A method for testing residual stress depth distribution based on constant temperature pulse electrolytic layer stripping

Abstract

The application discloses a kind of residual stress depth distribution test methods based on constant temperature pulse electrolytic stripping, belong to material mechanics performance detection field.The method is inhibited electrolytic thermal effect by low-temperature constant temperature constraint, realizes micro uniform stripping by pulse electrolysis, cooperates with layer-by-layer strain collection and recursive correction inversion, realizes the continuous, quasi-non-destructive, high-precision characterization of residual stress of metal component along depth direction.The application effectively solves the problems of traditional stripping method, such as large thermal disturbance, uneven surface corrosion, low depth resolution, poor test accuracy and the like, the test error is less than or equal to 3%, and is suitable for residual stress depth profile testing of high-strength steel, titanium alloy, welded structure and precision shaft components, and has the advantages of high precision, small disturbance, good repeatability and strong engineering applicability.

Description

Technical Field

[0001] This invention belongs to the field of material mechanical property testing technology, and in particular relates to a method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer. Background Technology

[0002] Residual stress is a key factor affecting the fatigue performance, dimensional stability, and stress corrosion cracking behavior of engineering components. In thick plate components, welded joints, and precision-machined parts, residual stress exhibits a gradient distribution along the depth direction, and its distribution pattern directly determines the structural service safety. Among the commonly used residual stress testing methods, blind hole methods and X-ray diffraction methods can only characterize surface stress information and cannot reflect internal stress gradients; deep hole methods and ring core methods cause significant damage to components and are not suitable for finished part testing; traditional electrolytic peeling methods have obvious defects: continuous electrolysis easily generates local overheating and thermal stress, altering the original stress state of the material; the peeling thickness control accuracy is low, and the surface is prone to pitting, over-corrosion, and unevenness; the lack of a layer-by-layer stress decoupling model leads to distorted test results and poor repeatability. These problems make it difficult for existing technologies to achieve high-precision, undisturbed, and high-resolution residual stress depth profile testing, failing to meet the testing needs of high-end equipment manufacturing. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of thermal disturbance, uneven peeling, low depth resolution, and insufficient testing accuracy in the existing technology, and to provide a method for testing the residual stress depth distribution based on isothermal pulse electrolytic peeling. Through low-temperature isothermal constraint, pulse micro-peeling, layer-by-layer strain acquisition and recursive correction inversion, continuous, quasi-non-destructive, and high-precision testing of residual stress from the surface to the subsurface of metal components can be achieved.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping, comprising the following steps:

[0006] (1) Sample pretreatment: The area to be tested is mechanically ground and polished step by step to remove oxide scale, rust and processing altered layer, and ensure that the surface roughness Ra≤0.1μm; ultrasonic cleaning with anhydrous ethanol for 5~10min, blow dry and then paste triaxial strain rosette, use special strain adhesive to cure at room temperature for more than 2h to complete the reference strain calibration.

[0007] (2) Thermostatic electrolysis system setup: The sample is loaded into a circulating water-cooled electrolysis fixture. The electrolyte is a 10% perchloric acid-ethanol solution. The electrolyte temperature is stably controlled at 0~5℃ through the refrigeration system, with temperature fluctuation ≤±0.5℃, to avoid thermal stress during the electrolysis process.

[0008] (3) Pulse electrolytic micro-peeling: Pulse DC power supply is used for layer-by-layer peeling, the electrolysis voltage is controlled at 10 / 16V, the pulse duty cycle is 10% / 30%, and the single-step peeling thickness is 0.01~0.05mm; after each layer is peeled, the power is immediately cut off, and the product is quickly rinsed with flowing deionized water, then dehydrated with anhydrous ethanol, and dried with clean cold air.

[0009] (4) Layer-by-layer strain acquisition: After each layer of erosion is completed, the strain release value at the current depth is acquired, and three sets of strain data are recorded to ensure that the signal is stable and drift-free;

[0010] (5) Gradient stress inversion calculation: Based on the multilayer strain release and peeling thickness sequence, the layer-by-layer recursive correction algorithm is used to eliminate interlayer interference and invert the principal stress, shear stress and equivalent stress distribution curves along the depth direction.

[0011] Furthermore, residual stress depth distribution tests were conducted on Q690 high-strength steel welded components with a thickness of 25 mm: the heat-affected zone 10 mm away from the center of the weld was selected as the test area.

[0012] Furthermore, the sample was successively ground using 240 grit, 400 grit, 600 grit, 800 grit, 1000 grit, and 2000 grit wet sandpaper under running water cooling conditions. Each time the sandpaper was changed, the sample was rotated 90° to ensure that the previous scratch was completely eliminated.

