CN117592267A - Self-adaptive indentation method for coupling detection scene-data acquisition-inversion algorithm - Google Patents
Self-adaptive indentation method for coupling detection scene-data acquisition-inversion algorithm Download PDFInfo
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Abstract
The invention provides a self-adaptive indentation method of a coupling detection scene-data acquisition-inversion algorithm, which comprises the steps of firstly carrying out indentation detection with multi-source data acquisition characteristics; secondly, matching a test scheme and an inversion algorithm according to a detection scene; then, preprocessing the press-in detection data, specifically including: proportion limit calculation based on indentation DIC, true indentation depth calculation based on compression bar DIC, loading-unloading curve fitting, elastic-plastic indentation energy calculation and effective Young modulus calculation; and finally, according to the indentation test scheme, selecting a proper algorithm from an incremental indentation algorithm, a power strengthening indentation energy algorithm, a simplified incremental indentation algorithm and a power strengthening database algorithm to finish the inversion of the equivalent stress-equivalent strain of the detected object. The invention adopts a targeted test and data acquisition scheme, and matches with a single-axis mechanical property inversion algorithm according to the scheme, so that the press-in detection method is ensured to face different actual engineering detection scenes, and has higher operability and detection precision all the time.
Description
Technical Field
The invention relates to the technical field of material performance detection, in particular to a self-adaptive indentation method of a coupling detection scene-data acquisition-inversion algorithm.
Background
In-service equipment is accumulated due to related damage such as fatigue, creep, corrosion, material degradation and the like, the failure risk is continuously increased, the inspection and evaluation difficulty is also greatly increased, serious potential safety hazards are brought, and a serious challenge is formed for social public safety. But the blind scrapping and the stop of the operation increase the burden of enterprises and cause the resource waste. How to accurately evaluate the current mechanical properties of the in-service equipment is the basis for realizing the structural integrity evaluation of the in-service equipment and the service life extension of the old equipment. Conventional mechanical property detection methods (such as uniaxial stretching, uniaxial compression and the like) all require destructive sampling with larger volume and cannot be applied to in-service equipment. In contrast, the near-lossless indentation detection without sampling becomes an emerging detection method with wide application prospect for mechanical properties.
In 2001, ahn et al, journal Journal of Materials Research, volume 16, pages 3170-3178, published paper "Derivation of plastic stress-strain relationship from ball indentations: examination of strain definition and pileup effect," proposed a method for inverting uniaxial mechanical properties of a material under test by a press-in load-press depth curve comprising multiple load-unload press-in tests.
In 2019, campbell et al in journal Acta materials, volume 168, pages 87-99 published paper Comparison between stress-strain plots obtained from indentation plastometry, based on residual indent profiles, and from uniaxial testing, introduced additional indentation profile acquisition based on the existing indentation load-indentation depth acquisition, further enriched data input, thereby improving the inversion accuracy of mechanical properties and avoiding the problem of lack of uniqueness of inversion results.
In 2019, zhang et al published paper "A study on determination of tensile properties of metals at elevated temperatures from spherical indentation tests" in journal Journal of Strain Analysis for Engineering Design, volume 54, pages 331-347, proposed a compliance correction strategy suitable for high temperature press-in detection, and indicated that compliance corrected unloading curves were still far less reliable than loading curves when loading systems were more compliant.
In 2021, hwang et al, journal International Journal of Mechanical Sciences, volume 197, 106291, published paper "Extracting plastic properties from in-plane displacement data of spherical indentation imprint," proposed that the in-plane displacement of the indentation surface be acquired by a numerical image correlation method, so as to obtain the radial displacement field of the indentation pit, and input it as data outside the indentation load-indentation depth.
The research current situation shows that the mode of single loading-unloading or multiple loading-unloading is dependent on the testing condition, and when the testing condition allows, additional data input is introduced on the basis of the existing indentation load-indentation depth acquisition, so that the reliability of the inversion result of the uniaxial mechanical property can be improved. However, the existing indentation detection method (including data acquisition and inversion method) with single-axis mechanical properties mainly aims at specific detection scenes, and cannot meet the universality requirements of engineering application and popularization when facing more complex detection scenes (such as incapacity of using an unloading curve due to insufficient rigidity of an indentation detection system, incapacity of manufacturing speckles necessary for digital image processing and acquisition on the surface state of detected equipment).
Disclosure of Invention
Aiming at the defect that the conventional indentation detection method with single-axis mechanical properties (comprising a data acquisition and inversion method) mainly aims at specific detection scenes and cannot meet the popularization requirement of engineering application, the invention provides the self-adaptive indentation detection method of the coupling detection scene-data acquisition-inversion algorithm, which can adopt a targeted data acquisition scheme according to the difference of detection scenes and select a matched single-axis mechanical property inversion algorithm, so that the indentation detection method always has higher operability and detection precision under different detection scenes of practical engineering application.
