The Effect of a Complex Stress State on Fatigue Crack Propagation and the Orientation of the Cracking Plane in VT3-1 Aeronautical Titanium Alloy

The subject of the paper is the investigations of fatigue crack imitation and propagation in notched specimens made of the VT3-1 aeronautical russian titanium alloy under combined bending - torsion loading. The presence of short cracks was revealed at various ratios of bending to torsion. Experimental courses of short and long crack growth rates have been proved by the SEM and TEM micrographs which illustrated the changes in the mechanism of cracking in the examined specimens. The attempt was undertaken in order to explain partly brittle fracture that was observed in the range of fatigue short crack growth in the VT3-1 titanium alloy specimens. The results of the study of atmospheric hydrogen absorption capability and its ability for penetration inside the faces of nucleated and propagated microcracks in the surface layer allowed for suggestion that the cleavage mechanism of fracture found in the regime of short crack growth in the VT3-1 titanium alloy specimens was induced by hydrogen.