Engineering Design of 3D Woven Composite T-joints against Delamination

Abstract

Composite T-joints has garnered significant attention as replacements for metal counterparts across various industries, making them subjected to complex stress fields. A key challenge is their vulnerability to delamination failure at the junction, particularly pronounced when they are reinforced with 2D laminates or 3D preforms with simple weave architectures. To addresses this challenge, this research develops advanced 3D woven architectures at the junction to resist delamination and enhance the mechanical properties of composite T-joints. This research introduces two structural concepts for the first time, crossing arrangement and position, developing 10 novel crossing warp architectures. Mechanical and imaging evaluations confirm that crossing warp architectures with different crossing arrangements and positions significant influence the failure mode and mechanical properties of 3D woven composite T-joints (3DWCTs). Under in-plane tensile loading, 3DWCTs with crossing warp yarns in external (EXT) arrangement primarily fail due to debonding and fibre breakage, while those in internal (INT) arrangement show severe delamination. Therefore, EXT 3DWCTs exhibit superior in-plane modulus, strength and strain, compared to their INT counterparts independent of crossing warp proportions, with maximum increases of 29.83%, 68.75% and 116.81% respectively. Interestingly, the failure modes are reversed under out-of-plane tensile loading. Accordingly, INT 3DWCTs have higher out-of-plane mechanical properties over their counterparts across all crossing warp proportions. The maximum differences are 105.22%, 67.70% and 12.15% in modulus, strength and strain respectively. The distinction between INT and EXT 3DWCTs diminishes as the crossing warp proportion increases. Regardless of crossing arrangements, increasing proportions creates a convex and concave relationship with in-plane and out-of-plane properties respectively. Varying the position of crossing and straight warp yarns in INT architecture changes the failure mode and mechanical properties. Separating neighboured straight warp yarns while keeping adjacent crossing warp yarns reduces delamination, increasing in-plane strength by up to 26.04%. However, separating both straight and crossing warps creates localised stress concentration, exacerbating debonding and delamination and therefore decreasing out-of-plane modulus and strength by up to 45.87% and 23.16% respectively. Overall, delamination resistance and mechanical properties of 3DWCTs are closely related to crossing yarn architectures and can be optimised with regard to crossing arrangement and position.

Date of Award	16 Dec 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Xiaogang Chen (Supervisor) & Constantinos Soutis (Supervisor)