Method and device for determining and using a diagnostic tool comprising a temperature ageing spectrum

Abstract

The invention relates to a method and a device for determining and using a diagnostic tool comprising a temperature ageing spectrum, the method (P) comprising a step (E1) of receiving at least one temperature curve relating to a given geographical location, a processing step (E2) comprising a sequence of consecutive substeps (E2A, E2B, E2C, E2D, E2E), implemented iteratively for different values of a characteristic time associated with a type of material, comprising a substep (E2A) of filtering the temperature curve using a first-order filter having the characteristic time as the time constant, a substep (E2B) of applying an ageing law, a substep (E2C) of performing a cumulative calculation over a given sliding time period, a substep (E2D) of extracting a value corresponding to an ageing criterion and a substep (E2E) of associating this extracted value with the characteristic time, wherein the pairs of values obtained at the end of the iterations form a temperature ageing spectrum, and a step (E3) of performing, from at least this spectrum, comparisons in order to carry out a diagnosis.

Description

Method and device for determining and using a diagnostic tool comprising a temperature aging spectrum.

[0001] The present invention relates to a method and device for determining and using a diagnostic tool comprising a temperature aging spectrum. State of the art

[0002] Although not exclusively applicable, the present invention is particularly relevant to the military field, and especially to any military equipment likely to be subjected to extreme conditions, such as a missile. This can include any type of equipment, such as electronic, pyrotechnical, or organic materials, thermal protection devices, etc.

[0003] To optimize the durability of equipment, particularly military equipment, over time, it is well known to implement a customization process (defining the precise requirements) of the mechanical demands, sometimes severe, to which the equipment may be or has been subjected. Specifically, to compare different mechanical environments, it is known to use a shock response spectrum and a fatigue damage spectrum. These spectra help to precisely specify the extremely severe stresses (vibrations, shocks, etc.) to which the equipment in question will be or has been exposed.

[0004] However, in addition to mechanical environments, equipment can also be subjected to climatic environments, particularly thermal ones, of varying severity. Yet, for climatic environments, a customization approach to equipment would require knowledge of real-world conditions. This would necessitate extremely long campaigns (requiring measurements over several years for meteorological parameters) at numerous sites worldwide (where the equipment could be deployed) to determine these real-world conditions, especially the temperature, to which the equipment might be subjected. Such a solution is therefore not feasible in practice.

[0005] However, the failure to consider actual thermal conditions (as well as the lack of knowledge regarding the thermal inertia of the equipment) prevents accurate specification of the equipment and generally leads to the environments to which the equipment is subjected being considered much more severe than they actually are. Consequently, the equipment is designed and adapted to withstand thermal conditions more severe than those it will actually encounter.

[0006] There is therefore a need to find a solution that makes available a diagnostic tool capable of determining the effect of thermal conditions, including average temperatures and temperature variations to which equipment will be subjected, particularly for customization during equipment design or to assess its level of stress.

[0007] The present invention relates to a method for determining and using a diagnostic tool, which makes it possible to meet the aforementioned need, the diagnostic tool comprising at least one temperature aging spectrum for a plurality of (different) types of material.

[0008] To this end, according to the invention, said method comprises at least the following steps: - a step of receiving at least one temperature curve, the temperature curve representing a variation of the temperature as a function of time at a given geographical location; - a processing step comprising a series of successive sub-steps, said series being implemented iteratively for each of a plurality of N different values ​​of a characteristic time Tau_i, N being an integer greater than 1 and i being an integer varying from 1 to N, the characteristic time Tau_i being associated with a given type of material and representative of the latter, said series of successive sub-steps comprising, for a given iteration: • a first sub-step consisting of filtering said temperature curve, using a first-order filter having as its time constant said characteristic time Tau_i, so as to obtain a first modified curve;• a second sub-step consisting of applying an aging law to said first modified curve to obtain a second modified curve illustrating instantaneous aging; • a third sub-step consisting of performing, from said second modified curve, a cumulative calculation over a given sliding period; • a fourth sub-step consisting of extracting a value corresponding to an aging criterion (average aging, maximum aging, minimum aging, ...); and • a fifth sub-step consisting of associating this extracted value with the characteristic time Tau_i corresponding to the iteration, to form a pair of values, the pairs of values ​​obtained at the end of the N iterations forming a set of pairs, said temperature aging spectrum comprising at least said set of pairs of values;and- a comparison step consisting of carrying out comparisons, based at least on said temperature aging spectrum, to perform at least one diagnosis.

[0009] Thus, thanks to the invention, a temperature aging spectrum is obtained that is representative of a temperature curve for a given geographical location, for example, a city, and that provides information and data on temperature aging as a function of the characteristic time that is representative of a type of material under consideration. Therefore, for a particular type of material, for example, missile equipment, it is possible to determine the temperature conditions and the associated aging to which it has been or will be subjected.

[0010] By making comparisons, for example with temperature aging spectra from different geographical locations or corresponding to different types of equipment, we have a diagnostic tool that allows us to determine the thermal conditions and associated aging to which equipment will be subjected. This is particularly useful for customizing equipment during the design phase (adapting it to the thermal constraints encountered so that it can withstand these temperatures without being oversized) or for assessing its stress level. This diagnostic tool is applicable to the main types of equipment (electronic, pyrotechnical, organic, thermal protection, etc.) used, notably, in the military sector.

[0011] Advantageously, said set of pairs of values ​​(forming the temperature aging spectrum) is represented in the form of a curve.

[0012] In a first embodiment, the reception step and the processing step are implemented for each of a plurality of different temperature curves (i.e. relating to different geographical locations) allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular geographical location, and the comparison step consists of making comparisons from at least two of these temperature aging spectra.

[0013] This allows us to compare the effects of temperature on a given piece of equipment, or on several pieces of equipment, for several different temperature curves, i.e., for several different geographical locations. This makes it possible, in particular, to adapt the equipment's protection to the thermal conditions to which it will be subjected in a given geographical location, for example, a city with very high temperatures.

