基于ANSYS二次开发地下工程材料非线性有限元分析

发布时间：2018-05-20 09:41

本文选题：地下工程 + Mohr-Coulomb模型　；参考：《华南理工大学》2015年硕士论文

【摘要】：地下工程中涉及的材料主要是岩土类材料,岩土的性质非常复杂,属于三相体摩擦类材料。由于地质体具有不连续性、非均质性、各向异性、存在地下水和初应力等特征,因此很多的岩土工程问题很难通过解析法求解,为此可以采用有限元等数值方法来解决;岩土具有明显的弹塑性特征,须进行弹塑性分析才能得到切合实际的计算结果。考虑以上因素并为了拓宽有限元软件ANSYS在地下工程的运用范围,本文利用ANSYS的二次开发功能—用户可编程特性UPFs,编制Mohr-Coulomb模型子程序usermat.F,对岩土结构进行材料非线性有限元分析。本文首先,在理解弹塑性理论中平面应变问题、屈服条件、硬化模型、流动法则、加卸载准则等基本概念的基础上。通过Mohr-Coulomb定律,导出用应力不变量表示的屈服准则,考虑各向同性硬化模型和相关联流动法则,采用简单的处理方法消去无法确定塑性流动方向的奇异点,推导了便于数值计算的弹塑性刚度矩阵。然后,根据usermat子程序有应力更新和输出一致切线算子矩阵的任务。详细阐述了求解应力更新的回退算法中弹性预测步和塑性修正步这两个步骤的数学和力学原理;通过增量型有限元说明一致切线算子矩阵即弹塑性刚度矩阵。据此,采用结构化程序设计方法,编制了子程序usermat.F。通过编译链接程序,将Mohr-Coulomb模型子程序导入ANSYS材料库中。最后,通过两个算例来验证本文模型的正确性和可靠性。通过算例一证明了子程序usermat.F能完成应力更新的任务,并在宏观上能反映土体从开始受力到剪切坡坏的整个过程。通过算例二,说明了自编的Mohr-Coulomb模型能达到ANSYS自带DP模型相近的效果;另外从安全因素和土所具有的本质属性来考虑,对于地下工程,采用弹塑性分析才能真实反映岩土的力学特性。
[Abstract]:The materials involved in underground engineering are mainly geotechnical materials. The properties of rock and soil are very complex and belong to three-phase friction materials. Because geological bodies have the characteristics of discontinuity, heterogeneity, anisotropy, groundwater and initial stress, many geotechnical engineering problems are difficult to be solved by analytical method, which can be solved by finite element method. The rock and soil have obvious elastic-plastic characteristics, so it is necessary to carry out elastic-plastic analysis to obtain practical results. Considering the above factors and in order to widen the application scope of finite element software ANSYS in underground engineering, this paper makes use of the secondary development function of ANSYS-user programmable characteristic UPFs, compiles the Mohr-Coulomb model subprogram usermat.F, carries on the material nonlinear finite element analysis to the geotechnical structure. In this paper, firstly, the basic concepts of plane strain problem, yield condition, hardening model, flow rule, loading and unloading criterion in elastic-plastic theory are understood. By means of Mohr-Coulomb 's law, the yield criterion expressed by stress invariants is derived. The isotropic hardening model and the associated flow rule are considered, and the singularity points in which the direction of plastic flow can not be determined are eliminated by a simple treatment method. The elastoplastic stiffness matrix which is easy to calculate numerically is derived. Then, according to the usermat subroutine, there are the tasks of updating the stress and outputting the uniform tangent operator matrix. The mathematical and mechanical principles of elastic prediction step and plastic correction step in the regression algorithm for stress updating are described in detail, and the uniform tangent operator matrix, i.e. the elastic-plastic stiffness matrix, is explained by the incremental finite element method. Based on this, the subprogram usermat.F. By compiling the link program, the Mohr-Coulomb model subroutine is imported into the ANSYS material library. Finally, two examples are given to verify the correctness and reliability of the model. An example is given to prove that the subroutine usermat.F can complete the task of stress renewal and can reflect the whole process from the beginning to the failure of the shear slope. The second example shows that the self-made Mohr-Coulomb model can achieve the similar effect of ANSYS self-contained DP model, in addition, considering the safety factors and the nature of soil, for underground engineering, The elastoplastic analysis can truly reflect the mechanical properties of rock and soil.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU43

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