A method for determining residual stress evolution based on prefabrication initial residual stress

Abstract

The present invention discloses a method for determining residual stress evolution based on prefabricated initial residual stress, comprising: designing multiple groups of initial target residual stresses of unidirectional stress states based on a certain processing and manufacturing process or service condition of a part to be studied and taking the initial residual stress distribution inside the part as the basis; designing a test piece, determining a central small cross-section area in the test piece as the area where residual stress is generated, adjusting the size of the test piece through finite element simulation, preparing a test piece of corresponding size using the same material as the part, and applying a tensile or compressive load to the test piece to generate initial target residual stress in the central small cross-section area; conducting tests under temperature conditions, load conditions, and temperature and load coupling conditions on a series of prepared test pieces corresponding to each group of initial target residual stresses; and determining the residual stress evolution law based on the test results.

Description

Technical Field

[0001] The present invention relates to the fields of materials and mechanical science, and in particular to a method for determining residual stress evolution based on prefabricated initial residual stress. Background Art

[0002] Residual stresses inevitably form within mechanical structures during the manufacturing process, significantly impacting the dimensional accuracy and mechanical properties of components. Residual stresses within structures relax and redistribute under high temperatures and cyclic loading. Understanding the evolution of residual stresses during manufacturing and service is crucial for improving component accuracy and service performance.

[0003] Residual stress evolution analysis typically uses standard or simulated test pieces to simulate the manufacturing process (such as welding, heat treatment, turbine disk pre-rotation) or surface mechanical strengthening process (such as shot peening, laser shock peening) to generate residual stress fields within the test piece, and then conduct residual stress evolution testing and analysis under different temperature and load environments. After the test piece is processed and mechanically strengthened, the residual stress distribution generated inside the test piece is complex and multi-directional, which greatly increases the difficulty of studying and clarifying the evolution law and mechanism of residual stress. On the other hand, when the test piece is processed from the part by cutting, the residual stress will be released and redistributed, making it difficult to obtain accurate residual stress at specific locations within the part on the test piece. Analyzing the residual stress evolution of complex residual stress fields within a structure by using the evolution law of simple unidirectional residual stress of the material is an effective method; therefore, it is necessary to develop methods that can pre-generate uniform unidirectional residual stress and facilitate evolution testing and analysis.

[0004] At present, simple unidirectional residual stress is mostly generated on flat plate or round rod test pieces with the help of additional mechanical devices or fixtures to facilitate residual stress calibration and research; the patent application with publication number CN102507318A provides a bending device that can simultaneously obtain tensile stress and compressive stress in different numerical ranges on the surface of a flat plate for indentation evaluation; CN208432361U provides a residual stress introduction device that can generate uniform, arbitrary tensile and compressive combinations and directly readable residual stress inside the specimen; CN114509339A provides a force application mechanism that can apply tensile stress or compressive stress along the axial direction on a cross-shaped specimen to simulate residual stress.

[0005] Although the use of additional mechanical devices or fixtures can generate uniform and simple residual stresses in a unidirectional or bidirectional stress state within the specimen, and the magnitude of the residual stress can be flexibly controlled, these are not suitable for testing and analyzing the evolution of residual stress under different temperature and load environments. The mechanical devices or fixtures will inevitably have a significant impact on the relaxation and redistribution of residual stress within the structure. If the mechanical device or fixture is removed, the residual stress within the flat plate or round bar specimen will be released, and it will be impossible to maintain the effective initial residual stress within the structure. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for determining residual stress evolution based on prefabricated initial residual stress, so as to solve the problem that the existing method is not suitable for carrying out evolution testing and analysis of residual stress in different temperature and load environments through unidirectional stress state.

