Fatigue Strength and Fracture Mechanisms in the Very-High-Cycle-Fatigue Regime of Automotive SteelsShow others and affiliations
2020 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 91, no 8, article id 2000060Article in journal (Refereed) Published
Abstract [en]
Very-high-cycle-fatigue (VHCF) strength properties are of interest to several technical applications assessed globally at different laboratories with long-life fatigue testing capabilities. Also, VHCF failure mechanisms are a scientific topic with remaining open research questions. Herein, three automotive bar grade steels are studied with respect to VHCF strength and initiation mechanisms. A microalloyed ferritic-pearlitic steel (38MnSiV5, 870 MPa tensile strength), a quenched and tempered martensitic steel (50CrV4, 1410 MPa tensile strength), and a carburizing steel (16MnCr5, 1180 MPa core structure tensile strength) are studied to reveal characteristics regarding initiation and VHCF failure mechanisms. A 20 kHz ultrasonic fatigue testing instrument is used to obtain fatigue lives up to and above 10(9) load cycles in uniaxial loading. Hour-glass specimens, smooth or notched, are tested at R = -1 and R = 0.1. Fatigue strength and stress life (SN)-diagram data are achieved, and crack initiation and growth mechanisms are studied using primarily field-emission gun-scanning electron microscopy (FEG-SEM). Fatigue strengths are explained by a modified life-dependent Murakami-expression, the Haigh diagram, and notch sensitivity. Interior and surface crack initiations by surface defects, triple points, and inclusions are found. The fine granular area (FGA) to fish-eye crack growth transition conditions are explored and schematic descriptions are given.
Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH , 2020. Vol. 91, no 8, article id 2000060
Keywords [en]
automotive steels, fish eyes, initiation mechanisms, stress life-curve, very high cycle fatigue
National Category
Metallurgy and Metallic Materials Materials Engineering
Research subject
Materials Science; Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-78092DOI: 10.1002/srin.202000060ISI: 000534036300001OAI: oai:DiVA.org:kau-78092DiVA, id: diva2:1439667
2020-06-122020-06-122025-10-17Bibliographically approved