Fiber Metal Laminates are a new class of advanced aerospace materials. They consist of thin metallic sheets bonded together with fiber reinforced adhesive matrices. Their most outstanding characteristic is exceptional fatigue resistance, which stems from the crack bridging effect of the fibers in the prepreg layers. Because of the many advantages they offer, such as higher strengths and lower densities than conventional aluminum and better machinability and impact resistance than thermoset composites, fiber metal laminates are being considered for a number of primary aircraft applications, including lower wing and pressurized fuselage skin panels. This paper presents a survey of published literature on the subject of fiber metal laminates, tracing their advancement over the past decade and a half, from bonded aluminum sheets to the commercially manufactured forms of ARALL and GLARE.

Fiber Metal Laminates — The Synthesis of Metals and Composites

In this research, dynamic progressive failure of Glass-Fiber-Reinforced aluminum laminates under low-energy impact was modelled. Intralaminar damage models, strain-based damage evolution laws, Puck failure criteria were used in ABAQUS-VUMAT software for modelling. Bilinear cohesive model was used for interface delamination, and the Johnson-Cook models were employed for aluminum layers. Damage evolution behaviours of this hybrid composite were calculated. After that, energy dissipation mechanisms were examined to identify the progressive failure and delamination of composite layers and plastic deformation of aluminum layers. In order to determine stress intensity at crack tip, the analytical model for constant-amplitude fatigue crack propagation according to Paris law was applied. Also, bridging stress along crack length in aluminum layer was investigated by correlation between the delamination growth rate and energy release rate in hybrid composite layers. The obtained findings indicated that the highest amount of peak low velocity impact force belonged to Glare 4 3/2. The presented numerical method based on bridging stress phenomena can successfully be used for predicting the post impact fatigue life of Glare.

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Numerical and Experimental Assessment of Post Impact Fatigue Life of Glass-fiber-reinforced Aluminum Laminates

The fatigue damage accumulation under variable amplitude loading conditions is significantly influenced by load sequence effects. It is shown that sequence effects can lead to significant accelerations of the fatigue damage process, not only for metallic materials but also for other types of materials, as the damage tolerant hybrid composite ARALL and fibre reinforced plastics. The parameters which are commonly used for fatigue life analysis methods are briefly described. It is then discussed that the actual physical damage phenomena, as they occur at the different types of materials, exhibit significant similarities after the influences of the presently known mechanics contributions are eliminated, despite of the fact that the microstructures are very different. In the last part of the study engineering fatigue life prediction methods are discussed.

H. Nowack

Papers

Fatigue analysis for variable amplitude loading: fundamental aspects and engineering applications