A method for detecting a titanium alloy welded joint rigidity restraint crack resistance test

Abstract

The application provides a detection method of a rigid restraint crack resistance test of a titanium alloy welding joint, and comprises the following steps: S1, determining a titanium alloy material to be detected, and obtaining mechanical and thermophysical performance parameters thereof; S2, obtaining a change rule of restraint degree with a test plate width through finite element simulation calculation; S3, obtaining a test plate width at which residual stress of the welding joint reaches stability through finite element simulation calculation; S4, obtaining the test plate width at which both the restraint degree and the residual stress reach stability; S5, manufacturing a test plate for the rigid restraint test by using the test plate width obtained in step S4; and S6, performing the rigid restraint test, and obtaining a critical restraint degree of the material to be detected without welding cracks. Different titanium alloy materials have different mechanical and physical properties, and in the crack resistance test, special crack resistance test plates are designed for different grades of titanium alloy materials, the test plate width is designed and adjusted, and the specification, rigor and economy of the crack resistance test process are improved.

Description

Technical Field

[0001] This invention relates to the field of weldability evaluation technology for metallic materials, and in particular to a test method for rigid restraint crack resistance testing of titanium alloy welded joints. Background Technology

[0002] Titanium alloys possess numerous advantages, including high strength, low density, and corrosion resistance. With continuous industrial and technological development, the demand for titanium alloys in industrial applications is gradually increasing, showing great promise in welded structural components for large marine equipment. However, the large temperature gradient and high structural constraint during the welding of these large titanium alloy structural components increase the tendency for cold cracking. Therefore, it is crucial to thoroughly study and understand the material's weld crack resistance before practical application.

[0003] The Rigid Restrain Crack Test (RRC) is the most effective method for testing weld cracks under actual restraint conditions. Rigid restraint involves using a testing machine or rigid base plate to firmly fix both ends of the test plate, constraining the weld joint's contraction during post-weld cooling and thus generating restraint stress. Greater restraint results in greater restraint stress and a greater tendency for weld cracks to develop. Therefore, by continuously adjusting the restraint degree during rigid restraint tests, the critical restraint degree under certain conditions can be obtained to prevent cracking in the material. This allows for a quantitative evaluation of the crack resistance of welded joints, which is of great significance.

[0004] Zhang Wenyue et al. published a paper titled "Study on Determining Weld Cold Crack Sensitivity Using Rigid Constraint Test on a Flat Plate," which provides a method for rigidly constraining test plates using a flat plate fixture. Jing Hongyang et al. published a paper titled "Development and Experimental Research of Test Device for Cold Crack Tendency in High-Strength Steel Welding," which provides a large-tonnage rigid constraint testing machine capable of performing rigid constraint crack testing at a certain tonnage. Existing technologies have, to some extent, solved the problem of how to achieve rigid constraint. However, different titanium alloys have different mechanical and physical properties, requiring the use of specialized test plates for rigid constraint crack resistance testing. According to welding stress theory, the parameters of the test plate are also a significant influencing factor. The existing methods for rigorously and systematically designing specialized crack resistance test plates for different materials have not been thoroughly studied, and this shortcoming significantly impacts the engineering application of this method. Summary of the Invention

[0005] In view of this, the present invention aims to propose a test method for the rigid restraint crack resistance test of titanium alloy welded joints. By standardizing the design of a dedicated crack resistance test plate, it is used to test different grades of titanium alloy materials, thereby improving the standardization, rigor and economy of the crack resistance test.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for testing the rigid restraint crack resistance of titanium alloy welded joints, the method comprising the following steps:

[0008] S1. Determine the titanium alloy material to be tested and obtain its mechanical and thermophysical property parameters;

[0009] S2. The variation law of restraint degree with the width of the test plate was obtained through finite element simulation calculation;

[0010] S3. The width of the test plate where the residual stress of the welded joint reaches a stable value is obtained through finite element simulation calculation;

[0011] S4. Obtain a test plate width where both restraint and residual stress are stable;

[0012] S5. Prepare a test plate for rigid restraint test using the test plate width obtained in step S4;

[0013] S6. Perform a rigid restraint test on the test plate prepared in step S5 to obtain the critical restraint degree to which the material to be tested will not develop welding cracks under certain welding process parameters.

