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Mechanical Behavior (mechanical + behavior)
Kinds of Mechanical Behavior Selected AbstractsStatistic Analysis of the Mechanical Behavior of Bulk Metallic Glasses,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Hai Bin Yu The Weibull distribution is used to characterize the mechanical behavior of a bulk metallic glass (BMG). The strength of the BMG is quite stable, while the plasticity is much less stable. The reason is attributed to the fraction and distribution of free volumes, which are sensitive to processing conditions. The results demonstrate the close relationship between the distribution and fraction of free volumes and plasticity in BMGs. [source] Molecular Origins of the Mechanical Behavior of Hybrid GlassesADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Mark S. Oliver Abstract Hybrid organic-inorganic glasses exhibit unique electro-optical properties along with excellent thermal stability. Their inherently mechanically fragile nature, however, which derives from the oxide component of the hybrid glass network together with the presence of terminal groups that reduce network connectivity, remains a fundamental challenge for their integration in nanoscience and energy technologies. We report on a combined synthesis and computational strategy to elucidate the effect of molecular structure on mechanical properties of hybrid glass films. We first demonstrate the importance of rigidity percolation to elastic behavior. Secondly, using a novel application of graph theory, we reveal the complex 3-D fracture path at the molecular scale and show that fracture energy in brittle hybrid glasses is fundamentally governed by the bond percolation properties of the network. The computational tools and scaling laws presented provide a robust predictive capability for guiding precursor selection and molecular network design of advanced hybrid organic-inorganic materials. [source] Bifurcated Mechanical Behavior of Deformed Periodic Porous SolidsADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Srikanth Singamaneni Abstract The transformation of periodic microporous structures fabricated by interference lithography followed by their freezing below glass transition is described. Periodic porous microstructures subjected to internal compressive stresses can undergo sudden structural transformation at a critical strain. The pattern transformation of collapsed pores is caused by the stresses originated during the polymerization of acrylic acid (rubbery component) inside of cylindrical pores and the subsequent solvent evaporation in the organized microporous structure. By confining the polymerization of acrylic acid to localized porous areas complex microscopic periodic structures can be obtained. The control over the mechanical instabilities in periodic porous solids at a sub-micron scale demonstrated here suggests the potential mechanical tunability of photonic, transport, adhesive, and phononic properties of such periodic porous solids. [source] Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Long-term Use In Vivo.JOURNAL OF PROSTHODONTICS, Issue 3 2008Part 1: Characterization of Adhesive Wear, Structure of Retaining Screws Abstract Purpose: The general aim of this study and those presented in Parts 2,4 of this series was to characterize the structure, properties, wear, and fracture of prosthetic retaining screws in fixed detachable hybrid prostheses after long-term use in vivo. This part of the overall investigation addresses whether there are differences in thread wear between the screws closest to the fulcrum and those that are farthest from the fulcrum in fixed detachable hybrid prostheses. Materials and Methods: The total number of prosthetic retaining screws used in this study was 100 (10 new and 90 used). New screws (controls) from Nobel Biocare (NB) were divided into Group 1 (slotted) and Group 2 (hexed). Ninety used screws (in service 18,120 months) were retrieved from fixed detachable hybrid prostheses in 18 patients (5 screws from each patient, 60 from NB and 30 from Sterngold). The used screws were divided into 18 groups. Additionally, each group was subdivided into A and B categories. Category A contained the middle three prosthetic screws, which were considered the farthest screws from the fulcrum line. Category B contained the most posterior two screws, which were considered the screws closest to the fulcrum line. All 100 screws were subjected to thorough, nondestructive testing. Results: Light and scanning electron microscopic examination of all used screws for each group revealed surface deterioration of the active profile of the screw threads consistent with adhesive wear. The observed thread profile deterioration ranged from mild to severe. The wear was aggressive enough to cause galling, which led to thinning of the threads and, in severe cases, to knife-edges at thread crests. In ten groups, the most anterior three screws exhibited more wear than the most posterior two screws. In addition to thread