Scientists at the Massachusetts Institute of Technology studying a phenomenon called a flow-stress upturn—in which material strength can abruptly soar as the applied strain rate increases—have hit upon an atomic-level explanation that may lead to a set of general principles.Those principles should apply to many kinds of materials and ultimately could help explain phenomena including the breakdown of concrete or metal structures under sudden stress.
The research, by associate professor Bilge Yildiz, professor emeritus Sidney Yip and Ph.D. candidate Yue Fan, will be published in the journal Physical Review Letters.
Swimmers know flow-stress upturn: While the water parts like silk when a diver enters the pool from its edge, it is rock-hard if the diver launches from a high point. Such variation in the rate materials deform is well known but not fully understood, the researchers say. From modeling a defect called a "screw dislocation" in an iron-crystal lattice, they now believe the key lies in how rapidly atoms can react to force applied at a confined location. When the rate of deformation exceeds the rate at which the atoms can move aside, strength soars.
