基于统一强度理论的土体应变局部化预测研究

发布时间：2018-03-21 23:16

本文选题：统一强度理论　切入点：应变局部化　出处：《长安大学》2013年博士论文　论文类型：学位论文

【摘要】：土体剪切带的形成机理与应变局部化理论是当今国际力学界和岩土工程界广泛研究的课题，应变局部化分叉理论预测为揭示岩土材料的破坏机理提供了有力依据。统一强度理论具有统一的力学模型、统一的理论和统一的数学表达式，可以有规律地变化以适用于各类工程材料，形成了一系列有序的破坏准则，可广泛适用于各种工程领域。但统一强度理论在剪切带形成机理以及非共轴本构模型和应变局部化分叉判别等方面还缺乏深入细致的系统应用研究，而且以往应变局部化没有考虑三维应力空间下混合硬化模型的影响。本文将混合硬化模型和统一强度理论用于应变局部化应力应变关系，应变局部化分叉点位置和剪切带倾角等预测研究。主要研究内容与结论如下：（1）建立了以压应力为正的统一强度理论公式，进而推导了新的加载函数和相应的塑性势函数及本构方程，并结合修正Euler积分方法编制了率型本构方程的积分程序对粘性土平面应变试验和密砂真三轴试验进行了模拟和验证，得出：当参数b取合适值时，预测值比已有文献结果更接近试验结果。对于所选的粘性土材料和密砂材料，可分别选用参数b=1和b=0.9所对应的强度理论进行应力应变关系预测。（2）在三维非共轴应力空间内，，考虑第三应力不变量对塑性变形非共轴性的影响，基于非共轴混合硬化法则，建立了更加符合土体实际受力性状的非共轴本构新模型、变形局部化分叉点判别准则和剪切带倾角公式，并对所得结果进行退化必要性验证；同时，结合修正Euler积分的基本步骤进行模拟，与已有成果和试验数据进行比较，验证了所得分叉点判别准则的初步合理性。（3）建立了基于统一强度理论和混合硬化法则的新的加载函数、塑性势函数、统一非共轴本构模型、应变局部化分叉点判别准则和剪切带倾角公式，并对粘性土平面应变试验和密砂真三轴试验进行了模拟和试验验证，得出：非共轴项的引入并不改变土体应力应变关系特性；对于所选的粘性土材料和密砂材料，可分别选用参数b=1和b=0.9所对应的强度理论来分析预测应变局部化分叉点和剪切带倾角。
[Abstract]:The formation mechanism and strain localization theory of soil shear zone are widely studied in the field of international mechanics and geotechnical engineering. The prediction of strain localization bifurcation theory provides a force basis for revealing the failure mechanism of rock and soil materials. The unified strength theory has a unified mechanical model, a unified theory and a unified mathematical expression. Can be changed regularly to apply to all kinds of engineering materials, forming a series of orderly failure criteria, It can be widely used in various engineering fields. However, the unified strength theory is still lack of systematic research on shear band formation mechanism, noncoaxial constitutive model and strain localization bifurcation, etc. In the past, strain localization did not consider the effect of mixed hardening model in three-dimensional stress space. In this paper, the mixed hardening model and the unified strength theory are applied to the strain localization stress-strain relationship. Prediction of strain localization bifurcation point location and shear band inclination. The main contents and conclusions are as follows:. 1) the unified strength theory formula with compressive stress as positive is established, and a new loading function, corresponding plastic potential function and constitutive equation are derived. Combined with the modified Euler integral method, the integral program of the rate constitutive equation is compiled to simulate and verify the plane strain test of cohesive soil and the true triaxial test of dense sand. The predicted values are closer to the experimental results than the results of previous literatures. For the selected cohesive soil materials and dense sand materials, the stress-strain relationship can be predicted by the strength theory corresponding to the parameters bt1 and BX 0.9, respectively. 2) considering the influence of the third stress invariant on the non-coaxial deformation of the soil, a new noncoaxial constitutive model is established based on the non-coaxial mixed hardening rule in the three-dimensional non-coaxial stress space. The deformation localization bifurcation criterion and shear band inclination formula are used to verify the degenerative necessity of the obtained results. At the same time, combined with the basic steps of the modified Euler integral, the results are simulated and compared with the existing results and experimental data. The preliminary rationality of the bifurcation criterion is verified. A new loading function, a plastic potential function, a unified noncoaxial constitutive model, a strain localization bifurcation criterion and a shear band inclination formula are established based on the unified strength theory and the mixed hardening rule. The plane strain test of cohesive soil and the true triaxial test of dense sand are simulated and verified. It is concluded that the introduction of non-coaxial term does not change the stress-strain relationship of soil, and for the selected cohesive soil and dense sand, The strength theory corresponding to the parameters bt1 and bt0. 9 can be used to analyze and predict the strain localization bifurcation point and shear band inclination respectively.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU43

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