Method for evaluating service life of compressed brittle solid material heated at high temperature

Abstract

The invention discloses a method for evaluating the service life of a compressed brittle solid material heated at high temperature, which comprises the following steps of: processing four types of specimens with specific sizes for the compressed brittle solid material heated at high temperature, measuring compressive strength, a strain-time curve and initial damage key parameters through multiple types of tests such as triaxial compression, compression rheology and CT (Computed Tomography) scanning, and evaluating the service life of the compressed brittle solid material. A deformation time evolution equation containing parameters such as temperature and stress is established based on fracture damage mechanics for life evaluation, the method is based on the fracture mechanics theory, it is verified that a theoretical curve and a test curve are similar in trend and comparable in numerical value, and it is ensured that the life evaluation result is reliable.

Description

Technical Field

[0001] This invention relates to the field of materials mechanics, and in particular to a method for evaluating the lifespan of compressible brittle solid materials after high-temperature heating. Background Technology

[0002] Many engineering construction fields, including building engineering, aerospace engineering, mechanical engineering, and transportation engineering, utilize a large amount of brittle solid materials, such as concrete, ceramics, and glass. During the operational phase of these projects, they are inevitably affected by fire. Therefore, considering the safety and stability of the engineering structure after fire impact is crucial in the early stages of construction. Brittle solid materials are the core materials for constructing these engineering structures. Exposure to high temperatures during a fire can cause internal damage to these brittle solid materials, which are constantly subjected to compressive loads, increasing the likelihood of material failure and leading to safety hazards in these brittle solid engineering structures. Therefore, effectively evaluating the lifespan of brittle solid materials under compressive loads after high-temperature heating is of significant application value for the design and reinforcement of brittle solid material engineering structures. A method for evaluating the lifespan of compressively brittle solid materials after high-temperature heating is needed. Summary of the Invention

[0003] The purpose of this invention is to provide a method for evaluating the lifespan of compressible brittle solid materials after high-temperature heating, in order to solve the problems of existing technologies.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: This invention includes the following steps: A. Select a target compressible brittle solid material and process it into four types of specimens, including cylindrical specimens, first cuboid specimens, second cuboid specimens and third cuboid specimens. Place the four types of specimens in an industrial oven for high-temperature heating treatment and then cool them to room temperature. B. The compressive strength of the cylindrical specimen was measured by a triaxial compression test. ; C conducts compression rheological tests and sets axial stress. The value is greater than 0 and less than the compressive strength. Lateral confinement The value range is 0- Pa; to obtain the compressive strain of the cylindrical specimen. With time The relationship curve, and the time corresponding to the complete failure of the sample, is characterized as the reference value of the initial lifetime of the material at that temperature; D. The proportion of microcracks inside the sample is measured by CT scan, and the initial damage size of the sample is determined based on the proportion of microcracks. We obtained multiple sets of initial damage data corresponding to different temperatures and fitted the relationship between initial damage and temperature. E measured the sliding friction coefficient of the first cuboid sample through a shear friction test. We obtained multiple sets of sliding friction coefficient data corresponding to different temperatures and fitted the relationship between sliding friction coefficient and temperature. F measured the fracture toughness of the second cuboid specimen at the point of fracture through a three-point bending load test. Multiple sets of fracture toughness data corresponding to different temperatures were collected, and the relationship between fracture toughness and temperature was obtained by fitting. G measured the stress erosion index of the third cuboid sample under the crack propagation state through a subcritical crack propagation test. With characteristic crack rate Multiple sets of stress erosion index and characteristic crack rate data corresponding to different temperatures were obtained, and the relationship between stress erosion index and temperature and the relationship between characteristic crack rate and temperature were obtained by fitting. H used fracture damage mechanics theory to establish the strain-time relationship of brittle solid materials under high temperature heating and derived the internal crack length value of the material under given load and temperature. The derived formula is as follows: ; ; ; ; ; ; In the formula: , , It is a material constant. It is the initial crack length, It is the initial crack angle. The number of internal cracks per unit volume of material. According to the formula Calculation determined; F determines parameters Initial crack length Initial crack angle The strain of the target compressive brittle solid material was then calculated and predicted under different temperatures and stresses. - Time evolution curves are used to evaluate the lifetime of compressible brittle solid materials after high-temperature heating.

[0005] Furthermore, the four types of samples are a cylindrical sample with a height of 10cm and a diameter of 5cm, a first cuboid sample with a height of 8cm, a diameter of 3cm, and a diameter of 1cm, a second cuboid sample with a height of 10cm, a diameter of 5cm, and a diameter of 2cm, and a third cuboid sample with a height of 18cm, a diameter of 6cm, and a diameter of 0.5cm.

