Seed Effort Toward "Multiscale Theoretical and Experimental Investigation of the Role of Structural Features on Damage Tolerance and Creep"

This report summarizes research ideas and some results in relation to effort conducted toward understanding the role of grain boundaries and grain boundary defects on the mechanical properties of metals, and with evolving interest in testing and learning the behavior of small specimens. It has been shown that by considering grain boundaries having different properties from grains, strengthening of metals as affected by grain size can be predicted. The analysis reveals that deformation in polycrystalline metals is heterogeneous and strain concentration evolves near grain boundary triple points and defects present on the grain boundary. An apparatus has been developed to perform tensile tests on small size samples within the chamber of the SEM. The tested samples of Ti-1100 alloy show considerably greater rate of strain hardening than specimens that are of conventional size. Because the grain size of these samples are the same, the higher hardening rate is believed to be a result of interaction of slip with specimen surface which occurs to a great extent per unit volume in the small size samples. Unfortunately, this seed effort remained as a seed effort and we were unable to continue the planned work due to inavailability of funds.