Small punch test apparatus and method for studying axial and circumferential creep of fuel cladding tubes

Abstract

This invention relates to a small punch test apparatus for studying the axial and circumferential creep of nuclear fuel cladding tubes. The apparatus, used to hold a sample of a nuclear fuel cladding tube, includes a lower die, a small punch, and an upper die. The lower die has a punched hole, and the upper die has a guide groove. The sample is located between the upper and lower dies, with the upper die pressing the sample against the lower die. The small punch passes through the guide groove and slides relative to it. The center of the sample is located between the small punch and the punched hole, and the position of the punch matches the movement path of the small punch. This invention also relates to a small punch test method for studying the axial and circumferential creep of nuclear fuel cladding tubes. By designing a small punch test apparatus for holding nuclear fuel cladding tubes, this invention accurately calculates the equivalent creep stress and equivalent creep strain of the nuclear fuel cladding tube, establishes a creep constitutive model, and achieves efficient and convenient research on the axial and circumferential creep behavior of nuclear fuel cladding tubes, belonging to the field of nuclear fuel cladding tube creep testing technology.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel cladding tube creep testing technology, specifically to a small punch test apparatus and method for studying axial and circumferential creep of fuel cladding tubes. Background Technology

[0002] Nuclear fuel cladding tubes operate at high temperatures for extended periods and may fail due to creep. Therefore, the creep behavior of nuclear fuel cladding tubes plays a crucial role in design and safety assessment. Standard creep testing methods are typically used to study the creep behavior of materials. However, nuclear fuel cladding tubes are thin-walled tubes, with an outer diameter of approximately 10 mm and a wall thickness of approximately 0.5 mm. Therefore, standard creep test specimens cannot be fabricated from nuclear fuel cladding tubes.

[0003] Small-pump testing is another method for studying the creep behavior of materials. It is widely used due to its small sample size and good correlation with standard creep testing. However, the creep behavior of nuclear fuel cladding tubes cannot be directly studied using standard small-pump testing because it requires thin-plate samples, which nuclear fuel cladding tubes cannot be directly fabricated into. Furthermore, nuclear fuel cladding tubes exhibit anisotropic creep behavior, with different creep behaviors in the circumferential and axial directions, which standard small-pump testing cannot test. Therefore, a new small-pump testing method is needed to test and study the axial and circumferential creep behavior of nuclear fuel cladding tubes. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the purpose of this invention is to provide a small punch test device for studying the axial and circumferential creep of fuel cladding tubes, thus solving the problem that the standard small punch test requires thin plate specimens and that nuclear fuel cladding tubes cannot be directly installed on the small punch test machine for testing.

[0005] Another objective of this invention is to provide a small punch test method for studying the axial and circumferential creep of fuel cladding tubes, thereby solving the problem that existing methods cannot effectively and conveniently study the axial and circumferential creep behavior of nuclear fuel cladding tubes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A small punch test apparatus for studying axial and circumferential creep of fuel cladding tubes is used to hold the sample of nuclear fuel cladding tubes. The apparatus includes a lower mold, a small punch, and an upper mold. The lower mold has a punch hole, and the upper mold has a guide groove. The sample is located between the upper and lower molds. The upper mold presses the sample against the lower mold. The small punch passes through the guide groove and slides relative to the guide groove. The middle part of the sample is located between the small punch and the punch hole. The position of the punch hole matches the movement path of the small punch.

[0008] As a preferred embodiment, the lower die has a concave arc surface, and the punch is located at the center of the concave arc surface, which matches the part of the upper die that presses the sample.

[0009] As a preferred embodiment, the upper mold has a convex arc surface, the guide groove is located at the center of the convex arc surface, and the convex arc surface matches the part of the lower mold that contacts the sample.

[0010] As a preferred embodiment, the small punch includes a connected guide post and a punch. The punch is semi-circular and passes through a guide groove. The guide post slides relative to the guide groove, and the movement path of the punch matches the position of the punch hole.

[0011] As a preferred option, the cross-section of the punch is rectangular.

[0012] As a preferred embodiment, the guide post has a rectangular cross-section, the guide groove has a rectangular cross-section, and the guide post and guide groove are matched.

[0013] As a preferred option, the sample was prepared using a nuclear fuel cladding tube.

[0014] The small punch test method for studying the axial and circumferential creep of fuel cladding tubes includes the following steps:

[0015] S1. Prepare a sample of the nuclear fuel cladding tube;

[0016] S2. Install the small punch test device on the small punch test machine, and then install the sample from step S1 into the small punch test device for testing. The small punch test device is a small punch test device for studying the axial and circumferential creep of fuel cladding tubes.

