JP2006162472A - Method, device and test piece for testing thermal fatigue - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly evaluate thermal fatigue strength of a thin sheet of a raw material for a thin wall member used in a high-temperature environment. <P>SOLUTION: A thermal fatigue test is carried out using this high-frequency induction heating type thermal fatigue testing device 20 of the present invention using a planar sheetlike thermal fatigue test piece 10, having a value with a ratio L<SB>0</SB>/t of a shoulder part length L<SB>0</SB>to a sheet thickness t, and the ratio L<SB>GL</SB>/t of a gauge length L<SB>GL</SB>to the sheet thickness t set down so as not to generate buckling, when heated in the thermal fatigue test, and is provided with heating coils 21, 21 arranged in substantially planar shape so as to face a plane of the thermal fatigue test piece 10 separated by a space and for heating the thermal fatigue test piece 10, and an extensometer 22 attached to a side face of the planar sheet-like thermal fatigue test piece 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermal fatigue test method, a thermal fatigue test apparatus, and a thermal fatigue test piece, for example, a thermal fatigue test method for evaluating the thermal fatigue strength of a thin plate that is a material of a thin member used in a high temperature environment, The present invention relates to a thermal fatigue test apparatus and a thermal fatigue test piece.

  In recent years, members that are used in a high temperature environment, such as an exhaust manifold for an automobile engine and a fuel cell reformer, have been manufactured by performing press molding or the like on a thin plate material.

  Since the temperature of this thin plate member generally varies greatly during use, the main failure mechanism of this member is thermal fatigue failure. For this reason, in order to design the durability of this member, it is necessary to grasp the thermal fatigue characteristics by conducting a thermal fatigue test using a thin plate as a test piece.

  The thermal fatigue test is a method of changing the mechanical load so as to change the strain of the test piece at the same time as changing the temperature of the test piece, and repeating the temperature change and strain change (load change). This is a test for measuring the number of repetitions until occurrence, that is, the thermal fatigue life.

  For this reason, in order to perform this thermal fatigue test, a test apparatus capable of simultaneously measuring and controlling the temperature and strain of the test piece and changing the temperature and strain of the test piece in a predetermined pattern is indispensable.

As a method for evaluating the thermal fatigue characteristics of a material, for example, there is a method described in Non-Patent Document 1. FIG. 12 is an explanatory diagram schematically illustrating the method described in Non-Patent Document 1.
As shown in FIG. 12, in this method, a round bar-shaped or cylindrical test piece 1 is used, a heating coil 2 is arranged concentrically with the central axis of the test piece on the outer periphery of the test part, and the test piece 1 is used as a high frequency induction system Heat by. In the case of a round bar test piece, the test piece 1 is cooled by blowing cooling air 3 from the outer periphery of the test section as shown in FIG. 12, and in the case of a cylindrical test piece, cooling air is blown into the inside. To do.

  A heat-resistant pressing rod 4 made of quartz glass, ceramics or the like is pressed at a predetermined interval on the outer periphery of the test piece 1, and the change in the interval accompanying the elongation of the test piece 1 results in the test piece 1. Measure the strain. In the present specification, the strain measuring device 5 having the pressing rod 4 is referred to as “extensometer”.

  In Non-Patent Document 2, as a dimension of a test piece used for a thermal fatigue test, a solid round bar test piece has a standard diameter of 10 mm, and a hollow cylindrical test piece has an outer diameter of 13 mm and a wall thickness of 1.5 mm. As a standard, it is described that the parallel part length and the gauge length (distance between two pressing rods) of the test piece are suitably 1 to 2 times the outer diameter.

  Furthermore, Non-Patent Document 3 describes that a thermal fatigue test was performed on a plate-like test piece having a thickness of 2 mm and a thermal fatigue life was evaluated by a predetermined heat pattern.

Edited by Shuji Hira, “Thermal Stress and Thermal Fatigue”, published by Nikkan Kogyosha, published on January 30, 1974, Chapter 4 Thermal Fatigue and High Temperature Low Cycle Test Method (pages 81-99) Japan Society of Materials High Temperature Strength Division Committee, Thermal Fatigue Test Method for Metal Materials (Revised 2nd Edition), Materials, Vol. 24, no. 258, (1975) Yuji Inoue, Masao Kikuchi, Satoshi Akamatsu, “Effect of Ti Addition on Thermal Fatigue Life of Nb-Containing Ferritic Stainless Steel”, CAMP-ISIJ, Vol. 16, (2003)

However, the inventions described in Non-Patent Documents 1 to 3 have the following problems.
Although Non-Patent Document 1 and Non-Patent Document 2 disclose a thermal fatigue test method using a round bar test piece or a cylindrical test piece, a thermal fatigue test method and a thermal fatigue test apparatus for a flat test piece are disclosed. It is not disclosed at all. For this reason, the thermal fatigue test method and the thermal fatigue test apparatus described in Non-Patent Documents 1 and 2 cannot properly evaluate the thermal fatigue characteristics of a member made of a flat plate.

