens were studied from the aspect of the effect of bond coat material behavior on low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) at various temperatures and under various loading conditions. Initially, monotonic tensile tests were carried out on a MCrAlY alloy bond coat material in the temperature range of 298 K to 1273 K (25 °C to 1000 °C). Special attention was paid to understand the ductile to brittle transition temperature (DBTT). Next, LCF and TMF tests were carried out on the thermal barrier coated Ni-based alloy IN738 specimen. After these tests, the specimens were sectioned to understand their failure mechanisms on the basis of DBTT of the bond coat material. Experimental results demonstrated that the LCF and TMF lives of the TBC specimen were closely related to the DBTT of the bond coat material, and also the TMF lives were different from those of LCF tests. It has also been observed that the crack density in the bond coat in the TBC specimen was significantly dependent on the test conditions. More importantly, not only the number of cracks but also the crack penetration probability into substrate were shown to be sensitive to the DBTT.

Probabilistic analysis of the behavior of polymer matrix composite materials reinforced by different types of fibers

NASA Astrophysics Data System (ADS)

Harb, N.; Bezzazi, B.; Mehraz, S.; Hamitouche, K.; Dilmi, H.

2017-11-01

The requests of lightening of the structures and gains in performance lead to search for new materials and the associated processes for aeronautical and space applications. Long-fiber composites have been used for many years for these applications; they make it possible to reduce the mass of the structures because of their excellent compromise of mass/rigidity / resistance. The materials in general contain defects which are essentially due to their nature and their mode of elaboration. To this purpuse, we carried out a probabilistic analysis of the mechanical behavior in three-point bending of composite materials with a thermosetting matrix in order to highlight the influence of the number of folds of the fibers and the nature of the fibers on the dispersion of the defects in the stratified structures fiberglass, carbon fiber laminates and hybrid (carbon / glass) laminates. From the results obtained, the dispersion of the defects is lower in the laminates of greater number of plies of the fibers and the hybrid laminates; the more the number of folds increases the more the mechanical characteristics increase; the hybrid laminates exhibit better mechanical properties compared to laminates of the same type of fiber. Finally, a morphological analysis of fracture structures and facies was investigated by scanning electron microscope (SEM) observations.

Recent advances in engineering science; Proceedings of the A. Cemal Eringen Symposium, University of California, Berkeley, June 20-22, 1988

NASA Technical Reports Server (NTRS)

Koh, Severino L. (Editor); Speziale, Charles G. (Editor)

1989-01-01

Various papers on recent advances in engineering science are presented. Some individual topics addressed include: advances in adaptive methods in computational fluid mechanics, mixtures of two medicomorphic materials, computer tests of rubber elasticity, shear bands in isotropic micropolar elastic materials, nonlinear surface wave and resonator effects in magnetostrictive crystals, simulation of electrically enhanced fibrous filtration, plasticity theory of granular materials, dynamics of viscoelastic media with internal oscillators, postcritical behavior of a cantilever bar, boundary value problems in nonlocal elasticity, stability of flexible structures with random parameters, electromagnetic tornadoes in earth's ionosphere and magnetosphere, helicity fluctuations and the energy cascade in turbulence, mechanics of interfacial zones in bonded materials, propagation of a normal shock in a varying area duct, analytical mechanics of fracture and fatigue.

Direct comparison of nanoindentation and tensile test results on reactor-irradiated materials

DOE PAGES

Krumweide, David L; Yamamoto, Takuya; Saleh, Tarik A.; ...

2018-03-13

Nanoindentation testing has been used for decades to assess materials on a local scale and to obtain fundamental mechanical property parameters. Nuclear materials research often faces the challenge of testing rather small samples due to the hazardous nature, limited space in reactors, and shallow ion-irradiated zones, fostering the need for small-scale mechanical testing (SSMT). As such, correlating the results from SSMT to bulk properties is particularly of interest. Here, this study compares macroscopic tensile test data (yield and flow stresses) to nanoindentation data (hardness) obtained on a number of different neutron-irradiated materials in order to understand the scaling behavior onmore » radiation-damaged samples.« less

Direct comparison of nanoindentation and tensile test results on reactor-irradiated materials

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

Krumweide, David L; Yamamoto, Takuya; Saleh, Tarik A.

Nanoindentation testing has been used for decades to assess materials on a local scale and to obtain fundamental mechanical property parameters. Nuclear materials research often faces the challenge of testing rather small samples due to the hazardous nature, limited space in reactors, and shallow ion-irradiated zones, fostering the need for small-scale mechanical testing (SSMT). As such, correlating the results from SSMT to bulk properties is particularly of interest. Here, this study compares macroscopic tensile test data (yield and flow stresses) to nanoindentation data (hardness) obtained on a number of different neutron-irradiated materials in order to understand the scaling behavior onmore » radiation-damaged samples.« less

Secondary emission conductivity of high purity silica fabric

NASA Technical Reports Server (NTRS)

Belanger, V. J.; Eagles, A. E.

1977-01-01

High purity silica fabrics were proposed for use as a material to control the effects of electrostatic charging of satellites at synchronous altitudes. These materials exhibited very quiet behavior when placed in simulated charging environments as opposed to other dielectrics used for passive thermal control which exhibit varying degrees of electrical arcing. Secondary emission conductivity is proposed as a mechanism for this superior behavior. Design of experiments to measure this phenomena and data taken on silica fabrics are discussed as they relate to electrostatic discharge (ESD) control on geosynchronous orbit spacecraft. Studies include the apparent change in resistivity of the material as a function of the electron beam energy, flux intensity, and the effect of varying electric fields impressed across the material under test.

The failure of brittle materials under overall compression: Effects of loading rate and defect distribution

NASA Astrophysics Data System (ADS)

Paliwal, Bhasker

The constitutive behaviors and failure processes of brittle materials under far-field compressive loading are studied in this work. Several approaches are used: experiments to study the compressive failure behavior of ceramics, design of experimental techniques by means of finite element simulations, and the development of micro-mechanical damage models to analyze and predict mechanical response of brittle materials under far-field compression. Experiments have been conducted on various ceramics, (primarily on a transparent polycrystalline ceramic, aluminum oxynitride or AlON) under loading rates ranging from quasi-static (˜ 5X10-6) to dynamic (˜ 200 MPa/mus), using a servo-controlled hydraulic test machine and a modified compression Kolsky bar (MKB) technique respectively. High-speed photography has also been used with exposure times as low as 20 ns to observe the dynamic activation, growth and coalescence of cracks and resulting damage zones in the specimen. The photographs were correlated in time with measurements of the stresses in the specimen. Further, by means of 3D finite element simulations, an experimental technique has been developed to impose a controlled, homogeneous, planar confinement in the specimen. The technique can be used in conjunction with a high-speed camera to study the in situ dynamic failure behavior of materials under confinement. AlON specimens are used for the study. The statically pre-compressed specimen is subjected to axial dynamic compressive loading using the MKB. Results suggest that confinement not only increases the load carrying capacity, it also results in a non-linear stress evolution in the material. High-speed photographs also suggest an inelastic deformation mechanism in AlON under confinement which evolves more slowly than the typical brittle-cracking type of damage in the unconfined case. Next, an interacting micro-crack damage model is developed that explicitly accounts for the interaction among the micro-cracks in brittle materials. The model incorporates pre-existing defect distributions and a crack growth law. The damage is defined as a scalar parameter which is a function of the micro-crack density, the evolution of which is a function of the existing defect distribution and the crack growth dynamics. A specific case of a uniaxial compressive loading under constant strain-rate has been studied to predict the effects of the strain-rate, defect distribution and the crack growth dynamics on the constitutive response and failure behavior of brittle materials. Finally, the effects of crack growth dynamics on the strain-rate sensitivity of brittle materials are studied with the help of the micro-mechanical damage model. The results are compared with the experimentally observed damage evolution and the rate-sensitive behavior of the compressive strength of several engineering ceramics. The dynamic failure of armor-grade hot-pressed boron carbide (B 4C) under loading rates of ˜ 5X10-6 to 200 MPa/mus is also discussed.

A Transversely Isotropic Thermo-mechanical Framework for Oil Shale

NASA Astrophysics Data System (ADS)

Semnani, S. J.; White, J. A.; Borja, R. I.

2014-12-01

The present study provides a thermo-mechanical framework for modeling the temperature dependent behavior of oil shale. As a result of heating, oil shale undergoes phase transformations, during which organic matter is converted to petroleum products, e.g. light oil, heavy oil, bitumen, and coke. The change in the constituents and microstructure of shale at high temperatures dramatically alters its mechanical behavior e.g. plastic deformations and strength, as demonstrated by triaxial tests conducted at multiple temperatures [1,2]. Accordingly, the present model formulates the effects of changes in the chemical constituents due to thermal loading. It is well known that due to the layered structure of shale its mechanical properties in the direction parallel to the bedding planes is significantly different from its properties in the perpendicular direction. Although isotropic models simplify the modeling process, they fail to accurately describe the mechanical behavior of these rocks. Therefore, many researchers have studied the anisotropic behavior of rocks, including shale [3]. The current study presents a framework to incorporate the effects of transverse isotropy within a thermo-mechanical formulation. The proposed constitutive model can be readily applied to existing finite element codes to predict the behavior of oil shale in applications such as in-situ retorting process and stability assessment in petroleum reservoirs. [1] Masri, M. et al."Experimental Study of the Thermomechanical Behavior of the Petroleum Reservoir." SPE Eastern Regional/AAPG Eastern Section Joint Meeting. Society of Petroleum Engineers, 2008. [2] Xu, B. et al. "Thermal impact on shale deformation/failure behaviors---laboratory studies." 45th US Rock Mechanics/Geomechanics Symposium. American Rock Mechanics Association, 2011. [3] Crook, AJL et al. "Development of an orthotropic 3D elastoplastic material model for shale." SPE/ISRM Rock Mechanics Conference. Society of Petroleum Engineers, 2002.

Anisotropic mechanical behavior of an injection molded short fiber reinforced thermoplastic

NASA Astrophysics Data System (ADS)

Lopez, Delphine; Thuillier, Sandrine; Bessières, Nicolas; Grohens, Yves

2016-10-01

A short fiber reinforced thermoplastic was injected into a rectangular mold, in order to prepare samples to characterize the mechanical behavior of the material. The injection process was simulated with Moldflow and a cutting pattern was deduced from the predicted fiber orientation, leading to samples with several well-defined orientations with respect to the injection direction. Monotonic tensile tests up to rupture, as well as complex cycles made of loading steps followed by relaxation steps at different strain levels were performed, in order to check the reproducibility for a given orientation. Moreover, the fiber orientation in the central part of the tensile samples was also analyzed with X-ray tomography. The results show that the mechanical behavior for each orientation (among 6) was rather reproducible, thus validating the cutting pattern.

Non-destructive thermo-mechanical behavior assessment of glass-ceramics for dental applications

NASA Astrophysics Data System (ADS)

Kordatos, E. Z.; Abdulkadhim, Z.; Feteira, A. M.

2017-05-01

Every year millions of people seek dental treatment to either repair damaged, unaesthetic and dysfunctional teeth or replace missing natural teeth. Several dental materials have been developed to meet the stringent requirements in terms of mechanical properties, aesthetics and chemical durability in the oral environment. Glass-ceramics exhibit a suitable combination of these properties for dental restorations. This research is focused on the assessment of the thermomechanical behavior of bio-ceramics and particularly lithium aluminosilicate glass-ceramics (LAS glass-ceramics). Specifically, methodologies based on Infrared Thermography (IRT) have been applied in order the structure - property relationship to be evaluated. Non-crystallized, partially crystallized and fully crystallized glass-ceramic samples have been non-destructively assessed in order their thermo-mechanical behavior to be associated with their micro-structural features.

Microstructure Analysis of Ti-xPt Alloys and the Effect of Pt Content on the Mechanical Properties and Corrosion Behavior of Ti Alloys

PubMed Central

Song, Ho-Jun; Han, Mi-Kyung; Jeong, Hyeon-Gyeong; Lee, Yong-Tai; Park, Yeong-Joon

2014-01-01

The microstructure, mechanical properties, and corrosion behavior of binary Ti-xPt alloys containing 5, 10, 15 and 20 wt% Pt were investigated in order to develop new Ti-based dental materials possessing superior properties than those of commercially pure titanium (cp-Ti). All of the Ti-xPt (x = 5, 10, 15, 20) alloys showed hexagonal α-Ti structure with cubic Ti3Pt intermetallic phase. The mechanical properties and corrosion behavior of Ti-xPt alloys were sensitive to the Pt content. The addition of Pt contributed to hardening of cp-Ti and to improving its oxidation resistance. Electrochemical results showed that the Ti-xPt alloys exhibited superior corrosion resistance than that of cp-Ti. PMID:28788660

NASA-UVA light aerospace alloy and structures technology program (LA(sup 2)ST)

NASA Technical Reports Server (NTRS)

Gangloff, Richard P.; Haviland, John K.; Herakovich, Carl T.; Pilkey, Walter D.; Pindera, Marek-Jerzy; Scully, John R.; Starke, Edgar A., Jr.; Stoner, Glenn E.; Thornton, Earl A.; Wawner, Franklin E., Jr.

1992-01-01

The general objective of the Light Aerospace Alloy and Structures Technology (LA(sup 2)ST) Program is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys, composites, and thermal gradient structures in collaboration with Langley researchers. Specific technical objectives are established for each research project. We aim to produce relevant data and basic understanding of material behavior and microstructure, new monolithic and composite alloys, advanced processing methods, new solid and fluid mechanics analyses, measurement advances, and critically, a pool of educated graduate students for aerospace technologies. Four research areas are being actively investigated, including: (1) Mechanical and Environmental Degradation Mechanisms in Advanced Light Metals and Composites; (2) Aerospace Materials Science; (3) Mechanics of Materials and Composites for Aerospace Structures; and (4) Thermal Gradient Structures.

Effect of Graphene Addition on Shape Memory Behavior of Epoxy Resins

NASA Technical Reports Server (NTRS)

Williams, Tiffany; Meador, Michael; Miller, Sandi; Scheiman, Daniel

2011-01-01

Shape memory polymers (SMPs) and composites are a special class of smart materials known for their ability to change size and shape upon exposure to an external stimulus (e.g. light, heat, pH, or magnetic field). These materials are commonly used for biomedical applications; however, recent attempts have been made towards developing SMPs and composites for use in aircraft and space applications. Implementing SMPs and composites to create a shape change effect in some aircraft structures could potentially reduce drag, decrease fuel consumption, and improve engine performance. This paper discusses the development of suitable materials to use in morphing aircraft structures. Thermally responsive epoxy SMPs and nanocomposites were developed and the shape memory behavior and thermo-mechanical properties were studied. Overall, preliminary results from dynamic mechanical analysis (DMA) showed that thermally actuated shape memory epoxies and nanocomposites possessed Tgs near approximately 168 C. When graphene nanofiller was added, the storage modulus and crosslinking density decreased. On the other hand, the addition of graphene enhanced the recovery behavior of the shape memory nanocomposites. It was assumed that the addition of graphene improved shape memory recovery by reducing the crosslinking density and increasing the elasticity of the nanocomposites.

Microgravity

NASA Image and Video Library

1996-09-18

One of three Mechanics of Granular Materials (MGM) test cells after flight on STS-79 and before impregnation with resin. Note that the sand column has bulged in the middle, and that the top of the column is several inches lower than the top of the plastic enclosure. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: University of Colorado at Boulder

Effect of particle morphology of Ni on the mechanical behavior of AZ91E-Ni coated nano Al2O3 composites

NASA Astrophysics Data System (ADS)

Sameer Kumar, D.; Suman, K. N. S.; Poddar, Palash

2017-06-01

The properties of any composite always depend on the bonding between the matrix and reinforcement phases. One way of improving the wettability of reinforcement in a matrix is to apply a layer of coating on reinforcing particles. The present study aims at developing Ni coating on nano Al2O3 ceramic particles and dispersing them in AZ91E magnesium matrix material. The electroless plating method has been employed to coat the particles and semi solid stir casting technique was adopted to prepare the composites. Several weight fractions of dispersed phase are considered to analyze the behavior of the fabricated composites. Field emission scanning electron microscopy (FESEM) and x-ray diffraction analysis has been carried out to investigate the distribution of particles and phase characteristics of the proposed material. The physical and mechanical behavior of the material was examined through density measurements, hardness, elastic modulus, ductility and tensile strength calculations. The metal coating on reinforcement aids to promote metal-metal bonding interface reactions which result in improved properties of the composite. Tensile fractography was carried out under FESEM and presented.

In-drop capillary spooling of spider capture thread inspires hybrid fibers with mixed solid–liquid mechanical properties

PubMed Central

Elettro, Hervé; Neukirch, Sébastien; Vollrath, Fritz; Antkowiak, Arnaud

2016-01-01

An essential element in the web-trap architecture, the capture silk spun by ecribellate orb spiders consists of glue droplets sitting astride a silk filament. Mechanically this thread presents a mixed solid–liquid behavior unknown to date. Under extension, capture silk behaves as a particularly stretchy solid, owing to its molecular nanosprings, but it totally switches behavior in compression to now become liquid-like: It shrinks with no apparent limit while exerting a constant tension. Here, we unravel the physics underpinning the unique behavior of this ”liquid wire” and demonstrate that its mechanical response originates in the shape-switching of the silk filament induced by buckling within the droplets. Learning from this natural example of geometry and mechanics, we manufactured programmable liquid wires that present previously unidentified pathways for the design of new hybrid solid–liquid materials. PMID:27185930

In-drop capillary spooling of spider capture thread inspires hybrid fibers with mixed solid-liquid mechanical properties.

PubMed

Elettro, Hervé; Neukirch, Sébastien; Vollrath, Fritz; Antkowiak, Arnaud

2016-05-31

An essential element in the web-trap architecture, the capture silk spun by ecribellate orb spiders consists of glue droplets sitting astride a silk filament. Mechanically this thread presents a mixed solid-liquid behavior unknown to date. Under extension, capture silk behaves as a particularly stretchy solid, owing to its molecular nanosprings, but it totally switches behavior in compression to now become liquid-like: It shrinks with no apparent limit while exerting a constant tension. Here, we unravel the physics underpinning the unique behavior of this "liquid wire" and demonstrate that its mechanical response originates in the shape-switching of the silk filament induced by buckling within the droplets. Learning from this natural example of geometry and mechanics, we manufactured programmable liquid wires that present previously unidentified pathways for the design of new hybrid solid-liquid materials.

In-drop capillary spooling of spider capture thread inspires hybrid fibers with mixed solid-liquid mechanical properties

NASA Astrophysics Data System (ADS)

Elettro, Hervé; Neukirch, Sébastien; Vollrath, Fritz; Antkowiak, Arnaud

2016-05-01

An essential element in the web-trap architecture, the capture silk spun by ecribellate orb spiders consists of glue droplets sitting astride a silk filament. Mechanically this thread presents a mixed solid-liquid behavior unknown to date. Under extension, capture silk behaves as a particularly stretchy solid, owing to its molecular nanosprings, but it totally switches behavior in compression to now become liquid-like: It shrinks with no apparent limit while exerting a constant tension. Here, we unravel the physics underpinning the unique behavior of this ”liquid wire” and demonstrate that its mechanical response originates in the shape-switching of the silk filament induced by buckling within the droplets. Learning from this natural example of geometry and mechanics, we manufactured programmable liquid wires that present previously unidentified pathways for the design of new hybrid solid-liquid materials.

