ANISOTROPY OF FRACTURE TOUGHNESS CHARACTERISTICS OF PRESTRAINED ORTHOTROPIC MATERIAL UNDER UNIAXIAL CYCLIC LOADING

Anisotropy of fracture toughness characteristics of an orthotropic plastically prestrained material under uniaxial cyclic loading is studied experimentally. The study was carried out using flat specimens with a lateral notch. The specimens are cut out from the rolled strip of titanium alloy at different angles to an anisotropy axis. As the fracture toughness characteristics, a number of cycles to failure, critical crack size, critical value of a stress intensity factor, and crack growth rate on the interval of crack stable propagation are used. It is shown that the more strong crack strength is observed, if the crack propagates perpendicularly to the direction of rolling. Such regularity is attributed to the fact that in the case under consideration the crack necessitates to cross the additional number of grain boundaries compared with the case, when it propagates along the rolling direction. Prestraining the sheet strip in the range of small plastic strains under uniaxial tension in the rolling direction leads to deterioration of the anisotropy of the fracture toughness characteristics. If the specimen axis is oriented at an angle to the anisotropy axis, the crack propagates not along the normal to the load applied, but at the angle to it. The value of such deviation depends on the load orientation relative to anisotropy axes. In this case fracture occurs by combination of opening and transverse-shear modes