Fatigue Properties of 3D Printed Carbon Fiber

Three-dimensional printing with carbon fiber has been used to create lower limb prosthetics. However, the fatigue resistance of carbon fiber is understudied. The goal of this work was to quantify the fatigue properties of three-dimensionally printed carbon fiber. Moore bending fatigue specimens were created using a commercially available printer (Markforged, Watertown, MA). Specimens were printed using (1) a chopped carbon fiber matrix or (2) chopped carbon fiber matrix with embedded continuous carbon fiber. Cycles to failure was measured for three bending stress levels: 11.8, 8.8, and 7.4 kpsi. Ultimately, adding continuous carbon fiber to the chopped matrix increased the short cycle fatigue life (i.e. 103) from 17 to 274 MPa and had no effect on the endurance limit. During a single stance phase of the gait cycle, the heel and toe portions of a prosthetic foot experience up to 262 MPa of von Mises stress. This means the carbon fiber produced from three-dimensional printing would last two gait cycles. Hence, lower limb prosthetics cannot yet be made completely from three-dimensionally printed carbon fiber.