Julie Yeomans

Professor Julie Yeomans


Professor of Ceramic Materials, Associate Dean (Research and Innovation)
MA, PhD, CEng, CSci, FIMMM
+44 (0)1483 689613
28 AB 03
Personal Assistant: Charlotte Gray

Academic and research departments

Department of Mechanical Engineering Sciences.

Biography

Affiliations and memberships

Institute of Materials, Minerals and Mining.
Member
American Ceramic Society.
Member

Research

Research interests

Research projects

My publications

Publications

D Hallam, A Heaton, B James, PA Smith, JA Yeomans (2015)The correlation of indentation behaviour with ballistic performance for spark plasma sintered armour ceramics, In: Journal of the European Ceramics Societypp. 2243-2252 Elsevier

The Knoop and Vickers indentation behaviour of spark plasma sintered SiC–5 wt.% B4 C, B4 C and SiC–2.5 wt.% AlN–3 wt.% C armour ceramics have been investigated and observations correlated with ballistic performance. Surface and sub-surface indentation-induced damage has been characterised via cross-sectioning and serial ceramographic polishing techniques. The nature of the damage appears to be less influential than hardness in relation to ballistic performance, but variability in indentation behaviour appears to correlate with variability in ballistic performance. Examination of the indentation size effect curves shows that both Knoop hardness and predicted transition velocities correlate with V50 ballistic performance against an armour-piercing threat, further supporting the importance of hardness and the potential for indentation to be used as a screening method for armour materials.

JA Yeomans (2008)Ductile particle ceramic matrix composites - Scientific curiosities or engineering materials?, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY28(7)pp. 1543-1550 ELSEVIER SCI LTD

This review is concerned with ductile particle ceramic matrix composites, which are a group of materials comprising micro- or nano-scale metallic particles in a ceramic matrix. The most studied materials have an alumina matrix; nickel, iron, molybdenum, copper, and silver are some of the more frequently used metals. In contrast to conventional cermets and composites containing an interconnected metallic phase, the particles are discrete. The larger particles provide a toughening increment by deforming plastically and bridging an advancing crack. For the nanoscale composites significant improvements in strength have been reported. Improvements in strength and toughness, coupled with changes to elastic properties and thermal conductivity, have led to improved thermal shock resistance and a consideration of these materials for wear applications.

AJ Harris, B Vaughan, Julie Yeomans, Paul Smith, ST Burnage (2017)Ballistic testing of surface treated alumina and silicon carbide with improved adhesive bond strength, In: International Journal of Applied Ceramic Technology: ceramic product development and commercialization14(3)pp. 323-330 Wiley

The laser treatment of ceramics can lead to increased concentrations of hydroxyl ions on the surface, resulting in improved adhesive bond strength in quasi-static tests. Whether the improvement can be translated to armor applications is investigated here. The ballistic testing of composite-backed, surface treated and non-treated ‘control’ alumina and silicon carbide panels was undertaken. The failure locus of the ceramic to adhesive/composite joint and the qualitative degree of damage were assessed. Laser surface treated samples performed better than control samples, with silicon carbide moving from single shot to multi-shot capability, thus giving significant advantages for the deployment of these materials.

KL Powell, JA Yeomans, PA Smith (1993)Localised damage in continuous fibre reinforced ceramic matrix composites, In: Ceramic Engineering and Science Proceedings14(9 -10)pp. 890-895

As a precursor to a study of erosive near behaviour of ceramic matrix composites fracture by indentation and single particle impact has been studied in two glass-ceramic/silicon carbide fibre composite systems. The damage has been characterised and quantified using a combination of confocal scanning laser microscopy and scanning electron microscopy. Lateral cracks which form approximately parallel to the surface, have been found to be the predominant damage event. In the calcium alumino-silicate (CAS)/Nicalon system, lateral cracks tend, to form in regions of the matrix which have a high local fibre volume fraction, whilst in the barium magnesium alumino silicate (BMAS)/Tyranno system they tend to avoid fibre-rich regions. These results are consistent with an analysis of residual thermal stresses in the two systems. In CAS/Nicalon the coefficient of thermal expansion of the matrix is greater than that of the fibre. This puts the matrix into axial tension at room temperature with the stress increasing with local fibre volume fraction. In BMAS/Tyranno the reverse in the case. Thus in both systems, the observed damage is a consequence of the residual stress as well as the stress due to the contact event.

