Method and System for Calculating Stress Intensity Factor at Deepest Point of Axial Circular Corner Crack

Abstract

The present invention discloses a method and a system for calculating the stress intensity factor at the deepest point of an axial circular corner crack, which relates to the field of fracture mechanics. The key points of its technical solution are as follows: establishing a crack-free grid finite element model in combination with the analysis object and completing the elastic calculation under the internal pressure load; assuming an axial circular corner crack of a certain size in the inner corner area and calculating the ratio of the crack depth to the shell wall thickness; obtaining a fitting coefficient by combining the normal stress on the crack surface calculated by the finite element method and the assumed crack; classifying the assumed cracks according to the classification basis; and obtaining the stress intensity factor by using the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack at the inner corner of the nozzle established. The present invention is applicable to the calculation of the stress intensity factor at the deepest point of the axial circular corner crack at the inner corner of the nozzle with different assumed crack sizes.

Description

Technical Field

[0001] The present invention relates to the field of fracture mechanics, and more specifically, to a method and system for calculating the stress intensity factor at the deepest point of an axial circular corner crack in the nozzle inner corner region. Background Art

[0002] The nozzle of the reactor pressure vessel of a pressurized water reactor is a typical discontinuous region. Due to the characteristics of high stress distribution, high stress gradient, and high stress concentration in the discontinuous region, key attention needs to be paid in the structural integrity evaluation.

[0003] In the anti-breakaway analysis and evaluation of the nozzle inner corner region during the design and R & D stage, according to the anti-breakaway evaluation process, first, a crack defect with a safe size such as an axial circular corner crack defect is assumed in the nozzle inner corner region. Secondly, the stress intensity factor K result at the deepest point of the crack is calculated by using the stress results of the crack-free finite element model combined with the engineering analysis method. Then, a certain safety factor is considered for the analysis working condition (the safety factor is generally greater than or equal to 1.0). Finally, the amplified stress intensity factor K is compared with the fracture toughness K IC limit value of the nozzle component material to complete the structural integrity evaluation. Based on the above process, it can be seen that the calculation of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region is an important parameter in the anti-breakaway evaluation.

[0004] Currently, the formula provided in the ASME-XI (2017 Edition) code for calculating the stress intensity factor of an axial circular corner crack in the nozzle inner corner region under pressure is:

[0005] where a is the crack depth, and the coefficients A0 to A3 are obtained by fitting the normal stress on the crack surface, and the corresponding fitting formula is:

[0006] σ = A0 + A1(x / a) + A2(x / a) 2 + A3(x / a) 3 , where x is the distance from the starting point to the ending point of the crack depth.

[0007] Further research finds that the analysis object of ASME-XI (2017 Edition) is a nozzle with a 90° transition inner corner with the shell (as Figure 1 shown), and this method is conservative for the analysis object of a nozzle with a rounded corner transition inner corner with the shell (as Figure 2 shown). Therefore, this way of using the right-angle transition calculation formula for analyzing the rounded corner transition object is commonly used in engineering analysis, and thus ASME-XI (2017 Edition) selects the above processing method.

[0008] However, by taking over the inner corner area to establish a comparison between the real crack defect and the deepest stress intensity factor result of the axial circular corner crack obtained by the calculation method of ASME-XI (2017) Code, it is known that with different assumed crack defect depths, the accuracy of the deepest point stress intensity factor result of the axial circular corner crack in the inner corner area of the nozzle calculated by ASME-XI (2017) Code is too low, that is, when assuming a small-sized crack, the result of the stress intensity factor engineering method of ASME-XI (2017) Code is on the low side, and when assuming a large-sized crack, the result of the stress intensity factor engineering method of ASME-XI (2017) Code is on the high side.

[0009] Therefore, the engineering calculation method of the deepest point stress intensity factor of the axial circular corner crack in the inner corner area provided by ASME-XI (2017) Code can only be applied to the stress intensity factor analysis of crack defects with a certain specified size, and the accuracy of the stress intensity factor calculation results for other assumed crack defects is too low. Summary of the Invention

[0010] The purpose of the present invention is to provide a method and system for calculating the deepest point stress intensity factor of an axial circular corner crack to solve the problem of too low accuracy of the deepest point stress intensity factor of an axial circular corner crack provided by the prior art.

