Justification for meso-scale modelling in quantifying constraint during creep crack growth
Justification for meso-scale modelling in quantifying constraint during creep crack growth
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DOI：
10.1016/j.msea.2003.09.014
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发表时间：
2004-01
期刊：
影响因子：
6.4
通讯作者：
K. Nikbin
中科院分区：
文献类型：
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作者：
K. Nikbin
50-500μm范围内的细观模型被用来预测蠕变范围内的裂纹扩展。它们利用断裂力学、多轴载荷下的蠕变损伤力学和极限分析技术。为了使该方法成为安全缺陷评估程序中可接受的工具，对建模过程中所需的几个级别的近似和验证进行了研究。之前开发的新南威尔士州中尺度模型已经用于比较在550°C下使用紧凑型拉伸(CT)和中心裂纹板(CCP)试件测试的316H不锈钢的裂纹扩展速率。这样，裂纹的稳定扩展区域可以用基于多轴约束水平的上下限裂纹率来解释。然而，该模型只量化了上/下平面的应力-应变界限，而没有量化中间的约束水平。因此，采用双参数约束预测的概念和不同的步骤来提高零件缺陷评估的预测精度。用平面应变条件下的CCP试件进行二维模拟的初步结果表明，与实验结果相比，该方法可以用来预测裂纹扩展速率的保守估计。使用实际几何尺寸的3D模型进行进一步的数值分析是必要的，以证实双参数方法在缺陷评估过程中的有效性。
Meso-scale models over a range of 50–500μm are employed for predicting crack growth in the creep range. They make use of fracture mechanics, creep damage mechanics under multi-axial loading and limit analysis techniques. A study is made of the several levels of approximations and validations in the modelling process that are needed in order to make the method an acceptable tool for use in a safe defect assessment procedure. The NSW meso-scale model developed previously has been used to compare crack growth rate in a 316H stainless steel tested at 550°C using compact tension (CT) and centre-cracked panel (CCP) specimens. In this way the steady crack growth region can be explained by an upper/lower bound cracking rate based on the level of multiaxial constraint. However, the model only quantifies the upper/lower plane stress–strain bounds and does not quantify the intermediate levels of constraint. Therefore, a two-parameter concept to predict constraint and the various steps is employed to improve the predictions for defect assessment in components. Preliminary results using 2D modelling of a CCP specimen under plane strain conditions suggest that the method could be used to predict conservative estimates for crack growth rates when compared to experimental results. Further numerical analysis using 3D models of actual geometric sizes are necessary to confirm the usefulness of the two parameter method in defect assessment procedures.