A test specimen design method reflecting the load characteristics of the electron beam weld of the combustion chamber casing of Ti2AlNb alloy.

Abstract

The application discloses a test piece design method for reflecting the weld load characteristics of a Ti2AlNb alloy electron beam welded combustion chamber case, and belongs to the technical field of test piece design reflecting load characteristics. The method comprises the following steps: determining model geometric shape parameters according to test piece size limit conditions and test piece size stress level limit conditions, and then building a test piece model and a pin model by using Abaqus; applying displacement load on the pin model, and applying contact control on the contact surface between the pin model and the pin hole, so as to solve the parallel section stress of the test piece model, the maximum stress at the pin hole and the maximum stress of the circular arc transition section, and then obtain the stress reserve coefficient of the pin hole and the stress concentration coefficient of the circular arc transition section; when the stress reserve coefficient of the pin hole and the stress concentration coefficient of the circular arc transition section meet the test piece size stress level limit conditions, a test piece is manufactured according to the model geometric shape parameters, and a weld is arranged on the test piece.

Description

Technical Field

[0001] This invention belongs to the field of test piece design technology that reflects load characteristics, and particularly relates to a test piece design method that reflects the load characteristics of the weld seam of the combustion chamber casing in electron beam welding of Ti2AlNb alloy. Background Technology

[0002] To reduce the weight of the engine combustion chamber casing, electron beam welding is typically used to connect its structural components. However, electron beam welding introduces significant residual stress fields into the weld seam and surrounding area. Even though post-weld heat treatment can reduce some of this residual stress, the residual stress field after heat treatment remains significant. When the combustion chamber casing operates under design conditions, the welding residual stress field and the operating stress field of the combustion chamber casing superimposed, potentially leading to stress levels at the weld seam exceeding the design stress level. Research literature indicates that the strength of electron beam welds on Ti2AlNb alloys is often lower than that of the base material. Therefore, the combustion chamber casing may fail prematurely at the vacuum electron beam weld seam during operation, before its design life.

[0003] Therefore, it is particularly necessary to reflect the load characteristics of the weld seam of the Ti2AlNb alloy electron beam welded combustion chamber casing through test specimens. Chinese patent CN118776893A discloses a combustion chamber test specimen, proposing to completely replicate the structural characteristics of the combustion chamber to study aerodynamic and deformation issues of the engine combustion chamber. However, this patent involves many components and assembly processes, considering multiple factors such as aerodynamics and deformation, resulting in a complex experimental procedure that cannot provide targeted analysis of welding load strength. Furthermore, the manufacturing of the test specimen requires numerous processing steps, leading to high experimental costs. Chinese patent CN113792398A discloses a design method for a simulated test specimen of the combustion chamber casing hole structure characteristics. By optimizing the size of the simulated hole structure characteristic segment in the simulated test specimen, the distribution of the stress intensity factor of the virtual crack with the crack size is consistent with the distribution of the stress intensity factor at the leading edge of a crack of the same specification in the actual combustion chamber casing, thus enabling the test specimen to accurately reflect the structural characteristics of the combustion chamber casing hole. However, this patent tends to focus on studying the stress intensity factor of the combustion chamber casing hole structure and the accuracy of the test specimen's reflection of the hole structure.

[0004] Based on GB / T 2651-2008 Tensile Testing Method for Welded Joints, GB 2656-81 Fatigue Testing Method for Weld Metal and Welded Joints, and general design experience for welded components, the weld direction of electron beam welded test pieces is often perpendicular to the length of the test piece. During the test, the load on the weld is perpendicular to the welding direction, which, reflected in the combustion chamber casing, means that the weld is mainly subjected to axial load. However, preliminary simulation results of the engine combustion chamber casing show that the actual working load characteristics at the weld of the engine combustion chamber casing are that the circumferential stress is greater than or close to the axial stress. Therefore, traditional welded test piece design cannot meet the test requirements. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a test specimen design method that reflects the load characteristics of the weld seam in the electron beam welded combustion chamber casing of Ti2AlNb alloy. The test specimen obtained by this method is suitable for high-temperature low-cycle fatigue testing and has sufficient safety redundancy.