[0014] In a second embodiment, as a variant or in addition to the first embodiment mentioned above, the processing step is implemented for a plurality of different aging criteria (maximum aging, minimum aging, …) allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular aging criterion, and the comparison step consists of making comparisons from at least two of these temperature aging spectra.

[0015] Advantageously, the said aging criterion corresponds to one of the following values: - a maximum value; - a particular percentage greater than 0 and less than 100 of the maximum value; - an average value; - a minimum value; - a particular percentage greater than 0 and less than 100 of the minimum value.

[0016] Furthermore, in a third embodiment, as a variant or complement to the first embodiment mentioned above and / or the second embodiment mentioned above, the processing step is implemented for a plurality of different sliding durations allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular sliding duration, and the comparison step consists of making comparisons from at least two of these temperature aging spectra.

[0017] Furthermore, in a first embodiment, the second substep of the processing step consists of applying the Coffin-Manson law as the aging law. Advantageously, the second substep of the processing step determines a number N of actual cycles of amplitude ΔTreal equivalent to one test cycle, based on the Coffin-Manson law, which is written as:

[0018] In which: - Tesmax and Tesmin are the maximum and minimum values ​​of the test cycle; is the variation of the actual temperature; et- q is a predetermined value.

[0019] This first embodiment makes it possible to clearly highlight the aging due to temperature variations.

[0020] Furthermore, in a second embodiment, the second substep of the treatment step consists of applying the Arrhenius law as the aging law. Advantageously, the second substep of the treatment step determines a test duration Dtest at a temperature Tref equivalent to a real situation of duration Dreal at a temperature T, based on the Arrhenius law which is written:

[0021] In which: -E corresponds to the activation energy, for example 70kJ; and -R corresponds to the universal ideal gas constant.

[0022] This second embodiment makes it possible to clearly highlight the aging due to the average temperature and the duration for which the material remained at that temperature.

[0023] Furthermore, advantageously, the process includes a preliminary step consisting of determining, for a plurality of different materials, the associated characteristic time.

[0024] Advantageously, at this preliminary stage, the characteristic time associated with a material is obtained from a so-called representative curve illustrating the temperature measured inside the material as a function of time, starting at the moment when said material (which initially has an initial internal temperature Ti) is subjected to a given external temperature Tf, and the characteristic time corresponds to one of the following times: - the time for the temperature measured inside the material to reach 63% of the temperature difference Tf-Ti between the external temperature Tf and the initial internal temperature Ti; - one third of the time for the temperature measured inside the material to reach 95% of the temperature difference Tf-Ti; - one fifth of the time for the temperature measured inside the material to reach 99% of the temperature difference Tf-Ti.

[0025] In a preferred embodiment, the temperature curve(s) received at the reception stage are sourced from one or more public, generally free, databases, thus enabling cost-effective implementation of the process. Furthermore, numerous temperature curves for various locations are currently available.

[0026] The present invention also relates to a device for determining and using a diagnostic tool comprising at least one temperature aging spectrum for a plurality of (different) types of material.

[0027] According to the invention, said device comprises at least the following units: - a receiving unit configured to receive at least one temperature curve, the temperature curve representing a variation of the temperature as a function of time at a given geographical location; - a processing unit performing iterative processing for each of a plurality of N different values ​​of a characteristic time Tau_i, N being an integer greater than 1 and i being an integer varying from 1 to N, the characteristic time Tau_i being associated with a given type of material and representative of the latter, said processing unit comprising: • a first subunit configured to filter said temperature curve, using a first-order filter having as its time constant said characteristic time Tau_i, so as to obtain a first modified curve;• a second subunit configured to apply an aging law to said first modified curve to obtain a second modified curve illustrating instantaneous aging; • a third subunit configured to perform, from said second modified curve, a cumulative calculation over a given sliding period; • a fourth subunit configured to extract a value corresponding to an aging criterion; and • a fifth subunit configured to associate this extracted value with the characteristic time Tau_i corresponding to the iteration, in order to form a pair of values, the pairs of values ​​obtained at the end of the N iterations forming a set of pairs, said temperature aging spectrum comprising at least said set of pairs of values; and - a comparison unit configured to perform, from at least said temperature aging spectrum, comparisons to carry out at least one diagnosis.

[0028] The present invention also relates to a method for assisting in the adaptation of equipment to future thermal constraints.

[0029] According to the invention, this method includes at least the following operations: - carrying out a diagnosis relating to the equipment at one or more geographical locations where it is expected to be used, by implementing the aforementioned process and using a characteristic time associated with the type of said equipment; and - a design of the equipment which is adapted to the result of this diagnosis.

[0030] Within the framework of the present invention, we therefore take into account, as a heat transfer function linking the external thermal conditions of a considered piece of equipment (whose thermal behavior is not exactly known) to the internal thermal conditions of this equipment, a simplified transfer function corresponding to a first-order filter which has as a time constant, a characteristic time Tau associated with (and representative of) this equipment (and of its storage and / or use conditions).

[0031] The present invention offers numerous advantages. In particular: - temperature aging spectra provide an advantageous solution in the field of thermal environment specification; - they allow, for currently used equipment, the determination of the stress level of that equipment; - above all, they allow for the design of future equipment, more precisely, to withstand the thermal stresses to which it is likely to be subjected; - they allow for early design, adapted to real thermal conditions; - the method is applicable to a wide range of equipment (equipment, missiles, containers, etc.) whose thermal behavior is not precisely known; and - the method can be implemented at reduced cost thanks to generally free access to temperature curves. Brief description of the figures

[0032] Other features and advantages of the device, process and / or method according to the invention will become clearer from the following description of illustrative and non-limiting examples of embodiments, annexed to the following figures.

[0033] This is the synoptic diagram of a device conforming to a particular embodiment of the invention.

[0034] This is a schematic view of an example system, in this case a missile, equipped with materials to which the present invention can be applied.

