Experimental characterization and analysis of fiber orientations in hemispherical thermostamping for unidirectional thermoplastic composites

Abstract

Nowadays there is seldom literature concerning in-plane fiber orientation variations in the thickness direction for composites after thermostamping. In present work, cross-section microscopy observations were carried out to characterize fiber orientations at different positions and in different plies for thermoformed unidirectional reinforced thermoplastic composite hemispheres. It is found that there is no fiber angle change in the thickness direction near the vertex; fiber angles of medial plies are lower than that of lateral plies in the middle region; fiber angles decrease from the outside ply to the inside ply on the hemisphere edge. Thermostamping simulations were performed and a constitutive model was applied with fiber reorientations considered. It is shown that embedding fiber reorientations and non-uniform temperature field of the blank into the constitutive model has an important influence on fiber orientations in simulation. The average condition of fiber orientations could be reasonably forecasted at different positions. Simulation shows agreements with experiments on distribution trends of in-plane fiber orientation variations through the thickness near the vertex and on the hemisphere edge. However, simulation failed to describe a distribution feature of in-plane fiber orientation variation through the thickness: fiber angles in medial plies are smaller than that in lateral plies.