Method for measuring the thermal history of a room

Abstract

Method for measuring the thermal history of a part. Method for analyzing the thermal history of a part (100) by an optical device, the part having a coating including a first marker, the optical device comprising a camera (20) and a light source (10), the method comprising: a calibration step in which a standard having the same coating as the part undergoes a predetermined thermal cycle, a step of acquiring images of the part and a step of acquiring images of the standard, a step of analyzing images of the part and a step of analyzing images of the standard, a step of determining a transfer function in which a transfer function relating the temperature, the processed optical information and the spatial dimensions is determined,An interpretation step in which a thermal history image is calculated, and the thermal history image represents the thermal history of the room according to the predetermined angle. Figure for the abbreviation: Fig. 2.

Description

Title of the invention: Method for measuring the thermal history of a room technical field

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

[0002] Such a method can be used for the analysis of parts of turbomachinery or turbojets, to name only these examples. Previous technique

[0003] Knowledge of the surface temperature of the components and / or parts of turbomachinery is information of interest for the design, maintenance and improvement of turbomachinery.

[0004] Several solutions exist for obtaining information on the surface temperature of such parts. The temperature can be measured using a thermocouple probe, using heat-sensitive crystals, or using thermochromic paints.

[0005] In the case of the thermocouple probe and the thermosensitive crystals, it is only possible to carry out spatially discrete measurements, at the location where these measuring means are arranged.

[0006] In these cases, the measuring device is applied locally to a location deemed critical by the operator. Thus, in order to obtain a surface temperature measurement, it is necessary to multiply the measurements, and consequently the measuring devices. The surface resolution is therefore limited by the number of measuring devices that can be placed on the part being studied.

[0007] This limitation can prove restrictive for parts with a small surface area or for parts with a complex geometry. Furthermore, in a turbomachine, some parts are required to rotate around an axis. Consequently, these rotating parts are poorly—or not at all—compatible with wired devices, as is the case for thermocouple probes.

[0008] On the other hand, the use of heat-sensitive crystals requires drilling to extract and analyze said heat-sensitive crystals. The method is therefore intrusive.

[0009] Furthermore, thermochromic paints provide subtle information regarding temperature. Indeed, thermochromic paints have the property of changing color when sufficiently exposed to a temperature above a threshold temperature. Under these circumstances, it is only possible to determine whether or not said temperature has been reached.

[0010] When a measurement is performed using thermochromic paint, the measurement is based on a colorimetric analysis by the naked eye. This type of measurement requires high contrast and saturation for the colors of the thermochromic paint in order to obtain satisfactory results.

[0011] Performing measurements using thermochromic paints is therefore complex.

[0012] Furthermore, the processing of measurements taken using thermochromic paints relies on methods of visual interpretation by the operator and the manual tracing of isothermal lines on the object or on a model of the object. Such methods are relatively imprecise and not very reproducible.

[0013] Thermochromic paints also contain substances that may be toxic and / or hazardous to the environment. They must therefore comply with current environmental standards. Furthermore, there is a risk that future standards will be more stringent regarding the use of such substances.

[0014] There is therefore a real need for means of measurement and methods of analysis which are free, at least in part, from the aforementioned inherent disadvantages. Description of the invention

[0015] The present description relates to a method for analyzing the thermal history of a part using an optical device, the part having a coating including a first optical marker, the optical device comprising a camera configured to acquire images of the part, a light source configured to illuminate the part, optionally a first filtering device configured to adjust the wavelength emitted by the light source, and a processing unit, the method comprising: a test step in which the part undergoes a thermal cycle, a calibration step in which a standard having the same coating as the part undergoes a predetermined thermal cycle, and in which a thermal image of the standard is acquired by the camera and saved by the processing unit,a part image acquisition step and a standard image acquisition step in which optical information of the part and the standard is respectively measured by the optical device and then recorded by the processing unit; a part image analysis step and a standard image analysis step in which the optical information of the part and the standard is respectively processed by the processing unit to obtain processed optical information of the part and the standard; a transfer function determination step in which a transfer function relating temperature, processed optical information, and spatial dimensions is determined by the processing unit based on the thermal image of the standard and the processed optical information of the standard; an interpretation step in which a thermal history image is calculated by the processing unit. using the transfer function and processed optical information of the part and the thermal history image represents the thermal history of the part.

[0016] In the present description, the thermal history of a point on the part or standard includes information relating to a temperature reached at that point during the past existence of the part or standard. For example, the thermal history may include the maximum temperature reached by the part or standard at that point during the thermal cycle they respectively undergo, and / or whether or not a threshold temperature was reached by the part or standard at that point.

[0017] In this description, the term "optical marker" or "marker" refers to a photoluminescent and / or thermochromic and / or thermochromoluminescent marker. More generally, an optical marker is a marker capable of providing optical information. The optical information may or may not depend on the parameter to be observed, in this case, the temperature. Typically, the first marker can be selected such that the optical information it provides depends on the temperature to which it has been subjected.

[0018] For the purposes of this description and unless otherwise indicated, the mention of a "first" element, such as a first optical marker, does not necessarily imply the existence of a "second" element, nor, where applicable, an order relationship between the first and second elements. Ordinal qualifiers are used in this context solely for the purposes of clarity and identification, without prejudice to any particular characteristics.

[0019] To say that the part and the standard have the same coating means that they both have a coating with the same density of the same markers, or even the same chemical composition. For example, the part and the standard may have been coated from a common source of coating product. Furthermore, the coatings may vary between the part and the standard, particularly in terms of their thickness, geometry, etc.

[0020] In this description, the term "optical information" refers to any information about luminescence or color obtained by studying the luminescence or color of one or more optical markers (photoluminescent and / or thermochromic and / or thermochromoluminescent) contained in the coating. For example, the intensity, wavelength, and lifetime of luminescence are optical information. Ratios between several luminescences or any other calculated and / or measured optical quantity can also be optical information.

[0021] In this document, the term "thermal image" refers to an image associating a temperature with each of its pixels. In the context of this document, it is understood that the thermal image of the standard represents the thermal history of the standard. The thermal image can be obtained by any means that allows a temperature to be measured in order to associate it with a pixel, for example a thermal camera (for example an infrared camera).

