A method of hoop tensile testing of ceramic-based pipe

Abstract

The present application relates to a kind of ceramic base pipe material circumferential tensile test method, it is related to test field, including the following steps: put expansion plug into the inside of tubular sample, and make expansion plug be located in the center of gauge section, again insert boss indenter with convex section into two ends of sample respectively;Preload is applied to boss indenter and is kept, after heating, keep for 5 minutes;Expansion plug is extruded by boss indenter to make it axial shortening and radial expansion, sample is not stressed;Subsequently, force value increases, expansion plug and sample inner wall are completely attached and begin to extrude inner wall, force value increases to drop load;Load and displacement data are collected throughout, after test, remove zero load data before preload and load sudden drop data after fracture and carry out smoothing processing;Finally, using the minimum method of residual sum of squares confirms inflection point and calculates the circumferential tensile strength and circumferential elastic modulus of sample, the present application has the advantage that can efficiently realize SiC pipe high temperature circumferential tensile mechanical property test.

Description

Technical Field

[0001] This invention relates to the field of testing technology, and in particular to a method for circumferential tensile testing of ceramic-based pipes. Background Technology

[0002] SiC ceramics, due to their high strength, high hardness, excellent wear resistance, corrosion resistance, and high-temperature stability, are widely used in piping systems in critical fields such as chemical engineering, metallurgy, aerospace, and semiconductor manufacturing. As a pressure-bearing component, its circumferential (ring) tensile strength is one of the most critical design parameters. However, due to the inherent brittleness of ceramic materials and the special shape of tubular specimens, conducting direct and accurate circumferential tensile tests presents significant technical challenges. Notably, for ceramic composite tubes that are slender (small diameter, large height), their mechanical properties cannot be reliably predicted using flat plate specimens, necessitating direct testing of tubular specimens.

[0003] Currently, the methods for measuring the circumferential tensile strength of tubular samples include the following: 1) The sample is fitted onto two symmetrical semicircular rings, arc-shaped pins, or semi-cylindrical core blocks, mounted on a fixture, and stretched by moving the fixture, as described in GB / T1458, CN202693413U, "Study on Stress Reorientation and Circumferential Tensile Test Method of Zirconium Alloy Tube Hydride". However, this loading method is problematic for high-strength, high-hardness materials like silicon carbide ceramics, especially given the rough internal surface of tubular samples. Point contact can easily lead to stress concentration, causing uneven stress distribution and ultimately, failure of the sample.

[0004] 2) An arc-shaped fixture is bonded to the side surface of the specimen, and the moving beam drives the positioning rod to stretch the specimen, as shown in CN113138121A. Although this method can avoid the above problems, the interlayer bonding strength of the specimen is unknown and cannot meet the test requirements.

[0005] 3) Create a sealed environment inside the sample, fill it with gas, and increase the gas pressure to circumferentially stretch the inner wall of the sample, as in "A Microstructure Study on an AZ31 Magnesium Alloy Tube after Hot MetalGas Forming Process". However, this method is mainly applied to the circumferential direction of metal tubes. For SiC ceramic-based tubes, it is difficult to ensure their compactness, and the end welding cost is extremely high and they are only for single use.

[0006] Therefore, to address the above shortcomings, a method for circumferential tensile testing of ceramic-based pipes is needed. Summary of the Invention

[0007] (a) Technical problems to be solved The technical problem to be solved by this invention is that the various current circumferential stretching methods are not suitable for testing SiC ceramic tubes.

[0008] (II) Technical Solution To address the aforementioned technical problems, this invention provides a method for circumferential tensile testing of ceramic-based pipes, comprising the following steps: Ⅰ. Place the expansion plug inside the tubular specimen and position the expansion plug at the center of the gauge length. Then insert the convex-shaped boss indenter into both ends of the specimen. II. Place the assembled components in the center of the parallel pressure plate of the testing machine, move the pressure plate to apply preload to the boss pressure head and maintain it, heat to 1000-1200℃ and hold for 5 minutes; III. The specimen is loaded in two stages. In the first stage, the expansion plug is squeezed by the boss head to shorten its axial length and expand its radial length, and the specimen is not under force. In the second stage, the force value increases rapidly, the expansion plug is completely attached to the inner wall of the specimen and begins to squeeze the inner wall, and the force value increases until the load drops. IV. Load and displacement data were collected throughout the test. After the test, the zero load data before preloading and the load drop data after fracture were removed and smoothed. Finally, the inflection point was confirmed by the minimum sum of squares method of residuals and the circumferential tensile strength and circumferential elastic modulus of the specimen were calculated.

[0009] As a further explanation of the present invention, preferably, the expansion plug is made of polymer or metal material, and the axial strain of the expansion plug is ≥5%.

