JP2021193341A - Fatigue limit identification device and fatigue limit identification method - Google Patents

Fatigue limit identification device and fatigue limit identification method Download PDF

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JP2021193341A
JP2021193341A JP2020099266A JP2020099266A JP2021193341A JP 2021193341 A JP2021193341 A JP 2021193341A JP 2020099266 A JP2020099266 A JP 2020099266A JP 2020099266 A JP2020099266 A JP 2020099266A JP 2021193341 A JP2021193341 A JP 2021193341A
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phase shift
fatigue
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JP7395426B2 (en
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淳嗣 赤井
Junji Akai
由梨 小島
Yuri Kojima
康元 佐藤
Yasumoto Sato
勇佐 大久保
Yusuke Okubo
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JTEKT Corp
Toyota Central R&D Labs Inc
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Toyota Central R&D Labs Inc
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Abstract

To identify easily the fatigue limit of a material.SOLUTION: A fatigue tester 14 applies a repeating load that gradually increases to a test piece 10 at a predetermined frequency. Measuring the temperature of the test piece by a temperature measuring device 16, a fluctuation waveform of the temperature is obtained. Based on the fluctuating waveform, amplitude of the second harmonic of the fluctuating waveform and a phase shift of the second harmonic with respect to the fundamental wave of the fluctuating waveform are calculated. Also, the phase shift at a small load under the repeating load sufficiently smaller than a fatigue limit and the phase shift at a large load at a repeating load sufficiently larger than the fatigue limit are obtained. Based on the amplitude of the second harmonic, the phase shift under the small load, and the phase shift at the large load, fatigue-related amplitude that is amplitude of the second harmonic related to fatigue damage for the fluctuating waveform is calculated for each load value of the repeating load and the fatigue limit is specified based on the fatigue-related amplitude.SELECTED DRAWING: Figure 2

Description

本発明は、材料の疲労限度を特定する装置および方法に関する。 The present invention relates to an apparatus and a method for specifying a fatigue limit of a material.

試験片に繰返し荷重を加えると、荷重の変動に対応して試験片の温度が変動する。この温度の変動の二次高調波の振幅が試験片の疲労限度に関係することが知られている。試験片に加える繰返し荷重の値を段階的に増加させると、温度の変動波形の二次高調波の振幅は増加し、特にある荷重から急激に増加するようになる。この二次高調波の振幅の急増が始まる荷重は疲労限度と関係する。 When a repeated load is applied to the test piece, the temperature of the test piece fluctuates in response to the fluctuation of the load. It is known that the amplitude of the second harmonic of this temperature fluctuation is related to the fatigue limit of the test piece. When the value of the repetitive load applied to the test piece is gradually increased, the amplitude of the second harmonic of the temperature fluctuation waveform increases, and in particular, it increases sharply from a certain load. The load at which the amplitude of this second harmonic begins to surge is related to the fatigue limit.

下記特許文献１には、試験片を赤外線カメラで撮影して二次高調波の振幅が大きい領域に関して、振幅の急増点から疲労限度を特定する技術が記載されている。 Patent Document 1 below describes a technique for identifying a fatigue limit from a point of rapid increase in amplitude in a region where a test piece is photographed with an infrared camera and the amplitude of the second harmonic is large.

下記非特許文献１では、温度変動の二次高調波には、疲労損傷に無関係な要因に起因する成分が含まれることが報告されている。 In Non-Patent Document 1 below, it is reported that the second harmonic of temperature fluctuation contains a component caused by a factor unrelated to fatigue damage.

下記非特許文献２には、疲労損傷に関係する特定の位相ずれを用いて、疲労損傷に関係する温度変動の二次高調波（散逸エネルギ）の計測精度を向上させる技術が示されている。 The following Non-Patent Document 2 discloses a technique for improving the measurement accuracy of the second harmonic (dissipated energy) of the temperature fluctuation related to fatigue damage by using a specific phase shift related to fatigue damage.

特開２０１６−２４０５６号公報Japanese Unexamined Patent Publication No. 2016-24506

河合亮悟，黒川悠，入江庸介，井上裕嗣，「温度変動に基づく疲労限度迅速推定法に関する研究（温度の第二高調波の発生原因）」，日本機械学会論文集，2018年2月6日，Vol.84,No.858(2018)Ryogo Kawai, Yu Kurokawa, Yosuke Irie, Yuji Inoue, "Study on Rapid Estimation of Fatigue Limit Based on Temperature Fluctuation (Cause of Second Harmony of Temperature)", Proceedings of the Japan Society of Mechanical Engineers, February 6, 2018 , Vol.84, No.858 (2018) D.Shiozawa，T.Inagawa，T.Washio，T.Sakagami，「Accuracy improvement in dissipated energy measurement by using phase information」，Measurement Science & Technology，2017年2月6日、Vol.28(2017)044004D.Shiozawa, T.Inagawa, T.Washio, T.Sakagami, "Accuracy improvement in dissipated energy measurement by using phase information", Measurement Science & Technology, February 6, 2017, Vol.28 (2017) 044004

上記の非特許文献２による疲労損傷に関係する温度変動の二次高調波の振幅の算出方法は、煩雑な演算処理が必要である。本発明は、疲労損傷に関係する温度変動の二次高調波の振幅を簡易に算出する装置および方法を提供する。 The method for calculating the amplitude of the second harmonic of the temperature fluctuation related to fatigue damage according to the above-mentioned Non-Patent Document 2 requires complicated arithmetic processing. The present invention provides an apparatus and method for easily calculating the amplitude of the second harmonic of temperature fluctuation related to fatigue damage.

