Strain rate change tests with the Split Hopkinson Bar method

In this paper, methods to produce rapid strain rate changes for strain rate sensitivity measurements in Split Hopkinson Bar arrangements are presented and discussed. Two different cases are considered: a strain rate change test within the high strain rate region in compression, and a tension test incorporating a large strain rate jump directly from the low strain rate region to high strain rates. The former method is based on the loading wave amplitude manipulation, while the latter method is based on the incorporation of a low strain rate loading device into a Tensile Split Hopkinson Bar apparatus.     

Numerical and experimental investigations of the effect of repeated cyclic thermal loads on the strength of materials of recoverable liquid-propellant rocket engines

Elements of the liquid-propellant rocket engines (LPREs) are subject to the action of intense mechanical and thermal loads, which are temporally related to the start-up, normal regime, and switch-off periods of the working cycle. Recoverable LPREs experience these loads many times. Repeated (cyclic) loads lead to the manifestation of processes typical of fatigue, whereby residual stresses and (plastic) deformations are retained and accumulated in the LPRE materials. Numerical investigations using models of the nonstationary thermal and stressed-strained state and the plastic behavior of materials have been performed in order to determine the limiting numbers of loading cycles for the structural materials employed in various units of LPREs. A special computational-experimental procedure is described, which allows these materials to be studied in a stressed-strained state close to that in real LPREs.     

Transformed steroids. 114. Direction of opening oxide ring of 16,17α-epoxy-17β-phenylandrost-4-en-3-one

Conclusions Starting with androst-5-en-3-ol-17-one, we synthesized 16,17-epoxy-17-phenylandrost-4-en-3-one. Cleavage of 17-C-O bond, adjacent to the phenyl ring, occurs during its nucleophilic opening, accompanied by 1,2-migration of the angular 18-CH₃ group.See [1] for Communication 113.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1889–1893, August, 1980.     

Why spin ice obeys the ice rules

The low-temperature entropy of the spin ice compounds, such as and , is well described by the nearest-neighbor antiferromagnetic Ising model on the pyrochlore lattice, i.e., by the "ice rules." This is surprising since the dominant coupling between the spins is their long ranged dipole interaction. We show that this phenomenon can be understood rather elegantly: one can construct a model dipole interaction, by adding terms of shorter range, which yields precisely the same ground states, and hence entropy, as the nearest-neighbor interaction. A treatment of the small difference between the model and true dipole interactions reproduces the numerical work by Gingras et al. in detail. We are also led to a more general concept of projective equivalence between interactions.     

Polarization of strontium-barium niobate crystals in pulsed fields

Polarization (ferroelectric switching) of SBN crystals in pulsed fields differs from the same process in model ferroelectrics. Polarization in most SBN crystals is characterized by slow kinetics, which can be approximated by a power-law dependence, with relaxation times of the order of seconds (in fields

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). The process smoothness results in the absence of a characteristic peak in the switching-current curve. Some crystals are characterized by fast (jumplike) polarization processes, whose characteristics (the kinetics and the field dependence of the switched charge) also differ from model ones.

     

Thermal ionization instability of an air discharge plasma in a microwave field

Results are presented from experimental studies of the initial stage of an air discharge initiated in a linearly polarized quasi-optical microwave beam. The discharge was excited at an air pressure at which the electron-neutral collision frequency in the discharge plasma was considerably higher than the circular frequency of the electromagnetic field and at a microwave field amplitude close to the threshold field for air breakdown. The experiments revealed relatively bright plasma channels stretched along the microwave electric field. The development rate of these channels and their characteristic transverse dimensions are estimated. A comparison of the experimental data and theoretical estimates indicates that the channels observed arise due to the onset of thermal ionization instability in the microwave discharge plasma.