金属材料の応力集中部における簡便疲労寿命予測手法の実用性について

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Fatigue crack initiation life (FCI life) of stress concentration can be predicted according to compare between elastic-plastic strain at there and total strain-fatigue life curve (Δεt-Nf curve) of smooth specimen. Elastic-plastic strain is estimated by use of Neubers rule etc., and Δεt-Nf curve is estimated by use of Mansons universal slope method (US method) etc. At this point, cyclic stress-strain curve (CSS curve) is needed in order to estimate the elastic-plastic strain using Neubers rule etc. However, CSS curve formulated by Ramberg-Osgood relation can be transform from Δεt-Nf curve formulated by Coffin-Manson & Basquin relation. Consequently, simplified fatigue life prediction methods can be constructed by only mechanical properties (tensile strength, true fracture ductility, Young modulus, etc.), according to combine these estimation methods (Neubers rule, US method, etc.).In this report, we compared actual fatigue fracture life (FF life) of some stress concentration specimens with predicted FCI life of them obtained by use of simplified methods, and then evaluated about a practical use of simplified methods. The conclusions are obtained as follows :(1) About the precision of predicted fatigue life, modified universal slope method (MUS method) was better for steels, and Median method was better for aluminum alloys and titanium alloys.(2) For steels, the predicted fatigue life using ESED rule was more effective than using Neubers rule.(3) In case of using elastic stress concentration factor Kt, the ratio of predicted FCI life Np and actual FF life Nf (Np/Nf) was conspicuously decreasing with increasing of Kt.(4) Taking account of decrease of Np/Nf, simplified method can be employed for preliminary fatigue design.

金属材料の応力集中部における簡便疲労寿命予測手法の実用性について

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