金属铝板弯折形变积累的超声兰姆波无损检测

Non-destructive detection for bending deformation of aluminum beams using ultrasonic Lamb waves

材料结构中疲劳微裂纹的产生和扩展是影响其寿命的重要因素,在疲劳裂纹产生初期就将其检测出来对于提高结构安全性至关重要。利用兰姆波探索了铝板反复弯折时判定材料疲劳积累到最终塑性形变断裂失效的方法。试验通过分析兰姆波各模式的频散曲线、振幅曲线和对比理论与实际的波包群速度,选定了在最佳激励频率下判定疲劳损伤积累的特征信号。还通过快速傅里叶变换分析频域的能量分布来判定疲劳累积。试验结果表明:在试样从弯折塑性形变积累到出现微裂纹的过程中,A0波包振幅有小幅度的减小,而在材料断裂失效前,该振幅幅度会急剧减小。

The formation and growth of fatigue cracks in structural materials is a crucial factor affecting their service life. Thus, it is important to detect the formation of the fatigue crack at the beginning and monitor its growth. Through the bending deformation simulation experiment, an approach by using Lamb wave was developed to detect the process from the accumulation of fatigue damages to the fracture of materials. By analyzing the dispersion curves and particle motion amplitudes of Lamb waves and comparing the theoretical and the actual group velocities, the characteristic mode packets under the optimum excitation frequency can be distinguished to evaluate the accumulation of the fatigues. And fast Fourier transform was used to reveal the energy distribution in frequency domain to detect damage accumulation. It is found that during the bending process from the fatigue accumulation to the appearance of micro-crack, the amplitude of A0 wave packet decreases. Especially, before the failure of materials, the amplitude decreases significantly.