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Showing papers on "Hydrostatic stress published in 1992"


Journal ArticleDOI
TL;DR: In this paper, the J-dominance is used to define the size scale over which large stresses and strains develop while Q scales the near-tip stress distribution and the stress triaxiality achieved ahead of the crack.
Abstract: C entral to the J-based fracture mechanics approach is the concept of J-dominance whereby J alone sets the stress level as well as the size scale of the zone of high stresses and strains. In Part I the idea of a J Q annulus was developed. Within the annulus, the plane strain plastic near-tip fields are members of a family of solutions parameterized by Q when distances are normalized by J σ 0 , where σ0is the yield stress, J and Q have distinct roles: J sets the size scale over which large stresses and strains develop while Q scales the near-tip stress distribution and the stress triaxiality achieved ahead of the crack. Specifically, negative (positive) Q values mean that the hydrostatic stress is reduced (increased) by Qσ0 from the Q = 0 plane strain reference state. Therefore Q provides a quantitative measure of crack-tip constraint, a term widely used in the literature concerning geometry and size effects on a material's resistance to fracture. These developments are discussed further in this paper. It is shown that the J Q approach considerably extends the range of applicability of fracture mechanics for shallow-crack geometries loaded in tension and bending, and deep-crack geometries loaded in tension. The J Q theory provides a framework to organize toughness data as a function of constraint and to utilize such data in engineering applications. Two methods for estimating Q at fully yielded conditions and an interpolation scheme are discussed. The effects of crack size and specimen type on fracture toughness are addressed.

791 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of inertia, strain hardening, and rate sensitivity on the short and long-term behavior of the void, as well as on its response to ramp loading, are investigated in detail.
Abstract: The problem studied in this paper concerns the dynamic expansion of a spherical void in an unbounded solid under the action of remote hydrostatic tension. The void is assumed to remain spherical throughout the deformation and the matrix to be incompressible. The effects of inertia, strain hardening, and rate sensitivity on the short and long-term behavior of the void, as well as on its response to ramp loading, are investigated in detail.

125 citations


Journal ArticleDOI
TL;DR: In this paper, finite element calculations have been carried out for spherical unit cells containing a concentric spherical hole to characterize the power law creep of a material containing voids, and the results of the unit cell calculations are approximated well by a creep potential for the macroscopic behavior of a porous material.
Abstract: Finite element calculations have been carried out for spherical unit cells containing a concentric spherical hole to characterize the power law creep of a material containing voids. Axisymmetric states of macroscopic stress were applied to the unit cells ranging from purely hydrostatic loading to purely deviatoric stressing. The results of the unit cell calculations are approximated well by a creep potential for the macroscopic behavior of a porous material. This potential agrees with the unit cell results for purely hydrostatic stress and purely deviatoric stress and involves a simple elliptical interpolation in between. The model predicts quite well the ratio of transverse to axial strain rate in uniaxial compression tests.

106 citations


Journal ArticleDOI
TL;DR: The use of hydrostatic pressure to apply mechanical stress to bone organ cultures is reviewed and local factors, such as prostaglandins and growth factors, seem to be involved in the tissue response to mechanical stress.
Abstract: The use of hydrostatic pressure to apply mechanical stress to bone organ cultures is reviewed. Ossifying long bones and calvarial rudiments are sensitive to this type of stress. Intermittent hydrostatic compression of near physiologic magnitude (ICF) has anabolic effects on mineral metabolism in such rudiments, and continuous hydrostatic stress of high magnitude (CCP) has catabolic effects. The effects of ICF may be ascribed to shear stress generated at tissue interphases of different chemical and mechanical properties. Local factors, such as prostaglandins and growth factors, seem to be involved in the tissue response to mechanical stress.

102 citations


Journal ArticleDOI
TL;DR: The static equilibrium conditions have been derived for piezoelectric-ceramic-polymer composite structures and it is shown that this enhancement effect not only depends on the volume percentage of the active component but also on the aspect ratio of the two components.
Abstract: Inhomogeneous displacement profiles have been derived for a single‐rod composite and a single‐tube 1‐3 ceramic‐polymer composite under both uniaxial and hydrostatic stress. The effective piezoelectric constants for the composites have been derived in terms of the ceramic content, the piezoelectric and elastic constants of each component, and the aspect ratio of the ceramic rod. The stress concentration inside both phases is derived from the calculated inhomogeneous displacement profiles. It is found that only a finite portion of the polymer in the vicinity of the ceramic‐polymer interface actually contributes to the stress transfer, and the induced additional stress on the ceramic also has a higher magnitude near the interface. The theoretical results quantitatively predict the performance of a given 1‐3 structure, and can be used to optimize the design parameters, such as ceramic content, aspect ratio of the ceramic rods, rod geometry and rod arrangement, resin hardness, etc., for 1‐3 structures designed for specific purposes.