The technical scheme adopted by the invention is as follows:
an adaptive push method of a coupling detection scene-data acquisition-inversion algorithm, comprising:
1) Self-adaptive press-in detection scheme for various detection scenes
1.1 Press-in detection with multisource data acquisition characteristics
1.1.1 According to the shape and material characteristics of the detected object, different fastening tools are arranged on the frame of the press-in detection instrument so as to tightly fix the press-in detection instrument and the detected object.
1.1.2 Under the drive of a motor and a transmission device, a compression bar with a hard alloy spherical pressure head at the bottom end is slowly pressed into the surface of a tested object, the loading mode of the compression bar is divided into single loading-unloading and multiple loading-unloading, real-time pressing load data are obtained through a load sensor connected with the compression bar in series, and real-time pressing displacement data are collected through a displacement sensor beside the compression bar.
1.1.3 Two sets of optical components are arranged on a rack of the press-in detection instrument, wherein the optical components facing the press rod are used for collecting real-time digital speckle distribution on the surface of the press rod in the press-in test process, and further press rod deformation (short for simplicity) is obtained according to a digital image correlation (digital image correlation, DIC) technology: compression bar DIC); the optical component facing the test sample is used for collecting real-time digital speckle distribution of the surface of the tested test sample near the indentation pit, and then indentation deformation (indentation DIC for short) is obtained according to the related technology of the digital image.
1.2 Test scheme and inversion algorithm selection based on detection scenario
1.2.1 Judging whether the detection scene has speckle manufacturing conditions, whether the detected object is in a high-temperature scene or not, and whether the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is enough or not, and selecting a test scheme and an inversion algorithm of equivalent stress-equivalent strain according to the judgment result.
Table 1 test scenario based test scenario and inversion algorithm selection
1.2.2 If the speckle manufacturing conditions are met, the detected object is at a height Wen Changjing, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is enough, the corresponding test scheme is selected as follows: the indentation test is completed in a manner that includes multiple load-unload, and the test procedure needs to include an indentation DIC and a compression bar DIC. The corresponding data processing flow is as follows: firstly, calculating the proportion limit of a detected object according to the step 2.1); secondly, calculating the real pressing depth according to the step 2.2); then, fitting an unloading curve according to the step 2.3.2); thirdly, calculating the elastic-plastic indentation energy according to the step 2.4); then, calculating the effective Young's modulus of the detected object according to the step 2.5); and finally, determining an equivalent stress-equivalent strain relation according to the incremental indentation algorithm in the step 3.1).
1.2.3 If the speckle manufacturing conditions are met, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is enough, but the detected object is not in a high Wen Changjing, the corresponding test scheme is selected as follows: the indentation test is done in a manner that includes multiple load-unload, and the test procedure needs to include an indentation DIC. The corresponding data processing flow is as follows: firstly, calculating the proportion limit of a detected object according to the step 2.1); secondly, fitting an unloading curve according to the step 2.3.2); then, the elastic-plastic indentation energy is calculated according to the step 2.4); thirdly, calculating the effective Young's modulus of the detected object according to the step 2.5); and finally, determining an equivalent stress-equivalent strain relation according to the incremental indentation algorithm in the step 3.1).
1.2.4 If the speckle manufacturing conditions are met and the detected object is at high Wen Changjing, but the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the indentation test is completed in a single load-unload manner and the test procedure needs to include an indentation DIC and a compression bar DIC. The corresponding data processing flow is as follows: firstly, calculating the proportion limit of a detected object according to the step 2.1); secondly, calculating the real pressing depth according to the step 2.2); then, fitting a loading curve according to the step 2.3.1); thirdly, calculating the elastic-plastic indentation energy according to the step 2.4); and finally, determining an equivalent stress-equivalent strain relation according to the power strengthening indentation energy algorithm in the step 3.3).
1.2.5 If the speckle manufacturing conditions are met, but the detected object is not at high Wen Changjing, and the system rigidity of the portable in-situ press-in detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the indentation test is completed in a single load-unload fashion and the test procedure needs to include an indentation DIC. The corresponding data processing flow is as follows: firstly, calculating the proportion limit of a detected object according to the step 2.1); secondly, fitting a loading curve according to the step 2.3.1); then, the elastic-plastic indentation energy is calculated according to the step 2.4); and finally, determining an equivalent stress-equivalent strain relation according to the power strengthening indentation energy algorithm in the step 3.3).
1.2.6 If the detected object is at a height Wen Changjing and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is sufficient, but the speckle manufacturing condition is not met, the corresponding test scheme is selected as follows: the press-in test is completed in a manner including multiple load-unload, and the test procedure needs to include a compression bar DIC. The corresponding data processing flow is as follows: firstly, calculating the real pressing depth according to the step 2.2); secondly, fitting a loading-unloading curve according to the step 2.3); then, the elastic-plastic indentation energy is calculated according to the step 2.4); thirdly, calculating the effective Young's modulus of the detected object according to the step 2.5); and finally, determining an equivalent stress-equivalent strain relation according to the simplified incremental indentation algorithm in the step 3.2).
