Neutron residual stress measurements in rails

Rails were among the first objects of study by neutron

diffraction strain measurement and the first experiments

were done as early as the late 1980s [1, 2]. This interest

is easy to explain: the problem of rail fracturing is critical

from the public safety point of view and the penetrating

ability of neutrons suggested the possibility of breakthrough

experiments and fast progress in this field. It was

well-established that residual stresses, both near-surface

and interior, played a signifi cant role in the development

of defects which led to rail failure. This suggested three

distinct approaches of neutron diffraction strain measurement

that could contribute to various problems of the rail

industry. The first method was to map the complete triaxial

stress distribution non-destructively in the interior

of an intact rail, ideally before and after significant service.

Another approach was to use slices, for example to

characterize how different processing methods produce

favourable or detrimental stress distributions in rails. A

third technique was to make non-destructive measurements,

but in critical and not very deep portions of rails,

for example, to examine defects and their relation to rail

failure in the top running surface of rails, e.g. “white

layer” formation.