Abstract:
A method for detecting a crack in a frame is disclosed. The method includes sensing with a first pressure sensor a first pressure within a first sealed cavity. The first sealed cavity is interior to a first structure of the frame. Additionally, the method includes detecting a first change in the sensed first pressure. The method also includes determining preliminarily that a crack has formed in the first structure based on the detected change in the sensed first pressure. In addition, the method includes determining a criticality of the crack.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a detection method and, more particularly, to a method for detecting a crack in a machine frame. 
       BACKGROUND 
       [0002]    Large machines such as, for example, wheel loaders, off-highway haul trucks, excavators, motor graders, and other types of earth-moving machines include frames to support their movement. Some of these frames are weld reparable (the frames are expected to crack during their economically useful life). Cracks in the frame are detected during regular inspections, and then repaired through welding. But, because of the size of the machines and/or the working environment of the machines, the frames can be difficult to inspect quickly and efficiently. In fact, it is not uncommon for a machine to be taken out of service for twenty-four hours while its frame is first completely cleaned, and then visually inspected for cracks. This problem can be exacerbated when parts of the frame are not easily accessible to maintenance crews. A frame that requires regular complete visual inspections can result in low productivity and efficiency. Also, potentially hazardous cracks may not be detected through a visual process. For example, a crack may form in a hidden side of a frame element. After an inspection, the crack may expand until it completely severs the frame element. When the frame element is severed, a portion of the machine may collapse, causing injury to an operator or nearby person, or extensive damage to the machine itself or a nearby machine or structure. 
         [0003]    One way to reduce inspection time associated with crack detection is described in U.S. Pat. No. 4,721,413 (the &#39;413 patent) issued to Crohas et al. on Jan. 26, 1988. The &#39;413 patent describes a marine platform with a structure consisting of a lattice of tubular elements sealingly connected to one another. When a crack forms in one of the tubular elements, a fluid passes into and/or out of the tubular element. Some of the tubular elements are submerged, and have attached pickups. Each pickup is configured to detect the passage of fluid into and/or out of a tubular element. The interiors of multiple tubular elements may be connected to each other, thereby increasing the detection region of a pickup. When a pickup detects fluid passage, the pickup acoustically transmits a signal to a submerged intermediate transmission means, which wiredly transmits the signal to an unsubmerged signal acquisition unit. The signal contains information about where the pickup is located and what the pickup detected. 
         [0004]    Although the pickups of the &#39;413 patent may help detect cracks in a tubular structure, the pickups may do little to pinpoint the exact location of a crack. Furthermore, though the pickups of the &#39;413 patent may communicate the general region of the crack to a signal acquisition unit, the signal acquisition unit may do little to assess the tolerability or criticality of the crack. In addition, though the pickups of the &#39;413 patent may detect the existence of the crack during the time period between inspections, permanent installation of pickups may be prohibitively expensive for certain applications. 
         [0005]    The disclosed method and system are directed to overcoming one or more of the problems set forth above. 
       SUMMARY 
       [0006]    In one aspect, the present disclosure is directed to a method for detecting a crack in a frame. The method includes sensing with a first pressure sensor a first pressure within a first sealed cavity. The first sealed cavity is interior to a first structure of the frame. Additionally, the method includes detecting a first change in the sensed first pressure. The method also includes determining preliminarily that a crack has formed in the first structure based on the detected change in the sensed first pressure. In addition, the method includes determining a criticality of the crack. 
         [0007]    In another aspect, the present disclosure is directed to a machine. The machine includes a frame. The frame includes a first sealed cavity. A first port is associated with the first sealed cavity. And, a first valve is configured to control communication of fluid to and from the first sealed cavity via the first port. The machine also includes a first pressure sensor. The first pressure sensor is associated with the first port to open the first valve. And, the first pressure sensor is configured to sense the pressure within the first sealed cavity and generate a corresponding first signal. Additionally, the machine includes a controller that is in communication with the first pressure sensor. The controller is configured to provide a first frame crack warning based on the first signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a pictorial illustration of an exemplary disclosed machine having an exemplary disclosed frame; 
           [0009]      FIG. 2  is an exploded-view illustration of the frame of  FIG. 1 ; 
           [0010]      FIG. 3  is a pictorial illustration of exemplary sealed cavities interior to the frame of  FIG. 1 ; 
           [0011]      FIG. 4  is an enlarged pictorial illustration of an exemplary sealed cavity interior to the frame of  FIG. 1 ; 
           [0012]      FIG. 5  is an enlarged cross-sectional illustration of an exemplary disclosed pressure sensor and port for use with the sealed cavity of  FIG. 4 ; and 
           [0013]      FIG. 6  is a diagrammatic illustration of an exemplary disclosed control system for use with the pressure sensor of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates an exemplary frame  10  for a machine  12 . The machine  12  is depicted as an off-highway haul truck. But, it is contemplated that machine  12  may be, for example, a wheel loader, an excavator, a motor grader, or another type of machine. 
