Experimental study on how free-edge effects impede CTE measurements

Abstract The present paper is focussed on the experimental quantification of free-edge effects and their relevance when laminates’ coefficients of thermal expansion (CTEs) are determined by means of thermo-mechanical analysis (TMA). TMA tests have been performed for specimens with in-plane dimensions of about 6 mm x 6 mm and 28 mm x 28 mm and a thickness of 5.56 mm. The examined 30-ply laminate with highly orthotropic stacking is made from HEXCEL’s M21E/IMA medium grade prepreg. The conducted tests clearly substantiate the strong effect of sample size. CTEs determined from the small sample data are found to exceed large-sample CTEs by 122% in the laminate’s x-direction and 76% in y-direction, even though both samples were cut from the same CFRP panel.