Effect Surface Roughness on Fatigue Crack Propagation Behaviour of Fibre Metal Laminates (FMLs)

In the present study, the effect of surface roughness of the metal lamina at the interface of fibre metal laminates (FMLs) on the crack propagation behaviours was investigated for different fibre orientation. The FMLs was made by combining the aluminium and the carbon fibre-epoxy composite lamina. The increasing of the aluminium surface roughness at the interface causes the tensile strength to increase for every fibre orientation. The highest tensile strength is 282 and 367 MPa., respectively for fibre orientation 0°/90° and -45°/45° when the surface roughness is 2.89 mm. The increasing surface roughness causes the development of the delamination taking place at the interface is more difficult, and it leads to the shear strength at the interface to increase. Because of this, the tensile strength increases. However, the lifetime is not only influenced by the interface shear strength but also the stress concentration just in front of the crack tip as well as the surface roughness itself leading to the crack to be initiated from the rougher surface. The longest fatigue life is 180 000 cycles in the case of the fibre orientation 0°/90° with the surface roughness of 1.78 mm, and in the case of fibre orientation of -45°/+45° the longest fatigue life is 420 000 cycles when the surface roughness is 0.33 mm. The results of the study show that the surface roughness affects the tensile strength and crack propagation behaviour.