Acoustic emission technology-based method for characterizing damage of composite material for molten salt reactor at high temperature

Abstract

The invention discloses a high-temperature damage in-situ characterization method for a composite material for a molten salt reactor based on an acoustic emission technology, and relates to the field of damage characterization of the composite material for the molten salt reactor, and the method comprises the following steps: preparing a C / C composite material under an approximate molten salt reactor working condition; stretching the prepared C / C composite material to obtain a time-stress curve in the stretching process; controlling a laser spot to completely cover the stretching section, and collecting the change condition of an acoustic emission signal; and after the change condition of the acoustic emission signal is correlated with the time-stress curve, judging and representing the change of the internal microstructure of the C / C composite material before and after molten salt infiltration according to a correlation result. According to the method, the internal damage of composite material components with different scales and different shapes in the performance evaluation stage before service under the working condition of the molten salt reactor can be effectively monitored, and the change of the internal microstructure of the material can be analyzed by combining the change of the characteristic frequency of the acoustic emission signal with the tensile curve, so that the method has important engineering practical significance.

Description

Technical Field

[0001] The present invention relates to the field of damage characterization of composite materials for molten salt reactors, and more particularly, to a method for characterizing the damage of composite materials for molten salt reactors at high temperatures based on acoustic emission technology. Background Art

[0002] The molten salt reactor is one of the six types of fourth-generation nuclear reactors, which uses molten salt as the fuel carrier and coolant. It has been increasingly favored from the perspectives of improving thermal utilization efficiency, realizing the nuclear energy utilization of thorium resources, fuel reprocessing, and inherent safety. In the molten salt reactor, materials are in harsh service environments such as high temperature, molten salt corrosion, and neutron irradiation. To further increase the temperature and energy efficiency of the molten salt reactor, it is necessary to develop new materials and their components that can work in the molten salt reactor environment.

[0003] Carbon fiber reinforced carbon matrix composites (referred to as C / C composites) are composed of carbon fibers or their fabrics as the reinforcement phase, and pyrolytic carbon infiltrated by chemical vapor or resin or pitch impregnated and graphitized by chemical liquid phase as the matrix. This material has the advantages of high tensile strength, high tensile elastic modulus, large specific strength, low coefficient of thermal expansion, excellent thermal shock resistance, corrosion resistance, fracture toughness, and creep resistance. The Oak Ridge National Laboratory (ORNL) in the United States has carried out systematic research on the application of C / C composites in nuclear energy systems and tested the high-temperature control rods made of graphite and C / C composites by General Atomics, believing that C / C composites are the preferred materials for manufacturing control rods. The Shanghai Institute of Applied Physics, Chinese Academy of Sciences, has carried out the design and experimental reactor construction of the thorium-based molten salt reactor (TSMR), and regarded composite materials as candidate materials for high-temperature reactor types. For the functional structure integrated components of molten salt reactors, it is very important to find a suitable monitoring method to monitor the material performance throughout the life cycle before service. Traditional non-destructive testing techniques (such as micro-CT and ultrasonic flaw detection) are limited by the poor transmissibility of molten salt media and insufficient adaptability to high-temperature environments (the upper limit of the detection temperature < 500 °C), and cannot achieve in-situ dynamic monitoring during service. At the same time, due to the complex internal fiber and matrix tissue structure of C / C composites, the mechanism of microstructural changes in C / C composites after molten salt infiltration is not yet clear.

[0004] As a new non-destructive testing technology, acoustic emission technology can quickly and real-time monitor the damage type and location of C / C composites, with high sensitivity and a large detection range. Current research gap: There is no research on the change of acoustic emission signals of C / C composites after molten salt infiltration. Therefore, the research on damage characterization based on acoustic emission technology has important scientific significance and engineering value for the application of C / C composites in molten salt reactors. Summary of the Invention

[0005] To solve the above problems, the object of the present invention is to provide a technology for characterizing the damage of composite materials for molten salt reactors at high temperatures based on acoustic emission technology, aiming to achieve in-situ monitoring of the characteristic frequency changes of acoustic emission signals of various types of internal damage during the tensile process of C / C composite materials under molten salt.

