James Marrow

University of Oxford, Materials, Faculty Member

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My research is focussed on the degradation of structural materials and the role of microstructure. A significant proportion of this work is related to materials utilised in the nuclear industry. This work has been funded by organisations including EPSRC, Rolls- Royce, British Energy, EdF, the Health and Safety Executive (Nuclear Installations Inspectorate) and the Nuclear Decommissioning Authority. 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.
Address: Department of Materials
University of Oxford

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Papers by James Marrow

Characterization of Material Properties Using an Inverse Method

Trans Tech Publications Ltd. eBooks, Oct 15, 2006

A simple finite-element-based inverse method has been devised with the aim of characterizing the ... more A simple finite-element-based inverse method has been devised with the aim of characterizing the properties of isotropic but heterogeneous materials under load. The method has been implemented into the commercial finite element code ABAQUS via its User Material (UMAT) Subroutine to facilitate the process of material characterization. Verification of the method has been carried out using simulated examples and the results showed rapid convergence of the method with good accuracy. The method has also been applied successfully to actual mechanical testing of graphite which has a porous microstructure and hence inhomogeneous distribution of material properties.

$Research paper thumbnail of In situ mechanical testing of nuclear graphite at elevated temperatures: Synchrotron x-ray tomography, neutron diffraction and Raman scattering$

In situ mechanical testing of nuclear graphite at elevated temperatures: Synchrotron x-ray tomography, neutron diffraction and Raman scattering

High temperature in situ tests of Gilsocarbon polygranular nuclear graphite have investigated the... more High temperature in situ tests of Gilsocarbon polygranular nuclear graphite have investigated the microstructure's deformation at two length scales. At the µm-scale, in situ bending tests observed by synchrotron radiation x-ray computed micro-tomography evaluated the bulk mechanical properties of flexural strength and fracture toughness and observed crack propagation at temperatures up to 1000°C; at the atomic-scale, neutron diffraction data correlated the lattice strain with bulk stress at temperatures up to 850°C. Raman scattering observations at temperatures up to 800°C showed the change of micro-scale residual strains. Gilsocarbon graphite was found to have a higher strength and fracture toughness with increased temperature. The mechanism leading to this behaviour has been attributed to the relaxation of residual strains

<i>In-Situ</i> Observation and Modelling of Intergranular Cracking in Polycrystalline Alumina

Key Engineering Materials, 2011

$Research paper thumbnail of In situ characterisation of the strain fields of intragranular slip bands in ferrite by high-resolution electron backscatter diffraction$

In situ characterisation of the strain fields of intragranular slip bands in ferrite by high-resolution electron backscatter diffraction

Acta Materialia, Oct 1, 2022

$Research paper thumbnail of X-ray diffraction contrast tomography: a novel technique for three-dimensional grain mapping of polycrystals. II. The combined case$

X-ray diffraction contrast tomography: a novel technique for three-dimensional grain mapping of polycrystals. II. The combined case

Journal of Applied Crystallography, Mar 8, 2008

The principles of a novel technique for nondestructive and simultaneous mapping of the three-dime... more The principles of a novel technique for nondestructive and simultaneous mapping of the three-dimensional grain and the absorption microstructure of a material are explained. The technique is termed X-ray diffraction contrast tomography, underlining its similarity to conventional X-ray absorption contrast tomography with which it shares a common experimental setup. The grains are imaged using the occasionally occurring diffraction contribution to the X-ray attenuation coefficient each time a grain fulfils the diffraction condition. The three-dimensional grain shapes are reconstructed from a limited number of projections using an algebraic reconstruction technique. An algorithm based on scanning orientation space and aiming at determining the corresponding crystallographic grain orientations is proposed. The potential and limitations of a first approach, based on the acquisition of the direct beam projection images only, are discussed in this first part of the paper. An extension is presented in the second part of the paper [

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Thermal Shock and Residual Strength Testing of SiC/SiC Composite Braided Tubes

Experimental Mechanics, May 12, 2023

Multi-scale damage modelling in a ceramic matrix composite using a finite-element microstructure meshfree methodology

Philosophical Transactions of the Royal Society A, Jul 13, 2016

One contribution of 22 to a Theo Murphy meeting issue 'Multiscale modelling of the structural int... more

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$Research paper thumbnail of J-integral analysis of the elastic strain fields of ferrite deformation twins using electron backscatter diffraction$

J-integral analysis of the elastic strain fields of ferrite deformation twins using electron backscatter diffraction