wear, severe plastic deformation was detected on the bottom part of each screw for three groups, and a long external longitudinal crack was detected in one screw of Group 2. Conclusions: The findings of this study and those presented in Parts 2,4 demonstrate that different retaining screws from the same manufacturer and/or from different manufacturers have different geometrical design, microstructures, major alloy constituents, and microhardness, and that these differences influence their preload and fractured load values. In this part of the overall investigation, the occurrence of galling as a result of wear involving prosthetic retaining screws appears to be an inevitable and unavoidable consequence of long-term use in vivo in fixed detachable hybrid prostheses regardless of the intended/original preload value. The galling rate is greater on the middle three screws compared to the most posterior two screws in fixed detachable hybrid prostheses. The wear pattern is consistent with an adhesive wear mechanism; however, this study does not provide enough data to support a definitive analysis. [source] Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Long-Term Use In Vivo.JOURNAL OF PROSTHODONTICS, Issue 3 2008Microhardness Analysis, Part 2: Metallurgical Abstract Purpose: This study involved testing and analyzing multiple retrieved prosthetic retaining screws after long-term use in vivo to: (1) detect manufacturing defects that could affect in-service behavior; (2) characterize the microstructure and alloy composition; and (3) further characterize the wear mechanism of the screw threads. Materials and Methods: Two new (control) screws from Nobel Biocare (NB) and 18 used (in service 18,120 months) retaining screws [12 from NB and 6 from Sterngold (SG)] were: (1) metallographically examined by light microscopy and scanning electron microscopy (SEM) to determine the microstructure; (2) analyzed by energy dispersive X-ray (EDX) microanalysis to determine the qualitative and semiquantitative average alloy and individual phase compositions; and (3) tested for Vickers microhardness. Results: Examination of polished longitudinal sections of the screws using light microscopy revealed a significant defect in only one Group 4 screw. No significant defects in any other screws were observed. The defect was considered a "seam" originating as a "hot tear" during original casting solidification of the alloy. Additionally, the examination of longitudinal sections of the screws revealed a uniform homogeneous microstructure in some groups, while in other groups the sections exhibited rows of second phase particles. The screws for some groups demonstrated severe deformation of the lower threads and the bottom part of the screw leading to the formation of crevices and grooves. Some NB screws were comprised of Au-based alloy with Pt, Cu, and Ag as alloy elements, while others (Groups 4 and 19) were Pd-based with Ga, Cu, and Au alloy elements. The microstructure was homogeneous with fine or equiaxed grains for all groups except Group 4, which appeared inhomogeneous with anomalous grains. SG screws demonstrated a typical dendritic structure and were Au-based alloy with Cu and Ag alloy elements. There were differences in the microhardness of gold alloy screws from NB and SG as well as palladium alloy screws from NB. Conclusions: Significant differences within NB retaining screws and between NB and SG screws were found for microstructure, major alloy constituents, and microhardness. [source] Processing and Mechanical Behavior of CrN/ZrO2(2Y) CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Yoshihiko Takano CrN powder consisting of granular particles of ,3 ,m has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2(2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness (KIC) of 3.3 MPa ·m1/2 and a bending strength (,b) of 400 MPa. In the latter materials almost all of the ZrO2(2Y) grains (0.36,0.41 ,m) are located in the grain boundaries of CrN (,4.6 ,m). The values of KIC (6.1 MPa · m1/2) and ,b (1070 MPa) are obtained in the composites containing 50 vol% ZrO2(2Y). [source] pH Tailoring Electrical and Mechanical Behavior of Polymer,Clay,Nanotube AerogelsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2009Matthew D. Gawryla Abstract Aerogels are low density (<0.1,g,·,cm,3), highly porous materials that are especially interesting for insulating applications. Combinations of clay and water-soluble polymers are commonly used to produce aerogels, but these materials are often mechanically weak. Single-walled carbon nanotubes (SWNT) were combined with clay and found to significantly improve mechanical behavior and impart electrical conductivity to these aerogels. Poly(acrylic acid) (PAA) as the matrix polymer provides a means of tailoring the electrical conductivity and mechanical behavior by altering the pH of the aqueous aerogel precursor suspensions prior to freeze drying. An aerogel, made from a pH 9 aqueous suspension containing 0.5,wt.-% PAA, 5,wt.-% clay, and 0.05,wt.