Method and apparatus for monitoring the integrity of components and structures

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.

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.