[0007] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0008] A method for determining residual stress evolution based on prefabrication initial residual stress comprises the following steps:

[0009] Step 1: Based on the initial residual stress distribution inside the part, design multiple sets of initial target residual stresses for unidirectional stress states for a certain manufacturing process or service condition of the part to be studied;

[0010] Step 2: Establish a test piece model in a computer; the test piece has a bilaterally symmetrical plate-like structure, with two rectangular tabs at the left and right ends of the test piece, and a variable cross-section region in the middle between the two tabs; the variable cross-section region is rectangular, with a circular arc transition between its outer side and the tabs, and the width of the variable cross-section region is smaller than the width of the tabs, so that the entire test piece has a dumbbell-shaped structure when viewed from above;

[0011] Two symmetrical T-shaped slots consisting of a transverse slot and a longitudinal slot are opened in the middle of the variable cross-section area of ​​the test piece. The area between the longitudinal slots of the upper and lower T-shaped slots is recorded as the central small cross-section area A;

[0012] Step 3: Import the test piece model into the finite element software and establish a finite element model of the test piece model; adjust the structural parameters and pre-tension or compression load of the test piece so that the initial residual stress generated in the central small cross-section area A after unloading the pre-tension or compression load is consistent with the selected initial target residual stress, and save the adjusted structural dimensions and corresponding pre-tension or compression load of the finite element model at this time;

[0013] Repeat step 3 to obtain the structural dimensions of the finite element model and the corresponding pre-tension or compression load when each set of initial target residual stresses is consistent;

[0014] Step 4, based on the structural dimensions of the finite element model for each set of initial target residual stresses, a test piece is manufactured using the same material as the part;

[0015] Step 5: For each test piece, clamp the lugs at both ends of the test piece onto the testing machine. Based on the pre-tension or compression load corresponding to the structural dimensions of the test piece saved in Step 3, the test piece is pre-stretched or compressed and then unloaded. This can pre-generate the corresponding initial target residual stress in the central small cross-sectional area A of the test piece.

[0016] The residual stress measurement method is used to evaluate the residual stress in the small cross-section area A at the center of the test piece. If there is a deviation from the initial target residual stress, the pre-tension or compression load is adjusted to make the residual stress consistent with the initial target residual stress;

[0017] Step 6: For a series of test pieces corresponding to each set of initial target residual stresses, tests are conducted under temperature conditions, load conditions, and temperature and load coupling conditions; and the residual stress evolution law is determined based on the test results.

[0018] Furthermore, the design of multiple sets of initial target residual stresses of unidirectional stress states based on the initial residual stress distribution inside the part includes:

[0019] The initial residual stress inside a part is generally a complex stress state, including normal stress components and shear stress components. For a certain point, the initial residual stress component in a certain direction of focus is selected as the reference target residual stress, or the complex stress is calculated as an equivalent stress as the reference target residual stress. If the initial residual stress state at this point is mainly compressive stress, a minus sign is added before the equivalent stress to indicate that the reference target residual stress is compressive residual stress. The distribution of normal stress components and shear stress components inside the part is obtained through modeling and simulation or measured using residual stress testing methods such as the contour method.

[0020] After obtaining the reference target residual stress distribution inside the part, a stress range is determined according to the maximum reference target residual stress and the minimum reference target residual stress; and multiple groups of stress values ​​are selected at intervals from the stress range as the initial target residual stress.

[0021] Furthermore, when preparing the test piece, the surface of the test piece is processed by mechanical polishing or electrolytic polishing to remove the residual stress introduced by processing factors as much as possible.

[0022] Furthermore, the corresponding initial target residual stress can be prefabricated in the central small cross-section area A of the test piece by:

[0023] A strain gauge is attached to the central small cross-sectional area A of the specimen to record the strain along the length direction of the specimen. When the strain of the central small cross-sectional area A reaches the strain of the central area A corresponding to the maximum pre-stretching or compression load in the finite element simulation during the pre-stretching or compression process of the specimen, the stretching or compression load is terminated and unloading begins, thereby achieving the purpose of using the strain gauge to monitor the maximum deformation of the central small cross-sectional area A, thereby pre-forming the corresponding initial target residual stress.

