Thermohydrodynamic description of adiabatic flow of He II, in which the high velocity region up to 100cm/s was studied, is given with a new-type mutual friction force. Experiments consist of various thermodynamic measurements and the NMR study of the motion of 3He atoms added to the system. There appeared various stages of the flow state of superfluid He II. Especially, there exist clearly two characteristic velocities vc1 and vc2. An interpretation of the results is given with the pinning-depinning model of quantized vortices, in which we made a conjecture that quantized vortices construct vortex-bundles in the presence of pinning-centers.
Effects of precracking temperatures and load on 4K fracture toughness, KIC, of tough 22Mn13Cr5Ni steel were investigated using an unloading compliance method. Compact tension specimens with a thickness of 25mm were precracked by fatigue at 298K, 77K and 4K. The stress intensity factor range, ΔKf, covered from 20 to 60MPa√m. The main results are as follows; (1) The experimental results showed that precracking temperatures and ΔKf hardly affected 4K-KIC of the 22Mn13Cr5Ni steel. (2) No α′ martensite was induced by precracking at all but ε martensite was induced at 4K. A subcritical crack growth started with a fracture of induced ε in 4K fracture toughness test. The dominant ε was not one induced by precracking but by fracture toughness test itself. Therefore the effects of ε by precracking at cryogenic temperature could be neglected. (3) Room temperature precracking produced a larger plastic zone than law temperatures. However its effect on 4K-KIC was very small because contraction of plastic zone could be expected and because ε was not induced at all.