An adaptive indentation method coupled with a scene-data acquisition-inversion algorithm

Abstract

The application provides an adaptive indentation method coupling a detection scene-data acquisition-inversion algorithm, first, indentation detection with multi-source data acquisition characteristics is carried out; second, a test scheme and an inversion algorithm are matched according to a detection scene; then, indentation detection data are pretreated, specifically including: proportional limit calculation based on indentation DIC, real indentation depth calculation based on a pressure bar DIC, loading-unloading curve fitting, elastic-plastic indentation energy calculation and effective Young's modulus calculation; finally, according to the indentation test scheme, a suitable algorithm is selected from an incremental indentation algorithm, a power strengthening indentation energy algorithm, a simplified incremental indentation algorithm and a power strengthening database algorithm to complete the equivalent stress-equivalent strain inversion of the detected object. The application adopts a targeted test and data acquisition scheme, and matches a uniaxial mechanical property inversion algorithm accordingly, so that the indentation detection method always has high operability and detection precision in the face of different actual engineering detection scenes.

Description

Technical Field

[0001] This invention relates to the field of material performance testing technology, and in particular to an adaptive input method for coupling detection scenario-data acquisition-inversion algorithm. Background Technology

[0002] Due to the accumulation of time-related damage such as fatigue, creep, corrosion, and material deterioration, the failure risk of in-service equipment is constantly increasing, significantly increasing the difficulty of inspection and evaluation, posing serious safety hazards and a severe challenge to public safety. However, blindly scrapping and decommissioning equipment increases the burden on enterprises and wastes resources. Accurately evaluating the current mechanical properties of in-service equipment is fundamental to assessing its structural integrity and extending the service life of aging equipment. Conventional mechanical property testing methods (such as uniaxial tension and uniaxial compression) require large-volume destructive sampling, making them unsuitable for in-service equipment. In contrast, indentation testing, which requires no sampling and is nearly non-destructive, has become a promising emerging method for mechanical property testing.

[0003] In 2001, Ahn et al. published a paper entitled "Derivation of plastic stress-strain relationship from ballindentations: Examination of strain definition and pileup effect" in Volume 16, pp. 3170-3178 of the Journal of Materials Research. They proposed a method to invert the uniaxial mechanical properties of the tested material by inverting the indentation load-indentation depth curve, which includes multiple loading-unloading indentation tests.

[0004] In 2019, Campbell et al. published a paper titled "Comparison between stress-strain plots obtained from indentationplastometry, based on residual indent profiles, and from uniaxial testing" in Acta Materialia, Volume 168, pp. 87-99. They proposed introducing additional indentation profile acquisition on top of existing indentation load-indentation depth acquisition to further enrich the data input, thereby improving the inversion accuracy of mechanical properties and avoiding the problem of lack of uniqueness in the inversion results.

[0005] In 2019, Zhang et al. published a paper entitled "A study on determination of tensile properties of metals at elevated temperatures from spherical indentation tests" in Volume 54, pp. 331-347 of the Journal of Strain Analysis for Engineering Design. They proposed a compliance correction strategy suitable for high-temperature indentation testing and pointed out that when the compliance of the loading system is large, the reliability of the unloading curve after compliance correction is still much lower than that of the loading curve.

[0006] In 2021, Hwang et al. published a paper entitled "Extracting plastic properties from in-plane displacement data of spherical indentation imprint" in Volume 197, 106291 of the journal International Journal of Mechanical Sciences. They proposed to acquire the in-plane displacement of the indentation surface by means of numerical image correlation, thereby obtaining the radial displacement field of the indentation pit, and using it as data input other than the indentation load and indentation depth.

[0007] The aforementioned research indicates that whether indentation testing employs a single load-unload or multiple load-unload methods depends on the testing conditions. Furthermore, when testing conditions permit, introducing additional data input on top of existing indentation load-indentation depth acquisition can improve the reliability of uniaxial mechanical property inversion results. However, existing uniaxial mechanical property indentation testing methods (including data acquisition and inversion methods) are primarily designed for specific testing scenarios. When faced with more complex testing scenarios (such as insufficient stiffness in the indentation testing system leading to unusable unloading curves, or the inability to create the speckle pattern necessary for digital image processing and acquisition of the tested equipment's surface condition), they cannot meet the universal requirements for engineering applications. Summary of the Invention

[0008] To address the shortcomings of existing uniaxial mechanical property indentation testing methods (including data acquisition and inversion methods) which are mainly targeted at specific testing scenarios and cannot meet the universal application requirements of engineering projects, this invention provides an adaptive indentation testing method that couples testing scenario, data acquisition, and inversion algorithm. This method can adopt targeted data acquisition schemes according to the differences in testing scenarios and select matching uniaxial mechanical property inversion algorithms accordingly, thereby ensuring that the indentation testing method always has high operability and testing accuracy in different testing scenarios in actual engineering applications.

[0009] The technical solution adopted in this invention is as follows:

[0010] An adaptive compression method for coupled detection scenario-data acquisition-inversion algorithm includes:

[0011] 1) Adaptive indentation detection scheme for various detection scenarios

[0012] 1.1) Indentation detection with multi-source data acquisition capabilities

[0013] 1.1.1) Depending on the shape and material characteristics of the object being tested, different fastening fixtures are installed on the frame of the pressing and testing instrument to secure it tightly to the object being tested.

