Method for measuring thermal history of component

Abstract

A method of analyzing the thermal history of a component (100) having a coating containing a first marker by means of an optical device comprising a camera (20) and a light source (10), the method comprising: a calibration step in which a reference component having the same coating as the component undergoes a predetermined thermal cycle; a step of acquiring an image of the component and a step of acquiring an image of a reference component, and a step of analyzing the image of the component and a step of analyzing the image of the reference component, and a step of determining a transfer function, in which the transfer function correlating the temperature, the processed optical information and the spatial dimensions is determined; and an interpretation step in which an image of the thermal history is calculated and the image of the thermal history represents the thermal history of the component according to the predetermined angle.

Description

Technical Field

[0001] The present disclosure relates to a method for measuring the thermal history of a component.

[0002] The method may be used to analyze components of a turbine engine or a turbojet engine, to name a few. Background Art

[0003] Knowing the surface temperature of components and / or parts of a turbine engine may provide interesting information for the design, maintenance, and improvement of the turbine engine.

[0004] To obtain information about the surface temperature of the component, several solutions exist. The temperature can be measured using thermocouple probes, thermosensitive crystals or thermochromic paints.

[0005] With thermocouple probes and temperature-sensitive crystals, spatially discrete measurements can only be made at the points where these measuring devices are placed.

[0006] In this case, the measurement device is applied locally to points determined by the operator as critical. Consequently, obtaining surface temperature measurements requires an increased number of measurements and corresponding measurement devices. Consequently, surface resolution is limited by the number of measurement devices that can be placed on the component to be inspected.

[0007] For components with small surface areas or complex geometries, this limitation can be severe. Furthermore, in turbine engines, some components rotate about their shafts. Consequently, these rotating components have little or no compatibility with wired devices such as thermocouple probes.

[0008] Furthermore, the use of heat-sensitive crystals requires puncture to extract and analyze the heat-sensitive crystals, making the method invasive.

[0009] Furthermore, thermochromic paints provide discrete information relative to temperature information. Thermochromic paints have the property of changing color when exposed to temperatures above a threshold temperature. In this case, only whether the temperature has been reached is known.

[0010] When measuring with thermochromic paints, the measurement is based on colorimetric analysis with the naked eye. This type of measurement requires the color of the thermochromic paint to have high contrast and saturation to obtain satisfactory results.

[0011] Therefore, measurements with thermochromic coatings are complicated.

[0012] Furthermore, the analysis of measurements taken with thermochromic paints relies on visual interpretation by the operator and the hand-drawing of isotherms on the object or object model. These methods are relatively imprecise and rarely reproducible. Thermochromic paints also contain substances that may be toxic and / or harmful to the environment. Therefore, they must comply with current environmental standards. Furthermore, there is a risk that future standards regarding the use of these substances may become even stricter.

[0013] Therefore, there is a real need for measuring devices and analytical methods that do not have at least some of the above-mentioned inherent disadvantages.

[0014] Description of the Invention

[0015] The invention relates to a method for analyzing the thermal history of a component, the component having a coating comprising a first optical marker, by means of an optical device, the optical device comprising a camera configured to acquire an image of the component, a light source configured to illuminate the component, optionally a first filter device configured to adjust the wavelength emitted by the light source, and a processing unit, the method comprising: a testing step in which the component is subjected to a thermal cycle;

[0016] A calibration step, in which a reference component undergoes a predetermined thermal cycle, and wherein a thermal image of the reference component is acquired by a camera and recorded by the processing unit; an acquisition step of acquiring an image of the component and an acquisition step of acquiring an image of the reference component, wherein optical information about the component and the reference component are respectively measured by the optical device and then recorded by the processing unit; an analysis step of analyzing the image of the component and an analysis step of analyzing the image of the reference component, wherein the optical information about the component and the reference component are respectively processed by the processing unit to obtain processed optical information about the component and the reference component; a determination step of determining a transfer function, wherein a transfer function correlating temperature, processed optical information and spatial size is determined by the processing unit based on the thermal image of the reference component and the processed optical information of the reference component; an interpretation step, wherein the processing unit uses the transfer function and the processed optical information of the component to calculate an image of the thermal history, the image of the thermal history representing the thermal history of the component.

[0017] In this description, the thermal history of a point on a component or reference component includes information about the temperatures reached at that point during the past existence of the component or reference component. For example, the thermal history may include the highest temperature reached at that point during the thermal cycle experienced by the component or reference component, and / or whether the component or reference component reached a threshold temperature at that point.

[0018] In this description, the term "optical marker" or "marker" refers to a photoluminescent and / or thermochromic and / or thermochromic luminescent marker. More generally, an optical marker is a marker capable of providing optical information. This optical information may or may not depend on the parameter being observed, in this case, temperature. Typically, a first marker can be selected such that the optical information it returns depends on the temperature to which it is subjected.

[0019] Within the meaning of the present disclosure, unless otherwise indicated, reference to a "first" element, such as a first optical marker, does not necessarily imply the presence of a "second" element, nor does it imply an order relationship between the first and second elements, where applicable. The use of ordinal adjectives in this context is purely for clarity and ease of identification and does not detract from any particular characteristics.

[0020] Having the same coating on a component and a reference part means they both have the same coating density, containing the same markers, and even the same chemical composition. For example, the component and reference part may have been coated with a common coating product source. However, the coating between the component and reference part may differ in thickness, geometry, etc.

[0021] In this description, the term "optical information" refers to any information about the luminescence or color obtained by analyzing the luminescence or color of one or more optical markers (photoluminescence and / or thermochromic and / or thermochromic luminescence) contained in a coating. For example, the intensity, wavelength, and lifetime of the luminescence are all examples of optical information. The ratio between several types of luminescence or any other calculated and / or measured optical quantity can also be considered optical information.

[0022] In this description, the term "thermal image" refers to an image that has a temperature associated with each of its pixels. In this description, it should be understood that a thermal image of a reference component represents the thermal history of the reference component. A thermal image can be obtained using any device capable of measuring temperature and associating it with pixels, such as a thermal imaging camera (e.g., an infrared camera).

[0023] This measurement method makes it possible to measure the thermal history of an entire surface in a single measurement. In other words, compared to known point-space measurements (such as those using thermocouple probes and thermosensitive crystals), the coating of the present invention allows for spatially continuous measurements. Consequently, the information collected using this method is more extensive and complete than that gathered using known methods.

