DISCRETE DAMAGE MODELING IN LAMINATED COMPOSITES UNDER FATIGUE LOADING

The Discrete Damage Modeling (DDM) method is extended for progressive failure analysis in laminated composites under fatigue loading. The essence of this technique is the insertion of true displacement discontinuities independent of mesh orientation to simulate matrix cracking. Multiple cracking in each ply is allowed. All plies are tied together by using cohesive interfaces, which are allowed to delaminate. Matrix cracks in two adjacent plies interact through the interface cohesive model, and their presence is a major delamination initiator. Failure criterion and cohesive zone model for initiation and propagation of cracking and delamination under fatigue loading were proposed. A material history variable in each integration point is introduced and updated after each loading increment, corresponding to certain load amplitude and the number of cycles. The computation begins without any matrix cracks present. A matrix crack is inserted when the material history variable value reaches unity. Delamination and matrix cracking extent under fatigue loading in open hole graphite epoxy laminates was predicted and showed good comparison with experiment.