Keywords: laminates, adhesion, stress concentrations, mechanical testing, out-of plane loadings, non-linear behaviour, finite element analysis.

The use of composite materials is a key element in energy reduction strategies, particularly in all areas of transportation. Therefore, the study of the behaviour of assemblies of composites is of great importance. Failure in bonded assemblies involving composites is often associated with crack initiation in the adhesive or delamination of the composite plies close to the adhesive joint caused by interlaminar or through-thickness stresses. Unfortunately, few experimental devices are proposed in the literature to characterize the mechanical behaviour of composites under out-of-plane loadings; and those which are available often use thick composite specimens or require special geometries which are often associated with subsequent large uncertainties in the experimental results. Ideally, to obtain experimental results representative of industrial applications, there is a need on the one hand to use composite plates with quite low thicknesses, which are easy to manufacture, and on the other hand to apply a large range of tensile-shear loadings.

This paper describes an experimental device, using a modified Arcan test, and optimized hybrid bonded assemblies, which limit the influence of edge effects. Different numerical studies have been developed in order to analyse and optimise the design of such a system (geometry of the composite plate, geometry of the substrates, fixing system). In order to obtain reliable experimental results, it is essential to limit the influence of edge effects. This test allows the mechanical behaviour of both composites and hybrid metal or composite bonded assemblies to be analysed under a large range of proportional tensile-shear out-of-plane loadings. Moreover, it is important to note that failure can occur in the composite, in the adhesive joint or at the composite-adhesive interface according to the tensile-shear loading ratio. An optimization of the adhesive must be performed, especially under shear loadings, as the shear strength of the composite can be higher than that of the adhesive. Experimental results show that the fibre orientations, the characteristics of different plies, and the surface preparation all have an influence on the out-of-plane strength of composites and of hybrid bonded assemblies. Test results, showing the potential of the approach, are presented in the form of failure envelope curves for radial out-of-plane loadings. This study makes it possible to optimize the strength of hybrid bonded assemblies. Moreover, inverse procedures are under development in order to characterize the damage evolution in the composite subject to out-of-plane loadings.

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