Strain rate and hydrostatic pressure effects on strength of iron

The strength of iron under high strain rate and high pressure loading was studied using magnetic and laser driven ramp compressions. Combining the data reported in literatures, the yield strength of iron at strain rate from 10−3/s to 107/s was given out. Obvious strain rate effect on yield strength of iron was observed: below 101/s, the yield strength of iron changes little; from 101/s to 104/s, the yield strength of iron increases about three times; above 104/s, the yield strength of iron continually increases to remarkable values: at 107/s strain rate, it is ten times larger than that at 10−3/s. Based on the thermal fluctuation model of dislocation, the correlation between thermally activated stress and loading strain rate was analyzed. A characteristics method was used to explore the stress-volume curve of bcc iron under magnetically driven ramp compression, and the theoretical isentrope of bcc iron was deduced from isothermal compression data. By subtracting the theoretical isentrope from longitudinal stress, yield stress of bcc iron was calculated during ramp wave loading. Further analysis show that yield stress of bcc iron has little dependence on hydrostatic pressure.