PSI - Issue 40

N.A. Makhutov et al. / Procedia Structural Integrity 40 (2022) 275–282 N. A. Makhutov, I. V. Makarenko / Structural Integrity Procedia 00 (2022) 000 – 000

277

3

samples -1 with surface semi-elliptical multi-oriented cracks were carried out on an electromechanical test machine UME with a maximum force of 1000 kN. 3. Test results The study obtains fracture resistance factorss based on strain criteria and the basic equations of linear and nonlinear fracture mechanics to describe the kinetics of destruction arising from the development of local elastic plastic strains along the front of inclined semi-elliptical cracks, taking into account their multidirectionality in a wide range of elastic and inelastic nominal strains and cryogenic temperature. The acceptability of these studies is assessed by special experiments on samples with inclined surface semi-elliptical cracks and numerical calculations. There exists a number of empirical and approximate analytical solutions of integral equations of second kind by the method of successive approximations, for the problems of cracked bodies, at thermoelastic equilibrium for critical crack opening by the corresponding fracture models j  , ( j = I, II, III) (Makhutov N. A., 2005, Andreykiv, A.E., 1982, Cherepanov G..P., 1976). A crack is assumed to start propagating over maximum tensile strain ( max  ) regions when the limiting equilibrium is reached, and local plastic strain achieves max  the critical value k  (Makhutov N. A., 2005, Makhutov N. A. and. Makarenko I. V., 1986): k    max (1)

This condition in view of the temperature factor is written in the following form:

] ( )[1 2 ( ) ( , , , , , , , , ) 1 0,2 2 0          T K T T F p q g IC

    

1

(2)





1 ( , , , , , , , , ) 4,5 ( ) ( ) { 1       f f F p q g T   

2 [ ( , , , , )(3cos 4  K p q g T I

cos 3

)

0 





0

0





2

(3)







2

2

2 3 ( , , , , )(sin  K p q g T II

sin 3

)]cos

( , , , , )cos 

sin 2 } 

K p q g T









III

2

2

Here  is the coordinate angle of the crack contour points,  and  are the angles aligning maximum local tensile stress regions, ( ) 0,2 T  is the yield limit as a function of the temperature T , ( ) K T IC ) is the fracture toughness of the material, p , q , and g are the external load values,   is the angle  value for the maximum plastic zone width, 0  and   are the material parameter and stress tensor value, respectively. 4. Materials and experimental procedure The experimental studies were carried out on two types of welded plates along the weld (WS) and fusion line (FL). Schemes of the samples are shown in Fig. 1. The samples of austenitic steel s of type 08Kh18N10Т were tested for eccentric tension according to current standards. Width of the welds was 20…100 mm, the temperature range was 77…295 K. On the basis of experimental results of testing of flat welded samples from austenitic steel 08Kh18 N10Т for extra centric stretching according to the relevant regulatory documents (RD 50 – 200 -81, 1982) and welding technique (I.I.Makarov, B.V., Grudzinsky, 1975) both for the weld and for the zone (line) of fusion, dependencies of the functions of critical opening of cracks are obtained: for the weld seam ( , ) f t T CW   and for the metal of the fusion zone ( , ) f t T CL   as functions of temperature T and thickness of the welded joint t. The fusion zone is a zone of partially fused grains on the border (Makhutov N. A., 2005, Makhutov N. A. and. Makarenko I. V., 1986) of the base metal and the seam metal.