[0017] S3. Perform a small punch creep test on the sample and record the punch force P and the punch displacement δ of the small punch.

[0018] S4. The equivalent creep stress σ is calculated using the impact force P recorded in step S3. The formula for calculating the equivalent creep stress σ is as follows:

[0019]

[0020] Where S is the initial cross-sectional area at the center of the sample, and K SP It is a constant;

[0021] S5. The equivalent creep strain ε is calculated from the punch displacement δ of the small punch recorded in step S3. The formula for calculating the equivalent creep strain ε is as follows:

[0022]

[0023] As a preferred embodiment, the specimens in step S1 include axial specimens and circumferential specimens.

[0024] As a preferred option, in step S4, KSP The value of K corresponds to the coefficient of friction between the sample and the small punch test device. When the coefficient of friction between the small punch test device and the small punch test device is 0.2, K... SP It is 0.55.

[0025] In summary, the present invention has the following advantages:

[0026] 1. This invention solves the problem that nuclear fuel cladding tubes cannot be directly installed on a small punch testing machine for testing in standard small punch tests by designing a lower mold with a concave arc surface and an upper mold with a convex arc surface, and then forming an arc-shaped sample from the nuclear fuel cladding tube. The upper and lower molds cooperate to clamp the arc-shaped sample.

[0027] 2. The small punch test apparatus and method for studying the axial and circumferential creep of fuel cladding tubes of the present invention can accurately calculate the equivalent creep stress of nuclear fuel cladding tubes according to the formula; the small punch test apparatus and method for studying the axial and circumferential creep of fuel cladding tubes can calculate the equivalent creep strain of the small punch creep test according to the calculation formula of the standard small punch creep test. Although the anisotropic creep characteristics will affect the accuracy of the calculation, the impact is small.

[0028] 3. This invention uses a small punch test device to conduct small punch tests on nuclear fuel cladding tubes, thereby measuring the calculation parameters required for axial and circumferential creep behavior, thus enabling effective and convenient study of the axial and circumferential creep behavior of nuclear fuel cladding tubes. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the nuclear fuel cladding tube of the present invention;

[0030] Figure 2 This is a schematic diagram of the circumferential sample of the present invention;

[0031] Figure 3 This is a cross-sectional view of a small punch test apparatus (quarter section) for circumferential creep behavior according to the present invention;

[0032] Figure 4 This is a cross-sectional view of the lower mold (quarter) of the small punch test device for circumferential creep behavior of the present invention;

[0033] Figure 5 This is a schematic diagram of the axial specimen of the present invention;

[0034] Figure 6 This is a cross-sectional view of a small punch test apparatus (quarter section) for axial creep behavior according to the present invention;

[0035] Figure 7 This is a cross-sectional view of the lower mold (quarter) of the small punch test device for axial creep behavior of the present invention;

[0036] Figure 8 This is a schematic diagram illustrating the principle of the sample being subjected to impact force in the small punch test device of the present invention;

[0037] Figure 9 The time-displacement curve obtained from the experiment when the punch force is fixed at P;

[0038] The markings of the components in the attached diagram are as follows: 1-lower die; 101-circular concave surface; 102-punch; 2-upper die; 201-circular convex surface; 202-guide groove; 3-small punch; 301-guide post; 302-punch; 4-sample; 41-circumferential sample; 411-circumferential hole; 42-axial sample; 421-axial hole; 5-clamp. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to specific embodiments.

[0040] Example 1

[0041] like Figure 2-7 As shown in the figure, the small punch test device provided in this embodiment for studying the axial and circumferential creep of fuel cladding tubes is used to clamp the sample of nuclear fuel cladding tubes. It includes a lower mold 1, a small punch 3, and an upper mold 2. The top of the lower mold 1 is provided with an arc concave surface 101, and a punch 102 is provided on the arc concave surface 101. The punch 102 is located at the center of the arc concave surface 101 and is recessed into or penetrates the arc concave surface 101. The length of the punch 102 is 4 mm and the width is 2.8 mm. The bottom of the upper mold 2 is provided with an arc convex surface 201, and a guide groove 202 is provided on the arc convex surface 201. The guide groove 202 is located at the center of the arc convex surface 201 and penetrates the arc convex surface 201. The arc concave surface 101 and the arc convex surface 201 match each other, and the punch 102 and the guide groove 202 correspond to each other.

