A Viscoelastic Based Mechanism for Improving Spring-In Angle Predictions in Compression Molded Thermoplastic Matrix Composites

In this paper, dimensional distortion during the compression molding of thermoplastic matrix composites, typically described as spring-in or spring forward, is investigated through a finite element model. Spring-in is the reduction of the enclosed angle of two surfaces on the final component shape with respect to the original mold shape. Spring-in of thermoplastic matrix composites has typically been attributed to the difference in the thermal expansion of in-plane and through thickness directions of the composite. However, using this mechanism alone during modeling has not shown complete agreement with the experimental data. A new meso-level mechanism based on the viscoelasticity effect of the thermoplastic matrix is proposed. With this mechanism, the predicted spring-in angle can be in good agreement with experiments.