         [0015]      FIG. 2  illustrates an exploded-view of frame  10 . Frame  10  may embody any structural unit that may support movement of machine  12 . Frame  10  may be, for example, a stationary base frame connecting a power source to a traction device, a moveable frame member of a linkage system, or another frame known in the art. 
         [0016]    Frame  10  may have one or more sub-assemblies. In particular, frame  10  may have a base sub-assembly  14 , which supports and stabilizes other sub-assemblies. Frame  10  may also have a drop tube sub-assembly  16 , which supports a work tool  17  (referring to  FIG. 1 ), and a cab sub-assembly  18 , which supports an operator station  19  (referring to  FIG. 1 ). Each sub-assembly may include one or more box sections. Box sections may be, for example, beams having substantially hollow cross-sections. Box sections of frame  10  may be connected to each other via welding or in another way known in the art. Alternatively, box sections of frame  10  may be connected to each other via castings, thereby moving welds to lower stress areas. Castings of frame  10  may be, for example, fabricated from mild steel, and have large radii with internal reinforcing ribs to dissipate stress in areas of high stress concentration. 
         [0017]    Base sub-assembly  14  may include two main rails  20 , one rear support  22 , one center tube  24 , two front rails  26 , and one bumper  28 . The rearward end of each main rail  20  may be connected to the forward end of an associated tail casting  30 , the tail casting  30  extending generally parallel to the main rail  20  toward the rear of machine  12 . Each tail casting  30  may be connected to an outward end of rear support  22 . Rear support  22  may thus connect the inward sides of each tail casting  30 . Forward of rear support  22 , a center tube support casting  32  may be connected to and extend inward from each main rail  20 . Each center tube support casting  32  may be connected to one outward end of a center tube  24 . Center tube  24  may thus connect the inward sides of each center tube support casting  32 . Forward of center tube  24 , the forward end of each main rail  20  may be connected to a main casting  34 , the main casting  34  extending generally parallel to the main rail  20 . Each main casting  34  may also be connected to an outward end of a steering box  36 . Steering box  36  may thus connect the inward sides of each main casting  34 . 
         [0018]    Each main casting  34  may also be connected to one front rail  26 , the forward end of the main casting  34  connecting to the rearward end of the associated front rail  26  and the front rail  26  extending generally parallel to the main casting  34  toward the front of machine  12 . The forward end of both front rails  26  may connect to the rearward side of bumper  28 . Bumper  28  may thus connect the forward ends of each front rail  26 . 
         [0019]    Drop tube sub-assembly  16  may be connected to the two main rails  20  of base sub-assembly  14 . Drop tube sub-assembly  16  may include one drop tube  38  and/or another box member and/or casting necessary to support work tool  17  (referring to  FIG. 1 ). Work tool  17  may embody, for example, a container, a bucket, a plow, a truss boom, or another work tool known in the art. And, it may be connected to drop tube sub-assembly  16  via hydraulic actuators, hinges, threaded fasteners, or other connection devices known in the art. Each end of drop tube  38  may connect to the inward side of one main rail  20 , thereby connecting the two main rails  20 . Drop tube  38  may be located gravitationally lower than and forward of rear support  22  and gravitationally lower than and rearward of center tube  24  when frame  10  is in an assembled upright position. Alternatively, drop tube  38  may be located forward of center tube  24 . 
