SMF Fracture and Shock Physics Group

Cambridge, United Kingdom

SMF Fracture and Shock Physics Group

Cambridge, United Kingdom
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Walley S.M.,SMF Fracture and Shock Physics Group
Strain | Year: 2014

The purpose of this review is to introduce the interested reader to the literature on the use of silica glasses in ballistic applications. These applications include optically transparent windows (where their amorphous nature, appropriate band gap, and cheapness make them ideal window materials) as well as layers in opaque armours designed to be resistant to shaped charges. In the latter application, their increase in volume (bulking) on fracture disrupts the shaped charge jet. Other topics covered in this review include low-velocity damage by windborne debris, liquid and solid impact, dynamic methods of testing (Hopkinson pressure bar, Taylor impact, and plate impact shock loading), and constitutive models. The use of glass as a shaped charge is also discussed. © 2013 Wiley Publishing Ltd.


Walley S.M.,SMF Fracture and Shock Physics Group
Advances in Applied Ceramics | Year: 2010

A brief outline is given of how ceramics came to be considered as armour materials. The major developments in understanding what mechanical properties are relevant to their use in this application are summarised along with experimental techniques for measuring them. © 2010 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute.


Taylor N.E.,SMF Fracture and Shock Physics Group | Williamson D.M.,SMF Fracture and Shock Physics Group | Jardine A.P.,SMF Fracture and Shock Physics Group
Journal of Physics: Conference Series | Year: 2014

Equations of state can be used to predict the relationship between pressure, volume and temperature. However, in shock physics, they are usually only constrained by experimental observations of pressure and volume. Direct observation of temperature in a shock is therefore valuable in constraining equations of state. Bloomquist and Sheffield (1980, 1981) and Rosenberg and Partom (1984) have attempted such observations in poly(methyl methacrylate) (PMMA). However, their results disagree strongly above 2GPa shock pressure. Here we present an improved fabrication technique, to examine this outstanding issue. We make use of the fact that the electrical resistivity of most metals is a known function of both pressure and temperature. If the change in resistance of a thin metal thermistor gauge is measured during a shock experiment of known pressure, the temperature can be calculated directly. The time response is limited by the time taken for the gauge to reach thermal equilibrium with the medium in which it is embedded. Gold gauges of thickness up to 200 nm have been produced by thermal evaporation, and fully embedded in PMMA. These reach thermal equilibrium with the host material in under 1 us, allowing temperature measurement within the duration of a plate impact experiment. © Published under licence by IOP Publishing Ltd.


Walley S.M.,SMF Fracture and Shock Physics Group | Field J.E.,SMF Fracture and Shock Physics Group | Biers R.A.,Dstl Fort Halstead | Proud W.G.,Imperial College London | And 2 more authors.
Propellants, Explosives, Pyrotechnics | Year: 2015

Conventional impact sensitiveness machines (e.g. Rotter and BAM) do not provide detailed information about hot-spot ignition mechanisms in energetic materials. To gain further insight, a glass anvil technique was developed at Cambridge in the early 1950s, which allowed high-speed photographic studies to be performed during impact on energetic liquids, explosive powders and crystals. Herein we review such investigations which continue up to the present day. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Dodd B.,Imperial College London | Walley S.M.,SMF Fracture and Shock Physics Group | Yang R.,CAS Institute of Mechanics | Nesterenko V.F.,University of California at San Diego
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2015

The standard story of the discovery of adiabatic shear bands is that it began with the American researchers Zener and Hollomon’s famous 1944 paper where the phenomenon was first reported and named. However, a recent discovery by one of us (SMW) in the Cambridge University Library has shown that the phenomenon was discovered and described by a Russian researcher, V.P. Kravz-Tarnavskii, in 1928. A follow-up paper was published by two of his colleagues in 1935. Translations of the 1928 and 1935 papers may be found at http://arxiv.org/abs/1410.1353. © 2015, The Minerals, Metals & Materials Society and ASM International.


Lea L.J.,SMF Fracture and Shock Physics Group | Jardine A.P.,SMF Fracture and Shock Physics Group
EPJ Web of Conferences | Year: 2015

Direct impact Hopkinson pressure bar systems offer many potential advantages over split Hopkinson pressure bars, including access to higher strain rates, higher strains for equivalent striker velocity and system length, lower dispersion and faster achievement of force equilibrium. Currently advantages are gained at a significant cost: the fact that input bar data is unavailable removes all information about the striker impacted specimen face, preventing the determination of force equilibrium, and requiring approximations to be made on the sample deformation history. Recently photon Doppler velocimetry methods have been developed, which can replace strain gauges on Hopkinson bars. In this paper we discuss an experimental method and complementary data analysis for using Doppler velocimetry to measure surface velocities of the striker and output bars in a direct impact bar experiment, allowing similar data to be recorded as in a split bar system, with the same level of convenience. We discuss extracting velocity and force measurements, and improving the accuracy and convenience of Doppler velocimetry on Hopkinson bars. Results obtained using the technique are compared to equivalent split bar tests, showing improved stress measurements for the lowest and highest strains. © 2015 Owned by the authors, published by EDP Sciences.


Lea L.J.,SMF Fracture and Shock Physics Group | Jardine A.P.,SMF Fracture and Shock Physics Group
Review of Scientific Instruments | Year: 2016

Direct impact Hopkinson pressure bar systems offer many potential advantages over split Hopkinson pressure bars, including access to higher strain rates, higher strains for equivalent striker velocity and system length, lower dispersion, and faster achievement of force equilibrium. Currently, these advantages are gained at the expense of all information about the striker impacted specimen face, preventing the experimental determination of force equilibrium, and requiring approximations to be made on the sample deformation history. In this paper, we discuss an experimental method and complementary data analysis for using photon Doppler velocimetry to measure surface velocities of the striker and output bars in a direct impact bar experiment, allowing similar data to be recorded as in a split bar system. We discuss extracting velocity and force measurements, and the precision of measurements. Results obtained using the technique are compared to equivalent split bar tests, showing improved stress measurements for the lowest and highest strains in fully dense metals, and improvement for all strains in slow and non-equilibrating materials. © 2016 AIP Publishing LLC.


Braithwaite C.H.,SMF Fracture and Shock Physics Group | Aydelotte B.,Georgia Institute of Technology | Jardine A.P.,SMF Fracture and Shock Physics Group
Journal of Physics: Conference Series | Year: 2014

A series of experiments were performed to probe the tensile behaviour of a cold sprayed reactive metal composite material containing a mixture of nickel and aluminium. Data were acquired at two different strain rates and were collected using high speed photography, strain gauges, force-extension measurements and were analysed using digital image correlation techniques. Comparisons were made with modelling on representative microstructural elements in the CTH code, supporting the conclusion that the material failed in shear rather than tension, in a manner dictated by the microstructure. Fairly high sample to sample variation was observed as well as minimal evidence of strain rate dependent behaviour. © Published under licence by IOP Publishing Ltd.

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