[0024] Furthermore, the test under temperature conditions, load conditions, and temperature and load coupling conditions includes:

[0025] Based on the temperature conditions of a part's manufacturing process or service conditions, different temperature environments are designed. The test pieces are placed in the temperature environment and taken out in batches at preset intervals. Residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in the small cross-section area A at the center of the test piece. A curve is constructed showing the relationship between residual stress release and initial residual stress, temperature environment, and time.

[0026] Based on the load conditions of a certain manufacturing process or service condition of the part, different load conditions are designed. Loads are applied to the ears at both ends of the test piece using a fixture. The test pieces are removed in batches at preset intervals or the number of cyclic load cycles. The residual stress in the small cross-sectional area A at the center of the test piece is evaluated using residual stress measurement methods such as X-ray diffraction. A curve is constructed showing the relationship between residual stress release and initial residual stress, load type, load size, and time or the number of cyclic load cycles.

[0027] Design the coupling conditions of different temperatures and loads for the parts, apply loads to the ears at both ends of the test piece through a fixture, take out the test pieces in batches at intervals of preset time or number of cyclic load cycles, and use residual stress measurement methods such as X-ray diffraction to evaluate the residual stress in the small cross-sectional area A in the center of the test piece to obtain the relationship curve between residual stress release and initial residual stress, temperature environment, load form, load size and time or number of cyclic load cycles.

[0028] Furthermore, the central small cross-section area A has a width of W1 and a length of L1; the rest of the transverse grooves between the upper and lower T-shaped grooves except area A is recorded as the large cross-section area B, whose width is W2, and the length of the transverse groove is L2; ​​the area between the upper T-shaped groove and the upper edge of the variable cross-section area, and the area between the lower T-shaped groove and the lower edge of the side cross-section area are recorded as the upper edge and the lower edge, both of which have a width of W3; the overall length of the test piece is L, the width is W, and the thickness is H.

[0029] Furthermore, in step 3, the structural parameters of the test piece are adjusted, specifically, the ratios of W2 / W1 and L1 / L2, and the size of W3 are adjusted, or the overall sizes L and W of the test piece are adjusted.

[0030] Compared with the prior art, the present invention has the following technical features:

[0031] The present invention simplifies the residual stress of the complex stress state at each spatial position inside the part into the residual stress of the discrete unidirectional stress state, which is convenient for analyzing the evolution law of the residual stress from a mechanism perspective. By designing a test piece with a special structure, a uniform and simple initial residual stress of the unidirectional stress state can be prefabricated in a specific area of ​​the test piece without the help of additional mechanical devices or fixtures, and the initial residual stress in the central area can be flexibly controlled by optimizing the geometric structure size and pre-tension (compression) load of the test piece; the special test pieces with different initial residual stresses obtained are placed in different temperature environments and cyclic load conditions, and residual stress evolution tests and analyses under unidirectional stress state can be carried out to determine the evolution law of residual stress, providing a basis and a convenient and feasible experimental determination method for analyzing and clarifying the evolution of residual stress inside the part structure during processing, manufacturing and service, revealing the residual stress evolution mechanism and constructing a residual stress prediction model. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the principle of the method of the present invention;

[0033] Figure 2 Schematic diagram of the test piece structure provided by the present invention, where region A is the region where the initial target residual stress is generated;

[0034] Figure 3 This is a schematic diagram of a pre-stretching-unloading finite element simulation of a test piece in an embodiment of the present invention. Based on the symmetry characteristics of the structural part, a quarter model is established;

[0035] Figure 4 For the finite element simulation structure of the embodiment of the present invention, an initial target residual compressive stress of 500 MPa with uniform distribution is generated in region A. DETAILED DESCRIPTION

[0036] The present invention provides a method for determining residual stress evolution based on prefabricated initial residual stress. For a certain processing and manufacturing process or service condition of a part, multiple groups of initial target residual stresses, temperatures and load conditions of unidirectional stress states are designed; a test piece is designed using the same material as the part, and by adjusting the geometric structure size and pre-deformation of the test piece, a uniform and unidirectional initial target residual stress is prefabricated in a preset area of ​​the test piece; the test piece after the prefabricated initial target residual stress is placed under the action conditions of multiple groups of temperature and load conditions, so as to realize residual stress evolution testing and analysis of the initial target residual stress under different temperature and load environments.

