GB2292610A - Crack detection in a sheet of material around a fastener hole - Google Patents
Crack detection in a sheet of material around a fastener hole Download PDFInfo
- Publication number
- GB2292610A GB2292610A GB9417083A GB9417083A GB2292610A GB 2292610 A GB2292610 A GB 2292610A GB 9417083 A GB9417083 A GB 9417083A GB 9417083 A GB9417083 A GB 9417083A GB 2292610 A GB2292610 A GB 2292610A
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- United Kingdom
- Prior art keywords
- sheet
- crack
- transducer
- transducers
- hole
- Prior art date
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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
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/221—Arrangements for directing or focusing the acoustical waves
-
- 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
- G01N29/043—Analysing solids in the interior, e.g. by shear waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/042—Wave modes
- G01N2291/0421—Longitudinal waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/042—Wave modes
- G01N2291/0422—Shear waves, transverse waves, horizontally polarised waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/042—Wave modes
- G01N2291/0428—Mode conversion
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/044—Internal reflections (echoes), e.g. on walls or defects
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/10—Number of transducers
- G01N2291/102—Number of transducers one emitter, one receiver
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/26—Scanned objects
- G01N2291/269—Various geometry objects
- G01N2291/2691—Bolts, screws, heads
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
Cracks (14) can be detected in one or more sheets (1, 2) of material such as aluminium in the vicinity of a fastener hole (3) through the sheet whilst the fastener remains in position in the hole (3). Two focussed longitudinal wave ultrasonic transducers (4, 5) are located at an angle to the top surface of the top sheet (1) on diametrically opposite sides of the fastener and hole (3), coupled to the sheet surface and pulsed ultrasonic energy is fed to one transducer (4) and converted therein to a focussed shear wave beam (6) which is passed in transmission obliquely into the material in the direction of the hole (3) and any crack if present. The presence of a crack creates a shadow region by relative changes in acoustic transparency through the sheet material which shadow region is picked up by scanning the other transducer (5) in synchronism with the transducer (4) and presented visually whereby both the position and size of the crack can be ascertained directly or indirectly from the visual image. <IMAGE>
Description
METHOD FOR CRACK DETECTION IN A SHEET OF MATERIAL AROUND A
FASTENER HOLE
This invention relates to a method for detection of cracks in at least one sheet of material in the vicinity of a fastener hole through the sheet whilst the fastener remains in place in the hole.
Non destructive testing for cracks in sheet material such as aluminium around fastener holes is of vital importance in many industries such as in the field of aviation. For example as part of the maintenance schedule for commercial aircraft there is a requirement to be able to detect and size fatigue cracks forming around fastener holes. In particular there is a need to know the size of the crack before starting a repair as this avoids unnecessary removal of material from around the fastener hole and leads to a more cost effective maintenance procedure. Removal of unnecessary material from around the fastener hole weakens the structure requiring either infill of fresh material, plating or use of oversize fasteners all of which could give rise to future maintenance problems and potential future stress problems which could lead to future incipient cracking.
Conventional non destructive testing techniques for the detection and sizing of cracks around fastener holes use either eddy currents or ultrasonic waves. Eddy currents are effective for detection of cracks but are inefficient at sizing the cracks particularly if they are located at any appreciable depth within the material being checked. This draw back is particularly exacerbated if testing is carried out with the fastener in situ.
Conventional ultrasonic testing methods generally rely on generating longitudinal sound waves incident normally at the surface of mechanically fastened sheet structures. These are difficult to use effectively because the crack if present is substantially shielded by the counterbore of the fastener hole and is also usually orientated in a plane perpendicular to the surface subtending little cross-sectional area to the incident beam. This results in small amounts of acoustic energy scattering back into a receiving transducer.
It has been proposed that shear waves be produced in the material beneath the counter bore to impinge obliquely incident on the crack. Shear waves are usually generated either by use of a contact shear wave transducer or of a longitudinal wave transducer immersed in water, both of which are aligned with their axis at an oblique angle with the surface of the test piece. A common procedure is the use of a hand-held transducer that is manually moved around the fastener. This of course is very operator skill dependent, relatively inefficient and does not provide any indication of crack size.
Conventional attempts to overcome or reduce these difficulties have involved mechanically locating the transducer on a scanning system relative to the fastener.
