JP2021076402A - Method and apparatus for specifying fatigue limit stress - Google Patents

Abstract

To specify fatigue limit stress of a measurement object at a lower cost and in a simple manner as compared to a case when using a quantum infrared camera by measuring dissipation energy without using an expensive quantum infrared camera.SOLUTION: An apparatus for specifying the fatigue limit stress includes: a vibrator 3 which applies successively increasing cyclic loads of tension and compression to a measurement object 2 at a predetermined frequency; a heat flow sensor 1 which is attached to the measurement object 2 and measures a heat flux; and an analyzer 6 which performs frequency analysis of the heat flux measured by the heat flow sensor 1 and measures dissipation energy from a frequency component of a second harmonic of the predetermined frequency. The fatigue limit stress of the measurement object is specified from the measurement result of the dissipation energy.SELECTED DRAWING: Figure 3

Description

本発明は、疲労限度応力の特定方法及び特定装置に関する。 The present invention relates to a method and an apparatus for specifying a fatigue limit stress.

引張と圧縮の繰り返し荷重を測定対象物に加え、測定対象物を赤外線カメラで撮影し、赤外線カメラで得られた温度データから散逸エネルギーを計測し、疲労破壊が進展するか否か特定する方法が特許文献１に開示されている。 A method of applying a repeated load of tension and compression to the object to be measured, photographing the object to be measured with an infrared camera, measuring the dissipated energy from the temperature data obtained by the infrared camera, and identifying whether fatigue failure progresses or not. It is disclosed in Patent Document 1.

また、順次増加する引張と圧縮の繰り返し荷重を所定の基本周波数で測定対象物に加え、測定対象物を量子型赤外線カメラで撮影し、量子型赤外線カメラで撮影した温度画像から散逸エネルギーを計測して、測定対象物の疲労限度応力を特定する方法が、特許文献２〜４に開示されている。特許文献２及び３では、温度の第２高調波成分を散逸エネルギーとして取得し、散逸エネルギーが急増する応力振幅を疲労限度応力として特定する方法が開示されている。特許文献４では、温度の基本周波数振幅と第２高調波振幅との関係から、測定対象物の疲労限度応力を特定する方法が開示されている。 In addition, a repeating load of tension and compression that gradually increases is applied to the object to be measured at a predetermined basic frequency, the object to be measured is photographed with a quantum infrared camera, and the dissipated energy is measured from the temperature image taken by the quantum infrared camera. A method for specifying the fatigue limit stress of the object to be measured is disclosed in Patent Documents 2 to 4. Patent Documents 2 and 3 disclose a method of acquiring the second harmonic component of temperature as dissipated energy and specifying the stress amplitude at which the dissipated energy rapidly increases as fatigue limit stress. Patent Document 4 discloses a method of specifying the fatigue limit stress of a measurement object from the relationship between the fundamental frequency amplitude of temperature and the second harmonic amplitude.

その他、安価に疲労限度応力を特定する試みとして、セラミックコンデンサーの容量の温度依存性を利用して、測定対象物の平均温度の上昇量を計測し、平均温度上昇量と応力振幅との関係において、平均温度上昇量が急増する応力振幅を疲労限度応力として特定する方法が非特許文献１に開示されている。また、熱型赤外線カメラを用いて、同様に測定対象物の平均温度の上昇量を計測し、平均温度上昇量と応力振幅との関係において、平均温度上昇量が急増する応力振幅を疲労限度応力として特定する方法が非特許文献２に開示されている。 In addition, as an attempt to identify the fatigue limit stress at low cost, the amount of increase in the average temperature of the object to be measured is measured using the temperature dependence of the capacitance of the ceramic capacitor, and the relationship between the amount of increase in the average temperature and the stress amplitude is measured. Non-Patent Document 1 discloses a method of specifying a stress amplitude in which an average temperature rise rapidly increases as a fatigue limit stress. In addition, the amount of increase in the average temperature of the object to be measured is measured in the same manner using a thermal infrared camera, and the stress amplitude at which the amount of increase in the average temperature increases rapidly in relation to the amount of increase in the average temperature and the stress amplitude is the fatigue limit stress. Non-Patent Document 2 discloses a method for specifying the above.

また、非特許文献３において、高価な量子型赤外線カメラ及び安価な熱型赤外線カメラを用いて、温度の第２高調波振幅及び平均温度上昇量を計測し、それぞれの場合における疲労限度応力の特定精度が検討されている。その結果、平均温度上昇量は熱伝導の影響を受け易いため、疲労限度応力を精度良く特定するためには温度の第２高調波振幅を用いる必要があることと、高価な量子型赤外線カメラでは温度の第２高調波振幅を計測できるが、安価な熱型赤外線カメラでは温度の第２高調波振幅を計測するのに感度が不十分であることが報告されている。 Further, in Non-Patent Document 3, the second harmonic amplitude and the average temperature rise of the temperature are measured by using an expensive quantum infrared camera and an inexpensive thermal infrared camera, and the fatigue limit stress in each case is specified. Accuracy is being considered. As a result, since the average temperature rise is easily affected by heat conduction, it is necessary to use the second harmonic amplitude of temperature in order to accurately identify the fatigue limit stress, and in an expensive quantum infrared camera, Although it is possible to measure the second harmonic amplitude of temperature, it has been reported that an inexpensive thermal infrared camera is insufficiently sensitive to measure the second harmonic amplitude of temperature.

また、非特許文献４には機械構造用炭素鋼Ｓ２５Ｃの引張圧縮疲労限度応力が開示されており、非特許文献５には散逸エネルギー（温度の第２高調波）から機械構造用炭素鋼Ｓ４５Ｃの疲労限度応力を特定する方法が開示されている。 Further, Non-Patent Document 4 discloses the tensile compressive fatigue limit stress of the carbon steel S25C for mechanical structure, and Non-Patent Document 5 discloses the carbon steel S45C for mechanical structure from the dissipated energy (second harmonic of temperature). A method of identifying the fatigue limit stress is disclosed.

