Mechanical properties and failure mechanisms of 3D layer-to-layer interlock woven composites

Three-dimensional layer-to-layer interlock woven composites (3D LTLIWCs) have been widely used in various aero-engine blade models because of their excellent near-net forming capabilities for complex components, as well as significant advantages in structural design flexibility and high damage tolerance. In this paper, a typical and two new 3D LTLIWCs, specifically including 1/3 twill (S-I), modified satin (S-II), and stuffer twill (S-III), were manufactured by two design methods: varying interweaving frequency and introducing stuffer yarns. Three-point bending and uniaxial tensile tests were conducted along the 0 degrees (warp) and 90 degrees (weft) directions. The damage morphology and failure mechanism of the specimens were revealed by nondestructive testing technology and topological structure analysis. The results showed that the fabric structure significantly influenced the mechanical properties and failure mechanisms of the 3D LTLIWCs. Compared with S-I and S-II, S-III demonstrated a 17.9%-80.2% increase in bending strength and a 35.3%-162.8% increase in tensile strength in the 0 degrees direction, while the bending strength and tensile strength in the 90 degrees direction increased by 1.1%-73.3% and 9.3%-50.4%, respectively. Notably, S-III exhibited lower bending and tensile damage in the 0 degrees direction than S-I and S-II, with a smaller propagation range of resin and interface cracks and less severe shear fracture of the load-bearing yarns. This study can provide a useful reference for the optimal design of fabric structure for 3D woven composite blades.Highlights Two design schemes for optimizing 3D LTLI fabric structure were compared. Introducing stuffer yarns improved the mechanical properties of 3D LTLIWCs. S-III composites exhibited the highest failure strength in all test directions. Full-field strain distribution was closely related to the interlocking patterns. Fabric structures had a great influence on the failure modes of 3D LTLIWCs.