VHCF Response up to 10⁹ Cycles of SLM AlSi10Mg Specimens Built in a Vertical Direction

• Main Authors: Davide S. Paolino, Andrea Tridello, Jacopo Fiocchi, Carlo A. Biffi, Giorgio Chiandussi, Massimo Rossetto, Ausonio Tuissi
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Applied Sciences
• Subjects: selective laser melting (SLM); AlSi10Mg alloy; building orientation; manufacturing defects; very high cycle fatigue (VHCF); ultrasonic testing
• Online Access: https://www.mdpi.com/2076-3417/9/15/2954

It is well-known that many manufacturing parameters affect the quasi-static and the fatigue response of additive manufacturing (AM) parts. In particular, due to the layer-by-layer production, the load orientation, with respect to the building direction, plays a fundamental role for the fatigue response. This paper investigates the fatigue response up to 10⁹ cycles (very high cycle fatigue (VHCF)) of selective laser melting (SLM) AlSi10Mg specimens built in a vertical direction. Ultrasonic tension-compression tests (stress ratio of −1) are carried out on as-built Gaussian specimens with a large loaded volume (2300 mm³). Fracture surfaces are investigated with the scanning electron microscope to analyze the defects originating the VHCF failure. Probabilistic S-N curves are estimated and analyzed. Experimental results confirm that the defect size controls the VHCF response, thus highlighting the importance of testing large risk volumes for a reliable assessment of VHCF behavior. The average value of the VHCF strength is close to that of the hourglass specimen tested in the literature. The variability of the VHCF strength is instead significantly larger, due to the scattered size distribution of the defects located near the specimen surface, which is the most critical region for crack initiation.