GB2029019A - Crack detection means - Google Patents

Crack detection means Download PDF

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Publication number
GB2029019A
GB2029019A GB7833168A GB7833168A GB2029019A GB 2029019 A GB2029019 A GB 2029019A GB 7833168 A GB7833168 A GB 7833168A GB 7833168 A GB7833168 A GB 7833168A GB 2029019 A GB2029019 A GB 2029019A
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United Kingdom
Prior art keywords
elements
detection means
crack
continuity
circuit
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Withdrawn
Application number
GB7833168A
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BAE Systems PLC
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British Aerospace PLC
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Filing date
Publication date
Application filed by British Aerospace PLC filed Critical British Aerospace PLC
Priority to GB7833168A priority Critical patent/GB2029019A/en
Publication of GB2029019A publication Critical patent/GB2029019A/en
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/20—Investigating the presence of flaws
    • 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

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  • General Physics & Mathematics (AREA)
  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Biochemistry (AREA)
  • Analytical Chemistry (AREA)
  • Electrochemistry (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
  • Testing Of Devices, Machine Parts, Or Other Structures Thereof (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

Means for detecting cracks in predetermined positions on the surface of a load bearing structure or a component thereof includes several electrically conducting elements, 2, 5, 9, some of which are electrically connected in series to form groups of elements, bonded to but insulated from said positions on the surface of the structure. Each element or group of elements is provided at its ends with connecting leads 3, 6, 11 electrically connecting the elements to a central site 4 such that each individual circuit may be remotely tested by a continuity testing unit. The elements are bonded to the structure such that cracks forming in the surface beneath them will sever the elements and thus break the electrical continuity. A trip latch may be incorporated in each circuit to ensure that the circuit, once broken, is not remade if the crack closes due, for example, to load changes in the structure. <IMAGE>

