Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


38027.pdf (4.65 MB)

ETD Abstract Container

Abstract Header

Nondestructive Residual Stress Assessment of Shot-Peened IN718 Using Hall Coefficient Spectroscopy

Velicheti, Dheeraj
http://rave.ohiolink.edu/etdc/view?acc_num=ucin161374262949063

Abstract Details

2020, PhD, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
In the past, substantial research effort was put towards studying the feasibility of high-frequency eddy current conductivity measurements for residual stress assessment of shot-peened aerospace superalloys. In precipitate hardened IN718, specifically, it was revealed that the influence of cold work and compressive residual stress on the electrical conductivity cancel each other out, rendering eddy current based residual stress assessment not feasible. The research presented in this dissertation investigates a novel galvanomagnetic NDE technique based on the Hall coefficient of the material under test, as an extension of high-frequency eddy current measurements, for the purpose of residual stress assessment in precipitate hardened IN718. Learning from the feasibility studies conducted in the case of eddy current measurements, significant efforts were made towards understanding the influence of residual stress, cold work and thermal aging on the Hall coefficient of IN718 in precipitate hardened state, before developing a broadband nondestructive Hall coefficient measurement system. These initial experiments were conducted in a destructive manner, and indicated that for fully hardened IN718, both cold work and compressive residual stress caused the Hall coefficient to decrease, i.e., the two effects add up, unlike the case of electrical conductivity where the two effects cancel each other out. This raises the possibility of separating the effects of cold work from that of residual stress on Hall coefficient of IN718 using additional eddy current measurements. Since all known Hall coefficient measurement techniques in the literature are inherently destructive in nature, new nondestructive electromagnetic inspection techniques were developed for Hall coefficient measurement. It was found that at low frequencies, constraining the bias magnetic field could replace constraining the dimensions of the specimen. At high inspection frequencies, the magnetic field of the Hall current induces a strong enough Hall electric field to obtain measurable potential differences between points lying on the path followed by the Hall current. Subsequently, it was found that the most promising experimental approach is based on inductive sensing of the Corbino current produced by an alternating current injected into the component under test and a first generation high-frequency Hall impedance measurement system was built that operated over a wide frequency range. A numerical inversion procedure was also developed for dual-mode electromagnetic characterization of shot-peened engine alloy IN718. This procedure allowed combining the measured frequency-dependent AECC and Hall impedance spectra and inverting them together to obtain the sought residual stress and cold work depth profiles. Finally, after developing an experimental Hall impedance measurement system with sufficient measurement accuracy, the dual-mode NDE technique was tested on IN718 coupons peened at Almen 4A, 6A, and 8A intensities. The inverted NDE results showed reasonable qualitative agreement with XRD based residual stress and cold work depth profiles. To suppress the remaining systematic differences, an empirical correction based on a single correction factor for all three peening intensities was introduced. As a result, both the maximum values and the depth at half maximum of the residual stress profiles were accurately assessed. Tests were also conducted on coupons after thermal exposure to 600°C for 100 hours, data from which hints towards thermally activated microstructural changes in the highly cold worked near-surface regions. The research presented in this dissertation highlights that the dual-mode galvanomagnetic method offers a potential answer to the daunting NDE problem of near-surface residual stress profiling in shot-peened aero engine components.
Peter Nagy, Ph.D. (Committee Chair)
Joseph Corcoran, Ph.D. (Committee Member)
Yao Fu (Committee Member)
Francesco Simonetti, Ph.D. (Committee Member)
232 p.
Aerospace Materials
Nondestructive Residual Stress Assessment; Hall Coefficient Spectroscopy; experimental Hall impedance measurement system; Shot-Peened IN718; galvanomagnetic NDE technique; inductive sensing of the Corbino current

Recommended Citations

Citations

  • Velicheti, D. (2020). Nondestructive Residual Stress Assessment of Shot-Peened IN718 Using Hall Coefficient Spectroscopy [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin161374262949063

    APA Style (7th edition)

  • Velicheti, Dheeraj. Nondestructive Residual Stress Assessment of Shot-Peened IN718 Using Hall Coefficient Spectroscopy. 2020. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin161374262949063.

    MLA Style (8th edition)

  • Velicheti, Dheeraj. "Nondestructive Residual Stress Assessment of Shot-Peened IN718 Using Hall Coefficient Spectroscopy." Doctoral dissertation, University of Cincinnati, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin161374262949063

    Chicago Manual of Style (17th edition)

ucin161374262949063
112
© 2020, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.