[0035] Laest is a graph used to explain the characteristics and method of determining a characteristic time associated with a given piece of equipment.

[0036] Laillustre schematically illustrates a particular embodiment of a process according to the invention.

[0037] This is a graph showing temperature curves associated with the first two cities.

[0038] This is a graph showing temperature curves associated with two other cities.

[0039] This is a graph derived from the processing of temperature curves, specifically the temperature curves in Figures 5 and 6, showing curves illustrating, each, the evolution of a number of test cycles to cover a real cycle, as a function of the characteristic time, and this for several different geographical locations.

[0040] This is a graph resulting from the processing of a temperature curve relative to a geographical location, showing curves illustrating, each, the evolution of a number of test cycles to cover a real cycle, as a function of the characteristic time, and this for several different aging criteria.

[0041] This is a graph resulting from the processing of a temperature curve relative to a geographical location, showing two curves illustrating, each, the evolution of a number of test cycles to cover a real cycle, as a function of the characteristic time, and this for two different sliding durations.

[0042] This is a graph resulting from the processing of a temperature curve relative to a geographical location, showing curves illustrating, each, the evolution of a test duration to simulate a real hour, as a function of the characteristic time, and this for several different aging criteria and several different sliding durations.

[0043] This is a graph resulting from the processing of a temperature curve relative to a geographical location, showing curves illustrating, each, the evolution of a test duration to simulate a real hour, as a function of the characteristic time, and this for several different aging criteria.

[0044] This is a graph resulting from the processing of temperature curves, showing curves illustrating, each, the evolution of a test duration to simulate a real hour, as a function of the characteristic time, and this for several different aging criteria, several different sliding durations and two different cities. Detailed description

[0045] Device 1 illustrating a particular embodiment of the invention and represented schematically on the diagram is a device for determining and using a diagnostic tool comprising at least one temperature aging spectrum (hereinafter referred to as "SVT").

[0046] Device 1 applies more specifically to the military sector, and in particular to any military equipment likely to be subjected to specific temperature conditions, such as a missile, for example. This can include any type of equipment, such as electronic, pyrotechnic, or organic materials, thermal protection devices, etc.

[0047] As an example, the equipment 2A and 2B shown on the diagram correspond to two components of a missile 3, for example, electronic equipment for missile 3 for equipment 2A and a propulsion unit for missile 3 for equipment 2B. The missile 3 is mounted in a container 4 which is installed on the ground 5 in a location where it is subjected to thermal conditions specified below and illustrated by a thermometer 6 and arrows 7.

[0048] In the context of the present invention, a parameter called the "characteristic time" Tau is associated with a given type of material. This characteristic time Tau represents the time required for the internal temperature of the material in question to adapt to the external temperature at the location of the material (or the system comprising this material). This characteristic time Tau varies, in particular, according to the size of the material in question (missile equipment, missile, etc.), its configuration, and its storage conditions (in a container or outside of a container, etc.). This characteristic time represents the time constant of a (simplified) heat transfer function used, relating the external conditions to the internal conditions of the material, as detailed below.

[0049] For example: - the time required to completely thermally stabilize a single cubic electronic device measuring 20 cm on each side is a few hours. In this case, the characteristic time Tau is considered, for example, to be on the order of 1 hour; and - the time required to completely thermally stabilize a propellant block for a long-range missile, when the missile is in logistical condition, can reach several tens of hours, or even a few days. In this case, the characteristic time Tau is considered, for example, to be on the order of 20 hours.

[0050] The device 1 comprises, as shown in Figure 5: - a receiving unit 8 configured to receive at least one temperature curve C1, C2, C3, C4 (Figures 5 and 6). The temperature curve represents the variation of the temperature T (expressed in °C) as a function of time t (expressed, for example, in hours) at a given geographical location, for example, at the level of a city as specified below; - a processing unit 9 receiving the temperature curve(s) C1, C2, C3, C4 from the receiving unit 8. The processing unit 9 is configured to perform processing using this or these temperature curve(s) C1, C2, C3, and C4. The processing unit 9 performs the processing iteratively, for each of a plurality of N values ​​of a characteristic time Tau_i, in order to determine at least one temperature aging spectrum (TAS). N is an integer greater than 1 and i is an integer ranging from 1 to N.Each characteristic time Tau_i is associated with a given type of material and is representative of the latter as specified below; and a comparison unit 10 configured to perform, from at least the temperature aging spectrum (SVT) (received from the processing unit 9), comparisons to perform at least one diagnosis, as also specified below.

[0051] Furthermore, the processing unit 9 comprises: - a subunit 11 configured to, at each iteration i, filter said temperature curve C1, C2, C3, C4, using a first-order filter having as its time constant said characteristic time Tau_i, so as to obtain a first modified curve; - a subunit 12 configured to apply an aging law to said first modified curve to obtain a second modified curve illustrating instantaneous aging; - a subunit 13 configured to perform, from said second modified curve, a cumulative calculation over a given sliding time period Di; - a subunit 14 configured to extract a value corresponding to a particular aging criterion; and - a subunit 15 configured to associate this extracted value with the characteristic time Tau_i corresponding to the iteration, to form a pair of values.

[0052] In the context of the present invention, the expression "aging criterion" encompasses one, several or all of the following values: - a maximum value; - at least a particular percentage greater than 0 and less than 100 of the maximum value; - an average value; - a minimum value; - at least a particular percentage greater than 0 and less than 100 of the minimum value.

[0053] The pairs of values ​​obtained at the end of the N iterations form a set of pairs. The temperature aging spectrum (TGS) includes at least this set of pairs of values.

[0054] The device 1 also includes a receiving unit 16 configured to receive the minimum and maximum characteristic times associated with the plurality of different materials considered. The minimum and maximum characteristic times are transmitted to the processing unit 9 and used by subunits 11, 12, 13, 14, and 15 during the processing operations performed. They can also be used by the comparison unit 10.

