Low temperature-operating load coupling test method for load-bearing structures and materials of high-altitude / polar equipment

Abstract

The present invention discloses a method for testing the load-bearing structure of high-cold / polar equipment and its materials under low-temperature-working-condition load coupling, and the steps include: determining the test spectrum of the test object, determining the test parameters, including the test temperature, the duration of low-temperature exposure, the number of fatigue cycle loading, and the interactive cycle period, and conducting the test according to the determined test parameters and test spectrum. The scheme of the present invention can fully and truly reflect the actual environmental damage history of the high-cold or polar equipment structure and its materials, can truly simulate and reproduce the synergistic effect of the low-temperature environment and low-temperature fatigue during the alternating process of "ground parking + mission execution", accelerate the equipment structure damage process, and facilitate the evaluation of the influence of simple low temperature and low-temperature-low-temperature fatigue coupling on the mechanical properties of the sample.

Description

Technical Field

[0001] The present invention belongs to the technical field of simulated environmental testing of load-bearing structures of high-altitude and cold (abbreviated as high-altitude and cold) or polar equipment, and specifically relates to a low-temperature-operating load coupling testing method for a load-bearing structure of high-altitude and cold / polar equipment and its materials. Background Art

[0002] The load-bearing structures of ground equipment in service in high-cold areas or polar regions will not only encounter the long-term cumulative effects of low temperatures of (-90 to 0)°C, but will also be subjected to the interaction or synergy of fatigue, impact, vibration and other working loads. In particular, low temperatures (the actual ambient temperature may be as low as -50°C to 70°C) increase the tendency of brittle fracture of metal materials. In addition, the coupling effect of loads causes the strength of metal materials to increase and the plasticity to decrease, often resulting in sudden damage and failure of structural parts when the actual working stress is far lower than the design allowable value. According to surveys, fracture damage caused by fatigue alternating loads in engineering structures accounts for 50% to 90% of all mechanical damage, and is the main form of structural failure.

[0003] The use of existing national or industry standards for testing and assessment, such as GJB 150.4A "Laboratory Environmental Test Methods for Military Equipment Part 4: Low Temperature Test", GB / T 3075 "Axial Force Control Method for Fatigue Test of Metallic Materials", HB 5287 "Axial Loading Fatigue Test Method for Metallic Materials" and other related test methods, can no longer meet the comprehensive assessment test requirements of the load-bearing structures and materials of this type of equipment at low temperature performance, and cannot fully and truly reflect the actual environmental damage history of equipment structures and materials, and cannot truly reflect the low-temperature environmental damage history of metal structures. If the aforementioned existing test methods and their results are used for low-temperature environment adaptability design, it will pose a hidden danger to the safe use of metal structures. Summary of the invention

[0004] At least in view of the problems mentioned in the background technology, the purpose of the present invention is to provide a low-temperature-operating load coupling test method for the load-bearing structure of high-altitude / polar equipment and its materials.

[0005] The present invention adopts the following technical solution.

[0006] A method for testing a load-bearing structure of high-cold / polar equipment and its materials under low-temperature-operating load coupling conditions, comprising the following steps: Step 1: Determine the test spectrum of the test subject (1) For structures or materials used in high-altitude cold regions, the test spectrum is: S11, conduct a normal temperature dynamic load test on the test object; S12, perform n cycles in the manner of “first conduct low temperature static exposure test → then conduct low temperature dynamic load test”, where n is an integer; S13, perform N cycles in the manner of "step S11 → step S12 → step S11", where N is an integer, and perform sampling and testing in the middle until the test is completed; (2) For structures or materials used in polar regions, the test spectrum is: S21, conduct low temperature static exposure test on the test object, S22, conduct low temperature dynamic load test on the test object, S23, perform N cycles in the manner of "step S21 → step S22", taking samples for testing in between, until the test is completed. Step 2, determine the test parameters, including: Test temperature: For metal structures or materials used in high-altitude cold regions of my country, the recommended test temperature is -43°C; for metal structures or materials used in polar regions, the recommended test temperature is -57°C; and the test temperature should meet the requirements of "the test temperature should not be lower than the ductile-brittle transition temperature of the test material; when the ductile-brittle transition temperature of the test material is higher than the recommended value, the test temperature should be determined based on the principle (method) of ductile-brittle transition temperature + 10°C"; Duration of low temperature exposure: 4 hours for the first cycle and 1 hour for the subsequent cycles; Fatigue cycle loading times: For the same batch of specimens, the test should be carried out under the same fatigue stress level, and 5000, 10000 or 20000 loading cycles should be selected for each cycle; Interactive cycle period: The recommended low-temperature-low-temperature fatigue interactive cycle period is 5 to 10 cycles. Step 3: Conduct the test according to the determined test parameters and test spectrum.

