Fatigue failure criteria for structural film adhesive bonded joints with considerations of multiaxiality, mean stress and temperature

Fatigue failure criteria for structural film adhesive joints considering multiaxiality, mean stress and temperature effects were investigated. Multiaxiality was addressed by testing butt, scarf and thick adherend shear test joints. Mean stress effect was evaluated under stress ratios of −1.0 and 0.1, and the temperature assessed at −55 C, RT and +100 C. Fatigue results were assessed using three fatigue criteria: (1) maximum principal stress, (2) linear Drucker-Prager stress or (3) Findley's critical plane. All criteria worked well on fitting the multiaxial fatigue behaviour of joints with criteria (2) and (3) performing slightly better. However, criterion (1) is parameter-free, which avoids data fitting. Mean stress effect was successfully described based on a Haigh transformation. Temperature effect was characterised using the criterion (1), which was capable of combining fatigue data at different temperatures. An increase of temperature led to fatigue strength reduction, meaning that a knock-down factor approach could be used.