US20090173827A1 - Method and apparatus for monitoring the integrity of components and structures - Google Patents
Method and apparatus for monitoring the integrity of components and structures Download PDFInfo
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- US20090173827A1 US20090173827A1 US12/390,545 US39054509A US2009173827A1 US 20090173827 A1 US20090173827 A1 US 20090173827A1 US 39054509 A US39054509 A US 39054509A US 2009173827 A1 US2009173827 A1 US 2009173827A1
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Images
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
- G01M3/28—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for pipes, cables or tubes; for pipe joints or seals; for valves ; for welds
- G01M3/2853—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for pipes, cables or tubes; for pipe joints or seals; for valves ; for welds for pipe joints or seals
- G01M3/2869—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for pipes, cables or tubes; for pipe joints or seals; for valves ; for welds for pipe joints or seals for seals not incorporated in a pipe joint
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
- G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
- G01M3/3236—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
- G01M5/0033—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining damage, crack or wear
Definitions
- the present invention is for a method and apparatus for monitoring the integrity of a component or structure, in particular though not exclusively, by monitoring a pressure state that can be maintained within cavities either inherently provided or specifically formed in the component or structure.
- the present invention has its genesis from consideration of the problems faced by aircraft designers in monitoring the integrity of: sandwiched structures typically encountered around splices and cut-outs in fuselages; and, substantially hollow components as encountered in composite structures such as flaps, doors, panels and the like; and, attempting to prevent the ingress of moisture into such structures and components.
- These structures and components are difficult to examine for the detection of cracking, corrosion and disbanding. Further they are prone to the ingress of moisture arising for various reasons including: capillary action and the substantially hollow nature of the structures, particularly those made from composite materials; exposure to temperature extremes; exposure to large ambient pressure variations; exposure to environments of high humidity and precipitation.
- Structural integrity monitoring has very wide application and can be used, for example, to monitor the adhesive bonds such as between anechoic tiles on a submarine or heat resistant tiles on a spacecraft.
- the present invention provides structures and methods for monitoring integrity of a permeable structure disposed in an environment containing a fluid at an ambient pressure at least one cavity being formed in or on the permeable structure.
- One method of monitoring the integrity of a structure or component may comprise forming one or more cavities internally of the structure or component, pressuring the one or more cavities with a gas, and monitoring for a change in rate of seepage of the gas from the at least one of the cavities.
- forming the cavities may comprise attaching at least two of the parts together in an overlapping relationship and wherein the cavities incorporate mutually adjacent surfaces of the attached overlapping at least two parts.
- a method of monitoring the integrity of a structure or component formed from two or more parts may comprise exposing the structure or component to an ambient pressure environment, pressurizing the one or more cavities with a gas at a pressure greater than the ambient pressure, and monitoring for a change in a rate of seepage of the pressurized gas from the at one or more cavities to the ambient pressure environment.
- a method of monitoring the integrity of a composite structure may comprise pressurizing the inner core with a gas at a pressure greater than air pressure outside the outer skin, and monitoring for a change in a rate of seepage of the pressurized gas from the inner core.
- a method of monitoring the integrity of an attachment between two or more parts may comprise forming one or more cavities between two or more of the parts, pressurizing the one or more cavities with a gas at a pressure greater than air pressure outside the one or more cavities, and monitoring for a change in a rate of seepage of the gas from at least one of the cavities.
- Another method may comprise providing a source of a first fluid at a first pressure greater than the ambient pressure, coupling the at least one cavity to the source through a high fluid flow impedance to establish a flow of the first fluid through the permeable structure via the cavity, allowing a rate of flow of the first fluid through the permeable structure to stabilize to a steady state rate, and monitoring for a change in the steady state rate of flow of the first fluid though the permeable structure.
- Another embodiment of the invention provides a method of constructing and monitoring the integrity of a permeable structure disposed in an environment containing a fluid at an ambient pressure.
- the method may comprise constructing the permeable structure of one or more elements and forming at least one cavity in or on the permeable structure, wherein a portion of a surface of at least one of the structural elements forms a part of an internal surface of the cavity, providing a source of a first fluid at a first pressure greater than the ambient pressure, placing the at least one cavity in fluid communication with the source, coupling a high fluid flow impedance in series between the at least one cavity and the source, the impedance being sufficiently high to create a pressure differential between the at least one cavity and the source resulting from a breach in the portion of the surface, and monitoring for a change in differential pressure.
- a further embodiment of the invention provides a method of monitoring the integrity of a permeable structure having an outer skin and an inner core of a honeycomb or cellular configuration composed of a plurality of adjoining cells, a number of the cells defining respective cavities internal of the permeable structure, the permeable structure disposed in an environment containing a fluid at an ambient pressure: providing a source of a first fluid at a first pressure greater than the ambient pressure, coupling at least one of the cavities to the source through a high fluid flow impedance to establish a flow of the first fluid through the permeable structure via the cavities, allowing a rate of flow of the first fluid through the permeable structure to stabilize to a steady state rate, and monitoring for a change in the steady state rate of flow of the first fluid through the permeable structure.
- the first fluid source pressure may be substantially constant with respect to the ambient pressure.
- providing the first fluid source at the first pressure may comprise setting the first pressure at a level which is sufficiently greater than the ambient pressure to overcome hygroscopic force and capillary action, but not sufficient to be detrimental to the integrity of the structure.
- the first fluid may be a gas.
- an embodiment of the invention may also comprise providing a moisture trap between the source and the at least one cavity to dry the gas prior to flowing into the permeable structure.
- a structural aspect of the invention may be directed to an aircraft having one or more structures or components provided with one or more internal cavities and a structural monitoring system for monitoring the integrity of one or more of the components or structures, wherein the structural monitoring may comprise a pressure source for pressuring the one or more cavities with a gas, one or more communication channels for placing the one or more cavities in fluid communication with the pressure source, and a monitoring apparatus for monitoring for a change in a rate of seepage of the pressurized gas from the cavities to an external environment.
- One of the structures or components may include a composite structure having an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, wherein the cells constitute the cavities.
- FIG. 1 is a schematic representation of a first embodiment of the present invention
- FIG. 2 is a schematic representation of an apparatus in accordance with a further embodiment of the present invention for monitoring the pressure state of cavities within a structure and hence the integrity of the structure;
- FIG. 3 is a schematic representation of a further embodiment of the present invention.
- FIG. 4 a is a schematic representation of a further embodiment of the present invention:
- FIG. 4 b is a schematic representation of a further embodiment of the present invention.
- FIG. 5 a is a schematic representation of a two-layer sandwich structure to which an embodiment of the present invention is applied;
- FIG. 5 b is a variation of the configuration of the embodiment of FIG. 5 a;
- FIG. 6 is a schematic representation of a three-layer sandwich structure to which an embodiment of the present invention is applied.
- FIG. 6 a is a variation of the configuration of the embodiment of FIG. 6 ;
- FIG. 6 b is a further variation of the configuration of the embodiment of FIG. 6 ;
- FIG. 7 is a schematic representation of a four-layer sandwich structure to which an embodiment of the invention is applied.
- FIG. 8 b is a schematic representation of a three-layer sandwich structure to which a further embodiment of the present invention is applied.
- FIG. 1 illustrates schematically, one embodiment of a method and apparatus of the present invention for preventing the ingress of a fluid F into a structure 10 .