特開２００６−２５０６８３号公報Japanese Unexamined Patent Publication No. 2006-250683 特開２０１０−２２３９５７号公報Japanese Unexamined Patent Publication No. 2010-223957 特開２０１６−２４０５６号公報Japanese Unexamined Patent Publication No. 2016-24506 特開２０１８−１０５７０９号公報JP-A-2018-105709

大野啓充，鯉渕興二，高見克己，“無接触温度測定による回転曲げ疲労限度の推定”，材料，Vol.16，No.161(1967)，pp.115-122Hiromitsu Ohno, Koji Koibuchi, Katsumi Takami, "Estimation of Rotational Bending Fatigue Limit by Non-contact Temperature Measurement", Materials, Vol.16, No.161 (1967), pp.115-122 早房敬祐，中本浩章，因幡和晃，岸本喜久雄，“サーモグラフィによる回転曲げ疲労限度の評価”，エバラ時報，No.230(2011)，pp.3-6Keisuke Hayafusa, Hiroaki Nakamoto, Kazuaki Inaba, Kikuo Kishimoto, "Evaluation of Rotational Bending Fatigue Limit by Thermography", Ebara Time Signal, No.230 (2011), pp.3-6 R．Kawai，T．Yoshikawa，Y．Kurokawa，Y．Irie，H．Inoue，“Rapid evaluation of fatigue limit using infrared thermography：comparison between two methods for quantifying temperature evolution”，Mechanical Engineering Journal，Vol.4，No.5(2017)，pp.17-00009．R. Kawai, T.K. Yoshikawa, Y. Kurokawa, Y. Irie, H. Inoue, “Rapid evaluation of fatigue limit using infrared thermography: comparison between two methods for quantifying temperature evolution”, Mechanical Engineering Journal, Vol.4, No.5 (2017), pp.17-00009. 金属材料技術研究所，“金属材料技術研究所疲れデータシート、機械構造用炭素鋼S25C(0.25C)の疲れ特性データシート”，No.1(1978)pp.1-11Metallic Materials Technology Laboratory, "Metallic Materials Technology Laboratory Tiredness Data Sheet, Tired Characteristic Data Sheet of Carbon Steel S25C (0.25C) for Machine Structure", No.1 (1978) pp.1-11 赤井淳嗣，稲葉健，塩澤大輝，阪上隆英“散逸エネルギー計測に基づく疲労き裂発生位置の推定”，材料，Vol.64，No.8(2015)，pp.668-674Atsushi Akai, Ken Inaba, Daiki Shiozawa, Takahide Sakagami "Estimation of Fatigue Crack Occurrence Position Based on Dissipated Energy Measurement", Materials, Vol.64, No.8 (2015), pp.668-674

上記のように疲労限度応力を精度良く特定するためには温度の第２高調波成分から散逸エネルギーを計測する必要があり、従来技術では、温度の第２高調波成分を計測するためには、高価な量子型赤外線カメラを使用しなければならなかった。更に、赤外線カメラを用いる場合、測定対象物の表面の放射率を向上させるため、試験前に測定対象物の表面に黒体化塗料を塗布する必要があった。これらは、疲労限度応力を安価かつ簡便に特定する上で課題となっていた。 As described above, in order to accurately identify the fatigue limit stress, it is necessary to measure the dissipated energy from the second harmonic component of temperature. In the prior art, in order to measure the second harmonic component of temperature, I had to use an expensive quantum infrared camera. Further, when an infrared camera is used, it is necessary to apply a blackbody paint to the surface of the object to be measured before the test in order to improve the emissivity of the surface of the object to be measured. These have been problems in identifying the fatigue limit stress inexpensively and easily.

そこで、本発明は、高価な量子型赤外線カメラを用いることなく散逸エネルギーを計測して、量子型赤外線カメラを用いる場合よりも安価かつ簡便に測定対象物の疲労限度応力を特定することを目的とする。 Therefore, an object of the present invention is to measure the dissipated energy without using an expensive quantum infrared camera and to specify the fatigue limit stress of the object to be measured cheaper and more easily than when the quantum infrared camera is used. To do.

本発明に係る疲労限度応力特定装置は、順次増加する引張と圧縮の繰り返し荷重を所定の周波数で測定対象物に加える加振機と、前記測定対象物に貼り付けて熱流束を測定する熱流センサと、前記熱流センサにより測定された熱流束を周波数解析して、前記所定の周波数の第２高調波の周波数成分から散逸エネルギーを計測する解析装置と、を備え、前記散逸エネルギーの計測結果から前記測定対象物の疲労限度応力を特定することを特徴とする。 The fatigue limit stress specifying device according to the present invention includes a vibration exciter that applies a repeatedly increasing tensile and compressive load to a measurement object at a predetermined frequency, and a heat flow sensor that is attached to the measurement object to measure heat flux. And an analyzer that frequency-analyzes the heat flux measured by the heat flow sensor and measures the dissipated energy from the frequency component of the second harmonic of the predetermined frequency. It is characterized by specifying the fatigue limit stress of the object to be measured.

引張と圧縮の繰り返し荷重を所定の周波数で測定対象物に加えた際に、散逸エネルギーは塑性変形に起因する不可逆な発熱により生じる。金属疲労による微視的な塑性変形が生じた場合、塑性変形による不可逆な発熱は、引張と圧縮の繰り返し荷重の１周期の間に、最大引張負荷時と最大圧縮負荷時の２回に渡って顕著に生じる。このように引張と圧縮の繰り返し荷重の１周期の間に２回生じる顕著な発熱は、熱流束の時系列データを周波数解析して、繰り返し荷重の第２高調波の周波数成分を抽出することで計測できる。この熱流束の第２高調波成分は温度の第２高調波成分に対応するため、熱流センサを用いることにより、散逸エネルギーを計測することができる。そして、熱流センサは量子型赤外線カメラよりも安価であり、赤外線カメラと異なり黒体化塗料を塗布しなくても熱流束を測定できる。そのため、このように熱流センサを用いて散逸エネルギーを計測することにより、量子型赤外線カメラを用いる場合よりも安価かつ簡便に測定対象物の疲労限度応力を特定することができる。 When a repeated tension and compression load is applied to the object to be measured at a predetermined frequency, the dissipated energy is generated by irreversible heat generation due to plastic deformation. When microscopic plastic deformation occurs due to metal fatigue, the irreversible heat generation due to plastic deformation occurs twice during one cycle of repeated tension and compression loads, at maximum tensile load and maximum compressive load. It occurs prominently. In this way, the remarkable heat generation that occurs twice during one cycle of the repeated load of tension and compression is caused by frequency analysis of the time series data of the heat flux and extracting the frequency component of the second harmonic of the repeated load. Can be measured. Since the second harmonic component of this heat flux corresponds to the second harmonic component of temperature, the dissipated energy can be measured by using a heat flow sensor. The heat flow sensor is cheaper than the quantum infrared camera, and unlike the infrared camera, the heat flux can be measured without applying a blackbody coating. Therefore, by measuring the dissipated energy using the heat flow sensor in this way, it is possible to specify the fatigue limit stress of the object to be measured more inexpensively and easily than when using the quantum infrared camera.

