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A Comparative Study on Pin Bending Effect Under Bearing Static and Fatigue Failure



Primary aerospace composite structures are often joined by bolted joints due to its capability in transferring high loads and ease in disassembling and assembling for inspections and repairs. Joint strength in composites can be significantly reduced with operational use beyond originally intended design life due to the accumulation of internal damage which necessitates more frequent inspections. Internal damage (delamination, matrix cracks) can continue to propagate without being seen through visual inspections, thus nondestructive testing is required. However, this may be costly, particularly for a full-scale aircraft. Thus, a comprehensive understanding of joint damage growth behavior is necessary to guide what damage modes to inspect for as well as the frequency of inspection. In this work, an experimental investigation was performed on single-countersunkbolted- joint specimens and semi-circular through-hole and countersunk hole specimens under static load to study the effect of pin bending on bearing damage (i.e. shear cracks). The static tests results were compared to cyclic loaded specimens from previous published work to develop a greater understanding of the relationship between hole elongation and damage growth in a double lap shear test configuration [1]. The static test results indicate pin bending did not contribute to the bearing failure. Shear crack formation at the shank was found to be caused by the compression-induced instability of fibers (fiber kinking) near the free surface of the laminate.


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