A method for testing and judging cracks of high-temperature alloy sheet

Abstract

The present application relates to a kind of high-temperature alloy sheet bending limit test and crack discrimination method, first, the constitutive model of accurate description material mechanics behavior is established by uniaxial tensile test;After combining constitutive model and yield criterion, carry out bending resilience test, simulate the bending resilience process;According to the constitutive model and yield criterion determined, carry out 90 ° bending resilience simulation, obtain the amount of pressing of punch under different punch round corner conditions;The sample blank is carried out 90 ° bending test on the front and back, according to the simulation result, set the amount of pressing of punch, measure bending angle;Observe whether there is crack in bending area;Finally, carry out 180 ° bending test, measure bending angle, and observe whether there is crack in bending area, if the sample has not yet broken, carry out re-bending test;The present application provides theoretical guidance for experiment, accurately controls the angle of high-temperature alloy sheet bending, improves work efficiency, further discriminates crack, and guarantees product quality.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy thin plate forming performance testing and application technology evaluation, and relates to a method for high-temperature alloy thin plate bending limit testing and crack identification. Background Technology

[0002] With the continuous development of materials synthesis technology, material properties are becoming increasingly sophisticated. High-temperature alloys based on iron, nickel, and cobalt can operate for extended periods under high temperatures and certain stresses, exhibiting high high-temperature strength, good oxidation and corrosion resistance, and excellent fatigue and fracture toughness. High-temperature alloys are widely used in aerospace, petroleum, chemical, and shipbuilding industries, primarily in critical components such as rocket launchers and fuel chambers for aero-engines. Many high-temperature alloy parts require bending processes before use, placing extremely high demands on their fatigue strength.

[0003] In existing high-temperature alloy bending technology, the process mainly relies on the experience of skilled workers to control the downward pressure of the punch to form the required bending angle. However, the bending of thin high-temperature alloy sheets is subject to springback, making it difficult to guarantee the accuracy of the bending angle. Furthermore, existing bending tests offer limited detection of cracks in the bending zone. Crack detection is crucial, as it relates to the fatigue strength of the part. Traditional methods, primarily relying on visual inspection or conventional optical testing, struggle to detect minute cracks in the bending zone, and the shortcomings of these traditional methods cannot be ignored. Summary of the Invention

[0004] The purpose of this invention is to propose a method for testing the bending limit and identifying cracks in high-temperature alloy thin plates. By conducting bending tests on the high-temperature alloy thin plates, the influence of springback during processing on the bending angle is fully considered, and an appropriate punch pressure is explored to ensure the accuracy of the bending angle. Simultaneously, a high-magnification optical microscope is used to identify cracks in the bending zone, providing theoretical guidance for obtaining the minimum relative bending radius of high-temperature alloy plates.

[0005] To solve this technical problem, the technical solution of the present invention is as follows:

[0006] A method for testing the bending limit and identifying cracks in high-temperature alloy thin plates is provided, the steps of which are as follows:

[0007] I. Establish a constitutive model that accurately describes the mechanical behavior of the material by conducting uniaxial tensile tests:

[0008] High-temperature alloy thin plate material was selected, and uniaxial tensile tests were conducted according to the national standard GB / T228-2010 Metallic Materials - Tensile Tests at Room Temperature. A constitutive model that can accurately describe its mechanical behavior was established to provide support for selecting a suitable material model for simulation.

[0009] 2. The high-temperature alloy material was processed into rectangular specimens, and a 60° "V" shaped bending springback test was conducted to simulate the bending springback process:

[0010] Compare the simulation results with the experimental results until the simulation accuracy is within an acceptable range; determine whether the selected constitutive model and yield criterion are reliable.

[0011] Third, conduct 90° bending springback simulation according to the standard to obtain the punch compression amount under different punch radius conditions; provide a reference for bending test; during simulation, the forming limit can be used to determine whether cracking occurs during bending.

[0012] IV. Perform 90° and 180° bending tests on both sides of the sample blank. Set the punch pressure based on simulation results. After the experiment, remove the high-temperature alloy sheet and measure the bending angle. According to the Ministry of Aviation Industry of the People's Republic of China standard on the principle of bending tests for the forming performance of metal sheets, 90° and 180° bending tests are required.

[0013] 5. Observe whether there are cracks in the bending area:

[0014] If there are cracks, increase the size of the punch by one level and repeat steps three and four; the navigation mark has grades of punch fillet radius, which can be selected according to the navigation mark;

[0015] If there are no cracks, determine if the punch radius has increased. If it has increased, then the punch radius at this time is the minimum relative bending radius Rmin, and the test ends. If it has not increased, proceed to step six.

