CALCULATION OF STRESS INTENSITY FACTORS FOR INTERLAMINAR CRACKS IN COMPOSITE LAMINATES

Owing to the oscillatory characteristics of stresses and displacements near the crack tip, individual strain-energy release rates for bimate rial interface cracks no longer exist. Strain-energy release rates for finite crack extension, Delta a, are introduced. For interface cracks lying between two monoclinic media, the explicit quadratic relationsh ips between stress intensity factors and these finite-extension strain -energy release rates are established. Very accurate stress intensity factors can be obtained by calculating these finite-extension strain-e nergy release rates in the finite element analysis and by using these quadratic relationships. An alternative and efficient method based on near-tip crack surface displacement ratio is also introduced to obtain these stress intensity factors. An infinite 'two-ply' graphite/epoxy laminate under remote uniform tension and an edge-delaminated symmetri c [theta/ - theta/ - theta/theta] graphite/epoxy laminate subjected to uniform axial extension are selected for numerical investigation. (C) 1997 Elsevier Science Limited.