Method for measuring the thermal history of a part

Abstract

The invention relates to a method for analysing the thermal history of a part (100) by means of an optical device, the part having a coating that includes a first marker, the optical device comprising a camera (20) and a light source (10), the method comprising: a calibration step, wherein a reference part 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 reference part, a step of analysing the images of the part and a step of analysing the images of the reference part, a step of determining a transfer function, wherein a transfer function linking the temperature, the processed optical information and the spatial dimensions is determined, an interpretation step, wherein an image of the thermal history is calculated and the image of the thermal history represents the thermal history of the part according to the predetermined angle.

Description

Description Title of the invention: Method for measuring the thermal history of a part Technical Field

[0001] This presentation concerns a method for measuring the thermal history of a part.

[0002] Such a method can be used for the analysis of turbomachinery or turbojet parts, to name just a few examples. Prior art

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

[0004] There are several solutions 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 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 the measuring devices accordingly. The surface resolution is therefore limited by the number of measuring devices that can be placed on the part to be studied.

[0007] This limitation can be restrictive for parts with a small surface area or for parts with complex geometry. Furthermore, in a turbomachine, certain parts are required to rotate around an axis. As a result, these rotating parts are not very compatible, if at all, with wired devices, as can be 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 information. Indeed, thermochromic paints have the property of changing color when they are sufficiently exposed to a temperature above a threshold temperature. In these circumstances, it is only possible to know whether or not the said temperature has been reached.

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

[0011] Carrying out measurements using thermochromic paints is therefore complex.

[0012] Furthermore, the exploitation of measurements made using thermochromic paints is based on visual interpretation methods by the operator, and tracing isothermal lines by hand 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 harmful to the environment. They must therefore comply with current environmental standards. Furthermore, there is a risk that future standards will be more restrictive regarding the use of such substances.

[0014] There is therefore a real need for measuring means and analysis methods which are free, at least in part, from the inherent drawbacks mentioned above. Statement of the invention

[0015] This disclosure relates to a method for analyzing the thermal history of a part by 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 are respectively measured by the optical device, then recorded by the processing unit,a workpiece image analysis step and a standard image analysis step in which the optical information of the workpiece and the standard are respectively processed by the processing unit to obtain processed optical information of the workpiece and the standard, a transfer function determination step in which a transfer function relating the temperature, the processed optical information and spatial dimensions is determined by the processing unit on the basis of 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 the processed optical information of the workpiece and the thermal history image represents the thermal history of the workpiece.,

[0016] In this disclosure, the thermal history of a point of the part or standard includes information relating to a temperature reached at this 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 this point, during the thermal cycle they undergo respectively, and / or the fact that a threshold temperature has been reached or not by the part or standard at this point.

[0017] In this disclosure, the term "optical marker" or "marker" means 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 temperature. Typically, the first marker can be selected so that the optical information it returns depends on the temperature it has experienced.

[0018] For the purposes of this disclosure 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 or, where applicable, an order relationship between the first and second elements. Ordinal qualifiers are, in this context, used for the sole purpose of clarity and identification, without prejudging 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 material. Furthermore, the coatings between the part and the standard may vary, including their thickness, geometry, etc.

[0020] In this disclosure, the term "optical information" means any information on the luminescence or on the color obtained by studying the luminescence or the color of one or more optical markers (photoluminescent and / or thermochromic and / or thermochromoluminescent) contained in the coating. For example, the intensity, the wavelength and the lifetime of the 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 disclosure, the term "thermal image" refers to an image associating a temperature with each of its pixels. In the case of this disclosure, 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 allowing 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 allows a measurement of the thermal history over an entire surface, in a single measurement. In other words, the The coating of the present invention allows spatially continuous measurements to be made, unlike known spatially point measurements (such as thermocouple probes and thermosensitive crystals). The information recovered by the method is therefore greater and more complete than that which could be recovered by known methods.

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

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

[0025] Also, since the process 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. In addition, this calibration and the Measurement of the part's history is carried out by the same optical device and does not require an external element, which saves time and limits measurement uncertainty. In particular, the closer the predetermined thermal cycle undergone by the standard is to the thermal cycle supposedly undergone by the part, the more precise the calibration of the process, which is materialized by the transfer function, will be.