本発明の疲労限度応力特定装置の一態様において、前記散逸エネルギーが急増する際の応力振幅を前記測定対象物の疲労限度応力として特定してもよい。 In one aspect of the fatigue limit stress specifying device of the present invention, the stress amplitude when the dissipated energy rapidly increases may be specified as the fatigue limit stress of the measurement object.

この態様によれば、熱流センサにより熱流束の第２高調波成分を測定して、散逸エネルギーが急増する際すなわち熱流束の第２高調波振幅が急増する際の応力振幅を前記測定対象物の疲労限度応力として特定することができる。 According to this aspect, the second harmonic component of the heat flux is measured by the heat flow sensor, and the stress amplitude when the dissipated energy suddenly increases, that is, when the second harmonic amplitude of the heat flux rapidly increases is the measurement object. It can be specified as the fatigue limit stress.

本発明の疲労限度応力特定装置の一態様において、前記熱流センサは少なくとも０．００８ｍＶ／Ｗ・ｍ^−２以上の感度を有しているとよい。 In one aspect of the fatigue limit stress specifying device of the present invention, the heat flow sensor is preferably having a sensitivity of ^{at least 0.008 mV / Wm-2 or more.}

この態様によれば、熱流束の第２高調波振幅の急増を検知できる感度を熱流センサが有するため、熱流束の第２高調波振幅の変動から測定対象物の疲労限度応力を特定することができる。 According to this aspect, since the heat flow sensor has a sensitivity capable of detecting a rapid increase in the second harmonic amplitude of the heat flux, it is possible to specify the fatigue limit stress of the object to be measured from the fluctuation of the second harmonic amplitude of the heat flux. it can.

本発明の疲労限度応力特定装置の一態様において、前記熱流センサは周波数が１０Ｈｚである第２高調波の周波数成分を測定できる応答性を有しているとよい。 In one aspect of the fatigue limit stress specifying device of the present invention, it is preferable that the heat flow sensor has a responsiveness capable of measuring the frequency component of the second harmonic having a frequency of 10 Hz.

この態様によれば、引張と圧縮の繰り返し荷重を５Ｈｚの周波数で測定対象物に加えた際に熱流束の第２高調波（１０Ｈｚ）の周波数成分を測定して測定対象物の疲労限度応力を特定することができる。 According to this aspect, when a repeated load of tension and compression is applied to the object to be measured at a frequency of 5 Hz, the frequency component of the second harmonic (10 Hz) of the heat flux is measured to determine the fatigue limit stress of the object to be measured. Can be identified.

本発明に係る疲労限度応力特定方法は、順次増加する引張と圧縮の繰り返し荷重を所定の周波数で測定対象物に加え、前記測定対象物に貼り付けた熱流センサで熱流束を測定し、前記熱流センサにより測定された熱流束を周波数解析して、前記所定の周波数の第２高調波の周波数成分から散逸エネルギーを計測し、前記散逸エネルギーの計測結果から前記測定対象物の疲労限度応力を特定することを特徴とする。 In the method for specifying fatigue limit stress according to the present invention, a repeatedly increasing tensile and compressive load is applied to an object to be measured at a predetermined frequency, the heat flux is measured by a heat flow sensor attached to the object to be measured, and the heat flow is measured. The heat flux measured by the sensor is frequency-analyzed, the dissipated energy is measured from the frequency component of the second harmonic of the predetermined frequency, and the fatigue limit stress of the measurement object is specified from the measurement result of the dissipated energy. It is characterized by that.

引張と圧縮の繰り返し荷重を所定の周波数で測定対象物に加えた際に、散逸エネルギーは塑性変形に起因する不可逆な発熱により生じる。金属疲労による微視的な塑性変形が生じた場合、塑性変形による不可逆な発熱は、引張と圧縮の繰り返し荷重の１周期の間に、最大引張負荷時と最大圧縮負荷時の２回に渡って顕著に生じる。このように引張と圧縮の繰り返し荷重の１周期の間に２回生じる顕著な発熱は、熱流束の時系列データを周波数解析して、繰り返し荷重の第２高調波の周波数成分を抽出することで計測できる。この熱流束の第２高調波成分は温度の第２高調波成分に対応するため、熱流センサを用いることにより、散逸エネルギーを計測することができる。そして、熱流センサは量子型赤外線カメラよりも安価であり、赤外線カメラと異なり黒体化塗料を塗布しなくても熱流束を測定できる。そのため、このように熱流センサを用いて散逸エネルギーを計測することにより、量子型赤外線カメラを用いる場合よりも安価かつ簡便に測定対象物の疲労限度応力を特定することができる。 When a repeated tension and compression load is applied to the object to be measured at a predetermined frequency, the dissipated energy is generated by irreversible heat generation due to plastic deformation. When microscopic plastic deformation occurs due to metal fatigue, irreversible heat generation due to plastic deformation occurs twice during one cycle of repeated tension and compression loads, at maximum tensile load and maximum compressive load. It occurs prominently. In this way, the remarkable heat generation that occurs twice during one cycle of the repeated load of tension and compression is caused by frequency analysis of the time series data of the heat flux and extracting the frequency component of the second harmonic of the repeated load. Can be measured. Since the second harmonic component of this heat flux corresponds to the second harmonic component of temperature, the dissipated energy can be measured by using a heat flow sensor. The heat flow sensor is cheaper than the quantum infrared camera, and unlike the infrared camera, the heat flux can be measured without applying a blackbody coating. Therefore, by measuring the dissipated energy using the heat flow sensor in this way, it is possible to specify the fatigue limit stress of the object to be measured more inexpensively and easily than when using the quantum infrared camera.

本発明の疲労限度応力特定方法の一態様において、前記散逸エネルギーが急増する際の応力振幅を前記測定対象物の疲労限度応力として特定してもよい。 In one aspect of the fatigue limit stress specifying method of the present invention, the stress amplitude when the dissipated energy rapidly increases may be specified as the fatigue limit stress of the object to be measured.

