Hydrostatic stress

About: Hydrostatic stress is a research topic. Over the lifetime, 1568 publications have been published within this topic receiving 37773 citations.

Synthesis and forming characteristics of Al–TiO2 powder metallurgy composites during cold upsetting under plane stress state conditions

Abstract: Aluminum-based metal matrix composites with various weight percentages of TiO2 reinforcement were synthesized by powder metallurgy technique and their forming characteristics were completely studied during cold upsetting under plane stress state conditions. The milled powders were characterized by scanning electron microscope, X-ray diffraction (XRD), and energy dispersive analysis using X-ray (EDAX) analysis. Green cylindrical compacts were made using a 400 kN hydraulic press using suitable punch and die, sintered at (590 ± 10)℃ for a period of 3 h, furnace cooled, and machined to obtain samples with 0.5 aspect ratio. The cold upset tests were carried out in steps of 10 kN and the true axial stress (σz), the true hoop stress (σθ), the true hydrostatic stress (σm), and the true effective stresses (σeff) were determined, and their behavior against the true axial strain (ɛz) was thoroughly analyzed. It was observed that, the addition of TiO2 to the Al matrix material increases the strength coefficient (K) a...

Gas Permeability Evolution with Deformation and Cracking Process in a White Marble Under Compression

Abstract: This paper presents an experimental study on the gas permeability evolution with deformation and cracking process in a white marble under compressive stresses. Uniaxial and triaxial compression tests with different confining pressures are firstly carried out to generate different states of deformation and induced cracks. The spatial distribution and geometrical form of induced cracks are investigated by the X-ray micro-tomographic imaging technique. Localized splitting-type macroscopic cracks are generated in the uniaxial test, while diffuse-oriented micro-cracks are induced in triaxial compression tests. Then, each of the cracked marble samples is subjected to a hydrostatic compression cycle, with the measurement of permeability and axial and lateral strains. It is found that the initial permeability of the sample with localized cracks is higher than that with diffuse cracks. The permeability of cracked samples exhibits an irreversible evolution between the hydrostatic loading and unloading, and the evolution trend is influenced by the initial crack state induced by the previous mechanical tests. The deformation of cracked samples under hydrostatic compression is clearly anisotropic due to oriented crack distributions and irreversible due to the unilateral closure—opening property of cracks. Finally, we propose to use the nonlinear regression method to formulate best-fitting models to capture the relationships between the permeability evolutions and effective hydrostatic stress or axial and lateral strains of cracked samples.

Analytical Solution for Coupled Diffusion Induced Stress Model for Lithium-Ion Battery

Abstract: Electric cycling is one of the major damage sources in lithium-ion batteries and extensive work has been produced to understand and to slow down this phenomenon. The damage is related to the insertion and extraction of lithium ions in the active material. These processes cause mechanical stresses which in turn generate crack propagation, material loss and pulverization of the active material. In this work, the principles of diffusion induced stress theory are applied to predict concentration and stress field in the active material particles. Coupled and uncoupled models are derived, depending on whether the effect of hydrostatic stress on concentration is considered or neglected. The analytical solution of the coupled model is proposed in this work, in addition to the analytical solution of the uncoupled model already described in the literature. The analytical solution is a faster and simpler way to deal with the problem which otherwise should be solved in a numerical way with finite difference method or a finite element model. The results of the coupled and uncoupled models for three different state of charge levels are compared assuming the physical parameters of anode and cathode active material. Finally, the effects of tensile and compressive stress are analysed.

Studies on the growth of voids in amorphous glassy polymers

Abstract: Numerical studies are presented of the localized deformations around voids in amorphous glassy polymers. This problem is relevant for polymer–rubber blends once cavitation has taken place inside the rubber particles. The studies are based on detailed finite element analyses of axisymmetric or planar cell models, featuring large local strains and recent material models that describe time-dependent yield, followed by intrinsic softening and subsequent strain hardening due to molecular orientation. The results show that plasticity around the void occurs by a combination of two types of shear bands, which we refer to as wing and dog-ear bands, respectively. Growth of the void occurs by propagation of the shear bands, which is driven by orientational hardening. Also discussed is the evolution of the local hydrostatic stress distribution between voids during growth, in view of possible craze initiation. © 1998 Kluwer Academic Publishers