[0022] This measurement method makes it possible to measure the thermal history over an entire surface in a single measurement. In other words, the coating of the present invention allows for spatially continuous measurements, unlike known spatially point-based measurements (such as thermocouple probes and heat-sensitive crystals). The information retrieved by the method is therefore more extensive and complete than that which could be retrieved by known methods.

[0023] In particular, the spatial resolution of the measurement is determined by the camera resolution. Compared to the spatial resolution limitations of known devices, which depend on the number of sensors that can be arranged on the part, the spatial resolution of the present method is significantly better. By way of non-limiting example, the spatial resolution of the thermal history measurement can be one-thousandth of the camera field of view in each direction of the plane acquired by the camera. For example, for a camera field of view of ten centimeters by ten centimeters, the spatial resolution is on the order of one hundred micrometers. In other words, the camera can provide a continuous thermal image of a continuous field, the discretization of which into pixels is solely due to the camera resolution.

[0024] Furthermore, the use of an optical device simplifies and accelerates the measurement process, and therefore speeds up the execution of the process. In particular, measurement procedures using an optical device are less restrictive than those of known measurement methods and can be adapted to any geometry that the part to be analyzed might have. They also have the advantage of being non-intrusive. This therefore represents a dual economic and time advantage.

[0025] Also, since the method is based on image acquisition and interpretation using a processing unit, all measurements can be processed digitally. The measurement is therefore more precise, easier, and more reproducible.

[0026] Calibration of the process is facilitated because the analysis of the standard during the calibration, image acquisition, and image analysis steps is sufficient to fully calibrate the process. In other words, the analysis of the standard alone makes it possible to determine the transfer function between optical information and thermal history, for a wide temperature range. Moreover, this calibration and the measurement of the part's history are performed by the same optical device and do not require any external elements, which represents a time saving and limits measurement uncertainty. In particular, the closer the predetermined thermal cycle undergone by the standard is to the thermal cycle assumed to be undergone by the part, the more accurate the calibration of the The process, which is materialized by the transfer function, will be precise.

[0027] In some embodiments, the part image acquisition step includes the use of three-dimensional reconstruction means, and the method further includes a reconstruction step in which a thermal history map of the part is deduced from the thermal history image of the part and the three-dimensional reconstruction means, and the thermal history map of the part links the thermal history of the part with the three dimensions of space.

[0028] In other words, reconstruction methods are used to determine the thermal history map from the thermal image. Thus, it is possible to construct a three-dimensional representation (here called a thermal history map) of the part, representing its thermal history. Such a representation allows for a more detailed analysis of the thermal history by directly linking the geometry of the part to its thermal history. For example, areas with particular thermal behavior can be identified.

[0029] In some embodiments, the optical device includes a target or a scanner.

[0030] These two examples are alternative methods for obtaining a thermal history map. The use of a target is particularly suitable for a part with a simple 3D geometry, while the scanner is more suitable for parts with complex 3D geometries. The target or the scanner can, in a manner known per se, acquire the three-dimensional geometry of the part, this geometry then being given as input to the reconstruction means.

[0031] In some embodiments, the standard has a conical shape. Alternatively or in addition, in some embodiments, the standard is made of an electrically conductive material.

[0032] In this configuration, during the calibration step, it is possible to predetermine a thermal cycle in a controlled manner. In particular, it is possible to impose a thermal cycle on the standard by passing an electric current through it. Thus, it is possible to predetermine a thermal cycle for the standard that is comparable—or even analogous—to the thermal cycle undergone by the part during the test step. The relevance of the calibration is therefore improved, which enhances the accuracy of the thermal history measurements.

[0033] The conical shape also allows for calibration across a significant temperature gradient in a single calibration. Under these circumstances, the calibration provides a continuous temperature gradient. In other words, by applying a temperature gradient to the standard, each temperature within this gradient is reached at a point on the standard, thus ensuring continuity of temperature calibration, which makes the analysis of thermal history more accurate.

[0034] In certain embodiments, during the part and standard image acquisition steps, the processing unit saves at least one average image, the at least one average image being an average of at least ten images acquired by the camera.

[0035] In this configuration, the noise appearing on the images acquired by the camera is compensated by calculating the average image. Thus, the accuracy of the measurement is increased.

[0036] In some embodiments, the coating includes a second optical marker, and during the part and standard image acquisition steps, the optical information measured by the optical device for the first optical marker includes 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 during the part and standard image analysis steps, the processing unit calculates a ratio of the luminescence intensity of the first optical marker to the luminescence intensity of the second optical marker, the processed optical information including said ratio of the luminescence intensity of the first optical marker to the luminescence intensity of the second optical marker.

[0037] This configuration is a first alternative for thermal history analysis according to the present method. This first alternative benefits from the advantages mentioned above. It is understood that the first optical marker and the second optical marker are photoluminescent markers.

[0038] A photoluminescent marker contained in the coating is susceptible to permanent physicochemical and / or microstructural modifications when exposed to certain temperatures. These modifications can include phase changes, volatilization of residual groups, diffusion of dopant ions, etc. Thus, the optical information that can be deduced from the marker is significantly altered by exposure to a temperature, for example, between 500°C and 1500°C. The process therefore makes it possible to deduce information on the thermal history with greater precision than known methods. In particular, the maximum temperatures experienced by the coating can be measured to the nearest degree.

[0039] Furthermore, the temperature range accessible to the marker is wider than the ranges covered by known techniques, particularly methods using thermochromic paints whose color changes are measured with the naked eye. The analysis of the thermal history is therefore more refined and precise.

[0040] In certain embodiments, the optical information obtained for the second marker is independent of temperature. Thus, the second The marker forms a control against which the optical information obtained for the first marker can be compared. Comparison with this control avoids taking into account parameters other than temperature.

[0041] In some embodiments, the first optical marker is unique, and during the part and standard image acquisition steps, the optical information measured by the optical device for the first optical marker includes a plurality of intensities reflected by the optical marker at a given plurality of wavelengths, and the processed optical information includes a spectral signature calculated by the processing unit for the plurality of wavelengths during the part and standard image analysis steps.

[0042] This configuration is a second alternative for thermal history analysis according to the present method. This second alternative benefits from the advantages mentioned above. According to this alternative, the markers can be photoluminescent and / or thermochromic and / or thermochromoluminescent. Since the spectral signature includes information at several wavelengths, it eliminates the effects independent of wavelength and temperature. The first optical marker being unique means that the coating can be devoid of any optical marker other than the first optical marker.

[0043] In some embodiments, the first optical marker is unique, and during part and standard image acquisition steps, the optical device performs, following a pulsed excitation of the luminescence of the first optical marker supplied by the light source, a sequence of measurements of the intensity of the luminescence of the first marker at a given wavelength, and the optical information processed includes the value of an integral of the intensity of the luminescence of the first optical marker as a function of time calculated by the processing unit during the part and standard image analysis steps.

[0044] In general, photoluminescent markers continue to be luminescent for a certain time after being exposed to an excitation wavelength. The intensity of the luminescence emitted by these markers is then expressed as a sum of decreasing exponentials, typically according to the following formula.

[0045] [Math.l]

[0046] In represents the emitted light intensity and tn the lifetime associated with this light intensity, for a given nth wavelength. The longest time tn is called the "lifetime" of the photoluminescent marker.

[0047] This configuration is a third alternative for history analysis thermal according to the present process. This third alternative benefits from the advantages mentioned above. According to this alternative, the markers can be photoluminescent and / or thermochromoluminescent.

[0048] Furthermore, this configuration has the advantage of being applicable to any luminescence signal. Indeed, calculating the integral of the luminescence intensity as a function of time allows any luminescence to be processed without presupposing its shape. It is therefore not necessary to know precisely the nature of the measured luminescence, nor to model it. This method also allows the result to be obtained without calculating the lifetime tn for each intensity In, which is simpler.

[0049] In some embodiments, the sequence of measures comprises more than ten measures.

[0050] The use of such parameters allows for greater accuracy in measuring the lifetime of the photoluminescence of the first photoluminescent marker, which increases the accuracy of the thermal history measurement.

[0051] The aforementioned features and advantages, as well as others, will become apparent from the following detailed description, examples of embodiments of the proposed device and method. This detailed description refers to the accompanying drawings. Brief description of the drawings

[0052] The attached drawings are schematic and are intended primarily to illustrate the principles of the exposition.

[0053] [Fig.1] Fig.1 represents an optical device configured to implement a thermal analysis method.

[0054] [Fig.2] Fig.2 schematically represents a method for analyzing the thermal history of a part according to a first embodiment.

[0055] [Fig.3A] Fig.3A represents images of a standard obtained during an acquisition step according to the first embodiment in greyscale.

[0056] [Fig.3B] [Fig.3B] represents thermal history images calculated during an analysis step from the images of [Fig.3A], in greyscale.

[0057] [Fig.4] Fig.4 schematically represents a method for analyzing the thermal history of a part according to a second embodiment.

[0058] [Fig.5] Fig.5 schematically represents a method for analyzing the thermal history of a part according to a third embodiment. Description of the implementation methods

[0059] To make the explanation more concrete, examples are described in detail below, with reference to the accompanying drawings. It should be noted that the invention is not limited to these examples.

[0060] The present invention proposes to analyze the thermal history of a part 100 by detecting the photoluminescence of one or more photoluminescent markers contained in a coating with which the part 100 is coated. In this example, the part 100 may be an aircraft part or, more generally, a part 100 that has undergone annealing.

[0061] Coating preparation

[0062] The coating provided on part 100 may include the following markers as dopants of an inorganic matrix: europium III, samarium III, dysprosium III, erbium III, thulium III or chromium III ions. Any matrix suitable for containing one or more of these markers may be suitable for the present process, for example metal oxides such as yttrium-stabilized zirconia (YSZ), alumina, yttrium oxide (or yttrium) or yttrium aluminum garnet (YAG).

[0063] We can cite the chromium-doped alumina marker, for example chromium-doped alumina marketed under CAS reference 99328-47-9, as suitable for use in a coating suitable for analysis by the present thermal history measurement method.

[0064] The markers A12O3:Cr3+, Y2O3:Eu3+, YAG:Eu3+, and YSZ doped with at least one of the ions europium III, samarium III, dysprosium III, erbium III, thulium III are particularly suitable for an intensity analysis, which will be described below.

[0065] The MC350-8 and MC520-7 markers marketed by TMCHallcrest © are particularly suitable for thermochromic analysis, which will be described below.

[0066] The markers A12O3:Cr3+ and YSZ doped with at least one of the ions europium III, samarium III, dysprosium III, erbium III, thulium III are particularly suitable for a lifetime analysis, which will be described below.

[0067] More generally, the coating can be obtained by depositing on the part and the standard a paint comprising a mixture of markers, a solvent, a binder and possible additives.

[0068] We can cite the commercial binders LK (ZYP COATINGS), HPC (ZYP COATINGS), ZAP (ZYP COATINGS), 644-S (AREMCO), Ceramabind 643-2 (AREMCO), Respond 791, 792, 793 & 795 (COTRONICS) suitable for the formation of a photoluminescent coating suitable for analysis by the present thermal history measurement method.

[0069] As a solvent, we can mention 1-propanol or any other commercial alcohol.

[0070] In the example of paints comprising photoluminescent markers, the latter are prepared from powders containing an inorganic matrix, which is functionalized or doped with ions exhibiting photoluminescent properties. As mentioned above, these ions can be lanthanides or metals of transition.

[0071] The inorganic matrix comprises a metal oxide. In the present example, the inorganic matrix may comprise yttrium-stabilized zirconia (YSZ), alumina, yttrium oxide, or yttrium aluminum garnet (YAG).

[0072] In the present example, the concentration of dopant, i.e., of ions in the inorganic matrix, is between 0.1 at% and 10 at%. Preferably, the concentration of dopant is between 0.5 at% and 5 at%.

[0073] The photoluminescent marker(s) to be introduced into the paint can thus be pre-heat-treated. For example, for a 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, the luminescence of such a marker will not vary according to the temperature to which it is exposed, provided that this temperature remains below 1500°C.

[0074] Once the paint is obtained, it is deposited onto an object, for example part 100 or the standard. The deposition can, for example, be carried out manually (typically using a brush or roller) or by spraying, dipping-removal, electrophoresis or spin-coating.

[0075] Method and device for implementing the method

[0076] Figure 1 represents an optical device configured to implement a thermal history analysis method. The optical device is configured to analyze part 100. The optical device comprises a light source 10, optionally a first filtering device 12 located after the light source 10, a light guide 14, and a collimator 16. The optical device further comprises a camera 20 and a second filtering element 22 arranged in front of the camera 20.

[0077] The light source 10 is configured to illuminate the room 100 while the light guide 14 and the collimator 16 are configured to adjust the illumination provided by the light source 10 to the room 100. Furthermore, the first filtering device 12 is configured to adjust the wavelength emitted by the light source 10, if necessary.

[0078] To improve the accuracy of the process, the light source 10 is configured to illuminate the part 100 so that the light rays arriving at the part 100 are substantially perpendicular to its surface. It is therefore understood that the angle between the incident light rays and the surface of the part is between 70° and 110°.

[0079] On the other hand, the camera 20 is configured to obtain images of the part 100 and the second filtering device 22 is configured to adjust the wavelength which is emitted by the coating provided on the part 100 and which is acquired by the camera 20.

[0080] The optical device also includes a configured processing unit 30 to save and analyze the images acquired by camera 20, and to calculate a thermal history mapping image. The processing unit 30 is also configured to control camera 20 as well as the first and second filtering devices 12, 22.

[0081] In the present example, the light source 10 can be a broad-spectrum source, capable of emitting radiation from 250 nm to 700 nm. The light source 10, together with the light guide 14 and the collimator 16, is configured to emit a homogeneous light field over a surface of at least 200 x 200 mm², for example. In other words, the light source 10 is an extended source configured to illuminate a surface.

[0082] First embodiment, intensity analysis of photoluminescent markers

[0083] Figure 2 schematically represents the sequence of steps of the process according to a first embodiment. The process includes a test step M1 and a calibration step M2, a part image acquisition step A1 and a standard image acquisition step A2, a part image analysis step E1 and a standard image analysis step E2, a transfer function determination step I, an interpretation step C, and a reconstruction step S.

[0084] In the example given for this first embodiment, the coating intended for part 100 is prepared according to Example 1 described above. Hereafter, the photoluminescent marker Al2O3:0.6% Cr3+ is referred to as the first photoluminescent marker and the photoluminescent marker Y2O3:5% Eu3+ is referred to as the second photoluminescent marker. This example of a pair of photoluminescent markers is not limiting, and other pairs such as Al2O3:Cr3+ / YAG:Eu3+ or YSZ:Er3+ / Y2O3:Eu3+ or even YSZ:Er3+ / YAG:Eu3+ may be used.

[0085] In this embodiment, the photoluminescence of the first photoluminescent marker provides information on the thermal history of the coating. On the other hand, the photoluminescence of the second photoluminescent marker is acquired as a control to neutralize the influence of other physical quantities, such as the coating thickness. More generally, the photoluminescence of the first photoluminescent marker depends on the thermal history, while the photoluminescence of the second photoluminescent marker does not. In this first embodiment, the light source 10 is configured to provide continuous broad-spectrum light in the visible and / or UV range. In the present example, the light source 10 is a xenon source emitting between 250 nm and 700 nm. Other light sources can be considered, such as laser diodes centered on the excitation wavelength of the photoluminescent markers.

[0086] During the test step M1, the part 100 undergoes a thermal cycle. For example, this thermal cycle can be undergone during a flight in an aircraft, or a simulation in the laboratory or test bench. The thermal cycle presents a number of parameters such as the maximum temperature experienced by the part, the heating rate, the cooling time, etc... These parameters can be known or estimated.

[0087] During the calibration step M2, the standard undergoes a predetermined thermal cycle. Preferably, the predetermined thermal cycle is parameterized in a way that is consistent with the thermal cycle of the part, i.e. for example at least the temperatures and heating rates undergone by the part 100 during the test step ML. For example, the temperatures may be of the same order of magnitude, the temperature variations may occur in the same direction (increase or decrease), the times of temperature change may be similar, etc.

[0088] This cycle is achieved using a hot source and a cold source. The hot source can, for example, be a laser, an infrared lamp, the Joule effect, induction, or a thermal torch. The cold source can, for example, be natural convection, a flow of cold air, a cold mass such as water or metal in contact with the standard, or a liquid flow. The shape of the standard can be a parameter affecting the thermal cycle.

[0089] In the present example, the hot source exploits the Joule effect, the cold source exploits natural convection and the standard is provided in a conical conductive material.

[0090] An electric current is applied to the standard, which generates a temperature gradient on its surface. Due to the conical shape, the temperature is higher at the top of the standard than at its base.

[0091] In the present example, the calibration step creates a temperature difference of between 100°C and 800°C between the temperature at the top of the standard and the temperature at its base. Furthermore, the maximum acceptable temperature for the standard is between 1200°C and 1400°C in this example. It is therefore understandable that it is possible to impose more or less precise temperature gradients on the standard over a chosen temperature range, from ambient temperature to 1400°C.

[0092] During this calibration step M2 and the establishment of the thermal cycle M1, it is possible to reach the chosen temperature gradients within a time ranging from a few minutes to a few hours, depending on the gradient to be explored and the desired heating rate. Accordingly, the heating rate is between 0°C and 70°C per second.

[0093] At the end of the thermal cycle, a thermal image of the standard is acquired using an infrared camera. This image may be an average of a plurality of thermal images. This thermal image of the standard is saved by the processing unit. 30.

[0094] In the present example, a size scale is acquired by the infrared camera or by another device so that the thermal image of the standard can be related to spatial dimensions. In other words, the image dimension in pixels is associated with an effective dimension in millimeters.

[0095] When part 100 and the standard have cooled to a temperature close to ambient temperature, the steps of acquiring images of part A1 and acquiring images of standard A2 are performed. We describe here the step of acquiring images of standard A2. It is understood that the step of acquiring images of part A1 is identical to the step of acquiring images of standard A2 but concerns part 100.

[0096] During the image acquisition step of standard A2, prior to image acquisition, the first filtering device 12 is placed in front of the light source 10 and is adjusted to filter the light. This filtering is of the bandpass type, centered on the excitation wavelength of the first photoluminescent marker. The second filtering device 22 is placed in front of the camera 20 and is configured similarly to the first filtering device 12, centered on the relaxation wavelength of the first photoluminescent marker.

[0097] In the present example, the first and second filtering devices 12 and 22 are sets of filters configured to filter light with a bandpass type filtering over a width of about ten nanometers, typically 50 nm, in a range from 400 nm to 700 nm.

[0098] In the present example, for the first photoluminescent marker, the first filter device is centered at 545 nm and the second filter device 22 is centered at 695 nm. Thus, the standard is illuminated by the light source 10 at a wavelength that allows excitation of the first photoluminescent marker provided in the coating, and the camera 20 perceives light representative of the luminescence of the first photoluminescent marker.

[0099] Next, image acquisition takes place. Thus, the camera 20 acquires a plurality of images of the standard at a wavelength corresponding to the relaxation of the first photoluminescent marker.

[0100] The acquisition time for 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 captured can be adjusted according to the desired accuracy of the average image that will be obtained from this plurality of acquired images.

[0101] After this acquisition, the processing unit 30 calculates a first average image of the luminescence of the first photoluminescent marker for the standard, from the plurality of images. This first average image is then saved by the unit treatment 30.

[0102] After recording this first average image, the first filtering device 12 is centered on the excitation wavelength of the second photoluminescent marker and the second filtering device 22 is centered on the photoluminescence wavelength of the second photoluminescent marker. This change can be performed by an operator or automatically.

[0103] In the present example, for the second photoluminescent marker, the first filter device is centered at 562 nm and the second filter device 22 is centered at 610 nm. Thus, the standard is illuminated by the light source 10 at a wavelength that allows excitation of the second photoluminescent marker provided in the coating, and the camera 20 perceives light representative of the luminescence of the second photoluminescent marker.

[0104] A new image acquisition takes place. Thus, the camera 20 acquires a plurality of images of the standard at a wavelength corresponding to the relaxation of the second photoluminescent marker. The acquisition time and the number of images acquired are the same as for the image acquisition for the first photoluminescent marker.

[0105] After this acquisition, the processing unit 30 calculates a second average image of the luminescence of the second photoluminescent marker for the standard, from the plurality of images. This second average image is then saved by the processing unit 30.

[0106] The first and second average images of the standard are acquired from the same angle, with identical camera geometric parameters. The first average image can therefore be compared pixel by pixel to the second average image. In other words, each pixel of each average image corresponds to a defined area of ​​the standard, identical from image to image.

[0107] Figure 3A represents the first and second average images of the analyzed standard obtained during the standard image acquisition step A2 according to the first embodiment. The images are presented in greyscale.

[0108] The illustration above in [Fig. 3A] represents the first average image, while the image below represents the second average image. In other words, the illustration above represents the photoluminescence of the first photoluminescent marker, while the image below represents the photoluminescence of the second photoluminescent marker. These images are shown in grayscale. Depending on the scale chosen, white corresponds to intense luminescence, while black corresponds to an absence of luminescence.

[0109] In the illustration above [Fig. 3A], an image is observed showing a light spot on the left side of the illustration. Furthermore, when moving towards the On the right side of the illustration, the spot gradually darkens, which reflects a lower luminescence on the right side.

[0110] Knowing that the first optical marker used is thermosensitive, it is understood that the left part which shows strong luminescence has been subjected to higher temperatures than the right part.

[0111] It is also observed that this high-intensity spot is slightly above the median axis of the illustration. It can therefore be deduced that the luminescence is not symmetrical with respect to the median axis. However, the test performed imposed a temperature field that was symmetrical with respect to the median axis. This observation shows that the measured luminescence can depend on parameters other than the thermal history, but the influence of these other parameters can be masked by taking into account the second thermal image, as described below.

[0112] In the illustration below [Fig. 3A], the grey level is more homogeneous than in the image above. However, a slightly lighter area is noted towards the upper centre of the illustration.

[0113] Since the second optical marker used is not heat-sensitive, the image below [Fig. 3A] is expected to be uniform. However, the lighter spot indicates stronger luminescence at the upper center. This suggests that the coating has a slight excess thickness in this area.

[0114] Furthermore, in the present example, a black image can be recorded during the A2 standard image acquisition step. In these circumstances, the camera lens 20 is shuttered, and a plurality of black images are acquired according to the same parameters as the photoluminescence acquisition of the photoluminescent markers. This plurality of black images is then transferred to the processing unit 30, which calculates an average black image. This average black image is then subtracted from the first average image and the second average image. These newly processed average images are saved by the processing unit 30 and replace the previous average images. The acquisition of the average black image can be performed before or after the acquisition of the first and second average images.

[0115] Next, during the analysis step E2, the processing unit 30 calculates the processed image of the standard. We describe here the acquisition of the processed image of the standard, it being understood that the processed image of the part 100 is obtained in the same way.

[0116] Initially, the processing unit 30 calculates a conversion from the pixel scale to the millimeter scale for one of the first or second average images of part 100. The scale is then transposed to the other image.

[0117] Next, the processing unit 30 constructs the processed image of part 100 by calculating, for each pixel, a ratio of the photoluminescence intensity of the first marker The photoluminescent intensity is related to the photoluminescence intensity of the second photoluminescent marker. In other words, the processing unit calculates I(first photoluminescent marker) / I(second photoluminescent marker) at every point in the processed image of the standard. This calculation also corrects for any variation in the photoluminescence of the first and second markers that is not due to temperature. Indeed, since these two markers are influenced in the same way by these external parameters, calculating the intensity ratio eliminates the need for these external parameters. For example, an external parameter could be a non-uniform illuminance of the light source or a non-uniform coating thickness.

