JP2019138828A - Fretting fatigue reduction structure of shaft member, shaft member, design method of shaft member, fretting fatigue strength test equipment for shaft member - Google Patents

Abstract

To reduce fretting fatigue generated in a press-fitting portion of a shaft member.SOLUTION: A shaft member 11 includes a non-press-fitting portion 13 having a diameter d, and a press-fitting portion 12 having a diameter D greater than the diameter d, and an outer peripheral surface of the press-fitting portion 12 is press-fit to an inner peripheral surface of a press-fitting hole 14a of the other member 14. The pitching generated in the protrusion 12c of the press-fitting portion 12 prevented by fretting from extending to cracks is thus prevented in the groove 12b since a large number of protrusions 12c surrounded by a large number of grooves 12b on the outer peripheral surface of the press-fitting portion 12 are formed, and the durability against fretting fatigue of the shaft member 11 is improved.SELECTED DRAWING: Figure 1

Description

  In the present invention, the shaft member includes a non-press-fit portion having a diameter d and a press-fit portion having a diameter D larger than the diameter d, and an outer peripheral surface of the press-fit portion is press-fitted into an inner peripheral surface of a press-fit hole of another member. The present invention relates to a fretting fatigue reduction structure for a shaft member, a shaft member to which the fatigue reduction structure is applied, a design method for the shaft member, and a fretting fatigue strength test apparatus for testing the fretting fatigue strength of the shaft member.

  Fretting is a phenomenon in which minute relative slip (several μm to several tens of μm) accompanied by friction force is repeatedly generated between contact surfaces of machine parts where surface pressure is applied. There is a problem that the surface of the component is fatigued and cracks are generated, and the fatigue strength of the component is greatly reduced.

  Non-Patent Document 1 below discloses fretting fatigue of a press-fitting portion where an axle of a railway vehicle is press-fitted into a wheel. As shown in FIG. 12, when a bending load is repeatedly input to the axle, the axially intermediate portion of the axle and the wheel press-fit portion becomes a fixed region where relative slip does not occur, but the axial end portions of the press-fit portion are relatively slippery. It is said that the generated slip region causes cracks due to fretting fatigue at the boundary between the fixed region and the slip region.

  Patent Document 1 below discloses a fretting fatigue strength test apparatus that generates fretting fatigue by inputting high-frequency torsional vibration to a test piece in a state where the contact piece is in contact with the surface of the test piece. Is not fixed to an external structure and brought into contact with the surface of the test piece, but is described in which the contact piece is directly supported in contact with the surface of the test piece. According to this fretting fatigue strength test apparatus, it is said that both a fixed region and a sliding region are generated at a portion where the test piece contacts the contact piece, and the fretting fatigue strength of the test piece can be accurately measured.

Fatigue characteristics of Shinkansen vehicle axles Nippon Steel & Sumikin Technical Report No. 395 (2013) pp. 56-63

JP2015-190874A

  Non-Patent Document 1 discloses a technique for reducing fretting fatigue generated in the press-fitting portion of the axle and the wheel by improving the induction hardening of the axle and the fitting shape of the press-fitting portion of the axle and the wheel. However, if fretting fatigue can be reduced by simply processing the outer peripheral surface of the axle that is press-fitted into the wheel, it is not necessary to make a major design change to the conventional axle, which can contribute to cost reduction. it can.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to reduce fretting fatigue occurring in a press-fitting portion of a shaft member.

  In order to achieve the above object, according to the first aspect of the present invention, the shaft member includes a non-pressed portion having a diameter d and a press-fit portion having a diameter D larger than the diameter d. The shaft member has a fretting fatigue reduction structure in which an outer peripheral surface is press-fitted into an inner peripheral surface of a press-fitting hole of another member, and a plurality of protrusions surrounded by a number of grooves are formed on the outer peripheral surface of the press-fitting portion. A fretting fatigue reduction structure for a shaft member is proposed.