[0013] Furthermore, after grinding, mechanical polishing is performed using 5.0 μm diamond polishing agent to achieve a mirror finish with a surface roughness Ra≤0.1μm.

[0014] Furthermore, the sample was ultrasonically cleaned in anhydrous ethanol for 8 minutes, and then dried with clean nitrogen gas.

[0015] Furthermore, a triaxial strain rosette was attached to the center of the sample to be tested using a high-temperature curing strain-specific adhesive, cured at a constant temperature of 25℃ for 2.5 hours to ensure a firm, bubble-free, and slip-free bond. The sample was then placed in a dedicated electrolysis fixture equipped with a circulating water cooling system. The electrolyte was a 10% perchloric acid-ethanol solution (by volume). The cooling system was activated to stabilize the electrolyte temperature at 0℃, with temperature fluctuations controlled within ±0.5℃. The pulse electrolysis parameters were set as follows: electrolysis voltage 14 V, pulse duty cycle 20%, and single-step peeling thickness 0.03 mm. The electrolyte was continuously stirred during the peeling process to ensure uniform concentration and temperature. Immediately after each peeling layer was completed, the power was cut off, and the sample was quickly transferred to flowing deionized water for 30 seconds, then immersed in anhydrous ethanol for 15 seconds, and finally thoroughly dried with clean, cold air.

[0016] Furthermore, the sample was fitted with a stress acquisition system to collect three sets of strain data at that depth, and the average value was taken as the effective strain release value of that layer. The erosion-cleaning-drying-acquisition process was repeated, completing 20 layers of erosion with a total depth of 0.6 mm. After testing, based on the layer-by-layer strain data and the layer thickness sequence, a self-developed layer-by-layer recursive correction model was used for calculation to eliminate the interference of previous layer erosion on subsequent stress release, ultimately obtaining the principal stress and equivalent stress distribution curves along the depth direction.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] 1) Low-temperature isothermal constraint completely eliminates the electrolytic heat effect and maintains the original stress state unchanged; 2) Pulse electrolysis achieves uniform micro-etching, with no pitting, over-corrosion, or additional deformation on the surface; 3) Micron-level step-by-step peeling with high depth resolution enables continuous profile characterization; 4) Recursive correction inversion significantly improves test accuracy with an error ≤3%; 5) The entire process is quasi-non-destructive, without damaging the overall structure of the component, and is suitable for finished part inspection. Detailed Implementation

[0019] Example 1

[0020] This embodiment focuses on the residual stress depth distribution test of a 25 mm thick Q690 high-strength steel welded component:

[0021] First, the heat-affected zone 10 mm from the center of the weld was selected as the test area. Unidirectional, progressive grinding was performed using 240 grit, 400 grit, 600 grit, 800 grit, 1000 grit, and 2000 grit wet sandpaper under running water cooling. Each time a grade of sandpaper was changed, the sample was rotated 90° to ensure complete removal of the previous scratch. After grinding, mechanical polishing was performed using 5.0 μm diamond polishing compound to achieve a mirror finish with a surface roughness Ra ≤ 0.1 μm.

[0022] The sample was ultrasonically cleaned in anhydrous ethanol for 8 minutes, then removed and dried with clean nitrogen. A triaxial strain rosette was then attached to the center of the test area using a high-temperature curing strain-specific adhesive and cured at a constant temperature of 25°C for 2.5 hours to ensure a firm, bubble-free, and slip-free bond.

[0023] The sample was placed in a special electrolysis fixture equipped with a circulating water cooling system. The electrolyte was a 10% perchloric acid-ethanol solution. The cooling device was turned on to stabilize the electrolyte temperature at 0℃, with temperature fluctuations controlled within ±0.5℃. The pulse electrolysis parameters were set as follows: electrolysis voltage 14 V, pulse duty cycle 20%, and single-step peeling thickness 0.03 mm.

[0024] During the ablation process, the electrolyte was continuously stirred to ensure uniform concentration and temperature. The power was immediately cut off after each layer of ablation was completed, and the sample was quickly transferred to flowing deionized water for 30 seconds, then immersed in anhydrous ethanol for 15 seconds, and finally thoroughly dried with clean cold air.

[0025] The sample was fitted with a stress-reflection acquisition system, and three sets of strain data were collected at that depth. The average value was taken as the effective strain release value of that layer. The etching-cleaning-drying-acquisition steps were repeated, and a total of 20 layers were etched, with a total depth of 0.6 mm.

[0026] After the test was completed, a self-developed layer-by-layer recursive correction model was used to calculate based on the layer-by-layer strain data and the peeling thickness sequence to eliminate the interference of the previous layer erosion on the subsequent stress release, and finally obtain the principal stress and equivalent stress distribution curves along the depth direction.