[0118] A processed image of the standard is then obtained, representing the relative intensity of the photoluminescence of the first photoluminescent marker compared to the photoluminescence of the second photoluminescent marker, the image being scaled to a spatial dimension. In this first embodiment, the ratio of the photoluminescence intensities is the optical information of interest, which allows the thermal history of part 100 to be deduced.

[0119] Figure 3B represents the processed image of the standard in Figure 3A, according to two different greyscale levels. This image is calculated by interpreting the two images in Figure 3A.

[0120] The illustration at the top of [Fig. 3B] shows a scale in which two similar intensity ratios are associated with similar gray levels. This reflects the difference in intensity ratio between the left and right sides of the standard. Conversely, the illustration at the bottom of [Fig. 3B] shows a scale in which similar intensity ratios are associated with contrasting gray levels, highlighting iso-intensity lines of the standard, corresponding to thermal isohistorical lines, which therefore underwent the same temperature during the M2 calibration step.

[0121] Calculating the intensity ratio therefore makes it possible to improve the accuracy of the measurement by compensating for external influences that could disrupt the measurement, such as excess thickness of the coating.

[0122] Similarly, a processed image of part 100 is calculated during the EL analysis step

[0123] During the transfer function determination step I, a transfer function between the temperature and the ratio of the photoluminescence intensities of the photoluminescent marker pair is determined using the thermal image of the standard obtained in the calibration step M2 and the processed image of the standard obtained during the standard image analysis step E2. In other words, a transfer function relating the processed optical information (here the intensity ratio), the temperature and The spatial dimensions are determined. It is understood that, in the case of part 100 and the standard, the temperature more concretely reflects the thermal history of part 100 or the standard. Indeed, this "temperature" indicates the maximum temperature experienced during the test steps M1 and calibration M2.

[0124] This relationship then makes it possible to convert an image representing the photoluminescence intensity ratio of the pair of photoluminescent markers into a thermal history image. It should be noted that such a conversion is only possible for images of parts coated with the same coating as the coating on the standard.

[0125] During the interpretation step C, the transfer function determined during the transfer function determination step I is used to transform the processed image of part 100 obtained during the analysis step E2 into a thermal history image of part 100.

[0126] During the reconstruction step S, the thermal history image of part 100 is made consistent with the geometry of part 100 to obtain a thermal history map of part 100. The reconstruction step S is able to establish the thermal history map of parts mainly in two dimensions and / or of parts in three dimensions.

[0127] In the case of parts with two-dimensional geometry, the consistency corresponds to a recalibration of the thermal history image on a reference linked to part 100.

[0128] In the case of parts with three-dimensional geometry, two cases can be distinguished. Generally, the three-dimensional geometry is reconstructed using three-dimensional reconstruction means, which may be, for example, a target, a grid, or a scanner.

[0129] In a first case, when the geometry is only slightly curved, as with a turbine blade, it can be obtained by an inverse function of a two-dimensional projection. In these circumstances, during the image acquisition step of part Al, images of part 100 are acquired, and part 100 includes a grid configured to be within the field of view of each of the acquired images. The grid can be directly affixed to part 100, or simply placed or drawn on it.

[0130] The processing unit 30 calculates, from the parts of images representing the grid on the plurality of acquired images, a geometric transformation relation (curvilinear abscissa) linking the pixels of the image to a reconstruction of the piece 100 in three dimensions.

[0131] In a second case, when the geometry of part 100 is complex, the optical device includes a scanner used to obtain a surface mesh of part 100. In these circumstances, the scanner cooperates with camera 20 to calculate a geometric transformation relation linking the pixel coordinates of the temperature image of the part with the 3D coordinates of the surface mesh of the part expressed in units of length.

[0132] Second embodiment, thermochromic analysis

[0133] In the following paragraphs, we will focus on a second embodiment schematically represented in [Fig. 4]. In the second embodiment, the process comprises a first variant of the image acquisition steps for part A1' and standard A2' and the image analysis steps for part E1' and standard E2'. The other steps are identical to the corresponding steps of the first embodiment.

[0134] In the example given for this second embodiment, the coating covering part 100 and the standard comprises a single thermochromic marker. This marker is, for example, one of the MC350-8 and MC520-7 markers marketed by TM-CHallcrest ©.

[0135] The image acquisition parameters of the image acquisition steps A1' and A2' of the second embodiment are identical to the parameters of the acquisition steps A1 and A2 of the first embodiment with regard to the general camera parameters (number of images acquired, acquisition time, black frame, etc.). It follows, in particular, that the acquisition steps A1' and A2' according to the second embodiment can be performed by an optical device comparable to the optical device of the first embodiment.

[0136] Furthermore, in the second embodiment, a white light source 10 is used and only the second filtering device 22 is used. The filtering device 22 is pre-positioned in front of the camera 20 and is adjusted to filter the light. This filtering is of the bandpass type, centered on a first arbitrary wavelength (visible or not) corresponding to an emission wavelength of the thermochromic marker whose intensity varies according to the thermal history.

[0137] We describe here the step of acquiring images of part Al' and the step of analyzing images of part El'. It is understood that the steps of acquiring images of standard A2' and analyzing images of standard E2' are respectively identical to the steps of acquiring images of part Al' and analyzing images of part El', but relate to the standard.

[0138] During the image acquisition step of part Al', a first image acquisition takes place. Thus, the camera 20 acquires a plurality of images of part 100 for the first wavelength. The light intensity reflected by the thermochromic marker is therefore recorded for this wavelength, using a first average image obtained for the first wavelength (or at a first color). This first average image is then saved by the processing unit 30.

[0139] After recording this first average image, the second filtering device 22 is centered on a second wavelength different from the first wavelength. A second average image is then acquired and recorded in the same way as the first average image. This process is repeated as many times as desired, for wavelengths all different from each other.

