Crack Detection Device and Monitoring System

Abstract

The present invention relates to a method and an apparatus for crack detection and monitoring of a material susceptible to potential cracks, delamination, or peeling that affect the material in aircraft, infrastructure, machinery, ships, enclosures, and other applications. The crack detector includes a base defining at least one sealed space formed between the material susceptible to potential cracks and the base, wherein at least one of the sealed spaces is filled with a first fluid, and at least one first detection means communicating with the at least one sealed space. The at least one first detection means measures a change in at least one physical or chemical parameter of the first fluid to detect the presence of a crack.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for detecting and monitoring potential cracks that affect materials in aircraft, infrastructure, machinery, ships, sealed enclosures, and other applications.

Background Art

[0002] Fatigue cracks in materials are a very important concern because they can cause catastrophic failures in mechanical systems or individual components. Nondestructive inspection requires a great deal of labor and time, and generally speaking, finding cracks is often as difficult as finding a needle in a haystack.

[0003] Cracks are not desirable, but the mere presence of a crack does not mean that the material cannot withstand the load, and therefore, monitoring the size of the crack also requires a great deal of labor. That effort involves the need to physically go to the location of the crack. For example, in the case of an aircraft, since it is necessary to inspect cracked parts more frequently, it is necessary to carefully remove the equipment, go to the location of the crack, and reassemble the equipment, which also involves additional risks and costs.

[0004] Rapidly growing industries such as electric vehicles using battery banks are also liable for potential legal responsibilities related to unnoticed cracks in the enclosures housing the batteries, because if a crack occurs in the enclosure, there is a risk of leakage of harmful chemicals.

[0005] The main known methods and apparatuses for crack detection are, as shown in FIGS. 1 to 3, electrical (acoustic, magnetic, high-frequency, nuclear, infrared imaging), penetrant (dyed liquid), visual, and continuous vacuum monitoring (CVM).

[0006] Apart from the methods available for crack detection, there is a prediction method (Autonomous Structural Health Monitor by Okulov, US 10,663,357). However, the prediction method used as an independent approach has a very large variation in the crack occurrence time (or per cycle) and a large variability in the crack propagation rate, so the uncertainty of the prediction itself becomes a problem.

[0007] The drawbacks encountered by most industries when using existing methods include, but are not limited to: i) inability to conduct inspections during the operation of an aircraft or machinery; ii) lack of a simple self - regulating crack indicator that functions under real - world conditions; iii) the acoustic method for crack detection is difficult to operate, more difficult to detect cracks, and the accuracy decreases because a large amount of acoustic noise is generated during flight or the operation of machinery.

[0008] Infrared (IR) cameras are used to detect the initial stage and progression of cracks and are very useful under laboratory conditions. However, in real - world applications where components experience large temperature change gradients in a short time (such as when an airplane climbs in altitude), detection becomes more difficult. Also, since the field - of - view angle of the IR camera is fixed, it needs to be installed at a considerable distance from the component, which is not always achievable in the case of an aircraft.

[0009] Real - time methods also include crack propagation sensing resistance gauges that contain an array of brittle conductive circuits applied to the surface. These usually cover a small area of the material surface and are commonly used where the location of potential cracks is already known. Also, there is a drawback that if the material mainly operates in a compressive state and the conductive elements of the gauge simply close and recover conductivity after damage, it will lead to incorrect results.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] During operation (e.g., in flight), it is desirable to be able to reliably identify cracks and continuously monitor cracks and their progression regardless of the load state (tension tends to open cracks and compression helps to close cracks), and a portable, autonomous, remotely accessible, low-power-consuming device is desired.

[0012] Such a device needs to be robust, have a wide operating temperature range, consume extremely low power, and in some cases have a passive indicator (e.g., visual) of cracks.

[0013] Ideally, such a device can locate cracks and is optically transparent to assist in visual inspection of the cracks after their location.

Means for Solving the Problems

[0014] According to one aspect of the present invention, there is provided means for providing a sealed space, cell or flow path sealed on a material. Such a space becomes a small, isolated "environmental ecosystem" in which parameters such as pressure, relative humidity, and the presence of certain gases or chemicals remain in equilibrium unless the space is connected to another environment via a passage provided by a crack.

[0015] One solution is based on the principle that a communication container equalizes or "exchanges" the physical or chemical properties of the fluid filling the container, or the fluids interact or react with each other, and generates a visible / optical or electrically detectable indicator when such communication is prohibited (no crack) or communication is effective (there is a crack).

[0016] For example, oxygen (O), carbon dioxide (CO2), or nitrogen (N), water vapor or moisture (H2O), and other gases present in the ambient environment (ambient atmosphere) initially diffuse into the interior of a sealed space (inside the container) containing a lower concentration of gas or vapor (compared to the concentration in the ambient atmosphere) through passages provided by cracks. The presence of such components can change the color of an indicator sensitive to them. Indicators or sensors sensitive to the oxygen, carbon dioxide, or nitrogen are readily available.