- the structure 10 is a fictitious structure made up from three types of composite structure and is provided merely for the purpose of illustrating the principles of embodiments of the invention.
- the structure 10 has an outer skin 12 and a plurality of internal cavities 14 a , 14 b and 14 c (hereinafter referred to in general as “cavities 14 ”).
- the actual geometry of the cavities 14 is a function of the type of structure 10 .
- Cavities 14 a are illustrative of a structure 10 having internal cavities of a random configuration; cavities 14 b are illustrative of a structure 10 having a honeycomb or cellular-type core, and cavities 14 c are illustrative of a structure 10 having a foam core.
- the structure 10 is disposed in an environment 16 containing fluid F at an ambient pressure that acts on the structure 10 .
- the environment 16 may be the atmosphere at 4000 meters above sea level, where the fluid F is air; or the environment 16 may be the ocean at depth of 100 meters in which case the fluid F is sea water.
- Apparatus 18 in accordance with an embodiment of the present invention acts to prevent or at least minimize the ingress of the fluid F into the structure 10 .
- the apparatus 18 includes a pressure source 20 for providing a first fluid such as, air or an inert gas at a pressure higher than the pressure of the fluid F.
- a communication channel in the form of a conduit 22 provides fluid communication between the source 20 and one or more of the internal cavities 14 of the structure 10 . If it is the case that the cavities 14 of structure 10 are all directly or indirectly in fluid communication with each other, then in order for the gas of source 20 to be in fluid communication with the cavities 14 , the conduit 22 need only extend into the structure 10 to a point where it pierces the skin 12 .
- a plurality of conduits 22 can be provided between the source 20 and the structure 10 .
- the communication path of apparatus 18 can include one or more galleries or conduits 24 contained within the skin 12 that communicate with the conduit 22 thereby providing fluid communication between the gas of the source 20 and the cavities 14 .
- small perforations can be made between the internal cavities 14 to allow fluid communication there between. This may for example be achieved using a laser.
- the pressure of source 20 is arranged to be greater than the pressure of fluid F (which may be either a static pressure or a dynamic pressure) so as to prevent the ingress of fluid F into the cavities 14 . More particularly, the pressure of source 20 is arranged to be sufficient to overcome hygroscopic force and capillary action to prevent moisture ingress into the structure 10 but is not sufficient to be detrimental to the integrity of the structure 10 .
- the skin 12 is absolutely impermeable to fluid F and such does not contain any faults or does not develop any faults throughout the life of the structure 10 then the fluid F of environment 16 cannot enter the structure 10 .
- the structure 10 has some degree of permeability. Hence fluid F communicated to the cavities permeates through the structure to the surrounding environment.
- PCT/AU94/00325 (WO 94/27130) a constant vacuum source is employed.
- the monitoring device 26 monitors for a change in the steady state rate of inflow of fluid from the source 20 into the cavities 14 .
- the monitoring device 26 includes a high fluid flow impedance 28 disposed in series in the conduit 22 a between the source 20 and the cavities 14 .
- the high fluid flow impedance 28 preferably comprises a very long length of small bore duct which allows a minuscule flow of fluid.
- the high fluid flow impedance 28 could comprise a permeable material such as sintered glass.
- the impedance 28 is sufficiently high to create a minimum discernable pressure differential between the cavities and the source 20 , as a result of permeability, and a measurable pressure differential between the cavities and source resulting from a breech (re crack or other failure) in the structure.
- the maximum rate of flow is at the minimum that can be detected by current digital flow meters.
- a duct having a bore of less than 0.3 mm and a length in excess of 3 meters and experiencing an air pressure drop of 20 kPa across its length would have a flow of approximately 2-3 micro liters/minute.
- sensitivity of the device increases at an exponential rate as zero is approached and, if desired magnitude of the high fluid flow impedance can be extended towards infinity, extremely small flow rates can be detected.
- the magnitude of the high fluid flow impedance should be sufficiently high as to produce significant pressure drop across the high impedance in response to minuscule flow through the high impedance.
- Measuring means in the form of a differential pressure transducer 30 is coupled across the impedance 28 .
- the transducer 30 is coupled across the impedance 28 by fluid connecting ducts 32 , and coupled to an amplifier and display 34 by electrical conductors 36 .
- the differential pressure transducer 30 coupled across the impedance 28 may be in the form of a non-electrical indicator where electrical circuitry is not desirable.
- FIG. 3 depicts an embodiment of the present apparatus and method when applied to a structure 10 b comprising anechoic tiles 38 adhered to the hull 40 of a submarine.
- a fillet of elastomeric grout 48 is deposited about the periphery of each tile in a manner so that cavities 50 are created underneath the grout 48 between adjacent tiles 38 or, under grout 48 between the edge of a tile 38 and the adjacent surface of the hull 40 .
- the cavities 50 are coupled to a monitoring apparatus 18 b.
- the apparatus 18 b is similar to the apparatus 18 a depicted in FIG. 2 and encloses a monitoring device 26 b which includes conduit 22 b that provides a fluid communication path between the cavities 50 and a fluid source 20 b (in this example a gas source) via a series connected high fluid flow impedance 28 .
- Differential pressure transducer 30 is coupled across the impedance 28 via ducts 32 .
- An amplifier and display 34 coupled to the transducer 30 via electrical conductors 36 provides a display of steady state pressure differential across the impedance 28 .
- the fluid from supply 20 is metered through a pressure regulator 52 which is disposed in the conduit 22 b between the impedance 28 and the source 20 .
- the regulator 52 is also pressure referenced to the surrounding atmosphere, in this case sea water, herein shown with the notation F.sup.s and associated white pressure indicating arrow heads, via a duct 54 .
- the regulator 52 maintains the pressure of the gas from source 20 at a substantially constant level above the water pressure.
- the system 18 b, and in particular the regulator 52 is able to dynamically vary the pressure of the gas from source 20 delivered to the cavities 50 .
- the monitoring device 26 b stabilizes with a relatively constant pressure differential across the high impedance irrespective of the ambient water pressure.
- the integrity monitoring of the adhesive bonding of the tiles 38 is facilitated by monitoring the differential pressure across the high impedance 28 for any increase resulting from minuscule air seepage from any of the cavities 50 giving ample warning of any disbond of a tile 38 or damage to the grout 48 .
- the imminence of disbanding and water ingress would be immediately obvious due to a rise in pressure differential across the impedance 28 and detected by the transducer 30 . Loss of a tile 38 would result in a dramatic rise in differential pressure.
- the monitoring device 26 b can also be provided with an adjustable bypass of the impedance 28 to allow high rates of flow of air from the source 20 to allow for some damage tolerance and maintain positive pressure protection for the cavities 50 .
- FIG. 4 a illustrates a further embodiment of the present invention applied to a structure 10 c comprising three components 56 , 58 and 60 which are coupled in a sandwich construction. More particularly, the structure 10 c is part of a pressurized fuselage of an aircraft.
- the components 56 , 58 and 60 are fastened together by rivets 62 which pass through holes 71 formed in the components 56 , 58 and 60 .
- Each rivet 62 has a head 64 that sits flush with the component 56 and a flattened tail 66 at an opposite end that sits on the component 60 .
- Flush head rivets are shown as an example but round head rivets and possibly bolt fasteners could be substituted.
- Apparatus 18 c, enclosing monitoring device 26 c is connected to the cavity 72 for monitoring the integrity of the structure 10 c .
