| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 99 === This thesis studies the evolution of yield surfaces for Al6061 under strain control in the axial and torsional directions and stress control in the hoop direction. A new method of automated yield stress probing is based on proof strain and used in
the determination of yield surfaces. The experimental determination of the subsequent yield surfaces in (σ_θz-σ_θθ), (σ_zz-σ_θθ) and (σ_zz-σ_θz) spaces after proportional and non-proportional loading paths were conducted to investigate the evolution of the yield surfaces. The experimental result showed that the rotation of the subsequent yield surfaces in the (σ_θz-σ_θθ) space was dependent on torsional pre-loading paths, and in the (σ_zz-σ_θθ) space, the subsequent yield surfaces of axial pre-loading paths showed obvious rotation. Finally, 3D yield surfaces of different pre-loading paths constructed by using the data of the yield points in the (σ_θz-σ_θθ), (σ_zz-σ_θθ) and (σ_zz-σ_θz) spaces were conducted to investigate the evolution of the yield surfaces in the 3D stress space. The result showed that the subsequent yield surfaces of torsional pre-loading paths rotated around the σ_zz axis , and the subsequent yield surfaces of axial pre-loading paths rotated around the σ_θz axis in the 3D stress space.
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