Local mechanical and electromechanical properties of the P(VDF-TrFE)-graphene oxide thin films

NASA Astrophysics Data System (ADS)

Silibin, M. V.; Bystrov, V. S.; Karpinsky, D. V.; Nasani, N.; Goncalves, G.; Gavrilin, I. M.; Solnyshkin, A. V.; Marques, P. A. A. P.; Singh, Budhendra; Bdikin, I. K.

2017-11-01

Recently, many organic materials, including carbon materials such as carbon nanotubes (CNTs) and graphene (single-walled carbon sheet structure) were studied in order to improve their mechanical and electrical properties. In particular, copolymers of poly (vinylidene fluoride) and poly trifluoroethylene [P(VDF-TrFE)] are promising materials, which can be used as probes, sensors, actuators, etc. Composite thin film of the copolymer P(VDF-TrFE) with graphene oxide (GO) were prepared by spin coating. The obtained films were investigated using piezoresponse force microscopy (PFM). The switching behavior, piezoelectric response, dielectric permittivity and mechanical properties of the films were found to depend on the presence of GO. For understanding the mechanism of piezoresponse evolution of the composite we used models of PVDF chain, its behavior in electrical field and computed the data for piezoelectric coefficients using HyperChem software. The summarized models of graphene oxide based on graphene layer from 96 carbon atoms C: with oxygen and OH groups and with COOH groups arranged by hydrogen were used for PVDF/Graphene oxide complex: 1) with H-side (hydrogen atom) connected from PVDF to graphene oxide, 2) with F-side (fluorine atom) connected from PVDF graphene oxide and 3) Graphene Oxide/PVDF with both sides (sandwich type). Experimental results qualitatively correlate with those obtained in the calculations.

A computational modeling approach for the characterization of mechanical properties of 3D alginate tissue scaffolds.

PubMed

Nair, K; Yan, K C; Sun, W

2008-01-01

Scaffold guided tissue engineering is an innovative approach wherein cells are seeded onto biocompatible and biodegradable materials to form 3-dimensional (3D) constructs that, when implanted in the body facilitate the regeneration of tissue. Tissue scaffolds act as artificial extracellular matrix providing the environment conducive for tissue growth. Characterization of scaffold properties is necessary to understand better the underlying processes involved in controlling cell behavior and formation of functional tissue. We report a computational modeling approach to characterize mechanical properties of 3D gellike biomaterial, specifically, 3D alginate scaffold encapsulated with cells. Alginate inherent nonlinearity and variations arising from minute changes in its concentration and viscosity make experimental evaluation of its mechanical properties a challenging and time consuming task. We developed an in silico model to determine the stress-strain relationship of alginate based scaffolds from experimental data. In particular, we compared the Ogden hyperelastic model to other hyperelastic material models and determined that this model was the most suitable to characterize the nonlinear behavior of alginate. We further propose a mathematical model that represents the alginate material constants in Ogden model as a function of concentrations and viscosity. This study demonstrates the model capability to predict mechanical properties of 3D alginate scaffolds.

Effects of Loading Frequency and Film Thickness on the Mechanical Behavior of Nanoscale TiN Film

NASA Astrophysics Data System (ADS)

Liu, Jin-na; Xu, Bin-shi; Wang, Hai-dou; Cui, Xiu-fang; Jin, Guo; Xing, Zhi-guo

2017-09-01

The mechanical properties of a nanoscale-thickness film material determine its reliability and service life. To achieve quantitative detection of film material mechanical performance based on nanoscale mechanical testing methods and to explore the influence of loading frequency of the cycle load on the fatigue test, a TiN film was prepared on monocrystalline silicon by magnetron sputtering. The microstructure of the nanoscale-thickness film material was characterized by using scanning electron microscopy and high-resolution transmission electron microscopy. The residual stress distribution of the thin film was obtained by using an electronic film stress tester. The hardness values and the fatigue behavior were measured by using a nanomechanical tester. Combined with finite element simulation, the paper analyzed the influence of the film thickness and loading frequency on the deformation, as well as the equivalent stress and strain. The results showed that the TiN film was a typical face-centered cubic structure with a large amount of amorphous. The residual compressive stress decreased gradually with increasing thin film thickness, and the influence of the substrate on the elastic modulus and hardness was also reduced. A greater load frequency would accelerate the dynamic fatigue damage that occurs in TiN films.

Comparison of in vivo and ex vivo viscoelastic behavior of the spinal cord.

PubMed

Ramo, Nicole L; Shetye, Snehal S; Streijger, Femke; Lee, Jae H T; Troyer, Kevin L; Kwon, Brian K; Cripton, Peter; Puttlitz, Christian M

2018-03-01

Despite efforts to simulate the in vivo environment, post-mortem degradation and lack of blood perfusion complicate the use of ex vivo derived material models in computational studies of spinal cord injury. In order to quantify the mechanical changes that manifest ex vivo, the viscoelastic behavior of in vivo and ex vivo porcine spinal cord samples were compared. Stress-relaxation data from each condition were fit to a non-linear viscoelastic model using a novel characterization technique called the direct fit method. To validate the presented material models, the parameters obtained for each condition were used to predict the respective dynamic cyclic response. Both ex vivo and in vivo samples displayed non-linear viscoelastic behavior with a significant increase in relaxation with applied strain. However, at all three strain magnitudes compared, ex vivo samples experienced a higher stress and greater relaxation than in vivo samples. Significant differences between model parameters also showed distinct relaxation behaviors, especially in non-linear relaxation modulus components associated with the short-term response (0.1-1 s). The results of this study underscore the necessity of utilizing material models developed from in vivo experimental data for studies of spinal cord injury, where the time-dependent properties are critical. The ability of each material model to accurately predict the dynamic cyclic response validates the presented methodology and supports the use of the in vivo model in future high-resolution finite element modeling efforts. Neural tissues (such as the brain and spinal cord) display time-dependent, or viscoelastic, mechanical behavior making it difficult to model how they respond to various loading conditions, including injury. Methods that aim to characterize the behavior of the spinal cord almost exclusively use ex vivo cadaveric or animal samples, despite evidence that time after death affects the behavior compared to that in a living animal (in vivo response). Therefore, this study directly compared the mechanical response of ex vivo and in vivo samples to quantify these differences for the first time. This will allow researchers to draw more accurate conclusions about spinal cord injuries based on ex vivo data (which are easier to obtain) and emphasizes the importance of future in vivo experimental animal work. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Finite Element Simulation of Compression Molding of Woven Fabric Carbon Fiber/Epoxy Composites: Part I Material Model Development

DOE PAGES

Li, Yang; Zhao, Qiangsheng; Mirdamadi, Mansour; ...

2016-01-06

Woven fabric carbon fiber/epoxy composites made through compression molding are one of the promising choices of material for the vehicle light-weighting strategy. Previous studies have shown that the processing conditions can have substantial influence on the performance of this type of the material. Therefore the optimization of the compression molding process is of great importance to the manufacturing practice. An efficient way to achieve the optimized design of this process would be through conducting finite element (FE) simulations of compression molding for woven fabric carbon fiber/epoxy composites. However, performing such simulation remains a challenging task for FE as multiple typesmore » of physics are involved during the compression molding process, including the epoxy resin curing and the complex mechanical behavior of woven fabric structure. In the present study, the FE simulation of the compression molding process of resin based woven fabric composites at continuum level is conducted, which is enabled by the implementation of an integrated material modeling methodology in LS-Dyna. Specifically, the chemo-thermo-mechanical problem of compression molding is solved through the coupling of three material models, i.e., one thermal model for temperature history in the resin, one mechanical model to update the curing-dependent properties of the resin and another mechanical model to simulate the behavior of the woven fabric composites. Preliminary simulations of the carbon fiber/epoxy woven fabric composites in LS-Dyna are presented as a demonstration, while validations and models with real part geometry are planned in the future work.« less

A study of hyperelastic models for predicting the mechanical behavior of extensor apparatus.

PubMed

Elyasi, Nahid; Taheri, Kimia Karimi; Narooei, Keivan; Taheri, Ali Karimi

2017-06-01

In this research, the nonlinear elastic behavior of human extensor apparatus was investigated. To this goal, firstly the best material parameters of hyperelastic strain energy density functions consisting of the Mooney-Rivlin, Ogden, invariants, and general exponential models were derived for the simple tension experimental data. Due to the significance of stress response in other deformation modes of nonlinear models, the calculated parameters were used to study the pure shear and balance biaxial tension behavior of the extensor apparatus. The results indicated that the Mooney-Rivlin model predicts an unstable behavior in the balance biaxial deformation of the extensor apparatus, while the Ogden order 1 represents a stable behavior, although the fitting of experimental data and theoretical model was not satisfactory. However, the Ogden order 6 model was unstable in the simple tension mode and the Ogden order 5 and general exponential models presented accurate and stable results. In order to reduce the material parameters, the invariants model with four material parameters was investigated and this model presented the minimum error and stable behavior in all deformation modes. The ABAQUS Explicit solver was coupled with the VUMAT subroutine code of the invariants model to simulate the mechanical behavior of the central and terminal slips of the extensor apparatus during the passive finger flexion, which is important in the prediction of boutonniere deformity and chronic mallet finger injuries, respectively. Also, to evaluate the adequacy of constitutive models in simulations, the results of the Ogden order 5 were presented. The difference between the predictions was attributed to the better fittings of the invariants model compared with the Ogden model.

Model and Simulation of an SMA Enhanced Lip Seal

NASA Astrophysics Data System (ADS)

Qiao, Rui; Gao, Xiujie; Brinson, L. Catherine

2011-07-01

The feasibility of using SMA wires to improve the seal effectiveness has been studied experimentally and numerically. In this article, we present only the numerical study of simulating the thermo-mechanical behavior for an SMA enhanced lip seal, leaving the test setup and results in the experimental counterpart. A pseudo 3D SMA model, considering 1D SMA behavior in the major loading direction and elastic response in other directions, was used to capture the thermo-mechanical behavior of SMA wires. The model was then implemented into ABAQUS using the user-defined material subroutine to inherit most features of the commercial finite element package. Two-way shape memory effect was also considered since the SMA material exhibits strong two-way effects. An axisymmetric finite element model was constructed to simulate a seal mounting on a shaft and the sealing pressure was calculated for both the regular seal and the SMA enhanced seal. Finally, the result was qualitatively compared with the experimental observation.

Autonomous healing materials based on epoxidized natural rubber and ethylene methacrylic acid ionomers

NASA Astrophysics Data System (ADS)

Arifur Rahman, Md; Penco, Maurizio; Peroni, Isabella; Ramorino, Giorgio; Janszen, Gerardus; Di Landro, Luca

2012-03-01

The development of autonomous healing material has an enormous scientific and technological interest. In this context, this research work deals with the investigation of autonomous healing behavior of epoxidized natural rubber (ENR) and its blends with ethylene methacrylic acid ionomers. The autonomous healing behavior of ENR and its blends containing two different ionomers [poly(ethylene-co-methacrylic acid sodium salt) (EMNa) and poly(ethylene-co-methacrylic acid zinc salt) (EMZn)] has been studied by ballistic puncture tests. Interestingly, EMNa/ENR blends exhibit complete healing just after the ballistic test but EMZn/ENR blends do not show full self-repairing. The healing efficiency has been evaluated by optical microscopy and a depressurized air-flow test. The healing mechanism has been investigated by characterizing thermal and mechanical properties of the blends. The chemical structure studied by FTIR and thermal analysis show that the ion content of ionomers and functionality of ENR has a significant influence on the self-healing behavior.

Stress-rupture behavior of small diameter polycrystalline alumina fibers

NASA Technical Reports Server (NTRS)

Yun, Hee Mann; Goldsby, Jon C.; Dicarlo, James A.

1993-01-01

Continuous length polycrystalline alumina fibers are candidates as reinforcement in high temperature composite materials. Interest therefore exists in characterizing the thermomechanical behavior of these materials, obtaining possible insights into underlying mechanisms, and understanding fiber performance under long term use. Results are reported on the time-temperature dependent strength behavior of Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Below 1000 C and 100 hours, Nextel 610 with the smaller grain size had a greater fast fracture and rupture strength than Fiber FP. The time exponents for stress-rupture of these fibers were found to decrease from approximately 13 at 900 C to below 3 near 1050 C, suggesting a transition from slow crack growth to creep rupture as the controlling fracture mechanism. For both fiber types, an effective activation energy of 690 kJ/mol was measured for rupture. This allowed stress-rupture predictions to be made for extended times at use temperatures below 1000 C.

Finite element simulation of location- and time-dependent mechanical behavior of chondrocytes in unconfined compression tests.

PubMed

Wu, J Z; Herzog, W

2000-03-01

Experimental evidence suggests that cells are extremely sensitive to their mechanical environment and react directly to mechanical stimuli. At present, it is technically difficult to measure fluid pressure, stress, and strain in cells, and to determine the time-dependent deformation of chondrocytes. For this reason, there are no data in the published literature that show the dynamic behavior of chondrocytes in articular cartilage. Similarly, the dynamic chondrocyte mechanics have not been calculated using theoretical models that account for the influence of cell volumetric fraction on cartilage mechanical properties. In the present investigation, the location- and time-dependent stress-strain state and fluid pressure distribution in chondrocytes in unconfined compression tests were simulated numerically using a finite element method. The technique involved two basic steps: first, cartilage was approximated as a macroscopically homogenized material and the mechanical behavior of cartilage was obtained using the homogenized model; second, the solution of the time-dependent displacements and fluid pressure fields of the homogenized model was used as the time-dependent boundary conditions for a microscopic submodel to obtain average location- and time-dependent mechanical behavior of cells. Cells and extracellular matrix were assumed to be biphasic materials composed of a fluid phase and a hyperelastic solid phase. The hydraulic permeability was assumed to be deformation dependent and the analysis was performed using a finite deformation approach. Numerical tests were made using configurations similar to those of experiments described in the literature. Our simulations show that the mechanical response of chondrocytes to cartilage loading depends on time, fluid boundary conditions, and the locations of the cells within the specimen. The present results are the first to suggest that chondrocyte deformation in a stress-relaxation type test may exceed the imposed system deformation by a factor of 3-4, that chondrocyte deformations are highly dynamic and do not reach a steady state within about 20 min of steady compression (in an unconfined test), and that cell deformations are very much location dependent.

Yielding to Stress: Recent Developments in Viscoplastic Fluid Mechanics

NASA Astrophysics Data System (ADS)

Balmforth, Neil J.; Frigaard, Ian A.; Ovarlez, Guillaume

2014-01-01

The archetypal feature of a viscoplastic fluid is its yield stress: If the material is not sufficiently stressed, it behaves like a solid, but once the yield stress is exceeded, the material flows like a fluid. Such behavior characterizes materials common in industries such as petroleum and chemical processing, cosmetics, and food processing and in geophysical fluid dynamics. The most common idealization of a viscoplastic fluid is the Bingham model, which has been widely used to rationalize experimental data, even though it is a crude oversimplification of true rheological behavior. The popularity of the model is in its apparent simplicity. Despite this, the sudden transition between solid-like behavior and flow introduces significant complications into the dynamics, which, as a result, has resisted much analysis. Over recent decades, theoretical developments, both analytical and computational, have provided a better understanding of the effect of the yield stress. Simultaneously, greater insight into the material behavior of real fluids has been afforded by advances in rheometry. These developments have primed us for a better understanding of the various applications in the natural and engineering sciences.

MECHANICAL PROPERTY CHARACTERIZATIONS AND PERFORMANCE MODELING OF SOFC SEALS

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

Koeppel, Brian J.; Vetrano, John S.; Nguyen, Ba Nghiep

2008-03-26

This study provides modeling tools for the design of reliable seals for SOFC stacks. The work consists of 1) experimental testing to determine fundamental properties of SOFC sealing materials, and 2) numerical modeling of stacks and sealing systems. The material tests capture relevant temperature-dependent physical and mechanical data needed by the analytical models such as thermal expansion, strength, fracture toughness, and relaxation behavior for glass-ceramic seals and other materials. Testing has been performed on both homogenous specimens and multiple material assemblies to investigate the effect of interfacial reactions. A viscoelastic continuum damage model for a glass-ceramic seal was developed tomore » capture the nonlinear behavior of this material at high temperatures. This model was implemented in the MSC MARC finite element code and was used for a detailed analysis of a planar SOFC stack under thermal cycling conditions. Realistic thermal loads for the stack were obtained using PNNL’s in-house multiphysics solver. The accumulated seal damage and component stresses were evaluated for multiple thermal loading cycles, and regions of high seal damage susceptible to cracking were identified. Selected test results, numerical model development, and analysis results will be presented.« less

Thermal-Mechanical Response of Cracked Satin Weave CFRP Composites at Cryogenic Temperatures

NASA Astrophysics Data System (ADS)

Watanabe, S.; Shindo, Y.; Narita, F.; Takeda, T.

2008-03-01

This paper examines the thermal-mechanical response of satin weave carbon fiber reinforced polymer (CFRP) laminates with internal and/or edge cracks subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to occur in the transverse fiber bundles and extend through the entire thickness of the fiber bundles. Two-dimentional generalized plane strain finite element models are developed to study the effects of residual thermal stresses and cracks on the mechanical behavior of CFRP woven laminates. A detailed examination of the Young's modulus and stress distributions near the crack tip is carried out which provides insight into material behavior at cryogenic temperatures.

Polyaryl ethers and related polysiloxane copolymer molecular coatings preparation and radiation degrdation

NASA Technical Reports Server (NTRS)

Mcgrath, J. E.; Hedrick, J. L.; Webster, D. C.; Johnson, B. C.; Mohanty, D. K.; Yilgor, I.

1983-01-01

Poly(arylene ether sulfones) comprise a class of materials known as engineering thermoplastics which have a variety of important applications. These polymers are tough, rigid materials with good mechanical properties over a wide temperature range, and they are processed by conventional methods into products typically having excellent hydrolytic, thermal, oxidative and dimensional stability. Wholly aromatic random copolymers of hydroquinone and biphenol with 4.4 prime dichlorodiphenyl sulfone were synthesized via mechanical nucleophilic displacement. Their structures were characterized and mechanical behavior studied. These tough, ductile copolymers show excellent radiation resistance to electron beam treatment and retain much of the mechanical properties up to at least 700 Mrads under argon.