[0027] In some embodiments, the part image acquisition step comprises the use of three-dimensional reconstruction means, and the method further comprises a reconstruction step in which a thermal history map of the part is derived from the part thermal history image and the three-dimensional reconstruction means, and the part thermal history map relates the part thermal history to 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 representation (here called thermal history map) of the part in three dimensions representing the thermal history. Such a representation allows for a more detailed analysis of the thermal history by directly linking the geometry of the part and the thermal history. For example, areas with particular thermal behavior can be identified.

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

[0030] These two examples are two alternative examples for obtaining a thermal history map. The use of a target is particularly suitable for a part with 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, allow the three-dimensional geometry of the part to be acquired, this geometry then being given as input to the reconstruction means.

[0031] In some embodiments, the standard has a conical shape. Alternatively or additionally, in some embodiments, the standard is provided in 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 improves the accuracy of the thermal history measurements.

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

[0034] In some 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 measurement accuracy is increased.

[0036] In some embodiments, the coating comprises a second optical marker, and during the steps of acquiring part and standard images, the optical information measured by the optical device for the first optical marker comprises the intensity of the luminescence 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 intensity of the luminescence of the second optical marker at a given second wavelength, and during the steps of analyzing images of part and standard, the processing unit calculates a ratio of the luminescence intensity of the first optical marker relative to the luminescence intensity of the second optical marker, the processed optical information comprising said ratio of the luminescence intensity of the first optical marker relative to the luminescence intensity of the second optical marker.

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

[0038] A photoluminescent marker contained in the coating is likely to undergo permanent physicochemical and / or microstructural modifications when exposed to certain temperatures. These modifications may be phase changes, volatilizations of residual groups, diffusion of doping ions, etc. Thus, the optical information that can be deduced from the marker is significantly modified by exposure to a temperature, for example between 500 °C and 1500 °C. The method 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] In addition, the temperature range accessible to the marker is wider than the ranges covered by known techniques, in particular methods using thermochromic paints whose tones are measured by the naked eye. The analysis of the thermal history is therefore more precise and accurate.

[0040] In some embodiments, the optical information obtained for the second marker is independent of temperature. Thus, the second marker forms a control against which it is possible to compare the optical information obtained for the first marker. The 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 comprises 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 the analysis of the thermal history according to the present method. This second alternative benefits from the advantages previously mentioned. 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 allows to overcome the independent effects of wavelength and temperature. To say that the first optical marker is unique means that the coating can be devoid of an optical marker different from the first optical marker.

[0043] In some embodiments, the first optical marker is unique, and during the part and standard image acquisition steps, the optical device performs, following a pulsed excitation of the luminescence of the first optical marker provided by the light source, a sequence of measurements of the intensity of the luminescence of the first marker at a given wavelength, and the processed optical information comprises 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] Generally, photoluminescent markers continue to luminesce for some 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 1]

[0046] L n represents the emitted light intensity and t n the lifetime associated with this light intensity, for a n ieme given wavelength. Time t n the longest is called the "lifetime" of the photoluminescent marker.

[0047] This configuration is a third alternative for the analysis of thermal history according to the present method. This third alternative benefits from the advantages previously mentioned. 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, the calculation of the integral of the luminescence intensity as a function of time makes it possible to process any luminescence without presupposing its form. It is therefore not necessary to know precisely the nature of the measured luminescence, nor to model it. This method also makes it possible to arrive at the result without calculating the lifetime t n for each intensity l n , which is simpler.

[0049] In some embodiments, the measurement sequence comprises more than ten measurements.

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

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

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

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

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

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

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

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

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

[0059] In order to make the disclosure more concrete, examples are described in detail below, with reference to the accompanying drawings. It is recalled 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 the present example, the part 100 may be an aircraft part or more generally a part 100 which has undergone annealing.

[0061] Preparation of the coating

[0062] The coating provided on the part 100 may comprise 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 capable of containing one or more of these markers may be suitable for the present method, for example metal oxides such as partially 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 the chromium-doped alumina marketed under the reference CAS 99328-47- 9, as suitable for use in a coating suitable for analysis by the present thermal history measurement method.

[0064] The AI2O3:Cr markers 3+ , Y2O3:Eu 3+ , YAG:Eu 3+ , and YSZ doped with at least one of the ions europium III, samarium III, dysprosium III, erbium III, thulium III are particularly suitable for intensity analysis, which will be described below.