[0024] In particular, the spatial resolution of the measurement is determined by the camera's resolution. This significantly improves the spatial resolution of known devices, which are limited by the number of sensors that can be placed on a component. As a non-limiting example, the spatial resolution of the thermal history measurement can be one thousandth of the camera's range in each direction across the camera's acquisition plane. For example, for a camera with a range of ten centimeters by ten centimeters, the spatial resolution is approximately one hundred microns. In other words, the camera can provide a continuous thermal image of a continuous field, where the pixel discretization is solely due to the camera's resolution.

[0025] Furthermore, the use of optical devices simplifies and accelerates the measurement process, thereby speeding up the implementation of this method. In particular, the measurement procedures using optical devices are less restrictive than those of known measurement methods and can accommodate all possible geometries of the components to be analyzed. They also offer the advantage of being non-invasive. This represents a dual advantage in terms of both cost and time.

[0026] Furthermore, since the method is based on image acquisition and interpretation by a processing unit, all measurements can be processed digitally. This makes measurements more accurate, easier, and more reproducible.

[0027] Calibration of the method is facilitated because analyzing a reference component during the measurement, image acquisition, and image analysis steps is sufficient for full calibration of the method. In other words, analyzing the reference component alone allows the transfer function between optical information and thermal history to be determined over a wide temperature range. Furthermore, this calibration and measurement of the component's thermal history are performed using the same optical setup and without the need for any external components, saving time and limiting measurement uncertainty. In particular, the closer the predetermined thermal cycle experienced by the reference component is to the assumed thermal cycle experienced by the component, the more accurate the calibration of the method, as reflected in the transfer function, will be.

[0028] In some embodiments, the acquiring step of acquiring an image of the component includes using a three-dimensional reconstruction means, and the method further includes a reconstruction step in which a map of the component thermal history is inferred from the image of the component thermal history and the three-dimensional reconstruction means, and the map of the component thermal history relates the thermal history of the component to the three dimensions of space.

[0029] In other words, reconstruction techniques are used to determine a thermal history map from the thermal image. This makes it possible to construct a three-dimensional representation of the component that represents its thermal history (referred to herein as a thermal history map). By directly linking the component's geometry to its thermal history, the map allows for a more refined analysis of the thermal history. For example, regions with specific thermal behavior can be identified.

[0030] In some embodiments, the optical device includes a test pattern or scanner.

[0031] These two examples are two alternative ways to acquire a thermal history map. Using a test pattern is particularly suitable for components with simple 3D geometries, while a scanner is more suitable for components with complex 3D geometries. The test pattern or the scanner can acquire the 3D geometry of the component in a known manner, which is then input into the reconstruction process.

[0032] In some embodiments, the reference component is conical. Alternatively or additionally, in some embodiments, the reference component is made of a conductive material.

[0033] With this configuration, a thermal cycle can be predetermined in a controlled manner during the calibration step. In particular, a thermal cycle can be applied to the reference component by passing an electric current through it. Thus, it is possible to predetermine a thermal cycle for the reference component that is comparable—or even similar—to the thermal cycle experienced by the component during the test step. This improves the relevance of the calibration, which in turn increases the accuracy of the thermal history measurement.

[0034] The conical shape also enables calibration of wide temperature gradients with a single calibration. Under these conditions, calibration allows for a continuous temperature gradient. In other words, by applying a temperature gradient to a reference component, every temperature within the gradient is reached at some point on the reference component, ensuring a continuous temperature calibration and making thermal history analysis more accurate.

[0035] In some embodiments, in the step of acquiring images of the component and the reference component, the processing unit records at least one mean image, where the at least one mean image is a mean of at least ten images acquired by the camera.

[0036] In this configuration, noise in the images captured by the camera is canceled out by calculating the mean image, thereby improving measurement accuracy.

[0037] In some embodiments, the coating comprises a second optical marker, and in the acquiring step of acquiring images of the component and the reference component, the optical information measured by the optical device for the first optical marker comprises the luminescence intensity of the first optical marker at a first given wavelength, the optical information measured by the optical device for the second optical marker comprises the luminescence intensity of the second optical marker at a second given wavelength, and in the analyzing step of analyzing the images of the component and the reference component, the processing unit calculates a ratio between the luminescence intensity of the first optical marker and the luminescence intensity of the second optical marker, the processed optical information comprising the ratio between the luminescence intensity of the first optical marker and the luminescence intensity of the second optical marker.

[0038] This configuration is a first alternative for analyzing thermal history according to the present method. This first alternative benefits from the advantages mentioned above. It should be understood that the first optical marker and the second optical marker here are photoluminescent markers.

[0039] The photoluminescent markers contained in the coating can undergo permanent physicochemical and / or microstructural changes upon exposure to certain temperatures. These changes can include phase transitions, volatilization of residual groups, diffusion of dopant ions, and so on. Consequently, the optical information that can be inferred from the markers can vary significantly upon exposure to temperatures between, for example, 500°C and 1500°C. Consequently, this method can infer thermal history information with greater accuracy than known methods. In particular, the maximum temperature experienced by the coating can be measured to the nearest whole degree. Furthermore, the temperature range covered by the markers is wider than that covered by known techniques, particularly thermochromic coating methods that measure color changes visually. Consequently, thermal history analysis is more refined and accurate.

[0040] In some embodiments, the optical information obtained for the second marker is independent of temperature. Thus, the second marker forms a reference against which the optical information obtained for the first marker can be compared. Comparison with this reference avoids consideration of parameters other than temperature.

[0041] In some embodiments, the first optical marker is a unique marker, and in the acquisition step of acquiring images of the component and the reference component, the optical information measured by the optical device for the first optical marker includes multiple intensities reflected by the optical marker at multiple given wavelengths, and the processed optical information includes spectral signatures calculated by the processing unit for multiple wavelengths in the analysis step of analyzing images of the component and the reference component.

[0042] This configuration is a second alternative for analyzing thermal history according to this method. This second alternative benefits from the advantages described above. In this alternative, the marker can be photoluminescent and / or thermochromic and / or thermochromically luminescent. Because the spectral signature contains information at multiple wavelengths, it can ignore wavelength- and temperature-independent effects. The fact that the first optical marker is unique means that there is no possibility that the coating has other optical markers that are different from the first optical marker.