本発明に係る疲労限度特定装置は、試験片に対して、所定周波数で、段階的に増加する繰返し荷重を加える疲労試験機と、試験片の温度を測定する温度測定装置と、試験片の測定された温度に基づき疲労限度を求める情報処理装置と、を備える。情報処理装置は、測定された温度の変動波形に基づき、繰返し荷重の荷重値ごとに、変動波形の二次高調波の振幅、および変動波形の基本波に対する二次高調波の位相ずれを算出し、疲労限度より十分小さい繰返し荷重における小荷重時の位相ずれと、疲労限度より十分大きな繰返し荷重における大荷重時の位相ずれを取得し、二次高調波の振幅と、小荷重時の位相ずれと、大荷重時の位相ずれとに基づき、繰返し荷重の荷重値ごとに、変動波形の疲労損傷に関係する二次高調波の振幅である疲労関連振幅を算出し、疲労関連振幅に基づき疲労限度を特定するように構成されている。 The fatigue limit specifying device according to the present invention is a fatigue tester that applies a repeating load that gradually increases at a predetermined frequency to a test piece, a temperature measuring device that measures the temperature of the test piece, and measurement of the test piece. It is equipped with an information processing device that obtains a fatigue limit based on the determined temperature. The information processing device calculates the amplitude of the second harmonic of the fluctuation waveform and the phase shift of the second harmonic with respect to the fundamental wave of the fluctuation waveform for each load value of the repeating load based on the measured fluctuation waveform of the temperature. , The phase shift at a small load with a repeating load sufficiently smaller than the fatigue limit and the phase shift at a large load with a repeating load sufficiently larger than the fatigue limit are acquired, and the amplitude of the second harmonic and the phase shift at the time of a small load are obtained. Based on the phase shift under heavy load, the fatigue-related amplitude, which is the amplitude of the second harmonic related to the fatigue damage of the fluctuating waveform, is calculated for each load value of the repeating load, and the fatigue limit is set based on the fatigue-related amplitude. It is configured to be specific.

本発明の他の態様に係る疲労限度特定方法は、試験片に対して、所定周波数で、段階的に増加する繰返し荷重を加えるステップと、試験片の温度を、繰返し荷重の荷重値ごとに測定し、温度の変動波形を取得するステップと、温度の変動波形に基づき、繰返し荷重の荷重値ごとに、変動波形の二次高調波の振幅、および変動波形の基本波に対する二次高調波の位相ずれを算出するステップと、疲労限度より十分小さい繰返し荷重における小荷重時の位相ずれと、疲労限度より十分大きな繰返し荷重における大荷重時の位相ずれを取得するステップと、二次高調波の振幅と、小荷重時の位相ずれと、大荷重時の位相ずれとに基づき、繰返し荷重の荷重値ごとに、変動波形の疲労損傷に関係する二次高調波の振幅である、疲労関連振幅に基づき疲労限度を特定するステップと、を含む。 In the fatigue limit specifying method according to another aspect of the present invention, a step of applying a repetitive load gradually increasing at a predetermined frequency to a test piece and a temperature of the test piece are measured for each load value of the repetitive load. Then, based on the step of acquiring the temperature fluctuation waveform and the load value of the repeated load, the amplitude of the second harmonic of the fluctuation waveform and the phase of the second harmonic with respect to the fundamental wave of the fluctuation waveform. The step of calculating the deviation, the phase shift at the time of a small load with a repeating load sufficiently smaller than the fatigue limit, the step of acquiring the phase shift at the time of a large load with a repeating load sufficiently larger than the fatigue limit, and the amplitude of the second harmonic. Fatigue based on fatigue-related amplitude, which is the amplitude of the second harmonic related to fatigue damage of the fluctuating waveform for each load value of repeated load, based on the phase shift under small load and the phase shift under heavy load. Includes steps to identify limits.

小荷重時の位相ずれと大荷重時の位相ずれは、それぞれあらかじめ定められた荷重値における位相ずれとすることができる。 The phase shift at the time of a small load and the phase shift at the time of a large load can be the phase shift at a predetermined load value, respectively.

繰返し荷重を加えたときの試験片の温度の変動波形の、基本波に対する二次高調波の位相ずれであって、小荷重時の位相ずれと、大荷重時の位相ずれを用いることで、簡便に疲労損傷に関係する二次高調波の振幅を求めることができ、疲労限度の測定精度を高めることができる。 It is the phase shift of the second harmonic with respect to the fundamental wave of the fluctuation waveform of the temperature of the test piece when a repeated load is applied. The amplitude of the second harmonic related to fatigue damage can be obtained, and the measurement accuracy of the fatigue limit can be improved.

