The present study investigates the effect of stress triaxiality on mechanical behavior and fracture of Ti-5Al-2.5Sn alloy in a practical relevant strain rate range from 0.1 to 1000 s−1. Tensile tests were carried out on flat smoothed and notched specimens using an Instron VHS 40/50-20 servo-hydraulic test machine. High-speed video registration was conducted by Phantom 711 Camera. Strain fields on the specimen gauge area were investigated by the digital image correlation method (DIC). The fracture surface relief was studied using digital microscope Keyence VHX-600D. Stress and strain fields during testing of the Ti-5Al-2.5Sn alloy were analyzed by the numerical simulation method. The evolution of strain fields at the investigated loading condition indicates that large plastic deformation occurs in localization bands. The alloy undergoes fracture governing by damage nucleation, growth, and coalescence in the localized plastic strain bands oriented along the maximum shear stresses. Results confirm that the fracture of near alpha titanium alloys has ductile behavior at strain rates from 0.1 to 1000 s−1, stress triaxiality parameter 0.33 < η < 0.6, and temperature close to 295 K.
Deformation and damage at the meso-scale level in representative volumes (RVE) of light ultrafine grained (UFG) alloys with distribution of grain size were simulated in wide loading conditions. The computational models of RVE were developed using the data of structure researches aluminum and magnesium UFG alloys on meso-, micro -, and nanoscale levels. The critical fracture stress on meso-scale level depends not only probabilistic of grain size distribution in RVE but relative volumes of coarse grains. Microcracks nucleation is associated with strain localization in UFG partial volumes in alloys with bimodal grain size distribution. Microcracks branch in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength. The distribution the shear stress and the local particle velocity takes place at mesoscale level under dynamic loading of UFG alloys with bimodal grain size. The increasing of fine precipitations concentration not only causes the hardening but increasing of ductility of UFG alloys with bimodal grain size distribution.
Bioinert metals are used for medical implants and in some industrial applications. This study was performed to detect and analyze peculiarities that appear in the temperature distributions during quasi-static tensile testing of bioinert alloys. These alloys include VT1-0 titanium, Zr-1%Nb and Ti-45%Nb in both coarse-grain (CG) and ultrafine-grain (UFG) states. The crystal structure, as well as the crystal domain and grain sizes of these alloys in the UFG state, may be different from the CG versions and identifying the thermal signatures that occur during their deformation and fracture is of interest, as it may lead to an understanding of physical processes that occur during loading. By comparing the surface temperature distributions of specimens undergoing deformation under tensile loading to the distributions at maximum temperatures it was found that the observed differences depend on the alloy type, the alloy structural state and the thermal properties of structural defects in the specimen. Macro-defects were found in some specimens of VT1-0 titanium, Zr-1Nb and Ti-45Nb alloys in both the CG and UFG states. The average tensile strength of specimens containing defects was lower than that of specimens with no defects. Infrared thermography documents change in the thermal patterns of specimens as they are deformed under tensile loading and when the load stops changing or the specimen breaks.
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