HK1056393B - System and method for the detection and propagation measurement of flaws in a component or structure - Google Patents

Description

System and method for detection and diffusion measurement of defects in a component or structure

Technical Field

The present invention relates to a system and method for continuously monitoring the structural integrity of a component or structure, and in particular, for detecting the integrity of a structure or component to provide an early indication and location of impending defects such as faults or cracks, and monitoring the development of faults or cracks.

Background

A very important function of design and maintenance engineers is to monitor to locate and evaluate the initial position of a surface fault or crack generated in a component or part under static or dynamic loading and then determine the likely propagation path and rate of development of the fault or crack. Examples of situations where monitoring of surface faults and cracks is critical include on the wing portion of an aircraft; turbine blades on jet engines, ship hulls and boilers in nuclear power plants. Monitoring is often done by visual observation only. However, it should be understood that when faults or cracks initially occur, they are typically very small and invisible to the naked eye. In addition, faults or cracks may develop within components or parts that are physically difficult or virtually impossible to access.

The system for measuring the rate of microcrack development must have a high sensitivity. International application PCT/AU94/00325 in the name of Tulip Bay (WO94/27130) discloses a monitoring device which may be used to detect faults or cracks in the surface of a component. The monitoring device described includes a substantially constant vacuum source connected in series with a high impedance device to a fluid flow device which is in turn connected to one or more small defect detecting cavities formed in the surface of the component. A differential pressure transducer is connected across the high impedance device to the fluid flow device to monitor the vacuum condition of the small defect detection cavity relative to a constant vacuum source. Thus, if a change in the vacuum state within the cavity occurs, which may be caused by the formation and propagation of a crack, the change is detected by the transducer. In this way, cracks as small as 250 microns long can be detected using a constant vacuum source of only 20kPa below atmospheric pressure reference. Upon initial indication, a slight increase in crack development may be detected. Embodiments of the present apparatus and method are suitable for use with the monitoring apparatus described in the above international application.

In US4145915 and US4109906, Oertle claims early crack detection, but lacks sensitivity and practicality for performing the proposed task. This occurs because in Oertle's apparatus the entire vacuum system volume forms part of the defect detection cavity and therefore a relatively high vacuum must be employed to provide some sensitivity to the method. This becomes apparent if a constant vacuum source of only 20kPa below atmospheric pressure reference is used by Oertle's device. Furthermore, the use of a high vacuum results in the use of low permeability materials, which limits practical applications.

Tulip Bay (WO94/27130) has the advantage that the crack detection cavity is largely isolated from the vacuum source and therefore can have a small volume.

Disclosure of Invention

The objects of the present invention include: a system and method of continuously inspecting a component or part is provided to give an early indication and location of an impending fault or crack; and monitor the development of faults or cracks.

For ease of description below (including in the claims), the term "member" is used to denote a member or component.

According to the present invention, there is provided a system for continuously monitoring the structural integrity of a component, the system comprising at least:

an elastomeric sensor pad (sensor pad) having a first member engaging surface and an opposing surface, the first member engaging surface being provided with a set of at least one first channel that forms a corresponding set of at least one first cavity when the first member engaging surface is sealingly engaged with the member;

a first fluid communication means for providing fluid communication between the set of at least one first channel and a constant vacuum source; and

isolation means for isolating each of said first cavities from fluid communication with said constant vacuum source,

the system further includes means for monitoring a change in vacuum state between a constant vacuum source and the first cavity.

In one embodiment, the sensor pad further comprises:

a set of at least one second channel formed in the first component bonding surface, the second channel forming a corresponding set of at least one second cavity when the first surface is in sealing engagement with the component;

the second channels alternate with the first channels; and

second fluid communication means for providing fluid communication between said second cavity and atmosphere or ambient at a different pressure than said constant vacuum source.

Preferably, the first communication means comprises a third channel provided in the first surface, the third channel being in fluid communication with each of the first channels and with the constant vacuum source.

In an alternative embodiment, the first fluid communication means comprises a plurality of conduits, each conduit providing fluid communication between a respective first channel and a constant vacuum source.

Preferably, the second flow-through means comprises a fourth channel provided in the first surface, the fourth channel being in fluid communication with each of the second channels and the atmosphere or ambient.

