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20 kHz 3-point bending fatigue of automotive steels
Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).ORCID-id: 0000-0001-6029-2613
Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
2018 (engelsk)Inngår i: MATEC Web of Conferences, EDP Sciences, 2018, Vol. 165, s. 1-7, artikkel-id 22020Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

The 20 kHz load frequency enables fatigue tests for very high cycle fatigue life, 109-1013 cycles, within conveniently short time. In automotive applications, many components are subjected to flexural loading and hence bending fatigue is an important test mode. Ultrasound fatigue test instruments have been used successfully in several assessments of fatigue strength and more commonly in uniaxial loading. Here, a 3-point bending fatigue test rig operating in resonance at 20 kHz load frequency has been designed to test plane specimens at R=0.1 loading. The test rig design and stress calculations are presented. Testing for fatigue strength was conducted using the staircase method with 15 specimens of each steel grade, specimens reaching 108 cycles were considered run-outs giving fatigue strength at 108 cycles. Additional 15 specimens of each grade were tested for S-N curves with the upper limit above 109 cycles. Two different common automotive steels, 38MnSiV5, a micro-alloyed ferritic-pearlitic steel, and 16MnCr5, a carburizing martensitic steel, were tested. The fatigue strengths achieved from the staircase testing are 340 and 419 MPa stress amplitudes for the 38MnSiV5 and 16MnCr5 steels, respectively. The S-N curves of the steels appear to be quite flat in the tested life range 107 - 109.

sted, utgiver, år, opplag, sider
EDP Sciences, 2018. Vol. 165, s. 1-7, artikkel-id 22020
Emneord [en]
Automotive steels, Carburized steel, Ferritic-pearlitic steel, Three-point bending, VHCF, Binary alloys, Chromium alloys, Fatigue of materials, Fatigue testing, Ferrite, Ferritic steel, Pearlite, Silicon alloys, Stairs, Steel metallography, Steel testing, Pearlitic steels, Three point bending, Manganese alloys
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
URN: urn:nbn:se:kau:diva-68076DOI: 10.1051/matecconf/201816522020ISI: 000478990600218Scopus ID: 2-s2.0-85048089977OAI: oai:DiVA.org:kau-68076DiVA, id: diva2:1224009
Konferanse
12th International Fatigue Congress, FATIGUE 2018, 27 May 2018 through 1 June 2018
Tilgjengelig fra: 2018-06-26 Laget: 2018-06-26 Sist oppdatert: 2019-12-19bibliografisk kontrollert
Inngår i avhandling
1. Very high cycle fatigue of automotive steels: Testing and computation at 20 kHz
Åpne denne publikasjonen i ny fane eller vindu >>Very high cycle fatigue of automotive steels: Testing and computation at 20 kHz
2020 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Mechanical fatigue failure occurs in components subjected to cyclic loading. A crack initiates at critical regions in the component and propagates during repeated loading. The expected fatigue life depends on the level, type and frequency of the loading. Generally, as implied by the Wohler’s SN curve, higher applied cyclic load leads to lower fatigue lifes and vice versa. When designing mechanical components carrying cyclic loading, engineers take into account the fatigue limit, i.e. the material specific maximum load allowed for the desired fatigue life. In automotive machinery, components are often required to withstand a very high amount of load cycles before failing. Hence, fatigue data for the very high cycle fatigue (VHCF) regime becomes significant.

In this thesis, an ultrasonic fatigue testing system, with 20 kHz loading frequency, was used to determine the fatigue properties of three high strength low alloyed automotive steels (a ferritic-pearlitic, a martensitic and a carburizing martensitic steel) in the VHCF regime. Theoretical modelling taking into account the influence of the high load frequency was developed and utilized to control the experimental testing. Fatigue strength, crack initiation mechanisms and crack propagation behaviour in the VHCF regime were studied. More specifically, fatigue strength (σN) at 108 cycles, in both uniaxial and bending loading, crack growth rate (da/dN) and threshold behaviour (ΔKth) in the low stress intensity factor regime were determined using specially designed specimens and test rigs.

The fatigue failure of the automotive steels in the VHCF regime, revealed fracture surfaces with fine granular area (FGA) formation close to the initiation point, with a transition to flat transgranular crack growth inside the fish-eye area. The stress intensity thresholds of FGA and fish-eye transitions are described and related to crack tip plastic zone sizes and steel strength.

The effect of damping at 20 kHz, on automotive steels, was thoroughly studied by experimental measurements and theoretical investigations. The effect of introducing damping in dynamic analysis of stress and stress intensity computations for fatigue strength and crack growth testing at 20 kHz was clarified. Best practice for theoretical modelling and computation of stress intensities in crack growth testing at 20 kHz, including the effect of damping, along with guidelines for best practice testing procedure are provided.

Abstract [en]

In automotive machinery, components are often required to withstand a very high amount of loading cycles before failing. Hence, fatigue data for the very high cycle fatigue (VHCF) regime are of importance for the engineers designing such components. In this thesis, the VHCF properties of three different high strength microalloyed automotive steel grades are investigated. Through theoretical computation and modelling, as well as experimental testing, knowledge of fatigue strength as well as crack initiation and propagation behaviour is gained.

The influence of high load frequency on both theoretical computation and experimental testing of fatigue properties was analyzed and conclusions were drawn. An ultrasonic fatigue testing system at 20 kHz load frequency was used to perform uniaxial and bending fatigue, and crack growth testing.

sted, utgiver, år, opplag, sider
Karlstad: Karlstads universitet, 2020. s. 41
Serie
Karlstad University Studies, ISSN 1403-8099 ; 2020:7
Emneord
Very high cycle fatigue, ultrasonic fatigue testing, automotive steels, fatigue strength, stress intensity computation, crack growth
HSV kategori
Forskningsprogram
Materialteknik
Identifikatorer
urn:nbn:se:kau:diva-76028 (URN)978-91-7867-090-1 (ISBN)978-91-7867-100-7 (ISBN)
Disputas
2020-02-14, 21A342, 10:15 (engelsk)
Opponent
Veileder
Prosjekter
FREQTIGUE
Tilgjengelig fra: 2020-01-27 Laget: 2019-12-19 Sist oppdatert: 2020-01-27bibliografisk kontrollert

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