Showing papers on "Hydrostatic stress published in 2005"
15 Nov 2005-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a new relation between hydrostatic stress and concentration of solute atoms is established, in which the normal stress is dependent on the mean curvature of the undeformed surface and tangential components of the surface displacement.
Abstract: The present work studies the interaction between chemical stresses and diffusion. A new relation between hydrostatic stress and concentration of solute atoms is established. For a solid free of action of body force, the Laplacian of the hydrostatic stress is proportional to the Laplacian of the concentration of solute atoms, that is, deviation of the hydrostatic stress from its local average is proportional to deviation of the local concentration of solute atoms. A general relationship among surface concentration of solute atoms, normal stress and surface deformation of a solid is then derived, in which the normal stress is dependent on the mean curvature of the undeformed surface and tangential components of the surface displacement. A closed-form solution of the steady state concentration of solute atoms in a thin plate is obtained. It turns out that linear distribution of solute atoms in the plate is non-existent due to the interaction between chemical stresses and diffusion.
227 citations
TL;DR: In this paper, the micromechanics of deformation of in situ formed metallic-glass-matrix composites consisting of Ta-rich particles dispersed in an amorphous matrix were examined.
95 citations
TL;DR: In this article, a constitutive model for predicting the time and temperature-dependent mechanical behavior of fluoropolymers, including PTFE, PFA and FEP, is presented.
72 citations
TL;DR: It is maintained that hydrostatic stress represents a suitable indicator for potential root resorptions caused by higher forces and moments, making it a helpful tool in the development of new orthodontic appliances.
Abstract: This study was undertaken to calculate the stress in the tooth, surrounding periodontal ligament, and in the alveolar bone when a lower first premolar is subjected to intrusion or torque movement using a constant moment. Root resorptions occur even when very low forces and moments are used in orthodontic therapy. It is therefore of great interest to determine and measure the stress that occurs under particular treatment conditions in the periodontal ligament. In this study, three finite element calculations were carried out with a realistic 3D model developed by CT data that consisted of a lower premolar, the surrounding periodontal ligament and alveolar bone. In close reference to the in-vivo experiments carried out by Faltin et al. [3, 5, 6] in Sao Paulo, Brazil, our model was subjected to an intrusive force on the premolar of 0.5 N and a lingual root torque of 3 Nmm. The three main stress directions and hydrostatic stress were quantified in all the surrounding tissues, revealing that the hydrostatic stress profile in the periodontal ligament correlated closely with resorption findings in Faltin et al.’s patients. Resorption occurred in the experimental study in Brazil when the hydrostatic stress exceeded capillary blood pressure in the periodontal ligament. We maintain that hydrostatic stress represents a suitable indicator for potential root resorptions caused by higher forces and moments, making it a helpful tool in the development of new orthodontic appliances. We must of course mention that there are many factors other than forces that are responsible for resorptions. But at the moment, only the force can be influenced by the orthodontist.
54 citations
TL;DR: In this paper, two approaches, namely, two-parameter fracture mechanics and micro-mechanical models are considered to investigate the feasibility of transferability of fracture parameters, and it is shown that if the triaxial conditions match for any two arbitrary geometries, it is feasible to transfer the fracture parameters.
45 citations
TL;DR: The multi-axial yield behavior of the aluminium alloy foam Alulight has been measured by Deshpande and Fleck as mentioned in this paper, who found that the degree of strain hardening in hydrostatic compression exceeds that for uniaxial compression, and the yield surface remains almost self-similar in shape after hydrostatic compaction.
Abstract: The multi-axial yield behaviour of the aluminium alloy foam Alulight has been measured Triaxial tests have been performed on a range of relative densities in order to compare the hydrostatic stress versus strain response with the uniaxial compressive response, and to probe the yield surface after prior hydrostatic compression It is found that the degree of strain hardening in hydrostatic compression exceeds that for uniaxial compression, and the yield surface remains almost self-similar in shape after hydrostatic compaction The measured yield surface provides support for the phenomenological yield model of Deshpande and Fleck (V S Deshpande, N A Fleck, Journal of Mechanics and Physics of Solids, 48, (2000), 1253) Upon reviewing the available experimental evidence from this and previous studies it is found that a broad correlation emerges between the relative density and the shape of the yield surface for metallic foams
42 citations
TL;DR: In this paper, a yield criterion based on a physical hypothesis was proposed to fulfill the experimental observations, which can well predict the yielding behavior arising from the yielding mechanism of the multiple-factor dependence.