[0011] The above technical purpose of the present invention is achieved through the following technical solutions:

[0012] In the first aspect of the present invention, a method for calculating the deepest point stress intensity factor of an axial circular corner crack is provided. The method is used to calculate the stress intensity factor of the deepest point of the axial circular corner crack in the inner corner area of the nozzle, and the method includes:

[0013] Establish a crack-free mesh finite element model of the inner corner area of the nozzle structure, and complete the elastic calculation under the internal pressure load according to the crack-free mesh finite element model to obtain the finite element calculation result;

[0014] Obtain the thickness of the shell connected to the nozzle and the crack depth of an axial circular corner crack with a certain size in the inner corner area of the nozzle, and calculate the ratio of the crack depth to the shell thickness;

[0015] Based on the finite element calculation result, obtain the normal stress of the crack surface of the axial circular corner crack, and substitute the normal stress of the crack surface and the crack depth into the fitting formula of the normal stress of the crack surface to calculate the fitting coefficient;

[0016] Preset the classification threshold of the ratio, classify the ratio according to the classification threshold, and obtain the size classification result of the axial circular corner crack;

[0017] Calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region according to the size classification result, the fitting coefficient, and the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region.

[0018] In one implementation, obtain the thickness of the shell connected to the nozzle, specifically: take the minimum dimension of the wall thickness of the shell connected to the nozzle as the shell thickness.

[0019] In one implementation, the fitting coefficient includes a first coefficient, a second coefficient, a third coefficient, and a fourth coefficient;

[0020] The normal stress fitting formula for the crack surface is: σ = A0 + A1(x / a) + A2(x / a) 2 + A3(x / a) 3 , where σ represents the normal stress of the crack surface of the axial circular corner crack, a represents the crack depth of the axial circular corner crack, x represents the distance from the crack depth starting point to the crack depth ending point, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, and A3 represents the fourth coefficient.

[0021] In one implementation, the classification threshold is 0.16.

[0022] In one implementation, preset the classification threshold for the ratio, classify the ratio according to the classification threshold, and obtain the size classification result, including:

[0023] When the ratio is less than the classification threshold, obtain the first size;

[0024] When the ratio is equal to the classification threshold, obtain the second size;

[0025] When the ratio is greater than the classification threshold, obtain the third size.

[0026] In one implementation, calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region according to the size classification result, the fitting coefficient, and the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region, including:

[0027] If the ratio is the first size, combine the fitting coefficient and use the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region;

[0028] If the ratio is the second size, combine the fitting coefficient and use the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region;

[0029] If the ratio is the third dimension, combining the fitting coefficient and using the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region, calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region.

[0030] In one implementation, if the ratio is the first dimension, the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack is: Wherein, a represents the crack depth of the axial circular corner crack, t shell represents the thickness of the shell connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c represents the pressure applied to the crack surface, m is the ratio function, and K1 represents the stress intensity factor at the deepest point of the crack with the ratio being the first dimension.

[0031] In one implementation, if the ratio is the second dimension, the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack is: Wherein, a represents the crack depth of the axial circular corner crack, t shell represents the thickness of the shell connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c represents the pressure applied to the crack surface, and K2 represents the stress intensity factor at the deepest point of the crack with the ratio being the second dimension.

[0032] In one implementation, if the ratio is the third dimension, the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack is: Wherein, a represents the crack depth of the axial circular corner crack, t shell represents the thickness of the shell connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c represents the pressure applied to the crack surface, m represents the ratio function, and K3 represents the stress intensity factor at the deepest point of the crack with the ratio being the third dimension.

