Experimental Investigation of Charpy Impact Resistance in Rail Vehicle Steel Wheels

Abstract

In this research the Charpy impact properties of the two steel wheels of grade B2N and R7 were investigated. The dynamic toughness levels of test materials were measured experimentally according to the general recommendations of International Union of Railways (UIC) test standards. To do this, two sets of standard Charpy U-notch impact specimens were taken from the original rail vehicle steel wheels (made from B2N and R7) in their circumferential direction. As the conventional Charpy impact machine gives only one output (i.e., total fracture energy), an instrumented Charpy rig was used for conducting the impact experiments. This provided novel impact test data as well as full failure information (appeared for the first time in the literature for rail vehicle steel wheels). The obtained data included elastic strain energy, fracture initiation, and fracture propagation energy. All these parameters were calculated by double integration of load history captured by a high frequency digital oscilloscope during impact tests. The results showed that the impact toughness of both steel wheels was above the minimum toughness specified by the UIC leaflet. Detailed analysis of instrumented fracture test data showed that a significant portion of total measured Charpy energy (more than 75%) was consumed in fracture initiation and non-related fracture processes in each test material. This is a direct result of high strain-hardening capacity of B2N and R7 steel wheels and their characteristics, which allows the material to absorb high amounts of energy and to deform plastically before any fracture initiation. The total fracture energy of the R7 wheel steel was 160% higher than the B2N (21J against 13J), which was indicative of better dynamic crack resistance of R7 wheel material.