JP2007278779A - Test method for thermal fatigue, test piece for thermal fatigue test, and test piece mounting joint for thermal fatigue test - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of performing an accurate thermal fatigue test without disturbing a temperature distribution between gage marks of a test piece by preventing induction heating of a gripper even in the case of a small-sized test piece, by using a hydraulic servo type material test machine capable of applying a constant repeated thermal strain to the test piece and a thermal fatigue test machine using a coil for high-frequency induction heating with a cooling nozzle. <P>SOLUTION: Each joint 1 made of a non-magnetic material comprising an adaptor 11 and a nut 12 is mounted and fixed on both ends of the test piece W, and the test piece W is gripped by grippers 21, 22 through each joint 1. As for the nut 12 of each joint 1, a chamfered part 12c having 60% or more of the thickness of the nut 12 is formed on a corner part between the end face 12a on the coil side for high-frequency induction heating and the outer circumferential surface 12b, to thereby suppress an influence exerted on a test caused by induction heating of the joint 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal fatigue test method for materials, a test piece used in the method, and a joint for mounting the test piece on a load mechanism in the thermal fatigue test, and more specifically, a small size cut out from an actual part. The present invention relates to a thermal fatigue test method for the test piece, its test piece, and a joint for mounting the test piece on a load mechanism.

  As a method of performing thermal fatigue tests on small test pieces cut out from actual parts, a temperature singularity where the coefficient of thermal expansion is smaller than that of the test piece and the coefficient of thermal expansion changes abruptly in the test temperature range. Each blade is press-fitted into both ends of the test piece so as to constrain both sides of the test piece with two holders each made of a low-expansion material and provided with blades at both ends. The test piece is constrained by a coupling means such as a bolt via an elastic member, and the heat distortion caused by the difference in thermal expansion between the test piece and the holder is repeated by repeating the heating / cooling cycle in the constrained state. A method of concentrating on the evaluation part has been proposed (see, for example, Patent Document 1).

Conventionally, a thermal fatigue testing machine that combines a hydraulic servo type material testing machine and a heating / cooling device with a high frequency induction heating coil equipped with a nozzle for blowing cooling gas directly onto the surface of the test piece. It has been known. In this thermal fatigue testing machine, the thermal strain of the test piece is constantly measured by an extensometer, and the strain of the test piece is controlled mechanically by hydraulic pressure, so that the thermal strain of the test piece is set to a preset target value. Can be matched.
JP 2003-35644 A

  By the way, according to the conventional thermal fatigue test method described above, it is possible to perform a thermal fatigue test with a relatively simple apparatus configuration. However, repeated thermal strain is caused by a difference in thermal expansion between the test piece and the holder. For this reason, there is a problem that a dimensional change accompanying a change with the lapse of time due to repeated cooling and heating of the test piece and the holder occurs, and it becomes difficult to apply the intended repetitive thermal strain.

  On the other hand, according to a thermal fatigue testing machine that combines a conventionally known hydraulic servo type material testing machine and a high frequency induction heating coil with a cooling nozzle, the elongation of each specimen is measured by an extensometer, and the measurement result Since the strain of the test piece is mechanically controlled by feedback control using the, it is possible to apply a constant thermal strain repeatedly.

  However, in a conventional thermal fatigue testing machine that combines a hydraulic servo type material testing machine and a high-frequency induction heating coil with a cooling nozzle, both ends of the test piece are directly gripped by the gripping tool, and thus cut out from the actual part. When a thermal fatigue test is performed using such a small test piece, the grip is also inductively heated because the grip is close to the high-frequency induction heating coil, and the temperature distribution of the test mark portion of the test piece There is a problem that it becomes difficult to give accurate cooling heat.

  The present invention has been made in view of such a situation. Basically, a high-frequency induction with a hydraulic servo type material tester and a cooling nozzle that can repeatedly apply a constant thermal strain to a test piece. Using a thermal fatigue testing machine with a heating coil, even for small test pieces as described above, the induction heating of the gripper is prevented and the temperature distribution in the area between the test specimens is destroyed. It is an object of the present invention to provide a thermal fatigue test method capable of performing accurate and accurate tests, a test piece for thermal fatigue test suitable for use in the method, and a joint for mounting a test piece suitable for use in the method It is said.