Further, Non-Patent Document 3 simply describes “a plate-shaped test piece having a thickness of 2 mm”, and the shape and heating method of this plate-shaped test piece are not disclosed at all.
In the thermal fatigue test, a mechanical load is applied to the test piece so as to constrain the free thermal expansion of the test piece. Therefore, a large compressive load is generated on the test piece at the time of temperature rise (during thermal expansion). . For this reason, if the shape of the test piece is not designed properly, this compressive load causes the test piece to buckle and deform in the middle of the thermal fatigue test. Since it is easy to buckle and deform, it is important to establish the shape and test method of a flat specimen that can prevent buckling in order to properly evaluate the thermal fatigue life. However, Non-Patent Document 3 does not disclose how the buckling of the plate-shaped test piece is prevented.

For this reason, even if the thermal fatigue test piece described in Non-Patent Document 3 is used, there is a high possibility that buckling occurs during the thermal fatigue test and the thermal fatigue characteristics cannot be properly evaluated.
An object of the present invention is to provide a thermal fatigue test method, a thermal fatigue test apparatus, and a thermal fatigue test piece capable of appropriately evaluating the thermal fatigue strength of a thin plate that is a material of a thin member used in a high temperature environment. It is.

  A flat specimen is more likely to buckle than a round specimen or a cylindrical specimen. For this reason, when a thermal fatigue test is performed using a flat test piece, the flat test piece buckles during this test, and the strain of the gauge part (between the gauge lengths) becomes uneven. There is a concern that the relationship between the amount and the thermal fatigue life cannot be accurately determined, or that the thermal fatigue test cannot be continued to the end. In order to prevent the occurrence of such buckling, it is effective to shorten the gauge length of the flat test piece and the length between jigs.

  On the other hand, in order to perform high-frequency induction heating of the flat test piece, the outer periphery of the test part of the flat test piece is measured in the same manner as the high-frequency induction heating method for the round bar test piece described in Non-Patent Document 1 and Non-Patent Document 2. It may be thought that the surrounding heating coil may be used.

FIG. 13 and FIG. 14 are explanatory diagrams showing a situation in which the flat-plate test piece 1 ′ is subjected to high-frequency induction heating using such a heating coil.
As shown in FIGS. 13 and 14, when the heating coil 2 ′ surrounding the outer periphery of the test portion of the flat test piece 1 ′ is used, the heating coil 2 ′ is formed in a rectangular shape from the viewpoint of heating efficiency. It is necessary to reduce the distance between “and the surface of the gauge part 7 of the flat plate-shaped test piece 1”. Further, as shown in FIG. 14, in order to heat the entire gauge portion 7 to a uniform temperature, a plurality of heating coils 2 'are arranged in parallel in the axial direction (the direction of the double arrows in FIGS. 13 and 14). It is necessary to make many windings.

  For this reason, if the gauge length of the flat test piece 1 ′ and the length between jigs are simply shortened in order to prevent buckling in the thermal fatigue test, a plurality of heating coils 2 ′ arranged in parallel are arranged. It becomes difficult to secure the axial distance to such an extent that the pressing rod 4 of the extensometer 5 can be inserted toward the gauge portion 7.

  Therefore, the present inventors can uniformly heat the entire gauge length of the flat test piece and attach an extensometer to prevent the occurrence of buckling during heating during the thermal fatigue test. In order to provide a flat plate-shaped thermal fatigue test piece, a thermal fatigue test method, and a thermal fatigue test apparatus, a gauge equipped with an extensometer of a high-frequency induction heating type thermal fatigue test apparatus as shown in FIG. A curvature formed on the left and right sides of the gauge portion 10a and gripped by the thermal fatigue test apparatus and connected to the gauge portion 10a and the grip portions 10c, 10c. Stress analysis and magnetic field analysis of the thermal fatigue test piece 10 when performing a thermal fatigue test by high frequency induction heating on a flat plate thermal fatigue test piece having the portions 10b and 10b, and further, By intensive studies prototyping and evaluation of ingredients, the present invention has been completed.

  In the present invention, except for at least one side surface of a flat plate-like thermal fatigue test piece, the thermal fatigue test piece is disposed in a substantially flat shape so as to face one plane or both planes while being spaced apart from each other. A thermal fatigue test method comprising performing a thermal fatigue test using a high-frequency induction heating type thermal fatigue test apparatus including a heating coil.

  In the thermal fatigue test method according to the present invention, the thermal fatigue test piece is formed on the gauge part to which the extensometer of the thermal fatigue test apparatus is attached, and both ends of the gauge part, and is gripped by the thermal fatigue test apparatus. Between the shoulder portion, which is a distance between the two shoulder portions that are the connection points between the curvature portion and the grip portion. It is desirable that the ratio between the length and the plate thickness, and the ratio between the gauge length and the plate thickness, which is the length of the gauge portion, have values determined so that buckling does not occur during the thermal fatigue test.

  From another viewpoint, the present invention is a high-frequency induction heating type thermal fatigue test apparatus for performing a thermal fatigue test on a flat plate-like thermal fatigue test piece, except for at least one side surface of the thermal fatigue test piece. A heating coil that heats the thermal fatigue test piece and is mounted on the side surface of the flat thermal fatigue test piece. It is a thermal fatigue testing apparatus characterized by comprising a meter.

In the thermal fatigue testing apparatus according to the present invention, it is desirable that the heating coil has a substantially planar shape by forming a spiral shape or a wave shape.
From another point of view, the present invention is a gauge part to which an extensometer of a high-frequency induction heating type thermal fatigue test apparatus is attached, and formed at both ends of the gauge part, and is gripped by the thermal fatigue test apparatus. A plate-shaped thermal fatigue test piece having a grip portion and a curved portion formed in a curved shape to connect the gauge portion and the grip portion, and used for a thermal fatigue test by high frequency induction heating, wherein the curvature portion and The ratio between the shoulder length, which is the distance between the two shoulders, which is the connection point with the grip, and the plate thickness, and the ratio between the gauge length, which is the gauge portion, and the plate thickness are the thermal fatigue test. It is a thermal fatigue test piece characterized by having a value determined so that buckling does not occur at the time.

In the thermal fatigue test piece according to the present invention, it is desirable that the ratio between the length between the shoulders and the plate thickness is 30 or less and the ratio between the gauge length and the plate thickness is 12 or less.
In these thermal fatigue test pieces according to the present invention, the high-frequency induction heating is performed by a heating coil arranged in a substantially planar shape so as to be opposed to the plane of the flat plate-like thermal fatigue test piece, desirable.

  With the thermal fatigue test method, the thermal fatigue test apparatus, and the thermal fatigue test piece according to the present invention, it is now possible to appropriately evaluate the thermal fatigue strength of a thin plate that is a material of a thin member used in a high temperature environment. . As a result, it has become possible to obtain useful information for developing a thin plate that is a material of a thin member used in a high-temperature environment and for designing a mechanical structure using the thin plate.

Hereinafter, the best mode for carrying out a thermal fatigue test method, a thermal fatigue test apparatus, and a thermal fatigue test piece according to the present invention will be described in detail with reference to the accompanying drawings.
Briefly, in this embodiment, a thermal fatigue test is performed on the flat thermal fatigue test piece according to the present invention using the high-frequency induction heating type thermal fatigue test apparatus according to the present invention. Then, after explaining this thermal fatigue test piece and a thermal fatigue test apparatus, the thermal fatigue test method performed using these is demonstrated.

[Thermal fatigue test piece 10]
FIG. 1 is a two-sided view showing the shape of a thermal fatigue test piece 10 used in the present embodiment.
The thermal fatigue test piece 10 has a flat plate shape with a plate thickness t. The plate thickness t is not particularly limited. However, since the high-frequency induction heating type thermal fatigue test apparatus 20 according to the present invention described later does not heat the thermal fatigue test piece 10 from the side, it does not heat from the side when the thickness t exceeds 3 mm. Due to the uneven heating, the temperature distribution in the thickness direction of the thermal fatigue test piece 10 becomes uneven. For this reason, it is desirable that the upper limit of the plate thickness t be 3 mm.

Further, the thermal fatigue test piece 10, in plan view, and a gauge portion 10a formed in a rectangular of L _GL length, gripping portion 10c of the formed width both ends thereof is L _1, and 10c, curve And a curvature portion 10b, 10b connecting the gauge portion 10a and the grip portions 10c, 10c. Here, connection points 10e, 10e, 10e, and 10e between the curvature portions 10b and 10b and the grip portions 10c and 10c are referred to as shoulder portions. The gauge portion 10a is a portion where the pressing rod 4 of the extensometer 5 of the high-frequency induction heating type thermal fatigue test apparatus 20 according to the present invention is disposed, and the grip portions 10c and 10c are chucks of the thermal fatigue test apparatus 20. 24 and 24 for gripping.

