Method for applying circumferential stress to hollow cylindrical members, and method for evaluating hollow cylindrical members

Abstract

To provide a circumferential stress loading method for a hollow cylindrical member that can simply find circumferential mechanical characteristics of a hollow cylindrical member, an evaluation method for the hollow cylindrical member, a test piece used therefor, and a manufacturing method for the test piece.SOLUTION: A circumferential stress loading method for a hollow cylindrical member has: a preparation process for preparing a test piece 17 for a hollow cylindrical member 11; and a stress loading process for sandwiching the test piece 17 in the diameter direction and loading the test piece 17 with a repeated load in the diameter direction to generate circumferential stress on a surface of the test piece 17. An evaluation method for a hollow cylindrical member has: a process for loading the test piece 17 with the stress; and a process for evaluating the mechanical characteristics of the test piece 17 after loading the test piece 17 with the stress.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for applying a circumferential stress to a hollow cylindrical member, a method for evaluating a hollow cylindrical member, a test piece used therefor, and a method for manufacturing the test piece. [Background technology]

[0002] To save energy, it is desirable to reduce the size and weight of components such as bearings and shafts used in vehicles. At the same time, as the power output of power sources increases, the load on components increases, so fatigue resistance of each component is also required. Therefore, heat treatment such as quenching is sometimes performed on each component as needed to improve fatigue resistance. However, there is a limit to the lifespan of materials in environments that cause metal fatigue, and it is important to clarify this limit in design. Therefore, various test methods have been established, such as fatigue testing and testing of residual stresses that affect fatigue strength.

[0003] For example, Patent Document 1 describes a fatigue testing method in which a cylindrical test piece made of the same material as the bearing raceway is set in an ultrasonic fatigue testing machine, vibrations are applied to the test piece to cause it to resonate, and the number of stress repetitions until the test piece peels off or breaks is determined. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-231974 Summary of the Invention [Problem to be solved by the invention]

[0005] In hollow cylindrical steel components such as bearings, cracks often propagate from the inner periphery to the outer periphery, or from the outer periphery to the inner periphery, leading to fracture (cracks), and it is believed that the strength of the component is dominated by the circumferential strength rather than the axial strength. Therefore, when it comes to stresses acting on hollow cylindrical components due to external forces and residual stresses generated by heat treatment, it is necessary to focus on the circumferential component. However, the fatigue testing method of Patent Document 1 applies repeated axial loads to test specimens, and is therefore unable to evaluate circumferential stress and residual stress. There are few examples of fatigue testing for evaluating circumferential stress and residual stress in hollow cylindrical members, and no established testing method has been established. Therefore, there is a need for the development of a technology that applies circumferential stress to hollow cylindrical members and can easily evaluate mechanical properties in the circumferential direction.

[0006] Therefore, the present invention aims to provide a method for applying circumferential stress to a hollow cylindrical member, which allows the circumferential mechanical properties of the hollow cylindrical member to be easily determined, a method for evaluating a hollow cylindrical member, a test piece to be used therefor, and a method for manufacturing the test piece. [Means for solving the problem]

[0007] The present invention comprises the following configurations. (1) a preparation step of preparing a test specimen of a hollow cylindrical member; a stress application step of clamping the test piece in a diameter direction and applying a repeated load in the diameter direction to the test piece to generate a circumferential stress on a surface of the test piece; A method for applying a circumferential stress to a hollow cylindrical member having the following structure. (2) applying stress to the test piece by the method for applying circumferential stress to a hollow cylindrical member according to (1); evaluating the mechanical properties of the test piece after applying the stress to the test piece; A method for evaluating a hollow cylindrical member having the following structure. (3) The test piece used in the circumferential stress loading method for a hollow cylindrical member according to (1), A test piece in which minute scratches are formed on at least one of the inner and outer peripheral surfaces of a hollow cylindrical steel material. (4) A method for producing the test piece according to (3), a step of quenching the hollow cylindrical steel material; cutting the quenched steel material into pieces having a specified axial width; forming the micro-incision in the cut piece to produce the test piece; A method for manufacturing a test piece having the above structure. [Effects of the Invention]