  In order to solve the above-described problems, the thermal fatigue test method of the present invention is configured such that the test piece is held by a high frequency induction heating coil disposed around the test piece in a state where both ends of the test piece are held by a pair of grippers. While repeating the step of heating and the step of cooling the test piece by blowing cooling gas through the nozzle provided in the high-frequency induction heating coil, each pair of detection rods of the extensometer is applied to each test point of the test piece. In the thermal fatigue test method in which a load is applied to the test piece through the pair of gripping tools so that the measurement result becomes a required value by contacting with each other, male screws are provided at both ends of the test piece. Then, each male screw is tightened to each adapter with a nut while being screwed into the female screw formed on the corresponding adapter, and the adapter is attached to each of the pair of grips. Then, the adapter and the nut are made of a non-magnetic material, and the nut has a thickness of the nut at the corner portion between the outer peripheral surface and the end surface on the high frequency induction heating coil side. It is characterized by using a chamfering of 60% or more of the thickness (Claim 1).

  Here, in the method of the present invention, the relationship between each nut and the male screw at both ends of the test piece is a relationship in which the thread of the male screw of the test piece is covered with the nut and not exposed to the outside with each nut tightened. (Claim 2) is desirable.

  In the method of the present invention, it is desirable to perform the test in a state in which the distance of the surface of the test piece with respect to the high frequency induction heating coil is 9 to 30 mm (Claim 3). Furthermore, in the method of the present invention, it is preferable that the pressing force of the extensometer detection rod against the test piece is 240 gf or more (Claim 4).

  On the other hand, the test piece for thermal fatigue test of the present invention is a test piece used in the thermal fatigue test method according to claim 1, 2, 3 or 4, and the deflection of the test piece relative to the adapter is 0.1 mm or less. (Claim 5) is desirable.

  The thermal fatigue test piece of the invention according to claim 6 is also a test piece used in the thermal fatigue test method according to claim 1, 2, 3 or 4, and the surface roughness between the gauge points is 1 .6z or less (claim 6).

  Moreover, the joint for mounting a test piece of the thermal fatigue test of the present invention is a joint comprising an adapter and a nut used in the thermal fatigue test method according to claim 1, 2, 3, 4 or 5, and the material thereof is: It is characterized by being a material having a thermal conductivity of 120 W / m · K or more.

  Further, the joint for mounting a test piece of the thermal fatigue test of the invention according to claim 8 is a joint comprising an adapter and a nut used in the thermal fatigue test method of claim 1, 2, 3, 4 or 5. The material is characterized by being a material having a tensile strength of 475 MPa or more.

  Furthermore, the joint for mounting a test piece in the thermal fatigue test of the invention according to claim 9 is a joint comprising an adapter and a nut used in the thermal fatigue test method according to claim 1, 2, 3, 4 or 5. The material is characterized by beryllium copper.

  The present invention employs a thermal fatigue testing machine that combines a hydraulic servo type material testing machine and a high-frequency induction heating coil with a cooling nozzle. The gripping tool is moved away from the high-frequency induction heating coil as much as possible, and the joint material is made of a non-magnetic material, and as a result of various experiments. .

  That is, in the thermal fatigue test method of the present invention, male threads are formed at both ends of the test piece, and the male threads at both ends are screwed into female threads formed on an adapter made of a non-magnetic material, respectively. Similarly, a nut made of a non-magnetic material is screwed and fastened to the adapter, so that a joint made of the adapter and the nut is attached to both ends of the test piece. In this state, each joint is gripped by a pair of grippers. That is, both ends of the test piece are gripped by the gripper via a joint made of a non-magnetic material so that a mechanical load is applied.

  And even if the joint is made of a non-magnetic material, it has been found that if there is a protrusion facing the high frequency induction heating coil, the joint temperature rises and an accurate test cannot be performed. Therefore, in the invention according to claim 1, the shape of the nut constituting the joint is formed in that portion in order to eliminate the protrusion (edge) at the corner portion where the end surface on the high frequency induction heating coil side and the outer peripheral surface intersect. A nut having a chamfering of 60% or more of the nut thickness was used. As a result, the temperature rise of the nut is suppressed, and as a result, it is possible to prevent the temperature distribution of the test piece from being disturbed.

  Further, in the invention according to claim 2, in addition to the above, in the state where the nut is screwed into the male screw of the test piece and tightened to the adapter, the thread of the male screw of the test piece is covered with the nut. . In other words, the thread of the test piece is hidden by the chamfered nut as described above. By adopting such a relationship between the thread and nut of the test piece, it is possible to prevent the temperature of the thread part of the male thread of the test piece from locally rising, and other than between the marks on the test piece. The part becomes difficult to be heated.

