3D printing, especially fused filament fabrication, presents a potentially attractive manufacturing technique for thermal applications such as polymer heat exchangers due to the ability to create complex internal geometries which can be used to enhance convective heat transfer. Recently, commercial and modified open-source printers have utilized continuous fibers such as carbon fiber to create continuous fiber reinforced polymer composites (FRPCs) which enhance the mechanical properties of the printed products. This continuous filler network can also serve to improve thermal conductivity. In this study, the effective thermal conductivity of 3D-printed FRPCs is characterized using a steady-state, modified, guarded hot plate apparatus. The effect of the fiber direction and volume fraction on the effective thermal conductivity of the 3D-printed composites was characterized experimentally and modeled analytically using series and parallel models. Thermal conductivities of up to 2.97 W/mK were measured for samples in which the fibers were aligned with the direction of heat flow. Measured values were in good agreement with analytical model predictions. The importance of fiber conductivity on overall performance of the FRPCs was further demonstrated using a handlaid-up, pitch-based carbon fiber sample which exhibited an effective thermal conductivity of 23.6 W/mK.
This study presents the electromechanical properties of three-dimensional (3D) printed unidirectional continuous wire polymer composite (CWPC) to study the correlation of the elastic mechanical deformation and the electrical resistance under uniaxial loading conditions. Two kinds of wires were used for this study: copper (Cu) and nichrome (NiCr). 3D printing was utilized due to its flexibility in design and structure for different applications. From mechanical testing, the NiCr CWPCs demonstrated an increase of 13.5% and 54% in ultimate tensile strength and Young’s modulus, respectively, compared to pure 3D printed Poly(lactic acid) while the Cu CWPC did not exhibit significant improvement in the mechanical properties. A direct linear relationship was observed between the applied tensile strain and the measured electrical resistance for both Cu and NiCr CWPCs indicating the ability of these 3D printed structures to be used as a sensor to measure stress/strain in the real time. In addition, the sensitivity of both composites in terms of gauge factor, representing the relative change in the electrical resistance with the tensile strain of the material, were found to be 1.17 ± 0.06 and 1.13 ± 0.07 for Cu and NiCr CWPCs, respectively. This sensitivity was compared with a simple analytical model and showed a good agreement with the experimental results. Finally, the reliability of these CWPCs was evaluated by conducting a cyclic loading test within their elastic ranges. The results of this work will enable the manufacture of integrated sensors within 3D printed components with improved mechanical properties and increased functionality. [ABSTRACT FROM AUTHOR]