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Hopkins C.,National University of Ireland | McHugh P.E.,National University of Ireland | O'Dowd N.P.,Materials and Surface Science Institute | Rochev Y.,National University of Ireland | McGarry J.P.,National University of Ireland
Computational Materials Science | Year: 2013

Reports from recent studies indicate that commercial stent coatings are susceptible to delamination, therefore warranting further research into their adhesion properties. In the present study a robust combined computational- experimental methodology to determine the characteristic interface properties for polyurethane stent coatings bonded to stainless steel is presented. Specifically, delamination of dry and hydrated stent coatings is investigated during 90° peel tests with the force and peel radius being experimentally measured. A comprehensive computational parametric study then establishes the relationship between peel force, peel radius, interface strength and interface characteristic length. Such uniquely determined interface properties are validated for different coating thickness and stiffness. Where accurate measurement of the peeling radius is not possible, it is demonstrated that the slope of the steady state load displacement curve can be used to uniquely characterise the interface. Results suggest that aging does not change the interfacial properties but stiffens the polymer coating. Hydration is found to reduce the interface strength by an order of magnitude, and also decreases the coating stiffness. Such alterations in interface and coating properties are of critical importance in prediction of coating delamination during stent deployment. © 2013 Elsevier B.V. All rights reserved.

Pavlova S.,RAS Boreskov Institute of Catalysis | Yaseneva P.,University of Cambridge | Sadykov V.,RAS Boreskov Institute of Catalysis | Rogov V.,RAS Boreskov Institute of Catalysis | And 4 more authors.
RSC Advances | Year: 2014

Using original hydrothermal technology honeycomb corundum monoliths with a peculiar porous structure and high water-adsorbing capacity facilitating procedures of active component loading have been produced. The detailed study of ethanol steam reforming over Ru/Ce0.5Zr0.5O 2(CZ), Ru/Ce0.4Zr0.4Sm0.2O 2-(δ + γ)Al2O3 (granulated) and Ru/Ce0.4Zr0.4Sm0.2O2/α-Al 2O3 (monolithic) has been performed. It has been revealed that the main route of the reaction over Ru/CZ is ethanol dehydrogenation while ethanol dehydration into ethylene mainly occurs over Ru/CZS-Al2O 3. Variation of the H2O-EtOH ratio, contact time and temperature allows hydrogen and CO yield to be governed. The monolithic catalyst has shown a high performance and stability at short contact time (0.1-0.4 s) and low water concentration (H2O-EtOH ∼ 1-3). © the Partner Organisations 2014.

Gray P.J.,Materials and Surface Science Institute | McCarthy C.T.,Materials and Surface Science Institute
Composites Part B: Engineering | Year: 2010

This paper presents the development and validation of a global bolted joint model (GBJM), a highly efficient modelling strategy for bolted composite joints. Shell elements are used to model the composite laminates and the bolt is represented by a combination of beam elements coupled to rigid contact surfaces. The GBJM can capture effects such as bolt-hole clearance, bolt-torque, friction between laminates, secondary and tertiary bending in the laminates as well as the load distribution in multi-bolt joints. The GBJM is validated using both three-dimensional finite element models and experiments on both single- and multi-bolt joints. The GBJM was found to be robust, accurate and highly efficient, with time savings of up to 97% realised over full three-dimensional finite element models. © 2010 Elsevier Ltd. All rights reserved.

Tanner D.A.,Materials and Surface Science Institute | Belochapkine S.,Materials and Surface Science Institute | Laffir F.,Materials and Surface Science Institute | Nakahara S.,Materials and Surface Science Institute | Nakahara S.,University of Limerick
Materials at High Temperatures | Year: 2012

The effect of room-temperature (~20°C) air-oxidation on void formation in sputter-deposited thin films of aluminum and its alloys was investigated using a transmission electron microscope. It was found that after air-oxidation, only lithium-bearing aluminum alloy films exhibited a high (~4×10 16 cm-3) density of small (~2 nm) voids, whereas pure aluminum or lithium-free aluminum alloy films did not contain any voids. In lithium-bearing aluminum alloy films, both aluminum and lithium atoms migrate to the surfaces to form their surface oxide during room-temperature ageing after film deposition. In the course of the atom migration, excess vacancies are generated as a result of the large diffusivity difference existing between aluminum and lithium atoms (DLi in Al≫DAl) in the alloy matrix. The agglomeration of these excess vacancies led to the formation of so-called Kirkendall voids inside the alloy. Thus the presence of both aluminum and lithium in the alloys was a key factor for generating these Kirkendall voids in the films.

McCarthy C.T.,Materials and Surface Science Institute | O'Higgins R.M.,Materials and Surface Science Institute | Frizzell R.M.,Materials and Surface Science Institute
Composite Structures | Year: 2010

An experimental study was carried out to characterise the constitutive response of carbon fibre-reinforced epoxy laminates. While maintaining essentially linear behaviour in the fibre and transverse directions, this material displays significant non-linear shear stress-strain behaviour to rupture. It is shown that the well known Hahn-Tsai non-linear shear model does not provide an acceptable fit for the strain range examined and so a novel approach was derived where a cubic spline interpolation method was used to capture the non-linear shear behaviour. The well known ply discount model, based on Hashin's failure criteria, was also used to predict fibre and transverse matrix damage in the laminates. The spline approach is coupled with maximum strain failure criteria to predict the response in the in-plane and out-of-plane shear directions. The material Jacobian matrix is fully defined, thus allowing a full implicit material model to be implemented. Hence, the model is suitable for both implicit and explicit finite element codes. It is shown that the model accurately predicts the response of the material for load cases in which shear stresses dominate. The performance of the model is demonstrated by considering a number of laminate configurations and failure of an open-hole tension specimen. © 2009 Elsevier Ltd. All rights reserved.

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