69 citations


Journal ArticleDOI
TL;DR: In this article, a model based on a sandwich structure was proposed to describe the deformation behavior of two-phase materials, which is found to hold, in good approximation, for particle composites with moderate amounts of soft phase as well.
Abstract: A model is proposed which describes the deformation behaviour of two-phase materials. It is based on a sandwich structure but is found to hold, in good approximation, for particle composites with moderate amounts of soft phase as well. The model emphasizes the mutual deformation constraint between the phases, which originates from the triaxiality of the stress state in soft phase regions close to hard phase boundaries, as long as the boundaries are to remain intact. The stress triaxility (or the hydrostatic stress component connected with it) causes a “harder” response of the soft phase, and a “softer” response of the hard phase. Elastic properties can be expressed analytically, and the flow behaviour in the elastic-plastic regime can be calculated by an iterative procedure, yielding data on stresses, stress triaxiality, and strains in the soft and in the hard phase. Good agreement with experiment is obtained for two-phase microstructures consisting of WC and Co and of martensite and austenite.

47 citations


Journal ArticleDOI
TL;DR: In this paper, an analytical study of the dynamic growth of microvoids is presented, with the help of a numerical study of void growth relationships derived; the conclusion is that both material viscosity and strain hardening may have an important influence on the tensile strength of ductile materials at high strain rates.

46 citations


Journal ArticleDOI
TL;DR: In this paper, a model for failure of encapsulated interconnect lines by stress voiding is developed. But the model is based on two limiting kinds of void growth: radial displacements and diffusion along grain boundaries.
Abstract: Stress-driven diffusive growth of voids in encapsulated interconnect lines is studied. By calculating the rate of growth of a single void in a passivated line subjected to an initial hydrostatic tension stress and by assuming that failure occurs when the void reaches a critical size, a model for failure of encapsulated interconnect lines by stress voiding can be developed. The model for the prediction of void growth and failure is based on two limiting kinds of void growth. In one limit, which applies at short times, radial displacements occur by diffusional flow processes around the growing void and relax the local hydrostatic tension stress. In the long time limit, vacancies flow to the void from distant parts of the line by diffusion along grain boundaries, thereby relaxing the stress in a growing section of the line. A model based on a combination of these behaviors leads to a failure law for aluminum lines of the form t f σ 2 / d = 10 19.2 exp( Q /R T ) where t f is the failure time in seconds, σ is the initial hydrostatic tension stress in the line in Pa, d is the grain size in meters, and the activation energy, Q = 80.9 kJ/mol, is close to that for grain boundary diffusion in aluminum. The model predictions appear to be in good agreement with the few experiments on stress voiding that have been conducted.

41 citations


Journal ArticleDOI
TL;DR: In this article, a new nonconventional microscopic fracture mode with a characteristic feature: the tearing topography surface (TTS), associated with hydrogen embrittlement processes in pearlitic steel, was investigated.
Abstract: This article deals with a new nonconventional microscopic fracture mode with a characteristic feature: the tearing topography surface (TTS), associated with hydrogen embrittlement processes in pearlitic steel. The TTS mode appeared in fracture tests on precracked and notched specimens when tested under hydrogen charging. Experimental results showed phenomenological relations between the size of the TTS region and variables such as the electrochemical potential and the maximum stress intensity factor during fatigue precracking (for cracked samples) or the time to failure and the geometry (for notched samples). A hydrogen diffusion model is proposed which explains, from the theoretical point of view, the phenomenological relations between the TTS size and the test variables. According to this model, hydrogen diffuses not only toward the places of minimum concentration, but also to the sites of maximum hydrostatic stress.