  In addition, in the thermal fatigue test, it is necessary that the temperature between the test marks of the test piece is as uniform as possible, but the small test piece has a small heat capacity, and a high frequency induction heating coil for heating the test piece and Sensitive to distance. That is, if the distance between the test piece and the coil is large, it is easy to be affected by variations in the ambient temperature, and the temperature difference between the gauge points becomes large. Conversely, when the distance is small, the test piece is easily affected by the degree of coaxiality with the high frequency induction heating coil, and the temperature difference between the gauge points becomes large. As in the invention according to claim 3, when the distance between the test piece and the high frequency induction heating coil is 9 to 30 mm, it has been found that the temperature difference between the gauge points is remarkably reduced (see FIG. 7).

  Furthermore, since the small test piece has small rigidity, it is sensitive to the pressing force of the extensometer detection rod. That is, if the pressing force of the detection rod is small, the thermal strain cannot be accurately detected because the detection rod slides on the surface of the test piece when thermal strain occurs in the test piece. As in the invention according to claim 4, when the pressing force of the extensometer detection rod against the test piece is 240 gf or more, the amount of slip of the detection rod is remarkably reduced (see FIG. 8).

  In a fatigue test, it is necessary that the strain generated between the test points of the test piece is as uniform as possible regardless of the position in the circumferential direction, but a small test piece is attached to the gripper via a joint. When gripping, since the test piece is sensitive, bending stress is likely to occur, and the distortion generated between the gauge points tends to be uneven. One of the main causes of the occurrence of bending stress in the test piece in this gripping state is the shake of the test piece with respect to the joint. Therefore, in the invention according to claim 5, the deflection amount of the test piece with respect to the joint is set to 0.1 mm or less. Such a mounting method significantly reduces the distortion difference between the gauge points (see FIG. 6).

  In a thermal fatigue test in which a test piece is heated to a high temperature, when the extensometer detection rod is brought into contact with the surface of the test piece to detect the momentary elongation, the test piece softens due to heating, and the extensometer detection rod gradually increases. It may bite into the specimen. Starting from the notch generated by this, thermal fatigue failure may occur earlier than the original life of the test piece. This is particularly likely to occur when using small test pieces. As in the invention according to claim 6, as a test piece used for this type of thermal fatigue test, when the surface roughness between the gauge points is 1.6 z or less, to the convex portion due to the roughness of the test piece surface As a result, the amount of biting into the test piece surface of the detection rod of the extensometer is remarkably reduced, and breakage from the biting portion can be suppressed (see FIG. 9).

  When a thermal fatigue test is performed by gripping a small test piece attached to a joint as in the present invention and performing a thermal fatigue test, the temperature drop rate becomes sensitive to the heat transfer coefficient of the joint because the heat capacity of the test piece is small. . When a material having a thermal conductivity of 120 W / m · K or more is used as the joint material as in the invention according to claim 7, the temperature drop rate during cooling of the test piece is remarkably increased (see FIG. 4).

  In the present invention, male screws are formed at both ends of the test piece, each male screw is screwed into a female screw formed in each adapter, and further, a nut is screwed into the male screw to fasten each adapter. The both ends of the test piece are gripped by the gripper via the joint, but with repeated heating and cooling during the test, the nut fastening torque decreases from the initial value, and the nut loosens. As a result, the stroke of the crosshead that imparts mechanical strain to the test piece becomes long, and if the time per cycle of the test conditions cannot be followed, the mechanical strain cannot be accurately applied. As described in claim 8, when a material having a tensile strength of 475 MPa or more is used as the adapter and the nut, the decrease rate of the fastening torque is remarkably reduced, and the mechanical strain initially set on the test piece is continuously increased. (See FIG. 5).

  Here, as is apparent from the above, the joint used in the present invention is not only the shape but also the material of which is an important point in conducting an accurate test. The material of the joint is preferably beryllium copper as in the invention according to claim 9. Beryllium copper is a non-magnetic material, has a high thermal conductivity, and has a corresponding tensile strength, and is suitable as a joint material when performing this type of thermal fatigue test.

