KR101956349B1 - Fatigue Life Prediction Method by High Frequency Heat Treatment of Automobile Drive Shaft Using Specimen and Specimen and Induction Heating Coil for Heat the Specimen - Google Patents

Abstract

The present invention relates to a method for predicting fatigue life according to a high frequency heat treatment of an automobile drive shaft using a specimen, and a specimen and an induction heating coil for heat treatment of the specimen. The fatigue life predicting method includes: a hardening depth calculating step of determining a hardening depth of a surface of a drive shaft through high frequency heat treatment; A torsional fatigue specimen processing step of using a metal material to be used as the drive shaft to process a specimen to be used in a twist test instead of an actual drive shaft; A specimen high frequency heat treatment step of subjecting the specimen prepared through the specimen processing step to a high frequency heat treatment and curing the specimen to a depth proportional to the hardening depth calculated through the hardening depth determination step; A test progress step of testing the specimen obtained through the high-frequency heat treatment step while applying a twisting force while setting the specimen on the test apparatus; And a life prediction and evaluation step of evaluating the fatigue life of the automobile drive shaft using the data obtained through the test progress step.
The fatigue life prediction method as described above can estimate the fatigue life and the property value of the drive shaft even when the shape of the drive shaft is changed by taking the material unit fatigue test method and predict the service life of the automobile drive shaft using the specimen .

Description

{Fatigue Life Prediction Method for High Temperature Heat Treatment of Automobile Driving Shaft Using Induced Heating Coil for Heat Piping for Specimen and Specimen Specimen}

More particularly, the present invention relates to a method for predicting fatigue life according to a high-frequency heat treatment of an automobile drive shaft using a specimen, and a specimen and an induction heating coil for heat treatment of the specimen.

The automotive drive shaft is a key part of the power transmission system that transmits the high torque generated by the engine to the wheels. Such a drive shaft must be able to withstand the torque of the engine and the actual load generated during running, and it must have high strength and rigidity as well as fatigue strength performance. In particular, a high frequency heat treatment as a post process is applied to satisfy the above physical properties.

On the other hand, the general drive shaft design has been developed to meet the safety factor through the design of static strength and stiffness, and evaluates the part demand performance through finite element analysis and simple test.

However, fatigue life, which is an index of fatigue failure performance, is difficult to evaluate using finite element analysis due to changes in material properties due to high frequency heat treatment. Therefore, the prototype is subjected to high frequency heat treatment and a fatigue test is performed to judge whether the life expectancy of the drive shaft is satisfied.

However, the fatigue test is carried out by subjecting the prototype product to high-frequency heat treatment and fatigue for a long period of time, which leads to an increase in the product development cost and a long development period.

Accordingly, in order to develop a reliable component in which short-term fatigue failure does not occur, a method of applying a fatigue life evaluation technique that reflects physical property values of a material varying with heat treatment degree to a high-frequency heat- Is required.

Korean Patent Registration No. 10-0851148 (Durability analysis method of weld portion of steel sheet for automobile)

The present invention has been made to overcome the above problems, and it is an object of the present invention to provide a method of predicting the service life of an automobile drive shaft using a test piece capable of evaluating a fatigue life and obtaining a physical property value even if the shape of a drive shaft is changed, The purpose is to provide.

It is another object of the present invention to provide a specimen which can be heat-treated to obtain a material property value reflecting a material characteristic according to a high-frequency heat treatment process.

It is another object of the present invention to provide an induction heating coil for heat treatment of a specimen, which can easily perform a high frequency heat treatment on a specimen and adjust a depth of curing.

In order to accomplish the above object, a fatigue life predicting method according to a high frequency heat treatment of an automobile drive shaft using a test piece of the present invention comprises: a curing depth calculating step of determining a curing depth of a surface of a drive shaft through high frequency heat treatment; A torsional fatigue specimen processing step of using a metal material to be used as the drive shaft to process a specimen to be used in a twist test instead of an actual drive shaft; A specimen high frequency heat treatment step of subjecting the specimen prepared through the specimen processing step to a high frequency heat treatment and curing the specimen to a depth proportional to the hardening depth calculated through the hardening depth determination step; A test progress step of testing the specimen obtained through the high-frequency heat treatment step while applying a twisting force while setting the specimen on the test apparatus; And a life prediction and evaluation step of evaluating the fatigue life of the automobile drive shaft using the data obtained through the test progress step.

