Prediction of the Degree of Bonding in the Extrusion Deposition Additive Manufacturing Process of Semi-Crystalline Polymer Composites

The Extrusion Deposition Additive Manufacturing (EDAM) process is a manufacturing process used to produce three-dimensional objects made by deposition of molten polymer composite in a layer-by-layer fashion. Printing with fiber reinforced, semi-crystalline polymers provides for the manufacture of molds that can be used in high-temperature composite prototype molding applications. Further, the EDAM is scalable and can provide printed geometries in the centimeter to meter scales. However, in plane (X-Y) fiber orientation of the extrudate results in mechanical properties in the stacking orientation (Z) that are governed by the bond formed between adjacent extrudate layers. The quality of this interlayer bond is strongly influenced by the processing conditions, namely temperature and printing history. Therefore, simulation tools are required to predict the influence of printing conditions on the interlayer bond strength and to optimize printing parameters for maximum interlayer bond strength. The degree of bonding is defined in the context of this work as the ratio of recovered mode-I critical energy release rate to the critical energy release rate of a fully bonded interface. The degree of bonding is predicted by coupling an autohesion model with the temperature history and the evolution of crystallinity. This method has been implemented in a UMATHT user subroutine and is used together with functionalities deployed in Abaqus 2017 for simulating additive manufacturing methods to predict the evolution of the degree of bonding in the EDAM process. Finally, the predictions for degree of bonding for multiple processing conditions are validated with experimental measurements.