Chiwei LUNG
,
Shenggang WANG
材料科学技术（英文）
After calculation on the fracture angles under various conditions of special surface energies with different symmetry operations of rotation, the complicated behavior of dependence of fractal dimension on the structure of crystal is shown. It is found that the crack propagates along the weakest crystal plane no matter what the direction of the maximum stress is if the anisotropy is sufficiently strong, and then, the fractal dimension of the fractured surfaces might be determined by the approximate fractal structure already existed in the material. Specificity of the fractal dimension of fractured surfaces would be easy to appear in this case. Reversely, the crack propagates along the direction of the maximum stress no matter what direction of the weakest crystal plane is if the anisotropy is sufficiently weak. Universality of the fractal dimension of fractured surfaces would be possible to appear in this case. In many real materials, universality and specificity of the materials are associated. The fractal dimension measured may more or less be influenced by the structure of materials and it shows its universality through the specificity of materials.
关键词:
Chiwei LUNG
,
Kang LONG
,
Enke TIAN
,
Zongjun LIANG
材料科学技术（英文）
The distortion regions near grain boundaries in cr-Fe-C solid solution were studied by use of internal friction method. It was found that the total thickness of these regions is quite large though the thickness of real grain boundaries is usually very thin. It was also found that the smaller the grain size, the thicker the total distortion region. A model for the structure of distortion regions near grain boundaries is proposed. Their effects on nanocrystalline materials are discussed.
关键词:
Chiwei LUNG
,
Jingyang WANG
材料科学技术（英文）
Experimental results of the temperature dependence of critical resolved shear stresses (CRSS) of Mo, Fe, Al and Mg single crystals are shown. Associating reports in recent years, we point out that the approximate exponential relationship between CRSS and the absolute temperature at least in the region of the steep temperature dependence range of many materials is more common, even for bcc, fcc, and hcp single crystals, polycrystals and other covalent crystals, provided that the slip plane and slip direction are kept the same. Successful explanation with atomic force law shows that the interatomic forces (electronic structure) play a decisive role in determining the temperature dependence of yield stresses for a large number of materials.
关键词:
Chiwei LUNG
,
Enke TIAN
,
Hengqiang YE
材料科学技术（英文）
Introducing the stress distribution near grain boundaries to improve the dislocation pileup model for the Halt-Petch (H-P) relation, the continuous distribution of dislocations in the pileup could be solved by means of Tschebysheff polynomials for the Hilbert transformation. An analytical formula of the stress intensity factor for the dislocation pileup is obtained. The reverse H-P relation may be explained by the modified dislocation-pileup-model.
关键词:
