This paper aims to illustrate the effect of the impact damage on fatigue behavior of CF/PEEK-titanium hybrid laminates. To achieve this end, a fatigue life model was proposed to predict the S–N curves of the laminates at various initial impact energy levels and stress ratios based on the energy dissipation approach. The energy dissipation behavior of the laminates during fatigue loading under different experimental conditions was analyzed through a large amount of post-impact fatigue tests, and the correlation between the initial impact damage and the total fatigue dissipation energy was determined. The full-field axial strain distribution of the titanium layer on the impacted side of the laminate was characterized in terms of initial impact energy level and maximum stress using digital image correlation, and then the post-impact fatigue failure mechanism of CF/PEEK-Ti hybrid laminates was summarized. Finally, the validity of the proposed model was verified by fatigue tests under other conditions of stress ratio and impact energy level. It is worth mentioning that the proposed model is also applicable to other types of FMLs, and can accurately predict the residual fatigue life of laminates after impact with only one set of S–N curve data.

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Finite-width-correction factors (FWCF) are required for GLARE to accurately predict fatigue crack growth using linear elastic fracture mechanics. As demonstrated in earlier work, these factors effectively correct for the change in specimen compliance, which in GLARE relates to intact fibre layers and the formation of delaminations between these layers and the cracked metal layers. Therefore, the development of delaminations in various GLARE grades were studied using digital image correlation during fatigue crack growth experiments under different maximum stresses and stress ratios. The elongation of GLARE in loading direction was recorded by crosshead displacement during fatigue testing, and was correlated to the observed development of the delamination area. The relationship between effective delamination area and effective GLARE specimen compliance is used as basis for determining explicit formulations for the FWCF for GLARE.

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In general, a finite width correction to stress intensity factor (SIF) is required in the fatigue crack growth. The finite width correction factor can be explained physically from the energy point of view. It is assumed that the finite width correction factor primarily constitutes an energy correction factor, i.e. it corrects the applied load for the work applied. To evaluate the finite width correction for FMLs, constant amplitude load fatigue crack growth tests were performed on monolithic aluminium 2024-T3 and the Fibre Metal Laminate GLARE containing 2024-T3 aluminium layers. The loads and displacements were recorded to quantify the total amount of work applied throughout each fatigue test. The crack length and delamination size were monitored by using digital image correlation technique to evaluate the dissipative energy. It appears that the Feddersen's and all other standard finite width correction significantly overestimates the effect for FMLs. The finite width correction to SIF for FMLs is small but cannot be neglected, and it is also greatly related to the Glare grades, stress ratio and stress level.@en