The Effect of Strain Rate on Critical COD of Structural Steels

The effect of strain rate and low temperature on the critical COD (δc) of structural steels has been experimentally investigated. The materials tested are 20 mm thick ordinary mild steel (KAS ; yield stress 28 kgf/mm2) and 60 kgf/mm2 class high tensile steel (HW 45; yield stress 56 kgf/mm2). The 3-point bend COD testings were carried out at temperatures from -150°C to -10°C with crosshead speeds varied from 0.05 mm/min to 500 mm/min. For highest strain rate test, drop weight impact load was applied.The results of the investigation are summarized as follows. Values of δc for KAS and HW 45 decrease with increase in strain rate. Particularly, the decrease in δc for both materials is remarkable at temperature below -50°C and at crosshead speed (strain rate) above 50 mm/min. The data plot of δc against rate-temperature parameter, Tln (A/e) showed rather wide scatter band for both tested steels.