Toughening and monitoring carbon fibre/epoxy composite delamination with electrospun PVDF interleaves

Abstract

Carbon fibre/epoxy composite (CF/EP) laminates have been extensively used in many structural applications owning to their high modulus and strength, and lightweight. As laminated materials, however, CF/EP laminates are easy to delaminate under cyclic and impact loadings. Several reinforcing methods such as through-thickness stitching or Z-pinning, fillers and interleaves have been utilized to enhance the interlaminar mechanical properties. However, few research has been reported on in-situ monitoring of damage of CF/EP laminates and to improve toughness simultaneously. Therefore, this project is aimed to fabricate hybrid PES/PVDF and PVDF piezoelectric interleaves by the electrospinning technique for dual-functions: (1) in-situ monitor of delamination of CF/EP laminates and (2) improve the fracture toughness of CF/EP laminates. Mode I and Mode II fracture toughness of CF/EP laminates with PES/PVDF or PVDF interleaves were studied. The Mode I results showed that only PVDF interleaves can increase the toughness, while PES/PVDF interleaves decreased the toughness. The matrix deformation was the major contribution to enhancing the Mode I toughness. All interleaves can enhance the Mode II fracture toughness. Matrix deformation and nanofibers pull-out were the main contributors. The Mode I delamination detection results showed that the output voltage from PVDF interleaves was increased by increasing applied extension at the same crack length. With increasing crack length, the output voltage initially increased and then sharply decreased at propagation. In Mode II tests, the output voltage initially increased, and then remained at a steady plateau value. After that, it increased significantly when the delamination started to propagate. The mechanism of in-situ monitoring using PVDF interleaves was revealed, and the theoretical equations were deduced.