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

A damage mechanics based general purpose interface/contact element

NASA Astrophysics Data System (ADS)

Yan, Chengyong

Most of the microelectronics packaging structures consist of layered substrates connected with bonding materials, such as solder or epoxy. Predicting the thermomechanical behavior of these multilayered structures is a challenging task in electronic packaging engineering. In a layered structure the most complex part is always the interfaces between the strates. Simulating the thermo-mechanical behavior of such interfaces, is the main theme of this dissertation. The most commonly used solder material, Pb-Sn alloy, has a very low melting temperature 180sp°C, so that the material demonstrates a highly viscous behavior. And, creep usually dominates the failure mechanism. Hence, the theory of viscoplasticity is adapted to describe the constitutive behavior. In a multilayered assembly each layer has a different coefficient of thermal expansion. Under thermal cycling, due to heat dissipated from circuits, interfaces and interconnects experience low cycle fatigue. Presently, the state-of-the art damage mechanics model used for fatigue life predictions is based on Kachanov (1986) continuum damage model. This model uses plastic strain as a damage criterion. Since plastic strain is a stress path dependent value, the criterion does not yield unique damage values for the same state of stress. In this dissertation a new damage evolution equation based on the second law of thermodynamic is proposed. The new criterion is based on the entropy of the system and it yields unique damage values for all stress paths to the final state of stress. In the electronics industry, there is a strong desire to develop fatigue free interconnections. The proposed interface/contact element can also simulate the behavior of the fatigue free Z-direction thin film interconnections as well as traditional layered interconnects. The proposed interface element can simulate behavior of a bonded interface or unbonded sliding interface, also called contact element. The proposed element was verified against laboratory test data presented in the literature. The results demonstrate that the proposed element and the damage law perform very well. The most important scientific contribution of this dissertation is the proposed damage criterion based on second law of thermodynamic and entropy of the system. The proposed general purpose interface/contact element is another contribution of this research. Compared to the previous adhoc interface elements proposed in the literature, the new one is, much more powerful and includes creep, plastic deformations, sliding, temperature, damage, cyclic behavior and fatigue life in a unified formulation.

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

Siranosian, Antranik Antonio; Schembri, Philip Edward; Luscher, Darby Jon

The Los Alamos National Laboratory's Weapon Systems Engineering division's Advanced Engineering Analysis group employs material constitutive models of composites for use in simulations of components and assemblies of interest. Experimental characterization, modeling and prediction of the macro-scale (i.e. continuum) behaviors of these composite materials is generally difficult because they exhibit nonlinear behaviors on the meso- (e.g. micro-) and macro-scales. Furthermore, it can be difficult to measure and model the mechanical responses of the individual constituents and constituent interactions in the composites of interest. Current efforts to model such composite materials rely on semi-empirical models in which meso-scale properties are inferredmore » from continuum level testing and modeling. The proposed approach involves removing the difficulties of interrogating and characterizing micro-scale behaviors by scaling-up the problem to work with macro-scale composites, with the intention of developing testing and modeling capabilities that will be applicable to the mesoscale. This approach assumes that the physical mechanisms governing the responses of the composites on the meso-scale are reproducible on the macro-scale. Working on the macro-scale simplifies the quantification of composite constituents and constituent interactions so that efforts can be focused on developing material models and the testing techniques needed for calibration and validation. Other benefits to working with macro-scale composites include the ability to engineer and manufacture—potentially using additive manufacturing techniques—composites that will support the application of advanced measurement techniques such as digital volume correlation and three-dimensional computed tomography imaging, which would aid in observing and quantifying complex behaviors that are exhibited in the macro-scale composites of interest. Ultimately, the goal of this new approach is to develop a meso-scale composite modeling framework, applicable to many composite materials, and the corresponding macroscale testing and test data interrogation techniques to support model calibration.« less

Influence of thermally activated processes on the deformation behavior during low temperature ECAP

NASA Astrophysics Data System (ADS)

Fritsch, S.; Scholze, M.; F-X Wagner, M.

2016-03-01

High strength aluminum alloys are generally hard to deform. Therefore, the application of conventional severe plastic deformation methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low temperature deformation in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically deform a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially deformed from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low temperatures, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic deformation at low temperatures. We then discuss how the deformation temperature and velocity influence the occurrence of PLC effects and the homogeneity of the deformed ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low temperature deformed materials as a function of deformation temperature.

Flow and fracture behavior of NiAl in relation to the brittle-to-ductile transition temperature

NASA Technical Reports Server (NTRS)

Noebe, R. D.; Bowman, R. R.; Cullers, C. L.; Raj, S. V.

1991-01-01

NiAl has only three independent slip systems operating at low and intermediate temperatures whereas five independent deformation mechanisms are required to satisfy the von Mises criterion for general plasticity in polycrystalline materials. Yet, it is generally recognized that polycrystalline NiAl can be deformed extensively in compression at room temperature and that limited tensile ductility can be obtained in extruded materials. In order to determine whether these results are in conflict with the von Mises criterion, tension and compression tests were conducted on powder-extruded, binary NiAl between 300 and 1300 K. The results indicate that below the brittle-to-ductile transition temperature (BDTT) the failure mechanism in NiAl involves the initiation and propagation of cracks at the grain boundaries which is consistent with the von Mises analysis. Furthermore, evaluation of the flow behavior of NiAl indicates that the transition from brittle to ductile behavior with increasing temperature coincides with the onset of recovery mechanisms such as dislocation climb. The increase in ductility above the BDTT is therefore attributed to the climb of the 001 line type dislocations which in combination with dislocation glide enable grain boundary compatibility to be maintained at the higher temperatures.

Mechanical Behavior of Spray-Coated Metallic Laminates

NASA Astrophysics Data System (ADS)

Vackel, Andrew; Nakamura, Toshio; Sampath, Sanjay

2016-06-01

Thermal spray (TS) coatings have been extensively utilized for various surface modifications such as enhancing wear/erosion resistance and thermal protection. In the present study, a new function of TS material is explored by studying its load-carrying capability. Due to the inherent microstructures containing voids and interfaces, it has been presumed TS materials were not suitable to bear loads. However, the recent advances in TS technology to manufacture near fully dense TS coatings have expanded their potential applications. In the current experiments, TS nickel coatings are deposited onto metallic substrates, and their mechanical behaviors are closely examined. Based on the measured data, the estimated elastic modulus of TS Ni is about 130 GPa (35% less than bulk value), and the maximum tensile strength is about 500 MPa (comparable to bulk value). It was found that such a high value is attainable because the coating is deposited onto a substrate, enabling a load-transfer mechanism and preventing coating failure at a much lower stress level. Three distinct deformation stages are identified to describe this behavior. Such a clarification is critical for enabling TS process to restore structural parts as well as to additively manufacture load-bearing components.

A review of mechanical and tribological behaviour of polymer composite materials

NASA Astrophysics Data System (ADS)

Prabhakar, K.; Debnath, S.; Ganesan, R.; Palanikumar, K.

2018-04-01

Composite materials are finding increased applications in many industrial applications. A nano-composite is a matrix to which nanosized particles have been incorporated to drastically improve the mechanical performance of the original material. The structural components produced using nano-composites will exhibit a high strength-to-weight ratio. The properties of nano-composites have caused researchers and industries to consider using this material in several fields. Polymer nanocomposites consists of a polymer material having nano-particles or nano-fillers dispersed in the polymer matrix which may be of different shapes with at least one of the dimensions less than 100nm. In this paper, comprehensive review of polymer nanocomposites was done majorly in three different areas. First, mechanical behaviour of polymer nanocomposites which focuses on the mechanical property evaluation such as tensile strength, impact strength and modulus of elasticity based on the different combination of filler materials and nanoparticle inclusion. Second, wear behavior of Polymer composite materials with respect to different impingement angles and variation of filler composition using different processing techniques. Third, tribological (Friction and Wear) behaviour of nanocomposites using various combination of nanoparticle inclusion and time. Finally, it summarized the challenges and prospects of polymer nanocomposites.

A thermomechanical constitutive model for cemented granular materials with quantifiable internal variables. Part II - Validation and localization analysis

NASA Astrophysics Data System (ADS)

Das, Arghya; Tengattini, Alessandro; Nguyen, Giang D.; Viggiani, Gioacchino; Hall, Stephen A.; Einav, Itai

2014-10-01

We study the mechanical failure of cemented granular materials (e.g., sandstones) using a constitutive model based on breakage mechanics for grain crushing and damage mechanics for cement fracture. The theoretical aspects of this model are presented in Part I: Tengattini et al. (2014), A thermomechanical constitutive model for cemented granular materials with quantifiable internal variables, Part I - Theory (Journal of the Mechanics and Physics of Solids, 10.1016/j.jmps.2014.05.021). In this Part II we investigate the constitutive and structural responses of cemented granular materials through analyses of Boundary Value Problems (BVPs). The multiple failure mechanisms captured by the proposed model enable the behavior of cemented granular rocks to be well reproduced for a wide range of confining pressures. Furthermore, through comparison of the model predictions and experimental data, the micromechanical basis of the model provides improved understanding of failure mechanisms of cemented granular materials. In particular, we show that grain crushing is the predominant inelastic deformation mechanism under high pressures while cement failure is the relevant mechanism at low pressures. Over an intermediate pressure regime a mixed mode of failure mechanisms is observed. Furthermore, the micromechanical roots of the model allow the effects on localized deformation modes of various initial microstructures to be studied. The results obtained from both the constitutive responses and BVP solutions indicate that the proposed approach and model provide a promising basis for future theoretical studies on cemented granular materials.

Nanoscale Protection Layers To Mitigate Degradation in High-Energy Electrochemical Energy Storage Systems.

PubMed

Lin, Chuan-Fu; Qi, Yue; Gregorczyk, Keith; Lee, Sang Bok; Rubloff, Gary W

2018-01-16

In the pursuit of energy storage devices with higher energy and power, new ion storage materials and high-voltage battery chemistries are of paramount importance. However, they invite-and often enhance-degradation mechanisms, which are reflected in capacity loss with charge/discharge cycling and sometimes in safety problems. Degradation mechanisms are often driven by fundamentals such as chemical and electrochemical reactions at electrode-electrolyte interfaces, volume expansion and stress associated with ion insertion and extraction, and profound inhomogeneity of electrochemical behavior. While it is important to identify and understand these mechanisms at some reasonable level, it is even more critical to design strategies to mitigate these degradation pathways and to develop means to implement and validate the strategies. A growing set of research highlights the mitigation benefits achievable by forming thin protection layers (PLs) intentionally created as artificial interphase regions at the electrode-electrolyte interface. These advances illustrate a promising-perhaps even generic-pathway for enabling higher-energy and higher-voltage battery configurations. In this Account, we summarize examples of such PLs that serve as mitigation strategies to avoid degradation in lithium metal anodes, conversion-type electrode materials, and alloy-type electrodes. Examples are chosen from a larger body of electrochemical degradation research carried out in Nanostructures for Electrical Energy Storage (NEES), our DOE Energy Frontier Research Center. Overall, we argue on the basis of experimental and theoretical evidence that PLs effectively stabilize the electrochemical interfaces to prevent parasitic chemical and electrochemical reactions and mitigate the structural, mechanical, and compositional degradation of the electrode materials at the electrode-electrolyte interfaces. The evidenced improvement in performance metrics is accomplished by (1) establishing a homogeneous interface for ion insertion and extraction, (2) providing mechanical constraints to maintain structural integrity and robust electronic and ionic conduction pathways, and (3) introducing spatial confinements on the electrode material matrix to alter the phase transformation (delaying the occurrence of the conversion reaction) upon Li insertion, which results in superior electrode performance, excellent capacity retention, and improved reversibility. Taken together, these examples portray a valuable role for thin protection layers synthesized over electrode surfaces, both for their benefit to cycle stability and for revealing insights into degradation and mitigation mechanisms. Furthermore, they underscore the impact of complex electrochemical behavior at nanoscale materials and nanostructure interfaces in modulating the behavior of energy storage devices at the mesoscale and macroscale.

Friction, wear, and lubrication in vacuum

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1971-01-01

A review of studies and observations on the friction, wear, and lubrication behavior of materials in a vacuum environment is presented. The factors that determine and influence friction and wear are discussed. They include topographical, physical, mechanical, and the chemical nature of the surface. The effects of bulk properties such as deformation characteristics, fracture behavior, and structure are included.

Hierarchically-Driven Approach for Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior in Aerospace Materials

DTIC Science & Technology

2016-08-31

crack initiation and SCG mechanisms (initiation and growth versus resistance). 2. Final summary Here, we present a hierarchical form of multiscale...prismatic faults in -Ti: A combined quantum mechanics /molecular mechanics study 2. Nano-indentation and slip transfer (critical in understanding crack...initiation) 3. An extended-finite element framework (XFEM) to study SCG mechanisms 4. Atomistic methods to develop a grain and twin boundaries database

A model for ferromagnetic shape memory thin film actuators

NASA Astrophysics Data System (ADS)

Lee, Kwok-Lun; Seelecke, Stefan

2005-05-01

The last decade has witnessed the discovery of materials combining shape memory behavior with ferromagnetic properties (FSMAs), see James & Wuttig1, James et al.2, Ullakko et al.3. These materials feature the so-called giant magnetostrain effect, which, in contrast to conventional magnetostriction is due motion of martensite twins. This effect has motivated the development of a new class of active materials transducers, which combine intrinsic sensing capabilities with superior actuation speed and improved efficiency when compared to conventional shape memory alloys. Currently, thin film technology is being developed intensively in order to pave the way for applications in micro- and nanotechnology. As an example, Kohl et al., recently proposed a novel actuation mechanism based on NiMnGa thin film technology, which makes use of both the ferromagnetic transition and the martensitic transformation allowing the realization of an almost perfect antagonism in a single component part. The implementation of the mechanism led to the award-winning development of an optical microscanner. Possible applications in nanotechnology arise, e.g., by combination of smart NiMnGa actuators with scanning probe technologies. The key aspect of Kohl's device is the fact that it employs electric heating for actuation, which requires a thermo-magneto-mechanical model for analysis. The research presented in this paper aims at the development of a model that simulates this particular material behavior. It is based on ideas originally developed for conventional shape memory alloy behavior, (Mueller & Achenbach, Achenbach, Seelecke, Seelecke & Mueller) and couples it with a simple expression for the nonlinear temperature- and position-dependent effective magnetic force. This early and strongly simplified version does not account for a full coupling between SMA behavior and ferromagnetism yet, and does not incorporate the hysteretic character of the magnetization phenomena either. It can however be used to explain the basic actuation mechanism and highlight the role of coupled magnetic and martensitic transformation with respect to the actuator performance. In particular will we be able to develop guidelines for desirable alloy compositions, such that the resulting transition temperatures guarantee optimized actuator performance.

A thermo-chemo-mechanically coupled constitutive model for curing of glassy polymers

NASA Astrophysics Data System (ADS)

Sain, Trisha; Loeffel, Kaspar; Chester, Shawn

2018-07-01

Curing of a polymer is the process through which a polymer liquid transitions into a solid polymer, capable of bearing mechanical loads. The curing process is a coupled thermo-chemo-mechanical conversion process which requires a thorough understanding of the system behavior to predict the cure dependent mechanical behavior of the solid polymer. In this paper, a thermodynamically consistent, frame indifferent, thermo-chemo-mechanically coupled continuum level constitutive framework is proposed for thermally cured glassy polymers. The constitutive framework considers the thermodynamics of chemical reactions, as well as the material behavior for a glassy polymer. A stress-free intermediate configuration is introduced within a finite deformation setting to capture the formation of the network in a stress-free configuration. This work considers a definition for the degree of cure based on the chemistry of the curing reactions. A simplified version of the proposed model has been numerically implemented, and simulations are used to understand the capabilities of the model and framework.

Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

NASA Astrophysics Data System (ADS)

Wang, Minghai; Wang, Hujun; Liu, Zhonghai

2011-05-01

Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

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

Li, Yang; Zhao, Qiangsheng; Mirdamadi, Mansour

Woven fabric carbon fiber/epoxy composites made through compression molding are one of the promising choices of material for the vehicle light-weighting strategy. Previous studies have shown that the processing conditions can have substantial influence on the performance of this type of the material. Therefore the optimization of the compression molding process is of great importance to the manufacturing practice. An efficient way to achieve the optimized design of this process would be through conducting finite element (FE) simulations of compression molding for woven fabric carbon fiber/epoxy composites. However, performing such simulation remains a challenging task for FE as multiple typesmore » of physics are involved during the compression molding process, including the epoxy resin curing and the complex mechanical behavior of woven fabric structure. In the present study, the FE simulation of the compression molding process of resin based woven fabric composites at continuum level is conducted, which is enabled by the implementation of an integrated material modeling methodology in LS-Dyna. Specifically, the chemo-thermo-mechanical problem of compression molding is solved through the coupling of three material models, i.e., one thermal model for temperature history in the resin, one mechanical model to update the curing-dependent properties of the resin and another mechanical model to simulate the behavior of the woven fabric composites. Preliminary simulations of the carbon fiber/epoxy woven fabric composites in LS-Dyna are presented as a demonstration, while validations and models with real part geometry are planned in the future work.« less

Sequential interpenetrating polymer networks produced from vegetable oil based polyurethane and poly(methyl methacrylate).

PubMed

Kong, Xiaohua; Narine, Suresh S

2008-08-01

Sequential interpenetrating polymer networks (IPNs) were prepared using polyurethane produced from a canola oil based polyol with primary terminal functional groups and poly(methyl methacrylate) (PMMA). The properties of the material were studied and compared to the IPNs made from commercial castor oil using dynamic mechanical analysis, differential scanning calorimetry, as well as tensile measurements. The morphology of the IPNs was investigated using scanning electron microscopy and transmission electron microscopy. The chemical diversity of the starting materials allowed the evaluation of the effects of dangling chains and graftings on the properties of the IPNs. The polymerization process of canola oil based IPNs was accelerated because of the utilization of polyol with primary functional groups, which efficiently lessened the effect of dangling chains and yielded a higher degree of phase mixing. The mechanical properties of canola oil based IPNs containing more than 75 wt % PMMA were comparable to the corresponding castor oil based IPNs; both were superior to those of the constituent polymers due to the finely divided rubber and plastic combination structures in these IPNs. However, when PMMA content was less than 65 wt %, canola oil based IPNs exhibited a typical mechanical behavior of rigid plastics, whereas castor oil based IPNs showed a typical mechanical behavior of soft rubber. It is proposed that these new IPN materials with high performance prepared from alternative renewable resources can prove to be valuable substitutes for existing materials in various applications.

