A Quantitative Analysis of the Thermoelastic Effect in CFRP Composite Materials

In this study the thermoelastic signal from carbon fibre-reinforced plastic (CFRP) laminates is investigated. A comparison between the theoretical and experimental values of the thermoelastic signal is reported, with the theoretical predictions obtained from two different quantitative models. These models are based on the classic thermoelastic effect law extended to the case of orthotropic materials (by using the mesomechanical or bulk approach), and the modified law assuming that the surface resin-rich layer behaves as a strain witness of the laminate. It is found that the theoretical predictions of the two models can be strongly and differently influenced by the intrinsic orthotropy of carbon fibres. Some effects are highlighted in particular such as the influence of the laminate lay-up and the strong mismatch between the thermal expansion coefficients of the polymer matrix and the fibres. These influences are investigated analytically, predicting the thermoelastic signal from various lay-ups and using strain-based and stress-based analytical models. Experimental evidence of some theoretical findings is provided by reporting on tests performed on CFRP tensile samples manufactured from low-crimp unidirectional fabrics.