Effect of fibre volume fraction and fibre direction on crack paths in unidirectional flax fibre-reinforced epoxy composites under static loading

Abstract

Nowadays, lightweight construction is of immense importance in many fields. Components and structures made of lightweight materials have extraordinary properties related to their densities. Fibre-reinforced composites are one of such materials. Besides their mechanical properties compared to conventional materials, fibres have benefits with regard to low densities, low manufacturing and processing costs. Environmental friendliness, biodegradability, and recyclability are to take into consideration as well. Regarding these criteria it is reasonable to take natural fibres into account. In this paper the fracture mechanical behaviour of unidirectional flax fibre-reinforced epoxy composites under static loading is investigated. Crack paths in compact tension specimens having five fibre directions and five fibre volume fractions are presented. Due to the anisotropic (transversal-isotropic) behaviour of the unidirectionally aligned flax fibre-reinforced epoxy composites the crack is not only governed by the stress state, but also affected by the fibre orientation and fibre volume fraction. From a certain fibre volume fraction onwards the crack path tends to propagate solely along the fibre direction. Furthermore, a mathematical model to estimate the crack kinking angles is presented.