[0033] In a second aspect of the present invention, there is provided a system for calculating the stress intensity factor at the deepest point of an axial circular corner crack. The system is used to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region, and the system includes:

[0034] A finite element calculation module, configured to establish a crack-free mesh finite element model of the inner corner region of the nozzle structure, and complete elastic calculation under internal pressure load according to the crack-free mesh finite element model to obtain a finite element calculation result;

[0035] A ratio calculation module, configured to obtain the thickness of the shell connected to the nozzle, and the crack depth of an axial circular corner crack with a certain size in the inner corner area of the nozzle, and calculate the ratio of the crack depth to the shell thickness;

[0036] A fitting coefficient calculation module, configured to obtain the normal stress on the crack surface of the axial circular corner crack based on the finite element calculation result, substitute the normal stress on the crack surface and the crack depth into the crack surface normal stress fitting formula, and calculate the fitting coefficient;

[0037] A depth classification module, configured to preset a classification threshold for the ratio, classify the ratio according to the classification threshold, and obtain a size classification result of the axial circular corner crack;

[0038] A stress intensity factor calculation module, configured to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the nozzle according to the size classification result, the fitting coefficient, and the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the nozzle.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention provides a method for calculating the stress intensity factor at the deepest point of an axial circular corner crack. By correcting the stress intensity factor through the ratio of the crack depth to the wall thickness of the shell, a highly reliable analysis method for calculating the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner of the nozzle is established, providing technical support for the analysis and evaluation of the resistance to brittle fracture in the inner corner area of the nozzle. Description of the Drawings

[0041] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0042] Figure 1 Shows a schematic diagram of a hypothetical circular corner crack in the 90° transition inner corner area between the nozzle and the shell provided by the prior art;

[0043] Figure 2 Shows a schematic diagram of a hypothetical circular corner crack in the inner corner area with a rounded transition between the nozzle and the shell provided by the prior art;

[0044] Figure 3 Shows a schematic flowchart of the method for calculating the stress intensity factor at the deepest point of the axial circular corner crack provided by the embodiment of the present invention;

[0045] Figure 4 Shows a specific step flowchart of the method for calculating the stress intensity factor at the deepest point of the axial circular corner crack provided by the embodiment of the present invention. Detailed implementation manners

[0046] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings. The illustrative implementation manners of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0047] It should be noted that the term "comprising" or "may comprise" that can be used in various embodiments of the present application indicates the presence of the claimed functions, operations or elements, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present application, the terms "comprising", "having" and their cognates are only intended to represent specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be construed as first excluding the existence or addition of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0048] It should be understood that terms such as "first", "second", "third" are only used for descriptive purposes 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", "second", "third" 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] Regarding the problem that the engineering calculation method of the stress intensity factor at the deepest point of the axial circular corner crack provided by the ASME-XI (2017) code can only be applied to the stress intensity factor analysis of crack defects of a certain specified size, and the accuracy of the calculation results of the stress intensity factors of assumed crack defects of other sizes is too low, an embodiment of the present invention provides a method for calculating the stress intensity factor at the deepest point of the axial circular corner crack. The method is used to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region. By means of correcting the stress intensity factor according to the ratio of the crack depth to the shell wall thickness, a highly reliable analysis method for calculating the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner is established, providing technical support for the analysis and evaluation of the resistance to brittle fracture in the nozzle inner corner region.

[0050] The following will make a detailed explanation and description of a method for calculating the stress intensity factor at the deepest point of the axial circular corner crack provided by the embodiments of the present application in conjunction with specific implementation manners. Please refer to Figure 3 , Figure 3 shows a schematic flow chart of the method for calculating the stress intensity factor at the deepest point of the axial circular corner crack provided by the embodiments of the present invention. AsFigure 3 As shown, the method includes:

[0051] S301, establish a crack-free mesh finite element model for the corner region of the takeover structure, and complete the elastic calculation under the internal pressure load according to the crack-free mesh finite element model to obtain the finite element calculation result.

[0052] In this embodiment, the construction of the crack-free mesh finite element model and the elastic calculation under the internal pressure load are both well-known technologies to those skilled in the art. Specifically, it can also be known from the discussion of the technical background. For example, in the anti-rapid fracture analysis and evaluation of the corner region of the takeover during the design and R & D stage of the existing technology, according to the anti-rapid fracture evaluation process, first assume a crack defect with a safe size such as an axial circular corner crack defect in the corner region of the takeover, and secondly use the stress result of the crack-free finite element model combined with the engineering analysis method to calculate the stress intensity factor K at the deepest point of the crack, then consider a certain safety factor for the analysis condition (the safety factor is generally greater than or equal to 1.0), and finally compare the amplified stress intensity factor K with the fracture toughness K IC limit value of the takeover component material to complete the structural integrity evaluation. It can be seen from the above process that the calculation of the stress intensity factor at the deepest point of the axial circular corner crack in the corner region of the takeover is an important parameter in the anti-rapid fracture evaluation. Therefore, this embodiment does not give a detailed description of how to establish a crack-free mesh finite element model and complete the elastic calculation under the internal pressure load.

