A method for predicting fracture toughness of a ship stop crack steel based on a fracture toughness test

Abstract

The application provides a method for predicting crack arrest toughness of marine crack arrest steel based on fracture toughness test, and relates to the field of fracture and crack arrest technology evaluation of high-strength crack arrest steel. ca The method adopts swallow tail crack arrest toughness test, double tension crack arrest toughness test, obtains data through fracture toughness test, and converts to establish a crack arrest toughness K ca Correlation model of fracture toughness δ, so as to predict the crack arrest toughness of the material by using the model. The method of the application has simple process, low operation difficulty, low cost for establishing the prediction model, high efficiency, high precision, and is beneficial to large-scale industrial application and promotion.

Description

Technical Field

[0001] This invention relates to the field of fracture and crack arrest technology evaluation of high-strength crack-arresting steel for marine applications, and in particular to a method for predicting the crack arrest toughness of crack-arresting steel for marine applications based on fracture toughness tests. Background Technology

[0002] High-strength steel plates used in critical components of large container ships, such as hatch coamings, webs, and upper deck keels, need to possess not only good low-temperature fracture toughness but also excellent crack arrest toughness. International classification societies require that marine high-strength steel plates undergo crack arrest performance verification before leaving the factory, and only those meeting the requirements can be used. Typically, crack arrest toughness at -10 °C is a crucial indicator for evaluating whether it meets the usage requirements.

[0003] Large-size wide-plate tensile testing (double tensile or ESSO) is an internationally accepted method for evaluating the crack arrest toughness of high-strength marine steel plates. The specimen size is typically 500mm × 500mm × B (B being the specimen thickness). This requires a large testing space and testing equipment with a tensile capacity of at least 1000 tons. Currently, only the Luoyang Shipbuilding Materials Research Institute in my country possesses the capability to conduct large-size double tensile tests and holds testing qualifications recognized by international classification societies. Typically, the successful completion of a single specimen's crack arrest toughness test takes 7-14 days. For the same batch of steel plates, obtaining crack arrest toughness at -10 °C requires the successful testing of at least 4-5 samples. Therefore, the large-size wide-plate tensile crack arrest toughness evaluation method suffers from drawbacks such as long testing cycles and high equipment requirements, making it difficult to meet the growing domestic demand for crack arrest toughness evaluation. Consequently, extensive research has been conducted both domestically and internationally, developing small-size crack arrest toughness evaluation methods and establishing various correlation models between crack arrest toughness and characterization parameters of small-size specimens. For example, small-size dovetail-shaped specimens are used instead of large-size wide-plate tensile tests to establish a crack arrest toughness K... ca Correlation model with non-plastic transformation temperature (NDT), crack arrest toughness K ca Correlation model with Charpy impact energy, crack arrest toughness K ca FATT (Fall Weight Transition Temperature) 50 Correlation models and other methods were used to establish the relationship between small-scale tests and large-scale crack arrest toughness tests, clarifying the basic mechanical parameters affecting crack arrest performance. This provided a clear direction for the regulation and evaluation of crack arrest performance and greatly promoted the development of crack arrest steel in China.

[0004] Chinese patent CN118566037A discloses a method for predicting the crack arrest temperature of crack-arresting steel based on a drop-weight tear test. This method involves conducting numerous double tensile tests on crack-arresting steels of different thicknesses and strength grades to obtain the crack arrest temperature T. kThen, for each specification and strength grade of crack-arresting steel, a series of drop-weight tear tests were conducted to obtain the drop-weight tear ductile-brittle transition curve and the drop-weight tear transition temperature (FATT). 50 Further analysis was conducted on the correlation between characteristic crack arrest temperature and drop hammer tear transition temperature (FATT50), and a correlation model was established to enable rapid prediction of crack arrest performance using FATT50. However, the drop hammer test equipment used in this invention is large in size, the test process is cumbersome, and in particular, the temperature control accuracy of the drop hammer test is insufficient, making it difficult to guarantee the authenticity of the fitted data.

[0005] Therefore, existing technologies employ large-scale double tensile tests, drop hammer tear tests, and dovetail tests to measure crack arrest toughness K. ca On the one hand, the required sample size is large, 4-5 samples are needed to complete a set of tests, and the testing cycle for a single sample is long and expensive. On the other hand, the equipment required for the test is large, the test process is cumbersome, and it is difficult to guarantee the authenticity of the fitted data.