Further, the thermal fatigue test piece 10 shown in FIG. 1 has a ratio (L ₀ / t) between the distance L ₀ between the shoulder portions 10e and 10e in the axial direction of the test piece (referred to as the length between the shoulder portions) and the plate thickness t. ), And the ratio (L _GL / t) of the gauge length L _GL which is the length of the gauge portion 10a and the plate thickness t, both using the high-frequency induction heating type thermal fatigue test apparatus according to the present invention. It has a value determined so that buckling does not occur during heating in the thermal fatigue test.

Specifically, the ratio (L ₀ / t) between the length L ₀ between the shoulders and the plate thickness t is 30 or less, and the ratio between the gauge length L _GL and the plate thickness t (L _GL / t). Is desirably 12 or less. When the ratio (L ₀ / t) is greater than 30 or the ratio (L _GL / t) is _greater than 12, heating in a thermal fatigue test using the high-frequency induction heating type thermal fatigue test apparatus according to the present invention In this case, buckling tends to occur, and the thermal fatigue characteristics cannot be properly evaluated.

The lower limit of the shoulder between the length L ₀ and the gauge length L _GL will not require limited from this point of view. However, to shorten the shoulder between the length L ₀ and the gauge length L _GL extends a total of 5 of the pressing installation interval is generally 5mm rods 4 of the high-frequency induction heating type thermal fatigue test apparatus according to the present invention From the above, it is difficult to make the gauge length L _GL less than 5 mm. For this reason, the lower limit of the gauge length L _GL is practically 5 mm.

On the other hand, reducing the between shoulder length L _0, the curvature portion 10b Along with this, although 10b becomes small, the curvature portion 10b and 10b is extremely small stress concentration on the curve portion becomes remarkable, the Since the possibility of breaking in the curved portion increases, it is desirable that the length L ₀ between the shoulders is about twice or more the gauge length L _GL .

In general, the regions 10g and 10g gripped by the chucks 24 and 24 of the thermal fatigue test apparatus 20 may be taken smaller than the gripping portions 10c and 10c, but prevent buckling during a compression load. In order to do so, it is desirable to grip the widest possible region of the gripping portions 10c, 10c. Therefore, the ratio (L _F / t) is desirably 30 or less.

  This thermal fatigue test piece 10 is for evaluating the thermal fatigue characteristics of a thin plate that is a material of a member used under a high temperature environment such as an exhaust manifold for a car engine or a fuel cell reformer, for example. Various materials are used as the material of the piece 10 in accordance with the purpose of the test, but typical materials include ferritic stainless steel such as SUS430J1L and austenitic stainless steel such as SUS310S. .

  Furthermore, since the surface roughness of the thermal fatigue test piece 10 affects the thermal fatigue characteristics, it is desirable that the thermal fatigue test piece 10 has a surface with a smoothness equal to or higher than that finished with No. 400 emery paper.

The thermal fatigue test piece 10 is obtained by high-frequency induction heating performed by heating coils 21 and 21 arranged in a substantially planar manner so as to be opposed to the flat surfaces 10d and 10d of the thermal fatigue test piece 10 which will be described later. Used for thermal fatigue test.
The thermal fatigue test piece 10 in the present embodiment is configured as described above.

[Thermal fatigue test apparatus 20]
FIG. 2 is an explanatory view showing the main part of the thermal fatigue testing apparatus 20 according to the present invention, in which FIG. 2 (a) is a perspective view, FIG. 2 (b) is a plan view, and FIG. It is a side view. FIG. 3 is a plan view showing a heating coil 21 and an extensometer 22 which are components of the thermal fatigue test apparatus 20.

As shown in FIG. 3, the thermal fatigue test apparatus 20 of the present embodiment includes a heating coil 21 and an extensometer 22 and performs a thermal fatigue test on the thermal fatigue test piece 10 described above.
As shown in FIGS. 2A to 2C, the high-frequency induction heating type heating coils 21 and 21 of the thermal fatigue test apparatus 20 for heating the gauge portion 10a of the thermal fatigue test piece 10 It arrange | positions so that the surface 10d and 10d of the test piece 10 may oppose at predetermined distance.

The heating coils 21 and 21 are disposed on a plane or a plane substantially parallel to the surfaces 10d and 10d of the thermal fatigue test piece 10 by, for example, forming a spiral shape or a wave shape.
In the present embodiment, the heating coil 21 shown in FIGS. 2 and 3 is configured in a circular spiral shape having a circular spiral shape. This is because the circular spiral shape makes the manufacture of the heating coil 21 the easiest. However, the present invention is not limited to this form.