41 citations
TL;DR: In this paper, it was shown that the thermal properties of foam neoprene under hydrostatic pressure cannot be predicted by theoretical means, and that uni-axial pressure cannot simulate hydrostatic compression.
Abstract: The purpose of this study was to show that the thermal properties of foam neoprene under hydrostatic pressure cannot be predicted by theoretical means, and that uni-axial pressure cannot simulate hydrostatic compression. The thermal conductivity and compressive strain of foam neoprene were measured under hydrostatic pressure. In parallel, uni-axial compressive strain data were collected. The experimental set-up and data were put into perspective with past published studies. It was shown that uni-axial compression yielded strains 20–25% greater than did hydrostatic compression. This suggests the need for direct hydrostatic pressure measurement. For comparison to hydrostatic experimental data, a series of thermal conductivity theories of two phase composites based on particulate phase geometry were utilized. Due to their dependence on the porosity and constituent thermal conductivities, a model to predict porosity under hydrostatic pressure was used and an empirical correlation was derived to calculate the thermal conductivity of pure neoprene rubber from experimental data. It was shown that, although some agreement between experimental data and thermal conductivity theories was present, no particular theory can be used because they all fail to model the complex structure of the pores. It was therefore concluded that an experimental programme, such as reported here, is necessary for direct measurement.
40 citations
TL;DR: In this article, the deformation behavior of Tertiary sandstones sampled from more than 13 formations was studied, and a constitutive model, involving nonlinear elastic/plastic deformation and volumetric deformation induced by shear stress, was proposed.
38 citations
TL;DR: Of the different failures models examined, the chain stretch failure model was found to capture uniaxial and multiaxIAL failure data most accurately for all of the UHMWPE materials.
37 citations
TL;DR: In this paper, the scaling laws for tensors with self-similar structure were determined using the differential self-consistent method, where the scaling is represented by power laws with the exponents determined by the microstructure, but not necessarily by the material fractal dimension.
TL;DR: In this article, the effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs-Ga 1− x Al x As quantum well are obtained.
Abstract: In this paper, the effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs–Ga 1− x Al x As quantum wells are obtained. We calculate the shallow-donor binding energy for different well widths and different values of hydrostatic stress. We find that for large well widths the binding energy increases slowly with hydrostatic stress, as opposed to the behavior of the binding energy for wells with small width. One of the results shows that the binding energy does not change appreciably with the impurity position when the width of the well is small and the hydrostatic stress is high. Two structures in both, the density of states and the optical absorption spectra, associated with impurities located close to the center and to the edges of the structure, are obtained. We have also observed that the density of states and the optical absorption spectra depend strongly on the applied hydrostatic stress.
TL;DR: In this paper, the von Mises stress in the via embedded in the low-k dielectric was analyzed, and it was shown that the yield strength of the via is severely reduced compared with that of the SiO2-embedded via.
Abstract: The stress of damascene Cu integrated with silicon dioxide (SiO2) and a low-k material was analyzed by x-ray diffraction, and that of the via-line structure was evaluated using finite element analysis. In both cases, the hydrostatic stress of the Cu line embedded in SiO2 was greater than that of the Cu line with low-k dielectric, whereas the opposite was true for the von Mises stress. In particular, the von Mises stress in the via embedded in the low-k dielectric was large. It was also shown that the yield strength of the via embedded in the low-k material is severely reduced compared with that of the via embedded in SiO2. Therefore, the deformation of the via, due to high von Mises stress and low yield strength, is expected to be the important failure mode in the interconnects made with low-k dielectrics which have higher coefficient of thermal expansion and lower elastic modulus.
