Monitoring delamination of laminated CFRP using the electric potential change method (two-stage monitoring for robust estimation)

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Detecting delaminations of carbon fiber reinforced plastic (CFRP) laminates is a difficult task for visual inspection. Delaminations cause large reductions in strength and stiffness of CFRP laminates, bringing deterioration of the structural reliability of a CFRP. Monitoring for delamination is, therefore, indispensable to maintain the reliability of a CFRP structure. In a previous study, we adopted the electric potential change method to detect delamination. This method shows good estimation performance for delamination cracks located near the edges of a specimen, but poor performance near the center where large errors that depend on the delamination shapes are created. A zigzag delamination caused by matrix cracking has a large effect on estimation performance; so the electric potential change method was not applicable to monitoring for delamination. In this paper, a mechanism that brings large errors of estimation due to the shape of the delamination is detailed. FEM analyses show a small electric current in the thickness direction in the center segment of a specimen causes large effects on the estimation performance. The problem is overcome by means of a newly proposed concept, a two-stage method. The effectiveness of the method is demonstrated using FEM analyses.