1.2.7 If the system rigidity of the portable in-situ press-in detection instrument after being fixed to the detected object is sufficient, but the detected object does not have the speckle manufacturing condition and is not at high Wen Changjing, the corresponding test scheme is selected as follows: the push test is completed in a manner that includes multiple load-unload. The corresponding data processing flow is as follows: firstly, fitting a loading-unloading curve according to the step 2.3); secondly, calculating elastic-plastic indentation energy according to the step 2.4); then, calculating the effective Young's modulus of the detected object according to the step 2.5); and finally, determining an equivalent stress-equivalent strain relation according to the simplified incremental indentation algorithm in the step 3.2).
1.2.8 If the detected object is at high Wen Changjing, but does not have the speckle manufacturing condition, and the system rigidity after the portable in-situ indentation detection instrument is fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the push test is completed in a single load-unload fashion and the test procedure needs to include a compression bar DIC. The corresponding data processing flow is as follows: firstly, calculating the real pressing depth according to the step 2.2); and secondly, determining an equivalent stress-equivalent strain relation according to the power strengthening database algorithm in the step 3.4).
1.2.9 If the detected object does not have the speckle manufacturing condition, is not in high Wen Changjing, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the indentation test is completed in a single loading-unloading manner, and the indentation DIC or the compression bar DIC is not needed in the test process. The corresponding data processing flow is as follows: determining an equivalent stress-equivalent strain relationship according to the power-enhanced database algorithm in step 3.4).
2) Data preprocessing
2.1 Proportional limit calculation based on indentation DIC
2.1.1 The optical component facing the sample is used for collecting real-time digital speckle distribution of the surface of the detected sample near the indentation pit, and digital image correlation technique analysis software is used for comparing the digital speckle distribution of the surface of the detected sample before and after the indentation test, so as to obtain the plastic strain distribution of the surface of the detected sample.
2.1.2 Using circular fitting to the plastic strain gradient line of the detected sample surface by setting the plastic strain threshold epsilon th Determining a maximum load P corresponding to the press-in test max (in the case of a press-in test involving N load-unload cycles, the maximum load is substantially the maximum load P of the Nth press-in cycle max (N) ) Radius r of indentation plastic region of (2) p 。
2.1.3 Calculating the stress proportion limit sigma of the tested material according to the formula (1) and the formula (2) respectively 0 And a strain ratio limit epsilon 0 。
Wherein E is the Young's modulus of the material being tested.
2.2 True press-in depth calculation based on compression bar DIC
2.2.1 And (3) calculating the displacement distribution of the compression bar by using a digital image correlation method through the real-time speckle distribution of the compression bar surface captured by the telecentric lens, and fitting the compression bar displacement change rule by using a formula (3).
U＝U 0 +f U (L) (3)
Wherein U is the displacement from the top end L of the pressure lever, U 0 For the integral translation of the compression bar, f U And (L) is a function of the change of the displacement gradient of the pressure rod along with the distance L of the top end of the pressure rod.
2.2.2 For any pressing load P, according to the plunger displacement gradient f in step 2.2.1) U (L) calculating the distance from the tip L of the plunger 0 Displacement gradient f at U (L 0 -P) and elastically compression-deforming it as a compression bar. Calculating a true indentation depth h corresponding to the indentation load P according to equation (4) t 。
h t ＝h-f U (L 0 -P) (4)
2.3 Load-unload curve fitting
2.3.1 Fitting a loading curve of the indentation load-indentation depth according to the formula (5) to obtain a loading coefficient C and a loading index m.
P＝Ch m (5)
2.3.2 Fitting an unloading curve of the ith indentation cycle of indentation load-indentation depth according to formula (6) to obtain an unloading slope S of the ith indentation cycle (i) And plastic press-in depth h p (i) 。
2.4 Elastic-plastic indentation energy calculation
Calculating the elastic indentation energy W of the ith indentation cycle according to the formula (7) and the formula (8), respectively e (i) And plastic indentation energy W p (i) 。
Wherein f load (i) And f unload (i) Loading curve and unloading curve of ith press-in cycle, h max (i) Is the maximum indentation depth for the ith indentation cycle.
2.5 Effective Young's modulus calculation
2.5.1 Calculating the effective Young's modulus E for the ith indentation cycle according to equation (9) eff (i) 。
Wherein R is the radius of a spherical pressure head, E ind And v ind Young's modulus and Poisson's ratio of the spherical indenter, respectively. h is a r (i) The secondary loading depth for the ith indentation cycle is calculated according to equation (10). R is R 0 (i) The radius of curvature of the residual indentation pit for the i-th indentation cycle is calculated according to equation (11).
2.5.2 For a press-in test involving multiple load-unload, the effective Young's modulus E for the first press-in cycle eff (1) Young's modulus E as a material to be tested; for a single loading-unloading press-in test, the Young modulus E of the material to be tested needs to be manually input and can be obtained through nondestructive testing such as nonlinear ultrasound or a table look-up method.
