【作者】 苏月；

【导师】 李国成；

【作者基本信息】 中国石油大学 ， 化工过程机械， 2007， 硕士

【摘要】 随着弹塑性断裂力学的发展,目前具有严格理论基础的双判据(断裂与塑性失稳)J积分失效评定图技术已成为缺陷断裂评定的主要依据。然而,J积分的计算是这一技术成功应用的关键。虽然EPRI给出了一套近似的工程解法,但实际上工程中构件的裂纹大多呈现内在的三维效应,若使用二维弹塑性或三维弹性分析必然不够精确,因为对裂纹的“等效”二维表达忽视了发生在靠近裂纹端部的应力和应变的再分配,所以对压力容器裂纹进行三维弹塑性分析及其J积分是研究压力容器裂纹扩展和安全评定的基础工作之一。本文在Rice提出的二维J积分表达式的基础上,推导出三维裂纹J积分表达式,验证了其与积分路径无关的这一特性,改变以往对裂纹前端普遍采用的“平行切片”积分,采用反映裂纹前端应力情况的“扇形切片”积分,将裂纹前沿的应力流变化考虑进去并减小了误差。以半椭圆表面裂纹和平面应变中心裂纹为计算模型,借助有限元法、高斯积分法,并采用六面体20节点单元,将公式转换成易于求解的数值积分形式——高斯积分形式,进而完成模型的三维J积分计算的全过程,利用ANSYS的二次开发工具APDL编写计算程序,使用Yagawa的拉伸解对该程序进行考核。更多还原

【Abstract】 At present, along with the development of elasto-plastio fracture mechanics, the double criterion (cracked and plastic instability) _J-integral disabled assessed-picture technique have become the primary basis of the defective cracked assessment, which based upon the strict theory. However, the key that the technique to be succeeded applied is the calculation of the J-integral. Although the EPRI give a set of the approximate engineering solution method, actually the crack of parts in engineering project mostly presents inner 3D effect. If using 2D elastic-plastic or 3D elastic analysis, the result can’t be precise. Because these methods have neglected the reassignation of the stress and strain which happened at nearly the top of cracks, carrying on 3D elastic-plastic analysis and J-integral calculation become the foundational work to study the expander and safety assessment of the pressure vessel cracks.On the basis of 2D J-integral expression by Rice, the text has deduced a 3D crack J-integral expression, verified it have nothing to do with the integral path, changed the "parallel slice" integral calculus which be widespread adopted in head of the cracks, adopted the "fan slice" integral calculus which reproduced the stress situation about the head of cracks. This kind of method takes full the stress-current change about the head of cracks into account, and reduces errors.The calculating model of semi-elliptical surface cracks is proposed by using the strong function of building model, analyzing and calculating in ANSYS. With the benefit of finite element method and Gaussian integral method, adopted the hexahedron 20 nodes element, 3D cracks J-integral formula will be converted into the numeric integral format_Gaussian integral format, which be prone to solve, and then the overall 3D J-integral calculating process is finished, program for calculating J-integral in the method of surrounding integral with APDL.更多还原