[0010] As a further explanation of the present invention, preferably, the sample is a SiC ceramic-based tube with a length not exceeding 30 mm.

[0011] As a further explanation of the present invention, preferably, the method for minimizing the sum of squared residuals is as follows: Let the processed data sequence be ( , ),in =1,2,3,…, , The total number of valid data points; iterate through all possible inflection point locations. , will go The points are fitted to a straight line in the first stage: The sum of squares of the residuals is then: in: This is the displacement value. Indicates the first Displacement values ​​of each data point; For load values, Indicates the first Load values ​​for each data point; The slope of the straight line in the first stage; This is the intercept of the line in the first stage.

[0012] As a further explanation of the present invention, preferably, The value range is 3~ -3.

[0013] As a further explanation of the present invention, preferably, the latter The points are fitted to form a straight line in the second stage: Its residual sum of squares is: in, The slope of the line in the second stage; This is the intercept of the line in the second stage.

[0014] As a further explanation of the present invention, preferably, the total residual sum of squares is calculated, and the method that minimizes the total residual sum of squares is found. Value, corresponding point ( , The optimal inflection point is the point at which the inflection point is reached.

[0015] As a further explanation of the present invention, preferably, the slope ratio of the two straight lines and the linear correlation coefficient are calculated. If the slope ratio is greater than 5:1, and the linear correlation coefficient of the first stage is greater than or equal to 0.98 and the linear correlation coefficient of the second stage is greater than or equal to 0.99, then the optimal inflection point is valid.

[0016] As a further explanation of the present invention, preferably, the acquisition is based on the obtained optimal inflection point. The value is used to calculate the circumferential elastic modulus of the specimen: in, The average wall thickness of sample (3); The outer diameter of the pipe; This refers to the inner diameter of the pipe. This is the correction factor at room temperature; is the Poisson's ratio of the pipe.

[0017] As a further explanation of the present invention, preferably, the load value at the fracture displacement is obtained based on the acquired optimal inflection point, and the circumferential tensile strength of the specimen is calculated as follows: in, The load value at the fracture location is the fitted straight line in the second stage. The temperature comprehensive correction factor is as follows: This is the temperature correction factor.

[0018] (III) Beneficial Effects The above-described technical solution of the present invention has the following advantages: This invention achieves automatic centering at the hardware level through the design of a boss indenter, eliminating the need for manual adjustment of the sample position and thus eliminating the ±0.2–0.5 mm eccentricity error caused by manual centering. At the software level, it utilizes the minimum sum of squared residuals method for global optimization to determine a unique inflection point, eliminating the need for manual visual selection of points and fitting of tangents, and eliminating the ±10%–20% difference in inflection point identification between different operators. Attached Figure Description

[0019] Figure 1 This is a diagram showing the assembly effect before testing of the present invention; Figure 2 This is a structural diagram of the boss pressure head of the present invention.

[0020] In the figure: 1. Boss indenter; 2. Expansion plug; 3. Sample. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] A method for circumferential tensile testing of ceramic-based pipes, combined with Figure 1 , Figure 2 This includes the following steps: Ⅰ. Select a SiC ceramic-based tube with a length not exceeding 30 mm as the sample 3. Place the expansion plug 2 made of polymer or metal material with axial strain ≥ 5% into the tube-shaped sample 3 and make the expansion plug 2 located at the center of the gauge length section. Then insert the convex-shaped boss head 1 into both ends of the sample 3 respectively.

[0023] II. Place the assembled components in the center of the parallel pressure plate of the testing machine, move the pressure plate to apply preload to the boss head 1 and maintain it, heat to 1000-1200℃ and keep it at that temperature for 5 minutes.

[0024] III. The sample 3 is loaded in two stages. In the first stage, the expansion plug 2 is squeezed by the boss head 1 to shorten its axial length and expand its radial length. At this time, the sample 3 is not under force. In the second stage, the force value increases, the expansion plug 2 is completely attached to the inner wall of the sample 3 and begins to squeeze the inner wall. The force value increases until the load drops.

[0025] IV. Load and displacement data were collected throughout the test. After the test, the zero-load data before preloading and the load drop data after fracture were removed and smoothed. Finally, the inflection point was confirmed using the method of minimizing the sum of squares of residuals, and the circumferential tensile strength and circumferential elastic modulus of the specimen were calculated. The method of minimizing the sum of squares of residuals is as follows: Let the processed data sequence be ( , ),in =1,2,3,…, , The total number of valid data points; iterate through all possible inflection point locations. , The value range is 3~ -3.

[0026] For each value: Before The points are fitted to a straight line in the first stage: The sum of squared residuals is calculated as follows: in: This is the displacement value. Indicates the first Displacement values ​​of each data point; For load values, Indicates the first Load values ​​for each data point; The slope of the straight line in the first stage; This is the intercept of the line in the first stage.

