Composite Material Acoustic Emission Signal Detection And AE Damage Source Localization Based On Time Reversal Method

Composite material which has become an emerging material is widely used in the field of aerospace, construction and medical career with its high specific strength, simple manufacturing process and corrosion resistance. However, complicated manufacturing process and environment in use of composite material products will give rise to defects and damage, which is threatened to the safety use. Thus, it is of practical significance studying on the Non-destructive Testing of composite material.The damage forms of composite material are various and obvious AE characteristics will come out in the process of damage. Acoustic Emission technology is a dynamic Non-destructive Testing technology, which is able to analyze the damage process of composite material timely and effective.This paper mainly studies on the detection of AE signals and source localization based on time reversal method with glass fiber composite material. The main work and research focus are as follows:(1)According to the national standard of GB/T1449-2005, the three-point bending experiments with glass fiber specimens were achieved in the condition of two types of loading rate, respectively 2 mm/min and 10 mm/min. Parameter analysis and research on damage mechanism were accomplished with the collected AE signals. The damage forms of glass fiber mainly consist of matrix cracking, interfacial damage and fiber breakage. The performance of these stages of AE signal parameters range from matrix cracking with low amplitude(40-65 d B), low duration(less than 1000 μs),low energy(less than 5000) to fiber breaking with high amplitude(greater than 95 d B), high duration(greater than 3000 μs), high energy(more than 10,000). That is to say, the intensity of AE signal changes from a low level to high.(2)Based on a parametric method, a wavelet packet-energy method was proposed to analyze the AE signal waveforms. AE signal frequency components distribution was obtained by waveform analysis, which are as follows: matrix cracking(0-187.5 k Hz), interfacial damage(187.5-375 k Hz), fiber breakage(562.5-750 k Hz). Based on the proposed method, the different damage patterns and stages during the process of glass fiber composite material deformation were successfully recognized.(3)For the characteristics of glass fiber composite material with its inhomogeneous and anisotropic, an acoustic emission source location method based on time reversal(TR) and reciprocal time reversal(inverse filtering, IF) using only one sensor was proposed. The present method exploits the benefits of a diffuse wave field and the reciprocity condition of acoustic field to achieve the focusing of the source with a high accuracy in a relative wide range of a glass fiber board(100 cm×100 cm×3 mm). Compared to a standard multi-sensor source location method, the TR method enhances its positioning accuracy to 34.8 %. On the basis of a standard TR approach, a reciprocity time reversal method was proposed to enhance a higher level of focusing accuracy, and its second matching coefficient can be increased to 36.4 %.