Graduation Semester and Year
Summer 2026
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Industrial Engineering
Department
Industrial and Manufacturing Systems Engineering
First Advisor
Dr. Emma Yang
Second Advisor
Dr. Victoria Chen
Third Advisor
Dr. Xin Liu
Fourth Advisor
Dr. Shuchisnigdha Deb
Abstract
Sustainable manufacturing is central to environmentally responsible development by reducing waste and carbon footprint. Metal repair is one important pathway toward achieving this goal, offering an eco-friendly alternative to premature disposal at the end of life. Since conventional methods often struggle to restore complex geometries, additive manufacturing (AM) provides an excellent alternative because of its layer-wise deposition, which offers both intricate fabrication and targeted repair. This work explored AM-assisted repair using a 5-axis hybrid laser metal deposition (LMD) system equipped with CNC machining and automatic tool change. The reliability and mechanical performance of repaired parts are essential for high-yield industries such as aerospace, defense, and energy. The existing studies emphasize interfacial defects as the primary source of weak bonding across dissimilar-metal joints. Efforts to mitigate these defects have concentrated on tuning process parameters, controlling thermal history, and preparing the interfacial surface. A comprehensive study understanding the interfacial surface and its link with defect formation and strategies to mitigate interfacial defects with improved bonding integrity has not been fully explored. To fill this knowledge gap in the current research on metal repair, this dissertation aims to study the interfacial surfaces to understand the bonding mechanisms and to explore a surface modification approach to improve the mechanical strength. An experimental investigation was carried out to evaluate the mechanical strength of the repair, accompanied by a multi-material finite element (FE) model that quantified the stress distribution in the repaired components. Interface roughening significantly improved the repair performance, raising the average yield strength by 36.36% and the ultimate tensile strength by 64.23% over the benchmark, while elongation at break increased from 17.50% to 39%. By mitigating interfacial defect formation, the controlled roughened interface prevented catastrophic failure at the repair joint. In addition, this dissertation implemented the interface roughening approach in the study of non-flat interfaces in order to further improve the bonding integrity in dissimilar metal repair. A non-flat interface strengthens the bond by increasing the contact area and reorienting the crack path. The study employed cohesive zone modeling that confirmed this strength gain, surrogate modeling that identified the governing design parameters, and a Gaussian heat flux model that yielded a sidewall energy correction restoring the interfacial energy deficit. Results demonstrated that the finger joint sustained a 17% higher peak force and about twice the displacement at peak load, failing gradually through post-peak softening. Moreover, ultimate strength improved from about 455 MPa to 530 MPa due to the longer, deflected crack path. Restoring the 26.90% energy deficit produced continuous, well-bonded deposition free of large lack-of-fusion defects. The findings of this research will enable AM designers, manufacturers, and practitioners to understand the effect of interfacial surface roughness to mitigate interfacial defects and achieve high mechanical strength in dissimilar metal repair using the AM process. In addition, by leveraging the surrogate model, a suitable finger design can be identified within the design space rapidly, without computationally expensive FE modeling. Meanwhile, the energy correction approach provides a guideline for defect mitigation in finger slot deposition.
Keywords
Additive manufacturing, Dissimilar metal repair, Joint interface, Non-flat interface, 5-axis hybrid additive subtractive manufacturing, Interfacial mechanics, Finite element modeling
Disciplines
Industrial Engineering | Manufacturing
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
KOBIR, MD HUMAUN, "A COMPREHENSIVE STUDY OF INTERFACIAL SURFACES TO IMPROVE MECHANICAL STRENGTH IN DISSIMILAR METAL REPAIR USING HYBRID ADDITIVE-SUBTRACTIVE MANUFACTURING" (2026). Industrial, Manufacturing, and Systems Engineering Dissertations. 3.
https://mavmatrix.uta.edu/industrialmanusys_dissertations2/3