JP2022143695A - Shaft member fitting structure, design method therefore and fretting fatigue test method - Google Patents

Abstract

To provide a fitting structure which can enhance the fretting fatigue strength of a shaft member, and a design method which can arbitrarily set a point at which the break of the shaft member occurs.SOLUTION: As a fitting structure of a shaft member 2 to a fitting hole 1a of a contact member 1, a stress relief groove 2A in which a stress concentration coefficient Kt reaches 1.08 to 1.13 is formed at a point corresponding to an end part of the contact member 1 of the shaft member 2 in an axial direction. Also, when the shaft member 2 receives a torsional load, the stress concentration coefficient Kt is set smaller than 1.08 in order to fretting-fatigue breaking the shaft member 2 at a fitting portion, the stress concentration coefficient Kt is set larger than 1.13 in order to fatigue-break the shaft member 2 at the stress relief groove 2A portion, and the stress concentration coefficient Kt is set to 1.08 to 1.13 in order to make the fretting-fatigue break at the fitting portion of the shaft member 2 and the fatigue break at the stress relief groove 2A portion substantially simultaneously occur.SELECTED DRAWING: Figure 10

Description

TECHNICAL FIELD The present invention relates to a fitting structure of a shaft member, a design method thereof, and a fretting fatigue test method.

Fretting issues must be taken into account in machine design. Here, fretting is a phenomenon in which minute (about several μm to several tens of μm) relative slippage accompanied by frictional force occurs repeatedly between the contact surfaces of mechanical structures on which surface pressure is acting. be. For example, at the joint between the blade root and the blade groove of a steam turbine, when the steam turbine is in operation, slight relative slip occurs repeatedly under surface pressure, causing fatigue due to fretting (fretting fatigue). .

The fretting fatigue described above may cause cracks in the structure or destroy the structure. When such fretting fatigue is involved, the strength of the structural member is greatly reduced compared to when it is not accompanied by fretting fatigue, so it is considered to be one of the problems to be considered when designing the structural member.

By the way, with regard to fretting fatigue of structural members, various proposals have been made so far (see, for example, Patent Document 1), and various research results have been reported (see, for example, Non-Patent Documents 1 to 5). .

That is, in Patent Document 1, as a fretting fatigue test device, a presser is attached to a pair of pads, a bolt inserted through these pads is tightened, and a high-frequency torsion is applied to the test piece in a state where the test piece is pressed by the presser. A device has been proposed in which fatigue testing is performed by applying vibration.

In addition, Non-Patent Document 1 proposes a configuration in which a stress relief groove and an overhang are formed in the fitting portion of the axle of a Shinkansen vehicle, and according to this, high fretting fatigue strength can be obtained. there is

Furthermore, Non-Patent Documents 2 and 3 report research results regarding the effect of the shape of stress relief grooves on the improvement of fretting fatigue strength.

Non-Patent Document 4 proposes a calculation formula for obtaining an accurate stress concentration factor for the entire range of notch dimensions when a rod member having a circumferential notch receives a torsional load.

Non-Patent Document 5 discloses materials concerning the effects of notches, dimensions, finishing and other various factors on the fatigue strength of machinery and structural parts.

Japanese Patent No. 6296860

Fatigue Characteristics of Shinkansen Axles, Nippon Steel & Sumikin Technical Review No.395 (2013) pp.56-63) Effect of Stress Relief Groove Shape on Fretting Fatigue Strength Improvement and Groove Shape Selection Conditions Materials Vol56, No.12, pp.1156-1162, Dec.2007 Effect of Stress Relief Groove Shape on Improvement of Fretting Fatigue Strength Journal of the Japan Society of Mechanical Engineers No.068-1 ('06-3-17, Kyushu Branch 59th General Assembly Lecture) Calculation formula for giving an accurate stress concentration factor for the entire range of notch shapes Transactions of the Japan Society of Mechanical Engineers (A) Vol.70 No.689 (2004-1) pp.93-98 Metallic materials Fatigue strength design data (I) Chapter 3 Effect of various factors on fatigue strength The Japan Society of Mechanical Engineers (1961)