- the monitoring device 26 c includes a conduit 22 c leading to a parallel connection of high fluid flow impedance 28 and pressure transducer 30 .
- the transducer 30 is coupled to an amplifier and display 34 via electrical conductors 36 .
- the differential pressure transducer 30 coupled across the impedance 28 may be in the form of a non-electrical indicator where electrical circuitry is not desirable.
- the pressure source 20 c of this embodiment is cabin pressure of the aircraft which feeds into both the impedance 28 and the transducer 30 .
- the cabin pressure is marked as “CP” and has associated pressure indicating black arrow heads.
- a fluid seepage flow path (indicated by small black flow indicating arrow heads) can be created around the rivet 62 and head 64 to the outside high altitude atmosphere F.sup.A, associated with white pressure indicating arrow heads, due to the crack 100 and subsequent loosening of the fastening.
- the resulting increase of the inflow of air into cavity 72 through the impedance 28 will be detected by the transducer 30 as a change in differential pressure thus providing an indication of the crack 100 in component 58 .
- the apparatus 18 ′ for monitoring the integrity of structure 10 c comprises a compliant container 76 of a fluid marker such as a liquid or gaseous dye, or detectable gas, which is coupled by conduit 22 ′ vice conduit 22 c to the cavity 72 .
- a fluid marker such as a liquid or gaseous dye, or detectable gas
- FIGS. 5-7 depict variations of “sandwich” structures to which embodiments of the present invention can be applied.
- a portion of a structure 10 d comprises two components 56 and 60 fastened together by rivets 62 .
- a gas permeable gap 70 exists between mutually facing adjacent surfaces of components 56 and 60 .
- a cavity 72 is formed by sealing the gap 70 with a perimeter seal 74 .
- the structure 10 d is a portion of an aircraft fuselage containing cabin pressure CP and is disposed in an environment of a fluid F.sup.A being ambient air pressure at high altitude.
- the integrity of the structure 10 d can be monitored by connecting the cavity 72 via a conduit 22 d to a monitoring apparatus 26 d similar to 26 c of FIG. 4 a of the type described herein above.
- any seepage of gas from the cavity 72 through component 56 will be to the outside environment F.sup.A.
- the apparatus 26 c could be connected between the cavity 72 and the outside atmospheric pressure F.sup.A.
- cavity 72 becomes a conduit for pressure source in form of cabin pressure (CP) in the event of a through flaw developing in component 60 .
- CP cabin pressure
- the structure 10 e is very similar to the structure 10 c in FIG. 4 a .
- the structure 10 e is now formed with two cavities, 72 s and 72 n.
- the cavity 72 s is formed between mutually adjacent faces of components 56 and 58 of the structure 10 e .
- the cavity 72 s is in fluid communication via conduit 22 s with the pressure source 20 e (CP) via monitoring apparatus 26 e of like structure and function as described above.
- the cavity 72 n however which exists between components 58 and 60 is placed in fluid communication with fluid pressure referenced to the outside environment F.sup.A.
- a dotted trail shows the flow path from pressure source 20 e, through duct 22 s and device 26 e, cavity 72 s, crack 101 cavity 72 n, duct 22 n and thence to the outside atmospheric “environmental” pressure F.sup.A.
- cavity 72 n could be communicated via duct 22 n to a similar apparatus to 26 e ( 26 x ) and thence to an atmospheric pressure reference F.sup.A.
- FIG. 6 a the employment of monitoring apparatus 26 x is basically the same arrangement as shown in FIG. 5 a. The purpose of this arrangement is to monitor the integrity of component 60 .
- a crack or flaw 102 developing in component 60 communicating cabin pressure CP (source 20 e ) with cavity 72 n would produce a pressure drop, due to seepage flow (small arrow heads and dots), across the fluid impedance of the apparatus 18 x to the outside environmental F.sup.A.
- connection of apparatus 26 x could be normally bypassed or carried out at intervals to prevent a continuous series connection of two monitoring devices 26 e and 26 x (as shown in FIG. 6 b ) which would halve the sensitivity of both apparatus 26 e and 26 x in response to a flaw 101 occurring in component 58 .
- the series flow problem is shown by small arrowheads and dots. Of course, if a crack developed in component 56 direct to the outside environmental F.sup.A, no such problem would arise.
- FIG. 8 a depicts a further embodiment of the invention.
- This embodiment is applied to a structure 10 g comprised of three sheets 56 , 58 and 60 formed as a sandwich construction coupled together by rivets 62 .
- a structure 10 g comprised of three sheets 56 , 58 and 60 formed as a sandwich construction coupled together by rivets 62 .
- the layer 68 is typically provided to prevent corrosion and fretting of the sheets 56 , 58 , 60 about the rivets 62 .
- the step of providing cavities 72 within the structure 10 g involves removing sections of the sealant 68 between adjacent pairs of sheets.
- sealant 68 areas of sealant 68 are maintained about the rivets 62 to maintain the function of minimizing fretting of the sheets 56 , 58 , and 60 , and also to form boundary seals for the cavities 72 .
- the removed sealant 68 produces the sealed cavities 72 which can be placed in fluid communication with a pressure source. Indeed alternate cavities 72 can be placed in fluid communication with the atmosphere and with the source as described above in relation to the embodiments depicted in FIGS. 6 and 7 .
- the removal of the sealant 68 to produce the cavities 72 is ideally achieved during the construction of the structure 10 g by placing masks on the sheets 56 , 58 and 60 to prevent the depositing of sealant 68 in selected regions. After the sealant layer 68 has been applied and the masks removed, the structure 10 g is pulled together by fastening with rivets 62 .
- FIG. 8 b depicts a structure 10 h which differs from that depicted in FIG. 8 a by the inclusion of recesses or depressions 80 deliberately formed in the surface of the sheets 56 , 58 and 60 in the regions where the sealant 68 is removed This provides larger, more definite cavities 72 .
- the recesses or depressions 80 can be formed by any known means including but not limited to, chemical milling.
- the cavities 72 can be placed in fluid communication with a constant pressure source by conduits typical of 22 c to 22 x in the manner described herein above in relation to FIGS. 4 a - 7 . Of course in a further variation alternate cavities 72 can be placed in communication with the source 20 (CP) and the ambient pressure F.sup.A.
- FIG. 9 shows a partly sectioned oblique view of a further structure in the form of lap splice 10 j in which preformed elastomeric, self adhesive, film pads 110 are sandwiched between sheets 56 and 60 which are fastened together by rivets 62 .
- the pads 110 comprise shapes cut and assembled so as to define multiple cavities 72 when sandwiched between the plates 56 and 60 .
- the cavities 72 as shown as thick lines.
- a moisture trap can be provided between the source 20 and impedance 28 , when the source 20 is a gas source to dry the gas prior to flowing into the structure 10 .
- the source 20 can be a source of an inert gas.
- anti corrosion agents can be induced into the defined cavities.
- the structure 10 is a composite material having a plurality of internal cavities that are sealed from each other, embodiments of the invention include forming communication paths in the composite material between the internal cavities. All such modifications and variations are deemed to be within the scope of the present invention the nature of which is to be determined from the above
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Abstract
A method for monitoring the integrity of a permeable structure that is disposed in an environment containing a fluid at ambient pressure is provided. At least one cavity is formed in or on the permeable structure. A source of first fluid is provided at a first pressure greater than the ambient pressure. The cavity is coupled to the source through a high-fluid-flow impedance to establish a flow of the first fluid through the permeable structure via the cavity. A rate of flow of the first fluid through the permeable structure is allowed to stabilize to a steady-state rate. A change in the steady-state flow rate of the first fluid through the permeable structure is monitored.