         [0020]    Cab sub-assembly  18  may be connected to a top side (gravitationally upper side when frame  10  is in an upright assembled position) of base sub-assembly  14 . Cab sub-assembly  18  may include the two main rails  20  of base sub-assembly  14 , the two front rails  26  of base sub-assembly  14 , two rear pedestals  40 , two front pedestals  42 , two fore-aft beams  44 , a main beam  46 , a front cross tube  48 , two slip castings  50 , and/or another box member and/or casting necessary to support operator station  19  (referring to  FIG. 1 ). Cab sub-assembly  18  may be connected to the top side of base sub-assembly  14  at four points. At two of these points, the lower end of each rear pedestal  40  may connect to an upper side of an associated main rail  20 . Rear pedestals  40  may be located forward of center tube  24  and drop tube  38 , and rearward of main castings  34 . At two other points, the lower end of each front pedestal  42  may be connected to the upper and outward sides of an associated front rail  26 . Front pedestals  42  may be located forward of main castings  34 , and rearward of bumper  28 . 
         [0021]    The upper end of both rear pedestals  40  may connect to the lower side of main beam  46 . Main beam  46  may thus connect the upper ends of each rear pedestal  40 . The forward side of main beam  46  may be connected to the rearward end of both fore-aft beams  44 . Main beam  46  may thus connect the rearward ends of each fore-aft beam  44 . Fore-aft beams  44  may extend forward from main beam  46  generally parallel to front rails  26 . The forward end of each fore-aft beam  44  may connect to the rearward end of an associated slip casting  50 , the slip casting  50  extending generally parallel to the fore-aft beam  44 . 
         [0022]    The forward end of each slip casting  50  may connect to the rearward side of one front pedestal  42 , thereby completing a chain of connections (main rails  20  to rear pedestals  40 , rear pedestals  40  to main beam  46 , main beam  46  to fore-aft beams  44 , fore-aft beams  44  to slip castings  50 , slip castings  50  to front pedestals  42 , and front pedestals  42  to front rails  26 ) to connect main rails  20  to front rails  26 . Front pedestals  42  may be connected to each other by front cross tube  48 . Each outward end of front cross tube  48  may connect to the inward side of one front pedestal  42 . Front cross tube  48  may be located gravitationally upward (when frame  10  is in an upright assembled position) of front rails  26  and forward of slip castings  50 . 
         [0023]      FIG. 3  illustrates drop tube sub-assembly  16  and cab sub-assembly  18  assembled to base sub-assembly  14 , thereby forming frame  10 . Each box section and/or casting of frame  10  (hereafter “tubular frame element  52 ”) may include a sealed cavity  54 . For example, main rails  20  may include sealed cavities  54   a , main castings  34  may include sealed cavities  54   b , and front rails  26  may include sealed cavities  54   c . It is contemplated that most, if not all, tubular frame elements  52  may include a sealed cavity  54 . Alternatively, two or more connected tubular frame elements  52  (hereafter “region  56 ”) may together have a single sealed cavity  54 . As illustrated in  FIG. 4 , for example, front rail  26  and main casting  34  may be connected by a weld  58 , which may wrap around the edges of a rearward end  60  of front rail  26  and the edges of a forward end  62  of main casting  34 . A central bore  64  may pass through rearward end  60  and forward end  62 , allowing fluid communication between sealed cavities  54   b  and  54   c , thereby forming a larger sealed cavity  54   d.    
         [0024]      FIG. 5  illustrates the cross section of a tubular frame element  52 , which may be part of a region  56  (referring to  FIG. 4 ), and which may include a sealed cavity  54 . Sealed cavity  54  may be accessible via a port  66 . Port  66  may be located on a surface of tubular frame element  52  that is easily accessible by maintenance personnel or other interested persons, and may allow intentional communication of a pressurized fluid  68  to and from sealed cavity  54 . In particular, port  66  may include a central bore  70  in fluid communication with sealed cavity  54 . A check valve  72  may be situated within central bore  70  to control the flow of fluid between central bore  70  and the atmosphere. Check valve  72  may normally be closed to inhibit the flow of fluid from central bore  70 . Fluid  68  may be a gas such as, for example, nitrogen, helium, argon, air, or another gas known in the art. And, fluid  68  may be easily distinguishable from another fluid  74  situated exterior to tubular frame element  52 . For example, fluid  68  may be, or may be dyed to be, a different color than fluid  74 . The dye may be, for example, disperse red number 9 (1-methylaminoanthraquinone), yellow number 7 (1,9-benz-10-anthrone), or another dye that is a different color than fluid  74 . It is contemplated that the dye may discolor tubular frame element  52 . Alternatively, fluid  68  may be gaseous while fluid  74  is liquid. In yet another alternative, fluid  68  may be, or may be altered to be, detectable by olfactory means. An alteration may include, for example, adding an odorant detectable by persons and/or devices to fluid  68 . This odorant may be, for example, mercaptan, or another odorant known in the art. A pressure sensor  76  may be associated with sealed cavity  54  to sense the pressure therein. 
