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COMPUTATIONAL ASPECT OF NONLINEAR FRACTURE MECHANICS APPLICATION

机译：非线性断裂力学应用的计算方面

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The development of powerful commercial computer programs made the concept of J-integral as computational parameter of fracture mechanics to be a very attractive one. It is equivalent to SIF in linear case, it converges in numerical calculation and the same results are obtained by different codes (programs). Besides, it is widely thought that elastic-plastic analysis gives bigger values than elastic SIF ones what is good from regulatory point of view. Such stand was reflected in the recommended by IAEA TECDOC 1627 (February 2010) devoted to pressurized thermal shock analysis of reactor pressure vessels, where the embedded crack in FEM mesh, elastic-plastic analysis with simultaneous determination of J-integral was stated as the best option of analysis. But at that time all the most widely used software were not able to treat the residual stresses, the thermal stresses in case of two different materials. Such a contradiction between requirements and the possibilities made a lot of problems for honest contractors especially in countries where the regulator had no own experience in calculation and completely relied on the authority of international documents. This means that at that time the said recommendations were harmful. The main reason of such a situation was the absence of the carefully elaborated examples. Now the capabilities and accuracy of such software are increasing. Nevertheless, some principal ambiguities and divergences of computations results in various J-integral contours around the crack tip still exist. They are exhibited when the large plastic zone emerges at the crack tip. Other problem is influence of the history of loading and the specification of the time of crack insertion in the mesh including the time of emergence of residual stress. This paper is invitation for discussion of the accuracy and restriction of computational J-integral. With this aim the detailed analysis of some simplified 2D examples of calculation of elastic -plastic J-integral for surface crack with accounting for residual stress, thermal stress and inner pressure are performed and commented. The attainment of consensus among the engineering society for treating the outcome results is the prerequisite for practical application of computational elastic plastic J-integral.
机译：强大的商用计算机程序的发展使作为断裂力学计算参数的J积分概念成为非常有吸引力的一个。在线性情况下等效于SIF，它在数值计算中收敛，并且通过不同的代码（程序）获得相同的结果。此外，人们普遍认为，从法规的角度来看，弹塑性分析比弹性SIF给出更大的值。这种立场反映在国际原子能机构TECDOC 1627（2010年2月）的建议中，该建议专门用于反应堆压力容器的加压热冲击分析，该方法在FEM网格中嵌入裂纹，同时确定J积分的弹塑性分析被认为是最好的分析选项。但是当时所有使用最广泛的软件都无法处理两种不同材料的残余应力（即热应力）。要求与可能性之间的这种矛盾给诚实的承包商带来了很多问题，尤其是在监管者没有自己的计算经验并且完全依赖国际文件权威的国家。这意味着当时的上述建议是有害的。出现这种情况的主要原因是缺乏精心阐述的例子。现在，此类软件的功能和准确性正在提高。然而，仍然存在一些主要的歧义和计算结果的分歧，导致裂纹尖端周围的各种J积分轮廓仍然存在。当大的塑性区出现在裂纹尖端时，它们就会出现。另一个问题是载荷历史的影响以及裂纹在网格中的插入时间（包括出现残余应力的时间）的规范。本文诚邀您讨论计算J积分的准确性和局限性。以此为目标，对一些简化的二维示例的详细分析进行了详细分析，并考虑了残余应力，热应力和内部压力，从而对表面裂纹的弹塑性J积分进行了计算。工程学会之间对于结果结果的处理达成共识是计算弹性塑料J积分实际应用的前提。

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