PSI - Issue 40

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Vladlen Nazarov et al. / Procedia Structural Integrity 40 (2022) 325–333 Vladlen Nazarov / Structural Integrity Procedia 00 (2022) 000 – 000

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Yield point MPa 348 s   are established from the experimental diagram. The process of the shape changing develops at the ultimate strength (logarithmic strain is 13%) is reached. When analyzing the deformation process of the plane specimen with a central circular hole with the 1/2 relative diameter (diameter of the central circular hole is comparable to the width of the rectangular plate), it was found that the stress concentrator leads to a noticeable weakening of the rectangular plate. MPa 180 y   and ultimate strength

a

b

Fig. 3. The dependence of the tensile force on elongation (a) and the dependence of the true stress on the logarithmic strain (b). The crosses indicate the initial time when the shape changes Nazarov et al. (2016).

The ultimate strength

MPa 311 s   for such the specimen is reached at 3% strain. At the same time local

MPa 240 y   is observed due to the stress concentrator.

hardening at

3. Uniaxial tension at high temperature Large elongations had been found of the creep test results of two titanium alloys VT5 (structure is represented by the   phase) and VT6 (structure is represented by the   ) (   phase) at 650 o C. These experimental data Nazarov (2015a) had been obtained on cylindrical specimens (Fig. 4) stretched at different values of the stationary force.

a

b

c

Fig. 4. Cylindrical specimens Nazarov (2015a) with the 5 mm diameter and the 25 mm length: before testing (a); tensioned to two different deformed states (b), after rupture (c).

The ultimate elongation at the rupture time was on average equal to 53% (Table 1) for the VT5 titanium alloy. The average ultimate elongation for titanium alloy VT6 was equal to 239% (Table 2) that much more than for titanium alloy VT5 at the same high temperature. Table 1. Experimental dependence Nazarov (2015a) of the ultimate elongation on the nominal stress for the VT5 (English equivalent is Grade−5) titanium alloy at 650 o C.

Stress at the initial creep time ( MPa )

80

100

120

140

160

Ultimate elongation taking into account the neck ( mm )

13.6 10.0 16.2 11.1 15.1