試験片の形状を示す図である。It is a figure which shows the shape of a test piece. 本実施形態の疲労限度特定装置の概略構成を示す図である。It is a figure which shows the schematic structure of the fatigue limit specifying apparatus of this embodiment. 繰返し荷重（応力振幅）と温度の二次高調波の振幅の関係を示す図である。It is a figure which shows the relationship between the cyclic load (stress amplitude) and the amplitude of the second harmonic of temperature. 繰返し荷重（応力振幅）と温度の基本に対する二次高調波の位相ずれの関係を示す図である。It is a figure which shows the relationship of the phase shift of the second harmonic with respect to the basic of a repeated load (stress amplitude) and temperature. 繰返し荷重（応力振幅）と温度の二次高調波の振幅、特に疲労損傷に関係する振幅との関係を示す図である。It is a figure which shows the relationship between the cyclic load (stress amplitude) and the amplitude of the second harmonic of temperature, particularly the amplitude related to fatigue damage.

以下、本発明の実施の形態を図面に従って説明する。図１は、試験片１０の形状を示す図であり、図２は、本実施形態の疲労限度特定装置１２の概略構成を示す模式図である。試験片１０は、長方形の板形状を有し、長方形の長辺の中央部分に円弧上の窪みが形成されている。疲労限度特定装置１２は、試験片１０に繰返し荷重を加える疲労試験機１４と、繰返し荷重が加えられている試験片１０の温度を測定する装置である赤外線カメラ１６と、測定された温度に基づき、疲労限度を特定する情報処理装置１８とを含む。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the shape of the test piece 10, and FIG. 2 is a schematic diagram showing a schematic configuration of the fatigue limit specifying device 12 of the present embodiment. The test piece 10 has a rectangular plate shape, and a depression on an arc is formed in the central portion of the long side of the rectangle. The fatigue limit specifying device 12 is based on a fatigue tester 14 that repeatedly applies a repeated load to the test piece 10, an infrared camera 16 that measures the temperature of the test piece 10 to which the test piece 10 is repeatedly loaded, and the measured temperature. , Including an information processing device 18 for specifying a fatigue limit.

疲労試験機１４は、試験片１０の両端をそれぞれ把持し、試験片１０に対して、所定の周波数で繰返し、引張荷重および圧縮荷重を加えることができる。情報処理装置１８は、演算装置２０、演算装置２０に所定の動作を実行させるためのプログラムおよび所定の数値などを記憶するための記憶装置２２を含む。赤外線カメラ１６は、他の温度測定装置、例えば試験片に接触して、その温度を特定する検出装置であってよい。 The fatigue tester 14 can grip both ends of the test piece 10 and repeatedly apply a tensile load and a compressive load to the test piece 10 at a predetermined frequency. The information processing apparatus 18 includes an arithmetic unit 20, a program for causing the arithmetic unit 20 to execute a predetermined operation, and a storage device 22 for storing a predetermined numerical value and the like. The infrared camera 16 may be a detection device that identifies the temperature by contacting another temperature measuring device, for example, a test piece.

次に、疲労限度の算出方法について説明する。疲労試験機１４を用いて試験片１０に対して、繰返し荷重を加える。繰返し荷重は、小さい荷重から大きい荷重に段階的に増加させる。例えば、周波数５Ｈｚで、試験片の応力振幅が２００ＭＰａから５００ＭＰａに段階的に増加するよう荷重を加える。まず、応力振幅が２００ＭＰａとなる荷重で１３００周期、荷重を加え、次に荷重を増加させて再び１３００周期の荷重を加える。これを応力振幅が５００ＭＰａになるまで繰り返す。繰返し荷重を加えている過程で、赤外線カメラで試験片１０を撮影し、荷重変動に応じて変化する温度変動を取得する。温度の測定は、１３００周期の中の定められた区間、例えば１０００〜１０９５周期の区間で計測する。 Next, a method of calculating the fatigue limit will be described. A fatigue tester 14 is used to repeatedly apply a load to the test piece 10. The repetitive load is gradually increased from a small load to a large load. For example, at a frequency of 5 Hz, a load is applied so that the stress amplitude of the test piece gradually increases from 200 MPa to 500 MPa. First, a load with a stress amplitude of 200 MPa is applied for 1300 cycles, then the load is increased and a load of 1300 cycles is applied again. This is repeated until the stress amplitude reaches 500 MPa. In the process of repeatedly applying the load, the test piece 10 is photographed with an infrared camera, and the temperature fluctuation that changes according to the load fluctuation is acquired. The temperature is measured in a defined section in 1300 cycles, for example, in a section of 1000 to 95 cycles.

