Characterization of Failure Modes in Composite Laminates Under Flexural Loading Using Time–Frequency Analysis

Abstract

Fiber reinforced composite materials are used as structural material in airplanes because of their high specific stiffness and strength. When composite materials are subjected to mechanical loading, it leads to many types of failures such as matrix cracking, debonding, delamination, and fiber breakage. To create a better understanding of the initiation, growth and interaction of the different types of damage, damage monitoring during mechanical loading is very important. Acoustic emission is a suitable technique for the detection of a wide range of micro-structural failures in composite materials. In this present paper, GFRP composite laminates with different stacking sequences such as [0°]4, [90°]4, angle ply [± 45°]4 and cross ply [0°/90°]4 are used to trigger different failure mechanisms when subjected to flexural test (three-point bending) with AE monitoring. Discrimination of the failure modes are done based on the predominance of the failure modes in each orientation. Parametric plots are used to discriminate the modes of fracture within the laminates. Range of frequency content in each orientation is investigated using fast Fourier transform (FFT) analysis. FFT enables calculating the frequency content of each damage mechanism. Short Time FFT highlights the possible failure mechanisms associated with each signal. Continuous wavelet transform allowed identifying frequency range and time history for failure modes in each signal. The predominance of failure modes in each orientation is used as a key in the study of discrimination of failure modes in composite laminates.