[0027] Comparative verification shows that the test results of this embodiment deviate from the standard cutting and release method by less than 3%. The sample surface is uniform and bright, without pitting, over-corrosion, or thermal damage, and can truly reflect the residual stress gradient characteristics inside the component. It is suitable for high-precision residual stress depth profile detection of large welded components.

[0028] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for testing the residual stress depth distribution based on isothermal pulsed electrolytic stripping, characterized in that, Includes the following steps: (1) Sample pretreatment: The area to be tested is mechanically ground and polished step by step to remove oxide scale, rust and processing altered layer, and ensure that the surface roughness Ra≤0.1μm; ultrasonic cleaning with anhydrous ethanol for 5~10min, blow dry and then paste triaxial strain rosette, use special strain adhesive to cure at room temperature for more than 2h to complete the reference strain calibration. (2) Thermostatic electrolysis system setup: The sample is loaded into a circulating water-cooled electrolysis fixture. The electrolyte is a 10% perchloric acid-ethanol solution. The electrolyte temperature is stably controlled at 0~5℃ through the refrigeration system, with temperature fluctuation ≤±0.5℃, to avoid thermal stress during the electrolysis process. (3) Pulse electrolytic micro-peeling: Pulse DC power supply is used for layer-by-layer peeling, the electrolysis voltage is controlled at 10 / 16V, the pulse duty cycle is 10% / 30%, and the single-step peeling thickness is 0.01~0.05mm; after each layer is peeled, the power is immediately cut off, and the product is quickly rinsed with flowing deionized water, then dehydrated with anhydrous ethanol, and dried with clean cold air. (4) Layer-by-layer strain acquisition: After each layer of erosion is completed, the strain release value at the current depth is acquired, and three sets of strain data are recorded to ensure that the signal is stable and drift-free; (5) Gradient stress inversion calculation: Based on the multilayer strain release and peeling thickness sequence, the layer-by-layer recursive correction algorithm is used to eliminate interlayer interference and invert the principal stress, shear stress and equivalent stress distribution curves along the depth direction.

2. The method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer according to claim 1, characterized in that, The residual stress depth distribution of Q690 high-strength steel welded components with a thickness of 25 mm was tested: the heat-affected zone 10 mm away from the center of the weld was selected as the test area.

3. The method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer according to claim 2, characterized in that, Use 240 grit, 400 grit, 600 grit, 800 grit, 1000 grit and 2000 grit wet sandpaper in sequence under running water cooling conditions to perform unidirectional progressive grinding. Rotate the sample 90° each time you change the grit of sandpaper to ensure that the previous scratch is completely eliminated.

4. The method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer according to claim 3, characterized in that, After grinding, mechanical polishing is performed using 5.0 μm diamond polishing agent to achieve a mirror finish with a surface roughness Ra≤0.1μm.

5. The method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer according to claim 4, characterized in that, The sample was ultrasonically cleaned in anhydrous ethanol for 8 minutes, and then dried with clean nitrogen gas.

6. The method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer according to claim 5, characterized in that, A triaxial strain rosette was attached to the center of the sample to be tested using a high-temperature curing strain-specific adhesive, cured at a constant temperature of 25℃ for 2.5 hours to ensure a firm, bubble-free, and slip-free bond. The sample was placed in a dedicated electrolysis fixture with a circulating water cooling system. The electrolyte was a 10% (v / v) perchloric acid-ethanol solution. The cooling system was activated to stabilize the electrolyte temperature at 0℃, with temperature fluctuations controlled within ±0.5℃. The pulse electrolysis parameters were set as follows: electrolysis voltage 14 V, pulse duty cycle 20%, and single-step peeling thickness 0.03 mm. The electrolyte was continuously stirred during the peeling process to ensure uniform concentration and temperature. The power was immediately cut off after each layer of peeling was completed, and the sample was quickly transferred to flowing deionized water for 30 s rinsing, followed by immersion in anhydrous ethanol for 15 s rinsing, and then thoroughly dried with clean, cold air.

7. The method for testing the residual stress depth distribution based on isothermal pulse electrolytic stripping layer according to claim 6, characterized in that, The sample was fitted with a stress acquisition system, and three sets of strain data were collected at that depth. The average value was taken as the effective strain release value of that layer. The ablation-cleaning-drying-acquisition steps were repeated, completing a total of 20 layers of ablation, reaching a total depth of 0.6 mm. After the test, based on the layer-by-layer strain data and the layer thickness sequence, a self-developed layer-by-layer recursive correction model was used for calculation to eliminate the interference of previous layer ablation on subsequent stress release, and finally the principal stress and equivalent stress distribution curves along the depth direction were obtained.