Finite Element Study on Delamination Identification in Quasi-Isotropic CFRP Laminate by Residual Stress Release Using the Electric Potential Change Method

Abstract

The electric potential change method (EPCM) was applied to identify delamination in quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate. The authors have introduced EPCM previously to detect delamination in a cross-ply CFRP laminate although it was difficult to apply to quasi-isotropic CFRP laminate because of its complicated electric anisotropy. In this study, a new concept was introduced to resolve this problem. Residual stress that developed during the curing process in CFRP laminate fabrication was utilized. This residual stress was released locally by the creation of a delamination which resulted in a local strain variation on the laminate surface. Since the electric conductivity of CFRP may change with applied strain because of its piezoresistivity a CFRP cloth was used as a strain sensor. The release of residual stress was detected as an electric potential change of the CFRP cloth by applying electric current to the laminate. The delamination location and size were estimated from electric potential changes. A finite element study was performed to investigate the applicability of the method. Two steps of finite element analysis were performed to calculate the electric potential change due to delaminations and matrix cracks, structural analyses to calculate strain variation due to release of the residual stress by the delamination and then electric field analyses to calculate electric potential change due to strain variation. The delamination location and size were estimated from electric potential changes using a response surface methodology. A numerical simulation was successful in estimating delaminations in quasi-isotropic CFRP laminate.