[0027] After The points are fitted to form a straight line in the second stage: The sum of squared residuals is calculated as follows: in, The slope of the line in the second stage; This is the intercept of the line in the second stage.

[0028] Calculate the total sum of squared residuals and find the value that minimizes the total sum of squared residuals. Value, corresponding point ( , The optimal inflection point is determined by finding the optimal two-stage division point from a global perspective. This completely eliminates the subjective error caused by manually selecting fitting points in the visual method. Even for curves with inflection points that are not obvious or whose slope changes gently, it can provide a unique and objective inflection point location. Moreover, the accuracy of inflection point identification obtained is more than 5 times higher than that of the double tangent method recommended by the ASTM standard, and the coefficient of variation is reduced from 7.8% to less than 1.5%.

[0029] V. To verify the validity of the inflection point, we begin by calculating the ratio of the slopes of the two straight lines, i.e.: The linear correlation coefficients of the two straight lines were then calculated separately. and And verify the slope ratio Is it greater than 5:1, first-stage linear correlation coefficient? Is it greater than or equal to 0.98? Second-stage linear correlation coefficient If the value is greater than or equal to 0.99, and all of the above conditions are met, then the optimal inflection point is valid. By quantitatively judging whether the curve conforms to the ideal two-stage morphology, the inflection point is ensured to have a clear physical meaning. Abnormal curves caused by improper selection of expansion plugs, poor lubrication, or sample defects are automatically identified, ensuring the reliability of the basic data for subsequent strength and modulus calculations and avoiding invalid data from entering the results statistics.

[0030] VI. Obtaining the optimal inflection point The value is used to calculate the circumferential elastic modulus of sample 3: in, The average wall thickness of sample (3); The outer diameter of the pipe; This refers to the inner diameter of the pipe. This is a correction factor at room temperature (25°C), preferably 0.042 for SiC pipes; is the Poisson's ratio of the pipe.

[0031] Based on the obtained optimal inflection point, the load value at the fracture displacement is obtained, and the circumferential tensile strength of specimen 3 is calculated as follows: in, The load value at the fracture location is the fitted straight line in the second stage. The temperature comprehensive correction factor is as follows: The temperature correction factor is preferably 2.1 × 10⁻⁶. -4 ℃ -1 .

[0032] Based on the above method, the present invention provides a set of detection and analysis tables, with specific data as follows: Statistical table of room temperature circumferential tensile strength data of tubular specimens 1 SiC-B-161-5#-1 52.1 2 SiC-B-161-4#-1 54.6 3 SiC-P-10-1#-1 47.2 4 SiC-B-161-1# ＞55.6 5 SiC-B-161-2# ＞28.8 6 SiC-P-28-1#-1 44.8 7 SiC-P-28-2#-1 49.5 Statistical table of room temperature circumferential tensile modulus and Poisson's ratio data for tubular specimens 1 SiC-B-161-5#-2 495 0.23 2 SiC-B-161-4#-2 366 0.34 3 SiC-P-10-1#-2 116 0.22 4 SiC-P-28-1#-2 98 0.079 5 SiC-P-28-2#-2 108 0.075 Circumferential tensile test at 350℃ Statistical table of circumferential tensile data of tubular specimens at 350℃ 1 SiC-B-161-6# 66.5 2 SiC-P-10-2# 45.0 3 SiC-P-10-3# 49.8 Circumferential tensile test at 450℃ Statistical table of circumferential tensile data of tubular specimens at 450℃ SiC-B-161-3# strength 69.4MPa SiC-B-161-7# strength 95.0MPa 800℃ Vacuum (Argon) Circumferential Tensile Test Statistical table of tubular specimens' circumferential tensile properties under vacuum at 800℃ 20240729-xgd-SiC-29-2# strength 62.6MPa 1200℃ Vacuum (Argon) Circumferential Tensile Test Statistical table of tubular specimens' circumferential tensile properties under vacuum at 1200℃ SiC-P-10-4# strength 61.9MPa As can be seen from the SiC-P series data in the table, the coefficient of variation of the calculated test results decreased to 5.1%, reaching the normal level of material inherent property dispersion. This indicates that the method of this invention can accurately eliminate systematic errors caused by geometrical differences, improving the matching degree with the true strength of the material by approximately 80%. Furthermore, this method completely eliminates the influence of the first-stage expansion deformation on the calculation results, improving the elastic modulus testing accuracy by more than 40% compared to the ASTM standard method. Moreover, by using the maximum load of the fitted straight line instead of the original peak value, the influence of load fluctuations at the moment of fracture is eliminated, while also correcting for the influence of interfacial friction, making the test results closer to the true circumferential tensile properties of the material.