-% SWNT, has a compressive modulus of 373,kPa. In the absence of nanotubes, this modulus is reduced to 43,kPa. Reducing suspension pH to 3, prior to freeze drying, also reduces modulus for these aerogels, but electrical conductivity is increased when nanotubes are present. It was found that bundled nanotubes provide better reinforcement for these low-density composites, which may provide some new insight into the use of nanotubes in materials that will be exposed to compressive loading. [source] Mechanical Behavior and Stability of the Internal Membrane of the InCor Ventricular Assist DeviceARTIFICIAL ORGANS, Issue 11 2001Pedro Baroni Da Costa Teixeira Abstract: This paper describes and analyzes the mechanical behavior of the internal membrane of the InCor VAD (Heart Institute [InCor], University of São Paulo, Brazil), applying the knowledge and tools of structural engineering analysis. This membrane plays an important role in the operation of the ventricular assist device (VAD) because it separates the blood chamber from the pneumatic one, transmitting the pneumatic load to the blood, thus making the desired blood flow possible. The loading repeats itself every time the VAD beats. Therefore the performance, reliability, and durability of the membrane are critical for the performance of the VAD. The mathematical model is based on the large deflection theory of thin shells and on the finite element method. The snap-through instability phenomenon, which is responsible for transmission of the pneumatic load to the blood, was observed in the membrane both when modeled mathematically and experimentally. Principal stresses and strain distributions were obtained with this model at certain load levels along the pre- and postbuckling paths. [source] Mechanical behavior of bovine periodontal ligament under tension-compression cyclic displacementsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2006Tatsuya Shibata In the present study, the mechanical response of bovine periodontal ligament (PDL) subjected to displacement-controlled tension,compression harmonic oscillations and subsequent rupture was examined. Specimens including dentine, cementum, PDL, and alveolar bone were extracted from different depths and locations of bovine first molars. They were immersed in a saline solution at room temperature and clamped on their bone and dentine extremities. The samples were tested at ±35% of the PDL's width, with a frequency of 1 Hz. The mechanical parameters evaluated were hysteresis, phase lag, and the modulus of the stress,stretch ratio curves in tension and compression. The tensile strength and the corresponding stretch ratio were also recorded. Stress,stretch ratio curves indicated a non-linear, time-dependent response with hysteresis and preconditioning effects. The hysteresis and phase lag in compression were much higher than in tension, suggesting that the dissipated energy was higher in compression than in tension. The root depth and location did not play essential roles for the tension or compression data, with the exception of limited statistical differences for tensile strength and corresponding stretch ratio. Thus, biological variability in the specimens, as a result of different bone contours, PDL width, and fiber orientation, did not affect the energy-absorbing capacity of the PDL. The evolution of the stress rate with stress demonstrated a constant increase of stiffness with stress. The stiffness values were twofold higher in tension than in compression. The data also showed that the stiffness of the PDL was comparable with data reported for other soft tissues. [source] Mechanical behavior of carbon nanofibre-reinforced epoxy compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010Sohel Rana Abstract Epoxy resins are widely used in a variety of applications because of their high chemical and corrosion resistance and good mechanical properties. But few types of epoxy resins are brittle and possess low toughness which makes them unsuitable for several structural applications. In this work, carbon nanofibres have been dispersed uniformly into the epoxy resin at a very low concentration (0.07 vol. %). Improvement of 98% in Young modulus, 24% in breaking stress and 144% in work of rupture was achieved in the best sample. The emphasis is on achieving uniform dispersion of carbon nanofibers into epoxy resin using a combination of techniques such as ultrasonication, use of solvent and surfactants. The fracture surfaces of the specimens were studied under scanning electron microscope to see the fracture mechanism of nanocomposites under tensile load and correlate it to the enhancement in their properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Mechanical behavior of recycled reinforced polyamide railway fastenersPOLYMER COMPOSITES, Issue 7 2010José Antonio Casado Modern railway tracks use short-fiber glass reinforced polyamide to inject insulating and mechanically resistant fasteners to connect the rails to the sleepers. Some of this material is later withdrawn, due either to defective production or