The impact of nozzle and bed temperatures on the fracture resistance of FDM printed materials

Additive manufacturing refers to a new technology in which physical parts are directly produced from a computer model by incremental addition of the constituent materials. Fused deposition modeling (FDM) is one of the most common types of additive manufacture processes. The ultimate mechanical performance of FDM printed parts is a function of the interlayer bond quality. Current literature however focuses only on the phenomenological evolution of standard mechanical properties (such as tensile and bending) as a function of printing conditions. Such studies do not provide direct information about the interlayer adhesion and in-practice failure characteristics. In this work, a fracture-mechanics-based methodology was used to characterize the fracture resistance of FDM 3D printed Acrylonitrile Butadiene Styrene (ABS) samples as a function of nozzle and bed temperatures. Double cantilever beam (DCB) specimens was printed in such pattern that the applied load exerted only tensile opening stresses at the crack front. This facilitated the measurement of crack growth under pure mode-I condition. A finite element model was then used to obtain the J-integral strain energy release rate values, as a measure of the fracture resistance. Since the crack propagated at the interlayer in all the cases, the fracture resistance was a direct indication of the interlayer adhesion. The results revealed that the critical crack growth load, the actual fracture surface area (governed by printed mesostructure) and the apparent fracture resistance all increased when the nozzle or bed temperature was increased; the nozzle temperature showed a much stronger effect. The layer-to-layer adhesion, as reflected by the interlayer fracture resistance, did not show monotonous increase with the temperatures and appeared to level off at higher temperatures, indicating that complete interlayer fusion was achieved. This work provides insight into and characterizes the relationships between the 3D printing conditions, the resultant mesostructure, the apparent fracture resistance and the interlayer adhesion in FDM 3D printed materials.