Sensor for in situ measurement of the ablation of a material surface and the amount of recession of the front of a carbonized layer

Abstract

This invention discloses a sensor for in-situ measurement of the ablation and carbonization layer front-receding amount of a material surface. The sensor includes an optical fiber surface receding measurement unit and a resistive carbonization depth measurement unit. The optical fiber surface receding measurement unit comprises a core rod and multiple optical fibers embedded in the core rod, distributed along the core rod axis and corresponding to different preset burial depths in a stepped manner. The resistive carbonization depth measurement unit comprises an inner polymer sheet, an outer polymer sheet, and a resistance wire, with the resistance wire encapsulated between the inner and outer polymer sheets. The optical fiber surface receding measurement unit is enclosed within the resistive carbonization depth measurement unit, forming an integrated probe structure. This sensor, benefiting from the designability of the number and position of the optical fibers, can not only accurately capture the ablation amount of the material but also meet specific ablation prediction requirements according to specific application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of ablation monitoring and sensing technology, and relates to an ablation sensor for high-temperature ablation environments, specifically a sensor that can simultaneously measure the ablation retreat of the material surface and the retreat of the carbonization front of the material interior. Background Technology

[0002] To ensure a spacecraft can successfully complete its mission, thermal protection systems often require excessively high safety margins to guarantee structural integrity and effective thermal protection, especially when aerodynamic conditions are difficult to accurately predict. However, more redundant thermal protection designs mean lower payload capacity. Accurately assessing the ablation retreat performance of materials is crucial for designing efficient thermal protection systems, with in-situ ablation measurements serving as a vital basis for evaluating material properties. Furthermore, such measurements are significant for obtaining the ablation thermal flow field on the spacecraft surface and verifying the effectiveness of computational models.

[0003] Under harsh aerodynamic heating environments, ablation-resistant heat-resistant materials undergo complex physicochemical changes, including thermochemical reactions between the surface material and the airflow, melting, sublimation, and mechanical ablation, as well as mass loss of internal materials due to thermochemical reactions, accompanied by the formation of a carbonized layer. Therefore, the ablation process is essentially accompanied by the evolution of two moving boundaries: the material surface and the carbonized layer interface. However, existing testing methods (such as melting point methods, radiometric methods, and electrical resistance methods) often struggle to simultaneously achieve continuous, high-precision measurements of these two interfaces.

[0004] Therefore, in order to meet the measurement requirements of ablation amount of ablation material during spacecraft reentry, it is of great significance to invent a high-precision ablation sensor that can simultaneously measure the surface ablation retreat and the carbonization layer front retreat. Summary of the Invention

[0005] This invention provides a sensor for in-situ measurement of the ablation and carbonization layer frontal retreat of a material surface. Thanks to the designability of the number and position of optical fibers, this sensor can not only accurately capture the ablation amount of the material, but also meet specific ablation amount prediction requirements according to specific application scenarios.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A sensor for in-situ measurement of the ablation and carbonization layer front-edge recession of a material surface includes an optical fiber surface recession measurement unit and a resistive carbonization depth measurement unit, wherein:

[0008] The optical fiber surface retraction measurement unit includes a core rod and multiple optical fibers embedded in the core rod. The optical fibers are distributed along the axis of the core rod and correspond to different preset burial depths, forming a stepped shape.

[0009] The resistive carbonization depth measurement unit includes an inner polymer sheet, an outer polymer sheet, and a resistance wire, with the resistance wire encapsulated between the inner and outer polymer sheets.

[0010] The optical fiber surface retraction measurement unit is wrapped in the middle by the resistive carbonization depth measurement unit, forming an integrated probe structure.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. Existing sensors can only acquire single ablation data. This invention can simultaneously measure the surface ablation retreat of the ablated material and the retreat of the carbonized layer front.

[0013] 2. It adopts a miniaturized design, with the overall diameter of the sensor being approximately 4 mm, which can effectively reduce the heat intrusion of the sensor during its service life.

[0014] 3. It has high measurement accuracy. The measurement error of the fiber optic surface retraction measurement unit can be kept within 10%, and the measurement error of the resistive carbonization depth measurement unit can also be kept within 10% by adjusting the number of optical fibers. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the fiber optic surface retraction measurement unit;

[0016] Figure 2 This is a schematic diagram of the resistive carbonization depth measurement unit.

