11:30   Design optimization and simulation of sports products
Chair: Marc van der Zande
11:30
20 mins 		A COMPARISON OF NOVEL AND CONVENTIONAL FABRICATION METHODS FOR AUXETIC FOAMS FOR SPORTS SAFETY APPLICATIONS
Olly Duncan, Leon Foster, Terry Senior, Tom Allen, Andrew Alderson
Abstract: Auxetic foams with a negative Poisson's ratio have previously been shown to increase impact force attenuation and resist 'bottoming out' when compared to their non-auxetic counterparts (Allen, Shepherd et al. 2015, Allen, Martinello et al. 2015). Improvements to the fabricated auxetic foams, as required with reference to previous research, will include; i) conversion of thinner foam samples to control variation of material properties through converted auxetic foam samples (Duncan, Foster et al. 2015, Lisiecki, Kłysz et al. 2014); ii) selection of candidate foams with material properties comparable to current foams in commercial protective equipment. Current candidate polymer foams utilised for conversion to auxetic foams typically exhibit a Young's Modulus ~30 times lower than the closed cell foams commonly found in commercial equipment for impact protection in sports (Allen, Shepherd et al. 2015, Ankrah, Mills 2004). In order to move towards commercial use, candidate foams with a higher Young's Modulus will be fabricated. Thermo-mechanical conversion methods will be applied to a variety of candidate materials and mould dimensions. A complete picture of material properties of each foam sample will be obtained through a combination of: i) Quasi-static testing on an Instron 3369 device to obtain stress/strain relationships and Poisson's Ratios. ii) Impact testing on a bespoke drop rig under conditions representative of those in the relevant standards (BS Online 2000, EN 2001). iii) Density measurements of dissected samples to obtain within sample variation of compression ratio after conversion (Duncan, Foster et al. 2015). These test methods will be repeated on a variety of materials found in current commercial protective equipment for comparison. The purpose of this study is to determine whether suggestions in previous studies (Duncan, Foster et al. 2015) can reduce variation and increase force attenuation of auxetic materials under impacts similar to those occurring in sports. This will pave the way for more extensive and focussed research into the relationships between the frequently described auxetic effect and whether this can improve the comfort and impact force attenuation of protective equipment in sport. Reference List ALLEN, T., SHEPHERD, J., HEWAGE, T., SENIOR, T., FOSTER, L. and ALDERSON, A., 2015. Low-kinetic energy impact response of auxetic and conventional open-cell polyurethane foams. Physica Status Solidi B, 252(7), pp. 1631-1639. ALLEN, T., MARTINELLO, N., ZAMPIERI, D., HEWAGE, T., SENIOR, T., FOSTER, L. and ALDERSON, A., 2015. Auxetic Foams for Sport Safety Applications. Procedia Engineering, 112, pp. 104-109. ANKRAH, S. and MILLS, N.J., 2004. Analysis of ankle protection in association football. Sports Engineering, 7(1), pp. 41-52. BS ONLINE, 2000. BS 6183-3:2000: Protective equipment for cricketers-leg protectors for batsmen, wicket-keepers and fielders, and thigh, arm and chest protectors for batsmen. British Standards Institute. DUNCAN, O., FOSTER, L., SENIOR, T., ALDERSON, A. and ALLEN, T., 2015. Quasi-static characterisation and impact testing of auxetic foam for sport safety applications. Smart Materials and Structures, In Prep. EN, B., 2001. 13061: 2001 Protective Clothing–shin guards for association football players. British Standards, London. LISIECKI, J., KŁYSZ, S., BŁAŻEJEWICZ, T., GMURCZYK, G. and REYMER, P., 2014. Tomographic examination of auxetic polyurethane foam structures. Physica Status Solidi (b), 251(2), pp. 314-320.
11:50
20 mins 		AN ASSESSMENT OF BICYCLE FRAME BEHAVIOUR UNDER VARIOUS LOAD CONDITIONS USING NUMERICAL SIMULATIONS
Derek Covill, Philippe Allard, Jean-Marc Drouet, Nicholas Emerson
Abstract: This paper outlines the use of a finite element model to simulate the behaviour of various steel bicycle frames under an extensive range of measured load cases. These load cases include those measured both in the laboratory setting and also in the field, and include loads transmitted at key areas such as the dropouts and hub, the bottom bracket and drive, the headset and handlebars, and the seatpost and saddle. The load cases analysed include extreme and highly dynamic situations which occur sporadically such as collisions or bumps and also those which occur constantly or regularly such as those generated at the drive and handlebars during climbing or cruising. The nature and variability of boundary conditions applied for each load case are also analysed highlighting the sensitivity of behavior to these boundary conditions. The resulting stresses and deflections within the bicycle are analysed in the context of frame performance relating to stiffness and comfort as well as static and fatigue strengths.
12:10
20 mins 		EXPLICIT FINITE ELEMENT METHODS FOR EQUESTRIAN APPLICATIONS
Karin Brolin, Jacob Wass
Abstract: A virtual human body model (HBM), developed for vehicle crash simulations, was used to study dangerous accidents that occur in equestrian sports. This pre-study was performed to illustrate the potential that the explicit finite element (FE) method has to improve rider safety and assess the protective capacity of the security vest. Four different questions were addressed: 1. When a rider is trampled by a horse, how does the injury risk vary with chest impact location? 2. Does the security vest provide protection if the rider is kicked by a horse and does the protection vary with the violence of the hoof impact? 3. Can a security vest provide any benefit when the rider is hit by the horse after a rotational fall? 4. How does the risk for thoracic injuries vary when the rider falls off the back of a horse at different angles? The HBM used was Total Human Model for Safety AM50 version 3.0 (Toyota Motor Corporation, Japan), improved for chest injury predictability in a previous automotive project. The FE code LS-DYNA (Livermore Software Technology Corporation, USA) was used for all simulations. Models of a generic security vest, a horse impactor and a hoof were developed as part of this project. The risk of thorax injury was evaluated with stresses and strains measured for each rib, as well as the total deformation of the ribcage, using the two criteria Dmax and DcTHOR. Dmax is a maximum relative deformation measure of compression at five points on the ribcage, where 100% means that the thorax was completely compressed at some point and 0% means no compression. DcTHOR is a measure of the maximum deformation between the same points as Dmax, but with emphasis on asymmetric deformation by adding terms measuring the difference of the deformation on the left and right side of the ribcage. The following results were obtained for each question: 1. The injury risk seemed to be higher for hoof impacts in the sternum compared to more lateral locations that have up to 25% less risk. Hence, this knowledge could be used to optimize novel safety vest designs with HBM simulations. 2. Yes, the security vest provided protection for hoof kicks and the protection varied with the violence of the kick. Therefore, if the range of violence that occurs in real world accidents is known, HBM simulations can be used to optimize the vest material properties. 3. No, the security vest did not provide any benefit when the horse lands on top of the rider. This suggests that safety measures should focused on preventing this type of accident, rather than designing personal protection for the rider. 4. When the rider falls with the head first, the number of predicted rib fractures increase compared to flat falls. However, the model predicts rib fractures for all the falls simulated from a height of 1.5 meters. To conclude, FE HBMs have the potential to improve equestrian safety and further studies on equestrian security vests designs are warranted.