TL;DR: In this article, a general expression of the stress field for an arbitrarily shaped QD structure with a non-uniform composition is presented, and it is found that the hydrostatic stress and strain are proportional to the initial misfit strain inside the QD but vanish outside it.
Abstract: Extensive research over the past several years has revealed graded composition and strong atomistic intermixing between a quantum dot (QD) and its surrounding material. In this paper, the strain and stress fields induced by a QD with an initial misfit strain due to its nonuniform composition are investigated. A general expression of the stress field for an arbitrarily shaped QD structure with a nonuniform composition is presented. It is found that the hydrostatic stress and strain are proportional to the initial misfit strain inside the QD but vanish outside it. The stress field in an arbitrarily shaped QD with a linearly graded composition is studied in detail, and a simple formula containing integrals over the boundary of the QD is derived. It can greatly simplify the numerical calculation of the elastic fields. Based on this formula, a closed-form analytical solution for a cuboidal QD with a linearly graded composition is obtained. It is also demonstrated that the strains inside and around the QD are s...
TL;DR: In this article, the authors used a simple fracture criterion based on the microscopic phenomena of void nucleation, growth and coalescence along with a simple criterion to predict the central burst in plane strain rolling.
TL;DR: In this article, a yield function taking into account the hydrostatic stress state is incorporated into a finite deformation concept in order to simulate void growth typically observed in ductile damage, and numerical aspects are addressed concerning the integration of the constitutive relations and the finite element equilibrium iteration.
TL;DR: In this article, the effects of compressive stress on the binding energy of an exciton in a cylindrical quantum dot (QD) using a variational procedure within the effective mass approximation was investigated.
Abstract: We investigate theoretically the effects of compressive stress on the binding energy of an exciton in a cylindrical quantum dot (QD) using a variational procedure within the effective mass approximation. The stress was applied in the z direction and the interaction between the charge carriers (electron and hole) and confined longitudinal optical (LO) phonon modes was taken into account. Specific applications of these results are given for GaAs QDs embedded in a Ga 1 - x Al x As semiconductor. The result shows that the binding energy and the polaronic correction increases linearly with increasing stress. Moreover, we obtain the binding energy and the polaronic contribution in the limit in which the QD turns into a quantum well.
TL;DR: The variations of the phase velocity of Rayleigh waves in dimensionless form with respect to the magnitude of the initial hydrostatic stress under certain practical assumptions have been depicted in graphs after numerical computations.
Abstract: The effect of the temperature and initial hydrostatic stress has been shown on the propagation of Rayleigh waves in a viscoelastic half-space. It has been explained how the velocity of Rayleigh waves depends not only on the parameters pertaining to the viscoelastic properties of the half-space, but on the temperature and the initial hydrostatic stress of the half-space also. The variations of the phase velocity of Rayleigh waves in dimensionless form with respect to the magnitude of the initial hydrostatic stress under certain practical assumptions have been depicted in graphs after numerical computations. If the temperature and the initial hydrostatic stress of the half-space are neglected, the results obtained are in perfect agreement with the classical case as obtained by Caloi for the propagation of Rayleigh waves in a viscoelastic medium.
Book•
01 Jan 2005
TL;DR: In this paper, a series of scaled hollow-cylinder tests were carried out on two model (cement-based) materials with varied maximum aggregate size, and the size effect was observed in the strength of the hollow cylinders with a consistent decease of strength with size.
