A high-precision and high-efficiency detection method for micro-scale micro-area stress

Abstract

The application discloses a kind of high-precision high-efficiency detection methods of micron-sized micro area stress.The surface of the metal sample to be tested is polished and polished, the difference of the work of loading section of stress-free load displacement curve and stress load displacement curve is calculated, and it is used as residual stress σ z In the work W of nanoindentation process rs =ΔU.Residual stress σ z Is decomposed into spherical tensor and deviatoric tensor, and the work ΔW of residual stress σ z Is calculated by integral method under the condition that contact area and indenter load change with indentation depth in the process of indenter indentation.Then ΔU=ΔW, the residual stress σ x At test position can be calculated.The numerical value of σ y At test position is obtained.The measurement accuracy of residual stress is greatly improved, and the test process is very simple.

Description

Technical Field

[0001] This invention relates to the field of precise measurement technology of residual stress in micron-scale regions, and particularly to a high-precision and high-efficiency method for detecting micron-scale micro-region stress. Background Technology

[0002] The accurate measurement methods and principles of residual stress in micrometer-scale regions remain a challenge. For example, in ceramic-metal brazing joints widely used in electronics, semiconductor packaging, and other industries, the thickness of the brazing metal is often ≤100μm. The difficulty in accurately detecting residual stress in such confined areas hinders effective product quality evaluation and control, ultimately compromising product reliability.

[0003] Currently, common methods for detecting residual stress include the pinhole method, magnetic measurement, ultrasonication, X-ray diffraction, neutron diffraction, and indentation. Among these methods, nanoindentation has attracted widespread attention due to its non-destructive nature and ability to measure residual stress in micro- and nanoscale regions.

[0004] When characterizing residual stress in materials using nanoindentation, data processing is required after the nanoindentation experiment to obtain measured values ​​of residual stress. Researchers have proposed numerous computational models for this purpose. These models can be divided into two main categories: the contact area method and the energy method. Each method has its advantages and disadvantages. The contact area method offers higher measurement accuracy, but it requires equipment such as atomic force microscopes to photograph the indentation morphology and calculate the contact area, making it relatively cumbersome and time-consuming. The energy method is very simple, requiring only the load-displacement curve directly obtained from the nanoindentation experiment, but its measurement error is relatively large.

[0005] like Figure 1 The diagram illustrates the basic principle of the David energy method for measuring residual stress. The details of this method for testing micro-area residual stress are as follows: Nanoindentation experiments are performed under both stressed and unstressed conditions to obtain load-displacement curves for each condition and calculate the work done in each. Then, the residual stress of the material is calculated based on the difference in work done under the two conditions. The formula for calculating the difference in work done under stressed and unstressed conditions using the David energy method model is as follows:

[0006] W t0 -W t1 =σA1sinαh max (compressive stress)

[0007] W t0 -W t1 =-σA1h max (Tensile stress)

[0008] Taking tensile stress as an example, in the existing David energy method model, the work done by residual stress is equivalent to the maximum load difference σA1 and the maximum indentation depth h. max The product σA1h max ,Right now Figure 1 The green rectangular area in the middle.

[0009] It is worth noting (still taking the tensile stress state as an example) that, during the actual pressing process, the work done by the residual stress obtained from the load-displacement curve should be the area S of the irregular region enclosed by the loaded portions of the stressed and unstressed curves. OAB ,Right now Figure 1 The blue area. Clearly, in the existing David energy method model, the calculation of work done by residual stress is based on... Figure 1 The area of ​​the green rectangular region in the middle is replaced by Figure 1 The area of ​​the irregular blue region will inevitably introduce measurement errors.

[0010] The classic energy-based David model approximates the work done by residual stress as the difference ΔP between the maximum load and the maximum indentation depth h in the stress-free and stress-free states at the maximum indentation depth. max The product ΔP·h max This leads to a significant underestimation of residual stress. To address this, this invention proposes a novel model (David-Zhang & Zeng model) for calculating the work done by residual stress using an integral method. In this new model, the contact area and indenter load during the indenter insertion process gradually change with the indentation depth. Results show that the calculation error of the David-Zhang & Zeng model is significantly smaller than that of other traditional models. Summary of the Invention

[0011] The purpose of this invention is to provide a high-precision and high-efficiency method for detecting micro-scale micro-region stress, in order to solve the above-mentioned problems of the existing David energy method model. This invention modifies the David energy method model.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A high-precision and high-efficiency method for detecting micron-level micro-region stress includes,

[0014] Step S1: The metal sample to be tested is subjected to surface grinding and polishing, and electrolytic polishing is performed to remove the surface stress caused by grinding and polishing.