[0017] As another example, moisture or humidity present in the ambient atmosphere can be utilized to activate an indicator or change the measured value (e.g., relative humidity) of a sensor connected to the sealed cell or space. In this case, a cell containing a space sealed on the surface of the material can contain an amount or "pixels" of a humidity-sensitive indicator that changes color in the presence of moisture. Furthermore, a small amount of hygroscopic material that absorbs the initial amount of moisture trapped in the cell during the installation process and can remain in the cell after installation can provide an additional positive effect. If moist air can pass from the ambient environment (or, for example, an adjacent space filled with an aqueous solution) into the cell, the hygroscopic process of the small amount of hygroscopic agent reaches a saturation stage, after which the moisture indicator changes to a different color, indicating the presence and location of cracks.

[0018] Also, absorption means arranged in the space can promote the inflow of gas from outside the cell by changing the gas partial pressure inside the cell, and as a result, provide reliable operation of the indicator film in the presence of cracks. Another advantageous effect of using an absorbent is to mitigate the influence of, for example, very slow penetration of moisture due to incomplete sealing of the space, and help maintain a low moisture content and a uniform "reading" of the indicator, while the larger openings provided by cracks ultimately cause the absorbent to become saturated and the inflowing moisture to change the color of the indicator.

[0019] Chemical indicators, such as pH, quality criteria index, kinetics, redox potential, reactive carbon, total organic carbon, total residue, dissolved oxygen (DO), chemical oxygen demand (COD), biological oxygen demand (BOD), phosphate (P), nitrogen (N2), anhydrous ammonia (NH3), nitrate (NO3), and copper (Cu2+), can function as crack indicators when the indicator is placed in a sealed space or cell where cracks can be detected by the seal interrupted by the crack.

[0020] The size of the cell or space can be made as small as technically possible, and it should be understood that the cells can be arranged in a grid covering the area of interest where individual cells function as visual pixels of the display system.

[0021] The luminescence effect of some indicators can also be used to indicate the location of cracks, for example, using a black light.

[0022] Another option is to provide a sensing cell with electrodes and provide an electrolyte or ionized gas to adjacent cells. When cracks are present, exchange occurs between the cells, and the sensing electrodes can conduct current between them. Electrical conductivity can also be achieved by exposing a pair of electrodes to the acidic or alkaline wetting provided by the absorbent substrate to which the electrodes are attached.

[0023] A similar concept is also feasible for remote monitoring or cracks. In this case, individual cells, flow paths, or spaces sealed on the surface of the material can be equipped with sensing means that communicate with an MCU or a processor. In such a variant, the sensing means can include a pressure sensor, a relative humidity sensor, a gas detector, or any suitable sensor capable of detecting changes in the state of the fluid within the cell (when the crack opens a passage to another cell filled with ambient air or fluid).

[0024] Such devices are passive and rely on natural variations, such as the atmospheric pressure or relative humidity of the air outside the sensing cell (and thus monitor only the "state" inside the cell), or can also include a "physical or chemical state exciter". As an example of such an exciter, a pressure sensor connected or integrated into the cell interior space is used to induce a pressure increase inside the cell by raising the temperature of the fluid inside the sensing cell. If the seal remains intact (no cracks), the response of the pressure sensing means is closely correlated with the nature of the excitation. In the presence of cracks and interruption of the hermetic seal, the response or pressure measurement has a lower correlation with the excitation.

[0025] Such an "exciter" can work on the principle of changing any of the detectable parameters of the fluid, i.e., the physical size of the temperature, volume, the partial pressure of the gas contained in the cell, and other conditions that can result in either a reaction correlated with the "crack-free situation" or a reaction correlated with the "cracked situation". By analyzing such a level of correlation, the relative size of the crack can be estimated.

[0026] The present invention provides a simple and reliable solution for crack detection and monitoring. It is less susceptible to interference from acoustic, vibration, electrical, RF, or other noise sources and can be used for actual crack detection and monitoring. This device can be manufactured in the form of a pressure-sensitive label, or a patch containing individual cells, flow channels, spaces, or grids, and such patterns (each representing a closed space sealed on or around the surface of the material). Such labels with passive indicators or electronically monitored sensing means can be manufactured inexpensively and deployed in large quantities.

[0027] According to one aspect of the present invention, there is provided a crack detector for a material, including a base defining at least one sealed space formed between a material potentially subject to cracks and the base, and at least one first detection means communicating with the at least one sealed space, wherein the at least one sealed space is filled with a first fluid. The at least one first detection means measures a change in at least one physical or chemical parameter of the first fluid to detect the presence of cracks.

[0028] The crack detector may further include a comparator for comparing the change in the at least one physical or chemical parameter of the first fluid with a characterized physical or chemical parameter of the first fluid.

[0029] The characterized parameter of the first fluid is expected, predicted, measured, or calculated.

[0030] The at least one sealed space may be surrounded by a second fluid.

[0031] The crack detector can further include at least one second detection means for measuring at least one physical or chemical parameter of the second fluid.

[0032] The crack detector further includes means for inducing or changing a physical or chemical parameter of the first fluid to facilitate a change, and observes a correlation between the at least one parameter and a predicted, measured, or calculated parameter of the first fluid.

[0033] The first fluid is a gas or a liquid, and the second fluid may be a gas or a liquid.

[0034] At least one first detection means is configured to measure one or more of the parameters selected from the group consisting of the pressure, temperature, mass, chemical composition, presence of chemical substances or gases, color, humidity or relative humidity, and any optical or electrical properties of the first fluid; wherein the electrical properties are selected from the group consisting of permittivity, resistance and capacitance.

