Issue 42

D. V. Orlova et alii, Frattura ed Integrità Strutturale, 42 (2017) 293-302; DOI: 10.3221/IGF-ESIS.42.31 299 The analysis of the  and 0  coefficients showed that 0 1 t   , where t is the time for the movement of zones at the pre-fracture stage, and the ratio * 0     is the deviation of the pole from a stationary zone. Then, in the laboratory reference system the location of the pole and the time required for reaching the pole by the localization zones are given by: * * 0 0 0 / X X X        (3a) * 0 1/ t t    (3b) where 0 t is the time when a pre-fracture stage is formed. The position of the pole and the time required for reaching the pole, calculated according to (3a) and (3b) for steel (G10080), were * X = 39.5 mm and * t = 6011 s. In fact, the sample was fractured in 5978 s after deformation at a distance of 38 mm from the fixed testing machine head. It can be seen that the space-time coordinates of the pole and the experimental values of location and fracture time are in satisfactory agreement. Tab. 4 shows the calculated values of location and fracture time for other materials. The calculated values obtained were compared with the real coordinates and fracture time of different materials. It is seen that the difference does not exceed 11%. Thus, the kinetic characteristics obtained for the autowaves of localized plasticity at the pre-fracture stage, which can be found experimentally, allow the space-time coordinates of the object fracture to be predicted long before the occurrence of external fracture signs. This can be used as a macroscopic criterion for the plasticity of structural steels and alloys. (a) (b) Figure 5 : Three-dimensional image of ε xx at the beginning (a) and end (b) of the pre-fracture stage for steel (G10080). Fracture time Material Fracture coordinate t ٭ exp , с t ٭ calc , с t ٭ exp /t ٭ calc X ٭ exp , mm X ٭ calc , mm X ٭ exp /X ٭ calc 5978 6011 0.99 G10080 38 39.5 0.96 6620 5895 1.11 321H 25 27 0.93 4014 3679 1.09 Fe+3%Si 35 35.5 0.99 930 871 1.07 AISI 420 43 42 1.02 Table 4 : Comparison of the experimental and calculated coordinates and the fracture time of the samples.  xx x, mm y, mm  xx x, mm y, mm