Smart characterisation of damage in carbon fibre reinforced composites under static and fatigue loading conditions by means of electrical resistivity measurements

This thesis investigates the smart damage sensing capabilities of the electrical resistivity measurement technique in carbon fibre reinforced composite materials. The static and fatigue damage mechanisms of unidirectional and cross-ply laminates are reviewed. The electrical resistivity measurement investigations of carbon fibre, epoxy resin and carbon fibre reinforced composites are described. Theoretical models related to damage and electrical conduction modelling are reviewed. The material properties, laminate fabrication, specimen design, tab design and electrode design details are presented. The experimental test set-up and test programme details are presented. The details of the formulation and algorithms of a proposed new random resistor network model and the three-dimensional unit cell assemblage model are described. The results related to the applicability and the validation of these models are presented. The influence of electrode effects on the electrical resistance are investigated. The relevant results are presented. The electrical properties of carbon fibre reinforced composites independent of specimen geometry and electrode configuration are established. The dependence of electrical resistance on the specimen geometry was investigated and the relevant results are presented. The smart damage sensing capabilities are demonstrated using computational simulation studies using the proposed new three-dimensional model. The strain sensing and damage sensing capabilities of electrical resistivity measurement technique under static and fatigue loading conditions are presented. The dependence of electrical resistance to the applied stress and fatigue life of the samples subjected to fatigue loading is presented. The smart sensing capabilities are highlighted based on the experimental and theoretical results. The static and fatigue behaviour of epoxy 914 and epoxy 920 based CFRP laminates is investigated. The failure mechanisms are established using the electrical resistance and other non-destructive test methods.