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

[0066] The markers AI2O3: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 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, 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 cite 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 transition metals.

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

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

[0073] The photoluminescent marker(s) to be introduced into the paint may thus be heat-treated beforehand. 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 depending on the temperature to which it will be exposed, provided that this temperature remains below 1500°C.

[0074] Once the paint is obtained, it is deposited on 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 even 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 the part 100. The optical device comprises a light source 10, optionally a first filtering device 12 placed 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] In order to improve the accuracy of the method, the light source 10 is configured to illuminate the part 100 so that the light rays arriving on 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 further comprises a processing unit 30 configured to save and analyze the images acquired by the camera 20, and to calculate a thermal history mapping image. The processing unit 30 is also configured to control the camera 20 as well as the first and second filtering devices 12, 22.

[0081] In the present example, the light source 10 may be a source having a broad spectrum, capable of emitting radiation from 250 nm to 700 nm. The light source 10, accompanied by the light guide 14 and the collimator 16, is configured to emit a homogeneous light field over a surface of at least 200x200 mm. 2 , for example. In other words, the light source 10 is an extended source that is configured to illuminate a surface.

[0082] First embodiment, intensity analysis of photoluminescent markers

[0083] Figure 2 schematically represents the succession of steps of the method according to a first embodiment. The method comprises 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 taken for this first embodiment, the coating provided on the part 100 is prepared according to example 1 described previously. Subsequently, the photoluminescent marker AI2O3:0.6% Cr 3+ is called the first photoluminescent marker and the photoluminescent marker Y2O3:5% Eu 3+ is called second photoluminescent marker. This example of a pair of photoluminescent markers is not limiting, and other pairs such as AI2O3:Cr3+ / YAG:Eu 3+ or YSZ:Er 3+ / Y203:Eu 3+ or YSZ:Er3+ / YAG:Eu3+ can be used.

[0085] In this embodiment, the photoluminescence of the first photoluminescent marker provides information on the thermal history of the coating. Furthermore, the photoluminescence of the second photoluminescent marker is acquired as a control to neutralize the influence of other physical quantities, such as the thickness of the coating. More generally, the photoluminescence of the first photoluminescent marker depends on the thermal history, while the photoluminescence of the second photoluminescent marker does not depend on its thermal history. In this first embodiment, the light source 10 is configured to provide broad-spectrum continuous light in the visible and / or UV range. In the present example, the light source 10 is a Xenon source that emits between 250 nm and 700 nm. Other light sources may 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 a laboratory or on a test bench. The thermal cycle has a certain number of parameters such as the maximum temperature undergone by the part, the heating rate undergone, the cooling duration, 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 manner consistent with the thermal cycle of the part, i.e. for example at least the temperatures and heating rates experienced by the part 100 during the test step M1. 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 instants of temperature change may be similar, etc.

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

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

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

[0091] In this example, the calibration step creates a difference of between 100°C and 800°C between the temperature of the top of the standard and the temperature of the base of the standard. Furthermore, the maximum acceptable temperature for the standard is between 1200°C and 1400°C, in this example. It is then understood that it is possible to impose more or less fine temperature gradients on the standard over a chosen temperature range, in an interval going from room 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 in a time between a few minutes and a few hours, depending on the gradient to be explored and the heating rate that we wish to impose. According to this aspect, the heating rate is between 0°C and 700 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 this example, a size scale is acquired by the infrared camera or other 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 the part 100 and the standard have cooled to a temperature close to room temperature, the steps of acquiring images of part A1 and acquiring images of standard A2 are carried out. Here we describe 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 the part 100.

[0096] During the step of acquiring standard images 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 in a similar manner 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 the light with bandpass type filtering over a width of around 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 on 545 nm and the second filter device 22 is centered on 695 nm. Thus, the standard is illuminated by the light source 10 at a wavelength allowing the excitation of the first photoluminescent marker provided in the coating, and the camera 20 perceives a light representative of the luminescence of the first photoluminescent marker.

[0099] Then, 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 the present example, the camera 20 is configured to capture 10 images. However, the number of images to be captured can be adjusted. depending on the precision sought for the average image which 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 processing unit 30.

