James Marrow

Professor James Marrow
Professor of Materials
+44-1865-273938
james.marrow@materials.ox.ac.uk

My research is focussed on the degradation of structural materials and the role of microstructure.  A key aspect is the investigation of fundamental mechanisms of damage accumulation using novel materials characterisation techniques. This has concentrated recently on computed X-ray tomography and strain mapping by digital image correlation, which I apply to studies of the degradation of Generation IV nuclear materials such as graphite and silicon carbide composites.

The next generation of nuclear power systems must be demonstrably safer, proliferation resistant and efficient. They will not provide power for some decades to come. Their development requires new high temperature fuels and structural materials with resistance to irradiation. This can only be achieved through fundamental understanding of materials microstructure and the mechanisms of materials ageing.

Research in engineering materials for energy generation is not a quick-fix topic. New materials take from 15-20 years to come into service, and then are expected to be in service for 40-80 years. The key physical mechanisms that determine manufactured performance, and how these properties age in service, are not very well understood, and mistakes in materials selection can have enormous financial and social implications.

Prediction is a major challenge, and deep understanding of the fundamental mechanisms of materials aging is essential to identify and avoid potential "cliff-edges" in future materials performance.

We use synchrotron tomographt and also laboratory tomography in our work.  You can follow some of the images we obtain on our laboratrory tomography instrument here www.instagram.com/xradia_oxford

 

Selected Publications

  • In situ measurement of elastic and total strains during ambient and high temperature deformation of a polygranular graphite

    2020
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    Journal article
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    Carbon
    © 2020 Elsevier Ltd In situ neutron diffraction and synchrotron X-ray diffraction, combined with image correlation analysis of 2D optical and 3D X-ray tomography datasets, have been used to investigate the relationship between elastic lattice strain and total strain during deformation of Gilsocarbon (IM1-24) polygranular nuclear grade graphite. The specimens were flat-end Brazilian discs under diametral loading, such that a compressive-tensile biaxial stress state was developed in the central region. The X-ray study was at ambient temperature, and the neutron diffraction was conducted at temperatures from ambient to 850 °C. When under compression, there is a temperature-insensitive linear relationship between the total strain and the lattice strain that is measured perpendicular to the graphite basal planes. However, when under tensile stress, the total strain and elastic strain relationship is temperature sensitive: below 600 °C, the lattice tensile strain saturates with increasing total tensile strain; above 600 °C, significantly higher tensile lattice strains are sustained. The saturation in tensile lattice strain is attributed to microcracking in the graphite microstructure. Improved resistance to microcracking and damage tolerance at elevated temperature explains the increase in tensile strength of polygranular graphite.

  • Unifying the Effects of in and out-of-plane constraint on the fracture of ductile materials by using synchrotron X-ray tomography and digital volume correlation

    2020
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    Journal article
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    Journal of the Mechanics and Physics of Solids

  • In-situ X-ray tomography of wear – a feasibility study

    2020
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    Journal article
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    Tribology International

  • A method for fracture toughness measurement in trabecular bone using computed tomography, image correlation and finite element methods

    2020
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    Journal article
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    Journal of the Mechanical Behavior of Biomedical Materials

  • J-Integral Analysis: An EDXD and DIC Comparative Study for a Fatigue Crack

    2020
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    Journal article
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    International Journal of Fatigue

  • Measuring the brittle-to-ductile transition temperature of tungsten–tantalum alloy using chevron-notched micro-cantilevers

    2020
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    Journal article
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    Scripta Materialia

  • Analysis of Interfacial Effects in All-Solid-State Batteries with Thiophosphate Solid Electrolytes.