[0006] Chinese patent CN118673739A discloses a crack evaluation method for crack-arresting steel based on finite element simulation calculation. This method combines relevant parameters from small laboratory sample tests with calculations from a full-size finite element model to calculate the crack-arresting performance of the steel. ca The value is given and a reasonable evaluation is provided; however, it is practically difficult to pre-create a crack of the same size as that in the experiment inside the specimen. The location, shape, and size of the pre-created crack are difficult to match those in the experiment, hence the calculated K value is... ca The value deviates significantly from the actual value, making its authenticity difficult to predict. Summary of the Invention

[0007] The purpose of this invention is to provide a method for rapidly predicting crack arrest toughness based on the fracture toughness of marine high-strength steel, in order to solve the technical problems existing in the crack arrest toughness testing method, such as long test cycle, high cost, large sample size, difficulty in obtaining relevant parameters in the way the pre-made crack location, shape and size are the same as those in the test, and large deviation between calculated values ​​and actual values.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing, the method comprising the following steps:

[0010] S1. Crack Arrest Toughness Test: Crack arrest toughness tests were conducted on marine crack-arresting steel at different thicknesses and temperatures to obtain the crack arrest toughness K of crack-arresting steel of different dimensions at different temperatures. ca Record the crack arrest temperature T during the experiment. ck ;

[0011] S2. Fracture toughness test: Using compact tensile specimens, fracture toughness tests were conducted at different crack arrest temperatures to obtain the corresponding CTOD data, denoted by δ.

[0012] S3. Data Conversion: Based on the crack arrest toughness dimension conversion relationship, convert the data obtained in S1 into a result with the same thickness as the fracture toughness specimen in step S2.

[0013] S4. Model Establishment: Based on the data transformation results from S3, establish the crack arrest toughness K. ca Correlation model with fracture toughness δ;

[0014] S5. Fracture Toughness Test Prediction: When predicting crack arrest toughness, CTOD data obtained through fracture toughness tests will be input into the correlation model in S4 to calculate the crack arrest toughness K during new research and development and trial production. ca predict.

[0015] Optionally, the marine crack arresting steel in S1 is EH47 crack arresting steel plate; the maximum thickness of the marine crack arresting steel shall not exceed 80mm.

[0016] Optionally, the crack arrest toughness test of S1 specifically includes the following steps:

[0017] S11. Fatigue cracks are pre-formed on the dovetail specimen using a fatigue testing machine. The length of the fatigue crack is about 5 mm, so that the brittle crack can be successfully initiated under tensile load.

[0018] S12. Install the sample and cooling device on the testing machine, establish a suitable gradient temperature field in the dovetail sample, apply a lower temperature source in the upper half of the gradient temperature field and apply a heat source in the lower half to form a stable temperature gradient within the entire temperature gradient field.

[0019] S13. Maintain the temperature gradient field for a duration that depends on the sample thickness. Once the temperature field stabilizes, activate the tensile device to initiate and rapidly propagate the brittle crack from the fatigue crack tip. After the test, pull the sample apart and record the crack length *a* and the temperature *T* at the crack tip. ck .

[0020] Optionally, the fracture toughness test of S2 includes the following steps:

[0021] S21. Install the compact tensile specimen on the testing machine and install a low-temperature COD extensometer on the specimen. The COD extensometer is used to measure the crack opening displacement in the specimen during loading in order to calculate δ.

[0022] S22. Adjust the temperature of the ambient chamber to ensure the stability of the test temperature. After the temperature reaches the predetermined temperature, maintain it for 25 minutes before starting the test. Finally, calculate δ using the following formula:

[0023]

[0024] In the formula, F is the fracture load, in kN; B is the thickness of the specimen, in mm; ν is Poisson's ratio; E is the elastic model of the material, in MPa; m and τ are both material coefficients; V p This represents the plastic component of the load-displacement curve.

[0025] Optionally, the crack arresting toughness K ca The calculation method is as follows: The J integral value at the crack tip of the arresting crack is obtained by integrating the contour plot in the finite element software ABAQUS. The conversion relationship between the J integral and the stress intensity factor K is shown in the following formula:

[0026] ;

[0027] In the formula, J is the J integral at the crack tip, in N / mm, E is the elastic modulus of the material, in MPa, and v is the Poisson's ratio of the material, usually 0.3.

[0028] The crack arrest toughness of the specimen at the moment of crack arrest was obtained.

