Staff publications (CDS)

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Open Access
A process for the fabrication of ceramic fibre reinforced titanium aluminide
(1992-01-07T00:00:00Z) Horsfall, Ian; Cundy, S. J.; Wachtman, J. B.
This paper describes initial work on a novel process for the production of titanium aluminide matrix composites reinforced with short alumina fibers. The processing route involves an adaption of existing metal matrix composite (MMC) fabrication technology used to produce hybrid particulate/short fiber composites. A preform is produced which contains alumina fibers and titanium metal powder with a fiber content of around 10% by volume and approximately 50% porosity. This preform is then infiltrated with pure aluminum by a squeeze casting process to produce a fully dense composite of titanium powder and alumina fibers in a metallic aluminum matrix. The composite is then heat treated in a hot isostatic press to react the aluminum and titanium to produce a titanium aluminide matrix.
Open Access
Impact perforation testing of stab-resistant armour materials
(1995-12-31T00:00:00Z) Horsfall, Ian; Pollitt, S. M.; Belk, J. A.; Angood, C.; Williams, J.G.; Pavan, A.
This paper describes the development of a method for the investigation and comparison of materials for use in stab resistant body armour. A number of polymer composite panels of different thicknesses and construction have been tested. A dynamic test which simulated the real threat has been used and the results compared to a simpler quasi-static test that might be used in initial materials selection. The materials tested were glass-epoxy, and glass-nylon composite panels of several thicknesses between 1.8 and 5.8mm. Additional tests were also performed on similar composites containing tungsten wires. An accelerated instrumented drop-tower was used to drive a knife through composite panels and record the force resisting penetration by the knife. The final penetration of the knife through the armour into a soft backing was also measured. For comparison,a similar geometry quasi-static test was carried out on the same specimens. It was found that energy absorbtion took the form of an initial resistance to perforation and then by a resistance to further penetration. This is thought to stem from resistance to cutting ofthe panel material and gripping of the knife blade. The energy required to produce a given penetration in dynamic tests was found to be in good agreement with the penetration achieved at similar energies under quasi-static conditions. For the materials tested there was no significant difference between the penetration resistance of single or two layer systems. The penetration achieved through a panel of a given material was approximately proportional to the inverse square of the panel's thickness. The relative performance of different armour materials was assessed by plotting the energy required to penetrate a fixed distance against the areal density of the panel.
Open Access
Crack softening damage model for ceramic impact and its application within a hydrocode
(American Institute of Physics, 1997-12-31T00:00:00Z) Hazell, P. J.; Iremonger, M. J.
A physically based crack softening damage model has been developed and used in a non-linear transient dynamic computer code (AUTODYN-2D). It is assumed that there is a finite number of orientated pre-existing flaws within the ceramic target. The mode I and mode II stress intensity factors are calculated in compression and tension and the strain energy release rate is then estimated and compared to a critical dynamic strain energy release rate. At initiation, a tension crack propagates at a velocity dependent on the mode I stress intensity factor and failure occurs in a computational cell when two neighbouring microcracks coalesce. The model was used to simulate two different plate impact experiments of alumina on alumina with encouraging results. The model was also used to analyze the impact of a steel sphere on alumina and shows strong correlation between experimental and predicted results.
Open Access
A note on the behind armour effects from perforated alumina/aluminium targets
(Elsevier Science B.V., Amsterdam., 1998-12-31T00:00:00Z) Hazell, P. J.; Fellows, N. A.; Hetherington, John G.
A thin, ceramic-faced armour, separated from a thick metal block, has been subjected to high-velocity impact by a 6.35 mm diameter steel sphere. Experimental work was carried out which compared firings into ceramic-faced aluminium armour, separated from thick aluminium witness blocks, with firings into the thick aluminium blocks alone. The depth of penetration and the area of damage were measured and an estimated percentage weight saving due to the inclusion of the ceramic-faced armour was calculated at varying velocity. This note yields useful information for the design and application of ceramic applique systems.