  FIG. 4 is a two-sided view showing a flat spiral heating coil 21-1 having a linear portion in a part of the spiral shape, and FIG. 5 shows an elliptical spiral heating coil 21-2 in which the spiral shape is an ellipse. FIG. 6 is a two-sided view showing a rectangular spiral heating coil 21-3, FIG. 7 is a two-sided view showing a wavy heating coil 21-4, and FIG. It is a two-plane figure which shows the conical spiral heating coil 21-5 arrange | positioned spirally within the planar conical surface.

  The heating coil in the present invention is not limited to the circular spiral heating coil 21, but also a flat spiral heating coil 21-1, an elliptical spiral heating coil 21-2, a rectangular spiral heating coil 21-3, and a wavy shape. Heating coil 21-4, conical spiral heating coil 21-5 arranged in a spiral shape in a substantially planar conical surface, and a shape that is technically equivalent to these heating coils 21 to 21-5 Even in this case, the same effects can be obtained.

  The shape and the number of turns of the heating coil 21 are not particularly limited. For example, the coil diameter may be about 3 to 5 mm, which is typical for this type of heating coil. Further, in the case of the circular spiral heating coil 21 of the present embodiment shown in FIGS. 2 and 3, the number of turns may be about 2 to 4 turns.

  The thermal fatigue test apparatus 20 according to the present embodiment includes the heating coil 21, an apparatus that energizes the heating coil 21 to start the heating coil 21, and the thermal fatigue test piece 10 that is induction-heated by the heating coil 21. However, these additional facilities are well-known from the above-mentioned Non-Patent Documents 1 and 2, etc., and are attached to the thermal fatigue testing apparatus for round bar test pieces and cylindrical test pieces. It is only necessary to divert the equipment, and since this well-known incidental equipment is also diverted and used in the present embodiment, description of the incidental equipment is omitted.

As shown in FIG. 3, the thermal fatigue test apparatus 20 of the present embodiment includes an extensometer 22 attached to the side surface of the flat plate-like thermal fatigue test piece 10. The extensometer 22 has two pressing rods 23 made of quartz glass, ceramics, or the like, which are arranged apart by a predetermined gauge length _LGL .

  Then, the two pressing rods 23 are from the side of the thermal fatigue test piece 10, that is, from the direction perpendicular to the plate thickness direction and the load axis direction of the thermal fatigue test piece 10 (left and right direction in FIG. 3), The heat fatigue test piece 10 is pressed against the side surface of the gauge portion 10a. When the interval between the two pressing rods 23 changes with the elongation of the thermal fatigue test piece 10 during the thermal fatigue test, the strain generated in the thermal fatigue test piece 10 is measured based on the change in the interval. Can do.

The thermal fatigue test apparatus 20 according to the present embodiment includes an apparatus for automatically recording the strain value continuously output from the extensometer 22 together with the extensometer 22, and a thermal fatigue test. In this case, there is also provided ancillary equipment such as a device for measuring the load applied to the thermal fatigue test piece 10 in the case of the round bar test. The incidental equipment of the thermal fatigue test apparatus for the piece or cylindrical test piece may be used, and since this known auxiliary equipment is also used in the present embodiment, the description of the auxiliary equipment is omitted.
The thermal fatigue test apparatus 20 in the present embodiment is configured as described above.

[Thermal fatigue test method]
In the present embodiment, a thermal fatigue test is performed on the flat thermal fatigue test piece 10 described above using the above-described high-frequency induction heating thermal fatigue test apparatus 20.

Specifically, the ratio (L ₀ / t) between the length L ₀ between the shoulders and the sheet thickness t, and the ratio (L _GL / t) between the gauge length L _GL and the sheet thickness t are determined in the thermal fatigue test. A flat plate-shaped thermal fatigue test piece 10 having a value determined so that buckling does not occur during heating is disposed in a substantially flat shape so as to face the plane of the thermal fatigue test piece 10 while being spaced apart. A high-frequency induction heating type thermal fatigue test apparatus 20 comprising heating coils 21 and 21 for heating the thermal fatigue test piece 10 and an extensometer 23 attached to the side surface of the flat plate thermal fatigue test piece 10 is used. And conduct a thermal fatigue test.

The operation and procedure of the thermal fatigue test may be carried out by diverting the operation and procedure of the thermal fatigue test of a round bar test piece and a cylindrical test piece, which are well known from Non-Patent Documents 1 and 2 described above.
For this reason, according to this Embodiment, the effect listed below is show | played.

  (A) In order to heat the gauge part 10a of the thermal fatigue test piece 10 by the heating coils 21 and 21 arranged so as to be opposed to the surfaces 10d and 10d of the thermal fatigue test piece 10, as shown in FIG. Furthermore, the pressing rods 23 of the extensometer 22 can be pressed against the gauge portion 10a of the thermal fatigue test piece 10 from the side of the thermal fatigue test piece 10 at a predetermined interval. For this reason, compared with the case where the pressing rods 23 and 23 are pressed from the surfaces 10d and 10d of the gauge part 10a, the risk of inducing buckling due to the lateral load of the pressing can be greatly reduced.