Some techniques employ rotary scanning around the fastener hole and others require linear scanning. Such known techniques work in pulsed echo mode.
There is thus a need for a generally improved non destructive testing procedure for detection of cracks around fastener holes in sheet material which at least minimises the aforegoing difficulties and which enables crack size measurements to be taken with improved accuracy.
According to one aspect of the present invention there is provided a method for detection of cracks in at least one sheet of material in the vicinity of a fastener hole through the sheet whilst the fastener remains in place in the hole, in which two focused longitudinal wave ultrasonic transducers are located at an angle with respect to the sheet's surface on diametrically opposite sides of the fastener and hole, coupled to said sheet surface, pulsed ultrasonic energy is fed to at least one said transducer, a focused shear wave beam generated thereby by mode conversion from a longitudinal wave is passed in transmission obliquely into the sheet material in the direction of the hole therethrough incident to any crack if present which thereby creates a shadow region, and an image of the shadow region, showing visually a crack if present, is formed by scanning the other of said transducers in synchronism with the one said transducer, which other said transducer acts as a receiver for the shear wave beam elements transmitted by the crack, sheet material and sheet surface most remote from the transducers to form the shadow region image by relative changes in acoustic transparency through the sheet material.
Preferably said two transducers are located at an angle of incidence in the range of from 13 to 29 degrees.
Conveniently said two transducers are located at an angle of incidence in the range of from 18 to 20 degrees.
Advantageously said two transducers are located such that the angle of incidence of the shear wave beam to a crack within the sheet of material is in the range of from 42 to 45 degrees to said crack.
Preferably said two transducers are coupled to said sheet surface by water.
Conveniently the or each transducer is operated at a frequency in the range of from 10 to 15 MHz.
Advantageously the method of the invention is employed for crack detection in a pair of sheets of material separated by a substantially acoustically transparent sealant layer, in which said pair of sheets is immersed in water for transducer coupling purposes.
Preferably the pulsed ultrasonic energy is provided by an ultrasonic pulser receiver and in which scanning is carried out using a C-scan system interfaced to the pulser receiver, and a computer controller.
Conveniently the length of a crack detected is ascertained directly or indirectly from the shadow region image.
For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:
Figure 1 is a graphic representation of the influence of transducer aperture size on the measured amplitude of shear waves for use in the method of the present invention,
Figure 2 is a diagrammatic shear and longitudinal ray diagram for a 25 mm radius of curvature, 6mm diameter transducer, for a water/aluminium interface,
Figure 3 is a shear and longitudinal ray diagram similar to that of Figure 2 but with the interface inclined at 19.5 degrees to the normal,
Figure 4 is a diagrammatic representation of possible ray paths for a shear wave incident on cracks adjacent to a fastener hole, shown in transmission mode according to the method of the present invention and showing shadow regions in a two plate system and,
Figure 5 is a transmission shear wave scan picture produced according to the method of the present invention, to an enlarged scale, using two focused wave transducers and showing a crack in a fastener hole in a plate with a fastener in situ.
The present invention as illustrated in the accompanying drawings provides a method for detection of cracks in at least one sheet of material such as the two aluminium sheets shown in Figure 4. In Figure 4 is shown a front sheet 1 of aluminium and a rear sheet 2 of aluminium. The method enables cracks to be detected in the sheets 1 and 2 in the vicinity of a fastener hole 3 therethrough whilst the fastener remains in place in the hole 3.
In the method two focused longitudinal ultrasonic transducers 4 and 5 are employed of which 4 provides a focused shear wave transmitted beam with rays 6, and 5 acts as a receiver. The transducers 4 and 5 are located at an angle of incidence a preferably in the range of from 13 to 29 degrees and more preferably in the range of from 18 to 20 degrees such as 18 as shown or 19.5 degrees, with respect to a normal to the surface of the sheet 1 on diametrically opposite sides of the fastener and hole 3.
The two transducers 4 and 5 are located such that the angle of incidence ss of the shear wave beam to a crack within the sheet of material is in the range of from 42 to 45 degrees and preferably 45 degrees as to the surface of the front sheet 1.