[0053] S302, obtain the thickness of the shell connected to the takeover and the crack depth of an axial circular corner crack with a certain size in the corner region of the takeover, and calculate the ratio of the crack depth to the shell thickness.

[0054] In this embodiment, obtaining the thickness of the shell connected to the takeover specifically means: taking the minimum size of the wall thickness of the shell connected to the takeover as the shell thickness. It can be understood that an axial circular corner crack with a certain size is assumed in the corner region of the takeover.

[0055] Correspondingly, the ratio of the crack depth to the shell thickness is a / t shell .

[0056] S303, obtain the normal stress of the crack surface of the axial circular corner crack based on the finite element calculation result, and substitute the normal stress of the crack surface and the crack depth into the crack surface normal stress fitting formula to calculate the fitting coefficient.

[0057] Specifically, the fitting coefficient includes the first coefficient, the second coefficient, the third coefficient, and the fourth coefficient. The crack surface normal stress fitting formula is: σ = A0 + A1(x / a) + A2(x / a) 2 + A3(x / a) 3, where σ represents the normal stress of the crack surface of the axial circular corner crack, a represents the crack depth of the axial circular corner crack, x represents the distance from the starting point to the ending point of the crack depth, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, and A3 represents the fourth coefficient.

[0058] S304, preset the classification threshold of the ratio, classify the ratio according to the classification threshold, and obtain the size classification result of the axial circular corner crack.

[0059] In this embodiment, the classification threshold of the preset ratio is 0.16. Classify the assumed crack in step S302 according to the classification basis of 0.16. When the ratio is less than the classification threshold, obtain the first size; when the ratio is equal to the classification threshold, obtain the second size; when the ratio is greater than the classification threshold, obtain the third size, as follows:

[0060]

[0061] S305, calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle internal corner region according to the size classification result, the fitting coefficient, and the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle internal corner region.

[0062] Specifically, if the ratio is the first size, combine the fitting coefficient and use the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle internal corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle internal corner region. If the ratio is the first size, the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack is: Among them, a represents the crack depth of the axial circular corner crack, t shell represents the thickness of the shell connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c represents the pressure applied to the crack surface, m represents the ratio function, and K1 represents the stress intensity factor at the deepest point of the crack with the first size ratio.

[0063] If the ratio is the second size, combine the fitting coefficient and use the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle internal corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle internal corner region. If the ratio is the second size, the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack is: Among them, a represents the crack depth of the axial circular corner crack, t shellDenote the thickness of the shell connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c Denote the pressure applied to the crack surface, and K2 represents the stress intensity factor at the deepest point of the crack with the ratio of the second dimension.

[0064] If the ratio is the third dimension, combine the fitting coefficients and use the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the nozzle to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the nozzle. If the ratio is the first dimension, the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack is: Among them, a represents the crack depth of the axial circular corner crack, t shell Denote the thickness of the shell connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c Denote the pressure applied to the crack surface, m represents the ratio function, and K3 represents the stress intensity factor at the deepest point of the crack with the ratio of the third dimension.

[0065] For the specific steps of the method for calculating the stress intensity factor at the deepest point of the axial circular corner crack provided above, this embodiment also provides a detailed implementation process. Please refer to Figure 4 S10 to S70.

[0066] First, the known parameters include the geometric dimensions of the nozzle structure, the applied internal pressure value of 1.0 MPa, and the pressure value applied to the crack surface of 1.0 Mpa.

