The fatigue test of industrial pure titanium notched specimens was carried out.Combined with digital image correlation(DIC)technology

the surface strain field of the specimen

the local strain at the notch root

and the fatigue crack propagation length were obtained

and the fatigue crack initiation and propagation stages were divided and characterized.The experimental results show that

in the fatigue crack initiation stage

the strain concentration factor obtained by DIC increases as the notch radius decreases

which is consistent with the theoretical stress concentration factor.When the cyclic strain at the notch root accumulates to a certain extent

the micro-cracks initiate.At this time

the increase of load causes the local strain rate to increase sharply

then decrease briefly and increases again until the appearance of macro-cracks.When macro-cracks appear

the fatigue crack propagation of TA2 is characterized by the stress intensity factor

which increases with the increase of load and crack length.The results show that the notch fatigue crack initiation and propagation can be characterized based on DIC technology

which can provide a basis for the safety assessment of titanium equipments.