to breakage in service. The recovery of the material for its later re-use would lead to a great saving, from both an environmental and an economic viewpoint. Mechanical recycling is a simple, economic process that only requires the crushing of the material and its subsequent molding, without the need for any chemical treatments. However, it has some drawbacks; as with any kind of recycling, there is a certain loss of material quality with some degradation of its properties. In this work, the physical and mechanical results for fasteners injected with recycled material are compared to others injected with pure material. The results show that the use of recycled fasteners is limited in-service by working conditions that increase the thermoplastic material temperature above its critical glass transition temperature, Tg. POLYM. COMPOS., 31:1142,1149, 2010. © 2009 Society of Plastics Engineers [source] Mechanical behavior of cold plasma,treated sisal and high-density polyethylene compositesPOLYMER COMPOSITES, Issue 3 2003Adriana R. Martin Sisal fibers and finely powdered high-density polyethylene were surface functionalized with dichlorosilane on a RF(radio frequency)-plasma reactor. Composites made from sisal and high-density polyethylene were compounded using a thermokinetic mixer. The discharged mass was cooled, granulated, and injected molded into composite specimens for testing. The mechanical behaviors (tensile, impact and thermal dynamical mechanical properties) of composites made from cold plasma-treated and untreated components are compared and discussed. The best mechanical performance was generally obtained for composites where only the inert thermoplastic matrix was plasma-functionalized. Plasma treatment of lignocellulosic fibers seems to induce decomposition processes of the surface layers structures exposed to the plasma that generally does not contribute to significant improvement on the mechanical behavior of the composite. [source] Rho plays a central role in regulating local cell-matrix mechanical interactions in 3D cultureCYTOSKELETON, Issue 6 2007N. Lakshman Abstract The purpose of this study was to assess quantitatively the role of the small GTPase Rho on cell morphology, f-actin organization, and cell-induced matrix remodeling in 3D culture. Human corneal fibroblasts (HTK) were infected with adenoviruses that express green fluorescent protein (GFP) or GFP-N19Rho (dominant negative Rho). One day later cells were plated inside collagen matrices and allowed to spread for 24 h. Cells were fixed and stained for f-actin. Fluorescent (for f-actin) and reflected light (for collagen fibrils) images were acquired using confocal microscopy. Fourier transform analysis was used to assess local collagen fibril alignment, and changes in cell morphology and collagen density were measured using MetaMorph. The decrease in matrix height was used as an indicator of global matrix contraction. HTK and HTK-GFP cells induced significant global matrix contraction; this was inhibited by N19Rho. HTK and HTK-GFP fibroblasts generally had a bipolar morphology and occasional intracellular stress fibers. Collagen fibrils were compacted and aligned parallel to stress fibers and pseudopodia. In contrast, HTK-GFPN19 cells were elongated, and had a more cortical f-actin distribution. Numerous small extensions were also observed along the cell body. In addition, both local collagen fibril density and alignment were significantly reduced. Rho plays a key role in regulating both the morphology and mechanical behavior of corneal fibroblasts in 3D culture. Overall, the data suggest that Rho-kinase dependent cell contractility contributes to global and local matrix remodeling, whereas Rho dependent activation of mDia and/or other downstream effectors regulates the structure and number of cell processes. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] Cost-Affordable Technique Involving Equal Channel Angular Pressing for the Manufacturing of Ultrafine Grained Sheets of an Al,Li,Mg,Sc Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Rustam Kaibyshev A two-step process consisting of modified equal channel angular pressing (ECAP) and subsequent isothermal rolling (IR) was developed to produce thin sheets of aluminum alloys with ultra-fine grained (UFG) structure. Significant increase in the efficiency of ECAP was attained by using flat billets and a back pressure system. The incorporation of final IR into technologic route provides a reduced strain which is necessary to impose for the fabrication of thin sheets with UFG structure. In addition, it allows producing relatively "long billets." In order to demonstrate the feasibility of this technique an Al,5.1Mg,2.1Li,0.17Sc,0.08Zr (wt %) alloy was subjected to ECAP at 325,°C to a total strain of ,8 using processing route CX. The operation time of this processing did not exceed 15,min. Subsequent IR at the same temperature with a total reduction of 88% was applied to produce thin sheets with a 1.8,mm thickness and an average size of recrystallized grains