[0043] In some embodiments, the first optical marker is the only marker, and in the step of acquiring images of the component and the reference component, after the light source pulses the luminescence of the first optical marker, the optical device performs a series of measurements of the luminescence intensity of the first marker at a given wavelength, and the processed optical information includes the time-dependent integrated luminescence intensity of the first optical marker calculated by the processing unit in the step of analyzing the images of the component and the reference component.

[0044] Generally speaking, photoluminescent markers emit light for a certain period of time after exposure to an excitation wavelength. The intensity of the light emitted by these markers is expressed as the sum of exponential decays, usually according to the following formula:

[0045] [Mathematical formula 1]

[0046]

[0047] For a given nth wavelength, I n represents the emitted light intensity and t n The longest time t is the lifetime related to the light intensity. n is called the "lifetime" of the photoluminescent marker.

[0048] This configuration is a third alternative for analyzing thermal history according to the present method. This third alternative benefits from the advantages mentioned above. In this alternative, the marker can be photoluminescent and / or thermochromic.

[0049] Furthermore, this configuration has the advantage of being applicable to any luminescence signal. Calculating the integrated luminescence intensity as a function of time allows processing any luminescence without having to assume its form in advance. Therefore, there is no need to know precisely the type of luminescence being measured, nor to model it. This approach also allows for the use of luminescence without having to calculate the integral luminescence intensity for each intensity I n The corresponding lifespan t n The result is obtained in the case of , so it is simpler.

[0050] In some embodiments, a series of measurements includes more than ten measurements.

[0051] Using the above parameters can improve the accuracy of the photoluminescence lifetime measurement of the first photoluminescent marker, thereby improving the accuracy of the thermal history measurement.

[0052] The above-mentioned characteristics and advantages as well as other aspects will become apparent on reading the following detailed description of an example of embodiment of the proposed device and method, which makes reference to the accompanying drawings.

[0053] Brief Description of the Drawings

[0054] The accompanying drawings are schematic and their primary purpose is to illustrate the principles of the present description.

[0055] [ Figure 1 ] Figure 1 An optical device configured for performing a thermal analysis method is illustrated.

[0056] [ Figure 2 ] Figure 2 The method of analyzing the thermal history of a component according to the first embodiment is schematically illustrated.

[0057] [ Figure 3A ] Figure 3A A grayscale image of the reference component acquired in the acquisition step according to the first embodiment is given.

[0058] [ Figure 3B ] Figure 3B Given in the analysis step according to Figure 3A Grayscale image of the thermal history calculated from the image in .

[0059] [ Figure 4 ] Figure 4 A method of analyzing the thermal history of a component according to the second embodiment is schematically illustrated.

[0060] [ Figure 5 ] Figure 5 A method of analyzing the thermal history of a component according to the third embodiment is schematically illustrated.

[0061] Description of the embodiment

[0062] For a clearer description, examples will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these examples.

[0063] The present invention proposes analyzing the thermal history of a component 100 by recording the photoluminescence of one or more photoluminescent markers contained in a coating applied to the component 100. In this example, the component 100 may be an aircraft component, or more generally, a component 100 that has undergone an annealing process.

[0064] Coating preparation

[0065] The coating provided on the component 100 may contain the following markers as dopants for the inorganic matrix: marker ions of europium III, samarium III, dysprosium III, erbium III, thulium III, or chromium III. Any matrix capable of containing one or more of these markers is suitable for the present method, for example, metal oxides such as yttrium partially stabilized zirconia (YSZ), aluminum oxide, yttrium oxide (or yttrium oxide), or yttrium aluminum garnet (YAG).

[0066] Mention may be made of chromium-doped alumina markers, such as the one sold under CAS number 99328-47-9, which are suitable for coatings that can be analyzed by the present thermal history measurement method.

[0067] Marker Al2O3:Cr 3+ ,Y2O3:Eu 3+ ,YAG:Eu 3+ YSZ doped with at least one of the ions europium III, samarium III, dysprosium III, erbium III, thulium III, or chromium III is particularly suitable for the intensity analysis described below.

[0068] Depend on The commercially available markers MC350-8 and MC520-7 are particularly suitable for use in thermochromic analysis as described below.

[0069] Marker Al2O3:Cr 3+ YSZ doped with at least one of the ions europium III, samarium III, dysprosium III, erbium III, thulium III, or chromium III is particularly suitable for lifetime analysis as described below.

[0070] More generally, the coating may be obtained by depositing a coating comprising a mixture of a marker, a solvent, a binder and optional additives on the component and the reference component.

[0071] Commercial binders suitable for forming photoluminescent coatings that can be analyzed by the present thermal history measurement method may be mentioned, such as LK (ZYP COATINGS), HPC (ZYP COATINGS), ZAP (ZYP COATINGS), 644-S (AREMCO), Ceramabind 643-2 (AREMCO), Respond 791, 792, 793 and 795 (COTRONICS).

[0072] As the solvent, there may be mentioned 1-propanol or any other commercially available alcohols.

[0073] In the case of coatings containing photoluminescent markers, these coatings are prepared from powders containing an inorganic matrix that is functionalized or doped with ions having photoluminescent properties. As mentioned above, these ions can be lanthanides or transition metals.

[0074] The inorganic matrix comprises a metal oxide. In this example, the inorganic matrix may comprise partially stabilized zirconia (YSZ), alumina, yttrium oxide, or yttrium aluminum garnet (YAG).

[0075] In this example, the concentration of the dopant in the inorganic matrix, ie, the ion concentration, is between 0.1 at % (atomic percent) and 10 at %. Preferably, the dopant concentration is between 0.5 at % and 5 at %.

[0076] The photoluminescent marker to be added to the coating can be pre-heated. For example, in the coating of the first embodiment, the photoluminescent marker corresponding to the second photoluminescent marker is treated at 1500°C and then ground. In this way, as long as the temperature to which the marker is exposed remains below 1500°C, its luminescence behavior remains constant with temperature changes.

[0077] Once the coating is obtained, it is deposited on an object, such as part 100 or a reference part. For example, deposition can be done manually (typically with a brush or roller), or by spraying, dipping, electrophoresis, or spin coating.