[0006] This invention proposes a test piece design method to reflect the load characteristics of the combustion chamber casing weld in electron beam welding of Ti2AlNb alloy. The test piece is divided into three sections: front, middle and rear. The middle section is a parallel section. The two ends of the parallel section are connected to the front and rear sections through arc transition sections, respectively. The center of the front and rear sections are provided with pin holes. The method includes: Step S1: Determine the size constraints of the test specimen based on the size of the sampled part; Step S2: Determine the stress level constraints for the test specimen dimensions based on design requirements; Step S3: Determine the geometric parameters of the model based on the size constraints and stress level constraints of the test specimen. Step S4: Using Abaqus, establish the test piece model and two pin models corresponding to the pin holes in the test piece model based on the model's geometric parameters. Step S5: Apply displacement load to the two pin models and apply contact control to the contact surface between the two pin models and the pin holes of the test piece model in order to solve for the stress in the parallel section of the test piece model, the maximum stress at the pin holes, and the maximum stress in the arc transition section. Step S6: Calculate the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section based on the stress of the parallel section, the maximum stress at the pin hole, and the maximum stress of the arc transition section. Step S7: Determine whether the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section meet the stress level limit conditions of the test piece size. If yes, proceed to step S8; otherwise, return to step S3. Step S8: Fabricate a test piece according to the geometric parameters of the model, and deploy welds on the test piece.

[0007] According to the method of the present invention, in step S1, the test specimen size limitation conditions specifically include: The minimum distance between the pin hole and the side wall of the test piece is greater than the width of the parallel section.

[0008] According to the method of the present invention, in step S2, the stress level limiting condition of the test specimen specifically includes: Is the stress concentration factor of the circular arc transition section less than or equal to the first threshold? The stress reserve coefficient of the pin hole is greater than or equal to the second threshold.

[0009] According to the method of the present invention, in step S3, the geometric parameters of the model include: the first arc radius and the second arc radius of the arc transition section of the test piece.

[0010] According to the method of the present invention, in step S5, applying a displacement load to the two pin models specifically includes: A fully fixed constraint is applied to the lower pin end face in the two pin models, and a tensile displacement load is applied to the upper pin end face in the two pin models. The tensile displacement load has a tensile speed of 0.008-0.012 mm / s and a duration of 9-11 s.

[0011] According to the method of the present invention, in step S5, applying contact control to the contact surface of the pin holes of the two pin models and the test piece model specifically includes: The tangential contact friction model between the pin model and the pin hole is controlled using a penalty function, while the normal contact is controlled using a hard contact penalty function constraint.

[0012] According to the method of the present invention, the method further includes: between step S5 and step S6, using a hexahedral mesh to mesh the two pin models and the test piece model; The mesh type is C3D8R.

[0013] According to the method of the present invention, in step S6, the stress reserve coefficient of the pin hole is the ratio of the stress in the parallel section to the maximum stress at the pin hole.

[0014] According to the method of the present invention, in step S6, the stress concentration factor of the arc transition section is the ratio of the maximum stress of the arc transition section to the stress of the parallel section.

[0015] According to the method of the present invention, in step S8, the weld is a straight weld or an oblique weld.

[0016] The solution proposed in this invention has the following technical effects: The test specimens obtained by the method of this invention are suitable for high temperature and low cycle fatigue testing and have sufficient safety redundancy. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a test specimen design method for reflecting the load characteristics of the weld seam of the combustion chamber casing in electron beam welding of Ti2AlNb alloy, according to one embodiment of the present invention.

[0019] Figure 2 This is a flowchart illustrating Embodiment 1 of the present invention.

[0020] Figure 3 The figure shows the simulation calculation results of the test piece designed in Embodiment 1 of the present invention.

[0021] Figure 4 This is a dimensional diagram of the test piece designed for Embodiment 1 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This embodiment proposes a test piece design method to reflect the load characteristics of the combustion chamber casing weld in electron beam welding of Ti2AlNb alloy. The test piece is divided into three sections: front, middle and rear. The middle section is a parallel section. The two ends of the parallel section are connected to the front and rear sections through arc transition sections, respectively. The center of the front and rear sections are provided with pin holes.