[0037] The flow chart of the method of the present invention is as follows Figure 1 , the specific implementation steps are as follows:

[0038] Step 1: Based on the initial residual stress distribution inside the part, multiple sets of initial target residual stresses of unidirectional stress states are designed for a certain manufacturing process or service condition of the part to be studied.

[0039] The initial residual stress inside a part is mostly a complex stress state, including normal stress components and shear stress components, which vary with the spatial position distribution. For a certain point, the initial residual stress component in a certain direction of focus can be selected as the reference target residual stress, or the complex stress can be calculated as an equivalent stress as the reference target residual stress using formula (1) (if the initial residual stress state at this point is mainly compressive stress, a negative sign is added before the equivalent stress to indicate that the reference target residual stress is residual compressive stress); the normal stress component and shear stress component inside the part can be obtained through modeling and simulation or measured using residual stress testing methods such as the contour method. After obtaining the reference target residual stress distribution inside the part, the stress range is determined based on the maximum reference target residual stress and the minimum reference target residual stress; multiple groups of stress values ​​are selected from this stress range as the initial target residual stress, so that the selected stress values ​​can cover the range of the reference target residual stress inside the part. The initial target residual stress can be selected at equal intervals or at variable intervals based on the distribution of the reference target residual stress.

[0040]

[0041] Where, is the calculated equivalent stress, σ x , σ y , σ z is the normal stress component in the x, y, and z directions at a certain position inside the part, τ xy , τ yz , τ zx is the shear stress component corresponding to this position.

[0042] Step 2: Construct the test piece model; the structure is as follows Figure 2 shown.

[0043] A test piece model was established in a computer. The test piece had a bilaterally symmetrical plate-like structure, with two rectangular tabs at the left and right ends. The middle area between the two tabs was a variable cross-section region. The variable cross-section region was rectangular, with an arc transition between its outer side and the tabs. The width of the variable cross-section region was smaller than the width of the tabs, resulting in a dumbbell-shaped structure when viewed from above.

[0044] Two symmetrical T-shaped slots consisting of transverse slots and longitudinal slots are opened in the middle of the variable cross-section area of ​​the test piece. The area between the longitudinal slots of the upper and lower T-shaped slots is recorded as the central small cross-section area A, whose width is W1 and length is L1; the rest of the transverse slots between the upper and lower T-shaped slots except area A is recorded as the large cross-section area B, whose width is W2 and the length of the transverse slot is L2; ​​the area between the upper T-shaped slot and the upper edge of the variable cross-section area, and the area between the lower T-shaped slot and the lower edge of the side cross-section area are recorded as the upper side and the lower side, both with a width of W3; the overall length of the test piece is L, the width is W, and the thickness is H.

[0045] This solution designs a variable cross-section area in the middle of the test piece so that the ears at both ends of the test piece are applied along the length direction ( Figure 2 When a tensile or compressive load is applied (in the horizontal direction), the central small-section area A, the large-section area B and the upper and lower edges of the specimen will undergo elongation or compression deformation; since the deformation of the central small-section area A of the specimen is large and the deformation of the large-section area B is small, after a certain amount of plastic deformation occurs in the central small-section area A, the tensile or compressive load of the ears at both ends is removed. Due to the different amounts of plastic deformation and elastic recovery between the central small-section area A and the upper and lower edges, residual stress along the length direction of the specimen will be generated in the central small-section area A.