  According to the invention described in claim 2, in addition to the structure of claim 1, there is proposed a fretting fatigue reduction structure for a shaft member, wherein the average contact width of the protrusion is 16 μm or less. The

According to the invention described in claim 3, the shaft member according to claim 1 or 2, wherein the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fit portion and the outer peripheral surface of the non-press-fit portion are provided. And the groove and the above-mentioned so that the value of D / d = (τ2 / τ1) ^1/3 calculated from the maximum allowable shear stress τ2 is 1.1 or less and the maximum allowable shear stress τ1 is the maximum value or more. A shaft member characterized by setting the shape of the protrusion is proposed.

According to the invention described in claim 4, the shaft member design method according to claim 1 or 2, wherein the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fit portion is measured; The step of measuring the maximum allowable shear stress τ2 of the outer peripheral surface of the non-pressed part and the diameter ratio D / d of the press-fitted part and the non-pressed part are calculated by D / d = (τ2 / τ1) ^1/3 And adjusting the shapes of the groove and the protrusion so that the value of the diameter ratio D / d is 1.1 or less and the maximum allowable shear stress τ1 is a maximum or more. A shaft member design method is proposed.

  According to the invention described in claim 5, the fretting fatigue strength test apparatus for testing the fretting fatigue strength of the shaft member according to claim 1, wherein the test corresponds to the shaft member. A contact piece fixed to the test piece so as to be in contact with the outer peripheral surface of the piece, a vibration device that applies high-frequency vibration to the test piece, and a displacement detection sensor that detects the occurrence of a crack from the displacement of the test piece. A fretting fatigue strength test apparatus characterized by comprising:

  According to the configuration of claim 1, the shaft member includes a non-press-fit portion having a diameter d and a press-fit portion having a diameter D larger than the diameter d, and an outer peripheral surface of the press-fit portion is an inner peripheral surface of a press-fit hole of another member. It is a fretting fatigue reduction structure of the shaft member that is press-fitted into the press-fitting portion, and since a large number of protrusions surrounded by a number of grooves are formed on the outer peripheral surface of the press-fitting part, the fretting generated the protrusions of the press-fitting part. Pitching is prevented by the grooves and prevented from extending into the cracks, and the durability of the shaft member against fretting fatigue is improved.

  Further, according to the configuration of the second aspect, since the average contact width of the protrusions is 16 μm or less, it is possible to reliably prevent the extension of the pitching generated in the protrusions and improve the durability of the press-fitting part of the shaft member. .

According to the third aspect of the present invention, D / d = (τ2 / τ1) ^{1 /} calculated from the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fit portion and the maximum allowable shear stress τ2 of the outer peripheral surface of the non-press-fit portion. ^Since the shape of the groove and the protruding portion was set so that the value of ³ was 1.1 or less and the maximum allowable shear stress τ1 was the maximum value, the fretting fatigue strength of the press-fit portion of the shaft member was determined as the groove and the protruding portion. The shaft member prevents the fatigue strength of the press-fitted part from becoming excessive with respect to the fatigue strength of the non-press-fitted part while minimizing the diameter ratio D / d of the press-fitted part and the non-fitted part while minimizing the fatigue strength of the non-press-fitted part. Can be reduced in size and weight.

According to the configuration of claim 4, the step of measuring the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fit portion, the step of measuring the maximum allowable shear stress τ2 of the outer peripheral surface of the non-press-fit portion, the press-fit portion and the non-press-fit And calculating the diameter ratio D / d of the portion by D / d = (τ2 / τ1) 1 ^1/3, and the value of the diameter ratio D / d is 1.1 or less and the maximum allowable shear stress τ1 is maximized. The step of adjusting the shape of the groove and the protruding portion so as to be equal to or higher than the value, so that the fretting fatigue strength of the press-fitted portion of the shaft member is effectively increased by the groove and the protruding portion, while the fatigue strength of the non-pressed portion is increased. On the other hand, the fatigue strength of the press-fitted part can be prevented from becoming excessive, and the diameter ratio D / d between the press-fitted part and the non-press-fitted part can be minimized to reduce the size and weight of the shaft member.

