Analysis of acoustic emission testing on the adherent layer thickness of lap joints under tensile loading

This paper aims to investigate the bonding strength of lap joints under tensile loading by altering the thickness of the adherent layer. The results show that increasing the adherent layer thickness of the bonded lap joint reduced stress concentration, indicating a higher stress transmission between the overlapping regions. Acoustic emission (AE) signals were used to identify the different failure modes and their frequency ranges by subjecting the AE signals to parametric analysis, fast Fourier transform (FFT) analysis, continuous wavelet transform (CWT) analysis and discrete wavelet transform (DWT) analysis. FFT analysis identified the frequency ranges of adhesive failure, fibre tear failure and mixed failure. At the same time, DWT was more effective at identifying the frequency ranges of the failure modes associated with varying adherent layer thicknesses in lap joints. Adhesive failure was characterised by low amplitudes, low frequency ranges and low energy levels. In contrast, delamination displayed moderate amplitudes, moderate frequency ranges and medium energy levels. High amplitudes, high frequency ranges, high energy levels and strong signal strength indicated mixed failures.