[0046] Therefore, applying a tensile load to the tabs at both ends of the specimen generates residual compressive stress along the length of the specimen in the central small cross-section area A in the middle of the specimen, and residual tensile stress along the upper and lower edges of the central area. Applying a compressive load to the tabs at both ends of the specimen generates residual tensile stress along the length of the specimen in the central small cross-section area A. W2 is greater than W1, and the residual stress in the central small cross-section area A increases with the increase of W2 / W1 and decreases with the increase of L1 / L2.

[0047] A certain length dimension L1 should be maintained to ensure that the residual stress generated in the central small cross-section area A is evenly distributed. If residual tensile stress needs to be generated in the middle area of ​​the test piece, the test piece needs to have a certain thickness dimension H to avoid bending instability during compression.

[0048] Step 3: Import the test piece model into the finite element software and establish a finite element model of the test piece model; adjust the ratio of W2 / W1 and L1 / L2 and the pre-tension or compression load in the test piece, and adjust the W3 size if necessary, or adjust the overall dimensions L and W of the test piece so that the initial residual stress generated at the central small cross-section area A is consistent with the initial target residual stress selected in step 1, and save the adjusted structural dimensions of the finite element model at this time and the corresponding pre-tension or compression load; the structural dimensions include W, H, L, W1, W2, W3, L1 and W2.

[0049] Repeat step 3 and use the same method to adjust, and you can get the structural dimensions of the finite element model and the corresponding pre-tension or compression load when each set of initial target residual stresses is consistent with step 1. Figure 3 and Figure 4 .

[0050] Step 4: Based on the structural dimensions of the finite element model for each set of initial target residual stresses established in step 3, a test piece is made of the same material as the part; the residual stress introduced by processing factors needs to be removed from the surface of the test piece as much as possible, such as by mechanical polishing or electrolytic polishing; thereby, a test piece prepared corresponding to each set of initial target residual stresses can be obtained.

[0051] In step 5, for each test piece, the ears at both ends are clamped onto the testing machine. Based on the pre-stretching or compressing load corresponding to the structural dimensions of the test piece saved in step 3, the test piece is pre-stretched or compressed and then unloaded. The corresponding initial target residual stress can be prefabricated in the central small cross-sectional area A of the test piece.

[0052] In actual operation, if the load applied by the ear piece of the test machine clamping the test piece deviates significantly from the pre-tension or compression load recorded when the finite element software is adjusted, a strain gauge can also be attached to the central small cross-sectional area A of the test piece to record the strain along the length of the test piece. When the strain of the central small cross-sectional area A of the test piece reaches the strain of the central area A corresponding to the maximum pre-tension or compression load in the finite element simulation during the pre-tension or compression process, the tension or compression load is terminated and unloading begins. This can also achieve the purpose of using strain gauges to monitor the maximum deformation of the central small cross-sectional area A without the help of the recorded pre-tension or compression load, thereby pre-setting the corresponding initial target residual stress.

[0053] Residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in the small cross-section area A at the center of the test piece. If there is a deviation from the initial target residual stress, the pre-tension or compression load is adjusted to make the residual stress consistent with the initial target residual stress.

[0054] Step 6: For a series of test pieces corresponding to each set of initial target residual stresses prepared in step 5, tests are conducted under temperature conditions, load conditions, and temperature and load coupled conditions; based on the test results, the residual stress evolution law is determined; specifically, as follows:

[0055] Based on the temperature conditions of a part's manufacturing process or service conditions, different temperature environments are designed. The test pieces are placed in the temperature environment and taken out in batches at preset intervals. Residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in the small cross-section area A at the center of the test piece. A curve is constructed showing the relationship between residual stress release and initial residual stress, temperature environment, and time.

[0056] or:

[0057] Based on the load conditions of a certain manufacturing process or service condition of the part, different load conditions are designed. Loads are applied to the ears at both ends of the test piece using a fixture. The test pieces are removed in batches at preset intervals (or the number of cyclic loading cycles). Residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in the small cross-sectional area A at the center of the test piece. A curve is constructed to show the relationship between residual stress release and initial residual stress, load type, load size, and time (or the number of cyclic loading cycles).

