Combined loading rate and specimen size effects on the material properties

The current interests in developing multiscale model-based simulation procedures have brought about the challenging tasks of bridging different spatial and temporal scales within a unified framework. However, the research focus has usually been on the scale effect in the spatial domain with the loading rate being assumed to be quasi-static. Although material properties are rate-dependent in nature, little has been done in understanding combined loading rate and specimen size effects on the material properties at different scales. On the other hand, the length and time scales that can be probed by the molecular level simulations are still fairly limited due to the limitation of existing computational capability. Based on the experimental and computational capabilities available, therefore, attempts have been made recently to formulate a hyper-surface in both spatial and temporal domains to predict combined size and rate effects on the mechanical properties of engineering materials. It appears from the preliminary results, with the use of tungsten and diamond specimens, that the proposed procedure might provide an effective means to bridge different spatial and temporal scales in a unified multiscale modeling framework, and facilitate the application of nanoscale research results to engineering practice. To provide a foundation for the future study of the combined rate and size effects on fracture mechanics, the recent research results are presented in this chapter.