Crack Initiation and Propagation of Bonded Metallic Joints under Mixed-Mode Cyclic Loading

Double Cantilever Beam (DCB) specimens have been used to carry out Fatigue tests to investigate mixed mode crack growth behaviour in bonded joints. Equal thickness mild steel DCB substrates bonded with FM73 adhesive were used. The bonded joints were tested under pure mode I and a range of fatigue mixed-mode conditions using a relatively simple, variable-mode loading fixture as described in [1and 2]. The fatigue testing was carried out at a load ratio (R) of 0.1, in displacement control such that the initial maximum fatigue load was 70% of the corresponding quasi-static fracture load. The fatigue load decreased as the fatigue crack grew and this load was recorded. Crack growth was monitored and measured using a video microscope. The strain energy release rate components were determined using corresponding values of fatigue crack length and fatigue load. The fatigue crack growth rates were characterised using a Paris Law approach and a significant influence of mode II component on the crack growth rate has been observed.