Computation of energy release rate for interfacial crack in orthotropic bimaterials

The interfacial crack in bimaterials is a very interesting problem for composite materials and which has received particular attention from several researchers. In this study, we will propose a numerical modeling of the interfacial crack between two orthotropic materials using a special mixed finite element. For the calculation of the energy release rate, a technique, based on the association of the present mixed finite element with the virtual crack extension method, was used. The numerical model proposed, in this work, was used to study a problem of interfacial crack in bimaterials. Two cases were treated: isotropic and orthotropic bimaterials. The results obtained, using the present element, were compared with the values of the analytical solution and other numerical models found in the literature.

Effective Methods to Determine Stress Intensity Factors for 2D and 3D Cracks

Increasing concern for crack assessment in the pipeline industry motivates analysis to quantify the crack driving force, with the linear-elastic fracture mechanics stress intensity factor, denoted K, viable for many vintage pipeline applications. This paper presents a brief review of numerical methods developed for calculating K via the finite element analysis (FEA) as a background to identify the “best” approaches for such purposes. The existing methods can be categorized into three groups: the displacement-based methods, the stress-based methods, and the energy-based methods. The first group involves the displacement extrapolation method, the quarter-point displacement method, and the displacement correction method. The second group involves the stress extrapolation method and the force method. The third group includes the J-integral method, the stiffness derivative method, the virtual crack extension method, the virtual crack closure technique (VCCT) and ABAQUS direct K output method. Based on the review, four methods were selected and evaluated for a central-cracked plate (CCP) specimen based on the FEA calculations via ABAQUS. The “best” methods are then applied in an analysis of K for through-wall cracks in a line pipe — important reference geometry for leak-versus-rupture analysis.

Development of an Automatic 3D Finite Element Crack Propagation System

When cracks are detected in piping in nuclear power plants during in-service inspections, the crack propagation is usually calculated using approximation formulas of stress intensity factor (SIF) provided in the ASME Code, the JSME Rules or the literature. However, when the crack is detected in complicated-shaped locations in components, finite element analysis (FEA) needs to be used to calculate the SIFs. Accordingly, a method of automatically conducting FEA for crack propagations in nuclear power plants is needed. Therefore, we, the Nuclear Regulation Authority (NRA, Japan) have developed an automatic 3D finite element crack propagation system (CRACK-FEM) for nuclear components. The developed CRACK-FEM uses three methods of SIF calculation: the Virtual Crack Extension Method (VCEM), the Virtual Crack Closure-Integral Method (VCCM) and the Domain Integral Method (DIM). Each method uses different meshes, so users can select a method which uses a suitable mesh for the problem. The software includes a geometry generator to create complicated weld models, and a mesh generator which can deal with interior boundaries formed between different materials. The functions and accuracy of the new software are demonstrated by solving several sample problems involving crack propagation. The contents of this paper were conducted as a research project of the Japan Nuclear Energy Safety Organization (JNES) when one of the authors (Doi) belongs to JNES. After this project, JNES was abolished and its staff and task were absorbed into NRA on March 1, 2014.

J Integral in Elasto-Plasticity by Path Integral Method and Virtual Crack Extension Method in 2-Dimensional Problem

This paper shows the two calculation method of J Integral in elastic-plastic behavior of central crack in 2-dimensional problem. The analysis of the J integral and the increment of J for a plate with a central crack under cyclic fatigue loadings are carried out by using path integration based on the numerical results of Finite Element (FE) analysis. The J integral is calculated by both elastic analysis and elasto-plastic analysis. The accuracy of numerical results for the increment of J is proved by comparison with the simplified method results. In this study, we also analyzed the J-integral using the virtual crack extension method based on the finite element method. Analysis model is a two-dimensional flat plate with a central crack, and by changing the crack length in the different FE analysis, the fundamental feature of J-integral by the virtual crack extension method under cyclic fatigue analysis is discussed.

Effect of Strength Matching Performance on J-Integral of Inhomogeneous Welded Joints

In this paper, J-integral of inhomogeneous welded joint is calculated by use of the combination of finite element method and virtual crack extension method, and the impact of strength matching on J-integral is studied as well. The analysis results show that the strength matching factor affects J-integral value greatly, that is, low matching of inhomogeneous welded joint of same steel can help to improve the ductility of the welded joint and the influence of the matching performance of dissimilar steel welded joint is more complex.