この態様によれば、熱流センサにより熱流束の第２高調波成分を測定して、熱流束の第２高調波振幅が急増する際すなわち散逸エネルギーが急増する際の応力振幅を前記測定対象物の疲労限度応力として特定することができる。 According to this aspect, the second harmonic component of the heat flux is measured by the heat flow sensor, and the stress amplitude when the second harmonic amplitude of the heat flux rapidly increases, that is, when the dissipated energy rapidly increases, is measured. It can be specified as the fatigue limit stress.

本発明の疲労限度応力特定方法の一態様において、前記熱流センサは少なくとも０．００８ｍＶ／Ｗ・ｍ^−２以上の感度を有しているとよい。 In one aspect of the fatigue limit stress identification method of the present invention, the heat flow sensor is preferably having a sensitivity of ^{at least 0.008 mV / Wm-2 or more.}

この態様によれば、熱流束の第２高調波振幅の急増を検知できる感度を熱流センサが有するため、熱流束の第２高調波振幅の変動から測定対象物の疲労限度応力を特定することができる。 According to this aspect, since the heat flow sensor has a sensitivity capable of detecting a rapid increase in the second harmonic amplitude of the heat flux, it is possible to specify the fatigue limit stress of the object to be measured from the fluctuation of the second harmonic amplitude of the heat flux. it can.

本発明の疲労限度応力特定方法の一態様において、前記熱流センサは周波数が１０Ｈｚである第２高調波の周波数成分を測定できる応答性を有しているとよい。 In one aspect of the fatigue limit stress specifying method of the present invention, it is preferable that the heat flow sensor has a responsiveness capable of measuring the frequency component of the second harmonic having a frequency of 10 Hz.

この態様によれば、引張と圧縮の繰り返し荷重を５Ｈｚの周波数で測定対象物に加えた際に熱流束の第２高調波（１０Ｈｚ）の周波数成分を測定して測定対象物の疲労限度応力を特定することができる。 According to this aspect, when a repeated load of tension and compression is applied to the object to be measured at a frequency of 5 Hz, the frequency component of the second harmonic (10 Hz) of the heat flux is measured to determine the fatigue limit stress of the object to be measured. Can be identified.

熱流センサによる散逸エネルギーの計測原理を説明する図である。It is a figure explaining the measurement principle of the dissipated energy by a heat flow sensor. 熱弾性効果と塑性変形による不可逆な発熱とを説明する図である。It is a figure explaining the thermoelastic effect and irreversible heat generation by plastic deformation. 本開示の実施形態の疲労限度応力特定装置の構成を示す図である。It is a figure which shows the structure of the fatigue limit stress identification apparatus of embodiment of this disclosure. 試験片の形状及び寸法を示す図である。It is a figure which shows the shape and dimension of a test piece. 引張と圧縮の繰り返し荷重の負荷条件を示す表である。It is a table which shows the loading condition of the repeated load of tension and compression. 熱流センサの貼り付け位置を示す図である。It is a figure which shows the sticking position of a heat flow sensor. 温度及び熱流束の測定条件を示す表である。It is a table which shows the measurement condition of temperature and heat flux. 応力振幅が４０ＭＰａで熱流束の時系列データを周波数解析した結果を示す図である。It is a figure which shows the result of the frequency analysis of the time series data of the heat flux with a stress amplitude of 40 MPa. 応力振幅が３００ＭＰａで熱流束の時系列データを周波数解析した結果を示す図である。It is a figure which shows the result of frequency analysis of the time series data of a heat flux with a stress amplitude of 300 MPa. 熱流センサにより熱流束の第２高調波振幅を測定した結果を示す図である。It is a figure which shows the result of having measured the 2nd harmonic amplitude of a heat flux by a heat flow sensor. 量子型赤外線カメラにより温度の第２高調波振幅を測定した結果を示す図である。It is a figure which shows the result of having measured the 2nd harmonic amplitude of temperature by the quantum type infrared camera. 熱流束の第２高調波振幅と温度の第２高調波振幅との関係を示す図である。It is a figure which shows the relationship between the 2nd harmonic amplitude of heat flux, and the 2nd harmonic amplitude of temperature.

本開示の実施形態の疲労限度応力特定装置１０の構成について説明する前に、図１及び図２を参照しながら、散逸エネルギーの計測原理について以下に説明する。 Before explaining the configuration of the fatigue limit stress specifying device 10 according to the embodiment of the present disclosure, the principle of measuring the dissipated energy will be described below with reference to FIGS. 1 and 2.

図１に示すように、金属製の試験片Ｐの表面に貼り付けた熱流センサ１では、試験片Ｐが発熱した場合に正の熱流束が測定され、試験片Ｐが吸熱した場合に負の熱流束が測定される。断熱状態で試験片Ｐに荷重を加えた場合、圧縮荷重で発熱が生じ、引張荷重で吸熱が生じることが熱弾性効果として知られている。このため、図２の一点鎖線ａで示す引張と圧縮の正弦波状の繰り返し荷重を試験片２に加えた場合、図２の実線ｂで示す熱弾性効果に起因する熱流束が測定されると考えられる。これに加えて、金属疲労による微視的な塑性変形が生じた場合、塑性変形による不可逆な発熱は、最大引張負荷時と最大圧縮負荷時の２回に渡って顕著に生じるため、図２の点線ｃで示す塑性変形に起因する熱流束が測定されると考えられる。 As shown in FIG. 1, the heat flow sensor 1 attached to the surface of the metal test piece P measures a positive heat flux when the test piece P generates heat, and negative when the test piece P absorbs heat. Heat flux is measured. It is known as a thermoelastic effect that when a load is applied to the test piece P in a heat-insulated state, heat is generated by a compressive load and heat is absorbed by a tensile load. Therefore, when a sinusoidal repeated load of tension and compression shown by the alternate long and short dash line a in FIG. 2 is applied to the test piece 2, it is considered that the heat flux due to the thermoelastic effect shown by the solid line b in FIG. 2 is measured. Be done. In addition to this, when microscopic plastic deformation occurs due to metal fatigue, irreversible heat generation due to plastic deformation occurs remarkably twice at the maximum tensile load and the maximum compression load. It is considered that the heat flux caused by the plastic deformation shown by the dotted line c is measured.