41 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the Raman spectrum associated with the transverse optical phonon of cubic SiC whiskers as a function of stress using a diamond anvil cell (for hydrostatic stress, X) and an individual whisker microtension apparatus (for uniaxial stress along P).
Abstract: We measured the Raman spectrum associated with the transverse optical (TO) phonon of cubic SiC (β‐SiC) whiskers as a function of stress using a diamond anvil cell (for hydrostatic stress, X) and an individual whisker microtension apparatus (for uniaxial stress along [111], P). These experiments were used to calibrate the shift and the splitting of the TO phonon mode with applied stress. The results of the calibration experiments were used to evaluate the residual stress in an Al2O3/SiC(w) composite (30% SiC by volume). The Raman spectra from the composite shows that residual stress in the SiC near the surface of the composite is (X+P/3)=−1050±100 MPa.

39 citations


Journal ArticleDOI
TL;DR: In this article, a partially fractured thin metal foil bonded between ceramic blocks subject to mode I loading was studied, and the maximum stress occurs at a distance of several foil thicknesses ahead of the crack tip, and can trigger cavitation or debonding.
Abstract: A partially fractured thin metal foil bonded between ceramic blocks subject to mode I loading was studied in a previous paper. The constrained plastic flow easily elevates the hydrostatic stress in the metal to more than 5 times the yield stress. The maximum stress occurs at a distance of several foil thicknesses ahead of the crack tip, and can trigger cavitation or debonding. The large spacing between the cavities and the crack tip allows the intact metal patches to bridge the crack, leading to rising crack growth resistance curves. The maximum foil thickness which would allow the above bridging mechanism to develop has been identified. In this paper mode mixity effects are investigated. As the mode II component increases, the plastic zone becomes longer while the stress triaxiality becomes smaller. The loss of constraint is detailed in this paper. Under mixed-mode loading, high tensile stresses also occur in the ceramics. These stresses are large enough to cause ceramic cleavage. Using a full-field large-deformation elastic-plastic analysis, the multi-mechanism competition is assessed. The dependence of nominal fracture toughness on failure mechanisms and on geometric and material parameters is also discussed.

Journal ArticleDOI
TL;DR: In this article, an analytical study of the dynamic plastic growth of microvoids under the combined action of hydrostatic and deviatoric stresses is presented, with the help of a numerical analysis of the void growth relationship derived, and applied to the case of spall fracture.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the stresses and strains induced by coefficient of thermal expansion (CTE) mismatch for a metal matrix composite with a spherical reinforcement particle and found that the critical internal pressure for plastic deformation is less than two-thirds of the yield stress of the matrix material and decreases with increasing range of thermal cycle.
Abstract: The stresses and strains, induced by coefficient of thermal expansion (CTE) mismatch, are analyzed for a metal matrix composite (MMC) with a spherical reinforcement particle. The spherical reinforcement particle is found to be in a hydrostatic stress state and remains in the elastic state. The stresses and strains are largest, and plastic deformation occurs in the matrix adjacent to the reinforcement particle. Accordingly, the reinforcement particle/matrix interface becomes a potential crack initiation site under thermal cycling. The critical internal pressure for plastic deformation is less than two-thirds of the yield stress of the matrix material and decreases with increasing range of thermal cycle.


Book ChapterDOI
01 Jan 1992
TL;DR: In this paper, the macrostresses and microstresses in composite materials were determined by using the macrostatic component of the stress tensor without the unstressed lattice parameters of individual phases.
Abstract: In two phase or composite materials it is possible to determine both the macrostresses in the material and the average microstresses present in each phase. The stress equilibrium relations allowing this separation are outlined. It is shown that errors in the unstressed lattice parameter lead to errors in only the hydrostatic component of the stress tensor. It is thus possible to accurately determine the entire deviatoric macrostress and microstress tensors without the unstressed lattice parameters of the individual phases. Two examples of the usefulness of macrostress and microstress measurements are given. In a SiC-TiB2 microcracking ceramic com-posite large hydrostatic microstresses develop during consolidation due to differential thermal contraction. Microcracks form during stressing, relaxing the thermal microstresses. Measurements of this relaxation have helped quantify the toughening in this system associated with microcracking. Measurements in both the ferrite and cementite phases of 1080 steel during low cycle fatigue show the proportion of the applied load carried by each phase. These results show that as the material yields in both tension and compression, the carbides take a higher fraction of the load and thus the stress range experienced by the carbide phase is much higher.