Preferably, the sensor pad is transparent or at least translucent.

Preferably, the system further comprises a supply of a dye indicating liquid in fluid communication with the second channel to provide a visual indication of the location of the defect.

In an alternative embodiment, the second fluid communication means comprises an opening in each of the first channels in fluid communication with the atmosphere through a sensor pad.

Preferably, the isolation means comprises means for applying a force to the sensor pad at a respective location over each or a selected one of the first and/or second channels to seal the first and/or second channels against the member and fluidly isolate the first and/or second cavities from the vacuum source.

Preferably, the isolation means is adapted to isolate the cavities individually and/or sequentially so that all of the cavities are progressively isolated from the vacuum source.

Preferably, the isolation means is programmable so that the order in which the cavities are isolated can be varied.

In one embodiment, the means for applying force comprises a plurality of actuators supported on or within the sensor mat on each of the channels for applying force to sealingly deform the channels against the member.

Preferably, the actuator is electrically, magnetically, hydraulically, pneumatically, or mechanically operated.

Preferably, the first communication means comprises a conduit formed on a second surface of the sensor mat opposite the first surface, and a corresponding aperture formed in the sensor mat to provide fluid communication between the first channel and the conduit, and the isolation means comprises means for applying a fluid isolation force at a corresponding location to occlude the conduit to fluidly isolate a selected one of the first channels from the vacuum source.

Preferably, said isolation means is adapted to isolate said cavities individually and/or sequentially so that all of said cavities are progressively isolated from said vacuum source.

Preferably, the isolation means is programmable so that the order in which the cavities are isolated can be varied.

In one embodiment, said means for applying force comprises a plurality of actuators supported on or within said sensor mat over each said length for applying force to said sensor mat to sealingly deform the respective said channels against the member.

Preferably, the actuator is electrically, magnetically, hydraulically, pneumatically or mechanically operated.

In another embodiment, the means for applying a fluid isolation force comprises a pair of miniature pinch rollers (pinch rollers) disposed on opposite sides of the conduit for sealing a length of the conduit from the vacuum source to progressively isolate the first passageway in communication with the length from the vacuum source.

In another embodiment, the means for applying a fluid isolation force comprises a movable seal disposed within the conduit for sealing a length of the conduit from the vacuum source to gradually fluidly isolate the first passage communicating with the length of the conduit from the vacuum source and means for moving the seal along the conduit.

In a further embodiment, the channel extends in a radial direction.

According to the invention, there is also provided a method for continuously monitoring the integrity of a component, the method comprising at least the steps of:

providing a sensor mat having a first component engagement surface and an opposing surface, the first surface being provided with a set of at least one first channel;

sealingly engaging the first surface of the sensor mat with a member such that the channels and member together form a respective set of first cavities;

connecting the first cavity to a constant vacuum source;

monitoring a change in vacuum state between the cavity and the constant vacuum source; and

isolating each of the first cavities from the constant vacuum source.

In one embodiment, isolating each of the first cavities includes venting the first cavity to atmosphere or ambient.

According to the invention there is also provided a method for continuously monitoring the integrity of a component, the method comprising at least the steps of:

providing a sensor mat having a first member engaging surface and an opposing surface, the first surface being provided with a set of at least one first channel and a set of at least one second channel, the first channels being spaced apart from and alternating with the second channels;

sealingly engaging said first surface of the sensor mat with the member such that said channels and member together form respective sets of first and second cavities;

connecting the first cavity to a constant vacuum source;

connecting the second cavity to an atmosphere or ambient at a different pressure or vacuum than the vacuum source;

monitoring a change in vacuum state between the first cavity and the vacuum source; and

isolating each of the first cavities from the constant vacuum source.

Preferably, the step of isolating the cavities comprises isolating the cavities individually and sequentially so that all of the cavities are progressively isolated from the vacuum source.

Preferably, the method further comprises forming the sensor pad of a transparent or translucent material.