[0008] According to the present invention, the mechanical properties of a hollow cylindrical member in the circumferential direction can be easily determined. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a process explanatory diagram showing steps (A) to (D) of a method for applying a circumferential stress to a hollow cylindrical member. [Figure 2A] FIG. 2A is a perspective view of the appearance of the test piece. [Figure 2B] FIG. 2B is an enlarged perspective view of the micro-injuries. [Figure 3A] FIG. 3A is a plan view of the microincision opening. [Figure 3B] FIG. 3B is a cross-sectional view taken along line III-III in FIG. 2B. [Figure 4] FIG. 4 is a schematic diagram showing how a load is applied to a test piece. [Figure 5] FIG. 5 is an explanatory diagram showing the measurement positions of the residual stress of the test piece. [Figure 6] FIG. 6 is a graph showing the measurement results of circumferential residual stress versus distance from the inner peripheral surface of the test piece in Test Example 1. [Figure 7] FIG. 7 is a graph showing the measurement results of circumferential residual stress versus distance from the inner peripheral surface of the test piece in Test Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The method for applying a circumferential stress to a hollow cylindrical member according to the present invention is a stress application method used, for example, in a crack growth test, in which a circumferential stress is applied to the hollow cylindrical member by pressing the hollow cylindrical member. The process generally includes a preparation step of preparing a test specimen with micro-defects formed on the surface of a hollow cylindrical member, and a stress application step of clamping the test specimen in the diametrical direction and applying a repeated load in the diametrical direction to the test specimen to generate circumferential stress in the micro-defects. The test specimen is evaluated according to the behavior of crack propagation originating from the micro-defects caused by this stress application step.

[0011] FIG. 1 is a process explanatory diagram showing steps (A) to (D) of a method for applying a circumferential stress to a hollow cylindrical member. First, as shown in FIG. 1A, a hollow cylindrical member 11 made of a steel material such as carburized steel is prepared as a rough-shaped material. The hollow cylindrical member 11 has a shape that resembles, for example, the inner or outer ring of a rolling bearing, but the shape of the rough-shaped material is not limited to this. The hollow cylindrical member 11 can be, for example, a cylindrical rod-like body having an outer diameter φD of φ50 mm to φ70 mm and an inner diameter φd of φ10 mm to φ30 mm. The above dimensions minimize deformation of the material during heat treatment and cutting, which will be described later, and allow the preparation of test pieces of a size that is favorable for ease of handling after cutting.

[0012] Next, the hollow cylindrical member 11 is quenched. The residual stress of the test piece obtained by cutting the rough shape changes depending on the quenching heat treatment conditions. Types of quenching include through quenching, carburizing quenching, carbonitriding quenching, and induction quenching. The magnitude of the residual stress of the test piece can be adjusted by varying the heat treatment conditions for each. Furthermore, it is preferable to appropriately temper the test piece after quenching by tempering or the like.

[0013] Then, as shown in FIG. 1B, the quenched hollow cylindrical member 11 is cut to a predetermined width to obtain cut pieces 13 with an axial width L. By setting the axial width L to, for example, 5 mm to 15 mm, the axial residual stress in the cut pieces 13 is easily released. Furthermore, the change (release) of the circumferential residual stress in the cut pieces 13 is suppressed even after cutting. The cut pieces 13 are desirably cut and cut out at a position at least one wall thickness ((φD-φd) / 2) of the hollow cylindrical member 11, preferably at least two times, and more preferably at least three times, away from the end of the hollow cylindrical member 11. This ensures that the residual stress distribution in the cut pieces 13 is uniform.

[0014] Next, as shown in Fig. 1(C), the circumferential residual stress is measured for the cut piece 13. The circumferential residual stress can be measured based on an X-ray stress measurement method using an X-ray diffraction device, for example. Here, micro-scratches are formed on the inner peripheral surface 13a of the cut piece 13, as will be described in detail later, and it is preferable to measure the residual stress near these micro-scratches. If it is difficult to directly measure the inner peripheral surface 13a with the micro-scratches, the residual stress near the micro-scratches may be estimated by extrapolating measurements taken at positions near the micro-scratches. For example, the circumferential residual stress may be measured at multiple locations along the radial direction of one side surface 13b of the cut piece 13, and the circumferential residual stress of the inner peripheral surface 13a may be estimated from the measurement results. This measurement of the circumferential residual stress may be performed after a crack propagation test under load, as described below.

