An investigation of the influence of the macroscopic heterogeneity on the thermoelstic response of fibre reinforced plastics

In this work the influence of the inherent heterogeneity in fibre reinforced plastic composites on the qualitative and quantitative evaluation of the thermoelastic signal is discussed. The role of two different levels of heterogeneity is identified, distinguishing between a micro-geometric scale characterized by the presence of different constituent materials, and a macro-geometric scale characterized by a non-uniform distribution of these constituents. Attention has been focused on the macro-scale level, presenting results of experiments performed on glass fibre - polyester resin samples, intended to highlight the influence on the thermoelastic signal of the fabric texture pattern and the surface pure resin layer. A hypothesis is proposed that the surface resin layer behaves as a strain witness towards the laminate and the consequences of this statement are investigated both experimentally and analytically, by deriving a mathematical model which has some potential advantages over the classical approach. (C) 2004 Elsevier Ltd. All rights reserved.