[0015] Step S2: In fixed depth mode, a Glass indenter is used to perform nanoindentation testing on the stressed metal sample to be tested, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve. t1 ,in Where p1 is the stressed load, h is the displacement, and h max This is the maximum pressing depth;

[0016] Step S3: In fixed depth mode, a Glass indenter is used to perform nanoindentation testing on the stress-free metal sample to be tested, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve. t0 ,in Where p0 is the load under stress-free conditions, h is the displacement, and h max This is the maximum pressing depth;

[0017] Step S4: Calculate the difference in work done by the loading segments of the stress-free load-displacement curve and the stress-laden load-displacement curve, and use this difference as the total work W done by the residual stress during the nanoindentation process. rs That is, W rs =W t0 -W t1 =ΔU;

[0018] Step S5: Apply the residual tension (σ) of the biaxial system. x , σ y It can be decomposed into a hydrostatic stress (σ). x , σ y , σ z ) and a uniaxial stress (-σ) parallel to the direction of the indenter load. z If the residual stress does work during the unit depth indentation dh, then the work done by the residual stress is expressed as dW = σ. z 24.5h 2 dh, the work done by residual stress during the entire pressing process is

[0019] Step S6: Let ΔU = ΔW, then we have Since the data required for the calculations on the right side are all obtained from nanoindentation experimental data, the residual stress σ at the test location is calculated. z Due to σ x , σ y , σ z The absolute values ​​of the three are equal, thus obtaining σ at the test location. x , σ y The value.

[0020] In the aforementioned high-precision and high-efficiency method for detecting micron-level micro-area stress, step S1: the polishing voltage is set to 5V, the polishing current to 0.5A, and the polishing time to 5min.

[0021] In the high-precision and high-efficiency detection method for micron-level micro-region stress, in step S2, the stress state of the metal sample to be tested is an equibiaxial stress state.

[0022] In the aforementioned high-precision and high-efficiency method for detecting micron-level micro-region stress, in step 4, for polycrystalline materials under both stressed and stress-free conditions, steps S2 and S3 are repeated within multiple different grains in the vicinity of the test location to obtain multiple W values. t0 Values ​​and multiple Ws t1 Calculate the average value of each. and The difference between the two average values ​​is then taken as the total work W done by the residual stress during the nanoindentation process. rs ,

[0023] In the aforementioned high-precision and high-efficiency method for detecting micron-level micro-region stress, the metal sample to be tested is an elastoplastic metal material.

[0024] In the high-precision and high-efficiency detection method for micron-level micro-region stress, the average grain size of the sample after electrolytic polishing to remove the surface stress caused by grinding and polishing is 50 μm.

[0025] In the aforementioned high-precision and high-efficiency method for detecting micron-level micro-area stress, the stress-relieved annealed metal sample to be tested is loaded into a nanoindenter. With the test point as the center and twice the average grain size as the radius, a nanoindentation experiment is performed on the grain that enters the marked point. A static loading is performed at a fixed depth of 350 nm. The distance between adjacent test points is 10 times the indentation radius. Two indentations are pressed into one grain, and the indentation position is located at the center of the grain.

[0026] In the aforementioned high-precision and high-efficiency method for detecting micro-scale micro-region stress, the energy method is the David energy method.

[0027] In the aforementioned high-precision and high-efficiency method for detecting micron-level micro-area stress, the experimental parameters for performing nanoindentation testing on a stressed metal sample using a Glass indenter are the same as those for performing nanoindentation testing on a stress-free metal sample using a Glass indenter. The experimental parameters include indenter type, indentation depth, loading speed, holding time, and unloading speed.

