Insulated rail joints (IRJs) are a primary component of the rail track safety and signalling
systems. Rails are supported by two fishplates which are fastened by bolts and nuts and, with the
support of sleepers and track ballast, form an integrated assembly. IRJ failure can result from
progressive defects, the propagation of which is influenced by residual stresses in the rail. Residual
stresses change significantly during service due to the complex deformation and damage effects
associated with wheel rolling, sliding and impact. IRJ failures can occur when metal flows over the
insulated rail gap (typically 6-8 mm width), breaks the electrically isolated section of track and
results in malfunction of the track signalling system.