Existing literature for additive manufacturing of composite materials almost always deals with short length (<1mm) fibers. Printing with longer fibers should theoretically increase the strength of the resulting composite, but it becomes difficult to print with long fibers as they increase the viscosity of the melt flow. Therefore, prints that use long fibers often contain lower fractions of carbon fiber, and consequently exhibit lower strength values during testing. By blending pellets that contain both long and short discontinuous fibers, we believe we are able to observe an increase in strength from longer fibers while maintaining the printability and high fiber fraction of the short fibers.

Currently, a variety of analysis have been performed to characterize the resulting material, including tensile, fiber length distribution, density, and surface roughness. While initial results showed a decrease in ultimate strength for the long fiber-short fiber hybrid compared to just the short fiber, this was concluded to largely be attributed to high porosity caused by the long fibers. Further experimentation will be conducted to compare samples with similar densities to further isolate the impact of the fiber on the tensile strength. If you'd like to learn more, be on the lookout for my publication at MSEC later this year! I'll be attending and would love to discuss my reserach in person too!