[0035] The second detection means is configured to measure one or more of the parameters selected from the group consisting of the pressure, temperature, mass, chemical composition, presence of chemical substances or gases, color, humidity or relative humidity, and any optical properties or electrical properties of the first fluid; wherein the electrical properties are selected from the group consisting of permittivity, resistance and capacitance.

[0036] The first detection means is configured to detect chemical reactions, diffusion or dilution in the first or second fluid caused by the fluids contacting each other.

[0037] The crack detector can further include means for changing the amount of any component of the first fluid.

[0038] The means for inducing or changing the physical or chemical parameters of the first fluid may be one that changes its pressure and is selected from the group consisting of a heater and a cooler.

[0039] The means for changing the pressure of the first fluid may further include volume change means by bending a diaphragm, moving a piston, or deforming the space itself.

[0040] This means can include an absorbent material for reducing the presence of a predetermined gas or liquid.

[0041] At least one sealed space may further include a plurality of compartments embedded in the sheet, and may include a transparent portion at least over the sealed space or the compartments, wherein the plurality of compartments includes a visual indicator of the presence or absence of the second fluid.

[0042] The at least one sealed space may further include a plurality of compartments embedded in a sheet including the at least one first detection means for detecting the second fluid entering the sealed space or the first fluid exiting the sealed space.

[0043] The sealed space may further include a plurality of compartments arranged in a matrix, pattern or grid extending over the material.

Brief Description of the Drawings

[0044] The present invention will be described in more detail below with reference to the accompanying drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0045] Figures 1 and 2 show the prior art related to a comparative vacuum monitoring system, where on the surface of a material 4 targeted by a crack 5, a patch 3 containing galleries 1 and 2 sealed with respect to the surface is provided. By applying a vacuum to a set of galleries (1) and comparing the value of the vacuum with a preset characteristic, or comparing it with the pressure in the second set of galleries (2), the concept of a crack can be derived when the vacuum in the galleries cannot be stably maintained.

[0046] Further disclosed is a differential pressure sensor 6 that is combined in parallel with a diffuser 7 and activated by a vacuum pump 8.

[0047] Another approach previously proposed by U.S. Patent No. 9,316,562 is shown in Figure 3, in which a flow path 9 is provided directly in the material 4, and the applied pressure or vacuum can monitor the stability over time when no crack is present and the instability when a crack 5 is present.

[0048] A schematic diagram of a first embodiment of a crack sensor 100 according to the present invention is shown in Figure 4. A sealed or closed space 14 associated with an extension 13 of a space 14 is provided on or within a material targeted by a potential crack 5 and is disposed adjacent to the potential crack 5. The space 14 communicates with an internal pressure sensor 17 via a port 18. The internal pressure sensor 17, in its simplest mode of operation, monitors pressure changes inside the space 14 and the extension 13 (e.g., in the form of a flow path, groove, bore, etc. associated with either the surface of the material 4 or the material itself). A passage / flow path 12a may be provided adjacent to the space 14 or / and the extension 13. The flow path 12a may open at or along its distal end 10 and communicate with the atmosphere.

[0049] Alternatively, as shown in Figure 5, a second passage / flow path 12b may be provided adjacent to the space 14 or / and the extension 13. The flow path 12b may be sealed / closed and may define a second sealed / closed space 14b.

[0050] Referring to FIGS. 4 and 5, when the crack 5 blocks the entire space 14 and / or the extension 13, the behavior of the reading value in the internal pressure sensor 17 changes from depending only on temperature (Gay-Lussac's law indicates that the pressure of a given amount of gas held at a constant volume is directly proportional to the Kelvin temperature) (or being correlated with temperature and altitude) to depending on other parameters, such as the atmospheric pressure measured by the pressure sensor 11. In other words, the crack 5 provides for the sealed space 14 to communicate with the atmosphere as shown in FIG. 4, or to communicate with a second sealed / closed space 14b as shown in FIG. 5. More precisely, when the space 14 contains a fluid different from the atmosphere as shown in FIG. 4, or when it contains a fluid different from the fluid in the closed space 14b as shown in FIG. 5, another fluid other than the fluid in the space 14 can be introduced through the crack 5.

[0051] These varying conditions can be easily detected as shown in FIGS. 6a) and 6b), FIGS. 7a) and 7b). FIG. 6a) is a graph showing the pressure measurement values of the atmospheric pressure sensor 11 and the internal pressure sensor 17. When there is no crack affecting the space 14 / extension 13 and the temperature is constant, it shows that even if the atmospheric pressure (APS) measured by the atmospheric pressure sensor 11 changes over time, the pressure (PS) from the internal pressure sensor 17 remains stable. Further, as shown in FIG. 6b), the correlation between the two pressures PS and ASP approaches zero.

[0052] Conversely, when there is a crack and it provides a microscopic flow path that allows the space 14 to communicate with the atmosphere, the two pressures APS and PS are correlated (as shown in FIGS. 7a) and 7b)). In short, by simply observing the physical conditions (pressure, humidity, chemical composition, etc.) of the closed space 14, reliable information regarding the presence or absence of cracks and their relative sizes can be derived. Thus, the present invention provides, in its minimal approach, a solid-state crack detection device that requires no pumps or moving parts, is extremely portable, and has low power consumption.