3) Equivalent stress-equivalent strain relationship calculation
3.1 Incremental indentation algorithm
The ratio limit sigma calculated based on the sample DIC using step 2.1) 0 -ε 0 . Calculating equivalent stress sigma of the ith press-in cycle according to the formula (12) and the formula (13), respectively eq (i) And equivalent strain ε eq (i) 。
In which W is p (i-1) For the plastic indentation energy of the (i-1) th indentation cycle, when i=1, W p (0) Is 0. Sigma (sigma) eq (i-1) And epsilon eq (i-1) Equivalent stress and equivalent strain for the (i-1) th press-in cycle, respectively, σ when i=1 eq (0) And epsilon eq (0) Respectively sigma 0 And epsilon 0 。E eff (i-1) For the (i-1) th press-in cycleE when i=1 eff (0) E is defined as E. P (P) max (i) And P max (i-1) The maximum press-in loads for the i-th and (i-1) -th press-in cycles, respectively.
3.2 Simplified incremental indentation algorithm
3.2.1 Assuming the stress ratio limit epsilon of the material being tested 0 0.002, and calculating the equivalent stress sigma of the ith press-in cycle according to the formula (12) and the formula (13) in the step 3.1), respectively eq (i) And equivalent strain ε eq (i) 。
3.2.2 Fitting 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 exponent n of the tested material.
3.2.3 Bringing the loading coefficient C obtained in the step 2.3.1) and the work hardening exponent n calculated in the step 3.2.2) into a formula (15), and fitting to obtain the strain proportion limit epsilon of the tested material 0 。
Wherein a is jk (j=0, 1,2; k=0, 1, 2) is a fitting coefficient.
3.2.4 If the stress proportion limit ε for the equivalent stress-equivalent strain data points is calculated in step 3.2.1) 0 If the error is smaller than the convergence criterion delta compared with the fitting result of step 3.2.3), the equivalent stress sigma calculated in step 3.2.1) is considered eq (i) And equivalent strain ε eq (i) The data is true. Otherwise, the strain proportion limit ε of the fit of step 3.2.3) should be calculated 0 Step 3.2.1) is carried over and the calculation is repeated until the convergence criterion delta is met.
3.3 Power strengthening indentation energy algorithm
The ratio limit sigma calculated based on the sample DIC using step 2.1) 0 -ε 0 . The work hardening exponent n in the equivalent stress-equivalent strain relationship shown in equation (14) is calculated according to equation (16).
In sigma eq-M Is an equivalent mean stress, calculated according to equation (17).
3.4 Power-enhanced database algorithm
The loading curve of the indentation load-indentation displacement is brought into a regression equation shown in a formula (18), and the strain proportion limit epsilon of the power function constitutive equation shown in a formula (14) is obtained by fitting 0 And a work hardening exponent n.
Wherein a is JKM Is the fitting coefficient.
The invention has the beneficial effects that:
1. the invention overcomes the defect that the existing indentation detection method of the single-axis mechanical property mainly aims at a specific detection scene and cannot meet the popularization requirement of engineering application, and whether the method has speckle manufacturing conditions, is high Wen Changjing-oriented and has enough system rigidity as the classifying basis of the detection scene, adopts a targeted test and data acquisition scheme according to the difference of the detection scene, and matches the single-axis mechanical property inversion algorithm according to the detection scene.
2. The proportion limit of the tested material can be determined by introducing an indentation DIC mode in the occasion with the speckle manufacturing condition, the universality of the optimization method on different materials is improved, and the calculation accuracy of the yield strength is improved; leading in compression bar deformation correction under a high-temperature scene, thereby obtaining the real pressing depth; when the system rigidity is insufficient, the system is automatically switched to a single loading-unloading loading mode, the dependence on an unloading curve is abandoned, and the influence of the system rigidity on an inversion result is reduced.
3. The method can be used for pressing detection under different detection scenes of actual engineering application, and has higher operability and detection precision all the time.
Drawings
FIG. 1 is a schematic illustration of a press-in detection instrument with multi-source data acquisition characteristics;
FIG. 2 is a press-in load-press-in depth curve including 12 load-off loads;
FIG. 3 is a natural speckle distribution prior to press-in testing;
FIG. 4 is a natural speckle distribution after press-in testing;
FIG. 5 is a graph showing the plastic strain distribution of the surface of a tested room temperature low alloy SA508 steel plate;
FIG. 6 is a press-in inversion of the equivalent stress-equivalent strain of the tested room temperature low alloy SA508 steel plate;
in the figure: 1. a load sensor; 2. an optical component facing the compression bar; 3. a frame; 4. tungsten carbide sphere-shaped pressure head; 5. a magnetic tool; 6. a displacement sensor; 7. a compression bar; 8. the room temperature low alloy SA508 steel plate is detected; 9. a transmission system; 10. a driving motor; 11. an optical component facing the sample.
Detailed Description
The present invention is further illustrated in the following drawings and detailed description, which are to be understood as being merely illustrative of the invention and not limiting the scope of the invention. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the drawings, and the words "inner" and "outer" refer to directions toward or away from, respectively, the geometric center of a particular component.
