基于横波检测柱状材料内部缺陷的数值模拟研究

Numerical Simulation of Cylindrical Material Internal Defects Detection Based on Shear Wave

小口径金属圆柱体的缺陷检测是无损检测领域的一个难题。通过有限元方法对金属圆柱中横波传播特性以及与缺陷作用机理进行数值模拟。探究了横波的方向性变化、圆孔缺陷半径对横波传播影响、不同位置和不同长度的缺陷对横波传播的影响。研究表明横波在传播过程中主要能量范围由15°~36°变为20°~35°,提出了近似正三角形的传播路径并进行验证,发现横波到达表面后发生模态转换,一部分声波以略面纵波的速度沿表面传播;对于圆孔缺陷,圆孔半径在3.4~4.6mm范围内可通过幅值变化判断孔径信息,半径在4.6~5.8mm范围内可通过接收时间判断孔径信息;对于不同位置的矩形缺陷,当缺陷进入到横波主要能量范围内,C扫图中出现近似线性的高能量区域,探测角度随着缺陷位置增加而增大,此范围内的缺陷可通过反射信号的探测角度判断位置信息;对于不同长度的矩形缺陷,随着缺陷长度增加,透射波能量减弱并且探测角度减小,呈现出近似线性的能量分布,通过探测透射波到达外表面的角度可判断缺陷长度信息。提出了相应的传播路径和长度计算公式,计算结果得到的误差百分比控制在6.5%以内,验证了该缺陷长度检测方法的有效性。

Defect inspection of small-diameter metal cylinders is a difficult problem in the field of nondestructive testing.In this paper,the propagation characteristics of shear wave in a cylinder and the interaction mechanism with defects were investigated by the finite element method.The directional change of the shear wave is explored by extracting the shear wave signals at different moments.The effect of the defect radius of the circular hole on the propagation of the shear wave was investigated by B-scan.The influence of different positions and different lengths of defects on the propagation of shear wave was investigated by C-scan.Results show that:the main energy range of shear wave in the propagation process changes from 15°-36°to 20°-35°.The propagation path of an approximate equilateral triangle is proposed and verified.For round hole defects of different radii,radius can be determined by the amplitude and receiving time changes.When the defects enter the main energy range of the shear wave,the detection angle increases with the increase of the defect position.The position information can be determined by the detection angle of the reflected signal.With the increase of defect length,the transmitted wave ST energy decreases and the detection angle decreases,presenting an approximately linear energy distribution.Defect length information can be determined by detecting the angle of the transmitted wave reaching the outer surface.The propagation path and length calculation formula are put forward,and the error percentage of the calculation result is controlled within 6.5%.