         [0025]    Pressure sensor  76  may be assembled to tubular frame element  52  via port  66 . When assembled, pressure sensor  76  may open check valve  72 , thereby providing fluid communication between pressure sensor  76  and sealed cavity  54 . Pressure sensor  76  may conduct signals to and from a controller  78  (referring to  FIG. 6 ). These signals may include the identity of pressure sensor  76 ; the current pressure within sealed cavity  54 , as sensed by pressure sensor  76 ; the rate of change of the pressure within sealed cavity  54 , as sensed by pressure sensor  76 ; and/or another signal representing desirable information regarding pressure sensor  76  or sealed cavity  54 . 
         [0026]    Referring to  FIG. 6 , controller  78  may be associated with one or more pressure sensors  76  to gather information about frame  10 . Controller  78  may include means for monitoring, recording, storing, indexing, processing, and/or communicating information. These means may include, for example, a memory, one or more data storage devices, a central processing unit, and/or another component that may be used to run the disclosed applications. Furthermore, although aspects of the present disclosure may be described generally as being stored in memory, one skilled in the art will appreciate that these aspects can be stored on or read from different types of computer program products or computer-readable media such as computer chips and secondary storage devices, including hard disks, floppy disks, optical media, CD-ROM, or other forms of RAM or ROM. 
         [0027]    Controller  78  may be attached directly or indirectly to frame  10 . Alternatively, controller  78  may be located in a hand held device.  FIG. 6  illustrates possible communications pathways between controller  78  and other devices. In particular, controller  78  may communicate wiredly or wirelessly with one or more pressure sensors  76  and a location index  80  to determine the location, tolerability, and criticality of pressure changes within sealed cavities  54 . Controller  78  may also communicate wiredly or wirelessly with a compressor  81  to repressurize sealed cavities  54 , thereby allowing controller  78  to analyze additional pressure changes within sealed cavities  54 . In addition, controller  78  may communicate wiredly or wirelessly with an operator interface device  82  to warn an operator or other interested person of pressure changes and, if necessary, schedule frame crack repairs. 
         [0028]    Location index  80 , electronic in form, may be stored in the memory of controller  78 . Location index  80  may be updated by an operator or other interested person to reflect the locations of pressure sensors  76 . Specifically, location index  80  may contain a unique identifier for each pressure sensor  76 . This unique identifier may be associated with a location value representing a certain sealed cavity  54  interior to a certain tubular frame element  52  or region  56  (hereafter “structure  84 ”). The location value may be associated with a tolerability value and/or a criticality value. 
         [0029]    The tolerability value may represent a minimum magnitude of a pressure change or a minimum rate of pressure change that signifies a potential crack, larger tolerability values representing poorly sealed cavities. For example, main casting  34  may have a very large tolerability value because it may be poorly sealed since it has a complex geometry and is joined to three other tubular frame elements  52 . But, rear support  22  may have a very small tolerability value because it may be very well sealed since it has a simple geometry and is joined to only two other tubular frame elements  52 . 
         [0030]    The criticality value may represent the hazardousness of a crack in structure  84 , larger criticality values representing more hazardous cracks (i.e. more urgently needed repair). For example, main rail  20  may have a very large criticality value since a crack in main rail  20  may lead to a collapse of work tool  17 , causing injury to an operator or nearby person, or damage to a nearby machine or structure. But, front cross tube  48  may have a very small criticality value since a crack in front cross tube  48  may only lead to the discomfort of an operator. 
         [0031]    As previously discussed, controller  78  may use compressor  81  to repressurize sealed cavity  54 . In particular, compressor  81  may be fluidly connected to sealed cavity  54  to increase the pressure within sealed cavity  54  (by compressing air into sealed cavity  54 ) to a pressure greater than that of fluid  74 . Compressor  81  may embody a fixed geometry compressor, a variable geometry compressor, or any other type of compressor known in the art. 
