JP3870266B2 - Material life evaluation method and fatigue failure prevention method - Google Patents
Material life evaluation method and fatigue failure prevention method Download PDFInfo
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- JP3870266B2 JP3870266B2 JP2003127357A JP2003127357A JP3870266B2 JP 3870266 B2 JP3870266 B2 JP 3870266B2 JP 2003127357 A JP2003127357 A JP 2003127357A JP 2003127357 A JP2003127357 A JP 2003127357A JP 3870266 B2 JP3870266 B2 JP 3870266B2
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【０００１】
【発明の属する技術分野】
本発明は、原子炉材料などの安全面への特別な配慮が必要な材料などに好適に用いることのできる材料の寿命評価方法、及び前記材料の疲労破壊防止方法に関する。
【０００２】
【従来の技術】
従来の非破壊検査法としては、磁粉探傷法及び電磁誘導探傷法などがあるが、これらの方法はいずれも疲労破壊により材料中に亀裂が発生して初めて異常を検出できるものがほとんどであり、疲労亀裂発生前の損傷過程を捉えることができなかった。このため、原子炉材料などの安全面への特別な配慮が必要な材料などに好適に用いることはできなかった。
【０００３】
【発明が解決しようとする課題】
本発明は、疲労亀裂発生前に材料の損傷過程を捉えることのできる新規な材料の寿命評価方法を提供するとともに、材料の疲労破壊を未然に防止する方法を提供することを目的とする。
【０００４】
【課題を解決するための手段】
上記目的を達成すべく、本発明は、所定の材料に対して応力を繰り返し負荷し、前記材料に対する前記応力の負荷開始から破断までの自発磁化の変化を予めモニターして、前記材料の、前記応力負荷の繰り返し数と前記自発磁化との相関を導出し、前記材料の実際の使用において、前記材料の自発磁化を随時モニターし、その自発磁化の大きさを前記応力負荷の繰り返し数と前記自発磁化との前記相関と比較することにより、前記材料に対して応力を繰り返し負荷し、前記材料中の、変形誘起磁気遷移を通じて生じた自発磁化の大きさから前記材料の寿命を評価することを特徴とする、材料の寿命評価方法に関する。
【０００５】
本発明者らは上記目的を達成すべく鋭意検討を実施した。その結果、本発明者らは、材料の変形に伴って生じる格子欠陥と、前記変形に伴って誘起される磁気遷移、すなわち変形誘起磁気遷移を通じて生じる自発磁化との間に相関があることを見出した。換言すれば、前記材料中に生じる格子欠陥の増大に伴って前記材料の自発磁化が増大し、前記材料の破断直前には前記自発磁化が急激に上昇することを見出した。
【０００６】
具体的には、前記材料に対する応力負荷の繰り返し数と前記材料の自発磁化との相関を、前記応力負荷の開始から前記材料の破断までの間で予め求めておく。定常的な使用においては、応力負荷の繰り返し数と使用時間とは略比例するので、現在使用中の前記材料の自発磁化を随時モニターし、前記自発磁化の大きさを前記相関と比較検討すれば、前記材料の現在の疲労度を定量的に見出すことができ、さらには破壊に至るまでの寿命を定量的に知ることができるようになる。
【０００７】
また、前記材料の使用において、前記材料の自発磁化が破断時の自発磁化より小さい状態で前記材料の使用を中断するようにすれば、前記材料の疲労破壊を未然に防止できるようになる。
【０００８】
したがって、本発明の疲労破壊の防止方法は、所定の材料に対して応力を繰り返し負荷し、前記材料に対する前記応力の負荷開始から破断までの自発磁化の変化を予めモニターして、前記材料の、前記応力負荷の繰り返し数と前記自発磁化との相関を導出し、前記材料の実際の使用において、前記材料の自発磁化を随時モニターし、その自発磁化の大きさを前記応力負荷の繰り返し数と前記自発磁化との前記相関と比較し、前記材料の疲労破壊を未然に防止することを特徴とする。
【０００９】
【発明の実施の形態】
以下、本発明を発明の実施の形態に則して詳細に説明する。
本発明の方法に供する材料として、Ｆｅ−４０ａｔ％Ａｌ単結晶を採用し、この材料に基づいて本発明を具体的に説明する。
【００１０】
Ｆｅ−４０ａｔ％Ａｌ単結晶に対して、所定の温度範囲において、例えば３００ＭＰａの引張応力及び圧縮応力を繰り返し負荷した後、振動試料型磁力計を用いて温度７７Ｋで自発磁化を測定する。本来、Ｆｅ−４０ａｔ％Ａｌ単結晶は常磁性体であるため、自発磁化を持たないが、上述した応力の繰り返し負荷により、前記単結晶中には変形によって逆位相境界と呼ばれる欠陥が導入される。
【００１１】
前記欠陥の導入により、前記単結晶の原子配列が乱れ、Ｆｅ原子が磁化を有するようになって、強磁性体へ遷移するようになる。この結果、前記単結晶は自発磁化を有するようになるが、その自発磁化の大きさは欠陥密度に依存して２次関数的に増大するようになる。
【００１２】
図１は、室温大気中において、前記Ｆｅ−４０ａｔ％Ａｌ単結晶に３００ＭＰａの引張応力及び圧縮応力を繰り返し負荷した際の、繰り返し数と自発磁化の大きさとの関係を示すグラフである。図１から明らかなように、繰り返し数の増大、すなわち欠陥密度の増大とともに自発磁化の大きさが２次関数的に増大し、破断直前においては急激に増大することが分かる。
【００１３】
定常的な使用においては、応力負荷の繰り返し数と使用時間とは略比例するので、現在使用中の前記Ｆｅ−４０ａｔ％Ａｌ単結晶の自発磁化を随時モニターし、前記自発磁化の大きさを図１における相関グラフと比較検討すれば、前記単結晶の現在の疲労度を定量的に見出すことができ、さらには破壊に至るまでの寿命を定量的に知ることができるようになる。
【００１４】
例えば、使用中のＦｅ−４０ａｔ％Ａｌ単結晶の自発磁化を測定した際、図中のプロットＸで示すような自発磁化の値を得、この時までの使用時間がＴ時間であるとすると、破断時までの使用時間ＴＢを導出することができ、前記単結晶の寿命を知ることができるようになる。さらには、ＴＢ−Ｔより前記単結晶の使用可能な残時間を導出することもできる。
【００１５】
また、使用中の前記Ｆｅ−４０ａｔ％Ａｌ単結晶の自発磁化を測定した際、図中のプロットＹで示すような自発磁化の値を得た場合、前記自発磁化の大きさは破断直前の自発磁化が急激に増大する過程の大きさに相当するので、前記単結晶の使用を中止することにより、前記単結晶の疲労破壊を未然に防止することができるようになる。
【００１６】
以上、具体例を示しながら発明の実施の形態に則して本発明を説明してきたが、本発明は上記内容に限定されるものではなく、本発明の範疇を逸脱しない範囲において、あらゆる変形や変更が可能である。例えば、上記具体例においては、Ｆｅ−４０ａｔ％Ａｌ単結晶の場合について説明したが、本発明は前記単結晶に限らずあらゆる種類の材料に対して適用することができる。特に、安全面で特別な配慮が必要な原子炉材料などに好適に用いることができる。
【００１７】
【発明の効果】
以上説明したように、本発明によれば、疲労亀裂発生前に材料の損傷過程を捉えることのできる新規な材料の寿命評価方法を提供するとともに、材料の疲労破壊を未然に防止する方法を提供することができる。
【図面の簡単な説明】