[0024] like Figure 1 As shown, the method includes: Step S1: Determine the size constraints of the test piece based on the size of the sampled part.

[0025] Step S2: Determine the stress level limits for the test specimen dimensions based on design requirements.

[0026] Step S3: Determine the geometric parameters of the model based on the size constraints and stress level constraints of the test specimen.

[0027] Specifically, when determining the geometric parameters of the model, it should also meet the requirements of GB / T 228.1-2021 "Metallic materials, tensile testing - Part 1: Test method at room temperature".

[0028] Step S4: Using Abaqus, establish the test piece model and two pin models corresponding to the pin holes in the test piece model based on the geometric parameters of the model.

[0029] Step S5: Apply displacement load to the two pin models and apply contact control to the contact surface between the two pin models and the pin holes of the test piece model to solve for the stress in the parallel section of the test piece model, the maximum stress at the pin holes, and the maximum stress in the arc transition section.

[0030] Specifically, in the Abaqus ODB calculation results, use the Tools → Query → Probe Values ​​function to query the stress of the parallel section and the maximum stress at the pin hole, and use the Options → Contour Plot OptionsLimits → Max:Show location function to obtain the maximum stress of the arc transition section.

[0031] Step S6: Calculate the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section based on the stress of the parallel section, the maximum stress at the pin hole, and the maximum stress of the arc transition section.

[0032] Step S7: Determine whether the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section meet the stress level limit conditions of the test piece size. If yes, proceed to step S8; otherwise, return to step S3.

[0033] Step S8: Fabricate a test piece according to the geometric parameters of the model, and deploy welds on the test piece.

[0034] In some embodiments, the test specimen size limitation conditions in step S1 specifically include: The minimum distance between the pin hole and the side wall of the test piece is greater than the width of the parallel section to ensure the structural strength at the pin hole.

[0035] In some embodiments, the stress level limiting conditions for the test specimen size in step S2 specifically include: The stress concentration factor of the arc transition section is less than or equal to the first threshold to ensure that there is no obvious stress concentration in the arc transition section, thereby avoiding the fracture of the test piece in the arc transition section. The stress reserve coefficient of the pin hole is greater than or equal to the second threshold to ensure the strength at the pin hole during high temperature and low cycle fatigue testing, thereby preventing the test piece from breaking at the pin hole.

[0036] Specifically, the second threshold is an empirical coefficient that varies depending on the material.

[0037] In some embodiments, in step S3, the model geometry parameters include the first and second arc radii of the arc transition section of the test piece.

[0038] In some embodiments, in step S5, applying a displacement load to the two pin models specifically includes: A fully fixed constraint is applied to the lower pin end face in the two pin models, and a tensile displacement load is applied to the upper pin end face in the two pin models. The tensile displacement load has a tensile speed of 0.008-0.012 mm / s and a duration of 9-11 s.

[0039] In some embodiments, in step S5, applying contact control to the contact surface of the pin holes of the two pin models and the test piece model specifically includes: The tangential contact friction model between the pin model and the pin hole is controlled using a penalty function, while the normal contact is controlled using a hard contact penalty function constraint.

[0040] The penalty function used in this invention has advantages such as high convergence efficiency, small computational cost, and effective handling of over-constraint problems.

[0041] In some embodiments, the method further includes: between step S5 and step S6, using a hexahedral mesh to mesh the two pin models and the test piece model; The mesh type is C3D8R.

[0042] In some embodiments, in step S6, the stress reserve coefficient of the pin hole is the ratio of the stress in the parallel section to the maximum stress at the pin hole.

[0043] In some embodiments, in step S6, the stress concentration factor of the arc transition section is the ratio of the maximum stress of the arc transition section to the stress of the parallel section.

[0044] In some embodiments, in step S8, the weld is a straight weld or a slanted weld.