[0140] It is understood that each average image acquires part 100 from the same angle, with identical camera parameters 20, except for the wavelength received by the camera 20, which has been filtered by the second filtering device 22. Each average image can therefore be compared pixel by pixel to another average image. In other words, each pixel of each of the average images corresponds to a defined area of ​​part 100, identical from image to image.

[0141] Then, during the part analysis step El', the processing unit 30 calculates respectively a processed spectral signature matrix of part 100 and a processed spectral signature matrix of the standard. We describe here the obtaining of the processed matrix of part 100, it being understood that the processed matrix of the standard is obtained in the same way.

[0142] Initially, the processing unit 30 calculates a conversion from the pixel scale to a millimeter scale (or other unit of length) for one of the average images of the part 100. This scale can then be transposed to all the other average images.

[0143] The processing unit 30 first records, for each pixel of the average images, the reflected intensities recorded on each of the average images during the acquisition step Al'. In other words, the processing unit 30 creates a matrix the size of the average images composed of reflected intensity vectors, each vector corresponding to a pixel, the vector being composed of each reflected intensity recorded for each measured wavelength, in relation to each average image calculated for that wavelength.

[0144] From the intensity vector matrix, the processing unit 30 calculates a spectral signature for each element of the matrix using an algorithm. A processed matrix is ​​then derived, associating each of its elements with the corresponding spectral signature. In this example, the spectral signature may include information on spectral moments, averages, and / or variances of reflection intensity. In this second embodiment, the spectral signature is the optical information of interest that allows the thermal history of part 100 to be deduced.

[0145] Similarly, a processed matrix is ​​obtained for the standard during the step E2' analysis.

[0146] The process can then continue according to the steps of determining transfer function I, interpretation C and reconstruction S.

[0147] In particular, a transfer function relating the spectral signature, temperature and spatial dimensions is determined during the transfer function determination step I using the processed matrix of the standard obtained during the analysis step E2' and the thermal image obtained during the calibration step M2.

[0148] The interpretation step C and the reconstruction step S then proceed as previously described.

[0149] Third embodiment, lifetime analysis

[0150] In the following paragraphs, we focus on a third embodiment schematically represented in [Fig. 5]. In the third embodiment, the process comprises a second variant of the image acquisition steps A1” and A2” and the image analysis steps E1” and E2”. The other steps are identical to the corresponding steps of the first embodiment.

[0151] The acquisition steps A1” and A2” according to the third embodiment can be performed by an optical device similar to the device described in the first and second embodiments. However, the camera used in the third embodiment is preferably an intensified camera. Indeed, given the durations involved in this process, it is desirable for the camera to have an intensifier to amplify a signal acquired over a duration that can be on the order of several nanoseconds, and is therefore of low intensity.

[0152] In the example given for this third embodiment, the coating covering part 100 and the standard comprises a single photoluminescent marker. This photoluminescent marker is YSZ:Er3+. This example of a photoluminescent marker is not limiting, and other photoluminescent markers may be used.

[0153] The lifespan of a photoluminescent marker can depend on its thermal history. On the other hand, this lifespan is independent of the thickness of the coating layer in which the photoluminescent marker is placed, the intensity of the lighting, and pollution, among other factors.

[0154] The light source 10 used in this embodiment is a monochromatic source configured to provide pulsed light. The wavelength of the light source 10 is chosen to match the excitation wavelength of the photoluminescent marker. The monochromatic nature can be achieved by the action of the filtering device 12 or by the nature of the light source 10. For example, the light source 10 could be a laser. In the present example, the pulse of the light source 10 is controlled by the processing unit 30.

[0155] The camera 20 is configured to take a sequence of images following a command of the processing unit 30. In this example, the camera 20 is configured to acquire a sequence of images, following the command of the processing unit 30, for an acquisition time significantly longer than the photoluminescence lifetime of the photoluminescent marker. This acquisition time is at least three times longer than the longest lifetime of the marker.

[0156] We describe here the image acquisition step of part Al” and the image analysis step of part El”. It is understood that the image acquisition steps of standard A2” and the image analysis steps of standard E2” are respectively identical to the image acquisition steps of part Al” and the image analysis steps of part El”, but relate to the standard.

[0157] During the acquisition step Al”, and prior to image acquisition, the second filtering device 22 is centered on the relaxation wavelength of the photoluminescent marker.

[0158] In the present example, the optical device is configured to provide illumination at 514 nm. Furthermore, the second filtering device 22 is centered at 545 nm. Thus, the part 100 is illuminated at a wavelength that allows excitation of the photoluminescent marker provided in the coating, and the camera 20 perceives light representative of the luminescence of the first photoluminescent marker.

[0159] Next, the acquisition takes place. The processing unit 30 jointly controls the light source 10 and the camera 20 to respectively perform a pulse and acquires a sequence of images. In the present example, the image sequence comprises a sufficient number of images to integrate the intensity of the photoluminescence as a function of time. In the present example, the image sequence comprises several dozen images, typically 30 images. The image sequence is then recorded by the processing unit 30.

[0160] It can be seen on the image sequence that the luminescence of the photoluminescent marker decreases as the images are passed.

[0161] Optionally, this acquisition is repeated at least ten times, according to the same parameters. The processing unit 30 then calculates an average image sequence where each image in the average image sequence is an average of the corresponding images in each of the previously acquired and recorded image sequences. This average image sequence is recorded by the processing unit 30.

[0162] Then, during the analysis steps E1” and E2”, the processing unit 30 calculates two processed matrices, one for part 100 and one for the standard, associating with each of their terms the integral of the photoluminescence intensity as a function of time for a given pixel of the image sequence of part 100, and the other of the image sequence of the standard. We describe here the obtaining of the processed matrix of part 100, it being understood that the processed matrix of the standard is obtained in the same way.

[0163] Initially, the processing unit 30 calculates a conversion from a pixel scale to a millimeter scale for one of the average images in the average image sequence. This scale can then be transposed to all the other average images in the average image sequence.