By the way, Patent Document 1 proposes a fretting fatigue test device that can quickly evaluate fatigue strength by ultrasonic excitation, and it is applicable to stress relief grooves in the vicinity of fine sliding portions. It is not clear whether

In addition, Non-Patent Documents 1 to 3 report that when stress relief grooves are formed, higher fretting fatigue strength can be obtained depending on the shape, compared to when stress relief grooves are not formed. However, all of them are shown by experimental results and are empirical methods. Furthermore, since the fatigue strength is about 10 ⁷ , it can be applied to a simple design method for stress relief grooves near fine sliding parts. Limited.
In addition, Non-Patent Document 4 provides a calculation formula for obtaining an accurate stress concentration factor for the entire range of notch dimensions when a round bar having a circumferential notch receives a torsional load. Document 5 provides a summary of the effects of various factors such as notches on the fatigue strength of various metal materials. is not mentioned.

SUMMARY OF THE INVENTION An object of the present invention is to provide a shaft member fitting structure capable of increasing the fretting fatigue strength of a shaft member that receives a torsional load.

By the way, in order to increase the fretting fatigue strength of the shaft member, it is known that it is effective to form a stress relief groove at a location corresponding to the axial end of the contact member. In some cases, when fatigue fracture occurs, a design is required in which fatigue fracture occurs not only in the portion where the shaft member is fitted to the contact member, but also in the stress relief groove portion.

Therefore, the present invention provides a shaft member fitting structure, a design method thereof, and a fretting fatigue test method, which can arbitrarily set the location where the shaft member breaks and can increase the degree of design freedom. intended to

In order to achieve the above object, the present invention provides a structure for fitting a shaft member (2) into a fitting hole (1a) formed in a contact member (1). The difference (σ _1.333 - σ _1.0 ) between the principal stress (σ _1.333 ) when tensile force is applied and the principal stress (σ _1.0 ) when only pressing force is applied is the nominal stress (σ _n ) at the minimum cross section When the value divided by ((σ _1.333 −σ _1.0 )/σ _n ) is defined as the stress concentration factor Kt, at a portion of the shaft member (2) corresponding to the axial end of the contact member (1), The stress relief groove (2A) is formed in such a shape that the stress concentration factor Kt is 1.08 to 1.13.

According to the present invention, when a stress relief groove having a shape with a stress concentration factor Kt of 1.08 to 1.13 is formed, when the shaft member receives a torsional load, the fretting fatigue strength at the fitting portion of the shaft member and the fatigue strength of the stress relief groove are substantially equal, and that these fatigue strengths exhibit the maximum value. Therefore, by forming such stress relief grooves in the shaft member, it is possible to increase the fretting fatigue strength of the shaft member that receives a torsional load. The range where the stress concentration factor Kt is 1.08 to 1.13 is a region where fretting fatigue fracture in the fitting portion of the shaft member and fatigue fracture in the stress relief groove coexist (both fatigue fractures occur almost simultaneously). be.

Here, it is desirable to form at least one escape groove (1A) along the entire circumference at an axially intermediate position of the fitting hole (1a) of the contact member (1).

According to the above configuration, the fixing area between the shaft member and the contact member is smaller than in the case where the escape groove is not formed, and the fixing between the shaft member and the contact member is evenly performed, so that the two are made uniform. can be firmly fixed.

Further, it is desirable to axially overhang the axial end of the contact member (1) to the stress relief groove (2A) formed in the shaft member (2).

According to the above configuration, by overhanging the axial end of the contact member in the axial direction to the stress relief groove of the shaft member, the stress concentration, the distribution of the contact surface pressure, the change in the relative slippage, etc., can cause the shaft member to be degraded. Fretting fatigue strength is increased.

Further, at a portion of the shaft member (2) axially outside the axial end of the contact member (1) and adjacent to the stress relief groove (2A) in the axial direction, the shaft member A brim portion (2a) having the same diameter as that of the portion to be fitted into the fitting hole (1a) of the contact member (1) of (2) may be formed.