Mechanics of Brittle Materials. Part 1. Preliminary Mechanical Properties and Statistical Representations

DTIC Science & Technology

1973-10-01

intensity computation are shown in Figure 17. Using the same formal procedure outlined by Winne & Wundt . a notch geometry can be chosen to induce...Nitride at Elevated Temperatures . Winne, D.H. and Wundt , B.M., "Application of the Gnffith-Irwm Theory of Crack Propagation to the Bursting Behavior

Deconvolution of the role of metal and pH in metal coordinating polymers

NASA Astrophysics Data System (ADS)

Cazzell, Seth; Holten-Andersen, Niels

Nature uses metal binding amino acids to engineer both mechanical properties and structural functionality. Some examples of this metal binding behavior can be found in both mussel foot protein and DNA binding protein. The mussel byssal thread contains reversible intermolecular protein-metal bonds, allowing it to withstand harsh intertidal environments. Zinc fingers form intramolecular protein-metal bonds to stabilize the tertiary structure of DNA binding proteins, allowing specific structural functionality. Inspired by both these metal-binding materials, we present mechanical and spectroscopic characterization of a model polymer system, designed to mimic this bonding. Through these studies, we are able to answer fundamental polymer physics questions, such as the role of pH and metal to ligand ratio, illuminating both the macroscopic and microscopic material behavior. These understandings further bio-inspired engineering techniques that are used to design viscoelastic soft materials. I was supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

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

NASA Astrophysics Data System (ADS)

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

2013-07-01

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

Influence of Severe Shot Peening on the Surface State and Ultra-High-Cycle Fatigue Behavior of an AW 7075 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Trško, Libor; Guagliano, Mario; Bokůvka, Otakar; Nový, František; Jambor, Michal; Florková, Zuzana

2017-04-01

The ever more pressing and concurrent requirements of light design, increased performances and reliability, energy savings together with acceptable costs, is always pushing researchers and engineers toward the definition and application of new materials and treatments, able to guarantee superior properties and adequate repeatability and reliability. This means that one step beyond the definition of a potentially successful solution, a complete characterization of the new materials is needed, in order to get the right data and use them in the design process. A promising severe plastic deformation surface treatment to improve the fatigue properties of materials and metal parts is considered in this paper. The used treatment is called the severe shot peening, and it is derived from the conventional shot peening but with use of unusually high peening parameters. It was proven that it is able to generate a nanostructured surface layer of material, which results in superior fatigue properties when applied to many structural materials. The severe shot peening is applied to an AW 7075 Al alloy, widely used in mechanical and aeronautic constructions and the effects of such a treatment on this material are investigated in this paper, with particular emphasis on the ultra-high-cycle fatigue behavior. The results address the choice of the correct treatment parameters for getting an evaluable advantage of this treatment and are critically discussed for a complete understanding of the mechanisms leading to the modified fatigue behavior, in view of the future developments and research in the field.

Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

NASA Technical Reports Server (NTRS)

Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

1972-01-01

Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

Advanced Energy Storage Devices: Basic Principles, Analytical Methods, and Rational Materials Design

PubMed Central

Liu, Jilei; Wang, Jin; Xu, Chaohe; Li, Chunzhong; Lin, Jianyi

2017-01-01

Abstract Tremendous efforts have been dedicated into the development of high‐performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery‐like behavior depending on the electrode design and the charge storage guest ions. Therefore, the underlying mechanisms and the electrochemical processes occurring upon charge storage may be confusing for researchers who are new to the field as well as some of the chemists and material scientists already in the field. This review provides fundamentals of the similarities and differences between electrochemical capacitors and batteries from kinetic and material point of view. Basic techniques and analysis methods to distinguish the capacitive and battery‐like behavior are discussed. Furthermore, guidelines for material selection, the state‐of‐the‐art materials, and the electrode design rules to advanced electrode are proposed. PMID:29375964

Advanced Energy Storage Devices: Basic Principles, Analytical Methods, and Rational Materials Design.

PubMed

Liu, Jilei; Wang, Jin; Xu, Chaohe; Jiang, Hao; Li, Chunzhong; Zhang, Lili; Lin, Jianyi; Shen, Ze Xiang

2018-01-01

Tremendous efforts have been dedicated into the development of high-performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery-like behavior depending on the electrode design and the charge storage guest ions. Therefore, the underlying mechanisms and the electrochemical processes occurring upon charge storage may be confusing for researchers who are new to the field as well as some of the chemists and material scientists already in the field. This review provides fundamentals of the similarities and differences between electrochemical capacitors and batteries from kinetic and material point of view. Basic techniques and analysis methods to distinguish the capacitive and battery-like behavior are discussed. Furthermore, guidelines for material selection, the state-of-the-art materials, and the electrode design rules to advanced electrode are proposed.

Calibration and Finite Element Implementation of an Energy-Based Material Model for Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hackl, Klaus

2016-09-01

Numerical simulations are a powerful tool to analyze the complex thermo-mechanically coupled material behavior of shape memory alloys during product engineering. The benefit of the simulations strongly depends on the quality of the underlying material model. In this contribution, we discuss a variational approach which is based solely on energetic considerations and demonstrate that unique calibration of such a model is sufficient to predict the material behavior at varying ambient temperature. In the beginning, we recall the necessary equations of the material model and explain the fundamental idea. Afterwards, we focus on the numerical implementation and provide all information that is needed for programing. Then, we show two different ways to calibrate the model and discuss the results. Furthermore, we show how this model is used during real-life industrial product engineering.

Final Report for DE-FG02-99ER45795

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

Wilkins, John Warren

The research supported by this grant focuses on atomistic studies of defects, phase transitions, electronic and magnetic properties, and mechanical behaviors of materials. We have been studying novel properties of various emerging nanoscale materials on multiple levels of length and time scales, and have made accurate predictions on many technologically important properties. A significant part of our research has been devoted to exploring properties of novel nano-scale materials by pushing the limit of quantum mechanical simulations, and development of a rigorous scheme to design accurate classical inter-atomic potentials for larger scale atomistic simulations for many technologically important metals and metalmore » alloys.« less

The Experiment and Numerical Simulation of Composite Countersunk-head Fasteners Pull-through Mechanical Behavior

NASA Astrophysics Data System (ADS)

Mu, Junwu; Guan, Zhidong; Bian, Tianya; Li, Zengshan; Wang, Kailun; Liu, Sui

2014-10-01

Fasteners made of the anisotropic carbon/carbon (C/C) composite material have been developed for joining C/C composite material components in the high-temperature environment. The fastener specimens are fabricated from the C/C composites which are made from laminated carbon cloths with Z-direction carbon fibers being punctured as perform. Densification process cycles such as the thermal gradient chemical vapor infiltration (CVI) technology were repeated to obtain high density C/C composites fastener. The fasteners were machined parallel to the carbon cloths (X-Y direction). A method was proposed to test pull-through mechanical behavior of the countersunk-head C/C composite material fasteners. The damage morphologies of the fasteners were observed through the charge coupled device (CCD) and the scanning electron microscope (SEM). The internal micro-structure were observed through the high-resolution Mirco-CT systems. Finally, an excellent simulation of the C/C composite countersunk-head fasteners were performed with the finite element method (FEM), in which the damage evolution model of the fastener was established based on continuum damage mechanics. The simulation is correspond well with the test result . The damage evolution process and the relation between the countersunk depth and the ultimate load was investigated.

FE-simulation of hot forging with an integrated heat treatment with the objective of residual stress prediction

NASA Astrophysics Data System (ADS)

Behrens, Bernd-Arno; Chugreeva, Anna; Chugreev, Alexander

2018-05-01

Hot forming as a coupled thermo-mechanical process comprises numerous material phenomena with a corresponding impact on the material behavior during and after the forming process as well as on the final component performance. In this context, a realistic FE-simulation requires reliable mathematical models as well as detailed thermo-mechanical material data. This paper presents experimental and numerical results focused on the FE-based simulation of a hot forging process with a subsequent heat treatment step aiming at the prediction of the final mechanical properties and residual stress state in the forged component made of low alloy CrMo-steel DIN 42CrMo4. For this purpose, hot forging experiments of connecting rod geometry with a corresponding metallographic analysis and x-ray residual stress measurements have been carried out. For the coupled thermo-mechanical-metallurgical FE-simulations, a special user-defined material model based on the additive strain decomposition method and implemented in Simufact Forming via MSC.Marc solver features has been used.

Phase transition induced strain in ZnO under high pressure

DOE PAGES

Yan, Xiaozhi; Dong, Haini; Li, Yanchun; ...

2016-05-13

Under high pressure, the phase transition mechanism and mechanical property of material are supposed to be largely associated with the transformation induced elastic strain. However, the experimental evidences for such strain are scanty. The elastic and plastic properties of ZnO, a leading material for applications in chemical sensor, catalyst, and optical thin coatings, were determined using in situ high pressure synchrotron axial and radial x-ray diffraction. The abnormal elastic behaviors of selected lattice planes of ZnO during phase transition revealed the existence of internal elastic strain, which arise from the lattice misfit between wurtzite and rocksalt phase. Furthermore, the strengthmore » decrease of ZnO during phase transition under non-hydrostatic pressure was observed and could be attributed to such internal elastic strain, unveiling the relationship between pressure induced internal strain and mechanical property of material. Ultimately, these findings are of fundamental importance to understanding the mechanism of phase transition and the properties of materials under pressure.« less

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

Enhanced densification under shock compression in porous silicon

NASA Astrophysics Data System (ADS)

Lane, J. Matthew D.; Thompson, Aidan P.; Vogler, Tracy J.

2014-10-01

Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. We demonstrate a molecular mechanism that drives this behavior. We also present evidence from atomistic simulation that silicon belongs to this anomalous class of materials. Atomistic simulations indicate that local shear strain in the neighborhood of collapsing pores nucleates a local solid-solid phase transformation even when bulk pressures are below the thermodynamic phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials.

Interconnected porosity analysis by 3D X-ray microtomography and mechanical behavior of biomimetic organic-inorganic composite materials.

PubMed

Alonso-Sierra, S; Velázquez-Castillo, R; Millán-Malo, B; Nava, R; Bucio, L; Manzano-Ramírez, A; Cid-Luna, H; Rivera-Muñoz, E M

2017-11-01

Hydroxyapatite-based materials have been used for dental and biomedical applications. They are commonly studied due to their favorable response presented when used for replacement of bone tissue. Those materials should be porous enough to allow cell penetration, internal tissue growth, vascular incursion and nutrient supply. Furthermore, their morphology should be designed to guide the growth of new bone tissue in anatomically applicable ways. In this work, the mechanical performance and 3D X-ray microtomography (X-ray μCT) study of a biomimetic, organic-inorganic composite material, based on hydroxyapatite, with physicochemical, structural, morphological and mechanical properties very similar to those of natural bone tissue is reported. Ceramic pieces in different shapes and several porous sizes were produced using a Modified Gel Casting Method. Pieces with a controlled and 3D hierarchical interconnected porous structure were molded by adding polymethylmethacrylate microspheres. Subsequently, they were subject to a thermal treatment to remove polymers and to promote a sinterization of the ceramic particles, obtaining a HAp scaffold with controlled porosity. Then, two different organic phases were used to generate an organic-inorganic composite material, so gelatin and collagen, which was extracted from bovine tail, were used. The biomimetic organic-inorganic composite material was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and 3D X-ray microtomography techniques. Mechanical properties were characterized in compression tests, obtaining a dramatic and synergic increment in the mechanical properties due to the chemical and physical interactions between the two phases and to the open-cell cellular behavior of the final composite material; the maximum compressive strength obtained corresponds to about 3 times higher than that reported for natural cancellous bone. The pore size distribution obtained could be capable to allow cell penetration, internal tissue in-growth, vascular incursion and nutrient supply and this material has tremendous potential for use as a replacement of bone tissue or in the manufacture and molding of prosthesis with desired shapes. Copyright © 2017 Elsevier B.V. All rights reserved.

A system structure for predictive relations in penetration mechanics

NASA Astrophysics Data System (ADS)

Korjack, Thomas A.

1992-02-01

The availability of a software system yielding quick numerical models to predict ballistic behavior is a requisite for any research laboratory engaged in material behavior. What is especially true about accessibility of rapid prototyping for terminal impaction is the enhancement of a system structure which will direct the specific material and impact situation towards a specific predictive model. This is of particular importance when the ranges of validity are at stake and the pertinent constraints associated with the impact are unknown. Hence, a compilation of semiempirical predictive penetration relations for various physical phenomena has been organized into a data structure for the purpose of developing a knowledge-based decision aided expert system to predict the terminal ballistic behavior of projectiles and targets. The ranges of validity and constraints of operation of each model were examined and cast into a decision tree structure to include target type, target material, projectile types, projectile materials, attack configuration, and performance or damage measures. This decision system implements many penetration relations, identifies formulas that match user-given conditions, and displays the predictive relation coincident with the match in addition to a numerical solution. The physical regimes under consideration encompass the hydrodynamic, transitional, and solid; the targets are either semi-infinite or plate, and the projectiles include kinetic and chemical energy. A preliminary databases has been constructed to allow further development of inductive and deductive reasoning techniques applied to ballistic situations involving terminal mechanics.

Multiscale Analysis of Structurally-Graded Microstructures Using Molecular Dynamics, Discrete Dislocation Dynamics and Continuum Crystal Plasticity

NASA Technical Reports Server (NTRS)

Saether, Erik; Hochhalter, Jacob D.; Glaessgen, Edward H.; Mishin, Yuri

2014-01-01

A multiscale modeling methodology is developed for structurally-graded material microstructures. Molecular dynamic (MD) simulations are performed at the nanoscale to determine fundamental failure mechanisms and quantify material constitutive parameters. These parameters are used to calibrate material processes at the mesoscale using discrete dislocation dynamics (DD). Different grain boundary interactions with dislocations are analyzed using DD to predict grain-size dependent stress-strain behavior. These relationships are mapped into crystal plasticity (CP) parameters to develop a computationally efficient finite element-based DD/CP model for continuum-level simulations and complete the multiscale analysis by predicting the behavior of macroscopic physical specimens. The present analysis is focused on simulating the behavior of a graded microstructure in which grain sizes are on the order of nanometers in the exterior region and transition to larger, multi-micron size in the interior domain. This microstructural configuration has been shown to offer improved mechanical properties over homogeneous coarse-grained materials by increasing yield stress while maintaining ductility. Various mesoscopic polycrystal models of structurally-graded microstructures are generated, analyzed and used as a benchmark for comparison between multiscale DD/CP model and DD predictions. A final series of simulations utilize the DD/CP analysis method exclusively to study macroscopic models that cannot be analyzed by MD or DD methods alone due to the model size.

Deformation Behavior of Recycled Concrete Aggregate during Cyclic and Dynamic Loading Laboratory Tests

PubMed Central

Sas, Wojciech; Głuchowski, Andrzej; Gabryś, Katarzyna; Soból, Emil; Szymański, Alojzy

2016-01-01

Recycled concrete aggregate (RCA) is a relatively new construction material, whose applications can replace natural aggregates. To do so, extensive studies on its mechanical behavior and deformation characteristics are still necessary. RCA is currently used as a subbase material in the construction of roads, which are subject to high settlements due to traffic loading. The deformation characteristics of RCA must, therefore, be established to find the possible fatigue and damage behavior for this new material. In this article, a series of triaxial cyclic loading and resonant column tests is used to characterize fatigue in RCA as a function of applied deviator stress after long-term cyclic loading. A description of the shakedown phenomenon occurring in the RCA and calculations of its resilient modulus (Mr) as a function of fatigue are also presented. Test result analysis with the stress-life method on the Wohler S-N diagram shows the RCA behavior in accordance with the Basquin law. PMID:28773905

In vitro investigation of the performance of different restorative materials under cast circumferential clasps for removable dental prostheses.

PubMed

Pospiech, Peter; Nagel, Florian; Gebhart, Florian; Nothdurft, Frank P; Mitov, Gergo

2012-12-01

The objective of this in vitro study was to investigate the behavior of different composite restorative materials under the load of cast circumferential clasps for removable dental prostheses (RDPs). In 60 human molars, standardized mesial-occlusal-distal cavities were prepared. The cavities were restored with the following materials: Definite, Tetric Ceram, SureFil, Heliomolar RO, Ariston pHc, and Oralloy, and provided with a rest seat. The rest seats were subjected to 5,000 cycles of thermal cycling and 1,200,000 masticatory cycles in a mastication simulator via cobalt-chromium circumferential clasps cast to standardized frameworks in a laboratory model designed to simulate the biomechanics of a free-end denture base. Fracture analysis of the restorations was performed by light microscopy. Before and after loading, material wear was measured with a 3D-laser scanner, and an analysis of the marginal quality was performed in an SEM at ×200 applying the replica technique. No significant differences in the fracture behavior among the composite materials were found; the amalgam control group showed a significantly higher fracture resistance. Regarding the wear of the materials, the composites Definite and SureFil exhibited a behavior similar to that of amalgam. The other composites demonstrated higher wear rates. The initial marginal quality was significantly worse for Ariston pHc. The marginal adaptation decreased significantly after thermal and mechanical loading for Definite and Ariston pHc. In terms of the investigated aspects of mechanical performance, the tested composites seemed to be inferior to amalgam. Further clinical studies are needed to evaluate the ability of composite restorations to provide support for RDP clasps. The use of composites as direct restoration materials should be avoided in teeth, which serve as abutments for clasp-retained RDPs.

The mechanics of delamination in fiber-reinforced composite materials. II - The delamination behavior and fracture mechanics parameters

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1983-01-01

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extension. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined. Previously announced in STAR as N84-13222

Extracellular matrix elasticity and topography: material-based cues that affect cell function via conserved mechanisms

PubMed Central

Janson, Isaac A.; Putnam, Andrew J.

2014-01-01

Chemical, mechanical, and topographic extracellular matrix (ECM) cues have been extensively studied for their influence on cell behavior. These ECM cues alter cell adhesion, cell shape, and cell migration, and activate signal transduction pathways to influence gene expression, proliferation, and differentiation. ECM elasticity and topography, in particular, have emerged as material properties of intense focus based on strong evidence these physical cue can partially dictate stem cell differentiation. Cells generate forces to pull on their adhesive contacts, and these tractional forces appear to be a common element of cells’ responses to both elasticity and topography. This review focuses on recently published work that links ECM topography and mechanics and their influence on differentiation and other cell behaviors, We also highlight signaling pathways typically implicated in mechanotransduction that are (or may be) shared by cells subjected to topographic cues. Finally, we conclude with a brief discussion of the potential implications of these commonalities for cell based therapies and biomaterial design. PMID:24910444

A continuum thermo-inelastic model for damage and healing in self-healing glass materials

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

Xu, Wei; Sun, Xin; Koeppel, Brian J.

Self-healing glass, a recent advancement in the class of smart sealing materials, has attracted great attention from both research and industrial communities because of its unique capability of repairing itself at elevated temperatures. However, further development and optimization of this material rely on a more fundamental and thorough understanding of its essential thermo-mechanical response characteristics, which is also pivotal in predicting the coupling and interactions between the nonlinear stress and temperature dependent damage and healing behaviors. In the current study, a continuum three-dimensional thermo-inelastic damage-healing constitutive framework has been developed for the compliant self-healing glass material. The important feature ofmore » the present model is that various phenomena governing the mechanical degradation and recovery process, i.e. the nucleation, growth, and healing of the cracks and pores, are described with distinct mechanism-driven kinetics, where the healing constitutive relations are propagated from lower-length scale simulations. The proposed formulations are implemented into finite element analyses and the effects of various loading conditions and material properties on the material’s mechanical resistance are investigated.« less

Experimental study on tissue phantoms to understand the effect of injury and suturing on human skin mechanical properties.