[0014] 1.1.2) Driven by a motor and transmission device, the pressure rod with a hard alloy spherical indenter at the bottom is slowly pressed into the surface of the object being tested. The loading method is divided into two types: single loading-unloading and multiple loading-unloading. Real-time pressing load data is obtained through a load sensor connected in series with the pressure rod, while real-time pressing displacement data is collected by a displacement sensor placed beside the pressure rod.

[0015] 1.1.3) Two optical components are installed on the frame of the indentation testing instrument. The optical component facing the indenter is used to collect the real-time digital speckle distribution on the surface of the indenter during the indentation test, and then obtain the indenter deformation (hereinafter referred to as: indenter DIC) based on digital image correlation (DIC) technology. The optical component facing the sample is used to collect the real-time digital speckle distribution on the surface of the sample under test near the indentation pit, and then obtain the indentation deformation (hereinafter referred to as: indentation DIC) based on digital image correlation technology.

[0016] 1.2) Selection of Test Scheme and Inversion Algorithm Based on Detection Scenario

[0017] 1.2.1) Determine whether the testing scenario has the conditions for speckle fabrication, whether the object under test is in a high-temperature environment, and whether the system stiffness is sufficient after the portable in-situ press-in testing instrument is fixed to the object under test. Based on the above judgment results, select the test scheme and the equivalent stress-equivalent strain inversion algorithm.

[0018] Table 1. Test Scheme and Inversion Algorithm Selection Based on Detection Scenarios

[0019]

[0020] 1.2.2) If speckle pattern fabrication conditions are available, the object under test is in a high-temperature environment, and the system stiffness of the portable in-situ indentation testing instrument after being fixed to the object under test is sufficient, then the corresponding test scheme is as follows: the indentation test is completed by including multiple loading-unloading cycles, and the test process needs to include both indentation DIC and indentation bar DIC. The corresponding data processing flow is as follows: First, calculate the proportional limit of the object under test according to step 2.1); second, calculate the true indentation depth according to step 2.2); then, fit the unloading curve according to step 2.3.2); third, calculate the elastic-plastic indentation energy according to step 2.4); then, calculate the effective Young's modulus of the object under test according to step 2.5); finally, determine the equivalent stress-equivalent strain relationship according to the incremental indentation algorithm in step 3.1).

[0021] 1.2.3) If the conditions for speckle fabrication are available, and the system stiffness of the portable in-situ indentation testing instrument after being fixed to the object under test is sufficient, but the object under test is not in a high-temperature environment, then the corresponding test scheme should be selected as follows: the indentation test should be completed by including multiple loading-unloading operations, and the test process should include indentation DIC. The corresponding data processing flow is as follows: first, calculate the proportional limit of the object under test according to step 2.1); second, fit the unloading curve according to step 2.3.2); then, calculate the elastic-plastic indentation energy according to step 2.4); third, calculate the effective Young's modulus of the object under test according to step 2.5); finally, determine the equivalent stress-equivalent strain relationship according to the incremental indentation algorithm in step 3.1).

[0022] 1.2.4) If speckle pattern fabrication is feasible and the object under test is in a high-temperature environment, but the system stiffness of the portable in-situ indentation testing instrument after being fixed to the object is insufficient, the corresponding test scheme should be: to complete the indentation test in a single loading-unloading manner, and the test process should include both indentation DIC and indentation bar DIC. The corresponding data processing flow is as follows: First, calculate the proportional limit of the object under test according to step 2.1); second, calculate the true indentation depth according to step 2.2); then, fit the loading curve according to step 2.3.1); third, calculate the elastic-plastic indentation energy according to step 2.4); finally, determine the equivalent stress-equivalent strain relationship according to the power-strengthened indentation energy algorithm in step 3.3).

[0023] 1.2.5) If speckle pattern fabrication is feasible, but the object under test is not in a high-temperature environment, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is insufficient, then the corresponding test scheme should be: to complete the indentation test in a single loading-unloading manner, and the test process should include indentation DIC. The corresponding data processing flow is as follows: first, calculate the proportional limit of the object under test according to step 2.1); second, fit the loading curve according to step 2.3.1); then, calculate the elastic-plastic indentation energy according to step 2.4); finally, determine the equivalent stress-equivalent strain relationship according to the power-strength indentation energy algorithm in step 3.3).

[0024] 1.2.6) If the object under test is in a high-temperature environment, and the system stiffness of the portable in-situ indentation testing instrument after being fixed to the object under test is sufficient, but the conditions for speckle fabrication are not available, then the corresponding test scheme should be selected as follows: the indentation test should be completed by including multiple loading-unloading cycles, and the test process should include the indenter DIC. The corresponding data processing flow is as follows: First, calculate the true indentation depth according to step 2.2); second, fit the loading-unloading curve according to step 2.3); then, calculate the elastic-plastic indentation energy according to step 2.4); third, calculate the effective Young's modulus of the object under test according to step 2.5); finally, determine the equivalent stress-equivalent strain relationship according to the simplified incremental indentation algorithm in step 3.2).

