Energetic materials cover a wide range of substances capable of releasing large amount of chemical energy quickly, and include propellants, pyrotechnics and explosives. Understanding the properties and mechanisms that control the behaviour of these materials is a substantial physical challenge, and requires a detailed understanding of the physical properties of the material. These properties can then be linked together using various theoretical techniques, including for example, the polymer Group Interaction Model (GIM) framework.
The group has a long history in studying the characteristics of energetic materials, dating back to the late 1940’s. Today we focus on applying modern methods to develop a much more complete understanding of the fundamental behaviour. A particular focus is on developing and instrumenting small scale experiments which can be used to provide fundamental insights enabling accurate models to be constructed, to understand larger scale response.
Structural, Mechanical & Thermal Properties
We use a variety of techniques to characterise the underlying physical properties of materials. These include thermal expansion (using direct and optical interferometric methods), heat capacity (using differential scanning calorimetry), thermal conductivity and differential mechanical analysis. Together, these can be combined to study the underlying thermodynamics and statistical mechanics of the materials.
We characterise the structures of complex energetic materials using various forms of microscopy and non-invasive 3-dimensional imaging techniques, such as X-ray Computed Tomography. We have several ongoing projects to characterise the adhesive interaction between different materials, and the corresponding effect this has on the ultimate strength on the material.
Damage Processes and Effects
Damage in energetic materials is a particularly important area. Damage can lead to an increased likelihood of energetic initiation, so understanding damage in detail is an important element of the explosive safety. We have several ongoing projects which include introducing controlled amounts of damage into energetic materials (propellants, PBXs) and studying the changes in both physical and energetic properties, as described in the papers below.
Novel Fabrication Methods
Novel fabrication methods for energetic materials are of particular interest. For example, we have recently been involved in a project to develop screen printable pyrotechnic inks, to reduce lead usage within the mining industry.
- 2012 Williamson D.M., Palmer S.J.P., Leppard C.L. and Gover R. "On the thermal expansion hysteresis of a UK PBX" in "Shock Compression of Condensed Matter - 2011" ed. M.L. Elert, J.P. Borg, J.L. Jordan and T.J. Vogler, pp. 725-728, publ. American Institute of Physics, Melville, NY
- 2012 Braithwaite C.H., Pachman J., Majzlik J. and Williamson D.M. "Recalibration of the large scale gap-test to a stress scale" Propell. Explos. Pyrotech. 37 614-620
- 2010 Drodge D.R., Williamson D.M., Palmer S.J.P., Proud W.G. and Govier R.K. "The mechanical response of a PBX and binder: Combining results across the strain-rate and frequency domains" J. Phys. D: Appl. Phys. 43 335403
- 2009 Williamson D.M., Palmer S.J.P., Proud W.G. and Govier R. "Thermodynamic work of adhesion between HMX and a UK PBX binder system" in "Shock Compression of Condensed Matter - 2009", ed. M.L. Elert, W.T. Buttler, M.D. Furnish, W.W. Anderson and W.G. Proud, pp. 478-481, publ. American Institute of Physics, Melville NY
- 2011 Grohn T, Williamson D. and Morgan G."Energetic inks for screen printing" in "Proc. 14th Seminar on New Trends in Research of Energetic Materials", pp. 204-213, publ. University of Pardubice, Czech Republic