According to the above configuration, the flange portion can reduce the influence of the rigidity of the shaft member on the stress relief groove, and the diameter of the portion extending axially outward from the flange portion of the shaft member can be reduced.

A method of designing a fitting structure for a shaft member (2) according to the present invention is any of the fitting structure designing methods for a shaft member (2) according to the present invention, wherein the shaft member (2) In a structure that receives a torsional load, when the shaft member (2) is designed so that fretting fatigue fracture occurs at the fitting portion of the contact member (1) into the fitting hole (1a), the stress concentration factor When Kt is set smaller than 1.08 and the shaft member (2) is designed so that fatigue fracture occurs in the stress relief groove (2A) portion, the stress concentration factor Kt is set larger than 1.13,
When designing so that both fretting fatigue fracture in the fitting hole (1a) of the contact member (1) of the shaft member (2) and fatigue fracture in the stress relief groove (2A) portion occur, the stress The concentration factor Kt is set to 1.08 to 1.13.

According to the design method according to the present invention, it is possible to arbitrarily set the location where the shaft member breaks depending on the value of the stress concentration factor Kt of the stress relief groove.

Further, in the fretting fatigue test method according to the present invention, the test member (12) is fitted to the contact member (11), and the test member (12) is placed relative to the contact member (11). A fretting fatigue test method for measuring the fretting fatigue of the test member (12) by sliding it, in which the principal stress (σ _1.333 ) when a tensile force is applied and the stress when only a pressing force is applied The difference (σ _1.333 - σ _1.0 ) from the principal stress (σ _1.0 ) divided by the nominal stress (σ _n ) at the minimum cross section ((σ _1.333 - σ _1.0 )/σ _n ) was defined as the stress concentration factor Kt. In this case, a predetermined stress concentration factor (Kt) is applied to the contact portion between the contact member (11) and the test member (12) in either one of the contact member (11) and the test member (12). forming an escape groove (12A) having a concave cross-sectional shape, and rotating either the contact member (11) or the test member (12) around the central axis of the test member (12) and a torsional load is applied to the contact portion between the contact member (11) and the test member (12).

According to the fretting fatigue test method according to the present invention, according to the value of the stress concentration factor of the stress relief groove having a concave cross section having a predetermined stress coefficient, fretting fatigue fracture at the contact part and fatigue at the stress relief groove Since it is possible to ascertain which of the fractures (groove fatigue fractures) will occur (first), it is possible to select the fracture mode in the design of the member. Therefore, for example, it is possible to design a portion where fretting fatigue fracture is not desired to cause groove fatigue fracture, so that the degree of freedom in designing the structure can be increased.

Further, in this fretting fatigue test method, by applying ultrasonic vibration to the contact member (11) in contact with the test member (12), the test member (12) and the contact member (11) Fine sliding may occur between them.

By performing the above steps in the fretting test method of the present invention, it is possible to provide a rapid fretting fatigue test method capable of confirming ultra-high cycle fatigue strength under torsional load.

ADVANTAGE OF THE INVENTION According to this invention, the effect that the fretting fatigue strength of the shaft member which receives a torsional load can be improved and the location where the shaft member breaks can be set arbitrarily is obtained.

It is a figure which shows the fitting structure of the shaft member which concerns on this invention. (a) is an enlarged detailed view of part A in FIG. 1, and (b) is a view similar to (a) when there is no escape groove. It is a figure which shows another form of the fitting structure of the shaft member which concerns on this invention. It is a figure which shows the basic composition of a fretting fatigue test apparatus. FIG. 2 shows the details of the specimen and the distribution of shear stress and torsion angle. (a) is a perspective view of a pressing jig, and (b) is a perspective view of a contact piece. 7(a) to 7(d) are diagrams showing test configurations for various test pieces, and FIG. 7(e) is an enlarged detailed view of the B portion of FIG. 7(c). 4 is a flow chart showing the procedure of fatigue strength test for various test pieces. FIG. 3 is an SN diagram showing test results for various test pieces. FIG. 3 is a diagram showing the relationship between the stress concentration factor Kt and fatigue strength of various test pieces.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[Fitting Structure of Shaft Member]
First, the fitting structure of the shaft member according to the present invention will be described below with reference to FIGS. 1 and 2. FIG.