Open Access
Recent developments in the study of failure of solid biomaterials and bone: 'Fracture' and 'pre-fracture' toughness
(Elsevier, 1999-02-15) Zioupos, Peter
Our understanding of the stress and energy requirements for the fracture of solid bio(logical)-materials has improved lately as a result of a number of investigations which highlighted some important new aspects of the failure process. The present short review article shows that under normal circumstances structural ‘damage’ precedes the creation of a fatal macrocrack and the onset of ‘failure’. The externally perceived material ‘toughness’ is a function of both: (i) the degree of prefailure accumulation of damage and (ii) of the properties of the final fracture surface. These two situations can be distinguished as ‘pre-fracture’ toughness and ‘fracture toughness’ and the relative contribution of each one in the overall toughness of the tissue is crucial for the final outcome of the failure process. Inevitably, materials which show remarkable toughness have to enhance their performance with respect to both the previous two defined quantities.
Open Access
Focused logistics: holy grail or poisoned chalice?
(Taylor & Francis, 1999-10-01T00:00:00Z) Moore, David M.; Antill, Peter D.
With logistics having become more important as the 20th century has progressed, and particularly since the end of the Cold War, the need for more efficient and effective logistics is becoming paramount, as it is seen as both a 'competitive advange' and a 'force enabler'. 'Focused Logistics' is the latest term to enter usage, and this paper will examine how different it is from what has gone before, and whether it is applicable to some of the operational challenges that the armed forces might face in the near future.
Open Access
Integrated Project Teams: The MoD's New Hot Potato?
(Taylor & Francis, 2000-02-01T00:00:00Z) Moore, David M.; Antill, Peter D.
Since the announcement of Smart Procurement, much has been written on the potential benefits that IPTs will hopefully bring. It is supposed that they will improve the interface with industry, create a better understanding of requirements and establish an environment where industry is motivated to perform and so reduce cost, risk and time into service while improving product quality. The formation of a team should provide continuity, consistency, flexibility and ~ increased performance due to the integration of a wide-range of functional activities and decision-making, as well as increased motivation. These may well be gallant objectives, but how achievable are they? What obstacles does the MoD face in the implementation of the IPTs? Have they grasped a 'hot potato'?
Open Access
Where do we go from here? Past present and future logistics of the British Army
(Common Services Establishment, 2000-09-01T00:00:00Z) Moore, David M.; Antill, Peter D.
This paper will focus on the logistics approach as used by the British Armed Forces during the Cold War, what it is today, and what future operations may involve. It will also look at certain aspects of commercial logistics practice to see what could be applied to the British Armed Forces.
Open Access
British Army logistics and contractors on the battlefield
(Taylor & Francis, 2000-10-01T00:00:00Z) Moore, David M.; Antill, Peter D.
The paper examines how the British Army has conducted logistic support during the last few decades and the pressures on it to change that have come about since the end of the Cold War. It also looks at the nature of future conflict and how industry could be used to aleviate some of those pressures (primarily financial) by supplying logistics support much closer to the frontline than has been the case.
Open Access
Is sea-basing a viable method of providing logistic support to the UK amphibious force?
(2000-10-01T00:00:00Z) Moore, David M.; Antill, Peter D.; MacLennan, W. R.
Maritime power has traditionally been a central part of the UK’s defence planning and is well suited to supporting a wide range of military operations. The littoral area has always created problems for naval planners as most landings historically have had to endure a tactical separation of the naval and land components, and hence an artificial seam between the Navy and the Marines. With the end of the Cold War, amphibious operations are going to be more difficult to conduct than in the past, and amphibious forces are going to have to adopt manoeuvre warfare capabilities in order to successfully complete their missions. It is very likely that amphibious forces will have to conduct operations against a numerically superior enemy, who is on his own terrain, and be surrounded by a neutral, if not hostile populace. As such, the concept of Operational Manoeuvre From The Sea (OMFTS) whereby the sea is used as a manoeuvre space, and command and control is fast enough to cope with large amounts of information, but at the same time allow subordinates maximum flexibility to use their initiative, is increasingly attractive. It will be important not only for the combat elements to be able to use this new concept, but the Combat Service Support (CSS) elements as well.
