Finite Element Modelling of Snowboard Wrist Protectors

Snowboarding has a higher injury risk than alpine skiing, with the upper extremities being the most common site for injuries. Wrist protectors are recommended to reduce injury risk by limiting wrist hyperextension and impact forces. There are different wrist protector designs but there is currently no recognised standardisation, with little consensus as to which are most effective. While experimental protocols are useful for analysing current products, they are limited when assessing the effect of design changes and predicting the performance of future protector concepts. The aim of this project was to develop finite element models to assess the impact performance of snowboard wrist protectors, whilst fitted to a surrogate. Two wrist protectors were chosen for modelling, both with palmar and dorsal splints and padding in the palmar region, with one classified as short and the other a long protector (based on splint length). The component materials within the protectors were characterised and impact tested. Using the measured material properties, finite element models replicating these impact tests were developed and compared to the experiment for validation. These models were developed into full protectors fitted to a wrist surrogate under impact. To validate the full protector models, experimental testing was conducted using a modified version of the pendulum impact rig developed by Adams (2018) across a range of energies (10 to 50 J). The validated models were then used to explore the effect of changing components (e.g. splint length, material) on impact performance, in order to enhance the understanding of wrist protector design. The research highlighted clear differences in the properties of wrist protector components from the same size/brand, re-iterating the need for standardisation. The palmar splint was found to have the largest influence on impact force and the dorsal splint on wrist angle, in agreement with the literature. Model outputs showed peak force and maximum wrist angle to decrease as splint length or stiffness (thickness or material) increased. Future work could develop the model into a tool for improving wrist protectors as well as to predict whether new designs would meet the requirements of the new ISO standard (once published)

Finite element model of an impact on a palmar pad from a snowboard wrist protector

Wrist injuries are the most common types of injury in snowboarding. Protectors can reduce injury risk by limiting wrist hyperextension and attenuating impact forces. There are a range of wrist protector concepts available, but it is unclear if any particular design is more effective. The aim of this study was to develop and validate a finite element model of an impact on the palmar pad from a protector. Pad material from a protector was characterised to obtain stress vs strain data, and determine whether it was rate dependent. Material data was implemented into a finite element model to predict impact behavior at 2.5 J. Four material models were investigated, with an Ogden model paired with a Prony series providing the best agreement to experimental data. Future work will build a model of a complete protector for predicting the protective levels of these products

Fabrication of auxetic foam sheets for sports applications

Auxetic materials have a negative Poisson's ratio, which can enhance other properties. Greater indentation resistance and energy absorption, as well as synclastic curvature, could lend auxetic materials well to protective sports equipment and clothing. Sheets of foam often form padding within protective equipment, but producing large homogenous auxetic foam samples is challenging. The aim of this work was to investigate techniques to fabricate large thin sheets of auxetic foam, to facilitate future production and testing of prototype sports equipment utilizing this material. A mold was developed to fabricate sheets of auxetic foam − with planar dimensions measuring 350 × 350 mm − using the thermo-mechanical process. The mold utilized through-thickness rods to control lateral compression of foam. Sheets of auxetic foam measuring 10 × 350 × 350 mmd were fabricated and characterized. Each sheet was cut into nine segments, with density measurements used to determine how evenly the foam had been compressed during fabrication. Specimens cut from corner and centre segments were subject to quasi-static extension up to 30% to obtain stress versus strain relationships, with Digital Image Correlation used to determine Poisson's ratio. Specimens cut from the corner tended to have a marginally higher density, lower stiffness and more consistent negative Poisson's ratio compared to those from the centre, indicating some inconsistency in the conversion process. Future work could look to improve fabrication techniques for large thin homogenous sheets of auxetic foam