[0025] 1.2.7) If the system stiffness of the portable in-situ indentation testing instrument after being fixed to the object under test is sufficient, but the object under test does not have the conditions for speckle fabrication and is not in a high-temperature environment, then the corresponding test scheme should be selected as follows: the indentation test should be completed by including multiple loading-unloading cycles. The corresponding data processing flow is as follows: First, fit the loading-unloading curve according to step 2.3); second, calculate the elastic-plastic indentation energy according to step 2.4); then, calculate the effective Young's modulus of the object under test according to step 2.5); finally, determine the equivalent stress-equivalent strain relationship according to the simplified incremental indentation algorithm in step 3.2).

[0026] 1.2.8) If the object under test is in a high-temperature environment but the conditions for speckle fabrication are not available, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is insufficient, the corresponding test scheme should be: to complete the indentation test in a single loading-unloading manner, and the test process should include the indenter DIC. The corresponding data processing flow is as follows: First, calculate the true indentation depth according to step 2.2); second, determine the equivalent stress-equivalent strain relationship according to the power-strengthened database algorithm in step 3.4).

[0027] 1.2.9) If the object under test does not have the conditions for speckle fabrication, is not in a high-temperature environment, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is insufficient, then the corresponding test scheme should be: to complete the indentation test in a single loading-unloading manner, and the test process does not require indentation DIC or indentation bar DIC. The corresponding data processing flow is: to determine the equivalent stress-equivalent strain relationship according to the power-strengthening database algorithm in step 3.4).

[0028] 2) Data preprocessing

[0029] 2.1) Calculation of proportional limits based on indentation DIC

[0030] 2.1.1) The real-time digital speckle distribution on the surface of the test specimen near the indentation pit is acquired by an optical component facing the specimen. The digital speckle distribution on the surface of the test specimen before and after the indentation test is compared using digital image correlation analysis software to obtain the plastic strain distribution on the surface of the test specimen.

[0031] 2.1.2) Fit the plastic strain gradient line on the surface of the specimen to be tested with a circle, by setting the plastic strain threshold ε. th Determine the maximum load P corresponding to the indentation test. max (If it is a push test that includes N load-unload cycles, then the maximum load is actually the maximum load P of the Nth push cycle.) max (N) The radius r of the indentation plastic zone p .

[0032] 2.1.3) Calculate the stress proportional limit σ0 and strain proportional limit ε0 of the tested material according to formula (1) and formula (2) respectively.

[0033]

[0034]

[0035] In the formula, E is the Young's modulus of the material being tested.

[0036] 2.2) Calculation of the actual indentation depth based on the DIC of the compression bar

[0037] 2.2.1) Using digital image correlation methods, the displacement distribution of the pressure bar is calculated by real-time speckle distribution on the surface of the pressure bar captured by the telecentric lens. The displacement variation law of the pressure bar is fitted by formula (3).

[0038] U = U0 + f U (L) (3)

[0039] In the formula, U is the displacement at a distance L from the top of the compression member, U0 is the overall translation of the compression member, and f U(L) is a function of the displacement gradient of the column as a function of the distance L from the top of the column.

[0040] 2.2.2) For any indentation load P, according to the column displacement gradient f in step 2.2.1) U (L) Calculate the displacement gradient f at a distance L0 from the top of the column. U (L0-P) is used as the elastic compression deformation of the compression member. The actual indentation depth h corresponding to the indentation load P is calculated according to formula (4). t .

[0041] h t =hf U (L0-P) (4)

[0042] 2.3) Load-unloading curve fitting

[0043] 2.3.1) Fit the loading curve of the indentation load-indentation depth according to formula (5) to obtain the loading coefficient C and the loading exponent m.

[0044] P = Ch m (5)

[0045] 2.3.2) Fit the unloading curve of the i-th pressing cycle based on the pressing load-pressing depth according to formula (6), and obtain the unloading slope S of the i-th pressing cycle. (i) and plastic indentation depth h p (i) .

[0046]

[0047] 2.4) Calculation of Elastic-Plastic Indentation Energy

[0048] The elastic indentation energy W of the i-th indentation cycle is calculated according to formulas (7) and (8) respectively. e (i) and plastic indentation energy W p (i) .

[0049]

[0050]

[0051] In the formula, f load (i) and f unload (i) The loading and unloading curves for the i-th push-in cycle are shown below, h. max (i) is the maximum indentation depth in the i-th indentation cycle.

[0052] 2.5) Calculation of Effective Young's Modulus

[0053] 2.5.1) Calculate the effective Young's modulus E of the i-th pressing cycle according to formula (9). eff (i) .

[0054]

[0055] In the formula, R is the radius of the spherical indenter, and E ind and v ind These are Young's modulus and Poisson's ratio for the spherical indenter, respectively. r (i) R0 is the secondary loading depth for the i-th pressing cycle, calculated according to formula (10). (i) Let be the radius of curvature of the residual indentation pit after the i-th pressing cycle, calculated according to formula (11).