Book ChapterDOI
01 Jan 1992
TL;DR: The rigid-plastic and viscoplastic finite-element techniques described in the previous chapters are useful approaches to the modelling of metal deformation when the elastic component of strain may reasonably be ignored as discussed by the authors.
Abstract: The rigid-plastic and viscoplastic finite-element techniques described in the previous chapters are useful approaches to the modelling of metal deformation when the elastic component of strain may reasonably be ignored. This is often the case, for example, for hot working conditions. In other situations, it is important to take into account the elastic as well as the plastic deformation of the material, and it is vital to do so if the unloading behaviour is to be predicted.

Journal ArticleDOI
F. Z. Li1
TL;DR: In this paper, the analytic solutions of plane-stress mode I perfectly-plastic near-tip stress fields for pressuresensitive materials are derived. And the effects of material pressure sensitivity on the near tip fields are discussed.
Abstract: Different from dense metals, many engineering materials exhibit pressure-sensitive yielding and plastic volumetric deformation. Adopting a yield criterion that contains a linear combination of the Mises stress and the hydrostatic stress, the analytic solutions of plane-stress mode I perfectly-plastic near-tip stress fields for pressuresensitive materials are derived. Also, the relevant characteristic fields are presented. This perfectly plastic solution, containing a pressure sensitivity parameter μ, is shown to correspond to the limit of low-hardening solutions, and when μ=0 it reduces to the perfectly plastic solution of near-tip fields for the Mises material given by Hutchinson [1]. The effects of material pressure sensitivity on the near-tip fields are discussed.

Journal ArticleDOI
TL;DR: In this paper, a new void growth model is presented to illustrate the ability of the model to predict porosity increases in metal forming, based on analyses of void growth under conditions of macroscopically isotropic and deviatoric stress states.


Journal ArticleDOI
TL;DR: In this article, the authors present the results of an analytical-experimental investigation of the effects of superposed hydrostatic stress on the mechanical properties of particulate reinforced metal-matrix composites.
Abstract: This paper presents the results of an analytical-experimental investigation of the effects of superposed hydrostatic stress on the mechanical properties of particulate reinforced metal-matrix composites. Tension experiments have been conducted with dif ferent levels of superposed pressure on aluminum alloys reinforced with Al2 O3 particu lates. Stress-strain curves have been experimentally generated as functions of pressure, while the behavior has been modeled analytically using the approximate mean-field theory developed by Weng and co-workers for plasticity of two-phase composites (Tandon and Weng, 1988; Zhao and Weng, 1990; Qiu and Weng, 1991). Using Berveiller-Zaoui's ap proximation (1979), the constraint due to the matrix phase is characterized by the secant moduli of the matrix, while the interaction of the inclusions is accounted for by the Mori- Tanaka mean-field theory. The stress-strain curves predicted by the analytical model show good agreement with those generated in the experimental program.

Book ChapterDOI
Alan Needleman1
01 Jan 1992
TL;DR: In this paper, the effect of imposed strain rate on the initiation of debonding is analyzed numerically for rigid spherical inclusions in an elastic-viscoplastic matrix subject to uniaxial tension with a superposed hydrostatic stress.
Abstract: The effect of imposed strain rate on the initiation of debonding is analyzed numerically for rigid spherical inclusions in an elastic-viscoplastic matrix subject to uniaxial tension with a superposed hydrostatic stress. The analyses are based on a cohesive zone type model that permits the prediction of interfacial decohesion without the necessity of introducing some additional failure criterion. Since the mechanical response of the interface is specified in terms of both a critical interfacial strength and the work of separation per unit area, dimensional considerations introduce a characteristic length. For the conditions analyzed, the strain rate dependence of the debonding initiation strain is found to increase with increasing inclusion size.

01 Jan 1992
TL;DR: In this article, the analytic solutions of plane-stress mode I perfectly-plastic near-tip stress fields for pressure sensitive materials are derived, which correspond to the limit of low-hardening solutions, and when /~ = 0 it reduces to the perfectly plastic solution for the Mises material given by Hutchinson.
Abstract: Different from dense metals, many engineering materials exhibit pressure-sensitive yielding and plastic volumetric deformation. Adopting a yield criterion that contains a linear combination of the Mises stress and the hydrostatic stress, the analytic solutions of plane-stress mode I perfectly-plastic near-tip stress fields for pressure- sensitive materials are derived. Also, the relevant characteristic fields are presented. This perfectly plastic solution, containing a pressure sensitivity parameter #, is shown to correspond to the limit of low-hardening solutions, and when /~ = 0 it reduces to the perfectly plastic solution of near-tip fields for the Mises material given by Hutchinson (1). The effects of material pressure sensitivity on the near-tip fields are discussed.

