铝合金型材对搭接搅拌摩擦焊接头中Hook缺陷的安全评定

Safety evaluation of Hook defects in joints of friction stir butt-lap welded aluminum alloy profiles

基于断裂力学理论对铝合金型材对搭接搅拌摩擦焊接头中Hook缺陷进行安全评定,并通过疲劳试验进行验证。金相显示Hook缺陷的本质是搭接面在搅拌头剧烈搅拌作用下向上迁移的结果,显现为裂纹的形式。将Hook缺陷归一化为延伸到焊缝内部的单边裂纹,裂纹扩展速率线性拟合得出应力强度因子幅度门槛值ΔK_(th)为2.509 MPa·m^(1/2)。依据裂纹扩展条件,得到评定Hook缺陷疲劳扩展的缺陷尺寸-应力幅关系曲线。疲劳试验结果与理论Hook缺陷临界扩展应力幅值有一定的误差,误差平均值为9.4%,整体趋势与理论曲线吻合度较好,可以将该理论公式应用到Hook缺陷疲劳扩展临界应力幅的预测中,对不同工作应力幅下接头中Hook缺陷进行安全评定。

In this paper,based on the theory of fracture mechanics,the safety evaluation of Hook defects in joints of friction stir butt-lap welded aluminum alloy profiles is carried out,and the fatigue test is used to verify it.The metallography shows that the essence of the Hook defect is the result of the upward migration of the overlapping surface under the vigorous stirring action of the stirring head,which appears as a crack.The Hook defect is normalized to a unilateral crack extending into the inside of the weld.The linear fitting of crack growth rate test shows that the threshold value of the stress intensity factor amplitudeΔK_(th) is 2.509 MPa·m^(1/2).According to the crack growth conditions,the defect size-stress amplitude relationship curve for evaluating the fatigue growth of Hook defects is obtained.There is a certain error between the fatigue test results and the theoretical Hook defect critical growth stress amplitude.The average error is 9.4%.The overall trend is in good agreement with the theoretical curve.The theoretical formula can be applied to the prediction of the critical stress amplitude of Hook defect fatigue growth,then it can be used to evaluate the safety of hook defects in joints under different working stress amplitudes.