【図１】 Ｆｅ−４０ａｔ％Ａｌ単結晶の、応力負荷の繰り返し数と自発磁化の大きさとの関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating the life of a material that can be suitably used for a material that requires special consideration for safety, such as a nuclear reactor material, and a method for preventing fatigue failure of the material.
[0002]
[Prior art]
As conventional nondestructive inspection methods, there are a magnetic particle inspection method and an electromagnetic induction inspection method, but most of these methods can detect an abnormality only when a crack occurs in a material due to fatigue failure. The damage process before fatigue cracks could not be captured. For this reason, it could not be suitably used for materials that require special safety considerations, such as reactor materials.
[0003]
[Problems to be solved by the invention]
It is an object of the present invention to provide a novel material life evaluation method capable of capturing the damage process of a material before the occurrence of fatigue cracks, and to provide a method for preventing fatigue fracture of the material.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention repeatedly applies stress to a predetermined material, and monitors in advance a change in spontaneous magnetization from the start of loading of the stress to breakage of the material. A correlation between the number of repetitions of stress load and the spontaneous magnetization is derived, and in the actual use of the material, the spontaneous magnetization of the material is monitored as needed, and the magnitude of the spontaneous magnetization is determined based on the number of repetitions of the stress load and the spontaneous magnetization. By comparing with the correlation with magnetization , stress is repeatedly applied to the material, and the lifetime of the material is evaluated from the magnitude of spontaneous magnetization generated through deformation-induced magnetic transition in the material. The present invention relates to a material life evaluation method.
[0005]
The inventors of the present invention have intensively studied to achieve the above object. As a result, the present inventors have found that there is a correlation between lattice defects caused by the deformation of the material and the magnetic transition induced by the deformation, that is, the spontaneous magnetization generated through the deformation-induced magnetic transition. It was. In other words, it has been found that the spontaneous magnetization of the material increases with an increase in lattice defects generated in the material, and the spontaneous magnetization rapidly increases immediately before the material breaks.
[0006]
Specifically, a correlation between the number of repeated stress loads on the material and the spontaneous magnetization of the material is obtained in advance from the start of the stress load to the fracture of the material. In steady use, the number of stress load repetitions and usage time are approximately proportional, so if you monitor the spontaneous magnetization of the material currently in use as needed and compare the magnitude of the spontaneous magnetization with the correlation Thus, the current fatigue level of the material can be found quantitatively, and further, the life until failure can be known quantitatively.
