PSI - Issue 32

A.Yu. Iziumova et al. / Procedia Structural Integrity 32 (2021) 93–100 Author name / Structural Integrity Procedi 00 (2019) 000 – 00

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carried out using the original heat flux sensor developed by Vshivkov et al. (2016). Displacements near the notch were registered by contact extensometer. Mechanical properties of titanium alloy Ti-0.8Al-0.8Mn were determined experimentally by quasi-static tensile test. True stress-true strain diagram is presented in Fig. 1b. To identify the thermal diffusivity and thermal conductivity of titanium alloy Ti-0.8Al-0.8Mn the transient technique based on infrared thermography was used (Zhelnin et al. (2019)). Thermal and mechanical properties were collected in the Table 1.

Table 1. Experimentally determined thermal and mechanical properties of titanium alloy Ti-0.8Al-0.8Mn. Material property Values Elastic modulus E, GPa 158 Ultimate tensile stress, MPa 625 Yield strength σ0.2%, MPa 259 Thermal conductivity, λ (W m -1 K -1 ) 14,0±1,3 Thermal diffusivity, α•10 6 (m 2 s -1 ) 5,5±0,2

3. Data processing According to the first law of thermodynamics the part of the mechanical work during plastic deformation is absorbed by the material, while the other is dissipated as a heat. Thus, the absorbed (stored) energy is calculated as the difference between the work of plastic deformation and the amount of heat dissipated into the environment: S dE dA dQ,   (1) where dE S is stored energy increment (J/cycle), dA is plastic work increment (J/cycle), dQ is heat dissipation increment (J/cycle). The plastic work can be experimentally estimated as the area of the hysteresis loop due to cyclic loading. The heat dissipation in plastic deformation zone near the crack tip was registered by original heat flux sensor. It allowed us to estimate the value of the internal energy stored in material by Eq. (1). Fig. 2 shows the typical time dependences of the crack length and heat flux near the crack tip area during deformation of titanium alloy Ti-0.8Al-0.8Mn specimens under constant maximum loading of 10.5 kN and 11 kN. Two different types of heat flux behaviour during crack propagation could be distinguished. Until about 12000 s of the experiment, the heat flux remains practically constant, despite the fact that the crack length is gradually increasing. After 12000 seconds of the experiment, the heat flux deviates from the constant value, and then demonstrates an avalanche-like growth up to the fracture moment of specimens. The time moment when the heat flux begins to deviate from the linear trajectory is marked by circles in Fig. 2 a, b. a b

Fig. 2. (a) experimental time dependence of crack length; (b) experimental time dependence of heat flux during cyclic deformation of titanium alloy Ti-0.8Al-0.8Mn.