Dynamic yielding in lithium fluoride and aluminum

Abstract

At a time immediately after shock loading, a kink ͑a weak discontinuity or a discontinuity in slope͒ occurs at a position in an unsteady portion in a smooth plane wave front in a lithium fluoride single crystal ͑material III b ͒ or in 1060-0 aluminum due to the instability of the wave front. After the occurrence of the kink, a zone is produced and broadened with time between a near steady precursor ahead of the kink and a plastic wave behind it in a weak-discontinuity plane wave by the difference in the propagation velocity between them. Stress relaxes in the zone, which is called a follower, and the precursor decay takes place due to the stress relaxation. During the decay process, the large increase in plastic flow occurs in the vicinity of the leading edge of the follower, causes yielding at the leading edge, and stabilizes the weak-discontinuity wave. The stress-strain ͑-͒ history caused by the follower rotates clockwise with time around the yield point. The rotation yields differenthistories behind the point and therefore different types of the dynamicrelation. Dynamic yield phenomena are illustrated by showing the schematic diagrams of three different types of the dynamicrelation, which are caused by weak-discontinuity plane waves composed of a precursor C, a follower ͑i͒ C, ͑ii͒ I or II, or ͑iii͒ RЈ or R b , and a plastic wave C behind the follower. Here C is the contraction ͑compression͒ wave, I and II are the degenerate contraction waves I and II, RЈ is the subrarefaction wave, and R b is the rarefaction wave.