[0029] Optionally, the crack arresting toughness K ca The calculation formula is:

[0030]

[0031] In the formula, σ is the tensile stress, in MPa; a is the crack arrest length, in mm; W s The width of the sample is in mm.

[0032] Optionally, the dovetail-shaped sample has dimensions of 250mm × 100mm × B, where B is the thickness of the sample in mm.

[0033] Optionally, the fracture toughness test specimen has dimensions of 62.5 mm × 60 mm × 25 mm.

[0034] Optionally, the crack arrest toughness dimension conversion formula described in S3 is:

[0035]

[0036] In the formula, K ca (B) represents the crack arrest toughness of a specimen with thickness B, and f(B) is a size factor related to the specimen thickness, which is calculated using the following formula:

[0037] .

[0038] Optionally, a model can be built in S4, and the crack arrest toughness K can be established using linear regression analysis. ca A correlation model between fracture toughness δ and fracture toughness δ.

[0039] Optionally, in S5, the fracture toughness test prediction is performed. Based on the crack arrest toughness prediction model, the predicted and measured values ​​of crack arrest toughness for each group of tests are compared. If the deviation between the predicted and measured values ​​is greater than 20%, S1-S4 need to be repeated to obtain a crack arrest toughness prediction model where the difference between the predicted and measured values ​​is less than 20%.

[0040] Technical principle of the invention:

[0041] Thanks to its excellent crack propagation resistance and low-temperature fracture toughness, crack-arresting steel is widely used in high-stress areas such as decks and webs of large container ships. In the research and application of crack-arresting steel, crack-arresting toughness testing is required for each batch of products; only those meeting the crack-arresting performance requirements are used. Current crack-arresting toughness testing typically employs large-scale double tensile tests. This method requires a tensile testing machine with a capacity of over 1000 tons, consumes a large amount of coolant to establish the temperature field, has a long testing cycle, is expensive, and requires a large amount of welding material for tooling connections. Therefore, in the research and application of crack-arresting steel, using small-sized samples to quickly evaluate its crack-arresting toughness is crucial for shortening research and development time and reducing testing costs.

[0042] Fracture toughness testing is one of the most common testing methods for the mechanical properties of metallic materials, primarily used to evaluate a material's resistance to crack propagation. Two types of specimens are used for fracture toughness testing: compact tension (CT) and three-point bending (TPB). These tests involve small specimen sizes, are easy to fabricate, and have well-established testing standards. Many steel mills have the necessary testing facilities, resulting in low testing costs and widespread application in the mechanical property testing of metallic materials.

[0043] The CT specimen is subjected to tensile load during the test, which is similar to the working condition of the specimen in the tensile test of large-size wide plate. If the correlation between fracture toughness and crack arrest toughness can be established, and then the crack arrest toughness of crack arrest steel at different temperatures can be quickly evaluated through small-size fracture toughness test, it will be of great significance for shortening the research and development process and promoting the rapid application of products.

[0044] The method for rapidly predicting crack arrest toughness based on fracture toughness testing described in this invention uses small-scale fracture toughness tests at different temperatures to replace large-scale crack arrest toughness tests for predicting the crack arrest toughness of crack-arresting steel, and establishes the crack arrest toughness K... caThe correlation model with CTOD can be used to predict crack arrest toughness in subsequent material development by combining the proposed correlation model with a series of low-temperature fracture toughness tests.

[0045] First, the low-temperature fracture toughness test method is mature, the equipment is simple, and the relevant test standards and specifications are complete, resulting in low test costs and short cycles. Second, the fracture toughness test uses a 25 mm thick standard CT specimen, which is small in size, saving a lot of material and specimen processing costs. Third, based on this, the crack arrest toughness can be predicted relatively accurately.

[0046] The correlation model is as follows:

[0047]

[0048] In the formula, K ca Crack stopping toughness, in N / mm 2 / 3 (MPa·mm) 1 / 2 ), δ represents the CTOD data obtained from the fracture toughness test, in µm; A, B, C, and D are fitting parameters.

[0049] The above technical solution has at least the following advantages compared with the existing technology:

[0050] The above-mentioned scheme, a method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test, is based on the inherent relationship between dovetail crack arrest toughness test and small-size fracture toughness test in terms of crack initiation, and establishes a correlation model that can predict crack arrest performance more accurately.

[0051] The fracture toughness test specimens of this invention are small in size and require low load on the test equipment, which can save a lot of materials and testing costs. It is suitable for batch testing in the research and development process of crack-arresting steel.