Description
- This application is a continuation of U.S. application Ser. No. 11/260,882, filed Oct. 27, 2005, which itself is a Continuation-In-Part of U.S. application Ser. No. 09/905,681, filed Jul. 13, 2001, claiming priority to and the benefit of Australian Provisional Application No. 0018, filed Sep. 8, 2001, the disclosures of which are hereby incorporated by reference herein in their entireties, and all commonly owned.
- The present invention is for a method and apparatus for monitoring the integrity of a component or structure, in particular though not exclusively, by monitoring a pressure state that can be maintained within cavities either inherently provided or specifically formed in the component or structure.
- The present invention has its genesis from consideration of the problems faced by aircraft designers in monitoring the integrity of: sandwiched structures typically encountered around splices and cut-outs in fuselages; and, substantially hollow components as encountered in composite structures such as flaps, doors, panels and the like; and, attempting to prevent the ingress of moisture into such structures and components. These structures and components are difficult to examine for the detection of cracking, corrosion and disbanding. Further they are prone to the ingress of moisture arising for various reasons including: capillary action and the substantially hollow nature of the structures, particularly those made from composite materials; exposure to temperature extremes; exposure to large ambient pressure variations; exposure to environments of high humidity and precipitation.
- Apart from corrosion in metallic structure, the ingress of moisture can lead to serious structural flaws such as disbanding due to progressive damage caused by the cyclic intrusion of the moisture followed by expansion as it freezes.
- Of course the above problems are not the exclusive domain of aircraft designers. Structural integrity monitoring has very wide application and can be used, for example, to monitor the adhesive bonds such as between anechoic tiles on a submarine or heat resistant tiles on a spacecraft.
- In view of the foregoing background, the present invention provides structures and methods for monitoring integrity of a permeable structure disposed in an environment containing a fluid at an ambient pressure at least one cavity being formed in or on the permeable structure. One method of monitoring the integrity of a structure or component may comprise forming one or more cavities internally of the structure or component, pressuring the one or more cavities with a gas, and monitoring for a change in rate of seepage of the gas from the at least one of the cavities. When the structure or component is comprised of two or more part, forming the cavities may comprise attaching at least two of the parts together in an overlapping relationship and wherein the cavities incorporate mutually adjacent surfaces of the attached overlapping at least two parts.
- Yet further, a method of monitoring the integrity of a structure or component formed from two or more parts, wherein the structure or component is provided with one or more cavities formed between the two or more parts, and wherein the cavities incorporate respective surface portions of at least two of the parts, may comprise exposing the structure or component to an ambient pressure environment, pressurizing the one or more cavities with a gas at a pressure greater than the ambient pressure, and monitoring for a change in a rate of seepage of the pressurized gas from the at one or more cavities to the ambient pressure environment.
- A method of monitoring the integrity of a composite structure, the composite structure having an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, one or more of the cells forming respective cavities, may comprise pressurizing the inner core with a gas at a pressure greater than air pressure outside the outer skin, and monitoring for a change in a rate of seepage of the pressurized gas from the inner core.
- A method of monitoring the integrity of an attachment between two or more parts may comprise forming one or more cavities between two or more of the parts, pressurizing the one or more cavities with a gas at a pressure greater than air pressure outside the one or more cavities, and monitoring for a change in a rate of seepage of the gas from at least one of the cavities.
- Another method may comprise providing a source of a first fluid at a first pressure greater than the ambient pressure, coupling the at least one cavity to the source through a high fluid flow impedance to establish a flow of the first fluid through the permeable structure via the cavity, allowing a rate of flow of the first fluid through the permeable structure to stabilize to a steady state rate, and monitoring for a change in the steady state rate of flow of the first fluid though the permeable structure.
- Another embodiment of the invention provides a method of constructing and monitoring the integrity of a permeable structure disposed in an environment containing a fluid at an ambient pressure. The method may comprise constructing the permeable structure of one or more elements and forming at least one cavity in or on the permeable structure, wherein a portion of a surface of at least one of the structural elements forms a part of an internal surface of the cavity, providing a source of a first fluid at a first pressure greater than the ambient pressure, placing the at least one cavity in fluid communication with the source, coupling a high fluid flow impedance in series between the at least one cavity and the source, the impedance being sufficiently high to create a pressure differential between the at least one cavity and the source resulting from a breach in the portion of the surface, and monitoring for a change in differential pressure.
- A further embodiment of the invention provides a method of monitoring the integrity of a permeable structure having an outer skin and an inner core of a honeycomb or cellular configuration composed of a plurality of adjoining cells, a number of the cells defining respective cavities internal of the permeable structure, the permeable structure disposed in an environment containing a fluid at an ambient pressure: providing a source of a first fluid at a first pressure greater than the ambient pressure, coupling at least one of the cavities to the source through a high fluid flow impedance to establish a flow of the first fluid through the permeable structure via the cavities, allowing a rate of flow of the first fluid through the permeable structure to stabilize to a steady state rate, and monitoring for a change in the steady state rate of flow of the first fluid through the permeable structure.
- The first fluid source pressure may be substantially constant with respect to the ambient pressure. In one embodiment, providing the first fluid source at the first pressure may comprise setting the first pressure at a level which is sufficiently greater than the ambient pressure to overcome hygroscopic force and capillary action, but not sufficient to be detrimental to the integrity of the structure.
- The first fluid may be a gas. In this event an embodiment of the invention may also comprise providing a moisture trap between the source and the at least one cavity to dry the gas prior to flowing into the permeable structure.
- A structural aspect of the invention may be directed to an aircraft having one or more structures or components provided with one or more internal cavities and a structural monitoring system for monitoring the integrity of one or more of the components or structures, wherein the structural monitoring may comprise a pressure source for pressuring the one or more cavities with a gas, one or more communication channels for placing the one or more cavities in fluid communication with the pressure source, and a monitoring apparatus for monitoring for a change in a rate of seepage of the pressurized gas from the cavities to an external environment. One of the structures or components may include a composite structure having an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, wherein the cells constitute the cavities.
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FIG. 1 is a schematic representation of a first embodiment of the present invention; -
FIG. 2 is a schematic representation of an apparatus in accordance with a further embodiment of the present invention for monitoring the pressure state of cavities within a structure and hence the integrity of the structure; -
FIG. 3 is a schematic representation of a further embodiment of the present invention; -
FIG. 4 a is a schematic representation of a further embodiment of the present invention: -
FIG. 4 b is a schematic representation of a further embodiment of the present invention; -
FIG. 5 a is a schematic representation of a two-layer sandwich structure to which an embodiment of the present invention is applied; -
FIG. 5 b is a variation of the configuration of the embodiment ofFIG. 5 a; -
FIG. 6 is a schematic representation of a three-layer sandwich structure to which an embodiment of the present invention is applied; -
FIG. 6 a is a variation of the configuration of the embodiment ofFIG. 6 ; -
FIG. 6 b is a further variation of the configuration of the embodiment ofFIG. 6 ; -
FIG. 7 is a schematic representation of a four-layer sandwich structure to which an embodiment of the invention is applied; -
FIG. 8 a is a schematic representation of a three-layer sandwich structure to which an embodiment of the present invention is applied; -
FIG. 8 b is a schematic representation of a three-layer sandwich structure to which a further embodiment of the present invention is applied; and -
FIG. 9 shows a partly sectioned oblique view of a further cavity arrangement. - The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternate embodiments.
