Analytical and numerical residual stress models for fiber metal laminates – comparison and application

Abstract

Fibre metal laminates (FML) consist of alternately stacked plies of polymer matrix composites and metallic foils. Such material systems exhibit advantageous properties regarding fracture toughness, impact resistance and structural strength. Glass fibre reinforced aluminium (GLARE) with the constituents glass fibres, epoxy resin and aluminium foils is state-of-the-art. To improve the processing of FML thermoplastic matrix systems are promising. Carbon fibres could enhance the stiffness of the laminates. However, both modifications have a serious influence on thermal residual stresses grown by the mismatch of coefficient of thermal expansion and the cooling down from processing temperature. Finite element analysis (FEA) provides a reliable tool to predict the state of thermal residual stresses for FML made of different constituents. Otherwise, analytical models are an under-estimated but powerful tool, too. Closed formulas based on mechanical relationships can be applied fast and easy. Both, numerical and analytical methods are used to analyse thermal residual stresses caused by processing of different material systems. This contribution provides an overview on the analytical and numerical models used. The results of both models are compared and discussed. For promising material systems a more detailed study is carried out to highlight the influence of fibre orientation and fibre material. The relevance of thermal residual stresses for mechanical properties is shown and validated by experimental results.