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Multi-Scale Computational Modeling of Ni-Base Superalloy Brazed Joints for Gas Turbine Applications

Wildofsky, Jacob
http://orcid.org/0000-0001-8645-7412
http://rave.ohiolink.edu/etdc/view?acc_num=osu1574809064215922

Abstract Details

2019, Master of Science, Ohio State University, Welding Engineering.
Brazing is a unique process capable of joining materials with minimal damage to the base material properties. Ni-base superalloy brazed joints are used for the manufacture and repair of high temperature gas turbine engines. However, the mechanical behavior of the brazed joint microstructure is still not fully understood. In addition, there are no standard test methods that include correction factors for the stress concentrations, high tri-axial stress, and potential defects that can reduce the strength of a brazed joint. This project’s goal was to develop a multi-scale model including the damage zone method for the prediction of brazed joint mechanical behavior by investigating shear and tensile loading conditions. The study investigated the impact of a variable braze joint geometry (lap, butt, and pin-in-collar), type of loading (tensile or shear), and form of braze filler metal (foil or paste) had on the mechanical performance of IN718/BNi-2 braze joints. The damage zone method was applied to model and predict the strain concentrations and joint strength of the brazed test samples using finite element analysis in Abaqus software and was validated through digital image correlation measurements. Ultrasonic immersion non-destructive flaw inspection and scanning election microscope fractography work was also completed to better understand the failure mechanisms and their correlation to the microstructure and quality of the brazed joints. Although all sample sets increased in strength with increasing joint area, changes in sample geometry, microstructure, and joint quality impacted the magnitude of the strength. Thermal cycle testing determined that a brazing temperature of 1065oC, a hold time of 10 minutes, and a joint gap of 75 um or lower is required to maintain a volume of fraction of brittle eutectic intermetallics below 10%. Applying the damage zone model to the foil type experimental results, the failure load was predicted for both double lap and pin-in-collar shear geometries using a single 0.5% maximum principle strain failure criterion at 0.015-in. damage zone length. The single lap shear geometry damage zone criteria differed, requiring an increased 0.6% maximum principle with twice the damage zone length. Overall, the individual damage zone model for each shear sample geometry successfully predicted the failure load with a higher accuracy than the current AWS C3.2 standard. A final set of modeling guidelines have been listed for the development and application of the damage zone method for brazed joints.
Boian Alexandrov, Dr. (Advisor)
Avraham Benatar, Dr. (Advisor)
Wei Zhang, Dr. (Committee Member)
216 p.
Engineering; Materials Science; Mechanical Engineering
Brazed Joints, Mechanical Properties, Modeling, Damage Zone Method, Nickel Supperalloys, Ultrasonic Non-destructive testing, Digital image correlation, Fractograghy

Recommended Citations

Citations

  • Wildofsky, J. (2019). Multi-Scale Computational Modeling of Ni-Base Superalloy Brazed Joints for Gas Turbine Applications [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574809064215922

    APA Style (7th edition)

  • Wildofsky, Jacob. Multi-Scale Computational Modeling of Ni-Base Superalloy Brazed Joints for Gas Turbine Applications. 2019. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1574809064215922.

    MLA Style (8th edition)

  • Wildofsky, Jacob. "Multi-Scale Computational Modeling of Ni-Base Superalloy Brazed Joints for Gas Turbine Applications." Master's thesis, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574809064215922

    Chicago Manual of Style (17th edition)

osu1574809064215922
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This open access ETD is published by The Ohio State University and OhioLINK.