of ,1.6,µm. These sheets exhibit extraordinary high superplastic ductilities. In addition, this material demonstrated almost isotropic mechanical behavior at room temperature. The maximum elongation-to-failure of ,2700% was attained at a temperature of 450,°C and an initial strain rate of 1.4,×,10,2 s,1. Thus it was demonstrated that the two-step processing consisting of ECAP with a back pressure followed by IR was a simple technique providing potential capability for the fabrication of superplastic sheets from an Al,Mg,Li,Sc alloy on a commercial scale. [source] Screening of the Interactions Between Mg-PSZ and TRIP-Steel and Its Alloys During Sintering,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Christian Weigelt Ceramic,steel compound materials are used in a wide range of applications up to date. Major advantages are the mechanical properties due to the combination of brittle ceramic with tough steel. This study deals with effects of the sintering process on austenitic TRIP-steel/Mg-PSZ composite materials for mechanical load applications. Both, the FeCrNisteel and partially stabilized zirconia offer their special mechanical behavior only in a metastable state. The ability of phase transformation depends mainly on the chemical composition. Mutual interactions of the alloying metals (Cr, Ni, Mn, and Fe) and the ceramic stabilizer (MgO) during sintering may prevent the martensitic phase transformation. This may cause disadvantageous mechanical behavior on mechanical load in use. [source] Statistic Analysis of the Mechanical Behavior of Bulk Metallic Glasses,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Hai Bin Yu The Weibull distribution is used to characterize the mechanical behavior of a bulk metallic glass (BMG). The strength of the BMG is quite stable, while the plasticity is much less stable. The reason is attributed to the fraction and distribution of free volumes, which are sensitive to processing conditions. The results demonstrate the close relationship between the distribution and fraction of free volumes and plasticity in BMGs. [source] The Effect of the Superconducting Transition on Plastic Deformation of Ultrafine-Grained Aluminum,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Yuri Estrin Abstract In this paper, the mechanical behavior of ultrafine- and coarse-grained Al at a record low temperature of 0.52,K is presented. It is demonstrated that grain refinement by equal channel angular pressing leads to increased flow stress and to a change in the strain hardening behavior of Al at this temperature. Special emphasis is placed on the effect of the superconducting transition on the mechanical behavior in the different microstructural conditions. It is shown that the magnitude of the stress jump associated with the transition correlates with the strain hardening behavior which, in turn, is related to the microstructure of the material. [source] Determination of Activation Volume in Nanocrystalline Cu Using the Shear Punch Test,ADVANCED ENGINEERING MATERIALS, Issue 10 2007K. Guduru Stress relaxation test (SRT) is very useful to study the dislocation dynamics and thus the deformation behavior. It becomes quite difficult to use conventional testing methods when the material availability is limited. In such instances, miniaturized specimen testing procedures such as shear punch test (SPT) becomes significantly useful for studying the mechanical behavior of materials. Current research deals with a novel SRT method employed on nanocrystalline Cu using SPT to study the deformation mechanism. [source] Bio-mimetic scaling of mechanical behavior of thin films, coatings, and surfaces by Laser Interference MetallurgyADVANCED ENGINEERING MATERIALS, Issue 9 2005C. Daniel Biological solutions to enhance strength and stability often use hierarchical composite structures. The effect is not based on large chemical variations, but instead is realized by structural composites with long-range order. Laser Interference Metallurgy is a newly developed technique that utilizes this biological approach to optimize the mechanical properties of surfaces and thin films. The possibility of scaling mechanical properties is quantitatively analyzed and compared with the biological approach. [source] High-Pressure Synthesis of Tantalum Nitride Having Orthorhombic U2S3 StructureADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Andreas Zerr Abstract Among binary compounds, there is a high potential for discovery of novel members (polymorphic phases or compounds) of the nitrides of transition metals group due to a pronounced dependence of the oxidation state of the metals (M) on pressure. The power of high pressure,high temperature (HP-HT) route for synthesis of binary nitrides has already been demonstrated by the discovery of cubic nitrides of the group 4 and 14 elements, of crystalline polymorphs of P3N5, and by reports on formation of four noble metal nitrides. It is anticipated that such HP products exhibit, in addition to enhanced elastic and mechanical behavior, other