このため、熱流センサ１を用いて得られる熱流束の時系列データを周波数解析し、繰り返し荷重と同じ周波数成分から熱弾性効果に起因する熱流束成分を抽出でき、繰り返し荷重の２倍の周波数成分から塑性変形に起因する熱流束成分を抽出できる。このように熱流センサ１を用いることにより、温度の第２高調波に相当する成分を熱流束の第２高調波成分として計測できれば、量子型赤外線カメラを用いて温度の第２高調波振幅から散逸エネルギーを計測する場合と同様に、熱流センサ１を用いて熱流束の第２高調波振幅から散逸エネルギーを計測することができる。 Therefore, the time-series data of the heat flux obtained by using the heat flow sensor 1 can be frequency-analyzed, and the heat flux component due to the thermoelastic effect can be extracted from the same frequency component as the repetitive load, and the frequency component is twice the repetitive load. The heat flux component due to plastic deformation can be extracted from. If the component corresponding to the second harmonic of the temperature can be measured as the second harmonic component of the heat flux by using the heat flow sensor 1 in this way, it dissipates from the second harmonic amplitude of the temperature using a quantum infrared camera. Similar to the case of measuring energy, the heat flow sensor 1 can be used to measure the dissipated energy from the second harmonic amplitude of the heat flux.

熱流束とは、単位時間に単位面積を通過する熱量であり、単位にはＷ／ｍ^２が用いられる。熱流束は、熱流束が平面状の熱流センサ１を貫通するとき、熱流束の大きさに比例した熱流センサ１の両面に生じる温度差を検出することによって測定できる。熱流センサ１の熱伝導率がλ（Ｗ／ｍＫ）で厚さがｄ（ｍ）であり、熱流センサ１の表裏両面間の温度差をΔＴとすると、熱流束Ｑ（Ｗ／ｍ^２）は、以下の式１で求められる。 The heat flux is the amount of heat that passes through a unit area in a unit time, and W / m ² is used as the unit. The heat flux can be measured by detecting the temperature difference that occurs on both sides of the heat flux sensor 1 in proportion to the size of the heat flux when the heat flux penetrates the planar heat flow sensor 1. If the thermal conductivity of the heat flow sensor 1 is λ (W / mK) and the thickness is d (m), and the temperature difference between the front and back surfaces of the heat flow sensor 1 is ΔT, the heat flux Q (W / m ² ) is , It is calculated by the following equation 1.

Ｑ＝（λ／ｄ）・ΔＴ ・・・ 式１ Q = (λ / d) ・ ΔT ・ ・ ・ Equation 1

そのため、熱流センサ１の熱伝導率λ及び厚さｄが既知であれば、温度差ΔＴを測定することによって熱流束Ｑを求めることができる。本実施形態の疲労限度応力特定装置１０に用いる熱流センサ１は、表裏両面間の温度差ΔＴに比例する電圧を出力する複数の熱電素子を直列に接続することによって感度を向上させている。 Therefore, if the thermal conductivity λ and the thickness d of the heat flow sensor 1 are known, the heat flux Q can be obtained by measuring the temperature difference ΔT. The heat flow sensor 1 used in the fatigue limit stress specifying device 10 of the present embodiment improves the sensitivity by connecting a plurality of thermoelectric elements in series that output a voltage proportional to the temperature difference ΔT between the front and back surfaces.

このように疲労限度応力特定装置１０に熱流センサ１を用いずに、接触式の温度センサとして、白金等の測温抵抗体やサーミスタや熱電対などを用いることも考えられる。しかし、測温抵抗体は応答性が悪く、電流を流すことによる自己発熱が生じる上、振動や衝撃に弱いため、測定対象物に継続して振動を加える疲労限度応力の試験に用いることは適切ではない。また、サーミスタも電流を流すことによる自己発熱が生じる上、振動や衝撃に弱いため、測定対象物に振動を加え続ける疲労限度応力の試験に用いることは適切ではない。熱電対は振動や衝撃に強く応答性が良いものの、複数の熱電素子を直列に接続した熱流センサ１よりも感度が低い。そのため、本実施形態の疲労限度応力特定装置１０では、熱流センサ１を用いて熱流束を測定する。 As described above, it is conceivable to use a resistance temperature detector such as platinum, a thermistor, a thermocouple, or the like as a contact type temperature sensor without using the heat flow sensor 1 for the fatigue limit stress specifying device 10. However, resistance temperature detectors have poor responsiveness, generate self-heating by passing an electric current, and are vulnerable to vibration and shock, so it is appropriate to use them for fatigue limit stress tests that continuously apply vibration to the object to be measured. is not it. In addition, the thermistor also generates self-heating by passing an electric current and is vulnerable to vibration and impact, so it is not appropriate to use it for the fatigue limit stress test in which vibration is continuously applied to the object to be measured. Although the thermocouple is strong against vibration and shock and has good responsiveness, it is less sensitive than the heat flow sensor 1 in which a plurality of thermoelectric elements are connected in series. Therefore, in the fatigue limit stress specifying device 10 of the present embodiment, the heat flux is measured by using the heat flow sensor 1.

次に、本実施形態の疲労限度応力特定装置１０の構成について、図３を参照しながら説明する。図３に示すように、疲労限度応力特定装置１０は、熱流センサ１、電気油圧サーボ式疲労試験機３、量子型赤外線カメラ４、データ収集記録装置５及び解析装置６を備える。電気油圧サーボ式疲労試験機３は、測定対象物となる試験片２に引張と圧縮の繰り返し荷重を加える加振機である。量子型赤外線カメラ４としてＦＬＩＲ製のＳＣ６０００が用いられており、熱流センサ１としてＤＥＮＳＯ製のＥｎｅｒｇｙ Ｅｙｅが用いられている。試験片２に貼り付けられた熱流センサ１の感度は０．００８３ｍＶ／Ｗ・ｍ^−２である。なお、量子型赤外線カメラ４は、量子型赤外線カメラ４を用いて温度の第２高調波振幅から散逸エネルギーを計測する場合と同様に、熱流センサ１を用いて熱流束の第２高調波振幅から散逸エネルギーを計測して疲労限度応力を特定することができるか評価するために設けられている。 Next, the configuration of the fatigue limit stress specifying device 10 of the present embodiment will be described with reference to FIG. As shown in FIG. 3, the fatigue limit stress identification device 10 includes a heat flow sensor 1, an electro-hydraulic servo type fatigue tester 3, a quantum infrared camera 4, a data collection / recording device 5, and an analysis device 6. The electro-hydraulic servo type fatigue tester 3 is a vibration exciter that repeatedly applies a tension and compression load to a test piece 2 to be measured. A FLIR SC6000 is used as the quantum infrared camera 4, and an Energy Eye made by DENSO is used as the heat flow sensor 1. The sensitivity of the heat flow sensor 1 attached to the test piece 2 is 0.0083 mV / Wm- ² . The quantum infrared camera 4 uses the heat flow sensor 1 to measure the dissipated energy from the second harmonic amplitude of the temperature, as in the case where the quantum infrared camera 4 is used to measure the dissipated energy from the second harmonic amplitude of the heat flux. It is provided to measure the dissipated energy and evaluate whether the fatigue limit stress can be specified.

