Study On The Single Crystal Yield Surfaces Of Cubic Metals And Evolution Of Rolling Textures Of Pure Aluminumh

The single-crystal yield surfaces (SCYS's) of cubic metals and the evolution of rolling textures of pure aluminum have been investigated on the crystal plasticity theory of Taylor/Bishop-Hill in this thesis. The SCYS's and their characteristics in face-centered cubic (f.c.c.) metals for {111}<110>slip and {111}<112>twinning have been analyzed and derived systematically. As far as body-centered cubic (b.c.c.) metals are concerned, the SCYS's and their characteristics are analyzed and calculated for {110}<111> {112}<111>and {123}<111>multiple slip under the different cases. The Taylor factors and yield strength anisotropies have also been calculated for axisymmetric and ideal plane plastic deformation. Using the Taylor-type models, a new principle, the minimum sum of shear displacementgradient tensor components (|e12 + el3| + |e23| = min.)?has been proposed to solve the ambiguityproblem in the selection of active slip systems. The rolling textures of pure aluminum are simulated with randomly distributed initial orientations and initial textures. The influences of lubrication conditions on formation of cold-rolling textures of high-purity aluminum foils are investigated.It has been demonstrated strictly that the SCYS's of f.c.c. metals can be described in terms of ξ, the ratio of the critical resolved shear stresses for twinning on {111}<112>and slip on {111}<110>systems. The complete yield stress states available for slip or/and twinning deformation mechanism(s) have been established. The results demonstrated that only ξ is within the range of l/3 <. ξ < 2/3, slip and twinning can occur together. There are only two types of co-yield surfaces and the critical value is 3/2.The maximum work principle of Bishop-Hill has been developed to analyze the axial symmetric and plane deformation for the case of mixed slip and twinning in f.c.c. metals. The influences ofξ on the yield stress states and the corresponding active systems have been investigated in detail. The concept of orientation factorμ has been introduced to describe the twinning ability. The orientationsthat have twinning tendency in the orientation space have been established in the case of the ideal plane strain. The formation and the development of cold-rolling textures of f.c.c. metals with medium , low stacking fault energy can be explained qualitatively.The SCYS's of b.c.c. metals are analyzed systematically for {110}<111> {112}<111>and {123}<111>separated slip modes. The yield stresses for separated and mixed slip modes have been calculated and derived. Especially, The complete yield stress states have been established for {123}<111>multiple slip, It has been found that there are 338 yield stresses altogether while Chin et al [421only found 212 ones. The results show that the obtained new 126 stress states are necessary in order to analyze others plastic flow such as three-axial deformation. Compared with pure {110}<111>slip, the fraction of vertices for which there is slip ambiguity (more than five active systems) is reduced considerably as the {112}<111>and {123}<111>multiple slip are introduced.The influences of randomly distributed orientations and cube textures on the rolling textures of pure aluminum are investigated. A convenient and effective method has been suggested to show theinitial textures in samples. The new principle, |e12| + |e13|+| e23 = min, has been introduced to solvethe ambiguity in the selection of active slip systems during the simulation of rolling textures of pure aluminum and thus to satisfy the strain compatibility to the maximum extent. The influences of lubrication conditions on formation of cold-rolling textures of high-purity aluminum foils are investigated. The influences of lubrications on the rolling textures of high pure aluminum have beenstudied. The results show that the cold-rolling textures mainly consist of B> C and S components using machine oil lubrication. In the case of the kerosene lubricant, the rolling textures were weaker compared with machine oil lubrication, and the shear textu...