PubMed

Chanda, Arnab; Unnikrishnan, Vinu; Flynn, Zachary; Lackey, Kim

2017-01-01

Skin injuries are the most common type of injuries occurring in day-to-day life. A skin injury usually manifests itself in the form of a wound or a cut. While a shallow wound may heal by itself within a short time, deep wounds require surgical interventions such as suturing for timely healing. To date, suturing practices are based on a surgeon's experience and may vary widely from one situation to another. Understanding the mechanics of wound closure and suturing of the skin is crucial to improve clinical suturing practices and also to plan automated robotic surgeries. In the literature, phenomenological two-dimensional computational skin models have been developed to study the mechanics of wound closure. Additionally, the effect of skin pre-stress (due to the natural tension of the skin) on wound closure mechanics has been studied. However, in most of these analyses, idealistic two-dimensional skin geometries, materials and loads have been assumed, which are far from reality, and would clearly generate inaccurate quantitative results. In this work, for the first time, a biofidelic human skin tissue phantom was developed using a two-part silicone material. A wound was created on the phantom material and sutures were placed to close the wound. Uniaxial mechanical tests were carried out on the phantom specimens to study the effect of varying wound size, quantity, suture and pre-stress on the mechanical behavior of human skin. Also, the average mechanical behavior of the human skin surrogate was characterized using hyperelastic material models, in the presence of a wound and sutures. To date, such a robust experimental study on the effect of injury and sutures on human skin mechanics has not been attempted. The results of this novel investigation will provide important guidelines for surgical planning and validation of results from computational models in the future.

A simplified in vivo approach for evaluating the bioabsorbable behavior of candidate stent materials.

PubMed

Pierson, Daniel; Edick, Jacob; Tauscher, Aaron; Pokorney, Ellen; Bowen, Patrick; Gelbaugh, Jesse; Stinson, Jon; Getty, Heather; Lee, Chee Huei; Drelich, Jaroslaw; Goldman, Jeremy

2012-01-01

Metal stents are commonly used to revascularize occluded arteries. A bioabsorbable metal stent that harmlessly erodes away over time may minimize the normal chronic risks associated with permanent implants. However, there is no simple, low-cost method of introducing candidate materials into the arterial environment. Here, we developed a novel experimental model where a biomaterial wire is implanted into a rat artery lumen (simulating bioabsorbable stent blood contact) or artery wall (simulating bioabsorbable stent matrix contact). We use this model to clarify the corrosion mechanism of iron (≥99.5 wt %), which is a candidate bioabsorbable stent material due to its biocompatibility and mechanical strength. We found that iron wire encapsulation within the arterial wall extracellular matrix resulted in substantial biocorrosion by 22 days, with a voluminous corrosion product retained within the vessel wall at 9 months. In contrast, the blood-contacting luminal implant experienced minimal biocorrosion at 9 months. The importance of arterial blood versus arterial wall contact for regulating biocorrosion was confirmed with magnesium wires. We found that magnesium was highly corroded when placed in the arterial wall but was not corroded when exposed to blood in the arterial lumen for 3 weeks. The results demonstrate the capability of the vascular implantation model to conduct rapid in vivo assessments of vascular biomaterial corrosion behavior and to predict long-term biocorrosion behavior from material analyses. The results also highlight the critical role of the arterial environment (blood vs. matrix contact) in directing the corrosion behavior of biodegradable metals. Copyright © 2011 Wiley Periodicals, Inc.

In Situ Microstructural Control and Mechanical Testing Inside the Transmission Electron Microscope at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Wang, Baoming; Haque, M. A.

2015-08-01

With atomic-scale imaging and analytical capabilities such as electron diffraction and energy-loss spectroscopy, the transmission electron microscope has allowed access to the internal microstructure of materials like no other microscopy. It has been mostly a passive or post-mortem analysis tool, but that trend is changing with in situ straining, heating and electrical biasing. In this study, we design and demonstrate a multi-functional microchip that integrates actuators, sensors, heaters and electrodes with freestanding electron transparent specimens. In addition to mechanical testing at elevated temperatures, the chip can actively control microstructures (grain growth and phase change) of the specimen material. Using nano-crystalline aluminum, nickel and zirconium as specimen materials, we demonstrate these novel capabilities inside the microscope. Our approach of active microstructural control and quantitative testing with real-time visualization can influence mechanistic modeling by providing direct and accurate evidence of the fundamental mechanisms behind materials behavior.

On 3-D inelastic analysis methods for hot section components (base program)

NASA Technical Reports Server (NTRS)

Wilson, R. B.; Bak, M. J.; Nakazawa, S.; Banerjee, P. K.

1986-01-01

A 3-D Inelastic Analysis Method program is described. This program consists of a series of new computer codes embodying a progression of mathematical models (mechanics of materials, special finite element, boundary element) for streamlined analysis of: (1) combustor liners, (2) turbine blades, and (3) turbine vanes. These models address the effects of high temperatures and thermal/mechanical loadings on the local (stress/strain)and global (dynamics, buckling) structural behavior of the three selected components. Three computer codes, referred to as MOMM (Mechanics of Materials Model), MHOST (Marc-Hot Section Technology), and BEST (Boundary Element Stress Technology), have been developed and are briefly described in this report.

Failure criterion for materials with spatially correlated mechanical properties

NASA Astrophysics Data System (ADS)

Faillettaz, J.; Or, D.

2015-03-01

The role of spatially correlated mechanical elements in the failure behavior of heterogeneous materials represented by fiber bundle models (FBMs) was evaluated systematically for different load redistribution rules. Increasing the range of spatial correlation for FBMs with local load sharing is marked by a transition from ductilelike failure characteristics into brittlelike failure. The study identified a global failure criterion based on macroscopic properties (external load and cumulative damage) that is independent of spatial correlation or load redistribution rules. This general metric could be applied to assess the mechanical stability of complex and heterogeneous systems and thus provide an important component for early warning of a class of geophysical ruptures.

EBSD characterization of low temperature deformation mechanisms in modern alloys

NASA Astrophysics Data System (ADS)

Kozmel, Thomas S., II

For structural applications, grain refinement has been shown to enhance mechanical properties such as strength, fatigue resistance, and fracture toughness. Through control of the thermos-mechanical processing parameters, dynamic recrystallization mechanisms were used to produce microstructures consisting of sub-micron grains in 9310 steel, 4140 steel, and Ti-6Al-4V. In both 9310 and 4140 steel, the distribution of carbides throughout the microstructure affected the ability of the material to dynamically recrystallize and determined the size of the dynamically recrystallized grains. Processing the materials at lower temperatures and higher strain rates resulted in finer dynamically recrystallized grains. Microstructural process models that can be used to estimate the resulting microstructure based on the processing parameters were developed for both 9310 and 4140 steel. Heat treatment studies performed on 9310 steel showed that the sub-micron grain size obtained during deformation could not be retained due to the low equilibrium volume fraction of carbides. Commercially available aluminum alloys were investigated to explain their high strain rate deformation behavior. Alloys such as 2139, 2519, 5083, and 7039 exhibit strain softening after an ultimate strength is reached, followed by a rapid degradation of mechanical properties after a critical strain level has been reached. Microstructural analysis showed that the formation of shear bands typically preceded this rapid degradation in properties. Shear band boundary misorientations increased as a function of equivalent strain in all cases. Precipitation behavior was found to greatly influence the microstructural response of the alloys. Additionally, precipitation strengthened alloys were found to exhibit similar flow stress behavior, whereas solid solution strengthened alloys exhibited lower flow stresses but higher ductility during dynamic loading. Schmid factor maps demonstrated that shear band formation behavior was influenced by texturing in these alloys.

Study on influence of vibration behavior of composite material damage by holography

NASA Astrophysics Data System (ADS)

Guo, Linfeng; Zhao, Zhimin; Gao, Mingjuan; Zhuang, Xianzhong

2006-01-01

Composite material has been applied widely in aeronautics, astronautics and some other fields due to their high strength, light weight and antifatigue and etc. But in the application, composite material may be destroyed or damaged, which may have impact on its further applications. Therefore, study on the influence of behavior of composite material damage becomes a hot research. In this paper, the common composite material for aircraft is used as the test object, and a study is conducted to investigate the influence of vibration behavior of composite material damage. The authors adopt the method of light-carrier wave and time-average holography. Compared the interference fringes of composite materials before and after damage, the width of the interference fringes of hologram of the damaged composite material is narrower than that of the fringes before. It means that the off-plane displacement of each point on the test object is larger than before. Based on the elastic mechanics theory, the off-plane displacement is inverse to the bending stiffness, and the bending stiffness of the test object will decrease after it is damaged. In other words, the vibration property of the composite material changes after damages occur. The research results of the paper show that the results accord with the analysis of theory.

Natural stiffening increases flaw tolerance of biological fibers

NASA Astrophysics Data System (ADS)

Giesa, Tristan; Pugno, Nicola M.; Buehler, Markus J.

2012-10-01

Many fibers in biomaterials such as tendon, elastin, or silk feature a nonlinear stiffening behavior of the stress-strain relationship, where the rigidity of the material increases severely as the material is being stretched. Here we show that such nonlinear stiffening is beneficial for a fiber's ability to withstand cracks, leading to a flaw tolerant state in which stress concentrations around cracks are diminished. Our findings, established by molecular mechanics and the derivation of a theoretical scaling law, explain experimentally observed fiber sizes in a range of biomaterials and point to the importance of nonlinear stiffening to enhance their fracture properties. Our study suggests that nonlinear stiffening provides a mechanism by which nanoscale mechanical properties can be scaled up, providing a means towards bioinspired fibrous material and structural design.

The use of a behavioral response system in the USF/NASA toxicity screening test method

NASA Technical Reports Server (NTRS)

Hilado, C. J.; Cumming, H. J.; Packham, S. C.

1977-01-01

Relative toxicity data on the pyrolysis effluents from bisphenol A polycarbonate and wool fabric were obtained, based on visual observations of the behavior of free-moving mice and on an avoidance response behavioral paradigm of restrained rats monitored by an instrumented behavioral system. The initial experiments show an essentially 1:1 correlation between the two systems with regard to first signs of incapacitation, collapse, and death from pyrolysis effluents from polycarbonate. It is hypothesized that similarly good correlations between these two systems might exist for other materials exhibiting predominantly carbon monoxide mechanisms of intoxication. This hypothesis needs to be confirmed, however, by additional experiments. Data with wool fabric exhibited greater variability with both procedures, indicating possibly different mechanisms of intoxication for wool as compared with bisphenol A polycarbonate.

Preface

NASA Astrophysics Data System (ADS)

Lexcellent, C.; Patoor, E.

2004-06-01

This international conference was held between the 18 and the 23th may 2003, in the "Villa Clythia" belonging to the CAES of the french "Comité National de la Recherche Scientifique CNRS" at Fréjus (France). The scope of this EMMC7 conference was about the use of smart materials which permits the conception of some adaptive systems for industrial applications. A special attention was devoted to active and passive controls of damping in structures. The use of this new class of materials (shape memory alloys, piezoelectric ceramics, TRIP steels, ferromagnetic shape memory alloys, ...) implies the development of numerical tools for computer assisted design process. Complexity of the involved material behaviour requires a deep understanding of strain mechanisms (martensitic phase transformation, reorientation process of domains), the use of accurate experimental techniques and advanced modelling approaches at various scale (micro, meso, macroscopic). In this purpose, it is necessary to use some coupled calculations connecting different fields of physics such as thermal, electromagnetism, electricity and mechanics of materials ones. The conference topic gave the opportunity of fruitful discussions between the mechanics of materials communauty and the specialists of damping or passive control. The scientific program contains nine oral sessions and one poster session. - Experimental characterization of the shape memory alloys thermomechanical behavior (two sessions) - Modeling of the shape memory alloy thermomechanical behavior (two sessions) - Ferromagnetic shape memory alloys behavior (one session) - Piezoelectric ceramics behavior (one session) - Transformation induced plasticity steel behavior (one session) - Hybrid structures including smart materials as sensor or actuator (one session) - Adaptive structure for vibration control (one session) - Poster session. The conference programm contains 50 lectures. 57 scientists were present and come from 14 different countries: 20 from France, 7 from Germany, 6 from Italy, 4 from Russia, 4 from Finland and 5 from USA ... This scientific programm allows all the participants interesting exchanges on "the state of art" about smart materials and adaptive systems. In the aim of its publication in the Proceedings of the EMMC7 Conference (EDP Sciences "Journal de Physique IV") each paper was expertised by two reviewers belonging to the International Scientific Committee and also other specialists. On that occasion, we will thank them for their very important contribution of the scientific level quality of the Proceedings. We will also thank: the sponsors of the Conference: Délégation Générale aux Armements (DGA), le Ministère de la Recherche, l'Université de Metz, l'ENSAM, le CNRS, l'Association Française de Mécanique et l'Institut des Microtechniques de Franche-Comté, the members of the organizing committee, the MECAMAT committee for trusting us, EDP Sciences for the Proceedings, The "Villa Clythia" team for his nice help in the material organization, ... and all the participants. The Co-chairmen Christian LEXCELLENT et Étienne PATOOR

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

NASA Astrophysics Data System (ADS)

Jiang, Can; Wang, Hongyu; Ma, Xiaobing

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

Reduction of Noise from Disc Brake Systems Using Composite Friction Materials Containing Thermoplastic Elastomers (TPEs)

NASA Astrophysics Data System (ADS)

Masoomi, Mohsen; Katbab, Ali Asghar; Nazockdast, Hossein

2006-09-01

Attempts have been made for the first time to prepare a friction material with the characteristic of thermal sensitive modulus, by the inclusion of thermoplastic elastomers (TPE) as viscoelastic polymeric materials into the formulation in order to the increase the damping behavior of the cured friction material. Styrene butadiene styrene (SBS), styrene ethylene butylene styrene (SEBS) and nitrile rubber/polyvinyl chloride (NBR/PVC) blend system were used as TPE materials. In order to evaluate the viscoelastic parameters such as loss factor (tan δ) and storage modulus (E‧) for the friction material, dynamic mechanical analyzer (DMA) were used. Natural frequencies and mode shapes of friction material and brake disc were determined by modal analysis. However, NBR/PVC and SEBS were found to be much more effective in damping behavior. The results from this comparative study suggest that the damping characteristics of commercial friction materials can be strongly affected by the TPE ingredients. This investigation also confirmed that the specimens with high TPE content had low noise propensity.

The hygroscopic behavior of plant fibers: a review.

PubMed

Célino, Amandine; Fréour, Sylvain; Jacquemin, Frédéric; Casari, Pascal

2013-01-01

Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper.

The hygroscopic behavior of plant fibers: a review

PubMed Central

Célino, Amandine; Fréour, Sylvain; Jacquemin, Frédéric; Casari, Pascal

2013-01-01

Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper. PMID:24790971

Creep Behavior of ABS Polymer in Temperature-Humidity Conditions

NASA Astrophysics Data System (ADS)

An, Teagen; Selvaraj, Ramya; Hong, Seokmoo; Kim, Naksoo

2017-04-01

Acrylonitrile-Butadiene-Styrene (ABS), also known as a thermoplastic polymer, is extensively utilized for manufacturing home appliances products as it possess impressive mechanical properties, such as, resistance and toughness. However, the aforementioned properties are affected by operating temperature and atmosphere humidity due to the viscoelasticity property of an ABS polymer material. Moreover, the prediction of optimum working conditions are the little challenging task as it influences the final properties of product. This present study aims to develop the finite element (FE) models for predicting the creep behavior of an ABS polymeric material. In addition, the material constants, which represent the creep properties of an ABS polymer material, were predicted with the help of an interpolation function. Furthermore, a comparative study has been made with experiment and simulation results to verify the accuracy of developed FE model. The results showed that the predicted value from FE model could agree well with experimental data as well it can replicate the actual creep behavior flawlessly.

Universal deformation pathways and flexural hardening of nanoscale 2D-material standing folds

NASA Astrophysics Data System (ADS)

Chacham, Helio; Barboza, Ana Paula M.; de Oliveira, Alan B.; de Oliveira, Camilla K.; Batista, Ronaldo J. C.; Neves, Bernardo R. A.

2018-03-01

In the present work, we use atomic force microscopy nanomanipulation of 2D-material standing folds to investigate their mechanical deformation. Using graphene, h-BN and talc nanoscale wrinkles as testbeds, universal force-strain pathways are clearly uncovered and well-accounted for by an analytical model. Such universality further enables the investigation of each fold bending stiffness κ as a function of its characteristic height h 0. We observe a more than tenfold increase of κ as h 0 increases in the 10-100 nm range, with power-law behaviors of κ versus h 0 with exponents larger than unity for the three materials. This implies anomalous scaling of the mechanical responses of nano-objects made from these materials.

Understanding the Effect of Ni on Mechanical and Wear Properties of Low-Carbon Steel from a View-Point of Electron Work Function

NASA Astrophysics Data System (ADS)

Lu, Hao; Huang, Xiaochen; Hou, Runfang; Li, D. Y.

2018-07-01

Electron work function (EWF) is correlated to intrinsic properties of metallic materials and can be an alternative parameter to obtain supplementary clues for guiding material design and modification. A higher EWF corresponds to a more stable electronic state, leading to higher resistance to any attempt to change the material structure and properties. In this study, effects of Ni as a solute with a higher EWF on mechanical, electrochemical, and tribological properties of low-carbon steel were investigated. Added Ni, which has more valence electrons, enhanced the electrons-nuclei interaction in the steel, corresponding to higher EWF. As a result, the Ni-added steel showed increased mechanical strength and corrosion resistance, resulting in higher resistances to wear and corrosive wear. Mechanism for the improvements is elucidated through analyzing EWF-related variations in Young's modulus, hardness, corrosion potential, and tribological behavior.

Understanding the Effect of Ni on Mechanical and Wear Properties of Low-Carbon Steel from a View-Point of Electron Work Function

NASA Astrophysics Data System (ADS)

Lu, Hao; Huang, Xiaochen; Hou, Runfang; Li, D. Y.

2018-04-01

Electron work function (EWF) is correlated to intrinsic properties of metallic materials and can be an alternative parameter to obtain supplementary clues for guiding material design and modification. A higher EWF corresponds to a more stable electronic state, leading to higher resistance to any attempt to change the material structure and properties. In this study, effects of Ni as a solute with a higher EWF on mechanical, electrochemical, and tribological properties of low-carbon steel were investigated. Added Ni, which has more valence electrons, enhanced the electrons-nuclei interaction in the steel, corresponding to higher EWF. As a result, the Ni-added steel showed increased mechanical strength and corrosion resistance, resulting in higher resistances to wear and corrosive wear. Mechanism for the improvements is elucidated through analyzing EWF-related variations in Young's modulus, hardness, corrosion potential, and tribological behavior.

Energy Conversion Alternatives Study (ECAS), Westinghouse phase 1. Volume 2: Materials considerations. [materials used in boilers and heat exchangers of energy conversion systems for electric power plants using coal

NASA Technical Reports Server (NTRS)

Thomas, D. E.

1976-01-01

Extensive studies are presented which were carried out on materials behavior in nine advanced energy conversion systems employing coal and coal-derived fuels. The areas of materials behavior receiving particular attention in this regard are: (1) fireside corrosion and erosion in boiler and heat exchanger materials, (2) oxidation and hot corrosion of gas turbine materials, (3) liquid metal corrosion and mass transport, (4) high temperature steam corrosion, (5) compatability of materials with coal slag and MHD seed, (6) reaction of materials with impure helium, (7) allowable stresses for boiler and heat exchanger materials, (8) environmental effects on mechanical properties, and (9) liquid metal purity control and instrumentation. Such information was then utilized in recommending materials for use in the critical components of the power systems, and at the same time to identify materials problem areas and to evaluate qualitatively the difficulty of solving those problems. Specific materials recommendations for critical components of the nine advanced systems under study are contained in summary tables.

