Modal-strain-based damage index of laminated composite structures using smooth transition of displacements

A modal-strain-based damage index is proposed to investigate the damage effects of discrete delaminations in a laminated composite structure. The Fermi-Dirac distribution function is incorporated with an improved layerwise laminate theory to model a smooth transition of the displacement and strain fields at the delaminated interfaces. The finite element technique is used to implement the proposed displacement field. Modal analysis is conducted to investigate the dynamic effects of delamination in a laminated structure and to obtain modal strains. The damage index is calculated based on fundamental modal strains of laminated structures. The damage effects of laminated structures are investigated using arbitrary size, number, location, and boundary conditions of discrete delaminations. It is observed that the proposed modal strain damage index provides accurate information of discrete delaminations.