Hydrostatic stress

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

Molecular Dynamics Study on Mechanical Properties in the Structure of Self-Assembled Quantum Dot

Abstract: Stress and strain in the structure of self-assembled quantum dots constructed in the Ge/Si(001) system is calculated by using molecular dynamics simulation. Pyramidal hut cluster composed of Ge crystal with {105} facets surfaces observed in the early growth stage are computationally modeled. We calculate atomic stress and strain in relaxed pyramidal structure. Atomic stress for triplet of atoms is approximately defined as an average value of pairwise (virial) quantity inside triplet, which is the product of vectors between each two atoms. Atomic strain by means of atomic strain measure (ASM) which is formulated on the Green’s definition of continuum strain. We find the stress (strain) relaxation in pyramidal structure and stress (strain) concentration in the edge of pyramidal structure. We discuss size dependency of stress and strain distribution in pyramidal structure. The relationship between hydrostatic stress and atomic volumetric strain is basically linear for all models, but for the surface of pyramidal structure and Ge-Si interface. This means that there is a reasonable correlation between atomic stress proposed in the present study and atomic strain measure, ASM.

Quasi-static crack tip fields in rate-sensitive FCC single crystals

Abstract: In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip fields in a FCC single crystal are studied. Finite element simulations are performed within a mode I, plane strain modified boundary layer framework by prescribing the two term (K-T) elastic crack tip field as remote boundary conditions. The material is assumed to obey a rate-dependent crystal plasticity theory. The orientation of the single crystal is chosen so that the crack surface coincides with the crystallographic (010) plane and the crack front lies along 101] direction. Solutions corresponding to different stress intensity rates K., T-stress values and strain rate exponents m are obtained. The results show that the stress levels ahead of the crack tip increase with K. which is accompanied by gradual shrinking of the plastic zone size. However, the nature of the shear band patterns around the crack tip is not affected by the loading rate. Further, it is found that while positive T-stress enhances the opening and hydrostatic stress levels ahead of crack tip, they are considerably reduced with imposition of negative T-stress. Also, negative T-stress promotes formation of shear bands in the forward sector ahead of the crack tip and suppresses them behind the tip.

Stress analysis for a laminated half-body in couple stress theory

Abstract: The paper contains an analysis of the distribution of stress and couple stress in a semi-infinite elastic laminated body when the body is deformed on the first plate due to surface pressure. In this analysis, the boundary conditions at the surface of the arbitrary numbered plate have been given without application of shearing stress nor couple stress, and the material constantsG, v andl on the all plates are taken as the same values. The particular solution of this case is constructed by applying the method of V. H. Bufler's recurrence relations for a stress transfer function with the aid, of displacement continuity. The problem is numerically calculated with three different new material constants and Poisson's ratiov=0.3; and in the results, the reduction rate of σzz in comparison with the classical value and μzθ distributions are influenced by the materials to a large degree.

Crack initiation under static loads including the influence of residual welding stresses

Abstract: Starting from the basic approaches for the reduction of ultimate strain for steel with increasing hydrostatic stress tensor a function is derived which reflects the different influences on ultimate strain abetting brittle fracture. This function, which via stress state includes the influence of residual stresses, e.g. due to welding, is a tool for predicting the formation of the crack. Nonlinear FE-analyses including a welding simulation macro are performed to describe the stress-strain situation up to the fracture state in component tests.

A model for the deformation behavior of amorphous alloys with application to the wear loading of the film-on-substrate geometry

Abstract: One method of addressing practical wear problems is via the creation of wear resistant films on the exposed surface by various surface modification techniques. A class of materials produced by such techniques, amorphous metals, is known to exhibit mechanical properties consistent with good wear resistance. In this paper we present a model for the mechanical behavior of these materials that is mechanistic in nature, yet sufficiently simple to allow treatment of the film-on-substrate geometry. The Eyring rate theory is used as a basis to describe the deformation rate, and agreement with stress sensitivity and activation energy data is shown to support this approach. The local creation of excess volume and its relaxation are integral parts of the deformation process in these materials. The kinetics of relaxation is analyzed, and the physical attributes of that process are examined. The effects on deformation of a hydrostatic stress component in the wear loading mode are addressed. The relation of all these factors to strain localization in the film is also studied. The strength of an amorphous film produced by ion implantation is estimated and correlations with plastic flow depth are established. Methods of predicting the wear responses of particular materials in this geometry are presented and compared with published wear data.