[0028] In the high-precision and high-efficiency detection method for micron-level micro-region stress, the residual stress of the metal sample to be tested is located in the micron-level region by nanoindentation measurement.

[0029] Compared with existing technologies, this invention has the following advantages: A high-precision and high-efficiency method for detecting micron-level micro-region stress utilizes load-displacement curves to obtain the work difference between different pre-stressed and stress-free states, and equates it to the integral of the work done by the residual stress on the indenter at each indentation depth from the start of indentation to the maximum indentation depth, thus obtaining the residual stress of the material. On the one hand, this method avoids measuring the actual contact area of ​​the indentation, and has advantages such as strong applicability and convenience. On the other hand, compared with the David energy method model and the energy method calculation model proposed by Yang et al., this method greatly improves the measurement accuracy. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the basic principle of the existing David energy method for measuring residual stress. The work done by the residual stress should be the area of ​​the irregular region enclosed by the loaded portions of the stress- and stress-free curves (i.e., the blue region OAB). Existing David energy method models calculate the work done by residual stress using... Figure 1 The area of ​​the green rectangular region in the middle is replaced by Figure 1 The area of ​​the irregular blue region will inevitably introduce measurement errors;

[0031] Figure 2 This is a schematic diagram of the volume change of the indentation under the indenter during the process of the indenter penetrating to depth dh. It can be seen that the increase in the volume of the indentation corresponding to dh is... Figure 2 The volume of the infinitesimal element shown is dA or dB, where dA = dB = 24.5 * h. 2 *dh;

[0032] Figure 3 The schematic diagram of the correction method proposed in this invention shows that the total work done on the residual stress is obtained by integrating the work done on the residual stress corresponding to each indentation depth element dh. Figure 1 The area of ​​the irregular blue region in the middle is higher than that of the existing David energy method in terms of the calculation accuracy of the work done by residual stress and the measurement error of residual stress can be reduced.

[0033] Figure 4 Schematic diagram of work done by residual stress during the indentation to depth dh;

[0034] Figure 5 This is a schematic diagram showing the calculation results of residual stress under different prestresses in an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram illustrating the calculation error of residual stress under different prestresses in an embodiment of the present invention;

[0036] Figure 7 This is a flowchart of a high-precision and high-efficiency method for detecting micro-scale micro-region stress according to the present invention. Detailed Implementation

[0037] The present application will now be described in further detail with reference to the accompanying drawings and embodiments to enable those skilled in the art to better understand the present invention. It is understood that the specific embodiments described herein are merely illustrative of the relevant invention and not intended to limit the invention. For ease of description, only the parts relevant to the invention are shown in the drawings. It should also be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other. The present application will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] See Figures 1 to 7 As shown, a high-precision and high-efficiency method for detecting micro-scale micro-region stress includes the following steps:

[0039] Step S1: The metal sample to be tested is subjected to surface grinding and polishing, and electrolytic polishing is performed to remove the surface stress caused by grinding and polishing.

[0040] Step S2: In fixed depth mode, a Glass indenter is used to perform nanoindentation testing on the stressed metal sample to be tested, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve. t1 ,in Where p1 is the stressed load, h is the displacement, and h max This is the maximum pressing depth;

[0041] Step S3: In fixed depth mode, a Glass indenter is used to perform nanoindentation testing on the stress-free metal sample to be tested, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve. t0 ,in Where p0 is the load under stress-free conditions, h is the displacement, and h max This is the maximum pressing depth;

[0042] Step S4: Calculate the difference in work done by the loading segments of the stress-free load-displacement curve and the stress-laden load-displacement curve, and use this difference as the total work W done by the residual stress during the nanoindentation process. rs That is, W rs =W t0 -W t1 =ΔU;

[0043] Step S5: Apply the residual tension (σ) of the biaxial system. x , σ y It can be decomposed into a hydrostatic stress (σ). x , σ y , σ z ) and a uniaxial stress (-σ) parallel to the direction of the indenter load. zIf the residual stress does work during the unit depth indentation dh, then the work done by the residual stress is expressed as dW = σ. z 24.5h 2 dh, the work done by residual stress during the entire pressing process is

[0044] Step S6: Let ΔU = ΔW, then we have Since the data required for the calculations on the right side are all obtained from nanoindentation experimental data, the residual stress σ at the test location is calculated. z Due to σ x , σ y , σ z The absolute values ​​of the three are equal, thus obtaining σ at the test location. x , σ y The value.