[0014] Furthermore, in step S4, the test plate width at which both restraint and residual stress have reached stability can be obtained using the following method: If the test plate width significantly affects the distribution pattern of restraint, then compare the test plate width B1 at which restraint has reached stability and the test plate width B2 at which residual stress has reached stability, and take the larger value as the test plate width. If the test plate width has no significant effect on restraint, then take the test plate width B2 at which residual stress has reached stability as the test plate width.

[0015] Furthermore, the change in the width of the test plate has an effect of less than 5% on the restraint degree, and it is considered that the width of the test plate has no significant effect on the restraint degree.

[0016] Furthermore, in step S1, the mechanical and thermophysical property parameters of the titanium alloy material to be tested are obtained through actual measurement or by searching for data.

[0017] Furthermore, in step S2, the constraint degree is defined as the force applied to a unit length of bevel when the weld joint bevel gap produces an elastic displacement of a unit length.

[0018] Furthermore, in step S2, the restraint degree calculation formula is C = P / δ, where C is the restraint degree; P is the force per unit length of the bevel, in N; and δ is the lateral elastic displacement of the bevel, in mm.

[0019] Furthermore, in steps S2 to S3, the finite element simulation calculation is performed using any one of the finite element calculation platforms Ansys, Abaqus, or Marc.

[0020] Furthermore, in step S6, the rigid constraint process is achieved using a rigid constraint testing machine.

[0021] Furthermore, in step S6, the weld joint cracks after the test are inspected by any one of the following methods: X-ray inspection, penetrant testing, or weld joint cross-section; and the restraint degree is adjusted and the test is repeated to obtain the critical restraint degree of the material.

[0022] The present invention provides a method for testing the rigid restraint crack resistance of titanium alloy welded joints, which has the following advantages compared with the prior art:

[0023] (1) Different titanium alloy materials have different mechanical and physical properties. When conducting crack resistance tests, special crack resistance test plates should be designed for different grades of titanium alloy materials, and the width of the test plates should be designed or adjusted to improve the standardization and rigor of the crack resistance test process.

[0024] (2) Under the premise of ensuring the reliability of the test results, optimizing the test plate size can help save unnecessary test materials and labor costs. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a flowchart of a test method for rigid restraint crack resistance testing of titanium alloy welded joints according to the present invention;

[0027] Figure 2 This is a schematic diagram of the finite element model of the rigid restraint test plate with a Y-shaped bevel in Embodiment 1 of the present invention;

[0028] Figure 3 The two ends of the finite element model in Embodiment 1 of this invention are rigidly fixed boundary conditions;

[0029] Figure 4 This is a bevel displacement cloud diagram from the constraint calculation process in Embodiment 1 of the present invention.

[0030] Figure 5 This illustrates the variation of the restraint degree with the width of the test plate in Embodiment 1 of the present invention.

[0031] Figure 6 This refers to the residual stress field of the welded joint in the rigid restraint test of Embodiment 1 of the present invention;

[0032] Figure 7 This is a schematic diagram of point A, the location for extracting the residual stress value path, in Embodiment 1 of the present invention.

[0033] Figure 8 The distribution pattern of residual stress along the weld direction in the 150mm wide test plate of Embodiment 1 of the present invention;

[0034] Figure 9 This is the crack morphology of the welded joint in the rigid restraint test of Embodiment 1 of the present invention. Detailed Implementation

[0035] To provide a more detailed understanding of the features and technical content of the embodiments of the present invention, the embodiments are described below in conjunction with the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of the present invention. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0036] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] like Figure 1 As shown, this invention proposes a method for testing the rigid restraint crack resistance of titanium alloy welded joints, the method specifically including the following steps:

[0038] S1. Determine the titanium alloy material to be tested and obtain its mechanical and thermophysical property parameters;

[0039] Specifically, the mechanical and thermophysical property parameters of the titanium alloy material to be tested can be obtained through actual measurement or by searching for relevant data.

