Spring-in angle as molding distortion for thermoplastic matrix composite

In this work, the spring-in angle behavior of a U-channel shaped thermoplastic matrix laminate is studied. The consolidation of the U-channel shaped profile having two different corner radii took place in an autoclave. Spring-in angle was measured at room temperature, after cooling in the autoclave, and during subsequent heating at different temperatures and after final cooling to room temperature. Different thermally induced spring-in angle behaviors were observed for the two inner radii of U-specimen. Thermal expansion coefficients in the through the thickness and in-plane directions were measured. Experimental spring-in angle data were then compared with a differential model derived from the Radford model. Some differences between the model results and experimental spring-in data were observed. The differences observed between the two radii and between experimental and model results were attributed to the existence of fibers distortion at the corner, leading to significant fibers misalignment and wrinkling. Consequently, the Radford model was modified to account for the increase of thermal expansion coefficient in the through the thickness direction. Results showed a better agreement with experimental data. Finally, the difference observed in the spring-in angle before and after heating of the composite indicates the relevance of non-thermoelastic effects in thermoplastic matrix composites.