Manipulating interfacial bond for controlling load transfer in 3D printed fiber reinforced polymer composites

The fiber/matrix interface is a critical item that affects Fiber Reinforced Polymer (FRP) composites mechanical performance due to its control of the load transfer mechanism. Partially bonded interfaces have been shown to affect the failure mode of FRP composites. This article examines the significance of manipulating the fiber/matrix interfacial bond in 3D printed FRP composites on the mechanical performance of multilayer 3D printed FRP composites. Three designs are investigated with different fiber stacking sequences, fiber orientation, and interfacial bond configurations. The designs have a low coefficient of variation in load fractions between layers to enable a gradual load transfer and progressive failure. Utilizing 3D printer chamber temperature changes, a composite with a controlled bond configuration is achieved using thermal blocks. It was observed that the controlled bond configurations resulted in promoting progressive failure and increased the strain at failure of 3D printed FRP composites. The observations of direct tension tests were supported with interlayer shear strength and interfacial adhesion tests which explained the weakened load transfer in the thermal block configurations. Using the interface manipulation strategy with thermal blocks in 3D printed specimens, a 25% lower interlayer shear strength and a 65% lower interfacial adhesion was achieved compared with un-modified interfaces. These changes attribute to the altered load transfer mechanism in 3D printed glass fiber reinforced composites and high strain to failure of up to 5% using high strength high stiffness fiber orientations. This work does not incorporate any new materials into the thermoplastic-fiber 3D printed structure which has been the strategy of past work to modify mechanical performance. Alternatively, a unique approach by using chamber and print bed temperature characteristics to modify the interfacial bond has been adopted that has shown to promote progressive failures and improve ductility in FRP composites. This study furthers the development of ductile designs in FRP composites with 3D printing technology in aerospace, wind, infrastructure, and automobile applications.