[0015] Next, when conducting a test by forming a micro-crack in the test piece 17, a micro-crack 15 is formed on the inner peripheral surface 13a of the cut piece 13. By forming a micro-crack in the test piece 17 in advance, it becomes easier to quantify the state in which damage occurs. Alternatively, the test may be conducted without forming a micro-crack. In this case, the cut piece 13 is treated as the test piece 17 as is. The micro-crack may be an artificial defect formed by machining. When formed by machining, the micro-crack 15 is preferably formed at the axial center of the inner peripheral surface 13a of the cut piece 13. Examples of methods for forming the micro-crack 15 include, but are not limited to, electrical discharge machining. Furthermore, the micro-crack 15 may be formed on the outer peripheral surface 13c in addition to the inner peripheral surface 13a, where tensile stress is likely to occur due to the load P.

[0016] 1(D), the test piece 17 is sandwiched in the diameter direction between a pair of jigs 21, 23 of a load application device, and a cyclic load P in the diameter direction is applied to the test piece 17. This generates a circumferential stress in the micro flaw 15. The load application device may be any device that can apply pressure between the jigs 21, 23, and a known pressure tester or the like may be used.

[0017] <Minor scratches> Fig. 2A is an external perspective view of test piece 17, and Fig. 2B is an enlarged perspective view of microcrack 15. Fig. 3A is a plan view of the opening of microcrack 15, and Fig. 3B is a cross-sectional view taken along line III-III in Fig. 2B. As shown in Figures 2A and 2B, the micro-crack 15 is a flat recessed groove along the axial direction of the test piece 17, and has a semicircular axial cross section. A V-shaped V-groove portion 15a is formed at each of the axial ends of the micro-crack 15 in a plan view. The groove width W, groove depth Dp, and apex angle θ of the V-groove portion of the micro-crack 15 shown in Figures 3A and 3B are each arbitrary. The shape of the micro-crack 15 described above is merely an example, and the shape is not limited to this and can be modified as appropriate.

[0018] <Stress load> FIG. 4 is a schematic diagram showing how a load is applied to the test piece 17. As shown in FIG. Here, the test piece 17 is clamped in the diameter direction between a pair of jigs 21, 23 of a load application device, and one of the jigs 21 is repeatedly pressed toward the test piece 17 at a predetermined cycle. As a result, maximum tensile stress is generated on the inner circumferential surface 13a of the test piece 17 at points S1, S2 where the line of action Lf of the load P connecting contact points P1, P2 between the test piece 17 and the jigs 21, 23 intersects with the inner circumferential surface 13a.

[0019] The micro scratches 15 are preferably placed at diametric positions (intersections S1 and S2) along the direction of the repeated load on the test piece 17. By placing the micro scratches 15 at either intersection S1 or S2 (in FIG. 4, they are placed at intersection S1), the maximum tensile stress is generated in response to the applied load, and a large circumferential stress can be efficiently applied to the micro scratches 15. The positions of the micro scratches 15 are not limited to this, and they may be offset, for example, within a range of ±20° or ±40° from the positions of intersections S1 and S2. Furthermore, if intersection S1 is represented as the 6 o'clock position and intersection S2 is represented as the 12 o'clock position on a clock, then the micro scratches 15 may be placed at the 3 o'clock and 9 o'clock positions on the outer peripheral surface 13c of the test piece 17, for example.

[0020] The stress generated in the test piece 17 by the load P can be calculated uniquely from the applied load P and the shape and size of the test piece 17, and the tensile stress generated in the minute flaw 15 can be obtained.

[0021] A load P is applied to the test piece 17 at a predetermined stress amplitude and a predetermined frequency, thereby generating repeated stress in the test piece 17. This causes tensile stress to act periodically on the minute flaws 15, causing fatigue failure (cracks) in the test piece 17. Then, the number of repeated stress loads N from the start of stress loading until fatigue failure occurs is calculated. Note that the test piece 17 is subjected to a load of up to 10 7 Repeated loading 10 times 7 It may be possible to evaluate whether the test piece breaks within the first 100 cycles.

[0022] <Evaluation of mechanical properties> The mechanical properties of the test piece 17 in the circumferential direction are evaluated based on the number of repetitions N of the stress measured as described above, or whether or not fracture occurs after a specified number of repetitions. Alternatively, the mechanical properties may be evaluated based on the relationship between the circumferential residual stress of the test piece 17 measured in advance and the number of repetitions N. Generally, a test piece having compressive residual stress has a larger stress intensity factor at fracture. In other words, as the compressive residual stress increases, the fatigue strength also increases.