Abstract: The influence of specimen size on measured material properties in solid heterogeneous materials, such as concrete and rock, has been an issue of research and discussions for a few decades. A thorough understanding of the size effect phenomenon and the physical processes involved is imperative. An appreciable amount of experimental data on size effect can be found in literature, which mainly focuses on direct and in-direct tension, bending, and uniaxial compression. These data are used for developing and validating numerical material models of fracture and size effect. To date, however, only few and limited experimental data exists for size effect in the biaxial and multiaxial compressive regimes. Size effect experiments under multiaxial stress conditions require three-dimensional scaling, which are experimentally challenging. For such experiments, the hollow-cylinder geometry lends itself for providing permutations of various multi-axial states of stress around its inner-hole depending on the stress path applied to its boundaries. Under external hydrostatic stress, it allows for a gradual and stable pre-peak failure development (in case of quasibrittle materials) across the wall thickness from the inner-hole outwards. Hollow-cylinder tests are commonly used in the oil and gas industry as model experiments for perforation and wellbore stability studies. In this thesis, series of scaled hollow-cylinder tests were carried out on two model (cement- based) materials with varied maximum aggregate size. The objective of these tests was to enhance the knowledge about size effect and fracture processes in multi-axial compressive failure of quasibrittle materials. The focus was to get insight into the physical mechanisms underlying the observed size effect. In addition, the deformation behaviour and fracture characteristics were closely examined and analyzed. For this purpose, a high-pressure test cell was developed that enables testing of hollowcylinders with dimensions up to 200 mm outer-diameter and 300 mm length. The cell was equipped to accommodate smaller specimens in a size range 1:4. The set-up was supplemented with novel measuring device for monitoring the deformations taking place inside the inner-hole, both in radial and axial directions for all sizes. Impregnation experiments were performed on all tested specimens using fluorescent epoxy resin. Obtained crack patterns were examined using both optical microscopes and Environmental Scanning Electron Microscope (ESEM). Numerical analyses using the distinct element program PFC2D were conducted in order to obtain a more thorough understanding of the phenomenon and experimental results. Modelling took place through firstly, developing a synthetic material that is calibrated for its (micro-) parameters using a set of laboratory mechanical tests. Afterwards, a model was developed to simulate the hollow-cylinder test in two-dimensions. Analyses of the hollow-cylinder test and its size dependence using the simulated model material and test procedure were performed. In addition, size effect simulations were performed for uniaxial compression and Brazilian splitting tests. Size effect was observed in the strength of the hollow-cylinders with a consistent de-cease of strength with size. The experimental/numerical results and the performed analysis revealed the size effect in hollow-cylinder tests as a result of complex combination of structural factors (e.g. stress gradients), mechanical processes of failure including deformation, and material characteristics in terms of heterogeneity and fabric. Emphasizing only one factor in a model or hypothesis and neglecting others brings an error to the model, which could be significant. Observed size effect was dependent on aggregate size, being stronger for the mixture with smaller aggregate size. The onset of size effect in the experiments was observed linked to the commencement of nonlinearity in the stress-strain response. Microscopic examination of fracture processes at this stage showed small boundary cracks to exist with barely any crack interaction or propagation activities. This implies that material related factors contributing to onset of size effect should be linked to processes taking place at crack initiation, which are largely due to heterogeneity and distribution of defects. The predicted size effect according to Weibull theory described with reasonable success the obtained size effect trends near crack initiation levels.
TL;DR: In this article, hot-torsion testing was used to establish the cavitation behavior of a typical alpha/beta titanium alloy, Ti-6Al-4V, with a colony microstructure, during simple-shear deformation.
Abstract: Hot-torsion testing was used to establish the cavitation behavior of a typical alpha/beta titanium alloy, Ti-6Al-4V, with a colony microstructure, during simple-shear deformation. For this purpose, sections of deformed specimens were examined by optical metallography, and by scanning and orientation-imaging microscopy (OIM). It was found that cavity nucleation occurred along prior beta boundaries as well as at triple points; in particular, most cavities nucleated along boundaries perpendicular to the axial direction of the specimen. Extensive growth was observed for cavities surrounded by both hard and soft orientations, with the soft colonies accommodating more of the imposed strain. At high degrees of deformation, dynamic globularization of the colony microstructure adjacent to the cavities was also observed. In addition, the metallographic observations revealed that the cavities did not grow in an equiaxed mode, but in an elliptical manner. A tensor describing the cavity-growth rate along the axial, radial, and hoop specimen directions was determined using measurements of individual cavity sizes. The cavity-growth behavior in torsion was compared to previous observations from hot-tension tests. This comparison indicated that the rate of cavity growth in shear was approximately one-tenth that in uniaxial tension. This finding is in broad agreement with models predicting the variation of the cavity-growth rate as a function of the ratio of the mean stress to the hydrostatic stress.
