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

Abstract

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 10 9 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 mm 3 ). 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.

VHCF response of AM materials: A literature review

“…In Paolino et al, 12 VHCF tests up to 10 9 cycles were carried out on Gaussian specimens manufactured in vertical direction. The S-N plot of the experimental dataset is shown in Figure 2C.…”

“…In Ref. fully reversed tension‐compression VHCF tests on Gaussian specimens (gage diameter of 11 mm) made of AlSi10Mg were carried out by using the ultrasonic testing machines developed at Politecnico di Torino. Spherical gas atomized AlSi10Mg powders (average size of approximately 45 μm) and an SLM Solutions (model 500 HL quad 4 × 400 W) Selective Laser Melting system were used for the specimen production.…”

“…Spherical gas atomized AlSi10Mg powders (average size of approximately 45 μm) and an SLM Solutions (model 500 HL quad 4 × 400 W) Selective Laser Melting system were used for the specimen production. All the SLM manufactured specimens were not subjected to a machining process; only manual polishing was applied to smooth the surface.…”

Ultrasonic Fatigue Device and Behavior of High-Temperature Superalloy Inconel 718 with Self-Heating Phenomenon

“…The insignificant influence of loading frequency was also reported in ferrous-type alloy [6] and nonferrous metals [7,8]. Tridello, Paolino, et al [9][10][11][12] evaluated the size effect analytically in the VHCF regime and validated on the full-scale specimen. It is important to monitor and record test parameters such as frequency, vibration amplitude, surface temperature of specimen, etc.…”

“…Pulse-pause mode or specimen temperature control were not decisive factors for the VHCF fatigue strength of superalloy Inconel 718. Shi's team [9,10] compared the very high cycle fatigue behavior of Inconel 718 by ultrasonic tension compression and rotary bending, as shown in Figure 8. Air cooling was applied during the whole process, ensuring the approximate room temperature.…”