The purpose of the proposed research is to evaluate the mechanical response of stitched T-joints under tension, bending, and combined tensile-flexure loading. The use of fiber-reinforced polymer matrix composites has increased in primary load-bearing structures due to their many attributes, such as their high strength and stiffness-to-weight ratio, and tailorability. Composite T-joints are often used in aerospace, marine, and wind turbine structures to provide load connectivity between orthogonal components, such as stiffeners to skins. However, one of the main drawbacks of polymer matrix composites is their low interlaminar strength, which can lead to delamination when subjected to out-of-plane loads. Techniques such as braiding, knitting, stitching, tufting, and z-pinning have been used to reinforce T-joints in the through-thickness direction. Most research has been focused on the tensile or bending behavior of T-joints, although these joints are often subjected to a combination of tensile and bending loads in service. A few experimental and analytical studies have been conducted on the mechanical response under combined tensile-flexure loading conditions, but no studies have been conducted on stitched T-joints. In this study, mechanical tests of 3D stitched and unstitched T-joints under tension, bending, and combined tensile-flexure were conducted, and the ultimate load, displacement, and absorbed energy were obtained. The average displacement at total failure under tension, bending, and combined tensile-flexure loading conditions for the stitched specimens were found to be 34%, 51%, and 24% greater, respectively, when compared to their unstitched counterparts. Similarly, the average absorbed energy for stitched specimens is 58%, 82%, and 51% greater under tension, bending, and combined tensile-flexure loading conditions. The failure surfaces of stitched and unstitched T-joints were analyzed using an optical microscope, and areas of interest, such as resin-rich regions, stitches, and different damage types, were identified. Furthermore, the skin-flange interface fracture surface of the combined loading T-joint specimens were analyzed using a scanning electron microscope. Significant differences in the fracture surface indicated varying degrees of mixed-mode loading conditions within a specimen for all specimen types. A numerical analysis of a stitched double cantilever beam specimen was conducted to evaluate smeared cohesive laws to represent stitched regions. Overall, stitching results in improved damage tolerance in T-joints subjected to various loading conditions.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-7225 |
| Date | 13 August 2024 |
| Creators | Shah, Aditya |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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