Damage summation in nonstationary cyclic loading of fiberglass-plastic

Abstract

1. Damage accumulation in stationary or nonstationary isothermal cyclic loading of fiberglass-plastic is described by the very same relationships and is determined by the instantaneous values of damage and stress. On the basis of data on the kinetics of damage buildup in a stationary regime, it is possible to predict lifetime for a number of nonstationary isothermal regimes. 2. More damage builds up in the stationary regimes at small loads. These differences lead to deviations from the linear hypothesis of summation of relative lifetimes in isothermal experiments. In a stepwise diminishing load, lifetime is larger, and in a rising and programmed load it is less than that calculated by the linear hypothesis. The linear hypothesis may be used to calculate lifetime in isothermal programmed experiments having a predominance of high loads. Comparison of the stationary and nonstationary nonisothermal regimes on the basis of the linear hypothesis may lead to appreciable errors in estimating lifetime.