[0045] In a preferred embodiment of the high-precision and high-efficiency method for detecting micron-level micro-area stress, step S1 is as follows: the polishing voltage is set to 5V, the polishing current to 0.5A, and the polishing time to 5min.

[0046] In a preferred embodiment of the high-precision and high-efficiency detection method for micron-level micro-region stress, in step S2, the stress state of the metal sample to be tested is an equibiaxial stress state.

[0047] In a preferred embodiment of the high-precision and high-efficiency method for detecting micron-level micro-region stress, in step 4, for both stressed and stress-free states of polycrystalline materials, steps S2 and S3 are repeated within multiple different grains in the vicinity of the test location to obtain multiple W values. t0 Values ​​and multiple Ws t1 Calculate the average value of each. and The difference between the two average values ​​is then taken as the total work W done by the residual stress during the nanoindentation process. rs ,

[0048] In a preferred embodiment of the high-precision and high-efficiency detection method for micron-level micro-region stress, the metal sample to be tested is an elastoplastic metal material.

[0049] In a preferred embodiment of the high-precision and high-efficiency method for detecting micron-level micro-region stress, the average grain size of the sample after electrolytic polishing to remove the surface stress caused by grinding and polishing is 50 μm.

[0050] In a preferred embodiment of the high-precision and high-efficiency detection method for micron-level micro-area stress, the stress-relieved annealed metal sample to be tested is loaded into a nanoindenter. With the test point as the center and twice the average grain size as the radius, a nanoindentation experiment is performed on the grain that enters the marked point. A static loading is performed at a fixed depth of 350 nm. The distance between adjacent test points is 10 times the indentation radius. Two indentations are pressed into one grain, and the indentation position is located at the center of the grain.

[0051] In a preferred embodiment of the high-precision and high-efficiency method for detecting micron-level micro-region stress, the energy method is the David energy method.

[0052] In a preferred embodiment of the high-precision and high-efficiency method for detecting micron-level micro-area stress, the experimental parameters for performing nanoindentation testing on a stressed metal sample using a Glass indenter are the same as those for performing nanoindentation testing on a stress-free metal sample using a Glass indenter. The experimental parameters include indenter type, indentation depth, loading speed, holding time, and unloading speed.

[0053] In a preferred embodiment of the high-precision and high-efficiency detection method for micron-level micro-region stress, the residual stress of the metal sample to be tested measured by nanoindentation is located in a micron-level region.

[0054] In one embodiment, to address the aforementioned problems of the existing David energy method model, the present invention modifies the David energy method model by using an integral method to obtain... Figure 1 The area of ​​the irregular blue region is used as the work done by residual stress. This method proposes defining the contact area as a function of the indentation depth and integrating the work difference between stressed and unstressed states at each indentation depth, equating it to the work done by residual stress on the indenter throughout the indentation process. Nano-indentation experiments are performed on the metal under stress, followed by stress-relief annealing and then nano-indentation testing at the test location, obtaining load-displacement curves under both stressed and unstressed states. This method uses code to process the points collected from the load-displacement curves under different prestressed and unstressed states to directly obtain the work difference, equating it to the integral of the work done by residual stress on the indenter at each indentation depth from the start of indentation to the maximum indentation depth, thus obtaining the residual stress of the material. The specific calculation model is as follows: This method has advantages such as strong applicability and convenience, and its calculation accuracy is greatly improved compared with the David energy method model.

[0055] This method, based on the David energy method, transforms the indentation contact area during the indentation process into a function of the indentation depth h. As the indenter indents to a unit depth dh, the volume of the "indentation" below the indenter increases, and the increase in "indentation" volume corresponding to dh is... Figure 2 The infinitesimal volume dA shown, or it can also be expressed as the infinitesimal volume dB, is determined by the geometry of the Bodeichter indenter, θ = 24.7°, and the following formula derivation confirms that the infinitesimal volume dA = dB.