取得した温度変動は、繰返し荷重の周波数と同じ周波数の成分と、繰返し荷重の周波数の２倍の周波数成分とを含む。前者を基本波、後者を二次高調波と記す。試験片１０の温度変動Ｔ(t)は、次式（１）で表される。 The acquired temperature fluctuation includes a component having the same frequency as the frequency of the repeating load and a frequency component having twice the frequency of the repeating load. The former is referred to as the fundamental wave and the latter is referred to as the second harmonic. The temperature fluctuation T (t) of the test piece 10 is represented by the following equation (1).

Figure 2021193341
ここで、Ｔmは平均温度、Ｔcは、周囲への温度損失、ωは繰返し荷重の角周波数、Ｔ1は温度の基本波の振幅、θ1は温度の基本波の初期位相、Ｔ2は温度の二次高調波の振幅、θ2は温度の二次高調波の初期位相である。
Figure 2021193341
 Here, T m is the average temperature, T c is the temperature loss to the surroundings, ω is the angular frequency of the cyclic load, T 1 is the amplitude of the fundamental wave of temperature, θ 1 is the initial phase of the fundamental wave of temperature, and T 2 Is the amplitude of the second harmonic of temperature, and θ 2 is the initial phase of the second harmonic of temperature.

疲労損傷となる微小な破壊は、引張荷重と圧縮荷重のそれぞれの最大時に発生するため、疲労損傷は温度変化の二次高調波に関係する。二次高調波成分は、次式（２）のように、疲労損傷に無関係な成分と、疲労損傷に関係する成分とを含む。式（２）の右辺第１項が疲労損傷に無関係な成分であり、第２項が疲労損傷に関係する成分である。 Fatigue damage is related to the second harmonic of temperature change, because minute fractures that result in fatigue damage occur at the maximum of each of the tensile load and the compressive load. The second harmonic component includes a component unrelated to fatigue damage and a component related to fatigue damage as in the following equation (2). The first term on the right side of the equation (2) is a component unrelated to fatigue damage, and the second term is a component related to fatigue damage.

Figure 2021193341
ここで、Ａnは疲労損傷に無関係な温度の二次高調波の振幅、Δθnは疲労損傷に無関係な位相ずれ、Ａdは疲労損傷に関係する温度の二次高調波の振幅、Δθdは疲労損傷に関係する位相ずれ、Δθ2は温度の基本波に対する二次高調波の位相ずれである。なお、温度の基本波に対する二次高調波の位相ずれΔθ2は、前述の非特許文献２に記載された式（３）で算出できる。
Figure 2021193341
 Here, A n is the amplitude of the second harmonic of the temperature unrelated to fatigue damage, Δθ n is the phase shift unrelated to fatigue damage, and A d is the amplitude of the second harmonic of the temperature related to fatigue damage, Δθ d. Is the phase shift related to fatigue damage, and Δθ 2 is the phase shift of the second harmonic with respect to the fundamental wave of temperature. The phase shift Δθ 2 of the second harmonic with respect to the fundamental wave of temperature can be calculated by the equation (3) described in the above-mentioned non-patent document 2.

式（２）を変形すると、式（４）、（５）を得る。

Figure 2021193341
By transforming the equation (2), the equations (4) and (5) are obtained.
Figure 2021193341

式（４）、（５）からＡnを消去すると、次式（６）を得る。

Figure 2021193341
Equation (4), clearing the A n from (5), we obtain the following equation (6).
Figure 2021193341

疲労損傷となる微小な破壊は疲労限度以上の繰返し荷重で発生する。よって、疲労限度に比べて十分小さな繰返し荷重では、式（２）の第１項、つまり疲労損傷に無関係な項が支配的であり、Δθ2は概ねΔθnとなると考えられる。一方、疲労限度に比べ十分大きな繰返し荷重では、式（２）の第２項、つまり疲労損傷に関係する項が支配的になり、Δθ2は概ねΔθdとなると考えられる。したがって、疲労限度に比べて十分小さな繰返し荷重のときに得られたΔθ2をΔθnとし、疲労限度に比べて十分大きな繰返し荷重のときに得られたΔθ2をΔθdとし、これらのΔθnおよびΔθdと、各繰返し荷重における温度変動のデータから得られるＴ2およびΔθ2とを式（６）に代入することで、疲労損傷に関係する二次高調波の振幅Ａdが算出できる。 Minor fractures that result in fatigue damage occur with repeated loads above the fatigue limit. Therefore, at a repeating load sufficiently smaller than the fatigue limit, the first term of Eq. (2), that is, the term unrelated to fatigue damage, is dominant, and it is considered that Δθ 2 is approximately Δθ n. On the other hand, at a repeating load sufficiently larger than the fatigue limit, the second term of Eq. (2), that is, the term related to fatigue damage, becomes dominant, and Δθ 2 is considered to be approximately Δθ d. Therefore, Δθ 2 obtained when the repetitive load is sufficiently smaller than the fatigue limit is Δθ n, and Δθ 2 obtained when the repetitive load is sufficiently larger than the fatigue limit is Δθ d, and these Δθ n are used. By substituting and Δθ d and T 2 and Δθ 2 obtained from the data of the temperature fluctuation at each repeated load into Eq. (6), the amplitude A d of the second harmonic related to fatigue damage can be calculated.