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FIG. 1 illustrates schematically, one embodiment of a method and apparatus of the present invention for preventing the ingress of a fluid F into astructure 10. Thestructure 10 is a fictitious structure made up from three types of composite structure and is provided merely for the purpose of illustrating the principles of embodiments of the invention. Thestructure 10 has anouter skin 12 and a plurality ofinternal cavities cavities 14”). The actual geometry of thecavities 14 is a function of the type ofstructure 10.Cavities 14 a are illustrative of astructure 10 having internal cavities of a random configuration;cavities 14 b are illustrative of astructure 10 having a honeycomb or cellular-type core, andcavities 14 c are illustrative of astructure 10 having a foam core. - The
structure 10 is disposed in anenvironment 16 containing fluid F at an ambient pressure that acts on thestructure 10. For example, theenvironment 16 may be the atmosphere at 4000 meters above sea level, where the fluid F is air; or theenvironment 16 may be the ocean at depth of 100 meters in which case the fluid F is sea water. -
Apparatus 18 in accordance with an embodiment of the present invention acts to prevent or at least minimize the ingress of the fluid F into thestructure 10. Theapparatus 18 includes apressure source 20 for providing a first fluid such as, air or an inert gas at a pressure higher than the pressure of the fluid F. A communication channel in the form of aconduit 22 provides fluid communication between thesource 20 and one or more of theinternal cavities 14 of thestructure 10. If it is the case that thecavities 14 ofstructure 10 are all directly or indirectly in fluid communication with each other, then in order for the gas ofsource 20 to be in fluid communication with thecavities 14, theconduit 22 need only extend into thestructure 10 to a point where it pierces theskin 12. Further, although not illustrated, a plurality ofconduits 22 can be provided between thesource 20 and thestructure 10. However, if thecavities 14 are not in mutual fluid communication with each other or are arranged in sealed layers or groups, the communication path ofapparatus 18 can include one or more galleries orconduits 24 contained within theskin 12 that communicate with theconduit 22 thereby providing fluid communication between the gas of thesource 20 and thecavities 14. Alternately small perforations can be made between theinternal cavities 14 to allow fluid communication there between. This may for example be achieved using a laser. - The pressure of
source 20 is arranged to be greater than the pressure of fluid F (which may be either a static pressure or a dynamic pressure) so as to prevent the ingress of fluid F into thecavities 14. More particularly, the pressure ofsource 20 is arranged to be sufficient to overcome hygroscopic force and capillary action to prevent moisture ingress into thestructure 10 but is not sufficient to be detrimental to the integrity of thestructure 10. - It is to be recognized that if the
skin 12 is absolutely impermeable to fluid F and such does not contain any faults or does not develop any faults throughout the life of thestructure 10 then the fluid F ofenvironment 16 cannot enter thestructure 10. However, in practice, for a variety of reasons including the effects of material permeability, dynamic loading, localized impact damage, practical imperfections in the manufacture ofstructure 10, or the use of fasteners to fabricate the structure it is often the case that theskin 12 is, or in time becomes, permeable to the fluid F. Thus in practice thestructure 10 has some degree of permeability. Hence fluid F communicated to the cavities permeates through the structure to the surrounding environment. -
FIG. 2 illustrates anapparatus 18 a that allows for the monitoring of the pressure state ofcavities 14 and hence the integrity ofstructure 10 a. Theapparatus 18 a includes afluid source 20 and aconduit 22 a serving a similar function asconduit 22 in the embodiment depicted inFIG. 1 and interconnecting amonitoring device 26 for monitoring the inflow of fluid from thesource 20 into thecavities 14. Themonitoring device 26 is based on that disclosed in International Application No. PCT/AU94/00325 (WO 94/27130), the contents of which is incorporated herein by way of reference. The substantive difference being that a constant (positive) pressure source is employed in embodiments of the present invention, whereas in International Application No. PCT/AU94/00325 (WO 94/27130) a constant vacuum source is employed. Themonitoring device 26 monitors for a change in the steady state rate of inflow of fluid from thesource 20 into thecavities 14. In this embodiment themonitoring device 26 includes a highfluid flow impedance 28 disposed in series in theconduit 22 a between thesource 20 and thecavities 14. The highfluid flow impedance 28 preferably comprises a very long length of small bore duct which allows a minuscule flow of fluid. Alternatively, the highfluid flow impedance 28 could comprise a permeable material such as sintered glass. Theimpedance 28 is sufficiently high to create a minimum discernable pressure differential between the cavities and thesource 20, as a result of permeability, and a measurable pressure differential between the cavities and source resulting from a breech (re crack or other failure) in the structure. - To gain an appreciation of the flow rates through the PCT/AU94/00325 (WO 94/27130) device, the maximum rate of flow is at the minimum that can be detected by current digital flow meters. As an example, a duct having a bore of less than 0.3 mm and a length in excess of 3 meters and experiencing an air pressure drop of 20 kPa across its length would have a flow of approximately 2-3 micro liters/minute. Bearing in mind that sensitivity of the device increases at an exponential rate as zero is approached and, if desired magnitude of the high fluid flow impedance can be extended towards infinity, extremely small flow rates can be detected.
- Generally, the magnitude of the high fluid flow impedance should be sufficiently high as to produce significant pressure drop across the high impedance in response to minuscule flow through the high impedance.
