应力比R对09CuPCrNi钢焊接接头疲劳裂纹扩展门槛值△K_(th)的影响

Influence of stress ratio R on threshold value △K_(th) of fatigue crack propagation for welded joints of 09CuPCrNi steel

本文根据国标GB6398-86,采用降K法分别求出在不同应力比R条件下,09CuPCrNi钢母材、焊缝和热响区(HAZ)的疲劳裂纹扩展门槛值△K_(?)的表达式,发现当应力比R达到某一值R_(?)之前,母材、焊缝和热影响区的门槛值△K_(?)随着应力比R的增大而减小;当R超过R_(?)之后,其门槛值均匀保持不变,同时还重点叙述了裂纹闭合应力强度因子K_(?)的计算方法,证实焊接接头的闭合效应高于母材金属,并对上述规律做了分析和解释.

The expressions of threshold value △K_(?) of fatigue crack propagation in base metal, weld metal and heat affected zone (HAZ) for 09CuPCrNi steel under various values of stress ratio have been obtained respectively by using gradual down K technique according to Chiness Standard GB6398-86. It was found that threshold values in the three parts of a welded joint would decrease with increasing stress ratio R when R≤R_((?)th), whereas the values would remain constant when R>R_((?)th). Meanwhile a calculating method for stress intensity factor K_(?) of crack closure has been described in detail. It was also indicated that the closure effect of the welded joint is greater than that of the base metal. The analysis and explanation for this viewpoint have been made.