各向异性弹黏塑性模型在ABAQUS中的研发

通过将Perzyna过应力理论与临界状态理论相结合，并引入Wheeler旋转硬化法则，提出一个能描述土体初始各向异性及应力诱发各向异性的三维弹黏塑性本构模型。模型考虑流变发生的下限，在三维应力空间，模型存在形状相似的静屈服面及动态加载面。采用缩放形式的幂函数。本构模型数值算法采用回映算法，借助ABAQUS软件UMAT子程序接口实现。并通过对三轴不排水蠕变试验的模拟，确定合适的积分步长。此后，分别对三轴不排水蠕变试验及常应变率三轴不排水剪切试验进行了模拟。模拟中通过设置不同参数值，可将模型退化为各向同性模型，并对这两种模拟结果进行了比较。模拟结果表明：(1) 对于三轴不排水蠕变，在低剪应力水平下，各向同性模型和各向异性模型模拟的结果相差不大，而在高剪应力水平下，各向异性模型模拟结果更接近试验结果；(2) 对于常应变率加载试验的模拟，模型合理反映了土体不排水强度随着加载速率的增大而增大现象。

Development of anisotropic elasto-viscoplastic model in ABAQUS software

This paper presents an improved three-dimensional anisotropic elasto-viscoplastic constitutive model which is based on overstress theory of Perzyna and critical state theory.In this model a rotational hardening law of Wheeler is also adopted to account for initial anisotropy and changes in anisotropy due to stress.The viscoplastic strain will not occur when the stress state is located within the static yield surface.A power-type scaling function is adopted for the viscoplastic strain-rate.The constitutive model is programmed in ABAQUS software by writing UMAT subroutine,which is integrated with Return Mapping Algorithm.Anisotropically consolidated undrained(CU) triaxial creep test for Sackville clay is simulated by proposed model and the suitable integration time step is determined.Then other CU triaxial creep tests and CU triaxial constant strain rate tests are simulated.By switching the anisotropic features off,the proposed model is degraded to the isotropic model.The simulation results show(1) The CU triaxial creep tests with rotational hardening law is more accurate than isotropic model in the high level of the shear stress;(2) The CU triaxial constant strain rate tests rationally reflect that the undrained strength of soil increase with loading rate.