Method for detecting residual stress of steel rail
By employing steps such as pickling, grinding, bonding strain gauges, and cutting, combined with ethanol solution and adhesive, the problem of cumbersome procedures and low accuracy in existing technologies for detecting residual stress in rails has been solved, achieving a simple and efficient detection result.
Patent Information
- Application Number
- CN202511114541.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-11
- Publication Date
- 2025-11-14
AI Technical Summary
Existing technologies for detecting residual stress in rails involve cumbersome procedures and low accuracy, making it difficult to effectively control the service life and safety of rails.
The process involves pickling, grinding, bonding strain gauges, zeroing, cutting, and testing. By combining the use of ethanol solution and adhesive, the influence of the oxide layer is reduced, ensuring accurate bonding of strain gauges and reading of residual stress.
It simplifies the operation steps, improves the accuracy and stability of the test, reduces the interference of the oxide layer on the test, and improves the efficiency and accuracy of the test.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of metal material testing technology, and in particular to a method for detecting residual stress in steel rails. Background Technology
[0002] Due to factors such as manufacturing processes, loads, and temperature variations, steel rails develop residual stresses of varying degrees. These residual stresses significantly impact the service life and safety of the rails. For example, persistent high levels of residual stress can lead to deformation or damage, and prolonged exposure to residual stress also drastically shortens the rail's lifespan. Therefore, high residual stress undoubtedly increases the cost of rail maintenance and replacement. To reduce costs and extend the service life of rails, it is essential to control residual stress.
[0003] Existing technologies use a cutting and releasing method for detection, which is cumbersome and has low accuracy. Summary of the Invention
[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for detecting residual stress in rails, which has simpler operation steps and higher accuracy.
[0005] This invention provides a method for detecting residual stress in steel rails, comprising the following steps:
[0006] A) Pickling: Pickling the test area of the rail sample to be tested;
[0007] B) Grinding: Grind the acid-washed test area until it is smooth;
[0008] C) Attaching strain gauges: Clean the area to be tested after step B) with ethanol solution, remove the ethanol solution, and attach the strain gauges to the test points on the area to be tested.
[0009] D) Zeroing: Connect the strain gauge to the terminals of the strain gauge to zero the stress and strain on the strain gauge, and then disconnect the terminals of the strain gauge and the strain gauge.
[0010] E) Cutting: Using the test point of the part to be tested as the center, cut the rail sample to be tested;
[0011] F) Test: Connect the strain gauge to the original strain gauge terminals on the cut specimen and read the final residual stress of the rail.
[0012] Preferably, in step A), the pickling includes:
[0013] The test area of the rail sample is immersed in the pickling solution.
[0014] The soaking time is 6 to 8 minutes;
[0015] The pickling solution used is a hot hydrochloric acid solution; the temperature of the hot hydrochloric acid solution is 70-80℃.
[0016] Preferably, after soaking, the method further includes: cleaning the area to be tested with a brush; the cleaning solution used is soap solution or laundry detergent solution;
[0017] During the cleaning process, the area to be tested is rinsed with boiling water at 85°C or higher every 5 to 10 seconds.
[0018] After the cleaning is completed, rinse the area to be tested with cold water, then rinse the area to be tested with boiling water above 85°C, and finally dry the area to be tested.
[0019] Preferably, in step B), the grinding process sequentially includes coarse grinding and fine grinding; or the grinding process is fine grinding.
[0020] The coarse grinding uses a 120-mesh grinding wheel; the fine grinding uses a 180-mesh grinding wheel.
[0021] The coarse grinding time is 1 to 4 minutes;
[0022] The fine grinding time is 2 to 6 minutes.
[0023] Preferably, in step C), the mass concentration of the ethanol solution is above 92%;
[0024] The method for removing ethanol solution is as follows:
[0025] After wiping the area to be tested clean from the center outwards, blow the ethanol solution dry from the center outwards.
[0026] Preferably, in step C), the adhesive used for pasting comprises, by weight, the following components:
[0027]
[0028] Preferably, in step C), the test point on which the strain gauge is attached to the part to be tested includes:
[0029] After stirring the adhesive evenly, apply it to the bottom of the strain gauge and then stick it to the test point on the part to be measured. After sticking, press the strain gauge repeatedly with polyethylene paper until all air bubbles are removed. Then, use a two-stage heating air blower to cure the adhesive.
