岩土材料弹塑性损伤模型及变形局部化分析

ELASTO-PLASTIC DAMAGE MODEL FOR GEOMATERIALS AND STRAIN LOCALIZAION ANALYSES

常规的弹塑性模型由于没有考虑到损伤和塑性的耦合作用,难以模拟破坏时由于内部损伤的累积导致的变形局部化剪切带的形成过程,因而,不能很好地反映实际结构的细观破坏机理。作者采用一种宏细观结合的思路,基于细观损伤力学提出了一个适用于岩土材料弹塑性损伤模型,研究均质材料在外部环境作用下由于损伤和塑性的耦合导致的局部化剪切带的形成过程。对基体材料服从 Drucker-Prager 准则的球形孔洞体胞单元提出了一个塑性损伤屈服面,为了反映岩土材料在拉应力和压应力作用下不同的孔洞形成机理,分别采用了球形拉应力和塑性应变的成核机制来建立孔隙率的演化方程,根据塑性损伤屈服面和孔隙率的演化方程,导出了关联流动法则下的岩土材料塑性损伤本构方程。将笔者提出的岩土材料弹塑性损伤模型,通过用户子程序嵌入到大型商业有限元软件MRAC中。为了研究塑性和损伤的耦合作用,分别采用Gurson弹塑性损伤模型和Mises弹塑性模型,对Tvergaard关于自由表面有周期性分布微小形状缺陷的半无限大板在平面应变拉伸作用下剪切带的形成进行了数值模拟,计算结果表明弹塑性损伤本构模型在模拟变形局部化方面具有明显的优势。采用作者提出的岩土材料弹塑性损伤模型,对平面应力条件下有一个缺陷单元的均质岩土材料单轴受压试?

Elasto-plastic models can not explain the micro mechanism of shear band formation caused by damage evolution in ductile material due to the neglecting of the interaction between damage and plastic flow. An elasto-plastic damage model for geo-materials based on micromechanics is proposed and the micro mechanism of shear band formation in homogeneous geo-material is studied. A macroscopic yield criterion for porous geo-materials with matrices of Drucker-Prager yield criterion is given,and a plastic strain-controlled void nucleation model as well as a tensile volumetric stress-controlled nucleation model are proposed for the compressive and tensile stresses,respectively. Moreover,the constitutive relationship of the elasto-plastic damage model with plastic normality flow rule is deduced. This elasto-plastic damage model for geo-materials is embeded into the commercial FEM software MARC as a user’s subroutine. A tensile plane strain specimen with initial shape imperfection on its upper bound which was first analyzed by Tvergaard is investigated through the elasto-plastic damage model and Mises elasto-plastic model,respectively. It is shown that the shear band development is only found in Gurson elasto-plastic damage model. Shear band formation due to void nucleation and growth in a plane stress specimen of homogeneous geo-material with one defect element subjected to uniaxial compression is analyzed by the model.