PSI - Issue 40

276 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 in the crack zones were recorded. The tests were carried out at temperatures T = 300 K, 150 K, 77 K on flat samples and samples with cracks at T = 300 K. On cylindrical samples, the tops of the original cracks were in the base metal, the weld and the fusion zone. The results of measurements of local strains s and displacements in the tops of cracks made it possible to determine both the strength (stress intensity factor) and the strain (strain intensity factor) factors of the crack resistance of the base metal and the welded joint. For inclined cracks, a computational model of nonlinear fracture mechanics is proposed, which meets the model I of normal separation. The test results are focused on their use in assessing the strength and crack resistance of critical products operating in a wide range of operating temperatures (up to cryogenic). This task is relevant for the designs of objects of new nuclear, rocket and space, aviation technology, taking into account the emergence and development of local elastic plastic destructions in them such as multi-oriented semi-elliptical cracks, in a wide range of temperatures - from room to cryogenic.

Nomenclature t

thickness

cycle asymmetry coefficient

R



initial angle of inclination of the crack decreasing initial angle of inclination factor of intensity elasto-plastic strain

 

je K

type of crack (normal, transverse or longitudinal)

j I II III , , 

ijk l

crack length

N

number of loading cycles

m 

nnominal stress load

local stress, а yield strength

Ti 

b 

tensile strength

relative narrowing

k 

yield strength t

T 

0.2 

conditional yield strength

k S

neck tear resistance relative narrowing modulus of elasticity

k  ,

E

Cj 

critical crack opening by the corresponding fracture models ( j = I, II, III)

temperature

T

2. Research methodology Tests were carried out on laboratory cylindrical and flat welded samples of austenitic stainless steel 08Kh18N10 Т (carbon 0,08%, chromium 18%, nickel 10%, titanium 1%). Mechanical properties of this steel: elasticity limit σ T = 179 MPa , yield strength σ T = 195 MPa , conditional yield strength σ 0.2 = 255 MPa , tensile strength σ b = 632 MPa , neck tear resistance S k = 1770 MPa , relative narrowing ψ k = 71 %, modulus of elasticity E = 1.98 · 10 5 MPa . The shape and size of the samples are shown in Fig. 1 and Fig.3. Tests of flat welded samples for extra-center stretching of different thicknesses were carried out on a machine with a hydraulic drive ZDM - 1000, providing a maximum tensile force of 1000 kN. The method of testing the samples met the methodological requirements (RD 50 – 200 -81, 1982) . Welding of flat images was performed on steel 08Kh18N10Т according to the appropriate methods (I.I.Makarov, B.V., Grudzinsky, 1975). Low-cycle tensile-compressive and cycle asymmetry tests of tubular