Fatigue Cracks in Fibre Metal Laminates in the Presences of Rivets and Cold Expanded Holes
In order for new composite materials like fiber metal laminates (FML) to gain acceptance in the aerospace field, it is important to understand the effect on them of common manufacturing techniques such as riveting and cold expansion. A comprehensive research program was initiated using two advanced strain measurement techniques; digital image correlation and thermoelastic stress analysis, to understand the failure mechanisms in FML materials that had been fatigue cycled after having undergone hole cold expansion or riveting. Prior theoretical work has shown the potential for improvement in fatigue life of FMLs, so one standard grade of FML (FML 4-3/2) and a novel FML variant were manufactured and tested. Thermoelastic stress analysis was employed to measure strains on the mandrel exit face while digital image correlation was used to measure strains on the mandrel entry face in the coupons and additional insight was gained regarding the effect of the cold expansion process and of riveting on fatigue crack growth. The results also highlighted the effect of material design on fatigue life as well as the interaction between residual strains and fatigue crack growth.
KeywordsFatigue Crack Fatigue Life Fatigue Crack Growth Digital Image Correlation Thermoelastic Stress Analysis
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