  According to the fifth aspect of the present invention, the contact piece fixed to the test piece so as to be in contact with the outer peripheral surface of the test piece corresponding to the shaft member, the vibration device for applying high-frequency vibration to the test piece, and the test piece It is equipped with a displacement detection sensor that detects the occurrence of cracks from the displacement of the test piece, so that both the fixed area and the sliding area are reliably generated at the part where the contact piece contacts the test piece, and the fretting fatigue strength of the test piece is accurately determined. Can be measured.

It is the longitudinal cross-sectional view and cross-sectional view of the shaft member and other member which were couple | bonded by press injection. It is a graph which shows the relationship between the width | variety of the protrusion part of a press-fit part, and the length of a crack. It is a figure which shows the shape of the test piece concerning 1st Embodiment. It is a figure which shows the manufacturing method of the test piece of FIG. It is a figure which shows the test piece concerning 2nd Embodiment. It is a figure which shows the manufacturing method of the test piece of embodiment of FIG. It is a figure which shows the manufacturing method of the test piece concerning 3rd Embodiment. It is a figure which shows a fretting fatigue strength test apparatus. It is a graph which shows the measurement result of the maximum permissible shear stress by an ultrasonic fretting test. It is a graph which shows the relationship between the axle diameter ratio D / d and the maximum allowable shear stress. It is a flowchart which shows the design method of a shaft member. It is a figure which shows the axle shaft press-fit in the wheel.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  As schematically shown in FIG. 1A, a shaft member 11 such as an axle of a conventional railway vehicle is sandwiched between press-fitting parts 12 and 12 having a diameter D and both press-fitting parts 12 and 12 located at both ends thereof. The inner peripheral surface of the press-fitting hole 14a at the center of another member 14 such as a wheel is fixed to the outer peripheral surface of each press-fitting portion 12 by press-fitting. The outer peripheral surface of the press-fitting portion 12 of the shaft member 11 that is press-fitted into the press-fitting hole 14a of the other member 14 is fretting fatigued by a load that is repeatedly input, and a surface deteriorated layer 12a that easily causes fine pitching is formed. When the pitching of the surface deteriorated layer 12a grows into cracks, the strength of the shaft member 11 is remarkably impaired. Therefore, the outer peripheral surface of the press-fit portion 12 is processed to prevent the pitching of the surface deteriorated layer 12a from growing into cracks. Is given.

  Since the strength of the press-fit portion 12 that undergoes fretting fatigue is lower than that of the non-press-fit portion 13 that does not undergo fretting fatigue, the diameter D of the press-fit portion 12 is set so that the strength of the press-fit portion 12 and the non-press-fit portion 13 is uniform. It is set larger than the diameter d of the non-press-fit portion 13. The diameter ratio D / d is an index representing the strength reduction of the press-fit portion 12 due to fretting fatigue. When the diameter ratio D / d is 1, the ideal state where the press-fit portion 12 is not affected by fretting fatigue at all. As the diameter ratio D / d is larger than 1, the press-fitting portion 12 is greatly affected by fretting fatigue.

  As schematically shown in FIGS. 1B and 1C, in the present embodiment, a large number of grooves extending in the circumferential direction and the axial direction and intersecting each other on the outer peripheral surface of the press-fitting portion 12 of the shaft member 11. Are formed, and the tops of a large number of protrusions 12c surrounded by the grooves 12b contact the inner peripheral surface of the press-fitting hole 14a of the other member 14. The depth of the grooves 12b is larger than the thickness of the surface deteriorated layer 12a. Therefore, the bottom of the grooves 12b extends beyond the bottom of the surface deteriorated layer 12a and reaches the inside of the press-fit portion 12. 1, the thickness of the surface degradation layer 12a, the width of the grooves 12b, and the width of the protrusions 12c are about several μm to several tens of μm.