Book ChapterDOI
01 Jan 1992
TL;DR: In this article, a large deformation finite element analysis has been performed to study the stress and strain fields near the crack-tip under mixed mode conditions, where the effects of microvoids on plastic flow are taken into account by using the continuum constitutive model introduced by Gurson.
Abstract: A large deformation finite element analysis has been performed to study the stress and strain fields near the crack-tip under mixed mode conditions. The effects of microvoids on plastic flow are taken into account by using the continuum constitutive model introduced by Gurson. Influence of hydrostatic stress and strain hardening exponent on the near-tip field is examined.

01 Jan 1992
TL;DR: In this paper, a modified Gurson's model was used to analyze the closing process of voids in rigid-plastic matrix materials, and it was found that the entire closing process requires the infinite hydrostatic stress or equivalent strain rate.
Abstract: microscopic damage model of ellipsoidal body containing ellipsoidal void for nonlinear matrix materials is developed under a particular coordinate. The change of void shape is considered in this model. The viscous restrained equation obtained from the model is affected by stress : ~ i i , void volume fraction f, material strain rate exponent m as well as the void shape. Gurson's equation is modifwd from the numerical solution. The modified equation is suitable for the case of nonlinear matrix materials and changeable voids. Lastly, the model is used to analyze the closingprocess of voids. Since GursonOl built the microscopic model of the'limited matrix containing a void, microscopic damage mechanics has greatly been developed. Gurson's model was xs;idely used because of its perfection and practicality. Yamamoto t2j used Gurson's equation to analyze the conditions for shear localization in ~e ductile fracture of void-containing materials. Gurson's constitutive model was used by Aravast3) in the analysis of void growth that leads to central bursts during extrusion. On the other hand, some modifications to Gurson's model were made. Tvergaardt41 considered the void interaction by. means of the finite element analysis. Strain hardening was indirectly taken:into account by Yamamotot2j through introducing the matrix average flow stress and Wang Tze-chiang |SJ considered directly the affection of the strain hardening matrix materials. In industral production, the manufacturing process of many parts such as the forge of heavy ingots and the forming of powder metallurgy is to eliminate all kinds of internal cavities in materials. So the study on the void closing in materials becomes significant. We t~ applied Gurson's model to analyze the closing process of voids in rigid-plastic matrix materials. It was found that the entire closing of voids requires the infinite hydrostatic stress or equivalent strain rate. This is because the void shape change was not taken into account in the model. In microscopic damage mechanics, studies were greatly, concentrated on void nucleation, growth, coalescence and forming a macro- crack at last. Therefore, the change of the void shape was ignored in Gurson's model and the modified Gurson's model. However, the void shape plays an important part in the void closing,

Journal ArticleDOI
TL;DR: In this article, the authors derived the generally analytical expressions of the hydrostatic stress-dependent perfectly-plastic stress fields at a stationary plane-stress crack-tip under the condition that all the stress components at a cracktip are the functions of θ only.
Abstract: Under the condition that all the stress components at a crack-tip are the functions of θ only, making use of equilibrium equations and hydrostatic stress-dependent yield condition, in this paper, we derive the generally analytical expressions of the hydrostatic stress-dependent perfectly-plastic stress fields at a stationary plane-stress crack-tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of hydrostatic stress-dependent perfectly-plastic stress fields at the tips of mode I and mode II cracks are obtained.

Book ChapterDOI
M. Itoh1, Fusahito Yoshida1, M. Ohmori1, T. Honda1, Y.Z. Tai2 
01 Jan 1992
TL;DR: In this article, the effect of hydrostatic stress on the ductile-to-brittle transition behavior of a sintered chromium has been studied at elevated temperatures under the tension and the torsion with superimposed axial compression.
Abstract: The effect of hydrostatic stress on the ductile-to-brittle transition behavior of a sintered chromium has been studied at elevated temperatures under the tension and the torsion with superimposed axial compression. Both the tension and the torsion tests revealed minimums in the fracture strain at 873K. This temperature of the ductility minimums corresponded to the temperature at which dynamic strain aging appeared. The superposition of a compressive stress of more than 50 % of the yield stress resulted in a very significant increase in the fracture ductility and a decrease in the ductile-to-brittle transition temperature.