Testing method for measuring longitudinal residual stress of deformed steel bar with diameter greater than 15mm
Through plane grinding and resistive strain gauge combined with wire cutting technology, the high accuracy and low cost problems of longitudinal residual stress detection of large-diameter rebar are solved, and simple and fast break warning is achieved.
Patent Information
- Application Number
- CN202510666948.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-22
- Publication Date
- 2025-07-18
AI Technical Summary
The prior art is difficult to detect the longitudinal residual stress of large diameter 30MnSi rebar with high accuracy and non-destructiveness, resulting in risk of fracture. The existing methods are complex, costly or have great impact on the surface morphology.
The plane grinding process, resistance strain gauge pasting and wire cutting technology are adopted, combined with the AFT-CM-10 strain meter, stress is released through local grinding and cutting, and the strain change value Δε is measured to achieve high-precision detection.
It realizes low-cost, simple and high-precision longitudinal residual stress detection, which can effectively warning of fracture risk, short single test time and accuracy up to ±5MPa.
Smart Images
Figure CN120333682A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of residual stress detection of metal materials, and particularly relates to a test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm. Background Art
[0002] 30MnSi deformed steel bars are widely used in engineering fields such as construction and bridges due to their high strength, good ductility and weldability. However, 30MnSi deformed steel bars with a larger diameter (>15 mm) are prone to generate uneven longitudinal residual stress during rolling or cooling, resulting in unexpected fractures during static storage or transportation, causing safety hazards and economic losses. Existing residual stress detection methods (such as X-ray diffraction method, drilling method, ultrasonic method) have the following limitations:
[0003] 1. The X-ray method requires complex equipment and is sensitive to surface roughness, and is not suitable for the ribbed surface of deformed steel bars.
[0004] 2. The drilling method damages the material and has complex operations, and it is difficult to be used for batch detection.
[0005] 3. The ultrasonic method is sensitive to the microstructure of the material, and the accuracy is greatly affected by the surface morphology of the deformed steel bar.
[0006] Therefore, there is an urgent need for a non-destructive, high-precision and easy-to-operate-on-site residual stress test method for deformed steel bars. Summary of the Invention
[0007] Aiming at the fracture problem caused by longitudinal residual stress in 30MnSi deformed steel bars, the purpose of the present invention is to provide a test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm. By optimizing the sample treatment, grinding process and test process, high-precision and low-cost detection of longitudinal residual stress is achieved.
[0008] To solve the above technical problems, the present invention adopts the following technical solutions:
[0009] A test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to the present invention includes the following steps:
[0010] 1). Sample preparation:
[0011] Cut a deformed steel bar specimen with a length of 50±0.5 mm, and use a grinding wheel to cut off the heat-affected zone at both ends; grind a plane with a width ≥10 mm along the longitudinal rib axis in the middle of the specimen. When grinding, grind along the transverse direction, and the grinding depth does not exceed 1 / 3 of the thread height to avoid damaging the internal stress distribution;
[0012] 2). Strain gauge pasting:
[0013] Select a resistance strain gauge with a gauge length of 3 mm, paste it along the longitudinal center line of the polished plane, evenly coat the covered area with epoxy resin glue and cure it under pressure;
[0014] 3). Stress release and measurement:
[0015] Use a wire cutting machine to cut two parallel grooves symmetric with respect to the strain gauge. The distance between the two cutting lines is 16 - 20 mm, and the cutting depth of the two cutting lines is 1 / 2 of the specimen diameter to release the longitudinal residual stress;
[0016] Use an AFT-CM-10 static resistance strain gauge to record the strain change value Δε before and after cutting.
[0017] Furthermore, take 30MnSi threaded steel, cut it into 50 mm specimens, and cut off 5 mm heat-affected zones at both ends.
[0018] Furthermore, use a belt sander to grind a 12 mm wide plane in the middle of the specimen, with a grinding depth of 0.5 mm and an original thread height of 1.5 mm.
[0019] Furthermore, after cleaning the surface, paste a KFG-3-120-C1-11 type strain gauge and cure it under pressure for 24 hours.
[0020] Furthermore, symmetrically cut release grooves with a depth of 8 mm and a width of 0.2 mm on both sides of the polished plane.
[0021] Furthermore, this method has low cost and is easy to operate, and the single test time ≤ 2 hours.
[0022] Furthermore, the accuracy of this method reaches ±5 MPa, and it can effectively warn of the fracture risk.
[0023] Compared with the prior art, the beneficial technical effects of the present invention:
[0024] Adopt a plane grinding process: make requirements for the grinding direction and depth, form a flat surface through local grinding, solve the problem of strain gauge fitting caused by the ribbed structure of threaded steel, and at the same time limit the grinding depth to retain the original residual stress distribution.
[0025] Short specimen, cutting line width and depth design: Select a 50 mm long specimen, combine the cutting width and depth, and take into account both the sufficiency of stress release and the operation convenience.
