内压圆筒中表面裂纹蠕变扩展的数值分析

NUMERICAL ANALYSIS OF SURFACE CRACK GROWTH IN PRESSURIZED CYLINDERS UNDER CREEP CONDITION

金属蠕变的研究逐渐趋向对含缺陷材料与结构进行探讨,但针对金属构件表面裂纹蠕变扩展特性的研究仍然有限。基于三维有限元方法,对高温内压下含轴向表面裂纹的低合金Cr-Mo钢圆筒进行研究。有限元计算得到的应力强度因子K和蠕变裂纹驱动力参量C*积分与前人的研究进行比较,提出一种基于软件ABAQUS的步步分析方法来描述蠕变裂纹的扩展行为。最后,通过对若干不同初始形状裂纹的研究,得到四种不同初始形状的表面裂纹的形貌变化特性,以及裂纹深度、裂纹长度、C*积分和剩余寿命的变化规律。

In the study of metal creep,more and more efforts are being devoted to the materials and structures containing defects.Surface crack shape variation is one of the important issues in the study of leak-before-break（LBB） procedure.However,little attention has been paid to creep crack growth of surface cracks by numerical simulation.In the present study,a numerical analysis has been conducted on a low alloy Cr-Mo steel cylinder subjected to internal pressure at high temperature,with semi-elliptical crack located at the inner surface.The stress intensity factors（SIFs） and creep crack driving force parameter C^＊-integrals,calculated by numerical methods,are compared with results from previous studies.Good agreement has been obtained by comparing SIF,which demonstrates the FE（finite elememnt） model is reliable.The empirical equations of C^＊-integral,however,may be inaccurate under some condition.Moreover,the creep crack growth described by C^＊-integral is investigated using three-dimensional finite element analyses and a step-by-step analysis procedure based on codes ABAQUS is illustrated.Finally,crack profile development,C^＊-integral variation,crack depth,crack length and remaining life prediction are presented by studying several cases of different initial aspect ratios.It is observed that under monotonic internal pressure,the magnitude of crack length increment decreases as the initial aspect ratio ranges from 1 to 1/6,which is always minor compared with the crack depth increment.The crack profiles vary approaching to semi-circles and the aspect ratios increase all the time whatever the initial aspect ratio would be.In the final stage of the analyses,the boundary effect has been observed in C^＊-integral calculations.