M Tillman, JA Yeomans, RA Dorey (2014)The effect of a constraint on the sintering and stress development in alumina thick films, In: Ceramics International4(7)pp. 9715-9721 Elsevier

The microstructural and stress evolution of thick (25 μm) alumina films on dense alumina substrates sintered at temperatures from 1300 °C to 1600 °C has been investigated. In this study the constraint on sintering was monitored in the absence of significant differences in thermal expansion between the film and the substrate. For comparison purposes unconstrained alumina pellets sintered at 1300 °C-1600 °C were also examined. Overall, the constrained alumina densified less than the free alumina, as expected, although at intermediate temperatures densification rates were comparable. Sintering in the direction perpendicular to the substrate was enhanced with respect to that parallel to the substrate as a means of stress relaxation. Using fluorescence spectroscopy the residual stresses of the films parallel to the substrates were measured; residual tensile stresses as high as 450±40 MPa were exhibited by the films. The considerable stress development resulted in cracking and delamination of the film from the substrate, subsequently film constraint was reduced and densification was not impeded. © 2014 The Authors.

C Kastritseas, PA Smith, JA Yeomans (2005)The onset of thermal shock damage in unidirectional-fibre-reinforced ceramic matrix composites, In: HIGH TEMPERATURE CERAMIC MATRIX COMPOSITES 5pp. 235-240
P Yates, Christopher Mallinson, P Mallinson, Mark Whiting, Julie Yeomans (2017)An Investigation into the Nature of the Oxide Layer Formed on Kovar (Fe-29Ni-17Co) Wires Following Oxidation in Air at 700 °C and 800 °C, In: Oxidation of Metals: an international journal of the science of gas-solid reactions88(5-6)pp. 733-747 Springer

This work provides new insight and evidence that challenges and extends the accepted view of the oxidation of Kovar (ASTM-15). Specimens of 2 mm diameter Kovar wire were oxidised in air at 700 °C or 800 °C for 10 minutes. The resulting oxide layers were analysed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, scanning transmission electron microscopy and Raman spectroscopy. Oxide layers of approximately 2 μm and 4 μm thick were formed at 700 °C and 800 °C, respectively. These were found to contain iron, cobalt and traces of nickel. The combination of analysis techniques revealed that the oxide contains Fe2O3 in addition to (Fe,Co,Ni)3O4, a spinel oxide, in contrast to the combinations of Fe3O4, Fe2O3 and FeO that are typically reported. The oxide layer was found to be complex, consisting of multiple layers with different compositions which is overlooked in the existing literature.

C Kastritseas, PA Smith, JA Yeomans (2008)Thermal shock behaviour of angle-ply and woven dense ceramic-matrix composites, In: JOURNAL OF MATERIALS SCIENCE43(12)pp. 4112-4118 SPRINGER
Adam Healey, J Cotton, S Maclachlan, Paul Smith, Julie Yeomans (2016)Understanding the Ballistic Event: Methodology and Initial Observations, In: Journal of Materials Science52(6)pp. 3074-3085 Springer

The purpose of the study is to accelerate the development of ceramic materials for armour applications, by substantially increasing the information obtained from a high-energy projectile impact event. This has been achieved by modifying an existing test configuration to incorporate a block of ballistic gel, attached to the strike face of a ceramic armour system, to capture fragments generated during the ballistic event such that their final positions are maintained. Three different materials, representative of the major classes of ceramics for armour applications, alumina, silicon carbide and boron carbide, have been tested using this system. Ring-on-ring biaxial disc testing has also been carried out on the same materials. Qualitative analysis of the fracture surfaces using scanning electron microscopy and surface roughness quantification, via stereoimaging, has shown that the fracture surfaces of biaxial fragments and ballistic fragments recovered from the edges of the tile are indistinguishable. Although the alumina and boron carbide fragments generated from areas closer to the point of impact were also similar, the silicon carbide fragments showed an increase in porosity with respect to the fragments from further away and from biaxial testing. This porosity was found to result from the loss of a boron-rich second phase, which was widespread elsewhere in the material, although the relevance of this to ballistic performance needs further investigation. The technique developed in this work will help facilitate such studies.

C Kastritseas, PA Smith, JA Yeomans (2010)Thermal shock fracture in cross-ply fibre-reinforced ceramic-matrix composites, In: PHILOSOPHICAL MAGAZINE90(31-32)PII 923938pp. 4209-4226 TAYLOR & FRANCIS LTD
Edward H. Williamson, Mark Gee, Daniel Robertson, John F. Watts, Mark J. Whiting, Julie A. Yeomans (2019)Wear performance and characterisation of coatings for nuclear applications: WC-(W,Cr)2C-Ni and hard chromium plate, In: Wear430pp. 169-182 Elsevier