Mechanisms of superconductivity investigated by nuclear radiation

NASA Technical Reports Server (NTRS)

Autler, S. H.; Coffey, H. T.; Keller, E. L.; Patterson, A.

1967-01-01

Investigation focused on the behavior of superconducting magnet and its constituent materials during and after exposure to nuclear radiation. The results will indicate the feasibility of their use in diverse applications and various environments.

Stress-dependent crystal structure of lanthanum strontium cobalt ferrite by in situ synchrotron X-ray diffraction

NASA Astrophysics Data System (ADS)

Geiger, Philipp T.; Khansur, Neamul H.; Riess, Kevin; Martin, Alexander; Hinterstein, Manuel; Webber, Kyle G.

2018-02-01

Lanthanum strontium cobalt ferrite La1-xSrxCo1-yFeyO3-δ (LSCF) is one of the most studied mixed ionic-electronic conductor materials due to electrical and transport properties, which are attractive for intermediate temperature solid oxide fuel cells (SOFCs), oxygen permeation membranes, and catalysis. The integration of such materials, however, depends on the thermal as well as mechanical behavior. LSCF exhibits nonlinear hysteresis during compressive stress-strain measurements, marked by a remanent strain and coercive stress, i.e., ferroelasticity. However, the origin of ferroelastic behavior has not been investigated under high compressive stress. This study, therefore, investigates the microscopic origin of stress-induced mechanical behavior in polycrystalline (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ using in situ synchrotron x-ray diffraction. The data presented here reveals that the strain response originates from the intrinsic lattice strain as well as the extrinsic domain switching strain without any apparent change in crystallographic symmetry. A comparison of the calculated microscopic strain contribution with that of a macroscopic measurement indicates a significant change in the relative contributions of intrinsic and extrinsic strain depending on the applied stress state, i.e., under maximum stress and after unloading. Direct evidence of the microscopic origin of stress-strain response outlined in this paper may assist in guiding materials design with the improved mechanical reliability of SOFCs.

A methodology for developing anisotropic AAA phantoms via additive manufacturing.

PubMed

Ruiz de Galarreta, Sergio; Antón, Raúl; Cazón, Aitor; Finol, Ender A

2017-05-24

An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of biomechanical factors for rupture risk assessment. AAA phantoms could be used for experimental validation of the numerical studies and for pre-intervention testing of endovascular grafts. We have applied multi-material 3D printing technology to manufacture idealized AAA phantoms with anisotropic mechanical behavior. Different composites were fabricated and the phantom specimens were characterized by biaxial tensile tests while using a constitutive model to fit the experimental data. One composite was chosen to manufacture the phantom based on having the same mechanical properties as those reported in the literature for human AAA tissue; the strain energy and anisotropic index were compared to make this choice. The materials for the matrix and fibers of the selected composite are, respectively, the digital materials FLX9940 and FLX9960 developed by Stratasys. The fiber proportion for the composite is equal to 0.15. The differences between the composite behavior and the AAA tissue are small, with a small difference in the strain energy (0.4%) and a maximum difference of 12.4% in the peak Green strain ratio. This work represents a step forward in the application of 3D printing technology for the manufacturing of AAA phantoms with anisotropic mechanical behavior. Copyright © 2017 Elsevier Ltd. All rights reserved.

Graphs of Soil Mechanics Tests in Orbit

NASA Technical Reports Server (NTRS)

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Planar biaxial testing of heart valve cusp replacement biomaterials: Experiments, theory and material constants.

PubMed

Labrosse, Michel R; Jafar, Reza; Ngu, Janet; Boodhwani, Munir

2016-11-01

Aortic valve (AV) repair has become an attractive option to correct aortic insufficiency. Yet, cusp reconstruction with various cusp replacement materials has been associated with greater long-term repair failures, and it is still unknown how such materials mechanically compare with native leaflets. We used planar biaxial testing to characterize six clinically relevant cusp replacement materials, along with native porcine AV leaflets, to ascertain which materials would be best suited for valve repair. We tested at least six samples of: 1) fresh autologous porcine pericardium (APP), 2) glutaraldehyde fixed porcine pericardium (GPP), 3) St Jude Medical pericardial patch (SJM), 4) CardioCel patch (CC), 5) PeriGuard (PG), 6) Supple PeriGuard (SPG) and 7) fresh porcine AV leaflets (PC). We introduced efficient displacement-controlled testing protocols and processing, as well as advanced convexity requirements on the strain energy functions used to describe the mechanical response of the materials under loading. The proposed experimental and data processing pipeline allowed for a robust in-plane characterization of all the materials tested, with constants determined for two Fung-like hyperelastic, anisotropic strain energy models. Overall, CC and SPG (respectively PG) patches ranked as the closest mechanical equivalents to young (respectively aged) AV leaflets. Because the native leaflets as well as CC, PG and SPG patches exhibit significant anisotropic behaviors, it is suggested that the fiber and cross-fiber directions of these replacement biomaterials be matched with those of the host AV leaflets. The long-term performance of cusp replacement materials would ideally be evaluated in large animal models for AV disease and cusp repair, and over several months or more. Given the unavailability and impracticality of such models, detailed information on stress-strain behavior, as studied herein, and investigations of durability and valve dynamics will be the best surrogates, as they have been for prosthetic valves. Overall, comparison with Fig. 3 suggests that CC and SPG (respectively PG) patches may be the closest mechanical equivalents to young (respectively aged) AV leaflets. Interestingly, the thicknesses of these materials are close to those reported for porcine and younger human AV leaflets, which may facilitate surgical implantation, by contrast to the thinner APP which has poor handling qualities. Because the native leaflets as well as CC, PG and SPG patches exhibit anisotropic behaviors, from a mechanistic perspective alone, it stands to reason that cardiac surgeons should seek to intraoperatively match the fiber and cross-fiber directions of these replacement biomaterials with those of the repaired AV leaflets. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Mechanical characterization and structural assessment of biocomposites for construction

NASA Astrophysics Data System (ADS)

Christian, Sarah Jane

The objective of this dissertation is to assess whether or not two particular biocomposite materials, made from hemp fabric and cellulose acetate or polyhydroxybutyrate matrices, are capable of being used for structural and/or construction purposes within in the construction and building industry. The objective of this dissertation was addressed by conducting research to meet the following three goals: (1) to measure the basic mechanical properties of hemp/cellulose acetate and hemp/PHB biocomposites and evaluate if they suitable for use in construction applications, (2) to determine how quickly moisture diffuses into the biocomposite materials and how the moisture affects the mechanical behavior, and (3) to determine how well simple models can predict behavior of structural scale laminates in tension and flexure using biocomposite ply behavior. Compression molding was used to manufacturing the biocomposites from hemp fabric and the themoplastic matrices: cellulose acetate and polyhydroxybutyrate. Four methods for determining the fiber volume fraction were evaluated, and the dissolution method, using different solvents for each matrix type, was used to determine the fiber volume fraction for each composite plate manufactured. Both types of biocomposite were tested in tension, compression, shear, and flexure and the measured properties were compared to wood and engineered wood products to assess whether the biocomposite properties are suitable for use in the construction industry. The biocomposites were conditioned in a humid environment to determine the rate of moisture diffusion into the materials. Then saturated specimens and specimens that were saturated and then dried were tested in tension to evaluate how moisture absorption affects the mechanical behavior of the biocomposites. Finally, simple models of laminate behavior based on laminate plate theory were evaluated to determine if ply level behavior could be used to predict structural scale laminate behavior. While the biocomposite strengths in flexure, compression, and shear were comparable to the strengths of wood and wood-based products parallel to grain, the biocomposite strengths exceeded the strengths perpendicular to the wood grain, as would be expected with fabric reinforcement. The biocomposite moduli of elasticity were between 35% and 75% of the wood moduli parallel to grain. While structural shape of the biocomposites could be manipulated to achieve a comparable structural stiffness to replace wood and short fiber FRPs, the biocomposites have comparable stiffness to the engineered wood-products. Thus, in terms of mechanical properties, the biocomposites can be used in place of engineered-wood products. Yet, the higher densities of the biocomposites as compared to wood and engineered-wood products may limit their implementation in construction. The diffusion coefficients for both biocomposites were comparable to wood and higher than the coefficients for synthetic composites as expected due to the hydrophilicity of the natural fibers. Significantly greater moisture absorption of the hemp/cellulose acetate composite as compared to the hemp/PHB composite was attributed to the cellulose acetate itself being hydrophilic whereas PHB is hydrophobic. The rate of diffusion for both materials was found to increase with increasing temperature. Moisture absorption negatively affected the biocomposites as shown through lower initial stiffnesses and higher strains at failure of saturated specimens. The hemp/cellulose acetate composites were much more affected by moisture absorption than the hemp/PHB composites likely because the moisture plasticized the cellulose acetate and also weakened the interfacial fiber-matrix bond. Moisture was assumed to cause permanent damage because the stress-strain behavior did not return to the unconditioned behavior upon drying of the saturated specimens. The degradation of mechanical properties upon introduction to humid environments limits the potential applications of these biocomposites. For these biocomposites to be used widely within the construction industry, they must therefore be protected from moisture for example through sealants and/or fiber treatments. Classical laminate plate theory was shown to be effective in predicting the initial linear behavior of all of the laminates in tension and flexure, but did not capture stiffness degradation or the full nonlinear stress-strain response of the biocomposites because the model was for linear elastic materials. Use of this model would be appropriate for design of deflection-limited applications within certain stress ranges. The modified nonlinear laminate plate theory predicted the initial stress-strain response well, but at higher strains overestimated the strength and stiffness. The overestimation was attributed to the constitutive model assuming uncoupled stress-strain behavior for each strain component and, additionally in flexure, to the use of tensile behavior as the constitutive behavior in compression. While the simple models provided an adequate prediction of laminate behavior at low strains, to predict behavior at higher strains, it is recommended instead to evaluate the use of finite element analysis to predict response using experimental stress-strain as models for orthotropic materials and non-linear behavior are well-established. (Abstract shortened by UMI.)

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

NASA Technical Reports Server (NTRS)

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

2006-01-01

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

Corrosion behavior of austenitic steels and their components in niobium-containing chloride melts

NASA Astrophysics Data System (ADS)

Abramov, A. V.; Polovov, I. B.; Rebrin, O. I.; Volkovich, V. A.; Lisienko, D. G.

2014-02-01

The mechanism of corrosion of austenitic steels 12Kh18N10T, 10Kh17N13M2T, and 03Kh17N14M3 and metals Cr, Fe, Ni, and Mo in a NaCl-KCl-NbCl n ( n = 3.5, Nb content is 5 ± 0.1 wt %) melt at 750°C is studied. The metal and steel corrosion rates under these conditions are determined. The character of material fracture and the mechanisms of material corrosion are found.

Theoretical prediction and experimental determination of the effect of mold characteristics on temperature and monomer conversion fraction profiles during polymerization of a PMMA-based bone cement.

PubMed

Vallo, Claudia I

2002-01-01

The present work is concerned with applications of a kinetic model for free-radical polymerization of a polymethylmethacrylate-based bone cement. Autocatalytic behavior at the first part of the reaction as well as a diffusion control phenomenon near vitrification are described by the model. Comparison of theoretical computations with experimental measurements for the temperature evolution during batch casting demonstrated the capacity of the proposed model to represent the kinetic behavior of the polymerization reaction. Temperature evolution and monomer conversion were simulated for the cure of the cement in molds made of different materials. The maximum monomer conversion fraction was markedly influenced by the physical properties of the mold material. The unreacted monomer acts as a plasticizer that influences the mechanical behavior of the cement. Hence, the same cement formulation cured in molds of different materials may result in different mechanical response because of the differences in the amounts of residual monomer. Standardization of the mold type to prepare specimens for the mechanical characterization of bone cements is recommended. Theoretical prediction of temperature evolution during hip replacement indicated that for cement thickness lower than 6 mm the peak temperature at the bone-cement interface was below the limit stated for thermal injury (50 degrees C for more than 1 min). The use of thin cement layers is recommended to diminish the risk of thermal injury; however, it is accompanied by an increase in the amount of unreacted monomer present in the cured material. Copyright 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 627-642, 2002

Modeling of the viscoelastic behavior of a polyimide matrix at elevated temperature

NASA Astrophysics Data System (ADS)

Crochon, Thibaut

Use of Polymer Matrix Composite Materials (PMCMs) in aircraft engines requires materials able to withstand extreme service conditions, such as elevated temperatures, high mechanical loadings and an oxidative environment. In such an environment, the polymer matrix is likely to exhibit a viscoelastic behavior dependent on the mechanical loading and temperature. In addition, the combined effects of elevated temperature and the environment near the engines are likely to increase physical as well as chemical aging. These various parameters need to be taken into consideration for the designer to be able to predict the material behavior over the service life of the components. The main objective of this thesis was to study the viscoelastic behavior of a high temperature polyimide matrix and develop a constitutive theory able to predict the material behavior for every of service condition. Then, the model had to have to be implemented into commercially available finite-element software such as ABAQUS or ANSYS. Firstly, chemical aging of the material at service temperature was studied. To that end, a thermogravimetric analysis of the matrix was conducted on powder samples in air atmosphere. Two kinds of tests were performed: i) kinetic tests in which powder samples were heated at a constant rate until complete sublimation; ii) isothermal tests in which the samples were maintained at a constant temperature for 24 hours. The first tests were used to develop a degradation model, leading to an excellent fit of the experimental data. Then, the model was used to predict the isothermal data but which much less success, particularly for the lowest temperatures. At those temperatures, the chemical degradation was preceded by an oxidation phase which the model was not designed to predict. Other isothermal degradation tests were also performed on tensile tests samples instead of powders. Those tests were conducted at service temperature for a much longer period of time. The samples masses, volume and tensile properties were recorded after 1, 4, 9 and 17 months. The results of those tests showed that after 17 months, the matrix lost about 5% of its mass and volume and as much as 19%, 30% and 10% of its Young's modulus, stress and strain at break, respectively. The second step consisted in studying the viscoelastic behavior of the matrix under various conditions and develop a constitutive theory to model its mechanical behavior. That theory was developed using the framework laid out by Schapery in 1964, using the Thermodynamics of Irreversible Processes. The main advantage of Schapery-type constitutive theories is that the effects of various parameters such as stresses, temperature and physical ageing can be taken into account by using user-defined explicit nonlinearizing functions. Tensile samples of the material were tested at service temperature using strain gages rosettes in order to study the matrix 3D behavior. It was found that the Poisson's ratio was time-independent, meaning that its retardation times spectrum was the same as the compliance function. Furthermore, at this temperature, it was found that the viscoelastic behavior was independent of the stress level. Those two observations led to the conclusion that the material was linearly viscoelastic and could be represented with a 1D constitutive theory. From this conclusion, and also due to the scarcity of material available, it was decided to use 3-point bending tests for studying the impact of temperature and physical ageing. Following Struik's methodology, the material was heated at ageing temperature and then series of creep tests at increasing intervals were performed. It was found that the material became stiffer as the ageing time increased, but it also became softer for increasing temperatures. A model was developed in which Schapery's nonlinearizing functions were obtained from experimental data. The model was validated with complex thermo-mechanical histories comprising several creep tests as well as temperature up- and down-jumps. The experimental data were predicted with excellent accuracy. Finally, the last step consisted in implementing the constitutive theory into a finite-element software. To that end, a new procedure was developed. Instead of the classical methods which deal with Schapery's hereditary integral, the method went back to the evolution equations which are the basis of the integral. The evolution equations were solved with well-known finite-difference schemes such as Backward-Euler, Crank-Nicholson or Runge-Kutta. The numerical model thus obtained could then easily be implemented into finite-element software. In this thesis, a thorough examination of the mechanical properties of a polyimide matrix was conducted. It was found that for such materials, the service temperature is so elevated that chemical ageing has a defining importance on components life. Furthermore, it was found that viscoelastic behavior was only dependent on temperature and physical ageing, but not on the stress levels. (Abstract shortened by ProQuest.).

Nanoindentation of HMX and Idoxuridine to Determine Mechanical Similarity

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

Burch, Alexandra; Yeager, John; Bahr, David

Assessing the mechanical behavior (elastic properties, plastic properties, and fracture phenomena) of molecular crystals is often complicated by the difficulty in preparing samples. Pharmaceuticals and energetic materials in particular are often used in composite structures or tablets, where the individual grains can strongly impact the solid behavior. Nanoindentation is a convenient method to experimentally assess these properties, and it is used here to demonstrate the similarity in the mechanical properties of two distinct systems: individual crystals of the explosive cyclotetramethylene tetranitramine (HMX) and the pharmaceutical idoxuridine were tested in their as-precipitated state, and the effective average modulus and hardness (whichmore » can be orientation dependent) were determined. Both exhibit a hardness of 1.0 GPa, with an effective reduced modulus of 25 and 23 GPa for the HMX and idoxuridine, respectively. They also exhibit similar yield point behavior. This indicates idoxuridine may be a suitable mechanical surrogate (or “mock”) for HMX. While the methodology to assess elastic and plastic properties was relatively insensitive to specific crystal orientation (i.e., a uniform distribution in properties was observed for all random crystals tested), the indentation-induced fracture properties appear to be much more sensitive to tip-crystal orientation, and an unloading slope analysis is used to demonstrate the need for further refinement in relating toughness to orientation in these materials with relatively complex slip systems and crystal structures. View Full-Text« less

Nanoindentation of HMX and Idoxuridine to Determine Mechanical Similarity

DOE PAGES

Burch, Alexandra; Yeager, John; Bahr, David

2017-11-01

Assessing the mechanical behavior (elastic properties, plastic properties, and fracture phenomena) of molecular crystals is often complicated by the difficulty in preparing samples. Pharmaceuticals and energetic materials in particular are often used in composite structures or tablets, where the individual grains can strongly impact the solid behavior. Nanoindentation is a convenient method to experimentally assess these properties, and it is used here to demonstrate the similarity in the mechanical properties of two distinct systems: individual crystals of the explosive cyclotetramethylene tetranitramine (HMX) and the pharmaceutical idoxuridine were tested in their as-precipitated state, and the effective average modulus and hardness (whichmore » can be orientation dependent) were determined. Both exhibit a hardness of 1.0 GPa, with an effective reduced modulus of 25 and 23 GPa for the HMX and idoxuridine, respectively. They also exhibit similar yield point behavior. This indicates idoxuridine may be a suitable mechanical surrogate (or “mock”) for HMX. While the methodology to assess elastic and plastic properties was relatively insensitive to specific crystal orientation (i.e., a uniform distribution in properties was observed for all random crystals tested), the indentation-induced fracture properties appear to be much more sensitive to tip-crystal orientation, and an unloading slope analysis is used to demonstrate the need for further refinement in relating toughness to orientation in these materials with relatively complex slip systems and crystal structures. View Full-Text« less

Coupled DDD-FEM modeling on the mechanical behavior of microlayered metallic multilayer film at elevated temperature

NASA Astrophysics Data System (ADS)

Huang, Minsheng; Li, Zhenhuan

2015-12-01

To investigate the mechanical behavior of the microlayered metallic thin films (MMMFs) at elevated temperature, an enhanced discrete-continuous model (DCM), which couples rather than superposes the two-dimensional climb/glide-enabled discrete dislocation dynamics (2D-DDD) with the linearly elastic finite element method (FEM), is developed in this study. In the present coupling scheme, two especial treatments are made. One is to solve how the plastic strain captured by the DDD module is transferred properly to the FEM module as an eigen-strain; the other is to answer how the stress field computationally obtained by the FEM module is transferred accurately to the DDD module to drive those discrete dislocations moving correctly. With these two especial treatments, the interactions between adjacent dislocations and between dislocation pile-ups and inter-phase boundaries (IBs), which are crucial to the strengthening effect in MMMFs, are carefully taken into account. After verified by comparing the computationally predicted results with the theoretical solutions for a dislocation residing in a homogeneous material and nearby a bi-material interface, this 2D-DDD/FEM coupling scheme is used to model the tensile mechanical behaviors of MMMFs at elevated temperature. The strengthening mechanism of MMMFs and the layer thickness effect are studied in detail, with special attentions to the influence of dislocation climb on them.