    2020
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    Journal article
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    ACS applied materials & interfaces
    All-solid-state batteries (ASSBs) present a promising route toward safe and high-power battery systems in order to meet the future demands in the consumer and automotive market. Composite cathodes are one way to boost the energy density of ASSBs compared to thin-film configurations. In this manuscript, we investigate composites consisting of β-Li3PS4 (β-LPS) solid electrolyte and high-energy Li(Ni0.6Mn0.2Co0.2)O2 (NMC622). The fabricated cells show a good cycle life with a satisfactory capacity retention. Still, the cathode utilization is below the values reported in the literature for systems with liquid electrolytes. The common understanding is that interface processes between the active material and solid electrolyte are responsible for the reduced performance. In order to throw some light on this topic, we perform 3D microstructure-resolved simulations on virtual samples obtained via X-ray tomography. Through this approach, we are able to correlate the composite microstructure with electrode performance and impedance. We identify the low electronic conductivity in the fully lithiated NMC622 as material inherent restriction preventing high cathode utilization. Moreover, we find that geometrical properties and morphological changes of the microstructure interact with the internal and external interfaces, significantly affecting the capacity retention at higher currents.
    microcomputer tomography, thiophosphate solid electrolyte, nickel-rich layered oxides, 3D microstructure-resolved simulations, all-solid-state batteries, impedance analysis

  • Characterisation of slip and twin activity using digital image correlation and crystal plasticity finite element simulation: Application to orthorhombic α-uranium

    2020
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    Journal article
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    Journal of the Mechanics and Physics of Solids
    © 2019 Calibrating and verifying crystal plasticity material models is a significant challenge, particularly for materials with a number of potential slip and twin systems. Here we use digital image correlation on coarse-grained α-uranium during tensile testing in conjunction with crystal plasticity finite element simulations. This approach allows us to determine the critical resolved shear stress, interaction mechanisms and hardening rate of the different slip and twin systems. The constitutive model is based on dislocation densities and twin volume fractions as state variables, and the simulated geometry is constructed from electron backscatter diffraction images that provide shape, size and orientation of the grains, allowing a direct comparison between virtual and real experiments. An optimisation algorithm is used to discriminate between different models for the slip-twin interactions and to find the parameters that reproduce the evolution of the average strain in each grain as the load is increased. A tensile bar, containing four grains aligned with the load direction, is used to calibrate the model with eight unknown parameters. The approach is then independently validated by simulating the strain distribution in a second tensile bar. Different mechanisms for the hardening of the twin systems are evaluated, based on the interaction between coplanar and non-coplanar twins. The latent hardening of the most active twin system turns out to be determined by coplanar twins and slip. The hardening rate of the most active slip system is lower than in fine-grained α-uranium. The method outlined here can be applied to identify the critical resolved shear stress and slip-twin interaction mechanisms of other coarse-grained materials.

  • Procedure for accurate calculation of the J-integral from digital volume correlation displacement data

    2020
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    Journal article
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    STRAIN
    © 2020 John Wiley & Sons Ltd The application of digital image and volume correlation techniques to obtain displacement fields from images has become ubiquitous in experimental fracture mechanics. In this paper, a procedure to extract the J-integral (J) from three-dimensional displacement fields obtained using digital volume correlation is presented. The procedure has been specially adapted to allow for experimental noise and errors, such as poorly defined crack front displacements, smearing of the displacement field across the crack faces, and knowledge of the imprecise crack front location. The implementation is verified using analytical crack-tip fields perturbed with synthetic image correlation errors to characterise the response of J. The method is then applied to experimental results using a Magnesium alloy WE43 loaded elastically in mixed mode. The steps outlined are intended as a guideline for the application of the volume integral from displacement fields to allow for accurate calculation of J along a crack front embedded within the volume.
    fracture mechanics, J-integral, digital volume correlation, X-ray computed tomography

  • Sodium/Na β″ Alumina Interface: Effect of Pressure on Voids.

    2020
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    Journal article
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    ACS applied materials & interfaces
    Three-electrode studies coupled with tomographic imaging of the Na/Na-β″-alumina interface reveal that voids form in the Na metal at the interface on stripping and they accumulate on cycling, leading to increasing interfacial current density, dendrite formation on plating, short circuit, and cell failure. The process occurs above a critical current for stripping (CCS) for a given stack pressure, which sets the upper limit on current density that avoids cell failure, in line with results for the Li/solid-electrolyte interface. The pressure required to avoid cell failure varies linearly with current density, indicating that Na creep rather than diffusion per se dominates Na transport to the interface and that significant pressures are required to prevent cell death, >9 MPa at 2.5 mA·cm-2.
    • More