Process Evaluation, Tensile Properties and Fatigue Resistance of Chopped and Continuous Fiber Reinforced Thermoplastic Composites by 3D Printing

The aim of this article was to comprehensively evaluate the manufacturing process, tensile properties and fatigue resistance of the chopped and continuous fiber reinforced thermoplastic composites (CFRTPCs) by 3D printing. The main results included: the common defects of the printed CFRTPCs contained redundant and accumulation defects, scratch and warping defects; the continuous fiber contributed to the dimensional stability and accuracy of width and thickness; associations between mass percentage of fiber reinforcement and the averages of elastic modulus, strain at break and ultimate tensile strength were approximately linear based on tensile test results; the fatigue resistance improved with the increasing fiber reinforcement based on fatigue test results. As for specimens with four fiber rings, there was a good linear relationship between the stress level and logarithm value of cycles during the whole life while those of pure matrix and specimens with one and two fiber rings were piecewise linear, taking about 10,000 cycles as boundary. The micro morphology showed that the fatigue failure behaved as matrix fracture, large and small fiber bundles and single fibers extracted from matrix. Under the tension-tension fatigue load, the deformations where easily concentrating stress behaved as sunken surfaces along thickness and width directions, and the deformation along width direction was greater than that along thickness direction.