[0055] Device 1, as described above, is intended to implement a method P for determining and using a diagnostic tool comprising at least one temperature aging spectrum (TVS). This method P, implemented by device 1, which is shown in Figure 1, is now described.

[0056] The said process P comprises at least the following steps: - a step E1 (implemented by the receiving unit 8) of receiving at least one temperature curve C1, C2, C3, C4 (figures 5 and 6) which shows a variation of the temperature T as a function of time t at a given geographical location;- a processing step E2 (implemented by processing unit 9) comprising a sequence of successive substeps E2A, E2B, and E2C. This sequence is implemented iteratively for each of a plurality of N values ​​of the characteristic time Tau_i. N is an integer greater than 1, and i is an integer ranging from 1 to N. A characteristic time Tau_i is associated with a given type of equipment, for example, equipment 2A or equipment 2B, and is representative of that equipment. The processing step E2 comprises, for a given iteration i: • a substep E2A (implemented by subunit 11) consisting of filtering the temperature curve C1, C2, C3, C4 using a first-order filter whose time constant is the characteristic time Tau_i, in order to obtain a first modified curve;• a sub-step E2B (implemented by sub-unit 12) consisting of applying an aging law to said first modified curve to obtain a second modified curve illustrating instantaneous aging; • a sub-step E2C (implemented by sub-unit 13) consisting of performing, from said second modified curve, a cumulative calculation over a given rolling period Di (for example 100 hours or 1000 hours) to obtain a third modified curve illustrating cumulative aging over the considered rolling period Di; • a sub-step E2D (implemented by sub-unit 14) consisting of extracting from the third modified curve a value corresponding to a particular aging criterion (maximum value, minimum value, …);and • a sub-step E2E (implemented by sub-unit 15) consisting of associating this value (thus extracted in sub-step E2D) with the characteristic time Tau_i corresponding to the iteration, to form a pair of values. The pairs of values ​​obtained at the end of the N iterations form a set of pairs. This set of pairs of values ​​is preferably represented as a curve. The SVT spectrum includes at least this set of pairs of values; and - a comparison step E3 (implemented by the comparison unit 10) consisting of performing comparisons, at least from said SVT spectrum, to carry out at least one diagnosis.

[0057] The main steps of process P are described in more detail below.

[0058] The temperature curves C1, C2, C3, and C4 that we wish to use are extracted from databases and received by the receiving unit 8 at the E1 reception stage. These temperature curves are generally sampled hourly, that is, with a temperature measurement every hour, and this sometimes extends over periods of several years.

[0059] In a preferred embodiment, the temperature curve(s) received in the E1 reception step are obtained from one or more commonly available public databases, including databases available on government websites. Access to information in such databases is generally free. This allows for the cost-effective implementation of the P process. Furthermore, numerous temperature curves for different locations, subjected to varying and sometimes extreme thermal conditions, are currently available. This provides a wide range of diagnostic possibilities.

[0060] After receiving the temperature curve(s) C1, C2, C3, C4, which we wish to use, subunit 11 performs, at substep E2A, for each temperature curve C1, C2, C3, C4, a usual filtering, using a first order filter having as its time constant the characteristic time Tau considered.

[0061] Within the framework of the present invention, the heat transfer function (HT) relating the external conditions to the internal conditions of the equipment under consideration is thus reduced to a first-order filter (with the characteristic time constant Tau). This simplified heat transfer function (HT) is described by: -- a thermal inertia Cth which slows the propagation of external conditions, which is described by: • m: the mass (in kg); and • Cp: the specific heat (in J / kg / K); and -- a thermal conductance 1 / Rth which promotes the propagation of external conditions.Thermal conductance is described: - by hS for convection phenomena, with: • h: the convective heat transfer coefficient (W / m² / K); and • S: the convective heat transfer surface area (m²); - or by λS / e for conduction phenomena, with: • e: the thickness through which the flux passes (in m); • λ: the thermal conductivity (in W / m / K); and • S: the conduction heat transfer surface area (in m²).

[0062] The internal temperature of the equipment is the solution to the first-order differential equation (1), which can be written as follows: With: • Text: the outside temperature; • T(t): the internal temperature as a function of time t; and • Tau: the characteristic time, namely a constant characteristic of the thermal behavior of the equipment.

[0063] When the equipment is subjected to a temperature step between 0 and Text, equation (1) has the following solution:

[0064] When the equipment is subjected to a temperature step between Ti and Tf ( ), equation (1) can be written as an equation:

[0065] The solution to this equation is:

[0066] The CR curve illustrates the response of a first-order filter with time constant Tau=20, when subjected to a temperature step between 15°C (Ti) and 50°C (Tf).

[0067] By observing the behavior (illustrated by this CR curve), we can identify the characteristic time Tau using one of the following properties: - after a duration of Tau, the heating is 63% of the temperature difference Tf-Ti considered; - after a duration of 3 Tau, the heating is 95% of the temperature difference Tf-Ti considered; - after a duration of 5 Tau, the heating is 99% of the temperature difference Tf-Ti considered.

[0068] The filtering performed in substep E2A yields a first modified curve, which is then used in substep E2B. Substep E2B applies an aging law to this first modified curve to obtain a second modified curve illustrating instantaneous aging. The implementation of this substep E2B is detailed below, in connection with the use of two specific aging laws.

[0069] Furthermore, then: - substep E2C performs, from this second modified curve, a cumulative calculation over a given sliding period Di (for example 100 hours or 1000 hours) to obtain a third modified curve illustrating cumulative aging over the considered sliding period Di; and - substep E2D extracts from this third modified curve a value corresponding to a particular aging criterion (maximum value, minimum value, …).

[0070] The extracted value is associated, in substep E2E (via subunit 15), with the characteristic time corresponding to the iteration, thus forming a pair of values ​​for that iteration. The set of pairs of values ​​obtained in substep E2E, at the end of the iterations, forms the SVT spectrum. This set of pairs of values ​​is preferably represented as a curve.

