The fracture stress of single-crystal zinc

Abstract

The basal plane fracture stress of 99.999 pct pure single-crystal zinc tensile specimens was determined from 77 to 298 K as a function of strain rate. The fracture stress was found to be dependent on the size of existing flaws associated with surface preparation, when the thermal variation of surface energy was taken into account. The stress at fracture was independent of strain and strain rate and was inversely proportional to the square root of the corrected flaw size, suggesting that a Griffith-type equation was obeyed to high strains. When flaws do not exist or are negligibly small, fracture is believed to be nucleated by the splitting of subboundaries as a result of plastic flow. The strain at fracture for constant fracture stress decreases with an increase in strain rate and a decrease in temperature and depends on the values of the work-hardening coefficient and exponent.