Strain-controlled fatigue life prediction of Flax-epoxy laminates using a progressive fatigue damage model

A finite element model that incorporates the progressive fatigue damage model (PFDM) is developed to predict the fatigue life of Flax-epoxy composites with [0](16), [90](16), [0/90](4S), [+/- 45](4S) and Quasi-isotropic [0/+45/90/-45](2S) layups under strain-controlled conditions. A stochastic distribution method is used to consider the manufacturing-induced variation of the material properties. The PFDM analysis includes stress analysis, sudden material property degradation as identified by the Hashin failure and maximum stress criteria, and gradual material property degradation in the longitudinal, transverse and in-plane shear directions. The gradual stiffness degradation is coupled with gradual strength degradation to avoid excessive testing. The PFDM is implemented via a user-defined material subroutine UMAT in ABAQUS that is written in FORTRAN. The predicted strain-life curves and residual stiffness degradation show a good agreement with the experimental results at different strain levels.