The transducers 4 and 5 operate as focused shear wave transducers with an angle of incidence to a normal to the the front plate 1 of 19.5 degrees and at a separation preferably of 3mm from the surface of the plate 1 to which they are coupled by a layer of water. For a plane wave transducer the size of aperture on each transducer effects the width of ultrasonic beam omitted therefrom. Figure 1 shows a curve 7 obtained with no aperture, a curve 8 obtained with a 5mm aperture, a curve 9 obtained with a 3mm aperture and a curve 10 obtained with a 1.5mm aperture. The plot in Figure 1 is shown of incidence angle of the wave to the surface of the plate 1 versus the shear wave amplitude in db. The shear waves were generated in the transducer under test which operated at a frequency of 1OMHz by mode conversion from a longitudinal sonic wave.
Figure 1 shows that with the plane wave transducer in question the best resolution was obtained at 1OMHz with a 1.5mm aperture with the transducer placed about 3mm from the surface of a scattering plate. Although these results were obtained from the measured amplitude of shear wave scattered from a 1.5mm cylindrical hole 8mm deep in an aluminium block they are generally applicable to the method of the present invention.
The most efficient angles over which shear waves are generated occurs between the longitudinal and shear critical angles which for an aluminium sheet and a transducer coupled by immersion in water were found to be 13.5 degrees and 28.2 degrees respectively. The shear wave is produced in the method according to the present invention by means of a longitudinal wave focused transducer.
Figure 2 shows a simple ray diagram for a 25mm radius of curvature transducer, diameter 6mm, oriented at an incidence angle of 19.5 degrees and located at a distance of 3mm from the upper surface of a sheet of aluminium 1 to which it is coupled by a water layer 11. Figure 2 shows a plane which is at right angles to a plane which contains the transducer axis and a normal to the surface to the aluminium sheet 1. The generated longitudinal waves are shown at 12 and the shear waves produced are shown at 13.
Figure 3 is a diagram similar to that of Figure 2 but taken in a plane which contains the transducer axis and a normal to the surface of the sheet 1. As shown in Figure 3 the shear focus is no longer a spot but is drawn out into a curve known as a caustic surface characterised by zero intensity on one side and large intensity on the other. Because the transducer subtends only a small area of its surface at angles less than the longitudinal critical angle, only a small longitudinal wave caustic is generated. The plane directions xy are shown also in
Figure 3.
Tests utilising reference test pieces in which test slots had been machined in the fastener hole area using a front sheet of aluminium of lOmm thickness attached by an acoustically transparent sealant to a rear sheet of aluminium of thickness 8mm showed that the best depth of penetration of the ultrasonic shear wave was produced by a 50mm radius of curvature transducer operating at a frequency of 1OMHz.
Ultrasonic signals were generated by a pulser receiver such as a Krautkramer USIP 12 receiver interfaced to a C-scan amplitude digitisation system with a computer controller. Suitable transducers are those manufactured by KB Aerotech. The standard C-scan software permitted positioning of an electronic gate over the required region of the time domain signal thus allowing the scan to be made over the whole area of the sheet 1.
In accordance with the method of the invention, pulsed ultrasonic energy is fed to the transmitter transducer 4 as shown in Figure 4 where cracks are shown at 14. The focused shear wave beam 6 generated thereby by mode conversion from a longitudinal wave is passed in transmission obliquely into the material of the sheets 1 and 2 in the direction of the hole 3 therethrough incident to the cracks 14 which are in effect provided in the test piece sample by machined slots. The cracks 14 thereby create a shadow region making use of the characteristic that images are formed by relative changes in acoustic transparency in the material being tested. There is no requirement for scattering or reflection of signals back into the transmitting transducer 4.
In the example shown in Figure 4 where there is a sealant layer between the two sheets 1 and 2 simply gating the signal on the rear wall 2a of the rear sheet 2 allows both sheets to be inspected simultaneously for cracks. It is preferred to conduct two scans, one with the gate placed over the rear wall la of the front plate and the other with the gate placed over the rear wall 2a of the rear plate 2. In both cases if focused transducers are being used, focusing should be optimised with the transmitting transducer 4 and receiving transducer 5 focused to the same depth.