[0071] Figures 7 to 12 show different sets of curves thus obtained, relating to SVT spectra, which will be specified below.

[0072] Then, in the E3 comparison step, comparisons are made, based on the SVT spectra determined in the E2 processing step, to perform at least one diagnosis concerning the material(s) considered.

[0073] Furthermore, in a particular embodiment, process P includes a preliminary step E0 implemented by the pretreatment unit 16. This preliminary step E0 consists of receiving, for a plurality of different materials, the minimum and maximum characteristic times.

[0074] The behavior of each piece of equipment is simplified by a single-parameter system, namely the time (characteristic time) required for its temperature to stabilize (thermal inertia).

[0075] In the preliminary step E0, the characteristic time associated with a given piece of equipment, such as the electronic equipment 2A or the propulsion unit 2B of missile 3, is obtained from a representative curve CR, such as the one shown in Figure 1. This representative curve CR indicates the temperature T (expressed in °C) measured inside the equipment 2A, 2B as a function of time t (expressed in hours). It is representative of the equipment in question. The measurement used begins when the equipment, which initially has an internal temperature Ti (initial) of 15°C, is subjected to a given external temperature Tf of 50°C. For the sake of simplicity in the diagram, Figure 1 shows a theoretical evolution of a representative curve CR, rather than a curve obtained from actual measurements, which generally have a less smooth and less consistent shape.

[0076] The characteristic time Tau associated with the CR representative curve is obtained from this CR representative curve by identifying one of the following times: - the time for the temperature measured inside the material to reach 63% of the temperature difference Tf-Ti. In the example above, the time to reach 63% is 20 h; - one-third of the time for the temperature measured inside the material to reach 95% of the temperature difference Tf-Ti. In the example above, the time to reach 95% is 60 h; - one-fifth of the time for the temperature measured inside the material to reach 99% of the temperature difference Tf-Ti.

[0077] Therefore, for a given material, for example material 2B, which has a representative CR curve like the one shown, we deduce in the preliminary step E0 that the characteristic time Tau associated with this material corresponds to 20 hours. The preliminary step E0 can be implemented for all types of materials that we wish to analyze.

[0078] Therefore, thanks to the P process, by making comparisons, for example with the SVT spectrum of another geographical location or for different types of equipment, we have a diagnostic tool that allows us to determine the thermal conditions to which equipment will be subjected. This is particularly useful for customizing equipment during the design phase (to adapt it to the thermal constraints encountered so that it can withstand these temperatures without being oversized) or for assessing its stress level. This diagnostic tool is applicable to the main types of equipment (electronic, pyrotechnical, organic, thermal protection, etc.), such as those used in the military sector.

[0079] Different types of diagnosis are possible thanks to the invention. Two different embodiments of the method P are specified below by way of illustration, with different examples of possibilities for comparison.

[0080] Furthermore, in a first implementation of process P, the reception step E1 and the processing step E2 are implemented for each of a plurality of different temperature curves C1, C2, C3, C4 (relating to different geographical locations) allowing to obtain a plurality of SVT spectra, each of which is associated with a particular geographical location, and the comparison step E3 consists of making comparisons from at least two of these SVT spectra.

[0081] In a second implementation of process P, as a variant or complement to the first implementation mentioned above, the E2 processing step is implemented for a plurality of different aging criteria (maximum value, minimum value, average value, …) allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular aging criterion, and the E3 comparison step consists of making comparisons from at least two of these SVT spectra.

[0082] Furthermore, in a third implementation of process P, as a variant or complement to the aforementioned first implementation and / or the aforementioned second implementation, the processing step E2 is implemented for a plurality of different sliding durations allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular sliding duration, and the comparison step E3 consists of making comparisons from at least two of these SVT spectra.

[0083] As an illustration, examples of implementation of the invention are presented below.

[0084] To do this, we refer to: - the temperature curves (or time series) C1 and C2 of two cities named V1 and V2, as shown in Figure 1. These temperature curves C1 and C2 are sampled hourly, between 2010 and 2016, meaning they include the external temperature values ​​measured respectively in cities V1 and V2, every hour, from 2010 to 2016. The maximum temperature is 50°C for city V1 and 47°C for city V2. The average diurnal temperature range is higher for city V1 (8.2°C) than for city V2 (5.3°C); and - the temperature curves (or time series) C3 and C4 of two cities named V3 and V4, as shown in Figure 1. These C3 and C4 temperature curves are sampled hourly, between 2010 and 2016, that is to say they include the values ​​of external temperatures measured respectively in cities V3 and V4, every hour, and this from 2010 to 2016.The maximum temperature is 40°C for city V3 and 37°C for city V4.

[0085] Various aging laws can be used to implement the present invention. Thermal aging phenomena are modeled by laws depending on the type of equipment considered.

[0086] By way of illustration, not limiting, we present below two particular aging laws, namely the Coffin-Manson law which can be used in particular for electronic equipment and the Arrhenius law which can be used in particular for energy and / or organic materials.

[0087] In a first embodiment of process P, substep E2B of treatment step E2 applies the Coffin-Manson law as the aging law.

[0088] In this first embodiment, substep E2B determines a number N of real cycles of amplitude ΔT_real equivalent to one test cycle, from the Coffin-Manson law which is written:

[0089] In which: -Tesmax and Tesmin are the maximum and minimum values ​​of the test cycle, for example 85°C and -45°C respectively; is the variation of the actual temperature; et-q is a predetermined value, for example between 2 and 3.

[0090] This first embodiment makes it possible to clearly highlight the aging due to temperature variation over time, to which the material in question is subjected.

[0091] Instantaneous aging is calculated day by day for the Coffin-Manson law.

[0092] We present below, with reference to figures 7, 8 and 9, for this first mode of embodiment, several examples of SVT spectra and the information that can be derived from them.

