平面应变条件下砂土局部化剪切带的有限元模拟

根据饱和砂土的排水平面应变压缩试验的应变场,分析研究砂土的应变局部化现象以及剪切带的形成。在平面应变压缩条件下,砂土在峰值应力状态附近出现应变局部化现象,在残余状态最终形成一条V型剪切带。剪切带的形成是一个渐进过程,砂土呈现出渐进性破坏特性。这种由软化特性引起的应变局部化剪切带是砂土材料非常重要的变形和强度特性之一。基于砂土的三要素弹黏塑性本构模型和动态松弛有限元求解技术,对砂土的应变局部化现象和剪切带的形成进行有限元模拟。其中,砂土本构模型中引入应变局部化参数S来表示砂土峰值以后的软化和剪切带效果,剪切带在单元内未考虑其方向性,而是假设剪切带方向与最大剪切应变的方向一致。分析结果表明,动态松弛有限元法及砂土三要素模型能合理地模拟砂土的应变局部化现象,剪切带附近的最大剪应变值也非常接近,从而实现对砂土材料从硬化→峰值→软化→残余的全过程模拟以及对砂土应变局部化剪切带的定量化分析。

FINITE ELEMENT SIMULATION OF STRAIN LOCALIZATION ON A SHEAR BAND OF SAND UNDER PLANE STRAIN CONDITION

On the basis of the local strain fields in the specimen obtained from the drained plane strain compression (PSC) test on saturated sand,the strain localization on a shear band induced by post-peak softening is investigated. Under plane strain condition,the strain localization starts around the peak stress state;and a V-shaped shear band is formed at the residual stress state. It can be seen that sand has progressive failure feature with shear banding. The strain localization on a shear band induced by post-peak softening is one of the most important deformations and strength characteristics of sand. On the basis of dynamic relaxation method,a nonlinear finite element analysis(FEA) technique incorporating the three-component elasto-viscoplastic constitutive model for sand is developed to simulate the strain localization on a shear band. A strain localization parameter,S,is introduced into the constitutive model to describe the post-peak softening and shear banding. No direction of shear banding is specified in the finite element simulation. The direction of shear banding is implicitly assumed to be consistent with the direction of maximum shear strain. It is shown that the presented FEA can well simulate the strain localization on a shear band;and the maximum shear strain around the shear band is very close between physical test and finite element simulation. Therefore,the whole process simulation from pre-peak hardening,peak,post-peak softening to the residual stress state is implemented in the FEA. And the quantitative analysis of strain localization on a shear band for sand could also be done by the presented FEA technique.