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Cambridge, United Kingdom

Walley S.M.,Fracture and Shock Physics Group
Materials Science and Technology (United Kingdom) | Year: 2012

Although it has been known for thousands of years that materials differ in hardness, quantitative methods of measuring hardness by performing careful indentation experiments only began to be developed during the nineteenth century. At the beginning of the twentieth century, hardness testing machines began to be commercially available. The methods that have persisted to this day may be divided into two broad categories: (1) those where a hardened steel ball or cone is pressed into a surface under a known load; and (2) those where sharp diamonds of various shapes are pressed into a surface also under a known load. An issue that has long been of interest is the relation of hardness to simpler measures of material strength, particularly the tensile strength. The review will cover the development of the various static and dynamic techniques and their subsequent application to a wide range of materials. © 2012 Institute of Materials, Minerals and Mining.


Proud W.G.,Fracture and Shock Physics Group | Proud W.G.,Imperial College London | Cross D.L.A.,Fracture and Shock Physics Group
AIP Conference Proceedings | Year: 2012

Scaled, reverse ballistic, long-rod experiments were performed at an impact velocity of ∼700 m s -1. The targets were tungsten alloy rods and the projectiles either 3 or 6 mm thick rolled homogeneous armour (RHA) plates. The plate was inclined at 60° to the direction of travel and the interaction was recorded using high-speed photography, strain gauges and laser velocimetry. The pitch of the rod was varied in steps of 3° over a total range of 15°. In this range the rod deformation changed dramatically the bending process moved from a flexing of the tip away from the plate, to a marked motion into the surface. Cross comparison of the diagnostic outputs reveals the time windows for these process and also the varying sensitivity of the measurement system to that process. Post-impact recovery was also performed. © 2012 American Institute of Physics.


Cross D.L.A.,Fracture and Shock Physics Group | Proud W.G.,Fracture and Shock Physics Group | Proud W.G.,Imperial College London
AIP Conference Proceedings | Year: 2012

A series of angled small-scale reverse ballistic long rod experiments were conducted using mild steel rods (6 mm dia., 90 mm long) against both 3 mm and 6 mm rolled homogeneous armour (RHA) plates at 60°. The impact velocity was varied from 450-780 m s -1 and the response of the system monitored by laser velocimetry, strain gauges and high-speed photography. This provided insight into the flexing of the rod during impact, the acceleration of the rear of the rod and the global penetration process. This experimental series involved ricochet, near-ricochet and full perforation, and so allows the sensitivity of the differing diagnostic outputs for these processes to be compared. © 2012 American Institute of Physics.


Forde L.C.,Fracture and Shock Physics Group | Proud W.G.,Fracture and Shock Physics Group | Walley S.M.,Fracture and Shock Physics Group | Church P.D.,QinetiQ | Cullis I.G.,QinetiQ
International Journal of Impact Engineering | Year: 2010

The ballistic impact properties of a borosilicate ('pyrex') glass was studied using mild steel rods accelerated using a light gas gun. High-speed photography at sub-microsecond framing rates was used along with schlieren optics to investigate the propagation of elastic shock waves and fracture fronts. Flash X-radiography was used to visualise the deformation of rods as they penetrated the comminuted glass normally. The rod was seen initially to dwell on the surface for at least 3 μs creating a Hertzian cone-crack. Later on, between 40 and 60 μs, self-sharpening of the projectile was observed as the 'wings' of the heavily deformed front end sheared off. After this event, the front of the rod speeded up. X-rays also showed that the pattern of fissures within the comminuted glass was observed to be very similar shot-to-shot. X-radiography was also used to examine the mechanisms occurring during oblique impact of rods at 45°. In oblique impact, bending of the rod rather than plastic deformation ('mushrooming') takes on the role of distributing the load over an area larger than that of the original rod diameter. High-speed photography of the rear surface of a glass block on which a fine grid had been placed confirmed that the comminuted glass moved as larger interlocked blocks. The experiments were modelled using the QinetiQ Eulerian hydrocode GRIM making use of the Goldthorpe fracture model. The model was found to predict well the transition from dwell to penetration. © 2009 Elsevier Ltd. All rights reserved.


Prentice H.J.,Fracture and Shock Physics Group | Proud W.G.,Fracture and Shock Physics Group | Walley S.M.,Fracture and Shock Physics Group | Field J.E.,Fracture and Shock Physics Group
International Journal of Impact Engineering | Year: 2010

This paper reports an initial study into the benefits of determining two-dimensional flow fields for low velocity impact on a small-scale model of explosive reactive armour (ERA) using digital speckle radiography (DSR). The model system consisted of a polymer-bonded sugar (PBS) (otherwise known as a sugar mock) confined between two mild steel plates. The DSR technique relies upon creating a layer within the specimen that is seeded with lead particles. So although radiography itself is mechanically non-invasive, the lead layer needed may change the mechanical properties of the material. DSR revealed where regions of intense shear occurred in normal impact. These regions are likely to be where a polymer-bonded explosive (PBX) would initiate. © 2010 Elsevier Ltd. All rights reserved.

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