Linear cutting auxiliary positioning measurement method for longitudinal residual stress under rail head tread of steel rail

Abstract

The invention discloses a linear cutting auxiliary positioning measurement method for longitudinal residual stress under a rail head tread of a steel rail, and belongs to the technical field of material mechanical property testing. Comprising the following steps of sample preparation, measurement point positioning, longitudinal cutting, surface treatment, strain gauge arrangement and stress calculation. According to the linear cutting auxiliary positioning measurement method for the longitudinal residual stress under the rail head tread of the steel rail, stress is released through directional cutting, strain measurement is matched, and accurate measurement of the longitudinal residual stress of any depth under the rail head tread of the steel rail is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material mechanical property testing, and particularly relates to a wire cutting assisted positioning measurement method for longitudinal residual stress under a rail head tread of a steel rail. BACKGROUND

[0002] Residual stress is formed in a steel rail during rolling, heat treatment and use, which directly affects the fatigue life and safety of the steel rail.

[0003] 1. The drilling method damages the integrity of the steel rail and is difficult to measure deep stress;

[0004] 2. The X-ray method is limited to surface measurement and cannot obtain stress distribution under the rail head tread;

[0005] 3. The existing cutting method is mainly for transverse or overall stress, and the longitudinal positioning precision is insufficient.

[0006] There is an urgent need for a method for accurately positioning and measuring longitudinal residual stress in a steel rail. SUMMARY

[0007] The purpose of the present application is to provide a wire cutting assisted positioning measurement method for longitudinal residual stress under a rail head tread of a steel rail, which realizes accurate measurement of longitudinal residual stress at any depth under the rail head tread of the steel rail by directional cutting to release stress and cooperating with strain measurement.

[0008] To solve the above technical problems, the present application adopts the following technical solutions:

[0009] The wire cutting assisted positioning measurement method for longitudinal residual stress under a rail head tread of a steel rail according to the present application comprises the following specific steps:

[0010] 1. Sample preparation: cut a certain length of complete steel rail sample, and fix it on the experimental platform after surface cleaning;

[0011] 2. Measurement point positioning: mark the vertical distance h of the measured point from the rail top along the rail head side surface based on the rail top surface;

[0012] 3. Longitudinal cutting:

[0013] a. Use a wire cutting machine to cut along the longitudinal direction of the steel rail to a depth of h, forming a cutting seam with a width of 3-5 mm;

[0014] b. Continue to cut and expand the gap to expose a smooth longitudinal section;

[0015] 4. Surface treatment: mechanically polish and electrolytically polish the cutting surface;

[0016] 5). Strain gauge layout: single-axis resistance strain gauges are pasted in the center of the cutting surface in the longitudinal direction, and a static strain meter is connected;

[0017] 6). Stress calculation: the longitudinal residual stress is calculated according to σ = E · ΔE by combining the material elastic modulus E with the strain change amount ΔE.

[0018] Further, the length of the sample cut in step 1) is 0.5-1.5m.

[0019] 3. The line cutting auxiliary positioning measurement method for the longitudinal residual stress of the rail head tread of a steel rail according to claim 1, characterized in that the length of the sample cut in step 1) is 1m.

[0020] Further, in step 2), 0<h≤the height of the rail head.

[0021] Further, the mechanical polishing of step 4 uses sandpaper polishing.

[0022] Further, the mesh number of the sandpaper is ≥800#.

[0023] Further, after the surface treatment in step 4), the roughness Ra is ≤0.8μm.

[0024] Compared with the prior art, the beneficial technical effects of the present application are:

[0025] 1. The longitudinal directional cutting precisely exposes the target depth stress field, overcoming the spatial limitations of traditional methods;

[0026] 2. The heat affected zone of the line cutting process is <0.1mm, significantly reducing the interference with the residual stress;

[0027] 3. Combined with the mechanical-electrolytic composite polishing technology, the strain gauge base adhesion is ensured, and the measurement error is <5%. BRIEF DESCRIPTION OF DRAWINGS

[0028] The present application will be further described below in conjunction with the drawings.