[0030] Preferably, the thickness of the adhesive coating is ≥0.5mm.
[0031] Preferably, the two-stage heating air blowing includes: maintaining an initial air temperature of 25-35°C for 110-130 seconds, and then adjusting the air temperature to 45-55°C and maintaining it for 50-70 seconds.
[0032] Preferably, in step C), after the pasting, the process further includes: applying silicone rubber to the strain gauge and its surrounding area so that the silicone rubber covers the strain gauge and its terminals;
[0033] The thickness of the coating is ≥1mm.
[0034] This invention provides a method for detecting residual stress in rails, comprising the following steps: A) Acid pickling: pickling the test area of the rail sample; B) Grinding: grinding the acid-washed test area until smooth; C) Applying strain gauges: cleaning the test area treated in step B) with ethanol solution, removing the ethanol solution, and then applying strain gauges to the test point on the test area; D) Zeroing: connecting the strain gauge to the terminals of the strain gauge, zeroing the stress and strain on the strain gauge, and then disconnecting the terminals of the strain gauge from the strain gauge; E) Cutting: cutting the rail sample with the test point as the center; F) Testing: connecting the strain gauge to the original terminals of the strain gauge on the cut sample, and reading the final residual stress of the rail. The detection method provided by this invention can reduce the influence of the oxide layer on residual stress testing, prevent the redistribution and concentration of residual stress inside the rail, make residual stress testing more accurate, and is simple to operate, showing good application prospects. Attached Figure Description
[0035] Figure 1 This is a schematic diagram of the measured points on the rail. Detailed Implementation
[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0037] This invention provides a method for detecting residual stress in steel rails, comprising the following steps:
[0038] A) Pickling: Pickling the test area of the rail sample to be tested;
[0039] B) Grinding: Grind the acid-washed test area until it is smooth;
[0040] C) Attaching strain gauges: Clean the area to be tested after step B) with ethanol solution, remove the ethanol solution, and attach the strain gauges to the test points on the area to be tested.
[0041] D) Zeroing: Connect the strain gauge to the terminals of the strain gauge to zero the stress and strain on the strain gauge, and then disconnect the terminals of the strain gauge and the strain gauge.
[0042] E) Cutting: Using the test point of the part to be tested as the center, cut the rail sample to be tested;
[0043] F) Test: Connect the strain gauge to the original strain gauge terminals on the cut specimen and read the final residual stress of the rail.
[0044] Regarding step A):
[0045] Pickling: The test area of the rail sample is pickled.
[0046] Specifically, the test area of the rail sample is immersed in an acid pickling solution. The immersion time is 6-8 minutes, for example, 7 minutes.
[0047] In some embodiments of the present invention, the pickling solution is a hydrochloric acid solution with a mass concentration of 38%. Further, the pickling solution used is a hot hydrochloric acid solution. The temperature of the hot hydrochloric acid solution is 70–80°C, preferably 75°C. The pickling is used to remove the oxide layer from the tested portion of the rail sample.
[0048] In some embodiments of the present invention, after the soaking is completed, the method further includes: cleaning the test area with a brush; the cleaning solution used is soap solution or laundry detergent solution with a mass concentration of 15% or higher, such as 30%. During the cleaning process, the test area is rinsed with boiling water at 85°C or higher (such as 90°C) every 5-10 seconds (such as 8 seconds); after cleaning, the test area is rinsed with cold water, then rinsed with boiling water at 85°C or higher (such as 90°C), and finally dried.
[0049] Regarding step B):
[0050] Grinding: Grind the acid-washed test area until it is smooth.
[0051] The grinding process includes coarse grinding and fine grinding in sequence; or the grinding process is fine grinding. That is, if the area to be tested is relatively flat or meets the conditions for direct fine grinding, the coarse grinding process can be skipped and fine grinding can be performed directly.