Further, in the test progressing step, A static torsional test process, a repeated strain control incremental test process, and a cyclic strain control fatigue test process.

In order to achieve the above object, the present invention provides a specimen for use in evaluating the torsional fatigue life of a high-frequency heat-treated automobile drive shaft, which is fixed to a repeated torsion test apparatus for providing a torsional force in the opposite direction, And a rupture portion located between the chuck portions and fractured by an applied twisting force, wherein a minimum diameter of the rupture portion is 0.66 times or more and less than 1 times the thickness of the chuck portion.

In order to achieve the above object, the induction heating coil of the present invention forms a desired hardening depth in a specimen by applying a high-frequency heat to a rod-shaped specimen used for evaluating a torsional fatigue life of a high- And a high-frequency induction unit for applying high-frequency energy applied from the outside to the high-frequency output unit, wherein the high-frequency induction unit is fixed while passing the specimen through the inner region thereof, .

Further, the high-frequency output section is characterized in that it takes the form of a partial arc having one side open.

The method of predicting the fatigue life according to the high-frequency heat treatment of the automobile drive shaft using the test piece of the present invention as described above is a method of estimating the fatigue life of the automobile drive shaft by using the material unit fatigue test method, The lifetime of the automobile drive shaft can be predicted by the high-frequency heat treatment.

In addition, the induction heating coil for heat treatment of a specimen according to the present invention can easily perform a high-frequency heat treatment on a specimen and adjust the depth of curing.

1 is a flowchart showing a method of predicting fatigue life according to high frequency heat treatment of an automobile drive shaft using a test piece according to an embodiment of the present invention.
FIGS. 2 and 3 are views showing a test piece and an induction heating coil used for the fatigue life prediction method according to an embodiment of the present invention.
4 is a side view of the specimen shown in FIG.

Hereinafter, one embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

As is known, the fatigue test is divided into two types. One is the component fatigue test method that tests the fatigue life of a structure or a component itself or a part to evaluate the fatigue life. The other is the fatigue test using the same material as the material used for the structure or machine parts. Material unit fatigue test.

The fatigue life prediction method covered in this embodiment corresponds to the material fatigue test. That is, a specimen having the same material as the drive shaft used in a car, as well as a high-frequency heat treatment (heat treatment depth is calculated in a proportional manner) identical to the high frequency heat treatment performed on a drive shaft of an automobile is manufactured, And a process of obtaining data.

1 is a flowchart showing a method of predicting fatigue life according to high frequency heat treatment of an automobile drive shaft using a test piece according to an embodiment of the present invention.

As shown in the figure, the method for predicting fatigue life according to the high-frequency heat treatment according to the present embodiment includes a curing depth calculating step 101, a torsional fatigue specimen processing step 103, a specimen high frequency heat treatment step 105, A step 107, and a life prediction and evaluation step 109. [ The depth of hardening refers to the depth of the metal structure of the hardened specimen through the high frequency heat treatment.

The hardening depth calculating step 101 is a process of determining a thermal processing depth to be formed on the test piece, and the hardening depth varies depending on the hardening depth formed on the actual driving shaft.

For example, if the heat treatment curing depth formed on a drive shaft having a diameter of 25 mm is 5 mm, the cure depth ratio is 40%. These ratios apply to the Psalms. For example, when the minimum diameter of a specimen is 8 mm, the depth of the specimen is 1.6 mm, which is 40% of the diameter.

If the hardening depth is determined through the elongation depth calculation step (101), the specimen is manufactured through the torsional fatigue specimen preparation step (103). The specimen can be fabricated using SAE10B38M2 steel and takes the form of Fig. The shape of the specimen 11 will be described later.

The subsequent specimen RF heat treatment step 105 is a process of forming a heat treatment layer having a hardened depth estimated by applying high frequency energy to the specimen.

An induction heating coil 13 of the type shown in FIG. 2 is used to perform the high frequency heat treatment step 105.