Preferably, the method further comprises the step of placing a supply of dye indicating liquid in fluid communication with the second channel to provide a visual indication of the location of the defect.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a first component engagement surface of a sensor mat included in a first embodiment of a system and method for detecting the generation of defects in a component;

FIG. 2 shows a section through a portion of the sensor pad shown in FIG. 1;

FIG. 3 shows an oblique view of the sensor pad shown in FIG. 1;

FIG. 4 shows a cross section through a portion of the sensor pad shown in FIG. 1 with a channel isolation device;

FIG. 5 shows a schematic form of the sensor pad shown in FIG. 1 with a liquid dye indicating the location of the defect;

FIG. 6 is a plan view of a first component engagement surface of a sensor pad included in the system and method configured for determining crack growth rate;

FIG. 7 is an oblique view of the sensor pad of FIG. 6 configured for determining crack growth rate and including an enlarged inset;

FIG. 8 is a schematic view of the sensor mat of FIG. 6 connected to an actuator for sequentially isolating the joints from the vacuum monitoring system;

FIG. 9 is a cross-sectional view of a sensor mat similar to that shown in FIGS. 6 and 7, showing an integrated isolation device including a plurality of actuators to sealingly deform corresponding channel counter-members for determining the rate of crack development;

FIG. 10 is a plan view of a first member engagement surface of a sensor mat configured as an integral isolation device suitable for use in determining a rate of crack development;

FIG. 11 is an oblique view of the sensor mat shown in FIG. 10, including portions of the integrated spacer;

FIGS. 12a and 12b show a widthwise cut-away view of a portion of the sensor mat of FIG. 11, illustrating the progressive function of the spacer of FIG. 11;

FIG. 13 is a view of a portion of the sensor mat shown in FIGS. 11 and 12 above, showing a lengthwise cut through the fluid isolation device of FIGS. 11, 12a and 12 b;

FIGS. 14 and 15 illustrate a mechanical drive arrangement for the isolation device shown in FIGS. 11, 12 and 13;

FIG. 16 is a view similar to FIG. 13 showing another isolation device;

FIG. 17 shows a complete system based on the embodiment of FIG. 16;

FIG. 18 shows a plan view of a first member engagement surface of a sensor pad for placement over a rivet fastener head for determining a strain field around the fastener;

FIG. 19 shows a cross-sectional view of the sensor pad of FIG. 18 applied to the head of a rivet fastener;

fig. 20 shows an oblique view of the sensor pad shown in fig. 18 and 19.

Detailed Description

As shown in FIGS. 1-4, a system 10 (FIG. 3) for continuously monitoring the integrity of a component 14 to detect the presence of a defect includes a sensor pad 16 having a first component engagement surface 18 and a second opposing surface 20. The first surface 18 is provided with a set of first channels 22 and a set of second channels 24. The channels 22, 24 appear as straight lines in the main part of fig. 1, since their width and spacing may be on the order of 250 microns. A portion of the enlarged view is included in fig. 1 as detail a to clearly illustrate their features.

The first channels 22 are isolated from and alternate with the second channels 24. As shown in fig. 2 and 4, when the surface 18 of the sensor mat 16 is sealingly engaged to the surface 12 of the member 14, the first and second channels 22 and 24 form, with the surface 12/member 14, respective sets of first and second cavities 26 and 28. A first fluid communication means in the form of a third channel 30, a through hole 31, and a conduit 32 (see fig. 3) provides fluid communication between the first channel 22/first cavity 26 and a constant vacuum source 101 of a monitoring device 100 of the type described in the aforementioned international application PCT/AU94/00325(WO94/27130), the contents of which are incorporated herein by reference. (thus, the channel 22/cavity 26 may be referred to as a "vacuum" channel/cavity). A second fluid communication means in the form of a fourth channel 34, a through hole 35 and a conduit 36 provides fluid communication between the second channel 24/second cavity 28 and the atmosphere at a different pressure or vacuum from the constant vacuum source. (thus, the channel 24/cavity 28 may be referred to as an "atmospheric" channel/cavity).

An isolation device in the form of a plunger or probe 38 (see fig. 4) is included within the system 10 for individually isolating the first channel 22/first cavity 26 from the vacuum source. In this embodiment, the entirety of the sensor pad 16 is made of an elastomeric material.

