Zhufeng YUE
材料科学技术（英文）
A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.
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Phenomenological anisotropic model
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Zhufeng YUE
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Zhenzhou Lü
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Deqiang WU
材料科学技术（英文）
Fracture behavior was studied for Ni-base single crystals and Ni-base bicrystals. The singlecrystals were machined from the bicrystal specimens to ensure that the single crystal samples had the same properties as those of the grains in the bicrystals. Using the three-point bend specimens, the fracture toughness Kc of single crystals and grain boundaries was measured, respectively. The two toughness values were little dependent on the ratio of the crack length to the height of the specimens. The grain boundary-induced shielding effect of fracture toughness was found in the grain-cracked bicrystals with normal front grain boundaries. The toughness varied with the distance between the crack tip and grain boundary. With the help of SEM analyses and numerical calculations, the mechanisms for the grain boundary-induced shielding are revealed. It is the grain boundary-induced redistribution of stresses and strains near the crack tip that induces the grain boundary-induced shielding. And the strain energy density criterion can be applied to the fracture of bicrystals. Agreement with experiments is good.
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