図３は、繰返し荷重による応力振幅に対する温度の二次高調波の振幅Ｔ2を示す図であり、図４は、繰返し荷重による応力振幅に対する温度の基本波に対する二次高調波の位相ずれΔθ2を示す図である。応力振幅が２００ＭＰａとなるように、試験片１０に対して繰返し荷重を加え、繰返しの所定の区間で赤外線カメラ１６を用いて試験片１０の表面温度を測定し、時系列の温度変動データＴ(t)を取得する。繰返し荷重の繰返し回数が所定数（例えば１３００周期）に達したら、応力振幅を例えば１０ＭＰａ増加させ、再び繰返し荷重を加える。これを応力振幅が５００ＭＰａになるまで繰返して、得られたグラフが図３および図４に示されている。繰返し荷重、つまり応力振幅の下限値と上限値は、経験的に得られる疲労限度σwよりも十分小さな、また十分大きな値とする。また、図３に示す二次高調波の振幅Ｔ2のグラフが得られれば、屈曲点が分かるので、繰返し荷重の下限値、上限値が適切であったかを判断し、適切でなければ、再度測定を行うこともできる。なお、試験は、２つの試験片１０に対して行い、図３、４には、それぞれの試験片の測定結果が示されている。また、同等の試験片に対して行われた一般的な疲労試験（材料学会標準（金属材料疲労信頼性評価標準［Ｓ−Ｎ曲線会期法］））により得られた疲労限度σwは３９６ＭＰａである。 FIG. 3 is a diagram showing the amplitude T 2 of the second harmonic of the temperature with respect to the stress amplitude due to the repeating load , and FIG. 4 is a diagram showing the phase shift Δθ 2 of the second harmonic with respect to the fundamental wave of the temperature with respect to the stress amplitude due to the repeating load. It is a figure which shows. A repeated load is applied to the test piece 10 so that the stress amplitude becomes 200 MPa, the surface temperature of the test piece 10 is measured using an infrared camera 16 in a predetermined section of the repetition, and the time-series temperature fluctuation data T ( get t). When the number of repetitions of the repeated load reaches a predetermined number (for example, 1300 cycles), the stress amplitude is increased by, for example, 10 MPa, and the repeated load is applied again. This was repeated until the stress amplitude reached 500 MPa, and the obtained graphs are shown in FIGS. 3 and 4. The repetitive load, that is, the lower and upper limits of the stress amplitude, should be sufficiently smaller and sufficiently larger than the empirically obtained fatigue limit σ w. Further, if the graph of the amplitude T 2 of the second harmonic shown in FIG. 3 is obtained, the bending point can be known. Therefore, it is determined whether the lower and upper limits of the repeating load are appropriate, and if not, the measurement is performed again. Can also be done. The test was performed on two test pieces 10, and FIGS. 3 and 4 show the measurement results of each test piece. In addition, the fatigue limit σ w obtained by a general fatigue test (standard of the Society of Materials Science (metal material fatigue reliability evaluation standard [SN curve session method])) conducted on the same test piece is 396 MPa. be.

図３に示されるように、繰返し荷重が小さいときには、温度の二次高調波振幅Ｔ2は、荷重の増加と共に緩やかに増加し、疲労限度σw付近を境に急増する。疲労限度σw未満の温度の二次高調波振幅Ｔ2が緩やかに増加する範囲の温度変動は、疲労損傷に無関係な温度振幅の影響を受けたものと考えられる。また、図４に示されるように、位相ずれΔθ2は、階段状に変化し、繰返し荷重が小さいときには低く概略一定値であり、疲労限度σw付近で大きく変化して疲労限度σwを超えると高くなり、ある値に漸近するように見える。 As shown in FIG. 3, when the repetitive load is small, the second harmonic amplitude T 2 of the temperature gradually increases with the increase of the load, and rapidly increases near the fatigue limit σ w. It is considered that the temperature fluctuation in the range where the secondary harmonic amplitude T 2 at the temperature below the fatigue limit σ w gradually increases is affected by the temperature amplitude unrelated to the fatigue damage. Further, as shown in FIG. 4, the phase shift [Delta] [theta] 2 is changed stepwise, a substantially constant value lower when repeated load is small, it exceeds the fatigue limit sigma w varies greatly around the fatigue limit sigma w It becomes high and seems to approach a certain value gradually.