Mechanical Properties of Plasma-Sprayed ZrO2-8 wt% Y2O3 Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

2004-01-01

Mechanical behavior of free standing, plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings, including strength, fracture toughness, fatigue, constitutive relation, elastic modulus, and directionality, has been determined under various loading-specimen configurations. This report presents and describes a summary of mechanical properties of the plasma-sprayed coating material to provide them as a design database.

Non-congruence of high-temperature mechanical and structural behaviors of LaCoO 3 based perovskites

DOE PAGES

Aman, Amjad; Jordan, Ryan; Chen, Yan; ...

2016-11-29

Our paper presents the mechanical behavior of LaCoO 3 and La 0.8Ca 0.2CoO3 ceramics under four-point bending in which the two cobaltites are subjected to a low stress of ~8 MPa at temperatures ranging from room temperature to 1000 °C. Unexpected stiffening is observed in pure LaCoO 3 in the 700–900 °C temperature range, leading to a significant increase in the measured Young’s modulus, whereas La 0.8Ca 0.2CoO 3 exhibits softening from 100 °C to 1000 °C, as expected for most materials upon heating. we use neutron diffraction, X-ray diffraction and micro-Raman spectroscopy to study the crystal structure of themore » two materials in the RT–1000 °C temperature range. Despite a detailed study, there is no conclusive evidence to explain the stiffening behavior observed in pure LaCoO 3 as opposed to the softening behavior in La 0.8Ca 0.2CoO 3 at high temperatures (above 500 °C).« less

On the Mechanisms for Martensite Formation in YAG Laser Welded Austenitic NiTi

NASA Astrophysics Data System (ADS)

Oliveira, J. P.; Braz Fernandes, F. M.; Miranda, R. M.; Schell, N.

2016-03-01

Extensive work has been reported on the microstructure of laser-welded NiTi alloys either superelastic or with shape memory effect, motivated by the fact that the microstructure affects the functional properties. However, some effects of laser beam/material interaction with these alloys have not yet been discussed. This paper aims to discuss the mechanisms for the occurrence of martensite in the heat-affected zone and in the fusion zone at room temperature, while the base material is fully austenitic. For this purpose, synchrotron radiation was used together with a simple thermal analytic mathematical model. Two distinct mechanisms are proposed for the presence of martensite in different zones of a weld, which affects the mechanical and functional behavior of a welded component.

Materials data handbook: Aluminum alloy 2014, 2nd edition

NASA Technical Reports Server (NTRS)

Muraca, R. F.; Whittick, J. S.

1972-01-01

A revised edition of the materials data handbook on the aluminum alloy 2014 is presented. The scope of the information presented includes physical and mechanical property data at cryogenic, ambient and elevated temperatures, supplemented with useful information in such areas as material procurement, metallurgy of the alloy, corrosion, environmental effects, fabrication and joining techniques. Design data are presented, as available, and these data are complemented with information on the typical behavior of the alloy.

Method and system for automated on-chip material and structural certification of MEMS devices

DOEpatents

Sinclair, Michael B.; DeBoer, Maarten P.; Smith, Norman F.; Jensen, Brian D.; Miller, Samuel L.

2003-05-20

A new approach toward MEMS quality control and materials characterization is provided by a combined test structure measurement and mechanical response modeling approach. Simple test structures are cofabricated with the MEMS devices being produced. These test structures are designed to isolate certain types of physical response, so that measurement of their behavior under applied stress can be easily interpreted as quality control and material properties information.

Mechanical Adaptivity as a Process: Implications to New Materials and Material System Design

DTIC Science & Technology

2012-08-01

Deliver. Rev. 2004 Microactuators and valves Uses: • Drug delivery • Microfluidic actuators, valves , and pumps • Chemical and biological Sensors... paper where they did a study with f the stoichiometric parameter involved in the reduction step, and they looked at 2 X* - both far away from the...through strain? How do varying material properties affect behavior? Smith, Vaia et al. submitted 2012 23 Fibrous Paper Next Step: Heterogeneous

A General Bioinspired, Metals-Based Synergic Cross-Linking Strategy toward Mechanically Enhanced Materials.

PubMed

Chen, Ke; Ding, Jin; Zhang, Shuhao; Tang, Xuke; Yue, Yonghai; Guo, Lin

2017-03-28

Creating lightweight engineering materials combining high strength and great toughness remains a significant challenge. Despite possessing-enhanced strength and stiffness, bioinspired/polymeric materials usually suffer from clearly reduced extensibility and toughness when compared to corresponding bulk polymer materials. Herein, inspired by tiny amounts of various inorganic impurities for mechanical improvement in natural materials, we present a versatile and effective metal ion (M n+ )-based synergic cross-linking (MSC) strategy incorporating eight types of metal ions into material bulks that can drastically enhance the tensile strength (∼24.1-70.8%), toughness (∼18.6-110.1%), modulus (∼21.6-66.7%), and hardness (∼6.4-176.5%) of multiple types of pristine materials (from hydrophilic to hydrophobic and from unary to binary). More importantly, we also explore the primarily elastic-plastic deformation mechanism and brittle fracture behavior (indentation strain of >5%) of the synergic cross-linked graphene oxide (Syn-GO) paper by means of in situ nanoindentation SEM. The MSC strategy for mechanically enhanced integration can be readily attributed to the formation of the complicated metals-based cross-linking/complex networks in the interfaces and intermolecules between functional groups of materials and various metal ions that give rise to efficient energy dissipation. This work suggests a promising MSC strategy for designing advanced materials with outstanding mechanical properties by adding low amounts (<1.0 wt %) of synergic metal ions serving as synergic ion-bonding cross-linkers.

Thermo-Mechanical and Thermal Behavior of High-Temperature Structural Materials.

DTIC Science & Technology

1980-12-31

glass insulating tape to prevent fracture due to unknown stresses at Lhe rod ends. Because of the very high density of cracks in the alumina, this...143. [31] 0. L. Bowie, J. Math. Phys. 35 (1956) 60. [32] F. Erdogan : in Fracture Mechanics of Ceramics, Vol. 1, ed. by R. C. f Bradt, D. P. H

Sociocultural Mechanisms of Intergenerational Values and Mindset Translation in Modern Family Development and Generational Change

ERIC Educational Resources Information Center

Nemova, Olga A.; Retivina, Veronika V.; Kutepova, Lubov I.; Vinnikova, Irina S.; Kuznetsova, Ekaterina A.

2016-01-01

The paper considers the issue of functioning of the mechanism of formation and translation of values of labor in family. Fundamental labor values and main channels of their distribution are revealed based on empiric material. Family influence on motivation of today's Russian youth's labor behavior was determined. An intergenerational comparative…

Student Assessment System. Domain Referenced Tests. Transportation/Automotive Mechanics. Volume II: Theory. Georgia Vocational Education Program Articulation.

ERIC Educational Resources Information Center

Watkins, James F., Comp.

These written domain referenced tests (DRTs) for the area of transportation/automotive mechanics test cognitive abilities or knowledge of theory. Introductory materials describe domain referenced testing and test development. Each multiple choice test includes a domain statement, describing the behavior and content of the domain, and a test item…

The effect of heat treatment on microstructure evolution in artificially aged carbon nanotube/Al2024 composites synthesized by mechanical alloying

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

Pérez-Bustamante, R.

Although carbon nanotubes/aluminum (CNT/Al) composites are promising materials in the production of structural components, their mechanical behavior under overaging conditions has not been considered. In this paper the effect of CNTs on the microstructural and mechanical behavior of a 2024 aluminum alloy (Al2024) synthesized by mechanical alloying (MA) and powder metallurgy routes is discussed, as well as the effect of aging heat treatments at different temperatures and aging times. The mechanical behavior of composites was screened by hardness measurements as function of aging time. After 96 h of aging time, composites showed mechanical stability in their hardness performance. Images frommore » transmission electron microscopy showed that the mechanical stability of composites was due to a homogeneous dispersion of CNTs in the aluminum matrix and a subsequent alteration in the kinetics of precipitation is due to their presence in the aluminum matrix. Even though strengthening precipitation took place during aging, this was not the main strengthening mechanism observed in composites. - Highlights: • Dispersion of carbon nanotubes during mechanical alloying • Microstructural evolution observed by HRTEM. • Mechanical performance evaluated through micro-hardness test. • Increased mechanical performance at high working temperatures • Acceleration of kinetics of precipitation due to CNTs, and milling conditions.« less

Volumetric influence on the mechanical behavior of organic solids: The case of aspirin and paracetamol addressed via dispersion corrected DFT

NASA Astrophysics Data System (ADS)

Adhikari, Kapil; Flurchick, Kenneth M.; Valenzano, Loredana

2015-06-01

The elastic and mechanical properties of the most stable polymorphs of aspirin and paracetamol are obtained at B3LYP-D2* level of theory to show how effects arising from volumetric expansions related to thermal variations influence the behavior of these materials. Results are in fair agreement with experimental values reported at temperatures far from 0 K, showing that the proposed approach can describe the elastic response of molecular crystals as rationalized in terms of inter-molecular forces. The computational approach, despite its semi-empirical nature, allows achieving a qualitative chemical understanding of the macroscopic mechanical properties of molecular crystals with respect to changes in temperature.

Evaluation of CVI SiC/SiC Composites for High Temperature Applications

NASA Technical Reports Server (NTRS)

Kiser, D.; Almansour, A.; Smith, C.; Gorican, D.; Phillips, R.; Bhatt, R.; McCue, T.

2017-01-01

Silicon carbide fiber reinforced silicon carbide (SiC/SiC) composites are candidate materials for various high temperature turbine engine applications because of their high specific strength and good creep resistance at temperatures of 1400 C (2552 F) and higher. Chemical vapor infiltration (CVI) SiC/SiC ceramic matrix composites (CMC) incorporating Sylramic-iBN SiC fiber were evaluated via fast fracture tensile tests (acoustic emission damage characterization to assess cracking behavior), tensile creep testing, and microscopy. The results of this testing and observed material behavior degradation mechanisms are reviewed.

NASA-UVA Light Aerospace Alloy and Structures Technology Program (LA2ST)

NASA Technical Reports Server (NTRS)

Gangloff, Richard P.; Starke, Edgar A., Jr.; Kelly, Robert G.; Scully, John R.; Shiflet, Gary J.; Stoner, Glenn E.; Wert, John A.

1997-01-01

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA2ST) Program was initiated in 1986 and continues with a high level of activity. Here, we report on progress achieved between July I and December 31, 1996. The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light-weight aerospace alloys, composites and thermal gradient structures in collaboration with NASA-Langley researchers. Specific technical objectives are presented for each research project. We generally aim to produce relevant data and basic understanding of material mechanical response, environmental/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and a pool of educated graduate students for aerospace technologies. The accomplishments presented in this report are summarized as follows. Three research areas are being actively investigated, including: (1) Mechanical and Environmental Degradation Mechanisms in Advanced Light Metals, (2) Aerospace Materials Science, and (3) Mechanics of Materials for Light Aerospace Structures.

Application of the time-temperature superposition principle to the mechanical characterization of elastomeric adhesives for crash simulation purposes

NASA Astrophysics Data System (ADS)

Rauh, A.; Hinterhölzl, R.; Drechsler, K.

2012-05-01

In the automotive industry, finite element simulation is widely used to ensure crashworthiness. Mechanical material data over wide strain rate and temperature ranges are required as a basis. This work proposes a method reducing the cost of mechanical material characterization by using the time-temperature superposition principle on elastomeric adhesives. The method is based on the time and temperature interdependence which is characteristic for mechanical properties of polymers. Based on the assumption that polymers behave similarly at high strain rates and at low temperatures, a temperature-dominated test program is suggested, which can be used to deduce strain rate dependent material behavior at different reference temperatures. The temperature shift factor is found by means of dynamic mechanical analysis according to the WLF-equation, named after Williams, Landel and Ferry. The principle is applied to the viscoelastic properties as well as to the failure properties of the polymer. The applicability is validated with high strain rate tests.

Mechanical stress modified ferroelectric aging behavior

NASA Astrophysics Data System (ADS)

Xu, Tingting; Kan, Yi; Jin, Yaming; Sun, Hui; Du, Yingchao; Wu, Xiumei; Bo, Huifeng; Cai, Wei; Huang, Fengzhen; Lu, Xiaomei; Zhu, Jinsong

2013-05-01

Mechanical stress effect on aging behavior of Bi3.25La0.75Ti3O12 (BLT) and PbZr0.53Ti0.47O3 (PZT) films was investigated. It is found that the remnant polarization decreases with time while the coercive field increases in stress-free BLT films. For unconfined PZT films, both the remnant polarization and the coercive field decrease as time elapses. The applied tensile stress weakens the aging of remnant polarization of BLT films but strengthens the aging of coercive field, while the applied tensile stress possesses opposite effect. In contrary, the applied compressive stress simultaneously improves the aging behavior of both remnant polarization and coercive field of PZT films. Mechanical-stress-induced variation of domain wall mobility in different materials was suggested as the possible origin of these observations. This work indicates that the aging behavior modification using stress could be realized, and it is helpful for promoting the reliability of ferroelectric films for industrial applications.

Family Material Hardship and Chinese Adolescents’ Problem Behaviors: A Moderated Mediation Analysis

PubMed Central

Sun, Wenqiang; Li, Dongping; Zhang, Wei; Bao, Zhenzhou; Wang, Yanhui

2015-01-01

In the current study, we examined a moderated mediation model using the risk and resilience framework. Specifically, the impact of family material hardship on adolescent problem behaviors was examined in a Chinese sample; we used the family stress model framework to investigate parental depression and negative parenting as potential mediators of the relation between family material hardship and adolescents’ problem behaviors. In addition, based on resilience theory, we investigated adolescents’ resilience as a potential protective factor in the development of their internalizing and externalizing problems. Participants included 1,419 Chinese adolescents (mean age = 15.38 years, SD = 1.79) and their primary caregivers. After controlling for covariates (age, gender, location of family residence, and primary caregiver), we found that parental depression and negative parenting mediated the association between family material hardship and adolescents’ problem behaviors. Furthermore, the adolescent resilience moderated the relationship between negative parenting and internalizing problems in a protective-stabilizing pattern; in addition, a protective-reactive pattern also emerged when adolescent resilience was examined as a moderator of the relationship between negative parenting and externalizing problems. These findings contribute to a comprehensive understanding of the mechanisms of risk and resilience in youth development. Moreover, the findings have important implications for the prevention of adolescent problem behaviors. PMID:26010256

A numerical and experimental study of temperature effects on deformation behavior of carbon steels at high strain rates

NASA Astrophysics Data System (ADS)

Pouya, M.; Winter, S.; Fritsch, S.; F-X Wagner, M.

2017-03-01

Both in research and in the light of industrial applications, there is a growing interest in methods to characterize the mechanical behavior of materials at high strain rates. This is particularly true for steels (the most important structural materials), where often the strain rate-dependent material behavior also needs to be characterized in a wide temperature range. In this study, we use the Finite Element Method (FEM), first, to model the compressive deformation behavior of carbon steels under quasi-static loading conditions. The results are then compared to experimental data (for a simple C75 steel) at room temperature, and up to testing temperatures of 1000 °C. Second, an explicit FEM model that captures wave propagation phenomena during dynamic loading is developed to closely reflect the complex loading conditions in a Split-Hopkinson Pressure Bar (SHPB) - an experimental setup that allows loading of compression samples with strain rates up to 104 s-1 The dynamic simulations provide a useful basis for an accurate analysis of dynamically measured experimental data, which considers reflected elastic waves. By combining numerical and experimental investigations, we derive material parameters that capture the strain rate- and temperature-dependent behavior of the C75 steel from room temperature to 1000 °C, and from quasi-static to dynamic loading.

Neutron and X-Ray Diffraction Studies of Advanced Materials

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

Barabash, Rozaliya; Tiley, Jaimie; Wang, Yandong

2010-01-01

The selection of articles in the special topic 'Neutron and X-Ray Studies of Advanced Materials' is based on the materials presented during the TMS 2009 annual meeting in San Francisco, CA, February 15-19, 2009. The development of ultrabrilliant third-generation synchrotron X-ray sources, together with advances in X-ray optics, has created intense X-ray microbeams, which provide the best opportunities for in-depth understanding of mechanical behavior in a broad spectrum of materials. Important applications include ultrasensitive elemental detection by X-ray fluorescence/absorption and microdiffraction to identify phase and strain with submicrometer spatial resolution. X-ray microdiffraction is a particularly exciting application compared with alternativemore » probes of crystalline structure, orientation, and strain. X-ray microdiffraction is nondestructive with good strain resolution, competitive or superior spatial resolution in thick samples, and with the ability to probe below the sample surface. Moreover, the high-energy X-ray diffraction technique provides an effective tool for characterizing the mechanical and functional behavior in various environments (temperature, stress, and magnetic field). At the same time, some neutron diffraction instruments constructed mainly for the purpose of engineering applications can be found at nearly all neutron facilities. The first generation-dedicated instruments designed for studying in-situ mechanical behavior have been commissioned and used, and industrial standards for reliable and repeatable measurements have been developed. Furthermore, higher penetration of neutron beams into most engineering materials provides direct measurements on the distribution of various stresses (i.e., types I, II, and III) beneath the surface up to several millimeters, even tens of millimeters for important industrial components. With X-ray and neutron measurements, it is possible to characterize material behavior at different length scales. It is predicted that the application of these techniques, in combination with theoretical simulations and numerical modeling, will lead to major breakthroughs in materials science in the foreseeable future, which will contribute to the development of materials technology and industrial innovation. Specifically, the use of these techniques provides bulk material properties that further augment new characterization tools including the increased use of atom probe tomography and high-resolution transmission electron microscopy systems. The combination of these techniques greatly assists the material property models that address multi-length-scale mechanisms. Different applications of diffuse scattering for understanding the fundamental materials properties are illustrated in the articles of Welberry et al., Goossens and Welberry, Campbell, Abe et al., Gilles et al., and Zhang et al. Analysis of thin films and two-dimensional structures is described in the articles of Gramlich et al., Brock et al., Vigliante et al., Kuzel et al., and Davydok et al. Recent advances in the line profile analysis are represented by the the articles of Scardi et al., Ungar et al., and Woo et al. Characterization of modern alloys is presented by the articles of Wollmershauser et al., Eidenberger et al., Garlea et al., Jia et al., Soulami et al., Wilson et al., and Wang et al. The collected articles are written by different scientific X-ray and neutron research groups. They represent a general trend in the development and application of diffraction techniques all over the world.« less

Analysis of CFRP Joints by Means of T-Pull Mechanical Test and Ultrasonic Defects Detection.

