Fatigue life prediction based on crack closure for 6156 Al-alloy laser welded joints under variable amplitude loading

• Fatigue crack growth of Al-alloy laser welded joints was investigated under variable amplitude loading.
• A fatigue life prediction approach based on crack closure was proposed.
• Welding residual stress and its relaxation are considered in the approach.

A fatigue prediction approach is proposed using fracture mechanics for laser beam welded Al-alloy joints under stationary variable amplitude loading. The proposed approach was based on the constant crack open stress intensity factor in each loading block for stationary variable amplitude loading. The influence of welding residual stress on fatigue life under stationary variable amplitude was taken into account by the change of crack open stress intensity factor in each loading block. The residual stress relaxation coefficient β = 0.5 was proposed to consider the residual stress relaxation for the laser beam welded Al-alloy joints during the fatigue crack growth process. Fatigue life prediction results showed that a very good agreement between experimental and estimated results was obtained.