Open Access
Structural ballistic armour for transport aircraft
(Elsevier Science B.V., Amsterdam., 2000-12-31T00:00:00Z) Horsfall, Ian; Austin, S. J.; Bishop, W.
This paper describes the structural response of a current ceramic-faced composite armour system and a proposed structural armour system for aircraft use. The proposed structural ballistic armour system is shown to be capable of providing significant structural integrity even after ballistic impact whilst providing ballistic protection equivalent to an existing applique system. The addition of a carbon fibre reinforced plastic front panel to the existing ceramic faced composite armour system improves the bendstrength by a factor of 3 and improves the energy to break by almost an order of magnitude.
Open Access
Strategy development for special operations force logistics
(2000-12-31T00:00:00Z) Moore, David M.; Allen, David; Antill, Peter D.
This article highlights the specific logistics problems which special operations forces have, given their highly specialist nature and the factors that act upon them such as external (political, economic and national culture) and internal influences as well as the changing face of warfare. It will examine the ways in which special operations forces are currently supported logistically and will go on to consider the ways by which commercial 'best-practice' could be used to enhance the mission effectiveness of forces employed in this role.
Open Access
The numerical analysis of dynamically loaded ceramic: A crack softening approach
(John Wiley & Sons, Ltd, 2000-12-31T00:00:00Z) Hazell, P. J.; Iremonger, M. J.
A physically based crack softening approach to modelling the failure of brittle materials that have been subjected to dynamic loading is presented and applied to a two-dimensional non-linear transient dynamic hydrocode. It is assumed that there are a number of evenly distributed and orientated micro flaws within the brittle material that are activated by a dynamically applied stress. Modes I and II stress intensity factors are calculated and compared to critical values, at which point the cracks grow at a velocity dependent on mode I stress intensity factor. The strength of the ceramic is degraded according to the length of the cracks. A simulation of a steel sphere impacting and penetrating a ceramic target at 1500 m/s is presented. Comparisons are drawn from experimental data.
Open Access
Mechanical properties of nacre and highly mineralized bone
(Royal Society, 2001-01-07) Currey, John D.; Zioupos, Peter; Peter, Davies; Casinos, Adrià
We compared the mechanical properties of ‘ordinary’ bovine bone, the highly mineralized bone of the rostrum of the whale Mesoplodon densirostris, and mother of pearl (nacre) of the pearl oyster Pinctada margaritifera. The rostrum and the nacre are similar in having very little organic material. However, the rostral bone is much weaker and more brittle than nacre, which in these properties is close to ordinary bone. The ability of nacre to outperform rostral bone is the result of its extremely well–ordered microstructure, with organic material forming a nearly continuous jacket round all the tiny aragonite plates, a design well adapted to produce toughness. In contrast, in the rostrum the organic material, mainly collagen, is poorly organized and discontinuous, allowing the mineral to join up to form, in effect, a brittle stony material.
Open Access
Supply chain management in SMEs within the defence / aerospace Industry - a case of simplification or increased complexity?
(2001-02-01T00:00:00Z) Moore, David M.; Neal, Derrick J.; Antill, Peter D.
This paper presents an overview of the rapidly changing nature of the European defence and aerospace industry. In particular the paper identifies a number of key issues associated with the dynamic of supply chain management in respect of Small to Medium-sized Enterprise’s (SME’s) at the 2nd, 3rd and 4th tier levels. A number of issues are raised concerning the current/future relationships between SME’s and prime contractors. Particular emphasis is placed on buyer/ supplier power and the development of SME strategies in response to the industry changes. The paper suggests a number of areas that need to be researched to investigate the developing view of strategy and strategic options for SME’s in light of the industry re-structuring within the context of the concept of strategic fit and
Open Access
Glass ceramic armour systems for light armour applications
(2001-05-07T00:00:00Z) Horsfall, Ian; Crewther, I. R.
