Weld examination

Weld metal contracts during post-welding cooilng. The strong forces generated by this process lead to the formation of significant residual stresses. Welded regions may therefore be zones of possible failures and therefore are of major concern to engineers.
For example, it was an inadequate knowledge of these stresses that lead to significant problems in the first pressurised-water nuclear power plants.

Residual stresses in railway rails

Residual stresses and their interaction with fatigue life is of particular importance in the rail industry. Diffraction techniques are uniquely able to measure high resolution residual stresses at depth in steels and allow the production of detailed stress maps. In the picture a worn US rail was measured using the synchrotron X-ray diffraction technique at the ESRF. The profiles indicate regions of near surface tension located at key points of the wheel-rail interface.

Using neutron analysis it is now possible to measure accurately the residual stresses and help engineers to imporve both welding techniques and post-welding treatments.

SALSA, the new ILL instrument for residual stress determination, set new frontiers in engineering and materials science