繰返し荷重が疲労限度σwより小さいときには、式（２）の第１項が支配的となり、このときの位相ずれΔθ2は、疲労損傷に無関係の位相ずれΔθnとみなすことができる。疲労限度σwから離れていた方が、疲労損傷による影響をより受けないと考えられるため、測定範囲の下限の繰返し荷重により得られた位相ずれΔθ2を疲労損傷に無関係な位相ずれΔθnとみなすことに合理性がある。また、繰返し荷重が疲労限度σwより大きいときには、式（２）の第２項が支配的となり、このときの位相ずれΔθ2は、疲労損傷に関係する位相ずれΔθdとみなすことができる。疲労限度σwから離れていた方が、疲労損傷に無関係な第１項が相対的に小さくなると考えられ、その影響を小さくすることができるため、測定範囲の上限の繰返し荷重により得られた位相ずれΔθ2を疲労損傷に関係する位相ずれΔθdとみなすことに合理性がある。 When the repetitive load is smaller than the fatigue limit σ w , the first term of Eq. (2) becomes dominant, and the phase shift Δθ 2 at this time can be regarded as the phase shift Δθ n irrelevant to fatigue damage. Since it is considered that the distance from the fatigue limit σ w is less affected by fatigue damage, the phase shift Δθ 2 obtained by the repeated load at the lower limit of the measurement range is referred to as the phase shift Δθ n unrelated to fatigue damage. It is rational to consider it. Further, when the repeated load is larger than the fatigue limit σ w , the second term of the equation (2) becomes dominant, and the phase shift Δθ 2 at this time can be regarded as the phase shift Δθ d related to fatigue damage. It is considered that the first term unrelated to fatigue damage becomes relatively smaller when the distance is far from the fatigue limit σ w , and the effect can be reduced. Therefore, the phase obtained by the repeated load at the upper limit of the measurement range It is rational to regard the shift Δθ 2 as the phase shift Δθ d related to fatigue damage.

位相ずれΔθn、Δθdは、温度の二次高調波の振幅Ｔ2のグラフの屈曲点を求め、この屈曲点の繰返し荷重（応力）から、所定値低い荷重時、所定値高い荷重時の位相ずれΔθ2を用いるようにしてもよい。例えば、屈曲点に対し２０％以下の荷重、２０％以上の荷重の時の位相ずれΔθ2を用いるようにしてもよい。また、位相ずれΔθn、Δθdは、それぞれ所定値より低い荷重範囲の平均値（例えば２０％以下の荷重の平均値）、所定値より高い荷重範囲の平均値（例えば２０％以上の荷重の平均値）としてもよい。さらにまた、位相ずれΔθn、Δθdは、図４に示す位相ずれΔθ2のグラフを用いてステップ形状の下段から上段に遷移する範囲を排除し、下段に相当する範囲の平均値、上段に相当する範囲の平均値としてもよい。 For the phase shifts Δθ n and Δθ d , the bending point of the graph of the amplitude T 2 of the second harmonic of the temperature is obtained, and from the repeated load (stress) of this bending point, when the load is low by a predetermined value and when the load is high by a predetermined value. The phase shift Δθ 2 may be used. For example, the phase shift Δθ 2 when the load is 20% or less and the load is 20% or more with respect to the bending point may be used. Further, the phase shifts Δθ n and Δθ d are the average value of the load range lower than the predetermined value (for example, the average value of the load of 20% or less) and the average value of the load range higher than the predetermined value (for example, the load of 20% or more). (Average value) may be used. Furthermore, for the phase shifts Δθ n and Δθ d , the range of transition from the lower stage to the upper stage of the step shape is excluded by using the graph of the phase shift Δθ 2 shown in FIG. It may be the average value in the corresponding range.

各繰返し荷重（応力）で測定された時系列温度変動データから得られた温度の二次高調波の振幅Ｔ2および位相ずれΔθ2と、疲労損傷に無関係な位相ずれΔθnおよび疲労損傷に関係する位相ずれΔθdとを式（６）に代入すると、疲労損傷に関係する温度の二次高調波の振幅Ａdを得ることができ、図５にこれを示す。図５では、図４に比べて、疲労限度σw未満の範囲における二次高調波の振幅の緩やかな増加が抑制され、ほぼ０となっており、疲労損傷に無関係な二次高調波の影響が低減されていると考えることができる。 It is related to the amplitude T 2 and phase shift Δθ 2 of the second harmonic of the temperature obtained from the time-series temperature fluctuation data measured at each repeated load (stress), and the phase shift Δθ n and fatigue damage unrelated to fatigue damage. If the phase shift [Delta] [theta] d that is substituted in equation (6), can be obtained amplitude a d of the second harmonic of the temperature related to fatigue damage, which is shown in FIG. In FIG. 5, as compared with FIG. 4, the gradual increase in the amplitude of the second harmonic in the range below the fatigue limit σ w is suppressed and becomes almost 0, and the influence of the second harmonic unrelated to fatigue damage is suppressed. Can be considered to be reduced.

