Combined Blast and Fragment Loading of Sandwich Systems

Protection of personnel and structures against the threat of an air-blast as a result of hostile actions requires a multi-hazard approach to design involving a complex series of trade-offs that must be balanced against other design constraints. The traditional strategy to counter blast and impact threats with thicker blast shields and armour plating are severely dated. Recent trend has moved towards high-strength, lightweight alternatives that do not compromise cost, performance and safety. The reduced weight also saves energy and fuel. Protection against blast and penetrating fragments is normally accomplished by a multi-layered strategy, often with different material combinations, to increase survivability. As a result, this has revived interests in using a sandwich construction for blast mitigation. The high flexural stiffness-to-weight ratio and strength of a traditional sandwich component can be exploited, in combination with the beneficial effects of fluid-structure interaction, as bases for designing 'all-metal' sandwich structures with improved blast resistances. Driven by these needs significant advances have been made over the last decade to design lightweight blast-resistant sandwich systems that employ novel 'micro-architectured' core topologies. The sandwich technology may also be implemented as structural components, designed to integrate several functions into a single component to reduce overall cost and weight, or as retrofits to existing structures for containing a blast to protect personnel and equipment in safety-critical compartments. However, the performance of these sandwich systems to the secondary effect of fragment impact is not well understood and it is, as yet, unclear how the sandwich systems will perform under the combined threat of blast and fragment impact often encountered during close-in explosions. The challenge in designing a combined blast and impact protection system is further complicated by their competing requirements as often the most efficient protection against each threat is, in general, different. The present proposal outlines a systematic study, by a combination of experiments and modelling, to assess and compare the performances and failure modes of 'all-metal' and 'ceramic/metal' sandwich panels subjected to the combined influence of blast and local impulse(s) imparted by a fragment field. The results from this work will be used to quantify the observed synergism which is essential to the future implementation of an optimal sandwich design for blast mitigation in close range.

The development of lightweight protective technology, using a sandwich strategy, for blast and impact protection will interest academic, governmental and industrial research communities in equal measures. The three major groups of beneficiaries and how they will, potentially, benefit from the proposed research is as follows: (1) Civilian population The development of lightweight blast and impact resistant sandwich structures, apart from the immediate relevance to the military, has a wider spin-off benefit into other areas of civilian survivability assessment and design. The technology and methodology developed can readily be extended or adopted for civilian applications. For example, the technology can be applied to retrofit key buildings and infrastructure against random acts of terrorism and to protect safety critical installations such as nuclear power-plants. With domestic terrorist threat predicted to rise in the foreseeable future (as indicated in a recent white paper presented to the Parliament in 2009 on 'The UK's Strategy for Countering International Terrorism'), the development of more efficient passive protective measures to safeguard lives and key infrastructures is both timely and challenging. Importantly, the light-weighting technology developed in this project saves energy, fuel and, therefore, contributes positively to the low carbon agenda. (2) Government and Classification Societies In the short to medium term, the project will have immediate benefits to the shipbuilding and ship owning communities for both commercial and defence (military) sectors. The results from this research will have direct input, through the involvement of Lloyd's Register and the Ministry of Defence, into the continual development of design rules and procedures against combined blast and fragment loading. As indicated in the Statement of Support by the Head of Strategic Research Group at Lloyd's Register, the topic of the proposed research is particularly urgent in view of increased pirate activities which demand the need to develop novel structural systems to give better protection to personnel sailing onboard ships . The technology developed is useful to the development of lightweight strategies to protect (a) machinery spaces against explosive loads and small arms attack; (b) large crowded spaces in passenger ships; (c) accommodation spaces against terrorist and pirate attack; and, (d) bulkheads in ships against internal blast and fragmentation. (3) Academic Researchers Despite significant advances in our understanding of the blast performance of metal sandwich systems in the last 10 years, the fundamental physics concerning the interaction of a blast wave and its ensuing fragments on the performance of sandwich panels are unclear and have not been studied systematically. The results from the proposed research will be an important valuable addition to the academic community and will help to further strengthen the technological basis for a sandwich strategy to protect personnel and structures against accidental explosions and/or acts of terrorism.