The work is aimed at establishing a relationship between the criteria for estimating the local stress state hmax / t (where hmax is the maximum depth of the plastic zone under the fracture surface, t is the thickness of the sample or part) and the criterion of fracture mechanics t / (K1C / σ0.2)2 for materials with an hcp lattice. The titanium alloys Ti-6Al-4Mo and Ti-6Al-4V were investigated in the initial coarse-grained (CG) and ultrafine-grained (UFG) states. The UFG state was processed by rotary forging (RF) in Ti-6Al-4Mo alloy and by equal-channel angular pressing (ECAP) and ECAP followed by isothermal forging (IF) in Ti-6Al-4V alloy. Testing of alloys for static crack resistance (K1C) was carried out on prismatic specimens with a thickness of 10 mm according to the three-point bending scheme in a liquid nitrogen environment (-196°C). The depth of the plastic deformation zones under the fracture surfaces was determined by the X-ray method. The test results showed that UFG alloys had a lower K1C value tha