STUDY ON FRACTURE OF WELDED CONNECTIONS IN STEEL STRUCTURES UNDER CYCLIC LOADS BASED ON NONLINEAR FRACTURE MECHANICS : Part 1 Formulation of multi-axial stress-strain relations of structural steel for cyclic loads

Safety, survivability, and serviceability of the equipment are governed by the strength characteristics of the separate units and elements which can contain initial or operational defects such as superficial differently oriented semi-elliptical cracks. Numerical methods of calculation provide a large bulk of information about the stress-strain state (SSS) of those elements proceeding from the given algorithms for calculating the corresponding fracture models. Change in the type of the SSS near the crack contour when going from the bulk to the surface depends on the constraint of deformations along their front, i.e., on the 3D character of the SSS. Diagnostics of the form change of the defects (surface differently oriented semi-elliptic low-cycle cracks) is carried out on the basis of experimental results and numerical solutions. The data of the finite element modeling are implemented on the basis of macros of the ANSYS program complex. The regularity of the directionality of developing the elastoplastic fracture under low-cycle loading is studied. The proposed methodology is proved by the parametric equations of the kinetics of forming changes of the cracks under study in the fractographic analysis of the surfaces of their development. The results of testing samples with semi-elliptic cracks under low-cycle loading are used in analysis of the parameters of the morphology of the surfaces of the developed defects. The results of measuring fields of elastoplastic deformation intensity in the crack tip and geometrical characteristics of the fracture surface development are presented. Analysis of the dynamics of the local stress-strain state near the contour of multi-oriented defects in parts and structural units of the equipment showed a good agreement between the experimental parameters of the geometry of developing cracks and characteristics obtained by numerical methods. The presented parametric equations specify the characteristics of nonlinear fracture mechanics thus providing reliable estimation and forecasting of survivability, and safety of serviceability of the critical equipment. The deformation criteria of nonlinear fracture mechanics are used to demonstrate the dependence of fracture development on the 3D character of the stress-strain state indicating to the directionality of the geometric development of the fracture surface form.

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On Relevant Ramberg-Osgood Fit to Engineering Nonlinear Fracture Mechanics Analysis

Journal of Pressure Vessel Technology ◽

10.1115/1.1760767 ◽

2004 ◽

Vol 126 (3) ◽

pp. 277-283 ◽

Cited By ~ 19

Author(s):

Yun-Jae Kim ◽

Nam-Su Huh ◽

Young-Jin Kim ◽

Young-Hwan Choi ◽

Jun-Seok Yang

Keyword(s):

Fracture Mechanics ◽

Three Dimensional ◽

Ferritic Steels ◽

Stress Strain ◽

Nonlinear Fracture Mechanics ◽

Practical Applications ◽

Nonlinear Fracture ◽

Mechanics Analysis ◽

Strain Data ◽

Deformation Plasticity

The present paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elastic-plastic J from the engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. The reliability of the proposed method for the R-O fit is validated against detailed three-dimensional FE analyses for through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as the reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

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Complex study of the fracture processes in materials and structures

Industrial laboratory Diagnostics of materials ◽

10.26896/1028-6861-2018-84-11-46-51 ◽

2018 ◽

Vol 84 (11) ◽

pp. 46-51 ◽

Cited By ~ 1

Author(s):

N. A. Makhutov

Keyword(s):

Fracture Mechanics ◽

Crack Resistance ◽

Scientific Basis ◽

Intensity Factors ◽

Nonlinear Fracture Mechanics ◽

Nonlinear Fracture ◽

Linear Fracture ◽

Science Technology ◽

Fracture Processes

The results of comprehensive studies of multifactor processes, mechanisms and criteria for fracture at a variation of the crack-like defect state, loading conditions and mechanical properties of structural materials carried out in the 20th - 21st centuries are presented on the basis of monographic publications and articles published in the journal “Zavodskaya Laboratoriya. Diagnostika Materialov.” Crack resistance of materials and structures has become a key problem of the material science, technology, design, manufacture and service of structures. Fracture mechanics including estimation of the stress-strain and limiting states in a cracks tip formed a scientific basis of the crack resistance analysis Stress intensity factors (linear fracture mechanics) and strain intensity factors (nonlinear fracture mechanics) are accepted as the basic criteria of those states. The basic computational relations for construction of the fracture diagrammes which link the cracks growth with conditions of a static, cyclic, long-term, dynamic loading are presented. Parameters of computational relations are put into correspondence with the features of fracture processes on nano-, micro-, meso- and macrolevels. Prospects of the research and guidelines of further studing crack resistance are discussed.

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Nonlinear Fracture Mechanics Analysis Considering Material Inhomogeneity of Welded Joints

Impact ◽

10.21820/23987073.2019.10.105 ◽

2019 ◽

Vol 2019 (10) ◽

pp. 105-107

Author(s):

Hiroshi Okada

Keyword(s):

Fracture Mechanics ◽

Solid Mechanics ◽

Crack Nucleation ◽

Intensity Factors ◽

Nonlinear Fracture Mechanics ◽

Material Inhomogeneity ◽

Computational Fracture Mechanics ◽

New Methods ◽

Nonlinear Fracture ◽

Mechanics Analysis

Professor Hiroshi Okada and his team from the Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science, Japan, are engaged in the field of computational fracture mechanics. This is an area of computational engineering that refers to the creation of numerical methods to approximate the crack evolutions predicted by new classes of fracture mechanics models. For many years, it has been used to determine stress intensity factors and, more recently, has expanded into the simulation of crack nucleation and propagation. In their work, the researchers are proposing new methods for fracture mechanics analysis and solid mechanics analysis.

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