1 is a view showing a fitting structure of a shaft member according to the present invention, FIG. 2(a) is an enlarged detailed view of part A in FIG. 1, and FIG. It is a similar figure.

The fitting structure of the shaft member 2 shown in FIGS. 1 and 2 is, as shown in FIG. It is used in a mechanical structure in which the member 2 is press-fitted. Specifically, stress relief grooves 2A having a curvature radius R, a depth d, and a width w are formed in the vicinity of both ends of the contact member 1 of the shaft member 2 in the axial direction. At an axially intermediate position of the fitting hole 1a of the contact member 1, one relief groove 1A having a rectangular cross section is formed along the entire circumference along the fitting hole 1a.

Further, as shown in detail in FIG. 2(a), the axial ends of the contact member 1 overhang the stress relief grooves 2A formed in the shaft member 2 in the axial direction by δ shown in the figure. .

Here, the difference (σ _{1.333 - σ 1 .0} ) divided by the nominal stress σ _n in the minimum cross section of the shaft member 2, that is, the value Kt obtained by the following equation:
Kt=( _σ1.333 − _σ1.0 )/ _σn (1)
is defined as a "stress concentration factor", a stress relief groove 2A having a shape with a stress concentration factor Kt of 1.08 to 1.13 is formed at a position corresponding to the axial end of the contact member 1 of the shaft member 2. formed.

By the way, when the torsional vibration is repeatedly applied to the contact member 1, the contact surface (fitting surface) between the contact member 1 and the shaft member 2 has the contact member 1 and the shaft member 2 as shown in FIG. 2, there are a fixed area S1 in which relative slip does not occur and a slip area S2 in which relative slip occurs, and cracks are known to occur near the boundary between both S1 and S2.

Here, since the relief groove 1A having a rectangular cross section is formed along the entire circumference along the fitting hole 1a at the axially intermediate position of the fitting hole 1a of the contact member 1 as described above, the clearance groove 1A is shown in FIG. 2(a). Thus, the shaft member 2 has a fixed area S1 and a sliding area S2 at the illustrated locations. On the other hand, as shown in FIG. 2(b), when the escape groove 1A shown in FIG. 2(a) is not formed in the contact member 1, the fixing region S11 and the sliding region Although S12 exists, it is enlarged as compared with the case where the fixed area S11 forms the relief groove 1A (see FIG. 2(a)). If the fixed area S11 expands in this way, there is a possibility that the contact member 1 and the shaft member 2 will not be uniformly fixed depending on the dimensional accuracy and surface roughness. For this reason, as described above, the contact member 1 and the shaft member 2 can be made uniform by forming the escape groove 1A having a rectangular cross section in the axially intermediate position of the fitting hole 1a of the contact member 1 over the entire circumference. It can be fixed firmly.

Further, as described above, if the axial end of the contact member 1 is axially overhanging the stress relief groove 2A formed in the shaft member 2 by δ shown in FIG. The fretting fatigue strength of the shaft member 2 is enhanced by the distribution of surface pressure, changes in the amount of relative slippage, and the like. This has been confirmed experimentally (also reported in Non-Patent Documents 1 to 3).

Here, another form of the fitting structure of the shaft member 2 is shown in FIG. A flange portion 2a having the same diameter as the portion of the shaft member 2 that is press-fitted into the fitting hole 1a of the contact member 1 is formed at a location adjacent to the stress relief groove 2A.

As described above, if the collar portion 2a is formed on the shaft member 2, the influence of the rigidity of the shaft member 2 on the stress relief groove 2A can be suppressed by the collar portion 2a. The diameter of the portion 2b extending in the axial direction can be reduced.

Next, a fretting fatigue test apparatus for the shaft member 2 will be described below with reference to FIG.

FIG. 4 is a diagram showing the basic configuration of a fretting fatigue test apparatus, and the illustrated fretting fatigue test apparatus 10 has the following components.

