Off-axis fatigue behaviour and its damage mechanics modelling for unidirectional fibre–metal hybrid composite: GLARE 2

Abstract

The fatigue behaviour of a unidirectional fibre–metal laminate GLARE 2 has been studied under various off-axis loading conditions. Tension–tension fatigue tests were first performed at room temperature on nine kinds of plain coupon specimen with a different off-axis angle. A non-dimensional effective stress defined on the basis of the classical static failure theory was applied as an off-axis fatigue strength parameter. A macroscopic fatigue damage mechanics model was then developed using the non-dimensional effective stress, and it was compared with the classical fatigue failure models for composites. The absolute off-axis fatigue strength decreases as the off-axis angle increases. The longitudinal fatigue strength of GLARE 2 is about two times as high as that of the high-strength aluminium alloy , while the transverse fatigue strength is almost one-half. The S – N relationships are almost linear for all off-axis angles in the intermediate range of fatigue life 10 3 < N f <10 5 , and they are followed by fatigue limits. The off-axis fatigue data plotted using the strength ratio (i.e. the maximum fatigue stress normalized by the static strength) are approximately represented by a single master S – N curve. The non-dimensional effective stress succeeds in describing this characteristic of the off-axis fatigue behaviour. The damage mechanics model developed using the non-dimensional effective stress can favourably reproduce the directional nature of the constant amplitude off-axis fatigue behaviour of GLARE 2. This model has an advantage over the classical fatigue failure models for composites with respect to the numerical procedure for fatigue life analysis.