The embodiment provides a self-adaptive indentation method of a coupling detection scene-data acquisition-inversion algorithm, which comprises the following specific steps:
1) Self-adaptive press-in detection schemes oriented to various detection scenes;
1.1 A press-in detection instrument with multi-source data acquisition characteristics as shown in fig. 1 is adopted, and a magnetic tool 5 is arranged on a frame 3 of the press-in detection instrument according to the shape and the ferromagnetic characteristics of a detected room temperature low alloy SA508 steel plate 8. Because the surface of the detected room temperature low alloy SA508 steel plate is flat, the magnetic attraction tool used is extremely strong in magnetism (effective load is 250 kg), and the rigidity of a system connected with the pressure detection instrument is enough.
1.2 Under the drive of a driving motor 10 and a transmission system 9, a pressing rod 7 of the spherical tungsten carbide pressing head 4 at the bottom end is slowly pressed into the surface of the room temperature low alloy SA508 steel plate to be detected in a loading-unloading mode for 12 times, real-time pressing load data are obtained through a load sensor 1 connected with the pressing rod in series, and real-time pressing displacement data are collected through a displacement sensor 6 beside the pressing rod. The indentation load-indentation depth profile containing 12 load-unload indentation tests is shown in fig. 2.
1.3 The optical component 2 facing the pressing rod is installed on the rack of the pressing detection instrument, the component can be used for collecting real-time digital speckle distribution on the surface of the pressing rod in the pressing test process, the detected low alloy SA508 steel plate is in a room temperature state and can be in direct contact with the displacement sensor, the pressing rod deformation has little influence on pressing displacement, and the optical component facing the pressing rod does not need to be started to collect digital speckle distribution.
1.4 The frame of the press-in detection instrument is also mounted with a specimen-facing optical assembly 11 that can be used to collect the real-time digital speckle distribution of the surface of the room temperature low alloy SA508 steel sheet being detected in the vicinity of the indentation pits. Considering that the detected low alloy SA508 steel plate is at room temperature, the surface of the steel plate is dry and smooth, and digital speckles are easy to manufacture, the 400# -600# -800# abrasive paper is adopted to polish the area to be detected step by step, and polishing marks shown in figure 3 are used as natural speckles.
2) Data preprocessing
2.1 Based on the scaling limits of the indentation DIC;
2.1.1 Collecting digital speckle distribution before and after the press-in test of the area to be tested of the low alloy SA508 steel plate through an optical component (a combination of a 2/3 inch CMOS,880 ten thousand pixels Sony camera and a 2-magnification magnifying telecentric lens) facing the sample, as shown in figures 3 and 4 respectively. And inputting the strain distribution into digital image correlation technique analysis software Correlated solutions VIC-2D to obtain the plastic strain distribution of the surface of the detected room temperature low alloy SA508 steel plate, as shown in figure 5.
2.1.2 Using circular fitting to the plastic strain gradient line of the surface of the detected room temperature low alloy SA508 steel plate, and using the plastic strain threshold epsilon th Set to 0.4%, a maximum load P corresponding to the 12 th press-in cycle was determined max (12) Is (r) p ＝0.68mm)。
2.1.3 Calculating the stress proportion limit sigma of the detected room temperature low alloy SA508 steel plate according to the formula (1) and the formula (2) respectively 0 And a strain ratio limit epsilon 0 。
Wherein E is Young's modulus of the room temperature low alloy SA508 steel sheet to be tested, and is set to 205GPa by a table look-up method.
2.2 Load-unload curve fitting
Fitting an unloading curve of the ith indentation cycle of indentation load-indentation depth according to the formula (3) to obtain an unloading slope S of the ith indentation cycle (i) And plastic press-in depth h p (i) 。
2.3 Elastic-plastic indentation energy calculation
Calculating the elastic indentation energy W of the ith indentation cycle according to the formula (4) and the formula (5) respectively e (i) And plastic indentation energy W p (i) 。
Wherein f load (i) And f unload (i) Loading curve and unloading curve of ith press-in cycle, h max (i) Is the maximum indentation depth for the ith indentation cycle.
2.4 Effective Young's modulus calculation
Calculating the effective Young's modulus E for the ith indentation cycle according to equation (6) eff (i) 。
Wherein R is the radius of a tungsten carbide spherical pressure head (R=0.38 mm), E ind And v ind Young's modulus and Poisson's ratio of a tungsten carbide sphere indenter, respectively (E ind ＝710GPa，v ind ＝0.21)。h r (i) The secondary loading depth for the ith indentation cycle is calculated according to equation (7). R is R 0 (i) The radius of curvature of the residual indentation pit for the i-th indentation cycle is calculated according to equation (8).
3) Equivalent stress-equivalent strain relation inversion based on incremental indentation algorithm
The ratio limit sigma calculated based on the sample DIC using step 2.1) 0 -ε 0 . Calculating equivalent stress sigma of the ith press-in cycle according to the formula (9) and the formula (10), respectively eq (i) And equivalent strain ε eq (i) The inversion results are shown in fig. 6. It can be seen that the equivalent stress-equivalent strain relationship inverted using the present invention is compared to the destructive uniaxial tensile test resultsThe method has good consistency and can be used as an alternative scheme for detecting the conventional uniaxial mechanical property.