[0056]

[0057]

[0058] 2.5.2) For push tests involving multiple load-unload cycles, the effective Young's modulus E of the first push cycle is... eff (1) The Young's modulus E of the material being tested; for single-load-unload indentation tests, the Young's modulus E of the material being tested needs to be manually input, which can be obtained through non-destructive testing such as nonlinear ultrasonic testing or by looking up a table.

[0059] 3) Calculation of equivalent stress-equivalent strain relationship

[0060] 3.1) Incremental Indentation Algorithm

[0061] The proportional limit σ0-ε0 calculated based on the sample DIC in step 2.1) is used. The equivalent stress σ of the i-th indentation cycle is calculated according to formulas (12) and (13) respectively. eq (i) And equivalent change ε eq (i) .

[0062]

[0063]

[0064] In the formula, W p (i-1) For the (i-1)th indentation cycle, W is the plastic indentation energy when i = 1. p (0) It is 0. σ eq (i-1) and ε eq(i-1) These are the equivalent stress and equivalent strain of the (i-1)th compression cycle, respectively. When i = 1, σ eq (0) and ε eq (0) σ0 and ε0 are respectively. E eff (i-1) For the effective Young's modulus of the (i-1)th push-in cycle, when i=1, E eff (0) For E. P max (i) and P max (i-1) These are the maximum indentation loads for the i-th and (i-1)-th indentation cycles, respectively.

[0065] 3.2) Simplified incremental indentation algorithm

[0066] 3.2.1) Assuming the stress proportionality limit ε0 of the tested material is 0.002, calculate the equivalent stress σ of the i-th indentation cycle according to formulas (12) and (13) in step 3.1). eq (i) And equivalent change ε eq (i) .

[0067] 3.2.2) Using the power function constitutive equation shown in formula (14), fit the equivalent stress-equivalent strain data points calculated in step 3.2.1) to obtain the work hardening index n of the tested material.

[0068]

[0069] 3.2.3) Substitute the loading coefficient C obtained in step 2.3.1) and the work hardening index n calculated in step 3.2.2) into formula (15) to obtain the strain proportional limit ε0 of the tested material.

[0070]

[0071] In the formula, a jk (j=0,1,2;k=0,1,2) are the fitting coefficients.

[0072] 3.2.4) If the stress proportionality limit ε0 used to calculate the equivalent stress-equivalent strain data points in step 3.2.1) has an error less than the convergence criterion δ compared to the fitting result in step 3.2.3), then the equivalent stress σ calculated in step 3.2.1) is considered to be valid. eq (i) And equivalent change ε eq (i)The data is true. Otherwise, the strain proportional limit ε0 fitted in step 3.2.3) should be substituted into step 3.2.1) and the above calculation process should be repeated until the convergence criterion δ is satisfied.

[0073] 3.3) Power-enhanced indentation energy algorithm

[0074] The proportional limit σ0-ε0 is calculated based on the DIC of the sample in step 2.1). The work hardening index n in the equivalent stress-equivalent strain relationship shown in formula (14) is calculated according to formula (16).

[0075]

[0076] In the formula, σ eq-M The equivalent mean stress is calculated according to formula (17).

[0077]

[0078] 3.4) Power-Strengthening Database Algorithm

[0079] Substituting the loading curve of indentation load-indentation displacement into the regression equation shown in formula (18), we obtain the strain proportional limit ε0 and work hardening index n of the power function constitutive equation shown in formula (14).

[0080]

[0081] In the formula, a JKM represents the fitting coefficient.

[0082] The beneficial effects of this invention are:

[0083] 1. This invention overcomes the shortcomings of existing uniaxial mechanical property indentation testing methods, which are mainly targeted at specific testing scenarios and cannot meet the needs of engineering application and promotion. It classifies the testing scenarios based on whether there are speckle fabrication conditions, whether it is for high-temperature scenarios, and whether the system stiffness is sufficient. According to the differences in testing scenarios, targeted testing and data acquisition schemes are adopted, and uniaxial mechanical property inversion algorithms are matched accordingly.

[0084] 2. When speckle pattern fabrication conditions are available, the proportional limit of the tested material can be determined by introducing indentation DIC method, optimizing the universality of the method for different materials and improving the calculation accuracy of yield strength; in high-temperature scenarios, bar deformation correction is introduced to obtain the true indentation depth; when the system stiffness is insufficient, it automatically switches to a single loading-unloading mode, abandoning the dependence on unloading curve and reducing the influence of system stiffness on the inversion results.

