Experimental and Theoretical Investigation of Discrete Damage and Residual Strength Prediction in Fatigue-Loaded CFRP Speciemns

Abstract

Ply level detailed prediction of fatigue performance of a nontraditional carbon fiber reinforced composite laminate with open hole has been accomplished and compared with experimental data. Discrete Damage Modeling (DDM) method was used for this purpose. 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. A material history variable in each integration point is introduced and updated after each loading increment, corresponding to certain load amplitude and number of cycles. The computation begins without any matrix cracks present. A matrix crack is inserted when the material history variable value reaches unity. Failure criterion and cohesive zone model for initiation and propagation of cracking and delamination under fatigue loading were proposed. The delamination and matrix cracking extent under fatigue loading in open hole [30/60/90/-60/-30]2s laminate was predicted and showed good correlation with experimental micro X ray CT imaging. In addition, static residual strength in tension and compression for the same laminate after 200,000 fatigue cycles was predicted and showed slight increase in tension and slight decrease in compression residual strength as compared to pristine laminate, which is in qualitative agreement with experimental observations.