[0052] In some embodiments of the present invention, the coarse grinding uses a 120-mesh grinding wheel; the fine grinding uses a 180-mesh grinding wheel. The coarse grinding time is 1–4 minutes. The coarse grinding smooths the test area, giving it a metallic luster. Because the oxide layer on the test surface is removed after acid pickling, the sides appear dark gray, necessitating coarse grinding. Furthermore, removing the oxide layer facilitates observation of the base material; for example, less grinding is needed in concave areas, and more grinding is needed in convex areas. In other words, acid pickling not only improves measurement accuracy but also facilitates grinding. The fine grinding time is 2–6 minutes, for example, 4 minutes. The fine grinding removes larger scratches and other defects based on the coarse grinding, smoothing the test area to a level surface without any visible scratches.
[0053] In some embodiments of the present invention, the grinding of the rail section to be tested should meet the testing requirements. After grinding, the width of the rail section to be tested should be at least twice the sawing thickness (for example, twice the sawing thickness), where the sawing thickness is the thickness after cutting in step E).
[0054] Regarding step C):
[0055] Applying strain gauges: Clean the area to be measured after step B) with ethanol solution, remove the ethanol solution, and then apply the strain gauges to the measurement points on the area to be measured.
[0056] In some embodiments of the present invention, the mass concentration of the ethanol solution is above 92%, for example 99.7%.
[0057] In some embodiments of the present invention, the method for removing the ethanol solution is as follows:
[0058] After wiping the area to be tested clean from the center outwards, blow the ethanol solution dry from the center outwards. A hairdryer can be used to dry it.
[0059] In some embodiments of the present invention, the adhesive used for bonding comprises, by weight, the following components:
[0060]
[0061] The preferred silane coupling agent is KH550.
[0062] The polyurethane prepolymer in this invention is an adhesive. This invention does not impose any special restrictions on the type and source of the polyurethane prepolymer, and it can be commercially available.
[0063] In some embodiments of the present invention, the adhesive used for bonding comprises, by weight, 45 parts of bisphenol A epoxy resin, 17 parts of polyurethane prepolymer, 4 parts of silane coupling agent, 68 parts of fumed silica, and 0.7 parts of benzoyl peroxide.
[0064] In some embodiments of the present invention, the test point on which the strain gauge is attached to the part to be measured includes:
[0065] After stirring the adhesive evenly, apply it to the bottom of the strain gauge and then stick it to the test point on the part to be measured. After sticking, press the strain gauge repeatedly with polyethylene paper until all air bubbles are removed. Then, use a two-stage heating air blower to cure the adhesive.
[0066] The adhesive coating is applied to a thickness of ≥0.5mm, for example, 1mm.
[0067] The two-stage heating and blowing process includes: maintaining an initial air temperature of 25–35°C for 110–130 seconds, and then adjusting the air temperature to 45–55°C and maintaining it for 50–70 seconds. Specifically, maintaining an initial air temperature of 30°C for 120 seconds, and then adjusting the air temperature to 50°C and maintaining it for 60 seconds, to ensure rapid curing of the adhesive.
[0068] In some embodiments of the present invention, if there are multiple test points, multiple strain gauges are used for bonding, and the strain gauges are oriented in the same direction when bonding.
[0069] In some embodiments of the present invention, after the bonding process, the method further includes: protecting the strain gauge. Specifically, silicone rubber is applied to the strain gauge and its surrounding area, covering the strain gauge and its terminals. This prevents the influence of emulsions, water, etc., on the contact surface between the strain gauge and the rail. The silicone rubber is room temperature vulcanizing silicone rubber, specifically 704 silicone rubber.
[0070] The thickness of the coating is ≥1mm, for example, 1mm.
[0071] Regarding step D):
[0072] Zeroing: Connect the strain gauge to the terminals of the strain gauge to clear the stress and strain on the strain gauge to zero, and then disconnect the terminals of the strain gauge and the strain gauge.
[0073] Regarding step E):
[0074] Cutting: The rail sample to be tested is cut with the test point as the center.
[0075] In some embodiments of the present invention, the rail sample to be tested is cut into a sample block with a thickness of 20 mm as specified in the standard; the standard may be GB / T2585-2016.
[0076] Regarding step F):
[0077] Test: Connect the strain gauge to the original strain gauge terminals on the cut specimen and read the final residual stress of the rail.
[0078] Beneficial effects:
[0079] This invention can reduce interference from other factors on the residual stress test of rails, such as oxide scale, making the test more accurate and improving the test efficiency. It has a wide range of applications.
[0080] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.
