Numerical analysis methods of surface cracks: Dissertation

The present work concentrates on developing methods for practical engineering fracture and fatigue analysis of flawed thick-walled components. It aims at improving the applicability of the three- dimensional (3D) finite element (FE) method in calculating fracture mechanical parameters for surface flaws. Furthermore a method for approximating weight functions for flawed structures is developed. The major contributions to the present state of the art are: (1) the method developed for approximating weight functions for 3D surface flaws and (2) the use of an accuracy indicator together with localized model refinement for systematic improvement of the accuracy of the FE analysis results. Other important components of the work are the automated capability of generating FE models developed for practically any flawed components and a weight function-based program for practical engineering fracture and fatigue analysis. The ACR (Automatic Finite Element Model Generation for Part Through Cracks) program was developed for modeling a surface crack in a structure with a 3D FE model. The modeling of the crack area was tested by analyzing a large matrix of surface crack sizes in a plate of finite thickness for which other published results were available. A local mesh refinement procedure was developed for systematic improvement of the accuracy of the fracture parameters. The weight function method developed was im plemented in the VTTSIF program which was designed in such a way that it can serve as a programmed fracture mechanical handbook. For each structural crack configuration the reference solutions are programmed in their own subroutines and they can be used for developing weight functions or for direct superpositioning of the results. The accuracy of the methods and applicability of the system developed to practical engineering problems was demonstrated by several examples.