Understanding the mechanisms that govern the impact behaviour of a football.

Football is one of the most popular sports in the world. The 2022 FIFA World Cup final was watched by approximately 1.5 billion people, with an estimated 250 million people participating in the sport globally. The ball is a fundamental piece of equipment necessary for participating in the sport and has undergone numerous developments in both the design and materials as manufacturers strive for a competitive advantage. The Fédération Internationale de Football Association (FIFA), as the international governing body of football, regulate the quality of footballs entering the professional game to uphold the integrity and safety of the sport. However, there is a need to greater understand the dynamic performance of footballs to ensure that the policy remains relevant to assess the standard of balls entering the sport as materials and manufacturing technologies evolve. This thesis details an in-depth investigation into the dynamic impact response of footballs, the development of appropriate experimental test protocols and a mathematical model to investigate the contribution of the mechanical properties of a football on its impact behaviour to inform the standards. The static and dynamic properties of twelve different footballs were obtained experimentally. Each football was projected at a force platform at a relatively low and high velocity. Measurements were captured using a combination of high-speed video and a force platform to characterise the impact response. The mechanical properties of each football were evaluated from a quasi-static compression test and the loading profile outputted from the force platform. The relationships between the mechanical properties and the impact response of a football were developed using multivariable regression. The models that used the properties derived from dynamic tests showed better ability to explain the variations in the impact response between the footballs than the properties obtained from static tests. The stiffness of a football showed significant influence on its impact response. The current policy for regulating the standard of footballs evaluates their ability to dissipate energy upon impact but lacks a direct or indirect quantification of a ball’s stiffness. However, the stiffness properties govern aspects such as contact time, deformation and impact force. Therefore, to ensure comprehensive assessment of the mechanisms that govern the impact behaviour of a football, it is recommended to incorporate an additional measurement of contact time in the FIFA Quality Programme. This measure can easily be incorporated into the existing test protocols to serve as a proxy of dynamic stiffness. This can provide a comprehensive evaluation of the properties of a football that govern its impact behaviour across diverse conditions.