One of the challenges faced by tennis players is the interaction of their shoes with the court. Tennis is played on a range of surfaces with different properties. For example, it it much easier to slide across a clay court than a hard court due to the lower friction with the less rough surface. Researchers at the University of Sheffield investigated tennis shoe-court interactions and subsequently developed a portable mechanical device that can assess the quality of a tennis court which will be utilised by the International Tennis federation.
The rubber used to make tennis shoes is viscoelastic which means if a force is briefly applied to the material it is deformed and then returns to its original shape but when a force is applied for longer the material is deformed permanently. The rubber soles are compressed against the surface of a tennis court and the rubber molds its shape to the roughness of the surface which is the cause of the friction. Therefore, when designing the test it was important to understand how load, surface roughness, shoe orientation, temperature and contact area contribute to the frictional force and a lab-based test rig was built for initial tests. The researchers concluded that friction is mainly affected by sole surface temperature and surface roughness, and also the presence of a tread in the shoe sole.
In the design of the portable test device, the main features considered were reliability, size and weight for transportation and the ability to represent match play conditions well. Also, the test shoe needed to be interchangeable to allow testing of different sole materials and sizes. The final design consists of a test shoe slider attached to a sled with weights mounted on it, a pneumatic ram which provides a horizontal force to drive the sled. The horizontal force is applied until the test shoe slider is initiated and friction is measured.
The researchers hope that with further development the device could become part of a standard test to assess the quality of courts for elite tennis competitions and eventually be used to improve the quality of tennis courts for all players.
Article by Naomi Brown; a PhD Student on the EPSRC Polymers, Soft Matter and Colloids CDT programme. For more information, please contact Dr Joe Gaunt at the Polymer Centre.
D. Ura, M Carré, Development of a Novel Portable Test Device to Measure the Tribological Behaviour of Shoe Interactions with Tennis Courts, Procedia Engineering, 147, 550-555, 2016.