The nuclear industry has used hard chromium plate for many years but is seeking alternatives, due to the adverse health effects of Cr(VI) employed in electroplating. In this study, testing and analysis regimes for the comparison of the sliding wear performance of candidate materials have been established and the performance of WC-(W,Cr)2C-Ni has been compared with that of hard chromium plate. WC-(W,Cr)2C-Ni was applied to Inconel 625 substrates using a detonation gun thermal spray technique. Sliding wear testing was performed using a ball-on-flat configuration reciprocating tribometer at 20 °C in three environments: dry, deionised water and simulated nuclear reactor water chemistry. Wear rates have been evaluated, using both mass and volume loss, and the worn samples were analysed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The WC-(W,Cr)2C-Ni coating had a broadly comparable wear performance to hard chromium plate in all three environments. There were differences between deionised and borated water, such that the latter needs to be used in further evaluation. SEM and XPS analyses enabled the wear mechanisms for WC-(W,Cr)2C-Ni and HCP to be elucidated, including pull-out and tribolayer formation. XPS has shown that the tribolayer on WC-(W,Cr)2C-Ni is stratified and undergoes chemical changes as a result of wear.

RA Dorey, JA Yeomans, PA Smith (2002)Effect of pore clustering on the mechanical properties of ceramics, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY22(4)pp. 403-409 ELSEVIER SCI LTD
RA Dorey, JA Yeomans, PA Smith, J Pan (2001)In situ optical dilatometric measurements of the initial stages of sintering of alumina, In: ACTA MATERIALIA49(3)pp. 519-527 PERGAMON-ELSEVIER SCIENCE LTD
MJ Blissett, PA Smith, JA Yeomans (1997)Thermal shock behaviour of unidirectional silicon carbide fibre reinforced calcium aluminosilicate, In: JOURNAL OF MATERIALS SCIENCE32(2)pp. 317-325 CHAPMAN HALL LTD
C Kastritseas, PA Smith, JA Yeomans (2005)Thermal shock fracture in unidirectional fibre-reinforced ceramic-matrix composites, In: COMPOSITES SCIENCE AND TECHNOLOGY65(11-12)pp. 1880-1890 ELSEVIER SCI LTD
MJ Whiting, MT Staff, JA Fernie, PM Mallinson, JA Yeomans (2016)Fabrication of a Glass-Ceramic-to-Metal Seal between Ti-6Al-4V and a Strontium Boroaluminate Glass, In: International Journal of Applied Ceramic Technology: ceramic product development and commercialization13(5)pp. 956-965 Wiley

Glass-ceramics are widely utilized in the electronics industry to provide electrical insulation and to form leak tight joints with a range of metals. The coefficient of thermal expansion (CTE) of the glass-ceramic can be controlled by the extent of crystallization to reduce detrimental tensile stresses in the joint. In recent years there has been interest in using titanium alloys, in place of stainless steels, due to their lower density and superior specific strength. In this study, the heat treatment of a strontium boroaluminate glass has been tailored to create glass-ceramics with mean CTEs ranging from 5.7 ± 0.1 × 10-6 K-1 to 9.7 ± 0.1 × 10-6 K-1 over the temperature range 303 K to 693 K. The resultant glass-ceramic consists of three crystalline phases and residual glass. A glass-ceramic with a mean CTE of 6.9 ± 0.1 × 10-6 K-1 was subsequently fabricated to form a compression seal with a Ti-6Al-4V housing and a pre-oxidized Kovar pin. Single pin assemblies were shown to be reproducible in terms of microstructure and all passed a standard helium leak test, indicating that a successful seal had been produced.

MJ Blissett, PA Smith, JA Yeomans (1998)Flexural mechanical properties of thermally treated unidirectional and cross-ply Nicalon-reinforced calcium aluminosilicate composites, In: JOURNAL OF MATERIALS SCIENCE33(16)pp. 4181-4190 KLUWER ACADEMIC PUBL
PM Delaforce, JA Yeomans, NC Filkin, GJ Wright, RC Thomson (2007)Effect of NiO on the phase stability and microstructure of yttria-stabilized zirconia, In: JOURNAL OF THE AMERICAN CERAMIC SOCIETY90(3)pp. 918-924 BLACKWELL PUBLISHING
C Kastritseas, P Smith, J Yeomans (2006)Thermal shock of ceramic matrix compositespp. 400-433
S Kiani, J Pan, JA Yeomans (2006)A new scheme of finding the master sintering curve, In: J AM CERAM SOC89(11)pp. 3393-3396 BLACKWELL PUBLISHING

The master sintering curve approach represents densification data in terms of a master variable that combines sintering time and temperature. Recently, a finite-element scheme to predict sintering deformation that requires only the master sintering curve instead of a full constitutive law as the input data has been developed. Here, a modification to the original master sintering curve approach, so that it is more suitable for finite-element analysis, is presented. Finite-element shape functions are used to represent the densification data as well as the master sintering curve. This approach confers extra flexibility to the master sintering curve approach, even when it is not used with finite-element analysis. For example, by using shape functions, a varying activation energy can be used to obtain a master sintering curve for a set of densification data that cannot be fitted using a constant activation energy.