[0085] 3. The method of the present invention can maintain high operability and detection accuracy in different detection scenarios in actual engineering applications. Attached Figure Description

[0086] Figure 1 An indentation testing instrument with multi-source data acquisition capabilities;

[0087] Figure 2 The indentation load-indentation depth curve includes 12 load-unload cycles;

[0088] Figure 3 The natural speckle distribution before the indentation test;

[0089] Figure 4 The natural speckle distribution after the indentation test;

[0090] Figure 5 The plastic strain distribution on the surface of the room temperature low alloy SA508 steel plate being tested;

[0091] Figure 6 Indentation inversion of equivalent stress-equivalent strain for the tested room temperature low alloy SA508 steel plate;

[0092] In the figure: 1. Load sensor; 2. Optical assembly facing the pressure bar; 3. Frame; 4. Tungsten carbide spherical pressure head; 5. Magnetic fixture; 6. Displacement sensor; 7. Pressure bar; 8. Room temperature low alloy SA508 steel plate to be tested; 9. Transmission system; 10. Drive motor; 11. Optical assembly facing the sample. Detailed Implementation

[0093] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0094] This embodiment provides an adaptive input method for coupling detection scenario-data acquisition-inversion algorithm, and the specific steps are as follows:

[0095] 1) An adaptive indentation detection scheme for various detection scenarios;

[0096] 1.1) Adopting as Figure 1 The indentation testing instrument shown features multi-source data acquisition capabilities. Based on the shape and ferromagnetic properties of the room-temperature low-alloy steel plate 8 being tested, a magnetic suction fixture 5 is installed on the instrument's frame 3. Because the surface of the room-temperature low-alloy steel plate being tested is flat, the magnetic suction fixture is extremely strong (effective load 250kg), and the system rigidity after the indentation testing instrument is connected to it is sufficient.

[0097] 1.2) Driven by the drive motor 10 and transmission system 9, the pressure rod 7, with a tungsten carbide spherical indenter 4 at its bottom, is slowly pressed into the surface of the room temperature low alloy SA508 steel plate under test in a loading-unloading manner, including 12 cycles. Real-time indentation load data is obtained through a load sensor 1 connected in series with the pressure rod, while real-time indentation displacement data is collected by a displacement sensor 6 placed beside the pressure rod. The indentation load-indentation depth curve of the 12-cycle loading-unloading indentation test is shown below. Figure 2 As shown.

[0098] 1.3) An optical component 2 facing the pressure bar is installed on the frame of the indentation testing instrument. This component can be used to collect the real-time digital speckle distribution on the surface of the pressure bar during the indentation test. Considering that the low alloy SA508 steel plate being tested is at room temperature and can directly contact the displacement sensor, the deformation of the pressure bar has little effect on the indentation displacement. Therefore, it is not necessary to start the optical component facing the pressure bar to collect the digital speckle distribution.

[0099] 1.4) An optical component 11 facing the sample is also installed on the frame of the indentation testing instrument. This component can be used to acquire the real-time digital speckle distribution on the surface of the room-temperature low-alloy SA508 steel plate near the indentation pit. Considering that the low-alloy SA508 steel plate being tested is at room temperature and its surface is dry, flat, and easy to produce digital speckle, the area to be tested is gradually polished using 400#-600#-800# sandpaper, and then... Figure 3 The polishing marks shown are natural speckles.

[0100] 2) Data preprocessing

[0101] 2.1) Calculation of proportional limits based on indentation DIC;

[0102] 2.1.1) Digital speckle distribution of the low-alloy SA508 steel plate before and after indentation testing was acquired using an optical assembly (a combination of a 2 / 3-inch CMOS sensor, an 8.8-megapixel Sony camera, and a 2x magnification telecentric lens) facing the sample. The results are shown below. Figure 3 and Figure 4 As shown. The data was then input into the digital image correlation analysis software Correlated Solutions VIC-2D to obtain the plastic strain distribution on the surface of the tested room temperature low-alloy SA508 steel plate, as shown. Figure 5 As shown.

[0103] 2.1.2) The plastic strain gradient line on the surface of the room temperature low alloy SA508 steel plate to be tested is fitted with a circle, and the plastic strain threshold ε is set. th Setting it to 0.4% yields the maximum load P corresponding to the 12th pressing cycle. max (12) The radius of the indentation plastic zone (r)p =0.68mm).

[0104] 2.1.3) Calculate the stress proportional limit σ0 and strain proportional limit ε0 of the tested room temperature low alloy SA508 steel plate according to formula (1) and formula (2), respectively.

[0105]

[0106]

[0107] In the formula, E is the Young's modulus of the tested room temperature low alloy SA508 steel plate, which is set to 205 GPa by looking up a table.

[0108] 2.2) Load-unloading curve fitting

[0109] Based on formula (3), the unloading curve of the i-th pressing cycle, which is the result of fitting the pressing load-pressing depth curve, is obtained as the unloading slope S of the i-th pressing cycle. (i) and plastic indentation depth h p (i) .

[0110]

[0111] 2.3) Calculation of Elastic-Plastic Indentation Energy

[0112] The elastic indentation energy W of the i-th indentation cycle is calculated according to formulas (4) and (5) respectively. e (i) and plastic indentation energy W p (i) .

[0113]

[0114]

[0115] In the formula, f load (i) and f unload (i) The loading and unloading curves for the i-th push-in cycle are shown below, h. max (i) is the maximum indentation depth in the i-th indentation cycle.

[0116] 2.4) Calculation of Effective Young's Modulus

[0117] The effective Young's modulus E for the i-th injection cycle is calculated according to formula (6). eff (i) .

