WO1993024830A1 - Ultrasonic evaluation of a sample - Google Patents

Ultrasonic evaluation of a sample Download PDF

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Publication number
WO1993024830A1
WO1993024830A1 PCT/GB1993/001184 GB9301184W WO9324830A1 WO 1993024830 A1 WO1993024830 A1 WO 1993024830A1 GB 9301184 W GB9301184 W GB 9301184W WO 9324830 A1 WO9324830 A1 WO 9324830A1
Authority
WO
WIPO (PCT)
Prior art keywords
sample
ultrasound signal
ultrasound
evaluating
contacting means
Prior art date
Application number
PCT/GB1993/001184
Other languages
French (fr)
Inventor
Christopher Edwards
Stuart Beaumont Palmer
Original Assignee
Lucas Industries Public Limited Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lucas Industries Public Limited Company filed Critical Lucas Industries Public Limited Company
Publication of WO1993024830A1 publication Critical patent/WO1993024830A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/07—Analysing solids by measuring propagation velocity or propagation time of acoustic waves

Definitions

  • This invention relates to a method of and to an apparatus for evaluating a sample using ultrasound, and is particularly applicable to the evaluation of the liquid fraction of a billet of metal being prepared for a semi-solid forming process.
  • Semi-solid forming processes involve heating a body or billet of metal until it reaches a plastic consistency, and then pressing the billet into a mould to form it into the required shape. It is necessary for the metal to exhibit the correct consistency (i.e. liquid fraction) before the forming or moulding operation and it is therefore necessary to monitor the consistency of the metal.
  • a method of evaluating a sample comprising transmitting an ultrasound signal through the sample, measuring the time taken for a longitudinal wave of the ultrasound signal to pass through the sample, measuring the time taken for a shear wave of the ultrasound signal to pass through the sample, and determining a parameter of the sample from these two measurements.
  • a value may be calculated which is independent of (and therefore does not require measurement of) the path length through the sample: for example this value may be calculated as the ratio of the two times-of-flight.
  • the calculated value provides a measure of the degree of plasticity, or liquid fraction, of the material.
  • the velocity of the shear wave is significantly less than the velocity of the longitudinal wave, so that a detector will firstly sense arrival of the longitudinal wave and then, after a delay, will sense arrival of the shear wave.
  • an apparatus for evaluating a sample comprising non- contacting means for generating an ultrasound signal for passing through the sample, means for measuring the respective times taken for a longitudinal wave and a shear wave of the ultrasound signal to pass through the sample, and for determining a parameter of the sample from these two measurements.
  • the non-contacting means for generating the ultrasound signal may comprise a pulsed laser directed at one side of the sample: incidence of the pulse of laser light on the sample causes generation of an ultrasound signal having both longitudinal and shear wave components.
  • Non-contacting detection of the ultrasound signal at the opposite side of the sample may be made using an interferometer: this requires a reflective surface finish on that side of the sample.
  • the arrangement may be modified so that the detector is positioned on the same side of the sample as the ultrasound generator, and the ultrasound waves pass through the sample in one direction, are reflected from the opposite side and pass through the sample in the return direction towards the detector.
  • Electromagnetic acoustic- transducers EMATs
  • a pulsed laser generator is used, together with an EMAT detector, the laser producing an intense ultrasound signal and the EMAT detector avoiding the need for a reflective surface on the sample, yet yielding good signal-to-noise ratio.
  • a pulsed switched laser for example a q-switched Nd:YAG laser 10, producing 200 mJ, 10 ns pulses, is directed at one side of a sample 12 (e.g. of aluminium alloy) , typically 8mm thick and 19mm in diameter.
  • a sample 12 e.g. of aluminium alloy
  • Incidence of the laser pulse against the side 13 of the sample causes an ultrasound pulse to be generated at the surface and this ultrasound pulse propagates through the sample to its opposite side 14, the ultrasound pulse comprising both longitudinal and shear wave components.
  • the velocity of the longitudinal wave is significantly greater than the velocity of the shear wave, so that the longitudinal wave is the first to arrive at the opposite side 14 of the sample, followed after a delay by the shear wave.
  • Arrival of each wave at the opposite side 14 of the sample causes vibration of the sample surface, the displacements of the surface being in a direction normal to itself but extremely small.
  • a detector 16 is used to sense these displacements.
  • the detector 16 comprises a stabilised HeNe Michelson interferometer directly aligned with the source laser 10.
  • the detector may comprise an EMAT positioned close to the surface 14 of the sample, the EMAT being water cooled.
  • a control and measurement system 20 of the apparatus is arranged to measure the respective times-of-flight of the longitudinal and shear waves (relative to the instant of emission of a pulse from laser 10) . From these measurements, a value is calculated which is independent of the path length, so that it is not necessary to measure the thickness of the sample: for example this value may be calculated as the ratio of the two times-of-flight.
  • the velocity decreases as the sample temperature increases, and decreases more sharply after partial melting has occurred.
  • this effect is more pronounced with the shear wave, consistent with the fact that the shear wave does not propagate in a liquid whilst the longitudinal wave velocity generally drops by approximately 10%.
  • the ratio of the two times-of-flight (being the inverse ratio of the respective velocities) gives a measure related to the temperature and hence the liquid fraction of the sample.
  • the detector 16' can be positioned on the same side of the sample as the ultrasound generating means: in this case the ultrasound waves pass through the sample in one direction, are reflected from the opposite side of the sample and then pass through the sample in the opposite direction, to be picked up by the detector.

Abstract

For evaluating the liquid fraction of a sample of metal (12), a pulsed laser (10) is directed at one side (13) of the sample (12) and an interferometer detector (16) is directed at the opposite side (14) of the sample. The pulsed laser (10) causes an ultrasound pulse to propagate through the sample (12), the ultrasound pulse comprising longitudinal and shear wave components which propagate at different velocities through the sample. The ratio of the times-of-flight of the two components can be measured to determine the liquid fraction of the sample.

Description

ULTRASONIC EVALUATION OF A SAMPLE
This invention relates to a method of and to an apparatus for evaluating a sample using ultrasound, and is particularly applicable to the evaluation of the liquid fraction of a billet of metal being prepared for a semi-solid forming process.
Semi-solid forming processes involve heating a body or billet of metal until it reaches a plastic consistency, and then pressing the billet into a mould to form it into the required shape. It is necessary for the metal to exhibit the correct consistency (i.e. liquid fraction) before the forming or moulding operation and it is therefore necessary to monitor the consistency of the metal.
Conventional monitoring techniques are crude and involve monitoring the force required to produce a given deformation of the metal, e.g. by slicing it with a blade. Ultrasound techniques are also known, and these make use of the phenomenon that the velocity of ultrasound through a body decreases as the material of the body passes from its solid phase to its liquid phase. However, the velocity is determined by measuring the time taken for an ultrasound signal to pass from one side to an opposite side of the body being monitored, but requires a precise measure of the path length through the sample. When the sample is contained within a vessel, and fills the space between two opposite sides of the vessel, the path length between those sides is constant, but in the case of a discrete item such as a metal billet, the width of the item is not accurately known because of expansion resulting from the heating process and also because of dimensional inaccuracies in the production of the billet. We have now devised a method of and an apparatus for evaluating a sample, which method and apparatus overcome the problems noted above.
In accordance with this invention there is provided a method of evaluating a sample, comprising transmitting an ultrasound signal through the sample, measuring the time taken for a longitudinal wave of the ultrasound signal to pass through the sample, measuring the time taken for a shear wave of the ultrasound signal to pass through the sample, and determining a parameter of the sample from these two measurements.
From the two time-of-flight measurements, a value may be calculated which is independent of (and therefore does not require measurement of) the path length through the sample: for example this value may be calculated as the ratio of the two times-of-flight. For a given material, the calculated value provides a measure of the degree of plasticity, or liquid fraction, of the material.
It is found that the velocity of the shear wave is significantly less than the velocity of the longitudinal wave, so that a detector will firstly sense arrival of the longitudinal wave and then, after a delay, will sense arrival of the shear wave.
Also in accordance with this invention, there is provided an apparatus for evaluating a sample, comprising non- contacting means for generating an ultrasound signal for passing through the sample, means for measuring the respective times taken for a longitudinal wave and a shear wave of the ultrasound signal to pass through the sample, and for determining a parameter of the sample from these two measurements.
The non-contacting means for generating the ultrasound signal may comprise a pulsed laser directed at one side of the sample: incidence of the pulse of laser light on the sample causes generation of an ultrasound signal having both longitudinal and shear wave components. Non-contacting detection of the ultrasound signal at the opposite side of the sample may be made using an interferometer: this requires a reflective surface finish on that side of the sample. However, the arrangement may be modified so that the detector is positioned on the same side of the sample as the ultrasound generator, and the ultrasound waves pass through the sample in one direction, are reflected from the opposite side and pass through the sample in the return direction towards the detector. Electromagnetic acoustic- transducers (EMATs) may be used as ultrasound generator and/or detector. Preferably a pulsed laser generator is used, together with an EMAT detector, the laser producing an intense ultrasound signal and the EMAT detector avoiding the need for a reflective surface on the sample, yet yielding good signal-to-noise ratio.
