裂纹长度和位置影响下声发射信号传播特性

针对再制造毛坯闭合裂纹检测较困难,采用声发射技术,从仿真和实验两个方面研究裂纹长度和裂纹位置对声发射信号传播特性的影响。根据裂纹中波的传输理论,采用时域有限差方法,仿真两个因素对声信号的影响,实验结果表明,裂纹长度对于信号衰减影响比裂纹位置明显;裂纹长度小于3 mm时信号的能量和幅值衰减系数(分别为-0.28和-0.15)明显大于裂纹长度大于6 mm的信号衰减系数(分别为-1.48和-0.9);裂纹长度为3 mm比裂纹长度为0.5 mm时能量和幅值相对衰减率分别大0.62 d B和0.2 d B,而其比裂纹长度为15 mm的能量和幅值相对衰减分别小14.7 d B和8 d B;裂纹位置的能量相对衰减率位于-6.4~-6.6 d B,幅值相对衰减率位于-1.4~-1.7 d B。实验研究了裂纹长度对声发射信号的影响,得出裂纹长度小于2 mm时的衰减系数明显大于裂纹长度超过6 mm的衰减系数,与仿真结果相符。因此,声发射参数与裂纹长度有明确的对应关系,声发射技术可有效检测再制造毛坯中的裂纹,尤其是长度小于3 mm的微裂纹。

Propagation characteristics of acoustic emission signals affected bythe length and the position of cracks

To address problem that closed crack detection of remanufacturing blank is more difficult, the acoustic emission technology is used to study propagation characteristics of acoustic emission signals due to the length and the position of cracks in remanufacturing blanks. The wave transmission theory in crack medium and the finite difference time domain method are used to simulate the influence of two factors on acoustic signals which indicates that the attenuation effect due to crack lengths is more obvious than that due to crack locations. The energy and amplitude attenuation coefficients (0.28 and 0.15, respectively) of the acoustic signals for the crack length less than 3 mm are greater than those for the crack length greater than 6 mm (1.48 and 0.9, respectively). The relative energy and amplitude attenuation rates of crack length 6 mm are 0.62 dB and 0.2 dB more than those of crack length 0.5 mm, 14 .7dB and 8 dB are decreased crack length 15 mm. The energy relative attenuation rates of the crack location are between -6.4 to -6.6 dB and its relative amplitude attenuation rates are between -1.4 to -1.7 dB. The influence of crack length on the acoustic emission signal is also discussed in experiments. The experiment result shows that the attenuation coefficient of the crack length less than 2 mm is bigger than that of the length more than 6 mm, which indicates that it is consistent with the simulation. Therefore, the acoustic emission parameters and the crack length have a definite corresponding relationship. The acoustic emission technique can effectively detect the crack in remanufacturing blank, especially for the detection of micro crack less than 3 mm.