  As shown in FIG. 1 (A), if there are no grooves 12b... And protrusions 12c... In the press-fit portion 12, the pitting generated in the surface deteriorated layer 12a of the press-fit portion 12 penetrates the surface deteriorated layer 12a. It extends to the inside of 12 and grows into a crack, so that the strength of the press-fit portion 12 is lowered.

  On the other hand, as shown in FIGS. 1 (B) and 1 (C), when grooves 12b ... and protrusions 12c ... exist in the press-fit portion 12, the pitching generated in the surface degradation layer 12a of the press-fit portion 12 is projected 12c. Since it reaches the grooves 12b from the side surfaces of the ... and cannot extend any more, the growth into cracks is prevented and the strength reduction of the press-fit portion 12 is suppressed.

  FIG. 2 is a graph showing the relationship between the maximum width of the protrusions 12c of the press-fitting portion 12 of the shaft member 11 and the length of the crack.

  The horizontal axis is the maximum width of the protrusions 12c after initial wear, and the vertical axis is the length of cracks generated in the protrusions 12c. As is clear from the figure, cracks are generated when the maximum width of the protrusions 12c exceeds 16 μm, but no crack is generated when the maximum width of the protrusions 12c is 16 μm or less. .

  The reason why cracks can be prevented if the maximum width of the protrusions 12c after initial wear is 16 μm or less is that even if pitching occurs at the top of the narrow protrusions 12c, the pitching is the top of the protrusions 12c. Since the width of the head is narrow, it does not extend in the depth direction, and even if it extends along the top, it stops at the end of the protrusion 12c. This is because it is scraped off by the metal and disappears. Eventually, when familiarity is found between the tops of the protrusions 12c and the other members 14, the average Hertz surface pressure is lowered and pitching is less likely to occur. Also, the top of the protrusions 12c ... wears and the surface roughness becomes very good, so that the lubricity is improved and the further progress of wear is stopped.

  Next, a test piece 21 for testing fretting fatigue characteristics will be described with reference to FIGS.

  As shown in FIG. 3, the dumbbell-shaped test piece 21 includes a shaft portion 22 formed in a round bar shape having a constant diameter at the center portion, and a pair of head portions 23, 23 bulging from both ends of the shaft portion 22. Are formed on the outer peripheral surface of the shaft portion 22 and a plurality of protrusions 22b are formed. The grooves 22a and the protrusions 22b of the test piece 21 correspond to the grooves 12b and the protrusions 12c of the shaft member 11 described above, and prevent the pitching generated by fretting from growing into cracks. It has a function.

  In order to manufacture the test piece 21, first, as shown in FIG. 4A, a plurality of annular relief grooves 22 c... Are processed on the outer peripheral surface of the shaft portion 22. Subsequently, as shown in FIG. 4B, a spur gear-shaped rolling roller 25 having a backup roller 24 having a flat outer peripheral surface on the outer peripheral surface of the shaft portion 22 and a number of protrusions 25a on the outer peripheral surface. Are rotated to form a large number of parallel grooves 22a and a large number of rectangular protrusions 22b in a region sandwiched between the adjacent escape grooves 22c. At this time, the material pushed out of the grooves 22a by the rolling roller 25 is released into the escape grooves 22c.

  FIG. 5 shows another embodiment of the test piece 21. The test piece 21 includes a large number of mesh-shaped grooves 22a and a large number of rhombus-shaped protrusions 22b. In order to manufacture the test piece 21, first, as shown in FIG. 6A, a plurality of annular relief grooves 22 c... Are processed on the outer peripheral surface of the shaft portion 22. Subsequently, as shown in FIG. 6B, the rolling roller 26 having a bevel gear-shaped outer peripheral surface having a number of protrusions 26a... Inclined in one direction on the outer peripheral surface of the shaft portion 22, and the other direction. A plurality of mesh-like grooves 22a in a region sandwiched between adjacent escape grooves 22c, by rotating and rotating a bevel gear-shaped rolling roller 27 having a large number of protrusions 27a ... A large number of diamond-shaped protrusions 22b are formed. At this time, the material extruded from the grooves 22a by the rolling rollers 26 and 27 is released to the escape grooves 22c.