functional properties making them interesting for industrial applications. Here, HP,HT synthesis research is extended to nitrides of group 5 elements, resulting in the discovery of a novel hard tantalum nitride, exhibiting U2S3 structure: , -Ta2N3 (Pbnm, a,=,8.1911(17),Å, b,=,8.1830(17),Å, c,=,2.9823(3),Å). The stoichiometry is supported by two independent means, verifying that , -Ta2N3 is the first thermodynamically stable transition metal nitride with a N:M ratio exceeding 4:3. Due to its high hardness and peculiar texture (needle-like and granular crystallites), , -Ta2N3 may find practical applications as a hard fracture resistant material. [source] Influence of inherent anisotropy on mechanical behavior of granular materials based on DEM simulationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2010Zafar Mahmood Abstract We study the influence of inherent anisotropy, i.e. bedding angle on stress,strain behavior and shear band formation in quasi-static granular media. Plane strain biaxial tests are carried out using two-dimensional distinct element method (DEM). Oval/elliptical-shaped particles are generated by overlapping the discrete circular elements. Particle assemblies with four different bedding angles are tested. Evolution of the microstructure inside and outside the shear band and effect of bedding angle on the microstructure are investigated. Influence of bedding angle on fabric and force anisotropy is studied. It is found that by using non-circular particles, generation of large voids and excess particle rotations inside the shear band are reproduced in a quite similar manner to those of the natural granular soils, which are difficult to produce with standard DEM simulations using circular particles. Copyright © 2009 John Wiley & Sons, Ltd. [source] A new Cosserat-like constitutive model for bedded salt rocksINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2009Yin-Ping Li Abstract Salt rocks are commonly used as geologic host rocks for storage of gas and crude oil, and are being considered for the disposal of radioactive waste. Different from the salt rock domes in many countries, the salt rock formations in China are usually laminar with many alternating layers, i.e. rock salt, anhydrite, and/or mudstone. Considering the unique stratigraphic characteristics of these salt rocks, a new Cosserat-like medium constitutive model is proposed in order to facilitate efficient modeling of the mechanical behavior of these formations. In this model, a new representative volume element, containing two different layers, is employed to simulate the compatibility of the meso-displacement between two different layers and also the bending effect. A new method for the deformation and failure analysis of bedded salt rocks is derived therefrom. Having the macro-average stresses, the conventional stresses in the different layers can be obtained in sequence. The conventional stresses can then be utilized in a routine way for the strength and failure analysis. For the initial numerical modeling, the new Cosserat-like medium is reduced to a transversely isotropic one. The simplified constitutive model for layered media is then implemented into FLAC3D codes. A test sample validates that the results by using the numerical model are in good agreement with that by using the built-in model, and the mesh size for the new model is reduced greatly. Finally, an application for the stability of oil storage caverns in deep thinly bedded salt rocks is carried out. The effects on convergence of storage caverns and on the failure of surrounding rock due to the presence of the mudstone interlayers (hard phase) are discussed in detail. Copyright © 2009 John Wiley & Sons, Ltd. [source] A multiscale modeling of damage and time-dependent behavior of cohesive rocksINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2009A. Abou-Chakra Guéry Abstract The present paper deals with a micromechanical approach to modeling the time-dependent mechanical behavior of a class of cohesive geomaterials. The considered material is Callovo-Oxfordian argillite, which is mainly composed of three constituents: an elastoviscoplastic clay matrix, elastic quartz minerals, and elastic damaged calcite grains. The macroscopic constitutive law is obtained by adapting the incremental method proposed by Hill (J. Mech. Phys. Solids 1965; 13:89,101). Its unified formulation allows a description of not only the time-dependent behavior of the argillite but also its elastoplastic damage response. The developed model is first validated by comparison with finite element solutions and then it is applied to the prediction of argillites' macroscopic responses in connection with their mineralogical compositions. The validity of the model is checked through comparisons between the model's predictions and experimental data. Copyright © 2008 John Wiley & Sons, Ltd. [source] A model for pore-fluid-sensitive rock behavior using a weathering state parameterINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 16 2008R. J. Hickman Abstract Chalk