試験片２は、図４に示す形状と寸法となるように機械構造用炭素鋼Ｓ２５Ｃの供試材から作製されている。図４に示すように、試験片２は、長さ７０ｍｍ、幅１０ｍｍ、厚さ２．５ｍｍの平板形状であり、半径２５ｍｍでＲ加工された２箇所のＲ部が形成されていることにより、中央部が括れて幅が狭くなっており、最小となる部分では幅が６ｍｍとなっている。 The test piece 2 is manufactured from a test material of carbon steel S25C for machine structure so as to have the shape and dimensions shown in FIG. As shown in FIG. 4, the test piece 2 has a flat plate shape having a length of 70 mm, a width of 10 mm, and a thickness of 2.5 mm, and has two R portions formed by R processing with a radius of 25 mm. The central part is constricted and the width is narrowed, and the width is 6 mm at the minimum part.

引張と圧縮の繰り返し荷重を試験片２に加える電気油圧サーボ式疲労試験機３は、室温かつ大気中において、図５に示す負荷条件で、応力振幅を規定の負荷繰り返し数（１３００サイクル）に達するごとに階段状に増加させていく。そして、このように試験片２に繰り返し荷重を加えながら、図３に示すように、試験片２に向かって設置した量子型赤外線カメラ４を用いて試験片２の表面の温度を測定し、その裏面に貼り付けた熱流センサ１を用いて熱流束を測定する。熱流センサ１は図６に示すように試験片２の中央部に両面テープを用いて貼り付けられる。そして、データ収集記録装置５は、熱流センサ１の出力電圧から感度定数（０．００８３ｍＶ／Ｗ・ｍ^−２）を用いて熱流束に変換して熱流束の値を記録する。なお、量子型赤外線カメラ４により温度を測定する試験片２の温度測定面には、放射率向上のため黒体化塗料が塗布されている。 The electro-hydraulic servo-type fatigue tester 3 that applies a repeated tension and compression load to the test piece 2 reaches a specified load repetition number (1300 cycles) at room temperature and in the air under the load conditions shown in FIG. Increase in steps for each step. Then, while repeatedly applying a load to the test piece 2 in this way, as shown in FIG. 3, the temperature of the surface of the test piece 2 is measured by using the quantum infrared camera 4 installed toward the test piece 2. The heat flux is measured using the heat flow sensor 1 attached to the back surface. As shown in FIG. 6, the heat flow sensor 1 is attached to the central portion of the test piece 2 using double-sided tape. Then, the data collection / recording device 5 converts the output voltage of the heat flow sensor 1 ^{into a heat flux using a sensitivity constant (0.0083 mV / Wm-2} ) and records the value of the heat flux. A blackbody paint is applied to the temperature measuring surface of the test piece 2 whose temperature is measured by the quantum infrared camera 4 in order to improve the emissivity.

疲労限度応力特定装置１０は、図７に示す測定条件で温度及び熱流束をそれぞれ測定する。熱流センサ１のセンサ部サイズが５ｍｍ×５ｍｍであるため、温度の時系列データも５ｍｍ×５ｍｍの範囲内の平均値を各時刻の温度の代表値として、温度及び熱流束の評価範囲を統一する。再現性確認のため、図３に示す形状と寸法の２本の試験片２（以下、試験片Ａ及び試験片Ｂと呼ぶ）を作製して、温度及び熱流束をそれぞれ測定した。 The fatigue limit stress identification device 10 measures the temperature and the heat flux under the measurement conditions shown in FIG. 7, respectively. Since the sensor unit size of the heat flow sensor 1 is 5 mm × 5 mm, the time series data of the temperature also uses the average value within the range of 5 mm × 5 mm as the representative value of the temperature at each time, and unifies the evaluation range of temperature and heat flux. .. In order to confirm the reproducibility, two test pieces 2 (hereinafter referred to as test piece A and test piece B) having the shape and dimensions shown in FIG. 3 were prepared, and the temperature and heat flux were measured, respectively.

解析装置６により、試験片Ａの応力振幅が４０ＭＰａ及び３００ＭＰａで熱流束の時系列データを周波数解析した結果をそれぞれ図８及び図９に示す。図８及び図９に示すように、４０ＭＰａと３００ＭＰａのいずれの応力振幅においても、繰り返し荷重と同じ周波数（５Ｈｚ）でスペクトルのピークが確認できる（以下、熱流束の基本波と呼ぶ）。更に、図９に示すように、応力振幅が３００ＭＰａでは、繰り返し荷重の２倍の周波数（１０Ｈｚ）においても、スペクトルのピークが確認できる（以下、熱流束の第２高調波と呼ぶ）。非特許文献４に記載された機械構造用炭素鋼Ｓ２５Ｃの引張圧縮疲労限度応力の文献値は２０９〜２２２ＭＰａであるから、４０ＭＰａは疲労限度応力未満の応力振幅に相当し、３００ＭＰａは疲労限度応力以上の応力振幅に相当し、熱流束の基本波及び第２高調波の成分が熱弾性効果及び塑性変形に起因する成分にそれぞれ相当すると考えられる。 The results of frequency analysis of the time series data of the heat flux by the analysis device 6 with the stress amplitudes of the test piece A of 40 MPa and 300 MPa are shown in FIGS. 8 and 9, respectively. As shown in FIGS. 8 and 9, the peak of the spectrum can be confirmed at the same frequency (5 Hz) as the repeating load at any stress amplitude of 40 MPa or 300 MPa (hereinafter, referred to as a fundamental wave of heat flux). Further, as shown in FIG. 9, when the stress amplitude is 300 MPa, the peak of the spectrum can be confirmed even at a frequency (10 Hz) twice the repeating load (hereinafter, referred to as the second harmonic of the heat flux). Since the document value of the tensile compressive fatigue limit stress of the mechanical structural carbon steel S25C described in Non-Patent Document 4 is 209 to 222 MPa, 40 MPa corresponds to the stress amplitude less than the fatigue limit stress, and 300 MPa corresponds to the fatigue limit stress or more. It is considered that the components of the fundamental wave and the second harmonic of the heat flux correspond to the stress amplitude of the above, and correspond to the components caused by the thermoelastic effect and the plastic deformation, respectively.

