Development of a strength model for the cocured stepped lap joints under tensile loading

The cocured stepped lap joints for composite structures were manufactured and tested under static and fatigue tensile loads. From the tests, it was found that the joints were shear-failed at the joining interfaces. As the length of the stepped lap of the joint increased, the average static tensile strength of the joint increased, while the average static shear strength decreased in proportion to the length of the stepped lap of the joint. The fatigue endurance limit was found to be 30–40% of the static strength.

Also, the cocured stepped lap joints were manufactured by curing plies laid-up on the composite plates which had machined stepped laps. The static strength of the joints manufactured by the latter method was found to be 70–80% of the static strength of the joints manufactured without machining and the fatigue endurance limit was found to be about 25% of the static strength.