Abstract This work describes the framework to model ductile damage based on phenomenological stress-modified critical strain criterion (SMCS) coupled with a softening law to predict the onset of ductile initiation and ductile propagation in typical fracture specimens, extracted from a flat plate made of ASTM A285 Gr. C steel. A very detailed and well-illustrated methodology has been developed for the identification of material parameters. Laboratory testing of cylindrical tensile bars and SE(B) specimens, at room temperature, provides necessary and sufficient information to calibrate the numerical parameters in the proposed model. For either geometry, the applied loading is measured by a continuous record of the load ( P ) and displacement ( Δ ) . After the model parameters have been set, verification studies are carried out for SE(B) specimens having shallow cracks with and without side-grooves. Consequently, parameter transferability, outside small-scale yielding condition between specimens having different crack tip conditions, can be addressed and the constraint influence on the driving force better understood. An additional check is performed by comparing the final crack front profile measured on the fracture surface of the SE(B) specimens with the numerical calculated in the finite element analyses. The phenomenological model adopted herein can reproduce and predict reasonably well the experimental data obtained for specimens with different levels of stress triaxiality (constraint). Overall, it is shown that the SMCS criterion combined with a softening law can be used to study and to predict the influence of stress state on ductile failure initiation and ductile crack growth by identifying nine model parameters through testing notched round bar geometries and SE(B) specimens. The proposed methodology shows great potential as an engineering tool for assessing the integrity of complex structures such as welded pipelines and pressure vessels.

中文翻译：

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使用典型压力容器钢的临界应变轨迹和软化定律模拟延性断裂

摘要 这项工作描述了基于现象学应力修正临界应变准则 (SMCS) 和软化定律的延性损伤建模框架，以预测典型断裂试样中延性起始和延性扩展的开始，从由 ASTM 制成的平板中提取。 A285 Gr。C钢。已经开发了一种非常详细且图解清楚的方法来识别材料参数。在室温下对圆柱形拉伸杆和 SE(B) 试样进行实验室测试，为校准所提出模型中的数值参数提供了必要和充分的信息。对于任一几何形状，施加的载荷是通过载荷 (P) 和位移 (Δ) 的连续记录来测量的。模型参数设置好后，对带有和不带侧槽的浅裂纹的 SE(B) 试样进行验证研究。因此，可以解决具有不同裂纹尖端条件的试样之间小规模屈服条件之外的参数可传递性，并更好地理解对驱动力的约束影响。通过将在 SE(B) 试样断裂表面上测量的最终裂纹前沿轮廓与有限元分析中计算的数值进行比较，进行了额外的检查。本文采用的现象学模型可以合理地再现和预测具有不同应力三轴性（约束）水平的试样获得的实验数据。全面的，结果表明，SMCS 准则结合软化定律可用于研究和预测应力状态对延性破坏萌生和延性裂纹扩展的影响，通过测试缺口圆棒几何形状和 SE(B) 试样确定九个模型参数. 所提出的方法显示出作为评估复杂结构（如焊接管道和压力容器）完整性的工程工具的巨大潜力。