Joining thick composite panels with the use of unitary 3-D woven couplers and patches
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abstract
Joining thick composite structural components (particularly those unequal in thickness) remains the primary problem of composites research and technology. If traditional single-lap or double-lap joining approaches are applied, the resulting large overlap thickness and sharp thickness variation may not only be unacceptable from the aesthetics design viewpoint but also due to increased stress concentration at the ends of the overlap resulting in premature failure. If butt joints are used, the difference in adherend thickness causes additional geometric stress concentration which also leads to the reduction of the joint strength efficiency. This paper presents several novel concepts of joining thick composite panels that are aimed at reducing these negative effects. The use of unitary 3-D woven preforms is their main distinctive feature. The preform design and manufacturing aspects are elaborated for a face patch and one coupler constructions which were selected for further experimental evaluation. The joint samples of thick composite adherends having two times thickness difference were fabricated by VARTM method with the use of (1) two thick flat unitary 3-D woven patches and (2) unitary 3-D woven X-coupler preform. The consolidated composite-to-composite joints were tested under in-plane tensile loading. The presented and discussed results include load-displacement curves and detailed observations of the failure initiation and progression mechanisms of each joint type. The obtained failure loads are compared to experimental results from the previous study of several single-lap and double-lap bonded and co-cured joints of 3-D woven F-glass fabric composites.
