Rapid fatigue life evaluation over time of PA12 obtained by Multijet Fusion printing process

Additive manufacturing (AM) allows the creation of structural components adopting several printing strategies and materials. Polyamide-12 (PA12) obtained by MultiJet-Fusion (MJF) printing process is taking place as one of the most adopted materials on the market, offering fast, economical and large production of functional parts which can undergo to several loading conditions, including fatigue. It was observed how MJF PA12 mechanical properties are characterized by wide dispersion associated with large processing window of this novel technology. Although the fatigue life of this material and the aging effect on its mechanical properties have already been investigated, there are no studies on aging influence on fatigue life. In the present work, two sets of PA12 specimens obtained by MJF technology, stored under ambient conditions, were tested after 90 days. Tensile properties were evaluated adopting DIC analysis while infrared camera was adopted to monitor the energy release of PA12 during quasi-static monotonic tensile and fatigue test conditions. Constant amplitude fatigue tests and stepwise fatigue tests have been carried out to investigate material's fatigue life. A novel and rapid approach, compared to fatigue test campaign prescribed by standards and staircase methodology, was adopted applying the Risitano's Thermographic Method and the Static Thermographic Method. They allow fast fatigue characterization providing reliable information, useful for mechanical design, monitoring the material behaviour over time rapidly. Experimental observations and comparisons with previous studies about HP PA12 MJF lead to validation of Thermographic Methods as a tool for rapidly monitoring fatigue properties of material subject to physical aging phenomena.