GB2057690A - Testing metal components for strain therein - Google Patents
Testing metal components for strain therein Download PDFInfo
- Publication number
- GB2057690A GB2057690A GB7929823A GB7929823A GB2057690A GB 2057690 A GB2057690 A GB 2057690A GB 7929823 A GB7929823 A GB 7929823A GB 7929823 A GB7929823 A GB 7929823A GB 2057690 A GB2057690 A GB 2057690A
- Authority
- GB
- United Kingdom
- Prior art keywords
- metal
- component
- resistance
- strain
- strip
- 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- Withdrawn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
- 239000002184 metal Substances 0.000 title claims abstract description 53
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 53
- 238000012360 testing method Methods 0.000 title claims description 13
- 238000000034 method Methods 0.000 claims abstract description 10
- 238000010998 test method Methods 0.000 claims abstract description 8
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 239000000523 sample Substances 0.000 abstract description 13
- 238000003825 pressing Methods 0.000 abstract description 7
- 238000005259 measurement Methods 0.000 description 3
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
A method of testing a metal component 12 to determine the level of strain therein comprises measuring the electrical resistance of the metal in a region of the component which has been stressed, and comparing the resistance of the metal with the resistance of the metal before the stress was applied thereto. Since the resistance increases with strain, the change in resistance can be used to indicate the level of strain in the component. The strain may be produced by compressive forces, in the component, e.g. where the component is secured by a bolted connection, or by tensile forces, e.g. where the component has been formed by pressing. The method may therefore be used in determining the quality of a metal component during or after assembly. Current is applied to the component via terminals 11a, 11b and a probe 9 including spring contacts 10a, 10b is positioned thereon. Probe 9 is connected to ohmmeter 8. <IMAGE>
Description
SPECIFICATION
Method of testing metal components for strain
This invention relates to a method of testing metal components for strain.
It is well known that the electrical resistance of metals alters in accordance with the strain produced therein by an applied stress. This phenomenon is utilised in the design of strain gauges. Such gauges comprise a strip of metal which is attached to a component to which a stress is applied so that changes in the dimentions of the component under stress produce corresponding changes in the strip. An electrical current is passed through the metal strip whilst the component is stressed, and the variation in resistance of the strip is observed. The change in resistance of the strip gives an indication of the strain caused in the component by the applied stress.
In many cases it is impossible to use a strain gauge in order to measure the level of strain in a component because the part of the component which is to be stressed is inaccessible or too small to carry a strain gauge. For example it is desirable to test metal components produced by pressing processes to ensure that the stresses applied to the component during production have not strained the component so far beyond the elastic limit of the metal that the metal is likely to fail. A strain gauge could not be used to determine the strain in the component after pressing because the gauge would not remain attached to the component during the pressing operation.In these circumstances, the strain in the article must be determined by marking the metal of the component before pressing with a reference mark, such as a rectangular grid, and measuring the alteration or deformation in the reference mark produced by the pressing operations. This measurement can then be used to calculate the strain produced in the component by the pressing operation. This technique is laborious and time consuming.
According to the present invention there is provided a method of testing a metal component to determine the level of strain therein comprising the step of measuring the electrical resistance of the metal in a region of the component which has been stressed and comparing the resistance of the metal with the resistance metal before the stress was applied thereto.
By measuring the resistance changes produced in the metal component by an applied stress, the strain produced in the component can be measured quickly and easily without the use of a strain gauge.
The method of the invention is particularly suitable for testing metal components for stress failure. In accordance with this aspect of the invention, the electrical resistance of the metal in a region of the component which has been stressed is measured, and it is then determined whether the resistance exceeds the resistance of the unstressed metal by more than a predetermined amount, eg. 20%. The value of the predetermined amount will vary with the metal and the maximum acceptable strain in the component.
The determinations of changes in electrical resistance in accordance with the present invention allow the method to be used in the manufacture of metal components of a required durability. If the resistance of the component indicates that it is undesirably strained, the component can be discarded.
The method of the invention may also be used to determine whether a required minimum level of strain has been produced in the component. For example, it may be possible to test the metal in the region of a bolted connection using the method of this invention to determine whether the connection is secure. The resistance of the metal in such a region will alter as the compressive force applied to the component by the bolted connection increases the strain in the metal.
Measurement of the resistance of the metal can therefore give an indication as to whether or not the bolted connection is secured to a required tightness. This method of testing has the advantage that the security of the connection is not measured indirectly by measuring the torque applied to the bolt and is therefore not subject to errors caused by friction losses in the threaded connection between the bolt and the component.
In order that the invention may be better understood, the results of a series of tests which we have carried out in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings in which:
Figure 1 is a diagram illustrating a test rig used in the method of the invention;
Figure 2 is a sketch illustrating equipment used to determine the resistance of sample metal components; and
Figures 3 and 4 are graphs showing the physical properties of the components tested in accordance with the invention.