In this embodiment, probe 38 pushes against surface 20 of sensor pad 16 to sealingly deform the portion of sensor pad 16 at location 21 over the major length of channel 22/cavity 26. In this manner, the channel 22/cavity 26 is in fluid communication with the channel 30 and conduit 32 and is thereby isolated from the vacuum source 101. As described in more detail below, the probes 38 may be moved or repositioned over and/or along the length of each channel 22/cavity 26 or common channel 30 to isolate the cavities from the vacuum source individually or in groups.

It is assumed that the catheter 32 is now connected to a monitoring device 100 (fig. 3) of the type described in the aforementioned international application PCT/AU94/00325(WO 94/27130).

The monitoring device 100 includes a vacuum source 101 connected in series with a high fluid flow impedance 102 and a differential pressure transducer 103 connected across the high impedance fluid flow device 102 to monitor various changes in vacuum conditions between the vacuum source and the vacuum within the channel 22/cavity 26. If a crack or fault 40 (shown in FIG. 2) develops in the component 14 and opens onto the surface 12 and propagates, thereby forming a fluid communication path between one of the channels 22/cavities 26 and the adjacent channel 24/cavity 28, a change in the vacuum state of the channel 22/cavity 26 under consideration occurs. This change is detected by the monitoring device 100, thereby providing an indication related to the initial formation of the crack or fault 40.

However, this merely provides an indication that a crack or fault 40 is present somewhere within the area of the sensor pad 16. To more specifically locate the position of the fault or crack 40, isolation devices in the form of probes 38 are sequentially applied to the surface 20 at various points along the common channel 30 above to identify the affected channel 22, and then along the affected channel 22 (applied). The amount of force applied by the probe 38 is sufficient to sealingly flatten the channel 30 or 22 against the member 14, thereby sealing the respective cavity 26. If, upon application of this force, there is no change in the readings of the monitoring device, then the crack or fault 40 is not below or in communication with that particular respective channel 22/cavity 26 or channel 22/cavity 26. However, in the event that the vacuum condition indicated by the monitoring device changes as the probe 38 applies force, then a portion of the crack or fault 40 is located beneath or contained within the particular respective channel 22/cavity 26 or the presently isolated portion of the channel 22/cavity 26.

The probe 38 may be of the form shown in fig. 4 so as to isolate only one individual channel 22 at a time. In addition, the isolation device may be formed to isolate each channel 22 in turn, so as to gradually seal each channel 22.

In the method described above, the probe 38 is applied to the vacuum channel 22/cavity 26. However, it will be appreciated that substantially the same effect may be achieved by applying a probe to the "atmosphere" passage 24/cavity 28. It is apparent that if the probe 38 is applied to a portion of the sensor mat 16 to seal the atmospheric passageway 24/cavity 28 at a location between the crack 40 and the fourth passageway 34 (and assuming that the crack 40 is also in fluid communication with the adjacent "vacuum" passageway 22/cavity 26), then the monitoring device will indicate a change in the vacuum condition as not presently leaking to the atmosphere. By progressively isolating with probe 38, the location of defect 40 can be determined.

Instead of probes 38, or in addition to probes 38, dyes may be used to visually indicate the location of the defect. This is illustrated in fig. 5, which shows a plan view of a transparent sensor pad 16 of transparent or translucent material attached to the surface 12. This is only shown schematically due to the scale issues noted above. In detecting defects, a supply 41 of liquid dye 5 is connected in fluid communication with the channel 24/cavity 28 via conduit 36, aperture 35 and channel 34. The dye 5 is slowly drawn into the cavity 28 and substantially stops when the crack 40 is encountered, since the crack 40 presents a higher fluid resistance to the dye than the previous air path. Thereby, a visual indication of the location of the crack 40 is provided.

6-8 illustrate how embodiments of the system 10a may be used to track the propagation of fault defects or cracks 40 in the event that a fault or crack has been detected or is known to exist. In this method, the other sensor mat 16a is in a position in which the crack 40 protrudes from the edge 15a of the sensor mat 16a and is thus in communication with the surroundings. The sensor mat 16a is configured with only channels 22a and the respective alternate ends are connected to respective conduits 32a via through holes 31a, as shown in fig. 6, 7 and 8. Further, the pitch of the channels 22a that are spread from the crack at the edge 15a may be configured to gradually increase. This is to facilitate the measurement of the rate of crack development due to the increased rate of fatigue crack propagation.

