Tunable soft–stiff hybridized fiber-reinforced thermoplastic composites using controllable multimaterial additive manufacturing technology

Abstract

As a revolutionary manufacturing technology, material extrusion exhibits great potential for fabricating thermoplastic composites. However, the application of controllable multiple-thermoplastic materials for producing a tunable soft–stiff hybridized fiber-reinforced thermoplastic composite (CCFRTP-TSSH) based on material extrusion has yet to be extensively studied. Thus, this study proposes a controllable multimaterial additive manufacturing process for integrating continuous carbon fibers (CCF) as reinforcement for the thermoplastic structures. Structural reinforcement and tunable soft–stiff hybridization were achieved by adopting thermoplastic polyurethane (TPU) and polylactic acid (PLA) as the soft and stiff materials, respectively. Additionally, the mechanical properties of the CCFRTP-TSSH specimens were systematically investigated and discussed based on various process parameters, such as nozzle temperature, layer thickness, and supporting resin volume ratio (SRVR). The experimental results revealed that the layer thickness had a significant influence on the tensile properties, followed by the SRVR and nozzle temperature, wherein the highest tensile strength obtained was 90.89 MPa. Moreover, the bending strength depends on both the layer thickness and loading direction, with the largest bending strength of 65.96 MPa. Furthermore, the influence of SRVR on various fusion interfaces, e.g., PLA/ TPU, PLA/CCF, and PLA/PLA, was analyzed using scanning electron microscopy, including the influence of process parameters on the wall thickness of the stiff and soft resins, to realize an enhanced tunable soft–stiff hybridization. Ultimately, several distinct components, including a thin-walled hollow cylinder, round table, and a socket for a limb prosthetic, were fabricated to demonstrate the feasibility and accuracy of the proposed method. Therefore, this study presents a novel approach for the integrated manufacturing of soft–stiff hybridized composites, particularly in the field of wearable devices.