[0052] The method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing, as described in this invention, is mature and has a short testing cycle. By replacing large-scale crack arrest toughness tests with fracture toughness tests, the testing cycle is shortened from 15 days to 0.5 days, and the sample cost is reduced from tens of thousands of yuan to several hundred yuan.

[0053] The crack arresting toughness K of the present invention ca The correlation model with fracture toughness δ shows that the deviation between the predicted value and the actual value can be as small as 0.15%. According to the results of 18 measured temperature points, the prediction deviation of 78% of the data is less than 10%.

[0054] In summary, compared with traditional fracture and crack arrest technology evaluation techniques for high-strength crack-arresting steel used in marine applications, the method of this invention uses dovetail crack arrest toughness tests and fracture toughness tests to obtain data, which are then converted to establish and obtain the crack arrest toughness K with the smallest deviation from the actual value.ca A correlation model between the fracture toughness δ and the model is used to predict the fracture toughness δ. This method is simple to implement, easy to operate, and the prediction model is low-cost, efficient, and accurate, which is conducive to large-scale industrial application and promotion. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a schematic diagram of the dovetail-type crack arrest toughness test in a method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness testing according to the present invention; wherein, Figure 1 a is the overall experimental diagram. Figure 1 b is a partial view of the experiment. Figure 1 c is a schematic diagram of the dovetail-shaped specimen;

[0057] Figure 2 This is a schematic diagram of a fracture toughness specimen in a method for predicting the crack arrest toughness of marine crack arresting steel based on fracture toughness test according to the present invention.

[0058] Figure 3a This is a comparison graph showing the relationship between the crack arrest toughness of 20 mm and 80 mm thick specimens and the test temperature in a method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test according to the present invention.

[0059] Figure 3b This is a comparison chart showing the relationship between the crack arrest toughness results of 20 mm and 80 mm thick samples and the crack arrest toughness of 25 mm thick samples versus the test temperature in a method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test according to the present invention.

[0060] Figure 4 This is a graph showing the relationship between the fracture toughness δ of a 25 mm thick sample and the test temperature in a method for predicting the crack arrest toughness of marine crack arresting steel based on fracture toughness test according to the present invention.

[0061] Figure 5 This invention relates to a method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing, where the crack arrest toughness K is... ca Correlation diagram between fracture toughness δ and fracture toughness δ;

[0062] Figure 6 This is a graph showing the relationship between the predicted crack arrest toughness and the measured crack arrest toughness in a method for predicting crack arrest toughness of marine crack arrest steel based on fracture toughness test according to the present invention.

[0063] Figure 7 This is a schematic diagram of the double tensile crack arrest toughness test in a method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test according to the present invention.

[0064] Figure 8 This invention relates to a crack arrest toughness K based on the results of a dual tensile crack arrest toughness test. ca Correlation diagram between fracture toughness δ and fracture toughness δ;

[0065] Figure 9 This is a graph showing the relationship between the predicted and measured values ​​of crack arrest toughness based on the results of a double tensile crack arrest toughness test, according to the present invention. Detailed Implementation

[0066] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0067] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0068] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0069] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0070] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0071] A method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing, the method comprising the following steps:

[0072] S1. Crack Arrest Toughness Test: Crack arrest toughness tests were conducted on marine crack-arresting steel at different thicknesses and temperatures to obtain the crack arrest toughness K of crack-arresting steel of different dimensions at different temperatures. ca Record the crack arrest temperature T during the experiment. ck ;

[0073] S2. Fracture toughness test: Using compact tensile specimens, fracture toughness tests were conducted at different crack arrest temperatures to obtain the corresponding CTOD data, denoted by δ.

[0074] S3. Data Conversion: Based on the crack arrest toughness dimension conversion relationship, convert the data obtained in S1 into a result with the same thickness as the fracture toughness specimen in step S2.

[0075] S4. Model Establishment: Based on the data transformation results from S3, establish the crack arrest toughness K. ca Correlation model with fracture toughness δ;

[0076] S5. Fracture Toughness Test Prediction: When predicting crack arrest toughness, CTOD data obtained through fracture toughness tests will be input into the correlation model in S4 to calculate the crack arrest toughness K during new research and development and trial production. ca predict.

[0077] Specifically, the marine crack arresting steel in S1 is EH47 crack arresting steel plate; the maximum thickness of the marine crack arresting steel is no more than 80mm.