  As other embodiment of the manufacturing method of the test piece 21, as shown in FIG. 7, the axial part 22 and a pair of head parts 23 and 23 were comprised by another member, and the groove | channel 22a ... and the protrusion part 22b ... were formed. A pair of heads 23 and 23 may be fixed to both ends of the shaft part 22 by press-fitting.

  3 to 7, the widths of the grooves 22a, the protrusions 22b, and the escape grooves 22c are about several μm to several tens of μm. .

  FIG. 8 shows a fretting fatigue strength test apparatus for measuring the strength reduction due to fretting of the test piece 21. A pair of contact pieces 32 and 32 that can come into contact with the shaft portion 22 of the test piece 21 are fixed to the center portions of the inner surfaces of the pair of plate-like pads 31 and 31 facing each other. The nuts 34 and 34 are screwed and fastened to a pair of bolts 33 and 33 penetrating both ends of the pair of pads 31 and 31 so that the contact pieces 32 and 32 have a predetermined load on the shaft portion 22 of the test piece 21. Pressed with. A vibration device 35 that generates high-frequency torsional vibration is connected to the upper head 23 of the test piece 21, and a pair of displacement detection sensors 36 and 36 that detect torsional displacement are a pair of the test piece 21. It arrange | positions so that it may oppose head 23,23.

  The test piece 21 and the contact piece 32 correspond to, for example, the shaft member 11 and the other member 14, and the material and the shapes of the grooves 22a and the protruding portions 22b are the shaft member 11 and the other member. 14 is set.

  When high-frequency torsional vibration is input to the upper head 23 of the test piece 21 with the vibration device 35 in a state where the pair of contact pieces 32 and 32 are fixed so as to sandwich the shaft portion 22 of the test piece 21, the test piece The shaft portion 22 of the test piece 21 is torsionally vibrated to cause relative slip between the contact pieces 32 and 32, and the shaft portion 22 of the test piece 21 is fretting fatigued. At this time, the twisting angle of the shaft portion 22 of the test piece 21 is detected from the outputs of the pair of displacement detection sensors 36, 36. When the detected twisting angle increases rapidly, the pitching generated by fretting does not occur. It grows into a crack, and it is judged that the test piece 21 has reached the fatigue limit. The shear stress of the outer peripheral surface of the shaft part 22 of the test piece 21 at this time is calculated from the torque applied to the test piece 21 and the diameter of the shaft part 22 of the test piece 21.

  Assuming that the contact pieces 32 and 32 are supported by a fixed portion such as a frame, the entire contact portion of the test piece 21 and the contact pieces 32 and 32 becomes a sliding region, and the fixing region and the sliding region coexist. It becomes difficult to realize the state to be performed, and the occurrence of cracks cannot be detected accurately. On the other hand, according to the present embodiment, since the contact pieces 32 and 32 are directly supported by the test piece 21, the fixing region and the sliding region are allowed to coexist in the contact portion between the test piece 21 and the contact pieces 32 and 32, thereby fixing the fixing region. In addition, it is possible to accurately detect the occurrence of cracks at the boundary of the sliding region.

  In order to verify the fatigue limit of the test piece 21 having the grooves 22a... And the protruding portions 22b..., The fretting fatigue limit of the test piece 21 having no grooves 22a. Can be measured. Further, by removing the contact pieces 32, 32, it is possible to measure a simple torsional fatigue limit without fretting of the test piece 21 which does not have the grooves 22a and the protrusions 22b.