An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawing, the single Figure of which is a schematic diagram of an apparatus in accordance with this invention for evaluating a sample.
Referring to the drawing, a pulsed switched laser, for example a q-switched Nd:YAG laser 10, producing 200 mJ, 10 ns pulses, is directed at one side of a sample 12 (e.g. of aluminium alloy) , typically 8mm thick and 19mm in diameter. Incidence of the laser pulse against the side 13 of the sample causes an ultrasound pulse to be generated at the surface and this ultrasound pulse propagates through the sample to its opposite side 14, the ultrasound pulse comprising both longitudinal and shear wave components. The velocity of the longitudinal wave is significantly greater than the velocity of the shear wave, so that the longitudinal wave is the first to arrive at the opposite side 14 of the sample, followed after a delay by the shear wave. Arrival of each wave at the opposite side 14 of the sample causes vibration of the sample surface, the displacements of the surface being in a direction normal to itself but extremely small. A detector 16 is used to sense these displacements.
In the example being discussed, the detector 16 comprises a stabilised HeNe Michelson interferometer directly aligned with the source laser 10. Alternatively, the detector may comprise an EMAT positioned close to the surface 14 of the sample, the EMAT being water cooled.
A control and measurement system 20 of the apparatus is arranged to measure the respective times-of-flight of the longitudinal and shear waves (relative to the instant of emission of a pulse from laser 10) . From these measurements, a value is calculated which is independent of the path length, so that it is not necessary to measure the thickness of the sample: for example this value may be calculated as the ratio of the two times-of-flight.
For each of the longitudinal and shear waves, the velocity decreases as the sample temperature increases, and decreases more sharply after partial melting has occurred. However, this effect is more pronounced with the shear wave, consistent with the fact that the shear wave does not propagate in a liquid whilst the longitudinal wave velocity generally drops by approximately 10%. Accordingly, the ratio of the two times-of-flight (being the inverse ratio of the respective velocities) gives a measure related to the temperature and hence the liquid fraction of the sample.
As shown in dotted lines in the drawings, the detector 16' can be positioned on the same side of the sample as the ultrasound generating means: in this case the ultrasound waves pass through the sample in one direction, are reflected from the opposite side of the sample and then pass through the sample in the opposite direction, to be picked up by the detector.

Claims

1) A method of evaluating a sample, comprising transmitting an ultrasound signal through the sample, measuring the time taken for a longitudinal wave of the ultrasound signal to pass through the sample, measuring the time taken for a shear wave of the ultrasound signal to pass through the sample and determining a parameter of the sample from said measurements.
2) A method of evaluating a sample as claimed in claim 1, comprising calculating the value of the ratio of said measurements.
3) An apparatus for evaluating a sample, comprising non- contacting means for generating an ultrasound signal for passing through the sample, means for measuring the respective times taken for a longitudinal wave and a shear wave of the ultrasound signal to pass through the sample, and for determining a parameter of the sample from these measurements.
4) An apparatus for evaluating a sample as claimed in claim 3, in which the non-contacting means for generating the ultrasound signal comprises a pulsed laser directed at one side of the sample.
5) An apparatus for evaluating a sample as claimed in claim 3 , in which the non-contacting means for generating the ultrasound signal comprises an electromagnetic acoustic transducer.
6) An apparatus as claimed in any of claims 3 to 5, comprising non-contacting means for detecting the ultrasound signal.
7) An apparatus as claimed in claim 6, in which the non- contacting means for detecting the ultrasound is disposed on the opposite side of the sample to the means for generating the signal. 8) An apparatus as claimed in claim 7, in which the non- contacting means for detecting the ultra-sound signal is disposed on the same side of the sample as the means for generating the signal.
9) An apparatus as claimed in claims 6 or 7, in which the non-contacting means for detecting the ultrasound signal comprises an interferometer.
10) An apparatus as claimed in claim 6, in which the non- contacting means for detecting the ultrasound signal comprises an electromagnetic acoustic transducer.
PCT/GB1993/001184 1992-06-03 1993-06-03 Ultrasonic evaluation of a sample WO1993024830A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9211778.7 1992-06-03
GB929211778A GB9211778D0 (en) 1992-06-03 1992-06-03 Ultrasonic evaluation of a sample

