科研之友
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摘要
We consider rolled sheets of cubic metals which are macroscopically orthorhombic and microscopically aggregates of tiny crystallites. The preferred orientations of the crystallites create crystallographic texture, which is a main cause for the plastic anisotropy of the sheet metal. Crystallographic texture is characterized by the orientation distribution function or, equivalently, the texture coefficients. In this paper we propose, for weakly textured sheets of cubic metals, a new generalization of the Hosford yield criterion, which is applicable for any state of stress and, as a distinguishing feature, incorporates explicitly the effects of crystallographic texture on plastic anisotropy. Besides the principal stresses, our new yield function depends on the principal stress directions, certain texture coefficients (which can be measured by X-ray diffraction or electron backscatter diffraction), and three material parameters, namely the exponent eta, the uniaxial yield stress Y-iso for the isotropic polycrystal, and a parameter beta which describes the strength of the effects of crystallographic texture. We derive formulas with which the three material parameters can be calibrated by uniaxial and/or balanced biaxial tension tests. As examples, the three material parameters are calibrated against (i) the predictions of the Taylor model in uniaxial and balanced biaxial tension tests and (ii) experimental data on directional dependence of the q-value and uniaxial yield stress that pertain to two aluminum alloys. The values of the exponent eta determined by calibration with the Taylor model are approximately 10 and 6.6 for FCC and BCC sheet metals, respectively, which square well with the earlier findings of Hosford and coworkers. For the two aluminum alloys studied, it is found that both the plastic anisotropy of the q-value and of the uniaxial yield stress can be described reasonably well by the new yield criterion.
- 出版日期2013-2
- 单位南昌大学