[0053] This method is effective, but the time required for the above-mentioned correlation evaluation can be very long and depends on the magnitude of the atmospheric pressure change. To facilitate a more rapid evaluation, an excitation device 15 for either internal physical or chemical properties can be optionally introduced into the enclosed space 14 or the extension 13. For example, by heating the fluid contained within the space 14, its pressure can be increased very rapidly, and the readings of the pressure sensor 17 can be observed and used to detect cracks and evaluate their relative magnitude. The excitation device 15 can be controlled by a control device 16.

[0054] When communication between the space 14 / extension 13 and the atmosphere is not desired (i.e., FIG. 4), the closed system described in FIG. 5 can be used. In this case, a second fluid filling the second space 14b and a first fluid filling the space 14 (which may be different from the second fluid) interact when cracks are present or when there are cracks. In a purely pressure-driven observation, an additional space in the second space 14b is added to the space 14 and the extension 13, thus enabling the first fluid to communicate with the second fluid. The pressure rises due to heat, and the level of pressure increase due to excitation within the space 14 is affected by the presence of the space 14b, and the difference can be measured and compared with a state indicating the presence of cracks.

[0055] Figures 8 to 17 further show different embodiments of an excitation device 15 (or excitation device) for using temperature, changes in the space itself, or processes of absorption, sublimation, or evaporation to facilitate changes in the environment of the enclosed space 14 and observe the effects of those changes for two different conditions, namely, i. no cracks (the space is sealed), and ii. cracks present (the space is not sealed), which serve the same purpose. Such methods and devices used for the excitation of conditions can be controlled by a control device 16, which can communicate with an MCU or a processor via a serial bus or a parallel bus.

[0056] For example, in the case of the resistance heater 22 shown in FIG. 9, the control device 16 can be an electronic circuit that supplies an electric pulse with a predetermined duration and intensity.

[0057] According to another embodiment of the present invention, the space 14 can be excited using a piezoelectric film 24 / actuator 23. In this case, as shown in FIG. 10, the piezoelectric actuator 23 bends the film 24 to excite the space 14.

[0058] According to still another embodiment of the present invention, the space 14 can be excited using an electromagnetic coil actuator 25a similar to those used in audio applications such as earphones / speakers. For example, as shown in FIG. 11, the electromagnetic coil 25a actuates the film 24a to change the space 14.

[0059] According to a further embodiment of the present invention, the space 14 can be excited using a Peltier cooler, a heater, or a thermoelectric heat pump 26. In this case, as shown in FIG. 12, the pressure increases when the space 14 is heated, and the pressure inside the space 14 decreases when the space 14 is cooled.

[0060] According to a further embodiment of the present invention, the space 14 can be excited by deforming its shape using means 27 as shown in FIG. 13.

[0061] According to still another embodiment of the present invention, the space 14 can contain a liquid 28 that evaporates / condenses within the operating temperature range of the sensor to excite the space 14, as shown in FIG. 14.

[0062] According to still another embodiment of the present invention, the space 14 can contain a sublimation material 30 that generates a gas or vapor within the operating temperature range of the sensor to excite the space 14, as shown in FIG. 15.

[0063] According to yet another embodiment of the present invention, the space 14 can contain a moisture-absorbing material 31 for absorbing moisture 32 in the space 14, as shown in FIG. 16. The moisture-absorbing material 31 can function as a hysteresis / buffer to avoid false detection of cracks because crack formation is detected only after the moisture-absorbing material 31 is saturated (when pressure / moisture is monitored to detect cracks).

[0064] According to yet another embodiment of the present invention, the space 14 may be monitored or / and excited by using a discharge. For example, referring to FIG. 17, an anode 33 and a cathode 34 are provided in the space 14 with a discharge 34 to monitor the emission / transmission of electricity in the fluid in the space 14 and detect the presence of cracks.

[0065] A crack sensor 100a according to an embodiment of the present invention is shown in FIGS. 18 and 19, where FIG. 18 is a top view and FIG. 19 is a cross-sectional view taken along A-A of FIG. 18. Here, the material 4 can be affected by a crack 5 that affects its surface 35. The crack detector 100a includes a housing 40 and a base or patch 37 made of a transparent pressure-sensitive film, and both can have a transparent cover 36 to facilitate visual observation or inspection of the surface 35 affected by the crack 5. A single continuous groove or gallery 38 is provided on the bottom surface of the base 37 in communication with the material 4. The groove 38 can be formed by machining, mechanical or chemical etching, engraving (e.g., laser engraving), casting, injection molding, or other means. The base 37 is attached to the material 4, and the groove 38 of the base connects to the material to form a sealed space that communicates with the internal space of the housing 40 via a port 42, thus providing a sealed space 14. The sealed space 14 can be filled with a first fluid containing a gas or a liquid. The internal pressure sensor 17 can be disposed inside the space 14, inside the housing 40 in communication with the space 14, or externally via a pressure conduit 43 in communication with the space 14. The resistive heating element 22 can also be sealed inside the housing 40 or the closed space 14, or alternatively, disposed in an additional space in communication with the housing 40 or the closed space 14. There is a groove 39 that communicates with the atmosphere and is arranged alternately with the groove 38.