[0093] A first example of the application of the Coffin-Manson law is shown in Figure 1. This graph is derived from the processing of temperature curves, specifically the temperature curves C1 to C4 in Figures 5 and 6, relating to cities V1, V2, V3, and V4. More precisely, Figure 1 comprises curves T1 to T6, where curves T1 to T4 are obtained, respectively, from the temperature curves C1 to C4 relating to cities V1 to V4, and curves T5 and T6 are obtained, respectively, from temperature curves relating to a temperate geographical zone Z1 (for T5) and a hot geographical zone Z2 (for T6). Each curve T1 to T6 represents the evolution of a number N of test cycles required to cover one actual cycle, as a function of the characteristic time Tau (expressed in hours).

[0094] These curves T1 to T6 are obtained for a sliding duration Di of 1000 hours (i.e. 41 days) and for a maximum value as an aging criterion.

[0095] To highlight the particularities of these curves and to make comparisons, the following tables were created, the values ​​of which are taken from these curves.

[0096] The table below shows, for three values ​​of Tau, the number of actual cycles covered by one test cycle. V1 V2 V3 V4 Z1 Z2 Tau=0.5h28843016230610771 Tau=5h10121470494934360200 Tau=10h28574443145729571251711

[0097] The table below shows, for the three values ​​of Tau, the number of test cycles (rounded up to the nearest whole number) needed to cover 10 years, i.e., 3650 diurnal cycles. V1 V2 V3 V4 Z1 Z2 Tau=0.5h13923123452 Tau=5h43841119 Tau=10h213236

[0098] Furthermore, the table below indicates, for the three values ​​of Tau, the number of actual years covered by 10 test cycles. V1 V2 V3 V4 Z1 Z2 Tau=0.5h 7.911.84 48.42.91.9 Tau=5h 27.740.313.525.69.95.5 Tau=10h 78.3121.739.980.234.319.5

[0099] By making comparisons (at the E3 comparison stage) using the data from these curves, we can notably observe that: - climate zone Z2 is always more severe than the others (2 to 6 times more severe); and - city V3 is twice as severe as cities V1 and V4, and three times as severe as city V2.

[0100] For the SVT spectrum obtained from the Coffin-Manson law, the characteristic time Tau always has a very large influence. The number N relating to the SVT spectrum is three times higher for τ=0.5h than for τ=5h, and the number N relating to the SVT spectrum is ten times higher for τ=0.5h than for τ=10h.

[0101] A second example of the application of the Coffin-Manson law is shown in Figure 1. Figure 1 is a graph derived from the processing of the temperature curve C2 of Figure 2, relating to city V2. More precisely, Figure 1 comprises curves TA, TB, TC, TD, and TE. Curves TA, TB, TC, TD, and TE represent the evolution of a number N of test cycles to cover a real cycle, as a function of the characteristic time Tau (expressed in hours), and this respectively for several different aging criteria but for the same rolling period Di of 1000 hours (i.e., 41 days). More precisely, curves TA, TB, TC, TD, and TE correspond, respectively, to the following values ​​of the aging criterion: - maximum value; - maximum value at 95%; - average value; - minimum value at 5%; and - minimum value.

[0102] To highlight the particularities of these curves and to make comparisons, the following tables were created, the values ​​of which are taken from these curves.

[0103] The table below shows, for two values ​​of τ, the number of actual cycles covered by one test cycle. Aging criterion: minimum value Aging criterion: average value Aging criterion: maximum value Tau=0.5h53321137430 Tau=5h1532139191470

[0104] The table below indicates, for the two Tau values, the number of test cycles (rounded up to the nearest whole number) required to cover 10 years, i.e., 3650 diurnal cycles. Aging criterion: minimum value; Aging criterion: average value; Aging criterion: maximum value. Tau = 0.5h149; Tau = 5h113

[0105] A third example of the application of the Coffin-Manson law is shown in Figure 1. Figure 1 is a graph derived from the processing of the temperature curve C2 of Figure 1, relating to city V2. More precisely, Figure 1 comprises two curves, TF and TG. The curves TF and TG represent the evolution of the number N of test cycles required to cover one actual cycle, as a function of the characteristic time Tau (expressed in hours), for the same aging criterion (maximum value) but for two different rolling durations. More precisely, the curves TF and TG correspond, respectively, to rolling durations of 1000 h (one thousand hours) and one year (i.e., 8760 h).

[0106] By making comparisons (at the E3 comparison stage) from the data from these TF and TG curves, we can notably observe that, for Tau=5h, it appears that 8.7 situations of 1000h (namely 8700h) are twice as less severe as a situation of one year (8760h).

[0107] Furthermore, in a second embodiment of process P, substep E2B of treatment step E2 applies the Arrhenius law as the aging law.

[0108] In this second embodiment, substep E2B of processing step E2 determines a test duration Dtest at a temperature Tref (for example 50°C) equivalent to a real situation of duration Dree at a temperature T, based on the Arrhenius law which is written:

[0109] In which: -E corresponds to the activation energy, for example 70kJ; and -R corresponds to the universal ideal gas constant.

[0110] Instantaneous aging is calculated hour by hour for the Arrhenius law.

[0111] This second embodiment makes it possible to clearly highlight the aging due to the average temperature and the duration for which the material has remained at that temperature.

[0112] Several examples of SVT spectra and the information that can be derived from them are presented below with reference to figures 10, 11 and 12.

[0113] A first example of the application of Arrhenius' law is shown on the graph. This graph is derived from the processing of the temperature curve C2 of the graph, relating to city V2. More precisely, the graph comprises curves FA, FB, FC, FD, and FE. Curves FA, FB, FC, FD, and FE represent the evolution of a test duration Dtest to simulate one real hour, as a function of the characteristic time Tau (expressed in hours), for several different aging criteria and several different sliding durations. More precisely, curves FA, FB, FC, FD, and FE correspond, respectively, to the following values ​​of the aging criterion and the sliding duration: - maximum value and duration of 100h (100 hours); - maximum value and duration of 1000h (1000 hours); - average value and duration of 100h; - minimum value and duration of 1000h; and - minimum value and duration of 100h.

