Improving fatigue properties of metallic components through a new surface treatment

Purpose and goal

Fatigue damage is the dominant cause of metallic component failure. The aim of this pre-study is to evaluate the potential of dengeling as an effective way to improve fatigue resistance of metallic materials with reference to shot peening. Aluminum alloys were studied in the project. The test results showed that a dengeling treatment with similar intensity as a shot peening process used in the production line gave much better fatigue performance than the shot peening process. The effectiveness of the dengeling method is thus confirmed.

Expected results and effects

The dengeling treatment with similar intensity as that of a production line shot peening process showed much better fatigue performance than the shot peening, in spite its somewhat higher surface roughness. Other investigated dengeling treatments that generated a deeper compression zone but with lower compressive stresses and lower surface plastic deformation are less effective in terms of fatigue resistance enhancement. The anisotropy of dengeling induced residual stress field may be utilized for optimizing fatigue resistance for different applied stress levels.

Planned approach and implementation

4-point bend fatigue tests sensitive to surface treatment and axial fatigue tests for studying samples with geometric stress concentration were carried out on samples of different surface conditions. The results were analysed with regard to residual stress, surface deformation, and etc. and to initiation sites of fatigue crack. The fatigue life could easily be compared, however it was generally difficult to evaluate the runout stresses due to scattered fatigue data in the low stress region. The project work was carried out through close collaboration of the project partners.