Characterisation of residual principal stresses and their implications on failure of railway rails

The residual principal stresses of an unused and four used railway rails of differing service times and loading conditions have been determined with a new magnetic stress measuring system (known as MAPS).The distributions of residual principal stresses on the transverse cross-sections of the rails have been mapped out. Results of the present work have complemented other recent research efforts which have established the residual principal stress component in the longitudinal direction.Due to wheel-rail contact loads, a hardened layer of about 10 mm in thickness developed in each of the used rails, irrespective of loading conditions and times. The contact loads also induced changes in the patterns of residual stresses after an unused rail is put to service.Besides residual stresses, the microstructures and ways of crack propagation in the used rails have been characterised. The severity of grain deformation in the rails has been qualitatively studied using optical microscopy and quantitative measured with image analysis. Contribution of residual stresses to crack growth is discussed.