         [0032]    Controller  78  may use operator interface device  82  to warn an operator or other interested person of the hazardous crack and schedule frame crack repairs. For example, operator interface device  82  may be a monitor, LCD screen, plasma screen, screen of a handheld device, warning lamp; alarm; horn; head-up display, offboard system, or another device operable to warn an operator or other interested person of pressure changes, and if necessary, schedule frame crack repairs. It is contemplated that controller  78  may also use operator interface device  82  to relay additional information about these pressure changes. For example, controller  78  may use operator interface device  82  to display the real-time pressure sensed by pressure sensor  76 , the sealed cavity  54  associated with pressure sensor  76 , the tolerability values associated with sealed cavity  54 , the criticality value associated with sealed cavity  54 , and/or other desirable information regarding pressure sensor  76  or sealed cavity  54 . 
       INDUSTRIAL APPLICABILITY 
       [0033]    The disclosed system may be applicable to any machine frame susceptible to cracking, for example, the frame of an off-highway haul truck. The system may detect information about the pressure within a sealed cavity of the frame, and report this information to interested persons. In particular, the disclosed system may detect when and where the frame cracks. Operation of the system will now be described. 
         [0034]    The disclosed system may pressurize a sealed cavity of frame  10 . Specifically, a filling device (not shown) may be connected to tubular frame element  52  via port  66 . During connection, the filling device may open check valve  72 , thereby providing fluid communication between the filling device and sealed cavity  54 . The filling device may pressurize sealed cavity  54  with fluid  68  to a pressure greater than that of fluid  74 . For example, the pressure difference between fluid  68  and fluid  74  may be greater than the minimum pressure change discernible by pressure sensor  76 . The filling device may then be disconnected from tubular frame element  52 , thereby closing check valve  72  to prevent fluid  68  from escaping sealed cavity  54  through port  66 . It is contemplated that it may be advantageous to repressurize sealed cavity  54 , possibly during machine  12  operation. For example, fluid  68  may slowly leak from sealed cavity  54  until the pressure difference between fluid  68  and fluid  74  is no longer greater than the minimum pressure change discernible by pressure sensor  76 . Therefore, the disclosed system may automatically use compressor  81  to repressurize sealed cavity  54  so that a pressure change within sealed cavity  54  is again discernible by pressure sensor  76 . 
         [0035]    The disclosed system may also detect pressure changes within the sealed cavity. Prior to operation of machine  12 , pressure sensor  76  may be assembled to tubular frame element  52  via port  66 . As pressure sensor  76  is assembled, it may open check valve  72 , thereby providing fluid communication between pressure sensor  76  and sealed cavity  54 . Maintenance personnel or other persons may update location index  80  to reflect that pressure sensor  76  is in fluid communication with sealed cavity  54 . Additionally, an operator or other interested person may update location index  80  to reflect the tolerability and criticality values of structure  84 . 
         [0036]    During operation of machine  12 , controller  78  may communicate with pressure sensor  76  to determine the unique identifier of pressure sensor  76 . Controller  78  may also communicate with location index  80  to determine, based on the unique identifier of pressure sensor  76 , the sealed cavity  54  with which pressure sensor  76  is in fluid communication. Additionally, controller  78  may communicate with location index  80  to determine, based on the unique identifier of pressure sensor  76 , the structure  84  exterior to sealed cavity  54 . 
         [0037]    Having determined pressure sensor  76  is in fluid communication with sealed cavity  54  interior to structure  84 , controller  78  may further communicate with location index  80  to determine the tolerability and criticality values of sealed cavity  54 . Controller  78  may compare the tolerability value (representing a minimum magnitude or rate of pressure change signifying a potential crack) to a detected pressure change. The detected pressure change may be of the same type as the tolerability value (i.e. a tolerability value representing a magnitude may be compared to a detected pressure change representing a magnitude and a tolerability value representing a rate may be compared to a detected pressure change representing a rate). 
         [0038]    When the detected pressure change is greater than the tolerability value, controller  78  may preliminarily determine that the pressure change is the result of a crack in structure  84  (i.e. controller  78  may preliminarily detect a crack in structure  84 ). But, when the pressure change and tolerability value each represent magnitudes (as opposed to rates) the preliminary determination may be a false positive. For example, a slow leak (possibly the result of sealed cavity  54  being poorly sealed) may, after sufficient time, lead to a pressure change greater in magnitude than the tolerability value. But, this pressure change may not represent a crack. Therefore, controller  78  may double check the structure  84  crack detection. Soon (within a few minutes) after using compressor  81  to repressurize sealed cavity  54 , controller  78  may again compare the tolerability value to another pressure change detected by pressure sensor  76 . When this pressure change is again greater than the tolerability value, controller  78  may confirm the preliminary structure  84  crack detection. Otherwise, controller  78  may determine the preliminary structure  84  crack detection is a false positive and disregard it. 