Acta Materialia, Oct 1, 2021

The strain fields of deformation twins in the ferrite matrix of an age-hardened duplex stainless-... more The strain fields of deformation twins in the ferrite matrix of an age-hardened duplex stainless-steel (Zeron 100: 25%Cr, 7%Ni) have been studied in situ under load, and ex situ (unloaded), using high-resolution electron backscatter diffraction (HR-EBSD). The local 2dimensional (2D) elastic strain field acting on the twin tip was parametrised for the first time using the strain energy release rate (J-integral) and then decomposed into the mode I and mode II stress intensity factors (KI and KII). An improved method to select the strain reference was used, based on the relationship between the HR-EBSD cross-correlation peak height and mean angular error. The elastic field described by KI increased with twin thickness. The inplane shear field, described by KII, relaxed when the load was removed. Some current limitations of the 2D analysis are discussed, which aims to provide an experimental methodology to quantify the fields that describe the local boundary conditions for twin thickening and propagation.

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$Research paper thumbnail of X-ray diffraction contrast tomography: a novel technique for 3D grain mapping of polycrystals. Part I: direct beam case$

X-ray diffraction contrast tomography: a novel technique for 3D grain mapping of polycrystals. Part I: direct beam case

HAL (Le Centre pour la Communication Scientifique Directe), 2008

By simultaneous acquisition of the transmitted and the diffracted beams, the applicability of the... more By simultaneous acquisition of the transmitted and the diffracted beams, the applicability of the previously introduced diffraction contrast tomography technique [Ludwig, Schmidt, Lauridsen and Poulsen (2008). J. Appl. Cryst. 41, 302-309] can be extended to the case of undeformed polycrystalline samples containing more than 100 grains per cross section. The grains are still imaged using the occasionally occurring diffraction contribution to the X-ray attenuation coefficient, which can be observed as a reduction in the intensity of the transmitted beam when a grain fulfils the diffraction condition. Automating the segmentation of the extinction spot images is possible with the additional diffracted beam information, even in the presence of significant spot overlap. By pairing the corresponding direct ('extinction') and diffracted beam spots a robust sorting and indexing approach has been implemented. The analysis procedure is illustrated on a real data set and the result is validated by comparison with a two-dimensional grain map obtained by electron backscatter diffraction. © International Union of Crystallography 2008

Cortical Bone Spherical Indentation Modulus Correlates with the Elastic Modulus from Compression Testing and CT-Measured Porosity

Orthopaedic Proceedings, Jan 30, 2019

With information about a patient's bone mechanical properties orthopaedic operations could be... more

Application of an independent parallel reactions model on the annealing kinetics of BEPO irradiated graphite

Journal of Nuclear Materials, Aug 1, 2012

ABSTRACT Stored energy release rates have been determined for neutron irradiated graphite samples... more ABSTRACT Stored energy release rates have been determined for neutron irradiated graphite samples machined from an early air-cooled nuclear reactor (British Experimental Pile Zero or BEPO). The rate of release of stored energy was measured for both isothermal and linear rise heating rate differential scanning calorimetry experiments. The rate of release data were analysed using a thermal kinetics, independent parallel reactions model. The effect of annealing on the graphite crystalline structure was evaluated by investigating changes to X-ray diffraction spectra. A correlation between the calculated crystallite size and stored energy release is presented. A method for calculating the kinetic parameters for the annealing reaction is proposed and tested against the data. The method shows excellent consistency for both the isothermal and linear heating rate experiments (with less than 3% standard deviation).

Small-Specimen Testing, with Image-Based Analysis, for Crack Propagation Resistance in Polygranular Nuclear Graphite

Graphite Testing for Nuclear Applications: The Validity and Extension of Test Methods for Material Exposed to Operating Reactor Environments

A Robust Finite Element-based Filter for Digital Image and Volume Correlation Displacement Data

Experimental Mechanics, 2021

Background: Digital Image and Volume Correlation (DIC and DVC) are non-contact measurement techni... more Background: Digital Image and Volume Correlation (DIC and DVC) are non-contact measurement techniques that are used during mechanical testing for quantitative mapping of full-field displacements. The relatively high noise floor of DIC and DVC, which is exasperated when differentiated to obtain strain fields, often requires some form of filtering. Techniques such as median filters or least-squares fitting perform poorly over high displacement gradients, such as the strain localisation near a crack tip, discontinuities across crack flanks or large pores. As such, filtering does not always effectively remove outliers in the displacement field. Objective: This work proposes a robust finite element-based filter that detects and replaces outliers in the displacement data using a finite element method-based approximation. Methods: A method is formulated for surface (2D and Stereo DIC) and volumetric (DVC) measurements. Its validity is demonstrated using analytical and experimental displacement data around cracks, obtained from surface and full volume measurements. Results: It is shown that the displacement data can be filtered in such a way that outliers are identified and replaced. Moreover, data can be smoothed whilst maintaining the nature of the underlying displacement field such as steep displacement gradients or discontinuities. Conclusions: The method can be used as a post-processing tool for DIC and DVC data and will support the use of the finite element method as an experimental-numerical technique.

