Author: An Lam
Lam, An, 2019 Optimisation and impact assessment of novel protective guards used in cricket, Flinders University, College of Science and Engineering
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Concerns about injury in cricket have been reported as a leading reason why participants choose to leave the sport (Sport Australia, 2019). With a 163g ball bowled at high speeds of up to 160km/h, batsmen are particularly vulnerable to impact trauma, ranging from contusions and fractures, to fatal tragedies that question the safety and public perception of the sport. While there has been great emphasis and progress in the development of helmets and shin pads, protection of other body parts have not been thoroughly evaluated or analysed in literature. This project is driven by a client with the aim of evaluating the protective properties of Isoblox, which is a thin, hexagonal mesh material that provides impact dispersion properties. Isoblox has successfully returned promising results in previous testing carried out by Ziegler (2016) in the United States, with comparison against padding from other reputable competitors showing a clear improvement. This thesis extended the impact assessment of the original Isoblox material, as well as three newly formed Isoblox compositions, in various configurations involving five different types of ethylene-vinyl acetate (EVA) or polyethylene (PE) foams. A testing protocol has been developed to apply impact energy in a drop test setting that is equivalent to that experienced in a competitive cricket game. While similarities can be drawn between this protocol and the official standard, BS 6183-3:2000, a key difference in this study is the use of ballistics gelatine, on which the materials are tested. This deformable layer imitated soft tissue in a human limb, and allowed for a more realistic simulation of the impact event. Due to the inclusion of this layer, new observations about the material could be made upon visual inspection, such as the potential for various types of damage. These characteristics were not previously identified in testing, and have prompted ideas for material improvement by strengthening the interconnecting hinges in the mesh. The combinations of interest were selected in collaboration with the client, and force data from drop tests were collected using a 20kN capacity load cell, recorded at 5kHz. Data acquisition was completed using the National Instruments SignalExpress software, and analysis was completed in MATLAB. The key parameter evaluated from the data was the peak force transmitted through the sample, which was taken from the maximum force of the first bounce of the impactor on the material. Peak forces were compared to draw conclusions about the best performing Isoblox composition, foam type, and lay-up configuration. From these results, the most effective materials were re-tested to assess repeatability, finding a range of variation between 148N – 1024N. The best-performing materials were then combined to create two superior lay- up configurations, with input from the client to ensure that the materials meet the requirements of flexibility and thickness required for a protective guard. The new combinations were found to provide the most protection out of all materials tested, with peak transmitted forces of 3974N and 4496N. This is a respective 2466N and 1944N less than the next best configuration. Since this is outside the range or variation found in the repeatability tests, it can be said that this is a significant improvement, although further repeats of testing would be recommended to properly distinguish between the best two configurations. Unlike all other samples, the best two material configurations were also successful in protecting the underlying ballistics gelatine from visible damage. Overall, the thesis presents an evaluation of protocols for sports guard impact testing, highlights the optimal materials that may be considered for further development, and provides many areas of improvement to be implemented in future testing.
Keywords: impact protection, protective guards, protective equipment, cricket, impact injuries, drop testing protocol, ballistics gelatine
Subject: Engineering thesis
Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: David Hobbs, Mark Taylor