Predicting fatigue transverse crack growth in cross-ply carbon-epoxy laminates from quasi static strength tests by using iso-damage curves

Cross-ply laminates made of carbon/epoxy IM7/977-2 system are investigated. The fatigue study is confined to ambient temperature conditions and zero loading ratio. Damage is characterized by the transverse crack density rho in the central 90-layer. The family of experimental fatigue cracking curves (rho versus N, where N is the number of cycles, for each tensile test maximum stress amplitude) can be replaced with a set of iso-damage curves, i.e. contour curves of constant rho in the sigma-log (N) plane. The iso-damage curves approximately constitute a fan of straight lines that intersect at a common point (sigma(e), log (N-s)), where N-s is a very large number of cycles beyond which no more crack appears, and sigma(e) is some fatigue limit. Our aim is to propose a simple method to predict fatigue cracking at an arbitrary maximum stress level loading by using data stemming from a constant strain rate test. This method essentially rests upon the construction of the above iso-damage curves, using very simple assumptions. (C) 2009 Elsevier Ltd. All rights reserved.