For example with cracks located at either the base of the front sheet 1 or the top of the rear plate 2, with the gate over the rear wall 2a of the rear plate 2, the transmitting transducer 4 should be focused at the rear wall la of the front plate 1 and the receiver transducer 5 should be focused to include the extra path length involved with the reflection at the rear wall 2a of the rear plate 2. As can be seen from Figure 4, each crack 14 provides a shadow region 15 which is picked up and presented on a display screen to show visually the presence of a crack such as is shown in Figure 5 in which one crack 14 is shown at 16 by dips in the normal transmitted outline shape of the fastener hole. the crack appears to be partly filled with a medium which provides some acoustic transmission.
In this instance both transducers used were 1OMHz focused wave transducers, one with a 50mm radius of curvature and the other with a 25mm radius of curvature.
The gate was positioned on the rear wall 2a of the rear sheet 2. All scans were made linearly using an incidence angle of approximately 18 degrees. A jig 17 was used which permitted both transducers 4 and 5 to be located on the front end of the scanning arm 18 so that they could be held at a fixed position from each other and at fixed angles and distances from the surface of the front sheet 1.
The front sheet 1 had a thickness of 4mm and the rear sheet 2 had a thickness of 7.5mm. The crack 14 in the rear sheet 2 had a length of 8mm, and imaging of the crack was via the sealant layer.
The image example shown in Figure 5 was produced using a 10 MHz frequency transducer with a radii of curvature of about 25mm for the transmitting transducer 4 and a 10 MHz frequency transducer of 50mm focal length for the receiver transducer 5. Preferably the receiving transducers should have a focal length of approximately 75mm. Estimates of slot size were made from the shadow image based on distances between 6db points at the edge of the slot and the edge of the fastener to give a value of 7.5mm. The actual size of the slot in question was 8mm.
Preferably the transducers are operated at a frequency in the range of from 10 to 15MHz.
With the method of the present invention it has been found that so long as the crack or slot casts a shadow, the orientation of the slot or crack was not critical for transmission. In general terms smaller beam width some waves emitted from the transducer 4 results in more accurate crack size estimation. The influence of crack reflectivity on apparent crack size is less with the transmission method of the present invention than with conventional pulse-echo ultrasonic techniques which require compromised gain levels to be set to avoid signal truncation and saturation. On the contrary in the transmission method of the present invention all that is required is that the "darkness" of the shadow region in the transmission mode falls below a defined level, for example 6db levels, as any further drop below this level will not affect the apparent size. With the method of the present invention cracks in the front sheet 1 can be sized to about 0.5mm error and slots in the rear sheet 2 can be sized to about 0.5mm error.
Claims (10)
1. A method for detection of cracks in at least one sheet of material in the vicinity of a fastener hole through the sheet whilst the fastener remains in place in the hole, in which two focused longitudinal wave ultrasonic transducers are located at an angle with respect to the sheet's surface on diametrically opposite sides of the fastener and hole, coupled to said sheet surface, pulsed ultrasonic energy is fed to at least one said transducer, a focused shear wave beam generated thereby by mode transmission from a longitudinal wave is passed in transmission obliquely into the sheet material in the direction of the hole therethrough, incident to any crack if present which thereby creates a shadow region, which is reflected at the sheet surface most remote from the transducers, and an image of the shadow region, showing visually a crack if present, is formed by scanning the other of said transducers in synchronism with the one said transducer, which other said transducer acts as a receiver for the shear wave beam elements transmitted by the crack, sheet material and sheet surface most remote from the transducers to form the shadow region image by relative changes in acoustic transparency through the sheet material.
2. A method according to claim 1, in which said two transducers are located at an angle of incidence in the range of from 13 to 29 degrees.
3. A method according to claim 1 or claim 2, in which said two transducers are located at an angle of incidence in the range of from 18 to 20 degrees.
4. A method according to claim 2 or claim 3, in which said two transducers are located such that the angle of incidence of the shear wave beam to a crack within the sheet of material is in the range of from 42 to 45 degrees to said crack.
5. A method according to any one of claims 1 to 4 in which said two transducers are coupled to said sheet surface by water.
6. A method according to any one of claims 1 to 5, in which the or each transducer is operated at a frequency in the range of from 10 to 15 MHz.
7. A method according to any one of claims 1 to 6, employed for crack detection in a pair of sheets of material separated by a substantially acoustically transparent sealant layer, in which said pair of sheets is immersed in water for transducer coupling purposes.
