Browsing by Author "Bourne, Neil K."

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    Deviatoric response of an armour-grade aluminium alloy
    (AIP American Institute of Physics, 2009-12-31T00:00:00Z) Appleby-Thomas, Gareth J.; Hazell, P. J.; Millett, J.; Bourne, Neil K.; Buttler, W. T.
    Aluminium alloys such as 5083 H32 are established light-weight armour materials. As such, the shock response of these materials is of great importance. The shear strength of a material under shock loading provides an insight into its ballistic performance. In this investigation embedded manganin stress gauges have been employed to measure both the longitudinal and lateral components of stress during plate-impact experiments over a range of impact stresses. In turn, these results were used to determine the shear strength and to investigate the time dependence of lateral stress behind the shock front to give an indication of material response.
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    The effects of changing chemistry on the shock response of basic polymers
    (2016-07-11) Millett, J.; Brown, E. N.; Gray III, G. T.; Bourne, Neil K.; Wood, D. C.; Appleby-Thomas, Gareth J.
    The shock response of four common semicrystalline thermoplastic polymers—polyethylene (PE), polyvinylchloride (PVC), polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE)—have been studied in terms of their Hugoniots, release velocities and shear strengths. Through the variations in behaviour caused by changes to the attached atoms to the carbon backbone, it has been possible to suggest that there are two main factors in play. The first is an electrostatic repulsion between adjacent polymer chains. Where this force is large, for example in PTFE with highly electronegative fluorine atoms, this results in this force dominating the shock response, with low shock velocities, high release velocities and little if no hardening behind the shock front. In contrast, in materials such as PE, this force is now weaker, due to the lower electronegativity of hydrogen, and hence this force is easier to overcome by the applied shock stress. Now the main factor affecting shock behaviour is controlled by the shape of the polymer chain allowing inter chain tangling (tacticity). This results in higher shock velocities, lower release speeds and significant hardening behind the shock front as the chains are forced together. This is prevalent in materials with a relatively open structure such as PE and is enhanced with the presence of large side groups or atoms off the main polymer chain.
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    Evaluation of the SPH method for the modelling of spall in anisotropic alloys
    (2005-06-27T00:00:00Z) De Vuyst, Tom; Vignjevic, Rade; Bourne, Neil K.; Campbell, James C.
    Spall caused by hypervelocity impacts at the lower range of velocities could result in significant damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pronounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation. The material failure observed in plate impact was simulated using an explicit finite element code and a smoothed particle hydrodynamics (SPH) code. A number of spall models where used, and the Hugoniot Elastic Limit (HEL) and spall strength have been studied as a function of orientation, and compared to experimental results.
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    Modeling shock waves in orthotropic elastic materials
    (American Institute of Physics, 2008-08-01T00:00:00Z) Vignjevic, Rade; Campbell, James C.; Bourne, Neil K.; Djordjevic, Nenad
    A constitutive relationship for modeling of shock wave propagation in orthotropic materials is proposed for nonlinear explicit transient large deformation computer codes (hydrocodes). A procedure for separation of material volumetric compression (compressibility effects equation of state) from deviatoric strain effects is formulated, which allows for the consistent calculation of stresses in the elastic regime as well as in the presence of shock waves. According to this procedure the pressure is defined as the state of stress that results in only volumetric deformation, and consequently is a diagonal second order tensor. As reported by Anderson et al. [Comput. Mech.15, 201 (1994)], the shock response of an orthotropic material cannot be accurately predicted using the conventional decomposition of the stress tensor into isotropic and deviatoric parts. This paper presents two different stress decompositions based on the assumption that the stress tensor is split into two components: one component is due to volumetric strain and the other is due to deviatoric strain. Both decompositions are rigorously derived. In order to test their ability to describe shock propagation in orthotropic materials, both algorithms were implemented in a hydrocode and their predictions were compared to experimental plate impact data. The material considered was a carbon fiber reinforced epoxy material, which was tested in both the through-thickness and longitudinal directions. The psi decomposition showed good agreement with the physical behavior of the considered material, while the zdeta decomposition significantly overestimated the longitudinal stresses.
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    Modelling of impact on a fuel tank using smoothed particle hydrodynamics
    (2005-06-27T00:00:00Z) Vignjevic, Rade; De Vuyst, Tom; Campbell, James C.; Bourne, Neil K.
    This paper describes a modelling approach for the simulation of hypervelocity impact on fuel tanks using the Smoothed Particle Hydrodynamics (SPH) method. To determine a suitable particle density, three two-dimensional axi-symmetric models were analysed. Then three-dimensional simulations with cylindrical and cubic penetrators were performed. For each analysis the transient pressure values at locations corresponding to experimental transducer locations were recorded. The pressure time histories are shown for the axi-symmetric and 3D models. The simulation results are compared with the experimental results. The purpose of the research was to demonstrate the capability and potential of SPH for simulating this type of problem.
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    The shock Hugoniot of hydroxy-terminated polybutadiene
    (AIP, 2004-08-04) Meziere, Y.; Akhavan, Jacqueline; Stevens, G. S.; Millett, Jeremy C. F.; Bourne, Neil K.
    The response of polymers to shock loading is becoming of increasing importance, both as binder systems in plastic-bonded explosives (PBXs) and as structural materials in their own right. In this paper, we report on the shock Hugoniot of hydroxy-terminated polybutadiene (HTPB), which is commonly used as a binder system in PBXs, but whose shock response has yet to be presented in the open literature. Results indicate that the shock velocity --- particle velocity relationship is linear, similar to some but not all polymer-based materials.