Nowadays, there is a tendency to use various materials in the aircraft structures. It is caused by weight and strength optimisation as well as manufacturing and service (including repairs) cost optimisation.

As there is a wide range of materials and numerous parts in aeroplane structures, the problem of joining different materials is very important. The design of the hole vicinity in composite elements (metal-composite joint) and, therefore, the improvement of load transfer is of great importance.

The main goal of PROJOINT is to design a metal-composite mechanical connection with improved bearing performance of a composite panel. The particular tasks of this project are to study the local phenomena in composite material during the bearing and riveting process as well as to investigate possible benefits of local laminate modification in the hole vicinity in mechanical joints of composite panels.

Although fibre reinforced composites have high tensile strength, the load transfer in mechanical joints of such components is limited. In this type of connection the load is transferred by bearing (local compression) determined by matrix strength. A proper solution of load transfer into the composite structure using shear stress in the resin matrix between metal and composite layers can improve bearing capacity of mechanically fastened joints. Bonding of titanium foils between laminate layers seems to be the most advantageous solution. The authors effort will be put on searching for the optimal solution for the mechanical joint of composite panels that creates a possibility of transferring the bearing load into the composite material in a gradual way and will be economically reasonable. Both different inserts (foils) shape and content will be taken into account. Joining panels will be made of CFRP laminate and aluminium alloy 2024T3 (typical materials used in aircraft industry). The insert material (metal alloy) is also important (e.g. due to galvanic corrosion problem). The application of titanium or aluminium alloy inserts will be considered due to cost reduction of experimental tests.

As there are many factors that influence joint strength, the finite element analysis is a very useful tool to solve such problems since some statements are possible to be made without many expensive experimental tests. A deep study of load transfer by means of shear stress and numerical analysis of various locally modified laminate configurations will be the principal investigation method. However, identification of material properties as well as validation and verification tests using DIC, strain gauges, SE and non-destructive methods will also be necessary.

The target groups of the project are scientists (due to new competences) and airplane manufacturers and services. The solution of load transfer into the composite structure by means of interlaminar shear stress can be profitable for bolted or riveted joints. This fact will cause great economical profit (due to simple and limited equipment, less demanding assembly and service conditions, reliable checking methods).