Characterization of the Fatigue Behavior of SLS Thermoplastics

Abstract

The selective laser sintering (SLS) is an additive manufacturing technology with clear potential for producing high quality polymeric components of various thermoplastic polymers and elastomers which can be used in demanding engineering applications under complex service loading conditions. The prerequisite for these applications is that the stiffness and the tensile strength of the SLS specimens is in the same range as for injection molded specimens using a proper parameter set of the SLS process and qualified materials. While the tensile strength of SLS printed polymers is recently determined by many researchers, hardly any data are available about the fatigue behavior of SLS polymers on specimen level and even less on component level. Cylindrical specimens with and without round notch have been designed and additively manufactured using PA12 and TPU SLS grades in two different printing directions (vertical and horizontal). The monotonic tensile behavior was characterized over a wide loading rate range (0.1 to 100 mm/s) and the tensile strength and failure strain values were determined. The fatigue behavior was characterized under cyclic loading conditions at various stress ratios (R=0.1, -1), at a constant frequency of 5 Hz at 5 stress levels. Stress vs. cycle number-to-failure, Nf points were determined for constructing conventional S-N curves for the materials investigated. A distinct anisotropy of the tensile strength and failure strain was recognized for the SLS TPU investigated.