Fig. 6 is a plan view of the first member engagement surface of sensor pad 16a, showing channels 22a, their progressively increasing spacing, and their respective connections to conduit 32a via through-holes 31a (fig. 7).

Fig. 7 is an oblique view of the sensor pad 16a shown in fig. 6, and shows the conduit 32a and the crack 40 a. An enlarged view of another portion of the crack 40a is included and shown as detail B.

Fig. 8 is a schematic view of the sensor pad 16a shown in fig. 6 and 7, the sensor pad 16a being connected to an actuator isolation device 38a for controllably isolating the channel 22a from the vacuum monitoring system 100 in turn. The isolation device 38a is in the form of a switch or multiplexer and selectively controls fluid communication between the conduit 32a (and thus the channel 22a) and the system 100, or more specifically, the vacuum source of the system 100. In turn, the isolation device 38a may be rotary, linearly movable, or otherwise desired and operates by selectively closing off fluid communication between the conduit 32a and the vacuum source 101. Similar fluid switching devices have been used in the past to individually connect test points in wind tunnels to pressure transducers that were expensive in the past. However, with the present arrangement, the volume of the isolation device 38a and associated catheter 32a should be as small as practical to reduce time delays and thereby increase the sensitivity of the system 10 a.

It is assumed that fault or crack 40a extends to edge 15a of sensor pad 16a but has not yet spread across the first of the intersecting channels 22 a. In this case, the monitoring device will not detect any change in the vacuum condition, thereby indicating that a fault or crack has not propagated to the first of the channels 22 a. If and when a fault or crack 30 propagates to the first of the channels 22a, the monitoring device 100 will detect a change in vacuum condition in time. At this point, the transected channel 22a may be isolated from the constant vacuum source by some form of isolation device 38a that closes off fluid communication between the respective channel 32a and the vacuum source 101. Alternatively, once isolated, the passageway 22a may be completely disconnected from the vacuum monitoring system and vented to atmosphere, if desired. This isolation/venting may occur automatically upon detection of a predetermined change in vacuum condition. There is a suitable feedback loop in which an electrical switching device included in the monitoring circuit 104 of the system 100 may be used to drive a miniature reduction gear motor or similar actuating device included in the isolation device 38a to in turn close the conduit 32a until the pressure differential drops due to the occurrence of the resulting fluid isolation and park the isolation device at the new location. Alternatively, a predetermined stepper motor/microprocessor programmable configuration may be employed.

Once the first of the transected channels 22a has been isolated and/or disconnected, the monitoring device 100 returns to a standby state reading until the crack or fault 40a propagates to transect the next vacuum channel 22 a. In this way, the propagation path of the crack can be recorded very accurately. Likewise, by moving the isolator probe 38 as shown in FIG. 4 along the affected vacuum passage 22a while detecting a crack intersecting the passage 22a, the location of the point where the crack 40 intersects the vacuum passage 22a can be ascertained so that the path of propagation of the crack or fault 40 can be accurately delineated.

In today's fatigue tests, optical verification measurements have shown that the method records crack length time scales (markers) in 0.5mm length increments with extreme accuracy. The lower limit has not been determined so far.

Fig. 9 shows another embodiment of the system in which the isolation device 38b is magnetically operated. Here, the isolation device 38b includes a plurality of actuators 60 embedded within the sensor pad 16 b. The actuator 60 is in the form of a magnetic plunger. The isolator 38b also includes a dynamic magnet 62 mounted on a support (not shown) so as to be movable along the portion of each actuator 60 above it. The actuator 60 and the magnet 62 are of the same magnetic polarity. Thus, by sliding the dynamic magnet 62 over a particular actuator 60, the actuator 60 is forced in a downward direction to sealingly compress the channel 22 a/cavity 26 therebelow. A programmable stepper motor (not shown) may be provided to control the movement and position of the dynamic magnet 62 to isolate the channel 22 a/cavity 26 in any suitable order.