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Cortical Bone Spherical Indentation Modulus Correlates with the Elastic Modulus from Compression Testing and CT-Measured Porosity

With information about a patient's bone mechanical properties orthopaedic operations could be... more

A 2 D mesoscale model for intergranular stress corrosion crack propagation

A mechanical model for simulating intergranular stress corrosion cracking is presented. The model... more A mechanical model for simulating intergranular stress corrosion cracking is presented. The model has been developed to address the limitations of percolation-like models, which do not account for the mechanical crack driving force and cannot capture experimentally observed phenomena such as the formation of ductile bridging ligaments by resistant boundaries. The model is based on a regular representation of the material’s microstructure and a categorisation of grain boundaries as susceptible and resistant to corrosion. Crack propagation in 2D microstructures with several fractions of experimentally observed susceptible boundaries is studied. Monte-Carlo type simulations with random distributions of boundaries and a range of susceptible and resistant boundaries failure strengths are performed. The effects of crack bridging and crack branching are quantified. It is concluded that together with the fraction of susceptible boundaries, the resistant boundaries failure strength is the si...

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

ACS Applied Materials & Interfaces, 2019

3-electrode studies coupled with tomographic imaging of the Na/Na-"-alumina interface reveal th... more 3-electrode studies coupled with tomographic imaging of the Na/Na-"-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 2 interface and that significant pressures are required to prevent cell death, > 9 MPa at 2.5 mA•cm-2 .

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In-situ X-ray tomography of wear – A feasibility study

Tribology International, 2020

Wear experiments using annular contacts were carried out to investigate the possibility of imagin... more Wear experiments using annular contacts were carried out to investigate the possibility of imaging wear scars and wear debris beds in-situ. Samples made of 6082T6 aluminium alloy were subjected to unidirectional wear under different conditions with the sample elements then locked in contact to preserve the end-of-wear condition. Post-wear 3D morphology was successfully imaged in-situ using X-ray tomography, with total depth of the wear scar, surface primary-profile roughness and real area of contact also obtained. This study is a proof-of-concept illustrating the utility of tomography for studying wear, without the need to disassemble the contact or disturb the debris bed and serves as a starting point for a new approach to the investigation of wear phenomena.

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Imaging Sodium Dendrite Growth in All‐Solid‐State Sodium Batteries Using 23Na T2‐Weighted Magnetic Resonance Imaging

Angewandte Chemie International Edition, 2020

Two‐dimensional, Knight‐shifted, T2‐contrasted 23Na magnetic resonance imaging (MRI) of an all‐so... more Two‐dimensional, Knight‐shifted, T2‐contrasted 23Na magnetic resonance imaging (MRI) of an all‐solid‐state cell with a Na electrode and a ceramic electrolyte is employed to directly observe Na microstructural growth. A spalling dendritic morphology is observed and confirmed by more conventional post‐mortem analysis; X‐ray tomography and scanning electron microscopy. A significantly larger 23Na T2 for the dendritic growth, compared with the bulk metal electrode, is attributed to increased sodium ion mobility in the dendrite. 23Na T2‐contrast MRI of metallic sodium offers a clear, routine method for observing and isolating microstructural growths and can supplement the current suite of techniques utilised to analyse dendritic growth in all‐solid‐state cells.

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$Research paper thumbnail of A method for fracture toughness measurement in trabecular bone using computed tomography, image correlation and finite element methods$

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

Journal of the Mechanical Behavior of Biomedical Materials, 2020

The fracture resistance of load-bearing trabecular bone is adversely affected by diseases such as... more The fracture resistance of load-bearing trabecular bone is adversely affected by diseases such as osteoporosis. However, there are few published measurements of trabecular bone fracture toughness due to the difficulty of conducting reliable tests in small specimens of this highly porous material. A new approach is demonstrated that uses digital volume correlation of Xray computed tomographs to measure 3D displacement fields in which the crack shape and size can be objectively identified using a phase congruency analysis. The criteria for crack propagation, i.e. fracture toughness, can then be derived by finite element simulation, with knowledge of the elastic properties.

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

Journal of the Mechanics and Physics of Solids, 2019

Calibrating and verifying crystal plasticity material models is a significant challenge, particul... more 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, and hardening rate of the different slip and twin systems. The constitutive model is based on dislocation densities 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 find the model 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. 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 developed in the present research can be applied to identify the critical resolved shear stress and hardening parameters of other coarse-grained materials.

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