[0006] Furthermore, by comparing the strain-time relationship curve of a brittle solid material after high-temperature heating with the strain-time relationship test curve, and when the two curves are substantially similar, the parameters of the equation are determined. Initial crack length Initial crack angle The parameters The range of values ​​is 0< <3, initial crack length The range of values ​​is 0< <0.004m, initial crack angle The range of values ​​is 0< <90°; Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes fracture damage mechanics theory to propose a deformation time evolution equation capable of evaluating the eventual failure of brittle solid materials after high-temperature heat treatment under prolonged compressive loading. The equation includes temperature, stress, strain, and time parameters. Temperature describes the external high-temperature heating environment, stress describes the magnitude of the external compressive load, deformation describes the magnitude of the deformation under external compressive loading after high-temperature heating, and time describes the time it takes for the material to ultimately fail under external compressive loading. The invention verifies the similarity and numerical comparability between the theoretical and experimental curves, ensuring the reliability of the life assessment results and providing a reference for the safety assessment of brittle solid material engineering structures after a fire. Attached Figure Description

[0007] Figure 1 The 300 method for evaluating the lifespan of compressible brittle solid materials after high-temperature heating according to the present invention 0 Theoretical calculation curve of strain versus time relationship under compressive load on granite under C; Figure 2 For the present invention 300 0 Comparison of theoretical and experimental strain-time relationship curves for granite under C-type compressive load. Detailed Implementation

[0008] Reference Figure 1-2 The following example of brittle solid granite is used to verify the reliability of the theoretical equations in this invention.

[0009] To achieve the above objectives, the present invention includes the following steps: 1. Select a brittle solid material and process it into four types of samples: cylinders (10cm high x 5cm diameter), cuboids (8cm x 3cm x 1cm), cuboids (10cm x 5cm x 2cm), and samples (18cm x 6cm x 0.5cm). Place these samples in an industrial oven and heat them at the maximum temperature (100-800 degrees Celsius) for one hour. Then, allow the heated brittle solid material samples to cool naturally to room temperature. These samples will then be used for the tests in steps 2-7. Furthermore, the heating time and temperature mentioned above can be adjusted according to engineering requirements.

[0010] 2. Place the 10cm*5cm cylindrical specimen of brittle solid obtained from the high-temperature heating in step 1 into a triaxial compression testing apparatus and set the confining pressure. (Value range 0-) Pa (the specific value is determined according to actual needs), and then the compressive strength of the sample is measured. The unit is Pa.

[0011] 3. Place the 10cm*5cm cylindrical specimen of brittle solid obtained from the high-temperature heating in step 1 into a compression rheology testing apparatus and set the axial stress. (The value is greater than 0 and less than the compressive strength measured in step 2) ), lateral confining pressure is (Value range 0-) (Pa), the unit is Pa, and then the test is carried out to measure the compressive strain of the sample. With time The relationship curve is used to terminate the test until the brittle solid material is completely destroyed. The time when the material finally fails is the material's lifespan.

[0012] 4. Place the 10cm*5cm cylindrical brittle solid sample from step 1, heated to high temperature, into a CT scanner and scan the proportion of microcracks inside the sample to determine the initial damage size. Then, based on the initial damage data at different temperatures, a formula relating initial damage to temperature is fitted. .

[0013] 5. Place the 10cm*5cm*2cm rectangular sample 1, which was heated to high temperature in step 1, into a shear friction testing instrument and measure the sliding friction coefficient of the material sample. Then, based on friction data at different temperatures, a formula relating the friction coefficient to temperature is fitted. .

[0014] 6. Place the brittle solid 8cm*3cm*1cm rectangular specimen 2 obtained from step 1 (after high-temperature heating) into a three-point bending load testing apparatus and measure the fracture toughness of the material specimen at the point of fracture. The unit is Then, based on the fracture toughness data at different temperatures, a formula relating fracture toughness to temperature was fitted. .

[0015] 7. Place the brittle solid 18cm*6cm*0.5cm rectangular sample 3 obtained from step 1 after high-temperature heating in a subcritical crack propagation test instrument, and measure the stress erosion index of the material sample under crack propagation. With characteristic crack rate The rate is measured in m / s. Then, based on the erosion index and characteristic crack rate data at different temperatures, a formula relating the erosion index, characteristic crack rate, and temperature is fitted. , .

[0016] 8. Using fracture damage mechanics theory, a strain-time relationship equation for brittle solid materials under high-temperature heating was established. This equation can describe temperature. ,stress ,strain ,time The interrelationships between these elements can effectively analyze the evolution of material deformation time under different loads and temperatures, thereby evaluating the material's lifespan.

[0017] Then, It is an ordinary differential equation that can be solved to determine the evolutionary crack length inside a material under specific loads and temperatures. The result of the time evolution, namely In the formula .

[0018] at last, The length of the internal crack in the material under given load and temperature can be determined, and this crack length can then be used as an ordinary differential equation. The initial condition value.

[0019] ; ; ; ; ; ; In the formula: , , It is a material constant. It is the initial crack length, It is the initial crack angle. The number of internal cracks per unit volume of material. According to the formula Calculation determined; 9. In the formula of step 8 , , , , It can then be determined based on the test results at the specific temperature in steps 4, 5, 6, and 7.

