Hydrostatic stress

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

Experimental Investigations on Microstructure, Properties and Workability Behavior of Zinc Oxide Reinforced Al–Si–Mg Matrix Composites

Abstract: Al-Si based alloy matrix composites are now broadly utilized by the industrial sectors like automobile, structural, aerospace and more practical industrial applications due to its noncompetitive economy range, good mechanical properties and less density. In order to widen its applications, it is very significant to improve its mechanical and workability behavior. So, in this work, an effort has been taken to develop a ZnO microparticles (3, 4.5 & 6 %) reinforced with Al-Si-Mg (AA6061) alloy by stir casting route.Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (X-RD) were employed for characterization studies of the composites. Tensile and hardness of the composites are investigated, compared and analyzed its effects. Another novel finding of the work is determining the workability behavior of the prepared samples with aspect ratio of 1 by incremental compressive loading of 25 kN through cold upsetting technique. For all developed samples, true axial stress (σz), hoop stress (σө), hydrostatic stress (σm), effective stress (σeff), formability stress index (β) and stress ratio parameters [(σz/σeff), (σө/σeff), (σm/σeff)] were determined and the results are correlated with the axial strain (ez). The results clearly infers that increasing weight contributions of ZnO particles increase the mechanical properties, all the stresses and stress ratio parameters of the composites.

Effect of Dielectric Materials on Stress-Induced Damage Modes in Damascene Cu Lines

Abstract: Various low-k materials are being pursued as dielectric materials for future interconnects. However, poor thermo-mechanical properties of low-k materials cause tremendous reliability concerns, thus the proper materials for integration with Cu are not suggested yet. In this study, the line width and spacing dependence of damascene Cu lines embedded by TEOS and low-k materials (CORAL) was analyzed using x-ray diffraction. Generally, the hydrostatic stress of Cu/TEOS was greater than that of Cu/CORAL, while the opposite for von-Mises stress. Using a three-dimensional finite analysis (FEA), the effect of low-k materials on the stress and its distribution in via-line structures of dual damascene Cu interconnects was studied. In the case of Cu/TEOS, the hydrostatic stress was concentrated at the via and on the top of the lines, where it was suspected that the void would nucleate. On the other hand, in the via-line structures integrated with organic low-k materials, large von-Mises stress was maintained in the via. Therefore, the deformation of via, rather than voiding, may be the main failure mode in the interconnects with low-k materials.

Modelling the crack initiation in unidirectional laminates under multiaxial fatigue loading

Abstract: In this chapter, a criterion to predict crack initiation in unidirectional laminae subjected to multiaxial cyclic loading is proposed. The criterion is based on experimental observations concerning the damage mechanisms occurring at the microscopic scale, of which the evolution leads to the initiation of a macro-crack. In particular, two stress parameters have been identified as representative of the driving forces for the damage evolution at the microscale. These parameters, that is the local maximum principal stress and the local hydrostatic stress in the matrix, are expressed in terms of local stresses in the matrix, calculated by means of finite element analyses of a fiber/matrix unit cell subjected to periodic boundary conditions. Applications of the proposed criterion to fatigue results from the literature show that only two scatter bands can be successfully used to predict the cycles spent for crack initiation in unidirectional laminae under multiaxial loading.

The Yield Condition of Nodular Cast Iron Subjected to Triaxial Stresses

Abstract: The yield stresses of ferritic nodular cast iron under triaxial stress states with various values of Lode's parameter over a wide range of hydrostatic stresses are obtained by operating testing apparatus under hydrostatic pressure. It is found that the yield stress is influenced by Lode's parameter and hydrostatic stress. The initial yield surface in principal stress space is derived from a model in which the stress concentration in matrix around spherical graphite nodules dispersed in the material is considered. Comparison of the experimental results with the theoretical results suggests that the initial yield surface of the material is unsymmetric with respect to the hydrostatic stress axis, swells in the negative side of the axis, and is a closed surface.

Rheological experimental investigation on surrounding rock mass of granite under high temperature and hydrostatic stress

Abstract: The research on rheological property,rheological mechanism of surrounding rock of granite under high temperature and high pressure is of great importance to extracting heat from hot dry rock(HDR) and stability of drilling borehole wall. Utilizing the 20 MN servo-controlled triaxial rock testing machine with high temperature and high pressure developed by the authors,the intensive research on the rheological property of large size granite with borehole samples of φ 200 mm×400 mm under high temperature and triaxial hydrostatic stress in depth is carried out. The research results can be found as follows. (1) The granite is a kind of brittle and hard rock,it is constituted with multi-crystal. Surrounding rock in granite shows of steady creep state,main with hydrostatic stress below than 5 000 m in depth and temperature below 600 ℃. However,it appears as unstable creep state when hydrostatic stress is over 5 000 m in depth and temperature above 600 ℃. (2) The creep of surrounding rock of granite has a creep threshold of stress and creep temperature threshold. (3) The main reason of surrounding rock possessing threshold of stress and temperature is the dislocation and cracking of grain and cement of grain under thermo-mechanical coupling. (4) At different temperatures and hydrostatic stresses in depths,the critical hydrostatic stress of rheodestruction of surrounding rock is 5 000–6 000 m;and the critical temperature of rheodestruction is 500 ℃–600 ℃. The failure modes commonly are compression fracture,transpression or both of them. At the same time,the parameters of steady creep state rates of surrounding rock within 600 ℃ and hydrostatic of stress of 6 000 m are obtained;thus it can provide significant mechanical parameter for the stability of HDR borehole wall.