[0045] Example 1 like Figure 2 As shown in the figure, this embodiment presents a test specimen design method suitable for high-temperature low-cycle fatigue testing and reflecting the load characteristics of the weld seam of the combustion chamber casing of Ti2AlNb alloy electron beam welding, including the following steps: 1. Determine the size constraints of the test specimen based on the size of the sampled part.

[0046] In this design, the test piece was taken from a welded cylinder with an inner diameter of Φ295 × outer diameter of Φ306 × 100 mm. To ensure successful sampling, the initial maximum sampling size of the test piece was set at 90 (length) × 20 (width) × 4 (thickness) mm. The thickness of the parallel section of the test piece was 2.5 mm. This size was determined by the actual size of the combustion chamber casing of the research object.

[0047] 2. Based on the size constraints of the test specimen and the initial maximum sampling size of the test specimen, the diameter of the pin hole of the test specimen is taken as 8mm, and the width of the parallel section of the test specimen is taken as 5mm. Under these data, the minimum distance between the pin hole and the side wall of the test specimen is 6mm ((20-8) / 2 mm), which is greater than the width of the parallel section of 5mm, and meets the size constraint requirements.

[0048] 3. Based on the stress level constraints of the test specimen size, the initial thickness of the clamping section of the test specimen is taken as 4mm. At this time, the stress reserve coefficient of the pin hole is 1.25, which is sufficient. At the same time, the sufficiently large clamping end thickness can avoid the problem that the clamping part will be severely deformed due to stress concentration at the pin hole position after the tensile test for thinner plates, strips, etc., which would affect the accuracy of the tensile test curve.

[0049] 4. Determine the first arc radius R1 and the second arc radius R2 of the circular transition section of the test specimen based on the dimensional constraints and stress level constraints of the test specimen. The positions of R1 and R2 are as follows: Figure 2 As shown.

[0050] 5. Using Abaqus, establish a test specimen model and two pin models corresponding to the pin holes in the test specimen model based on the first arc radius R1 and the second arc radius R2 of the arc transition section of the test specimen. 6. Apply a fully fixed constraint to the lower pin end face in the two pin models, and apply a tensile displacement load to the upper pin end face in the two pin models, wherein the tensile displacement load has a tensile speed of 0.008-0.012 mm / s and a duration of 9-11 s.

[0051] 7. Apply contact control to the contact surfaces of the pin holes of the two pin models and the test piece model. The tangential contact friction model between the pin model and the pin hole is controlled by a penalty function, and the normal contact is controlled by a hard contact penalty function constraint.

[0052] 8. Use a hexahedral mesh to mesh the two pin models and the test piece model, and set the mesh type to C3D8R.

[0053] 9. Use the Abaqus Static, General analysis step to solve for the tensile stress field of the test specimen. In the Abaqus ODB calculation results, use the Tools → Query → Probe Values ​​function to query the stress in the parallel section and the maximum stress at the pin hole. Use the Options → Contour Plot Options Limits → Max:Show location function to obtain the maximum stress in the circular transition section.

[0054] 10. Based on the stress in the parallel section, the maximum stress at the pin hole, and the maximum stress in the arc transition section, calculate the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section.

[0055] Specifically, the stress reserve coefficient of the pin hole is the ratio of the stress in the parallel section to the maximum stress at the pin hole. The stress concentration coefficient of the arc transition section is the ratio of the maximum stress in the arc transition section to the stress in the parallel section.

[0056] 11. Determine whether the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section meet the stress level constraints of the test specimen dimensions; specifically, the simulation calculation results of the test specimen are as follows: Figure 3 As shown, a lower stress concentration factor (≤1.10) can be obtained when R1≥16mm and R2≥10mm. To increase the redundant strength of the test piece, the radius of the arc transition section is taken as R1=16mm and R2=30mm. At this time, the stress concentration factor of the arc transition section is 1.057. The overall dimensions of the test piece are as follows. Figure 4 As shown.

[0057] 12. After determining the geometric parameters of the test piece, arrange 45° oblique welds and straight welds on the weld seam, with the relative positions of the welds as follows: Figure 2 As shown. The 45° angled weld seam corresponds to the actual weld seam angle of the combustion chamber casing.