[0066] When the electrical resistance heater 22 is activated, the pressure within the closed space 14 formed by the groove 38, the port 42, the interior of the housing 40, and any external pressure conduits or other enclosed spaces increases. When heat is present in the first fluid within the space 14 and a thermal equilibrium is provided, the pressure within the space 14 is maintained constant. If a crack interrupts the sealed gallery 38 and provides communication with the atmosphere, the pressure gradually decreases. When the heating pulse applied by the resistance heater 22 is removed and the temperature within the space 14 returns to its original value, the pressure decreases, and if some of the fluid has already exited the space 14, the pressure at the original temperature will be different from the initial measured value (determined prior to applying the heating pulse). Subsequently, the fluid can reverse its direction, enter the space 14 again through the crack, and then return its pressure to a value similar to that observed at the beginning of the cycle, as shown in FIG. 43.

[0067] There are various configurations that can create the closed space 14. FIG. 20 shows a closed space 14 defined as an individual cell 45 with a sealed seal 46 on the surface of the material 4 that is the subject of the potential crack 5. Any sensor or sensors 47 can be placed within the cell 45 without compromising the sealed seal (it should be understood that the control, power, and communication lines required for the sensor / sensors 47 must also be sealed). In this embodiment, the sensor 47 can be selected from the group consisting of a pressure sensor, a relative humidity sensor, and a gas detector.

[0068] The material of such a cell 45 is desirably made transparent so that the material 4 can be visually confirmed / observed.

[0069] In addition to, or independently of, the sensor 47, an indicator 49 can be disposed within the cell 47. Such an indicator 49 can, for example, change color or dielectric properties in response to a change in the physical or chemical state inside the space 14 that constitutes the cell 47 when fluid outside the cell 47 penetrates therein through the crack 5. As an example, there is a simple moisture indicator installed inside the cell 47, and the moisture in the cell 47 is removed during installation. For example, when a crack occurs and the sealed / closed space defined between the cell and the material 4 is impaired, moisture from the fluid (such as air) surrounding the cell 47 enters the interior of the closed space, and the color of the indicator 49 changes. In this way, the individual cells 47 become passive indicators of cracks.

[0070] Needless to say, such individual cells can be arranged in various shapes and ways, including forming grids, patterns and matrices that are strategically designed to assist in crack blocking and more accurate visualization, as shown in FIGS. 24, 25 and 26.

[0071] If it is not desired to rely on moisture or gas content in the atmosphere as a means of inducing the reaction of the indicator 49 (for example, when placing a crack detector on an unprotected material surface where contact with the atmosphere must be prevented), adjacent cells 45 can be provided, where the two adjacent cells 45 contain different fluids 50a, 50b. When the crack 5 is formed, such a crack becomes a conduit 52, and since different fluids can pass through the crack 5 / conduit 52, a measurable change occurs as shown in FIG. 22. One of the closed spaces formed between the two adjacent cells 45 and the material 4 can be designated as a sensing space 51.

[0072] As shown in FIG. 23, yet another configuration can be realized, in which one cell 45a forms a sensing space 51 having a fluid 50a, and the sensing space 51 is surrounded by another cell 45b to form a surrounding space 51b containing another fluid 50b. However, simply providing an additional space filled with any fluid 50b increases the total volume of the sensing space 51 and can be used to identify the crack 5 using a sensor disposed within the sensing space 51.

[0073] In the case of the repeating pattern or grid 53 shown in FIGS. 24 - 25, for example, the pattern 53 shown in FIG. 24 employs the same principle as shown in FIG. 22 and is illustrated here, where the sensing cell 55 is surrounded by a cell 54 containing a fluid (not shown) different from that contained in the sensing cell 55.

[0074] The pattern 53 having the sensing cell 56 shown in FIG. 25 can employ the same principle as shown in FIGS. 20, 21, and 23.

[0075] The repeating pattern or grid 53 shown in FIGS. 24 - 25 can be applied when the environment surrounding the sensing cell or space 55 contains either the same fluid or a different fluid, or is simply exposed to the atmosphere. The purpose of the shape and orientation of the individual cells of the grid is to provide a structure that blocks any possible direction of crack propagation.

[0076] A practical device incorporating such a crack detection grid is shown in Fig. 27 (elevation view). The vertical wall 61 is provided for the division between adjacent cells 54 (for example, the honeycomb matrix shown in Fig. 24), and the sensing cell 55 is equipped with sensors 62 for pressure, relative humidity, chemical content, temperature, etc.; the sensors 62 and the heating element 22 (or other means devised to facilitate changes in the environment within the closed space 14) can be attached to a printed circuit board (PCB) 60 that functions as a cover providing a hermetic seal for all cells, and together with the wall 61 and the surface of the material 4, form the closed / sealed space 14. If communication with the atmosphere is desired, the PCB 60 can have an opening 59. Thus, when the cracks 5 provide a passage or path 63 for the interconnection between adjacent cells, the properties of the fluid filling them change, enabling crack detection.

[0077] A crack detector 100b according to another embodiment of the present invention is shown in Fig. 28, where the crack detector 100b includes a first cell 100b1 and a second cell 100b2. The first cell 100b1 has a first pressure sensor 17 communicating with a sealed space 14 having an extension 13 via a port 18, and the second cell 100b2 has a second pressure sensor 64 communicating with a second sealed space 12c via a second port 65. The first cell 100b1 optionally includes a state excitation device 15. The arrangement described here represents a closed system where the crack does not provide communication with the atmosphere in either such space. This configuration is useful for applications where the material 4 is submerged or its surface is prohibited from being exposed to the external environment.

