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Title: Discrete crack dynamics and its application to study fracture in polycrystalline diamond
Author: Tajabadi Ebrahimi, Mahdieh
ISNI:       0000 0004 7657 9258
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Mechanical properties of polycrystalline materials are affected by the microstructure of the components. All cracks and inclusions present in a body subjected to external forces cannot act independently even if their density is relatively low. The elastic fields generated by the presence of each crack and inclusion extends throughout the system. Thus, not only the external load but also the neighbouring cracks and inclusions determine the stress experienced by each individual defect. In this work, the Multipole Method (MM) is used to simulate the many-body self-consistent problem of interacting elliptical micro-cracks and inclusions in an unbounded solid. Finite-sized problem can be solved using the superposition scheme and incorporating the complex variable boundary element method. A criterion is employed to determine the crack propagation path based on the stress distribution; the evolution of individual micro-cracks and their interactions with existing cracks and inclusions is then predicted using what we coin the Discrete Crack Dynamics (DCD) method. DCD is fast (semi-analytical) and particularly suitable for the simulation of evolving low-speed crack networks in brittle or quasi-brittle materials. Furthermore, effects of the grain boundary strength and the interfacial strength of inclu- sions on the deflection of crack paths were studied. Results of each step of the analysis are validated against finite element analysis predictions and previously published experimental data and modelling results. New results for propagating cracks interacting with hard and soft inclusions in finite bodies are presented. Finally, the methodology developed by the author is used to determine the effect of residual stresses in general, and the residual thermal stresses associated with the second phase inclusion in particular, on the crack propagation path. The study is then extended to characterise the influence of residual stresses and thermal stresses on crack propagation in PCD structures.
Supervisor: Dini, Daniele ; Balint, Daniel ; Sutton, Adrian Sponsor: Element 6 Ltd
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral