Process monitoring with FBG sensors during vacuum infusion of thick composite laminates

Abstract

During manufacturing of thick (>20 mm) laminates, thermal gradients through the thickness may arise due to, for example, exothermal reactive heat release. These thermal variations may result in residual strain gradients through the thickness as well as variations in polymer matrix properties, such as degree of cure. For prediction and simulation of the residual strains, it is essential that the manufacturing process is monitored, in order to identify the parameters responsible for the residual strain build-up. The research described in this paper, proposes the use of Fibre Bragg Grating sensors as an experimental tool to determine variations in (thermal) residual strain levels through the thickness in a thick glass fibre reinforced thermoset laminate. In addition, other manufacturing issues, such as the flow behaviour that could be identified with these sensors were addressed. Moreover, the results of a first attempt to identify polymer property variations through the thickness by means of the microhardness test are reported