[0023] In addition to the number of repetitions N for the specified stress described above, the mechanical properties may be evaluated by varying the magnitude of the repetitive stress to examine the effect of increasing or decreasing the stress on the number of repetitions N. Furthermore, a parameter that takes into account the defect shape and the maximum stress, such as the maximum stress intensity factor K, which represents the strength of the stress distribution near the tip of the crack under the maximum load, may also be used. max The maximum stress intensity factor K max By using this, evaluation can be performed in accordance with fracture toughness.

[0024] In general, when a crack exists on the xy plane in an infinite body to which a uniform stress σ acts in the z-axis direction, if the area of ​​the crack on the xy plane (the area projected in the z-axis direction) is Area, the maximum stress intensity factor K at the edge of the crack is max can be approximately calculated using formula (1) (see Metal Fatigue: The Effects of Minute Defects and Inclusions, Takayoshi Murakami, Yokendo, 1993, p. 17). If the contour shape of the crack edge is uneven, find the envelope of the convex part and define the area inside this envelope as Area.

[0025]

number

[0026] Here, the stress σ is the maximum stress σ on the inner peripheral surface 13a of the test piece 17. max The maximum stress σ maxcan be calculated from the shape of the test piece using equations (2) to (4) (see Stress Intensity Factor Handbook Vol. 1, Y. MURAKAMI, Pergamon, 1987, pp. 340-341).

[0027]

number

[0028] R1: Radius of the inner surface of the test piece R2: Radius of the outer surface of the test piece

[0029] As described above, according to this embodiment, a hollow cylindrical test piece having residual stress in the circumferential direction can be easily fabricated, and circumferential stress can be easily generated in the test piece without using a complicated device. Therefore, a life test such as a crack propagation test can be easily performed in the circumferential direction of a hollow cylindrical member. As a result, it becomes possible to perform a more detailed evaluation of the mechanical properties of a hollow cylindrical member by adding circumferential properties to the conventional evaluation of axial properties. [Example]

[0030] The results of measuring the circumferential residual stress for two types of test pieces with different properties cut from a raw material of a hollow cylindrical member will be described as Test Examples 1 and 2. The test conditions and test results for Test Examples 1 and 2 are summarized in Table 1.

[0031] [Table 1]

[0032] <Production of test specimens> Two types of hollow cylindrical blanks were prepared. One blank (Material 1) was heat-treated and then cut. The other blank (Material 2) was cut and then heat-treated. Micro-scratches were then formed on the surface of each of the resulting cut pieces to prepare test specimens. (raw material) Material 1: Carburized steel 18NiCrMo14-6 (ISO standard) Material 2: High carbon chromium bearing steel SUJ2 (JIS G 4805)

[0033] (shape of raw material) hollow cylindrical rod Outer diameter: φ60mm Inner diameter: φ20mm Axial length of test piece before cutting: 240 mm (Test piece shape) Axial length: 8 mm Radial width (thickness of one side): 20 mm

[0034] (Heat treatment conditions) In Test Example 1, a raw material of Material 1 was carburized and quenched at 820°C, and then tempered at 180°C. The raw material was then cut into a test piece shape. In Test Example 2, a raw material of Material 2 was cut into a test piece shape, and the cut piece was then through-quenched at 840°C, and then tempered at 200°C.

[0035] (residual stress measurement) FIG. 5 is an explanatory diagram showing the measurement positions of the residual stress of the test piece (cut piece) 17. The circumferential residual stress was measured by X-ray stress measurement in the range from the inner peripheral surface (position R1) along the radial direction R to the outer peripheral surface (position R2) on one side 13b of the heat-treated test piece (cut piece) 17.

