Understanding the ballistic event: methodology and initial observations

Journal of Materials Science, Dec 2016

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 stereo imaging, 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.

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Understanding the ballistic event: methodology and initial observations

Understanding the ballistic event: methodology and initial observations Adam Healey 0 1 John Cotton 1 Stuart Maclachlan 1 Paul Smith 0 Julie Yeomans 0 0 University of Surrey , Stag Hill Campus, Guildford, Surrey GU2 7XH , UK 1 Lucideon Limited , Queens Road, Penkhull, Stoke-on-Trent, Staffordshire ST4 7LQ , UK 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 stereo imaging, 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. - Ceramic armour material systems have been in use for over one hundred years and since the Vietnam War they have provided protection from high-velocity projectiles to vehicles, aircraft, and personnel on the battlefield. The key property for an armour system is the ability to resist high-energy projectile impacts, which is referred to as ballistic performance. If this can be combined with a low weight (by using low density materials), this offers the prospect of increased fuel economy and/or manoeuvrability. Ideally, these properties will be delivered at a low cost. Common ceramic materials used for armour systems are aluminium oxide (Al2O3), known as alumina, silicon carbide (SiC), and boron carbide (B4C). Of these, the most widely used is alumina, due to its comparatively low cost of manufacture and effectiveness in protecting against common battlefield threats. Silicon carbide is of lower density and able to resist higher energy impacts but is more expensive. Finally, boron carbide has very low density and high impact resistance, but the high cost often restricts it to applications where weight-saving is critical, such as in aircraft [1]. New ceramic materials are currently in development to improve on these baseline materials. A significant obstacle in armour development is an incomplete understanding of the phenomena that occur when a high-velocity projectile strikes an armour target. Upon penetration, the bullet and the ceramic strike face undergo a number of processes, such as fragmentation, to dissipate the kinetic energy of the projectile to the extent that what remains is completely stopped by the composite backing of the armour system. The high speed nature (strain rates of approximately 108 s-1) and resulting damage to samples inflicted during this interaction, known as the ballistic event, make it difficult to identify the individual mechanisms that dissipate the kinetic energy of an incoming projectile [2, 3]. Further, it is very problematic to systematically alter one property of a ceramic, such as grain size, to gauge its effect on ballistic performance, without inadvertently altering other microstructural parameters. Some properties of ceramics, such as compressive strength, are also known to be strain-rate dependent, causing changes in the material behaviour between test regimes and affecting the nature of brittle fragmentation [4]. Furthermore, the ballistic event is sensitive to changes in strike face and backing material combinations, as well as projectile type, speed, and other variables. Thus, predicting the outcome is challenging [5, 6]. Consequently, the only widely accepted method of assessing how effective a new system or material is at resisting impact is to subject it to ballistic testing. Due to the statistical nature of the mechanical properties of ceramics this is a very expensive process; a robust test requires a minimum of 25 armour samples [7], and over 100 are required for a full understanding of the statistics of the material. This high cost is a significant barrier in the development of new armour materials. A new test (or suite of (...truncated)


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Adam Healey, John Cotton, Stuart Maclachlan, Paul Smith, Julie Yeomans. Understanding the ballistic event: methodology and initial observations, Journal of Materials Science, 2017, pp. 3074-3085, Volume 52, Issue 6, DOI: 10.1007/s10853-016-0594-0