[0016] VI. Reduce the fillet radius of the first-stage punch and perform bending springback simulation:

[0017] If the forming limit diagram breaks, the radius of the punch fillet before reduction is Rmin, and the test ends.

[0018] If the forming limit diagram does not break, perform 90° and 180° bending tests and observe whether there are cracks in the bending area. If there are cracks, reduce the original punch fillet radius to Rmin, and the test ends.

[0019] If there are no cracks, determine whether the fillet radius of the punch has reached the minimum value in the navigation mark. If it has not, repeat step six; if it has, perform the overlap bending test and the test ends.

[0020] The absence of cracks indicates a very small minimum relative bending radius and good bending performance.

[0021] In step three, the standard used is the aviation standard "HB6140.5-87 Test Method for Formability of Sheet Metals". Finite element software is used to simulate the 90° bending springback.

[0022] The simulation described in step three uses a bending angle of 90°±1° after bending and springback as the standard.

[0023] In step one, the thickness of the high-temperature alloy sheet material is typically selected to be 1 to 10 mm.

[0024] In step two, the specifications of the rectangular specimen are selected based on the mold size, and a bending springback test is performed on an electronic universal testing machine.

[0025] In the preferred embodiment, step four involves using an electronic universal testing machine to perform a 90° bending test on both sides of the sample blank.

[0026] In the preferred embodiment, a high-magnification optical microscope is used to identify cracks in the bending zone in steps five and six.

[0027] The beneficial effects of this invention are:

[0028] This invention utilizes bending tests on thin high-temperature alloy sheets, fully considering the influence of springback on the bending angle during processing, to explore suitable punch pressure to ensure bending angle accuracy. Simultaneously, a high-magnification optical microscope is used to identify cracks in the bending zone, providing theoretical guidance for obtaining the minimum relative bending radius of high-temperature alloy sheets. Its significant advantages are as follows:

[0029] (a) Precise control of bending angle. This invention establishes a material model in finite element software, taking into account the springback that will occur after the high-temperature alloy thin plate is bent and unloaded, and performs bending simulation of the high-temperature alloy thin plate to obtain a downward pressure, which provides theoretical guidance for experiments, precisely controls the bending angle of the high-temperature alloy thin plate, and improves work efficiency.

[0030] (b) Determining whether cracks or fractures have occurred. Traditional visual inspection or observation of cracks in the bending area using a regular microscope is easily affected by subjective factors. Before the test, the present invention uses finite element simulation to determine whether cracks have occurred during the bending process based on the forming limit. During the test, the displacement-load curve is observed. A decrease in the curve indicates instability, and the appearance or fracture of cracks. After the test, a high-magnification optical microscope is used to carefully observe the outer surface of the bending area of ​​the high-temperature alloy sheet to further identify cracks and ensure product quality.

[0031] (c) Determining bending limits by combining simulation and experiment. Traditional bending limit testing involves repeated attempts using experimental methods. This invention, however, uses a combination of basic experiments on tensile strength and forming limits, simulation, and physical experiments to determine the experimental range of bending angles before testing. This effectively reduces the testing cycle and improves testing efficiency. Attached Figure Description

[0032] Figure 1 This is a flowchart of the implementation method of the present invention;

[0033] Figure 2 This is a comparison chart of the theoretical predictions and experimental results of the constitutive model of this invention;

[0034] Figure 3 The device and bending angle before and after the "V"-shaped bending springback of the present invention;

[0035] Figure 4 This is the finite element model of the "V"-shaped bending of the present invention;

[0036] Figure 5 This is a comparison of the simulation and experimental results of the "V"-shaped bending springback of the present invention;

[0037] Figure 6 This is a schematic diagram of the invention at a 90° bend.

[0038] Figure 7 This is the finite element model of a 90° bend in this invention;

[0039] Figure 8 This is the simulation result of a 90° bend in this invention;

[0040] Figure 9 This invention relates to a 90° bending test device;

[0041] Figure 10 The results of the 90° bending test of this invention;

[0042] Figure 11 This is a diagram showing the absence of cracks in the bending region of this invention.

[0043] Figure 12 The diagram shows cracks in the bending area of ​​this invention.

[0044] In the figure, 1-punch; 2-sample; 3-die; 4-base. Detailed Implementation

[0045] 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, not all, of the embodiments of the present invention. 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.

[0046] Figure 1 The flowchart shown is a method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to the present invention. The steps are as follows:

[0047] (A) Select a high-temperature alloy sheet material and conduct a uniaxial tensile test according to the national standard GB / T228-2010 Metallic Materials Tensile Test at Room Temperature. Establish a constitutive model that can accurately describe its mechanical behavior to provide support for selecting a suitable material model for simulation.

