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Fracture mechanics analysis of multiple edge cracks

Abdul Manan, M.S.; (2008) Fracture mechanics analysis of multiple edge cracks. Doctoral thesis, UCL (University College London).

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Abstract

This thesis is concerned with the evaluation of crack propagation in the presence of other cracks within the same two-dimensional body. The parameter known as the Stress Intensity Factor (SlF) is used within Linear Elastic Fracture Mechanics (LEFM) to predict crack propagation rate knowing the appropriate material properties. Unfortunately the number of SIF solutions for multiple cracks is very small especially for real engineering cases. This thesis investigates the use of the SIF weight function for the efficient evaluation of SlFs for two one-dimensional cracks in close proximity to each other. The SIF weight function has proved to be a powerful tool for the evaluation of single cracks however, has not before been used to solve multiple crack problems. The main objective of the thesis is to investigate the mechanics of multiple cracks through an experimental and numerical analysis programme and to develop engineering solutions for prediction of multiple crack behaviour in steels and materials that exhibit LEFM characteristics. A Finite Element (FE) approach was employed to model multiple crack interaction. In addition, the FE model was used to study the non-unifom stress distribution caused by the interaction effect between cracks. Over one hundred FE models were analysed for this study. A major experimental programme was conducted to study the interaction effect between two edge cracks. A totel of seven specimens with different crack geometries were completed under fatigue loading in tension. The purpose of this experimental work was to better understand the mechanisms of crack interaction and to provide information for validation of the numerical anlayses. The experimental results show that cracks in close proximity to each other interact to varying degrees depending on relative crack lengths, crack separation and plate width. A novel weight function method was developed in order to predict SlFs of two edge cracks under uniform tension. The crack interaction effect was established using the idea of non-uniform stress distributions along the potential crack plane due to the presence of an additional edge crack. Generally the novel weight function approach shows good results compared to finite element analysis. Finally, further work to explore the wide range of SlFs for multiple cracks using the weight function method is identified and proposed.

Type:Thesis (Doctoral)
Title:Fracture mechanics analysis of multiple edge cracks
Language:English
Additional information:Authorisation for digital version not received
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Mechanical Engineering

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