Abstract In this paper, a continuum damage enhanced formulation of effective (undamaged) material properties is proposed to predict fracture behaviour of various notched tensile specimens and a compact tension (CT) specimen for a high-strength rail steel that is commonly known to be insensitive to change in hydrostatic stress. The presented constitutive model considers a thermodynamically nonlinear, isotropic continuum damage, and stress-triaxiality-dependent effective stress using a viscoplastic regularization method to reduce strain and damage localization at the sharp notch tip. Conventional loading-unloading tensile test for damage measurement and monotonic tensile test on a notched specimen are used to calibrate the constitutive equation which consists of a set of eight model parameters. Further validation is performed on the geometry transferability of the model parameters to three different notched tensile specimens in the high stress triaxiality regime. The calibrated constitutive model is then applied to simulate crack initiation and propagation in the mode I plane-strain condition, where the computed result of load versus crack mouth opening displacement shows good agreement with those determined from CT specimens. The study concludes that the critical damage parameters for fracture are relatively constant among different notched specimens of high-strength rail steel, and thus as a proper fracture criterion for crack initiation at and crack propagation from the sharp notch tip. The study also found that the complementing mechanisms for the stress-triaxiality-dependent damage evolution and strain-hardening-induced enhancement of effective matrix material properties, respectively, result in the overall hydrostatic-stress insensitivity, and thus is often regarded as a material that belongs to the classical J2 plasticity.

中文翻译：

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高强钢轨裂纹萌生与扩展的应力-三轴耦合损伤粘塑性模型

摘要 在本文中，提出了一种有效（未损坏）材料特性的连续损伤增强公式来预测各种缺口拉伸试样的断裂行为和通常已知不敏感的高强度轨道钢的紧凑拉伸 (CT) 试样的断裂行为。改变静水应力。所提出的本构模型考虑了热力学非线性、各向同性连续介质损伤和应力三轴相关的有效应力，使用粘塑性正则化方法来减少尖锐缺口尖端的应变和损伤局部化。用于损伤测量的常规加载-卸载拉伸试验和缺口试样的单调拉伸试验用于校准由一组八个模型参数组成的本构方程。进一步验证了模型参数在高应力三轴状态下对三个不同缺口拉伸试样的几何可转移性。然后应用校准的本构模型来模拟模式 I 平面应变条件下的裂纹萌生和扩展，其中载荷与裂纹开口位移的计算结果与 CT 试样确定的结果非常吻合。研究得出的结论是，高强度钢轨钢不同缺口试样的断裂临界损伤参数相对恒定，因此可作为裂纹在尖锐缺口尖端处萌生和裂纹扩展的适当断裂准则。