基于非线性超声波的疲劳损伤检测试验研究

EXPERIMENTAL STUDY ON FATIGUE DAMAGE DETECTION BASED ON NONLINEAR ULTRASONIC

对完整铝板、含孔铝板以及用复合材料补片修补后的铝板分别进行疲劳试验和非线性超声波检测试验,提取三组试件不同疲劳周期下的基波幅值和二次谐波幅值,得到其相对二阶超声非线性系数,并拟合出相对二阶超声非线性系数随疲劳周期变化的曲线图,以研究相对二阶超声非线性系数与疲劳损伤过程的对应关系。结果表明:随着疲劳周期增加,三组试件的相对二阶超声非线性系数均呈现先缓慢上升,然后快速上升并到达峰值,最后下降的趋势,这与疲劳损伤过程中位错和裂纹的产生及扩展过程相一致;同时发现:孔损伤会加剧微裂纹向宏观裂纹的过渡,而用复合材料补片修补孔损伤可减缓裂纹的扩展。

The fatigue testing and nonlinear ultrasonic testing are carried out on the complete aluminum plates, the aluminum plates containing the hole and the aluminum plates repaired with the composite patches. The amplitudes of fundamental ultrasonic and the second harmonic of the three sets of specimens under different fatigue cycles areextracted. The relative second-order ultrasonic nonlinear coefficients are obtained, and the graph of the relative second-order ultrasonic nonlinear coefficient with the fatigue cycles is fitted to study the corresponding relationship between the relative second-order ultrasonic nonlinear coefficients and the fatigue damage process. The results show that with the increase of fatigue cycles, the second-order ultrasonic nonlinear coefficients of the three sets of specimens show a slow rise first, then rise rapidly and reach the peak value, and finally decrease, which is consistent with the process of dislocation and crack generation and propagation during fatigue damage. At the same time, it is found that the pore damage will aggravate the transition of microcracks to macroscopic cracks, while repairing pore damage with composite patches can slow crack propagation.