Whole-field residual stress measurement in rail using Moire interferometryand Twyman/Green interferometry via thermal annealing

A novel whole-field residual stress measurement technique is developed usin g moire interferometry and Twyman/Green interferometry coupled with thermal annealing. The technique is successfully applied to residual stress measur ement in rail. In the measurement, a high temperature resistant 1200-lines/ mm cross grating is made on a rail transverse slice surface. The whole-fiel d residual stress relief is achieved by thermal annealing. Moire interferom etry and Twyman/Green interferometry are employed to obtain the in-plane an d out-of-plane deformations generated by the residual stress relaxation. Th e whole-field strain redistribution due to the residual stress relief is ca lculated, and the whole-field residual stress distribution, including the p ossible stress concentration, is then obtained. Because of the three-dimens ional nature of the residual stress relaxation and the measurement, the thr ee-dimensional residual stress reconstruction sometimes becomes possible ba sed on some plausible assumptions. In this paper, the principle of the expe rimental theory, technique and procedures are described. Three-dimensional residual stress reconstruction in a rail using a transverse slice is shown. Its comparison to the hole-drilling method with moire interferometry is al so presented.