Novel Analytical and Experimental Methods for Evaluating Bolted Joint Repairs in Composite Structure

In today"s composite aircraft structures, bolted joints are frequently subject to abuse, overloads, heat damage, or lightning strikes which can damage both the fastener and the surrounding composite material. This damage, when detected, must be repaired. However, little information currently exists to guide the maintainer in the design, analysis, or certification of the repair. SCS proposes to solve this problem through the use of a combined analytical/empirical approach using series of coupon and element tests to establish and validate the empirical parameters needed to accurately match joint strength behavior. This procedure, consisting of an analytical approach combined with a material-specific strength database, would be used to predict the strength of a repaired fastened joint relative to its undamaged strength. Used by itself, this tool will enable maintainers to evaluate repair options and qualitatively determine whether the proposed repair restores the joint to its original, undamaged strength. When combined with the original joint analysis and/or material properties database, the tool could be used to determine the resulting strength. With knowledge of the loads and margins of safety of the individual fasteners, these predictions can then be used to determine repair approaches and techniques. BENEFIT: This testing and development of bolt repair methodology will benefit both commercial and DOD aircraft. This technology will improve the ease and reliability of bolted hole repair on all aircraft. This should increase the safety across the entire DOD and commercial aircraft fleet.