[0078] Figure 29 is a graph of the pressure measurement values by the first and second pressure sensors 17 and 64, showing the difference in the pressure values read by the first pressure sensor 17 and the second pressure sensor 64 during the pressure excitation cycle 66 of the space 14 while there are no cracks. When there are no cracks, the second pressure sensor 64 does not respond to the change in pressure read by the first pressure sensor 17. In other words, both spaces remain isolated. When there is a crack as shown in Figure 30, the fluid passes through the crack 5 between the space 14a and the space 12c, and through this process, the pressure of the fluid in the space 12c measured by the second sensor 64 increases.

[0079] It should be noted that the amount of pressure increase is about 5 to ings of the space, nor is there a possibility of damaging the seal. Of course, it is understandable that the higher the pressure difference, the faster the evaluation of the crack is completed. With the above pressure difference (5 to 15 hPa), in order to identify very small cracks, the time required for evaluation is 5 to 30 minutes.

[0080] Next, turning to a usage method other than the pressure detection means, let's look at an example of a relative humidity sensor. Figure 31 shows a crack detector 100d according to yet another embodiment of the present invention, where a relative humidity sensor (or RH sensor) 69 is arranged to monitor the relative humidity of the space 14. When there are no cracks, the RH sensor 69 provides a fairly stable measurement value regardless of the moisture level in the surrounding atmosphere, which can be monitored by a second relative humidity sensor (or second RH sensor) 70 represented by the flow path 12d that surrounds the crack detector 100d and is open to the atmosphere. Optionally, a humidity / moisture absorbent 68 such as silica gel or calcium chloride may be arranged in the space 14. To explain in simpler terms, it is possible to assume a tightly sealed bottle with an unchanging internal environment. Any crack, regardless of its size, will damage this environment and cause it to approach the environment surrounding such a bottle.

[0081] When the second relative humidity sensor 70 monitors the external environment, as shown in FIGS. 32 and 33 respectively, it is possible to analyze the correlation between the two and derive information useful for crack identification.

[0082] Since it is very difficult to ensure that there is no moisture during the installation process of the crack detector, it is desirable to include a certain amount of moisture absorbent in the space 14. After a while, the initial amount of moisture trapped in the space 14 is absorbed by the absorbent 68, and the measured value of the relative humidity sensor 69 approaches 0%. When cracks occur that allow moisture to diffuse and penetrate into the space 14 without limit over time, the absorbent 68 will eventually become saturated, and the measured value of the sensor 69 will begin to rise. When using a single sensor 69, it will exceed a certain threshold or stabilize near the average value of the relative humidity measured by the sensor 70.

[0083] It is important to mention that the same principle can also be applied when detecting other parameters, such as the amounts of oxygen, nitrogen, CO2, etc. that can pass through the cracks into the space 14. Alternatively, if the adjacent space contains not just any component of the atmosphere but a second fluid, sensing the presence of such a fluid entering the space 14 will also result in the same outcome of crack detection.

[0084] As yet another option, it is also possible to observe the chemical reactions that occur when the fluid from the space 14 mixes with the fluid outside the space 14.

[0085] Obviously, the same methodology can be further enhanced by using electronic indicators, changes in material properties, and any other means for identifying the fact that the space 14 has become unsealed due to cracks. Those means can include, for example, using changes in dielectric constant, resistivity, vibration patterns of microelectromechanical systems, and any other method useful for identifying changes in either the physical or chemical state of the fluid filling the space 14.

[0086] Figure 34 shows another crack detector 100e according to an embodiment of the present invention, corresponding to the devices also shown in FIGS. 18 and 19. The crack detector 100e is disposed on the surface 73 of the material 4 and forms a closed space 14 having an extension in the form of a flow path 38 that can have different geometric shapes or patterns so as to be blocked by cracks. The resistance heater 43 supplies heat pulses that cause a change in pressure measured and monitored by the pressure sensor 17.

[0087] Figure 35 is a time diagram of the heating and the electrical pulses that provide the corresponding change in pressure read by the sensor 17.

[0088] As the crack 5 occurs and progresses, the magnitude of the pressure change decreases because the fluid (such as gas / air) from the space 14 escapes through the crack 5. One simple method and algorithm for evaluation is to integrate the pressure values read by the sensor 17 over time and derive the parameter N = A / I / V, where A is the integrated area of the pressure plot, I is the current passing through the resistance heater, and V is the voltage applied during the heating pulse. This method is shown in FIG. 36. The parameter N gradually decreases as the crack grows.

[0089] It should be noted that the method introduced above is only one of many available methods. By having multiple input parameters and adopting various detection means, it can be ensured that machine learning and artificial intelligence methodologies can be quite applicable not only to the identification and characterization of cracks, but also to the removal, correction, or cancellation of parameters that interfere with the accuracy of the crack detection process. Furthermore, it can be imagined that it is also useful for providing algorithms aimed at correcting the influence of temperature, the stress received by the material around the crack, and other factors.