[0114] By making comparisons (at the E3 comparison step) using the data from these curves, we can observe the following.

[0115] In the example above, the characteristic time Tau only has an influence for short sliding duration situations, well below 1000h (approximately 100h).

[0116] This example highlights the effect of seasons and years.

[0117] It appears that, for a rolling duration of 1000h and a characteristic time Tau of 5h, a test of at least 120h, on average 212h and at most 370h is required to simulate the most severe situations of 1000h.

[0118] The effect of seasons increases for short sliding periods. For a sliding period of 100 hours and a characteristic time Tau of 5 hours, a test of at least 10 hours and at most 60 hours will be required.

[0119] This approach can be further developed by calculating not extreme spectra (maximum, minimum) but spectra relative to different percentages, as considered below.

[0120] A second example of the application of Arrhenius' law is shown in Figure 1. Figure 2 is a graph derived from the processing of the temperature curve C2 of Figure 1, relating to city V2. More precisely, Figure 1 comprises curves FF, FG, FH, FI, FJ, FK, and FL. Curves FF, FG, FH, FI, FJ, FK, and FL represent the evolution of a test duration Dtest to simulate one real hour, as a function of the characteristic time τ (expressed in hours), for several different aging criteria but for the same rolling duration of 100 hours. More precisely, curves FF, FG, FH, FI, FJ, FK, and FL correspond, respectively, to the following values ​​of the aging criterion: - maximum value; - maximum value at 99.9%; - maximum value at 99%; - maximum value at 95%; - average value; - minimum value at 5%; - minimum value.

[0121] By making comparisons (in comparison step E3) using data from these curves, we can observe that: - for a characteristic time Tau of 5 hours, to simulate a real-world situation of 100 hours (rolling duration of 100 hours), a maximum of 60 hours of testing will be required, 50 hours to cover 99.9% of cases, and 36 hours to cover 95% of cases. This difference decreases as the characteristic time Tau increases; - however, the type of extremum has no effect on the minimum value of the SVT spectrum (FK and FL curves).

[0122] A third example of the application of Arrhenius' law is shown in Figure 1. Figure 2 is a graph derived from the processing of the temperature curves C1 and C2 of Figure 3, relating to cities V1 and V2. More precisely, Figure 3 comprises curves F1A, F1B, F1C, F2A, F2B, F2C, F2D, and F2E. Curves F1A, F1B, F1C, F2A, F2B, F2C, F2D, and F2E represent the evolution of a test duration Dtest to simulate one real hour, as a function of the characteristic time Tau (expressed in hours), for several different aging criteria, several different moving durations, and for the two cities V1 and V2.More specifically, curves F1A, F1B, F1C, F2A, F2B, F2C, F2D and F2E correspond, respectively, to the following values ​​of the aging criterion and the sliding duration: - maximum value and duration of 100h (100 hours) for city V1; - maximum value and duration of 1000h (1000 hours) for city V1; - minimum value and duration of 100h for city V1; - maximum value and duration of 100h for city V2; - maximum value and duration of 1000h for city V2; - average value and duration of 1000h for city V2; - minimum value and duration of 1000h for city V2; and - minimum value and duration of 100h for city V2.

[0123] By making comparisons (at the E3 comparison stage) using the data from these curves, we can notably observe that: - for situations with sliding durations greater than or equal to 1000h, and regardless of the value of the characteristic time Tau, there is no difference between the maximum SVT spectrum of city V1 and city V2 (curves F1B and F2B); and - city V1 has "cold" periods which are up to twice as less severe than city V2: the minimum SVT spectra of city V1 never exceed 0.06 while those of city V2 can reach 0.12.

[0124] The preceding examples, with reference to figures 7 to 12, clearly highlight the numerous and varied comparisons that can be implemented with the P process, particularly with variable criteria (geographic location, aging criterion, sliding duration) and different characteristic times Tau (therefore for different materials).

[0125] Device 1 and process P thus use a "standard" model allowing comparison of the effect of temperature curves (or time curves) on a material whose heat transfer function is not precisely known, namely the time required for the temperature to propagate from the outside to the core of the material in question.

[0126] Device 1 and process P, as described above, thus offer numerous advantages. In particular: - the temperature aging spectra obtained provide an advantageous solution in the field of thermal environment specification; - they allow, for currently used equipment, the determination of the stress level of that equipment; - above all, they allow for the design of future equipment, more precisely, to withstand the thermal stresses to which it is likely to be subjected, i.e., to achieve customization.Such customization (to climatic environments) allows for the best possible sizing of equipment to thermal constraints, regardless of the type of equipment; - they allow for early design, adapted to real thermal conditions; - the process is applicable to a wide range of equipment (equipment, missile, container, etc.) whose thermal behavior is not precisely known; and - the process can be implemented at reduced cost thanks to generally free access to temperature curves.

