The static and fatigue responses of aged metal laminate doublers joints under tension loading

Experimental studies have been undertaken to investigate the static and fatigue responses of metal laminate doublers (MLD) joints under tension loading after ageing in deionised water at a temperature of 50 °C up to 2 years. It was found that absorbed water did not have a significant effect on the static and fatigue degradation of the MLD; however, corrosion pits located on the aluminium surfaces caused a reduction in fatigue life. Inevitably, the laminate contained butts where co-planar aluminium sheets were joined, and it was found that the position of the butt affected the static response of the MLD but, due to a restricted data set, it has not been possible to assess the effect under fatigue loading. The backface strain technique in conjunction with video microscopy has been utilised to monitor the damage of the adhesive bondlines, the butts and the aluminium layers and successfully identified both the localised and the global damage in the MLD. Most of fatigue failures initiated at the stringer bondline edge and at the aluminium layers where the butt was located. A careful design should be made to reduce the stress concentration at the stringer edge and to avoid positioning the butts at the upper layer of aluminium close to the stringer edge.