1) A contact piece 11 fixed to the test piece 12 so as to contact the outer peripheral surface of the test piece 12 corresponding to the shaft member 2
2) Vibrator 13 that generates high-frequency torsional vibration
3) An amplifier 14 that amplifies the high-frequency torsional vibration generated by the vibrating device 13 and applies it to the test piece 12
4) Displacement detection sensor 15 for detecting displacement of test piece 12
5) a displacement measuring device 16 that receives a signal from the displacement detection sensor 15 and determines the displacement of the test piece 12;
6) A computer (PC) 17 that detects the occurrence of cracks from the displacement of the test piece 12 detected by the displacement detection sensor 15 and obtains the fatigue strength of the test piece 12;
7) A transmitter 18 that receives a command signal from a computer (PC) 17 and transmits a high-frequency pulse signal to the vibrating device 13
The computer (PC) 17 has a function of detecting the occurrence of cracks from the displacement of the test piece 12 detected by the displacement detection sensor 15 and obtained by the displacement measuring device 16 .

Here, FIG. 5 shows the details of the test piece 12 and the distribution of shear stress and twist angle. ) A tempered material is used, and has a Young's modulus of 203 GPa, a tensile strength of 1195 MPa, a proof stress of 855 MPa, a breaking strain of 5.8%, and a Vickers hardness of about 450 HV.

The test piece 12 has large-diameter heads 12a at both ends in the axial direction, a small-diameter shaft portion 12b in the center in the axial direction, and an arc-shaped concave curved surface portion 12c connecting the head portions 12a and the shaft portions 12b. The contact piece 11 is pressed against the central shaft portion 12b having a constant shear stress using a pressing jig 20 shown in FIG. Here, the configuration of the pressing jig 20 will be described below with reference to FIG.

6(a) is a perspective view of a pressing jig, and FIG. 6(b) is a perspective view of a contact piece. As shown in FIG. 6(a), the pressing jig 20 is a pair of rectangular plate-like pads 21, and these pads 21 are arranged so as to sandwich the test strip 12 from both sides. A contact piece 11 as shown in FIG. 6B is attached to the inner surfaces of the pair of pads 21 facing each other, and a strain gauge 22 is attached to the outer surface of one of the pads 21 . Bolts 23 are inserted through the pair of pads 21 on both sides of the test piece 12, respectively. is pressed by the contact piece 11 with a predetermined pressing force. At this time, the pressing force applied from the contact piece 11 to the test piece 12 is detected by the strain gauge 22 , and the detection signal is sent to the computer (PC) 17 . The computer (PC) 17 then calculates the pressing force applied from the contact piece 11 to the test piece 12 .

Next, the procedure and results of the fatigue test using the fretting fatigue test apparatus 20 will be described below with reference to FIGS. 7 to 10. FIG.

7 (a) to (d) are diagrams showing test configurations for various test pieces, FIG. 7 (e) is an enlarged detailed view of B part in FIG. 7 (c), and FIG. 8 is a fatigue strength test procedure for various test pieces. 9 is an SN diagram showing test results for various test pieces, and FIG. 10 is a diagram showing the relationship between stress concentration factor Kt and fatigue strength of various test pieces.

Here, fatigue strength tests are performed in various forms on various test pieces 12, 12' shown in FIGS. 7(a) to 7(d). That is, FIG. 7(a) shows a configuration in which a contact piece 11 presses a test piece (smooth material) 12' in which no stress relief groove is formed (referred to as "fretting fatigue test of press-fit portion without groove" (see FIG. 8). See step S1)). In the following description, the stress relief groove may be simply referred to as "groove".

FIG. 7(b) shows a configuration in which a test piece (smooth material) 12′ in which no stress relief groove is formed is subjected to a torsional fatigue test without being pressed by the contact piece 11 (referred to as a “non-press-fit portion torsional fatigue test”). See step S2 in FIG. 8)). In addition, FIG. 7(c) shows a mode in which a fretting fatigue test is performed in a state in which a test piece 12 having a stress relief groove 12A formed therein is pressed by a contact piece 11 (referred to as "a fretting fatigue test of a press-fit portion with a groove"). See step S4 in FIG. 8)). FIG. 7(d) shows a configuration in which a torsional fatigue test is performed in a state in which the test piece 12 in which the stress relief groove 12A is formed is not pressed by the contactor (referred to as "torsion fatigue test of non-press-fitted portion with groove" (FIG. 8). (see step S5)).

