Backscattered microstructural noise in ultrasonic toneburst inspections

Ultrasonic Grain Noise Modeling: Recent Applications to Engine Titanium Inspections

“…The models used in this work are based upon three principal assumptions [1]: (1) that multiple scattering can be neglected; (2) that the total noise signal is an incoherent Superposition of the echoes from the individual scatterers; and (3) that the microstructure is spatially uniform in the region under inspection (although it may be anisotropic). Initial modeling efforts centered on the prediction of the root-mean-squared (rms) noise level.…”

“…There the random variable of interest was the RF noise voltage (v) seen at some fixed observation time. For an incident tonehurst pulse, the position-averaged mean squared voltage seen at time t in a scanning experimentwas written as the product of two factors, one which depended on the microstructure, and one which was independent of microstructure and primarily depended on details of the measurement system [1]: <v 2 (t)> = [microstructure factor][system factor] = 11 2 [system factor] .…”

“…[5], the calculation of P(V rrl requires the partitioning of the 8 llS gate into statistically independent subintervals of duration ll.t. In the present work we have consistently chosen D.t to equal the "equivalent square wave duration" [1] of the reference signal, in this case 0.2261-ls. From P(VP) the mean GPN valtage <Vpp> can easily be deduced (Fig.…”

“…Under the sponsorship of the U.S. Air Force and the FAA Engine Titanium Consortium, models have been developed which endeavor to predict characteristics of the backscattered microstructural noise observed in focused-probe pulse/ echo inspections of titanium billets and forgings [1][2][3][4][5]. In this paper we briefly review the history of the model development work at Iowa State University, and then compare noise model predictions with experiment for several cases of interest.…”

“…microstructure which enters the model calculations through certain frequency-dependent factors known as "backscatter coefficients" or "Figures-of-Merit" (FOM) [1]. Fora typical industrial inspection of a billet or forging, such FOM information is not generally available, although it could be deduced by analyzing backscattered noise waveforms from regions where the microstructure is spatially uniform [1][2]. In the absence of specific FOM information it is still possible to use the noise models in a productive manner, namely to predict how changes in the inspection procedure or component geometry will affect the backscattered noise from some microstructure at hand.…”