[0078] Method and device for implementing the method

[0079] Figure 1 An optical device configured to implement a method for analyzing thermal history is illustrated. The optical device is configured to analyze a component 100. The optical device includes a light source 10, an optional first filter device 12 located after the light source 10, a light guide 14, and a collimator 16. The optical device also includes a camera 20 and a second filter device 22 arranged in front of the camera 20.

[0080] The light source 10 is configured to illuminate the component 100, while the light guide 14 and the collimator 16 are configured to adjust the illumination provided by the light source 10 to the component 100. The first filter device 12 is configured to adjust the wavelength emitted by the light source 10 if necessary.

[0081] To improve the accuracy of the method, the light source 10 is configured to illuminate the component 100 so that the light reaching the component 100 is substantially perpendicular to the surface of the component 100. Therefore, it can be understood that the angle between the incident light and the component surface is between 70° and 110°.

[0082] Furthermore, the camera 20 is configured to capture an image of the component 100 , and the second filter device 22 is configured to adjust the wavelength emitted by the coating included in the component 100 and captured by the camera 20 .

[0083] The optical device additionally comprises a processing unit 30 configured to record and analyze images acquired by the camera 20 and calculate a mapping image of the thermal history. The processing unit 30 is also configured to control the camera 20 and the first and second filtering devices 12 and 22 .

[0084] In this example, light source 10 can be a light source with a broad spectrum capable of emitting radiation from 250 nm to 700 nm. For example, light source 10, accompanied by light guide 14 and collimator 16, is configured to emit a uniform light field onto a surface of at least 200 x 200 mm2. In other words, light source 10 is an extended light source configured to illuminate a surface.

[0085] First embodiment, intensity analysis of photoluminescent markers

[0086] Figure 2 A series of steps of a method according to a first embodiment are schematically illustrated. The method comprises a testing step M1 and a calibration step M2, an acquisition step A1 of acquiring an image of a component and an acquisition step A2 of acquiring an image of a reference component, an analysis step E1 of analyzing the image of the component and an analysis step E2 of analyzing the image of the reference component, a determination step I of determining a transfer function, an interpretation step C, and a reconstruction step S.

[0087] In the example chosen for this first embodiment, the coating provided on the component 100 is prepared according to the example 1 described above. In the remainder of this document, the photoluminescent marker Al2O3:0,6% Cr 3+ Known as the first photoluminescent marker, photoluminescent marker Y2O3:5% Eu 3+ This example of a pair of photoluminescent markers is not limited thereto, and other marker pairs such as Al2O3:Cr may also be used. 3+ / YAG:Eu 3+ or YSZ:Er 3+ / Y2O3:Eu 3+ or YSZ:Er 3+ / YAG:Eu 3+ .

[0088] In this embodiment, the photoluminescence profile of the first photoluminescent marker provides information about the thermal history of the coating. Furthermore, the photoluminescence profile of the second photoluminescent marker is collected as a reference to eliminate the influence of other physical quantities, such as coating thickness. More generally, the photoluminescence profile of the first photoluminescent marker depends on the thermal history, while the photoluminescence profile of the second photoluminescent marker does not. In this first embodiment, light source 10 is configured to provide a broad-spectrum continuous light in the visible and / or ultraviolet range. In this example, light source 10 is a xenon light source emitting wavelengths between 250 nm and 700 nm. Other light sources, such as laser diodes centered around the excitation wavelength of the photoluminescent marker, are also contemplated.

[0089] In test step M1, component 100 is subjected to a thermal cycle. For example, such a thermal cycle can be applied during flight on an aircraft or simulated in a laboratory or on a test bench. The thermal cycle has several parameters, such as the maximum temperature encountered by the component, the heating rate, and the cooling time. These parameters can be known or estimated.

[0090] In the calibration step M2, the reference component is subjected to a predetermined thermal cycle. Preferably, the parameters of the predetermined thermal cycle are parameterized to be consistent with the thermal cycle of the component, i.e., consistent at least with the temperature and temperature ramp rate experienced by the component 100 in the test step M1. For example, the order of magnitude of the temperature can be the same, the direction of the temperature change can be the same (increasing or decreasing), the timing of the temperature change can be similar, etc.

[0091] This cycle is achieved through a heat source and a heat sink. The heat source can be, for example, a laser, an infrared lamp, a Joule effect or induction effect, or a thermal spray gun. The heat sink can be, for example, natural convection, a stream of cold air, cold water or a cold metal block in contact with the reference component, or a liquid stream. The shape of the reference component can be a parameter that influences the thermal cycle.

[0092] In this example, the heat source utilizes the Joule effect, the heat sink utilizes natural convection, and the reference component is made of a conductive material and has a conical shape.

[0093] Applying an electric current to the reference component creates a temperature gradient across its surface. Due to its conical shape, the top of the reference component is hotter than the bottom.

[0094] In this example, the calibration step can produce a temperature difference between the top and bottom temperatures of the reference component of between 100° C. and 800° C. In this example, the maximum acceptable temperature of the reference component is between 1200° C. and 1400° C. It will be appreciated that a larger or smaller temperature gradient can be applied to the reference component within a selected temperature range from ambient temperature to 1400° C.

[0095] During the calibration step M2 and the establishment of the thermal cycle M1, it is possible to reach the selected temperature gradient in a period of between a few minutes and a few hours, depending on the temperature gradient to be explored and the heating rate to be applied. In this respect, the heating rate is between 0°C and 70°C per second.

[0096] At the end of the thermal cycle, a thermal image of the reference component is acquired by means of an infrared camera. This image may be the average of multiple thermal images. This thermal image of the reference component is recorded by the processing unit 30.

[0097] In this example, a scale is acquired by an infrared camera or other device so that the thermal image of the reference component can be correlated to its spatial dimensions. In other words, the image's dimensions in pixels are correlated to its actual dimensions in millimeters.

[0098] When component 100 and the reference component have cooled to approximately ambient temperature, step A1 of capturing an image of the component and step A2 of capturing an image of the reference component are performed. Here, step A2 of capturing an image of the reference component is described. It will be appreciated that step A1 of capturing an image of the component and step A2 of capturing an image of the reference component are identical, but are applied to component 100.