and other porous rocks are known to behave differently when saturated with different pore fluids. The behavior of these rocks varies with different pore fluids and additional deformation occurs when the pore fluid composition changes. In this article, we review the evidence that behavior in porous rocks is pore-fluid-dependent, present a constitutive model for pore-fluid-dependent porous rocks, and present a compilation of previously published data to develop quantitative relationships between various pore fluids and mechanical behavior. The model proposed here is based on a state parameter approach for weathering and has similarities to models previously proposed for weathering-sensitive rocks in that the values for parameters that characterize material behavior vary as a function of weathering. Comparisons with published experimental data indicate that the model is capable of reproducing observed behavior of chalk under a variety of loading conditions and changes in pore fluid composition. Copyright © 2008 John Wiley & Sons, Ltd. [source] Implicit integration of a chemo-plastic constitutive model for partially saturated soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2008H. W. Zhang Abstract A chemo-plastic constitutive model for partially saturated soils is proposed in this paper based on the existing models developed in Hueckel (Int. J. Numer. Anal. Meth. Geomech. 1997; 21:43,72) and Gallipoli et al. (Geotechnique 2003; 53:123,135). The chemical softening effects due to the increase in contaminant mass concentration are considered based on Hueckel's chemo-plastic model. Gallipoli's model is used to simulate the effects of suction and degree of saturation on mechanical behavior of partially saturated porous materials. In order to implement the proposed model in a finite element code, a fully implicit backward-Euler integration algorithm is put forward. Numerical solutions for the tests at local level and the application of the algorithm to the real boundary value problem demonstrate the accuracy and convergence properties of the proposed integration scheme. Copyright © 2008 John Wiley & Sons, Ltd. [source] Random porosity fields and their influence on the stability of granular mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2008José E. Andrade Abstract It is well established that the mechanical behavior of granular media is strongly influenced by the media's microstructure. In this work, the influence of the microstructure is studied by integrating advances in the areas of geostatistics and computational plasticity, by spatially varying the porosity on samples of sand. In particular, geostatistical tools are used to characterize and simulate random porosity fields that are then fed into a nonlinear finite element model. The underlying effective mechanical response of the granular medium is governed by a newly developed elastoplastic model for sands, which readily incorporates spatial variability in the porosity field at the meso-scale. The objective of this study is to assess the influence of heterogeneities in the porosity field on the stability of sand samples. One hundred and fifty isotropic and anisotropic samples of dense sand are failed under plane-strain compression tests using Monte Carlo techniques. Results from parametric studies indicate that the axial strength of a specimen is affected by both the degree and orientation of anisotropy in heterogeneous porosity values with anisotropy orientation having a dominant effect, especially when the bands of high porosity are aligned with the natural orientation of shear banding in the specimen. Copyright © 2007 John Wiley & Sons, Ltd. [source] A uniform nodal strain tetrahedron with isochoric stabilizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2009M. W. Gee Abstract A stabilized node-based uniform strain tetrahedral element is presented and analyzed for finite deformation elasticity. The element is based on linear interpolation of a classical displacement-based tetrahedral element formulation but applies nodal averaging of the deformation gradient to improve mechanical behavior, especially in the regime of near-incompressibility where classical linear tetrahedral elements perform very poorly. This uniform strain approach adopted here exhibits spurious modes as has been previously reported in the literature. We present a new type of stabilization exploiting the circumstance that the instability in the formulation is related to the isochoric strain energy contribution only and we therefore present a stabilization based on an isochoric,volumetric splitting of the stress tensor. We demonstrate that by stabilizing the isochoric energy contributions only, reintroduction of volumetric locking through the stabilization can be avoided. The isochoric,volumetric splitting can be applied for all types of materials with only minor restrictions and leads to a formulation that demonstrates impressive performance in examples provided. Copyright © 2008 John Wiley & Sons, Ltd. [source] Molecular mechanics in the context of the finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2009Jens Wackerfuß Abstract In molecular mechanics, the formalism of the finite element method can be exploited in order to analyze the behavior of atomic structures in a computationally efficient way. Based on the atom-related consideration of the atomic interactions, a direct correlation between the type of the underlying interatomic potential and the design of the related finite element is established. Each type of potential is represented by a specific finite element. A general formulation that unifies the various finite elements is proposed. Arbitrary diagonal- and cross-terms dependent on bond length, valence angle, dihedral angle, improper dihedral angle and inversion angle can also be considered. The finite elements are formulated in a geometrically exact setting; the related formulas are stated in detail. The mesh generation can be performed using well-known procedures typically used in molecular dynamics. Although adjacent elements overlap, a double counting of the element contributions (as a result of the assembly process) cannot occur a priori. As a consequence, the assembly process can be performed efficiently line by line. The presented formulation can easily be implemented in standard finite element codes; thus, already existing features (e.g. equation solver, visualization of the numerical results) can be employed. The formulation is applied to various interatomic potentials that are frequently used to describe the mechanical behavior of carbon nanotubes. The effectiveness and robustness of this method are demonstrated by means of several numerical examples. Copyright © 2008 John Wiley & Sons, Ltd. [source] Influence of Interface Characteristics on the Mechanical Properties of Hi-Nicalon type-S or Tyranno-SA3 Fiber-Reinforced SiC/SiC MinicompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010C. Sauder The tensile behavior of CVI SiC/SiC composites with Hi-Nicalon type-S (Hi-NicalonS) or Tyranno-SA3 (SA3) fibers was investigated using minicomposite test specimens. Minicomposites contain a single tow. The mechanical behavior was correlated with microstructural features including tow failure strength and interface characteristics. The Hi-NicalonS fiber-reinforced minicomposites exhibited a conventional damage-tolerant response, comparable to that observed on composites reinforced by untreated Nicalon or Hi-Nicalon fibers and possessing weak fiber/matrix interfaces. The SA3 fiber-reinforced minicomposites exhibited larger interfacial shear stresses and erratic behavior depending on the fiber PyC coating thickness. Differences in the mechanical behavior were related to differences in the fiber surface roughness. [source] Flexural Strength Evaluation of Nonconstant Thickness Ceramic Floorings by Means of the Finite-Element MethodINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2010Beatriz Defez The ceramic tile industry has become an extremely competitive sector. The entry of new Asian and South American manufacturers into the market is shifting the leadership in production and exports from the traditional clusters of Europe to China, Turkey, and Brazil. In this uncertain environment, enterprises should raise the quality and cut costs by means of new products and processes. Ceramic tiles lightened by carving of a deep back relief could give rise to a generation of new, efficient products. These tiles could be manufactured with fewer raw materials than the traditional ones, which may lead to saving of weight and energy. Additionally, a lighter final product improves working conditions on the shopfloor and at the building site. Nevertheless, lightened tiles are structurally different from traditional ones, and so is their mechanical behavior. Because tiles are constructive elements, it is necessary to know their response under typical loads and assure fulfillment of the valid standards. This paper aims at evaluating the flexural strength (R) of lightened ceramic floorings using solid three-dimensional modelling and the finite-element method, establishing a new formula for the application of the international standard ISO 10545 "Ceramic Tiles." In order to achieve this objective, one reference model and 48 different relief versions were designed, which underwent a simplified computational simulation of the bending test. In accordance with the Rankine criterion, the maximal stresses of each version were calculated, as much as their distribution. Next, we correlated the results defining a new parameter called "normalized thickness," defined as the thickness that a carved tile should have to behave as a traditional flooring under flexion. This parameter allowed the adjustment of the international standard ISO 10545 to this kind of a product, facilitating their certification and therefore their real introduction in the market. Finally, thanks to the collaboration of the company Keros Cerámica S. A., it was verified that the methodology used was appropriate. [source] | ||||||||||||||||||||||||||||||||||||||||