[0006] To achieve the above technical object, the present application provides a method for characterizing the damage of composite materials for molten salt reactors at high temperatures based on acoustic emission technology, including the following steps:

[0007] Prepare C / C composite materials under conditions approximating those of molten salt reactors;

[0008] Tensile the prepared C / C composite materials to obtain a time-stress curve during the tensile process;

[0009] Control the laser spot to completely cover the tensile section and collect the changes in acoustic emission signals;

[0010] After correlating the changes in acoustic emission signals with the time-stress curve, based on the correlation results, judge and characterize the changes in the internal microstructure of C / C composite materials before and after molten salt infiltration.

[0011] Preferably, during the process of obtaining C / C composite materials under conditions approximating those of molten salt reactors, infiltrate the C / C composite materials in molten salt at 650 °C and 0.3 MPa for 1 hour to obtain C / C composite materials under conditions approximating those of molten salt reactors.

[0012] Preferably, when obtaining the changes in acoustic emission signals, collect the changes in acoustic emission signals through an acoustic emission signal acquisition system, wherein the acoustic emission signal acquisition system includes a platinum metal waveguide rod, an acoustic emission signal detector, an acoustic emission signal amplifier, and an acoustic emission signal memory.

[0013] Preferably, when using the acoustic emission signal acquisition system, evenly apply vaseline on the ceramic surface on the front of the acoustic emission signal detector to ensure that the acoustic emission signal detector is completely fitted with the platinum metal waveguide rod without gaps to reduce the influence of noise, and fix the acoustic emission signal detector to the platinum metal waveguide rod with raw tape.

[0014] Preferably, when using the acoustic emission signal acquisition system, set the parameters of the acoustic emission signal collector as threshold 10 mV, impact discrimination time 2000 μs, impact lockout time 2000 μs, peak discrimination time 500 μs, and the gain of the preamplifier is 40 dB, wherein the universal testing machine for tensile testing of C / C composite materials runs synchronously with the acoustic emission signal acquisition system.

[0015] Preferably, when collecting the change of acoustic emission signals, an acoustic emission signal acquisition system is used to record in real time the acoustic emission signals monitored by an acoustic emission detector. The acoustic emission signals include peak frequency signals, quantity signals, and energy signals.

[0016] Preferably, when characterizing the change of the internal microstructure of C / C composites before and after molten salt infiltration, the damage types and damage locations of internal damage during the stress application process of composites with different scales and shapes are judged and characterized.

[0017] Preferably, when characterizing the change of the internal microstructure of C / C composites before and after molten salt infiltration, the stress application process of the composites includes tensile, compressive, and creep processes.

[0018] Preferably, a high-temperature damage characterization system for composites used in molten salt reactors for the high-temperature damage characterization method of composites used in molten salt reactors includes:

[0019] A material preparation module for preparing C / C composites under conditions approximating those of molten salt reactors;

[0020] A material tensile module for tensile testing of the prepared C / C composites to obtain a time-stress curve during the tensile process;

[0021] A data acquisition and control module for controlling the laser spot to completely cover the tensile section and collecting the change of acoustic emission signals;

[0022] A judgment and characterization module for correlating the change of acoustic emission signals with the time-stress curve and then judging and characterizing the change of the internal microstructure of C / C composites before and after molten salt infiltration according to the correlation result.

[0023] Preferably, the material tensile module is a CMT6104 microcomputer-controlled electronic universal testing machine.

[0024] The present invention discloses the following technical effects:

[0025] The present invention can effectively monitor the damage types and damage locations of internal damage during the stress application process of composites with different scales and shapes, such as tensile, compressive, and creep processes, in a high-temperature environment, which has important engineering practical significance.

[0026] The present invention can analyze the change of the internal microstructure of materials by combining the change of the characteristic frequency of acoustic emission signals with the tensile curve. Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0028] Figure 1 It is a flowchart of the method for in-situ high-temperature damage characterization of composite materials for molten salt reactors based on acoustic emission technology according to the present invention;

