INITIATION AND GROWTH OF DELAMINATION FROM THE TIPS OF TRANSVERSE CRACKS IN CFRP CROSS-PLY LAMINATES

Delamination initiation and growth from the tips of the transverse cracks in toughened-type CFRP (T800H/3631) cross-ply laminates was measured by the replica technique as a function of the applied laminate strain. In addition, loading/unloading tests were performed to obtain the relationship between the measured material damage and Young's modulus reduction. ENF (end-notched flexure) tests were also performed to obtain the mode II interlaminar fracture toughness in order to understand the delamination growth behavior. A simple shear-lag stress analysis was extended to the laminates containing delaminations at the tips of transverse cracks. This stress analysis was used to obtain Young's modulus reduction and the energy release rate associated with the delamination growth. The shear-lag prediction of Young's modulus reduction was compared with experimental data. The total delamination length was predicted as a function of the applied laminate strain by using the energy release rate and the experimentally obtained mode II interlaminar fracture toughness.