[0042] This embodiment solves the problem that nuclear fuel cladding tubes cannot be directly installed on a small punch testing machine for testing in standard small punch tests by designing a lower mold with a concave arc surface and an upper mold with a convex arc surface. The upper and lower molds cooperate to clamp the arc-shaped (axial / circumferential) sample.

[0043] The small punch 3 includes a connected guide post 301 and a punch 302. The guide post 301 passes through the guide groove 202. The arc-shaped concave surface 101 and the arc-shaped convex surface 201 hold the sample 4 (i.e., the axial sample 42 or the circumferential sample 41). Figure 1 (The sample 4 is made of nuclear fuel cladding tube shown), with the middle part located between the punch 102 and the punch 302.

[0044] The lower die 1 cooperates with the upper die 2 to clamp the sample 4; the small punch 3 is used to impact the middle of the sample 4; the guide post 301 guides the impact direction of the punch 302; the punch 302 is a semi-circular punch with a radius of 1mm, a length of 2.8mm, and a width of 2mm, used to impact the sample 4; the upper die 2 is used to clamp the sample 4; the outer radius of the arc convex surface 201 and the inner radius of the arc concave surface 101 depend on the outer radius and inner radius of the sample 4.

[0045] The cross-section of the punch is rectangular, the cross-section of the guide post is rectangular, and the cross-section of the guide groove is rectangular. The guide post and the guide groove are matched. Since the punch is semi-circular, the extrusion of the sample is first line contact and then surface contact. That is to say, the contact surface of the punch extruding the sample is always rectangular.

[0046] The samples are prepared directly from nuclear fuel cladding tubes without damaging the microstructure of the nuclear fuel cladding tubes, and the size of the nuclear fuel cladding tubes is determined by the tubes themselves.

[0047] Installation process: First, fix the upper and lower dies on the worktable of the small punch testing machine. The concave arc surface of the lower die matches the convex arc surface of the upper die, and the guide groove and punch hole correspond to each other. During the test, place the sample between the upper and lower dies, fix the upper die on the lower die, and make the convex arc surface of the upper die contact with the top arc surface of the sample and press it against the concave arc surface of the lower die. The concave arc surface of the lower die contacts and supports the bottom arc surface of the sample. Then, install the small punch to the punching end of the small punch testing machine, calibrate the position of the small punch so that the small punch corresponds to the guide groove, and insert part of the guide post and the punch into the guide groove. The guide post and the punch are driven by the punching end of the small punch testing machine, so that the movement path of the small punch passes through the guide groove and the punch hole in sequence, realizing that the small punch slides in the guide groove, and the punch continues to move through the guide groove to the punch hole, thereby impacting the sample with the force of the punch.

[0048] Example 2

[0049] like Figure 1-9 As shown, a small punch test method is used to study the axial and circumferential creep of fuel cladding tubes. This method, employed to investigate the axial and circumferential creep behavior of nuclear fuel cladding tubes, includes the following steps:

[0050] S1, Install the nuclear fuel cladding tube (such as...) Figure 1 (As shown) Directly fabricate axial specimen 42 (e.g.) Figure 5 (as shown) and circumferential specimen 41 (as shown) Figure 4 (As shown). The circumferential hole 411 or the axial hole 421 is a rounded rectangle with a length of 2mm, a width of 2mm, and a radius of 1mm. The distance between the two circumferential holes 411 or the axial hole 421 is 2mm.

[0051] S2. Install the small punch test device for axial creep behavior or the small punch test device for circumferential creep behavior on the small punch test machine. Then, clamp the axial specimen 42 between the upper mold 2 and the lower mold 1 of the small punch test device for axial creep behavior (or clamp the circumferential specimen 41 between the upper mold 2 and the lower mold 1 of the small punch test device for circumferential creep behavior). Then, install the small punch 3. Finally, apply force to the small punch punch 302 in the area between the two circumferential holes 411 or the axial hole 421 of the specimen, and then start testing the specimen 4.

[0052] The specific steps are as follows: After the sample is installed, the testing machine is heated. Once the temperature reaches the specified level, a fixed force P is applied to the small punch, and then the test begins. During the test, the test time and the displacement caused by the deformation of the sample under force are recorded, resulting in a test-time-displacement curve when the punch force is fixed at P (e.g., ...). Figure 9 (As shown), the machine was shut down after the test.

[0053] After the small punch creep test is performed on S3, axial specimen 42 and circumferential specimen 41 respectively, the force P applied by the small punch and the displacement δ curve of the punch 302 over the test time will be obtained.