[0058] High-temperature low-cycle fatigue tests were conducted on specimens without welds, with 45° oblique welds, and with straight welds. The test conditions were: temperature 650℃, maximum stress 570MPa, stress ratio 0.1, and frequency 1Hz. The results showed: The Ti2AlNb test piece without welds showed no cracks at the pin holes and did not break. The Ti2AlNb test piece with a 45° beveled weld showed no cracks at the pin holes and the test piece did not break. The Ti2AlNb test piece with a straight weld had no cracks at the pin holes, but the test piece broke at the weld. The results above show that the test piece design of this invention is reliable.

[0059] In summary, the solution proposed in this invention has the following technical effects: The test specimens obtained by the method of this invention are suitable for high temperature and low cycle fatigue testing and have sufficient safety redundancy.

[0060] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A test specimen design method reflecting the load characteristics of the weld seam of the combustion chamber casing in electron beam welding of Ti2AlNb alloy, characterized in that, The test piece is divided into three sections: front, middle and rear. The middle section is a parallel section. The two ends of the parallel section are connected to the front and rear sections by arc transition sections. The center of the front and rear sections are provided with pin holes. The method includes: Step S1: Determine the size constraints of the test specimen based on the size of the sampled part; Step S2: Determine the stress level constraints for the test specimen dimensions based on design requirements; Step S3: Determine the geometric parameters of the model based on the size constraints and stress level constraints of the test specimen. Step S4: Using Abaqus, establish the test piece model and two pin models corresponding to the pin holes in the test piece model based on the model's geometric parameters. Step S5: Apply displacement load to the two pin models and apply contact control to the contact surface between the two pin models and the pin holes of the test piece model in order to solve for the stress in the parallel section of the test piece model, the maximum stress at the pin holes, and the maximum stress in the arc transition section. Step S6: Calculate the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section based on the stress of the parallel section, the maximum stress at the pin hole, and the maximum stress of the arc transition section. Step S7: Determine whether the stress reserve coefficient of the pin hole and the stress concentration coefficient of the arc transition section meet the stress level limit conditions of the test piece size. If yes, proceed to step S8; otherwise, return to step S3. Step S8: Fabricate a test piece according to the geometric parameters of the model, and deploy welds on the test piece.

2. The method according to claim 1, characterized in that, In step S1, the test specimen size constraints specifically include: The minimum distance between the pin hole and the side wall of the test piece is greater than the width of the parallel section.

3. The method according to claim 1, characterized in that, In step S2, the stress level limiting conditions for the test specimen dimensions specifically include: Is the stress concentration factor of the circular arc transition section less than or equal to the first threshold? The stress reserve coefficient of the pin hole is greater than or equal to the second threshold.

4. The method according to claim 1, characterized in that, In step S3, the geometric parameters of the model include the first and second arc radii of the arc transition section of the test piece.

5. The method according to claim 1, characterized in that, In step S5, applying a displacement load to the two pin models specifically includes: A fully fixed constraint is applied to the lower pin end face in the two pin models, and a tensile displacement load is applied to the upper pin end face in the two pin models. The tensile displacement load has a tensile speed of 0.008-0.012 mm / s and a duration of 9-11 s.

6. The method according to claim 1, characterized in that, In step S5, applying contact control to the contact surface of the pin holes of the two pin models and the test piece model specifically includes: The tangential contact friction model between the pin model and the pin hole is controlled using a penalty function, while the normal contact is controlled using a hard contact penalty function constraint.

7. The method according to claim 1, characterized in that, The method further includes: between step S5 and step S6, using a hexahedral mesh to mesh the two pin models and the test piece model; The mesh type is C3D8R.

8. The method according to claim 1, characterized in that, In step S6, the stress reserve coefficient of the pin hole is the ratio of the stress in the parallel section to the maximum stress at the pin hole.

9. The method according to claim 1, characterized in that, In step S6, the stress concentration factor of the arc transition section is the ratio of the maximum stress of the arc transition section to the stress of the parallel section.

10. The method according to claim 1, characterized in that, In step S8, the weld is a straight weld or an oblique weld.

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