In which W is p (i-1) For the plastic indentation energy of the (i-1) th indentation cycle, when i=1, W p (0) Is 0. Sigma (sigma) eq (i-1) And epsilon eq (i-1) Equivalent stress and equivalent strain for the (i-1) th press-in cycle, respectively, σ when i=1 eq (0) And epsilon eq (0) Respectively sigma 0 And epsilon 0 。E eff (i-1) For the effective Young's modulus of the (i-1) th press-in cycle, E when i=1 eff (0) E is defined as E. P (P) max (i) And P max (i-1) The maximum press-in loads for the i-th and (i-1) -th press-in cycles, respectively.
The technical means disclosed by the scheme of the invention is not limited to the technical means disclosed by the embodiment, and also comprises the technical scheme formed by any combination of the technical features.
Claims (7)
1. The self-adaptive indentation method of the coupling detection scene-data acquisition-inversion algorithm is characterized by comprising the following steps of: the method comprises the following steps:
step 1: performing press-in detection with multi-source data acquisition characteristics; then matching the test scheme and inversion algorithm according to the detection scene
Step 2: preprocessing the press-in detection data; the method comprises the following steps:
step 2.1 calculation of the proportionality limit based on indentation DIC:
step 2.1.1: collecting real-time digital speckle distribution of the surface of the detected sample near the indentation pit through an optical component facing the sample, comparing the digital speckle distribution of the surface of the detected sample before and after the indentation pit is pressed into the sample by using digital image correlation technique analysis software, and obtaining plastic strain distribution of the surface of the detected sample;
step 2.1.2: fitting the plastic strain gradient line of the surface of the detected sample by using circles, and setting a plastic strain threshold epsilon th Determining a maximum load P corresponding to the press-in test max In the case of a press-in test involving N load-unload cycles, the maximum load is substantially the maximum load P of the Nth press-in cycle max (N) Radius r of indentation plastic region of (2) p ；
Step 2.1.3: calculating the stress proportion limit sigma of the tested material according to the formula (1) and the formula (2) respectively 0 And a strain ratio limit epsilon 0 ；
Wherein E is Young's modulus of the tested material;
step 2.2: calculating the true pressing depth based on the compression bar DIC;
step 2.2.1: calculating pressure lever displacement distribution by using a digital image correlation method through pressure lever surface real-time speckle distribution captured by a telecentric lens, and fitting a pressure lever displacement change rule by using a formula (3);
U＝U 0 +f U (L) (3)
wherein U is the displacement from the top end L of the pressure lever, U 0 For the integral translation of the compression bar, f U (L) is a function of the displacement gradient of the plunger as a function of the distance L from the plunger tip;
step 2.2.2: for any pressing load P, according to the compression rod displacement gradient f in step 2.2.1) U (L) calculating the distance from the tip L of the plunger 0 Displacement gradient f at U (L 0 -P) and elastically deforming it as a compression bar; according to the formula(4) Calculating a true press-in depth h corresponding to the press-in load P t ；
h t ＝h-f U (L 0 -P) (4)
Step 2.3: fitting a loading-unloading curve;
step 2.3.1: fitting a loading curve of the pressing-in load-pressing-in depth according to a formula (5) to obtain a loading coefficient C and a loading index m;
P＝Ch m (5)
step 2.3.2: fitting an unloading curve of the ith indentation cycle of indentation load-indentation depth according to formula (6) to obtain an unloading slope S of the ith indentation cycle (i) And plastic press-in depth h p (i) ；
Step 2.4: calculating the elastic-plastic indentation energy;
calculating the elastic indentation energy W of the ith indentation cycle according to the formula (7) and the formula (8), respectively e (i) And plastic indentation energy W p (i) ；
Wherein f load (i) And f unload (i) Loading curve and unloading curve of ith press-in cycle, h max (i) The maximum press-in depth for the ith press-in cycle;
step 2.5: calculating effective Young's modulus;
step 2.5.1: calculating the effective Young's modulus E for the ith indentation cycle according to equation (9) eff (i) ；
Wherein R is the radius of a spherical pressure head, E ind And v ind Young's modulus and Poisson's ratio of the spherical indenter, respectively; h is a r (i) The secondary loading depth for the ith press-in cycle is calculated according to formula (10); r is R 0 (i) The radius of curvature of the residual indentation pit for the ith indentation cycle is calculated according to formula (11);
step 2.5.2: for a press-in test involving multiple load-unload, the effective Young's modulus E for the first press-in cycle eff (1) Young's modulus E as a material to be tested; for a single loading-unloading press-in test, the Young modulus E of the tested material needs to be manually input and can be obtained through nondestructive testing such as nonlinear ultrasound or a table look-up method;
step 3: according to the indentation test scheme, selecting a proper algorithm from an incremental indentation algorithm, a power strengthening indentation energy algorithm, a simplified incremental indentation algorithm and a power strengthening database algorithm to finish the inversion of equivalent stress-equivalent strain of the detected object;
the step 3 specifically comprises the following steps:
step 3.1: an incremental indentation algorithm;
using step 2.1, the proportional limit σ calculated based on the sample DIC 0 -ε 0 The method comprises the steps of carrying out a first treatment on the surface of the Calculating equivalent stress sigma of the ith press-in cycle according to the formula (12) and the formula (13), respectively eq (i) And equivalent strain ε eq (i) ；
