I.G. Cullis

THE DYNAMIC COMPACTION OF SAND AND RELATED POROUS SYSTEMS

Porous and granular materials are widely found in a number of environments. One of the most important groups both geographically and in the construction industry are the sands. A review of the response of sand (42% porous) over a wide range of strain rates is presented. Factors such as water content and density variation are addressed. In addition a very low‐density silica dust (95% porous) is also discussed in relation to its contrasting behaviour.

Using the split Hopkinson pressure bar to validate material models.

This paper gives a discussion of the use of the split-Hopkinson bar with particular reference to the requirements of materials modelling at QinetiQ. This is to deploy validated material models for numerical simulations that are physically based and have as little characterization overhead as possible. In order to have confidence that the models have a wide range of applicability, this means, at most, characterizing the models at low rate and then validating them at high rate. The split Hopkinson pressure bar (SHPB) is ideal for this purpose. It is also a very useful tool for analysing material behaviour under non-shock wave loading. This means understanding the output of the test and developing techniques for reliable comparison of simulations with SHPB data. For materials other than metals comparison with an output stress v strain curve is not sufficient as the assumptions built into the classical analysis are generally violated. The method described in this paper compares the simulations with as much validation data as can be derived from deployed instrumentation including the raw strain gauge data on the input and output bars, which avoids any assumptions about stress equilibrium. One has to take into account Pochhammer–Chree oscillations and their effect on the specimen and recognize that this is itself also a valuable validation test of the material model.

Characterising the Response of Energetic materials and Polymer-Bonded Explosives (PBXs) to High-Rate Loading.

Polymer-bonded explosives (PBXs) are being increasingly used as energetic fillings and components in many systems. They are perceived as more chemically and mechanically stable than traditional fillings such as RDX/TNT. They are castable into predetermined shapes, machinable and can be used as structural components. However, along with all these undeniable advantages, as a class, these materials are now undergoing extensive characterisation to ensure they comply with both the legal and technical requirements in energetic systems. It is well-known that polymers display non-linear behaviour and are much more complex than, for example, simple metal systems at any rate of strain. The understanding of PBX systems involves areas as diverse as polymer chemistry, chemical compatibility, mechanical properties, impact tests, and thermal stability. In this paper, aspects of energetic material response are outlined which are relevant to the understanding of PBX sensitivity.

Cost-Effective Simulation and Prediction of Explosions for Military and Public Safety, and for Improved Oil Extraction

An MoD-funded research programme based in Applied Mathematics at Leeds University has resulted in demonstrable long-term and ongoing benefits on diverse fronts for beneficiaries in a range of public and private sectors. First, by guaranteeing robustness and reliability of bespoke numerical methods for the MoD, the joint research led to substantial financial savings in ballistic-development programmes, thereby enabling the delivery of advanced research output cost-effectively under severe budgetary pressures. As a result, QinetiQ was placed as a world leader in the simulation of explosions, which supported the MoD to rapidly assess and develop countermeasures to the ever-changing threats faced by British Forces in Afghanistan and Iraq, and to reduce casualties. It also enabled government agencies to assess threats to transport and public-building infrastructure. Second, the joint research underpinned substantial recurrent income for QinetiQ, who has additionally developed the codes with the oil industry to develop a new explosive perforator for oil extraction that has not only led to demonstrable improvements in both extraction efficiency and research-and-development costs, but has also yielded recurrent licensing royalties.