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

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. (C) 2000 Elsevier Science Ltd. All rights reserved.