試験片Ａ及びＢの各応力振幅で得られた、熱流束の第２高調波振幅の測定結果を図１０に示し、温度の第２高調波振幅の測定結果を図１１に示す。図１０に示すように、熱流束の第２高調波振幅は、試験開始後は概ね一定で、応力振幅が２４０ＭＰａ付近を境に急増した。また、図１１に示すように、温度の第２高調波振幅も熱流束の第２高調波振幅と同様に、試験開始後は概ね一定で、応力振幅が２４０ＭＰａ付近を境に急増した。更に、各応力振幅で得られた熱流束の第２高調波振幅と温度の第２高調波振幅との関係を図１２に示す。図１２に示すように、熱流束の第２高調波振幅と温度の第２高調波振幅との間には強い正の相関がある。これらのことから、高価な量子型赤外線カメラ４を用いて計測される温度の第２高調波に相当する成分を、熱流束の第２高調波成分により評価できることが分かる。 FIG. 10 shows the measurement results of the second harmonic amplitude of the heat flux obtained at each stress amplitude of the test pieces A and B, and FIG. 11 shows the measurement results of the second harmonic amplitude of the temperature. As shown in FIG. 10, the second harmonic amplitude of the heat flux was substantially constant after the start of the test, and the stress amplitude rapidly increased around 240 MPa. Further, as shown in FIG. 11, the second harmonic amplitude of the temperature was also substantially constant after the start of the test, and the stress amplitude rapidly increased around 240 MPa, similarly to the second harmonic amplitude of the heat flux. Further, FIG. 12 shows the relationship between the second harmonic amplitude of the heat flux obtained at each stress amplitude and the second harmonic amplitude of the temperature. As shown in FIG. 12, there is a strong positive correlation between the second harmonic amplitude of the heat flux and the second harmonic amplitude of the temperature. From these facts, it can be seen that the component corresponding to the second harmonic of the temperature measured by using the expensive quantum infrared camera 4 can be evaluated by the second harmonic component of the heat flux.

更に、非特許文献５に示される機械構造用炭素鋼Ｓ４５Ｃの散逸エネルギー（温度の第２高調波振幅）が急増する応力振幅と耐久試験で得られた疲労限度応力とが良く一致すること、温度及び熱流束の第２高調波振幅が急増する応力振幅（２４０ＭＰａ）が非特許文献４に示される機械構造用炭素鋼Ｓ２５Ｃの引張圧縮疲労限度応力の文献値と概ね一致することを考慮すると、熱流束の第２高調波振幅から疲労限度応力を精度良く特定できると評価できる。 Further, the stress amplitude at which the dissipated energy (second harmonic amplitude of temperature) of the mechanical structural carbon steel S45C shown in Non-Patent Document 5 rapidly increases and the fatigue limit stress obtained in the durability test are in good agreement with each other, and the temperature. Considering that the stress amplitude (240 MPa) in which the second harmonic amplitude of the heat flux rapidly increases is almost the same as the document value of the tensile compression fatigue limit stress of the mechanical structural carbon steel S25C shown in Non-Patent Document 4, the heat flow It can be evaluated that the fatigue limit stress can be accurately specified from the second harmonic amplitude of the bundle.

疲労限度応力特定装置１０において、解析装置６は、散逸エネルギーが急増する際の応力振幅を疲労限度応力として特定する。例えば、図１０に示す熱流束の第２高調波振幅の測定データが得られた場合は、解析装置６は、熱流束の第２高調波振幅が急増する応力振幅である２４０ＭＰａを疲労限度応力として特定する。 In the fatigue limit stress specifying device 10, the analysis device 6 specifies the stress amplitude when the dissipated energy suddenly increases as the fatigue limit stress. For example, when the measurement data of the second harmonic amplitude of the heat flux shown in FIG. 10 is obtained, the analyzer 6 sets 240 MPa, which is the stress amplitude at which the second harmonic amplitude of the heat flux rapidly increases, as the fatigue limit stress. Identify.

このように疲労限度応力特定装置１０は、熱流センサ１を用いて散逸エネルギーを計測し、測定対象物の疲労限度応力を特定することができる。熱流センサ１は量子型赤外線カメラ４よりも安価であり、測定対象物に黒体化塗料を塗布しなくても熱流束を測定できる。そのため、疲労限度応力特定装置１０は、このように熱流センサ１を用いて散逸エネルギーを計測することにより、量子型赤外線カメラ４を用いる場合よりも安価かつ簡便に測定対象物の疲労限度応力を特定することができる。 In this way, the fatigue limit stress specifying device 10 can measure the dissipated energy using the heat flow sensor 1 and specify the fatigue limit stress of the object to be measured. The heat flow sensor 1 is cheaper than the quantum infrared camera 4, and can measure the heat flux without applying a blackbody paint to the object to be measured. Therefore, the fatigue limit stress specifying device 10 specifies the fatigue limit stress of the object to be measured more inexpensively and easily than when the quantum infrared camera 4 is used by measuring the dissipated energy using the heat flow sensor 1 in this way. can do.

また、熱流センサ１は０．００８ｍＶ／Ｗ・ｍ^−２以上の感度を有しており、図１０に示すように熱流束の第２高調波振幅の急増を検知できるため、熱流センサ１を用いた疲労限度応力特定装置１０は、測定対象物の疲労限度応力を特定することができる。 Further, since the heat flow sensor 1 has ^{a sensitivity of 0.008 mV / Wm-2} or more and can detect a rapid increase in the second harmonic amplitude of the heat flux as shown in FIG. 10, the heat flow sensor 1 is used. The fatigue limit stress specifying device 10 can specify the fatigue limit stress of the object to be measured.

また、熱流センサ１は周波数が１０Ｈｚである第２高調波の周波数成分を測定できる応答性を有しているため、疲労限度応力特定装置１０は、引張と圧縮の繰り返し荷重を５Ｈｚの周波数で測定対象物に加えた際に熱流束の第２高調波（１０Ｈｚ）の周波数成分を測定して測定対象物の疲労限度応力を特定することができる。 Further, since the heat flow sensor 1 has a responsiveness capable of measuring the frequency component of the second harmonic having a frequency of 10 Hz, the fatigue limit stress specifying device 10 measures the repeated load of tension and compression at a frequency of 5 Hz. When applied to an object, the frequency component of the second harmonic (10 Hz) of the heat flux can be measured to specify the fatigue limit stress of the object to be measured.