[0058] or:

[0059] The coupling conditions of different temperatures and loads are designed for the parts. The load is applied to the ears at both ends of the test piece through a fixture. The test pieces are taken out in batches at preset time intervals (or number of cyclic load cycles). The residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in the small cross-sectional area A in the center of the test piece, and the relationship curve between the residual stress release and the initial residual stress, temperature environment, load form, load size and time (or number of cyclic load cycles) is obtained.

[0060] Using the above relationship curve, the evolution law of initial residual stress under different temperature environments and loads is analyzed, laying the foundation for building a prediction model and revealing the residual stress evolution mechanism.

[0061] Example:

[0062] The following will illustrate the residual stress evolution of a structure during service with reference to the accompanying drawings.

[0063] The part targeted by this embodiment is a metal part, the elastic modulus and Poisson's ratio of its material are 225 GPa and 0.303 respectively. Assuming that the material has linear plastic hardening behavior, the yield strength is 1060 MPa, and the stress when the plastic strain is 0.3 is 1520 MPa.

[0064] S1: Select the residual stress component in a particular direction of focus for the part as the reference target residual stress. The reference target residual stress range for this part is: -700MPa to 100MPa (the negative sign indicates compressive residual stress). The initial design target residual stresses are -700MPa, -500MPa, -300MPa, -100MPa, and 100MPa.

[0065] S2, based on the test and material size requirements, preliminarily determine the test piece structure and outline size, such as Figure 2 As shown, the length dimension L, width dimension W and thickness dimension H are: 116mm, 44mm, 3mm respectively.

[0066] S3, based on the required initial target residual stress, preliminarily design the structural dimensions L1, L2, W1, W2, and W3 of the special test piece. Taking the uniaxial tensile mechanical behavior of the material as input, based on the symmetric characteristics of the test piece, and applying symmetric boundary conditions, a quarter finite element model is established, and pre-tension-unloading loads are applied to the ears at both ends of the test piece, such as Figure 3 As shown, the simulation generates initial residual stress in the central small cross-section area A. In this example, the pre-tension load is applied through a reference point at the end of the ear, which is bound to a part of the ear area through a rigid body constraint.

[0067] S4, optimize the geometric structure dimensions (L1, L2, W1, W2, W3) and pre-tension or compression load of the test piece model so that the initial residual stress generated in the central small cross-section area A is consistent with the initial target residual stress, such as Figure 3 shown.

[0068] Taking the initial target residual stress of -500 MPa as an example, the optimized sizes of L1, L2, W1, W2, and W3 are 20 mm, 46 mm, 4 mm, 20 mm, and 7 mm, respectively, and the pre-tension load is 27920 N.

[0069] S5, processing the test piece according to the test piece structure dimensions designed in steps 2 and 4.

[0070] S6, clamping the ears at both ends of the test piece on the tensile machine, pre-stretching and unloading the test piece based on the pre-stretching load recorded during the adjustment in S4, and generating the initial target residual stress in area A.

[0071] S7, using X-ray diffraction to evaluate the stress in region A. If there is a deviation from the initial target residual stress, the pre-tensioning load is adjusted to make the stress consistent with the initial target residual stress.

[0072] S8, pre-stretching-unloading is performed on the special test piece to obtain an initial target residual stress consistent with the target compressive residual stress at region A, thereby completing the prefabrication of the initial target residual stress of the test piece.

[0073] S9, the service operating temperature of the structure is 400℃-500℃. Three temperature conditions of 400℃, 450℃ and 500℃ are designed. The test pieces after prefabricating the initial target residual stress are placed in the temperature environment. The test pieces are taken out in batches at intervals. The residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in area A of the test piece, and the relationship curve between residual stress release and initial residual stress, temperature environment and time is obtained.