[0099] In step A2 of capturing an image of the reference component, before capturing the image, a first filter device 12 is positioned in front of the light source 10 and adjusted to filter the light. This filtering is a bandpass type centered around the excitation wavelength of the first photoluminescent marker. A second filter device 22 is positioned in front of the camera 20 and is configured similarly to the first filter device 12, centered around the relaxation wavelength of the first photoluminescent marker.

[0100] In this example, the first and second filter devices 12 and 22 are a set of filters configured to perform bandpass filtering of light having a width of about several tens of nanometers (typically 50 nanometers) in the range of 400 nanometers to 700 nanometers.

[0101] In this example, for the first photoluminescent marker, the first filter device is centered at 545 nanometers and the second filter device 22 is centered at 695 nanometers. Thus, the reference component is illuminated by the light source 10 at a wavelength that allows excitation of the first photoluminescent marker in the coating, and the camera 20 is able to sense light that represents the emission of light by the first photoluminescent marker.

[0102] Image acquisition is then performed. The camera 20 acquires a plurality of images of the reference component at a relaxation wavelength corresponding to the first photoluminescent marker.

[0103] The acquisition time of each image and the number of images to be acquired are predetermined. In this example, the camera 20 is configured to capture 10 images. However, the number of images to be acquired can be adjusted according to the accuracy required for the mean image obtained from the acquired multiple images.

[0104] After this acquisition, the processing unit 30 calculates a first mean image of the luminescence of the first photoluminescent marker of the reference component based on the plurality of images. The processing unit 30 records this first mean image.

[0105] After recording this first mean image, the first filter device 12 is adjusted to center on the excitation wavelength of the second photoluminescent marker, and the second filter device 22 is adjusted to center on the photoluminescence wavelength of the second photoluminescent marker. This switching can be performed by the operator or automatically.

[0106] In this example, for the second photoluminescent marker, the first filter device is centered at 562 nanometers and the second filter device 22 is centered at 610 nanometers. In this way, the reference component is illuminated by the light source 10 at a wavelength that allows the second photoluminescent marker in the coating to be excited, and the camera 20 is able to sense light that represents the emission of the second photoluminescent marker.

[0107] Image acquisition is further performed. The camera 20 acquires multiple images of the reference component at the relaxation wavelength corresponding to the second photoluminescent marker. The image acquisition time and the number of images acquired are the same as those when acquiring the first photoluminescent marker image.

[0108] After this acquisition, the processing unit 30 calculates a second mean image of the luminescence of the second photoluminescent marker of the reference component based on the plurality of images. The processing unit 30 records this second mean image.

[0109] The first and second mean images of the reference part are acquired from the same angle and using the same geometric parameters of camera 20. Therefore, the first mean image can be compared with the second mean image on a pixel-by-pixel basis. In other words, each pixel of each mean image corresponds to a defined region of the reference part and is identical in each image.

[0110] Figure 3A The first and second mean images of the analyzed reference component obtained in the acquisition step A2 of acquiring an image of the reference component according to the first embodiment are illustrated. These images are grayscale images.

[0111] Figure 3A The top image in the figure shows the first mean image, while the bottom image shows the second mean image. In other words, the top image illustrates the photoluminescence of the first photoluminescent marker, while the bottom image illustrates the photoluminescence of the second photoluminescent marker. These images are presented in grayscale. Depending on the selected scale, white corresponds to high-intensity luminescence, while black corresponds to no luminescence.

[0112] exist Figure 3A In the image above, you can see an image with a bright patch on the left side of the image. Furthermore, as you move to the right side of the image, the patch becomes gradually darker, meaning that the light on the right side is weaker.

[0113] Since the first optical marker used is temperature-sensitive, it can be understood that the left portion showing strong luminescence experiences a higher temperature than the right portion.

[0114] It can also be noted that this patch of high intensity lies slightly above the central axis of the diagram. This suggests that the luminescence is asymmetric with respect to the central axis. However, the tests performed imposed a temperature field that was symmetric with respect to the central axis. This observation suggests that the measured luminescence may depend on parameters other than the thermal history, although, as will be described below, the influence of these other parameters can be masked by considering a second thermal image.

[0115] exist Figure 3A In the lower image, you can see that the grayscale is more uniform than in the upper image. However, you can notice a slightly brighter area towards the upper center of the image.

[0116] Since the second optical marker used is known to be temperature insensitive, it is expected that Figure 3A The lower image in the figure should be uniform. However, this brighter patch indicates that the glow is stronger in the upper center. This suggests that the coating is slightly too thick at that point.

[0117] Furthermore, in this example, a dark image can be recorded during step A2 of capturing an image of the reference component. Under these conditions, the lens of camera 20 is covered, and multiple dark images are captured using the same parameters as those used to capture the photoluminescence of the photoluminescent marker. These multiple dark images are transmitted to processing unit 30, which calculates a mean dark image. This mean dark image is then subtracted from the first and second mean images. These new, processed mean images are recorded by processing unit 30 and replace the previous mean images. The acquisition of the mean dark image can be performed before or after the acquisition of the first and second mean images.

[0118] Next, during an analysis step E2, the processing unit 30 calculates a processed image of the reference component. The acquisition of the processed image of the reference component is described here, but it is clear that the processed image of the component 100 is obtained in the same way.

[0119] First, processing unit 30 calculates a conversion from pixel scale to millimeter scale for one of the first or second mean images of component 100. This scale conversion is then applied to the other image.

[0120] The processing unit 30 then constructs a processed image of the component 100 by calculating, for each pixel, the ratio between the photoluminescence intensity of the first photoluminescent marker and the photoluminescence intensity of the second photoluminescent marker. In other words, the processing unit 30 calculates I(first photoluminescent marker) / I(second photoluminescent marker) at each point in the processed image of the reference component. This calculation also corrects for any variations in the photoluminescence of the first and second markers that are not due to temperature. Because both markers are affected by these external parameters in the same way, the calculation of the intensity ratio allows these external parameters to be ignored. For example, an external parameter could be non-uniform illumination from a light source or a non-uniform thickness of a coating.

[0121] A processed image of the reference component is obtained, which represents the relative intensity of the photoluminescence of the first photoluminescent marker relative to the photoluminescence of the second photoluminescent marker, the image being related to the spatial ratio. In this first embodiment, the ratio of the photoluminescence intensities is the optical information of interest, which allows the thermal history of the component 100 to be inferred.

