Development of a High Pressure Torsion Test for Recreating Deformed Layers in Rail

This thesis outlines work carried to develop a method for recreating plastically
deformed layers to allow fatigue crack growth testing material with properties and
microstructure equivalent to those found in the actual rail. The top layer of the rail
experiences high contact pressure (above material yield) and shear from wheel
passage. This leads to the creation of a highly deformed layer. Rail damage such as
wear and rolling contact fatigue are initiated in this layer.
Design work has been carried out to develop the set-up and testing approach for
high pressure torsion (HPT) testing to create a deformed layer representative of that
on wheels and rails and for a fatigue crack growth (FCG) test to assess properties of
specimens taken from the deformed layer created from the HPT process.
Tests have been completed under different conditions and using varying rail grades,
R260, R350HT and R400HT. Consistent deformed layers were created which
compare well with those found in field rail in terms of microstructure and hardness.
A new method was established for extracting fatigue crack growth (FCG) specimens
from the specimens so that the deformed layer could be tested in a cyclic fatigue
test.
A pilot test set-up was iterated through several machines that would allow the very
small FCG specimens to be tested. Unfortunately, this could not be run successfully
as the string of components within the set-up were not stiff enough and the
connections were taking up the load rather than it being transferred to the specimen.
A new approach has been defined that will allow larger deformed layer specimens to
be created and a different FCG test to be carried out.