Abstract
Rail corrugation is identified on the running surface around track curves of a twenty seven kilometer long railway line with the smallest and largest curve radii of 140m and 484m respectively. The railway line runs from Belfast to Steelpoort in the Limpopo Province of South Africa. Given that corrugation has not formed on rails for track curves with steel sleepers, the study contributes to the body of knowledge by investigating the difference in dynamic response of rail track with steel and concrete sleepers. This results in significant findings as to why the dynamic response of track with concrete sleepers could be associated with the formation of short pitch rail corrugation in the railway line. In the recent accepted literature researchers are starting to believe frictional self-excited vibration of the wheel-rail system to be an important culprit for short pitch rail corrugation formation. The dynamics of ballasted railway tracks is not studied sufficiently in the recent literature, particularly those installed with steel sleepers, which is key in developing means to prevent short pitch rail corrugation formation. A corrugation-borne vibration frequency is dependent on wavelengths and train velocities. In the current study these frequencies are matched with natural frequencies of a locomotive traction wheelset, to investigate whether wheels have a resonant influence on the short pitch rail corrugation formation. Experimental modal test is conducted to obtain natural frequencies of a traction wheelset that was used by a locomotive operating in the affected railway line. Finite Element Analysis (FEA) is used to validate dynamic mode shapes at important natural frequencies of the traction wheelset, obtained through experimental modal test. The natural frequencies of the wheelset are correlated with corrugation frequencies for each affected track curve selected for the purpose of the current study. Experimental modal tests are also conducted on tracks with steel and concrete sleepers to obtain natural frequencies of rail tracks with these two types of sleepers. The FEA complex eigenvalue method is used to validate dynamic mode shapes at important natural frequencies of rail tracks with the two types of sleepers. An important traction wheelset axial bending mode is excited at 108Hz when the traction wheelset is free of boundary conditions. This frequency was found to be the short pitch rail corrugation formation frequency for the affected railway line. This traction wheelset vibration mode was found to reasonably match with corrugation frequencies around each track curve. This axial bending mode of the traction wheelset becomes more damped and shifts to 120Hz when the traction wheelset is coupled to a traction motor and installed in a bogie. Another important resonance mode is also excited at 103Hz in...
Ph.D.