[0122] Figure 3B Given in two different shades of gray Figure 3A The processed image of the reference part in Figure 3A Calculated from the two images in .

[0123] Figure 3B The figure above shows the ratios of two close intensity ratios associated with close grayscales. This reflects the difference in intensity ratios between the left and right sides of the reference part. Figure 3B The lower figure in shows the close intensity ratios associated with contrasting grayscales, making it possible to highlight the isointensity lines of the reference part, which correspond to thermal isohystokes and therefore experienced the same temperature in calibration step M2.

[0124] The calculation of the intensity ratio improves the accuracy of the measurement by counteracting external influences that may interfere with the measurement (such as excessive coating thickness).

[0125] Similarly, a processed image of the component 100 is calculated in an analysis step E1 .

[0126] In a transfer function determination step I, a transfer function is determined between the temperature and intensity ratio of the photoluminescence of a pair of photoluminescent markers using the thermal image of the reference component obtained in the calibration step M2 and the processed image of the reference component obtained in the analysis step E2 of analyzing the image of the reference component. In other words, a transfer function is determined that relates the processed optical information (here, the intensity ratio), temperature, and spatial dimension. It will be appreciated that for component 100 and the reference component, the temperature more specifically reflects the thermal history of component 100 or the reference component. This "temperature" effectively represents the highest temperature encountered during the test step M1 and the calibration step M2.

[0127] This relationship enables the conversion of an image representing the ratio of the photoluminescent intensities of a pair of photoluminescent markers into an image of the thermal history. Note that the conversion is only applicable to images of parts coated with the same coating as the reference part.

[0128] In an interpretation step C, the processed image of the component 100 obtained in the analysis step E2 is converted into an image of the thermal history of the component 100 using the transfer function determined in the transfer function determination step I.

[0129] In a reconstruction step S, the image of the thermal history of the component 100 is coordinated with the geometry of the component 100 to obtain a map of the thermal history of the component 100. The reconstruction step S enables the mapping of the thermal history of a primarily two-dimensional component and / or a three-dimensional component to be drawn.

[0130] For a component having a two-dimensional geometry, coordination corresponds to aligning the image of the thermal history with reference points relative to the component 100 .

[0131] For components with three-dimensional geometry, two cases can be distinguished: Generally, a three-dimensional reconstruction means (which can be, for example, a test pattern, a grid or a scanner) is used to reconstruct the three-dimensional geometry.

[0132] In the first case, when the geometry is slightly curved, such as a turbine blade, it can be obtained by the inverse function of the two-dimensional projection. Under these conditions, in step A1 of acquiring images of the component, images of component 100 are acquired, and component 100 includes a grid configured to be located within the field of view of each acquired image. This grid can be directly attached to component 100 or simply placed or drawn on it.

[0133] The processing unit 30 calculates a geometric transformation relationship (curve X axis) linking the image pixels to the three-dimensional reconstruction of the component 100 based on those image portions of the plurality of acquired images that represent the grid.

[0134] In the second case, when the geometry of the component 100 is complex, the optical device comprises a scanner for capturing the surface mesh of the component 100. Under these conditions, the scanner cooperates with the camera 20 to calculate a geometric transformation that links the pixel coordinates of the temperature image of the component to the three-dimensional coordinates of the surface mesh of the component expressed in units of length.

[0135] Second Example: Thermochromic Analysis

[0136] In the following paragraphs, focus on Figure 4 The second embodiment is schematically illustrated in FIG. In the second embodiment, the method includes a first variant of an acquisition step A1′ for acquiring an image of a component and an acquisition step A2′ for acquiring an image of a reference component, as well as an analysis step E1′ for analyzing the image of the component and an analysis step E2′ for analyzing the image of the reference component. The remaining steps are identical to the corresponding steps in the first embodiment.

[0137] In the example used for this second embodiment, the coatings on component 100 and the reference component comprise a single thermochromic marker. For example, this marker is One of the marketed markers MC350-8 and MC520-7.

[0138] The image acquisition parameters of acquisition steps A1' and A2' in the second embodiment are the same as the general camera parameters (number of acquired images, acquisition time, dark image, etc.) of acquisition steps A1 and A2 in the first embodiment. In particular, it can be seen that acquisition steps A1' and A2' in the second embodiment can be performed using an optical device similar to the optical device in the first embodiment.

[0139] Furthermore, in the second embodiment, a white light source 10 is used, and only a second filter device 22 is used. The filter device 22 is pre-placed in front of the camera 20 and adjusted to filter the light. This filtering is of the bandpass type centered around an arbitrary first wavelength (visible or invisible) corresponding to the emission wavelength of the thermochromic marker, the intensity of which varies according to the thermal history.

[0140] Here, the acquisition step A1' for acquiring an image of a component and the analysis step E1' for analyzing the image of the component are described. It should be understood that the acquisition step A2' for acquiring an image of a reference component and the analysis step E2' for analyzing the image of the reference component are respectively the same as the acquisition step A1' for acquiring an image of a component and the analysis step E1' for analyzing the image of a component, but involving a reference component.

[0141] During step A1', a first image acquisition process is performed. Camera 20 captures multiple images of component 100 at a first wavelength. The intensity of light reflected by the thermochromic marker is measured at this wavelength, and a first average image at the first wavelength (or first color) is obtained. This first average image is recorded by processing unit 30.

[0142] After recording this first mean image, the second filter device 22 is centered at a second wavelength different from the first wavelength. The second mean image is acquired and recorded in the same manner as the first mean image. This method is repeated as many times as needed for different wavelengths.

[0143] It will be appreciated that each mean image captures an image of component 100 from the same angle and using the same camera 20 parameters, with the sole exception of the wavelength of light received by camera 20 and filtered by second filter device 22. Therefore, each mean image can be compared pixel by pixel with another mean image. In other words, each pixel of each mean image corresponds to a defined region of component 100, and this region is the same in each image.

[0144] In the subsequent component analysis step E1', the processing unit 30 calculates the processed spectral signature matrix of the component 100 and the processed spectral signature matrix of the reference component. Here, the acquisition of the processed matrix of the component 100 is described, and it should be understood that the processed matrix of the reference component is obtained in the same manner.