[0056]

[0057]

[0058] Therefore, for ease of calculation, we use the projected area of ​​the indentation, i.e., A = 24.5h. 2 The residual stress work done during the pressing process is obtained by integrating the infinitesimal volume dA.

[0059] like Figure 3 As shown, during the pressing process, when the pressing depth is h, the projected contact area between the indenter and the material can be expressed as A = 24.5h. 2 Our modified model does not consider the promoting or hindering effect of residual stress on the indenter; therefore, the work done by residual stress during the subsequent indentation to a unit depth dh can be expressed as:

[0060] dW=σ24.5h 2 dh

[0061] The detailed derivation of the above formula is as follows:

[0062] When there is equibiaxial residual tensile stress (σ) in the material x , σ y When the David model is used, it decomposes the residual stress of a particle in the material below the indenter into a hydrostatic stress (σ). x , σ y , σ z ) and a uniaxial stress (-σ) parallel to the direction of the indenter load. z ),Right now

[0063] (Equal biaxial tensile stress)

[0064] In the above formula, the first term on the left represents the biaxial stress component, the first term on the right represents the hydrostatic stress, and the second term on the right represents the uniaxial stress component.

[0065] If a material contains biaxial residual compressive stress, the residual stress can be decomposed into a hydrostatic stress and a uniaxial stress opposite to the direction of the indenter load, i.e.

[0066] (Equal biaxial compressive stress)

[0067] The stress state of the material can be decomposed into a hydrostatic stress and a deviatoric stress parallel to the direction of the indenter load. During the indentation process, in addition to the load P applied to the material by the indenter, an effective stress of magnitude p can be introduced in the z-direction. z =σ z A(h) represents the additional force caused by residual stress. Therefore, the difference in work done during the pressing process between the stress-free and stress-laden states of the indenter, i.e., the work done by residual stress, can be considered as p. z The work done.

[0068] like Figure 4 As shown, under stress, during the downward movement of the indenter dh, the additional force p z It can be decomposed into components perpendicular to and parallel to the side of the indenter, and the displacements in these two directions are as follows: Figure 4 As shown in (c). Therefore, the work dW done by the residual stress when the indenter moves downward dh can be expressed as:

[0069] dW=σ z A(h)cosθdhcosθ+σ z A(h)sinθdhsinθ

[0070] =σ z (cos 2 θ+sfn 2 θ)A(h)dh

[0071] =σ z A(h)dh

[0072] During the pressing process, when the pressing depth is h, the projected area of ​​the indentation can be expressed as A(h) = 24.5h. 2 .

[0073] Right now

[0074] dW=σ z 24.5h 2 dh

[0075] The total work done in the entire indentation process can be calculated by integrating the work corresponding to each indentation depth element dh, thus yielding the modified model proposed in this invention:

[0076]

[0077] Right now

[0078]

[0079] p1 and p0 are the load values ​​collected from the load-displacement curves with and without stress, respectively. Their integral values ​​are obtained by directly processing the points on the curve using code.

[0080] Thus, the numerical value of the residual stress has been obtained.

[0081] In one embodiment, the method includes,

[0082] The metal samples to be tested are subjected to surface grinding and polishing, and electropolishing is performed to remove the surface stress caused by grinding and polishing.

[0083] At a fixed depth (maximum compression depth h) max In this mode, a Glass indenter is used to perform nanoindentation tests on the stressed test material, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve (p1-h curve). t1 ,in

[0084] At a fixed depth (maximum compression depth h) max In this mode, a Glass indenter is used to perform nanoindentation tests on the stress-free material under test, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve (p0-h curve). t0 ,in

[0085] The difference in work done by the load-displacement curves of the stress-free sample and the load-displacement curves of the stressed sample during the loading segment is calculated and used as the total work W done by the residual stress during the nanoindentation process. rs That is, W rs =W t0 -W t1 =ΔU;

[0086] The residual tension (σ) of the biaxial axis x , σ y It can be decomposed into a hydrostatic stress (σ). x , σ y , σ z ) and a uniaxial stress (-σ) parallel to the direction of the indenter load. z If the residual stress does work during the unit depth indentation dh, then the work done by the residual stress can be expressed as dW = σ²4.5h. 2 dh, the work done by residual stress during the entire pressing process is

[0087] Let ΔU = ΔW, then we have Since the data required for the calculation on the right can all be obtained from nanoindentation experimental data, the residual stress σ at the test location can be calculated. z According to the theory of elasticity, σ x, σ y , σ z The absolute values ​​of the three are equal, thus we can know σ at the test location. x , σ y The value.