- Measuring means in the form of a
differential pressure transducer 30 is coupled across theimpedance 28. Thetransducer 30 is coupled across theimpedance 28 byfluid connecting ducts 32, and coupled to an amplifier anddisplay 34 byelectrical conductors 36. Alternatively, thedifferential pressure transducer 30 coupled across theimpedance 28 may be in the form of a non-electrical indicator where electrical circuitry is not desirable. - Assuming that the
skin 12 of thestructure 10 a has some degree of inherent permeability, after initial start up of theapparatus 18 a, there will be a characteristic steady state rate of seepage of fluid through and from thestructure 10 a. If there is a change in the permeability of the skin 12l structure 10 a, there will be a corresponding increase in the rate of inflow of the fluid from thesource 20 into thestructure 10 a. This will be monitored and detected by themonitoring device 26. A typical application of this embodiment could be an aircraft door, flap, aileron, and the like supplied with nitrogen at a pressure above ambient. -
FIG. 3 depicts an embodiment of the present apparatus and method when applied to astructure 10 b comprisinganechoic tiles 38 adhered to thehull 40 of a submarine. - A fillet of
elastomeric grout 48 is deposited about the periphery of each tile in a manner so thatcavities 50 are created underneath thegrout 48 betweenadjacent tiles 38 or, undergrout 48 between the edge of atile 38 and the adjacent surface of thehull 40. Thecavities 50 are coupled to amonitoring apparatus 18 b. Theapparatus 18 b is similar to theapparatus 18 a depicted inFIG. 2 and encloses amonitoring device 26 b which includesconduit 22 b that provides a fluid communication path between thecavities 50 and afluid source 20 b (in this example a gas source) via a series connected highfluid flow impedance 28.Differential pressure transducer 30 is coupled across theimpedance 28 viaducts 32. An amplifier anddisplay 34 coupled to thetransducer 30 viaelectrical conductors 36 provides a display of steady state pressure differential across theimpedance 28. The fluid fromsupply 20 is metered through apressure regulator 52 which is disposed in theconduit 22 b between theimpedance 28 and thesource 20. Theregulator 52 is also pressure referenced to the surrounding atmosphere, in this case sea water, herein shown with the notation F.sup.s and associated white pressure indicating arrow heads, via aduct 54. Theregulator 52 maintains the pressure of the gas fromsource 20 at a substantially constant level above the water pressure. As ambient water pressure varies with depth thesystem 18 b, and in particular theregulator 52, is able to dynamically vary the pressure of the gas fromsource 20 delivered to thecavities 50. In operation, themonitoring device 26 b stabilizes with a relatively constant pressure differential across the high impedance irrespective of the ambient water pressure. - The integrity monitoring of the adhesive bonding of the
tiles 38 is facilitated by monitoring the differential pressure across thehigh impedance 28 for any increase resulting from minuscule air seepage from any of thecavities 50 giving ample warning of any disbond of atile 38 or damage to thegrout 48. The imminence of disbanding and water ingress would be immediately obvious due to a rise in pressure differential across theimpedance 28 and detected by thetransducer 30. Loss of atile 38 would result in a dramatic rise in differential pressure. Themonitoring device 26 b can also be provided with an adjustable bypass of theimpedance 28 to allow high rates of flow of air from thesource 20 to allow for some damage tolerance and maintain positive pressure protection for thecavities 50. - As ambient pressure of the sea water F.sup.s surrounding the
hull 40 of the submarine would vary significantly from the top of the conning tower fin to the belly of the hull, it may be necessary to group thetiles 38 into several vertically tiered layers which are monitored separately to ensure that the pressure of the gas supplied to a particular group of tiles remains only slightly above the ambient pressure acting on those tiles thereby preventing excess positive pressure in upper groups of tiles. This can be achieved by providing a manifold in the portion ofconduit 22 b between thesource 20 andregulator 52 and having a plurality ofregulators 52 each feeding from the manifold and coupled to identical arrangements of highfluid flow impedance 28,transducer 30, andambient pressure reference 54. -
FIG. 4 a illustrates a further embodiment of the present invention applied to astructure 10 c comprising threecomponents structure 10 c is part of a pressurized fuselage of an aircraft. Thecomponents rivets 62 which pass throughholes 71 formed in thecomponents rivet 62 has ahead 64 that sits flush with thecomponent 56 and a flattenedtail 66 at an opposite end that sits on thecomponent 60. Flush head rivets are shown as an example but round head rivets and possibly bolt fasteners could be substituted. - Sandwich components generally have a layer of a sealant material between each fastened layer partly to prevent corrosion and fretting. To facilitate the provision of a cavity, this arrangement is modified in the present embodiment such that a
sealant layer 68 is provided betweencomponents components permeable gap 70 there between. In accordance with the present embodiment thegap 70 can be formed into acavity 72 by providing aperimeter seal 74 about the perimeter ofgap 70.Sealant 75 should also be employed sparingly around the flattenedend 66 ofrivets 62 and adjacent surface ofcomponent 60.Apparatus 18 c, enclosingmonitoring device 26 c is connected to thecavity 72 for monitoring the integrity of thestructure 10 c. Themonitoring device 26 c includes aconduit 22 c leading to a parallel connection of highfluid flow impedance 28 andpressure transducer 30. Thetransducer 30 is coupled to an amplifier anddisplay 34 viaelectrical conductors 36. Alternatively, thedifferential pressure transducer 30 coupled across theimpedance 28 may be in the form of a non-electrical indicator where electrical circuitry is not desirable. - The
pressure source 20 c of this embodiment is cabin pressure of the aircraft which feeds into both theimpedance 28 and thetransducer 30. The cabin pressure is marked as “CP” and has associated pressure indicating black arrow heads. - If a crack 100 was to form in the
intermediate component 58 about therivet 62, a fluid seepage flow path (indicated by small black flow indicating arrow heads) can be created around therivet 62 andhead 64 to the outside high altitude atmosphere F.sup.A, associated with white pressure indicating arrow heads, due to the crack 100 and subsequent loosening of the fastening. The resulting increase of the inflow of air intocavity 72 through theimpedance 28 will be detected by thetransducer 30 as a change in differential pressure thus providing an indication of the crack 100 incomponent 58. - In an alternate embodiment depicted in
FIG. 4 b, theapparatus 18′ for monitoring the integrity ofstructure 10 c comprises acompliant container 76 of a fluid marker such as a liquid or gaseous dye, or detectable gas, which is coupled byconduit 22′vice conduit 22 c to thecavity 72. As with the previously described embodiment, if a crack 100 were to develop in thecomponent 58 that extends to therivet 62, there will be a flow of marker from thecontainer 76 throughconduit 22′,cavity 72, the crack 100 and around rivet 62 to seep to the outside atmosphere. This arises because thecompliant container 76 is also subject to cabin pressure CP. The detection of dye or gas about therivet 62 provides an indication of the crack in thecomponent 58. - When the fluid marker is a liquid, detection can be by means of visual inspection of the structure The appearance of the dye say around the head of a
rivet 62 is potentially due to the existence of a crack. When a detectable gas is used as the marker, such as helium, gas monitoring and detecting equipment is required to detect the escape of the gas from the structure. In the case where the structure has some inherent permeability, there will be of course a steady state flow of the gas through the structure in which case one is required to monitor for a change in the steady state condition. On the other hand, if the structure is after initial manufacture absolutely impermeable, then one is required to detect for any presence of the gas marker. This of course is the same as monitoring for the appearance of a significant pressure differential across themonitoring apparatus 26 c indicating a flow where previously no flow existed. However, because of the sensitivity of thefluid impedance device 26 c, the fluid marker method is more likely to be useful in a secondary roll as an indicator of the location of a flaw. -
FIGS. 5-7 depict variations of “sandwich” structures to which embodiments of the present invention can be applied. - In
FIG. 5 a, a portion of astructure 10 d comprises twocomponents rivets 62. A gaspermeable gap 70 exists between mutually facing adjacent surfaces ofcomponents cavity 72 is formed by sealing thegap 70 with aperimeter seal 74. Similar toFIG. 4 a, thestructure 10 d is a portion of an aircraft fuselage containing cabin pressure CP and is disposed in an environment of a fluid F.sup.A being ambient air pressure at high altitude. The integrity of thestructure 10 d can be monitored by connecting thecavity 72 via aconduit 22 d to amonitoring apparatus 26 d similar to 26 c ofFIG. 4 a of the type described herein above. - As the