[0029] Figure 2 It is a schematic diagram of the device for realizing the method for in-situ high-temperature damage characterization of composite materials for molten salt reactors. Among them, 1 represents a laser heater, 2 represents a CMT6104 microcomputer-controlled electronic universal testing machine, 3 represents a C / C composite material after molten salt infiltration treatment, 4 represents a platinum metal waveguide rod, 5 represents an acoustic emission signal detector, 6 represents a signal amplifier, 7 represents a signal collector, and 8 represents an industrial computer. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Usually, the components of the embodiments of the present application described and marked in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application required to be protected, but only represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0031] As Figure 1-2 shown, the present invention discloses a method for in-situ high-temperature damage characterization of composite materials for molten salt reactors based on acoustic emission technology. First, the C / C composite material is infiltrated in molten salt at 650 °C and 0.3 MPa for 1 hour to obtain a C / C composite material under approximate molten salt reactor conditions. Then, the acoustic emission signal test platform is used to test the changes in the characteristic frequencies of various internal damage acoustic emission signals of the C / C composite material before and after molten salt infiltration during the tensile process. The specific steps are as follows:

[0032] 1. An acoustic emission signal monitoring experimental platform was built to monitor various damages during the tensile process of C / C composites after molten salt infiltration in a high-temperature environment. The acoustic emission signal monitoring experimental platform includes a CMT6104 microcomputer-controlled electronic universal testing machine, a laser heater, an acoustic emission signal acquisition system, and a signal processing workstation. The acoustic emission signal acquisition system includes a platinum metal waveguide rod, an acoustic emission signal detector, an acoustic emission signal amplifier, and an acoustic emission signal memory.

[0033] 2. Place the acoustic emission signal detector at the center of the specimen: Apply vaseline evenly on the ceramic surface of the front of the acoustic emission signal detector to ensure that the acoustic emission signal detector fits perfectly with the platinum metal waveguide rod without gaps to reduce noise interference, and fix the acoustic emission signal detector to the platinum metal waveguide rod with raw tape.

[0034] 3. Set the parameters of the acoustic emission signal collector as follows: threshold 10 mV, impact discrimination time 2000 μs, impact lockout time 2000 μs, peak discrimination time 500 μs, and the gain of the preamplifier is 40 dB. Set the trigger mode as manual trigger. To prevent the missing of acoustic emission signals or the influence of useless ambient signals on the acoustic emission test results, the universal testing machine and the acoustic emission signal acquisition system need to click the start working button simultaneously to start at the same time.

[0035] 4. Start the laser heater, and the laser spot needs to completely cover the tensile section of the specimen to be tested.

[0036] 5. During the test, use the acoustic emission signal acquisition system to record the acoustic emission signals monitored by the acoustic emission detector in real time. The acoustic emission signals include peak frequency signals, quantity signals, and energy signals.

[0037] 6. Relate the change of the acoustic emission signal to the time-stress curve obtained during the tensile process, and judge the change of the internal microstructure of the C / C composite before and after molten salt infiltration according to the change of the acoustic emission signal.

[0038] As Figure 2 mentioned in the schematic diagram of the device, it specifically includes the following designs: 1. The model of the laser heating device is FS-10-100LD, and the variable range of the light spot is 10x10 - 100x1001mm 2 , and the built-in temperature control system can achieve a temperature detection range that always remains consistent with the size of the light spot.

[0039] 2. The CMT6104 microcomputer-controlled electronic universal testing machine is mainly used for the mechanical property test and analysis research of non-metallic materials such as tensile, compression, and bending. It has three closed-loop control modes of stress, strain, and displacement, and can calculate parameters such as maximum force, tensile strength, bending strength, compression strength, elastic modulus, fracture elongation, and yield strength.

[0040] 3. It is the test sample of the C / C composite material to be measured, with variable shape and size;

[0041] 4. The platinum metal waveguide rod is made of platinum metal and can work in a high-temperature environment of 1000 °C, conducting the acoustic emission signal inside the specimen to the acoustic emission detector;

[0042] 5. The acoustic emission signal detector, model RS-5A, can collect acoustic emission signals in the frequency range of 50KHz - 800KHz;

[0043] 6. The signal amplifier is a 20 / 40 / 60dB gain adjustable amplifier, which can amplify the signal by 10 / 100 / 1000 times and is used to amplify tiny acoustic emission signals;

[0044] 7. The signal collector is a DS128 high-speed data acquisition instrument, which collects acoustic emission signals at a sampling speed of 500kHz per channel, connects to the corresponding sensors, can monitor various parameters such as strain, pressure, temperature, vibration, displacement, voltage, and current in real time, and records and saves complete waveform data;

[0045] 8. The industrial computer is a OptiPlex tower model with a running memory of 16GB and is used for acoustic emission signal data processing operations.

