Library of geometric influences for stress intensity factor weight functions

• Main Author: Teh, Lay Seong
• Published: University College London (University of London) 2002
• Subjects: 620.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566060

This research thesis reports the development of a novel concept for Linear Elastic Fracture Mechanics (LEFM) analysis - Composition Theory of Stress Intensity Factor Weight Functions (CToWF). A generic closed form composition model has been derived to generate Mode I SIFs for an edge crack propagating in a symmetrically loaded two-dimensional body. The CToWF concept has demonstrated, by verification with published solutions and Finite Element Analysis (FEA), that the SIF weight function for a new cracked body can be evaluated by isolating and combining appropriate constituent geometries. Being a unique property of crack and component geometry, the newly determined weight function enables rapid generation of SIFs for the same cracked component under different stress systems. Over two thousand Finite Element (FE) models were analysed to provide constituent geometrical configurations and to validate the SIFs calculated from the CToWF model where published solutions were not available. These are Mode I SIFs for edge cracks emanating from two-dimensional notches i. e. semi-elliptical, U- and V-notches in semi-infinite bodies along with their associated stress distributions. Hence, a comprehensive database has been established. Using the versatile composition model with the database, a large number of new SIF solutions for edge cracks from equivalent notches in finite bodies have been obtained. This `Library' of geometric influences, which are presented as weight function coefficients in tabular form, can now be composed by the CToWF approach to generate SIFs for modelling crack propagation through residual stress fields and other complex stress systems. In general, this universal approach, which is easy-to-implement yet maintaining high accuracy, has tremendous potential in allowing rapid assessment of defects prone to linear elastic fracture behaviour via the evaluation of SIFs. Further work to enhance the understanding of this novel concept is proposed to develop a broader practical use in real engineering applications.