[0048] (B) The high-temperature alloy material is processed into a rectangular specimen and subjected to a 60° "V" bend test on an electronic universal testing machine;

[0049] (C) Based on the established constitutive model, select an appropriate yield criterion, use finite element software to perform “V”-shaped bending springback simulation, compare the simulation results with the experimental results, and determine whether the selected constitutive model and yield criterion are reliable.

[0050] (D) Based on the constitutive model and yield criterion determined in the previous step, and in accordance with the aviation standard "HB6140.5-87 Test Method for Formability of Thin Metal Sheets" (hereinafter referred to as the aviation standard), finite element software was used to simulate 90° bending and 180° bending springback. Using a bending angle of 90°±1° after springback as the standard, the punch compression under different punch radius conditions was obtained, providing a reference for the bending test. During the simulation, the forming limit can be used to determine whether cracking occurs during the bending process.

[0051] (E) Based on the navigation mark, use an electronic universal testing machine to perform a 90° bending test on both sides of the sample blank. Set the punch pressure according to the simulation results in step (D). After the experiment, remove the high-temperature alloy sheet and measure the bending angle.

[0052] (F) Carefully observe the outer surface of the curved area using a high-powered optical microscope. If cracks appear, increase the size of the punch and repeat steps (D) and (E) until no cracks appear.

[0053] (G) Coincidence Bending Test. If no cracks appear in the bending zone after the 180° bending test, then the punch radius at this point is the minimum relative bending radius value R. min Perform coincident bending tests. When performing 180° bending and coincident bending tests, simulate and test according to the above method to determine whether cracks appear, using the same method as above.

[0054] The following example uses a 1mm thick high-temperature alloy GH4169 sheet, combined with the attached... Figures 2 to 12 The present invention is further described in the following specific process:

[0055] (A) Design the shape and dimensions of the uniaxial tensile specimen according to GB / T 228.1-2010 standard as follows: Figure 2As shown. High-temperature alloy GH4169 plates were machined into specific shapes and dimensions at angles of 0°, 45°, and 90° to the rolling direction, and then subjected to uniaxial static tensile tests on an MTS electronic tensile testing machine. Each test was repeated three times, and the average value was taken. The initial yield stress was the stress corresponding to 0.2% plastic strain. The initial yield stresses in the three directions were calculated. The Voce++ model was used to fit the true stress-true plastic strain curve in the rolling direction, and its expression is:

[0056]

[0057] Where, σ s A, B, C, and m are all fitting parameters, such as... Figure 3 As shown, the theoretical curve can accurately describe the experimental results.

[0058] (B) The high-temperature alloy GH4169 sheet was machined into a rectangular specimen of 150mm × 30mm. A 60° "V"-shaped bending springback test was then performed on an electronic universal testing machine. A schematic diagram of the bending device is shown below. Figure 3 As shown in (a), the punch's downward movement rate was 5 mm / min. After the experiment, the specimen was removed and its springback angle was measured to be 65°. Figure 3 As shown in (b).

[0059] (C) Using the constitutive model established above, and selecting the Hill48 yield criterion, a "V"-shaped bending springback simulation was performed in Dynaform. The finite element simulation model is as follows: Figure 4 As shown in the figure (R5 in the figure is the fillet radius of the punch and die), the simulation results are compared with the above experimental results, such as... Figure 5 As shown, the simulated rebound angle was 65.5°, which is close to the experimental result. The error is within an acceptable range, and the established simulation model is reliable.

[0060] (D) Based on the above constitutive model and yield criterion, Dynaform was used to simulate the 90° bending springback of high-temperature alloy GH4169 sheet. According to the aviation standard "HB6140.5-87 Test Method for Formability of Sheet Metal" (hereinafter referred to as the aviation standard), the sample width was 50±0.5mm, the length was 150±2.0mm, the punch radius was selected as R=2.5mm, and the die radius was r. d =2.0mm, the span B between the two recessed modules is 8mm, such as Figure 6 As shown in the figure (B is the span between the two concave modules, and S is the downward pressure of the punch), the established finite element model is as follows: Figure 7 As shown.

[0061] (E) By adjusting the punch's downward displacement, the bending angle after springback in both directions is kept within the range of 90°±1°. When the punch's downward displacement is 2.95mm, the bending angle after springback in the forward direction is 89.2°; when the punch's downward displacement is 2.82mm, the bending angle after springback in the reverse direction is 90.6°. Figure 8 As shown, observing the forming limit diagram, there is no crack in the bending area, and the bending angle is within the tolerance range, which meets the aviation standard.

[0062] (F) Based on navigational aids, perform a 90° bending test using an electronic universal testing machine, such as... Figure 9 As shown. The downward pressure of the punch was taken as the simulated downward pressure, and the downward movement rate of the punch was 5 mm / min. When the downward pressure reached the preset value, the experiment ended. The specimen was removed, and the angle of the bending zone after unloading and springback was measured with a protractor. The measurement results are shown in the figure. Figure 10 As shown, the bending angle is within the allowable error range, and the experimental results are in good agreement with the simulation results. At the same time, a 180° bending test was conducted.

[0063] (G) Careful observation of the outer surface of the curved area using a high-powered optical microscope revealed that the surface of the curved area was relatively smooth and flat, such as... Figure 11 As shown, there are no cracks. Reduce the radius of the first-stage punch fillet and repeat steps (D), (E) and (F). Carefully observe the outer surface of the bending area using a high-powered optical microscope until cracks appear in the forming limit diagram or test results. At this point, the radius of the punch fillet before the breakage is Rmin, and the test ends.

[0064] If no crack occurs, perform a coincident bending test, and the test is then complete.

[0065] If the curved surface is uneven and has tiny cracks, such as Figure 12 As shown, in the navigation mark, select to increase the fillet radius of the first-level punch (the navigation mark has a selection value for the punch radius) and repeat steps (D), (E), and (F) until no cracks appear. At this time, the fillet radius of the punch is Rmin, and the test ends.

[0066] This invention establishes a material model in finite element software. Considering that the high-temperature alloy thin plate will rebound after bending and unloading, the bending and springback simulation of the high-temperature alloy thin plate can be performed to obtain a downward pressure, which provides theoretical guidance for experiments, accurately controls the bending angle of the high-temperature alloy thin plate, and improves work efficiency.

Claims

1. A method for testing the bending limit and identifying cracks in high-temperature alloy thin plates, characterized in that: The method steps are as follows: I. Establish a constitutive model that accurately describes the mechanical behavior of the material by conducting uniaxial tensile tests: High-temperature alloy thin plate material was selected, and uniaxial tensile tests were conducted according to the national standard GB / T228-2010 Metallic Materials - Tensile Tests at Room Temperature. A constitutive model that can accurately describe its mechanical behavior was established to provide support for selecting a suitable material model for simulation.

2. The high-temperature alloy material is processed into rectangular specimens, and a 60° "V" shaped bending springback test is conducted. The bending springback process is simulated, and the simulation results are compared with the experimental results until the simulation accuracy is within an acceptable range. The reliability of the selected constitutive model and yield criterion is then determined. Third, conduct 90° bending springback simulation according to the standard to obtain the punch compression amount under different punch radius conditions; provide a reference for bending test; during simulation, the forming limit can be used to determine whether cracking occurs during bending. IV. Perform a 90° bending test on both sides of the sample blank. Set the punch pressure based on the simulation results. After the experiment, remove the high-temperature alloy sheet, measure the bending angle, and perform a 180° bending test at the same time.

5. Observe whether there are cracks in the bending area: If there are cracks, increase the size of the punch and repeat steps three and four; If there are no cracks, determine if the punch radius has increased. If it has increased, then the punch radius at this time is the minimum relative bending radius Rmin, and the test ends. If it has not increased, proceed to step six. VI. Reduce the fillet radius of the first-stage punch and perform bending springback simulation: If the forming limit diagram breaks, the radius of the punch fillet before reduction is Rmin, and the test ends. If the forming limit diagram does not break, perform 90° and 180° bending tests and observe whether there are cracks in the bending area. If there are cracks, reduce the original punch fillet radius to Rmin, and the test ends. If there are no cracks, determine whether the fillet radius of the punch has reached the minimum value in the navigation mark. If it has not, repeat step six; if it has, perform the overlap bending test and the test ends.

2. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: Step 3 is based on the standard HB6140.5-87 Test Method for Formability of Sheet Metal.

3. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: Step 3 involves using finite element software to simulate 90° bending and springback.

4. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: The simulation described in step three uses a bending angle of 90°±1° after bending and springback as the standard.

5. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: In step one, the thickness of the high-temperature alloy sheet material is 1~10mm.

6. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: In step two, the specifications of the rectangular specimen are determined based on the mold size range, and a bending springback test is performed on an electronic universal testing machine.

7. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: In step four, an electronic universal testing machine is used to perform a 90° bending test on both sides of the sample blank.

8. The method for testing the bending limit and identifying cracks in high-temperature alloy thin plates according to claim 1, characterized in that: In steps five and six, a high-powered optical microscope is used to identify cracks in the bending area.

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