Rule of Mixtures Model to Determine Tensile Strength of 3D-Printed Kevlar-Reinforced Nylon: Thermal Gravimetric Analysis of Kevlar Filaments

Incorporation of high strength composite materials into additive manufacturing by fused deposition modeling (FDM) has opened the doors to new lightweight, robust, and efficient structures. However, our knowledge of the behavior of these structures under various loading conditions is still not completely understood. Further, with the large number of fiber and matrix options to choose from, the number of possible combinations of composites is quickly increasing. This is making experimental testing of every possible combination prohibitive due to its large time and cost investment. The issue gets more complicated when structures with complicated geometries need to be analyzed. This calls for designing a model that can use the data from simple experiments to accurately predict the behavior of structures under various loading conditions. This work highlights an experimental procedure to determine the elastic modulus and tensile strength of Kevlar fiber-reinforced nylon (KFRN) samples produced with FDM. The thermal gravimetric analysis (TGA) was employed to quantify the volume fraction of fiber and matrix in the filament. Samples with varying fiber reinforcement layer configurations were manufactured based on standards. Tensile tests were performed to determine the elastic modulus and tensile strength of the samples. A rule of mixtures model was used to estimate the load borne by each layer configuration. The results demonstrate that the relation between volume fraction and load-bearing capacity follows the rule of mixtures. This work provides a straightforward method to determine the tensile strength and elastic modulus of KFRN parts produced by FDM. The approach may decrease development time by simplifying the design process.