Fatigue crack growth and fracture toughness of shot peened 6060 T6 aluminium alloy

Aluminium alloys are widely used in many industrial sectors due to their high strength-to-weight ratio. The structural integrity of aluminium components is a fundamental issue when these components are subjected to fatigue loading. Some surface treatments such as shot peening, or laser shock peening can induce compressive residual stresses in the treated material and thus may be effective at delaying crack propagation. In this research, the fracture toughness of a 6060 T6 aluminium alloy was evaluated according to ASTM E1820 standard. SE(B) specimens were analysed in the non-treated condition and after different shot peening treatments. The crack propagation behaviour of these specimens was evaluated during the fatigue precrack stage of the tests by fitting the crack growth rates to Paris law. Then, a fracture toughness value was determined using the resistance curve procedure method. The results of these tests demonstrated that the shot peening treatments had little or no significant effect on the fracture toughness values, or the crack propagation rates. The reason behind these results is probably the shallow depth of the strain hardened layer affected by the shot peening treatments.