[0145] First, processing unit 30 calculates a pixel scale to millimeter scale (or other unit length) conversion for one of the mean images of part 100. This scale can then be converted to all other mean images.

[0146] Processing unit 30 first counts, for each pixel of the mean image, the reflection intensity recorded in each mean image during acquisition step A1′. In other words, processing unit 30 creates a matrix the size of the mean image, consisting of reflection intensity vectors, one for each pixel, consisting of each reflection intensity recorded in each mean image calculated at that wavelength for each measurement wavelength.

[0147] From the intensity vector matrix, processing unit 30 uses an algorithm to calculate a spectral signature for each element of the matrix. A processed matrix is ​​thereby derived, associating each element with a corresponding spectral signature. In this example, the spectral signature may include information about the spectral moments, mean, and / or variance of the reflected intensity. In this second embodiment, the spectral signature is the optical information of interest, allowing the thermal history of component 100 to be inferred.

[0148] In an analogous manner, a processed matrix is ​​obtained for the reference component in an analysis step E2 ′.

[0149] The method may then continue with a transfer function determination step I, an interpretation step C and a reconstruction step S.

[0150] In particular, in the transfer function determination step I, the transfer function linking the spectral signature, the temperature and the spatial dimensions is determined using the processed matrix of the reference component obtained in the analysis step E2 ′ and the thermal image obtained in the calibration step M2 .

[0151] The interpretation step C and the reconstruction step S are then performed as described above.

[0152] Third embodiment, life analysis

[0153] The third embodiment is described in the following paragraphs. Figure 5 In the third embodiment, the method includes a second variant of the image acquisition steps A1″ and A2″ and the image analysis steps E1″ and E2″. The other steps are the same as the corresponding steps of the first embodiment.

[0154] The acquisition steps A1″ and A2″ of the third embodiment can be performed by optical equipment similar to the equipment described in the first and second embodiments. However, the camera used in the third embodiment is preferably an intensified camera. Considering the time involved in the method, it is desirable that the camera be equipped with an intensifier to amplify the signal acquired within a time period of perhaps a few nanoseconds and therefore of low intensity.

[0155] In the example used for this third embodiment, the coatings on component 100 and the reference component contain a single photoluminescent marker. This photoluminescent marker is YSZ:Er 3+ This example of a photoluminescent marker is not limiting, and other photoluminescent markers may be used.

[0156] The lifetime of the photoluminescent marker may depend on the thermal history of the photoluminescent marker. Furthermore, the lifetime is independent of factors such as the thickness of the coating provided on the photoluminescent marker, the intensity of the illumination, and contamination.

[0157] The light source 10 used in this embodiment is a monochromatic light source configured to provide pulsed light. The wavelength of the light source 10 is selected to correspond to the excitation wavelength of the photoluminescent marker. The monochromatic nature can be achieved by the action of the filter device 12 or the type of light source 10. For example, the light source 10 can be a laser source. In this example, the pulsing of the light source 10 is controlled by the processing unit 30.

[0158] The camera 20 is configured to capture a series of images in response to instructions received from the processing unit 30. In this example, the camera 20 is configured to capture a series of images after receiving instructions from the processing unit 30, for a period of time substantially longer than the photoluminescent lifetime of the photoluminescent marker. The period of time is at least three times the maximum lifetime of the marker.

[0159] Here, the image acquisition step A1" for acquiring the image of the component and the image analysis step E1" for analyzing the image of the component are described. It should be understood that the image acquisition step A2" for acquiring the image of the reference component and the image analysis step E2" for analyzing the image of the reference component are respectively the same as the image acquisition step A1" for acquiring the image of the component and the image analysis step E1" for analyzing the image of the component, but involve the reference component.

[0160] In an acquisition step A1 ″, and before acquiring an image, the second filter device 22 is centered on the relaxation wavelength of the photoluminescent marker.

[0161] In this example, the optical device is configured to provide illumination at 514 nanometers. The second filter device 22 is centered at 545 nanometers. The component 100 is thus illuminated at a wavelength that allows the photoluminescent marker contained in the coating to be excited, and the camera 20 is able to sense light representing the luminescence of the first photoluminescent marker.

[0162] Then, acquisition is performed. Processing unit 30 jointly instructs light source 10 and camera 20 to emit pulses and capture a series of images, respectively. In this example, the series of images includes a sufficient number of images to integrate the photoluminescence intensity as a function of time. In this example, the series of images includes several dozen images, typically 30 images. The series of images is recorded by processing unit 30.

[0163] It can be seen from this series of images that the luminescence intensity of the photoluminescent marker decreases as the images are scrolled.

[0164] Optionally, this acquisition is repeated at least ten times using the same parameters. The processing unit 30 calculates a sequence of mean images, wherein each image in the sequence of mean images is the mean image of the corresponding image in each previously acquired and recorded sequence of images. The series of mean images is recorded by the processing unit 30.

[0165] In subsequent analysis steps E1″ and E2″, processing unit 30 calculates two processed matrices for component 100 and the reference component, relating their respective entries to the time-dependent integrated photoluminescence intensity of a given pixel in the image sequence of component 100 and the corresponding pixel in the image sequence of the reference component. While the case of acquiring the processed matrix of component 100 is described herein, it should be understood that the processed matrix of the reference component is obtained in the same manner.

[0166] First, the processing unit 30 calculates a pixel-to-millimeter scale conversion for the mean image in the mean image sequence, and then this scale can be converted to all other mean images in the mean image sequence.

[0167] From the mean image sequence, processing unit 30 integrates the luminescence intensity at each pixel as a function of time. This value is entered into a matrix of the same size as the pixel size of one image in the mean image sequence, at the position corresponding to the processed pixel. Thus, when all pixels have been processed, a processed matrix is ​​formed. In this third embodiment, the integrated photoluminescence intensity as a function of time is the optical information of interest, allowing the thermal history of component 100 to be inferred.

[0168] Similarly, a processed matrix is ​​obtained for the reference component in analysis step E2 ″.

[0169] The method may then continue with a transfer function determination step I, an interpretation step C and a reconstruction step S.

[0170] In particular, in the transfer function determination step I, the transfer function relating integrated intensity, temperature and spatial size is determined using the processed matrix of the reference component obtained in the analysis step E2″ and the thermal image obtained in the calibration step M2.