TL;DR: In this article, a lower bound on all r th moments of the hydrostatic stress inside each phase is obtained for r 2, where r 2 is the maximum value of the stress.
Abstract: Composites made from two linear isotropic elastic materials are subjected to a uniform hydrostatic stress. It is assumed that only the volume fraction of each elastic material is known. Lower bounds on all r th moments of the hydrostatic stress eld inside each phase are obtained for r 2. A lower bound on the maximum value of the hydrostatic stress eld is also obtained. These bounds are given by explicit formulas depending on the volume fractions of the constituent materials and their elastic moduli. All of these bounds are shown to be the best possible as they are attained by the hydrostatic stress eld inside the Hashin{Shtrikman coated sphere assemblage. The bounds provide a new opportunity for the assessment of load transfer between macroscopic and microscopic scales for statistically dened microstructures. Keywords. A Composite materials; B Failure criteria; C Stress concentrations
TL;DR: In this article, the effect of particle distribution on the macroscopic and microscopic response has been studied using three distinct types of three-dimensional (3D) finite-element model: a repeating unit cell, a multiparticle model, and a clustered particle model.
Abstract: The ductility of particle-reinforced metal matrix composites (PR MMCs) is reduced by the localization of stress and strain, which is exacerbated by microstructural heterogeneity, especially particle clustering. Herein, the effect of particle distribution on the macroscopic and microscopic response has been studied using three distinct types of three-dimensional (3D) finite-element model: a repeating unit cell, a multiparticle model, and a clustered particle model. While the repeating unit cell model represents a cubic periodic array of particles, the multiparticle model represents a random distribution of particles contained in a cube of matrix material, and the clustered particle model represents an artificially clustered distribution of particles. These models were used to study the macroscopic tensile stress-strain response as well as the underlying stress and strain fields. The results indicate that a clustered microstructure leads to a stiffer response with more hardening than that of random and periodic microstructures. Plastic flow and hydrostatic stress localization in the matrix and maximum principal stress localization in the particles are significantly higher in the clustered microstructure. Damage is expected to initiate in the cluster regions leading to low ductility.
Journal Article•
TL;DR: In this article, the applicability of a failure criterion for the strain energy density of rock under static-dynamic loading is proposed, and the critical value of strain energy densities of rock is mainly determined by preceding irreversible deformation process and current environmental state.
Abstract: The applicability of a failure criterion for the strain energy density of rock under static-dynamic loading is proposed. According to the analysis,critical value of strain energy density of rock is mainly determined by preceding irreversible deformation process and current environmental state;and the irreversible deformation is mainly caused by nonelastic deformation,damage and other possible intrinsic dissipative mechanisms of rock in a mechanical system;and volume deformation energy associated with hydrostatic stress effects can not be neglected on some stress states. Using mechanical model to represent the reduction of elasticity,occurrence of inelasticity deformation and effect of loading rate are proposed. On the basis of mechanical model,the critical value of strain energy density of rock under static-dynamic loading is derived. According to the catastrophe model for impact buckling of static-loading structures,a new catastrophe model for impact disturbance fragmentation of a rock system under static loading is established to analyze the rock failure under static-dynamic coupling loading ulteriorly. Finally,by using of the Instron electro-hydraulic and servo-controlled material testing machine and adopting low-cycle-index fatigue loading method,the test of red sandstone failure with medium strain rate under dynamic loading is carried out to verify the strain energy density criterion and catastrophe theory model. There is a good agreement between theoretic and experimental results.
TL;DR: In this paper, the effective second invariant ~ J2 is defined as the integration of the square of the effective shear stress over the unit sphere, which is the form of the Hill (1950) anisotropic yield function.
