Improving the Damage Tolerance of Durable Redundant Joints

A previous analysis and test program demonstrated that the Durable Redundant Joint (DRJ), a patented concept that features multiple adhesive load paths, exhibited superior performance compared to a conventional joint design. This paper describes follow-on investigations on design improvements to the DRJ to further understand its damage tolerance characteristics. Before embarking on this particular study, it was necessary to further investigate the failure sequence of the DRJ. One short flaw and one large flaw were intentionally manufactured between the doubler termination and the facesheet. Surprisingly, fracture analysis predicted the shorter flaw to be more critical than the larger flaw, and it was confirmed with examination of the coupons. Using the insight gained from these studies, three design attributes are investigated relative to increasing damage tolerance characteristics of the DRJ: (1) Insert stiffness, (2) Relative length between the doubler and the insert, and (3) The use of tapers at the ends of doublers. The paper will include findings from all these ongoing studies.