This paper descries an experimental evaluation of lithium-zinc-silicate glass ceramics when used as the strike face of an armour system. It is shown that against soft cored 7.62mm rounds (lead or mild steel cores) glass ceramics offer protection at an areal density which is equal to or better than alumina faced systems. The lithium zinc silicate system has a relatively low hardness (Hv 600) when compared to conventional ceramics such as alumina (typically Hv1300-1500). Consequently the performance of the glass ceramic system against hard cored projectiles is poor.
Open Access
Integrated Project Teams: the way forward for UK defence procurement
(2001-09-30T00:00:00Z) Moore, David M.; Antill, Peter D.
This paper looks at a particular aspect of the Smart Procurement Initiative, which was announced in the Strategic Defence Review, that of Integrated Project Teams. These teams aim to bring together all the relevent stakeholders from the Ministry of Defence, armed forces and industry. Much has been written on the perceived benefits these teams will bring to the procurement process in their management of a project from 'cradle to grave'. This paper examines the potential pitfalls that lay ahead and the factors the Ministry of Defence will have to take into account in order for them to succeed.
Open Access
Performance Issues for Vertex Elimination Methods in Computing Jacobians using Automatic Differentiation.
(Springer, 2002) Tadjouddine, Mohamed; Forth, Shaun A.; Pryce, John D.; Reid, John K.
In this paper, we present first results from EliAD, a new automatic differentiation tool. EliAD uses the Elimination approach for Automatic Differentation first advocated by Griewank and Reese (Automatic Differentiation of Algorithms, SIAM, 1991 p126-135). EliAD implements this technique via source-transformation, writing new Fortran code for the Jacobians of functions defined by existing Fortran code. Our results are from applying EliAD to the Roe flux routine commonly used in computational fluid dynamics. We show that we can produce code that calculates the associated flux Jacobian approaching or in excess of twice the speed of current state-of-the-art automatic differentiation tools. However, in order to do so we must take into account the architecture on which we are running our code. In particular, on processors that do not support out-of-order execution, we must reorder our derivative code so that values may be reused while in arithmetic registers in order that the floating point arithmetic pipeline may be kept full.
Open Access
A Discrete Sensitivity Solver for an Industrial CFD Code via Automatic Differentiation.
(2002-01-01T00:00:00Z) Standingford, David W. F.; Forth, Shaun A.
We report on development and validation of a discrete sensitivity solver for the BAE SYSTEMS/Airbus UK CFD code FLITE-3D. We used the Odyssee automatic differentiation (AD) tool to create a discrete forward sensitivity version of FLITE-3D. Validation is via comparing sensitivities of integrated forces (lift, drag, side force) with respect to (w.r.t) angle-of-attack (AoA) , calculated using the sensitivity solver and central-differencing. Validation, w.r.t. changes in the surface and field mesh, is performed by setting sensitivities of all mesh related quantities as if rotated by an infinitesimal angle D alpha. Such sensitivities correspond to those calculated w.r.t AoA alpha. We investigate calculating discrete sensitivities under 2 approximations regarding so-called mesh sensitivities, concluding that they are not applicable to FLITE- 3D. We present results of a wing geometry optimisation using forward sensitivities.
Open Access
Aerofoil Optimisation via AD of a Multigrid Cell-Vertex Euler Flow Solver.
(2002-01-01T00:00:00Z) Forth, Shaun A.; Evans, Trevor P.
We report preliminary results in the use of ADIFOR 2.0 to determine aerodynamic sensitivities of a 2-D airfoil with respect to geometrical variables. Meshes are produced with a hyperbolic interpolation technique. The flow field is calculated using the cell-vertex method of Hall, which incorporates local time-stepping, mesh sequencing and multigrid. We present results and timings using both Finite Differences (FD) and Automatic Differentiation (AD). We investigate the effect of starting the perturbed calculation for FD and the derivative calculation for AD from either the current or freestream conditions and highlight the need for careful implementation of convergence criteria. We attempt to make a comparative study of AD and FD gradients in an aerofoil optimisation, using the DERA CODAS method from the perspective of DERA's eventual aim, 3D viscous optimisation of wing-body configurations.