  According to the present invention, even a small test piece cut out from an actual part is held in a state where both ends thereof are gripped by a pair of grippers via a joint made of a nonmagnetic material, and the high frequency induction heating coil is used. While repeating heating by cooling and cooling by blowing cooling gas from the cooling nozzle provided on the coil, the strain is detected by bringing the extensometer detection rod into contact with each gauge point, and the detected value is the target value. It became possible to perform an accurate thermal fatigue test that applied a load to the test piece by a hydraulic servo mechanism so that

  In addition, by conducting the test with the male screw thread formed on the test piece covered with a nut, the temperature of the test piece is prevented from locally rising and the temperature distribution between the gauge points is made uniform. In addition, when the amount of deflection of the test piece with respect to the adapter is 0.1 mm or less, the distortion difference between the gauge points is reduced, and an accurate test can be performed.

  Furthermore, by performing the test with the distance of the test piece surface from 9 to 30 mm with respect to the high frequency induction heating coil, the temperature difference between the gauge points can be reduced, and the pressing force of the extensometer detection rod against the test piece By setting the value to 240 g or less, the detection rod can be prevented from sliding against the surface of the test piece, and accurate distortion can be imparted.

  Furthermore, as a test piece to be used for such a test, by setting the surface roughness between the gauge points to 1.6 z or less, it is possible to suppress the high-frequency heating from being concentrated on the peak portion of the roughness, The occurrence of premature destruction of the test piece due to the biting into the test piece surface can be prevented.

  And, as a joint consisting of an adapter and nuts attached to both ends of the test piece, by using a material having a thermal conductivity of 120 w / m · K or more, the temperature drop rate is improved particularly when the test piece is cooled. Moreover, when the tensile strength of these adapters and nuts is set to 475 MPa or more, it is possible to suppress a decrease in the fastening torque of the nuts when heating and cooling are repeated, and to give an accurate distortion. By using beryllium copper as a material for such a joint, it is possible to perform an accurate test with high reproducibility that satisfies the above-mentioned conditions.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of a main part of an embodiment of the present invention, FIG. 2 is a partial cross-sectional view of the high-frequency induction heating coil 2 for one turn, and FIG. FIG.

  The test piece W has a total length of about 60 mm, and the distance between the gauge points is 20 mm. The test piece W is held by a pair of upper and lower grips 21 and 22 via each joint 1 with joints 1 to be described later attached to both ends thereof. Each of the grips 21 and 22 is attached to a hydraulic servo type material testing machine, of which a lower grip 21 is attached to a table and an upper grip 22 is attached to a crosshead. The cross head is moved up and down in the vertical direction with respect to the table by a hydraulic servo mechanism, and a load is applied to the test piece W.

  Around the test piece W, a three-turn high-frequency induction heating coil 3 is arranged. Each turn is connected to each other in series by a connection portion (not shown), and both ends of the connection portion are connected to a high-frequency power source, and a high-frequency voltage is passed from the high-frequency power source to the coil 3, whereby a test piece is obtained. W is heated by induction.

  The high frequency induction heating coil 3 has a double pipe structure in which two square pipes 31 and 32 are arranged inside and outside as shown in FIG. A cooling gas is flowed inside, and a number of nozzles 31a are formed in the circumferential direction on the inner wall body. By blowing the cooling gas from each nozzle 31a toward the inner test piece W, The test piece W can be cooled. Cooling water for cooling the coils themselves flows through each outer pipe 32.

  As shown in FIG. 3, the test piece W is gripped by the grips 21 and 22 with the joints 1 attached to both ends thereof. That is, the joint 1 is constituted by an adapter 11 and a nut 12, and the adapter 11 is formed with a female screw 11 a at one end surface thereof. A male thread Wa is formed at both ends of the test piece W. The male thread Wa is screwed into the female thread 11a of the adapter 11 and is tightened with a nut 12 from the center side, so that a joint is formed at both ends of the test piece W. 1 is attached and fixed. In this state, the adapters 11 of the joints 1 on both sides are gripped by the grips 21 and 22, and the test is performed.

  The nut 12 is chamfered to 60% or more of its thickness (axial dimension) at the corner portion between the end surface (end surface opposite to the adapter 11) 12a and the outer peripheral surface 12b on the high frequency induction heating coil 3 side. 12c is formed. The nut 12 is in a state in which the thread 1 of the male screw Wa formed on the test piece W is covered with the joint 1 mounted and fixed to the test piece W. The adapter 11 and the nut 12 are both made of beryllium copper.

  The two detection bars 41 and 42 of the extensometer 4 are in contact with the two test points of the test piece W so as to pass between the high frequency induction heating coils 3. The momentary elongation between the test marks of the test piece W is measured.

  In the above configuration, the test piece W is repeatedly heated by the high-frequency induction heating coil 3 and cooled by blowing a cooling gas from the nozzle 31a. The crosshead to which the upper gripping tool 22 is attached moves up and down so that the preset elongation is applied to the test piece W by feeding back the measurement result of the momentary elongation to the target value.

