PSI - Issue 28

S.V. Suknev et al. / Procedia Structural Integrity 28 (2020) 903–909 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Keywords: Quasi-Brittle fracture, Nonlocal fracture criteria, Theory of Critical Distances, Size effect, Circular hole, Biaxial loading.

Nomenclature TCD

Theory of critical distances Linear elastic fracture mechanics Finite fracture mechanics Size of the prefracture zone

LEFM FFM

d

Intrinsic material length

0 d K , e L

Stress-intensity factor, critical stress-intensity factor

c K

Size of the stress concentration zone Parameter of plasticity of the material



Radius of the hole Crack length Size of the insert

a

l

B

1  , 2 

Stresses

Critical stress

c  e  0 

Equivalent stress

Uniaxial tensile strength

Uniaxial compressive strength Pressure, critical pressure

0 C

p , c p

Asymptotic value of the critical pressure

s T 0 T

Asymptotic value of the critical pressure for brittle material

Tensile-to-compressive strength ratio Loading biaxiality ratio Coefficients of proportionality





1 k , 2 k

 , s  Parameters 1 J , 2 J , 12 J Parameters

1. Introduction The urgent task is to develop new approaches, which make it possible to assess the strength of structural members with a blunt notch and a crack from a single point of view. These requirements are met by nonlocal fracture criteria, which are based on the idea of the formation of a prefracture zone around the most stressed point in the material, with local redistribution of elastic stresses occurring in this zone. Outside this region, which is small as compared to the dimensions of a deformable body, the material is deformed elastically up to failure. The foundations of nonlocal fracture criteria were laid in the works by Wieghardt (1907), Neuber (1937), Peterson (1959), Novozhilov (1969). A common property of these criteria is the introduction of an additional parameter, which is an intrinsic material length 0 d , characterizing the microstructure of the material. This allows one to describe the size effect under stress concentrations, thereby expanding the field of application as compared to traditional criteria that do not take into account the size effect. Currently, nonlocal criteria are developed within the framework of the theory of critical distances. Although the criteria are based on different approaches, Taylor (2007 and 2008) notes that the predictions of failure made by these methods yield very close results and suggests regarding them as different manifestations of a certain general theory, which refers to as the Theory of Critical Distances (TCD). This theory deals with four methods: