Doctoral theses of the School of Engineering are available in the open access repository maintained by Aalto, Aaltodoc.
Public defence in Fatigue of Welded Joints, M.Sc. Abinab Niraula
Public defence from the Aalto University School of Engineering, Department of Energy and Mechanical Engineering.
When
–
Where
Lecture Hall 215 Meyer, Otakaari 4, K1 Building, 02150 Espoo
Event language(s)
English
Title of the thesis: Quantifying Weld Undercut Severity on the Fatigue of Marine Structures
Thesis defender: Abinab Niraula
Opponent: Prof. Grzegorz Glinka, University of Waterloo, Canada
Custos: Prof. Heikki Remes.,Aalto University School of Engineering
Fusion welding is the most common metal-to-metal joining method in the fabrication of large metallic structures, such as ships. It necessitates localized melting via high-energy application to forge robust joints. The inherent volatility of this process introduces geometric imperfections like undercuts, compromising the structural integrity and service life of the welded structure. While modern manufacturing techniques have improved welding quality, local imperfections such as undercuts are almost impossible to avoid due to the volatile nature of the welding process.
This dissertation investigates the influence of the local undercut geometry on fatigue life through a systematic evaluation of 3D undercut geometric parameters. Employing high-resolution geometry measurements and a library of realistic undercut profiles, the study utilizes fatigue experiments, statistical analysis, and thorough numerical simulations. Strain-based approach is applied to uncover the interplay between fatigue and undercut geometry, material variants, stress ranges, as well as weld geometry.
Key finding highlights the significant influence of the local undercut geometry on the fatigue life of welded joints. An innovative 3D Undercut Indicator is introduced to characterize complex undercut shapes. Furthermore, a novel Undercut Severity Index (Ψ_USI) is defined as a robust metric to quantify the fatigue deteriorating effect of local undercuts considering their geometry, materials, stress range, and weld geometry. This index promotes a flaw-tolerant philosophy in design and enables rigorous quality control protocols across industries.
Keywords: Fatigue, Strain-based analysis, Laser hybrid weld, Local undercut, 3D geometry
Thesis available for public display 7 days prior to the defence at .
Contact information:
E-mail: abinab.niraula@aalto.fi
LinkedIn:
Doctoral theses of the School of Engineering
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