[0102] After recording this first average image, the first filter device 12 is centered on the excitation wavelength of the second photoluminescent marker and the second filter device 22 is centered on the photoluminescence wavelength of the second photoluminescent marker. This change can be carried out by an operator or in an automated manner.

[0103] In the present example, for the second photoluminescent marker, the first filter device is centered on 562 nm and the second filter device 22 is centered on 610 nm. Thus, the standard is illuminated by the light source 10 at a wavelength allowing the excitation of the second photoluminescent marker provided in the coating, and the camera 20 perceives a 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 acquisition of images 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 20. The first average image can therefore be compared pixel by pixel with the second average image. In other words, each pixel of each of the average images 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 grayscale.

[0108] The top illustration of Figure 3A represents the first average image while the bottom image represents the second average image. In other words, the top illustration represents the photoluminescence of the first photoluminescent marker, while the bottom image represents the photoluminescence of the second photoluminescent marker. These images are illustrated in grayscale. Depending on the scale chosen, white corresponds to intense luminescence while black corresponds to no luminescence.

[0109] In the top illustration of Figure 3A, we see an image with a bright spot on the left side of the illustration. Furthermore, as we move towards the right side of the illustration, the spot gradually darkens, which indicates a weaker luminescence on the right side.

[0110] Knowing that the first optical marker used is heat-sensitive, we understand that the left part which shows strong luminescence has undergone higher temperatures than the right part.

[0111] It is also noted that this high intensity spot is slightly above the median axis of the illustration. We therefore deduce that the luminescence is not symmetrical with respect to the median axis. However, the test carried out imposed a temperature field 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 now.

[0112] In the bottom illustration of Figure 3A, we observe that the gray level is more homogeneous than that of the top image. However, we note a slightly lighter range towards the top center of the illustration.

[0113] Knowing that the second optical marker used is not heat-sensitive, the bottom image in Figure 3A is expected to be uniform. However, the lighter spot indicates stronger luminescence in the center high. We deduce that the coating has a slight excess thickness at this point.

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

[0115] Then, during the analysis step E2, the processing unit 30 calculates the processed image of the standard. We describe here the obtaining 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] First, 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 the part 100. The scale is then transposed to the other image.

[0117] Then, the processing unit 30 constructs the processed image of the part 100 by calculating for each pixel a ratio of the photoluminescence intensity of the first photoluminescent marker to the photoluminescence intensity of the second photoluminescent marker. In other words, the processing unit calculates l(first photoluminescent marker) / l(second photoluminescent marker) at any point of the processed image of the standard. This calculation also makes it possible to correct any variation in the photoluminescence of the first and second markers that would not be due to the temperature. Indeed, as these two markers are influenced in the same way by these external parameters, the calculation of the intensity ratio makes it possible to overcome said external parameters. For example, a parameter exterior can be a non-uniform illumination of the light source or a non-uniform thickness of the coating.

[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 reported on a spatial scale. In this first embodiment, the ratio of the photoluminescence intensities is the optical information of interest which makes it possible to deduce the thermal history of the part 100.

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

[0120] The top illustration of Figure 3B shows a scale in which two close intensity ratios are associated with close gray levels. This accounts for the difference in intensity ratio between the left part of the standard and its right part. On the other hand, the bottom illustration of Figure 3B shows a scale in which close intensity ratios are associated with contrasting gray levels, which makes it possible to highlight iso-intensity lines of the standard, corresponding to iso-thermal history lines, having therefore undergone 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 which could disrupt the measurement, such as excess coating thickness.

[0122] Similarly, a processed image of part 100 is calculated during analysis step E1.

[0123] During the transfer function determination step I, a transfer function between the temperature and the ratio of the intensity of the photoluminescences of the pair of photoluminescent markers 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 linking the processed optical information (here the intensity ratio), the temperature and the spatial dimensions is determined. It is understood that, for the case of the 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 M1 test and M2 calibration steps.

[0124] This relationship then allows the conversion of 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 coating 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 the part 100 obtained during the analysis step E2 into a thermal history image of the part 100.

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

[0127] In the case of parts with two-dimensional geometry, 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 weakly curved, as for a turbine blade, it can be obtained by a reciprocal function of a projection on two dimensions. In these circumstances, during the part image acquisition step A1, images of the part 100 are acquired and the part 100 comprises a grid configured to be in the field of each of the acquired images. The grid can be directly glued onto the part 100, or simply placed or drawn on it.

