Research On Lamb Wave Detecting Delamination In Composite Laminates

With the rapid development of industrial technology, the requirements for engineering application material properties are becoming increasingly higher.Composite is widely used in industrial field because of the advantage of higher strength,bigger elasticity modulus and lighter quality. The health of composite structures is directly related to the integrity and security of system. In the composite laminates, the most common defects are fiber breakage, matrix crack, and delamination and the most difficult for examination is the internal delamination, and this defect seriously affects the characteristics of the composite material. Meanwhile, it bears safety risks during its usage. There are many large accidents made by delamination in home and abroad.Therefore, delamination examination to the composite material is very significant. This paper using Lamb wave to examine delamination defects, analyzing the propagation principle of Lamb wave in the composite and conducting finite element simulation,using the time reversal method and wavelet analysis method to achieve free baseline purpose, and displaying composite delamination defects in two-dimensional image according to probability imaging.Firstly, this paper studies propagation theory equation and the detecting principle of Lamb wave in the composite plate, obtains the disperse equation, draws out the dispersion curves, makes the detailed theoretical analysis about the time reversal method(TRP), and establishes free baseline delamination examination basis with TRP principle and wavelet analysis method. By analyzing the focusing signal after time reversal processing and comparing the difference between the original input signals and focusing signal, we propose time-reverse focused property evaluation indexes about the focusing signals and wavelet otherness coefficient evaluation indexes, and they will be used as an important parameter in imaging damage in the following section.Based on the study about theory method, by using the finite element analysis software ABAQUS, we build the propagation model of Lamb wave in composite plate,then carry out deep study on the propagation characteristics of guided waves on theone-dimensional Line propagation model and two-dimensional Plane propagation model. According to the analysis result of acquired signal after TRP, we find out if there is any delamination defects, location delamination and the effect of delamination size on signal waves. for the examination waveform that is difficult to deal with, "Removal of the central peak method" is put forward which solves the problem of weak signal, the defect reflected echo wave and the ongoing wave mixing, therefore improving the effectiveness and accuracy of the signal analysis.We use the reconstructed probability of time reversal method and wavelet otherness coefficient to realize two-dimensional imaging in composite laminates,realizing successfully the imaging display of single and multiple delamination, and then the imaging results can be corrected accurately. It enables us to precisely locate the default position.