[0033] In summary, this invention achieves automatic centering at the hardware level by designing the boss pressure head 1, eliminating the need for manual adjustment of the sample position and thus eliminating the ±0.2–0.5 mm eccentricity error caused by manual centering. At the software level, it utilizes the minimum sum of squared residuals method for global optimization to determine the unique inflection point, eliminating the need for manual visual selection of points and fitting of tangents, and eliminating the ±10%–20% difference in inflection point identification between different operators. From sample 3 placement to result output, there is no step requiring subjective human judgment; the test results are entirely determined by experimental data and objective algorithms, achieving true blind testing. For SiC / SiC composite tube samples with unit prices ranging from 20,000 to 150,000 yuan, the effective sample rate is increased from 60% to 100%, meaning a 40% reduction in single-test cost and a 50% reduction in the test cycle. This allows a complete testing system to be reduced to below 200,000 yuan, enabling more universities and small and medium-sized enterprises to conduct related research.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of hoop tensile testing of ceramic-based pipe material, characterized by: Includes the following steps: Ⅰ. Place the expansion plug (2) inside the tubular sample (3) and position the expansion plug (2) at the center of the gauge length. Then insert the convex-shaped boss indenter (1) into both ends of the sample (3). II. Place the assembled components in the center of the parallel pressure plate of the testing machine, move the pressure plate to apply preload to the boss pressure head (1) and maintain it, heat to 1000~1200℃ and keep it at that temperature for 5 minutes; Ⅲ. The sample (3) is loaded in two stages. In the first stage, the expansion plug (2) is squeezed by the boss head (1) to shorten its axial length and expand its radial length. The sample (3) is not subjected to force. In the second stage, the force value increases, the expansion plug (2) is completely attached to the inner wall of the sample (3) and begins to squeeze the inner wall. The force value increases until the load drops. IV. Load and displacement data were collected throughout the test. After the test, the zero load data before preloading and the load drop data after fracture were removed and smoothed. Finally, the inflection point was confirmed by the minimum sum of squares of residuals and the circumferential tensile strength and circumferential elastic modulus of the specimen (3).

2. A method of hoop tensile testing of a ceramic-based pipe material according to claim 1, characterized in that: The expansion plug (2) is made of polymer or metal material, and the axial strain of the expansion plug (2) is ≥5%.

3. A method of hoop tensile testing of a ceramic-based pipe material according to claim 1, characterized in that: Sample (3) is a SiC ceramic-based tube with a length not exceeding 30 mm.

4. The method of claim 1, wherein: The method for minimizing the sum of squared residuals is as follows: Let the processed data sequence be (x , ), where =1,2,3,…, , is the total number of valid data points; traverse all possible inflection point positions , and fit the first points as a first-stage straight line: The sum of squares of the residuals is then: in: displacement value, representing the displacement value of the first data point; for the load value, denotes the load value of the data point; The slope of the straight line in the first stage; is the intercept of the first stage straight line.

5. A method of hoop tensile testing of a ceramic-based pipe material according to claim 5, characterized in that: the value range of a is 3 ~ 5 -3.

6. A method of hoop tensile testing of a ceramic-based pipe material according to claim 5, characterized in that: Fitting the last points as a second stage line: Its residual sum of squares is: in, is the slope of the second phase straight line; is the intercept of the second stage straight line.

7. A method of hoop tensile testing of a ceramic-based pipe material according to claim 6, characterized in that: The total residual sum of squares is calculated, and the value that minimizes the total residual sum of squares is found The corresponding point (xopt, yopt) is the optimal inflection point. , ​ 8. A method of hoop tensile testing of a ceramic-based pipe material according to claim 7, characterized in that: Calculate the slope ratio of the two straight lines and the linear correlation coefficient. If the slope ratio is greater than 5:1, and the linear correlation coefficient of the first stage is greater than or equal to 0.98 and the linear correlation coefficient of the second stage is greater than or equal to 0.99, then the optimal inflection point is valid.

9. A method of hoop tensile testing of a ceramic-based pipe material according to claim 8, characterized in that: Based on the acquired optimal inflection point acquisition The circumferential elastic modulus of the sample (3) is calculated as: in, t is the average wall thickness of the test specimen (3); D is the outer diameter of the pipe; D is the inside diameter of the pipe; This is the correction factor at room temperature; is the Poisson's ratio of the pipe.

10. A method of hoop tensile testing of a ceramic-based pipe material according to claim 9, characterized in that: Based on the obtained optimal inflection point, the load value at the fracture displacement is obtained, and the circumferential tensile strength of specimen (3) is calculated as follows: in, Fitting a straight line to the load values at the break positions for the second stage; T is the temperature correction coefficient, specifically: is the temperature correction coefficient.

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