材料の分岐変形に関する弾塑性変形解析と微小疲労き裂進展挙動解明への応用

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Elastoplastic analysis of bifurcation and application to fatigue threshold analysis of small cracksBifurcation :Analytical solutions are presented for the localized and diffuse bifurcations of an incompressible circular cylinder subjected to axisymmetric loading, whose constitutive behavior is described by adopting the tangential-subloading surface model falling within the framework of tangential plasticity. The analysis includes the conditions for shear band formation, shear band inclination, diffuse buckling formation, and the long and short wavelength limits of diffuse buckling modes in relation to material properties and stress. It becomes well-informed that the normal-yield ratio describing the degree of approach to the normal-yield state, the tangential-plastic strain rate due to the tangential-stress rate effect and the kinematic hardening variable influence the onset of localized and diffuse bifurcations.Fatigue and Fracture :The characterization of the elastoplastic zone at the tip of a blunt crack under mixed mode loading was discussed. The deformed zone appearing at the crack front is described by presenting a criterion based on the subloading surface concept falling within the framework of unconventional plasticity. It is revealed that the mixed mode crack propagates along the minimum value of the elastoplastic region.A study was conducted to clarify the behavior of a dislocation located on the inclined plane near a finite crack. Equations were presented for the forces based on the interactions between a finite crack and the dislocations near the crack tip. The influences of crack length on the forces applied to a dislocation were investigated using the extended equations.