[0164] From the average image sequence, the processing unit 30 integrates, for each pixel, the luminescence intensity at that pixel as a function of time. This value is stored in a matrix whose size is equal to the pixel size of an image from the average image sequence, in the space corresponding to the processed pixel. Thus, when all the pixels are processed, the processed matrix is ​​formed. In this third embodiment, the integral of the photoluminescence intensity as a function of time is the optical information of interest, which allows the thermal history of the part 100 to be deduced.

[0165] Similarly, a treated matrix is ​​obtained for the standard during the analysis step E2”.

[0166] The process can then continue according to the steps of determining transfer function I, interpretation C and reconstruction S.

[0167] In particular, a transfer function relating the integrated intensity, temperature and spatial dimensions is determined during the transfer function determination step I using the processed matrix of the standard obtained during the analysis step E2” and the thermal image obtained during the calibration step M2.

[0168] A variant of this third embodiment consists, during the acquisition steps A1 and A2, of providing a light source 10 configured to supply continuous amplitude-modulated light. In such circumstances, during the analysis steps A1 and A2, the processing unit 30 calculates the phase shift and / or the 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 relation tan φ = 27πrf, where P is the phase shift, φ is the modulation frequency of the incident light, and T is the lifetime to be determined. This lifetime corresponds to the maximum of the lifetimes tn.

[0169] Fourth embodiment, thermochromoluminescent marker analysis

[0170] In the following paragraphs, we focus on a fourth embodiment. In this fourth embodiment, a thermochromoluminescent marker, such as Zn3(PO4)2: 2%Mn2+, is used. These markers have the characteristic of emitting a spectrum with peaks at several defined wavelengths when they receive excitation at a defined excitation wavelength. The intensity of the peaks in the emitted spectrum depends on the thermal history.

[0171] The thermal history analysis method is identical to the analysis method of the second embodiment, except for the configuration of the light source. 10 and the first filtering device 12.

[0172] Indeed, in the fourth embodiment, the optical device includes a filtering device 12 and the part is illuminated by light centered on an excitation wavelength of the thermochromoluminescent marker, as in the first embodiment.

[0173] The second filtering device 22 is then centered on each of the emission wavelengths of the thermochromoluminescent marker, and the spectral signature is measured, as for the second embodiment.

[0174] The present description was based on the example of thermal history analysis, but this method could be applied mutatis mutandis to history analyses of any thermomechanical quantity (stress, strain, pressure, temperature, etc.) using markers whose optical information varies according to said thermomechanical quantity.

[0175] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

[0176] It is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Demands

1. Method for analyzing the thermal history of a part (100) using an optical device, the part (100) having a coating including a first optical marker, the optical device comprising a camera (20) configured to acquire images of the part (100), a light source (10) configured to illuminate the part (100) and to illuminate a standard having the same coating as the part (100), and a processing unit (30), the process comprising: a test step (M1) in which the part undergoes a thermal cycle, a calibration step (M2) in which the standard undergoes a predetermined thermal cycle, and in which a thermal image of the standard is acquired by a thermal camera, and saved by the processing unit (30), a part image acquisition step (A1; A1'; A1") and a standard image acquisition step (A2; A2'; A2") in which optical information of the part (100) and the standard are respectively measured by the optical device, then recorded by the processing unit (30), a part image analysis step (E1; E1'; E1") and a standard image analysis step (E2; E2'; E2") in which the optical information of the part (100) and the standard are respectively processed by the processing unit (30) to obtain processed optical information of the part and the standard, a transfer function determination step (I) in which a transfer function relating temperature, processed optical information and spatial dimensions is determined by the processing unit (30) on the basis of the thermal image of the standard and the processed optical information of the standard, an interpretation step (C) in which a thermal history image is calculated by the processing unit (30) using the transfer function and the processed optical information of the part (100) and the thermal history image represents the thermal history of the part (100).

2. A method according to claim 1, wherein the acquisition step of part images (Al; Al'; A1”) includes the use of three-dimensional reconstruction means, and wherein the method further includes a reconstruction step (S) in which a thermal history map of the part (100) is deduced from the thermal history image of the part (100) and the three-dimensional reconstruction means, and the thermal history map of the part links the thermal history of the part with the three dimensions of space.

3. Method according to claim 2, wherein the optical device comprises a target or a scanner.

4. A method according to any one of claims 1 to 3, wherein the standard has a conical shape and is made of an electrically conductive material.

5. Method according to any one of claims 1 to 4, during the part image acquisition steps (A1; A1'; A1") and standard image (A2; A2'; A2") the processing unit saves at least one average image, the at least one average image being an average of at least ten images acquired by the camera (20).

6. A method according to any one of claims 1 to 5, wherein the coating comprises a second optical marker, and during the part and standard image acquisition steps (A1, A2), the optical information measured by the optical device for the first optical marker comprises the luminescence intensity of the first optical marker at a given first 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 given second wavelength, and during the part and standard image analysis steps (E1, E2), the processing unit (30) calculates a ratio of the luminescence intensity of the first optical marker to the luminescence intensity of the second optical marker,the processed optical information including said ratio of the luminescence intensity of the first optical marker relative to the luminescence intensity of the second optical marker.

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

8. Method according to any one of claims 1 to 5, the first optical marker is unique, and during the part and standard image acquisition steps (Al', A2'), the optical information measured by the optical device for the optical marker includes a plurality of intensities reflected by the optical marker at a given plurality of wavelengths, and the processed optical information includes a spectral signature calculated by the processing unit (30) for the plurality of wavelengths during the part and standard image analysis steps (El, E2).

9. A method according to any one of claims 1 to 5, wherein the first optical marker is unique, and during part and standard image acquisition steps (A1”, A2”), the optical device performs, following a pulsed excitation of the luminescence of the first optical marker supplied by the light source (10), a sequence of measurements of the intensity of the luminescence of the first optical marker at a given wavelength, and the processed optical information includes the value of an integral of the intensity of the luminescence of the first optical marker as a function of time calculated by the processing unit (30) during the part and standard image analysis steps (A1”, E2”).

10. Method according to claim 9, wherein the sequence of measurements comprises more than 10 measurements.

Images