Effect of interface profile and incident wave characteristics on aluminum/epoxy dynamic adhesion strength

The effect of interface profile on aluminum/epoxy adhesion strength under extreme dynamic loading condition is investigated. Test samples are prepared by depositing thick epoxy film onto polished aluminum substrates of roughness less than 200 nm. Failure is instigated at the interface by using laser induced stress waves. The adhesion strength of the film, evaluated by employing hybrid experimental/numerical approach, is observed to increase with decreasing interface roughness. To get more insight into the effect of interface profile and the incident wave characteristics on transient stress fields, two dimensional bi-material geometries are modeled with sinusoidal interface and the wave propagation analyses are performed. The simulations indicate increasing stress amplification at crest locations with an increase in the wavy interface amplitude (Aint). The interface wave length (λint) on the other hand shows a reverse trend. While the interface stress peaks appear to be uniquely dependent upon Aint/λint2, the effect of asperity remains constrained to the vicinity of the interface. It is demonstrated that the stress amplification at wavy interface increases with increasing incident energy flux whereas the shape of the loading pulse has no effect on the interface stress magnitude. On the contrary the peak stress at a planar thick film interface is only influenced by the incident pulse amplitude and not by its shape or the energy content.