Modeling the effects of thermal contact resistance on mechanical properties in material extrusion additive manufacturing

This study investigates the role of thermal contact resistance and material thermophysical properties on the mechanical properties of fused filament fabrication (FFF) parts. Experiments were conducted to determine material conductivity, contact resistance, and conductivity through the print bed/first layer interface, which accounts for the contact resistance at the interface. This data was used to develop a two-dimensional heat transfer model, simulating a single-, three-, and five-road-width polycarbonate structure with equivalent layer times. The predicted tensile strength was compared to models neglecting thermal contact resistance. Accounting for thermal contact resistance leads to no change in the tensile strength of parts with 8-s layer time, but leads to 2.8% increase in tensile strength in parts with 20-s layer time. Assumption of full contact between roads leads to 6–8% decrease in tensile strength. In parts with 8-s layer time, which previously showed no effect for thermal contact resistance in a single-road system, the predicted tensile strength varies by 1 and 5% for the three- and five-road structures, respectively. The results demonstrate that thermal contact resistance influences the tensile strength, especially as layer deposition time increases and the decreasing interface temperature slows the welding kinetics. Thermal contact resistance is also critical to consider in complex, multi-road structures due to the presence of multiple interfaces.