[0081] To further illustrate the present invention, the following detailed description of a method for detecting residual stress in rails provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.
[0082] Example 1
[0083] The longitudinal residual stress test was performed on the bottom of a 1.02m long U71Mn 60N steel rail. The steps are as follows:
[0084] 1) Pickling: Prepare a hydrochloric acid solution using 38wt% hydrochloric acid and 62wt% water. Heat the hydrochloric acid solution to 75°C. Immerse the area to be tested (60mm from the center of the rail) in the 75°C hydrochloric acid solution for 7 minutes. After immersion, clean the area with a brush using a 30% (w / w) laundry detergent solution. During cleaning, rinse the area with 90°C boiling water every 8 seconds. After cleaning, rinse the area with cold water, then rinse with 90°C boiling water again. Finally, dry the area.
[0085] 2) Grinding: After pickling, the test area was observed to be relatively flat after removing the oxide layer, meeting the conditions for direct fine grinding. Therefore, a 180-grit grinding wheel was used for 4 minutes to grind the test area until it was smooth and level, with no visible scratches. After grinding, the width of the test area of the rail was twice the sawing thickness, which was the thickness after cutting in step 5).
[0086] 3) Applying the strain gauge: Clean the area to be measured after step 2) with an ethanol solution (99.7% mass concentration), wiping it clean from the center outwards. Then, use a hairdryer to dry the ethanol solution from the center outwards. Mark the measurement points, such as... Figure 1 As shown. Figure 1 This is a schematic diagram of the test points on the rail. 1, 2, and 3 are test point numbers, 2 is the center point of the rail base, the distance between 1 and 2 is 15mm, and the distance between 2 and 3 is 15mm.
[0087] The adhesive is prepared in the following proportions by weight: 45 parts bisphenol A epoxy resin, 17 parts polyurethane prepolymer, 4 parts silane coupling agent KH550, 68 parts fumed silica, and 0.7 parts benzoyl peroxide.
[0088] After thoroughly mixing the adhesive, apply it to the bottom of the strain gauge to a thickness of 1 mm. Attach the strain gauge to the measurement point. After attachment, press the strain gauge repeatedly with polyethylene paper to completely remove air bubbles. Then, use a two-stage heating airflow (initial air temperature 30℃, maintained for 120 seconds, then adjusted to 50℃ and maintained for 60 seconds) to rapidly cure the adhesive. Ensure the strain gauges are oriented evenly during attachment. After completion, apply 704 silicone sealant to the strain gauge and its surrounding area, ensuring the silicone sealant covers the strain gauge and its terminals to a thickness of 1 mm.
[0089] 4) Zeroing: Connect the strain gauge to the terminals of the strain meter and strain gauge, clear the stress and strain on the strain gauge to zero, and then disconnect the terminals of the strain gauge and strain gauge.
[0090] 5) Cutting: Using the test point of the part to be tested as the center, cut the sample into a 20mm thick sample block as specified in the standard.
[0091] 6) Testing: Connect the strain gauge to the original strain gauge terminals on the cut specimen and read the final residual stress of the rail, as shown in Table 1.
[0092] Table 1. Final Residual Stress Test Results of the Rails
[0093] Test point number Residual stress / MPa 1 136 2 134 3 131
[0094] Comparative Example 1
[0095] The longitudinal residual stress test was also performed on the bottom of a 1.02m long U71Mn 60N steel rail using the conventional method. The sample was taken from an adjacent location on the same rail as the sample in the example. The steps are as follows:
[0096] 1) Grinding: Use 90-grit and 110-grit grinding wheels to grind the test area of the sample to be tested until it is smooth and flat (resulting in more scratches).
[0097] 2) Cleaning: Clean the test area treated in step 1) with an ethanol solution (99.7% mass concentration), wiping it clean from the center outwards. Then use a hairdryer to dry the ethanol solution from the center outwards. Mark the test points, such as... Figure 1 As shown. Figure 1 This is a schematic diagram of the test points on the rail. 1, 2, and 3 are test point numbers, 2 is the center point of the rail base, the distance between 1 and 2 is 15mm, and the distance between 2 and 3 is 15mm.
[0098] 3) Attaching the strain gauge: Use 502 glue to attach the strain gauge to the measurement point, pressing continuously to ensure there are no air bubbles or other defects between the strain gauge and the rail. (This process is time-consuming and inefficient.)
