Experiment and analysis on evolution of yield surface in three-dimensional stress space for aluminum alloy
Date Issued
2012
Date
2012
Author(s)
Chang, Ruei-Cheng
Abstract
The evolution of yield surface in three dimentional axial-torsional-hoop stress space for
aluminum alloy Al 6061 was studied in this thesis. Yield surface of three dimensional stress
space was conducted by the yield points of several planer detections under a pre-loading path.
By virtue of specified experiments and qualitative analysis, we found the elastic behavior of Al
6061 is not isotropic but cubic. Therefore, we designed a criterion of yield stress determination
based on the incremental relationsof linear elasticity for cubic material. It enable us to conduct
probing paths not only on the plane of constant hoop stress but also on the plane of constant
torsional stress. After five kinds of different pre-loading paths, we observed that the subsequent
yield surfaces move toward pre-loading directions, and show a sharp front in the pre-loading
directions. Different characteristics of rotation are exhibited in our experiments. The sub-
sequent yield surfaces for axial pre-strain and for free-end pre-torsion rotate each around an
axis on the σ θθ = 0 plane. The yield surfaces for axial-hoop proportional pre-stress and hoop
pre-stress show the rotation around the pre-loading direction and the σ zθ axis respectively. The
rotation axis of free-end pre-torsion with σ θθ = 20 MPa is not on the coordinate planes. The
fitted results of cubic polynominals in three variables are supplemented our observation on yield
surface evolution in the (σ zz , σ zθ , σ θθ ) stress space.
Subjects
Al 6061
cubic material
yield surface
axial-torsional-hoop dimentional stress space
rotation
cubic polynominal
Type
thesis
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