[0088] Optionally, the processing of the metal sample to be tested specifically includes: grinding and polishing the metal sample to be tested, followed by electrolytic polishing (polishing voltage set to 5V, polishing current 0.5A, polishing time 5min). The surface treatment of the annealed stress-free sample should be exactly the same as that of the stress-bearing sample.

[0089] Optionally, the nano-indentation test parameters of the specimens under both stressed and stress-free conditions should be exactly the same, including indenter type, indentation depth, loading speed, holding time, and unloading speed.

[0090] Optionally, for polycrystalline materials, steps S2 and S3 can be repeated in multiple different grains in the vicinity of the test location under both stressed and stress-free conditions to obtain multiple W values. t0 Values ​​and multiple Ws t1 Calculate the average value of each. and The difference between the two average values ​​is then taken as the total work W done by the residual stress during the nanoindentation process. rs ,Right now

[0091] Optionally, the method for measuring residual stress in a metal micro-region based on a residual stress work algorithm is characterized in that it is applicable to elastoplastic metal materials.

[0092] Optionally, the method for measuring residual stress in a metal micro-region based on a residual stress work algorithm is characterized in that it is applicable to equibiaxial stress states.

[0093] To further illustrate the technical effect of the residual stress measurement method for metal micro-regions based on the residual stress work algorithm correction provided by the present invention, the method is applied as follows:

[0094] (1) The metal sample to be tested is subjected to stress-relief annealing.

[0095] (2) The metal sample to be tested is ground and polished, and then electropolished to obtain a sample with good surface quality and clear grains, with an average grain size of about 50 μm. Specifically, the sample is ground and polished, and then electropolished (polishing voltage is set to 5V, polishing current is 0.5A, and polishing time is 5min). The surface treatment of the annealed stress-free sample should be exactly the same as that of the stressed sample.

[0096] (3) The stress-relieved annealed metal sample was loaded into a nanoindenter. With the test point as the center and twice the average grain size as the radius, a nanoindentation experiment was performed on the grains that entered the marked point (marking circle). Quasi-static loading was performed with a fixed depth of 350 nm. The distance between adjacent test points was 10 times the indentation radius. Two indentations were pressed into one grain, and the indentation position was as close as possible to the center of the grain.

[0097] The specific steps of the nanoindentation experiment are as follows: the experimental parameters used for each indentation point should be exactly the same, including loading speed, holding time, unloading speed, etc.

[0098] (4) Metal samples with different pre-applied known stresses (-100MPa, 147MPa, 215MPa, 255MPa, and 290MPa) were loaded into a nanoindenter. Nanoindentation experiments were performed on grains entering the marked points (marking circles) with the test point as the center and twice the average grain size as the radius. A fixed depth of 350nm was used for quasi-static loading. The distance between adjacent test points was 10 times the indentation radius. Two indentations were pressed into each grain, with the indentation positions as close to the grain center as possible.

[0099] (5) Integrate the loading segments of all load-displacement curves obtained under both stress-free and stress-affected conditions to obtain multiple W values. t0 Values ​​and multiple Ws t1 The value is then calculated by averaging. as well as The difference between the two is calculated and substituted into the residual stress energy method correction model proposed in this invention, that is:

[0100]

[0101]

[0102]

[0103] W t0 W is the integral of the stress-free load displacement curve under loading. t1 σ is the integral of the stress-loaded displacement curve during the loaded segment; σ is the calculated residual stress, h max The maximum indentation depth is given by p0, where p0 represents the load on the stress-free specimen at each indentation depth collected by the load-displacement curve, and p1 represents the load on the stressed specimen at each indentation depth collected by the load-displacement curve. The residual stress σ can be calculated from these parameters.

