CTOD试验焊缝表面开缺口试样裂纹前沿平直度研究

Study on Fatigue Crack Front Straightness of Weld Surface Notched Specimen in CTOD Test

对于裂纹尖端张开位移(CTOD)试验,焊缝试样中预制疲劳裂纹前沿平直度直接影响了试样制备的合格率,是试验的关键难题之一.试验中常对试样进行预处理以提高裂纹前沿平直度,但由此也使试验结果与实际情况产生一定差异.本文深入研究规范BS7448:Part2中对焊缝试样取样方向的规定,对表面开缺口试样裂纹尖端焊接残余应力进行分析,运用大型有限元软件ANSYS模拟90mm厚钢板焊接过程,求解了横向残余应力沿板厚方向及焊缝方向的分布规律,研究出横向残余应力分布是影响焊缝试样预制裂纹前沿平直度的主要原因,并通过试验进行验证.试验结果表明,表面开缺口试样可不经过局部韧带压缩等预处理而得到合格的裂纹前沿平直度,试验不改变原焊缝残余应力,可测得更加接近焊缝实际情况的CTOD韧度值,给CTOD试验中合理选取焊缝试样取样方向提供了新思路.

Fatigue crack front straightness of the weld specimen in CTOD test directly affects the passing rate of the specimen preparation. It＇s an important issue in CTOD test. Pretreatments are often applied to improve the straightness of the crack front, but they may cause discrepancies between the test results and the actual situation. Based on a thorough examination of the sampling orientation in Standard BS7448： Part2, the welding residual stress near the crack tip of the surfaces notched specimen was analyzed. The finite element software ANSYS was used to simulation the welding process of a 90 mm thick plate. The distributions of the lateral residual stress along the thickness direction and the weld direction were determined. It indicates that the main influential parameter for the fatigue crack front straightness is the distribution of the lateral residual stress, which is verified by tests. The results show that a qualified crack front straightness in the surfaces notched specimen can be obtained without the pretreatments, such as local compression. The tests can get accurate CTOD toughness values in welding position because they do not change the welding residual stress. This paper provides novel perspective for the selection of weld specimen sampling orientation in CTOD tests.