Description

SPECIFICATION Crack detection means This invention relates to detection means for detecting cracks in load bearing structures or components thereof.
Undetected cracks in such structures may continue to grow as the structure is subjected to load cycles during use and this growth can naturally lead to catastrophic faiiure when the crack reaches a certain critical length at which the structure tends to break apart.
It is an object of the present invention to provide a load bearing structure or a component thereof with means to facilitate detection of these cracks at an early, non-catastrophic stage.
According to the present invention detection means for detecting formation of a crack at a predetermined position in the surface of a load bearing structure or a component thereof, comprises an electrically conducting element bonded to but electrically insulated from said surface and extending across said position whereby formation of a crack at that position will break the electrical continuity of the element, and means for connecting the element to circuit continuity testing means.
Preferably the detection means comprises a group of such elements arranged to extend across a plurality of predetermined positions, and connecting means electrically connecting the elements of the group in series.
Conveniently the detection means comprises a plurality of such groups of elements, and connecting means for connecting each group of elements to a common circuit continuity testing means such that the continuity of each group of elements may be individually tested.
A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows diagrammatically a portion of an aircraft load bearing structure provided with crack detection means according to the invention.
Figure 2 shows diagrammitically a zig-zag form of crack detection element.
Referring now to Figure 1, the portion of the aircraft load bearing structure 1 is provided with a number of conducting elements 2 bonded to but electrically insulated from the surface of the structure in positions of high stress. Each element 2 is in the form of a metallic strip positioned longitudinally along the length of the portion and each element is provided at its ends with connecting leads 3 electrically connecting the element 2 with a continuity test site 4.
Three groups of strip elements 5 having connecting wires 6 connecting the elements of each group in series are arranged circumferentially, each group having elements positioned on both sides of circumferential joints 7, the free ends of each group being connected by connecting leads 8 to the test site 4.
Further elements 9 are positioned along rivet lines in the lap joints 10, and are connected by connecting leads 11 to the test site 4. These elements are of a generally zig-zag form (see figure 2) and weave between the rivet holes 1 2 whilst passing close to the holes to detect cracks of short length. The shape of the element is chosen to provide substantial angular detection coverage for cracks emanating from the holes. In order to provide additional strength for the element during the handling stages before bonding to the structure, the element is formed with reinforcing side strips 9a, 9b (shown in broken outline) and when the element has been bonded to the structure 1 the two side strips are cut away.
The elements comprise an electrically conducting metallic foil having an approximate composition of 97% aluminium and 3% magnesium. This foil has substantiaily the same coefficient of expansion as the material to which it is bonded. Bonding is effected by an epoxy resin adhesive, Hysol 9309A which has a room temperature cure and has reasonably high strength at high temperature. The foil is such that formation of a crack in the area of the structure to which it is bonded will sever the foil.
All the elements or groups of elements are connected to the central test site as individual circuits. An electrical continuity monitoring unit (not shown) may be coupled to the test site to test the continuity of each of the circuits in turn. The monitoring unit may record and display the state of continuity of each circuit thus indicating a general location of the crack. Further inspection of the elements in a broken circuit is necessary to locate the crack. This monitoring unit may be carried on the aircraft or may be used only on the ground.
In some cases it would be possible that an element may break whilst the aircraft is in flight and then close up to re-make the continuity, due to load changes when the aircraft is on the ground. In such cases a trip latch could be incorporated in each circuit to ensure that the circuit is not re-made when the crack closes.
These elements may be bonded to the inside or the outside of the structure 1 depending upon the circumstances. If they are bonded to the inside surface, obstructions such as stringers will have to be cleared. Elements could profitably be attached along the edge of stringers.
1. Detection means for detecting formation of a crack at a pre-determined position in the surface of a load bearing structure or a component thereof, comprising an electrically conducting element bonded to but electrically insulated from said surface and extending across said position whereby formation of a crack at that position will break the electrical continuity of the element, and means for connecting the element to circuit continuity testing means.
2. Detection means according to claim 1 including a group of such elements arranged to
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Crack detection means This invention relates to detection means for detecting cracks in load bearing structures or components thereof. Undetected cracks in such structures may continue to grow as the structure is subjected to load cycles during use and this growth can naturally lead to catastrophic faiiure when the crack reaches a certain critical length at which the structure tends to break apart. It is an object of the present invention to provide a load bearing structure or a component thereof with means to facilitate detection of these cracks at an early, non-catastrophic stage. According to the present invention detection means for detecting formation of a crack at a predetermined position in the surface of a load bearing structure or a component thereof, comprises an electrically conducting element bonded to but electrically insulated from said surface and extending across said position whereby formation of a crack at that position will break the electrical continuity of the element, and means for connecting the element to circuit continuity testing means. Preferably the detection means comprises a group of such elements arranged to extend across a plurality of predetermined positions, and connecting means electrically connecting the elements of the group in series. Conveniently the detection means comprises a plurality of such groups of elements, and connecting means for connecting each group of elements to a common circuit continuity testing means such that the continuity of each group of elements may be individually tested. A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows diagrammatically a portion of an aircraft load bearing structure provided with crack detection means according to the invention. Figure 2 shows diagrammitically a zig-zag form of crack detection element. Referring now to Figure 1, the portion of the aircraft load bearing structure 1 is provided with a number of conducting elements 2 bonded to but electrically insulated from the surface of the structure in positions of high stress. Each element 2 is in the form of a metallic strip positioned longitudinally along the length of the portion and each element is provided at its ends with connecting leads 3 electrically connecting the element 2 with a continuity test site 4. Three groups of strip elements 5 having connecting wires 6 connecting the elements of each group in series are arranged circumferentially, each group having elements positioned on both sides of circumferential joints 7, the free ends of each group being connected by connecting leads 8 to the test site 4. Further elements 9 are positioned along rivet lines in the lap joints 10, and are connected by connecting leads 11 to the test site 4. These elements are of a generally zig-zag form (see figure 2) and weave between the rivet holes 1 2 whilst passing close to the holes to detect cracks of short length. The shape of the element is chosen to provide substantial angular detection coverage for cracks emanating from the holes. In order to provide additional strength for the element during the handling stages before bonding to the structure, the element is formed with reinforcing side strips 9a, 9b (shown in broken outline) and when the element has been bonded to the structure 1 the two side strips are cut away. The elements comprise an electrically conducting metallic foil having an approximate composition of 97% aluminium and 3% magnesium. This foil has substantiaily the same coefficient of expansion as the material to which it is bonded. Bonding is effected by an epoxy resin adhesive, Hysol 9309A which has a room temperature cure and has reasonably high strength at high temperature. The foil is such that formation of a crack in the area of the structure to which it is bonded will sever the foil. All the elements or groups of elements are connected to the central test site as individual circuits. An electrical continuity monitoring unit (not shown) may be coupled to the test site to test the continuity of each of the circuits in turn. The monitoring unit may record and display the state of continuity of each circuit thus indicating a general location of the crack. Further inspection of the elements in a broken circuit is necessary to locate the crack. This monitoring unit may be carried on the aircraft or may be used only on the ground. In some cases it would be possible that an element may break whilst the aircraft is in flight and then close up to re-make the continuity, due to load changes when the aircraft is on the ground. In such cases a trip latch could be incorporated in each circuit to ensure that the circuit is not re-made when the crack closes. These elements may be bonded to the inside or the outside of the structure 1 depending upon the circumstances. If they are bonded to the inside surface, obstructions such as stringers will have to be cleared. Elements could profitably be attached along the edge of stringers. CLAIMS
1. Detection means for detecting formation of a crack at a pre-determined position in the surface of a load bearing structure or a component thereof, comprising an electrically conducting element bonded to but electrically insulated from said surface and extending across said position whereby formation of a crack at that position will break the electrical continuity of the element, and means for connecting the element to circuit continuity testing means.
2. Detection means according to claim 1 including a group of such elements arranged to extend across a plurality of predetermined positions, and connecting means electrically connecting the elements of the group in series.
3. Detection means according to claim 2 including a plurality of such groups of elements and connecting means for connecting each group of elements to a common circuit continuity testing means such that the continuity of each group of elements may be individually tested.
4. Detection means according to any preceding claim wherein the or each element is arranged to extend across a plurality of pre-determined positions whereby formation of a crack in any one of the positions will result in the electrical continuity of the element being broken.
5. Detection means according to any preceding claim wherein the electrically conducting element comprises thin aluminium alloy foil.
6. Detection means according to any preceding claim wherein at least one of the elements is positioned to detect cracks emanating from plain areas of high stress in the load bearing structure and is in the form of a straight strip.
7. Detection means according to any of claims 1 to 5 wherein at least one of the elements is positioned to detect cracks emanating from rivet holes and wherein the element is shaped so that it weaves between and close to the holes.
8. Detection means according to claim 7 wherein the shaped element is preformed with two side strips to maintain its shape, the side strips being removed after the element has been bonded to the aircraft structure.
9. Detection means according to any preceding claim including circuit continuity testing means connected to said elements.
10. Detection means according to claim 9 wherein the circuit continuity testing means includes means for maintaining an indication of a broken circuit regardless of the continuity of the circuit being remade due to reclosure of the crack.
11. Detection means substantially as described herein with reference to the accompanying drawings.
GB7833168A 1978-08-12 1978-08-12 Crack detection means Withdrawn GB2029019A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7833168A GB2029019A (en) 1978-08-12 1978-08-12 Crack detection means