The dimensions of the stress relief groove 12A formed in the test piece 12 shown in FIGS. 7(c) and (d) are shown in FIG. 7(e). is set to d, the width is set to w, and the amount of overhang of the contact piece 11 to the stress relief groove 12A is set to δ.
A pair of flat portions 12B, 12B with which the pair of contact pieces 11, 11 come into contact are formed on the test piece 12 shown in FIGS. 7(c) and 7(d). The pair of plane portions 12B, 12B are so-called width across flats surfaces arranged on both sides of the central portion of the test piece 12 in the axial direction so as to face each other 180 degrees. When the pair of contact pieces 11 and 11 come into contact with the pair of flat portions 12B and 12B, the contact pieces 11 and 11 apply pressure to the test piece 12 .

Here, Table 1 shows the types of various test pieces with different specifications.

表１においては、「溝なし」の試験片とは、図７（ａ），（ｂ）に示す応力逃がし溝（溝）が形成されていない試験片１２’であって、この試験片１２’の応力集中係数Ｋｔは１である。また、図７（ｃ），（ｄ）に示す応力逃がし溝（溝）１２Ａが形成された試験片１２の応力逃がし溝１２Ａの深さｄが０．０３ｍｍ、曲率半径Ｒが３．００ｍｍ、幅ｗが０．８５ｍｍ、応力集中係数Ｋｔが１．０７０のものを「Ｇ_0.03」としている。以下、同様に、応力逃がし溝１２Ａの深さｄが０．０４ｍｍ、曲率半径Ｒが２．４５ｍｍ、幅ｗが０．８８ｍｍ、応力集中係数Ｋｔが１．０８６のものを「Ｇ_0.04」、応力逃がし溝１２Ａの深さｄが０．０５ｍｍ、曲率半径Ｒが１．５０ｍｍ、幅ｗが０．７７ｍｍ、応力集中係数Ｋｔが１．１２７のものを「Ｇ_0.05」、応力逃がし溝１２Ａの深さｄが０．１０ｍｍ、曲率半径Ｒが１．００ｍｍ、幅ｗが０．８７ｍｍ、応力集中係数Ｋｔが１．１９３のものを「Ｇ_0.1」としている。なお、「Ｇ_0.03」、「Ｇ_0.04」、「Ｇ_0.05」、「Ｇ_0.1」にて示される試験片１２における接触片１１のオーバーハング量δは０．３ｍｍ（一定）に設定されている。

In Table 1, the "no groove" test piece is the test piece 12' in which the stress relief groove (groove) shown in Figs. 7(a) and (b) is not formed. has a stress concentration factor Kt of 1. 7(c) and 7(d), the test piece 12 formed with the stress relief groove (groove) 12A had a depth d of 0.03 mm, a radius of curvature R of 3.00 mm, and a width “G _0.03 ” means that w is 0.85 mm and the stress concentration factor Kt is 1.070. Similarly, the depth d of the stress relief groove 12A is _0.04 mm, the radius of curvature R is 2.45 mm, the width w is 0.88 mm, and the stress concentration factor Kt is 1.086. The depth d of the relief groove 12A is 0.05 mm, the radius of curvature R is 1.50 mm, the width w is 0.77 mm, and the stress concentration factor Kt is _1.127 . d is 0.10 mm, the radius of curvature R is 1.00 mm, the width w is 0.87 mm, and the stress concentration factor Kt is 1.193 is defined as "G _0.1 ". The overhang δ of the contact piece 11 in the test piece 12 indicated by "G _0.03 ", "G _0.04 ", "G _0.05 ", and "G _0.1 " is set to 0.3 mm (constant).

Next, the procedure and test results (fatigue strength) of the fatigue strength test for various test pieces 12, 12' will be described below with reference to FIGS. 8 to 10. FIG.

