Browsing by Author "Iremonger, M. J."

Now showing 1 - 3 of 3
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    Crack softening damage model for ceramic impact and its application within a hydrocode
    (American Institute of Physics, 1997-12-31T00:00:00Z) Hazell, P. J.; Iremonger, M. J.
    A physically based crack softening damage model has been developed and used in a non-linear transient dynamic computer code (AUTODYN-2D). It is assumed that there is a finite number of orientated pre-existing flaws within the ceramic target. The mode I and mode II stress intensity factors are calculated in compression and tension and the strain energy release rate is then estimated and compared to a critical dynamic strain energy release rate. At initiation, a tension crack propagates at a velocity dependent on the mode I stress intensity factor and failure occurs in a computational cell when two neighbouring microcracks coalesce. The model was used to simulate two different plate impact experiments of alumina on alumina with encouraging results. The model was also used to analyze the impact of a steel sphere on alumina and shows strong correlation between experimental and predicted results.
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    From capability to concept: Fusion of systems analysis techniques for derivation of future
    (Cranfield University, 2007-03-27T09:11:22Z) Sparks, Emma S.; Couldrick, C. A.; Iremonger, M. J.; Allsop, Derek F.
    The intent of this thesis is to define a set of processes for use within UK Government dismounted soldier systems research that will provide stakeholders with auditable and traceable information to understand gaps in military capability and justify future procurement decisions. The need for this approach is linked to organisational shifts within the UK Ministry of Defence, and more specifically Government research with the move towards procurement of capability rather than equipment. In conjunction with reducing defence budgets and increased scrutiny, there is a need to prioritise spending to those areas that will provide the most significant enhancement to operational effectiveness. The proposed process suite provides underpinning data to support Government decisions, from definition of military need through to concept design and prioritisation of future research activities. The approach is grounded in the field of systems thinking and systems engineering providing the logical and systematic constructs required for highly complex systems where the human is a central focus. A novel fusion of existing systems tools and techniques enables both subjective data from domain experts and objective data in the form of operational analysis and field trials to be utilised for analysis across the five NATO capability domains, with output defining the relative importance of survivability, sustainability, mobility, lethality and C4I in the context of operational and strategic level military goals as well as wider challenges represented by the doctrinal defence lines of development. Future developments should include alignment with developing pan-MoD initiatives in the form of MODAF, if required by the customer organisation. This would enable generic versions of the process suite to be applied to any defence domain and problem.
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    The numerical analysis of dynamically loaded ceramic: A crack softening approach
    (John Wiley & Sons, Ltd, 2000-12-31T00:00:00Z) Hazell, P. J.; Iremonger, M. J.
    A physically based crack softening approach to modelling the failure of brittle materials that have been subjected to dynamic loading is presented and applied to a two-dimensional non-linear transient dynamic hydrocode. It is assumed that there are a number of evenly distributed and orientated micro flaws within the brittle material that are activated by a dynamically applied stress. Modes I and II stress intensity factors are calculated and compared to critical values, at which point the cracks grow at a velocity dependent on mode I stress intensity factor. The strength of the ceramic is degraded according to the length of the cracks. A simulation of a steel sphere impacting and penetrating a ceramic target at 1500 m/s is presented. Comparisons are drawn from experimental data.