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Gavalda Diaz, Oriol (2018) On understanding the material removal mechanism when cutting Ceramic Matrix Composites (CMCs). PhD thesis, University of Nottingham.

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Abstract

The continuous increase in Turbine Entry Temperature (TET) in aerospace gas-turbines is the main driving force behind research efforts in the development of Ceramic Matrix Composites CMCs. Among different ceramic composites, SiC-based \CMCs are the material choice for aero-engine manufacturers for employment in structural components of turbines such as seal segments and turbine blades/vanes. Hence, because of their non-oxide ceramic nature and their exposure to harsh environments (i.e. high temperatures and stresses), the risk of these materials to suffer environmental degradation is a matter of concern for the aerospace industry. Consequently, the importance of understanding the state of the CMCs surface (e.g. cracks or residual stresses) after the manufacturing processes is of critical importance to achieve the desired life in service. Hence, as CMCs components need some machining operations to achieve the final features and dimensions, this thesis focuses on understanding the material removal mechanism and its effects on the machined surface. Moreover, because of the unique nature of SiC-based CMCs (i.e. orthotropic, brittle, hard and heterogeneous) its machining process becomes very challenging, especially when drilling small holes, and for this reason hole-making has been chosen as a target operation.

After an in-depth literature survey of the state-of-the-art in machining CMCs, conventional drilling is selected as a reference process to drill small holes (i.e. 0.8-5 mm) in SiC-based CMCs. Thus, to fill the research gaps found in the literature, the present thesis has the following objectives: (i) to understand how the orthotropic-brittle nature of CMCs affects the mechanical material removal process, (ii) to provide a comprehension and optimisation of the performance presented by "off-the-shelf" drills while reporting the material-related limitations and (iii) to determine the material characterisation techniques most suitable to identify and quantify the machining-induced damages. Furthermore, the understanding of the limitations found in the currently available solutions has allowed to define the design pathway needed for the novel generation of drill bits.

The work of this thesis thus provides a scientific step forward in the understanding of the material removal mechanism by analysing the unique material nature of SiC-based CMCs. Furthermore, this work has also contributed to understand and optimise an industrially relevant process such as drilling which is currently being used in real aero-engine components.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Axinte, Dragos Butler-Smith, Paul Novovic, Donka
Keywords:	CMCs, material removal, material characterisation, cutting, drilling, machining
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	55445
Depositing User:	Gavaldà Díaz, Oriol
Date Deposited:	09 Mar 2021 09:05
Last Modified:	29 Feb 2024 15:37
URI:	https://eprints.nottingham.ac.uk/id/eprint/55445

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