[0067] In Example 1, enter S10, establish a meshless finite element model of the nozzle structure and complete the elastic calculation; enter S20, assume the crack size in the inner corner area of the nozzle is a = 36.73 mm; enter S30, obtain the coefficients A0 = 14.52, A1 = -4.12, A2 = 0.78, A3 = 0.09 obtained by fitting the normal stress of the crack surface; enter S40, classify the assumed crack by size. Since the a / t of the assumed crack shell = 0.1068, which is less than 0.16, so the assumed crack is the first dimension; enter S50, calculate the stress intensity factor K1 = 4.30 MPa·m at the deepest point of the assumed crack 1 / 2 .

[0068] Example 2, enter S10, establish a meshless finite element model of the takeover structure and complete the elastic calculation; enter S20, assume the crack size in the inner corner area of the takeover is a = 74.23 mm; enter S30, obtain the coefficients A0 = 14.52, A1 = -8.56, A2 = 4.66, A3 = -1.19 obtained by fitting the normal stress on the crack surface; enter S40, classify the assumed crack by size. Since a / t of the assumed crack shell = 0.2158, which is greater than 0.16, so the assumed crack is of the third size; enter S50, calculate the stress intensity factor K3 = 4.91 MPa·m at the deepest point of the assumed crack 1 / 2 .

[0069] The present invention also provides a system for calculating the stress intensity factor at the deepest point of an axial circular corner crack. This system can be used to execute the method for calculating the stress intensity factor at the deepest point of an axial circular corner crack provided in the above embodiments. The system is used to calculate the stress intensity factor at the deepest point of an axial circular corner crack in the inner corner area of the takeover. The system includes:

[0070] A finite element calculation module, which is used to establish a meshless finite element model of the inner corner area of the takeover structure, and complete the elastic calculation under the internal pressure load according to the meshless finite element model to obtain the finite element calculation result;

[0071] A ratio calculation module, which is used to obtain the thickness of the shell connected to the takeover and the crack depth of an axial circular corner crack with a certain size in the inner corner area of the takeover, and calculate the ratio of the crack depth to the shell thickness;

[0072] A fitting coefficient calculation module, which is used to obtain the normal stress on the crack surface of the axial circular corner crack based on the finite element calculation result, and substitute the normal stress on the crack surface and the crack depth into the crack surface normal stress fitting formula to calculate the fitting coefficient;

[0073] A depth classification module, which is used to preset the classification threshold of the ratio, classify the ratio according to the classification threshold, and obtain the size classification result of the axial circular corner crack;

[0074] A stress intensity factor calculation module, which is used to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the takeover according to the size classification result, the fitting coefficient and the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the takeover.

[0075] The system for calculating the stress intensity factor at the deepest point of an axial circular corner crack in the embodiments of this application, compared with the above Figure 3The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack shown is an invention based on the same concept. Through the above detailed description of the method for calculating the stress intensity factor at the deepest point of an axial circular corner crack, those skilled in the art can clearly understand the implementation process of the system for calculating the stress intensity factor at the deepest point of an axial circular corner crack in this embodiment. Therefore, for the sake of brevity of the specification, it will not be repeated here.

[0076] Correspondingly, the system for calculating the stress intensity factor at the deepest point of an axial circular corner crack provided in the embodiment of the present application establishes a highly reliable analysis system for calculating the stress intensity factor at the deepest point of an axial circular corner crack at the inner corner of a nozzle by adopting a stress intensity factor correction method corresponding to the ratio of the assumed crack size to the wall thickness of the shell.

[0077] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the stress intensity factor at the deepest point of an axial circular corner crack, characterized in that, A method for calculating the stress intensity factor at the deepest point of an axial circular corner crack in the nozzle inner corner region, the method comprising: Establishing a crack-free mesh finite element model of the nozzle inner corner region of the nozzle structure, and performing elastic calculation under internal pressure load according to the crack-free mesh finite element model to obtain finite element calculation results; Obtaining the thickness of the shell connected to the nozzle and the crack depth of an axial circular corner crack with a certain size in the nozzle inner corner region, and calculating the ratio of the crack depth to the shell thickness; Obtaining the normal stress of the crack surface of the axial circular corner crack based on the finite element calculation results, and substituting the normal stress of the crack surface and the crack depth into the crack surface normal stress fitting formula to calculate the fitting coefficient; Presetting a classification threshold for the ratio, classifying the ratio according to the classification threshold, and obtaining a size classification result of the axial circular corner crack; Calculating the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region according to the size classification result, the fitting coefficient, and the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region.

