The Effect of Hydrostatic Pressure on the Fracture of Polycrystalline Zinc

Abstract

The pressure-induced brittle ductile transition in polycrystalline zinc was examined, with special reference to the variation of transition pressure with the grain size of specimens. Fracture stress σ_fr in the brittle pressure range increases linearly with pressure P applied and is expressed as
(This article is not displayable. Please see full text pdf.)
where a constant η is nearly 0.35 and σ_fr(0) is the fracture stress at ambient pressure.
The pressure-induced transition has been found to occur when the fracture stress reaches the necking stress σ_n. The variation of transition pressure P_c with grain size comes from the dependence of σ_fr(0) on grain diameter d of specimens, i.e. σ_fr(0)=K_frd^−1⁄2, where K_fr is a constant, and the following relation is established:
(This article is not displayable. Please see full text pdf.)
Generally speaking, P_c does not vary linearly with d^−1⁄2, since the necking stress σ_n also depends on grain size. However, within a narrow grain size range in which the variation of σ_n is rather small, P_c satisfies the relation P_c∝d^−1⁄2.
Finally, the rapid or discontineous increase of ductility of zinc at the transition pressure has been explained on the basis of the previously proposed criterion of ductile fracture, viz. “the constancy of hydrostatic tensile stress”.