Blast and Impact Dynamics,
The University of Sheffield, UK
I research how the properties of soils can be used to protect people from explosions and high-velocity fragments.About me
I'm a research associate in the Department of Civil and Structural Engineering at The University of Sheffield. This page gives an overview of my work in the Blast and Impact Dynamics group, where my main focus is the behaviour of materials at high pressures and under dynamic loading. Links to some relevant publications () are included for more technical information, but get in touch if you'd like to know more!
Sand and gravel filled walls are used in military bases to protect people and equipment from explosions and fragmentation. Soils are very effective at stopping high-velocity fragments because of the way the particles reorganise and fracture as the projectile tries to pass through. I research the influence that soil properties, such as particle size and moisture content, have on this attenuating ability to help designers create more efficient protective structures.Under pressure
The stresses involved in explosions and impacts are very high, and so my research involves testing materials at pressures of up to a gigapascal (GPa). 1 GPa is the equivalent of balancing 85 double decker buses in the palm of your hand, and is enough to make a pile of dry sand into a block of sandstone!Research themes
The designers of protective structures use computer models to help guide decision making and test designs against specific threats. My research provides information about how the materials in the models should respond under different loading conditions, ensuring that the predictions are accurate and that the final design performs well.
Computer models usually need at least two things to make a prediction of a material's mechanical behaviour: an equation of state (how much its volume changes under a particular pressure) and the shear behaviour (how its shape changes if the loads on each side are not equal). The experiments required to find this information had not previously been carried out at the pressures needed to make accurate models, and so I use the unique mac2T apparatus to test soils in compression and shear. Different particle sizes and moisture contents are used to analyse how sensitive the behaviour is to these properties.
Some materials, such as copper and aluminium, behave differently depending on how quickly you apply a load, usually becoming stronger and stiffer the faster you compress or stretch them: this is called a strain-rate effect. Because explosions and projectiles are travelling very quickly when they impact a soil-filled structure, understanding whether soils exhibit a strain-rate effect is important, as this information will also need to be added to the computer model. I use experiments with very slow and very fast loading to look for potential strain-rate effects in soils under compression and shear.
The characterisation and strain-rate experiments provide a lot of information about how the mechanical properties of soils are dependent on geotechnical properties like moisture content and particle size. To use this information in a computer model, the designers need to know how these geotechnical properties vary in real soil-filled walls, which will be affected by factors such as rainfall and temperature changes. I am currently assessing this with a long-term monitoring project which records the changes in moisture content and density of a gabion structure as the weather changes throughout the year.