[0036] (Formation of micro-scratches) An artificial defect was formed in each of the cut pieces of Test Examples 1 and 2 by electrical discharge machining. Test Example 1: Semicircular shape with a radius of 400 μm Groove width W: 35μm Axial length L: 800 μm Groove depth Dp: 400 μm Test example 2: Semicircular shape with a radius of 100 μm Groove width W: 35μm Axial length L: 200 μm Groove depth Dp: 100 μm

[0037] (residual stress measurement results) Fig. 6 is a graph showing the measurement results of circumferential residual stress versus the distance from the inner peripheral surface (R1) to the outer peripheral surface (R2) of the test piece (cut piece) in Test Example 1. Fig. 7 is a graph showing the measurement results of circumferential residual stress versus the distance from the inner peripheral surface (R1) to the outer peripheral surface (R2) of the test piece (cut piece) in Test Example 2. In Test Example 1, the circumferential residual stress on the inner peripheral surface (R1) was −200 MPa (compressive stress) based on the approximation line LM obtained from the measured values ​​near the inner peripheral surface in Figure 6. In Test Example 2, the circumferential residual stress on the inner peripheral surface (R1) was estimated to be 0 MPa based on the approximation line LM shown in Figure 7 obtained in the same manner.

[0038] The maximum stress intensity factor K was calculated by substituting the estimated residual stress value and the size of the micro-flaw into the above-mentioned equation (1). max In Test Example 1, it was 17.9 MPa m 1 / 2 In Test Example 2, it was 7.1 MPa m 1 / 2 In this way, the maximum stress intensity factor K max It can be seen that there is a clear difference.

[0039] Next, the test pieces of Test Examples 1 and 2 were sequentially set in a load tester so that the micro-flaw was at the position S1 in FIG. 4, and repeated stress was applied to the test pieces. In Test Example 1, the maximum load P max :48kN (maximum stress σ max :690MPa), minimum load P min :4.8kN (minimum stress σ min In Test Example 2, a load of 69 MPa was applied. max :38kN (maximum stress σ max :550MPa), minimum load P min :3.8kN (minimum stress σ min In both Test Examples 1 and 3, the stress ratio was 0.1 and the load frequency was 10 Hz.

[0040] As a result, in Test Example 1, the number of repeated stresses N until the test piece broke due to repeated load application was 2.2 × 10 5 In Test Example 2, the cycle was 0.85 × 10 5 As a result of comparing the compressive residual stress and the number of stress cycles N in Test Example 1 and Test Example 2, it was confirmed that Test Example 1, which had a larger compressive residual stress, had a larger number of stress cycles N until fracture than Test Example 2, despite the larger test load.

[0041] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these are included in the scope of protection sought.

[0042] As described above, the present specification discloses the following: (1) a preparation step of preparing a test specimen of a hollow cylindrical member; a stress application step of clamping the test piece in a diameter direction and applying a repeated load in the diameter direction to the test piece to generate a circumferential stress on a surface of the test piece; A method for applying a circumferential stress to a hollow cylindrical member having the following structure. This method for applying a circumferential stress to a hollow cylindrical member allows repeated application of a circumferential stress to the surface of the hollow cylindrical member, and is therefore suitable for testing the mechanical properties of the hollow cylindrical member in the circumferential direction.

[0043] (2) The method for applying a circumferential stress to a hollow cylindrical member according to (1), wherein minute scratches are formed on the surface of the hollow cylindrical member. According to this method for applying a circumferential stress to a hollow cylindrical member, a circumferential stress can be repeatedly applied to the minute scratches formed on the surface of the hollow cylindrical member.

[0044] (3) The method for applying a circumferential stress to a hollow cylindrical member according to (2), wherein the micro-flaws are arranged at diametric positions along the direction of the repeated load on the test piece. According to this method for applying a circumferential stress to a hollow cylindrical member, minute flaws are placed at positions where maximum tensile stress occurs, so that a large circumferential stress can be applied efficiently.

[0045] (4) The method for applying a circumferential stress to a hollow cylindrical member according to (2) or (3), wherein the minute scratches are formed on the inner peripheral surface of the hollow cylindrical member. According to this method of applying circumferential stress to a hollow cylindrical member, minute scratches can be placed in positions where tensile stress due to load is particularly likely to occur.

[0046] (5) The method for applying a circumferential stress to a hollow cylindrical member according to any one of (1) to (4), wherein the test piece is quenched. According to this method of applying circumferential stress to a hollow cylindrical member, the residual stress of the test piece can be changed by changing the heat treatment conditions of quenching.

[0047] (6) The method for applying a circumferential stress to a hollow cylindrical member according to (5), wherein the quenching is one of through quenching, carburizing quenching, carbonitriding quenching, and induction quenching. According to this method of applying circumferential stress to a hollow cylindrical member, different residual stresses can be generated by various types of hardening.

