Mecatheque
Scientific and technical publications
HFMI : understanding the mechanisms for fatigue life improvement and repair of welded structures
Fatigue resistance of High Frequency Mechanical Impact (HFMI) treatment is investigated on high strength welded steel S690. Cyclic four points bending tests are performed on butt weld samples and hammer peening samples with different conditions of treatment with or without stress-relieving heat treatment. Microstructural characterizations with EBSD observations and residual stress analyses are presented. The main objective of this paper is to reveal and identify the parameters (residual stresses, geometry, strain hardening, etc.) which have an effect during the HFMI operation and to understand the phenomena involved during fatigue stressing. The optimization of the geometry of the fatigue specimen allowed us to repetitively obtain failures in the hammer peened areas, thereby showing the relationship between the geometry, the strain hardening, the residual stresses and the fatigue strength.
The main conclusions of this paper showed that HFMI treatment improves the fatigue performance of welded joints (in keeping with the IIW results). The residual compressive stresses are prominent. The microstructure does not seem to have any effect, despite the nanostructured layer. The geometry is of secondary importance despite a significant change in the local geometry due to the presence of laps generated by the hammer peening operation. This does not jeopardise the improvement of the service life if the residual compressive stress field is not relieved. In this paper, some recommendations are proposed for the hammer peening process in terms of sweeping strategy and HFMI as reparation treatment is also presented.
Authors : Fabien Lefebvre, Catherine Peyrac du Cetim, C. Revilla-Gomez, Catherine Verdu, Jean-Yves Buffière de l'INSA
Log in to download
HFMI : understanding the mechanisms for fatigue life improvement and repair of welded structures
