A Power Law Fatigue Damage Model for Fibre-Reinforced Plastic Laminates

Abstract
Following an earlier comparative investigation of the tensile fatigue response, in terms of stress versus log life curves, of three epoxy-resin-based laminates of 0/90 lay-up and reinforced with carbon, glass and Kevlar-49 fibres, the authors now present a study of the accumulation of fatigue damage in terms of the residual strengths of the fatigued laminates. A stress-independent parametric relationship between normalized stress and normalized number of cycles is found to describe the behaviour of all three composites, suggesting a single major mode of fatigue damage despite the widely different mechanical characteristics of the different materials. The model is a two-parameter power law model, derived from a consideration of the appropriateness of various curve-fitting methods, and permits the incorporation of all modes of damage accumulation, from gentle ‘wear-out’ to ‘sudden death’ simply by the adjustment of this pair of power law exponents.

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