Papers by Author: W. Yang

Abstract: A new technique for investigating 3D grain growth in polycrystalline materials using white x-ray microdiffraction with micron point-to-point spatial resolution is presented. This technique utilizes focused polychromatic x-rays at the Advanced Photon Source, differential aperture depth-profiling, CCD measurements, and automated analysis of spatially-resolved Laue patterns to measure local lattice structure and orientation. 3D thermal grain growth studies of hotrolled aluminum have been initiated to demonstrate the capabilities of this method. Complete 3D grain orientation maps were obtained from a hot-rolled aluminum polycrystal. The sample was then annealed to induce grain growth, cooled to room temperature, and re-mapped to measure the thermal migration of all grain boundaries within the same volume region. Initial observations reveal significant grain growth above 360°C, involving movement of both low- and high-angle boundaries. Systematic measurements have been obtained of the as-rolled grain structure and of the microstructural evolution after annealing at successively higher temperatures. Small second-phase precipitates have been identified. Such measurements will provide the detailed 3D experimental link needed for testing theories and computer models of 3D grain growth in bulk materials.

Abstract: The issues of intersonic and supersonic fracture become the frontier of dynamic fracture mechanics. We describe in this paper the recent progresses in obtaining the analytical continuum solution for the initial-boundary valued problem of intersonic fracture under mode II loading, and construct an plausible analytical solution for mode III supersonic fracture.

Abstract: Reciprocal Tribocontact has been manifested to be responsible for the certain attrition of artificial components in dental fields. But confusion on the aspects of friction and wear pattern was found between fretting and sliding, the two items often emerging in reports about friction and wear of biomaterials, due to the ambiguity on definition. By refining the definition of fretting with partial slip concept, this work compared friction and wear behaviors of three dental alloys under fretting and sliding conditions. Results indicate that friction force waveform and surface damage topography created by fretting quite differs from by sliding. The curve of friction force vs time under fretting is of nearly perfect sine waveform; some micro disturbance occurs on the peaks and valleys of the waveform while the amplitude is big enough. Wear patterns from fretting consist of a central stick region, a surrounding slip region and sometimes crack between the two regions, but wear patterns from sliding are of linear tracks running through the entire scar, scraped trace or severe surface deformation.