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

[0131] In a second case, when the geometry of the part 100 is complex, the optical device comprises a scanner used to obtain a surface mesh of the part 100. In these circumstances, the scanner cooperates with the camera 20 to calculate a geometric transformation relationship 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 are interested in a second embodiment schematically represented in Figure 4. In the second embodiment, the method comprises a first variant of the steps of acquiring images of part A1' and standard A2' and of the steps of analyzing images of part E1' and standard E2'. The other steps are identical to the corresponding steps of the first embodiment.

[0134] In the example taken for this second embodiment, the coating covering the 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 TMCHalIcrest ©.

[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 parameters of the camera (number of images acquired, acquisition time, black image, etc.). This results in particular in that the acquisition steps A1' and A2' according to the second embodiment can be operated 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 previously placed 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] Here we describe the part image acquisition step A1' and the part image analysis step E1'. It is understood that the standard image acquisition steps A2' and standard image analysis steps E2' are respectively identical to the part image acquisition steps A1' and part image analysis steps E1', but relate to the standard.

[0138] During the part image acquisition step A1', a first image acquisition takes place. Thus, the camera 20 acquires a plurality of images of the 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 for the first average image. This process is iterated as many times as desired, for wavelengths all different from each other.

[0140] It is understood that each average image acquires the room 100 from the same angle, with identical camera 20 parameters, 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 ​​the room 100, identical from image to image.

[0141] Then, during the part analysis step E1', the processing unit 30 respectively calculates a processed spectral signature matrix of the part 100 and a processed matrix of spectral signature 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] First, the processing unit 30 calculates a conversion from the scale in pixels to the scale in millimeters (or other unit of length) for one of the average images of the room 100. This scale can then be transposed to all the other average images.

[0143] The processing unit 30 firstly lists, for each pixel of the average images, the reflected intensities recorded on each of the average images during the acquisition step A1'. In other words, the processing unit 30 creates a matrix of 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 this 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 deduced, associating each of its elements with the corresponding spectral signature. In the present example, the spectral signature may comprise information on the spectral moments, averages and / or variances of reflection intensity. In this second embodiment, the spectral signature is the optical information of interest which makes it possible to deduce the thermal history of the part 100.

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

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

[0147] In particular, a transfer function linking the spectral signature, the temperature and the 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 reconstruction step S then take place as previously described.

[0149] Third embodiment, lifetime analysis

[0150] In the following paragraphs, we are interested in a third embodiment schematically represented in Figure 5. In the third embodiment, the method comprises a second variant of the image acquisition steps A1” and A2” and of 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 carried out 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 method, it is desirable for the camera to have an intensifier to amplify a signal acquired over a duration which can be of the order of several nanoseconds, and therefore not very intense.

[0152] In the example taken for this third embodiment, the coating covering the 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 can be used.

[0153] The lifespan of a photoluminescent marker may depend on the thermal history of the photoluminescent marker. 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 others.

[0154] The light source 10 used for 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 character may 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 may 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 from the processing unit 30. In the present example, the camera 20 is configured to acquire a sequence of images, following the command from the processing unit 30 during an acquisition duration significantly greater than the lifetime of the photoluminescence of the photoluminescent marker. This acquisition duration is at least three times greater than the longest lifetime of the marker.

[0156] Here we describe the part image acquisition step A1” and the part image analysis step E1”. It is understood that the standard image acquisition steps A2” and standard image analysis steps E2” are respectively identical to the part image acquisition steps A1” and part image analysis steps E1”, but relate to the standard.

[0157] During the acquisition step A1”, and prior to the acquisition of images, 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 on 545 nm. Thus, the part 100 is illuminated at a wavelength allowing the excitation of the photoluminescent marker provided in the coating, and the camera 20 perceives a light representative of the luminescence of the first photoluminescent marker.

[0159] Then, 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 sequence of images comprises a sufficient number of images to be able to integrate the intensity of the photoluminescence as a function of time. In the present example, the sequence of images comprises several dozen images, typically 30 images. The sequence of images is then recorded by the processing unit 30.

[0160] We can see from the sequence of images that the luminescence of the photoluminescent marker decreases as the images scroll by.