[0099] 4) After completion, apply 704 silicone to the strain gauge and its surroundings, so that the 704 silicone covers the strain gauge and its terminals, with a coating thickness of 1mm.
[0100] 5) Zeroing: Connect the other end of the connection terminal of the strain gauge to the strain meter to zero the stress and strain on the strain gauge, and then disconnect the connection terminal of the strain gauge and strain meter.
[0101] 6) Cutting: Using the test point of the part to be tested as the center, cut the sample into a 20mm thick sample block as specified in the standard.
[0102] 7) Test: Connect the strain gauge to the original strain gauge terminals on the cut specimen and read the final residual stress of the rail, as shown in Table 2.
[0103] Table 2. Final Residual Stress Test Results of the Rails
[0104] Test point number Residual stress / MPa 1 146 2 167 3 132
[0105] Comparing Embodiment 1 and Comparative Example 1, it can be seen that the detection method provided by the present invention has simpler operation steps, more stable testing, smaller stress difference at different test points, and higher accuracy.
[0106] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for detecting residual stress in steel rails, comprising the following steps: A) Pickling: Pickling the test area of the rail sample to be tested; B) Grinding: Grind the acid-washed test area until it is smooth; C) Attaching strain gauges: Clean the area to be tested after step B) with ethanol solution, remove the ethanol solution, and attach the strain gauges to the test points on the area to be tested. D) Zeroing: Connect the strain gauge to the terminals of the strain gauge to zero the stress and strain on the strain gauge, and then disconnect the terminals of the strain gauge and the strain gauge. E) Cutting: Using the test point of the part to be tested as the center, cut the rail sample to be tested; F) Test: Connect the strain gauge to the original strain gauge terminals on the cut specimen and read the final residual stress of the rail.
2. The detection method according to claim 1, characterized in that, In step A), the pickling includes: The test area of the rail sample is immersed in the pickling solution. The soaking time is 6 to 8 minutes; The pickling solution used is a hot hydrochloric acid solution; the temperature of the hot hydrochloric acid solution is 70-80℃.
3. The detection method according to claim 2, characterized in that, After the soaking is completed, the process further includes: cleaning the area to be tested with a brush; the cleaning solution used is soap solution or laundry detergent solution; During the cleaning process, the area to be tested is rinsed with boiling water at 85°C or higher every 5 to 10 seconds. After the cleaning is completed, rinse the area to be tested with cold water, then rinse the area to be tested with boiling water above 85°C, and finally dry the area to be tested.
4. The detection method according to claim 1, characterized in that, In step B), the grinding process sequentially includes coarse grinding and fine grinding; or the grinding process is fine grinding. The coarse grinding uses a 120-mesh grinding wheel; the fine grinding uses a 180-mesh grinding wheel. The coarse grinding time is 1 to 4 minutes; The fine grinding time is 2 to 6 minutes.
5. The detection method according to claim 1, characterized in that, In step C), the mass concentration of the ethanol solution is above 92%; The method for removing ethanol solution is as follows: After wiping the area to be tested clean from the center outwards, blow the ethanol solution dry from the center outwards.
6. The detection method according to claim 1, characterized in that, In step C), the adhesive used for pasting comprises, by weight, the following components:
7. The detection method according to claim 1, characterized in that, In step C), the test points where the strain gauges are attached to the area to be measured include: After stirring the adhesive evenly, apply it to the bottom of the strain gauge and then stick it to the test point on the part to be measured. After sticking, press the strain gauge repeatedly with polyethylene paper until all air bubbles are removed. Then, use a two-stage heating air blower to cure the adhesive.
8. The detection method according to claim 7, characterized in that, The adhesive coating is applied to a thickness of ≥0.5mm.
9. The detection method according to claim 7, characterized in that, The two-stage heating and blowing process includes: maintaining an initial air temperature of 25-35℃ for 110-130 seconds, and then adjusting the air temperature to 45-55℃ and maintaining it for 50-70 seconds.
10. The detection method according to claim 1, characterized in that, In step C), after the pasting, the process further includes: applying silicone rubber to the strain gauge and its surrounding area so that the silicone rubber covers the strain gauge and its terminals. The thickness of the coating is ≥1mm.