[0090] Figure 38 is a schematic diagram of a passive crack detector 53 according to yet another embodiment of the present invention. The crack detector 53 includes a patch 74w adhered to the surface of the material. The patch 74 has a plurality of sealed cavities 75.

[0091] Figure 39 is a cross-sectional view taken along line A-A of Figure 38. The base having the cell 76 and the surface of the material 4 define a cavity 75. Any or all of the cavities 75 can have an indicator that reacts with a fluid or gas entering the cavity through the crack 5. The indicator can, for example, change its color when such a reaction occurs. And since the cover 77 of the patch 74 is transparent, such a plurality of cavities are configured as passive visual indicators for detecting cracks, and the individual cavities constitute the pixels of the display. Therefore, the crack leaves a permanent trace of different-colored indicators, enabling not only the detection of the crack but also the identification of its progression. Needless to say, as a simple indicator, there is a moisture indicator or an oxygen indicator, and by using an appropriate gas / fluid absorbent, the crack detector 53 can be reset to a desired state after installation.

[0092] Finally, cross-sectional views of a crack detector 100f according to yet another embodiment of the present invention are shown in FIGS. 40 and 41. The crack detector 100f having a space 14 and its extension in the form of a blind bore 81 protruding into the thickness of the material 4 (e.g., a composite material) provides a periodic heating pulse using a heater 22 and the detection of the pressure in a closed space composed of the internal space 14 of the housing 82 and the internal space of the bore 81. When delamination 84 occurs, the total volume of the space 14 and the space 81 increases and becomes larger than the initial total volume. Therefore, considering that the heat input during the heating pulse supplied by the heater 22 remains the same, the increase in pressure monitored by the pressure sensor 17 is lower than the increase in pressure when not affected by the delamination configuration. This makes it possible to detect internal cracks caused by delamination even when the delamination itself does not lead to the opening of the affected area to the atmosphere.

[0093] Therefore, the present invention is also useful for identifying, characterizing, and monitoring not only cracks but also voids, delamination between components or between a protective cover and a coating. In summary, the described method can be applied to detect and monitor any voids that may occur during the life of any structure due to the use of materials.

[0094] Figure 42 is a block diagram of one possible configuration of the present invention. This includes an MCU or processor 91, a memory 92, an interface 93 (such as UART, I2C, CAN, RS485, etc.), a temperature sensor 94, a real-time clock (RTC) 95, visual means (such as LED indicators, displays, etc.) for displaying information regarding the presence and relative size of cracks, sensing means, such as a pressure sensor 17, a control circuit 16, and a serial or parallel bus or multiple buses for communicating with an excitation device 15. This system can communicate with an external data management system, a network of sensors, monitors, wireless communication means, etc. (generally denoted as an external monitoring system 98).

[0095] Figure 43 shows the pressure response when a thermal pulse is applied for 10 minutes under the following conditions: 1. There are no cracks. The pressure PS remains stable. When the heating pulse ends in 10 minutes, the pressure PS becomes zero. If the heating pulse continues, the pressure remains stable; 2. A crack with a length of 3 mm. Positive strain, +1000 μ strain, tension; 3. A crack with a length of 3 mm. Positive strain, +500 μ strain, tension; 4. A crack with a length of 3 mm. Negative strain, -1000 μ strain, compression.

[0096] As can be seen from the figure, the pressure drop becomes more significant as the crack is under tension, and the crack opens wider, allowing more air to pass through the space 14 during the heating cycle. Therefore, after the heating pulse is removed, the pressure PS drops below the original value (for simplicity, the original pressure PS is close to 1000 hPa but is represented as zero).

[0097] Figure 45 schematically shows the shape of a test piece in which a crack has grown on the side surface of a hole (concentrator) in a plate made of an aluminum alloy.

[0098] All of the figures show the importance of knowing the strain / stress level at which pressure measurements and crack size evaluations are performed. Therefore, a combination with the device described in the present invention and US 10,663,357 or a device similar thereto that can simultaneously monitor the strain in the crack region is desirable. It will be apparent to those skilled in the art that by knowing the relationship between the relative crack size, strain / stress, and the output of the crack detector of the present invention, the accuracy of the characteristic evaluation of the crack size can be significantly improved.

[0099] Finally, Figure 45 shows the evaluation process of a crack and its progression based on a series of N-value measurements, where N0 is a value derived and established based on the observation of the N-value over time in the absence of a crack. Therefore, a threshold can be set, and when the N-value exceeds it, the crack state can be determined. Note that, as described above, some variations in the N-value are related to the strain / stress state that the material is subjected to.

[0100] Regarding crack determination, the value measured by the sensor can be compared with an expected, predicted, measured, or calculated value for detecting the presence of a crack using a comparator or a processor.

