压力容器有限元应力分析中应力的正确评定--压力容器应力分析设计中的六个重要问题(一)

ISSUES ON THE CORRECT ASSESSMENT OF STRESS IN FINITE ELEMENT ANALYSIS FOR PRESSURE VESSELS

讨论了标准中关于一次弯曲应力限制准则的理论依据,经过比较得出结论,分析设计标准中关于一次弯曲应力的评定不适用于容器圆筒大开孔问题,压力容器圆筒大开孔孔边弯曲应力必须按SⅢ评定,不能直接以SⅣ评定,而且SⅢ不能按1.5 Sm评定,SⅢ评定可依据极限载荷确定,其承载潜力系数远大于1.5。有限元方法(如ANSYS软件)计算结果只能给出所考察的路径(截面)上的三部分应力:薄膜应力(均匀部分),弯曲应力(线性分布部分)和峰值应力(非线性部分),但无法分清前两部分应力中的一次应力与二次应力的成分,长期以来其应力的评定存在不确定性。同时介绍了一次结构法的原理及在压力容器上的应用。一次结构法为合理解决有限元分析结果评定不确定性问题开辟了新途径。

This paper discusses the theoretical foundation for the restriction criteria of primary bending stress in current codes.After comparison and analysis,the paper arrives at the conclusions that the assessment criteria for primary bending stress in design code is not applicable to large opening in vessel cylinder;the bending stress of large opening in pressure vessel cylinder should be assessed according to S_Ⅲ other than S_Ⅳ.And S_Ⅲ cannot be assessed according to 1.5 S_m and can be determined by limit load.Its loading potential coefficient is far more than 1.5.And results from FEA method,such as ANSYS software,can only provide three parts of stress on the checking path or section:membrane stress(uniform part),bending stress(liner distribution part) and peak stress(nonlinear distribution part).But the components of the primary and secondary stress cannot be separated from the first two parts of stress.So the assessment on the stress of these parts has been uncertain for a long time.Meanwhile,this paper introduces the principles of primary structure method and its application to pressure vessels as well.The primary structure method opens up a new way for the reasonable solution to the uncertain problem of stress assessment on FEA results.