In which W is p (i-1) For the plastic indentation energy of the (i-1) th indentation cycle, when i=1, W p (0) Is 0; sigma (sigma) eq (i-1) And epsilon eq (i-1) Equivalent stress and equivalent strain for the (i-1) th press-in cycle, respectively, σ when i=1 eq (0) And epsilon eq (0) Respectively sigma 0 And epsilon 0 ；E eff (i-1) For the effective Young's modulus of the (i-1) th press-in cycle, E when i=1 eff (0) E is; p (P) max (i) And P max (i-1) Maximum press-in loads for the i-th and (i-1) -th press-in cycles, respectively;
step 3.2: simplifying an incremental indentation algorithm;
step 3.2.1) assume the stress proportion limit ε of the tested material 0 0.002, and calculating the equivalent stress sigma of the ith press-in cycle according to the formula (12) and the formula (13) in the step 3.1), respectively eq (i) And equivalent strain ε eq (i) ；
Step 3.2.2: fitting the equivalent stress-equivalent strain data points calculated in the step 3.2.1) by using a power function constitutive equation shown in the formula (14) to obtain a work hardening exponent n of the tested material;
step 3.2.3: bringing the loading coefficient C obtained in the step 2.3.1 and the work hardening index n calculated in the step 3.2.2 into a formula (15), and fitting to obtain the strain proportion limit epsilon of the tested material 0 ；
Wherein a is jk (j=0, 1,2; k=0, 1, 2) is a fitting coefficient;
step 3.2.4: if the stress proportion limit epsilon used for calculating the equivalent stress-equivalent strain data point in the step 3.2.1 0 If the error is smaller than the convergence criterion delta compared with the fitting result of step 3.2.3, the equivalent stress sigma calculated in step 3.2.1) is considered to be eq (i) And equivalent strain ε eq (i) The data is true; otherwise, the strain proportion limit ε of the fit of step 3.2.3 should be calculated 0 Carrying out the step 3.2.1, and repeating the calculation process until the convergence criterion delta is met;
step 3.3: a power-enhanced indentation energy algorithm;
the proportional limit σ calculated based on the sample DIC using step 2.1 0 -ε 0 The method comprises the steps of carrying out a first treatment on the surface of the Calculating a work hardening exponent n in an equivalent stress-equivalent strain relationship shown in formula (14) according to formula (16);
in sigma eq-M Calculating according to a formula (17) for equivalent mean stress;
step 3.4, a power strengthening database algorithm;
the loading curve of the indentation load-indentation displacement is brought into a regression equation shown in a formula (18), and the strain proportion limit epsilon of the power function constitutive equation shown in a formula (14) is obtained by fitting 0 And a work hardening exponent n;
wherein a is JKM Is the fitting coefficient.
2. The adaptive push method of a coupling detection scenario-data acquisition-inversion algorithm of claim 1, wherein: the step 1 specifically includes:
step 1.1: the press-in detection with the multi-source data acquisition characteristic specifically comprises the following steps:
step 1.1.1: according to the shape and material characteristics of the detected object, different fastening tools are arranged on a frame of the press-in detection instrument so as to tightly fix the press-in detection instrument and the detected object;
step 1.1.2: under the drive of a motor and a transmission device, a compression bar of which the bottom end is a hard alloy spherical pressure head is slowly pressed into the surface of a tested object, the loading mode is divided into single loading-unloading and multiple loading-unloading, real-time pressing load data are obtained through a load sensor connected with the compression bar in series, and real-time pressing displacement data are collected through a displacement sensor arranged beside the compression bar;
step 1.1.3: two sets of optical components are arranged on a rack of the press-in detection instrument, wherein the optical components facing the press rod are used for collecting real-time digital speckle distribution on the surface of the press rod in the press-in test process, and further, press rod deformation is obtained according to the digital image related technology; the optical component facing the test sample is used for collecting real-time digital speckle distribution of the surface of the tested test sample near the indentation pit, and further obtaining indentation deformation according to a digital image correlation technique;
step 1.2: the test scheme and inversion algorithm selection based on the detection scene is specifically as follows:
step 1.2.1: judging whether the detection scene has speckle manufacturing conditions, whether the detected object is in a high-temperature scene or not and whether the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is enough or not, and selecting a test scheme and an inversion algorithm of equivalent stress-equivalent strain according to the judgment result;
step 1.2.2: if the speckle manufacturing conditions are met, the detected object is at a height Wen Changjing, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is enough, the corresponding test scheme is selected as follows: the press-in test is completed in a mode of multiple loading-unloading, and the test process needs to comprise an indentation DIC and a compression bar DIC;
step 1.2.3: if the speckle manufacturing conditions are met, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is enough, but the detected object is not in a high Wen Changjing, the corresponding test scheme is selected as follows: the indentation test is completed in a manner comprising multiple loading-unloading, and the test process needs to comprise indentation DIC;
