Delaminations induced by constrained transverse cracking in symmetric composite laminates

Abstract

Transverse ply cracking and its induced delaminations at the φ/90° interfaces in [. /φ i / φ m /90 n ] s laminates are theoretically investigated. Three cracked and delaminated model laminates, one five-layer model (FLM) laminate [ S L / φ m /90 2 n / φ m / S R ] T and two three-layer model (TLM) laminates I and II, [ φ m /90 2n / φ m ] T and [ S′ L /90 2n / S′ R ] T , are designed to examine constraining mechanisms of the constraining plies of the center 90°-ply group on transverse crack induced delaminations, where S L , S R , S′ L and S′ R are sublaminates [./ φ i ] T , [ φ i /.] T , [./ φ i / φ m ] T and [ φ m / φ i /.] T , respectively. A sublaminate-wise first-order shear laminate theory is used to analyze stress and strain fields in the three cracked and delaminated laminates loaded in tension. The extension stiffness reduction of the constrained 90°-plies and the strain energy release rate for a local delamination normalized by the square of the laminate strain are calculated as a function of delamination length and transverse crack spacing. The constraining effects of the immediate neighboring plies and the remote plies are identified by conducting comparisons between the three model laminates. It is seen for the examined laminates that the nearest neighboring ply group of the 90°-plies primarily affects the stiffness reduction and also the normalized strain energy release rate, whereas the influences of the remote constraining layers are negligible.