Fracture of Titanium Alloys at High Strain Rates and under Stress Triaxiality

Abstract

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.

Mechanical behavior of the Zr-1%Nb alloy at high strain rates and stress triaxiality from 0.33 to 0.5

“…Для моделирования развития повреждений и вязкого разрушения сплава была использована кинетическая модель [6,9]. Предполагалось, что зарождение повреждений в материале связано с развитием пластических деформаций и может быть описано кинетическими уравнениями (9) [9].…”

“…Сплав Zr-1 % Nb используется для изготовления оболочек тепловыделяющих элементов ядерных реакторов, трубопроводов и других конструкций ядерного энергетического оборудования. Результаты исследований свидетельствуют, что характер разрушения ГПУ поликристаллических металлов и сплавов, к которым относится сплав Zr-1 % Nb, зависит от температуры, скорости деформации, параметра трехосности напряженного состояния [1][2][3][4], и что деформация разрушения монотонно уменьшается при увеличении трехосности напряжений при квазистатическом растяжении циркониевых сплавов [5,6]. Было обнаружено, что величина деформации до разрушения уменьшается с ростом скорости деформации в диапазоне от 10 −3 до 10 4 с −1 [1].…”

Failure Mechanisms of Alloys with a Bimodal Graine Size Distribution

“…The mechanical behavior of HCP alloys under quasistatic and dynamic loading at temperatures T /T m less than 0.5 is determined by dislocation mechanisms and twinning [25][26][27][28][29]. Authors used modifications of the constitutive equations developed in the framework of the micro-dynamical approach and taking into account the thermally activated dislocation mechanisms [15][16][17][30][31][32].…”

“…the function ϕ( f ) establishes a relation between the effective stresses of the damaged medium and the stresses in the condensed phase, is the Grüneisen coefficient, ρ 0 is the initial mass density of the condensed phase of the alloy, γ R , ρ R , n, B 0 , B 1 are the material's constants, C p is the specific heat capacity, D(•)/Dt is the Jaumann derivative, μ is the shear modulus,ḟ growth is the void growth rate, f is the void volume fraction in the damaged medium,λ is the plastic multiplier derived from the consistency condition˙ = 0, and is the plastic potential. The plastic potential was described using the Gurson-Tvergaard model (GTN) [32,[37][38][39]. The Grüneisen coefficient was equal to 1.42 and 1.09 for Mg-3Al-1Zn and Ti-5Al-2.5Sn, respectively.…”

“…The temperature rise associated with energy dissipation during plastic flow can be evaluated by relation [25,32]:…”