[0054] S4. The equivalent creep stress σ of the axial specimen 42 and the circumferential specimen 41 is calculated using the impact force P recorded in step S3. The calculation formula (4) for the equivalent creep stress σ of the axial specimen 42 and the circumferential specimen 41 is as follows:

[0055]

[0056] Where S is the initial cross-sectional area at the center of sample 4, and K SP K is a constant, which is affected by the material properties of the sample and the friction coefficient of the small punch test device. SP It is approximately 0.55. The derivation of formula (4) is as follows:

[0057] The circumferential specimen 41 is fixed at its symmetrical edge relative to the yoz plane, and deforms after being impacted by the punch 302. A contact boundary line exists between the circumferential specimen 41 and the punch 302, with a contact angle of [missing information]. ,like Figure 8 As shown. According to thin film theory, under the action of impact force P, the circumferential specimen 41 has only a single thin film stress σ, which is the equivalent stress, equal to the uniaxial creep stress of the uniaxial standard creep specimen.

[0058] If there is no friction between the circumferential sample 41 and the punch 302, then:

[0059]

[0060] Where l is the width of the circumferential specimen 41, and h is the thickness of the deformed circumferential specimen 41. Calculation formula (1) can be rewritten as formula (2):

[0061]

[0062] During the steady-state creep stage, the thickness h and contact angle of the circumferential specimen 41 It is almost a constant value. Therefore, the calculation of stress σ in the steady-state creep stage can be simplified to formula (3):

[0063]

[0064] Where h0 is the initial thickness of the sample, formula (3) can be further written as:

[0065]

[0066] Formula (4) can also be used to calculate the equivalent stress of axial specimen 42 in the steady-state creep stage.

[0067] S5. The equivalent creep strain ε of the axial specimen 42 and the circumferential specimen 41 is calculated from the punch displacement δ of the small punch recorded in step S3. The formula (5) for calculating the equivalent creep strain ε is:

[0068]

[0069] The parts not mentioned in this embodiment are the same as in Embodiment 1.

[0070] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A small punch test method for studying the axial and circumferential creep of fuel cladding tubes, characterized in that, Includes the following steps: S1. Prepare a sample of the nuclear fuel cladding tube; The specimens in step S1 include axial specimens and circumferential specimens; S2. Install the small punch test device on the small punch test machine, and then install the sample from step S1 in the small punch test device for testing. The small punch test device includes a lower die, a small punch, and an upper die. The lower die has a punch hole, and the upper die has a guide groove. The sample is located between the upper die and the lower die. The upper die presses the sample against the lower die. The small punch passes through the guide groove and slides relative to the guide groove. The middle part of the sample is located between the small punch and the punch hole. The position of the punch hole matches the movement path of the small punch. S3. Perform a small punch creep test on the sample and record the punch force P and the punch displacement δ of the small punch. S4. Calculate the equivalent creep stress using the impact force P recorded in step S3. The equivalent creep stress The calculation formula is ， Where S is the initial cross-sectional area at the center of the sample. It is a constant; In step S4, The value corresponds to the coefficient of friction between the sample and the small punch test device. When the coefficient of friction between the small punch test device and the small punch test device is 0.2... It is 0.55; S5. The equivalent creep strain is calculated using the punch displacement δ of the small punch recorded in step S3. Equivalent creep strain The calculation formula is 。 2. The small punch test method for studying axial and circumferential creep of fuel cladding tubes according to claim 1, characterized in that: The lower die has a concave arc surface, and the punch is located at the center of the concave arc surface. The concave arc surface matches the part of the upper die that presses the sample.

3. The small punch test method for studying axial and circumferential creep of fuel cladding tubes according to claim 1, characterized in that: The upper mold has a convex arc surface, and the guide groove is located at the center of the convex arc surface. The convex arc surface matches the part of the lower mold that contacts the sample.

4. The small punch test method for studying axial and circumferential creep of fuel cladding tubes according to claim 1, characterized in that: The small punch includes a connected guide post and a punch. The punch is semi-circular and passes through a guide groove. The guide post slides relative to the guide groove, and the movement path of the punch matches the position of the punch hole.

5. The small punch test method for studying axial and circumferential creep of fuel cladding tubes according to claim 4, characterized in that: The cross-section of the punch is rectangular.

6. The small punch test method for studying axial and circumferential creep of fuel cladding tubes according to claim 5, characterized in that: The guide post has a rectangular cross-section, the guide groove has a rectangular cross-section, and the guide post and guide groove are matched.

7. The small punch test method for studying axial and circumferential creep of fuel cladding tubes according to claim 1, characterized in that: The samples were prepared using nuclear fuel cladding tubes.

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