Fatigue Strength Optimization of Bonded Joints

Abstract

The possibility of improving the fatigue strength of bonded double strap joints by reducing the stress concentration, inherently encountered at the conventional square (90 deg) strap edge, was studied. A 10 deg bevel on the strap edges was used for this purpose and joint specimens of both types were fatigue tested. The test data were plotted as S-N curves and compared with those of plain metal specimens. The metal employed was 2024-T3 clad aluminum alloy and the adhesive, FM-123-2. The results indicate that stress concentrations on square strap edges are in practice, due to plastic relaxation, much lower than theory predicts and that, therefore, the resulting but limited gains in fatigue strength due to bevelling of the strap edges doesn’t seem worth the extra effort.