PSI - Issue 20

E.S. Oganyan et al. / Procedia Structural Integrity 20 (2019) 42–47

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E.S. Oganyan et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Task statement To substantiate safe and efficient operation of rolling stock and railway infrastructure at all stages of the life cycle, it is necessary to develop methods for calculation and durability prediction of structural elements of railway equipment with regular and irregular cyclic loading in elastic and elastoplastic domains relying on force and deformation criteria of damageability. The solution of this problem is connected with the search for general laws describing the kinetics of damageability accumulation in a metal under conditions that are closest to operational ones. Considering that the operational loading of an object is mostly random in nature, problems of such loading simulation and its use in the damageability analysis arise. The growth of rail freight traffic, the increased speed of shunting impacts of cars, the increase of the average mass in network and the maximum mass of trains have led to more intensive loading of automatic coupling units by longitudinal forces.

Nomenclature C

empirical parameter of the material elasticity modulus of the material

E

m р N ℓ s N 1 Р 0.2 Р lim UM Δ ε р

index of the hardening diagram beyond the elastic limit of the material number of low-cycle quasistatic loads (in this case – longitudinal forces in the coupler) number of cycles in the single (annual) block of longitudinal loads on the coupler load at the material yield strength of the considered element of the part

ultimate load for the same element in the elastoplastic range

Universal Mechanism software

range or one-sided plastic relative strain in a loading cycle

σ -1

fatigue limit of the part

ψ

relative reduction of area in the specimen neck at rupture

2. Initial data Actual data on the operational loading of the coupler is the basis for the calculations of durability. The loading is characterized by the statistics of occurrence of tensile and compressive forces of various level at different operating modes in the form of a load block. This block is formed by operating loads on locomotives and cars through their automatic coupling units by Kostina (1981), Standards (1996), GOST 33211 (2014). It should be noted that the loading nature is determined by the type of work and the conditions of rolling stock operation. In this regard, two loading modes are considered below. 3. Methodology and calculation results 3.1. During shunting operations with train: in the process of their formation at the stations, including humps, as well as during transient modes of train movement (starting, braking), on the track changes The longitudinal forces arising in this case are maximum and reach the standard limit values (standard loading mode I by Standards (1996)). These loads (from 1.0–1.5 MN to 2–3 MN and more), having a low-cycle nature, cause stresses close to or reaching the yield point, with possible occurrence and accumulation of elastoplastic strains in the metal of the coupler elements, and these strains can lead to its fracture. The most frequent (up to 70%) of the automatic coupler damages is the fracture of the CA-3 coupler bar. More than 50% of these is accounted for sections in the area of the draft key opening (fig. 1a). Distribution of the longitudinal forces acting on the car through automatic coupling units is normalized by Standards (1996), GOST 33211 (2014), GOST 33788 (2016). There are other distributions which however are not fundamentally different between each other by Kostina (1981), Kostenko and Nikolskiy (1971).