[0074] S10, the service load of the structure is a cyclic load. In this example, the structural service load is simulated by a cyclic load controlled by an axial force. Three force amplitude load conditions are designed, and pin holes are made on the ears at both ends of the test piece. The cyclic load is applied by the pins. The test pieces are taken out in batches at intervals of the cyclic load cycles. The residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in area A of the test piece, and a relationship curve between the residual stress release and the initial residual stress, load form, load size and cyclic load cycle number is obtained.

[0075] S11, design coupling conditions of different temperatures (400℃, 450℃ and 500℃) and loads, place the test pieces after prefabricating the initial target residual stress in different temperature environments and apply loads to the ears at both ends, take out the test pieces in batches at intervals of the number of cyclic load cycles, and use residual stress measurement methods such as X-ray diffraction to evaluate the residual stress in area A of the test piece, and obtain the relationship curve between residual stress release and initial residual stress, temperature environment, load form, load size and number of cyclic load cycles.

[0076] S12, combining the residual stress release relationship curves obtained in S9, S10, and S11, analyzes the evolution law of the residual stress of the material under different temperature environments and loads.

[0077] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for determining residual stress evolution based on prefabricated initial residual stress, characterized in that: The following steps are involved: Step 1: Based on the initial residual stress distribution inside the part, design multiple sets of initial target residual stresses for unidirectional stress states for a certain manufacturing process or service condition of the part to be studied; Step 2: Establish a test piece model in a computer; the test piece has a bilaterally symmetrical plate-like structure, with two rectangular tabs at the left and right ends of the test piece, and a variable cross-section region in the middle between the two tabs; the variable cross-section region is rectangular, with a circular arc transition between its outer side and the tabs, and the width of the variable cross-section region is smaller than the width of the tabs, so that the entire test piece has a dumbbell-shaped structure when viewed from above; Two symmetrical T-shaped slots consisting of a transverse slot and a longitudinal slot are opened in the middle of the variable cross-section area of ​​the test piece. The area between the longitudinal slots of the upper and lower T-shaped slots is recorded as the central small cross-section area A; Step 3: Import the test piece model into the finite element software and establish a finite element model of the test piece model; adjust the structural parameters and pre-tension or compression load of the test piece so that the initial residual stress generated in the central small cross-section area A after unloading the pre-tension or compression load is consistent with the selected initial target residual stress, and save the adjusted structural dimensions and corresponding pre-tension or compression load of the finite element model at this time; Repeat step 3 to obtain the structural dimensions of the finite element model and the corresponding pre-tension or compression load when each set of initial target residual stresses is consistent; Step 4, based on the structural dimensions of the finite element model for each set of initial target residual stresses, a test piece is manufactured using the same material as the part; Step 5: For each test piece, clamp the lugs at both ends of the test piece onto the testing machine. Based on the pre-tension or compression load corresponding to the structural dimensions of the test piece saved in Step 3, the test piece is pre-stretched or compressed and then unloaded. This can pre-generate the corresponding initial target residual stress in the central small cross-sectional area A of the test piece. The residual stress measurement method is used to evaluate the residual stress in the small cross-section area A at the center of the test piece. If there is a deviation from the initial target residual stress, the pre-tension or compression load is adjusted to make the residual stress consistent with the initial target residual stress; Step 6: For a series of test pieces corresponding to each set of initial target residual stresses, tests are performed under temperature conditions, load conditions, and temperature and load coupled conditions. The residual stress evolution law is determined based on the test results.

2. The method for determining residual stress evolution based on prefabrication initial residual stress according to claim 1, characterized in that: The initial residual stress distribution inside the part is used as a basis to design multiple sets of initial target residual stresses of unidirectional stress states, including: The initial residual stress inside the part is a complex stress state, including normal stress components and shear stress components. For a certain point, the initial residual stress component in a certain direction of focus is selected as the reference target residual stress, or the complex stress is calculated as an equivalent stress as the reference target residual stress; if the initial residual stress state at this point is mainly compressive stress, a minus sign is added before the equivalent stress, indicating that the reference target residual stress is residual compressive stress; wherein, the distribution of normal stress components and shear stress components inside the part is obtained through modeling and simulation or measured using residual stress testing methods such as the contour method; after obtaining the reference target residual stress distribution inside the part, the stress range is determined based on the maximum reference target residual stress and the minimum reference target residual stress; and multiple groups of stress values ​​are selected from the stress range at intervals as the initial target residual stress.

3. The method for determining residual stress evolution based on prefabrication initial residual stress according to claim 1, characterized in that: When preparing the test piece, the surface of the test piece is processed by mechanical polishing or electrolytic polishing to remove the residual stress introduced by processing factors as much as possible.

4. The method for determining residual stress evolution based on prefabrication initial residual stress according to claim 1, characterized in that: The corresponding initial target residual stress is prefabricated in the central small cross-section area A of the test piece. Alternatively, the following method can be used: A strain gauge is attached to the central small cross-sectional area A of the specimen to record the strain along the length direction of the specimen. When the strain of the central small cross-sectional area A reaches the strain of the central area A corresponding to the maximum pre-stretching or compression load in the finite element simulation during the pre-stretching or compression process of the specimen, the stretching or compression load is terminated and unloading begins, thereby achieving the purpose of using the strain gauge to monitor the maximum deformation of the central small cross-sectional area A, thereby pre-forming the corresponding initial target residual stress.

5. The method for determining residual stress evolution based on prefabrication initial residual stress according to claim 1, characterized in that: The tests under temperature conditions, load conditions, and temperature and load coupling conditions include: Based on the temperature conditions of a part's manufacturing process or service conditions, different temperature environments are designed. The test pieces are placed in the temperature environment and taken out in batches at preset intervals. Residual stress measurement methods such as X-ray diffraction are used to evaluate the residual stress in the small cross-section area A at the center of the test piece. A curve is constructed showing the relationship between residual stress release and initial residual stress, temperature environment, and time. Based on the load conditions of a certain manufacturing process or service condition of the part, different load conditions are designed. Loads are applied to the ears at both ends of the test piece using a fixture. The test pieces are removed in batches at preset intervals or the number of cyclic load cycles. The residual stress in the small cross-sectional area A at the center of the test piece is evaluated using residual stress measurement methods such as X-ray diffraction. A curve is constructed showing the relationship between residual stress release and initial residual stress, load type, load size, and time or the number of cyclic load cycles. Design the coupling conditions of different temperatures and loads for the parts, apply loads to the ears at both ends of the test piece through a fixture, take out the test pieces in batches at intervals of preset time or number of cyclic load cycles, and use residual stress measurement methods such as X-ray diffraction to evaluate the residual stress in the small cross-sectional area A in the center of the test piece to obtain the relationship curve between residual stress release and initial residual stress, temperature environment, load form, load size and time or number of cyclic load cycles.

6. The method for determining residual stress evolution based on prefabrication initial residual stress according to claim 1, characterized in that: The central small cross-section area A has a width of W1 and a length of L1; the rest of the transverse grooves between the upper and lower T-shaped grooves except area A is recorded as the large cross-section area B, with a width of W2 and a length of L2; the area between the upper T-shaped groove and the upper edge of the variable cross-section area, and the area between the lower T-shaped groove and the lower edge of the side cross-section area are recorded as the upper side and the lower side, both with a width of W3; the overall length of the test piece is L, the width is W, and the thickness is H.

7. The method for determining residual stress evolution based on prefabrication initial residual stress according to claim 6, characterized in that: In step 3, the structural parameters of the test piece are adjusted, specifically, the ratios of W2 / W1 and L1 / L2, and the size of W3, or the overall sizes L and W of the test piece are adjusted.

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