Variable amplitude fatigue of bonded aluminum joints

The effect of variable amplitude loading on the fatigue life and failure mode of adhesively bonded double strap (DS) joints made from clad and bare 2024-T3 aluminum was investigated. Under constant amplitude loading, the clad specimens failed through the adhesive or the substrate at high and low stress levels, respectively. The presence of overload cycles shifted the failure mode towards adhesive failure. The specimens made from bare aluminum failed only in the adhesive. Effective stress range vs. failure life curves developed for the bare and clad specimens were used in conjunction with a linear damage summation to predict the failure lives of double strap specimens subjected to two variable amplitude aircraft load spectra with reasonable accuracy.