Search

The paper presents a shear strength model used to evaluate information of interest from shock experiments aimed at studying the properties of the hardened 30KhGSA steel and the MA14 magnesium alloy subjected to low- and high-intensity loadings. The model parameters are adjusted by experimental deformation curves obtained from static and dynamic tests at different temperatures and the data from shock experiments to account for strength variation at high strain rates. The simulation of low-intensity loading tests helped to improve the description of elastic-plastic properties and to adjust our failure model. The data from the shock experiments with high-intensity loading of 30KhGSA steel samples and unloading of the shocked samples in window materials were used to verify the phase diagram and the kinetics of direct and inverse phase transitions, and to determine more exactly how the changed phase state influences the strength. The model presented here has allowed us to reproduce the complicated strength behavior of the MA14 alloy at different loading intensities. [ABSTRACT FROM AUTHOR]

The paper is concerned with the skin effect of plastic deformation, which was discovered circa ninety years ago. The study is carried out with the help of the hydrogen diagnostics. Accumulation of hydrogen is shown to occur due to the dissociation of atmospheric moisture under the process of plastic deformation of metals in a thin surface layer comparable to the grain size. Hydrogen is accumulated in pores and microcracks, whose volume in the surface layer increases hundred-fold. The zones of localization of plastic deformation coincide with the local surface zones of hydrogen storage. The obtained experimental data lead to the conclusion that the surface layer cannot be considered as a continuous medium. [ABSTRACT FROM AUTHOR]

The paper consists of two parts united by the central idea of the random field of the microstructure of the material. The first part addresses a discrete static approach to describing the localization effect of plastic deformation known with the help of finite-element analysis under the assumption that the deformation of each of the grains obeys a bilinear law with a normal distribution of the yield stress over the grains. The result is a surface relief in the form of diagonally directed strips, which allows one to treat the deformed surface as Panin’s "chessboard". The second part is concerned with a dynamic continuum approach to the description of the random microstructure of materials. The problem of the propagation of stochastic waves modeled by waves in media with random elastic and mass properties is solved by means of the integral decomposition of the wave amplitude over the wave numbers. [ABSTRACT FROM AUTHOR]

Homogenization theory has been well accepted by the applied mechanics modeling community for its ability to integrate small-scale microstructure phenomena into bulk continuum equations using convergent features of asymptotics. This paper describes an extension of the method to handle asymptotically small atomic scale systems at zero temperature embedded within a deforming continuum. A so-called inner displacement naturally arises in the formulation that enables the consideration of distributed anharmonic crystalline effects that would otherwise be unapproachable with bulk continuum methods alone. The result is a simple computational mechanics method that, first, maps instantaneous continuum deformation gradients to deforming defected crystalline arrangements then, second, provides convergent effective material properties to be used for consistent continuum calculations. The intended applications are those involving patterned defects, either in bulk or on surfaces, which allude to possible manufacturing scenarios. Simple 2-D examples are shown for in-plane deformation of graphene possessing various types of point defects. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]