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Abstract

Fibre Metal Laminates (FML) consist of bonded alternating thin aluminium and fibre/epoxy layers. Post-stretching of FML after curing is accompanied by plastic deformation which causes a reversal of the internal stresses due to curing which is favourable for their fatigue properties. The influence of this post-stretching on the delamination resistance was studied. The GI, of FML with aramid fibre (ARALL) was increased by post-stretching. No influence was found on the GI, of glass fibre based FML (GLARE). The GI,, of FML was hardly influenced. The mode I and II delamination resistance of GLARE is significantly higher than that of ARALL. There appeared to be no relationship between these G,-values and the delamination of realistic structural details: the delamination of doublers as applied in aircraft wing panels. Post-stretching increased the delamination resistance of doubler specimens and despite its higher G,-values GLARE doubler specimens showed the same delamination resistance as ARALL. Although the delamination resistance of post-stretched doubler specimens was increased, the delamination progression after exceeding the delamination stress was for post-stretched material much faster than for as cured material, due to the larger amount of strain energy stored in the laminates during the post-stretching operation. Delamination fatigue tests indicated two competing mechanisms on the delamination growth rate. Therefore the delamination fatigue behavior is largely influenced by post-stretching, but the effect can be either positive or negative.

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References

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Delamination Resistance of Post-Stretched Fibre Metal Laminates

Abstract

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