Co-authors​ :

 Weijie ZHANG (CHINA), Yiding LI (CHINA), Junru LI , Shibo YAN (CHINA) 

The design of composite I-sections in aerostructures faces a significant challenge with conventional laminates because they are prone to delamination subject to out-of-plane loads. To address the issue, this study explores the fabric design, manufacture, and mechanical properties of 3D woven near-net-shaped composite I-sections. The study compares the mechanical behavior of 3D woven structures with equivalent 2D laminated structures and examines the influence of weave patterns. Firstly, both 2D laminated and 3D woven test specimens were designed according to the fiber volume content and geometric size requirements, and manufactured using the vacuum-assisted resin transfer molding technique. In particular, using 3D woven preforms to manufacture composite I-sections exhibits shortened production time observably in terms of layup and resin infusion. Different types of specimens, including 2D laminated and 3D woven with three distinct weave patterns, were utilized to carry out quasi-static tensile, compressive, and bending tests on I-sections to assess their mechanical properties. The testing equipment was specifically designed and verified for different tests. The findings indicate that the introduction of binder yarns and crossed weft yarns in the junction for the weave pattern significantly enhances the ultimate strength and damage tolerance of the structures under pull-off load. The test of 3D woven specimens showed a significant increase in ultimate strength compared to their 2D laminated counterparts, with enhancements of 531%, 89%, and 13% using different designs, respectively. In particular, for three types of 3D woven specimens, the crossing weft yarns were found to be more effective than the non-crossing pattern in maintaining the integrity of the webs and limiting crack propagation. The test results indicate that incorporating crossing weft increases the ultimate strength of the test specimens by nearly 100%. This implies that the manipulation of the weave pattern within the bifurcation region can serve as a viable strategy for tailoring the mechanical properties of 3D woven I-section composites. In summary, the 3D woven I-section specimens exhibited superior damage tolerance and ultimate strength compared to the 2D laminated specimens. Furthermore, 3D woven specimens show a larger weave pattern design space and require less time to produce. This highlights the potential of 3D weaving technology in the development of high-performance composite structures.