図５のグラフから屈曲点を求め、屈曲点に対応する応力を疲労限度と特定することができる。屈曲点の求め方は、例えば次のとおりである。まず、仮の屈曲点を定め、この仮の屈曲点より低い繰返し荷重による測定点の近似直線を求め、この近似直線と各測定点の残差を二乗した値の総和を算出する。同様に仮の屈曲点より高い繰返し荷重による測定点について、近似直線と各測定点の残差を二乗した値の総和を算出する。複数の仮の屈曲点に対して同様に残差の二乗の総和を算出し、これらの総和の和が最も小さくなる仮の屈曲点を、このグラフの屈曲点とする。この屈曲点に対応する繰返し応力を疲労限度とすることができる。図５のグラフから、２つの試験片１０の疲労限度は、それぞれ３９７ＭＰａ、３８６ＭＰａと求められた。 The bending point can be obtained from the graph of FIG. 5, and the stress corresponding to the bending point can be specified as the fatigue limit. For example, the method of obtaining the bending point is as follows. First, a temporary bending point is determined, an approximate straight line of the measurement points with a repeating load lower than the temporary bending point is obtained, and the sum of the squared values of the approximate straight line and the residual of each measurement point is calculated. Similarly, for the measurement points with a repeating load higher than the temporary bending point, the sum of the approximate straight lines and the squared residuals of each measurement point is calculated. Similarly, the sum of the squares of the residuals is calculated for a plurality of temporary bending points, and the temporary bending point at which the sum of these sums is the smallest is defined as the bending point of this graph. The repeated stress corresponding to this bending point can be set as the fatigue limit. From the graph of FIG. 5, the fatigue limits of the two test pieces 10 were determined to be 397 MPa and 386 MPa, respectively.

情報処理装置は、疲労試験機の繰返し荷重の切替えなどを制御する制御装置として機能してもよい。また、情報処理装置は、疲労試験機から繰返し荷重に係る情報を取得し、この情報に基づき、赤外線カメラによる測定の制御、および測定された時系列温度変動のデータの処理を行うようにしてよい。 The information processing device may function as a control device for controlling switching of repeated loads of the fatigue tester. Further, the information processing apparatus may acquire information related to the repetitive load from the fatigue tester, control the measurement by the infrared camera, and process the measured time-series temperature fluctuation data based on this information. ..

１０ 試験片、１２ 疲労限度特定装置、１４ 疲労試験機、１６ 赤外線カメラ（温度測定装置）、１８ 情報処理装置、２０ 演算装置、２２ メモリ、Ｔ1 温度の基本波の振幅、θ1 温度の基本波の初期位相、Ｔ2 温度の二次高調波の振幅、θ2 温度の二次高調波の初期位相、Ａn 疲労損傷に無関係な温度の二次高調波の振幅、Δθn 疲労損傷に無関係な位相ずれ（小荷重時位相ずれ）、Ａd 疲労損傷に関係する温度の二次高調波の振幅、Δθd 疲労損傷に関係する位相ずれ（大荷重時位相ずれ）、Δθ2 温度の基本波に対する二次高調波の位相ずれ。
10 Test piece, 12 Fatigue limit identification device, 14 Fatigue tester, 16 Infrared camera (temperature measuring device), 18 Information processing device, 20 Computing device, 22 Memory, T 1 Temperature fundamental wave amplitude, θ 1 Temperature basics wave of the initial phase, T 2 temperature of the secondary harmonic amplitudes, theta 2 temperature of the secondary harmonic of the initial phase, a n second harmonic of the amplitude of the extraneous temperature fatigue damage, regardless of the [Delta] [theta] n fatigue damage a phase shift (small load when the phase shift), the second harmonic of the amplitude of the temperature related to a d fatigue damage, the phase shift (large load at the time phase shift) which is related to the [Delta] [theta] d fatigue damage, the fundamental wave of the [Delta] [theta] 2 temperature Phase shift of the second harmonic with respect to.

Claims (6)