[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 of the average image sequence is an average image of the corresponding images of 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 for the part 100 and 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 sequence of images of the part 100, respectively of the sequence of images of the standard. We describe here the obtaining of the processed matrix of the part 100, it being understood that the processed matrix of the standard is obtained in the same way.

[0163] First, the processing unit 30 calculates a conversion from the pixel scale to the 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 intensity of the luminescence at said pixel, as a function of time. This value is noted in a matrix of size equal to the size in pixels of an image of the average image sequence, in the place 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 makes it possible to deduce the thermal history of the part 100.

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

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

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

[0168] A variant of this third embodiment consists, during the acquisition steps A1 ”and A2”, in providing a light source 10 configured to provide 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 linked to the lifetime for example by the relation tan <p = 2TT T avec <p le déphasage, f la fréquence de modulation de la lumière incidente et T le temps de vie à déterminer. Ce temps de vie correspond au maximum des durées de vie t n .

[0169] Fourth embodiment, thermochromoluminescent marker analysis

[0170] In the following paragraphs we are interested in a fourth embodiment. In the fourth embodiment, a thermochromoluminescent marker, such as for example Zn3(PO4)2: 2%Mn 2+ , is used. These markers have the particularity of emitting a spectrum presenting peaks at several defined wavelengths when they receive an excitation at a defined excitation wavelength. The intensity of the peaks of the emitted spectrum depends on the thermal history.

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

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

[0173] The second filter 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] This description is based on the example of thermal history analysis, but this method could be applied mutatis mutandis to history analyses of any thermomechanical quantity (stress, deformation, pressure, temperature, etc.) using markers whose optical information varies as a function of said thermomechanical quantity.

[0175] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may 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 illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0176] It is also obvious that all the characteristics described with reference to a method 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 method.

Claims

Claims

1. A method for analyzing the thermal history of a part (100) by 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 method 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 step of acquiring part images (A1; A1'; A1") and a step of acquiring standard images (A2; A2';A2") in which optical information of the workpiece (100) and the standard are respectively measured by the optical device and then recorded by the processing unit (30), a workpiece image analysis step (E1; E1'; E1") and a standard image analysis step (E2; E2'; E2") in which the optical information of the workpiece (100) and the standard are respectively processed by the processing unit (30) to obtain processed optical information of the workpiece and the standard, a transfer function determination step (I) in which a transfer function relating the temperature, the 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 function of; transfer and processed optical information of the part (100) and the thermal history image represents the thermal history of the part (100).

2. The method of claim 1, wherein the step of acquiring part images (Al; Al'; Al") comprises the use of three-dimensional reconstruction means, and wherein the method further comprises a reconstruction step (S) in which a thermal history map of the part (100) is deduced from the image of the thermal history 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. The method of claim 2, wherein the optical device comprises a target or a scanner.

4. Method according to one of claims 1 to 3, in which the standard has a conical shape and is provided in an electrically conductive material.

5. Method according to one of claims 1 to 4, during the steps of acquiring part images (A1; A1'; A1") and standard images (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. Method according to one of claims 1 to 5, wherein the coating comprises a second optical marker, and during the steps of acquiring part and standard images (A1, A2), the optical information measured by the optical device for the first optical marker comprises the intensity of the luminescence 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 intensity of the luminescence of the second optical marker at a given second wavelength, and during the steps of analyzing part and standard images (E1, E2), the processing unit (30) calculates a ratio of the intensity of the luminescence of the first optical marker relative to the intensity of luminescence of the second optical marker, the processed optical information comprising said ratio of the luminescence intensity of the first optical marker to the luminescence intensity of the second optical marker.

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

8. Method according to one of claims 1 to 5, the first optical marker is unique, and during the steps of acquiring part and standard images (A1', A2'), the optical information measured by the optical device for the optical marker comprises a plurality of intensities reflected by the optical marker at a given plurality of wavelengths, and the processed optical information comprises a spectral signature calculated by the processing unit (30) for the plurality of wavelengths during the steps of analyzing part and standard images (E1, E2).

9. Method according to one of claims 1 to 5, in which the first optical marker is unique, and during the steps of acquiring part and standard images (A1", A2"), the optical device performs, following a pulsed excitation of the luminescence of the first optical marker provided 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 comprises 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 steps of analyzing part and standard images (E1", E2").

10. The method of claim 9, wherein the sequence of measurements comprises more than 10 measurements.

Images