[0026] AFT-CM-10 strain gauge adaptation: Combine with a high-sensitivity strain gauge to achieve micro-strain level (με) precision measurement.
[0027] 1. This method has low cost and is easy to operate, and the single test time ≤ 2 hours.
[0028] 2. The accuracy of this method reaches ±5 MPa, and it can effectively warn of the fracture risk. Brief Description of the Drawings
[0029] The present invention will be further described below in conjunction with the drawings.
[0030] Figure 1 : Schematic diagram of the polished plane of the specimen (indicating the plane position and dimensions).
[0031] Figure 2 : Diagram of the wire cutting groove position and strain gauge arrangement. Detailed Implementation Manner
[0032] A test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm includes the following steps:
[0033] 1. Sample preparation:
[0034] Cut a 30MnSi deformed steel bar specimen with a length of 50 ± 0.5 mm, and cut off the heat affected zone at both ends using a grinding wheel; grind a plane with a width ≥ 10 mm along the longitudinal rib axis in the middle of the specimen (see Figure 1 ), and grind transversely, with the grinding depth not exceeding 1 / 3 of the thread height to avoid damaging the internal stress distribution.
[0035] 2. Strain gauge pasting:
[0036] Select a resistance strain gauge with a gauge length of 3 mm, paste it along the longitudinal center line of the polished plane, and evenly coat the covered area with epoxy resin glue and cure it under pressure.
[0037] 3. Stress release and measurement:
[0038] Use a wire cutting machine to cut two parallel grooves symmetric about the strain gauge in the Figure 2 direction, with a distance of 18 mm between the two cutting lines and a cutting depth of 1 / 2 of the specimen diameter for the two cutting lines to release the longitudinal residual stress (see Figure 2 ).
[0039] Use an AFT-CM-10 static resistance strain gauge to record the strain change value Δε before and after cutting.
[0040] Example 1
[0041] 1. Take a 30MnSi deformed steel bar with a diameter of 16 mm, cut it into a 50 mm specimen, and cut off 5 mm of the heat affected zone at both ends.
[0042] 2. Use a sanding machine to grind a 12 mm wide plane in the middle of the specimen, with a grinding depth of 0.5 mm (the original thread height is 1.5 mm).
[0043] 3. After cleaning the surface, paste a KFG-3-120-C1-11 type strain gauge and cure it under pressure for 24 hours.
[0044] 4. Symmetrically cut release grooves with a depth of 8 mm and a width of 0.2 mm on both sides of the polished plane.
[0045] 5. Read Δε = 85 με through an AFT-CM-10 strain gauge, and calculate the residual stress σ = 210×10 3 MPa×85×10 -6 = 17.85 MPa.
[0046] The method of the present invention not only has low cost and simple operation, with a single test time ≤ 2 hours, but also has an accuracy of ±5 MPa, and can effectively warn of the fracture risk.
[0047] The embodiments described above are only used to describe the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.
Claims
1. A test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm, characterized in that, It includes the following steps: 1). Sample preparation: Cut a deformed steel bar specimen with a length of 50 ± 0.5 mm, and use a grinding wheel to remove the heat-affected zone at both ends; grind a plane with a width ≥ 10 mm along the longitudinal rib axis in the middle of the specimen. When grinding, grind along the transverse direction, and the grinding depth does not exceed 1 / 3 of the thread height to avoid damaging the internal stress distribution; 2). Strain gauge pasting: Select a resistance strain gauge with a gauge length of 3 mm and paste it along the longitudinal center line of the ground plane. The covered area is evenly coated with epoxy resin glue and cured under pressure; 3). Stress release and measurement: Use a wire cutting machine to cut two parallel grooves symmetric about the strain gauge. The distance between the two cutting lines is 16 - 20 mm, and the cutting depth of the two cutting lines is 1 / 2 of the specimen diameter to release the longitudinal residual stress; Use an AFT-CM-10 static resistance strain gauge to record the strain change value Δε before and after cutting.
2. The test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to claim 1, wherein Take 30MnSi deformed steel bar, cut it into 50 mm specimens, and cut off 5 mm of the heat-affected zone at both ends.
3. The test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to claim 1, characterized in that, Use a belt grinder to grind a 12 mm wide plane in the middle of the specimen, with a grinding depth of 0.5 mm and an original thread height of 1.5 mm.
4. The test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to claim 1, characterized in that, After cleaning the surface, paste a KFG-3-120-C1-11 type strain gauge and cure it under pressure for 24 hours.
5. The test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to claim 1, characterized in that, Symmetrically cut release grooves with a depth of 8 mm and a width of 0.2 mm on both sides of the ground plane.
6. The test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to claim 1, wherein This method has low cost and simple operation, and the single test time ≤ 2 hours.
7. The test method for measuring the longitudinal residual stress of deformed steel bars with a diameter greater than 15 mm according to claim 1, characterized in that, The accuracy of this method reaches ±5 MPa, and it can effectively warn of the fracture risk.