cavity 72 in thestructure 10 d is completely enveloped by the fluid F, any seepage of gas from thecavity 72 throughcomponent 56 will be to the outside environment F.sup.A. - In a variation of the above arrangement of
FIG. 5 a, shown inFIG. 5 b, theapparatus 26 c could be connected between thecavity 72 and the outside atmospheric pressure F.sup.A. In this example,cavity 72 becomes a conduit for pressure source in form of cabin pressure (CP) in the event of a through flaw developing incomponent 60. This arrangement is further discussed inFIGS. 6 a and 6 b following. - In
FIG. 6 , thestructure 10 e is very similar to thestructure 10 c inFIG. 4 a. However thestructure 10 e is now formed with two cavities, 72 s and 72 n. Thecavity 72 s is formed between mutually adjacent faces ofcomponents structure 10 e. Thecavity 72 s is in fluid communication viaconduit 22 s with thepressure source 20 e (CP) via monitoring apparatus 26 e of like structure and function as described above. Thecavity 72 n however which exists betweencomponents crack 101 in theintermediate component 58 that extends between thecavities component 56. A dotted trail shows the flow path frompressure source 20 e, throughduct 22 s and device 26 e,cavity 72 s, crack 101cavity 72 n,duct 22 n and thence to the outside atmospheric “environmental” pressure F.sup.A. - As a further measure,
cavity 72 n could be communicated viaduct 22 n to a similar apparatus to 26 e (26 x) and thence to an atmospheric pressure reference F.sup.A. This is shown inFIG. 6 a and the employment ofmonitoring apparatus 26 x is basically the same arrangement as shown inFIG. 5 a. The purpose of this arrangement is to monitor the integrity ofcomponent 60. A crack orflaw 102 developing incomponent 60 communicating cabin pressure CP (source 20 e) withcavity 72 n would produce a pressure drop, due to seepage flow (small arrow heads and dots), across the fluid impedance of the apparatus 18 x to the outside environmental F.sup.A. If this feature was desired, the connection ofapparatus 26 x could be normally bypassed or carried out at intervals to prevent a continuous series connection of twomonitoring devices 26 e and 26 x (as shown inFIG. 6 b) which would halve the sensitivity of bothapparatus 26 e and 26 x in response to aflaw 101 occurring incomponent 58. See page flow fromcavity 72 s through a crack (101) incomponent 58, intocavity 72 n, would have to pass through the two high fluid impedances in series ofmonitor 26 e and 26 x and the two associated differential pressure sensors would share the pressure drop resulting in halved sensitivity. The series flow problem is shown by small arrowheads and dots. Of course, if a crack developed incomponent 56 direct to the outside environmental F.sup.A, no such problem would arise. -
FIG. 7 depicts afurther sandwich structure 10 f having four layers orsheets rivets 62.Layer 57 comprises two abutted sheets.Structure 10 f is once again a portion of an aircraft fuselage containing cabin pressure CP and is disposed in an environment of a fluid being ambient air pressure at high altitude. The method of monitoring the integrity ofstructure 10 f includes formingcavities 72 s that are in fluid communication, viaconduits 22 s, with the pressure source CP of a monitoring apparatus of the type described herein above typically 26 c to 26 x and formingcavities 72 n that are in fluid communication viaconduits 22 n with the environmental ambient pressure F.sup.A, withcavities 72 n interspersed betweencavities 72 s. The arrangement for monitoring the integrity ofcomponent 60 ofFIGS. 5 a and 6 a could similarly be applied toFIG. 7 . -
FIG. 8 a depicts a further embodiment of the invention. This embodiment is applied to astructure 10 g comprised of threesheets rivets 62. As explained in relation to the embodiment depicted inFIG. 4 a, it is common for such structures to incorporate a layer ofsealant material 68 between adjacent sheets. Thelayer 68 is typically provided to prevent corrosion and fretting of thesheets rivets 62. In the present embodiment, the step of providingcavities 72 within thestructure 10 g involves removing sections of thesealant 68 between adjacent pairs of sheets. However areas ofsealant 68 are maintained about therivets 62 to maintain the function of minimizing fretting of thesheets cavities 72. The removedsealant 68 produces the sealedcavities 72 which can be placed in fluid communication with a pressure source. Indeedalternate cavities 72 can be placed in fluid communication with the atmosphere and with the source as described above in relation to the embodiments depicted inFIGS. 6 and 7 . The removal of thesealant 68 to produce thecavities 72 is ideally achieved during the construction of thestructure 10 g by placing masks on thesheets sealant 68 in selected regions. After thesealant layer 68 has been applied and the masks removed, thestructure 10 g is pulled together by fastening withrivets 62. -
FIG. 8 b depicts astructure 10 h which differs from that depicted inFIG. 8 a by the inclusion of recesses ordepressions 80 deliberately formed in the surface of thesheets sealant 68 is removed This provides larger, moredefinite cavities 72. The recesses ordepressions 80 can be formed by any known means including but not limited to, chemical milling. Thecavities 72 can be placed in fluid communication with a constant pressure source by conduits typical of 22 c to 22 x in the manner described herein above in relation toFIGS. 4 a-7. Of course in a further variationalternate cavities 72 can be placed in communication with the source 20 (CP) and the ambient pressure F.sup.A. -
FIG. 9 shows a partly sectioned oblique view of a further structure in the form of lap splice 10 j in which preformed elastomeric, self adhesive,film pads 110 are sandwiched betweensheets rivets 62. Thepads 110 comprise shapes cut and assembled so as to definemultiple cavities 72 when sandwiched between theplates cavities 72 as shown as thick lines. By interspersing the connections of thecavities 72 with both atmospheric pressure reference and with cabin pressure interconnected to the monitoring apparatus typical of 26 c to 26 e of previous examples, cracks that may transit asheet surface rivet 62, confirmation of the growth of a crack, by recording a second interception can be achieved to aid the elimination of false positives. For additional reference, the examiner is directed to the specification International Application No PCTIAU94/00325 (WO 94/27130) which shows disclosure of crack detection. - Now that the embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the broad inventive concepts. For example, a moisture trap can be provided between the
source 20 andimpedance 28, when thesource 20 is a gas source to dry the gas prior to flowing into thestructure 10. Additionally, thesource 20 can be a source of an inert gas. Further, anti corrosion agents can be induced into the defined cavities. When thestructure 10 is a composite material having a plurality of internal cavities that are sealed from each other, embodiments of the invention include forming communication paths in the composite material between the internal cavities. All such modifications and variations are deemed to be within the scope of the present invention the nature of which is to be determined from the above
Claims (27)
1. A method of monitoring the integrity of a structure or component comprising:
forming one or more cavities internally of the structure or component;
pressuring the one or more cavities with a gas; and
monitoring for a change in rate of seepage of the gas from the at least one of the cavities.
2. The method according to claim 1 , wherein, when the structure or component is comprised of two or more parts, forming the cavities comprises attaching at least two of the parts together in an overlapping relationship and wherein the cavities incorporate mutually adjacent surfaces of the attached overlapping at least two parts.
3. The method according to claim 2 , wherein the attaching at least two of the parts together comprises attaching the two parts with one or more mechanical fasteners and wherein at least one of the mechanical fasteners has a surface disposed in at least one of the cavities.
4. The method according to claim 2 , wherein forming the cavities comprises providing a sealant between the two overlapping parts and circumscribing the cavities.
5. The method according to claim 1 , wherein pressurizing the cavities comprises pressurizing the cavities to a pressure which is sufficiently greater than pressure outside of the structure or component to overcome hygroscopic force and capillary action, but not sufficient to be detrimental the integrity of the structure or component.
6. The method according to claim 1 , wherein forming the cavities comprises forming a reference cavity in the structure or component, wherein the reference cavity is separated from the one or more cavities, and wherein the reference cavity is vented to ambient pressure.
7. The method according to claim 1 , wherein, when the structure or component is a composite structure having an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, forming the cavities comprises utilizing one or more of the cells as the cavities.