         [0039]    Having determined that there is a crack in structure  84 , when the criticality value for structure  84  is sufficiently large (i.e. the crack is hazardous), the disclosed system may warn an operator or other interested person of the crack and, if necessary, schedule frame crack repairs. Specifically, controller  78  may use an operator interface device  82  to warn an operator or other interested person of the crack in structure  84  and, if necessary, automatically interface with a repair database (not shown) to schedule frame crack repairs. Additionally, controller  78  may use operator interface device  82  to notify the operator or other interested person of what triggered the structure  84  crack detection. In particular, operator interface device  82  may be used to display the real-time and/or historical pressures sensed by pressure sensor  76 , and the tolerability and criticality values associated with structure  84 . 
         [0040]    The disclosed system may also be used to locate the exact position of a crack. In particular, escaping fluid  68  may be detectable by maintenance personnel or other interested persons because it is visibly and/or olfactorily distinguishable from fluid  74 . It is contemplated that the pressure of fluid  68  may equalize with that of fluid  74  before maintenance personnel or other interested persons may inspect structure  84 . When this occurs, sealed cavity  54  may be repressurized (using the filling device or compressor  81 ). Once repressurized, fluid  68  may again escape from sealed cavity  54 , and be detectable by maintenance personnel or other interested persons. Alternatively, escaping fluid  68  may discolor structure  84  in the exact position of a crack. The discoloration may remain visible to maintenance personnel or other interested persons after the pressure of fluid  68  has equalized with that of fluid  74 . 
         [0041]    The disclosed system may be operated continuously without needlessly distracting an operator. When operated continuously, it is contemplated that controller  78  may be connected directly or indirectly to frame  10 . Controller  78  may periodically communicate with one or more pressure sensors  76  to determine when the pressure within individual sealed cavities  54  changes. When this pressure changes, controller  78  may automatically use operator interface device  82  to warn an operator or other interested person of a hazardous crack, based on a preliminary or confirmed structure  84  crack detection, and a sufficiently large structure  84  criticality value. The operator or other interested person may then appropriately handle the situation. For example, the operator or other interested person may proceed to a maintenance facility, call a maintenance team, or act in another way known in the art. Additionally, controller  78  may automatically use operator interface device  82  to schedule frame crack repairs. It is contemplated that preliminary and/or confirmed structure  84  crack detections with insufficiently large structure  84  criticality values (i.e. detected structure  84  cracks that are not hazardous) may be of little concern to the operator. Therefore, controller  78  may store information regarding these detections. The detections may then be handled by maintenance personnel or other interested persons during routine inspections and/or at other more convenient times. 
         [0042]    The disclosed system may alternatively be operated only during routine inspections. When operated during routine inspections, pressure sensors  76  and controllers  78  may be shared between more than one frame  10 , thereby reducing total equipment costs. In particular, a routine inspection may begin with one or more sealed cavities  54  being pressurized with fluid  68 . A pressure sensor  76  may then be assembled to each structure  84 . It is contemplated that controller  78  and operator interface device  82  may be integral components within a handheld device. Controller  78  may periodically communicate with one or more pressure sensors  76  over a fixed period of time to determine when the pressure within individual sealed cavities  54  changes. When the pressure changes, controller  78  may automatically use operator interface device  82  to warn maintenance personnel or other interested persons of a hazardous crack, based on a preliminary or confirmed structure  84  crack detection. Maintenance personnel or other interested persons may then appropriately handle the situation. For example, a hazardous crack may be immediately repaired. But, a non-hazardous crack may be scheduled for repair on a later date. After the fixed period of time has elapsed, pressure sensors  76  may be disassembled from their associated structures  84 . Sealed cavities  54  may then be depressurized through their ports  66 . It is contemplated that maintenance personnel or other interested persons may have fewer pressure sensors  76  than there are sealed cavities  54  in frame  10 . Therefore, the maintenance personnel or other interested persons may repeat the above process as necessary until a pressure sensor  76  has been assembled to and disassembled from each structure  84  of frame  10 . 
         [0043]    It will be apparent to those skilled in the art that various modifications and variations can be made to the method and system of the present disclosure. Other embodiments of the method and system will be apparent to those skilled in the art from consideration of the specification and practice of the method and system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.