Analysis of selected parameters influence on failure in metal-composite mechanical joint

The never-ending attempt to obtain as low mass as possible is the reason for using material of high specific strength (stiffness) in the aerospace industry. High strength titanium or aluminium alloys (e.g. 2024T3) and composite laminates (e.g. CFRP or Glare) are the examples of such materials. Despite a large number of composite types, fibre reinforced composites in the form of laminates are commonly used in aircraft structures. One-half of modern aircrafts is made of composites. However, the second one is still made of metallic alloys. The usage of different materials in aircraft structures results in the necessity of joining composite and metallic components. There are three connection methods for aircraft primary structures: mechanical (riveting, bolting), adhesive (bonding) and hybrid where both mentioned methods are used. The paper deals with metal-composite mechanical joint. Although fibre reinforced composites have high tensile strength, the load transfer in mechanical joints of such components is limited. Strength of composite laminates is dependent on the joint geometry; however, it is strongly influenced by laminate lay-up. There are five global failure modes for mechanically fastened composite laminates: tension, bearing, shear-out, cleavage and pull-through. The bearing failure mechanism is a safe progressive mechanism not leading to catastrophic failure and therefore it is acceptable. Problems with strength assessment of composite mechanical joints are drawn. Some geometrical (joint width), material (bolt material, stacking sequence) as well as numerical parameters (failure criterion) are analysed.