点焊试件中兰姆波传播的有限元模拟及其应用

Finite Element Modulation of Lamb Wave Propagation for Nondestructive Evaluation of Spot Weld

提出兰姆波评价汽车钢板点焊质量的理论依据及试验方法,评价对象包括点焊焊核的直径及最大拉伸载荷。兰姆波中的多模态频散特性及在复杂结构中的模式转换导致超声检测信号难于区分,通过解析方法难以获得兰姆波在点焊试样中的传播规律,因此采用有限元法模拟兰姆波在点焊试样中的传播。有限元法的模拟结果显示:经焊核传播的A0模态兰姆波特征峰值随焊核直径的增大而减小、随凹痕深度的增大而增大。因此,A0模态兰姆波的特征幅值可望用于评价焊核的形状及力学性能。试验通过调整斜探头入射角度激励A0模态兰姆波对高强度镀锌钢板的点焊试件进行检测试验,结果显示:A0模态兰姆波特征峰值随焊核直径及焊核最大拉伸载荷的增大而减小,该规律与有限元模拟的结果一致,可以用于实际结构点焊质量的无损评价。

The Lamb wave testing for the automobile spot weld is proposed,which can be used for evaluating the diameter and the maximum tension load of the spot weld.The propagation mechanics of Lamb wave in the sample of spot weld is difficult to be investigated by analytical method because of the wave dispersion and type transformation in the wave conductor with complex shape,so the finite element method is adopted to simulate the Lamb wave propagation in the samples.The simulation results reveal that the A0 modal Lamb wave transmitted through the weld nugget has a close relationship with the characters of nugget shape such as the nugget diameter and the indentation depth.Thus,the shape and mechanical property of spot weld may be evaluated by Lamb wave method.A0 modal Lamb wave can be excited by adjusting the incident angle of probe.Experimental results indicate that the peak value of received A0 modal Lamb wave decreases with the increase of the nugget diameter and the maximum tension load of the spot weld,which are consistent with the finite element modulation,and can be used in the nondestructive evaluation on practical spot-welded structure.