Browsing by Author "Iremonger, M J"

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    The Effects of fibre pre-stressing on the impact performance of composite laminates
    (2011-09-19) Jevons, M P; Iremonger, M J
    This thesis has presented the results and findings of a study carried out into the effects of fibre pre-stressing on the impact performance of composite laminates. Fibre prestress has been explained as a way of mechanically altering the internal residual stress state of a composite, which typically is a result of thermal, moisture and chemical expansions. It has been suggested that pre-stressing can offer potential benefits to composites by reducing or reversing the hygro-thermal stresses in a composite. It has also been suggested that the impact performance could be improved through fibre prestressing, which has given rise to this study. In this study panels have been made with various levels of pre-stress. A special system was developed to apply pre-stress to the laminates and the produced laminates were tested under low- and high-velocity impact regimes. To apply these regimes, an instrumented falling weight and a gas gun were used respectively. A short finite element study was carried out to supplement the experimental study and offer further insight into the failure mechanics. The main findings of the study were that although pre-stressing had no discernable effect on the high-velocity impact performance of the composite laminate considered, there was a noted effect on the low-velocity impact performance. Under low-velocity impacts the laminate showed an improved impact performance for increase levels of pre-stress, except at one critical pre-stress level (60 MPa), where the laminate absorbed less energy per damage area compared with unpre-stressed laminates.
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    A systems approach to the design of personal armour for explosive ordnance disposal
    (Cranfield University, 2004-11) Couldrick, C A; Iremonger, M J; Gotts, P L; John, Philip
    A qualitative description of the personal armour design system is elicited by comparing armour throughout the ages. Inputs that 'shape' designs are the materials technology, threat, wearer, task and environment. The emergent properties of protection, ergonomic effectiveness and financial cost form the basis of trade-offs to select final solutions. Work on the protection subsystem refines the key positive emergent property of personal armour. Existing quantifications of protection effectiveness are rejected in favour of a novel measure named the Usefulness Factor, UF. This is the first measure that accounts for the real benefit of armour. A five-stage model is proposed for the assessment of protection. Two feedback loops - due to making tasks as safe as possible and the ergonomic penalty of armour are evident. These must be considered in order to assess protection correctly. Casualty reduction analysis software (CASPER) is used to produce 'approach plots' and 'zones of usefulness' in order to make tasks safer and map the benefit of armour. This approach is demonstrated with the UK's Lightweight Combat EOD Suit against L2A2 and No. 36 Mills grenades, an HB876 area denial mine, a BL 755 sub-munition and a 105mm artillery shell. Assessment of secondary fragmentation from antipersonnel (AP) blast mines defines a threat input that is specific to Explosive Ordnance Disposal (EOD). Trials are carried out with explosive charges of 50g to 500g, buried under 5 or 10cm of stones and sand at a range of 1m. The threat is defined in terms of the probabilities of (a) being hit, (b) a hit perforating armour and (c) a hit incapacitating an unarmoured person. The chances of being hit close to the ground decrease to approximately 15% of the value when directly above the mine. Secondary fragmentation is not likely to perforate armour that protects against primary fragments. However, it is likely to incapacitate an unarmoured person. Protection is traded-off against proxies for ergonomic and financial cost effectiveness by using quantitative optimisation of personal armour. This introduces the concept of a 'protection optimisation envelope', which defines the bounds of possibility rather than a single solution. CASPER is adapted to produce weight and cost as well as incapacitation parameters. This provides a model that generates both benefits and constraints of armour. Hence, the foundations are laid for the world's first fully integrated personal armour design tools. The ergonomic effectiveness subsystem is the primary constraint of personal armour. Visor demisting for the UK's Mk 5 EOD Suit provides a simple example. Existing methods of assessment of the ergonomic penalty of armour are considered. A novel development of biomechanics computational models is proposed to predict both the mechanical and thermal burdens of armour.