9531187 Marder Using both analytical and numerical methods, this grant will study the connection between the interatomic forces and the behavior of materials during brittle fracture. Some questions to be asked are: "How does fracture occur on the atomic scale?" "When do the cracks propagate in a stable manner and when do the instabilities set in?" "What sorts of interatomic forces lead to brittle, or to ductile materials?" "What are the effects of thermal fluctuations upon fracture?" "What are the differences between fracture of amorphous and crystalline materials?" The proposed program of research also contains a strong collaboration with experiments. %%% In spite of more than sixty years of development in the modern understanding of materials, very little is known about the atomic nature of the strength of materials or how they fail under stress. This grant plans to develop an atom- level understanding of the mechanical properties, especially the ones related to failure. What are the atoms doing when a material fractures? On an atomic level, how is brittle fracture different from ductile fracture? What are the atoms doing when a glass fractures, and when a metal fractures? ***