[0017] Figure 3 This is a schematic diagram of the overall structure of the sensor. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0019] This invention provides a sensor for in-situ measurement of the ablation and carbonization layer front-edge retreat of a material surface. The sensor is an embedded sensor, which is entirely embedded inside an ablation insulation material. It consists of two relatively independent parts: an optical fiber surface retreat measurement unit and a resistive carbonization depth measurement unit. The optical fiber surface retreat measurement unit includes a core rod made of ablation material and multiple optical fibers embedded along the axial direction of the core rod, with the probe tips of the multiple optical fibers located at different preset depths along the longitudinal direction of the core rod. The resistive carbonization depth measurement unit has a thin-film structure, including two layers of insulating polymer sheets that can carbonize and conduct electricity at high temperatures, and resistance wires etched on the polymer sheets. The optical fiber surface retreat measurement unit is wrapped in the resistive carbonization depth measurement unit, forming an integrated probe structure. In terms of manufacturing, the two parts can be prepared separately and then assembled.

[0020] In this invention, multiple micro-grooves parallel to the axis are formed on the cylindrical surface of the core rod, and multiple optical fibers are placed in the micro-grooves respectively and fixed by filling material so that the optical fibers and the core rod form a solid whole.

[0021] In this invention, the mandrel and filling material are made of the heat-resistant material to be tested, in order to match the ablation characteristics of the heat-resistant material to be tested.

[0022] In this invention, the optical fiber is made of quartz and is used to transmit the thermal radiation signal received at its tip. When the ablated surface retreats to the tip of a certain optical fiber, the light intensity signal output by the optical fiber drops sharply, which serves as the basis for determining whether the surface has reached that depth.

[0023] In this invention, the resistance wire is made of an alloy material with a low temperature coefficient of resistance; the resistance wire is arranged in an "S" shape between two layers of insulating polymer sheets.

[0024] In this invention, the insulating polymer sheet is a polyimide sheet; during the ablation process, as the carbonized layer advances deeper, the polyimide sheet carbonizes and becomes a conductor in the carbonized area, thereby short-circuiting part of the resistance wire. The amount of retreat of the carbonized layer front is calculated by measuring the change in the total resistance of the resistance wire.

[0025] In this invention, the resistive carbonization depth measuring unit comprises, from the inside out: an inner polyimide sheet, a resistance wire layer etched on the inner sheet, and an outer polyimide insulating layer covering the resistance wire; the resistance wire is encapsulated between the two polyimide sheets.

[0026] In this invention, the tip position of the optical fiber is non-uniformly distributed, for example: 1 mm, 2 mm, 3 mm, 4 mm, 6 mm, 10 mm, so as to realize discrete point measurement of the surface ablation retreat rate.

[0027] In this invention, the overall diameter of the integrated probe structure of the sensor is less than 4 mm, and the diameter of the core rod is approximately 3 mm.

[0028] In this invention, the working principle of the optical fiber surface retraction measurement unit is as follows:

[0029] 1. A micro-groove is made axially on the surface of the sensor core rod, and multiple optical fibers for transmitting optical signals are embedded in the micro-groove.

[0030] 2. The detection tips of each optical fiber are distributed in a stepped manner along the axis of the core rod, each corresponding to a different preset depth.

[0031] 3. In the initial state, the fiber tip is completely covered by the core rod and filling material, and is in a light-blocking state, so the output signal is a low horizontal line.

[0032] 4. When the sensor is ablated and retreats along with the heat-resistant material under the scouring of high-temperature airflow, the shielding material on the surface of the core rod is gradually consumed.

[0033] 5. When the ablation front advances to a certain fiber tip position, the shielding layer disappears, and the external high-intensity radiation light instantly enters the fiber, causing a step change in the probe light intensity signal.

[0034] 6. Process the signals collected by the detector, extract the time when the light intensity signal of each fiber changes abruptly, and then calculate the process and rate of surface ablation retreat.

[0035] The working principle of the resistive carbonization depth measurement unit in this invention is as follows:

[0036] 1. Two layers of polyimide sheets are set in the sensor body, one inside and one outside.

[0037] 2. Etch continuous KM alloy resistance wires on the inner polyimide sheet, and then cover it with the outer polyimide sheet.

[0038] 3. The resistance wire is in an open circuit or high-resistance state with respect to the external circuit at room temperature.

