VHCF response of as‐built SLM AlSi10Mg specimens with large loaded volume

Abstract

It is well known in the literature that fatigue is particularly critical for Additive Manufacturing (AM) parts, because internal defects originating during the AM process represent a critical site for crack initiation. In the literature, the High‐Cycle‐Fatigue (HCF) response of AM parts has been extensively investigated; however, there are few results on the Very‐High‐Cycle‐Fatigue (VHCF) behavior of AM parts, even if the number of machinery components that may sustain VHCF is rapidly increasing in the last years. The present paper investigates the VHCF response of an AlSi10Mg alloy produced through Selective Laser Melting. Ultrasonic tests are carried out on Gaussian specimens with a large loaded volume and show that fatigue failures in VHCF originate from surface and sub‐surface defects with the same mechanism of HCF failures. P‐S‐N curves and fatigue strength at 109 cycles are finally estimated to show the effect of defect size on the VHCF strength. Research highlights Ultrasonic VHCF tests on AlSi10Mg Gaussian specimens produced through SLM. Identification and analysis of critical AM defects inducing VHCF failure. Statistical estimation of models for the prediction of the VHCF response of AM parts. Statistical prediction of effect of defect size on the VHCF response of AM parts.

VHCF Response of Two AISI H13 Steels: Effect of Manufacturing Process and Size-Effect

“…where is the number of cycles to failure; , , and are constant coefficients; is the standardized normal random variable; and is the standard deviation. Through easy passages [32], the VHCF strength (corrected VHCF strength, ) at the reference number of cycles can be expressed by: Finally, the inclusion size was analyzed. According to Reference [3], the inclusion originating the failure with size √ a d,0 (i.e., the square root of the projected area of the inclusion) was considered as the largest defect in the risk-volume.…”

“…The influence of size-effect and ESR on the VHCF strength is investigated in this section. Following a procedure adopted in the VHCF literature [31,32], data were gathered together at the reference fatigue life, N f ,re f , by considering the relationship between mean fatigue life, stress amplitude, and defect size (Equation (1)):…”

“…where N f is the number of cycles to failure; c Y , m Y , and n Y are constant coefficients; Z is the standardized normal random variable; and σ Y is the standard deviation. Through easy passages [32], the VHCF strength (corrected VHCF strength, s corr ) at the reference number of cycles can be expressed by:…”

“…According to Equation (2), depends only on the inclusion size and therefore permits the assessment of the influence of the different inclusion size on the VHCF strength. According to Reference [32], it can be shown that is a normal random variable with mean, , equal to − + , − log , and standard deviation, , equal to − . The probabilitydensity function (pdf) of , denoted as , can be finally expressed as:…”

“…All the experimental failures (except one) are included within the 98% confidence interval. The 0.01th P-S-N curves (99% reliability), which ensure an appropriate safety margin with respect to failures [32], can be considered for comparison. Figure 8 shows the 0.01th P-S-N curves for the investigated H13 and H13-ESR steel: In the figure, h refers to the hourglass specimens and G refers to the Gaussian specimens.…”