Publications (1)

Publication Number Publication Date
WO1993024830A1 true WO1993024830A1 (en) 1993-12-09

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AU (1) AU4341293A (en)
GB (1) GB9211778D0 (en)
WO (1) WO1993024830A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999044051A1 (en) * 1998-02-25 1999-09-02 American Iron And Steel Institute Laser-ultrasound spectroscopy apparatus and method with detection of shear resonances for measuring anisotropy, thickness, and other properties
US9585692B2 (en) 2007-10-19 2017-03-07 Pressure Products Medical Supplies Inc. Transseptal guidewire
CN107967911A (en) * 2016-10-18 2018-04-27 南京理工大学 A kind of optical transducer and method for producing single ultrasonic shear waves

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3416365A (en) * 1965-09-28 1968-12-17 Atomic Energy Commission Usa Method of determining elastic properties of a metal sample
EP0019002A1 (en) * 1978-06-20 1980-11-26 Sumitomo Metal Industries, Ltd. Method and apparatus for non-contact ultrasonic flaw detection
US4602511A (en) * 1985-06-20 1986-07-29 J. A. Green Company Method for measuring fastener stress utilizing longitudinal and transverse ultrasonic wave time-of-flight
WO1988001054A1 (en) * 1986-07-25 1988-02-11 J.A. Green Company Measuring metal hardness utilizing ultrasonic wave time-of-flight
US4790188A (en) * 1986-07-18 1988-12-13 Canadian Patents And Development Limited Method of, and an apparatus for, evaluating forming capabilities of solid plate
WO1989006796A1 (en) * 1988-01-22 1989-07-27 Kline Ronald A System for nondestructively determining composite material parameters
WO1991017009A1 (en) * 1990-05-01 1991-11-14 The Broken Hill Proprietary Company Limited The inspection of continuously cast metals

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3416365A (en) * 1965-09-28 1968-12-17 Atomic Energy Commission Usa Method of determining elastic properties of a metal sample
EP0019002A1 (en) * 1978-06-20 1980-11-26 Sumitomo Metal Industries, Ltd. Method and apparatus for non-contact ultrasonic flaw detection
US4602511A (en) * 1985-06-20 1986-07-29 J. A. Green Company Method for measuring fastener stress utilizing longitudinal and transverse ultrasonic wave time-of-flight
US4790188A (en) * 1986-07-18 1988-12-13 Canadian Patents And Development Limited Method of, and an apparatus for, evaluating forming capabilities of solid plate
WO1988001054A1 (en) * 1986-07-25 1988-02-11 J.A. Green Company Measuring metal hardness utilizing ultrasonic wave time-of-flight
WO1989006796A1 (en) * 1988-01-22 1989-07-27 Kline Ronald A System for nondestructively determining composite material parameters
WO1991017009A1 (en) * 1990-05-01 1991-11-14 The Broken Hill Proprietary Company Limited The inspection of continuously cast metals

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999044051A1 (en) * 1998-02-25 1999-09-02 American Iron And Steel Institute Laser-ultrasound spectroscopy apparatus and method with detection of shear resonances for measuring anisotropy, thickness, and other properties
US6057927A (en) * 1998-02-25 2000-05-02 American Iron And Steel Institute Laser-ultrasound spectroscopy apparatus and method with detection of shear resonances for measuring anisotropy, thickness, and other properties
US9585692B2 (en) 2007-10-19 2017-03-07 Pressure Products Medical Supplies Inc. Transseptal guidewire
CN107967911A (en) * 2016-10-18 2018-04-27 南京理工大学 A kind of optical transducer and method for producing single ultrasonic shear waves
CN107967911B (en) * 2016-10-18 2022-03-15 南京理工大学 Optical transducer and method for generating single ultrasonic transverse wave

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Publication number Publication date
AU4341293A (en) 1993-12-30
GB9211778D0 (en) 1992-07-15

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