2004 Fiscal Year Annual Research Report
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
| Project/Area Number |
04F04078
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| Research Institution | Kyushu University |
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Principal Investigator |
村上 敬宜 九州大学, 大学院・工学研究院, 教授
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| Co-Investigator(Kenkyū-buntansha) |
KHOJASTEHPOUR M 九州大学, 大学院・工学研究院, 外国人特別研究員
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| Keywords | Shear Band / Bifurcation / Constitutive Behavior / Elastoplastic Materials / Elastoplasticity / Subloading Surface Model / Crack tip Plasticity / Mixed Mode Fracture |
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| Research Abstract |
Elastoplastic analysis of bifurcation and application to fatigue threshold analysis of small cracks
Bifurcation :
The constitutive equation for metallic and granular materials was first reviewed, in which the material functions were incorporated into the subloading surface model with the tangential stress rate effect. Then, based on the constitutive equation, both diffuse bifurcation modes, such as those corresponding to bulging (symmetric modes) and buckling (antisymmetric modes) in compressive loading or necking (symmetric modes) in tensile loading, and localized modes corresponding to the development of shear bands, for the rectangular and cylindrical specimen were analyzed. It was well-informed that the normal-yield ratio describing the degree of approach to the normal-yield state, and the tangential-plastic strain rate due to the tangential stress rate effect influence the onset of localized and diffuse bifurcations.
Fatigue and Fracture :
The characterization of the fracture process zone at the tip of a blunt crack in elastoplastic materials under mixed mode loading was discussed. Also, the description of elastoplastic zone geometry around the blunt crack tip for predicting crack growth direction was presented. The deformed zone appearing at the crack front was described by presenting a criterion based on the subloading surface concept falling within the framework of unconventional plasticity. It was well-informed that the mixed mode crack propagates along the minimum value of the elastoplastic region.
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