PSI - Issue 28

A. Vshivkov et al. / Procedia Structural Integrity 28 (2020) 1839–1845 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Experimental setup Two types of experiments were carried out to analyse energy dissipation under fatigue crack propagation in metals. We conducted uniaxial and biaxial fatigue tests with a constant stress amplitude. Figures 1, 2 show the geometry of samples. Flat samples made of Graid-2 titanium alloy with stress concentrators were tested. The chemical composition of Grade 2 is presented in table 1:

Fig. 1. Geometry of biaxial samples, the thickness is 1 mm. (all sizes are in millimeters).

Fig. 2. Geometry of uniaxial samples, the thickness is 3 mm. (all sizes are in millimeters)

Table 1. The chemical composition of titanium alloy. Fe C Si N Ti

O

H

0.25 0.07 0.01 Uniaxial test was carried out with different levels of applied stresses and a stress ratio R equal to 0.1. The crack length was measured by potential drop method. During biaxial tests the samples were subjected to cyclic loading of 10 Hz with different biaxial coefficient η=P x /P y (1, 0.5, 0) and ratios R (0.1, 0.5). The crack length was measured by optic method. The biaxial fatigue test was carried out by servo-hydraulic biaxial test system Biss BI-00-502 at the Kazan Scientific Center of the Russian Academy of Sciences. uniaxial test was carried out by servo-hydraulic testing machine Instron 8802 loacated in the center of experimental mechanics, Perm National Research Polytechnic University. To analyze the dissipated energy at the crack tip a contact heat flux sensor was designed and assembled. The sensor is based on the Seebeck effect which is reversed to Peltier effect. The Peltier effect is a thermoelectric phenomenon, according to which the passage of electric current through conducting medium leads to the generation or absorption of heat at the point of contact (junction) of two dissimilar conductors. The quantity of heat and its sign depend on the type of materials in contact, the direction and the strength of the electric current. The detailed description of the gauge is presented by Bowlen (2006). The quantity of heat absorbed or dissipated by the element is directly proportional to the current intensity and the time of its passage: AB P I   (1) 0.1 0.04 99.24 — 99.7 0.2