[0040] S2. The variation law of restraint degree with the width of the test plate was obtained through finite element simulation calculation;

[0041] In step S2, the restraint degree refers to the force applied to a unit length of bevel when the weld joint bevel gap produces an elastic displacement of a unit length.

[0042] The constraint degree is defined as C = P / δ, where C is the constraint degree; P is the force per unit length of the bevel, in N; and δ is the lateral elastic displacement of the bevel, in mm. The constraint degree value can be obtained by extracting the lateral displacement δ at the root of the bevel from the finite element analysis results and substituting it into the constraint degree definition.

[0043] S3. The width of the test plate where the residual stress of the welded joint reaches a stable value is obtained through finite element simulation calculation;

[0044] Specifically, in steps S2-S3, this invention introduces the parameter of test plate width. According to welding stress theory, test plate width is an important parameter. Below the critical width, the peak transverse stress of the test plate after welding increases with the width. After reaching the critical width, the peak stress no longer increases, reaching a stable state. Whether the stress state reaches stability directly affects the crack behavior of the specimen and also affects the reliability of the results. Therefore, different titanium alloy materials have different mechanical and physical properties. When conducting crack resistance tests, the test plate size should be designed or adjusted according to its characteristics. However, existing methods do not consider the influence of test plate size on the test results, making it difficult to guarantee the stability and reliability of the test results. Furthermore, under the premise of ensuring the reliability of test results, optimizing the test plate size can significantly save unnecessary test material costs, which is of great significance for engineering applications.

[0045] The finite element simulation calculations described in steps S2 and S3 are performed using any one of the finite element computing platforms: Ansys, Abaqus, or Marc. Based on the principle of rigid restraint testing, a finite element model of the rigid restraint test is established. The degrees of freedom of the nodes on both ends of the finite element model are set to 0, simulating rigid constraint at both ends. The restraint degree calculation is based on the linear elastic theory of solid mechanics, and the residual stress calculation of the welded joint is based on the thermo-elastic-plastic theory.

[0046] S4. Obtain a test plate width where both restraint and residual stress are stable;

[0047] S5. Prepare a test plate for rigid restraint test using the test plate width obtained in step S4;

[0048] S6. Perform a rigid restraint test on the test plate prepared in step S5 to obtain the critical restraint degree to which the material to be tested will not develop welding cracks under certain welding process parameters.

[0049] Specifically, in step S6, the rigid constraint process is achieved using a rigid constraint testing machine. After the test, the weld joint cracks are inspected using any of the following methods: X-ray inspection, penetrant testing, or macro- and micro-observation of weld joint sections. The constraint degree is then adjusted and the test is repeated to obtain the critical constraint degree of the material.

[0050] In one embodiment of the present invention, the test plate width at which both restraint and residual stress reach stability can be obtained using the following method: If the test plate width significantly affects the distribution pattern of restraint, then compare the test plate width B1 at which restraint reaches stability and the test plate width B2 at which residual stress reaches stability, and take the larger value as the test plate width. If the test plate width has no significant effect on restraint, then take the test plate width B2 at which residual stress reaches stability as the test plate width. Generally, it is considered reasonable for changes in test plate width to have an effect of less than 5% on restraint, and the test plate width can be considered to have no significant effect on restraint.

[0051] This invention provides a method for testing the rigid restraint crack resistance of titanium alloy welded joints. Considering the influence of test plate width, the test plate dimensions were designed and adjusted for the mechanical and physical properties of different titanium alloy materials to ensure the reliability and broad applicability of the crack resistance test results. This method also provides support for the process evaluation, material selection comparison, and structural optimization design of titanium alloy welded structures.

