Fibre-reinforced composites with nacre-inspired interphase: a route towards high performance toughened hierarchical composites

Abstract

Conventional fibre-reinforced polymer composite materials are well known for their high strength, stiffness, low weight and chemical resistance but composites do fail catastrophically, in a brittle manner, with little prior warning. When a fibre breaks in tension, shear stresses transfer load previously carried by the broken fibre to neighbouring fibres through the matrix, leading to local stress concentrations. As tensile loading continues, fibre breaks accumulate in the composite, eventually leading to the formation of a critical cluster, which triggers the failure of the composite. The aim of this research was to develop a novel hierarchical composite architecture consisting of fibres decorated with a nanostructured coating embedded in a matrix. A high performance and tough nanostructured composite interphase, inspired by nacre, should provide additional toughness in tension. A Layer-by-Layer assembly method was used to assemble inorganic nanometre-wide platelets and a polyelectrolyte into a well-organised nanostructure, mimicking the “brick-and-mortar” architecture of nacre, which was developed and characterised. The nanostructure was successfully deposited around conventional reinforcing-fibres, such as carbon and glass fibres, and allowed for absorption of the energy arising from fibre breaks and substantial increase in debonding toughness in single fibre composite models. Impregnated fibre bundle composites were manufactured and tested in tension, which exhibited an increased tensile strength, strain to failure and work of fracture when the nanostructured composite interphase was incorporated. This work was part of the HiPerDuCT programme grant, collaboration between the departments of Aeronautics, Chemical Engineering, Chemistry and Mechanical Engineering of Imperial College London and the University of Bristol.