中文摘要：

近年来结构健康监测与损伤识别研究中广泛采用非线性振动与非线性超声方法。由于作动器和测试设备环节产生的超谐波成分作为背景噪声掩盖了损伤信号,降低了信噪比,利用亚谐波信号成分来识别闭合型疲劳裂纹。建立了闭合型裂纹的单自由度定性模型,分段迟滞型作用力模拟了裂纹界面间的相互作用以及裂纹张开与闭合过程,研究了产生亚谐波的激励频率和激励幅值条件,讨论了模型参数对亚谐波产生的阈值影响。利用压电作动器/传感器进行了铝制裂纹梁损伤检测实验,得到了裂纹损伤亚谐波识别的激励电压与频率的范围。数值仿真与实验结果表明了闭合型疲劳裂纹的亚谐波损伤识别方法的有效性。

英文摘要：

In recent years,researchers have focused on more efficient procedures in SHM and damage detection using nonlinear vibration and nonlinear acoustic methods.Because superharmonics are also generated by the piezoelectric transducers and by the electronic equipments,these harmonics increase the background noise deteriorating the S/N ratio.The objective of the paper is to demonstrate the application of nonlinear ultrasonic subharmonic method for detecting fatigue crack.The closed fatigue crack is qualitatively modeled as a single-degree-of-freedom（SDOF）system with non-classical hysteretic nonlinear interface force at both sides of the crack interface.The threshold of subharmonic is discussed and the influence of model parameters on the subharmonic resonance parameter condition is investigated.An aluminum beam with a fatigue crack is used to quantitatively verify the excitation voltage amplitude and frequency subharmonic resonance region.Two surface-bonded piezoelectric transducers are used to generate and receive ultrasonic wave signals.The experimental results demonstrate that the subharmonic components increase in magnitude with increasing amplitude of the input signal and can be used to accurately detect the fatigue cracks.