[0046] The present invention can effectively monitor the internal damage during the performance evaluation stage of composite material components with different scales and shapes under the working conditions of molten salt reactors, and can analyze the changes in the internal microstructure of materials by combining the changes in the characteristic frequencies of acoustic emission signals with the tensile curve, which has important engineering practical significance.

[0047] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the specified functions in one Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0048] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0049] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A damage characterization method for composite materials for molten salt reactors at high temperatures based on acoustic emission technology, characterized in that: The following steps are involved: Preparation of C / C composite materials under conditions similar to molten salt reactor; Stretching the prepared C / C composite material to obtain a time-stress curve during the stretching process; The laser spot must be controlled to completely cover the stretching section, and the changes in the acoustic emission signal must be collected; After correlating the change of the acoustic emission signal with the time-stress curve, the change of the internal microstructure of the C / C composite material before and after molten salt infiltration is judged and characterized according to the correlation result.

2. According to claim 1, the damage characterization method for composite materials for molten salt reactors at high temperature based on acoustic emission technology is characterized by: In the process of obtaining the C / C composite material under the condition approximating the molten salt reactor, the C / C composite material is infiltrated in a molten salt at 650° C. and 0.3 MPa for 1 hour to obtain the C / C composite material under the condition approximating the molten salt reactor.

3. According to claim 2, the method for characterizing damage of composite materials for molten salt reactors at high temperatures based on acoustic emission technology is characterized in that: When obtaining the change of the acoustic emission signal, the change of the acoustic emission signal is collected through the acoustic emission signal collection system, wherein the acoustic emission signal collection system includes a platinum metal waveguide rod, an acoustic emission signal detector, an acoustic emission signal amplifier and an acoustic emission signal storage.

4. The damage characterization method for composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to claim 3 is characterized in that: When using the acoustic emission signal acquisition system, apply Vaseline evenly on the ceramic surface on the front of the acoustic emission signal detector to ensure that the acoustic emission signal detector and the platinum metal waveguide rod are completely fitted without gaps to reduce the impact of noise, and use raw tape to fix the acoustic emission signal detector to the platinum metal waveguide rod.

5. The damage characterization method for composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to claim 4 is characterized in that: When using the acoustic emission signal acquisition system, the acoustic emission signal acquisition parameters are set to a threshold of 10 mV, an impact identification time of 2000 μs, an impact lock time of 2000 μs, a peak identification time of 500 μs, and a gain of the preamplifier of 40 dB, wherein a universal testing machine for stretching C / C composite materials runs synchronously with the acoustic emission signal acquisition system.

6. The damage characterization method for composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to claim 5 is characterized in that: When collecting changes in the acoustic emission signal, the acoustic emission signal acquisition system is used to record in real time the acoustic emission signal monitored by the acoustic emission detector, wherein the acoustic emission signal includes a peak frequency signal, a quantity signal, and an energy signal.

7. The damage characterization method for composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to claim 6 is characterized in that: When characterizing the changes in the internal microstructure of C / C composites before and after molten salt infiltration, the damage type and damage location of the internal damage during the stress process of composite materials of different scales and shapes are judged and characterized.

8. The method for characterizing damage of composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to claim 7, characterized in that: When characterizing the changes in the internal microstructure of C / C composites before and after molten salt infiltration, the stress process of the composite material includes tension, compression, and creep processes.

9. The damage characterization method for composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to any one of claims 1 to 8, characterized in that: The damage characterization system for composite materials used in molten salt reactors at high temperatures is used for the damage characterization method of composite materials used in molten salt reactors at high temperatures, including: Material preparation module, used to prepare C / C composite materials under conditions similar to molten salt reactor; A material stretching module is used to stretch the prepared C / C composite material and obtain the time-stress curve during the stretching process; Data acquisition and control module, used to control the laser spot to completely cover the stretching section and collect changes in acoustic emission signals; The judgment and characterization module is used to correlate the change of the acoustic emission signal with the time-stress curve, and then judge and characterize the change of the internal microstructure of the C / C composite material before and after molten salt infiltration according to the correlation result.

10. The method for characterizing damage of composite materials for molten salt reactors at high temperatures based on acoustic emission technology according to claim 9, characterized in that: The material stretching module is a CMT6104 microcomputer-controlled electronic universal testing machine.

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