Delamination Identification in Quasi-Isotropic CFRP Laminate Using Electric Potential Technique

Carbon fiber reinforced plastic (CFRP) laminate is very sensitive to an impact. Even a low impact creates a delamination, which deteriorates the compression strength of the laminate. Monitoring for delamination is indispensable to maintain the reliability of CFRP structures. Electric potential change method (EPCM) has been applied for CFRP as a nondestructive testing method although it has not yet been reported for the successful application to a quasi-isotropic CFRP laminate which is commonly used for various applications. Strong electrical anisotropy and inhomogenity of the laminate makes simple application of the method difficult. In this paper, a new concept was introduced to resolve the problem of the conventional method. The new method utilizes the piezoresistivity of CFRP woven fabric. Variation of strain on laminate surface due to delamination was measured as electric potential change of CFRP woven fabric. As CFRP woven fabric is generally stacked on the laminate on purpose to protect laminate surface, no additional sensor is required in the method. Delaminations were estimated from the electric potential changes as an inverse problem. Finite element studies were performed to investigate the applicability of the method. The simulation results indicated the validity of the method for delamination identification in quasi-isotropic CFRP laminate.