Residual strain measurement by synchrotron diffraction

Third generation synchrotron X-ray sources such as the European Synchrotron Radiation Facility and the Advanced Photon Source (USA) have made very intense beams of very high energy X-rays available for the first time. At energies in excess of 60 keV penetration lengths of the order of centimetres are possible in most engineering materials. The associated low scattering angles limit the strain measurement directions available at depth. Gauge dimensions as small as microns and sub-second measurement times give the technique unique characteristics, making 2 and 3 dimensional strain mapping economically feasible. The current state of the art is reviewed and the potential assessed, primarily using illustrative case studies made at the ESRF. These include the measurement of near surface strains caused by peening, TIG welding stresses for the development of finite element models, the mapping of crack bridging during fatigue crack growth in Ti/SiC fibre composites and crack field mapping in 3D.