2 and 3, the induction heating coil 13 includes a partially arc-shaped high-frequency output section 13a which is open to one side, and a high-frequency generating section 13b which is integrated with the high-frequency output section 13a, And a high frequency induction portion 13b connected to the high frequency induction portion 15a.

In particular, the induction heating coil 13 takes the form of a hook, and the specimen 11 can be received at an arbitrary position in the longitudinal direction of the specimen 11 to be accommodated therein. The diameter of the high frequency output portion 13a is sufficiently large to accommodate the test piece 11.

The high-frequency output section 13a outputs high-frequency energy in a state of accommodating the test piece 11 to harden the metal structure of the test piece 11. In particular, while the high-frequency output section 13a outputs high-frequency energy, the specimen 11 is linearly moved in the longitudinal direction so that the entire surface of the specimen 11 is heat-treated.

It is natural that the curing depth of the specimen 11 can be varied depending on the setting conditions of the high frequency heat treatment process such as the feed rate and the delay time of the specimen and the output of the high frequency output section 13a. The desired setting depth can be formed by appropriately adjusting the setting conditions.

The subsequent test progressing step 107 is a step of proceeding with the specimen 11 having been subjected to the high-frequency heat treatment in a state where it is mounted on the testing apparatus. The static torsion testing step 107a, the repeated strain control incremental step testing step 107b, And a control fatigue testing process 107c.

For reference, the test apparatus is a device for applying repetitive twisting forces in a state where the two side portions 11a of the specimen are fixed by being fixed, and has a fixing chuck, a rotary shaft, a control panel portion, and the like. The control panel unit collects and stores data acquired through the torque sensor.

The static torsional test process 107a is a process of looking at the static torsional behavior of the specimen 11 and calculating the shear modulus (G).

In addition, the repeated strain control incremental step test step 107b is a test for observing the hardening or softening phenomenon caused by the repeated deformation of the material and obtaining the repeated stress-strain curve.

The stress-strain curve in the form of a stabilized hysteresis loop as shown below can be obtained by proceeding to the repeated strain control incremental step test step 107b. By connecting the vertices in a stabilized hysteresis loop graph, you can obtain the cyclic stress-strain curve by curve fitting on the formula.

,

= 비틀림 전단변형률 진폭

,

= Torsional shear strain amplitude

= 비틀림 전단응력 진폭

= Torsional shear stress amplitude

= 재료의 전단 탄성계수 (Shear Modulus)

= Shear modulus of material (shear modulus)

= 반복 강도계수 (Cyclic Strength Coefficient)

= Cyclic Strength Coefficient

= 반복 변형률 경화지수 (Cyclic Strain Hardening Exponent)

= Cyclic Strain Hardening Exponent

[Equation 1]

[Stress-strain diagram]

On the other hand, the cyclic strain control fatigue testing process 107c is a process of using several identical specimens to obtain a strain-life diagram.

The strain-life diagram is expressed as the sum of the elastic deformation fatigue life relation and the plastic deformation fatigue life relation. The elastic deformation fatigue life relation is based on the elastic deformation fatigue life relation proposed by Basquin, The relational expression uses the relation proposed by Manson-Coffin. The fatigue properties of the strain-life diagram can be obtained through the following graph.

= 피로 전단강도계수 (Fatigue Shear Strength Coefficient)

Fatigue Shear Strength Coefficient (Fatigue Shear Strength Coefficient)

= 피로 전단연성계수 (Fatigue Shear Ductility Coefficient)

Fatigue Shear Ductility Coefficient

 bt = Fatigue Strength Exponent

 ct = Fatigue Ductility Exponent

[Equation 2]

This cyclic strain control fatigue test 107c proceeds by determining 8 to 10 different strain amplitudes. At this time, the infinite life-time criterion (Run-out) of the fatigue test is set to 2,000,000 cycles.

In order to estimate the elastic strain and plastic strain at a given strain amplitude, it is necessary to obtain a stress-strain curve in the form of a stabilized hysteresis loop obtained in a state in which the fatigue test is sufficiently advanced. In the fatigue test, Torque data can be collected and utilized as a stabilized hysteresis loop by temporarily delaying the test equipment when it is determined that the variation has remained constant as the number of iterations has been sufficiently maintained while monitoring the angle-torque data.

