Resource–saving Reserve of Strength Characteristics of Longitudinal Beam of the Metro Wagon Truck

In this paper, an analysis of methods for calculating structures from allowable stresses and from limiting states is made. It is shown that when the transition from the longitudinal beam calculation to the allowable stresses to the calculation of the limiting state, the strength limit increases by 1.5 times.A mathematical model of the stress–strain state of a longitudinal beam of metro wagon truck without taking into account the transverse force is developed. The mathematical modeling with the given margin of strength of the power calculation of the longitudinal beam metro wagon track, which is a simple beam of a constant hollow rectangular section, pinched at its ends and loaded along the middle of the span by a concentrated stationary force, is carried out.Thus, the application of the method of calculation for the limiting state makes it possible to identify the resource–saving reserve of the strength characteristics of the longitudinal beam of the metro wagon truck – a 3-fold increase in the maximum permissible load

Nonlogarithmic magnetization relaxation at the initial time intervals and magnetic field dependence of the flux creep rate in Bi2Sr2Ca(sub I)Cu2Ox single crystals

At the initial time intervals, preceding the thermally activated flux creep regime, fast nonlogarithmic relaxation is found. The fully magnetic moment Pm(t) relaxation curve is shown. The magnetic measurements were made using SQUID-magnetometer. Two different relaxation regimes exist. The nonlogarithmic relaxation for the initial time intervals may be related to the viscous Abrikosov vortices flow with j is greater than j(sub c) for high enough temperature T and magnetic field induction B. This assumption correlates with Pm(t) measurements. The characteristic time t(sub O) separating two different relaxation regimes decreases as temperature and magnetic field are lowered. The logarithmic magnetization relaxation curves Pm(t) for fixed temperature and different external magnetic field inductions B are given. The relaxation rate dependence on magnetic field, R(B) = dPm(B, T sub O)/d(1nt) has a sharp maximum which is similar to that found for R(T) temperature dependences. The maximum shifts to lower fields as temperature goes up. The observed sharp maximum is related to a topological transition in shielding critical current distribution and, consequently, in Abrikosov vortices density. The nonlogarithmic magnetization relaxation for the initial time intervals is found. This fast relaxation has almost an exponentional character. The sharp relaxation rate R(B) maximum is observed. This maximum corresponds to a topological transition in Abrikosov vortices distribution