Stochastic Processes and the Strength of Metals Containing a Limited Number of Dislocations
讲座名称：
Stochastic Processes and the Strength of Metals Containing a Limited Number of Dislocations
讲座时间：
2014-09-12
讲座人：
George Pharr
形式：
校区：
兴庆校区
实践学分：
讲座内容：
讲座名称：Stochastic Processes and the Strength of Metals Containing a Limited Number of Dislocations
讲座时间：9月12日（周五）上午 9:00-11:00
讲座地点：材料学院 205 会议室
讲座内容：
Since its development in the mid-1980's, nanoindentation and other related mechanical testing techniques have led to the discovery of a variety of unique small-scale deformation phenomena in materials. Among these are the indentation size effect, in which hardness at small indenter penetration depths increases; indentation pop-in, in which sudden displacement excursions are caused by homogenous nucleation of dislocations at stresses approaching the theoretical strength; and micro-pillar compression testing, in which the nanoindenter is used as a small-scale compression testing apparatus to explore deformation phenomena in samples small enough to probe single dislocation events. One common theme in these observations is that "smaller is stronger", and a great deal of research over the past decade has focused on the physical origin of these effects. In this presentation, a simple stochastic model based on the behavior of specimens containing a small number of dislocations is presented that explains many of the observations. The model is tested by comparing its predictions to recent experimental observations of the yield strengths of sub-micron diameter Mo alloy fibers tested in tension and compression as well as nanoindentation pop-in data for pure single crystals. The model correctly predicts not only the size dependence of strength, but also how the scatter in the strength should vary with specimen size.
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