GB2220493A - Extensometer probe - Google Patents
Extensometer probe Download PDFInfo
- Publication number
- GB2220493A GB2220493A GB8816242A GB8816242A GB2220493A GB 2220493 A GB2220493 A GB 2220493A GB 8816242 A GB8816242 A GB 8816242A GB 8816242 A GB8816242 A GB 8816242A GB 2220493 A GB2220493 A GB 2220493A
- Authority
- GB
- United Kingdom
- Prior art keywords
- probe arrangement
- arrangement according
- extensometer
- strain
- protuberances
- Prior art date
- Legal status (The legal status 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 status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
- G01B7/18—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge using change in resistance
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
A probe is provided for application to a location on the surface of an object (1) for measuring mechanical strain in the object (1) at the location. It comprises three strain gauge extensometer devices (2, 3, 4) mechanically interconnected in series to present a base of substantially triangular shape and is provided with three sharp protuberances (13, 14, 15) extending from the base such that one protuberance is provided at each apex region of the triangular base where the extensometer devices (2, 3, 4) interconnect. The arrangement is applied to the surface of the object (1) such that the sharp protuberances (13, 14, 15) make pressure-contact with the surface, strain gauges (9) on the extensometers being adapted to be connected to circuit means whereby a measure of the mechanical strain in the object (1) in three directions at the location thereon may be provided. <IMAGE>
Description
TITLE: PROBE ARRANGEMENT
This invention concerns a probe arrangement which may conveniently be hand-held and which can be readily and temporarily applied to a location on the surface of an object for measuring mechanical strain in the object at the location. In particular, the invention provides such a probe arrangement which provides output data for the strain in three predetermined directions in the surface of the object and enables values of principal stress and strain to be readily computed.
The present invention provides a probe arrangement for application to a location on the surface of an object, for measuring mechanical strain in the object at the said location, said arrangement comprising three strain gauge extensometer devices mechanically interconnected in series to present a base of substantially triangular shape, said arrangement being provided with three sharp protuberances extending from the base such that one protuberance is provided at each apex region of the triangular base where said extensometer devices interconnect, said arrangement being adapted to be applied to the surface such that the sharp protuberances make pressure-contact with the surface, strain gauges on the extensometers being adapted to be electrically connected to circuit means whereby a measure of the mechanical strain in the structure in three directions at the location thereon may be provided.
Each of tne protuberances is suitably provided with one or more sharp points or edges. The sharp points or edges may suitably be of a hard metal or a hard crystal such as diamond.
The probe arrangement may be suitably clamped against the surface of the object by a variety of means while being used to measure the strain. Such means may include hand, finger or thumb pressure or magnetic or suction arrangements. Temporary bonding means, including spot welding, may also be adopted. It is, however, important that the means used to clamp the probe arrangement to the surface does not interfere with the operation of the extensometers.
A separate frame or structure is suitably provided for application to the probe arrangement to enable pressure to be applied to the region of the protuberances from above the probe arrangement. Such a frame or structure conveniently comprises legs arranged to extend from a plate above the probe arrangement to the region of the protuberances, the legs being provided with feet suitably shaped to engage with the protuberances.
The protuberances may suitably be mounted on shafts which fit into appropriately dimensioned holes in the probe arrangement. Such shafts may also conveniently serve as link pins for interconnecting the three extensometer devices.
The strain gauge extensometer devices suitably comprise well-known forms which are also used in load-cell constructions. Such extensometers may involve parallelogram, cantilever, caliper, or double bending beam arrangements.
The strain gauges employed in the extensometer devices may comprise any of the well-known forms, such as foil, deposited film, or wire, electrical resistance gauges, or semiconductor gauges.
The gauges on each extensometer device may be suitably electrically interconnected in part or full Wheatstone bridge configuration with terminations provided for connection to external circuits.
In a preferred embodiment, the said base of substantially triangular shape is in the shape of an equilateral triangle with strain-sensing axes of the extensometer devices along the sides of the triangle.
