PSI - Issue 39

N.A. Makhytov et al. / Procedia Structural Integrity 39 (2022) 266–272 Makhutov N.A./ Structural Integrity Procedia 00 (2019) 000–000

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and Makarenko and et al, 2017; Makhutov and Makarenko and et al, 2013; Makhutov and Makarenko and et al, 1999; ANSYS, 2010; Makhutov and Makarenko and et al, 2020; C.Q. Li et al, 2016; Fu GY et al, 2017), the results of studying the kinetics of fracture surfaces and the parameters of nonlinear fracture mechanics near the contour of surface semi-elliptic inclined low-cycle cracks are obtained. Based on the deformation criteria of fracture(Makhutov, 2005), experimental, analytical and numerical methods of research, compact elasto-plastic solutions for strain intensity factors and stresses are proposed. Functional relations are proposed to determine a stress-strain state along randomly oriented low-cycle surface semielliptical cracks that provide refined estimation of strength and residual life of NPP equipment with deformation fracture criteria and numerical methods based on experimental data.

Nomenclature t

thickness

cycle asymmetry coefficient

R

β

initial angle of inclination of the crack decreasing initial angle of inclination

∗ β

/

e K K α =

σ

relative factor of intensity elasto-plastic strain

e

T

α

e K α

factor of intensity elasto-plastic strain ec K α critical value relative factor of intensity elasto-plastic strain I II III , , = α type of crack (normal, transverse or longitudinal) ijk l crack length N number of loading cycles ∗ ∆ i e

range of intensity relative elasto-plastic strain in a concrete local volume range of intensity elasto-plastic strain in a concrete local volume

∗ ∆ i e

Ti e

local strain at yield strength Ti m σ σ /

σ

=

nominal relative stress and elasto-plastic strain

mi

m σ nominal stress load Ti σ local stress, а yield strength e mi e m e Ti / =

nominal relative elasto-plastic strain

e m

nominal elasto-plastic strain

q K

relative equivalent stress intensity factor

2. Method and investigation results The kinetics of defects such as surface semi-elliptic cracks was studied on tubular specimens (Fig. 1) with a wall thickness t = 0.010 m , on which the initial inclined semi-elliptical cracks were applied by the electro erosion method, through a polished surface. Specimens (Fig. 1) made of austenitic cyclically stable stainless steel 08Kh18N10T, with the initial angle of inclination of the crack / 6 / 2 π π β = ⋅ − , were tested under soft saw tooth loading (central tension-compression) with a cycle asymmetry coefficient of R = -1 and a loading frequency of 0.01 Hz.