Plastic Flow in hcp ⁴He. II

The plastic flow in hcp 4 He was investigated by using a new equipment which was designed to improve the accuracy of measurements. The pronounced yield drop is always observed at moderately low temperatures or in high speed tests, but the yield drop becomes almost undetectable in low speed tests at high temperatures, where the steady flow stress is proportional to one fourth power of the flow rate. At low temperatures and at high pressures flattened upper yield points are observed frequently, and the steady flow stress becomes independent of the flow rate in low speed tests.

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