9531930 Grujicic The objective of the proposed research is a multi-scale analysis of the role of martensitic phase transformation in inhibiting crack propagation. The key idea is that this mechanism of crack closure would be better understood if one could link the stress-assisted and strain-induced martensite formation to the state of stress imposed on the actual atoms at the extreme tip of a crack. The modeling effort will use computer simulation techniques (molecular dynamics and the finite element method) to analyze the fracture behavior of transformation toughened metallic materials and the predictions will be validated through metallic systems investigated in earlier work. This research should help to bridge the gap between information gained at different microstructural length scales, atomistic and macroscopic. ***