[0078] Specifically, the crack arrest toughness test of S1 includes the following steps:

[0079] S11. Fatigue cracks are pre-formed on the specimen using a fatigue testing machine. The length of the fatigue crack is about 5 mm, so that the brittle crack can be successfully initiated under tensile load.

[0080] S12. Install the sample and cooling device on the testing machine, establish a suitable gradient temperature field in the sample, apply a lower temperature source in the upper half of the gradient temperature field and a heat source in the lower half, so as to form a stable temperature gradient in the entire temperature gradient field.

[0081] S13. Maintain the temperature gradient field for a duration that depends on the sample thickness. Once the temperature field stabilizes, activate the tensile device to initiate and rapidly propagate the brittle crack from the fatigue crack tip. After the test, pull the sample apart and record the crack length *a* and the temperature *T* at the crack tip. ck .

[0082] Specifically, the fracture toughness test of S2 includes the following steps:

[0083] S21. Install the compact tensile specimen on the testing machine and install a low-temperature COD extensometer on the specimen. The COD extensometer is used to measure the crack opening displacement in the specimen during loading in order to calculate δ.

[0084] S22. Adjust the temperature of the ambient chamber to ensure the stability of the test temperature. After the temperature reaches the predetermined temperature, maintain it for 25 minutes before starting the test. Finally, calculate δ using the following formula:

[0085]

[0086] In the formula, F is the fracture load, in kN; B is the thickness of the specimen, in mm; ν is Poisson's ratio; E is the elastic model of the material, in MPa; m and τ are both material coefficients; V p This represents the plastic component of the load-displacement curve.

[0087] Specifically, the crack arrest toughness K ca The calculation method is as follows: The J integral value at the crack tip of the arresting crack is obtained by integrating the contour plot in the finite element software ABAQUS. The conversion relationship between the J integral and the stress intensity factor K is shown in the following formula:

[0088] ;

[0089] In the formula, J is the J integral at the crack tip, in N / mm, E is the elastic modulus of the material, in MPa, and v is the Poisson's ratio of the material, usually 0.3.

[0090] The crack arrest toughness of the specimen at the moment of crack arrest was obtained.

[0091] Specifically, the sample size is 250mm × 100mm × B, where B is the thickness of the sample in mm.

[0092] Specifically, the fracture toughness test specimen has dimensions of 62.5 mm × 60 mm × 25 mm.

[0093] Specifically, the formula for converting crack arrest toughness dimensions described in S3 is:

[0094]

[0095] In the formula, K ca (B) represents the crack arrest toughness of a specimen with thickness B, and f(B) is a size factor related to the specimen thickness, which is calculated using the following formula:

[0096] .

[0097] Specifically, a model was established in S4, and the crack arrest toughness K was determined using linear regression analysis. ca A correlation model between fracture toughness δ and fracture toughness δ.

[0098] Specifically, in S5, the fracture toughness test prediction is conducted. Based on the crack arrest toughness prediction model, the predicted and measured values ​​of crack arrest toughness for each group of tests are compared. If the deviation between the predicted and measured values ​​is greater than 20%, S1-S4 need to be repeated to obtain a crack arrest toughness prediction model where the difference between the predicted and measured values ​​is less than 20%.

[0099] Example 1

[0100] A method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test is proposed. According to the requirements of the rapid prediction method of crack arrest toughness, 18 crack arrest steels were selected for test, and the crack arrest toughness and fracture toughness at different temperatures were measured. A correlation model between crack arrest toughness and fracture toughness was constructed.

[0101] The method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing is combined with Figure 1 a and Figure 1 b includes the following steps:

[0102] S1. Crack Arrest Toughness Test: 18 groups of dovetail-shaped crack arrest toughness test specimens were selected for marine crack-arrest steel, such as... Figure 1 As shown in Figure c, dovetail-shaped crack arrest toughness tests were conducted at different thicknesses and temperatures. The dimensions of the dovetail-shaped crack arrest toughness specimens were 250mm × 100mm × B, where B is the thickness of the specimen. The test material was EH47 marine crack arresting steel. The crack arrest toughness K of different sizes of crack arresting steel at different temperatures was obtained. ca Record the crack arrest temperature T during the experiment. ck ;

[0103] S2, Fracture toughness test: The following method is used... Figure 2 The compact tensile specimen shown was subjected to fracture toughness tests at different crack arrest temperatures. The specimen dimensions were 62.5 mm × 60 mm × 25 mm. The corresponding CTOD data were obtained, denoted by δ. The test temperature is related to the crack arrest temperature T in S1. ck Consistent. The crack arrest toughness and fracture toughness results for all specimens at different temperatures and thicknesses are shown in Table 1 and... Figure 3a , Figure 3b As shown:

[0104] Table 1. Fracture and crack arrest toughness results of specimens at different temperatures and thicknesses.