step 1.2.4: if the speckle manufacturing conditions are met and the detected object is at high Wen Changjing, but the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the press-in test is completed in a single loading-unloading mode, and the test process needs to comprise an indentation DIC and a compression bar DIC;
step 1.2.5: if the speckle manufacturing conditions are met, but the detected object is not at high Wen Changjing, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the press-in test is completed in a single loading-unloading mode, and the test process needs to comprise an indentation DIC; step 1.2.6: if the object to be inspected is at a height Wen Changjing and the system stiffness after the portable in-situ indentation detection instrument is fixed to the object to be inspected is sufficient, but the speckle manufacturing condition is not provided, the corresponding test scheme is selected as follows: the press-in test is completed in a mode of multiple loading-unloading, and the test process needs to comprise a compression bar DIC;
step 1.2.7: if the system rigidity of the portable in-situ press-in detection instrument after being fixed to the detected object is sufficient, but the detected object does not have the speckle manufacturing condition and is not at high Wen Changjing, the corresponding test scheme is selected as follows: performing a push test in a manner including multiple load-unload;
step 1.2.8: if the detected object is at high Wen Changjing, but does not have the speckle manufacturing condition, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the press-in test is completed in a single loading-unloading mode, and the test process needs to comprise a compression bar DIC; the corresponding data processing flow is as follows: firstly, calculating the real pressing depth according to the step 2.2); secondly, determining an equivalent stress-equivalent strain relation according to the power strengthening database algorithm in the step 3.4;
step 1.2.9: if the detected object does not have the speckle manufacturing condition, is not in high Wen Changjing, and the system rigidity of the portable in-situ indentation detection instrument after being fixed to the detected object is insufficient, the corresponding test scheme is selected as follows: the press-in test is completed in a single loading-unloading mode, and the indentation DIC or the compression bar DIC is not needed in the test process; the corresponding data processing flow is as follows: determining an equivalent stress-equivalent strain relationship according to the power-enhanced database algorithm in step 3.4).
3. The adaptive push method of a coupling detection scenario-data acquisition-inversion algorithm of claim 1, wherein: the data processing flow corresponding to the step 1.2.2 is as follows: firstly, calculating the proportion limit of a detected object according to the step 2.1; secondly, calculating the real pressing depth according to the step 2.2; then, fitting an unloading curve according to the step 2.3.2; thirdly, calculating elastic-plastic indentation energy according to the step 2.4; then, calculating the effective Young's modulus of the detected object according to the step 2.5; and finally, determining an equivalent stress-equivalent strain relation according to the incremental indentation algorithm in the step 3.1).
4. The adaptive push method of a coupling detection scenario-data acquisition-inversion algorithm of claim 1, wherein: step 1.2.3 thus corresponds to the data processing flow: firstly, calculating the proportion limit of a detected object according to the step 2.1; secondly, fitting an unloading curve according to the step 2.3.2; then, the elastic-plastic indentation energy is calculated according to the step 2.4; thirdly, calculating the effective Young's modulus of the detected object according to the step 2.5; and finally, determining an equivalent stress-equivalent strain relation according to the incremental indentation algorithm in the step 3.1.
5. The adaptive push method of a coupling detection scenario-data acquisition-inversion algorithm of claim 1, wherein: the data processing flow corresponding to the step 1.2.5 is as follows: firstly, calculating the proportion limit of a detected object according to the step 2.1; secondly, fitting a loading curve according to the step 2.3.1; then, the elastic-plastic indentation energy is calculated according to the step 2.4; and finally, determining an equivalent stress-equivalent strain relation according to the power strengthening indentation energy algorithm in the step 3.3.
6. The adaptive push method of a coupling detection scenario-data acquisition-inversion algorithm of claim 1, wherein: the data processing flow corresponding to the step 1.2.6 is as follows: firstly, calculating the real pressing depth according to the step 2.2; secondly, fitting a loading-unloading curve according to the step 2.3); then, the elastic-plastic indentation energy is calculated according to the step 2.4; thirdly, calculating the effective Young's modulus of the detected object according to the step 2.5); and finally, determining an equivalent stress-equivalent strain relation according to the simplified incremental indentation algorithm in the step 3.2.
7. The adaptive push method of a coupling detection scenario-data acquisition-inversion algorithm of claim 1, wherein: the data processing flow corresponding to the step 1.2.7 is as follows: firstly, fitting a loading-unloading curve according to the step 2.3; secondly, calculating elastic-plastic indentation energy according to the step 2.4; then, calculating the effective Young's modulus of the detected object according to the step 2.5; and finally, determining an equivalent stress-equivalent strain relation according to the simplified incremental indentation algorithm in the step 3.2.
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