An embedded fibre optic sensor for impact damage detection in composite materials

A structurally embedded fibre optic damage detection sensor for composite materials is described. The system is designed specifically for the detection of barely visible damage resulting from low velocity impacts in Kevlar-epoxy laminates. By monitoring the light transmission properties of optical fibre embedded in the composite, it has been shown that the integrity of the material can be accurately determined. The effect of several parameters on the sensitivity of the system has been investigated, including the effect of the optical fibre orientation and depth of embedding within the composite. A novel surface treatment has also been developed for the optical fibres to ensure they will fracture at the requisite damage level. The influence of the optical fibre sensors on the tensile and compressive material properties and on the impact resistance of the laminate has also been studied. Extensive experimental results from impact tests are reported and a numerical model of the impact event is presented which is able to predict and model the damage mechanism and sensor system. A new and powerful method of nondestructive evaluation of translucent composite materials is also described, based on image enhanced backlighting.