[0105] Temperature (°C) <![CDATA[Fracture arrest toughness (N / mm 3 / 2 )]]> Thickness of the crack-arresting specimen (mm) Result converted to 25mm thickness Fracture toughness (µm) Sample thickness (mm) -92 3961 20 3301 36 25 -80 5643 20 4703 38 25 -56 6076 20 5063 74 25 -54 5923 20 4936 85 25 -50 7011 20 5843 113 25 -40 9523 20 7936 254 25 -35 10688 20 8907 366 25 -31 10742 20 8952 466 25 -27 12508 20 10423 564 25 -20 7000 80 13542 698 25 -17 15758 20 13132 738 25 -15 18919 20 15766 760 25 -10 9494 80 18366 797 25 -1.4 8189 80 15842 829 25 8 24962 20 20802 841 25 5 22337 20 18614 838 25 3.1 10176 80 19686 836 25 1.2 9289 80 17970 833 25

[0106] S3. Data Conversion: Based on the crack arrest toughness dimension conversion relationship, convert the data obtained in S1 into results for the same thickness of the fracture toughness specimen as in step S2; the relationship between the fracture toughness δ of the 25 mm thick specimen and the test temperature is as follows. Figure 4 As shown;

[0107] S4. Model Establishment: Based on the data transformation results from S3, establish the crack arrest toughness K. ca Correlation model with fracture toughness δ; crack arrest toughness K ca The correlation between fracture toughness δ and the following is as follows: Figure 5 As shown;

[0108] Based on the transformed crack arrest toughness and fracture toughness results, a polynomial fitting method was used to directly perform regression analysis on the fracture toughness and crack arrest toughness results, and the correlation coefficient r was obtained. 2 The regression model has a coefficient of 0.97.

[0109] The relationship between the two is K ca =2624.096+37.618×δ-0.085×δ 2 +7.651×10 -5 ×δ 3 In the formula, K ca Crack stopping toughness, in N / mm 3 / 2 δ represents fracture toughness, with units of µm;

[0110] S5. Fracture Toughness Test Prediction: When predicting crack arrest toughness, CTOD data obtained through fracture toughness tests will be input into the correlation model in S4 to calculate the crack arrest toughness K during new research and development and trial production. ca Prediction. The relationship between predicted crack arrest toughness and measured crack arrest toughness is as follows: Figure 6 As shown, the predicted value and the measured value in this embodiment have a good linear relationship, indicating that the predicted value can well represent the measured value. This has important guiding significance for evaluating the crack arrest toughness in the research and development and trial production stages of crack arrest steel.

[0111] Example 2

[0112] A method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test is proposed. According to the requirements of the rapid prediction method of crack arrest toughness, eight groups of crack arrest steel were selected for testing. The crack arrest toughness and fracture toughness at different temperatures were measured. In order to ensure the universality of the prediction method, the crack arrest toughness of the material was tested by double tensile test. And a correlation model between crack arrest toughness and fracture toughness was established by polynomial fitting.

[0113] The method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing includes the following steps:

[0114] S1. Crack Arrest Toughness Test: Eight groups of dovetail-shaped crack arrest toughness test specimens were selected for marine crack-arrest steel, such as... Figure 7 As shown, double tensile crack arrest toughness tests were conducted at different thicknesses and temperatures. The double tensile specimens were 500mm × 500mm × 80mm in size, and the test material was EH47 marine crack arresting steel. The crack arrest toughness K of crack arresting steels of different sizes at different temperatures was obtained. ca Record the crack arrest temperature T during the experiment. ck ;

[0115] Crack arrest toughness K ca The calculation formula is:

[0116]

[0117] In the formula, σ is the tensile stress, in MPa; a is the crack arrest length, in mm; W s The width of the sample is in mm.

[0118] S2, Fracture toughness test: The following method is used... Figure 2 The compact tensile specimen shown was subjected to fracture toughness tests at different crack arrest temperatures. The specimen dimensions were 62.5 mm × 60 mm × 25 mm. The corresponding CTOD data were obtained, denoted by δ. The test temperature is related to the crack arrest temperature T in S1. ck Consistent results were obtained for crack arrest toughness and fracture toughness of all specimens at different temperatures and thicknesses, as shown in Table 2.