  (B) By using the heating coils 21, 21 arranged in this way, for example, the thermal fatigue test piece in which the width of the heating coil must be larger than the width of the grip portion 10 c of the thermal fatigue test piece 10. Since the restriction on the shape of the heating coil due to the size of 10 is eliminated, the shape of the heating coils 21 and 21 can be freely designed.

  (C) The heating coils 21 and 21 are shaped so as to be substantially planar so as to be opposed to the flat surface 10d of the thermal fatigue test piece 10 and to cover the entire flat surface of the gauge portion 10a. Therefore, the gauge portion 10a can be uniformly heated by the heating coils 21 and 21.

(D) Since the shape of the thermal fatigue test piece 10 can be set freely by using the heating coils 21 and 21, the length L ₀ between the shoulders is set so as not to cause buckling due to the compression load in the thermal fatigue test. The ratio (L ₀ / t) with the plate thickness t and the ratio (L _GL / t) between the gauge length L _GL and the plate thickness t can be set.

(E) Specifically, by making the ratio (L ₀ / t) 30 or less and the ratio (L _GL / t) 12 or less, occurrence of buckling in the thermal fatigue test is surely prevented. Can do.
As described above, according to the present embodiment, it is possible to appropriately evaluate the thermal fatigue strength of a thin plate that is a material of a thin member used in a high temperature environment. As a result, it is possible to obtain useful information for developing a thin plate that is a material of a thin member used in a high temperature environment and for designing a mechanical structure using the thin plate.

Furthermore, the present invention will be described more specifically with reference to examples.
Plate-like heat having the test piece shape (plate thickness t, gauge length L _GL , shoulder-to-shoulder length L ₀ , ratio (L _GL / t) and ratio (L ₀ / t)) shown in FIG. 1 and Table 1 Using the thermal fatigue test apparatus 20 having the heating coil (shape, number of turns, arrangement) shown in FIG. 2, FIG. 4 or FIG. 13 and Table 1 and the extensometer 22 shown in FIG. The thermal fatigue test was conducted by pressing the pressing rods 23 and 23 of the extensometer 22 to the extensometer pressing position shown in Table 1.

  A in the column of the shape of the heating coil in Table 1 indicates a rectangular shape (comparative shape) of a form surrounding the outer periphery of the thermal fatigue test piece 1 ′ shown in FIG. 13, and B indicates a circular spiral shape shown in FIG. (Shape according to the present invention), and C represents a flat spiral shape (shape according to the present invention) having a straight portion shown in FIG.

  The thermal fatigue test piece subjected to this thermal fatigue test was collected from a cold rolled steel sheet made of ferritic stainless steel (SUS430J1L) used for automobile exhaust gas parts and the like so that the load axis direction coincides with the rolling direction. did.

  In the thermal fatigue test, the strain and temperature waveforms shown in the graph of FIG. 9 were given to the thermal fatigue test piece. That is, the temperature is varied in the range of 200 ° C. to 900 ° C., and at the same time, the elongation (strain) associated with the thermal expansion during heating is mechanically constrained by 30% and 50% (these numerical values are referred to as the constraining rate). A fatigue test was conducted. If the coefficient of linear expansion of the thermal fatigue test piece is α and the temperature fluctuation range is ΔT (700 ° C. in this embodiment), the strain fluctuation range in the graph of FIG. 9 is 0.7 when the constraint rate is 30%. × α × ΔT, and 0.5 × α × ΔT when the constraint rate is 50%. The thermal fatigue test piece was cooled by blowing cooling air from its outer periphery.

Table 1 shows the specimen shape (plate thickness t, gauge length L _GL , shoulder-to-shoulder length L ₀ , ratio (L _GL / t) and ratio (L ₀ / t) of the flat plate-like thermal fatigue test piece described above. )) And the heating coil (shape, number of windings, arrangement), as well as test no. The test result (heating suitability to 900 degreeC) about 1-13 is shown. Table 2 shows the test No. in which the thermal fatigue test could be performed. The test result about 1-10 (the presence or absence of buckling at the time of a thermal fatigue test, and the possibility of test implementation) is shown.

  Test No. in Tables 1 and 2 In Nos. 1 to 5 and 9, the shape of the thermal fatigue test piece and the shape and arrangement of the heating coil all satisfy the range defined by the present invention. In either case, the thermal fatigue test could be performed to the end while heating the thermal fatigue test piece to a predetermined temperature without causing buckling of the thermal fatigue test piece. Regardless of whether the shape of the heating coil is a circular spiral shape (heating coil shape: B) or a flat spiral shape (heating coil shape: C), the thermal fatigue test piece is at a target temperature of 900. It was also possible to heat to ° C.

