Fatigue crack growth kinetics in titanium alloys at different interaction of cyclic loading amplitudes

Fatigue crack growth kinetics of various titanium alloys BT6 (α+β structure) and 3M (α-structure) under constant amplitude loading with different types of cyclic disturbances in the form of over- and underloading at a loading frequency of 25 Hz was investigated.The tests were conducted on a servohydraulic testing machine under controlled load with simultaneous automatic recording of loading parameters and readings from a crack opening gauge. Tests were carried out on compact specimens with an edge crack which were subjected to off-centre loading. The crack opening data was converted into crack length using a yield strength measurement method. Experimental results, namely fatigue crack growth curves and fatigue fracture kinetic diagrams, were analyzed. It is shown that crack growth kinetics depends mainly on the type of alternating loading amplitude sequences. Reliability estimation of crack growth on the basis of crack opening gauge and study of fractographic features of materials fracture has been carried out.