Abstract: This paper addresses some issues of the application of the effective stress tensor to coupled damage-plasticity from the point of view of a microplane. In this paper, damage and effective stress are defined on microplanes. The effective stress tensor of Murakami (1988) can be recovered as the second-order fabric tensor of the effective stress vector. The effective second invariant ~ J2 is defined as the integration of the square of the effective shear stress over the unit sphere. It is revealed that the ~ J2 possesses the form of the Hill (1950) anisotropic yield function based on the definition. Therefore, one can also use the Hill (1950) model to describe coupled anisotropic-damage-plasticity except for the conventional approach of effective stress.
TL;DR: In this paper, an experimental technique based on a plane strain test for the description of the elastic-plastic transition zone at small strain is proposed and achieved in a biaxial testing machine.
Abstract: The determination of the yield surface of cellular and porous materials requires experimental procedures under multi-axial stress states as the yield behavior is sensitive to the hydrostatic stress and as simple uniaxial tests aim only to determine one single point of the yield surface. Therefore, an experimental technique based on a plane strain test for the description of the elastic-plastic transition zone at small strain is proposed and achieved in a biaxial testing machine. A simple cubic model of a periodic cellular metal is used to demonstrate the method for materials of relatively high relative density. In contrast to common analytical and numerical models, experimental samples of the same geometry are easy to manufacture and to simulate. Furthermore, this experimental technique enables the determination of Poisson's ratio in the elastic range without any strain measurement. The experimental procedure is verified by the finite element method.
TL;DR: In this article, the length changes during torsion of solid bars with axial freedom of deformation were analyzed theoretically for polycrystalline copper, where the texture development was simulated with the help of the Taylor viscoplastic polycrystal model.
Abstract: The Swift effect, i.e. the length changes during torsion of solid bars with axial freedom of deformation is analysed theoretically for polycrystalline copper. In the simulations, the bar is divided into 5 tubes and in each tube the texture development is simulated with the help of the Taylor viscoplastic polycrystal model. The distribution of the hydrostatic stress is obtained from the equilibrium equation and the zero axial force requirement is satisfied with the help of an iterative scheme. The simulations reproduce faithfully the observed axial deformation and texture development. A second technique, based on the minimum plastic power is also applied to predict the length changes and textures. This technique leads to results which are nearly equivalent to the results obtained from the technique based on the equilibrium equation.
17 Apr 2005
TL;DR: In this paper, a stress model based on microstructure was constructed and the contribution of the growth and thermal stress of the damascene lines were quantified using finite element analysis.
Abstract: The line width dependence of stress in damascene Cu was examined experimentally as well as with a numerical simulation. The measured hydrostatic stress was found to increase with increasing line width. The larger stress in an interconnect with large dimension is attributed to the larger grain size, which induces higher growth stress in addition to thermomechanical stress. A stress model based on microstructure was constructed and the contribution of the growth and thermal stress of the damascene lines were quantified using finite element analysis. It was found that the stress of the via is lower than that of wide lines when both the growth stress and thermal stress were considered. Therefore, the characteristic failure mode, i.e. voiding in a via neighboring a wide line, was successfully explained by our stress model.
01 Aug 2005-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the authors investigated the high-pressure behavior of carbon nanotubes (single-walled and multi-walled, pristine and Fe-filled) by in situ powder X-ray diffraction (XRD) studies.
Abstract: High-pressure behavior of novel one-dimensional material - carbon nanotubes (single-walled and multi-walled, pristine and Fe-filled) have been investigated by in situ powder X-ray diffraction (XRD) studies.Single-walled nanotubes show remarkable mechanical resilience. The presence of non-hydrostatic stresses makes compression behavior much different from that under the hydrostatic stress. Our results also suggest pressure-induced elliptization of the tubes in a bundle.Iron-filled multi-walled nanotubes, unlike pristine, show a structural modification at a pressure of similar to 9 GPa where the outer component $(Fe_{3}C)$ of the encapsulated nanowire undergoes aniso-structural transition. Also the high-pressure behavior of the \alpha-Fe is quite different from the bulk.