Matrix crack initiation and progression in composite laminates subjected to bending and extension

An experimental investigation of matrix crack initiation and progression in glass/epoxy laminates of different stacking sequences is presented. The la minates have been loaded in extension and bending, and the degree of damage as function of the load has been recorded. The changes in certain elastic properties caused by the damage were also measured, and are compared to res ults from a previously developed approximate analytic model. An energy rele ase rate resistance curve is adopted in an attempt to describe the initiati on and progression of matrix cracks in the laminates. The amount of crackin g is also viewed in relation to the strain transverse to the fibres in the ply under consideration, and the ply stresses at the onset of cracking are calculated. The different damage evolution criteria are compared to the exp erimental results, and their validity and reliability are discussed. By use of the ply strain transverse to the fibres as a critical parameter for dam age evolution, the load-deformation curves of the tested laminates are simu lated taking damage progression into account. (C) 1999 Elsevier Science Ltd . All rights reserved.