Estimating the Parameters of Signals Observed during Ultrasonic Testing of a Cylindrical Article with a Normal Probe on the End Surface

Abstract

The first and second signals observed during ultrasonic testing of a cylindrical article with a normal probe set on the article's end surface are studied. The amplitude of the second pulse caused by a reflection from a lateral wall with transformation of elastic waves is estimated relative to the amplitude of the first (ordinary bottom-reflected) pulse. It is ascertained that, under certain conditions, the amplitude of the second pulse can be comparable to or even exceed the amplitude of the first pulse. The effect of a change in the specimen radius-to-length ratio on the amplitude of the bottom signal is estimated.The necessity of testing cylindrical articles from ends using normal probes is encountered during ultrasonic testing of appropriately shaped forged pieces, axles of rolling-stock wheel pairs, etc.[1]. In acceptance tests of axles according to the regulatory document RD 32.144-2000 [2], a method of testing their sounding is used, which consists in determining the difference (in decibels) between bottom echo signals obtained from a face of a standard specimen CO-2 (at a distance of 59 mm) and from the opposite end of an axle. This axle is considered inconsistent with the requirements of the acceptance test if this difference exceeds 46 dB.It is known that, in the far-field zone of a normal probe, the amplitude of the bottom signal falls (without allowance for a decrease due to the absorption and scattering by microinhomogeneities) as a result of a divergence of the wave front of a longitudinal wave in inverse proportion to the increasing distance to the reflecting surface; this decrease in the bottom signal occurs more slowly than a decrease with the distance of echo signals from cylindrical, spherical, flat-bottomed, and other reflectors [1,3]. However, when cylindrical articles are tested from their ends, signal reflections from lateral surfaces can be observed. This leads to the appearance of additionally detected pulses (false signals), the amplitude of which, owing to a certain focusing effect of these surfaces, can be comparable with the amplitudes of signals reflected directly from the ends (bottom signals). This may complicate the discrimination of bottom signals since their selection by the time of arrival becomes obligatory. The author of this paper has performed studies of the first two echo pulses observed during ultrasonic testing from the ends of cylindrical specimens. The corresponding results are presented below.The specimens used in this study were steel cylinders no. 1 of radius b = 35 mm and length h = 142 mm and steel cylinders no. 2 with b = 45 mm and h = 210 mm. Elastic waves were emitted and received by a èêàá -Ñ 11 normal probe at a frequency of 2.5 MHz ( è 111-2.5-K12-002). Figure 1 shows (in arbitrary units) the first and second pulses observed on the screen of the AVGUR computer apparatus upon excitation and reception of elastic waves by the probe located axisymmetrically at the end of specimen no. 1. Fig. 1, pulse 1 corresponds to a bottom signal (from the opposite end). The d...

Estimation of a Bottom Echo-Signal Level Reflected from a Plane Surface of a Cylindrical Article Using a Normal Probe Operating in a Pulsed Mode

“…The relationship obtained in [5] between pressure δ P bc of the bottom echo signal in a cylindrical article and pressure δ P bp of the bottom echo signal reflected from an infinite plane boundary can be expressed as (1) In formula (1), a is the radius of a round-shaped normal probe,…”

“…For the axles of railway vehicles subjected to the acceptance inspection, their "sounding" is estimated according to the document êÑ 32.144-2000 [4] by the difference between the bottom echo signals received from the face of a CO-2 (calibration block) sample (from a 59-mm distance) and the butt end of the axle. However, as was mentioned in [5], during detecting of a bottom echo signal reflected from the end surface using a normal probe that is attached to the opposite end surface of the cylindrical article at its center and creates pressure P acting normally on the surface (Fig. 1), it is rather difficult to estimate the signal level because it is determined not only by article length h (distance from the reflecting end) but also by ratio b / h , where b is the radius of the cylinder.…”

“…1), it is rather difficult to estimate the signal level because it is determined not only by article length h (distance from the reflecting end) but also by ratio b / h , where b is the radius of the cylinder. If b decreases to values several times smaller than the radius for the first Fresnel zone [6] of the operating wavelength of the normal probe or even smaller, the amplitude of the bottom echo signal will decrease.In [5], an expression was obtained for the pressure applied to a normal probe by longitudinal waves forming a bottom echo signal. This expression is expressed as a sum of pressures created by a wave reflected from an infinite plane boundary and a wave reflected from the angle between a cylinder's lateral surface and end surfaces over the entire round profile.…”

“…In [5], an expression was obtained for the pressure applied to a normal probe by longitudinal waves forming a bottom echo signal. This expression is expressed as a sum of pressures created by a wave reflected from an infinite plane boundary and a wave reflected from the angle between a cylinder's lateral surface and end surfaces over the entire round profile.…”

“…In [5], this dependence was considered for the case of a continuous operating regime (at a nominal frequency) of a normal probe. The objective of this study was to understand the specifics of changes in the bottom echo-signal level reflected from the plane surface of a cylindrical article in the pulsed mode.…”