Ultrasonic VHCF Tests on Very Large Specimens with Risk-Volume Up to 5000 mm3

Abstract

The research on the size-effects in Very-High-Cycle Fatigue (VHCF) has recently drawn the attention of several scholars. The fatigue cracks in VHCF originate from the largest defect present within the loaded material volume (risk-volume) and the larger the risk-volume, the larger the probability of critical defects affecting the VHCF response (size-effect). Many models have been proposed in the literature to deal with size-effects in VHCF. However, the proposed models cannot be validated on full-scale components, since VHCF tests are typically carried out with ultrasonic fatigue testing machines. The authors have proposed a specimen geometry, the so-called Gaussian specimens, to enlarge as much as possible the risk-volume in ultrasonic VHCF tests. In this study, fully reversed tension–compression ultrasonic VHCF tests up to 109 cycles were carried out on AISI H13 steel Gaussian specimens with a risk-volume of 5000 mm3, two times larger than the largest tested in the literature. The stress distribution and the absence of bending loads were verified with strain gages, proving that VHCF tests on risk-volumes of 5000 mm3 can be reliably carried out. Ultrasonic VHCF tests were also carried out on small hourglass specimens, confirming that larger risk-volumes allow for a more reliable design against VHCF failures.