Vodka O. Development of methods for assessing life-time of bolted connection of Kaplans turbine runner

Object of study: the process of the accumulation of the high cycle fatigue damage in water turbine impeller bolted joints. Purpose of research: the creation of methods for assessing structural strength and reliability of threaded fasteners in the elements of power machines allowing for the technological and operational load, and degradation of the material; using the developed approach to determine the parameters of reliability and life-time of the water turbines impeller bolted joints. Methods of research: theoretical basis of the thesis are methods of mechanics of deformable solid body; theory of vibrations; continuum damage mechanics; probability theory and stochastic processes. Calculation of stress-strain state of bolted joints is performed within the finite element method. For the experimental research methods strain gauges, vibration measurement and digital signal processing is used. Theoretical and practical results: the generalized probabilistic mathematical model of accumulation of fatigue damage for life-time prediction of the bolted joints, taking into account the random nature of the frequency of starts / stops of water turbine and degradation of the material. A study of the influence of the pretightening on the life-time of bolted connection. The results for bolted connections of water turbine impeller 40 PL-V-700 installed on the Dnipro II power station is obtained, showed that the mathematical expectation of the life-time of the bolted connection based on the random nature of the occurrence of transients regimes and degradation of the material is 31 year with confidence range from 25 to 40 years. It is recommended to replace bolted joints after 25 years of operation of the hydraulic unit. Scientific novelty: first proposed probabilistic model of accumulation of fatigue damage accumulation, which, unlike existing, taking into account the random nature of load frequency and the degradation (aging) of the material. A new approach to the analysis of bolted joints stress-strain state impeller turbines, which, unlike existing technology to allow for the installation and operation features and is based on the use of three-dimensional finite-element models with a high degree of detail. On the basis of approaches and models revealed regularities of pre-stress state of the life-time of the turbine impeller bolted joints. Degree of implementation: research results implemented in the practice of designing turbines at OJSC "Turboatom" (Kharkiv). Measurement complex ULTRA-V-I is used to study vibration of turbine foundation (case studies at JSC "Prombudremont", Donetsk) and to determine the vibration state of centrifugal pumps (patent of Ukraine № u201211397). Application area: The results can be used in the design of bolted joints and to determine their project and the residual life-time.