[0119] Table 2. Fracture and crack arrest toughness results of specimens at different temperatures and thicknesses.

[0120] Temperature (°C) <![CDATA[Fracture arrest toughness (N / mm 3 / 2 )]]> Thickness of the crack-arresting specimen (mm) Result converted to 25mm thickness Fracture toughness (µm) Thickness of fractured specimen (mm) -35 6000 80 11607 366 25 -27 6489 80 12553 564 25 -20 7000 80 13541 698 25 -10 9494 80 18366 789 25 -10 8732 80 16892 797 25 -14.9 7704 80 14904 761 25 -1.4 8729 80 16886 829 25 1.2 9289 80 17970 833 25 3.1 9667 80 18701 836 25

[0121] S3. Data conversion: Based on the crack arrest toughness size conversion relationship, the data obtained in S1 is converted into the result with the same thickness as the fracture toughness specimen in step S2. The conversion method is the same as in Example 1.

[0122] S4. Model Establishment: Based on the data transformation results from S3, establish the crack arrest toughness K. ca Correlation model with fracture toughness δ; crack arrest toughness K ca The correlation between fracture toughness δ and the following is as follows: Figure 8 As shown;

[0123] Based on the transformed crack arrest toughness and fracture toughness results, a polynomial fitting method was used to directly perform regression analysis on the fracture toughness and crack arrest toughness results, and the correlation coefficient r was obtained. 2 The regression model has a coefficient of 0.90.

[0124] The relationship between the two is K ca =6043.109+37.786×δ-0.088×δ 2 +7.190×10 -5 ×δ 3 In the formula, K ca Crack stopping toughness, in N / mm 3 / 2 δ represents fracture toughness, with units of µm;

[0125] S5. Fracture Toughness Test Prediction: When predicting crack arrest toughness, CTOD data obtained through fracture toughness tests will be input into the correlation model in S4 to calculate the crack arrest toughness K during new research and development and trial production. caPrediction. The relationship between predicted crack arrest toughness and measured crack arrest toughness is as follows: Figure 9 As shown, the predicted value and the measured value in this embodiment have a good linear relationship, indicating that the predicted value can well represent the measured value. This has important guiding significance for evaluating the crack arrest toughness in the research and development and trial production stages of crack arrest steel.

[0126] The above-mentioned scheme, a method for predicting the crack arrest toughness of marine crack arrest steel based on fracture toughness test, is based on the inherent relationship between dovetail crack arrest toughness test and small-size fracture toughness test in terms of crack initiation, and establishes a correlation model that can predict crack arrest performance more accurately.

[0127] The fracture toughness test specimens of this invention are small in size and require low load on the test equipment, which can save a lot of materials and testing costs. It is suitable for batch testing in the research and development process of crack-arresting steel.

[0128] The method for predicting the crack arrest toughness of marine crack-arresting steel based on fracture toughness testing, as described in this invention, is mature and has a short testing cycle. By replacing large-scale crack arrest toughness tests with fracture toughness tests, the testing cycle is shortened from 15 days to 0.5 days, and the sample cost is reduced from tens of thousands of yuan to several hundred yuan.

[0129] The crack arresting toughness K of the present invention ca The correlation model with fracture toughness δ shows that the deviation between the predicted value and the actual value can be as small as 0.15%. According to the results of 18 measured temperature points, the prediction deviation of 78% of the data is less than 10%.

[0130] In summary, compared with traditional fracture and crack arrest technology evaluation techniques for high-strength crack-arresting steel used in marine applications, the method of this invention uses dovetail crack arrest toughness tests and fracture toughness tests to obtain data, which are then converted to establish and obtain the crack arrest toughness K with the smallest deviation from the actual value. ca A correlation model between the fracture toughness δ and the model is used to predict the fracture toughness δ. This method is simple to implement, easy to operate, and the prediction model is low-cost, efficient, and accurate, which is conducive to large-scale industrial application and promotion.