  In such a thermal fatigue test, the joint 1 is a non-magnetic material, and the nut 12 is not chamfered due to the chamfering of the nut 12, so that it is not locally induction heated. In addition, since all the threads of the male thread Wa of the test piece W are covered by the nut 12, high-frequency heating does not concentrate on the thread of the male thread Wa of the test piece W.

  Beryllium copper has an advantage of 120 to 130 W / m · K in thermal conductivity, and has an advantage that the temperature drop rate when the test piece W is cooled is fast, and the test time can be shortened. The result of investigating the relationship between the thermal conductivity and the rate of temperature decrease between the test points of the test piece W, specifically the rate at which the temperature decreases from 250 ° C. to 50 ° C., by changing the material of the joint 1 in various ways Is shown graphically in FIG. As is apparent from this graph, it was found that the use of a material having a thermal conductivity of 120 W / m · K or more as the material of the joint 1 markedly increases the cooling rate in the cooling process of the test piece W.

  Moreover, the tensile strength of beryllium copper is 500 MPa or more, and the decrease rate of the fastening torque between the adapter 11 and the nut 12 is small even after repeated cycles, and mechanical strain can be continuously applied. The material of the joint 1 was changed in various ways, and the relationship between the tensile strength and the decrease rate of the fastening torque between the adapter 11 and the nut 12 after a certain cold / heat cycle elapsed was investigated. That is, the result of investigating the decrease rate of the fastening torque between the adapter 11 and the nut 12 after 100 cycles at 50 to 250 ° C. is shown in a graph in FIG. As is apparent from this graph, by using a material having a tensile strength of 475 MPa or more, the reduction rate of the fastening torque is remarkably reduced, and the mechanical strain set initially can be continuously applied to the test piece W. understood.

  Moreover, when attaching the test piece W with respect to the coupling 1, it turned out that a bending stress will generate | occur | produce in the test piece W and the distortion difference within a gauge will arise if these mutual deflection | deviation amounts become large. That is, FIG. 6 is a graph showing the result of measuring the total strain range difference between the test points of the test piece W by changing the shake amount in various ways. As shown in this graph, it has been clarified that the distortion difference between the gauge points is remarkably reduced by setting the shake amount to 0.1 mm or less.

  Furthermore, as a result of changing the distance between the surface of the test piece W and the high frequency induction heating coil 3 in various ways and measuring the temperature difference between the gauge points of the test piece W, the distance is preferably 9 to 30 mm. I found out. FIG. 7 shows the result. By setting the distance between the surface of the test piece W and the high-frequency induction heating coil 3 to 9 to 30 mm, the temperature difference between the gauge points is significantly reduced. In the thermal fatigue test, it is desirable that the temperature between the marks of the test pieces is as uniform as possible. If the temperature is 9 mm or less, the test piece and the high frequency induction heating coil 3 are easily affected by the coaxiality. It has been found that the temperature difference is large, and when it is 30 mm or more, it is easily affected by variations in the ambient temperature.

  Since the rigidity of the small test piece is small, thermal strain occurs in the test piece W unless the pressing force of the detection rods 41 and 42 of the extensometer 4 on the surface of the test piece W is increased to some extent. As a result, it was found that the detection rods 41 and 42 slipped on the surface of the test piece W, and the thermal strain cannot be measured accurately. FIG. 8 shows the results of measuring the amount of slip of the detection rods 41 and 42 of the extensometer 4 with respect to the surface of the test piece W by variously changing the pressing force. As is clear from this graph, it has been found that the slip amount is remarkably reduced by setting the pressing force to 240 gf or more.

  When the detection rods 41 and 42 of the extensometer 4 are pressed with a certain level of force while the test piece W is heated, the detection rods 41 and 42 gradually bite into the test piece W due to softening of the test piece due to heating. As a result, the test piece may be subject to thermal fatigue failure, and an accurate test result cannot be obtained. This problem is likely to occur particularly in a small test piece in which the diameter of the parallel part of the test piece is small. Softening due to induction heating of the test piece W can be suppressed by reducing the surface roughness of the test piece W. That is, it has been found that by suppressing the concentration of high-frequency induction heating on the minute convex portions caused by the surface roughness of the test piece W, the detection rods 41 and 42 caused by softening of the test piece W can be prevented. . FIG. 9 is a graph showing the results of performing a thermal fatigue test with various changes in the surface roughness of the test piece W, and measuring the relationship between the surface roughness of the test piece W and the penetration depth of the detection rods 41 and 42 into the test piece W. It shows with. As shown in this graph, when the surface roughness (between marks) of the test piece W is 1.6 z or less, the biting depth of the detection rods 41 and 42 is remarkably reduced, and the test starting from the biting portion is performed. Breakage of the piece W can be suppressed.

