Crack localisation in composite cantilever beams using natural frequency measurements

Crack localisation is a fundamental step of damage identification. Most of the published research on crack localisation based on natural frequency consists in model updating which requires a great deal of calculation. This paper presents a simple method of crack localisation in composite cantilever beam-type structures. The proposed method consists of classifying the reduction of the first four measured natural frequencies and deducing the damage position from a table. For these purposes, a finite element model is first used to study the direct problem: the vibration behaviour of an intact beam and the changes caused in the damaged state. Then it is shown that the classification of the frequency reduction ratio is different for each damaged zone. Consequently, the beam is discretized into several areas according to the classifications of the first four frequency ratios. Therefore, this discretization is represented in a table to be used in damage localisation. The robustness of the suggested technique is first tested numerically by using the Abaqus/CAE finite element software environment. Then, the applicability of the localisation method is validated experimentally on a cracked glass fibre-reinforced epoxy beam. The results show that the proposed method can successfully localise damage in composite beams.