[0171] A variant of this third embodiment is to provide, during the acquisition steps A1″ and A2″, a light source 10 configured to provide continuous light with amplitude modulation. Under these conditions, the processing unit 30 calculates the phase shift and / or amplitude variation between the light source and the light intensity acquired by the camera 20. This parameter can be related to the lifetime, for example by the equation (in is the phase shift, f is the incident light modulation frequency, and τ is the lifetime to be determined). This lifetime corresponds to the maximum lifetime t n .

[0172] Example 4: Thermochromic-Luminescent Marker Analysis

[0173] The following paragraphs relate to the fourth embodiment. In the fourth embodiment, a thermochromic-luminescent marker, such as Zn3(PO4)2:2%Mn 2+ These markers have the property that, when excited at a specific excitation wavelength, they emit a spectrum with peaks at several specific wavelengths. The peak intensity of the emitted spectrum depends on the thermal history.

[0174] The method of analyzing the thermal history is the same as that of the second embodiment, except that the configurations of the light source 10 and the first filter device 12 are different.

[0175] In a fourth embodiment, the optical device comprises a filter device 12 and the component is illuminated with light centred on the excitation wavelength of the thermochromic-luminescent marker as in the first embodiment.

[0176] The second filter device 22 is centered on each emission wavelength of the thermochromic-luminescent marker and measures the spectral signature as in the second embodiment.

[0177] This description is based on an example of analysis of thermal history, but the method can be applied, with appropriate modifications, to historical analysis of any thermomechanical quantity (stress, deformation, pressure, temperature, etc.) using markers whose optical information varies according to the quantity.

[0178] Although the present invention has been described with reference to specific examples of embodiments, it will be apparent that modifications and variations may be made to these examples without departing from the overall scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in other embodiments. The description and drawings are therefore to be interpreted in an illustrative rather than a restrictive sense.

[0179] Obviously, all features described with reference to a method can be transferred to a device individually or in combination, and conversely, all features described with reference to a device can also be transferred to a method individually or in combination.

Claims

1. A method for analyzing the thermal history of a component (100) by means of an optical device, The component (100) has a coating comprising a first optical marker, The optical device comprises a camera (20) configured to acquire an image of the component (100), a light source (10) configured to illuminate the component (100) and a reference component having the same coating as the component (100), and a processing unit (30), The method comprises: a test step (M1) in which the component is subjected to thermal cycling; a calibration step (M2), in which the reference component is subjected to a predetermined thermal cycle, and in which a thermal image of the reference component is acquired by a thermal imaging camera and recorded by the processing unit (30); an acquisition step (A1; A1'; A1") of acquiring an image of the component and an acquisition step (A2; A2'; A2") of acquiring an image of the reference component, wherein optical information about the component (100) and the reference component are respectively measured by the optical device and then recorded by the processing unit (30); an analyzing step (E1; E1'; E1") of analyzing the image of the component and an analyzing step (E2; E2'; E2") of analyzing the image of the reference component, wherein the optical information about the component (100) and about the reference component are processed by the processing unit (30) in order to obtain processed optical information about the component and the reference component, respectively; a determining step (I) of determining a transfer function, wherein the processing unit (30) determines a transfer function that relates temperature, processed optical information, and spatial size based on the thermal image of the reference component and the processed optical information of the reference component; Explain step (C), wherein the processing unit (30) calculates an image of thermal history using the transfer function and the processed optical information of the component (100), the image of thermal history representing the thermal history of the component (100).

2. The method according to claim 1, wherein The acquisition step (A1; A1'; A1") of acquiring an image of the component comprises using three-dimensional reconstruction means, and wherein the method additionally comprises a reconstruction step (S) in which a map of the thermal history of the component (100) is derived from the image of the thermal history of the component (100), and the map of the thermal history of the component relates the thermal history of the component to three dimensions of space.

3. The method according to claim 2, wherein The optical device includes a test pattern or a scanner.

4. The method according to any one of claims 1 to 3, characterized in that The reference component has a conical shape and is made of a conductive material.

5. The method according to any one of claims 1 to 4, wherein in the acquisition step (A1; A1'; A1") of acquiring an image of the component and in the acquisition step (A2; A2'; A2") of acquiring an image of the reference component, the processing unit records at least one mean image, wherein the at least one mean image is the mean of at least ten images acquired by the camera (20).

6. The method according to any one of claims 1 to 5, characterized in that the coating comprises a second optical marker, and in the acquisition steps (A1, A2) of acquiring images of the component and the reference component, the optical information measured by the optical device for the first optical marker comprises the luminescence intensity of the first optical marker at a first given wavelength, The optical information measured by the optical device for the second optical marker includes the luminescence intensity of the second optical marker at a second given wavelength, and In the analyzing steps (E1, E2) of analyzing the images of the component and the reference component, the processing unit (30) calculates the ratio between the luminescence intensity of the first optical marker and the luminescence intensity of the second optical marker, the processed optical information including the ratio between the luminescence intensity of the first optical marker and the luminescence intensity of the second optical marker.

7. The method according to claim 6, wherein The optical information obtained for the second optical marker is independent of temperature.

8. The method of any one of claims 1 to 5, wherein the first optical marker is the only marker, and In the acquisition step (A1', A2') of acquiring images of the component and the reference component, The optical information measured by the optical device for the optical marker comprises a plurality of intensities reflected by the optical marker at a plurality of given wavelengths, and the processed optical information comprises spectral signatures calculated by the processing unit (30) for the plurality of wavelengths in the analysis steps (E1, E2) of analyzing the images of the component and the reference component.

9. The method according to any one of claims 1 to 5, characterized in that The first optical marker is the only marker, and In the acquisition step (A1", A2") of acquiring images of the component and the reference component, After the light source (10) provides a pulsed excitation of the luminescence of the first optical marker, the optical device performs a series of measurements of the luminescence intensity of the first optical marker at a given wavelength, and the processed optical information includes the time-dependent integrated luminescence intensity of the first optical marker calculated by the processing unit (30) in the analysis step (E1", E2") of analyzing the images of the component and the reference component.

10. The method according to claim 9, wherein The series of measurements comprises more than 10 measurements.

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