[0007] In order to more accurately reflect the actual environmental damage history of the equipment structure and its materials, the total low temperature static exposure time t is determined as follows: 总 , Step 101, obtaining the low temperature cumulative index A of the test area according to formula (1); Where: A represents the low temperature accumulation index, ℃·h; T 均 represents the average daily temperature in winter in the test area, ℃; t c represents the number of hours per day below the critical temperature (0°C), h; N represents the expected winter use time of the test object, d; Step 102: Obtain the total low temperature static exposure time t of the test object according to formula (2): 总 ;

[0008] As a preferred solution, the fatigue load spectrum of equal amplitude is used for testing; the fatigue stress is determined according to the following method: at room temperature, the tensile strength and elongation of the standard specimen are obtained by static tensile test; a preliminary test is carried out at 50% or 60% of the tensile strength, and the stress ratio is 0.1, so that the fatigue life is within (5×10 4 ~10 5 ), 5×10 5 , 10 6 About times of cycles are performed to determine the three fatigue stress levels: high, medium and low.

[0009] Beneficial effects: The scheme of the present invention can fully and truly reflect the actual environmental damage history of high-cold or polar equipment structures and their materials, can truly simulate and reproduce the synergistic effect of low-temperature environment and low-temperature fatigue during the alternating process of "ground parking + mission execution", accelerate the damage process of equipment structures, and facilitate the evaluation of the influence of simple low temperature and low-temperature-low-temperature fatigue coupling on the mechanical properties of specimens. The present invention is based on the low-temperature damage mechanism of metal structures and materials in high-cold environments, highlights the influence of the interaction of low temperature and fatigue and other working condition loads on the performance of metal structures and materials, and quantitatively characterizes the cumulative effect of low temperature based on the low-temperature cumulative index, which is more consistent with the actual environmental effect, and at the same time improves the effectiveness and accuracy of the simulation acceleration test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Test spectrum for structures or materials used in high-altitude cold regions; Figure 2 Test spectra for structures or materials used in polar regions; Figure 3 This is a schematic diagram of the structure of the butt welding simulation specimen in Example 1; Figure 4 This is the low temperature-low temperature fatigue interaction test spectrum in Example 1. DETAILED DESCRIPTION

[0011] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0012] Example 1: Combination Figures 2 to 4 As shown in the figure, a method for coupling low temperature and working load of polar equipment load-bearing structure and its materials is presented. A typical butt welding simulation specimen of a vehicle body used in polar regions is used as an example to carry out a low temperature-low temperature load interaction test. The specimen specifications and dimensions are as follows: Figure 3 As shown, the specific steps include: (1) Determine the test temperature: For metal structures used in polar regions, the test temperature is -57°C. (2) Determine the interactive test spectrum of the test object, such as Figure 4 As shown, the specific test spectrum is: S11, conduct low temperature static exposure test on the test object in advance (i.e. Figure 4 Low temperature exposure in the test), sampling and testing to obtain the initial fatigue life; S12, then follow the "Low Temperature Fatigue Test (i.e. Figure 4 Low temperature exposure in Figure 2 The test was repeated for 2, 4, or 6 cycles in the form of "low-temperature dynamic load test)-low-temperature exposure test-low-temperature fatigue test", with samples taken in the middle to detect the remaining fatigue life until the end of the test. (3) Determine the total low temperature exposure time and cycle time: Taking 5 days of continuous use in the Antarctic as an example, according to the monitoring data of Zhongshan Station in Antarctica in 2015, the lowest monthly average temperature was -21.9℃, and the temperature was below 0℃ throughout the month. Calculate the low temperature cumulative index according to formula (1): Calculate the total low temperature exposure time according to formula (2): Since the effect of low temperature on the weld and heat-affected zone may have a long induction period, the first low-temperature exposure time is designed to be 24 h, and the low-temperature exposure time of subsequent cycles is designed to be (46-24) / 6≈4 h to reflect the coupling effect of low temperature and fatigue load. (4) Determine the fatigue load value and the number of cyclic loading: Take three butt-welded simulated specimens for static tensile test. Initially, 45% of the static strength is used as the maximum load of the fatigue test. The stress ratio is 0.1. Preliminary tests are carried out to determine the fatigue life within 10 5 The fatigue load value is about 85KN. According to the preliminary test results (see Table 1), the maximum fatigue load of the interactive test is determined to be 85KN. Based on the expected intensity and frequency analysis of the vehicle, the number of fatigue loading cycles per cycle is determined to be 5000. Table 1 Preliminary test results This test spectrum is closer to actual service conditions and truly reflects the synergistic effect of low temperature environment and low temperature fatigue during the alternating process of "ground parking + sports car". Low-temperature-low-temperature fatigue interaction tests were carried out according to the determined test conditions. The results show (see Table 2) that, compared with the low-temperature fatigue life of the original specimens without interactive tests, the fatigue life of the specimens first increased and then decreased, which truly reproduced the actual damage history of the welded structure. Table 2 Remaining fatigue life after different cycles of low temperature-fatigue interaction tests

