A stochastic jump and deterministic dynamics model of impact failure evolution with rate effect

Motivated by the observation of the rate effect on material failure, a model of nonlinear and nonlocal evolution is developed, that includes both stochastic and dynamic effects. In phase space a transitional region prevails, which distinguishes the failure behavior from a globally stable one to that of catastrophic. Several probability functions are found to characterize the distinctive features of evolution due to different degrees of nucleation, growth and coalescence rates. The results may provide a better understanding of material failure

损伤断裂图型演化的统计描述

本文采用动力学演化与随机跃迁并存的模型;研究损伤断裂图型的演化规律。根据演化的终态;损伤演化可分为整体稳定(GS)和演化引起剧变(EIC)两种模式;后者联系于断裂现象。本文引入统计描述;并指出;即使微损伤的连接规律是确定性的;无序介质中断裂的出现亦应以概率分布函数描写

从“哥伦比亚”号悲剧看多尺度力学问题

航空航天安全蕴含着大量的涉及多个物理层次的多尺度力学问题.多尺度力学问题对现有的力学概念和理论是一个巨大的挑战.以铝合金层裂和岩石脆性破坏为典型案例,讨论了多尺度力学问题的特点、难点以及可能的处理方法,说明合理表征和处理多尺度问题的跨尺度耦合及跨尺度敏感性是解决多尺度问题的关键

微裂纹串级连接及临界破坏

对一铝合金材料层裂过程的实验研究发现;当损伤累积到一定程度时;受损材料的残余强度突然丧失;表现出临界破坏现象。层裂表面具有分形特征;其分形断面的形成归因于大量微裂纹的串级连接。据此提出了一重正化群弱面模型;并对损伤演化后期的临界破坏现象进行了初步的分析和探讨

Long-Range Stress Redistribution Resulting From Damage in Heterogeneous Media

It has been shown in CA simulations and data analysis of earthquakes that declustered or characteristic large earthquakes may occur with long-range stress redistribution. In order to understand long-range stress redistribution, we propose a linear-elastic but heterogeneous-brittle model. The stress redistribution in the heterogeneous-brittle medium implies a longer-range interaction than that in an elastic medium. Therefore, it is surmised that the longer-range stress redistribution resulting from damage in heterogeneous media may be a plausible mechanism governing main shocks

Critical Sensitivity and Trans-Scale Fluctuations in Catastrophic Rupture

Rupture in the heterogeneous crust appears to be a catastrophe transition. Catastrophic rupture sensitively depends on the details of heterogeneity and stress transfer on multiple scales. These are difficult to identify and deal with. As a result, the threshold of earthquake-like rupture presents uncertainty. This may be the root of the difficulty of earthquake prediction. Based on a coupled pattern mapping model, we represent critical sensitivity and trans-scale fluctuations associated with catastrophic rupture. Critical sensitivity means that a system may become significantly sensitive near catastrophe transition. Trans-scale fluctuations mean that the level of stress fluctuations increases strongly and the spatial scale of stress and damage fluctuations evolves from the mesoscopic heterogeneity scale to the macroscopic scale as the catastrophe regime is approached. The underlying mechanism behind critical sensitivity and trans-scale fluctuations is the coupling effect between heterogeneity and dynamical nonlinearity. Such features may provide clues for prediction of catastrophic rupture, like material failure and great earthquakes. Critical sensitivity may be the physical mechanism underlying a promising earthquake forecasting method, the load-unload response ratio (LURR)

Closed Trans-Scale Statistical Microdamage Mechanics

Damage and failure due to distributed microcracks or microvoids are on the challenging frontiers of solid mechanics. This appeals strongly to tools not yet fully developed in continuum damage mechanics, in particular to irreversible statistical thermodynamics and a unified macroscopic equations of mechanics and kinetic equations of microstructural transformations. This review provides the state of the art in statistical microdamage mechanics. (1) It clarifies on what level of approximation continuum damage mechanics works. Particularly, D-level approximation with dynamic function of damage appears to be a proper closed trans-scale formulation of the problem. (2) It provides physical foundation of evolution law in damage mechanics. Essentially, the damage-dependent feature of the macroscopic evolution law is due to the movement of microdamage front, resulting from microdamage growth. (3) It is found that intrinsic Deborah number D*, a ratio of nucleation rate over growth rate of microdamage, is a proper indication of critical damage in damage mechanics, based on the idea of damage localization. (4) It clearly distinguishes the non-equilibrium damage evolution from equilibrium phase transition, like percolation. Finally, some comments on its limitations are made

细观力学面临的新挑战国际会议简介

“细观力学面临的新挑战国际会议”(“International Conference on New Challenges in Mesomechanis”)于2002年8月26～30日在丹麦奥尔堡(Aalborg)召开，由奥尔堡大学(Aalborg University)主办。与会人数约120人，分别来自丹麦、中国、希腊、俄国、德国、美国、英国、日本等20多个国家。会议上报告论文100余篇。我国有12人(包括大陆、香港、台湾)参加会议，在会上作了10个报告

波驱动电流的临界密度效应

近来,在低杂波驱动托卡马克电流的实验中,发现当等离子体密度超过某个临界值时波驱动的电流突然降到很低的值。对这种现象尚无比较肯定的解释,研究波驱动电流的目的是要建立稳态托卡马克反应堆,当然希望能在较高密度下运行,临界密度的存在对这种方