[0052] Example 1

[0053] Taking a 50mm thick TC4ELI titanium alloy plate as an example, this invention provides a detailed description of a method for testing the rigid restraint crack resistance of a titanium alloy welded joint.

[0054] S1. Mechanical and thermophysical property parameters of TC4ELI titanium alloy plates were obtained by searching literature and used for finite element calculations.

[0055] S2. A finite element model of a test plate with a slanted Y-shaped bevel was established using Ansys Apdl finite element software, such as... Figure 2 As shown. Input the mechanical property parameters of the TC4ELI titanium alloy, and set the degrees of freedom of each node at both ends of the model to 0, i.e., simulate the boundary conditions where both ends are rigidly fixed, as shown. Figure 3 As shown in the figure. A uniformly distributed transverse load of 200 MPa was applied at the bevel, causing elastic contraction deformation of the bevel gap, and the elastic deformation contour diagram was obtained, as shown in the figure. Figure 4 As shown.

[0056] Based on the elastic displacement data of the root node of the bevel, the restraint degree is calculated using the definition of restraint degree C = P / δ, where C is the restraint degree, P is the force per unit length of the bevel (N), and δ is the lateral elastic displacement of the bevel (mm). In this embodiment, the restraint degree of test plates with different widths was calculated to obtain the variation law of the restraint degree of the welded joint with the width of the test plate, as follows. Figure 5 As shown.

[0057] Depend on Figure 5 As can be seen, in this embodiment, the width of the test plate is increased from 100mm to 400mm, and the restraint is increased from 9.37kN (mm).-1 ·mm -1 Increased to 9.72 kN (mm) -1 ·mm -1 The increase was only 3.7%, indicating that the restraint degree was only slightly affected by the width of the test plate. The results show that the restraint degree of this titanium alloy is not significantly affected by the width of the test plate.

[0058] S3. Using Ansys Apdl finite element software, after completing parametric modeling, inputting material parameters, and meshing, the welding temperature field is first simulated. Then, the temperature field calculation results are used for thermal stress coupling calculation to obtain the residual stress distribution cloud map of the weld joint. (See [link]). Figure 6 Further analysis was conducted to extract the variation pattern of residual stress at point A at the weld root along the weld length, as follows: Figures 7-8 As shown. Calculations show that when the test plate width is 150mm, the residual stress of the welded joint of TC4ELI titanium alloy reaches a stable value. (See [reference]). Figure 8 .

[0059] S4. Analysis of the results of steps S2 and S3 shows that since the width of the test plate has little effect on the restraint degree, the width B2 of the test plate where the residual stress reaches a stable value is taken as the width of the test plate. Therefore, 150 mm is used as the width of the test plate for this titanium alloy.

[0060] S5. Using the test plate width obtained in step S4, fabricate a pair of 150mm wide test plates for rigid restraint tests, and machine the inclined Y-shaped test bevel using a milling method. In this example, the length of a single-sided test plate is 1200mm, which is suitable for the clamping distance of the testing machine in this embodiment;

[0061] S6. The test plates prepared in step S5 are subjected to rigid restraint tests under different restraint degrees to obtain the critical restraint degree under certain welding process parameters that prevents welding cracks from occurring.

[0062] The rigid restraint test is conducted through the following steps:

[0063] (1) Specimen assembly

[0064] The test plate is assembled onto the clamping end of the rigid restraint testing machine with a bevel gap of 2 mm. Extensometers are mounted on both sides of the test plate; the distance between the extensometers is the restraint distance L.

[0065] (2) Welding of the test weld

[0066] In this embodiment, manual TIG welding is used. Before welding, the oxide scale on the bevel and the surrounding 20mm area is removed with an angle grinder, and oil and metal shavings are wiped clean with alcohol. A suitable method is needed to fix a drag shield on the back of the bevel to achieve back protection. The welding process parameters in this embodiment are shown in Table 1.