試験片に対して、所定周波数で、段階的に増加する繰返し荷重を加える疲労試験機と、
前記試験片の温度を測定する温度測定装置と、
前記試験片の測定された前記温度に基づき疲労限度を求める情報処理装置と、
を備え、
前記情報処理装置は、
測定された前記温度の変動波形に基づき、前記繰返し荷重の荷重値ごとに、前記変動波形の二次高調波の振幅、および前記変動波形の基本波に対する二次高調波の位相ずれを算出し、
前記位相ずれであって、疲労限度より十分小さい前記繰返し荷重における小荷重時位相ずれと、疲労限度より十分大きな前記繰返し荷重における大荷重時位相ずれを取得し、
前記二次高調波の振幅と、前記小荷重時位相ずれと、前記大荷重時位相ずれとに基づき、前記繰返し荷重の荷重値ごとに、前記変動波形の疲労損傷に関係する二次高調波の振幅である疲労関連振幅を算出し、
前記疲労関連振幅に基づき疲労限度を特定する、
ように構成されている、
疲労限度特定装置。 A fatigue tester that applies a repeating load that gradually increases to a test piece at a predetermined frequency,
A temperature measuring device that measures the temperature of the test piece, and
An information processing device that obtains a fatigue limit based on the measured temperature of the test piece, and
Equipped with
The information processing device is
Based on the measured fluctuation waveform of the temperature, the amplitude of the second harmonic of the fluctuation waveform and the phase shift of the second harmonic with respect to the fundamental wave of the fluctuation waveform are calculated for each load value of the repeating load.
The phase shift at a small load, which is sufficiently smaller than the fatigue limit, and the phase shift at a large load, which is sufficiently larger than the fatigue limit, are obtained.
Based on the amplitude of the second harmonic, the phase shift at the time of a small load, and the phase shift at the time of a large load, the second harmonic related to the fatigue damage of the fluctuation waveform is generated for each load value of the repeating load. Calculate the fatigue-related amplitude, which is the amplitude,
Specifying the fatigue limit based on the fatigue-related amplitude,
Is configured as
Fatigue limit identification device. 請求項１に記載の疲労限度特定装置であって、前記小荷重時位相ずれと前記大荷重時位相ずれは、それぞれあらかじめ定められた荷重値における位相ずれである、疲労限度特定装置。 The fatigue limit specifying device according to claim 1, wherein the phase shift at a small load and the phase shift at a large load are phase shifts at predetermined load values, respectively. 請求項１または２に記載の疲労限度特定装置であって、前記情報処理装置は、前記小荷重時位相ずれをΔθn、前記大荷重時位相ずれをΔθd、前記温度の変動波形の基本波に対する二次高調波の位相ずれをΔθ2、前記温度の変動波形の二次高調波の振幅をＴ2としたとき、前記疲労関連振幅Ａdを、
Figure 2021193341
 に基づき算出するよう構成されている、疲労限度特定装置。 The fatigue limit specifying device according to claim 1 or 2, wherein the information processing device has a phase shift under a small load of Δθ n , a phase shift at a large load of Δθ d , and a fundamental wave of a fluctuation waveform of the temperature. when the second harmonic [Delta] [theta] 2 the phase shift, the amplitude of the second harmonic of the variation waveform of the temperature was T 2 relative to, the fatigue associated amplitude a d,
Figure 2021193341
 Fatigue limit identification device configured to calculate based on. 試験片に対して、所定周波数で、段階的に増加する繰返し荷重を加えるステップと、
前記試験片の温度を、前記繰返し荷重の荷重値ごとに測定し、前記温度の変動波形を取得するステップと、
前記温度の変動波形に基づき、前記繰返し荷重の荷重値ごとに、前記変動波形の二次高調波の振幅、および前記変動波形の基本波に対する二次高調波の位相ずれを算出するステップと、
前記位相ずれであって、疲労限度より十分小さい前記繰返し荷重における小荷重時位相ずれと、疲労限度より十分大きな前記繰返し荷重における大荷重時位相ずれを取得するステップと、
前記二次高調波の振幅と、前記小荷重時位相ずれと、前記大荷重時位相ずれとに基づき、前記繰返し荷重の荷重値ごとに、前記変動波形の疲労損傷に関係する二次高調波の振幅である、
前記疲労関連振幅に基づき疲労限度を特定するステップと、
を含む、疲労限度特定方法。 A step of applying a stepwise increasing repetitive load to the test piece at a predetermined frequency,
The step of measuring the temperature of the test piece for each load value of the repeated load and acquiring the fluctuation waveform of the temperature, and
A step of calculating the amplitude of the second harmonic of the fluctuation waveform and the phase shift of the second harmonic with respect to the fundamental wave of the fluctuation waveform for each load value of the repeating load based on the fluctuation waveform of the temperature.
The step of acquiring the phase shift at a small load in the repeating load, which is sufficiently smaller than the fatigue limit, and the phase shift at the time of a large load in the repeating load, which is sufficiently larger than the fatigue limit.
Based on the amplitude of the second harmonic, the phase shift at the time of a small load, and the phase shift at the time of a large load, the second harmonic related to the fatigue damage of the fluctuation waveform is generated for each load value of the repeated load. Amplitude,
The step of specifying the fatigue limit based on the fatigue-related amplitude and
Fatigue limit identification methods, including. 請求項４に記載の疲労限度特定方法であって、前記小荷重時位相ずれと前記大荷重時位相ずれは、それぞれあらかじめ定められた荷重値における位相ずれである、疲労限度特定方法。 The fatigue limit specifying method according to claim 4, wherein the phase shift at a small load and the phase shift at a large load are phase shifts at predetermined load values, respectively. 請求項３または５に記載の疲労限度特定方法であって、前記疲労関連振幅を算出するステップは、前記小荷重時位相ずれをΔθn、前記大荷重時位相ずれをΔθd、前記温度の変動波形の基本波に対する二次高調波の位相ずれをΔθ2、前記温度の変動波形の二次高調波の振幅をＴ2としたとき、前記疲労関連振幅Ａdを、
Figure 2021193341
 に基づき算出する、疲労限度特定方法。
In the method for specifying the fatigue limit according to claim 3 or 5, in the step of calculating the fatigue-related amplitude, the phase shift under a small load is Δθ n , the phase shift under a large load is Δθ d , and the temperature fluctuation. when [Delta] [theta] 2 phase shift of the second harmonic to the fundamental wave of the waveform, the amplitude of the second harmonic of the variation waveform of the temperature was T 2, the fatigue associated amplitude a d,
Figure 2021193341
 Fatigue limit identification method calculated based on.
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