Referring to Figure 1, tests were carried out on eight strips 1 of mild steels identified as samples A to H. Each strip was sheared from a sheet of mild steel 0.79mm in thickness, and measured 1 50 mm in length and 25 mm in width. The ends of each strip were clamped in the upper and lower jaws of an hydraulic tensioning device 4 equipped with a-gauge for indicating the applied load. The load, applied to the strip was controlled so that the strips were elongated by increasing amounts. The load on the strip when the required elongation had been achieved was noted together with the elongation produced.
Figure 3 is a graph showing the variation in final load on the strip (L) with the elongation produced (E). The points on the graph indicated by the letters A and H represent the data for the strips
A to H respectiveiy.
Strip A was not subjected to any loading in the device 4. The test on sample B was terminated when the metal reached its lower yield point (Y).
The tests on samples C and D were terminated after increasing the load beyond the upper and lower yield points of the metal (Yu and Y). The test on sample E was terminated when the maximum load point of the metal had been reached, and the tests on samples G and H were terminated when the load required to produce further increases in length of the strip began to fall, thereby indicating the onset of failure of the metal. The breaking point R of the metal is indicated by the intersection of the extrapolated part of the line of the graph with the abscissa.
Samples B C and D showed no visible signs of stress failure. Sample E was reduced in width.
Samples F and G were also found to be reduced in width but in addition exhibited a V-shaped line of dull metal extending across the strip from a small crack in one edge of the strip, indicating a region of high stress.
Tests of electrical resistance of the strips were then carried out using a digital microhmeter 8 and a hand held probe 9, carrying two spring loaded contact-points 1 0a, lOb, as illustrated in Figure 2.
In each case the microhmeter was connected by two connectors 11 a, 11 b, to opposite ends of the strip to provide a reference current through the strip, and the probe 9 was applied to the strip along the line 12 between the two connectors 11 so that the resistance of the metal of the strip between the two contact points 11 of the probe 9 was determined. The spacing between the two contact points 11 of the probe was 50 mm and the determinations of resistance were carried out along the strips at 10 mm intervals.
Figure 4 is a graph of the resistance R (in microhms) of strips A D, E and F along their lengths, the length d being the distance (in mm) of the leading contact lOb from one connector 1 a as the probe is advanced along the strip towards the other connector 1 lb.
It will be noted from Figures 3 and 4 that the resistance of the metal of the strips increases with the strain, ie. the elongation E, produced by the applied load.
Strip E is the sample which was subjected to the maximum load. The increase in resistance of the metal in this strip compared with that of the metal before stressing (strip A) is about 20%.
Consequently, where an increase in resistance of more than 20% is detected, the metal would be expected to exhibit signs of failure. This is confirmed by the graph for strip F which illustrates an increase in resistance of over 20%, especially in the region a of the curve. This part of the curve represents measurements of resistancy of the strip as the leading contact 1 0b of the probe 9 traversed the region of the strip showing visible signs of stress fatigue.
Claims (5)
1. A method of testing a metal component to determine the level of strain therein comprising the step of measuring the electrical resistance of the metal in a region of the component which has been stressed and comparing the resistance of the metal with the resistance of the metal before the stress was applied thereto.
2. A method of testing a metal component for stress failure comprising the steps of measuring the electrical resistance of the metal in a region of the component which has been stressed, and determining whether the resistance of the metal exceeds the resistance of the unstressed metal by more than a predetermined amount.
3. A method according to Claim 2 wherein the predetermined amount is 20%.
4. A method of manufacturing metal components comprising the steps of forming the components from sheet metal, testing the components for stress failure by a method according to Claim 2 or Claim 3 and discarding those components in which the electrical resistance of a region of the component exceeds the resistance of the sheet metal by more than the predetermined amount.
5. A method of testing a metal component substantially as hereinbefore described with reference to the drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7929823A GB2057690A (en) | 1979-08-28 | 1979-08-28 | Testing metal components for strain therein |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7929823A GB2057690A (en) | 1979-08-28 | 1979-08-28 | Testing metal components for strain therein |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2057690A true GB2057690A (en) | 1981-04-01 |
Family
ID=10507460
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7929823A Withdrawn GB2057690A (en) | 1979-08-28 | 1979-08-28 | Testing metal components for strain therein |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2057690A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007102754A1 (en) * | 2006-03-02 | 2007-09-13 | Igor Gennadievich Korolev | Method for testing carrying capacity of reinforced concrete roof or floor |
| WO2008133540A1 (en) * | 2007-04-25 | 2008-11-06 | Igor Gennadievich Korolev | Building construction accident warning |
| CN114660126A (en) * | 2022-03-18 | 2022-06-24 | 为天(深圳)检测科技有限公司 | Metal structure health monitoring method and low-temperature welding method for monitoring |
-
1979
- 1979-08-28 GB GB7929823A patent/GB2057690A/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007102754A1 (en) * | 2006-03-02 | 2007-09-13 | Igor Gennadievich Korolev | Method for testing carrying capacity of reinforced concrete roof or floor |
| WO2008133540A1 (en) * | 2007-04-25 | 2008-11-06 | Igor Gennadievich Korolev | Building construction accident warning |
| CN114660126A (en) * | 2022-03-18 | 2022-06-24 | 为天(深圳)检测科技有限公司 | Metal structure health monitoring method and low-temperature welding method for monitoring |
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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) |