[0029] Figure 1 It is a schematic diagram and sectional view of the cutting of a steel rail;

[0030] Figure 2 It is a local enlarged view of the strain gauge layout of the cutting surface;

[0031] Figure 3 It is a local enlarged view of the strain gauge layout of the cutting surface;

[0032] Figure 4 It is a schematic diagram of the cutting of a measurement surface;

[0033] Figure 5 for the post-cutting sample block;

[0034] Figure 6 for the residual stress calculation flowchart. DETAILED DESCRIPTION

[0035] A wire cutting auxiliary positioning measurement method for longitudinal residual stress under the rail head tread of a steel rail, comprising the following steps: sample preparation, measurement point positioning, longitudinal cutting, surface treatment, strain gauge layout, and stress calculation; the specific steps are as follows:

[0036] 1. Sample preparation: cut a complete steel rail sample with a length of 1 m, and fix it on the experimental platform after surface cleaning;

[0037] 2. Measurement point positioning: take the rail top surface as the reference, and mark the vertical distance h (0 < h ≤ rail head height) of the measured point from the rail top along the rail head side;

[0038] 3. Longitudinal cutting:

[0039] a. Use a wire cutting machine to cut along the longitudinal direction (parallel to the rail length direction) of the steel rail to a depth of h, forming a cutting seam with a width of 3-5 mm;

[0040] b. Continue to cut to enlarge the gap to expose a smooth longitudinal section;

[0041] 4. Surface treatment: mechanically polish (sanding paper grit number ≥800#) and electrolytically polish the cutting surface, with a roughness Ra ≤0.8 μm;

[0042] 5. Strain gauge layout: paste a single-axis resistance strain gauge along the longitudinal direction at the center position of the cutting surface, and connect a static strain meter;

[0043] 6. Stress calculation: calculate the longitudinal residual stress according to σ = E · ΔE by combining the material elastic modulus E with the strain change amount ΔE.

[0044] Example: select a U75V hot-rolled steel rail with a length of 1 m, and the measurement point h = 15 mm. Wire cutting parameters: molybdenum wire diameter 0.18 mm, wire speed 8 m / s, cooling liquid deionized water. Strain gauge model BE120-3AA, sampling frequency 10 Hz. The measurement results are shown in the table below:

[0045]

[0046] The above-described embodiments are only descriptions of the preferred modes of the present application and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A wire-cut-assisted positioning measurement method for longitudinal residual stress under the rail head tread of a steel rail, characterized in that, The specific steps are as follows: 1). Specimen preparation: Cut a complete rail specimen of a certain length, and fix it on the experimental platform after cleaning the surface; 2). Measurement point positioning: Taking the rail top surface as the reference, mark the vertical distance h from the measurement point to the rail top along the side surface of the rail head; 3). Longitudinal cutting: a. Use a wire cutting machine to longitudinally cut the rail to a depth of h, forming a cutting seam with a width of 3 - 5 mm; b. Continue cutting to expand the seam until a flat longitudinal section is exposed; 4). Surface treatment: Mechanically polish and electro-polish the cutting surface; 5). Strain gauge layout: Paste a uniaxial resistance strain gauge longitudinally at the center position of the cutting surface, and connect it to a static strain gauge; 6). Stress calculation: Calculate the longitudinal residual stress according to σ = E·Δε through the strain change amount Δε and combined with the material elastic modulus E.

2. The wire-cut-assisted positioning measurement method for longitudinal residual stress under the rail head tread as described in claim 1, characterized in that, The length of the specimen intercepted in step 1) is 0.5 - 1.5 m.

3. The wire-cut-assisted positioning measurement method for longitudinal residual stress under the rail head tread as described in claim 1, characterized in that, The length of the specimen intercepted in step 1) is 1 m.

4. The wire-cut-assisted positioning and measurement method for longitudinal residual stress under the rail head tread as described in claim 1, characterized in that, In step 2), 0 < h ≤ rail head height.

5. The wire-cut-assisted positioning measurement method for longitudinal residual stress under the rail head tread as described in claim 1, characterized in that, In step 4), mechanical polishing is carried out using sandpaper.

6. The wire-cut-assisted positioning measurement method for longitudinal residual stress under the rail head tread as described in claim 5, characterized in that, The grit number of the sandpaper ≥ 800#.

7. The wire-cut-assisted positioning measurement method for longitudinal residual stress under the rail head tread as described in claim 1, characterized in that, After the surface treatment in step 4), the roughness Ra ≤ 0.8 μm.

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