  Now, since the strength of the outer peripheral surface of the press-fitting portion 12 of the shaft member 11 is reduced due to fretting fatigue, the diameter D of the press-fit portion 12 is set to be that of the non-press-fit portion 13 in order to ensure the maximum strength of the shaft member 11. It is necessary to set larger than the diameter d. However, unnecessarily increasing the diameter D of the press-fit portion 12 is not desirable because the weight and dimensions of the shaft member 11 increase. Therefore, the grooves 12b and the protrusions 12c are formed in the press-fit portion 12 to reduce fretting fatigue, and the diameter D of the press-fit portion 12 is suppressed to the minimum necessary, that is, the diameter ratio D / d is made as small as possible. Thus, it is desirable to reduce the weight and size of the shaft member 11.

When adding torque T to the press-fitting portion 12 of the shaft member 11 having a diameter D, the shear stress .tau.1 at the outer circumferential surface is given by τ1 = 16T / πD ^3. Also when adding torque T in the non-press-fitting portion 13 of the shaft member 11 having a diameter d, shear stress .tau.2 at the outer circumferential surface is given by τ2 = 16T / πd ^3. Since the press-fitting portion 12 and the non-press-fitting portion 13 of the shaft member 11 are integrally continuous and the same torque T acts, the diameter ratio D / d is given by D / d = (τ2 / τ1) ^1/3 . That is, if the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fit portion 12 and the maximum allowable shear stress τ2 of the outer peripheral surface of the non-press-fit portion 13 are applied to the equation D / d = (τ2 / τ1) ^1/3 , It is possible to obtain a diameter ratio D / d at which cracks occur in the press-fitted portion 12 at the same time as cracks occur in the non-press-fit portion 13, that is, a minimum diameter ratio D / d where the diameter D of the press-fit portion 12 is not unnecessarily large. .

  The graph of FIG. 9 shows the measurement result of the maximum allowable shear stress of the test piece by the fretting fatigue strength test. The horizontal axis is the number of cycles of vibration applied to the test piece, and the vertical axis is cracks in the test piece. Shear stress (maximum allowable shear stress) when generated. ■ and ● indicate the maximum allowable shear stress when the specimen is subjected to simple torsional fatigue without fretting fatigue, and ■ indicates carbonitriding and fine particle shot peening (WPC) ), And the ● mark indicates that the test piece was only carburized. The □ and ○ marks indicate the maximum allowable shear stress when the test piece is subjected to torsional fatigue accompanied by fretting fatigue. Both marks are given, and the circles indicate that the test piece was only carburized.

  The maximum allowable shear stress of a specimen subjected to both carbonitriding and fine particle shot peening is 900 MPa when subjected to mere torsional fatigue (marked with ■), whereas that with fretting fatigue When subjected to fatigue (□ mark), it is reduced to 480 MPa. In addition, the maximum allowable shear stress of a specimen subjected only to carburizing treatment is 750 MPa when subjected to mere torsional fatigue (marked with ●), but torsional fatigue with fretting fatigue. (Circle mark) has fallen to 440 MPa.

When this test result is applied to the equation D / d = (τ2 / τ1) ^1/3 , the diameter ratio D / d of the test piece subjected to both carbonitriding and fine particle shot peening is 1.19. The diameter ratio D / d of the test piece subjected to only carburizing treatment is 1.20.

  FIG. 10 is a graph showing the maximum allowable shear stress of the press-fitted portion 12 in which the shaft member 11 of the railway vehicle described in FIG. 12 is press-fitted into the other member 14. The horizontal axis shows the diameter ratio D / d, and the vertical axis shows The maximum allowable shear stress when a crack occurs in the press-fit portion 12 is shown.