8. A method according to any one of claims 1 to 7, in which the pulse ultrasonic energy is provided by an ultrasonic pulser receiver and in which scanning is carried out using a C-scan system interfaced to the pulser receiver, and a computer controller.
9. A method for detection of cracks in at least one sheet of material in the vicinity of a fastener hole through the sheet whilst the fastener remains in place in the hole, substantially as hereinbefore described and as illustrated in Figure 1, Figures 2 and 3, Figure 4 or
Figure 5 of the accompanying drawings.
10. A method according to any one of claims 1 to 9, in which the length of a crack detected is ascertained directly or indirectly from the shadow region image.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9417083A GB2292610B (en) | 1994-08-24 | 1994-08-24 | Method for crack detection in a sheet of material around a fastener hole |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9417083A GB2292610B (en) | 1994-08-24 | 1994-08-24 | Method for crack detection in a sheet of material around a fastener hole |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9417083D0 GB9417083D0 (en) | 1994-10-19 |
| GB2292610A true GB2292610A (en) | 1996-02-28 |
| GB2292610B GB2292610B (en) | 1998-08-05 |
Family
ID=10760322
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9417083A Expired - Fee Related GB2292610B (en) | 1994-08-24 | 1994-08-24 | Method for crack detection in a sheet of material around a fastener hole |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2292610B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7328619B2 (en) * | 2002-07-30 | 2008-02-12 | R/D Tech Inc. | Phased array ultrasonic NDT system for fastener inspections |
| WO2009133384A1 (en) | 2008-05-01 | 2009-11-05 | Airbus Uk Limited | Ultrasound inspection method and apparatus |
| US20150320383A1 (en) * | 2014-05-06 | 2015-11-12 | University Of Washington | Methods and Systems for Estimating a Size of an Object in a Subject with Ultrasound |
| CN106315444A (en) * | 2016-08-11 | 2017-01-11 | 辽宁工程技术大学 | Lifting device used for deep hole shear wave velocity testing |
| US11047831B2 (en) | 2019-07-15 | 2021-06-29 | Kellogg Brown & Root Llc | Nondestructive inspection apparatus and methods of use |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1203854A (en) * | 1967-06-09 | 1970-09-03 | Automation Ind Inc | Material tester |
| GB2151786A (en) * | 1983-12-19 | 1985-07-24 | Atomic Energy Authority Uk | Ultrasonic flaw detection |
| EP0177053A2 (en) * | 1984-10-04 | 1986-04-09 | Mitsubishi Denki Kabushiki Kaisha | Method of detecting flaws in thick wall steel pipe with ultrasonic angle beam technique and apparatus therefor |
-
1994
- 1994-08-24 GB GB9417083A patent/GB2292610B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1203854A (en) * | 1967-06-09 | 1970-09-03 | Automation Ind Inc | Material tester |
| GB2151786A (en) * | 1983-12-19 | 1985-07-24 | Atomic Energy Authority Uk | Ultrasonic flaw detection |
| EP0177053A2 (en) * | 1984-10-04 | 1986-04-09 | Mitsubishi Denki Kabushiki Kaisha | Method of detecting flaws in thick wall steel pipe with ultrasonic angle beam technique and apparatus therefor |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7328619B2 (en) * | 2002-07-30 | 2008-02-12 | R/D Tech Inc. | Phased array ultrasonic NDT system for fastener inspections |
| WO2009133384A1 (en) | 2008-05-01 | 2009-11-05 | Airbus Uk Limited | Ultrasound inspection method and apparatus |
| CN102027365B (en) * | 2008-05-01 | 2012-09-05 | 空中客车操作有限公司 | Ultrasound inspection method and apparatus |
| US20150320383A1 (en) * | 2014-05-06 | 2015-11-12 | University Of Washington | Methods and Systems for Estimating a Size of an Object in a Subject with Ultrasound |
| CN106315444A (en) * | 2016-08-11 | 2017-01-11 | 辽宁工程技术大学 | Lifting device used for deep hole shear wave velocity testing |
| US11047831B2 (en) | 2019-07-15 | 2021-06-29 | Kellogg Brown & Root Llc | Nondestructive inspection apparatus and methods of use |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2292610B (en) | 1998-08-05 |
| GB9417083D0 (en) | 1994-10-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20000824 |