[0013] Embodiment 2: A method for testing a load-bearing structure of equipment used in high-cold areas and its materials under low-temperature and working load coupling conditions, comprising the following steps: Step 1: Determine the test spectrum of the test subject (1) For structures or materials used in high-altitude cold regions, Figure 1 As shown, the test spectrum is: S11, conduct a normal temperature dynamic load test on the test object; S12, perform n cycles in the manner of “first conduct low temperature static exposure test → then conduct low temperature dynamic load test”; S13, perform N cycles in the manner of "step S11 → step S12 → step S11", taking samples for testing in between, until the test is completed.

[0014] The scheme adopted in the embodiment can fully and truly reflect the actual environmental damage history of high-cold or polar equipment structures and their materials, can truly simulate and reproduce the synergistic effect of low-temperature environment and low-temperature fatigue during the alternating process of "ground parking + mission execution", accelerate the damage process of equipment structure, and facilitate the evaluation of the influence of simple low temperature and low-temperature-low-temperature fatigue coupling on the mechanical properties of the specimen. This scheme is based on the low-temperature damage mechanism of metal structures and materials in high-cold environments, highlights the influence of the interaction of low temperature and fatigue and other working condition loads on the performance of metal structures and materials, and quantitatively characterizes the cumulative effect of low temperature based on the low-temperature cumulative index, which is more consistent with the actual environmental effect, and at the same time improves the effectiveness and accuracy of the simulation acceleration test results.

Claims

1. A method for testing the load-bearing structure of high-cold / polar equipment and its materials under low temperature and working load coupling conditions, characterized in that the steps include: Step 1: Determine the test spectrum of the test subject (1) For structures or materials used in high-altitude cold regions, the test spectrum is: S11, conduct a normal temperature dynamic load test on the test object; S12, perform n cycles in the manner of "first conduct low temperature static exposure test → then conduct low temperature dynamic load test"; S13, perform N cycles in the manner of "step S11→step S12→step S11", sampling and testing in the middle, until the test is completed; or, (2) For structures or materials used in polar regions, the test spectrum is: S21, conduct low temperature static exposure test on the test object, S22, conduct low temperature dynamic load test on the test object, S23, perform N cycles in the manner of "step S21→step S22", taking samples for testing in between, until the test is completed. Step 2, determine the test parameters, including: Test temperature: For metal structures or materials used in high-altitude cold regions of my country, the recommended test temperature is -43°C; for metal structures or materials used in polar regions, the recommended test temperature is -57°C; and the test temperature should meet the requirements of "the test temperature should not be lower than the ductile-brittle transition temperature of the test material; when the ductile-brittle transition temperature of the test material is higher than the recommended value, the test temperature should be determined based on the principle of ductile-brittle transition temperature + 10°C"; Duration of low temperature exposure: 4 hours for the first cycle and 1 hour for the subsequent cycles; Fatigue cycle loading times: For the same batch of specimens, the test should be carried out under the same fatigue stress level, and 5000, 10000 or 20000 loading cycles should be selected for each cycle; Interactive cycle period: The recommended low-temperature-low-temperature fatigue interactive cycle period is 5 to 10 cycles. Step 3: Conduct the test according to the determined test parameters and test spectrum.

2. The test method according to claim 1, characterized in that Determine the total low temperature static exposure time t as follows 总 : Step 101, obtaining the low temperature cumulative index A of the test area according to formula (1); Where: A represents the low temperature accumulation index, ℃·h; T 均 represents the average daily temperature in winter in the test area, ℃; t c represents the number of hours per day below the critical temperature (0°C), h; N represents the expected winter use time of the test object, d; Step 102: Obtain the total low temperature static exposure time t of the test object according to formula (2): 总 ; Where: T 试 Indicates the test temperature.

3. The test method according to claim 1 or 2, characterized in that: The test was carried out using a fatigue load spectrum of equal amplitude; the fatigue stress was determined according to the following method: at room temperature, the tensile strength and elongation of the standard specimen were obtained by static tensile test; a preliminary test was carried out at 50% or 60% of the tensile strength, with a stress ratio of 0.1, so that the fatigue life was within (5×10 4 ~10 5 ), 5×10 5 , 10 6 About times of cycles are performed to determine the three fatigue stress levels: high, medium and low.

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