[0039] 4. When the thermal insulation material undergoes pyrolysis under high-temperature aerodynamic load, the polyimide gradually carbonizes, and the carbonized products generated by thermal decomposition have high electrical conductivity.

[0040] 5. When the carbonization front advances to the location of the resistance wire, a new conductive path is formed through the carbonization layer, causing the sensor circuit to close or its overall resistance to decrease significantly.

[0041] Example:

[0042] The ablation measurement system in this embodiment is embedded inside the ablation insulation material and consists of an optical fiber surface retreat measurement unit and a resistance carbonization depth measurement unit. When a high-temperature airflow or arc-heated wind tunnel heat flow acts on the surface of the specimen, the surface of the insulation material is ablated and gradually retreats inward. At the same time, the internal resin matrix gradually transforms from an uncarbonized area to a conductive carbonized area, thereby forming two moving interfaces in the material: the surface ablation front and the carbonization layer front.

[0043] 1. Working principle and data processing of the fiber optic surface retraction measurement unit:

[0044] The optical fiber surface retraction measurement unit consists of two parts: the core material and the optical fiber. The specific fabrication steps are as follows:

[0045] Step 1: The fiber optic surface retraction measurement unit uses a core rod of the same material as the material being measured as a carrier and is processed using a CNC machine tool to produce a core rod with a diameter of 30 mm.

[0046] Step 2: Machining several parallel grooves along the axial direction on the sidewall of the core rod, and embedding multiple optical fibers in the grooves, so that the end faces of each optical fiber are located at different burial depths. (Such as 1 mm, 2 mm, 3 mm, 4 mm, 6 mm, 10 mm, etc.).

[0047] The working principle of the fiber optic surface retraction measurement unit is as follows:

[0048] The fiber optic head can receive radiation signals from the surrounding environment and transmit them to the fiber optic tail. The radiation signals are then connected to the data acquisition system via photodetectors and amplification circuits, forming a multi-point radiation signal channel.

[0049] For any depth of fiber optic channel, the photodiode in time upper output current The current and the fiber optic outlet are in the same band. The integral of the radiation intensity within is proportional to the total radiation intensity, and can be expressed as:

[0050]

[0051] in, The spectral radiation intensity at the end of the optical fiber. For the spectral response of silicon photodiodes, The conversion factor is determined by factors such as the numerical aperture of the optical fiber and the effective light-receiving area.

[0052] As the ablation surface gradually recedes, the material covering the fiber head gradually thins, increasing the spectral radiation intensity at the fiber tail and ultimately leading to an increase in output current. When the ablation surface recedes to the fiber head, the exposed fiber is physically broken or completely burned by the high-temperature airflow, interrupting the optical path and causing the current to drop back to 0 instantly.

[0053] As the ablation front approaches, the signal rises sharply from zero to a peak, then drops precipitously back to zero due to fiber optic cable breakage. This is displayed as a sharp peak on the image; the location of the peak is used to determine the moment when the ablated surface reaches the fiber. .

[0054] In actual testing, the output current is sampled at a fixed interval. Discrete acquisition. To suppress noise, this invention first discards the data from the first 5 seconds after heating begins, treating this as the noise range.

[0055] 2. Working principle and calculation of the resistance-type carbonization depth measurement unit

[0056] The resistance-type carbonization depth measurement unit is designed based on the principle of resistance method. During the ablation process, the material being tested forms a conductive carbonization layer and establishes electrical contact with the resistance wire. As the ablation proceeds, the leading edge of the carbonization layer retreats, and the effective circuit of the connected circuit becomes shorter. By monitoring the change in the resistance of the resistance wire, the position of the leading edge of the carbonization layer and its retreat process can be reflected.

[0057] The resistance-type carbonization depth measurement unit consists of a core material, a resistance wire, and an insulating material. The specific preparation steps are as follows:

[0058] Step 1: Use laser etching to remove Fe 70 Cr 25 Al5 thin films are etched into the designed circuit. Two polyimide thin films are thermo-pressed together using a thin film thermo-pressing technique in a manner of "polyimide thin film - etched circuit - polyimide thin film" to form a flexible resistor sheet.

[0059] Step 2: The fiber optic surface retraction measurement unit serves as the core material for the resistive carbonization depth measurement unit. The core material is placed on the back of the flexible resistive sheet, and the flexible resistive sheet is wrapped around the core material using adhesive.