It is a fragmentary sectional view which shows the principal part structure of embodiment of this invention. It is a fragmentary sectional view for 1 turn of the high frequency induction heating coil 3 in FIG. FIG. 2 is a partial cross-sectional front view showing a state in which a joint 1 is mounted on a test piece W used in FIG. 1. 4 is a graph showing the results of investigation on the relationship between the thermal conductivity of the joint 1 and the temperature drop rate between the test marks of the test piece W. It is a graph which shows the result of having investigated the tensile strength of the adapter 11 and the nut 12 which comprise the coupling 1, and the decreasing rate of the fastening torque between these after giving a heat cycle. 4 is a graph showing the results of investigating the relationship between the amount of deflection of a test piece W relative to a joint 1 and the strain difference between gauge points. It is a graph which shows the investigation result of the relationship between the distance of the surface of the test piece W and the high frequency induction heating coil 3, and the temperature difference between the test marks of the test piece W. 4 is a graph showing the results of an investigation of the relationship between the pressing force of the detection rods 41 and 42 of the extensometer 4 on the surface of the test piece W and the amount of slip on the surface of the test piece W. 4 is a graph showing the results of an investigation of the relationship between the surface roughness of a test piece W and the amount of biting of a detection rod of an extensometer 4;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Joint 11 Adapter 11a Female thread 12 Nut 12c Chamfering 21, 22 Grasping tool 3 High frequency induction heating coil 31a Cooling nozzle 4 Extensometer 41, 42 Detection rod W Test piece Wa Male thread

Claims (9)

With both ends of the test piece held by a pair of grippers, the test piece is heated by a high frequency induction heating coil arranged around the test piece, and a nozzle provided in the high frequency induction heating coil is used. While repeating the process of cooling the test piece by blowing a cooling gas, the pair of detection rods of the extensometer is brought into contact with each test point of the test piece and the elongation is measured. In the thermal fatigue test method of applying a load to the test piece through the pair of grips so as to be a value,
Male screws are formed at both ends of the test piece, and each male screw is tightened to each adapter with a nut in a state of being screwed into a female screw formed on the corresponding adapter, and the adapter is attached to each of the pair of grips. The adapter and the nut are made of a non-magnetic material, and the nut has a thickness of the nut at the corner portion between the outer peripheral surface and the end surface on the high frequency induction heating coil side. A thermal fatigue test method characterized by using a chamfering of 60% or more of the thickness.   2. The relationship between the nuts and the male screws at both ends of the test piece is such that the thread of the male screw of the test piece is covered with the nut and not exposed to the outside when the nuts are tightened. The thermal fatigue test method described in 1.   The thermal fatigue test method according to claim 1 or 2, wherein the test is performed in a state where the distance of the surface of the test piece with respect to the high frequency induction heating coil is 9 to 30 mm.   The thermal fatigue test method according to claim 1, 2 or 3, wherein a pressing force of the extensometer detection rod against the test piece is 240 gf or more. A test piece used in the thermal fatigue test method according to claim 1, 2, 3, or 4,
A test piece for a thermal fatigue test, characterized in that the amount of deflection of the test piece relative to the adapter is 0.1 mm or less. A test piece used in the thermal fatigue test method according to claim 1, 2, 3, or 4,
A test piece for thermal fatigue testing, characterized in that the surface roughness between the gauge points is 1.6 z or less. A joint comprising an adapter and a nut used in the thermal fatigue test method according to claim 1, 2, 3 or 4,
A joint for mounting a test piece in a thermal fatigue test, characterized in that the material is a material having a thermal conductivity of 120 W / m · K or more. A joint comprising an adapter and a nut used in the thermal fatigue test method according to claim 1, 2, 3 or 4,
A joint for mounting a test piece in a thermal fatigue test, characterized in that the material is a material having a tensile strength of 475 MPa or more. A joint comprising an adapter and a nut used in the thermal fatigue test method according to claim 1, 2, 3 or 45,
A joint for mounting a test piece for a thermal fatigue test, characterized in that the material is beryllium copper.

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