[0007]
Further, in the use of the material, if the use of the material is interrupted in a state where the spontaneous magnetization of the material is smaller than the spontaneous magnetization at the time of rupture, the material can be prevented from fatigue fracture.
[0008]
Therefore, the fatigue fracture prevention method of the present invention repeatedly applies stress to a predetermined material, monitors in advance the change in spontaneous magnetization from the start of stress loading to fracture of the material, A correlation between the number of repetitions of the stress load and the spontaneous magnetization is derived, and in actual use of the material, the spontaneous magnetization of the material is monitored as needed, and the magnitude of the spontaneous magnetization is determined based on the number of repetitions of the stress load and the Compared with the correlation with spontaneous magnetization, the material is prevented from fatigue fracture in advance.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail according to embodiments of the invention.
Fe-40 at% Al single crystal is adopted as a material to be used in the method of the present invention, and the present invention will be specifically described based on this material.
[0010]
For example, after repeatedly applying tensile stress and compressive stress of 300 MPa to a Fe-40 at% Al single crystal in a predetermined temperature range, spontaneous magnetization is measured at a temperature of 77 K using a vibrating sample magnetometer. Originally, the Fe-40 at% Al single crystal is a paramagnetic material and does not have spontaneous magnetization. However, due to the repeated loading of the stress described above, defects called antiphase boundaries are introduced into the single crystal due to deformation. .
[0011]
Due to the introduction of the defects, the atomic arrangement of the single crystal is disturbed, and the Fe atoms become magnetized and transition to a ferromagnetic material. As a result, the single crystal has spontaneous magnetization, but the magnitude of the spontaneous magnetization increases in a quadratic function depending on the defect density.
[0012]
FIG. 1 is a graph showing the relationship between the number of repetitions and the magnitude of spontaneous magnetization when 300 MPa tensile stress and compressive stress are repeatedly applied to the Fe-40 at% Al single crystal in room temperature air. As is clear from FIG. 1, it can be seen that as the number of repetitions increases, that is, as the defect density increases, the magnitude of the spontaneous magnetization increases as a quadratic function, and increases rapidly immediately before fracture.
[0013]
In steady use, the number of stress load repetitions and use time are approximately proportional, so the spontaneous magnetization of the Fe-40 at% Al single crystal currently in use is monitored as needed to show the magnitude of the spontaneous magnetization. If the comparison graph is compared with the correlation graph in FIG. 1, the present fatigue degree of the single crystal can be found quantitatively, and further, the life until failure can be quantitatively known.
[0014]
For example, when the spontaneous magnetization of the Fe-40 at% Al single crystal in use is measured, the value of the spontaneous magnetization as shown by the plot X in the figure is obtained, and the usage time up to this time is T time. The use time TB until the time of fracture can be derived, and the lifetime of the single crystal can be known. Furthermore, the remaining usable time of the single crystal can be derived from TB-T.
[0015]
In addition, when the spontaneous magnetization of the Fe-40 at% Al single crystal in use was measured, when the value of the spontaneous magnetization as shown by the plot Y in the figure was obtained, the magnitude of the spontaneous magnetization was Since this corresponds to the magnitude of the process in which the magnetization rapidly increases, it is possible to prevent fatigue breakdown of the single crystal by stopping the use of the single crystal.
[0016]
As mentioned above, the present invention has been described according to the embodiments of the present invention by showing specific examples. However, the present invention is not limited to the above contents, and all modifications and changes can be made without departing from the scope of the present invention. It can be changed. For example, in the above specific example, the case of an Fe-40 at% Al single crystal has been described, but the present invention is not limited to the single crystal and can be applied to all kinds of materials. In particular, it can be suitably used for nuclear reactor materials that require special considerations in terms of safety.
[0017]
【The invention's effect】
As described above, according to the present invention, a novel material life evaluation method that can grasp the damage process of a material before occurrence of a fatigue crack is provided, and a method for preventing fatigue fracture of the material is provided. can do.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the number of repeated stress loads and the magnitude of spontaneous magnetization of an Fe-40 at% Al single crystal.
Claims (6)
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| JP2003127357A JP3870266B2 (en) | 2003-05-02 | 2003-05-02 | Material life evaluation method and fatigue failure prevention method |
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| JP2003127357A JP3870266B2 (en) | 2003-05-02 | 2003-05-02 | Material life evaluation method and fatigue failure prevention method |
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| JP4805046B2 (en) * | 2006-07-20 | 2011-11-02 | 聰 島本 | Metal material damage evaluation apparatus using high sensitivity magnetic flux density meter, damage evaluation method and damage evaluation system |
| JP5325194B2 (en) | 2010-02-26 | 2013-10-23 | 株式会社神戸製鋼所 | Method for evaluating fatigue characteristics of T-joints in T-type welded joint structures |
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