As shown by the solid line in FIG. 10, the maximum allowable shear stress of the press-fit portion 12 increases as the diameter D of the press-fit portion 12 increases, that is, the diameter ratio D / d increases. It can be seen that the shear stress (the maximum allowable shear stress of the press-fit portion 12 when the diameter ratio D / d = 1) is 70 MPa, and the maximum allowable shear stress of the press-fit portion 12 is 124 MPa. When the maximum allowable shear stress of the non-pressed portion 13 = 70 MPa and the maximum allowable shear stress of the press-fit portion 12 = 124 MPa are applied to the equation D / d = (τ2 / τ1) ^1/3 , the diameter ratio D / d = 1. It can be seen that the diameter ratio is almost equal to the diameter ratio D / d = 1.15 that can be read from the graph.

  Next, a design method for reducing the size and weight of the shaft member 11 by minimizing the diameter ratio D / d will be described based on the flowchart of FIG.

  First, in step S1, a test piece 21 simulating the press-fitted portion 12 of the shaft member 11 having no grooves 12b and protrusions 12c is applied to a fretting fatigue strength test apparatus, and the maximum allowable shear is generated in a state where fretting fatigue is generated. The stress τ1 ′ is measured. In the subsequent step S2, the test piece 21 simulating the non-pressed portion 13 of the shaft member 11 is applied to the fretting fatigue strength test apparatus, and the maximum allowable value is obtained in a state where only the torsional fatigue is generated without generating fretting fatigue. The shear stress τ2 is measured. In step S2, since it is not necessary to generate fretting fatigue, it is not necessary to bring the contact pieces 32, 32 into contact with the test piece 21. In the subsequent step S3, the diameter ratio (D / d) ′ is calculated from the maximum allowable shear stress τ1 ′ and the maximum allowable shear stress τ2. This diameter ratio (D / d) ′ corresponds to the diameter ratio of the shaft member 11 (see FIG. 1A) of the comparative example having no grooves 12b.

  In the subsequent step S4, the test piece 21 simulating the press-fitting portion 12 of the shaft member 11 having the grooves 12b... And the projecting portions 12c is subjected to a fretting fatigue strength test device, and the maximum allowable shear stress is generated in the state where fretting fatigue is generated. τ1 is measured. In the subsequent step S5, the diameter ratio (D / d) is calculated from the maximum allowable shear stress τ1 and the maximum allowable shear stress τ2. This diameter ratio (D / d) corresponds to the diameter ratio of the shaft member 11 of the embodiment having the grooves 12b... And the protrusions 12c (see FIGS. 1B and 1C).

  In subsequent step S6, the diameter ratio (D / d) ′ of the comparative example and the diameter ratio (D / d) of the embodiment are compared, and if (D / d) ≦ (D / d) ′ is satisfied, step S7 is established. If not established, the process proceeds to step S8. The case where (D / d) ≦ (D / d) ′ is not satisfied means that the fatigue strength of the shaft member 11 of the comparative example not having the grooves 12b and the protrusions 12c is that the grooves 12b and the protrusions 12c are not. This corresponds to a case where the fatigue strength of the shaft member 11 of the embodiment is greater than that, and the case where the design of the grooves 12b and the protrusions 12c is inappropriate and the effect is not exhibited.

  In that case, in step S8, the shape, depth, angle, pitch, etc. of the groove of the test piece 21 or the shape, area, etc. of the protrusion are changed, and the above steps S4 to S6 are repeated. As a result, if (D / d) ≦ (D / d) ′ is established in step S6, it is determined that the fatigue strength of the embodiment has improved with respect to the comparative example, and the process proceeds to step S7.

  In step S7, if (D / d) ≦ threshold value is not satisfied, it is determined that the fatigue strength is not sufficiently improved by the groove and the protrusion, and the properties of the groove and the protrusion are further changed in step S8. Later, steps S4 to S7 are further repeated. As a result, if (D / d) ≦ threshold value is established, it is determined that the fatigue strength has been sufficiently improved, and this routine is terminated.