With this embodiment, principal stresses and strains can be readily canputed from the output data received from the extensometer devices, using known standard equations applicable to 'delta' type bondable strain gauge rosettes.
Other variations in the triangular shape would require computations of the principal stresses and strains to be carried out using 'rectangular' rosette equations or more general standard equations.
Circular means graduated according to angular notation may be provided for securing to the probe arrangement or the associated frame or structure, said circular means also having means for indicating a reference axis relative to one of the extensometer devices, pointer means being provided arranged for rotation relative to the circular graduated means whereby a direction of principal stress or strain may be indicated on the surface of the object by setting the pointer means to an angle of principal stress or strain following computation thereof from data derived from the three extensometer devices.
The said circular means may conveniently be provided in the shape of a top hat, with graduations provided on a rim thereof.
The pointer means is suitably provided on a band which is frictionally rotatable about the top hat shaped circular means and such that the pointer means traverses the graduations. Preferably the pointer means incorporates two diametrically opposed pointers provided on the band.
The means for indicating a reference axis preferably comprises two diametrically opposed pointers on the said circular means.
The invention is now described by way of example with reference to the accompanying drawings in which:
Figure 1 represents a view, in elevation, of a probe arrangement according to the invention;
Figure 2 represents a plan view of the arrangement of Figure 1;
Figure 3 represents a view, in elevation, of a structure for clamping the probe arrangement of Figure 1 to the surface of an object under test;
Figure 4 represents a sectional view through A-A' in the structure of
Figure 3.
Figure 5 represents a part-sectional view of the structure of Figure 3 provided with an added arrangement for indicating a reference axis and direction of a computed principal stress or strain.
Figure 6 represents a top plan view of the structure shown in Figure 5.
Figure 7 represents an exploded view of the added arrangement of
Figures 5 and 6.
Referring to Figures 1 and 2, a probe arrangement is provided for application to a location on the surface of an object 1 for measuring mechanical strain at that location in the object 1. The object 1 may, for example, be a material test sample or a vehicle structure or a pressure vessel, or possibly a ship or a structure such as a bridge.
The probe arrangement comprises three identical strain gauge extensometer devices 2, 3, 4 interconnected in series to present an equilateral triangular base as shown in Figure 2. The extensometers are suitably constructed from a metal or alloy of suitable transducer quality, according to well-known transducer flexure design principles and substantially of known parallelogram form. Only extensometer 2 is shown completely in Figure 1 and is shaded to aid identification.
Extensometer 2 has an end portion 2A which is mechanically connected to an end portion 3B of extensometer 3 and has an opposite end portion 2B which is mechanically connected to an end portion 4A of extensometer 4. Extensometers 3 and 4 have correspondingly connected end portions 3A and 4B. As shown for extensometer 2, each extensometer has a slot 5 provided in it and two holes 6, 7 interconnected by a further slot 8.
Arrangements of this nature are well known in transducer technology.
Strain gauges 9 of well known form (eg metal foil resistance type) are bonded to the exterior surface of each extensometer adjacent the holes 6, 7 and electrically connected in known Wheatstone bridge configuration. Terminal lead wires (not shown) are provided for connecting the strain gauge networks to appropriate external signal conditioning and computation circuitry.
It will be apparent to those skilled in the art that the strain gauges 9 will respond to deflections of the extensometer 2 which causes end portions 2A, 2B to move closer together or further apart.
(Similarly for end portions 3A, 3B and end portions 4A, 4B of extensometers 3 and 4).
The extensometers 2, 3 and 4 are connected together by pins 10, 11, 12 (Figure 2) which permit some degree of pivotability of the interconnected parts. Pins 10, 11, 12 are conveniently joined to three protuberances 13, 14, 15 which have sharp pointed ends 13A, 14A, 15A and which are adapted to be pressed in contact with the surface of the object 1. The pointed ends 13A, 14A, 15A may be of hard metal or be coated with fine particles of a hard material such as diamond.
