GB2215056A

GB2215056A - Ultrasonic non-destructive testing apparatus with adjustably mounted transducer

Info

Publication number: GB2215056A
Application number: GB8900044A
Authority: GB
Inventors: Mark Bourock
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-01-30
Filing date: 1989-01-04
Publication date: 1989-09-13
Also published as: GB8802105D0; GB8900044D0

Abstract

A non-destructive ultrasonic apparatus, which is particularly useful in measuring the elastic constants of materials is based on the principle of wave reflection and refraction. A liquid interface F2 is used to couple transducers at positions T1, T2 to the specimen. The specimen SUT is prism shaped in order to get the desired angles for wave reflection and refraction. Different kinds of materials could be tested using the apparatus, including rock specimens. The apparatus comprises oil filled cavities C1, C2, clamps CL1, CL2 and a guide G. The transducers are used as both transmitters and receivers to measure transit times through the specimen of both P and S waves and the elastic constant is derived from the P and S wave velocities. To remove the sample SUT oil is transferred from cavity C2 to cavity C1, the clamps CL1, CL2 are released and the guide G slides away. <IMAGE>

Description

NON-DESIPUCTIVE TLTIN$ liF'FARP.?1'S This invention relates to non-destructive testing apparatus and more particularly to a transducer cell used in the field of non-destructive testing of materials.

Non-destructive testing of materials is one of the subjects which have-many challenges to researchers and scientists. Over the last decade, there has been a growing interest in designing systems for measuring the elastic constants of materials using ultrasounds. To determine the elastic constants, two parameters have to be measured, namely, the longitudinal and shear wave velocities of ultrasound in the specimen concerned. Many instruments have been designed using different methods, which give more or less accurate results in measuring longitudinal waves. The problem, however, is the measurement of shear wave velocity which has been always tedious. Hence, most of the time, the final resultsare either doubtful or inaccurate, unless a lengthy process of comparison of results and elimination of wrong values is used.

It is an object of the present invention to provide an apparatus for the non-destructive testing of materials in which a measurement of shear wave velocities can be determined in a relatively simple manner.

The present invention provides apparatus for the non-destructive testing of a material specimen including means for holding the material sample in a relatively rotatable manner with respect to a transducer at a desired distance from the transducer, means for adjusting the relative angle of the transducer with respect to the sample, means for maintaining a liquid interface between the transducer and the specimen such that waves transmitted by the transducer are tansmitted as compressional waves within the liquid and as shear or compressional waves within the material specimen.

The material sample is prism shaped.

The apparatus preferably includes a first cavity and a second cavity for containing the liquid which is preferably an oil, the first cavity being a reservoir cavity and the second cavity being an active cavity containing the oil through which the waves are transmitted, the first and second cavities being connected by pipe means such that the oil can be transferred from the second cavity to the first cavity thereby allowing the material specimen to be exchanged without spillage of the oil.

Preferably the means for adjusting the rotational angl- includes a fine screw thread drive acting on one side of a pivoted member holding the transducer the other side of the member being spring biased.

The same ultrasonic transducer is used to both transmit and detect the waves.

Preferably a similar transducer is provided for mounting on a further surface of the specimen to provide a measurement of compressional waves and preferably a change over switch is interposed between a source of electrical pulses and the transducers.

The material specimen is preferably held by two clamps.

The means for maintaining a liquid interface between the transducer and the material specimen includes a flexible rubber seal.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows the top view of the transducer cell with a crosssection DD through cavity 1 and cavity 2; Figure 2 shows the side view AA; Figure 3 shows the side view BB; and Figure 4 to Figure 6 illustrate the techniques involved in designing the system.

Referring to the drawing, the teansducer cell comprises a base, an electric switch SW, two cavities C1 and C2 filled with liquid, two clamps CLi and CL2, two identical transducers T1 and T2 which are not shown in Figures 1 to 3, (the letters T1 and T2 indicate where the two transducers are going to be put) and a guide G.