[0118]

[0119] In the formula, R is the radius of the tungsten carbide spherical indenter (R = 0.38 mm), and E ind and v ind These are Young's modulus and Poisson's ratio (E) of the tungsten carbide spherical indenter. ind =710GPa, v ind =0.21). h r (i) R0 is the secondary loading depth for the i-th pressing cycle, calculated according to formula (7). (i) The radius of curvature of the residual indentation pit in the i-th pressing cycle is calculated according to formula (8).

[0120]

[0121]

[0122] 3) Inversion of equivalent stress-equivalent strain relationship based on incremental indentation algorithm

[0123] The proportional limit σ0-ε0 calculated based on the sample DIC in step 2.1) is used. The equivalent stress σ of the i-th indentation cycle is calculated according to formulas (9) and (10) respectively. eq (i) And equivalent change ε eq (i) The inversion results are shown in Figure 6. It can be seen that the equivalent stress-equivalent strain relationship obtained using this invention exhibits good consistency with the results of destructive uniaxial tensile testing, and can serve as an alternative to conventional uniaxial mechanical property testing.

[0124]

[0125]

[0126] In the formula, W p (i-1) For the (i-1)th indentation cycle, W is the plastic indentation energy when i = 1. p (0) It is 0. σ eq (i-1) and ε eq (i-1) These are the equivalent stress and equivalent strain of the (i-1)th compression cycle, respectively. When i = 1, σ eq (0) and ε eq (0) σ0 and ε0 are respectively. E eff (i-1) For the effective Young's modulus of the (i-1)th push-in cycle, when i=1, E eff (0) For E. Pmax (i) and P max (i-1) These are the maximum indentation loads for the i-th and (i-1)-th indentation cycles, respectively.

[0127] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims

1. An adaptive input method for coupled detection scenario-data acquisition-inversion algorithm, characterized in that: Includes the following steps: Step 1: Conduct push-in testing with multi-source data acquisition capabilities; then match the test plan and inversion algorithm according to the testing scenario. Step 2: Preprocess the indentation detection data; specifically: Step 2.1 Calculation of proportional limits based on indentation DIC: Step 2.1.1: The real-time digital speckle distribution on the surface of the test sample near the indentation pit is acquired by the optical component facing the sample. The digital speckle distribution on the surface of the test sample before and after the indentation test is compared by digital image correlation analysis software to obtain the plastic strain distribution on the surface of the test sample. Step 2.1.2: Fit the plastic strain gradient line on the surface of the sample to be tested to a circle, by setting the plastic strain threshold ε. th Determine the maximum load P corresponding to the indentation test. max If the test involves N load-unload cycles, then the maximum load is actually the maximum load P of the Nth load cycle. max (N) The radius r of the indentation plastic zone p ; Step 2.1.3: Calculate the stress proportional limit σ0 and strain proportional limit ε0 of the tested material according to formula (1) and formula (2) respectively; In the formula, E is the Young's modulus of the tested material; Step 2.2: Calculation of the actual indentation depth based on the DIC of the pressure bar; Step 2.2.1: Apply digital image correlation method to calculate the displacement distribution of the pressure bar by capturing the real-time speckle distribution on the surface of the pressure bar with a telecentric lens. The displacement variation law of the pressure bar is fitted by formula (3). U=U0+f U (L) (3) In the formula, U is the displacement at a distance L from the top of the compression member, U0 is the overall translation of the compression member, and f U (L) is a function of the displacement gradient of the column as a function of the distance L from the top of the column; Step 2.2.2: For any compressive load P, according to the column displacement gradient f in step 2.2.1) U (L) Calculate the displacement gradient f at a distance L0 from the top of the column. U (L0-P) is used as the elastic compression deformation of the compression bar; the actual indentation depth h corresponding to the indentation load P is calculated according to formula (4). t ; h t =h-f U (L0-P) (4) Step 2.3: Load-unload curve fitting; Step 2.3.1: Fit the loading curve of indentation load-indentation depth according to formula (5) to obtain the loading coefficient C and loading exponent m; P=Ch m (5) Step 2.3.2: Fit the unloading curve of the i-th pressing cycle based on the pressing load-pressing depth according to formula (6), and obtain the unloading slope S of the i-th pressing cycle. (i) and plastic indentation depth h p (i) ; Step 2.4: Calculation of elastic-plastic indentation energy; The elastic indentation energy W of the i-th indentation cycle is calculated according to formulas (7) and (8) respectively. e (i) and plastic indentation energy W p (i) ; In the formula, f load (i) and f unload (i) The loading and unloading curves for the i-th push-in cycle are shown below, h. max (i) The maximum indentation depth in the i-th indentation cycle; Step 2.5: Calculation of effective Young's modulus; Step 2.5.1: Calculate the effective Young's modulus E of the i-th pressing cycle according to formula (9). eff (i) ; In the formula, R is the radius of the spherical indenter, and E ind and v ind These are Young's modulus and Poisson's ratio of the spherical indenter, respectively; h r (i) R0 is the secondary loading depth for the i-th pressing cycle, calculated according to formula (10); (i) The radius of curvature of the residual indentation pit in the i-th pressing cycle is calculated according to formula (11); Step 2.5.2: For push tests involving multiple load-unload cycles, the effective Young's modulus E of the first push cycle is... eff (1) The Young's modulus E of the material being tested; for single loading-unloading indentation tests, the Young's modulus E of the material being tested needs to be manually input, which can be obtained through non-destructive testing such as nonlinear ultrasonic testing or by looking up a table. Step 3: Based on the indentation test plan, select a suitable algorithm from incremental indentation algorithm, power-strength indentation energy algorithm, simplified incremental indentation algorithm and power-strength database algorithm to complete the equivalent stress-equivalent strain inversion of the tested object; Step 3 specifically involves: Step 3.1: Incremental indentation algorithm; Using step 2.1, the proportional limit σ0-ε0 is calculated based on the sample DIC; the equivalent stress σ of the i-th indentation cycle is calculated according to formulas (12) and (13), respectively. eq (i) And equivalent change ε eq (i) ; In the formula, W p (i-1) For the (i-1)th indentation cycle, W is the plastic indentation energy when i = 1. p (0) =0; σ eq (i-1) and ε eq (i-1) These are the equivalent stress and equivalent strain of the (i-1)th compression cycle, respectively. When i = 1, σ eq (0) and ε eq (0) σ0 and ε0 are respectively; E eff (i-1) For the effective Young's modulus of the (i-1)th push-in cycle, when i=1, E eff (0) For E; P max (i) and P max (i-1) These are the maximum indentation loads for the i-th and (i-1)-th indentation cycles, respectively; Step 3.2: Simplify the incremental indentation algorithm; Step 3.2.1) Assuming the stress proportionality limit ε0 of the tested material is 0.002, calculate the equivalent stress σ of the i-th indentation cycle according to formulas (12) and (13) in Step 3.1). eq (i) And equivalent change ε eq (i) ; Step 3.2.2: Fit the equivalent stress-equivalent strain data points calculated in step 3.2.1) using the power function constitutive equation shown in formula (14) to obtain the work hardening index n of the tested material; Step 3.2.3: Substitute the loading coefficient C obtained in step 2.3.1 and the work hardening index n calculated in step 3.2.2 into formula (15) to fit and obtain the strain proportional limit ε0 of the tested material; In the formula, a jk (j = 0, 1, 2; k = 0, 1, 2) are the fitting coefficients; Step 3.2.4: If the stress proportionality limit ε0 used to calculate the equivalent stress-equivalent strain data points in step 3.2.1 has an error less than the convergence criterion δ compared to the fitting result in step 3.2.3, then the equivalent stress σ calculated in step 3.2.1) is considered to be... eq (i) And equivalent change ε eq (i) If the data is true, then the strain proportional limit ε0 fitted in step 3.2.3 should be substituted into step 3.2.1 and the above calculation process should be repeated until the convergence criterion δ is satisfied. Step 3.3: Power-enhanced indentation energy algorithm; The proportional limit σ0-ε0 calculated based on the sample DIC in step 2.1 is used; the work hardening index n in the equivalent stress-equivalent strain relationship shown in formula (14) is calculated according to formula (16); In the formula, σ eq-M The equivalent mean stress is calculated according to formula (17); Step 3.4 Power-enhanced database algorithm; Substituting the loading curve of indentation load-indentation displacement into the regression equation shown in formula (18), we can obtain the strain proportional limit ε0 and work hardening index n of the power function constitutive equation shown in formula (14). In the formula, a JKM represents the fitting coefficient.