In particular, the fatigue life is defined as the number of repetitions when the load carrying capacity is reduced by 50% of the initial load, citing ASTM E606 / E606M.

The material properties and the fatigue properties obtained by the above tests are used as quantitative evaluation of the fatigue life evaluation of the drive shaft through the fatigue analysis, which is a finite element analysis.

If the test progress step 107 is completed, the horizontal prediction and evaluation step 109 is performed. The lifetime and evaluation step 109 is a process for evaluating the fatigue life of an automobile drive shaft by synthesizing the data collected through the above test step 107. [

FIGS. 2 and 3 are views showing a test piece 11 and an induction heating coil 13 used for the fatigue life prediction method according to an embodiment of the present invention. 4 is a side view of the specimen shown in Fig. 2. Fig.

As shown in the drawing, the specimen 11 used for the progress of the fatigue life prediction method according to the present embodiment takes the form of a rod and has a chuck portion 11a at both ends and a rupture portion 11b at the center . This structure is considered to allow sufficient torsional shear deformation to occur even at small angles.

The chuck portion 11a has a square cross-sectional shape as a portion of the chuck portion of the test apparatus. The rupture portion 11b is a portion that is broken by the twisting force applied to the chuck portion 11a. That is, the portion to be broken is included in the inner range of the rupture portion 11b.

In addition, as described above, the minimum diameter D2 of the breaking portion 11b is smaller than the thickness D1 of the breaking portion 11b. As described above, the minimum diameter D2 is 0.66 times or more and less than 1 times the thickness D2 of the rupture portion.

3, the high frequency output portion 13a of the induction heating coil 13 has a minimum diameter capable of accommodating the chuck portion 11a therein. In particular, the specimen 11 can be held in the inside of the specimen 11 by taking the form of a hook, anywhere in the longitudinal direction of the specimen 11.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

11: Psalm 11a: chuck
11b: rupture portion 13: induction heating coil
13a: high frequency output section 13b: high frequency induction section
15:

Claims (5)

Frequency heat is applied to the rod-shaped specimen used for evaluating the torsional fatigue life of the high-frequency heat-treated automobile drive shaft to form a desired hardening depth in the specimen,
Wherein the specimen includes a chuck portion having a square cross section fixed to a repeated torsion testing apparatus provided with a twisting force in the opposite direction and a rupture portion located between the chuck portions and fractured by an applied twisting force, The diameter is 0.66 times or more and less than 1 times the thickness of the chuck,
A high-frequency output unit having a predetermined inner region that can be fixed while passing through the specimen and applying a high-frequency heat to the specimen when the specimen is moved in the longitudinal direction;
And a high frequency induction unit for applying high frequency energy externally applied to the high frequency output unit,
Wherein the high-frequency output unit and the high-frequency induction unit are integrally formed. The method according to claim 1,
Wherein the high-frequency output section takes the form of a partial arc having one side opened. A method for predicting fatigue life using an induction heating coil for heat treatment of a specimen according to claim 1 or 2,
A hardening depth calculating step of determining a hardening depth of the surface of the drive shaft through high frequency heat treatment;
A torsional fatigue specimen processing step of processing a specimen to be used for a torsional test instead of an actual drive shaft by using the same material as the metal material to be used as the drive shaft;
A specimen high frequency heat treatment step of subjecting the specimen prepared through the specimen preparation step to a high frequency heat treatment and curing the specimen to a depth proportional to the depth of curing calculated through the curing depth calculation step;
A test progress step of testing the specimen obtained through the high-frequency heat treatment step while applying a twisting force while setting the specimen on the test apparatus;
And estimating a fatigue life of the automobile drive shaft using the data obtained through the test progression step. The method of predicting fatigue life according to the high frequency heat treatment of an automobile drive shaft using a specimen. The method of claim 3,
In the test progress step,
A static torsional test process, a repeated strain control incremental test process, and a cyclic strain control fatigue test process. The method of predicting fatigue life according to high frequency heat treatment of automobile drive shafts using a specimen. delete

Images