8. The method according to claim 1 , wherein the monitoring comprises coupling a high fluid flow impedance in series between the one or more cavities and a source of pressurized gas used to pressurize the cavities, the high fluid flow impedance being sufficiently high to create a pressure differential between at least one of the cavities and the source in the event of seepage of gas through the at least one of the cavities to a lower pressure environment, and monitoring for a change in the differential pressure.
9. The method according to claim 1 , wherein the component or structure is a component or structure of an aircraft.
10. The method according to claim 1 , wherein the gas is nitrogen.
11. A method of monitoring the integrity of a structure or component formed from two or more parts, wherein the structure or component is provided with one or more cavities formed between the two or more parts, and wherein the cavities incorporate respective surface portions of at least two of the parts, the method comprising:
exposing the structure or component to an ambient pressure environment;
pressurizing the one or more cavities with a gas at a pressure greater than the ambient pressure; and
monitoring for a change in a rate of seepage of the pressurized gas from the at one or more cavities to the ambient pressure environment.
12. The method according to claim 11 , wherein the cavities are formed by attaching at least two of the parts together in an overlapping relationship, and wherein the cavities incorporate mutually adjacent surfaces of the attached overlapping two parts.
13. The method according to claim 12 , wherein the attaching at least two of the parts together comprises attaching the parts with one or more mechanical fasteners, and wherein at least one of the mechanical fasteners is disposed in at least one of the cavities.
14. The method according to claim 13 , wherein the formed cavities are formed by providing a sealant or bonding material between the two overlapping parts and circumscribing the cavities.
15. The method according to claim 11 , wherein pressurizing an interior of the at least one or more cavities comprises pressurizing the at least one or more cavities to a pressure which is sufficiently greater than the ambient pressure to overcome hygroscopic force and capillary action, but not sufficient to be detrimental the integrity of the structure or component.
16. The method according to claim 11 , further comprising separating at least one of the cavities from the one or more cavities to form at least one corresponding reference cavity in the structure or component, and venting at least one of the reference cavities to the ambient pressure environment.
17. The method according to claim 11 , wherein the monitoring comprises coupling a high fluid flow impedance in series between the one or more cavities and a source of the pressurized gas, the high fluid flow impedance being sufficiently high to create a pressure differential between at least one of the cavities and the source in the event of a flow of air from an interior of the structure or component through the at least one of the cavities to the ambient pressure environment and monitoring for a change in the differential pressure.
18. A method of monitoring the integrity of a composite structure, the composite structure having an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, one or more of the cells forming respective cavities, the method comprising:
pressurizing the inner core with a gas at a pressure greater than air pressure outside the outer skin; and
monitoring for a change in a rate of seepage of the pressurized gas from the inner core.
19. The method according to claim 18 , further comprising forming one or more galleries or conduits between two or more of the cells.
20. The method according to claim 18 , wherein pressurizing the inner core comprises pressurizing an interior of the composite structure to a level which is sufficiently greater than air pressure outside the outer skin to overcome hygroscopic force and capillary action but not sufficient to be detrimental to the integrity of the composite structure.
21. A method of monitoring the integrity of an attachment between two or more parts, the method comprising:
forming one or more cavities between two or more of the parts;
pressurizing the one or more cavities with a gas at a pressure greater than air pressure outside the one or more cavities; and
monitoring for a change in a rate of seepage of the gas from at least one of the cavities.
22. The method according to claim 21 , wherein the attachment is a lap joint comprising the two or more parts and the attachment comprises a plurality of mechanical joiners coupling the parts together.
23. The method according to claim 21 , wherein the attachment is a composite structure and two of the parts comprise an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, wherein the attachment comprises a bond between the skin and the inner core, and wherein the cavities comprise the cells.
24. An aircraft comprising:
one or more structures or components provided with one or more internal cavities; and
a structural monitoring system for monitoring the integrity of one or more of the components or structures, the structural monitoring comprising;
a pressure source for pressuring the one or more cavities with a gas;
one or more communication channels for placing the one or more cavities in fluid communication with the pressure source; and
a monitoring apparatus for monitoring for a change in a rate of seepage of the pressurized gas from the cavities to an external environment.
25. The aircraft according to claim 24 , wherein one of the structures or components is a composite structure having an inner core of a honeycomb or cellular configuration composed of adjoining cells and an outer skin bonded to and surrounding the inner core, and wherein the cells constitute the cavities.
26. The aircraft according to claim 24 , wherein one of the structures or components is a lap joint between two or more overlapping parts and wherein the cavities are formed between adjacent surfaces of the overlapping parts.
27. The aircraft according to claim 24 , wherein the lap joint comprises a plurality of mechanical fasteners and wherein one or more of the mechanical fasteners joiner pass through one of the cavities.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US12/390,545 US20090173827A1 (en) | 2001-07-13 | 2009-02-23 | Method and apparatus for monitoring the integrity of components and structures |
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AU0018 | 1985-04-04 | ||
US09/905,681 US20020029614A1 (en) | 2000-08-09 | 2001-07-13 | Method and apparatus for monitoring the integrity of components and structures |
AUPR001801 | 2001-09-08 | ||
US11/260,882 US7500383B2 (en) | 2001-07-13 | 2005-10-27 | Method and apparatus for monitoring the integrity of components and structures |
US12/390,545 US20090173827A1 (en) | 2001-07-13 | 2009-02-23 | Method and apparatus for monitoring the integrity of components and structures |
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US11/260,882 Continuation US7500383B2 (en) | 2001-07-13 | 2005-10-27 | Method and apparatus for monitoring the integrity of components and structures |
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US20090173827A1 true US20090173827A1 (en) | 2009-07-09 |
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US11/260,882 Expired - Fee Related US7500383B2 (en) | 2001-07-13 | 2005-10-27 | Method and apparatus for monitoring the integrity of components and structures |
US12/390,545 Abandoned US20090173827A1 (en) | 2001-07-13 | 2009-02-23 | Method and apparatus for monitoring the integrity of components and structures |
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US11/260,882 Expired - Fee Related US7500383B2 (en) | 2001-07-13 | 2005-10-27 | Method and apparatus for monitoring the integrity of components and structures |
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ES2739379T3 (en) * | 2006-03-16 | 2020-01-30 | Structural Monitoring Systems Ltd | Component cracking monitoring procedure |
US7942032B2 (en) * | 2006-04-04 | 2011-05-17 | Structural Monitoring Systems Ltd. | Method for detecting impact damage in a structure |
EP2044417A4 (en) * | 2006-04-04 | 2015-06-24 | Structural Monitoring Sys Ltd | Method for detecting separation in a structure |
EP2329106B1 (en) * | 2008-09-24 | 2019-09-18 | Schlumberger Technology Corporation | Method, device, and system for determining water or liquid in the annulus of a flexible riser or flowline |
US9128020B2 (en) * | 2012-08-31 | 2015-09-08 | Johnson & Johnson Comsumer Inc. | Permeability flow cell and hydraulic conductance system |
BR112015028037A2 (en) * | 2013-05-06 | 2017-09-12 | Univ Brussel Vrije | effective structural health monitoring |
ES2903551T3 (en) * | 2016-04-21 | 2022-04-04 | Structural Monitoring Systems Ltd | Detection system for monitoring the integrity of a structure |
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Also Published As
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US7500383B2 (en) | 2009-03-10 |
US20070107496A1 (en) | 2007-05-17 |
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