Richard Todd

Professor Richard Todd
Professor of Materials
+44-1865-273718
richard.todd@materials.ox.ac.uk

Mechanical properties and processing of ceramics and metals. Current interests include processing and properties of ceramic nanocomposites, the use of carbon nanotubes and graphene in ceramic composites, mechanical testing and stress measurement in ceramics at the microscale, high strain rate performance of ceramics for armour applications, "flash sintering" of ceramics, probing of stress and structure using neutrons and synchrotron radiation, improved metal forming for automobiles and mechanisms of superplastic deformation.

Selected Publications

  • Characterisation of damage mechanisms in oxide ceramics indented at dynamic and quasi-static strain rates

    Dancer, CEJ, Spawton, JNF, Falco, S, Petrinic, N, Todd, RI
    2019
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    Journal article
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    Journal of the European Ceramic Society
    © 2019 The Authors Ceramic materials are known to display rate dependent behaviour under impact. Tests to establish the strain-rate dependent variations in damage mechanisms have been carried out on debased alumina, an alumina-zirconia composite, and 3Y-TZP. Materials were indented dynamically and quasi-statically using identical sharp hardened steel projectiles while recording the load profile. Characteristics typical of both sharp and blunt indentation types were observed using scanning electron microscopy and piezospectroscopic mapping. At dynamic strain rates both the depth of the indentation and the residual stress in the material were lower than for quasi-static tests. This was attributed to temperature-induced softening of the projectile. Unusual behaviour was observed in the 3Y-TZP samples due to the reversible transformation from tetragonal to monoclinic crystal structures during mechanical loading. These effects and the observed superior mechanical strength against impact suggest that zirconia or zirconia-composite materials may have advantages over debased alumina for application as ceramic armour materials.

  • Nacre-like alumina with unique high strain rate capabilities

    Evers, K, Falco, S, Grobert, N, Todd, RI
    2019
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    Journal article
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    Journal of the European Ceramic Society
    © 2019 The Authors Nacre-like alumina manufactured using spark plasma sintering shows a strikingly different mechanical behaviour compared to conventional alumina. A range of sintering conditions were applied to micron-sized alumina platelet powders to form alumina with different nacre-like microstructures, density, grain size and flexural strength. We show that a microstructure of aligned sintered platelets not only mitigates the typical issue of brittleness, but also has extraordinary energy absorption capabilities. It can withstand an impact with up to three times the kinetic energy required to break monolithic alumina while maintaining structural integrity. The high-rate compressive strength is shown to be more than 50% higher than that of monolithic alumina and we show energy absorption mechanisms such as crack deflection and branching to be present. Our approach provides a fast and effective way of manufacturing aligned nacre-like ceramic microstructures that maintain structural integrity through energy dissipation and interlocking mechanisms.

  • MWCNT-coated alumina micro-platelets for nacre-like biomimetic composites

    Evers, K, Porwal, H, Todd, RI, Grobert, N
    2019
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    Journal article
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    Carbon
    © 2019 The Authors A novel building block material for the generation of non-brittle ceramic composites consisting of micron-sized alumina platelets homogeneously coated with multi-wall carbon nanotubes (MWCNTs) bound to their surface is described. The MWCNT phase is grown in situ from immobilised metal catalyst particles using chemical vapour deposition techniques. In-depth Raman and scanning electron microscope studies revealed that this approach solves the typical issue of MWCNT-agglomeration in ceramic matrices and paves the way to excellent control over MWCNT purity and concentration within the resulting composite material. Moreover, we show that the preparation of the catalyst is the most important factor for the generation of uniformly distributed MWCNTs of high-quality on these platelets. With these MWCNT-coated alumina building blocks, we have manufactured nacre-like biomimetic composites using spark plasma sintering. The resulting composites are electrically conductive and three-point bending tests show a transition from brittle/catastrophic failure to graceful failure, holding great promise towards multifunctional, tough and strong lightweight ceramic composite manufacturing.

  • Statistical effects in X-ray diffraction lattice strain measurements of ferritic steel using crystal plasticity

    Erinosho, TO, Collins, DM, Todd, RI, Wilkinson, AJ, Dunne, FPE
    2018
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    Journal article
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    MATERIALS & DESIGN
    Lattice strain, Statistics, Crystal plasticity, X-ray diffraction, Texture, Hardening

  • Measurement and modelling of electrical resistivity by four-terminal method during flash sintering of 3YSZ

    Yoshida, M, Falco, S, Todd, RI
    2018
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    Journal article
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    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN
    Zirconia, Flash sintering, Electrical resistivity

  • Ultra-fast firing: Effect of heating rate on sintering of 3YSZ, with and without an electric field

    Ji, W, Parker, B, Falco, S, Zhang, JY, Fu, ZY, Todd, RI
    2017
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    Journal article
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    Journal of the European Ceramic Society
    © 2017 Elsevier Ltd.It has recently been reported that ceramics can be sintered in a few seconds with the aid of an electric field ("flash sintering"). This investigation tests the possibility that the accelerated sintering is a consequence of the rapid heating rate involved rather than a direct effect of the electric field on mass transport. The sintering of 3YSZ powder compacts at a temperature of ∼1300. °C was compared (i) in flash sintering, (ii) with rapid heating rates produced without the application of an electric field, and (iii) with conventional heating rates. The results show that rapid heating can accelerate sintering by over 2 orders of magnitude compared with heating to the same temperature at conventional rates, even without the application of an electric field. It is concluded that the rapid densification in flash sintering of 3YSZ is at least partly a consequence of the rapid heating involved. Possible explanations are discussed.

  • A synchrotron X-ray diffraction study of non-proportional strain-path effects

    Collins, DM, Erinosho, T, Dunne, FPE, Todd, RI, Connolley, T, Mostafavi, M, Kupfer, H, Wilkinson, AJ
    2017
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    Journal article
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    ACTA MATERIALIA
    Synchrotron radiation, X-ray diffraction (XRD), Lattice strain, Texture, Crystal plasticity

  • Liquid-phase assisted flash sintering of SiC from powder mixtures prepared by aqueous colloidal processing

    Candelario, VM, Moreno, R, Todd, RI, Ortiz, AL
    2017
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    Journal article
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    JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
    SiC, Flash sintering, Liquid-phase assisted densification, Microstructure, Aqueous colloidal processing

  • Abrasive wear rate of boron carbide ceramics: Influence of microstructural and mechanical aspects on their tribological response

    Moshtaghioun, BM, Gomez-Garcia, D, Dominguez-Rodriguez, A, Todd, RI
    2016
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    Journal article
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    Journal of the European Ceramic Society

  • Assessment of X-ray diffraction and crystal plasticity lattice strain evolutions under biaxial loading

    Erinosho, TO, Collins, DM, Wilkinson, AJ, Todd, RI, Dunne, FPE
    2016
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    Journal article
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    INTERNATIONAL JOURNAL OF PLASTICITY
    Finite element, Crystal Plasticity, Microstructures, X-ray diffraction