Delamination cracking between plies of different orientation angles in composite laminates

Delaminations initiating at the 90 degrees-ply crack tips, and growing along the phi/90 interfaces in [.../phi(p)/phi(m)/90(n)](s) laminates are theoretically investigated. The cracked and delaminated laminates are subdivided by the cross-section separating the laminated and delaminated intervals. A sublaminate-wise first-order shear laminate theory is used to analyze stress and displacement fields in the cracked and delaminated laminates loaded in tension. The strain energy release rate (SERR) for a local delamination normalized by the square of the laminate strain is calculated as a function of delamination length and transverse crack spacing. It is found that the SERR for a delamination is substantially affected by the relative orientation angle of the associated two ply groups.