2. The adaptive input method for a coupled detection scenario-data acquisition-inversion algorithm according to claim 1, characterized in that: Step 1 specifically includes: Step 1.1: Push-in detection with multi-source data acquisition characteristics, specifically: Step 1.1.1: Based on the shape and material characteristics of the object being tested, install different fastening fixtures on the frame of the pressing and testing instrument to secure it tightly to the object being tested; Step 1.1.2: Driven by the motor and transmission device, the pressure rod with a hard alloy spherical indenter at the bottom is slowly pressed into the surface of the object being tested. The loading method is divided into two types: single loading-unloading and multiple loading-unloading. Real-time pressing load data is obtained through a load sensor connected in series with the pressure rod, while real-time pressing displacement data is collected by a displacement sensor placed beside the pressure rod. Step 1.1.3: Two sets of optical components are installed on the frame of the indentation testing instrument. The optical component facing the indenter is used to collect the real-time digital speckle distribution on the surface of the indenter during the indentation test, and then obtain the deformation of the indenter based on digital image correlation technology. The optical component facing the sample is used to collect the real-time digital speckle distribution on the surface of the sample under test near the indentation pit, and then obtain the indentation deformation based on digital image correlation technology. Step 1.2: Selection of test scheme and inversion algorithm based on detection scenario, specifically as follows: Step 1.2.1: Determine whether the testing scene meets the conditions for speckle fabrication, whether the object under test is in a high-temperature environment, and whether the system stiffness is sufficient after the portable in-situ press-in testing instrument is fixed to the object under test. Based on the above judgment results, select the test scheme and the equivalent stress-equivalent strain inversion algorithm. Step 1.2.2: If the conditions for speckle fabrication are available, the object under test is in a high-temperature environment, and the system rigidity of the portable in-situ indentation testing instrument after it is fixed to the object under test is sufficient, then the corresponding test scheme is to complete the indentation test by including multiple loading-unloading, and the test process needs to include indentation DIC and indentation bar DIC. Step 1.2.3: If the conditions for speckle fabrication are available, and the system rigidity of the portable in-situ indentation testing instrument after it is fixed to the object under test is sufficient, but the object under test is not in a high-temperature environment, then the corresponding test scheme should be selected as follows: the indentation test is completed by including multiple loading and unloading, and the test process needs to include indentation DIC. Step 1.2.4: If the conditions for speckle fabrication are available and the object under test is in a high-temperature environment, but the system rigidity of the portable in-situ indentation testing instrument after it is fixed to the object under test is insufficient, then the corresponding test scheme should be selected as follows: the indentation test is completed by a single loading-unloading method, and the test process should include indentation DIC and indentation bar DIC. Step 1.2.5: If speckle pattern fabrication is possible, but the object under test is not in a high-temperature environment, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is insufficient, then the corresponding test plan should be: to complete the indentation test in a single loading-unloading manner, and the test process should include indentation DIC; Step 1.2.6: If the object under test is in a high-temperature environment, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is sufficient, but speckle pattern fabrication is not possible, then the corresponding test plan should be: to complete the indentation test in a manner that includes multiple loading-unloading, and the test process should include pressure bar DIC; Step 1.2.7: If the system stiffness of the portable in-situ indentation testing instrument after it is fixed to the object under test is sufficient, but the object under test does not have the conditions for speckle fabrication and is not in a high-temperature environment, then the corresponding test scheme is to complete the indentation test by including multiple loading and unloading. Step 1.2.8: If the object under test is in a high-temperature environment but does not have the conditions for speckle fabrication, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is insufficient, then the corresponding test scheme should be selected as follows: the indentation test should be completed in a single loading-unloading manner, and the test process should include the indenter DIC; the corresponding data processing flow is as follows: first, calculate the actual indentation depth according to step 2.2); second, determine the equivalent stress-equivalent strain relationship according to the power-strengthened database algorithm in step 3.

