A Finite Element Approach for Thermal-Structural Response in Fibre Reinforced Composite Systems

Abstract

This paper presents a finite element analysis of coupled and semi-coupled thermal structural response of composite laminated plates. Our purpose is to use the results in order to quantify and’ calibrate’ the SPATE ( Stress Pattern Analysis by Thermal Emission ) experimental procedure. SPATE uses the thermoelastic effect, first quantified by Lord Kelvin [1], in order to obtain the stress distribution in a structure. Unfortunately the application of SPATE as NDT method on composite materials has so far been limited. The main problem has been identified to be associated with the existence of true adiabatic conditions, therefore the valid application of Kelvin’s law and the specimen motion due to the cyclic loading, known as’ motion effect’ [2-4].

In the first part we deal with the semi-coupled thermoelasticity. We evaluate the stress field in all the plies of the laminate, calculate the heat source term as a function of the principal stresses and thermal expansion coefficient of every layer and then proceed in the heat conduction finite element analysis. As a result we have the temperature and the heat flux on the surface area. This is what the infared detector of the SPATE apparatus measures. In the second part we make the finite element formulation of coupled thermoelasticity with starting point at the first and second thermodynamic laws. Then compare the results with the previous case and with SPATE results. By the comparison of the analytical and experimentalresults we can give an answer to the question’ how deep SPATE sees ?’ .