SN curve

Japanese: S-N 曲線 - えすえぬきょくせん

...The former includes stress concentrations at openings in plates such as deck hatches, manholes in the web of girders, and longitudinal penetrations, as well as localized stress concentrations at welds in ribs and stiffeners. In either case, the stress or strain amplitude calculated by experiments or the finite element method is applied to the S - N curve (a curve showing the relationship between the magnitude of repeated stress and the number of cycles at which fatigue failure occurs under that stress) of the hull structural material to estimate the fatigue life, and measures to reduce stress concentrations are taken as necessary, such as increasing the radius of bends, thickening, and welding finishes. On the other hand, with regard to buckling, the buckling strength of corners of trans-rings, member joints, and web openings is examined, and measures to prevent buckling are taken, such as thickening and arranging stiffeners.

From [Fatigue]

… Fatigue tests (also called fatigue tests) can be classified into those that use smooth, i.e., unnotched test pieces to determine the fatigue limit, and those that use notched test pieces to measure crack growth behavior. When fatigue tests are performed using smooth test pieces with various values for the difference between maximum and minimum stress (stress width), the relationship between the stress width σ _a and the number of cycles N leading to fracture is called the S - N curve (Wöhler curve). An example is shown in the figure, where the curve is bent at N = 10 ⁶ to 10 ^7. …

*Some of the terminology that refers to the "SN curve" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…前者には甲板の倉口や桁材の腹板における人孔，縦通材貫通部などの板の開口部における応力集中，さらに局部的には肋骨，防撓（ぼうとう）材などの溶接部における応力集中が含まれる。いずれも実験，あるいは有限要素法で算定された応力，あるいはひずみの振幅を船体構造材料のS‐N曲線(繰返し応力の大きさと，その応力のもとで疲労破壊が生ずる繰返し数との関係を示す曲線)にあてはめて疲労寿命を推定し，必要に応じて曲り部半径の増大，増厚，溶接仕上げの実施などによる応力集中の緩和策がとられる。一方，座屈に関しては，トランスリングの隅角部，部材結合部，腹板の開口部などにおける座屈強度が検討され，座屈防止のための増厚，防撓材配置などの対策がとられる。…

【疲労】より

…　疲労試験(疲れ試験ともいう)は，平滑な，すなわち切欠きのない試験片を用いて疲労限度を求めるものと，切欠きのある試験片を用いて亀裂進展挙動を計測するものとに分類できる。平滑な試験片を用いて，最大応力と最小応力との差(応力幅)をいろいろな値に変えて疲労試験を行ったとき，応力幅σ_aと，破壊に至る繰返し数Nとの関係をS‐N曲線(ウェーラー曲線)と呼ぶ。その例を図に示すが，N＝10⁶～10⁷で曲線が折れ曲がっている。…

※「S-N 曲線」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典第２版について | 情報

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