Modelling of inter-rivet buckling of hybrid composites

In aircraft construction, hybrid composites have obtained an increased use as a skin material due to its beneficial characteristics in terms of fatigue and fire resistance. The material, consisting of alternate layers of aluminium and glass fibre reinforced epoxy, is however complicated to model numerically. This paper deals with the modelling of hybrid composites and is focused on a detailed simulation of the inter-rivet buckling behaviour in a stiffened fuselage shell. The skin material consists of a hybrid composite and is modelled with solid elements, layer by layer. Each of the constituents are provided with their respective material model. For the glass fibre reinforced epoxy the user subroutine UMAT is employed for description of the failure modes, such as matrix cracking and fibre failure. The behaviour of the delamination between the metal layer and the fibre reinforced epoxy is also described with a user subroutine for interfaces, which is an optional contact definition. This subroutine contains a failure criterion for the delamination. The rivets between the stiffener and the skin of a fuselage are modelled by elastic solid elements with a plastic material model, but without any failure criterion. This reflects the design, where no rivet failure is allowed prior to buckling of the skin. A specially designed experimental test, which captures the main characteristics of inter-rivet buckling, is modelled and simulated. The numerical results are compared to the experimental data. Finally, conclusions and recommendations are given for future research.