FIGS. 10-14 illustrate components of another embodiment of the system. This embodiment includes a sensor pad 16c having a plurality of first channels 22c, only the first channels being spaced at progressively increasing distances from an edge 15c of the sensor pad to an opposite edge 17 c. The end of each channel 22c near the longitudinal edge 19c of the sensor mat is provided with a respective through hole 31 c. The through hole 31c communicates with a first communication means, which in this embodiment is in the form of a conduit (common conduit) 30c, which conduit 30c is formed integrally with the sensor mat 16c and extends along the opposite or back side 20c of the sensor mat 16 c. Common conduit 30c is provided in fluid communication with a system 100 of the type shown in fig. 3 to provide fluid communication between channel 22c and a constant vacuum source 101.

The conduit 30c in this embodiment also forms part of an isolation device 38c for controllably isolating the passage 22c (and associated cavity 24c) from the vacuum source. Isolation device 38c includes a pair of pinch rollers 50 disposed on opposite sides of catheter 30 c. A reverse torque is applied to puck 50 to cause the puck to travel along tube 30c and pinch tube 30c closed therebetween. As this occurs, the length L1 of tube 30c behind puck 50 is effectively isolated from vacuum source 101. Thus, the passage 22c communicating with the length L1 through the corresponding hole 31c is also isolated from the vacuum source 101. In this manner, the isolation device 38c can gradually isolate all of the channels 22c from the vacuum source.

Figure 14 illustrates one method and structure for applying a torque to puck 50. In this embodiment, each of the press wheels 50 is attached to a flexible wire drive shaft 80 that is driven by a separate motor and gearbox or by two separate motors (not shown).

Figure 15 shows another drive configuration for puck 50. In this embodiment, worm 90 meshes with a corresponding toothing 91 formed at the end of the shaft adjacent to puck 50, worm 90 being connected to flexible drive shaft 80, which in turn is driven by a motor (not shown).

Fig. 16 shows yet another embodiment of an isolation device 38 d. In this embodiment, the isolation device 38d includes a spherical seal 93 and a device 90 in the form of a worm screw, the device 90 being used to move the seal 93 along the conduit 30 d. Seal 93 seals length L1 of conduit 30d from the vacuum source of system 100. In this regard, the system 100 communicates with the end of the conduit 30d on the side of the seal 93 opposite the worm 90. Drive is imparted to the worm 90 from a motor (not shown) by a flexible wire drive shaft 80. It will be appreciated that the seal 93 effectively seals the passageway 22d and its associated cavity 26d, which communicates with the length L1, from the vacuum source. The worm 90 taps its way along the inside of the conduit 30d itself. Although the seal 93 is shown in this embodiment as a spherical seal, other shapes such as a cylindrical block with a rounded front end or bullet shape are also possible. It is contemplated that this embodiment 38d with the worm 90 and seal 93 in this environment is the best choice from an engineering standpoint, as the bore of the conduit 30d is typically only nominally 0.5 mm.

In each example driven by a flexible wire shaft, a small reduction gear drive motor, stepper motor/programmable microprocessor arrangement, or similar actuation device controlled by the alarm circuit of the monitoring system 100 forms the remainder of the isolation devices 38c and 38 d.

Fig. 17 shows an example of a complete system 10d, which system 10d utilizes the isolation device 38d and the actuation device 37d of fig. 16, the actuation device 37d including a reduction geared motor 70 to drive a longitudinally splined shaft connected drive shaft 80 to allow free movement in the length direction thereof. In response to the negative vacuum being detected through conduit 32d, power is supplied to motor 70 through conductor 99 and by the power source of vacuum monitoring system 100.

A crack 40d within the substrate 14d is shown propagating beneath the sensor pad 16 d. As it progressively intersects each cavity 26d, a pressure differential of predetermined value is generated, which is detected by monitor 100 via conduit 32 d. In response to this, current is communicated to the reduction geared motor 70 via conductor 99. The motor drive shaft 80/auger screw 90/and seal 93 pass through the common conduit 30d to the next isolated position causing the pressure differential to drop below a predetermined value and is detected by the vacuum monitoring system 100, which system 100 terminates the current to the motor 70. In this way, the precise time scale of crack development can be combined with the fatigue time or period to predict the diffusion rate.

Fig. 18, 19 and 20 relate to defects resulting from yield values rather than from actual cracks.

FIG. 18 shows a plan view of a first member engagement surface 18e of a sensor pad 16e for placement on a rivet fastener head to determine a strain field around the fastener. Which have vacuum channels 22e of radial configuration and are jointly connected to a conduit 32e via a through hole 31 e. Further, the atmosphere passages 24e are alternately arranged, and the atmosphere passages 24e communicate at the outer ends thereof with the atmosphere conduit 36e via the through holes 35 e.

FIG. 19 shows a view of the sensor pad 16e of FIG. 18, the sensor pad 16e being sectioned through line A-A and placed on a similar cross-section through the rivet fastener head 92e and the fastened component 14 e.

Fig. 20 shows an oblique view of sensor pad 16e placed on surface 12e of component 14 e. The circumference of the lower rivet head 92e is shown lightly in phantom. The conduit 32e is connected to a vacuum monitoring system 100, which is not shown. A segment 41e of the circumferential bold dashed line is the separation of the interface between the rivet 92e and the adjacent portion of the hole in the component 14e (see also fig. 19). This is due to elastic or plastic flow in the fastened material. The leakage flow between the vacuum cavity 22e/26e and the atmospheric cavity 24e/28e is detected and measured by the vacuum monitoring system 100. By selectively isolating conduit 36e, the separation 41e of the interface in the fastened condition can be determined. Thus, the system gives an initial indication of yielding. This is often difficult to achieve, especially if a tightening prestress has been applied.

Now that embodiments of the apparatus and method for monitoring the condition of a surface have been described in detail, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the basic inventive concept. The sensor pad may be made in any shape to suit or suit the application at hand. Likewise, channels 22, 22a, 22b, 22c, 22d, and 22e, 24e, 30c, 30d, and 34 are shown only on surface 18 of sensor pads 16, 16a, 16b, 16c, 16d, and 16 e. However, similar channels may also be formed on the opposite surface 20 of the sensor mat so that the sensor mat can simultaneously monitor the surface condition of adjacent components. In this regard, the sensor mat may form part of the bond between the components, and in particular may be made of an elastomeric adhesive or sealant material.

Embodiments are described in which the channels 22 and 22 a/cavity 26 are sealed by applying a force directly to the channels 22 and 22 a/cavity 26 (e.g., in fig. 4 and 9), or to a conduit 32c (see fig. 7 and 20) in fluid communication with the channels and cavity. However, in alternative embodiments, sensor pads 16 and 16a may be provided with conduits of the type shown in fig. 7 and 8, which, instead of being acted upon from the outside by a squeezing force, may each be provided with an internally-spaced actuatable valve for opening or closing a fluid communication path with a vacuum source. It is contemplated that other embodiments may be constructed in which each of the passages 22 and 22a is provided with its own internal valve that may be individually controlled to open and close communication between the passages 22 and 22a and the passage 30. The application of micro-electro-mechanical devices will be improved in relation to the use of micro-scale isolation devices.

All such modifications and variations, together with others which will be obvious to those skilled in the art, are deemed to be within the scope of the present invention, the characteristics of which are to be determined from the foregoing description and the appended claims.

Claims (21)

1. A system for continuously monitoring the structural integrity of a component, the system comprising at least:

an elastomeric sensor mat having a first member engaging surface and an opposing surface, the first member engaging surface being provided with a set of at least one first channel that forms a corresponding set of at least one first cavity when the first member engaging surface is sealingly engaged with the member;

a first fluid communication means for providing fluid communication between the set of at least one first channel and a constant vacuum source; and

isolation means for fluidly disconnecting each of said first cavities from said constant vacuum source,

the system further includes means for monitoring a change in vacuum state between a constant vacuum source and the first cavity.

2. The system of claim 1, wherein the sensor pad further comprises:

a set of at least one second channel formed on the first component engagement surface, the second channel forming a corresponding set of at least one second cavity when the first surface is sealingly engaged with the component;

the second channels alternate with the first channels; and

second fluid communication means for providing fluid communication between said second cavity and atmosphere or ambient at a different pressure than said constant vacuum source.