It is required to maintain the probe arrangement with the protuberances 13, 14, 15 pressed in contact with the surface of the object 1 for a period long enough to enable the necessary measurements of strain in the surface of the object 1 to be made. Any changes in strain will result in the protuberances moving away from or towards one another by a very small amount and such movement will be transmitted to the extensometers 2, 3, 4 and sensed by the strain gauges 9. Electrical outputs from the three extensometers provide a measure of the strain in the surface of the object in the three directions of the extensometers on the surface.With dedicated signal conditioning, analogue to digital conversion and an appropriately programmed computer, measurement of changes in the surface stress or strain at the location of the probe arrangement can be readily and instantly obtained, with little regard to the condition of the surface of the object 1, ie whether it is rough or smooth, hard or soft, clean or dirty, coated or uncoated, hot or cold.
Computation of the principal stresses and strains is effected using the standard well-known equations derived for 'delta' type bonded strain gauge rosettes.
The probe arrangement is readily moved from one location to another on the surface of the object 1 as required.
It is important that pressure applied to the probe arrangement to hold it in good contact with the surface does not hamper operation of the extensometers 2, 3, 4. A structure shown in Figures 3 and 4 provides a convenient way of applying pressure directly to the protuberances 13, 14, 15 on the probe arrangement, from above the arrangement without contacting the extensometers themselves.
This structure, which may have a degree of inherent mechanical flexibility, comprises a circular plate 16 from which- three legs 17 extend, the legs having slotted feet 18. The circular plate 16 overlies the extensometers 2, 3, 4 without contacting them and the legs 17 extend down the outside of the probe arrangement without contacting it. The feet 18 locate with the protuberances 13, 14, 15 on the probe arrangement. By this means, pressure applied, eg by hand, to the plate 16 is transmitted directly to the protuberances 13, 14, 15 and the probe arrangement is thereby clamped to the surface of the object 1 for test purposes.
Because stress and strain are vector quantities, values of principal stress or strain computed in respect of the object 1 have both magnitude and direction The appropriate direction, which is obtained by calculation from the output data provided by the three extensometer devices 2, 3, 4, is referenced to a particular extensometer axis and it is desirable to be able to indicate on the surface of the object 1, at the location where the probe arrangement is placed, the reference axis and the direction of the principal stress or strain. An arrangement for achieving this is shown in Figures 5, 6, 7 and is mounted on and secured to the structure described with reference to
Figures 3 and 4.
A top-hat shaped housing 19, constructed of a plastics or light metal alloy material, is secured to the top plate 16 by one or more threaded fasteners (not shown). A circular rim 20 of the housing has graduations 21 in degrees marked on it in clockwise and anti-clockwise directions from a reference axis 22 which is identified by two diametrically opposed pointers or arrows 22A and 22B marked on the rim 20. The reference axis 22 is arranged to be aligned with axis 23 of one of the extensometers which is selected as a reference.A circular band 24, provided with two diametrically opposed pointers 25 A and 25 B, appropriately of transparent plastics material, is located around the top-hat shaped housing so that it can be rotated thereon with the pointers 25A, 25B traversing the graduations 21 on the rim 20 of the housing, but such that there is friction between the band 24 and the housing 19 sufficient to hold the band in a pre-set position of rotation while allowing easy rotation by hand to a desired position. With the probe arrangement held in a desired location on the surface of the object 1, the reference axis 22 can be marked on the surface of the object.
When an angle defining the direction of principal stress or strain has been computed from output data derived from the extensometer devices 2, 3, 4, the band 24 is rotated by hand until the pointers 25A, 25B lie over the graduation 21 on the rim 20 of the housing denoting that particular angle. The direction of the principal stress or strain can then be marked on the surface of the object by drawing a line passing through the positions of pointers 25A, 25B.
Claims (17)
1A probe arrangement for application to a location on the surface of an
object, for measuring mechanical strain in the object at the said
location, said arrangement comprising three strain gauge extensometer
devices mechanically interconnected in series to present a base of
substantially triangular shape, said arrangement being provided with
three sharp protuberances extending from the base such that one
protuberance is provided at each apex region of the triangular base
where said extensometer devices interconnect, said arrangement being
adapted to be applied to the surface such that the sharp protuberances
make pressure-contact with the surface, strain gauges on the
extensometers being adapted to be electrically connected to circuit
means whereby a measure of the mechanical strain in the object in
three directions at the location thereon may be provided.
