Microstrain Yield Stress in Neutron-Irradiated Copper Single Crystals

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Abstract
τ0, the stress necessary to produce a plastic strain of 2×10−6, has been measured with the use of electrical resistance strain gauges in neutron‐irradiated copper single crystals as a function of neutron dose (∼1016 to 1020 neutrons/cm2) and testing temperature (77° and 300°K). τ0 increases from about 0.3 kg/mm2 for ∼1016 neutrons/cm2 to over 5 kg/mm2 for ∼1020 neutrons/cm2; in annealed copper crystals, τ0 is ∼0.02 kg/mm2 (previously determined by other researchers). At all neutron doses, τ0 is about 75% of the macroscopic flow stress. τ0 is observed to increase with the cube root of the neutron dose; the macroscopic flow stress shows the same dose dependence. The results are explained on the basis of dislocation generation and obstacle cutting mechanisms controlling the yielding. These mechanisms are thought to be simultaneously operative.