Prediction of Fatigue Damage Development in Undirectional Long fibre Composites

Cyclic damage development in polymer matrix composites reinforced with long fibres may be modelled by a two stage process. The first stage involves transverse and shear cracking of the matrix which is particularly significant in cross-ply laminates. Its development may be described using a two-parameter Weibull model. The damage rate continuously decreases until saturation is reached. This stage also occurs in unidirectional glass’ polyester rods pultruded under industrial conditions. The second stage exhibits an increasing rate of damage development resulting from longitudinal splitting, delamination, fibre pull-out and fracture. This may be described by applying continuum damage mechanics. The summation of the two expressions results in a comprehensive description of the fatigue damage evolution process. Using this approach it is possible to predict complete damage accumulation in undirectional long fibre composites.