Crack initiation in VHCF regime on forged titanium alloy under tensile and torsion loading modes

Alexander Nikitin (1, 2) , Thierry Palin-Luc (1) , Andrey Shanyavskiy (3, 2)

1 I2M - Institut de Mécanique et d'Ingénierie de Bordeaux
2 MAI - National research university
3 RAS - Russian Academy of Sciences [Moscow]

This paper is focused on the VHCF behavior of aeronautical titanium alloy under tensile and torsion fatigue loadings. Tensile tests were carried out with two different stress ratios: R = À1 and R = 0.1. Both surface and subsurface crack initiations were observed. In the case of subsurface crack initiation several fatigue life controlling mechanisms of crack initiation were found under fully-reversed loading conditions: initiation from (1) strong defects; (2) ‘macro-zone’ borders; (3) quasi-smooth facets and (4) smooth facets. Tests with stress ratio R = 0.1, have shown that initiation from the borders of ‘macro-zones’ becomes the dominant crack initiation mechanism in presence of positive mean stress. Like for the tensile results, surface and subsurface crack initiations were observed under ultrasonic torsion in spite of the maximum shear stress location on the specimen surface. But the real reason for the subsurface crack initiation under torsion was not found.

Mots clés: Very-high cycle fatigue; Titanium alloy; Crack initiation; Ultrasonic torsion

Domaines: Mécanique des matériaux [physics.class-ph]

Alexander Nikitin, Thierry Palin-Luc, Andrey Shanyavskiy. Crack initiation in VHCF regime on forged titanium alloy under tensile and torsion loading modes. International Journal of Fatigue, 2016, 93 Part2, pp.318-325. ⟨10.1016/j.ijfatigue.2016.05.030⟩. ⟨hal-01372854⟩