2 A probe arrangement according to Claim 1 in which each of the
protuberances is provided with one or more sharp points or edges.
3 A probe arrangement according to Claim 2 in which the sharp points or
edges comprise a hard metal or a hard crystal.
4 A probe arrangement according to Claim 3 in which the crystal
comprises a diamond.
5 A probe arrangement according to any preceding Claim, adapted to be
clamped against the surface of the object while being used to measure
the strain.
6 A probe arrangement according to Claim 5 adapted to be clamped against
the surface of the object by means selected from hand, finger or thumb
pressure, or magnetic or suction arrangements, or temporary bonding
means
7 A probe arrangement according to any preceding Claim in which a
separate frame or structure is provided for application thereto to
enable pressure to be applied to the region of the protuberances from
above the probe arrangement.
8 A probe arrangement according to Claim 7 in which the frame or
structure comprises legs arranged to extend from a plate above the
probe arrangement to the region of the protuberances, the legs being
provided with feet suitably shaped to engage with the protuberances.
9 A probe arrangement according to any preceding Claim in which the
protuberances are mounted on shafts which fit into appropriately
dimensioned holes in the probe arrangement.
10 A probe arrangement according to Claim 9 in which the shafts also
serve as link pins for interconnecting the three extensometer devices.
11 A probe arrangement according to any preceding Claim in which the
extensometers involve parallelogram, or cantilever, or caliper, or
double bending beam arrangements.
12 A probe arrangement according to any preceding Claim incorporating
strain gauges selected from foil, deposited film, and wire, electrical
resistance gauges, or from semiconductor gauges.
13 A probe arrangement according to Claim 12 in which the gauges on each
extensometer device are electrically interconnected in part or full
Wheatstone bridge configuration with terminations provided for
connection to external circuits.
14 A probe arrangement according to any preceding Claim in which the base
of substantially triangular shape is in the shape of an equilateral
triangle with strain-sensing axes of the extensometer devices along
the sides of the triangle.
15 A probe arrangement according to any preceding Claim in which circular
means graduated according to angular notation is provided for securing
thereto or to the associated frame or structure, where provided, the
circular means also having means for indicating a reference axis
relative to one of the extensometer devices, pointer means being
provided arranged for rotation relative to the circular graduated
means whereby a direction of principal stress or strain may be
indicated on the surface of the object by setting the pointer means to
an angle of principal stress or strain following computation thereof
from data derived from the three extensometer devices.
16 A probe arrangement according to Claim 15 in which the circular means
is provided in the shape of a top hat, with graduations provided on a
rim thereof.
17 A probe arrangement constructed and arranged substantially as hereinbefore
described with reference to the accompanying drawings.
17 A probe arrangement according to Claim 16 in which pointer means is
provided on a band which is frictionally rotatable about the top hat
shaped circular means and such that the pointer means traverses the
graduations.
18 A probe arrangement according to Claim 17 in which the pointer means
incorporates two diametrically opposed pointers provided on the band.
19 A probe arrangement according to any of Claims 15 to 18 in which the
means for indicating a reference axis comprises two diametrically
opposed pointers on the circular means.
20 A probe arrangement constructed and arranged substantially as
hereinbefore described with reference to the accompanying drawings.
Amendments to the claims have been filed as follows 1 A probe arrangement for application to a location on the surface of an
object, for measuring mechanical strain in the object at the said
location, said arrangement comprising three strain gauge extensometer
devices mechanically interconnected in series to present a base of
substantially triangular shape, said arrangement being provided with three
sharp protuberances extending from the base such that one protuberance is
provided at each apex region of the triangular base where said
extensometer devices interconnect, said arrangement being adapted to be
applied to the surface such that the sharp protuberances make
pressure-contact with the surface, strain gauges on the extensometers
being adapted to be electrically connected to circuit means whereby a
measure of the mechanical strain in the object in three directions at the
location thereon may be provided, a frame or structure being provided
which is adapted and arranged to enable pressure to be applied to the
region of the protuberances from above the arrangement.
