Electronic Theses and Dissertations

Ahmad Razi

Date

2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Committee Chair

Ali Fatemi

Committee Member

Gladius Lewis

Committee Member

John Williams

Committee Member

Majid Farajian

Committee Member

Yue Guan

Abstract

Welding is arguably the most widely used method for joining parts, which often experience fluctuating loads during service and cyclic damage accounts for most mechanical failures in weldments. Hence, fatigue and failure assessment of the welded joints is an essential step in design process to ensure reliable performance. This work investigates experimental and predictive determination of weld metal properties, evaluates multiaxial fatigue of welded tubular joints featuring important geometric traits of welds (i.e., start/stop and partial penetration), and demonstrates application of the results to fatigue analysis of a welded component. Monotonic, cyclic, and fatigue properties of steel weld specimens of ER70S-3 were obtained under axial and shear loading conditions. The predictive framework to estimate shear properties include classical failure criteria and empirical equations based on the readily available properties from monotonic uniaxial testing or hardness measurements. Welded joints with preserved start/stop points and full/partial weld penetrations were tested under different loading conditions including single- and multi-channel, constant and variable amplitude and analyzed for life estimation. Multiaxial fatigue life prediction of the welded joints was carried out by a comprehensive framework of crack initiation- and growth-based damage models. The crack initiation-based methods include nominal stress-life, local strain-life, and critical plane approach which resulted in the highest robustness, accuracy and conservatism in life prediction. Micro-crack (< ~2 mm) orientations based on the critical plane approach were also accurately predicted. The critical plane concept was also used with fracture mechanics as a crack growth-based approach to predict macro-crack growth orientation and fatigue lives to failure with reasonable accuracy compared to experimental observations. Furthermore, popular weldment design guidelines by International Institute of Welding, British Standard, and Eurocode were evaluated and their application to life prediction of welded joints under multi-channel variable amplitude loading is discussed. Based on the weld metal and welded joint analyses, fatigue damage in a welded coupled torsion beam axle of an automobile chassis was calculated and lives were accurately predicted within a factor of two of the experimental data. This dissertation provides an efficient and effective fatigue life prediction framework of welded components with complex geometries and service loading conditions.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest/Clarivate.”

Notes

Open Access

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