Elastic/viscoplastic characterization of additively manufactured composite based on continuous carbon fibers

Additive manufacturing (AM) of continuous carbon fiber thermoplastic matrix composites (CFRPs) allows for producing bowtie geometries that are more appropriate to probe the mechanical behavior of these composites. The quasistatic thermomechanical behaviors of different 3D printed composites laminae and laminate were investigated at temperatures below the glass transition of the thermoplastic matrix. The influence of the fiber orientation revealed weak performance of off-axis samples compared to the on-axis lamina and multidirectional laminate. Fractography attributed this degradation to the low fiber volume fraction of carbon fibers; 20-21%, and the inherent defects of the fused filament fabrication (FFF) process. The degradation was most significant along the direction transverse to the loading direction where the stiffness and strength dropped by 44% and 35%, respectively at 90 degrees C compared to the room temperature values. The viscoplastic behavior of the 3D printed composites were probed via series of load relaxation and creep tests at different thermal environments. The results of the experimental tests were utilized to both construct and validate a phenomenological viscoplastic constitutive model of the 3D printed FRPs. The experiments and the model predictions established that 3D printed composites with off-axis fiber orientation exhibit significant stress relaxation and creep deformation. The results also emphasized that the prediction of the viscoplastic model is less accurate for the off-axis AM composite configuration. (C) 2021 Elsevier Masson SAS. All rights reserved.