Monte-Carlo Simulation of Ultrasonic Grain Noise

Embrittlement of many important metal alloys has been related to the accumulation of undesirable materials at grain boundaries, a condition which may be detectable through measurement of ultrasonic scattering from the material's microstructure. Grains with decorated grain boundaries are modeled as shelled microspheres embedded in an isotropic elastic host, and a practical means of predicting scattering from these particles is developed. The incident field often used for measuring backscattered grain noise is focused; both plane and focused incident fields are treated. Theoretical predictions of scattering from isolated scatterers are compared with experimental measurements on metal microspheres embedded in plastic to validate the computational procedure, then predictions of scattering from similar spherical structures embedded in a metal host are presented. In the former case theoretical predictions are found consistent with observations, although differences between shelled and nonshelled scatterers are obscured by the great contrast between host and scatterer. In the latter case, where host and core are quite similar, even thin shells can produce scattering readily distinguishable from the weak scattering in polycrystals that may be due to locally inhomogeneous properties. Results of this study can be used to calculate a backscattering coefficient for calculations of grain noise in metals containing, or composed of, numerous shelled scatterers. Embrittlement of many important metal alloys has been related to the accumulation of undesirable materials at grain boundaries, a condition which may be detectable through measurement of ultrasonic scattering from the material's microstructure. Grains with decorated grain boundaries are modeled as shelled microspheres embedded in an isotropic elastic host, and a practical means of predicting scattering from these particles is developed. The incident field often used for measuring backscattered grain noise is focused; both plane and focused incident fields are treated. Theoretical predictions of scattering from isolated scatterers are compared with experimental measurements on metal microspheres embedded in plastic to validate the computational procedure, then predictions of scattering from similar spherical structures embedded in a metal host are presented. In the former case theoretical predictions are found consistent with observations, although differences between shelled and nonshelled scatterers are obscured by the great contrast between host and scatterer. In the latter case, where host and core are quite similar, even thin shells can produce scattering readily distinguishable from the weak scattering in polycrystals that may be due to locally inhomogeneous properties. Results of this study can be used to calculate a backscattering coefficient for calculations of grain noise in metals containing, or composed of, numerous shelled scatterers.

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“…These results are suitable input for scattering predictions of grain noise based on the independent scattering model. 3,41,42 …”

Section: Numerical Studiesmentioning

confidence: 99%

Elastic wave scattering by shelled spherical scatterers in a focused field

Mittleman

Thompson

Han

1996

The Journal of the Acoustical Society of America

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“…The geometry shown in Figure 2 is being studied numerically, with several distinct types of scatters. Scattering from single crystals, randomly rotated, and embedded in an effective medium [7,8], has been studied through the Independent Scattering Model [9,10]. We extend this work to numerical studies of scattering from anisotropic shells, where shell properties have been chosen to represent the possible effects of precipitates or microvoids on the grain boundaries.…”

Section: An Exacf Solution To the Anisotropic Field Equationsmentioning

confidence: 99%

Ultrasonic Scattering from Spherically Orthotropic Shells

Mittleman¹,

Roberts

Thompson

1993

Review of Progress in Quantitative Nondestructive Evaluation

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“…In this work, we present a Monte Carlo method ͑MCM͒ 16 for simulating time-domain noise signals observed in pulse/echo immersion inspections of polycrystalline components. The method predicts simulated time-domain noise signals, and hence can be used to determine average and peak noise levels, as well as other statistical quantities.…”

Section: Introductionmentioning

confidence: 99%

Predicting ultrasonic grain noise in polycrystals: A Monte Carlo model

Yalda

Margetan

Thompson

1996

The Journal of the Acoustical Society of America

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A Monte Carlo technique is described for predicting the ultrasonic noise backscattered from the microstructure of polycrystalline materials in a pulse/echo immersion inspection. Explicit results are presented for equiaxed, randomly oriented aggregates of either cubic or hexagonal crystallites. The model is then tested using measured noise signals. Average and peak noise levels and the distribution of the noise voltages are studied as the density of grains changes. A Monte Carlo technique is described for predicting the ultrasonic noise backscattered from the microstructure of polycrystalline materials in a pulse/echo immersion inspection. Explicit results are presented for equiaxed, randomly oriented aggregates of either cubic or hexagonal crystallites. The model is then tested using measured noise signals. Average and peak noise levels and the distribution of the noise voltages are studied as the density of grains changes.

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Monte-Carlo Simulation of Ultrasonic Grain Noise

Cited by 13 publications

References 6 publications

Elastic wave scattering by shelled spherical scatterers in a focused field

Elastic wave scattering by shelled spherical scatterers in a focused field

Ultrasonic Scattering from Spherically Orthotropic Shells

Predicting ultrasonic grain noise in polycrystals: A Monte Carlo model

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