More on the Fatigue Resistance Assessment of the Freight Car Bogies’ Cast Parts

Quality of solebars and bolsters is assessed by the value of fatigue safety factor. In the respective calculations they use experimental fatigue limits of individual component parts obtained in the course of their fatigue testing. Enhancement of the railway car axle-loads, development of freight car bogie advanced design versions as well as increase in the number of part fracture events demand for revision of certain issues of the existing fatigue testing procedure. Component parts testing of the new high-strength structures ought to be conducted under higher maximum loads within the loading cycle. However loads’ maximum to minimum ratios depend on the permanent loads average, thus making impossible to employ all the necessary spectrum of testing loads. Meanwhile application of higher testing loads may result in emergence of plastic flow deformations and residual compression stresses, thus leading to overestimation of the testing results. Survival of the tested parts is also possible. So it is recommended: - To conduct the tests at fixed value of the loading cycle asymmetry coefficient; - To assess testing results specifically for the normalized number of the loading cycles at each testing load value. It has been found that fractures occurred in operation under summer and winter conditions are practically similar in their character. They are characterized with small area of the fatigue crack retarded development, which is evidence of the action of high stresses. Fatigue tests of bolsters at temperature values of +20 ° and -60 °С demonstrated that negative temperature contributes to some extent to higher fatigue resistance of the component parts, thus delaying initiation of fatigue cracking process. However it also contributes to lesser critical size of the crack area, and as a consequence to worse survivability of the parts. It has been indicated that the relationships obtained in the course of rig and field tests explain the reasons of a large number of solebar fracture events during cold seasons (emergence of critically-sized cracks, their extremely quick development and subsequent fracture in between the routine inspections).

solebars, bolsters, fatigue resistance, durability, temperature, methodology

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