[0101] The proposed configuration has many variations with the following features and means, but is not limited thereto: 1. The acid or base can be used as the fluid in the sensing space or the space surrounding the cell; 2. The sterile indicator can be used, for example, to detect the presence of oxygen and functions as a visual indicator; 3. A wireless system can be used to communicate with the crack detector for remote monitoring of the crack; 4. The battery-driven system can be used for autonomous operation; 5. Energy harvesting can be used to power a system or assist in power supply; 6. Each cell or enclosed space arranged in a grid can be equipped with an LED or passive display means (such as electronic paper) for visualizing the position and propagation of cracks; 7. A UV - resettable indicator sensitive to gas or moisture can also be used; 8. A heat - resettable indicator sensitive to gas or moisture can be used; 9. The diffuser can be used to release pressure in a controllable manner or equalize pressure between the surrounding environment, adjacent parts of the enclosed space cells, or a combination thereof; 10. The crack detector can be provided in the form of a label or patch with a pressure - sensitive adhesive, regardless of the presence of a protective cover; 11. Customized shapes can be provided to fit various components and surfaces; 12. The electronic circuit can be integrated with the device or label / patch or housed separately; 13. Any type of pattern and grid can be adopted; 14. To facilitate the observation of crack details during the installation process, the material surface or the entire label / patch can be sealed with paint or a transparent sealant; 15. In combination with at least one pressure sensor, a space or flow path connected in series, parallel (or any combination thereof) can be used to evaluate the progress of cracks, and optionally, a diffuser between the spaces can be adopted to assist in evaluating the size and growth rate of cracks; 16. Independent spaces (cells), each equipped with a pressure, relative humidity, and / or temperature sensor, can be connected to the MCU using a serial or parallel interface; ​ 18. The temperature sensor is a desirable component for most of the configurations described above; 19. The MEMS actuator can be used for the excitation of spatial variations; 20. Measurements of gas content and chemical analysis can be used; 21. A vibrating mass with an absorptive mass or a sublimative mass can be used as a detection means by observing a change in the natural vibration frequency of such a vibrating mass; 22. Vaporization, phase change, and sublimation can be used to change the state of a fluid within any space; 23. A liquid emerging from the space can be placed to leave a stained trace by evaporating through a crack; 24. The ionized gas and the change in electrical characteristics when ions are released through a crack can be further developed.

[0102] In addition to the above-described modifications, the foregoing embodiments of the present invention are merely examples, and it is obvious that they can be variously modified. Such current and future modifications are not considered to depart from the spirit and scope of the present invention, and all such modifications that would be apparent to those skilled in the art are intended to be included within the possible scope of the claims.

Claims

Claim 1 A crack detector for a material, comprising: a. a base defining at least one sealed space formed between the material and the base, which is a target of potential cracks, wherein at least one of the sealed spaces is filled with a first fluid; and b. at least one first detection means communicating with the at least one sealed space, wherein the at least one first detection means measures a change in at least one physical or chemical parameter of the first fluid to detect the presence of cracks. Claim 2 The crack detector according to claim 1, further comprising a comparator for comparing the change in the at least one physical or chemical parameter of the first fluid with a characterized physical or chemical parameter of the first fluid. Claim 3 The crack detector according to claim 2, wherein the characterized parameter of the first fluid is expected, predicted, measured, or calculated. Claim 4 The crack detector according to claim 1, wherein the at least one sealed space is surrounded by a second fluid. Claim 5 The crack detector according to claim 4, further comprising at least one second detection means for measuring at least one physical or chemical parameter of the second fluid. Claim 6 The crack detector according to claim 3, further comprising means for inducing or changing a physical or chemical parameter of the first fluid. Claim 7 The crack detector according to claim 4, wherein the first fluid is a gas or a liquid, and the second fluid is a gas or a liquid. Claim 8 The at least one first detection means is configured to measure one or more of the parameters selected from the group consisting of pressure, temperature, mass, chemical composition, presence of a chemical substance or gas, color, humidity or relative humidity, and any optical or electrical properties of the first fluid; and the electrical properties are selected from the group consisting of permittivity, resistance, and capacitance. The crack detector according to claim 5. Claim 9 The second detection means is configured to measure one or more of the parameters selected from the group consisting of pressure, temperature, mass, chemical composition, presence of a chemical substance or gas, color, humidity or relative humidity, and any optical or electrical properties of the first fluid; and the electrical properties are selected from the group consisting of permittivity, resistance, and capacitance. The crack detector according to claim 8. Claim 10 The crack detector according to claim 9, wherein the first detection means is configured to detect a chemical reaction, diffusion, or dilution in the first or second fluid caused by the fluids coming into contact with each other.

11. The crack detector according to claim 6, further comprising means for changing the amount of any component of the first fluid.

12. The crack detector according to claim 6, wherein the means for inducing or changing a physical or chemical parameter of the first fluid changes its pressure and is selected from the group consisting of a heater and a cooler.

13. The crack detector according to claim 12, wherein the means for changing the pressure of the first fluid further comprises a volume change means by bending a diaphragm, moving a piston, or deforming the space itself.

14. The crack detector according to claim 11, wherein the means comprises an absorbent material for reducing the presence of a predetermined gas or liquid.

15. The crack detector according to claim 4, wherein the at least one sealed space further comprises a plurality of compartments embedded in a sheet, the sheet comprises a transparent portion at least over the sealed space or the compartments, and the plurality of compartments comprise a visual indicator of the presence or absence of the second fluid.

16. The crack detector according to claim 4, wherein the at least one sealed space further comprises a plurality of compartments embedded in a sheet including the at least one first detection means for detecting the second fluid entering the sealed space or the first fluid exiting the sealed space.

17. The crack detector according to claim 1, wherein the sealed space comprises a plurality of compartments arranged in a matrix, pattern, or grid extending over the material.

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