Crack propagation behavior on metal laminate of FMLs after a high tensile overload under high constant amplitude load

The crack propagation behaviour on the metal laminate of the FMLs is investigated under constant amplitude loads, which is higher compared to the fatigue strength of the metal laminate, and the subsequent crack propagation behaviours after being highly overloaded. The observation was carried out on the FMLs with the various surface roughness of the metal laminate at the interface between the metal and fibre-reinforced composite laminate. The overload leads to delay of the crack propagation following the overload, and the higher surface roughness increases the number of delay cycles. The overload together with the surface roughness affects stress condition in front of the crack tip and the crack tip condition as well as the compressive residual stress in front of the crack tip after the overload. In addition, the higher surface roughness strengthens the shear strength of the interface leading to the delamination caused by cyclic loads to be more difficult to take place. Therefore, the delay cycles after the overloading become longer.