Analysis of spectra of external impacts, reactions to them and limit states under the non-stationary modes of loading

It is noted that under real operating conditions of technical systems the so-called non-stationary loading in which external loadings increase or decrease arbitrarily is realized most often. At the same time final ratios between strains and stresses are of practical interest to engineering calculations. It is shown that for simple cyclic loadings the state equations in final ratios which are based on the theory of small elastic-plastic strains can be used. In this case the existence of the uniform generalized deformation diagram assuming a final relation between the corresponding components of stresses and strains both for initial and cyclic stages of deformation is essential for the analysis of considered conditions of a non-stationary cyclic loading. The analysis of conditions of achieving limit states at all stages of the life cycle the criteria base and the system of the computation equations become more complicated and more saturated by the factors taken into account and among them first external and internal impacts of natural, technogenic, anthropogenous origin, load from these impacts, and the reactions of installations to such impacts and loads as well. At the same time a set of criteria defining a limit state is presented in the form of a functional dependence characterizing a set of force and deformation parameters of the state of technical system on the one hand, and, on the other hand, a complex of criterion characteristics of constructional materials taking into account their change during operation. The most important step of determining conditions for achievement of the limit state causing fracture is establishing the critical parts that determine risks of emergency and catastrophic situations in which processes of local and main fractures are initiated. In this case transition of the operated installation from design area to the area of initiation of refusals, accidents and disasters occurs when the parameters of damage, defectiveness and risk reach their critical values.