PubMed

Casavola, Caterina; Palano, Fania; De Cillis, Francesco; Tati, Angelo; Terzi, Roberto; Luprano, Vincenza

2018-04-18

Defects detection within a composite component, with the aim of understanding and predicting its mechanical behavior, is of great importance in the aeronautical field because the irregularities of the composite material could compromise functionality. The aim of this paper is to detect defects by means of non-destructive testing (NDT) on T-pull samples made by carbon fiber reinforced polymers (CFRP) and to evaluate their effect on the mechanical response of the material. Samples, obtained from an industrial stringer having an inclined web and realized with a polymeric filler between cap and web, were subjected to ultrasonic monitoring and then to T-pull mechanical tests. All samples were tested with the same load mode and the same test configuration. An experimental set-up consisting of a semiautomatic C-scan ultrasonic mapping system with a phased array probe was designed and developed, optimizing control parameters and implementing image processing software. The present work is carried out on real composites parts that are characterized by having their intrinsic defectiveness, as opposed to the previous similar results in the literature mainly obtained on composite parts with artificially produced defects. In fact, although samples under study were realized free from defects, ultrasonic mapping found defectiveness inside the material. Moreover, the ultrasonic inspection could be useful in detecting both the location and size of defects. Experimental data were critically analyzed and qualitatively correlated with results of T-pull mechanical tests in order to better understand and explain mechanical behavior in terms of fracture mode.

Analysis of CFRP Joints by Means of T-Pull Mechanical Test and Ultrasonic Defects Detection

PubMed Central

Casavola, Caterina; Palano, Fania; De Cillis, Francesco; Tati, Angelo; Terzi, Roberto; Luprano, Vincenza

2018-01-01

Defects detection within a composite component, with the aim of understanding and predicting its mechanical behavior, is of great importance in the aeronautical field because the irregularities of the composite material could compromise functionality. The aim of this paper is to detect defects by means of non-destructive testing (NDT) on T-pull samples made by carbon fiber reinforced polymers (CFRP) and to evaluate their effect on the mechanical response of the material. Samples, obtained from an industrial stringer having an inclined web and realized with a polymeric filler between cap and web, were subjected to ultrasonic monitoring and then to T-pull mechanical tests. All samples were tested with the same load mode and the same test configuration. An experimental set-up consisting of a semiautomatic C-scan ultrasonic mapping system with a phased array probe was designed and developed, optimizing control parameters and implementing image processing software. The present work is carried out on real composites parts that are characterized by having their intrinsic defectiveness, as opposed to the previous similar results in the literature mainly obtained on composite parts with artificially produced defects. In fact, although samples under study were realized free from defects, ultrasonic mapping found defectiveness inside the material. Moreover, the ultrasonic inspection could be useful in detecting both the location and size of defects. Experimental data were critically analyzed and qualitatively correlated with results of T-pull mechanical tests in order to better understand and explain mechanical behavior in terms of fracture mode. PMID:29669992

Hierarchies, multiple energy barriers, and robustness govern the fracture mechanics of α-helical and β-sheet protein domains

PubMed Central

Ackbarow, Theodor; Chen, Xuefeng; Keten, Sinan; Buehler, Markus J.

2007-01-01

The fundamental fracture mechanisms of biological protein materials remain largely unknown, in part, because of a lack of understanding of how individual protein building blocks respond to mechanical load. For instance, it remains controversial whether the free energy landscape of the unfolding behavior of proteins consists of multiple, discrete transition states or the location of the transition state changes continuously with the pulling velocity. This lack in understanding has thus far prevented us from developing predictive strength models of protein materials. Here, we report direct atomistic simulation that over four orders of magnitude in time scales of the unfolding behavior of α-helical (AH) and β-sheet (BS) domains, the key building blocks of hair, hoof, and wool as well as spider silk, amyloids, and titin. We find that two discrete transition states corresponding to two fracture mechanisms exist. Whereas the unfolding mechanism at fast pulling rates is sequential rupture of individual hydrogen bonds (HBs), unfolding at slow pulling rates proceeds by simultaneous rupture of several HBs. We derive the hierarchical Bell model, a theory that explicitly considers the hierarchical architecture of proteins, providing a rigorous structure–property relationship. We exemplify our model in a study of AHs, and show that 3–4 parallel HBs per turn are favorable in light of the protein's mechanical and thermodynamical stability, in agreement with experimental findings that AHs feature 3.6 HBs per turn. Our results provide evidence that the molecular structure of AHs maximizes its robustness at minimal use of building materials. PMID:17925444

The Interaction of Radio-Frequency Fields With Dielectric Materials at Macroscopic to Mesoscopic Scales

PubMed Central

Baker-Jarvis, James; Kim, Sung

2012-01-01

The goal of this paper is to overview radio-frequency (RF) electromagnetic interactions with solid and liquid materials from the macroscale to the nanoscale. The overview is geared toward the general researcher. Because this area of research is vast, this paper concentrates on currently active research areas in the megahertz (MHz) through gigahertz (GHz) frequencies, and concentrates on dielectric response. The paper studies interaction mechanisms both from phenomenological and fundamental viewpoints. Relaxation, resonance, interface phenomena, plasmons, the concepts of permittivity and permeability, and relaxation times are summarized. Topics of current research interest, such as negative-index behavior, noise, plasmonic behavior, RF heating, nanoscale materials, wave cloaking, polaritonic surface waves, biomaterials, and other topics are overviewed. Relaxation, resonance, and related relaxation times are overviewed. The wavelength and material length scales required to define permittivity in materials is discussed. PMID:26900513

Magnetismo Molecular (Molecular Magentism)

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

Reis, Mario S; Moreira Dos Santos, Antonio F

The new synthesis processes in chemistry open a new world of research, new and surprising materials never before found in nature can now be synthesized and, as a wonderful result, observed a series of physical phenomena never before imagined. Among these are many new materials the molecular magnets, the subject of this book and magnetic properties that are often reflections of the quantum behavior of these materials. Aside from the wonderful experience of exploring something new, the theoretical models that describe the behavior these magnetic materials are, in most cases, soluble analytically, which allows us to know in detail themore » physical mechanisms governing these materials. Still, the academic interest in parallel this subject, these materials have a number of properties that are promising to be used in technological devices, such as in computers quantum magnetic recording, magnetocaloric effect, spintronics and many other devices. This volume will journey through the world of molecular magnets, from the structural description of these materials to state of the art research.« less

Modeling material interfaces with hybrid adhesion method

DOE PAGES

Brown, Nicholas Taylor; Qu, Jianmin; Martinez, Enrique

2017-01-27

A molecular dynamics simulation approach is presented to approximate layered material structures using discrete interatomic potentials through classical mechanics and the underlying principles of quantum mechanics. This method isolates the energetic contributions of the system into two pure material layers and an interfacial region used to simulate the adhesive properties of the diffused interface. The strength relationship of the adhesion contribution is calculated through small-scale separation calculations and applied to the molecular surfaces through an inter-layer bond criterion. By segregating the contributions into three regions and accounting for the interfacial excess energies through the adhesive surface bonds, it is possiblemore » to model each material with an independent potential while maintaining an acceptable level of accuracy in the calculation of mechanical properties. This method is intended for the atomistic study of the delamination mechanics, typically observed in thin-film applications. Therefore, the work presented in this paper focuses on mechanical tensile behaviors, with observations in the elastic modulus and the delamination failure mode. To introduce the hybrid adhesion method, we apply the approach to an ideal bulk copper sample, where an interface is created by disassociating the force potential in the middle of the structure. Various mechanical behaviors are compared to a standard EAM control model to demonstrate the adequacy of this approach in a simple setting. In addition, we demonstrate the robustness of this approach by applying it on (1) a Cu-Cu 2O interface with interactions between two atom types, and (2) an Al-Cu interface with two dissimilar FCC lattices. These additional examples are verified against EAM and COMB control models to demonstrate the accurate simulation of failure through delamination, and the formation and propagation of dislocations under loads. Finally, the results conclude that by modeling the energy contributions of an interface using hybrid adhesion bonds, we can provide an accurate approximation method for studies of large-scale mechanical properties, as well as the representation of various delamination phenomena at the atomic scale.« less

A novel dental implant abutment with micro-motion capability--development and biomechanical evaluations.

PubMed

Chen, Yen-Yin; Chen, Weng-Pin; Chang, Hao-Hueng; Huang, Shih-Hao; Lin, Chun-Pin

2014-02-01

The aim of this study was to develop a novel dental implant abutment with a micro-motion mechanism that imitates the biomechanical behavior of the periodontal ligament, with the goal of increasing the long-term survival rate of dental implants. Computer-aided design software was used to design a novel dental implant abutment with an internal resilient component with a micro-motion capability. The feasibility of the novel system was investigated via finite element analysis. Then, a prototype of the novel dental implant abutment was fabricated, and the mechanical behavior was evaluated. The results of the mechanical tests and finite element analysis confirmed that the novel dental implant abutment possessed the anticipated micro-motion capability. Furthermore, the nonlinear force-displacement behavior apparent in this micro-motion mechanism imitated the movement of a human tooth. The slope of the force-displacement curve of the novel abutment was approximately 38.5 N/mm before the 0.02-mm displacement and approximately 430 N/mm after the 0.03-mm displacement. The novel dental implant abutment with a micro-motion mechanism actually imitated the biomechanical behavior of a natural tooth and provided resilient function, sealing, a non-separation mechanism, and ease-of-use. Copyright © 2013 Academy of Dental Materials. All rights reserved.

Constitutive Theory Developed for Monolithic Ceramic Materials

NASA Technical Reports Server (NTRS)

Janosik, Lesley A.

1998-01-01

With the increasing use of advanced ceramic materials in high-temperature structural applications such as advanced heat engine components, the need arises to accurately predict thermomechanical behavior that is inherently time-dependent and that is hereditary in the sense that the current behavior depends not only on current conditions but also on the material's thermomechanical history. Most current analytical life prediction methods for both subcritical crack growth and creep models use elastic stress fields to predict the time-dependent reliability response of components subjected to elevated service temperatures. Inelastic response at high temperatures has been well documented in the materials science literature for these material systems, but this issue has been ignored by the engineering design community. From a design engineer's perspective, it is imperative to emphasize that accurate predictions of time-dependent reliability demand accurate stress field information. Ceramic materials exhibit different time-dependent behavior in tension and compression. Thus, inelastic deformation models for ceramics must be constructed in a fashion that admits both sensitivity to hydrostatic stress and differing behavior in tension and compression. A number of constitutive theories for materials that exhibit sensitivity to the hydrostatic component of stress have been proposed that characterize deformation using time-independent classical plasticity as a foundation. However, none of these theories allow different behavior in tension and compression. In addition, these theories are somewhat lacking in that they are unable to capture the creep, relaxation, and rate-sensitive phenomena exhibited by ceramic materials at high temperatures. The objective of this effort at the NASA Lewis Research Center has been to formulate a macroscopic continuum theory that captures these time-dependent phenomena. Specifically, the effort has focused on inelastic deformation behavior associated with these service conditions by developing a multiaxial viscoplastic constitutive model that accounts for time-dependent hereditary material deformation (such as creep and stress relaxation) in monolithic structural ceramics. Using continuum principles of engineering mechanics, we derived the complete viscoplastic theory from a scalar dissipative potential function.

Miniaturization of Micro-Solder Bumps and Effect of IMC on Stress Distribution

NASA Astrophysics Data System (ADS)

Choudhury, Soud Farhan; Ladani, Leila

2016-07-01

As the joints become smaller in more advanced packages and devices, intermetallic (IMCs) volume ratio increases, which significantly impacts the overall mechanical behavior of joints. The existence of only a few grains of Sn (Tin) and IMC materials results in anisotropic elastic and plastic behavior which is not detectable using conventional finite element (FE) simulation with average properties for polycrystalline material. In this study, crystal plasticity finite element (CPFE) simulation is used to model the whole joint including copper, Sn solder and Cu6Sn5 IMC material. Experimental lap-shear test results for solder joints from the literature were used to validate the models. A comparative analysis between traditional FE, CPFE and experiments was conducted. The CPFE model was able to correlate the experiments more closely compared to traditional FE analysis because of its ability to capture micro-mechanical anisotropic behavior. Further analysis was conducted to evaluate the effect of IMC thickness on stress distribution in micro-bumps using a systematic numerical experiment with IMC thickness ranging from 0% to 80%. The analysis was conducted on micro-bumps with single crystal Sn and bicrystal Sn. The overall stress distribution and shear deformation changes as the IMC thickness increases. The model with higher IMC thickness shows a stiffer shear response, and provides a higher shear yield strength.

Microgravity

NASA Image and Video Library

1997-09-09

A test cell for the Mechanics of Granular Materials (MGM) experiment is shown in its on-orbit configuration in Spacehab during preparations for STS-89. The twin locker to the left contains the hydraulic system to operate the experiment. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Note: Because the image on the screen was muted in the original image, its brightness and contrast are boosted in this rendering to make the test cell more visible. Credit: NASA/Marshall Space Flight Center (MSFC)

From elasticity to capillarity in soft materials indentation

NASA Astrophysics Data System (ADS)

Pham, Jonathan T.; Schellenberger, Frank; Kappl, Michael; Butt, Hans-Jürgen

2017-06-01

For soft materials with Young's moduli below 100 kPa, quantifying mechanical and interfacial properties by small scale indentation is challenging because in addition to adhesion and elasticity, surface tension plays a critical role. Until now, microscale contact of very soft materials has only been studied by static experiments under zero external loading. Here we introduce a combination of the colloidal probe technique and confocal microscopy to characterize the force-indentation and force-contact radius relationships during microindentation of soft silicones. We confirm that the widespread Johnson-Kendall-Roberts theory must be extended to predict the mechanical contact for soft materials. Typically a liquid component is found within very soft materials. With a simple analytical model, we illustrate that accounting for this liquid surface tension can capture the contact behavior. Our results highlight the importance of considering liquid that is often associated with soft materials during small scale contact.

Mechanical Properties of Air Plasma Sprayed Environmental Barrier Coating (EBC) Materials

NASA Technical Reports Server (NTRS)

Richards, Bradley; Zhu, Dongming; Ghosn, Louis; Wadley, Haydn

2015-01-01

Development work in Environmental Barrier Coatings (EBCs) for Ceramic Matrix Composites (CMCs) has focused considerably on the identification of materials systems and coating architectures to meet application needs. The evolution of these systems has occurred so quickly that modeling efforts and requisite data for modeling lag considerably behind development. Materials property data exists for many systems in the bulk form, but the effects of deposition on the critical properties of strength and fracture behavior are not well studied. We have plasma sprayed bulk samples of baseline EBC materials (silicon, ytterbium disilicate) and tested the mechanical properties of these materials to elicit differences in strength and toughness. We have also endeavored to assess the mixed-mode fracture resistance, Gc, of silicon in a baseline EBC applied to SiCSiC CMC via four point bend test. These results are compared to previously determined properties of the comparable bulk material.

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.

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.

ICME for Crashworthiness of TWIP Steels: From Ab Initio to the Crash Performance

NASA Astrophysics Data System (ADS)

Güvenç, O.; Roters, F.; Hickel, T.; Bambach, M.

2015-01-01

During the last decade, integrated computational materials engineering (ICME) emerged as a field which aims to promote synergetic usage of formerly isolated simulation models, data and knowledge in materials science and engineering, in order to solve complex engineering problems. In our work, we applied the ICME approach to a crash box, a common automobile component crucial to passenger safety. A newly developed high manganese steel was selected as the material of the component and its crashworthiness was assessed by simulated and real drop tower tests. The crashworthiness of twinning-induced plasticity (TWIP) steel is intrinsically related to the strain hardening behavior caused by the combination of dislocation glide and deformation twinning. The relative contributions of those to the overall hardening behavior depend on the stacking fault energy (SFE) of the selected material. Both the deformation twinning mechanism and the stacking fault energy are individually well-researched topics, but especially for high-manganese steels, the determination of the stacking-fault energy and the occurrence of deformation twinning as a function of the SFE are crucial to understand the strain hardening behavior. We applied ab initio methods to calculate the stacking fault energy of the selected steel composition as an input to a recently developed strain hardening model which models deformation twinning based on the SFE-dependent dislocation mechanisms. This physically based material model is then applied to simulate a drop tower test in order to calculate the energy absorption capacity of the designed component. The results are in good agreement with experiments. The model chain links the crash performance to the SFE and hence to the chemical composition, which paves the way for computational materials design for crashworthiness.

Symposium II: Mechanochemistry in Materials Science, MRS Fall Meeting, Nov 30-Dec 4, 2009, Boston, MA

DTIC Science & Technology

2010-09-02

Dynamic Mechanical Analysis (DMA). The fracture behavior of the mechanophore-linked polymer is also examined through the Double Cleavage Drilled ...multinary complex structures. Structural, microstructural, and chemical characterizations were explored by metrological tools to support this...simple hydrocarbons in order to quantitatively define structure-property relationships for reacting materials under shock compression. Embedded gauge

Core-shell chromium silicide-silicon nanopillars: a contact material for future nanosystems.

PubMed

Chang, Mu-Tung; Chen, Chih-Yen; Chou, Li-Jen; Chen, Lih-Juann

2009-11-24

Chromium silicide nanostructures are fabricated inside silicon nanopillars grown by the vapor-liquid-solid mechanism. The remarkable field-emission behavior of these nanostructures results from extensive improvement of carrier transport due to the reduced energy barrier between the metal and semiconductor layers. The results warrant consideration of chromium silicide as a potentially important contact material in future nanosystems.

Materials characterization and fracture mechanics of a space grade dielectric silicone insulation

NASA Technical Reports Server (NTRS)

Abdel-Latif, A. I.; Tweedie, A. T.

1982-01-01

The present investigation is concerned with the DC 93-500 high voltage silicone insulation material employed to pot the gun and the collector end of a traveling wave tube (TWT) used on the Landsat D Satellite. The fracture mechanics behavior of the silicone resin was evaluated by measuring the slow crack velocity as a function of the opening mode of the stress intensity factor at +25 and -10 C, taking into account various uniaxial discrete strain values. It was found that the silicone resins slow crack growth is faster than that for a high voltage insulation polyurethane material at the same stress intensity factor value and room temperature.