Before starting any measurements, transducer T2 has to be inserted into place and adjusted in position until it reaches the axis aa. Grease is used to seal the transducer against cavity 1. Next, the specimen under test (SUT) is put into place and clamped by means of CL1 and CL2 ( a rubber seal is used between the specimen and cavity C2). After that cavity 1 is filled with oil or any suitable liquid. The oil level has to be about 15mm below the hole H4 (Figure 3 ). The oil will move to cavity C2 through pipe P1 (Figure 3 ). The rubber seal around cavity C2 enables cavity C1 to pivot freely around point P (Figure 2 ). Cavity C1 is held in position by means of a spring SF and a screw S.The angle # is ther fixed at a desired value to ensure that the waves generated by T2 are receive back at T2 after passing through the specimen SUT. Now, the system is set for taking both shear and compressional wave measurements.

Figure 4 shows the method used for transit time measurement. When the system is switched on by connecting the switch SW to a source of electrical pulses; T2 starts radiating ultrasonic waves into the liquid. The ultrasonic beam travels the length L1 along dd axis before getting refracted at point O on the face F2 of the liquid-solid interface. A change in mode occurs, whereby the initial compressional wave becomes a shear wave due to refraction.

(The change in mode occurs only in the case of shear wave measurement). The latter travels the length L2 before getting reflected on the same axis (since the beam incidence angle is 90 degrees). Once again the wae gets refracted and the change in mode occurs, but this time the shear wave becomes converted back to a compressional wave. The beam travels back the distance L1 and gets detected by the same transducer T2.Shear wave velocity (Vs) is computed from the following formula: Vs = L2 = a + 2 Voto ( tan 190 - tan e (1) Tt-Ll/Vl 2 ( Tt - to/cos 8) Where, Vo : Longitudinal wave velocity in the oil interface; Tt : Transit time of the pulse along L1 and L2, to : Transit time of the pulse when the beam is perpendicular to F2; a : Lateral dimension of the specimen.

Figure 5 shows transducer T1 on the face F1 of the specimen for measuring longitudinal wave velocity. V1 is calculated by dividing distance by the transit time of the pulse.

To make any measurement, the angle e is first put to zero. From the echo train which appears, to can be measured. By increasing the angle, a second echo will apppear, this time it gives Tt for compressional waves.

If e is increased further, a third echo train will appear, which gives Tt for shear waves. Therefore, both waves can be measured from the same formula (1) using the same transducer. The second transducer is used to crosscheck the measurement of compressional wave velocity.

In order tc remove the specimer. after finishing measurement, the transducer cell is turned into an upright position (with the switch SW to the top). The oil in cavity C2 is then transferred to cavity C1 through pipe P1. The liquid tranfer principle is illustrated in Figure 6 (by turning the system upside down the liquid can be transferred from one cavity to another). The cavity C2 is then empty of oil and the sample can be removed by releasing clamps CII and CL2 and sliding guide G backwards away from cell C2.

Claims

1 This invention provides an apparatus for the non-destructive testing of a material specimen including means for holding the material sample in a relatively rotatable manner with respect to a transducer at a desired distance from the transducer, means for adjusting the relative angle of the transducer with respect to the sample, means for maintaining a liquid interface between the transducer and the specimen such that waves transmitted by the transducer are transmitted as compressional waves within the liquid and as shear or compressional waves within the material specimen.

2 A non-destructive testing apparatus as claimed in claim 1 wherein the material sample is prism shaped.

3 A non-destructive testing apparatus as claimed in claim 1 wherein the apparatus preferably includes a first cavity and a second cavity for containing a liquid which is preferably an oil, the first cavity being a reservoir cavity and the second cavity being an active cavity containing the oil through which the waves are transmitted, the first and second cavities being connected by pipe means such that the oil can be transferred from the second cavity to the first cavity thereby allowing the material specimen to be exchanged without the spillage of the oil.

4 A non-destructive apparatus as claimed in claim 1 wherein preferably the means for adjusting the rotational angle includes a fine screw thread drive acting on one side of a pivoted member holding the transducer thevother side of the member being spring biased, the same transducer is used to both transmit and detect the waves.

5 A non-destrucive testing apparatus as claimed in claim 1 wherein a similar transducer is provided for mounting on a further surface of the specimen to provide a measurement of compressional waves and preferably a change over switch is interposed between a source of electrical pulses and the transducers.

6 A non-destructive testing apparatus as claimed in claim 1 wherein the material sample is preferably held by two clamps.

7 A non-destructive testing apparatus substantially as described herein with reference to Figure 1-6 of the accompanying drawings.

7 A non-destructive testing apparatus as claimed in claim 1 wherein means for maintaining a liquid interface between the transducer and the material specimen include a flexible rubber seal.