Edge-reflected lamb wave exploitation for defect localization in square orthotropic CFRP laminates

The edge reflection of Lamb waves contains rich information about the structure, and is a promising tool for the structural health monitoring (SHM) of composite laminates. However, related investigation on its applicability in orthotropic composite laminates are still limited. To address this issue, this paper presents a defect localization method based on multipath edge reflected Lamb waves, which can be used for the SHM of square carbon fiber reinforced plastics (CFRP) laminates that have orthotropic material properties. Firstly, the feasibility of using edge reflections to detect defects in orthotropic materials is analyzed, laying the foundation for the construction of a multipath model. A modified dispersion compensation algorithm is then developed based on the equivalent dispersion relations, so as to minimize the influence of the orthotropic property on the signal waveform. On the basis, a four-step implementation process of the detection method is established, including identifying edge reflected wave packets, tracking theoretical virtual wave paths, matching wave packets with virtual paths, and imaging the detection area by fusing images of multipath wave packets. Experiments on three different defect cases show that the method can localize the defect on orthotropic CFRP laminates accurately, even its position is near the edges. Compared with the widely-used delay-and-sum algorithm, the method also performs better in the presence of strong edge reflections, thus can be an efficient SHM tool for the orthotropic CFRP laminates of small sizes.