Object-Oriented System for Evaluation of Fracture Mechanics Parameters of Linear and Nonlinear 3D Cracks

Abstract

Fracture mechanics is widely used to evaluate the structural integrity and safety of various components. In the fields of linear elastic fracture mechanics (LEFM), numerous formulas of the stress intensity factors (SIFs) for various types of specimens have been developed theoretically or numerically. The SIFs for a semi-elliptical surface crack in a plate subjected to tension or bending moment were formulated as a simplified scheme through intensive 3D finite element calculations [1]. Useful influence functions of the SIFs for various 3D cracks subjected to arbitrarily distributed loading were also developed [2]. Most of them are now available to ordinary engineers as handbooks [3]. In the fields of nonlinear or elastic-plastic fracture mechanics, a situation is more difficult. As for fracture toughness testing specimens, i.e. standardized specimens such as three-point bending and compact tension (CT) types, some simplified formulas have been developed to easily evaluate fracture mechanics parameters such as the J-integral [4] from measured load vs. load-line displacement curves [5–7]. In general, numerical simulation tools such as the finite element method are known to be powerful tools to deal with 2D and 3D cracks in complex geometry and to deal with elastic-plastic crack problems. However, it takes tremendous time for routine analyses such as crack growth prediction, so that the numerical tools are not such convenient tools as the simplified formulas. Some simplified schemes for evaluating 3D and nonlinear crack parameters have also been proposed and widely utilized in practical situations [8–10].