PSI - Issue 23

I.A. Volkov et al. / Procedia Structural Integrity 23 (2019) 281–286 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

285

5

Integrating evolutionary equation of damage accumulation (11) in combination with defining relations of thermal viscoplasticity (1) – (7) and failure criterion (12) for the known history of thermal-mechanical loading in the given elementary volume of the material, one can predict the moment when a macrocrack forms in the presence of creep. 3. Results of the study Paper by К apustin et al. (2008), presents the results of experimentally studying processes of short-term high temperature creep of the VZh-159 heat-resistant alloy, which were obtained in the Laboratory for Testing Physical Mechanical Properties of Structural Materials, Research Institute for Mechanics, Nizhny Novgorod Lobachevski State University. The tests were conducted on cylindrical specimens of solid cross-section, with the length of the working parts being equal to 50mm l  and the diameter of 8mm d  , in the conditions of uniaxial tension for various levels of normal stresses 11  and temperatures Т . The short-term creep process up to the formation of a macrocrack according to the long-term strength mechanism was numerically analyzed using the «EXPMODEL» program designed for numerically modeling non -isothermal viscoplastic deformation and damage accumulation in structural materials (metals and their alloys) under non regular non-stationary thermal-mechanical loading by Volkov et al (2016). The physical-mechanical characteristics of the VZh-159 heat-resistant alloy and the mathematical parameters of the MDM model are listed in the Table. Figs. 1 – 4 depict the creep curves for: temperature 750 o T C  and stresses 11 350MPa   and 450 М P а , respectively (Fig. 1); temperature 850 o T C  and stresses 11 120MPa   and 150MPa, respectively (Fig. 2); temperature 750 o T C  and the transition from stress level 11 350MPa   to level 11 450MPa   (Fig. 3); temperature 850 o T C  and the transition from stress level 11 120MPa   to level 11 150MPa   (Fig. 4).

Table 1. Physical-mechanical characteristics and material parameters of the MDM model of the VZh-159 heat-resistant alloy.

f с W , М J/ m 3 57,5

a с W , М J/ m 3 14,3

  1

c 

с С , МPа

(0) с  , 1/МPahr 0,0005 0,00068

(1) с  , 1/М Pahr 0,0005 0,00068

с k

Т, °С

К, МPа

g 1 c , МPа 1100 1000

G, МPа

f 

α с

g 2

r c

c

  2

c 

750 850

137000 113000

64000 52000

265

150 150

1 1

0,1 1 0,1 1

0 0

0,025

0,83 0,83

85

14

5

0,06

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.