直管外表面轴向半椭圆裂纹应力强度因子KⅠ的有限元分析

Finite Element Analysis of Stress Intensity Factor for Straight Pipes' Axial Semi-elliptical External Surface Cracks

利用有限元法对含外表面轴向裂纹的直管进行了分析,应用有限元软件ANSYS建立了裂纹有限元模型,采用参数化建模对内压下裂纹的应力强度因子KI进行计算,得出了影响应力强度因子的主要因素。计算表明,应力强度因子随a/t及a/c成线性变化,并与t/Do为乘幂关系。一般情况下,表面裂纹在最深点(90°)处应力强度因子最大,然后随着角度的减小应力强度因子依次减小。但是在最浅点(0°)处应力强度因子有回升趋势,且随着a/t的增加,这种回升趋势逐渐明显,当a/t=0.8时,甚至出现最浅点KI超过最深点KI的现象,这时对于结构的脆性起裂位置要慎重判断,不能单纯地以最深点KI为断裂依据。

Straight pipes with axial semi-elliptical external surface cracks has been analysed by three-dimensional finite element method.A finite element model of the cracks has been built using ANSYS,and a parametric model has been conducted to calculate the stress intensity factors（SIFs） of the semi-elliptical cracks under internal pressure,and the main factors that impact the SIFs has been obtained.Caculation shows that the SIFs changes linearly with a/t and a/c,in addition,the it＇s exponentiation relationship between SIFs with t/Do.Usually,the SIFs is biggest at the deepest point（90 degree） and gradually decrease with the degree＇s decrease,but the SIFs has uptrend at the shallowest point（0 degree）,and the uptrend is noticeable with the increase of a/t.Even when a/t is equal to 0.8,the SIFs＇ value at the shallowest point is bigger than the deepest＇s,then the location of brittle crack must be judged cautiously,it＇s could＇t simply judged by the SIFs at the deepest point.