[0020] 10. Parameters in the formula of step 8 The strain value at which the material ultimately fails can be determined based on the strain value measured by the rheological testing instrument in step 3.

[0021] 11. Parameters in the formula of step 8 , , , The strain-time relationship curves obtained from the theoretical calculations in step 8 and the experimental measurements in step 3 can be repeatedly compared and analyzed. When the two curves are basically similar, then... , , The value is a fixed value, and its range is 0 < <3, 0< <1, 0< <0.004m, 0< <90.

[0022] 12. After determining all the model parameters in step 8 based on the above process, and verifying the rationality of the formula in step 8 through the experimental results in step 3, the influence of different temperatures and loads on the lifespan of the analyzed brittle solid material can be further predicted and analyzed based on the formula in step 8, thereby serving engineering structural design.

[0023] In this implementation example, granite, a brittle solid material, is selected as an example. The strain-time relationship curve of granite under compressive load after high-temperature heating is calculated and compared with the experimental results to verify the reliability of the theory.

[0024] The following are the specific values ​​of the theoretical parameters for granite materials.

[0025] , , , , , .

[0026] , , , , , .

[0027] Figure 1-2 300 was given 0 The strain-time curves of granite samples tested under a rheological testing apparatus at temperature C are presented, along with the strain-time curves calculated using the theoretical formula proposed in this invention. A comparative analysis of the theoretical and experimental curves shows that the trends are similar and the values ​​are comparable, verifying the rationality of the proposed method for evaluating the lifespan of compressively brittle solid materials after high-temperature heating.

[0028] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for evaluating the life of a high-temperature heated compressed brittle solid material, characterized by, The method comprises the following steps: Target compression brittle solid materials are selected and processed into four types of samples, including a cylindrical sample, a first cuboid sample, a second cuboid sample, and a third cuboid sample. The four types of samples are placed in an industrial oven for high-temperature heating treatment and then cooled to room temperature. B The compressive strength of the cylinder sample is measured by triaxial compression test ; C Conduct compression rheological test, set the value of axial stress greater than 0 and less than the compressive strength , the value of lateral confining pressure range from 0 to 10 7 Pa; obtain the compression strain of the cylindrical sample and time curve, the corresponding time when the sample is completely destroyed is characterized as the initial life reference value of the material at this temperature; D The proportion of micro-cracks in the sample is measured by CT scanning, and the initial damage size of the sample is determined based on the proportion of micro-cracks And a plurality of groups of initial damage data corresponding to different temperatures are obtained, and the relationship between the initial damage and the temperature is fitted. E The first cuboid sample is measured for the sliding friction coefficient by a shear friction test Obtain a plurality of groups of sliding friction coefficient data corresponding to different temperatures, and fit the relationship between the sliding friction coefficient and the temperature. F The second cuboid sample is measured by a three-point bending loading test to obtain the fracture toughness of the sample when fracture occurs A plurality of groups of fracture toughness data corresponding to different temperatures are obtained, and a relationship between the fracture toughness and the temperature is fitted. G measuring the stress corrosion index of the third cuboid sample in the crack propagation state by a subcritical crack propagation test with a characteristic crack rate , obtaining a plurality of groups of stress corrosion index and characteristic crack rate data corresponding to different temperatures, and respectively fitting to obtain the relationship between the stress corrosion index and the temperature and the relationship between the characteristic crack rate and the temperature; HUsing the fracture damage mechanics theory, the strain-time relationship of the compressed brittle solid material after high-temperature heating is established, and the internal crack length of the material under the given load and temperature is derived, and the derivation formula is as follows: ； ； ； ； ； ； where: , , is a material constant, is the initial crack length, is the initial crack angle, is the number of cracks inside the unit volume of material, is calculated according to the formula ; F determining parameters , initial crack length , initial crack angle Post-computation predicts the strain-time evolution curve of the target compressive brittle solid material under different temperatures and different stress actions for evaluating the life of the compressive brittle solid material after high-temperature heating.

2. The method for evaluating the lifetime of a compressed brittle solid material after high-temperature heating according to claim 1, characterized by, The four types of samples are respectively a cylindrical sample with a height of 10 cm and a diameter of 5 cm, a first cuboid sample with a size of 8 cm*3 cm*1 cm, a second cuboid sample with a size of 10 cm*5 cm*2 cm, and a third cuboid sample with a size of 18 cm*6 cm*0.5 cm.

3. The method for evaluating the lifetime of a compressed brittle solid material after high-temperature heating according to claim 1, characterized by, The strain-time relationship curve of the brittle solid material compressed after high-temperature heating is similar to the strain-time relationship test curve, and parameters of the equation are determined when the two curves are basically similar , the initial crack length , the initial crack angle , the value range of the parameter 0 < 3, the value range of the initial crack length 0 < 0.004 m, the value range of the initial crack angle 0 < 90°.

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