基于超磁致伸缩换能器的CFRP板孔裂纹缺陷检测

Hole crack damage detection of CFRP plate based on super-magneto-strictive transducer

孔劈裂损伤是碳纤维增强复合材料板(Carbon Fibre Reinforced Plastics,CFRP)承接服役中的主要损伤形式。由于CFRP材料的各向异性,致使超声导波信号衰减大,多种模态波包混叠,难以实现对CFRP螺接或铆接孔劈裂损伤的定量检测。针对CFRP孔裂纹损伤量化,研制Galfenol换能器,作为超声导波的高能激励源,采用PZT-5作为接收端,对孔裂纹进行超声导波检测。建立换能器动力学模型,利用扫频方法结合S0模态捕捉对比确定换能器检测最优激励频率;对获取的超声导波信号采用小波分解与短时傅里叶变换(Short-time Fouruer Transform,STFT),并计算调控云图色阈值显著化S0模态与损伤模态信息,得到时频云图谱;建立CFRP板的力学模型,利用Floquet边界固有的周期性,对板单元波长布利渊区扫描获取频散曲线,在云图谱上依据频散曲线群速度计算获得裂纹损伤时域位置;依据云图谱阈值色度量化波包幅值,获取损伤程度信息。实验结果发现云图谱中裂纹损伤模态与原有模态之间具有良好的辨识度,根据获取频散曲线计算直达与反射S0模态的时间误差为2.3μs、0.6μs。

Hole crack damage is the main damage form of carbon fiber reinforced plastics(CFRP)plate in service.Due to the anisotropy of CFRP material,ultrasonic guided wave signals are greatly attenuated and multiple mode wave packets are overlapped,so it is difficult to realize the quantitative detection of hole crack damage of CFRP bolted or riveted.Here,aiming at the damage quantification of CFRP hole cracks,Galfenol transducer was developed as the high-energy excitation source of ultrasonic guided wave,and PZT-5 was used as the receiving end to detect ultrasonic guided wave of hole cracks.The dynamic model of transducer was established,and the optimal excitation frequency was determined with the sweep frequency method combined with S0 mode capture comparison.Wavelet decomposition and short-time Fourier transform(STFT)were performed for the obtained ultrasonic guided wave signals,and the color threshold of the control cloud chart was calculated to highlight information of S0 mode and damage mode,and obtain the time-frequency cloud atlas.The mechanical model of CFRP plate was established,and the natural periodicity of Floquet boundary was adopted to gain the dispersion curve through scanning plate element wavelength Brillouin region.The time-domain location of crack damage was obtained by calculating the group velocity of dispersion curve on the cloud atlas.According to the threshold chromaticity of cloud atlas,the amplitude of wave packet was quantized,and the information of damage degree was obtained.The experimental results showed that there is a good discernibility between crack damage mode and the original mode;according to the obtained dispersion curve,the time errors for S0 mode to directly reach and reflect are 2.3μs and 0.6μs,respectively.