The conventional flow rule and plasticity constitutive models implicitly assume that the principal stress and plastic strain rate are coaxial, which often result in various setbacks in modeling, for example, the bifurcation and the evolution of shear band cannot be accurately and adequately captured. In this work, we investigate the non-coaxial effects of an elastoplastic constitutive model on strain localization in the framework of micropolar plasticity theory. The vertex-like yield surface is introduced in the flow rule, and a non-coaxial Drucker–Prager model is implemented in a user-defined finite element subroutine (UEL) in ABAQUS. The simple shear test and the plane strain compression test have been conducted to study the non-coaxial stress–strain response and the strain localization behavior. Effects of boundary condition on bifurcation, shear band orientation and thickness are investigated. Results indicate that the proposed model shows a good performance in the simulation of the non-coaxial behavior of geomaterials. On the premise of overcoming mesh dependency, the shear band orientation and width predicted by the non-coaxial model possess higher values than those predicted by the coaxial model, and a better agreement with the experimental results are achieved by the non-coaxial model. Moreover, by analyzing stress–strain responses, we have found that material strength may be systematically overestimated by the coaxial model.

传统的流动规律和塑性本构模型隐含地假设主应力和塑性应变率是同轴的，这往往会导致建模中的各种挫折，例如不能准确和充分地捕捉分岔和剪切带的演变。在这项工作中，我们在微极塑性理论的框架内研究了弹塑性本构模型对应变局部化的非同轴效应。在流动规则中引入了类顶点屈服面，并在 ABAQUS 中用户定义的有限元子程序 (UEL) 中实现了非同轴 Drucker-Prager 模型。进行了简单剪切试验和平面应变压缩试验以研究非同轴应力应变响应和应变局部化行为。边界条件对分岔的影响，研究了剪切带的取向和厚度。结果表明，所提出的模型在模拟岩土材料的非同轴行为方面表现出良好的性能。在克服网格依赖性的前提下，非同轴模型预测的剪切带方向和宽度比同轴模型预测的值更高，非同轴模型与实验结果的一致性更好。此外，通过分析应力应变响应，我们发现同轴模型可能会系统地高估材料强度。非同轴模型预测的剪切带方向和宽度均高于同轴模型预测的值，非同轴模型与实验结果更加吻合。此外，通过分析应力应变响应，我们发现同轴模型可能会系统地高估材料强度。非同轴模型预测的剪切带方向和宽度均高于同轴模型预测的值，非同轴模型与实验结果更加吻合。此外，通过分析应力应变响应，我们发现同轴模型可能会系统地高估材料强度。