颗粒物质在等比例应变加载下的分散性失稳模式

由地下水引起的静力液化可能是边坡失稳的隐含机制之一，松砂在不排水剪切条件下可能发生静力液化，密实的颗粒集合体在特定的应变路径下也会出现相似的现象，即试样整体发生急剧的失稳，应力状态尚处于峰值强度线以内。该种失稳模式称为分散性失稳，是为了强调失稳模式中没有出现应变局部化或者剪切带。采用连续-离散耦合分析方法，研究由不规则形状颗粒组成的密实集合体在等比例应变加载路径下的力学特性。根据Hill的材料失稳理论，当试样的应力增量 和应变增量 对应的2阶功 为负时，试样即发生不可逆的整体失稳破坏。以根据不同等比例应变路径得到 曲线为界，在 平面内将试样的应力状态分为剪缩区、剪胀-稳定区和剪胀-非稳定区，连接不同围压下试样发生分散性失稳时的应力状态形成失稳线发现，峰值强度线高于临界状态线，临界状态线高于失稳线。

Diffusion failure mode of granular materials under proportional strain path loading

Loose sandy soil subject to undrained shearing manifests deviatoric softening, and such a behavior has been referred to collapse of static liquefaction. Feedback analysis of some slope failures reveals that the static liquefaction induced by underground water may be one of the implicit mechanisms of the slope failure. Densely packed assemblies exhibit similar phenomenon when sheared along certain proportional strain loading paths. For granular materials, such as soils, which are non-associated materials, diffusion failure can occur for stress states strictly included within the plastic limit condition. The expression “diffusion failure” is used in contrast to “localized failure”, to highlight the failure mode characterized by the lack of localization patterns. The mechanical response of dense assembly of irregular shaped particles subjected to proportional strain loading paths was studied using the combined finite-discrete element method(FDEM). According to Hill’s instability theory, a stress-strain state is stable if the stress and strain increments linked by the constitutive behavior of the material produce a strictly positive second-order work. The second-order work criterion is linked to the occurrence of a diffusing failure mode. In the meridian plane, the stress space is divided into dilation and compaction as distinguished by the controlling parameter of proportional strain loading path. The instability line is built by joining the points marking the onset of diffusion failure from each confining pressure.