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB7833168A GB2029019A (en) 1978-08-12 1978-08-12 Crack detection means

Publications (1)

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GB2029019A true GB2029019A (en) 1980-03-12

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2478311A1 (en) * 1980-03-17 1981-09-18 Cit Alcatel Crack detector for ceramic substrate - provides continuity measurement during application of torsional force from inflatable bladder between two arm members
WO1983003472A1 (en) * 1982-03-25 1983-10-13 Smith, Alan, Wilfred Improvements in or relating to profile change sensors
US4641539A (en) * 1984-08-08 1987-02-10 Texas Instruments Incorporated Sensor responding to the action of a force
EP0450000A1 (en) * 1989-10-17 1991-10-09 Bell Helicopter Textron Inc Electrical detection of shear pin operation.
US5145127A (en) * 1990-02-13 1992-09-08 Dunlop Limited A British Company Wheels
EP0526855A1 (en) * 1991-07-31 1993-02-10 Hughes Aircraft Company Conformal circuit for structural health monitoring and assessment
FR2728677A1 (en) * 1994-12-21 1996-06-28 Bidim Geosynthetics Sa Deformation detection method for civil engineering works
EP1195600A2 (en) * 2000-09-21 2002-04-10 Phasor Limited Pallet testing
EP1353139A1 (en) * 2002-04-12 2003-10-15 J.C. Bamford Excavators Limited Detecting damage to a structural member
WO2012010307A1 (en) * 2010-07-20 2012-01-26 Airbus Operations Gmbh Planking panel for a structural component, flow body comprising such a planking panel and device for monitoring material damage on such a planking panel

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2478311A1 (en) * 1980-03-17 1981-09-18 Cit Alcatel Crack detector for ceramic substrate - provides continuity measurement during application of torsional force from inflatable bladder between two arm members
WO1983003472A1 (en) * 1982-03-25 1983-10-13 Smith, Alan, Wilfred Improvements in or relating to profile change sensors
EP0092323A1 (en) * 1982-03-25 1983-10-26 Johnson Matthey Public Limited Company A bursting disc failure indicator
US4641539A (en) * 1984-08-08 1987-02-10 Texas Instruments Incorporated Sensor responding to the action of a force
EP0450000A1 (en) * 1989-10-17 1991-10-09 Bell Helicopter Textron Inc Electrical detection of shear pin operation.
EP0450000A4 (en) * 1989-10-17 1992-04-08 Bell Helicopter Textron Inc. Electrical detection of shear pin operation
US5145127A (en) * 1990-02-13 1992-09-08 Dunlop Limited A British Company Wheels
EP0526855A1 (en) * 1991-07-31 1993-02-10 Hughes Aircraft Company Conformal circuit for structural health monitoring and assessment
FR2728677A1 (en) * 1994-12-21 1996-06-28 Bidim Geosynthetics Sa Deformation detection method for civil engineering works
EP1195600A2 (en) * 2000-09-21 2002-04-10 Phasor Limited Pallet testing
EP1195600A3 (en) * 2000-09-21 2004-03-03 Phasor Limited Pallet testing
EP1353139A1 (en) * 2002-04-12 2003-10-15 J.C. Bamford Excavators Limited Detecting damage to a structural member
US6842119B2 (en) 2002-04-12 2005-01-11 J. C. Bamford Excavators, Limited Detecting damage to a structural member
WO2012010307A1 (en) * 2010-07-20 2012-01-26 Airbus Operations Gmbh Planking panel for a structural component, flow body comprising such a planking panel and device for monitoring material damage on such a planking panel
US9296463B2 (en) 2010-07-20 2016-03-29 Airbus Operations Gmbh Main-load-bearing planking shell and structural component and flow body comprising such a main-load-bearing planking shell
US9371128B2 (en) 2010-07-20 2016-06-21 Airbus Operations Gmbh Structural component comprising at least one main-load-bearing covering shell and a carrier structure for fixing the main-load-bearing covering shell, and flow body comprising such a structural component

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732 Registration of transactions, instruments or events in the register (sect. 32/1977)
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)