＜実施形態の補足＞
本開示の疲労限度応力特定装置は、上述した形態に限定されず、本開示の要旨の範囲内において種々の形態にて実施できる。例えば、上述の実施形態では、熱流センサによる測定データと量子型赤外線カメラによる測定データとを比較するために量子型赤外線カメラも備えているが、量子型赤外線カメラを備えていない形態であってもよい。また、熱流センサはＤＥＮＳＯ製のＥｎｅｒｇｙ Ｅｙｅに限定されず、同程度の感度や応答性を有する他社製の熱流センサを用いてもよい。また、上述の形態では、各応力振幅の負荷繰り返し数を１３００サイクルとしているが、各応力振幅の負荷繰り返し数はもっと少ない数であってもよい。 <Supplement to the embodiment>
The fatigue limit stress specifying device of the present disclosure is not limited to the above-described form, and can be implemented in various forms within the scope of the gist of the present disclosure. For example, in the above-described embodiment, the quantum infrared camera is also provided in order to compare the measurement data by the heat flow sensor with the measurement data by the quantum infrared camera, but even in the embodiment without the quantum infrared camera. Good. Further, the heat flow sensor is not limited to the Energy Eye manufactured by DENSO, and a heat flow sensor manufactured by another company having the same sensitivity and responsiveness may be used. Further, in the above-described embodiment, the number of load repetitions of each stress amplitude is set to 1300 cycles, but the number of load repetitions of each stress amplitude may be a smaller number.

１ 熱流センサ、２ 試験片、３ 電気油圧サーボ式疲労試験機、４ 量子型赤外線カメラ、５ データ収集記録装置、６ 解析装置、１０ 疲労限度応力特定装置。
1 Heat flow sensor, 2 Test piece, 3 Electro-hydraulic servo type fatigue tester, 4 Quantum type infrared camera, 5 Data collection / recording device, 6 Analysis device, 10 Fatigue limit stress identification device.

Claims (8)

順次増加する引張と圧縮の繰り返し荷重を所定の周波数で測定対象物に加える加振機と、
前記測定対象物に貼り付けて熱流束を測定する熱流センサと、
前記熱流センサにより測定された熱流束を周波数解析して、前記所定の周波数の第２高調波の周波数成分から散逸エネルギーを計測する解析装置と、
を備え、
前記散逸エネルギーの計測結果から前記測定対象物の疲労限度応力を特定することを特徴とする疲労限度応力特定装置。 A vibration exciter that applies a repeating load of tension and compression that gradually increases to the object to be measured at a predetermined frequency,
A heat flow sensor that is attached to the object to be measured and measures the heat flux,
An analyzer that frequency-analyzes the heat flux measured by the heat flow sensor and measures the dissipated energy from the frequency component of the second harmonic of the predetermined frequency.
With
A fatigue limit stress specifying device, characterized in that the fatigue limit stress of the object to be measured is specified from the measurement result of the dissipated energy. 請求項１に記載の疲労限度応力特定装置であって、
前記散逸エネルギーが急増する際の応力振幅を前記測定対象物の疲労限度応力として特定することを特徴とする疲労限度応力特定装置。 The fatigue limit stress specifying device according to claim 1.
A fatigue limit stress specifying device, characterized in that the stress amplitude when the dissipated energy rapidly increases is specified as the fatigue limit stress of the measurement object. 請求項２に記載の疲労限度応力特定装置であって、
前記熱流センサは少なくとも０．００８ｍＶ／Ｗ・ｍ^−２以上の感度を有することを特徴とする疲労限度応力特定装置。 The fatigue limit stress specifying device according to claim 2.
The fatigue limit stress specifying device, wherein the heat flow sensor has a sensitivity of at least 0.008 mV / W · m- ^{2 or more.} 請求項３に記載の疲労限度応力特定装置であって、
前記熱流センサは周波数が１０Ｈｚである第２高調波の周波数成分を測定できる応答性を有することを特徴とする疲労限度応力特定装置。 The fatigue limit stress specifying device according to claim 3.
The fatigue limit stress identification device is characterized in that the heat flow sensor has a responsiveness capable of measuring a frequency component of a second harmonic having a frequency of 10 Hz. 順次増加する引張と圧縮の繰り返し荷重を所定の周波数で測定対象物に加え、
前記測定対象物に貼り付けた熱流センサで熱流束を測定し、
前記熱流センサにより測定された熱流束を周波数解析して、前記所定の周波数の第２高調波の周波数成分から散逸エネルギーを計測し、
前記散逸エネルギーの計測結果から前記測定対象物の疲労限度応力を特定することを特徴とする疲労限度応力特定方法。 A repeating load of increasing tension and compression is applied to the object to be measured at a predetermined frequency.
The heat flux is measured by the heat flow sensor attached to the measurement object, and the heat flux is measured.
The heat flux measured by the heat flow sensor is frequency-analyzed, and the dissipated energy is measured from the frequency component of the second harmonic of the predetermined frequency.
A method for specifying a fatigue limit stress, which comprises specifying the fatigue limit stress of the object to be measured from the measurement result of the dissipated energy. 請求項５に記載の疲労限度応力特定方法であって、
前記散逸エネルギーが急増する際の応力振幅を前記測定対象物の疲労限度応力として特定することを特徴とする疲労限度応力特定方法。 The method for specifying fatigue limit stress according to claim 5.
A method for specifying a fatigue limit stress, which comprises specifying the stress amplitude when the dissipated energy suddenly increases as the fatigue limit stress of the object to be measured. 請求項６に記載の疲労限度応力特定方法であって、
前記熱流センサは少なくとも０．００８ｍＶ／Ｗ・ｍ^−２以上の感度を有することを特徴とする疲労限度応力特定方法。 The method for specifying fatigue limit stress according to claim 6.
A method for identifying fatigue limit stress, wherein the heat flow sensor has a sensitivity of at least 0.008 mV / W · m- ^{2 or more.} 請求項７に記載の疲労限度応力特定方法であって、
前記熱流センサは周波数が１０Ｈｚである第２高調波の周波数成分を測定できる応答性を有することを特徴とする疲労限度応力特定方法。
The method for specifying fatigue limit stress according to claim 7.
The fatigue limit stress identification method, wherein the heat flow sensor has a responsiveness capable of measuring a frequency component of a second harmonic having a frequency of 10 Hz.

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