PSI - Issue 30

N.A. Makhutov et al. / Procedia Structural Integrity 30 (2020) 87–92 N.A. Makhutov et al. / Structural Integrity Procedia 00 (2020) 000–000

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Keywords: ultimate strength; ductile-brittle transition; lifetime; cold resistance; railway transport; rolling stock

1. Introduction Being operated under conditions of thermal effects and low temperatures, wear and corrosion, objects of railway equipment, their critical elements and other essential parts are subjected to static, quasi-static and dynamic loads, which cause elastic and elastic-plastic deformations in some areas and constructional elements. Operational integrity of load-bearing and critical structures of rolling stock is important for a safe operation of objects of railway transport. Prevention of failures and crashes based on structural features requires a focused effort to study circumstances of failures and their causes, to establish limit values of influencing parameters and ranges of their changes by Kossov et al. (2018) and Oganyan et al. (2013). An example of a difficult task to identify determining factors may be the analysis of the performance of rails during their long-term operation, the assessment of their damageability and the definition of reasons for their withdrawal. Processes of the operation of rails and their interaction with rolling stock wheels are influenced by natural and climatic factors, which are characterized by an extremely wide range of temperatures, humidity, features of the geological structure of soils in areas of laying the railway bed, which largely determine an actual track state and requirements to its maintenance. In this regard, relevant, complex and science-based research trends become problems of the lifetime of rails at various stages of their life cycle, its calculation, experimental confirmation, maintenance of an operating state, diagnostics and monitoring during their operation. One of the main factors leading to failures of objects of rolling stock and railway transport infrastructure are natural climatic conditions of the operation typical for Russia. The climate pattern of territories of our country is its sharp continentality, which manifests itself in large annual temperature fluctuations and a relatively small amount of precipitation. In the coldest places, the air temperature drops to -60 ° С and lower. Severe natural climatic conditions for the operation of equipment in Siberian, northern and Arctic regions lead to a decrease in its main performance indicators. So the goal of this work is the formulation of the research trends and tasks, which solution will ensure a safe service life of critical systems and high-risk objects both in normal and in low-temperature climatic conditions by Security of Russia (2014) and Golubeva et al. (2018).

Nomenclature ψ K

lateral contraction of a standard sample neck during its tear

σ B σ C

ultimate strength actual failure stress

σ 0.2

conventional yield stress of a standard sample (at the relative residual deformation of 0.2%)

σ T

yield stress

t C 1 , t C 2 e i max

first and second critical temperatures of a ductile-brittle transition local plastic strain in the most stressed area of a structure critical value of the stress intensity factor area of a fracture ductile constituent of a metal sample

К 1 С F B

2. Methodological background To assess the service lifetime, the principle of a safe operation according to a technical state is taken as a basic approach: the service lifetime is assessed according to defining parameters of a technical state, based on established patterns of their change, the analysis of mechanisms of the damage accumulation, the origin and development of defects, as well as results of measuring functional indicators during tests and operation by Design-experimental assessment (2015), Approaches to assess (2015) and Oganyan et al. (2019). In accordance with damage processes, which are taken into account when designing structures of railway equipment to be operated in standard climatic conditions, the strength and service lifetime are substantiated according to the following criteria: