The Influence of High Strength Steel on the Fatigue Life of Welded Joints in the Automotive Industry.

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dc.contributor.advisorVenter, Gerharden_ZA
dc.contributor.advisorBredell, JRen_ZA
dc.contributor.authorRamsay, Gareth Allanen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.en_ZA
dc.date.accessioned2022-03-02T10:14:32Zen_ZA
dc.date.accessioned2022-04-29T09:36:40Zen_ZA
dc.date.available2022-03-02T10:14:32Zen_ZA
dc.date.available2022-04-29T09:36:40Zen_ZA
dc.date.issued2022-04en_ZA
dc.descriptionThesis (MEng)--Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH SUMMARY: The ability to predict and protect against fatigue failure of structurally critical components, while still being able to produce high performance and costefficient designs is of great importance to the automotive industry. This study investigates the influence of high strength steels on the fatigue life of welded joints commonly used in the automotive industry, and compares the experimental fatigue data to commonly used fatigue design approaches, namely the BS 7608 approach and Shigley’s approach. Two joint details of interest are considered, namely a non-load bearing fillet welded T-joint and a load bearing fillet welded cruciform joint. Each joint geometry has three different base and filler material combinations, with varying material strengths, i.e. a total of six different specimen configurations. Two material combinations have a high strength steel (Strenx® 700 MC D) for the base material, with one combination having a matched filler material and the other having an undermatched filler material. The third material combination has a lower strength steel (S 355 JR AR) for the base material, with a matched filler material. Tensile tests were performed to confirm the base material mechanical properties and weld quality of the manufactured specimens. The welded specimens of both joint geometries were fatigue tested and the obtained data was used to generate experimental S-N curves. The experimental S-N curves for each joint geometry and material combination were compared with each other, as well as with the two fatigue design approaches. The investigation showed that there is no significant benefit to using high strength steel as the base material for fatigue loaded welded joints. Moreover, in some cases the use of high strength steel actually proved to be detrimental to the fatigue performance of the joint, compared to the use of a lower strength steel (e.g. T-joint with non-load bearing weld attachment). The results suggest that the fatigue performance of a non-load bearing weld attachment (T-joint) is highly dependent on material combination and strength, with lower strength base materials offering better fatigue performance than higher strength base materials. In this case the material combination and strength seems to be the dominating factors in fatigue performance over joint geometry. In contrast, the load bearing welded joint (cruciform joint) was shown to be less dependent on material combination and strength, with the joint geometry potentially being the more dominating factor on fatigue performance, as shown by the similarity in fatigue performance with the varying material combinations. The BS 7608 design curves generally tended to be quite conservative depending on the joint geometry and material combination considered. The BS 7608 does not account for material strengths and this could be why its fatigue performance predictions are quite conservative in certain cases. In general, Shigley’s material strength dependent approach overestimated the fatigue performance of the investigated welded joint details and is therefore not recommended for use in the fatigue design of these joints.en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: In die voertuigindustrie is dit van groot belang om die vermoeidheidsfaling van kritieke strukturele komponente te voorspel en voorkom, terwyl hoë werkverrigting en kostedoeltreffendheid steeds verseker word. Hierdie studie ondersoek die invloed van hoë-sterkte staal op die vermoeidheidslewe van sweisverbindings wat algemeen in die voertuigindustrie gebruik word, en vergelyk die eksperimentele vermoeidheidsdata met standaard vermoeidheids-ontwerpsbenaderings, naamlik die BS 7608 benadering en Shigley se benadering. Twee verskillende verbindingdetails word oorweeg, naamlik ’n nie-lasdraende hoeksweis T-las en ’n lasdraende hoeksweis kruisvormige las. Vir beide details, word drie verskillende moedermateriaal- en vulmateriaal-kombinasies ondersoek, dit wil sê ’n totaal van ses verskillende toetsmonster-konfigurasies. Twee materiaalkombinasies het ’n hoë-sterkte staal (Strenx® 700 MC D) vir die moedermateriaal, een kombinasie met soortgelyke vulmateriaal en die ander met ’n laer-sterkte vulmateriaal. Die derde materiaalkombinasie het ’n laer-sterkte staal (S 355 JR AR) vir die moedermateriaal met soortgelyke vulmateriaal. Trektoetse is uitgevoer om die meganiese eienskappe van die moedermateriaal en die sweiskwaliteit van die vervaardigde toetsmonsters te bevestig. Vermoeidheidstoetse vir beide verbindingdetails is uitgevoer en die toetsdata is gebruik om S-N krommes te genereer. Die eksperimentele S-N data vir elke verbindingdetail en materiaalkombinasie is met mekaar vergelyk, sowel as met twee standaard ontwerpsbenaderings. Die ondersoek het getoon dat daar geen beduidende voordeel is vir die gebruik van hoë-sterkte staal as die moedermateriaal in terme van die vermoeidheidslewe in vermoeidheidsbelade sweisverbindings nie. Boonop blyk dit dat in sekere gevalle die gebruik van hoë-sterkte staal nadelig is in vergelyking met die gebruik van ’n laer-sterkte staal. Byvoorbeeld, die resultate dui daarop dat die vermoeidheidslewe van ’n T-verbinding sterk afhanklik is van die materiaalkombinasie en -sterkte, met ’n laer-sterkte moedermateriaal wat beter vermoeidheidslewe bied as ’n hoër-sterkte moedermateriaal. In hierdie geval blyk dit dat die materiaalkombinasie en -sterkte die oorheersende faktore is in vermoeidheidslewe, in vergelyking met die verbindings-geometrie. Daarteenoor is getoon dat die kruisvormige-las minder afhanklik is van materiaalkombinasie en -sterkte, met die verbindings-geometrie potensieel moontlik die meer oorheersende faktor vir vermoeidheidslewe, soos blyk uit die eendersheid in vermoeidheidsdata vir die verskillende materiaalkombinasies. Die BS 7608 ontwerpskrommes was oor die algemeen redelik konserwatief, afhangende van die verbindingdetail en materiaalkombinasie. Die BS 7608 neem nie materiaalsterkte in ag nie, en mag verklaar waarom die voorspelde vermoeidheidslewe in sekere gevalle konserwatief is. In die algemeen oorskat Shigley se materiaalsterkte afhanklike benadering die vermoeidheidslewe van die ondersoekte sweisverbindings wat onderskat is en word dus nie aanbeveel vir vermoeidheidsontwerp van hierdie verbindings nie.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentxvii, 129 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/124847en_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectLoad bearing weldsen_ZA
dc.subjectNon-load bearing weldsen_ZA
dc.subjectHigh strength steelen_ZA
dc.subjectAutomobile industry and tradeen_ZA
dc.subjectSteel, High strengthen_ZA
dc.subjectWelded joints -- Fatigueen_ZA
dc.subjectUCTDen_ZA
dc.titleThe Influence of High Strength Steel on the Fatigue Life of Welded Joints in the Automotive Industry.en_ZA
dc.typeThesisen_ZA
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