4. Step 1.2.9: If the object under test does not have the conditions for speckle fabrication, is not in a high-temperature environment, and the system stiffness after the portable in-situ indentation testing instrument is fixed to the object under test is insufficient, then the corresponding test scheme is to complete the indentation test by a single loading-unloading method, and the test process does not require indentation DIC or indentation bar DIC; the corresponding data processing flow is to determine the equivalent stress-equivalent strain relationship according to the power-strengthening database algorithm in step 3.4).

3. The adaptive input method for a coupled detection scenario-data acquisition-inversion algorithm according to claim 1, characterized in that: The data processing flow corresponding to step 1.2.2 is as follows: First, calculate the proportional limit of the object being detected according to step 2.1; second, calculate the actual indentation depth according to step 2.2; and then, fit the unloading curve according to step 2.3.

2. Next, calculate the elastic-plastic indentation energy according to step 2.4; Next, calculate the effective Young's modulus of the object being tested according to step 2.5; finally, determine the equivalent stress-equivalent strain relationship according to the incremental indentation algorithm in step 3.1).

4. The adaptive input method for a coupled detection scenario-data acquisition-inversion algorithm according to claim 1, characterized in that: The corresponding data processing flow for step 1.2.3 is as follows: First, calculate the proportional limit of the object under test according to step 2.1; second, fit the unloading curve according to step 2.3.2; then, calculate the elastic-plastic indentation energy according to step 2.4; third, calculate the effective Young's modulus of the object under test according to step 2.5; finally, determine the equivalent stress-equivalent strain relationship according to the incremental indentation algorithm in step 3.

1.

5. The adaptive input method for a coupled detection scenario-data acquisition-inversion algorithm according to claim 1, characterized in that: The data processing flow corresponding to step 1.2.5 is as follows: First, calculate the proportional limit of the object being tested according to step 2.1; second, fit the loading curve according to step 2.3.1; then, calculate the elastic-plastic indentation energy according to step 2.4; finally, determine the equivalent stress-equivalent strain relationship according to the power-strength indentation energy algorithm in step 3.

3.

6. The adaptive input method for a coupled detection scenario-data acquisition-inversion algorithm according to claim 1, characterized in that: The data processing flow corresponding to step 1.2.6 is as follows: First, calculate the true indentation depth according to step 2.2; second, fit the loading-unloading curve according to step 2.3); then, calculate the elastic-plastic indentation energy according to step 2.4; third, calculate the effective Young's modulus of the object being tested according to step 2.5; finally, determine the equivalent stress-equivalent strain relationship according to the simplified incremental indentation algorithm in step 3.

2.

7. The adaptive input method for a coupled detection scenario-data acquisition-inversion algorithm according to claim 1, characterized in that: The data processing flow corresponding to step 1.2.7 is as follows: First, fit the loading-unloading curve according to step 2.3; second, calculate the elastic-plastic indentation energy according to step 2.4; then, calculate the effective Young's modulus of the tested object according to step 2.5; finally, determine the equivalent stress-equivalent strain relationship according to the simplified incremental indentation algorithm in step 3.2.

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