In the fatigue strength test, first, a fatigue test (“fretting fatigue test of press-fit portion without groove”) is performed in the form of the test shown in FIG. 7(a) (step S1 in FIG. 8). The fatigue strength _τW0 in this case is 205 MPa, as shown in FIGS.

Next, a torsional fatigue test (“non-press-fit portion torsional fatigue test”) is performed in the form of the test shown in FIG. 7(b) (step S2). The fatigue strength τ _W1 in this case is 300 MPa, as shown in FIGS.

After that, a plurality of test pieces having stress relief grooves 12A formed thereon and having different stress concentration _{factors Kt} as shown in FIGS. _0.05 " and " _G0.1 ") 12 are prepared (step S3). Then, the two types of test pieces 12 indicated by "G _0.03 " and "G _0.04 " are subjected to the test mode shown in FIG. S4). The fretting fatigue strengths τ _W3 for the test pieces "G _0.03 " and "G _0.04 " obtained in this fretting fatigue strength test are 230 MPa and 266 MPa, respectively, as shown in FIGS.

In addition, the test _{form shown} in FIG. (step S5). The torsional fatigue strengths τ _W4 for the test pieces "G _0.05 " and "G _0.10 " obtained in this torsional fatigue test are 263 MPa and 212 MPa, respectively, as shown in FIGS.

The straight lines X and Y shown in FIG. 10 are as follows.

That is, when the shape factor α and the notch factor β for the notch (stress relief groove) formed in the shaft member are defined by the following formulas (2) and (3), respectively:
Shape factor α = maximum stress at notch bottom/nominal stress at notch bottom (2)
Notch factor β = fatigue limit of smooth test piece/fatigue limit of notched test piece (3)
The straight line X indicates the predicted value of the fatigue strength obtained using the data provided in Non-Patent Document 5 based on the notch factor β represented by the above equation (3), and the straight line Y indicates β = α and It shows the predicted value of the fatigue strength in the hypothetical case.

Next, whether the fretting fatigue strength τ _W3 obtained by the fretting fatigue test in step S4 and the torsional fatigue strength τ _W4 obtained in the torsional fatigue test in step S5 are substantially equal (τ _W3 ≈ τ _W4 ) is determined (step S6), and when the fretting fatigue strength τ _W3 and the torsional fatigue strength τ _W4 are substantially equal (step S6: Yes), a series of fatigue tests are completed (step S7), and fretting When the fatigue strength τ _W3 and the torsional fatigue strength τ _W4 are different (Step S6: No), the fretting fatigue test and the torsional fatigue test are continued for other test pieces 12 having different stress concentration factors Kt. (Steps S4 and S5).

According to the test results shown in FIG. 10, the fretting fatigue strength τ _W3 and the torsional fatigue strength τ _W4 are substantially equal and exhibit the highest values when the stress concentration factor is in the range of 1.08 to 1.13.

As is clear from the results of the above fatigue strength test, when the stress relief groove 2A having a shape with a stress concentration factor Kt of 1.08 to 1.13 is formed in the shaft member 2 that receives a torsional load, the shaft member 2 It was experimentally confirmed that the fretting fatigue strength of the fitting portion and the fatigue strength of the stress relief groove 2A are substantially equal, and that these fatigue strengths exhibit the maximum value. Therefore, by forming such a stress relief groove 2A in the shaft member 2, the fretting fatigue strength of the shaft member 2 that receives a torsional load can be increased.

[Method of designing the shaft member]
Next, a method of designing the shaft member 2 according to the present invention will be described.

As is clear from the fatigue test results shown in FIG. 10, when the stress concentration factor Kt is in the range of 1.08 to 1.13, fretting fatigue fracture at the fitting portion of the shaft member 2 and fatigue fracture at the stress relief groove 2A. is mixed (region where both fatigue fractures occur almost simultaneously), and the region where the stress concentration factor Kt is smaller than 1.08 is the region where fretting fatigue fracture occurs in the fitting portion of the shaft member 2, the stress concentration factor A region where Kt is greater than 1.13 is a region where fatigue fracture occurs in the stress relief groove 2A.

