Abstract
Polymeric particulate composites are widely used in engineering systems where they are subjected to impact loading – at a variety of temperatures – leading to high strain rate deformation. These materials are highly rate and temperature dependent, and this dependence must be well understood for effective design. It is not uncommon for many of these materials to display mechanical responses that range from glassy and brittle to rubbery and hyperelastic [1-3], due to their polymeric constituents. This makes accurate measurements and modelling not only necessary, but challenging. This is made more difficult by experimental artefacts present when traditional tools such as the split Hopkinson pressure (SHPB) or Kolsky bar are used to interrogate the high rate response of low-impedance materials. The transition from isothermal to adiabatic conditions as the rate of deformation increases also has an effect on the mechanical response, which cannot be neglected if the high rate behaviour is to be accurately predicted. In this paper, time-temperature superposition based frameworks that have enabled the high rate behaviour of neoprene rubber [4] and (plasticised) poly(vinyl chloride) [5] to be captured, will be extended to explore the high strain rate behaviour of unfilled natural rubber and several grades of glass microsphere filled natural rubber particulate composites.
Highlights
Particulate composites are commonplace in Engineering applications, ranging from concrete used in construction through to polymer bonded explosives (PBX) used in advanced weapons systems [6,7]
Dynamic Mechanical Analysis (DMA) experiments form the basis of the time-temperature superposition method, allowing the modulus at an ambient reference temperature to be obtained for a wide range of frequencies
This paper has shown that a damage augmented hyper-viscoelastic model can be calibrated using simple, low-rate data and subsequently used to predict the high-rate response of both unfilled and filled natural rubber particulate composites
Summary
Particulate composites are commonplace in Engineering applications, ranging from concrete used in construction through to polymer bonded explosives (PBX) used in advanced weapons systems [6,7] As in these examples, the filler may enhance the mechanical properties of the material, or the overall material may be designed to transport the filler itself. When the matrix constituent in these composites is a polymer, the overall behaviour is likely to be highly temperature and rate dependent This makes characterisation and modelling challenging, and necessary. The main challenges are low wave-speeds leading to a time to static stress equilibrium on the order of the experimental duration [9], and experimental signals from which force is calculated are too small to measure accurately [10]. An advantage of focusing on lower strain rate experiments to understand the high rate behaviour (either through experimental simulations [13,14] or calibrated models [4,5]) is that a wider range of diagnostic tools may be used to interrogate the mechanical response (e.g. Scanning Electron Microscope, X-ray tomography, etc.)
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