[0060] The working principle of the resistance-type carbonization depth measurement unit is as follows:

[0061] Step 1: Calibrate the resistance per unit length of the resistance-type carbonization depth measurement unit. (Unit: Ω / mm) and the circuit resistance in the initial uncarbonized state. Two wires are led out from the end of the sensor, and the total resistance of the wires is measured. .

[0062] Step 2: Apply a constant excitation current across both ends (For example, 1~2mA) Measure at any time The loop voltage is According to Ohm's law, the instantaneous resistance can be obtained as follows:

[0063]

[0064] The resistance of the entire circuit is:

[0065]

[0066] In the formula, This represents the resistance of the carbonized layer between two wires. This represents the remaining effective circuit length, and is the equivalent carbonization layer front retreat amount corresponding to the advancement of the carbonization front. It can be represented as:

[0067]

[0068] In the formula, That is, the resistance drop corresponding to the resistance length short-circuited by the carbonized layer. This represents the initial length of the effective circuit.

[0069] definition The carbonization rate at time is:

[0070]

[0071] In the formula: express The rate at which the carbonized layer recedes at any given moment. This indicates the amount of retreat of the carbonized layer front at a given moment.

[0072] 3. Comprehensive Judgment and Application

[0073] Using the above algorithm, this invention can simultaneously obtain: the surface ablation retreat arrival time at several discrete depth points. ablation rate between adjacent measuring points The curve of the retreat of the carbonized layer front over time and its propulsion rate .

[0074] By comparing and analyzing the two, the kinetic characteristics of surface ablation and internal carbonization of materials can be obtained under the same thermal environment, providing basic data for the evaluation of the thermal protection performance of insulation materials and the calibration of numerical models.

Claims

1. A sensor for in-situ measurement of the ablation and carbonization layer frontal retreat of a material surface, characterized in that... The sensor includes an optical fiber surface retraction measurement unit and a resistive carbonization depth measurement unit, wherein: The optical fiber surface retraction measurement unit includes a core rod and multiple optical fibers embedded in the core rod. The optical fibers are distributed along the axis of the core rod and correspond to different preset burial depths, forming a stepped shape. The resistive carbonization depth measurement unit includes an inner polymer sheet, an outer polymer sheet, and a resistance wire, with the resistance wire encapsulated between the inner and outer polymer sheets. The optical fiber surface retraction measurement unit is wrapped in the middle by the resistive carbonization depth measurement unit, forming an integrated probe structure.

2. The sensor for in-situ measurement of the ablation and carbonization layer frontal retreat of a material surface according to claim 1, characterized in that... The cylindrical surface of the core rod has multiple micro-grooves parallel to the axis. Multiple optical fibers are placed in the micro-grooves and fixed by filling material, so that the optical fibers and the core rod form a solid whole.

3. The sensor for in-situ measurement of the ablation and carbonization layer frontal retreat of a material surface according to claim 2, characterized in that... The mandrel and filling material are made of the heat-resistant material to be tested.

4. The sensor for in-situ measurement of the ablation and carbonization frontal retreat of a material surface according to claim 1 or 2, characterized in that... The optical fiber is made of quartz.

5. The sensor for in-situ measurement of the ablation and carbonization layer frontal retreat of a material surface according to claim 1, characterized in that... The resistance wires are arranged in an "S" shape and are closely packed between two layers of insulating polymer sheets.

6. The sensor for in-situ measurement of the ablation and carbonization frontal retreat of a material surface according to claim 1 or 5, characterized in that... The resistance wire is made of an alloy material with a low temperature coefficient of resistance.

7. The sensor for in-situ measurement of the ablation and carbonization frontal retreat of a material surface according to claim 1 or 5, characterized in that... The insulating polymer sheet is a polyimide sheet.

8. The sensor for in-situ measurement of the ablation and carbonization frontal retreat of a material surface according to claim 7, characterized in that... The resistive carbonization depth measurement unit comprises, from the inside out: an inner polyimide sheet, a resistance wire layer etched on the inner sheet, and an outer polyimide insulating layer covering the resistance wire; the resistance wire is encapsulated between the two polyimide sheets.

9. The sensor for in-situ measurement of the ablation and carbonization frontal retreat of a material surface according to claim 1, characterized in that... The sensor's integrated probe structure has an overall diameter of less than 4 mm, with the core rod having a diameter of 3 mm.

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