Therefore, in designing the shaft member 2, in order to cause the shaft member 2 to be fatigue-destructed at the fitting portion to the contact member 11, the stress concentration factor Kt is set smaller than 1.08, and the shaft member 2 is provided with a stress relief groove. In order to cause fatigue fracture at the 2A portion, the stress concentration factor Kt should be set larger than 1.13. In order to cause the shaft member 2 to undergo fretting fatigue fracture in the fitting hole 1a of the contact member 1 and fatigue fracture in the stress relief groove 2A portion at substantially the same time, the stress concentration factor Kt should be 1.08 to 1.13. should be set to

As a result, according to the method of designing the shaft member 2 according to the present invention, it is possible to arbitrarily set the location where the shaft member 2 breaks.

It should be noted that the present invention is not limited in application to the embodiments described above, and that various modifications are possible within the scope of the technical ideas described in the scope of claims, the specification, and the drawings. is of course.

Reference Signs List 1 contact member 1A relief groove of contact member 1a fitting hole of contact member 2 shaft member 2A stress relief groove 2a collar portion of shaft member 10 fretting fatigue test device 11 contact piece 11A relief groove of contact piece 12, 12' test piece 12A Stress relief groove of test piece 20 Pressing jig d Depth of stress relief groove Kt Stress concentration factor R Curvature radius of stress relief groove w Width of stress relief groove δ Overhang amount of contact member

Claims (7)

A fitting structure for fitting a shaft member into the fitting hole formed in the contact member,
When the stress concentration factor Kt is defined as the value obtained by dividing the difference between the principal stress when tensile force is applied and the principal stress when only pressing force is applied by the nominal stress at the minimum cross section,
A fitting of a shaft member characterized in that a stress relief groove having a shape with a stress concentration factor Kt of 1.08 to 1.13 is formed in a portion of the shaft member corresponding to an axial end of the contact member. Synthetic structure. 2. The fitting structure of the shaft member according to claim 1, wherein at least one relief groove is formed along the entire circumference at an axially intermediate position of the fitting hole of the contact member. 3. The fitting structure of the shaft member according to claim 1, wherein the axial end portion of the contact member axially overhangs the stress relief groove formed in the shaft member. A portion of the shaft member axially outside the axial end portion of the contact member and adjacent to the stress relief groove in the axial direction is fitted into the fitting hole of the contact member of the shaft member. 4. The fitting structure of the shaft member according to claim 1, wherein a flange portion having the same diameter as that of the fitting portion is formed. A method of designing a fitting structure for a shaft member according to any one of claims 1 to 4,
In the structure in which the shaft member receives a torsional load,
When the shaft member is designed so that fretting fatigue fracture occurs in the fitting portion of the contact member into the fitting hole, the stress concentration factor Kt is set to be smaller than 1.08,
When designing the shaft member so that fatigue fracture occurs in the stress relief groove portion, the stress concentration factor Kt is set to be greater than 1.13,
When designing so that both fretting fatigue failure in the fitting hole of the contact member of the shaft member and fatigue failure in the stress relief groove portion occur, the stress concentration factor Kt is set to 1.08 to 1.13. set,
A method of designing a fitting structure of a shaft member, characterized by: A fretting fatigue test method for measuring the fretting fatigue of the test member by fitting the test member to the contact member and sliding the test member relative to the contact member,
When the stress concentration factor Kt is defined as the value obtained by dividing the difference between the principal stress when tensile force is applied and the principal stress when only pressing force is applied by the nominal stress at the minimum cross section,
Forming a relief groove having a concave cross-sectional shape with a predetermined stress concentration factor in a contact portion between the contact member and the test member in either one of the contact member and the test member,
A torsional load is applied to a contact portion between the contact member and the test member by rotating either the contact member or the test member about the central axis of the test member. Fretting fatigue test method. 7. The fretting fatigue according to claim 6, wherein a contact member in contact with the test member is ultrasonically vibrated to generate fine sliding between the test member and the contact member. Test method.

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