2. The method for calculating the stress intensity factor of the deepest point of an axial circular corner crack according to claim 1, characterized in that, Obtaining the thickness of the shell connected to the nozzle, specifically: taking the minimum size of the wall thickness of the shell connected to the nozzle as the shell thickness.

3. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 1, characterized in that, The fitting coefficient includes a first coefficient, a second coefficient, a third coefficient, and a fourth coefficient; The fitting formula for the normal stress of the crack surface is: σ = A0 + A1(x / a) + A2(x / a) 2 + A3(x / a) 3 , where σ represents the normal stress of the crack surface of the axial circular corner crack, a represents the crack depth of the axial circular corner crack, x represents the distance from the starting point of the crack depth to the ending point of the crack depth, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, and A3 represents the fourth coefficient.

4. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 1, wherein The classification threshold is 0.

16.

5. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 1, wherein Presetting a classification threshold for the ratio, classifying the ratio according to the classification threshold, and obtaining a size classification result, including: When the ratio is less than the classification threshold, obtaining a first size; When the ratio is equal to the classification threshold, obtaining a second size; When the ratio is greater than the classification threshold, obtaining a third size.

6. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 5, wherein Calculating the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region according to the size classification result, the fitting coefficient, and the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region, including: If the ratio is the first size, combining the fitting coefficient and using the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region; If the ratio is the second size, combining the fitting coefficient and using the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region; If the ratio is the third size, combining the fitting coefficient and using the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the nozzle inner corner region.

7. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 6, characterized in that, If the ratio is the first size, the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack is: Among them, a represents the crack depth of the axial circular corner crack, t shell represents the shell thickness connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c represents the pressure applied to the crack surface, m is the ratio function, and K1 represents the stress intensity factor at the deepest point of the crack with a ratio of the first dimension.

8. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 6, characterized in that, If the ratio is the second size, the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack is: Among them, a represents the crack depth of the axial circular corner crack, and t shell represents the shell thickness connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, and p c represents the pressure applied to the crack surface, and K2 represents the stress intensity factor at the deepest point of the crack with a ratio of the second dimension.

9. The method for calculating the stress intensity factor at the deepest point of an axial circular corner crack according to claim 6, characterized in that, If the ratio is the third size, the calculation formula for the stress intensity factor at the deepest point of the axial circular corner crack is: Among them, a represents the crack depth of the axial circular corner crack, t shell represents the shell thickness connected to the nozzle, A0 represents the first coefficient, A1 represents the second coefficient, A2 represents the third coefficient, A3 represents the fourth coefficient, p c represents the pressure applied to the crack surface, m is the ratio function, and K3 represents the stress intensity factor at the deepest point of the crack with a ratio of the third dimension.

10. A system for calculating the stress intensity factor at the deepest point of an axial circular corner crack, characterized in that, A system for calculating the stress intensity factor at the deepest point of an axial circular corner crack in the nozzle inner corner region, the system comprising: A finite element calculation module is used to establish a crack-free mesh finite element model for the inner corner area of the nozzle structure, and complete elastic calculations under internal pressure loads according to the crack-free mesh finite element model to obtain finite element calculation results; A ratio calculation module is used to obtain the thickness of the shell connected to the nozzle and the crack depth of an axial circular corner crack with a certain size in the inner corner area of the nozzle, and calculate the ratio of the crack depth to the shell thickness; A fitting coefficient calculation module is used to obtain the normal stress on the crack surface of the axial circular corner crack based on the finite element calculation results, substitute the normal stress on the crack surface and the crack depth into the crack surface normal stress fitting formula, and calculate the fitting coefficient; A depth classification module is used to preset the classification threshold of the ratio, classify the ratio according to the classification threshold, and obtain the size classification result of the axial circular corner crack; A stress intensity factor calculation module is used to calculate the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the nozzle according to the size classification result, the fitting coefficient, and the calculation formula of the stress intensity factor at the deepest point of the axial circular corner crack in the inner corner area of the nozzle.

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