As shown by a solid line in FIG. 10, the maximum allowable shear stress τ of the press-fitted portion 12 in which the shaft member 11 of the conventional railway vehicle is press-fitted into the other member 14 increases as the diameter ratio (D / d) increases. When the diameter ratio (D / d) reaches 1.1, saturates to τ = 124 MPa and does not increase any more. The broken lines indicate the characteristics of the present embodiment in which the shapes of the grooves 12b and the protrusions 12c are optimized by the above design method, and the maximum allowable shear stress τ increases as the diameter ratio (D / d) increases. However, when the diameter ratio (D / d) is smaller than 1.1 of the conventional example (D / d) _min , saturates to τ = 124 MPa and does not increase any more. Therefore, by optimizing the shapes of the grooves 12b and the protrusions 12c so that the diameter ratio (D / d) is 1.1 or less and (D / d) _min , the diameter ratio is compared with the conventional example. The shaft member 11 can be reduced in size and weight by reducing (D / d).

  As described above, according to the present embodiment, the fretting fatigue strength of the press-fit portion 12 of the shaft member 11 is effectively increased by the grooves 12b and the protrusions 12c, while the fatigue strength of the non-press-fit portion 13 is increased. Thus, the fatigue strength of the press-fit portion 12 can be prevented from becoming excessive, and the diameter ratio D / d of the press-fit portion 12 and the non-press-fit portion 13 can be minimized to reduce the size and weight of the shaft member 11.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, the shaft member 11 and the other member 14 of the present invention are not limited to the axle and wheels of a railway vehicle.

  Further, the dimensions, shape, number, and the like of the grooves and protrusions of the shaft member of the present invention are not limited to the embodiments.

11 Shaft member 12 Press-fit portion 12b Groove 12c Projection portion 13 Non-press-fit portion 14 Other member 14a Press-fit hole 21 Test piece 32 Contact piece 35 Excitation device 36 Displacement detection sensor

Claims (5)

The shaft member (11) includes a non-press-fit portion (13) having a diameter d and a press-fit portion (12) having a diameter D larger than the diameter d, and the outer peripheral surface of the press-fit portion (12) is the other member (14). The fretting fatigue reduction structure of the shaft member press-fitted into the inner peripheral surface of the press-fitting hole (14a),
A fretting fatigue reduction structure for a shaft member, wherein a plurality of protrusions (12c) surrounded by a number of grooves (12b) are formed on an outer peripheral surface of the press-fitting portion (12).   2. The fretting fatigue reduction structure for a shaft member according to claim 1, wherein an average contact width of the protrusions (12 c) is 16 μm or less. A shaft member (11) according to claim 1 or 2, wherein
D / d = (τ2 / τ1) ^1/3 calculated from the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fitted portion (12) and the maximum allowable shear stress τ2 of the outer peripheral surface of the non-pressed portion (13). The shape of the groove (12b) and the protrusion (12c) is set so that the value is 1.1 or less and the maximum allowable shear stress τ1 is the maximum value or more. The shaft member according to claim 2. A method for designing a shaft member (11) according to claim 1 or 2,
A step of measuring the maximum allowable shear stress τ1 of the outer peripheral surface of the press-fit portion (12), a step of measuring the maximum allowable shear stress τ2 of the outer peripheral surface of the non-press-fit portion (13), the press-fit portion (12) and A step of calculating a diameter ratio D / d of the non-press-fit portion (13) by D / d = (τ2 / τ1) ^1/3, and a value of the diameter ratio D / d of 1.1 or less and a maximum allowable shear Adjusting the shape of the groove (12b) and the protruding portion (12c) so that the stress τ1 is equal to or greater than the maximum value. A fretting fatigue strength test apparatus for testing the fretting fatigue strength of the shaft member (11) according to claim 1 or 2,
A contact piece (32) fixed to the test piece (21) so as to come into contact with the outer peripheral surface of the test piece (21) corresponding to the shaft member (11), and high frequency vibration is applied to the test piece (21). A fretting fatigue strength test apparatus comprising: a vibration exciter (35); and a displacement detection sensor (36) for detecting occurrence of a crack from the displacement of the test piece (21).

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