[0131] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0132] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0133] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0134] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method of predicting the crack arrest toughness of a marine crack arrest steel based on a fracture toughness test, characterized by, The method for predicting the arrest toughness of marine arrest steel based on the fracture toughness test comprises the following steps: S1. Crack Arrest Toughness Test: Crack arrest toughness tests were conducted on marine crack-arresting steel at different thicknesses and temperatures to obtain the crack arrest toughness K of crack-arresting steel of different dimensions at different temperatures. ca Record the crack arrest temperature T during the experiment. ck ; S2, fracture toughness test: using compact tension specimens, carrying out fracture toughness tests at different arrest temperatures, obtaining corresponding CTOD data, denoted as δ; S3, data conversion: converting the data obtained in S1 into results of the same thickness as the fracture toughness specimens in step S2 according to the arrest toughness size conversion relationship; S4, model establishment: according to the data conversion result of S3, the crack arrest toughness K ca Correlation model with fracture toughness δ S5, Fracture toughness test prediction: when predicting the subsequent crack arrest toughness, CTOD data is obtained by carrying out fracture toughness test, and the correlation model in S4 is used to predict the crack arrest toughness K ca of new research and trial process.

2. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 1, characterized by, The marine arrest steel in S1 is an EH47 arrest steel plate; the thickness of the marine arrest steel is not more than 80 mm.

3. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 1, characterized in that, The arrest toughness test in S1 specifically comprises the following steps: S11, by means of a fatigue testing machine, preforming a fatigue crack on a dovetail specimen, the fatigue crack length is 5 mm, so as to facilitate the brittle crack to initiate and propagate under the action of tensile load; S12, installing the specimen and cooling device on the testing machine, establishing a suitable gradient temperature field in the dovetail specimen, applying a lower temperature source in the upper half of the gradient temperature field and a heat source in the lower half, so as to form a stable temperature gradient in the whole temperature gradient field; S13, the temperature gradient field formed is kept for a time related to the thickness of the sample; after the temperature field is stable, the stretching device is started, so that the brittle crack is initiated from the fatigue crack tip and expands rapidly; after the test is completed, the sample is pulled apart, and the crack length a and the temperature T of the arrest crack tip are recorded ck .

4. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 1, characterized in that, The fracture toughness test in S2 comprises the following steps: S21, installing the compact tension specimen on the testing machine and installing a low-temperature COD extensometer on the specimen, the COD extensometer is used to measure the crack mouth opening displacement in the specimen during the loading process, so as to calculate δ; S22, adjusting the temperature of the environmental chamber to ensure the stability of the test temperature, waiting for the temperature to reach the predetermined temperature, and then keeping the temperature for 25 min before starting the test, finally calculating δ by the following formula: ； In the formula, F is the breaking load, unit kN; B is the thickness of the sample, unit mm; v is the Poisson's ratio; E is the elastic modulus of the material, unit MPa; m and τ are both material coefficients; V p is the plastic component of the load-displacement curve.

5. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 4, characterized in that, The crack arrest toughness K ca The calculation method is that the J integral value of the crack arrest crack tip is obtained by the cloud integration method in the finite element software ABAQUS, and the conversion relationship between the J integral and the stress intensity factor K is shown in the following formula: ； In the formula, J is the J integral of the arrest crack tip, the unit is N / mm, E is the elastic modulus of the material, the unit is MPa, v is the Poisson's ratio of the material, which is 0.3; The arrest toughness of the arrest instant specimen is obtained.

6. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 3, characterized in that, The size of the dovetail specimen is 250mm×100mm×B, wherein B is the thickness of the specimen.

7. The method of predicting crack arrest toughness of a crack arrest steel for a ship based on a fracture toughness test according to claim 1, characterized by, The size of the fracture toughness specimen is 62.5mm×60mm×25mm.

8. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 1, characterized in that, The arrest toughness size conversion formula in S3 is: ； wherein K ca (B) represents the fracture toughness of a sample having a thickness B, and f(B) is a size factor related to the thickness of the sample, and is calculated by the following equation: 。 9. The method of predicting crack arrest toughness of a ship use crack arrest steel based on a fracture toughness test according to claim 1, characterized in that, In S4, the model is established, and the crack arrest toughness K ca The correlation model of the crack arrest toughness K and the fracture toughness δ.

10. The method of predicting crack arrest toughness of a crack arrest steel for a ship based on a fracture toughness test according to claim 1, characterized in that, In the fracture toughness test prediction in S5, according to the arrest toughness prediction model, the comparison between the predicted value and the measured value of the arrest toughness of each group of tests is obtained; if the deviation between the predicted value and the measured value is greater than 20%, S1-S4 need to be repeated to obtain an arrest toughness prediction model with a deviation between the predicted value and the measured value of less than 20%.

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