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Title: Novel self-healing systems : expanding and inhibited healing agents
Author: Rae, Steven Inglis
ISNI:       0000 0004 5994 9309
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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The concept of self-healing materials has emerged from the reticence that exists in composite design, especially in aerospace structures. This concern emanates from composite materials' poor interlaminar properties and therefore tendency to perform badly when subject to impact events, typically manifesting as matrix cracking, delamination, and fibre debonding. With even microscopic damage having the potential to grow under fatigue loading until the structure's mechanical properties are diminished, composite structures are manufactured with high built in safety factors and structural redundancy to counteract inevitable defect creation. By developing self-healing materials, these defects can be addressed before (or after) they are allowed to grow, thus reducing the requirement for structural redundancy and capitalise on the mass savings that result. The chemistry behind healing mechanisms, and. methods of incorporating healing functionality itself, has been intensely researched by many groups in recent years. Whilst impressive results have been observed, and respecting the advancements that have been achieved, there still exist challenges which need to be addressed to allow for effective and fully autonomous self-healing systems. Many studies report thermal activation of polymerisation reactions, pre-mixing of healing agents, manual closing of crack planes to increase the relative volume of healing agent, or artificial opening of crack planes to increase infiltration and alleviate tensile stresses on the healing agent. Fundamentally however, achieving high healing efficiencies relies on delivering an adequate volume of healing agent(s) in a stoichiometric ratio and achieve effective mixing, or relies on exposing embedded catalyst to initiate and sustain polymerisation. We aim to address some of these challenges and reduce the dependency on external stimulus to increase healing efficiency in an autonomous manner through two different approaches. Firstly, the problems associated with incorporation of catalyst into the matrix, achieving stoichiometric ratios, and effective mixing, can be addressed using a single part healing chemistry that requires no additional stimulus or catalyst after release to polymerise. We have therefore investigated a potential route to 'inhibited healing' whereby a resin is actively prevented from undergoing polymerisation until released from the delivery vessel, whereupon polymerisation occurs rapidly and autonomously., Secondly, problems associated with mixing, reducing fibre disruption from vascule incorporation, delivering adequate volume from smaller reserves, achieving high proportions of infiltration, or to address larger damage voids and bridge wider separations, can be achieved by creation of volume in the healing agent , itself. We have investigated different chemical systems to produce a structural polymer with a volume greater than the sum of its constituent parts, explored methods of tailoring its chemical and structural properties, and assessed its ability to repair not only the relatively small volumes associated with damage within laminate structures, but also the larger damage volumes associated with impacted sandwich structures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available