D Mahdi, A Riches, M Gester, J Yeomans, P Smith (2015)Rolling and sliding: Separation of adhesion and deformation friction and their relative contribution to total friction, In: TRIBOLOGY INTERNATIONAL89pp. 128-134 ELSEVIER SCI LTD
S Kiani, J Pan, JA Yeomans, M Barriere, P Blanchart (2007)Finite element analysis of sintering deformation using densification data instead of a constitutive law, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY27(6)pp. 2377-2383 ELSEVIER SCI LTD
GJ Wright, JA Yeomans (2009)Three-step sintering of constrained yttria stabilised zirconia layers and its effect on microstructure and gas permeance, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY29(10)pp. 1933-1938 ELSEVIER SCI LTD
GJ Wright, JA Yeomans (2008)The influence of screen-printing parameters on the microstructure and gas permeance of a zirconia electrolyte, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY28(4)pp. 779-785 ELSEVIER SCI LTD
Simon Parker, Mark Whiting, Julie Yeomans (2017)Control of carbon content in WC-Co hardmetal by heat treatment in reducing atmospheres containing methane., In: International Journal of Refractory Metals and Hard Materials66pp. 204-210 Elsevier

Pressed WC-Co hardmetal compacts of two different compositions, 6 and 10 wt.% Co, were heat treated under flowing atmospheres of nitrogen, hydrogen and methane at temperatures from 500 to 900 °C prior to sintering under argon. Microstructural examination showed excessive carburisation up to 2.5 mm into the compacts with regions most exposed to heat treatment atmospheres showing greatest carburisation. η-phase was present in the 6 wt.% Co samples heat treated at low temperatures without methane but was not present with heat treatment temperatures of 700 °C or above with methane present. The hardness of both materials was significantly lower in highly carburised regions, highlighting the need for careful control of heat treatment parameters.

AJ Harris, B Vaughan, ST Burnage, JA Yeomans, PA Smith (2013)Surface preparation of silicon carbide for improved adhesive bond strength in armour applications, In: Journal of the European Ceramic Society33(15-16)pp. 2925-2934

Surface treatments of silicon carbide have been investigated with the aim of improving the strength of the bond between the ceramic and an epoxy adhesive. Three surface conditions have been characterised; as-fired, air re-fired and KrF laser processed. A number of characterisation techniques have been used to determine the morphological and chemical changes that have occurred to the surface. Scanning electron microscopy of the re-fired and laser processed samples showed surfaces that appeared glassy, with the laser processed surface showing a different morphology. X-ray photoelectron spectroscopy indicated both treatments had oxidised the surface and the laser processed surface also had a greater concentration of hydroxyl groups. The wettability of both surfaces had improved and the laser processed surface was found to be highly hydrophilic. Mechanical testing of joints prepared with this technique showed them to have the highest strength in tension, with the locus of failure being cohesive. © 2013 The Authors.

AJ Harris, B Vaughan, ST Burnage, JA Yeomans, PA Smith (2013)Surface preparation of alumina for improved adhesive bond strength in armor applications, In: Ceramic Engineering and Science Proceedings33(5)pp. 149-159 Wiley Blackwell

Surface treatments of alumina have been investigated with the aim of increasing the strength of the bond created between the alumina and a toughened epoxy adhesive. Four surface conditions have been assessed: as-fired; grit blasted; and krypton fluoride excimer laser treated under two sets of conditions. Compared with the as-fired surface, the grit blasted surface was rougher with poorer wettability, probably due to surface contamination. It was found that the laser treatments removed some of the sintering additives and caused rounding of the alumina grains, slightly increasing the surface roughness. Further, the laser treatment led to an increased surface energy and wettability, which has been linked tentatively to an observed increase in the hydroxyl groups on the surface. The adhesive bond strength was assessed by testing joints in tension and shear. It was found that the laser treated surfaces demonstrated slight improvements in bond strength, with a cohesive failure of the adhesive in tension for surfaces subjected to one of the two laser treatments, compared with failure at the interface for the as-fired, grit blasted and other laser treated samples in tension and for all samples in shear. Thus, it has been demonstrated that modifications to the surface of alumina can result in mechanical and chemical changes which affect roughness, wettability, bond strength and the locus of failure.

C Kastritseas, PA Smith, JA Yeomans (2006)Damage characterisation of thermally shocked cross-ply ceramic composite laminates, In: JOURNAL OF MATERIALS SCIENCE41(3)pp. 951-962 SPRINGER