Energy features of an adiabatically loaded anharmonic oscillator

An excited anharmonic oscillator is considered under conditions of adiabatic (i.e., slow, as compared to the oscillation period) loading with an external force tending to a constant value at long times. The energy characteristics of the adiabatically loaded anharmonic oscillator, such as the instantaneous energy of the oscillator, the maximum kinetic (oscillation) energy, and the kinetic and potential energies averaged over the period, are analytically calculated as a function of the steady-state force. The analytical results are confirmed by the data of numerical calculations. It is established that the external force gives rise to a redistribution of the average kinetic and potential components of the initial energy of the anharmonic oscillator and that the transferred energy portions at a small external force considerably exceed the average work done by the external force.     

On elementary events in the electrical failure kinetics of polymers

The kinetics of electrical failure of poly(ethylene terephthalate) under different experimental conditions is studied. Process variables are the film thickness, electrode configuration and material, presence of partial discharges, and field application conditions. It is found that the potential barrier for elementary events, which controls the failure kinetics, is nearly the same irrespective of the process, 1.1–1.3 eV. The control process is discussed.     

Energetics of the thermoelastic effect in solids

The dependence of the temperature on the external adiabatic deformation is determined for a one-dimensional model of a solid — chains of atoms with an anharmonic interaction. The resulting dependences of the average kinetic and potential components of the internal energy on this deformation are compared with a model of adiabatic loading of a single oscillator. Fiz. Tverd. Tela (St. Petersburg) 40, 1548–1551 (August 1998)     

Effect of submicroscopic crack formation and relaxation phenomena in polymers

The development of submicrocracks and the changes taking place in their concentration during loading and unloading cycles were studied by the low-angle x-ray scattering method in oriented amorphous-crystalline polymers (capron and polypropylene). The deformation () of the polymers was compared with the changes in submicrocrack concentration (N_cr).A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 387–392, May–June, 1970.     

Behavior of the supermolecular structure of oriented amorphous-crystalline polymers under cyclic loading

Equipment has been developed for investigating small-angle X-ray diffraction in various phases of the loading period in cyclically extended polymers. The behavior of the large-period structure of oriented polycaprolactam (kapron) films in cyclic extension has been studied. The results are compared with the data on the behavior of the same structure in static tests.Mekhanika Polimerov, Vol. 4, No. 2, pp. 195–199, 1968     

Embryonic submicroscopic cracks in loaded polymers

The experimental work on embryonic fracture cracks in polymers recently carried out in the A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, is reviewed. The cracks have been studied by diffraction methods, chiefly by small-angle x-ray scattering. A principal result of this research is the possibility of formulating the general principle of a micromechanics of polymer fracture. The theory is based on data on the behavior of submicrocracks in polymers (size, concentration), the structural conditions and molecular mechanism of crack formation, the enlargement of submicrocracks, their influence on microcrack formation, and the growth of the macrocracks.     

Mechanisms of elementary events in the kinetics of electrical breakdown of polymer and ceramic dielectrics

The kinetics of electrical breakdown of thin (15–70 μm) layers of polymers and ceramics in a constant-sign field at 77–480 K has been investigated. The temperature dependences of the longevity (breakdown waiting time) of both dielectrics have been found to be similar to each other. At elevated temperatures, the longevity of the dielectrics varies exponentially with increasing temperature, and at reduced temperatures, it is temperature-independent (there is an athermal plateau). The mechanisms of elementary events controlling the process of preparation of the dielectrics for breakdown at elevated and reduced temperatures are the thermal-fluctuation over-barrier electron transition from trap to trap and the tunneling (under-barrier) transition, respectively. The hopping electron transport in the field direction gives rise to critical space charges causing breakdown of the dielectrics. The transition barrier heights (trap depths) have been determined. The low-temperature longevities of the polymer and the ceramic have been found to be similar, whereas the transition barrier for the ceramic is much higher than that for the polymer and the applied field in the former case is significantly (by a factor of tens) lower than that in the latter case. Electron traps in the polymer are adequately described by the Coulomb center model, whereas this is not the case for the ceramic.     

Features of the kinetics of electrical damage of polymers

The kinetics of electrical damage (breakdown) of polymer films 20–50 μm thick in a constant-sign field of 0.5–0.6 GV/m at 77–300 K has been studied. At elevated temperatures (250–300 K), the exponential temperature dependence of the durability and the above-barrier thermal-fluctuation mechanism of electron emission from traps, i.e., space charge accumulation leading to breakdown, take place. At low temperatures (77–200 K), there are separate local decreases in the durability (minima) at the athermal durability level. The identity of the temperatures of durability minima and measured thermoluminescence maxima of polymers was found. A conclusion is made about the mechanism of thermally stimulated tunneling (subbarrier emission) of electrons from traps.