Claims

Method for determining and using a diagnostic tool comprising at least one temperature aging spectrum for a plurality of types of equipment, the diagnostic tool being capable of determining the effect of thermal conditions, characterized in that it comprises at least the following steps: - a step (E1) of receiving at least one temperature curve (C1, C2, C3, C4), the temperature curve (C1, C2, C3, C4) representing a variation of the temperature as a function of time at a given geographical location;- a processing step (E2) comprising a series of successive sub-steps (E2A, E2B, E2C, E2D, E2E), said series being implemented iteratively for each of a plurality of N different values ​​of a characteristic time Tau_i, N being an integer greater than 1 and i being an integer ranging from 1 to N, the characteristic time Tau_i being associated with a given type of material (2A, 2B) and representative of the latter, said series of successive sub-steps comprising, for a given iteration: • a first sub-step (E2A) consisting of filtering said temperature curve (C1, C2, C3, C4), using a first-order filter having as its time constant said characteristic time Tau_i, so as to obtain a first modified curve; • a second sub-step (E2B) consisting of applying an aging law to said first modified curve to obtain a second modified curve illustrating instantaneous aging;• a third sub-step (E2C) consisting of performing, from said second modified curve, a cumulative calculation over a given sliding period; • a fourth sub-step (E2D) consisting of extracting a value corresponding to a particular aging criterion; and • a fifth sub-step (E2E) consisting of associating this extracted value with the characteristic time Tau_i corresponding to the iteration, to form a pair of values, the pairs of values ​​obtained at the end of the N iterations forming a set of pairs, said temperature aging spectrum comprising at least said set of pairs of values; and - a comparison step (E3) consisting of performing, from at least said temperature aging spectrum, comparisons to carry out at least one diagnosis. A method according to claim 1, characterized in that the reception step (E1) and the processing step (E2) are implemented for each of a plurality of different temperature curves (C1, C2, C3, C4) allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular geographical location, and in that the comparison step (E3) consists of making comparisons from at least two of these temperature aging spectra. A method according to any one of claims 1 and 2, characterized in that the treatment step (E2) is implemented for a plurality of different aging criteria allowing a plurality of temperature aging spectra to be obtained, each of which is associated with a particular aging criterion, and in that the comparison step (E3) consists of making comparisons from at least two of these temperature aging spectra. A method according to any one of claims 1 to 3, characterized in that the processing step (E2) is carried out for a plurality of different sliding durations allowing to obtain a plurality of temperature aging spectra, each of which is associated with a particular sliding duration, and in that the comparison step (E3) consists of making comparisons from at least two of these temperature aging spectra. A method according to any one of the preceding claims, characterized in that said aging criterion corresponds to one of the following values: - a maximum value; - a particular percentage greater than 0 and less than 100 of the maximum value; - an average value; - a minimum value; - a particular percentage greater than 0 and less than 100 of the minimum value. A method according to any one of claims 1 to 5, characterized in that the second substep (E2B) of the treatment step (E2) consists of applying, as the aging law, the Coffin-Manson law. A method according to claim 6, characterized in that the second sub-step (E2B) of the processing step (E2) determines a number N of real cycles of amplitude ΔT_real equivalent to one test cycle, from the Coffin-Manson law which is written: in which: - Tesmax and Tesmin are the maximum and minimum values ​​of the test cycle; is the variation of the actual temperature; et-q is a predetermined value. A method according to any one of claims 1 to 5, characterized in that the second substep (E2B) of the treatment step (E2) consists of applying, as the aging law, the Arrhenius law. A method according to claim 8, characterized in that the second substep (E2B) of the treatment step (E2) determines a test duration Dtest at a temperature Tref equivalent to a real situation of duration Dreal at a temperature T, from the Arrhenius law which is written: in which: -E corresponds to the activation energy; and -R corresponds to the universal gas constant. A method according to any one of the preceding claims, characterized in that it comprises a preliminary step (E0) consisting of determining, for a plurality of different materials (2A, 2B), the associated minimum and maximum characteristic times. A method according to claim 10, characterized in that in the preliminary step (E0), the characteristic time associated with a material (2A, 2B) is obtained from a so-called representative curve (CR) illustrating the temperature measured inside the material (2A, 2B) as a function of time, starting at the moment when said material (2A, 2B), which initially has an initial internal temperature Ti, is subjected to a given external temperature Tf, and in that the characteristic time corresponds to one of the following times: - the time for the temperature measured inside the material (2A, 2B) to reach 63% of the temperature difference Tf-Ti between the external temperature Tf and the initial internal temperature Ti; - one third of the time for the temperature measured inside the material (2A, 2B) to reach 95% of the temperature difference Tf-Ti;- one fifth of the time for the temperature measured inside the material (2A, 2B) to reach 99% of the temperature difference Tf-Ti.; A method according to any one of the preceding claims, characterized in that the temperature curve(s) (C1, C2, C3, C4), received at the (E1) reception stage, are from a public database. A method according to any one of the preceding claims, characterized in that said set of pairs of values ​​is represented in the form of a curve. Device for determining and using a diagnostic tool comprising at least one temperature aging spectrum for a plurality of material types, the diagnostic tool being capable of determining the effect of thermal conditions, characterized in that it comprises at least the following units: - a receiving unit (8) configured to receive at least one temperature curve, the temperature curve (C1, C2, C3, C4) representing a variation of temperature as a function of time at a given geographical location;- a processing unit (9) performing iterative processing for each of a plurality of N different values ​​of a characteristic time Tau_i, N being an integer greater than 1 and i being an integer ranging from 1 to N, the characteristic time Tau_i being associated with a given type of material (2A, 2B) and representative of the latter, said processing unit (9) comprising: • a first subunit (11) configured to filter said temperature curve (C1, C2, C3, C4), using a first-order filter having as its time constant said characteristic time Tau_i, so as to obtain a first modified curve; • a second subunit (12) configured to apply an aging law to said first modified curve to obtain a second modified curve illustrating instantaneous aging; • a third subunit (13) configured to perform, from said second modified curve, a cumulative calculation over a given sliding period;• a fourth subunit (14) configured to extract a value corresponding to a particular aging criterion; and • a fifth subunit (15) configured to associate this extracted value with the characteristic time Tau_i corresponding to the iteration, to form a pair of values, the pairs of values ​​obtained at the end of the N iterations forming a set of pairs of values, said temperature aging spectrum comprising at least said set of pairs of values; and - a comparison unit (10) configured to perform, from at least said temperature aging spectrum, comparisons to carry out at least one diagnosis. Method for assisting in the adaptation of equipment to future thermal constraints, characterized in that it comprises at least the following operations: - carrying out a diagnosis relating to the equipment (2A, 2B) at one or more geographical locations where it is expected to be used, by implementing the process (P) according to any one of claims 1 to 13 and using a characteristic time associated with the type of said equipment (2A, 2B); and - a design of the equipment which is adapted to the result of this diagnosis.

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