2 A probe arrangement according to Claim 1 in which the frame or structure
comprises legs arranged to extend from a plate above the probe arrangement
to the region of the protuberances, the legs being provided with feet
suitably shaped to engage with the protuberances.
3 A probe arrangement according to Claim 1 or 2 in which each of the
protuberances is provided with one or more sharp points or edges.
4 A probe arrangement according to Claim 3 in which the sharp points or
edges comprise a hard metal or a hard crystal.
5 A probe arrangement according to Claim 4 in which the crystal comprises a
diamond.
6 A probe arrangement according to any preceding Claim in which the
protuberances are mounted on shafts which fit into appropriately
dimensioned holes in the probe arrangement.
7 A probe arrangement according to Claim 6 in which the shafts also serve as
link pins for interconnecting the three extensometer devices.
8 A probe arrangement according to any preceding Claim in which the
extensometers involve parallelogram, or cantilever, or caliper, or double
bending beam arrangements.
9 A probe arrangement according to any preceding Claim incorporating strain
gauges selected from foil, deposited film, and wire, electrical resistance
gauges, or from semiconductor gauges.
10 A probe arrangement according to Claim 9 in which the gauges on each
extensometer device are electrically interconnected in part or full
Wheatstone bridge configuration with terminations provided for connection
to external circuits.
11 A probe arrangement according to any preceding Claim in which the base of
substantially triangular shape is in the shape of an equilateral triangle
with strain-sensing axes of the extensometer devices along the sides of
the triangle.
12 A probe arrangement according to any preceding Claim in which circular
means graduated according to angular notation is provided for securing
thereto or to the associated frame or structure, the circular means also
having means for indicating a reference axis relative to one of the
extensometer devices, pointer means being provided arranged for rotation
relative to the circular graduated means whereby a direction of principal
stress or strain may be indicated on the surface of the object by setting
the pointer means to an angle of principal stress or strain following
computation thereof from data derived from the three extensometer devices.
13 A probe arrangement according to Claim 12 in which the circular means is
provided in the shape of a top hat, with graduations provided on a rim
thereof.
14 A probe arrangement according to Claim 13 in which pointer means is
provided on a band which is frictionally rotatable about the top hat
shaped circular means and such that the pointer means traverses the
graduations.
15 A probe arrangement according to Claim 14 in which the pointer means
incorporates two diametrically opposed pointers provided on the band.
16 A probe arrangement according to any of Claims 12 to 15 in which the means
for indicating a reference axis comprises two diametrically opposed
pointers on the circular means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8816242A GB2220493A (en) | 1988-07-07 | 1988-07-07 | Extensometer probe |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8816242A GB2220493A (en) | 1988-07-07 | 1988-07-07 | Extensometer probe |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8816242D0 GB8816242D0 (en) | 1988-08-10 |
| GB2220493A true GB2220493A (en) | 1990-01-10 |
Family
ID=10640074
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8816242A Withdrawn GB2220493A (en) | 1988-07-07 | 1988-07-07 | Extensometer probe |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2220493A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4315387A1 (en) * | 1993-05-08 | 1994-11-10 | Industrieanlagen Betriebsges | High temperature strain gauges |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB843515A (en) * | 1957-11-19 | 1960-08-04 | Saab Scania Ab | Improvements in or relating to extensometers |
-
1988
- 1988-07-07 GB GB8816242A patent/GB2220493A/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB843515A (en) * | 1957-11-19 | 1960-08-04 | Saab Scania Ab | Improvements in or relating to extensometers |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4315387A1 (en) * | 1993-05-08 | 1994-11-10 | Industrieanlagen Betriebsges | High temperature strain gauges |
| US5699624A (en) * | 1993-05-08 | 1997-12-23 | Industrieanlagen-Betriebsgesellschaft Mbh | High-temperature extensometer |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8816242D0 (en) | 1988-08-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |