title: Forward models for extending the mechanical damage evaluation capability of resonant ultrasound spectroscopy.
abstract: Finite element (FE) modeling has been coupled with resonant ultrasound spectroscopy (RUS) for nondestructive evaluation (NDE) of high temperature damage induced by mechanical loading. Forward FE models predict mode-specific changes in resonance frequencies (ΔfR), inform RUS measurements of mode-type, and identify diagnostic resonance modes sensitive to individual or multiple concurrent damage mechanisms. The magnitude of modeled ΔfRcorrelate very well with the magnitude of measured ΔfRfrom RUS, affording quantitative assessments of damage. This approach was employed to study creep damage in a polycrystalline Ni-based superalloy (Mar-M247) at 950°C. After iterative applications of creep strains up to 8.8%, RUS measurements recorded ΔfRthat correspond to the accumulation of plastic deformation and cracks in the gauge section of a cylindrical dog-bone specimen. Of the first 50 resonance modes that occur, ranging from 3 to 220kHz, modes classified as longitudinal bending were most sensitive to creep damage while transverse bending modes were found to be largely unaffected. Measure to model comparisons of ΔfRshow that the deformation experienced by the specimen during creep, specifically uniform elongation of the gauge section, is responsible for a majority of the measured ΔfRuntil at least 6.1% creep strain. After 8.8% strain considerable surface cracking along the gauge section of the dog-bone was observed, for which FE models indicate low-frequency longitudinal bending modes are significantly affected. Key differences between historical implementations of RUS for NDE and the FE model-based framework developed herein are discussed, with attention to general implementation of a FE model-based framework for NDE of damage.
authors.affiliation: Materials, University of California, Santa Barbara 93106, USA. Electronic address: bgoodlet@engineering.ucsb.edu.
authors.forename: B R
authors.initials: BR
authors.lastname: Goodlet
authors.affiliation: Materials, University of California, Santa Barbara 93106, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Torbet
authors.affiliation: Vibrant Corporation, Albuquerque, NM 87113, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Biedermann
authors.affiliation: Vibrant Corporation, Albuquerque, NM 87113, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Jauriqui
authors.affiliation: Computational Tools, Gurnee, IL 60031, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Aldrin
authors.affiliation: Computational Tools, Gurnee, IL 60031, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Pollock
keywords: Creep; Damage; Evaluation; Finite element; Modeling; NDE; RUS; Resonance