Abstract
Framatome and EDF have launched an important R&D program which aims at evaluating the effective impact of residual stresses on the fracture initiation in the brittle-to-ductile transition regime, on vessel low alloy steel plates.
The paper presented here deals with the process used for introduction the residual stresses in the selected mock up. The goal of the process is to generate residual stresses over 300 MPa in the thickness at the vicinity of the crack. The principle retained is to locally produce small inelastic compression strains, around the crack, using a thermal spot imposed in the centre of a plate on both sides. The vicinity of the defect is then quickly heated by induction so as its prevented thermal expansion induces compression stresses, which, in the case sufficiently high temperatures are reached, cause both inelastic creep and plastic strains, inducing tensile residual stressing at the end of the cooling phase.
The process has been designed by finite elements modelling based on a fine material behaviour modelling in the plastic-viscous domain. The thermal cycle has been defined to reach a residual stresses level between 300 MPa and 400 MPa up to the mid-thickness of the plate.
The experimental developments confirm the relevance of the thermal cycle defined through the numerical investigation, showing a good reproducibility, and expected residual stresses levels.
