Stress corrosion crack depth investigation using the time reversed elastic nonlinearity diagnostic

2018

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All Rights Reserved ii iii ABSTRACT Characterizing stress corrosion cracking in stainless steel using nonlinear resonant ultrasound spectroscopy Spent nuclear fuel rods are stored in stainless steel containers and may be stored for decades. In order prevent radiation leakage, the stainless steel structure must not be compromised. These containers are susceptible to stress corrosion cracking (SCC). Traditional nondestructive evaluation methods have been developed to detect open cracks but these cannot detect the closed portion of the crack that may extend further. Nonlinear Resonant Ultrasound Spectroscopy (NRUS) is used here to determine if it can be used to quantify a cumulative amount of SCC in a structure. To induce SCC in a timely manner, cylindrical, 304L stainless steel rods are immersed in a heated 42% magnesium chloride solution. A set of rods are removed one by one after different lengths of exposure to the hot magnesium chloride solution. NRUS measurements are then conducted on longitudinal modes in the rods. Rods exposed longer did indeed result in a larger resonance frequency shift, and therefore a larger nonlinear parameter, , in NRUS measurements. It is observed that α can be used to detect SCC before visible cracks appear on the rods. iv

Section: Appendix Amentioning

confidence: 99%

“…Elastic Nonlinearity Diagnostic to explore the depth dependence of SCC near welds. 18 The majority of the nonlinear acoustic techniques were applied to a single sample for proof of concept of the technique's ability to detect SCC rather than being applied to a set of samples with progressive damage.…”

Section: Chapter 1 Introductionmentioning

confidence: 99%

Characterizing stress corrosion cracking in stainless steel using nonlinear resonant ultrasound spectroscopy

Hogg

2018

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“…3,4 In 2001, Guyer first proposed using high-amplitude TR focusing for nonlinear imaging of cracks, 5 and Ulrich et al demonstrated this experimentally a few years later by locating a surficial crack in a doped glass sample. 6 Studies since then have used TR to find nonlinearity in various types of surface cracks, [7][8][9][10] near-surficial cracks and delaminations, 10,11 and even buried cracks. 10,12 The detection of cracks using nonlinear methods is rooted in the premise that cracks will generate nonlinear frequency mixing when excited with sufficient amplitude.…”

Section: Introductionmentioning

confidence: 99%

“…The nonlinear NDE of cracks and defects using TR is usually accomplished through the detection of a relative increase in harmonics 8,11,32 or sum and difference frequencies 6,7 (i.e., through the introduction of nonlinear frequency content). Some techniques have been developed to detect distortions in the focal signal when the focusing experiment is conducted multiple times.…”

Section: Introductionmentioning

confidence: 99%

A comparison of impulse response modification techniques for time reversal with application to crack detection

Young

Willardson

et al. 2019

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Time reversal (TR) focusing used for nonlinear detection of cracks relies on the ability of the TR process to provide spatially localized, high-amplitude excitation. The high amplitude improves the ability to detect nonlinear features that are a signature of the motion of closed cracks. It follows that a higher peak focal amplitude than what can be generated with the traditional TR process will improve the detection capability. Modifying the time-reversed impulse response to increase the amplitude of later arrivals in the impulse response, while maintaining the phase information of all arrivals, increases the overall focal signal amplitude. A variety of existing techniques for increasing amplitude are discussed, and decay compensation TR, a technique wherein amplitude is increased according to the inverse of the amplitude envelope of the impulse response decay, is identified as the best modification technique for nonlinear crack detection. This technique increases the focal signal amplitude with a minor introduction of harmonic content, a drawback in two other methods studied, one-bit TR and clipping TR. A final study employs both decay compensation TR and traditional TR, focusing on a rod with stress corrosion cracking, and compares the merits of each in detecting nonlinearity from cracks in a real system. V

“…4,5 This early experiment utilized what has been termed reciprocal time reversal (RTR), 2 where a signal is broadcast from location A, a recording of the signal is made at location B, this recording is then flipped in time, sent electronically to location A, subsequently broadcast from location A, and a TR focus is then created at location B. Subsequently, researchers have named the technique time reversal acoustics and have recently applied it to underwater communications, 6,7 medical applications, 8,9 nondestructive evaluation, [10][11][12][13] and infrasound.…”

Section: Introductionmentioning

confidence: 99%

The effect of transducer directivity on time reversal focusing

Clemens

Willardson

2017

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This letter explores the effect of the directivity of a source on time reversal acoustic focusing of energy. A single loudspeaker produces an airborne focus of sound in a reverberation chamber and in a classroom. Individual foci are created at microphone positions that surround the loudspeaker. The primary axis of the loudspeaker is then rotated and experiments are repeated to average out the room response. Focal amplitude, temporal quality of the foci, and spatial focusing quality are compared to determine the optimal angle to aim a directional source axis relative to the desired focal position.