Sports tribology

Tribology is a term used to define combination of friction, wear and lubrication. Tribology has been used in various fields to improve reliability and longevity of systems. Sports engineering applies engineering disciplines like mathematics, physics, and material science in order to solve sporting problems [1]. Tribological problems are often encountered with many sporting equipment’s which can deplete the performance of an athlete or even a team.  Let’s discuss some cases where sports engineers have used their knowledge of tribology in order to solve a problem.

In India, cricket is a religion. It is a popular sport among people of all ages. The cricket bat is one of the most important part of the game. The cricket bat is made by joining, a cane handle to the willow blade. The handle is then covered with a rubber grip to ensure proper handling and control of the blade. This rubber grip has to provide high friction so that it remains attached to the palm. If the surface of the rubber grip is very smooth, the handle will slip from the hands of a batsman while playing. The bat can also slip due to moisture in weather or on the field or due to formation of sweat.

In order to provide an efficient solution to these problems, researchers have been doing experiments on finger pad/palm surface. Through experiments it was discovered that if the counter surface (the grip of bat in this case) is having higher roughness, the friction coefficient can be significantly increased. As the roughness increases, the asperities of the counter surface starts to interlock with the ridges of the fingers. One of the ways of increasing roughness of the counter surface is by modifying the surface topography/texture of the counterpart.

A protruded pattern such as pimple pattern or geometrical scales on surface helps in improving friction between the contacts. The pimples and scales pattern can be widely spaced, closely spaced, can be of small and big size, depending upon the nature of the sport. These pimples/protruded scales also help when the contact interface gets lubricated via moisture or sweat. The pimples/protruded scales can break through this lubricating film and can provide efficient handling of the bat.

Even wicket keeping gloves are having pimples/protruded scales for better grasping of the ball by wicket keepers. This solution has been utilized even in the manufacturing of rugby balls. The outer surface of rugby balls are also having pimple like pattern to provide efficient gripping of rugby ball during passing and catching [2].

Fig. 1. Image showing surface topography of a cricket bat grip, wicketkeeping glove and rugby ball
Fig. 1. Image showing surface topography of a cricket bat grip, wicketkeeping glove and rugby ball

The Rio Olympics ended two months ago. Gymnastics has always been a part of Olympics. Vault, Uneven Bars, Balance Beam, Floor Exercise are some of the categories of gymnastics. We all have noticed that before any performance, gymnasts apply chalk powder on their hands and sometimes even on feet. Chalk absorbs moisture/sweat from palms and feet that could make gymnasts slip or make the equipment slip from their hands. In both the cases a serious injury can occur which could even ruin ones career. It also helps decrease friction, allowing a smooth spin on bars. Tribological tests carried out on four kinds of gripping agents (Powdered and Liquid Chalk, Rosin and Venice Turpentine) have revealed that chalk offers the highest friction for wet finger/dry surface contact [2].

Fig. 2. Image showing chalk applied on hands before lifting weight
Fig. 2. Image showing chalk applied on hands before lifting weight

The Ski industry is booming. According to 2016 International Report on Snow & Mountain Tourism, the Western Europe (except the Alpine countries mentioned separately above) alone is home to more than 30 million skiers. A ski is a narrow strip of semi-rigid material worn underfoot to glide over snow. In this sport our focus would be on the interaction of the ski running base with the snow. At the interface of ski running base and snow, a thin water layer between the base and the snow develops as a consequence of solar heating and friction. Adhesion of the water layer to the ski surface can bring a certain amount of rise in friction. This friction can deteriorate the maneuvering capabilities of ski. Hence it is desirable to produce bases with low water adhesion properties. Research work have shown that this can be achieved to a certain degree by treatment of the bases with hydrocarbon and/or fluorocarbon waxes, thermal embossing [3] and through surface patterning via stone grinding or milling processes [4].

Fig. 3. Image of a ski
Fig. 3. Image of a ski

Tennis is a very popular sport. It is played on a tennis court and can be played individually against a single opponent or in doubles format. The tennis court are of three main types – the grass court (Wimbledon tournament), the clay court (French Open) and the hard court (Australian open). The hard courts generally used in tennis tournaments are blue in color and are also referred as blue courts. Hard courts are generally made by coating a mixture of rubber, latex and plastic particles over the concrete asphalt base. A small amount of sand is mixed for impart proper bounce of tennis ball [5]. These courts are not easy to adapt to and even big players are not finding it comfortable. Complaining about the blue court World No. 1 Novak Djokovic said that it was “impossible to move” on the Manolo Santana show court during the Madrid open qualifiers [6].

Fig. 4. Image of a blue court
Fig. 4. Image of a blue hard court

The soles of tennis shoes are made of viscoelastic rubber. When this rubber is compressed against hard courts, adhesive friction forces develops due to interaction between asperities of the two contacts. In order to solve this problem, we would need a better tribological understanding of shoe-surface interaction. Researchers have come out with many test setups in order to simulate the shoe-surface interaction but it seems to be very difficult to mimic especially loads as it depends on the player’s own body weight and load variation while a shot such as serve, smash or dropshot is played. Researchers are also working on different types of material for shoe soles that can provide proper grip on hard courts [7].

Sports engineering and tribology can prove to be a beneficial combo for the sports industry and for players.

References:

  1. Hdriscoll, By. “What Is Sports Engineering?” Engineering Sport, 09 Aug. 2012. Web. 01 Nov. 2016 https://engineeringsport.co.uk/2012/08/09/what-is-sports-engineering/
  2. Lewis, R., M.J. Carre, and S.E. Tomlinson. “Skin Friction at the Interface between Hands and Sports Equipment.” Procedia Engineering 72 (2014): 611-17
  3. Nordin, Nurul A., and Peter Styring. “Superhydrophobic Ski Bases for Reduced Water Adhesion.” Procedia Engineering 72 (2014): 605-10
  4. Breitschädel, Felix. “A New Approach for the Grinding of Nordic Skis.” Procedia Engineering 112 (2015): 385-90
  5. “Tennis Guide – Surfaces.” YouTube, 16 Dec. 2013. Web. 01 Nov. 2016 https://www.youtube.com/watch?v=0AS7amVYkH8
  6. “Madrid Open: Djokovic Hits out at Organisers over Blue Court.” Rediff.com/sports., 09 May 2012. Web. 01 Nov. 2016 http://www.rediff.com/sports/report/djokovic-hits-out-at-madrid-organisers-over-blue-court/20120509.htm
  7. Carre, Matt J., James D. Clarke, Loic Damm, and Sharon J. Dixon. “Friction at the Tennis Shoe-court Interface: How Biomechanically Informed Lab-based Testing Can Enhance Understanding.” Procedia Engineering72 (2014): 883-88
  8. All images are used from google images “can be reused with modification” category. 

HARSHVARDHAN SINGH
About HARSHVARDHAN SINGH 17 Articles
Harshvardhan Singh is an Automotive Engineer and has good experience in lubrication science and experimental tribology. He loves to write about tribology and related fields such as coating technology, surface engineering and others.

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