Numerical Modeling of Crack Growth under Mixed-Mode Loading

The aim of this paper is to simulate the propagation of linear elastic crack in 3D structures using the latest innovation developed using Ansys software, which is the Separating Morphing and Adaptive Remeshing Technology (SMART), in order to enable automatic remeshing during a simulation of fracture behaviors. The ANSYS Mechanical APDL 19.2 (Ansys, Inc., Canonsburg, PA, USA), is used by employing a special mechanism in ANSYS, which is the smart crack growth method, to accurately predict the crack propagation paths and associated stress intensity factors. For accurate prediction of the mixed-mode stress intensity factors (SIFs), the interaction integral technique has been employed. This approach is used for the prediction of the mixed-mode SIFs in the three-point bending beam, which has six different configurations: three configurations with holes, and the other three without holes involving the linear elastic fracture mechanics (LEFM) assumption. The results indicated that the growth of the crack was attracted to the hole and changes its trajectory to reach the hole or floats by the hole and grows when the hole is missing. For verification, the data available in the open literature on experimental crack path trajectories and stress intensity factors were compared with computational study results, and very good agreement was found.

Modified duality methods for solving an elastic crack problem with Coulomb friction on the crack faces

We consider an equilibrium problem for an elastic body with a crack, on the faces of which unilateral non-penetration conditions and Coulomb friction are realized. This problem can be formulated as quasi-variational inequality. To solve it, the successive approximation method is applied. On each outer step of this method, we solve an auxiliary problem with given friction. We solve the auxiliary problem by using modified Lagrange functionals. Numerical results are presented.

Validation of a Finite Element Toolbox for Studying Flaw Interaction

Structural integrity assessment often requires the interaction of multiple closely-spaced cracks or flaws in a structure to be considered. Although many procedures for structural integrity assessment include rules for determining the significance of flaw interaction, and for re-characterising interacting flaws, these rules can be difficult to validate in a fracture mechanics framework. int_defects is an open-source MATLAB toolbox which uses the Abaqus finite element suite to perform large-scale parametric studies in cracked-body analysis. It is designed to allow developers of assessment codes to check the accuracy of simplified interaction criteria under a wide range of conditions, e.g. for different interacting flaw geometries, material models and loading cases. int_defects can help analysts perform parametric studies to determine linear elastic crack tip stress field parameters, elastic-plastic parameters and plastic limit loads for simple three-dimensional cracked bodies relevant to assessment codes. This article focusses on the validation of int_defects using existing fracture mechanics results. Through a set of validation examples, int_defects is shown to produce accurate results for a very wide range of cases in both linear and non-linear cracked-body analysis. Nevertheless, it is emphasised that users of this software should be conscious of the inherent limitations of LEFM and EPFM theory when applied to real fracture processes, and effects such as constraint loss should be considered when formulating interaction criteria.

Linear elastic fracture mechanics

This chapter introduces the basics of linear elastic fracture mechanics. It starts by recalling the asymptotic elastic crack tip solutions and the concept of stress intensity factors for Mode-I, Mode-II, and Mode-III loading. The concept of critical stress intensity factor is next introduced as a model for fracture under small scale yielding conditions. In this context the limits of linear elastic facture mechanics are discussed. Further, methods and requirements for fracture toughness testing are discussed.