  Table 3 also shows test numbers. The thermal fatigue test result of 1 is shown. The “thermal fatigue life (cycle)” in the table means the number of repetitions when the stress fluctuation range in one cycle starts to decrease due to the occurrence of cracks. It can be seen that the thermal fatigue life could be properly evaluated regardless of the constraint rate of 50% or 30%.

  Test No. 1 in Table 1 6, 7, 8, and 10 all satisfy the range defined by the present invention in the shape and arrangement of the heating coil, but the thermal fatigue test piece has a gauge part, a grip part, and a curvature part. The ratio between the length between the shoulders and the plate thickness, and the ratio between the gauge length and the plate thickness do not have values determined so that buckling does not occur during the thermal fatigue test. As a result, the thermal fatigue test could not be performed to the end.

  In addition, Test No. 11 and 12, although the shape of the thermal fatigue test piece is within the range defined by the present invention, the shape of the heating coil is a rectangular shape surrounding the outer periphery of the thermal fatigue test piece 1 'shown in FIG. Therefore, in order to secure a gap for inserting the pressing rods 23, 23 of the extensometer 22, the number of turns of the heating coil must be one or two, and the thermal fatigue test piece is up to 900 ° C. which is the target temperature. It was not possible to heat and a thermal fatigue test could not be performed.

  Furthermore, test no. 13, test no. Although the number of turns of the heating coil was increased to 3 with respect to 11 and 12, it became possible to heat the thermal fatigue test piece to the target temperature of 900 ° C., but with the increase in the number of turns of the heating coil As a result, the gap between the adjacent heating coils is narrowed, and the pressing rods 23 and 23 of the extensometer cannot be pressed against the thermal fatigue test piece, and the thermal fatigue test cannot be performed.

As described above, according to the present invention, it is possible to appropriately evaluate the thermal fatigue characteristics of a flat test piece.
In general, in order to properly evaluate the thermal fatigue characteristics of a thermal fatigue test piece by performing a thermal fatigue test, it is also important to make the temperature inside the gauge part of the thermal fatigue test piece as uniform as possible. . Therefore, also in this example, the relationship between the temperature distribution inside the gauge portion of the thermal fatigue test piece and the shape of the heating coil was examined.

FIG. 10 is an explanatory diagram showing the dimensions of the respective portions of the flat plate-like thermal fatigue test piece used in this study.
In this study, test no. 1 (heating coil shape: B (circular spiral), number of windings: 3) and test no. 2 (heating coil shape: C (flat spiral), number of turns: 3) was heated to a maximum temperature of 900 ° C., and the temperature inside the gauge portion was measured. The measurement results are shown in Table 4. For comparison, Test No. The result of 11 (heating coil shape: A (periphery surrounding shape), number of turns: 1) is also shown in the table.

  In the above three examples, the shape of the thermal fatigue test piece is the same, and as shown in FIG. 10, the plate thickness is 2 mm, the gauge portion length is 12 mm (parallel portion length is 14 mm), and the shoulder portion. The interspace length was 34 mm.

  Test No. 1 and no. In No. 2, both could be heated to 900 ° C., and the temperature difference between the central portion and the end of the gauge portion was as small as 3 ° C. or less. In contrast, test no. No. No. 11 could not be heated up to a maximum temperature of 900 ° C., and the temperature difference between the central portion and the end of the gauge portion was as large as 10 ° C.

  In order to consider the reason for the difference in temperature distribution as described above, a magnetic field analysis was performed using a finite element method, and the heat generation was evaluated using the thermal fatigue test piece shown in FIG. 10 as the analysis target. Table 5 summarizes the analysis conditions of the finite element magnetic field analysis conditions.

  Moreover, the shape of a heating coil is the coil A (periphery surrounding, 1 winding), B (circular spiral, 3 winding), and C (flat spiral, 3 winding) which were shown in the Example, and coils B and C are thermal fatigue. It arrange | positioned on both sides of the front and back of a test piece. The distance between the coil and the test piece surface was 1 mm in all cases.

  FIG. 11 is a graph showing the calorific value distribution on the central axis in the gauge on the surface of the thermal fatigue test piece. However, the vertical axis in the graph of FIG. 12 shows the dimensionless calorific value as dimensionless with the maximum value. Further, the horizontal axis is as shown in FIG. 10, and the center of the thermal fatigue test piece is the origin O.

  From the graph of FIG. 12, when the thermal fatigue test piece is heated using the coil A, only the center (X = 0) of the thermal fatigue test piece is locally heated. It can be explained that the temperature distribution cannot be made uniform.

  On the other hand, when the thermal fatigue test piece is heated using the coils B and C, there is a peak of the calorific value in the vicinity of both ends of the gauge part (X = ± 4 to 5), and the heat from the gauge part starts from these positions. It is thought that a uniform temperature distribution was obtained for the entire gauge part.

  As described above, according to this example, the thermal fatigue strength of a thin plate that is a material of a thin member used in a high temperature environment can be appropriately evaluated.

It is a two-plane figure which shows the shape of the thermal fatigue test piece used by embodiment. It is explanatory drawing which extracts and shows the principal part of the thermal fatigue testing apparatus based on this invention, Fig.2 (a) is a perspective view, FIG.2 (b) is a top view, FIG.2 (c) is a side view. It is a top view which shows the heating coil and extensometer which are the components of a thermal fatigue test apparatus. It is a double view which shows a flat spiral heating coil. It is a double view which shows an elliptical spiral heating coil. It is a double view which shows a rectangular spiral heating coil. It is a double view which shows a wavy heating coil. It is a two-view figure which shows the conical spiral heating coil arrange | positioned spirally within the substantially planar conical surface. It is a graph which shows the distortion and temperature waveform which were given to the thermal fatigue test piece in the thermal fatigue test of the Example. It is explanatory drawing which shows the dimension of each part of a flat thermal fatigue test piece. It is a graph which shows the emitted-heat amount distribution on the central axis in a gauge in the surface of a thermal fatigue test piece. It is explanatory drawing which shows the method described in the nonpatent literature 1 typically. It is explanatory drawing shown supposing the condition which carries out the high frequency induction heating of the flat test piece using a heating coil. It is explanatory drawing shown supposing the condition which carries out the high frequency induction heating of the flat test piece using a heating coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Thermal fatigue test piece 10a Gauge part 10b, 10b Curvature part 10c, 10c Grasp part 10d, 10d Plane 20 Thermal fatigue test apparatus 21, 21, 21-1 to 21-5 Heating coil 22 Extensometer 23 Pushing rod

Claims (7)

  Except at least one side surface of the flat plate-like thermal fatigue test piece, a heating coil is provided which is disposed in a substantially flat shape so as to be opposed to one plane or both planes and which heats the thermal fatigue test piece. A thermal fatigue test method comprising performing a thermal fatigue test using a high-frequency induction heating type thermal fatigue test apparatus.   The thermal fatigue test piece includes a gauge portion to which an extensometer of the thermal fatigue test device is attached, a grip portion formed on both ends of the gauge portion and gripped by the thermal fatigue test device, and in a curved shape. A length between the shoulder portion and a plate thickness that is a distance between two shoulder portions that are formed and have a curvature portion that connects the gauge portion and the grip portion, and is a connection point between the curvature portion and the grip portion. And the ratio of the gauge length, which is the length of the gauge part, and the plate thickness have values determined so that buckling does not occur during the thermal fatigue test. Thermal fatigue test method.   A high-frequency induction heating type thermal fatigue test apparatus for performing a thermal fatigue test on a plate-shaped thermal fatigue test piece, except for at least one side surface of the thermal fatigue test piece, separated from one plane or both planes. And a heating coil for heating the thermal fatigue test piece disposed substantially in a plane so as to face each other, and an extensometer attached to the side surface of the flat plate thermal fatigue test piece, Thermal fatigue testing equipment.   The thermal fatigue testing apparatus according to claim 3, wherein the heating coil exhibits the substantially planar shape by forming a spiral shape or a wave shape.   A gauge part to which an extensometer of a high-frequency induction heating type thermal fatigue test apparatus is attached, a grip part formed on both ends of the gauge part and gripped by the thermal fatigue test apparatus, and formed in a curved shape A flat plate-shaped thermal fatigue test piece for use in a thermal fatigue test by high-frequency induction heating, having a curvature portion for connecting the gauge portion and the grip portion, at a connection point between the curvature portion and the grip portion The ratio between the shoulder length and the plate thickness, which is the distance between two shoulders, and the ratio between the gauge length and the plate thickness, which is the length of the gauge portion, are buckled during the thermal fatigue test. A thermal fatigue test piece having a value determined so as not to occur.   The thermal fatigue test piece according to claim 5, wherein the ratio between the length between the shoulder portions and the plate thickness is 30 or less, and the ratio between the gauge length and the plate thickness is 12 or less.   7. The thermal fatigue according to claim 5, wherein the high-frequency induction heating is performed by a heating coil arranged in a substantially planar shape so as to be opposed to a plane of the flat plate-like thermal fatigue test piece. Test pieces.

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