Thermoelastic stress measurement on epoxy and fiber of CFRP

Thermoelasticity is the physical effect of temperature changing due to the strain distribution of the material of a dynamically loaded mechanical component. By measuring the temperature changes by a thermocamera on the component surface, it is possible to measure the strain field in a non intrusive way. A simple relation exist between stress and temperature for homogeneous material but the application of this measurement techniques to composite materials is more complex. Some theory has been proposed to analyse the thermoelastic effects on composite materials since more than 30 years, in order to perform stress pattern measurements by thermoelasticity. In this work measurements with high spatial resolution up to 22µm are performed by an infrared zoom on some special Carbon Fiber Reinforced Plastic (CFRP) specimens, realized with the hand lay-up technique. Results obtained was very useful in order to separate the thermal emission from the different composite components. By the analysis of different thermal emission it was possible to measure the stress on the epoxy layer and on the carbon fiber. The proposed technique is better analysed by a FEM model, useful to correlate the stress distribution measured and better understand the reason of the thermal emission of the different specimen parts.