Accession Number : ADA259035
Title : Nondestructive Evaluation of Grain Size Distributions Using Multifractal Analysis of Backscattered Ultrasonic Signals.
Descriptive Note : Final rept. 15 Jul 1989-14 Oct 1992
Corporate Author : DREXEL UNIV PHILADELPHIA PA DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
Personal Author(s) : Bilgutay, N ; Onaral, B ; Nicoletti, D
Report Date : Dec 1992
Pagination or Media Count : 46
Abstract : Grain size is one of the factors which influence mechanical properties of metals like strength and fracture toughness. Ultrasonic waves propagating in polycrystalline materials are subject to attenuation dominated by grain boundary scattering. The importance of grain size estimation for industrial applications warrants the investigation of alternative methods of nondestructive grain size determination. Analysis of the power-law behavior of ultrasonic attenuation experimental data is used to link the wavelength dependence of the attenuation coefficient directly to the grain size distribution. The outcome is a simple relationship between the power-law which describes the grain size distribution and the power-law dependence of attenuation on wavelength. Justifications for the use of the power-law for the grain size distribution include scaling and self-similarity. Careful attention is given to the limitations in terms of a practical grain size distribution with finite limits. Two types of measurements are presented to verify the theoretical development: grain size distribution and ultrasonic attenuation. Nickel samples were prepared using three different annealing durations. The attenuation exponent is experimentally shown to be an appropriate nondestructive measurement of the gain size distribution exponent. Further scaling properties for different annealing durations are also explored. A nondestructive evaluation procedure is suggested for metal samples with identical grain size distribution exponents, where the shifts of the log-log representations of the attenuation curves can be used to characterize the different grain size distributions.
Descriptors : *GRAIN SIZE , *BACKSCATTERING , *NICKEL , *ULTRASONIC PROPERTIES , METALS , MEASUREMENT , SCATTERING , ANNEALING , MECHANICAL PROPERTIES , STRENGTH(MECHANICS) , ULTRASONICS , ULTRASONIC FREQUENCIES , POLYCRYSTALLINE , GRAIN BOUNDARIES , BEHAVIOR , ATTENUATION , SIGNALS , LIMITATIONS , WAVE PROPAGATION , FRACTURE(MECHANICS) , EXPERIMENTAL DATA , NONDESTRUCTIVE TESTING , DISTRIBUTION , MATERIALS , DAMPING , TOUGHNESS
Subject Categories : Metallurgy and Metallography
Distribution Statement : APPROVED FOR PUBLIC RELEASE