THE DEPENDENCE OF THE STRENGTH OF ZINC-SULFIDE ON TEMPERATURE AND ENVIRONMENT

The dependence of the strength of zinc sulphide on temperature, enviro nment, surface finish and specimen size has been assessed. Room-temper ature fracture stresses were determined using a bursting disc geometry for a number of different surface finishes and for two different samp le sizes. High- and low-temperature fracture stresses in a dry nitroge n atmosphere were obtained from experiments using the Brazilian test g eometry and showed that the average strength of the material remained above or equal to the room-temperature value within the range -70 to 600-degrees-C. The Brazilian test is an indirect tensile technique whi ch is attractive for its experimental simplicity but gives fracture st ress values which are consistently below those obtained by direct tens ile techniques. The data from this test were therefore compared at roo m temperature to results obtained from the bursting disc test on sampl es which had been prepared using the same techniques. The possibility of delayed failure through environmentally enhanced slow crack growth was evaluated using the double-torsion technique which revealed slow c rack growth below the critical stress intensity factor.