FUSION BONDING OF FIBER REINFORCED SEMI-CRYSTALLINE POLYMERS IN EXTRUSION DEPOSITION ADDITIVE MANUFACTURING
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Extrusion deposition additive manufacturing (EDAM) has enabled upscaling the dimensions of the objects that can be additively manufactured from the desktop scale to the size of a full vehicle. The EDAM process consists of depositing beads of molten material in a layer-by-layer manner, thereby giving rise to temperature gradients during part manufacturing. To investigate the phenomena involved in EDAM, the Composites Additive Manufacturing Research Instrument (CAMRI) was developed as part of this project. CAMRI provided unparalleled flexibility for conducting controlled experiments with carbon fiber reinforced semi-crystalline polymers and served as a validation platform for the work presented in this dissertation.
Since the EDAM process is highly non-isothermal, modeling heat transfer in EDAM is of paramount importance for predicting interlayer bonding and evolution of internal stresses during part manufacturing. Hence, local heat transfer mechanisms were characterized and implemented in a framework for EDAM process simulations. These include local convection conditions, heat losses in material compaction as well as heat of crystallization or melting. Numerical predictions of the temperature evolution during the printing process of a part were in great agreement with experimental measurements by only calibrating the radiation ambient temperature.In the absence of fibers reinforcing the interface between adjacent layers, the bond developed through the polymer is the primary mechanisms governing the interlayer fracture properties in printed parts. Hence, a fusion bonding model was extended to predict the evolution of interlayer fracture properties in EDAM with semi-crystalline polymer composites. The fusion bonding model was characterized and implemented in the framework for EDAM process simulation. Experimental verification of numerical predictions obtained with the fusion bonding model for interlayer fracture properties is provided. Finally, this fusion bonding model bridges the gap between processing conditions and interlayer fracture properties which is extremely valuable for predicting regions with frail interlayer bond within a part.