[0104] Figure 5The results show the residual stress calculations under different prestresses in the embodiments of the present invention. As can be seen from the calculation results, under tensile and compressive stress states, the residual stress prediction accuracy of the energy method correction model proposed in this invention is significantly improved compared with the energy method proposed by David et al. and the energy method proposed by Yang et al.

[0105] Figure 6 The residual stress calculation error under different prestresses in the embodiments of the present invention is represented by (1 - residual stress calculation result / prestress) × 100%. Figure 6 As shown, compared with the energy method proposed by David and Yang et al., the error of the residual stress prediction results of the energy method correction model proposed in this invention is significantly reduced.

[0106] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0107] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A high-precision and high-efficiency method for detecting micro-region stress at the micrometer level, characterized in that, Includes the following steps: Step S1: The metal sample to be tested is subjected to surface grinding and polishing, and electrolytic polishing is performed to remove the surface stress caused by grinding and polishing. Step S2: In fixed depth mode, a Glass indenter is used to perform nanoindentation testing on the stressed metal sample to be tested, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve. t1 ,in Where p1 is the stressed load, h is the displacement, and h max This is the maximum pressing depth; Step S3: In fixed depth mode, a Glass indenter is used to perform nanoindentation testing on the stress-free metal sample to be tested, and the total work W of the indentation process is obtained by integrating the loading portion of the load-displacement curve. t0 ,in Where p0 is the load under stress-free conditions, h is the displacement, and h max This is the maximum pressing depth; Step S4: Calculate the difference in work done by the loading segments of the stress-free load-displacement curve and the stress-laden load-displacement curve, and use this difference as the total work W done by the residual stress during the nanoindentation process. rs That is, W rs =W t0 -W t1 =ΔU; Step S5: Apply the residual tension (σ) from the biaxial direction. x , σ y Decomposed into a hydrostatic stress (σ) x , σ y , σ z ) and a uniaxial stress (-σ) parallel to the direction of the indenter load. z If the residual stress does work during the unit depth indentation dh, then the work done by the residual stress is expressed as dW = σ. z 24.5h 2 dh, the work done by residual stress during the entire pressing process is Step S6: Let ΔU = ΔW, then we have Since the data required for the calculation on the right side are all obtained from nanoindentation experimental data, the residual stress σ at the test location is calculated. z Due to σ x , σ y , σ z The absolute values ​​of the three are equal, thus obtaining σ at the test location. x , σ y The value.

2. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, Preferably, in step S1: the polishing voltage is set to 5V, the polishing current to 0.5A, and the polishing time to 5min.

3. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, In step S2, the stress state of the metal sample to be tested under stress is an isobiaxial stress state.

4. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, In step 4, for both stressed and stress-free states of the polycrystalline material, steps S2 and S3 are repeated within multiple different grains in the vicinity of the test location to obtain multiple W values. t0 Values ​​and multiple Ws t1 Calculate the average value of each. and The difference between the two average values ​​is then taken as the total work W done by the residual stress during the nanoindentation process. rs , 5. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, The metal sample to be tested is an elastoplastic metal material.

6. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, The average grain size of the sample after electropolishing to remove the surface stress caused by grinding and polishing was 50 μm.

7. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, The stress-relieved annealed metal sample to be tested is loaded into a nanoindenter. With the test point as the center and twice the average grain size as the radius, a nanoindentation experiment is performed on the grain that enters the marked point. A static loading is performed with a fixed depth of 350 nm. The distance between adjacent test points is 10 times the indentation radius. Two indentations are pressed into one grain, and the indentation position is located at the center of the grain.

8. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, The energy method is the David energy method.

9. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, The experimental parameters for nanoindentation testing of stressed metal samples using a Glass indenter are the same as those for nanoindentation testing of unstressed metal samples using a Glass indenter. These experimental parameters include indenter type, indentation depth, loading speed, holding time, and unloading speed.

10. The high-precision and high-efficiency method for detecting micron-level micro-region stress according to claim 1, characterized in that, The residual stress in the metal sample being tested by nanoindentation measurement is located in the micrometer-scale region.

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