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The Application of Auxetic Structures for Rugby Shoulder Padding

Moroney, Charlotte (2021) The Application of Auxetic Structures for Rugby Shoulder Padding. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Auxetic materials have a negative Poisson’s ratio (NPR), they laterally expand under stretch, laterally shrink under compression and conform to curved surfaces through the formation of synclastic curvature. It was identified that these qualities could enhance the current standard of personal protective equipment (PPE) often embedded within sports apparel (sPPE) at regions of the body exposed to soft tissue injury through collision, fall or impact. Current pads can inhibit movement, breathability and wicking, whilst moulded pads are prone to saddling; segmentation techniques including vacuum moulding and cut segmenting are applied to improve the conformability of padding. It is unclear as to whether the impact performance of auxetic sPPE is affected under a state of synclastic curvature or biaxial expansion and as such sPPE applications are limited to date. User-centred design strategies for functional clothing have not yet been established for sPPE with auxetic elements, this could improve accessibility for implementation by pad designers. Therefore, this research set out to determine strategies for the application of auxetic sPPE with enhanced conformability. In order to achieve the overall aims of this research a multi-method research strategy was employed investigating the problem first through the user and product. A quantitative survey was designed to assess user perceptions of commercial rugby shoulder padding comfort. Commercial rugby shoulder padding featuring different segmentation types were assessed for conformability to the shoulder region through fit and pressure comfort measurements. Following this the research investigated how auxetic structures of different geometries could enhance the conformability of rugby shoulder padding. Data collection included pressure comfort assessments, impact tests over curved surfaces and lateral expansion of pads through tensile displacement and fitting pads to a mannequin. A user-perception survey of commercial rugby shoulder pads found that fit and protection were the most important of six realms of respondents perceived comfort. iii Current regulations for rugby shoulder padding suggest that pads must not hinder comfort and mobility yet only stipulate test methods for impact protection. The commercial rugby pads provided poor pressure comfort and conformability across the different types of segmentation and segment (unit cell) shapes. It was also identified that poor conformability was of detriment to product function where pads moved out of position. The findings from the survey and product analysis showed that the main cause of poor fit and pressure comfort was padding bulkiness caused by larger circumferences and less conforming segmentation techniques. Cutsegmented pads provided the best route to conformability but none of the pads provided the ideal pressure comfort range identified for this research. Rugby shoulder pads were cut-segmented with different auxetic structures and following this manipulation of an auxetic geometry was investigated. It was found that sPPE with auxetic elements conformed to curvatures and expanded laterally compared to the non-auxetic alternative. Parameters for use were identified including that opening consistency of the individual auxetic geometries had potential to affect sPPE function. Auxetic geometries in an arrangement of singular cuts had the most consistent opening mechanism throughout the pad when subject to a tensile load. Additionally, the manipulation of an auxetic geometry showed that anisotropy can be applied to offer higher displacement in specific directions, which may have use for sPPE not subject to rotational forces such as knee pads. It was also found that increasing the difference between rib (unit cell wall) length and separation between ribs led to the auxetic structure opening out less, which could be applied at specific regions of a pad that require restriction. The findings of this research showed that auxetic structures could be manipulated for different sPPE applications. A recommended strategy for development of sPPE with auxetic elements was presented, influenced by user-centred design strategies. The first stage of the strategy focused on defining the problem via the user, sport, body region and product. Ideation of possible solutions formed the second stage, by assessing manipulations of auxetic geometry in relation to requirements of the user, product, sport and body region, and was repeated until the product was found to provide a solution to the defined problem; implementation completed stage 3.

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