Simulation of RPG load:Study of Fatigue Crack Propagation Behavior Based upon RPG Load (5th Report)

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Newman showed crack opening/closing model during fatigue crack propagation under uniform stress field which was based on the Dugdale model, but modified to leave plastically deformed materials along the crack surface as the crack advances. In his model, however, he neglected the change of stress distribution ahead of a crack during loading process in the calculation of crack opening load. Moreover he also neglected the elastic deformation for a materials along the crack surface. Therefore he introduced plastic constrainted factor of 3.5 which was larger than the appropriate value of 1.21 obtained from comparison between COD's by elasto plastic FEM and those by Dugdale model for center notched specimens for the purpose of fitting experimental crack opening load.In this paper, Newman's model is modified to solve his neglected problems mentioned above and is expanded to arbitrary stress distribution field for the purpose of obtaining re-tensile plastic zone's generated load (RPG load). Moreover we consider plastic shrinkage at newly generated fracture surface during unloading process which corresponds to a part of deformation due to emancipation of acting force with a magnification of yield stress at an immediate growth of a crack in the region of fictitious crack in Dugdale model.Some calculation results are shown for understanding the effect of the plastic shrinkage at newly generated surfaces and the change of loading. Simulated results suggest that the effect of stress ratio and the effect of delayed reterdation due to decreasing maximum load become small as the plastic shrinkage becomes large.
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Simulation of RPG load:Study of Fatigue Crack Propagation Behavior Based upon RPG Load (5th Report)

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