[0067] Table 1 Welding process parameters

[0068]

[0069] (3) Rigid restraint

[0070] Rigid restraint means that the displacement of the extensometer remains constant under the displacement control function of the testing machine. After welding, rigid restraint needs to be maintained for 48 hours. If the test plate is removed after 48 hours or if obvious fracture occurs during the test, it should be removed.

[0071] (4) Crack rate detection

[0072] After the test, the unbroken joints were sectioned and dissected, and the crack rate was statistically analyzed using microscopic observation. Cold cracking was observed in the TC4ELI weld joint. (See [link to relevant documentation]). Figure 9 ;

[0073] (5) Change the degree of restraint

[0074] Repeated tests were conducted by gradually decreasing or increasing the restraint, with each test strictly following the above steps. The critical restraint of the material was ultimately obtained, which is the maximum restraint at which the welded joint will not crack in this test. The test results for the TC4ELI alloy in this embodiment are shown in Table 2.

[0075] Table 2 Results of Rigid Restraint Crack Resistance Test of TC4ELI Welded Joints

[0076]

[0077] As shown in Table 2, under the welding process parameters in this implementation, the critical restraint of the welded joint of TC4ELI and its matching welding materials is 12800 N / (mm·mm), which achieves the purpose of standardized and quantitative evaluation of the crack resistance of the weld.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting the rigid restraint crack resistance of titanium alloy welded joints, characterized in that, The detection method includes the following steps: S1. Determine the titanium alloy material to be tested and obtain its mechanical and thermophysical property parameters; S2. The variation law of restraint degree with the width of the test plate was obtained through finite element simulation calculation; S3. The width of the test plate where the residual stress of the welded joint reaches a stable value is obtained through finite element simulation calculation; S4. Obtain a test plate width where both restraint and residual stress are stable; S5. Prepare a test plate for rigid restraint test using the test plate width obtained in step S4; S6. Perform a rigid restraint test on the test plate prepared in step S5 to obtain the critical restraint degree to which the material to be tested will not develop welding cracks under certain welding process parameters.

2. The detection method according to claim 1, characterized in that, In step S4, the following method is used to obtain the test plate width where both restraint and residual stress have reached a stable state: If the test plate width significantly affects the distribution pattern of restraint, then compare the test plate width B1 where restraint has reached a stable state and the test plate width B2 where residual stress has reached a stable state, and take the larger value as the test plate width; if the change in the test plate width has an impact of less than 5% on restraint, it is considered that the test plate width has no significant impact on restraint, and then take the test plate width B2 where residual stress has reached a stable state as the test plate width.

3. The detection method according to claim 1, characterized in that, In step S1, the mechanical and thermophysical property parameters of the titanium alloy material to be tested are obtained by means of actual measurement or by searching for information.

4. The detection method according to claim 1, characterized in that, In step S2, the constraint degree is defined as the force applied to a unit length of bevel when the weld joint bevel gap produces an elastic displacement of a unit length.

5. The detection method according to claim 1, characterized in that, In step S2, the restraint degree is calculated using the formula C=P / δ, where C is the restraint degree; P is the force per unit length of the bevel, in N; and δ is the lateral elastic displacement of the bevel, in mm.

6. The detection method according to claim 1, characterized in that, In steps S2 to S3, the finite element simulation calculation is performed using any one of the finite element calculation platforms Ansys, Abaqus, or Marc.

7. The detection method according to claim 1, characterized in that, In step S6, the rigid constraint process is achieved using a rigid constraint testing machine.

8. The detection method according to claim 1, characterized in that, In step S6, the cracks in the welded joint after the test are inspected by any one of the following methods: X-ray inspection, penetrant testing, or welded joint cross-section; and the restraint is adjusted and the test is repeated to obtain the critical restraint of the material.

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