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Towards Understanding the Effects of Current Input on Fatigue Mechanisms in Resistance Spot Welding of Advanced High Strength Steels

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dc.contributorJordon, Brian
dc.contributorAllison, Paul
dc.contributorBewer, Luke
dc.contributor.advisorJordon, Brian
dc.contributor.advisorAllison, Paul
dc.contributor.authorCleek, Conner
dc.contributor.otherUniversity of Alabama Tuscaloosa
dc.date.accessioned2022-04-13T20:33:55Z
dc.date.available2027-09-01
dc.date.issued2020
dc.descriptionElectronic Thesis or Dissertationen_US
dc.description.abstractIn this study, the relationship of welding parameters to fatigue mechanisms is examined in spot welding of advanced high strength steels. Lightweighting efforts in the automotive industry are part of a push for greater fuel economy and improved consumer safety. TBF-1180 is an advanced high strength steel being developed for use in structurally critical components, however its fatigue behavior is not well understood. Electro galvanized TBF-1180 possesses corrosion resistant properties, however the additional zinc layer allows for the possibility of zinc-penetrative liquid metal embrittlement (LME) to occur during resistance spot welding (RSW). Additionally, variations in weld input and correspondingly heat input can affect the performance of welds due to microstructural changes that occur. In this study, the effect of LME and changes in microstructure were assessed in separate experiments for their fatigue impact in TBF-1180. Welds were fabricated in a traditional lap shear geometry in order to investigate the effects of LME, while an hourglass shaped cap geometry was used for welds with microstructural variation. Fatigue testing revealed that for lap-shear coupons containing LME cracks, no deleterious effect was observed. Cap geometry specimens were assessed for performance in a control and a high-current low-time condition, and a significant fatigue knockdown factor was found. Post-mortem fractography on both specimen geometries revealed that fatigue cracks initiated at the inner faying surface, regardless of the presence of LME. Finite element analysis confirmed that the LME cracks in the lap shear weld experience compressive stresses during loading, contributing to the lack of fatigue impact. Experimental conditions used for the cap geometry had lower heat input, which can result in less retained metastable austenite after welding, leading to reduced crack growth resistance. To tests the hypothesis that less retained metastable austenite after welding can cause a reduction in the number of cycles to failure in the spot weld, life prediction were made using fracture mechanics concepts coupled with reported knockdown factors on crack growth rates in relation to the amount of transformed martensite. The life predictions generated with this method strongly matched the observed fatigue behavior for the cap geometry specimens.en_US
dc.format.mediumelectronic
dc.format.mimetypeapplication/pdf
dc.identifier.otherhttp://purl.lib.ua.edu/182069
dc.identifier.otheru0015_0000001_0004222
dc.identifier.otherCleek_alatus_0004M_14224
dc.identifier.urihttps://ir.ua.edu/handle/123456789/8401
dc.languageEnglish
dc.language.isoen_US
dc.publisherUniversity of Alabama Libraries
dc.relation.hasversionborn digital
dc.relation.ispartofThe University of Alabama Electronic Theses and Dissertations
dc.relation.ispartofThe University of Alabama Libraries Digital Collections
dc.rightsAll rights reserved by the author unless otherwise indicated.en_US
dc.subjectFatigue
dc.subjectLiquid Metal Embrittlement
dc.subjectResistance spot welding
dc.titleTowards Understanding the Effects of Current Input on Fatigue Mechanisms in Resistance Spot Welding of Advanced High Strength Steelsen_US
dc.typethesis
dc.typetext
etdms.degree.departmentUniversity of Alabama. Department of Mechanical Engineering
etdms.degree.disciplineEngineering
etdms.degree.grantorThe University of Alabama
etdms.degree.levelmaster's
etdms.degree.nameM.S.

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