[0048] (7) A step of applying stress to the test piece by the method for applying circumferential stress to a hollow cylindrical member according to any one of (1) to (6); evaluating the mechanical properties of the test piece after applying the stress to the test piece; A method for evaluating a hollow cylindrical member having the following structure. According to this method for evaluating a hollow cylindrical member, the mechanical properties of the test piece in the circumferential direction can be evaluated.

[0049] (8) The method for evaluating a hollow cylindrical member according to (7), wherein the mechanical properties include the number of repetitions to which the stress is repeatedly applied until the test piece breaks. According to this method for evaluating hollow cylindrical members, the fatigue strength of the test piece can be evaluated based on the number of times stress loading is repeated.

[0050] (9) The method for evaluating a hollow cylindrical member according to (7) or (8), wherein the mechanical properties include a maximum stress intensity factor of the test specimen. According to this method for evaluating hollow cylindrical members, evaluation can be performed in accordance with fracture toughness as a material property, and the mechanical properties of the material can be evaluated more accurately.

[0051] (10) The method for evaluating a hollow cylindrical member according to any one of (7) to (9), wherein the mechanical properties include a residual compressive stress of the test piece. According to this method for evaluating a hollow cylindrical member, the test piece can be evaluated according to the residual stress.

[0052] (11) A test piece used in the method for applying a circumferential stress to a hollow cylindrical member according to any one of (1) to (6), A test piece in which minute scratches are formed on at least one of the inner and outer peripheral surfaces of a hollow cylindrical steel material. This test piece is suitable for evaluating the mechanical strength in the circumferential direction of a hollow cylindrical steel material.

[0053] (12) A method for producing a test piece according to (11), a step of quenching the hollow cylindrical steel material; cutting the quenched steel material into pieces having a specified axial width; forming the micro-incision in the cut piece to produce the test piece; A method for manufacturing a test piece having the above structure. According to this method of manufacturing a test piece, a steel material is cut to a specified axial width, thereby obtaining a test piece in which the release of circumferential residual stress is suppressed.

[0054] (13) A method for manufacturing a test piece according to (12), in which the cut piece is cut from a position that is at least one wall thickness of the hollow cylindrical steel material away from the end of the steel material. According to this method of manufacturing the test piece, the distribution of residual stress in the cut piece can be made uniform. [Explanation of symbols]

[0055] 11 Hollow cylindrical member 13 Cut piece 13a Inner surface 13b One side 13c Outer surface 15 Minor scratches 15a V groove 17 Test pieces 21,23 Jig

Claims

1. a preparation step of preparing a test piece of a hollow cylindrical member; a stress application step of clamping the test piece in a diameter direction and applying a repeated load in the diameter direction to the test piece to generate a circumferential stress on a surface of the test piece; and Micro-scratches are formed on the surface of the hollow cylindrical member, A method for applying circumferential stress to a hollow cylindrical member, in which the micro-flaws are arranged at diametric positions along the direction of application of the cyclic load to the test piece.

2. 2. The method for applying a circumferential stress to a hollow cylindrical member according to claim 1, wherein the minute scratches are formed on the inner peripheral surface of the hollow cylindrical member.

3. The test specimen is quenched.

3. The method for applying a circumferential stress to a hollow cylindrical member according to claim 1 or 2.

4. The quenching is any one of deep quenching, carburizing quenching, carbonitriding quenching, and induction quenching. The method for applying a circumferential stress to a hollow cylindrical member according to claim 3.

5. a step of applying stress to the test piece by the method for applying circumferential stress to a hollow cylindrical member according to any one of claims 1 to 4; evaluating the mechanical properties of the test piece after applying the stress to the test piece; A method for evaluating a hollow cylindrical member having the following structure.

6. The mechanical properties include the number of times the stress is repeatedly applied to the test piece until the test piece breaks. The method for evaluating a hollow cylindrical member according to claim 5 .

7. The mechanical properties include a maximum stress intensity factor of the test specimen. The method for evaluating a hollow cylindrical member according to claim 5 or 6.

8. The mechanical properties include residual compressive stress of the test specimen. The method for evaluating a hollow cylindrical member according to any one of claims 5 to 7.

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