X-ray 3D microscopy analysis of fracture mechanisms for 3D orthogonal woven E-glass/epoxy composites with drilled and moulded-in holes

As a promising structural material, three dimensional woven fabric reinforced composites are subjected to machining or drilling during manufacturing processes for components assembly. In-plane tensile and flexural properties of a three dimensional orthogonal woven E-glass/epoxy composites (3DOWC) with 4 and 6 mm drilled holes (DH) and moulded-in holes (MH) are investigated. 2D woven E-glass/epoxy laminated composites (2DWC) with the same drilled hole sizes are also tested for comparison. Two different calculation methods based on gross and net sectional area are adopted to evaluate the effects of the holes on mechanical performance of the composites. The 3DOWC-MH possesses the highest tensile and flexural strength, followed by 3DOWC-DH and 2DWC-DH. As the hole diameter increases, the mechanical properties of all the composites degrade, while those of the 3DOWC-MH increases when the net sectional areas are used for calculation. X-ray 3D microscopy and scanning electron microscopy are employed to analyze damages at submicron level resulted from the tests. Various failure modes such as fiber fracture, matrix cracking and tow debonding are observed, while serious delamination occurs in 2DWC but not in 3DOWC.