3. The system of claim 1, wherein the first flow-through device comprises a third channel disposed within the first surface, the third channel in fluid communication with each of the first channels and with the constant vacuum source.

4. The system of claim 1, wherein the first fluid communication means comprises a plurality of conduits, each conduit providing fluid communication between a respective first channel and a constant vacuum source.

5. The system of claim 2, wherein the second communication means comprises a fourth channel disposed in the first surface, the fourth channel being in fluid communication with each of the second channels and with the atmosphere or ambient.

6. The system of claim 2 or 5, wherein the second fluid communication means comprises an opening in each of the second channels providing fluid communication through the sensor mat to the atmosphere.

7. The system of claim 1, wherein the sensor mat is transparent or at least translucent.

8. The system of claim 7, further comprising a supply of a dye indicating liquid in fluid communication with the second channel to provide a visual indication of the location of the defect.

9. The system of claim 1, wherein the isolation means comprises means for applying a force to the sensor mat at a respective location over each or a selected one of the first and/or second channels to seal the first and/or second channels from the member and fluidly isolate the first and/or second cavities from the vacuum source.

10. The system of claim 1, wherein said isolation means is adapted to isolate said cavities individually and/or sequentially so that all of said cavities are progressively isolated from said vacuum source.

11. The system of claim 1, wherein the isolation device is programmable so that the order in which the cavities are isolated can be varied.

12. The system of claim 9, wherein the means for applying force comprises a plurality of actuators supported on or within the sensor mat over each of the channels for applying force to sealingly deform the channels against the member.

13. The system of claim 1, wherein the first flow-through device comprises a conduit formed on a second surface of the sensor mat opposite the first surface and a corresponding hole formed in the sensor mat to provide fluid communication between the first channel and the conduit, and the isolation device comprises a device for applying a fluid isolation force at respective locations to block the conduit to fluidly isolate a selected one of the first channels from the vacuum source.

14. The system of claim 13, wherein the means for applying a fluid isolation force comprises a pair of micro-pressure rollers disposed on opposite sides of the conduit for sealing a length of the conduit from a vacuum source, thereby progressively isolating the first channel in communication with the length from the vacuum source.

15. The system of claim 13, wherein said means for applying a fluid isolation force comprises a movable seal disposed within said conduit for sealing a length of said conduit from said vacuum source, and means for moving said seal along said conduit to progressively fluidly isolate said first passageway communicating with said length of said conduit from said vacuum source.

16. A method for continuously monitoring the integrity of a component, the method comprising at least the steps of:

providing a sensor mat having a first component engagement surface and an opposing surface, the first surface being provided with a set of at least one first channel;

sealingly engaging the first surface of the sensor mat with a member such that the channels and member together form a respective set of first cavities;

connecting the first cavity to a constant vacuum source;

monitoring a change in vacuum state between the cavity and the constant vacuum source; and

isolating each of the first cavities from the constant vacuum source.

17. The method of claim 16, wherein isolating each of the first cavities comprises venting the first cavity to atmosphere or ambient.

18. A method of continuously monitoring the integrity of a component, the method comprising at least the steps of:

providing a sensor mat having a first member engaging surface and an opposing surface, the first surface being provided with a set of at least one first channel and a set of at least one second channel, the first channels being spaced apart from and alternating with the second channels;

sealingly engaging said first surface of the sensor mat with the member such that said channels and member together form respective sets of first and second cavities;

connecting the first cavity to a constant vacuum source;

connecting the second cavity to an atmosphere or ambient different from the constant vacuum source pressure or vacuum state;

monitoring a change in vacuum state between the first cavity and the vacuum source; and

isolating each of the first cavities from the constant vacuum source.

19. The method of claim 18, wherein said step of isolating said cavities comprises individually and sequentially isolating said cavities so that all of said cavities are progressively isolated from said vacuum source.

20. The method of claim 18 or 19, further comprising forming the sensor pad of a transparent or translucent material.

21. The method of claim 20, further comprising the step of placing a supply of dye indicating liquid in fluid communication with the second channel to provide a visual indication of the location of the defect.