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Title: Micro-scale hybrid fibres for low cost polymer armours
Author: Del Rosso, Stefano
ISNI:       0000 0004 6423 0649
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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High performance polymer fibres are extensively used to make personal protective textiles and as reinforcing phase in polymer reinforced composite materials. This because of their excellent mechanical properties such as high tenacity and toughness, low elongation to break, and their ability to dissipate shock waves over a large area in a short amount of time. Over the past decades, braiding has become a very popular manufacturing technique and widely exploited in the composite industry for the production of advanced engineering parts. Braided reinforced structures offer certain advantages over conventional reinforced composite materials such as damage and impact resistance, high delamination resistance due to a greater through-the-thickness reinforcement. Moreover, the investment and labour cost can be minimised due to the inexpensive machinery, high rate of production and level of automation. This work aimed at studying the mechanical response of polymer structures rein- forced by high performance microbraids for ballistic impact applications. The mechanical properties of different high performance fibres were experimentally investigated under different conditions, from quasi-static to dynamic loads. Quasi-static tensile tests were performed on yarns and microbraids at constant strain rate and the effect of different gauge lengths studied; high strain rate tests were performed by transversely impacting yarns and microbraids using flat-face lead projectiles. Tensile tests performed on dry microbraids showed a significant improvement up to 96.2% over the constituent materials in terms of toughness and energy absorption. Dry microbraids also proved to offer greater ability to capture impactors with respect to unidirectional fibres, although with greater deformation. A novel and unique manufacturing technique was also developed for the manufacture of microbraid reinforced polymer composites (mBRPC). The microbraids were wound, at controlled tension, onto a spinning plate via a robotised lament winding system. The dry fabric was then consolidated into a prepreg via the hot-press technique using a thermoplastic resin film. The final composites were manufactured by stacking the prepregs in a cross-ply fashion. Quasi-static tests performed on mBRPC showed a different mechanical behaviour with respect to cross-ply composites manufactured using the same technique but with unidirectionally aligned fibres. mBRPC showed enhanced tensile strength, strain to failure and toughness for certain materials and architectures with respect to the UD counterpart. The ballistic performance of mBRPC were assessed by firing mild steel balls using a gas gun. Two high speed cameras were employed to record the behaviour of the mBRPC during the impact event. Test results showed a higher ballistic limit, up to 19%, for certain mBRPC with respect to the UD counterpart.
Supervisor: Iannucci, Lorenzo ; Curtis, Paul Sponsor: Defence Science and Technology Laboratory ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral