Innovative uses of composites in sport

Materials World magazine
,
4 Jan 2017

Composite materials are a driving force in sports technology, as Ellis Davies found out. 

The sports sector was one of the first to take up composite materials, and is a significant consumer of carbon fibre, accounting for 14% of industry consumption. Composites in Sport, an event presented by NetComposites, UK, heavily focused on presentations by various composite related professionals covering the technical aspect of recent developments in sports equipment. 

Dr Paul Sherratt of the Sports Technology Institute at Loughborough University began the series of presentations, giving an overview of the 460-acre campus and its extensive range of sporting facilities. Sherratt posited that the reason for the high level of composites in sport is because of lower levels of regulation, quick concept-to-market turnaround, multiple niches and general enthusiasm from consumers. 

Warning signs

Joe Summers, Sales and Marketing Director at North Thin Ply Technology (NTPT), UK, headed the first manufacturer’s presentation of the day. NTPT is a developer of composite and thin ply materials and supplier of various products for sailing, cycling and motorsport.

3Di, a technology developed and licensed in 2008 to international sailmaker North Sails by NTPT, is used to make sails that are durable and, NTPT claims, the world’s fastest. Summers explained, ‘They are composed of ultra-thin unidirectional spread filament tapes, pre-impregnated with thermo adhesive, arranged in a complex multiple-axis array and 3D moulded into a one-piece, flexible composite membrane.’

The material provides a high-strength laminate because delayed first ply failure increases the usable strength, with 20% higher average compressive strength than thick ply. Summers claimed NTPT’s thin ply has shown first ply damage onset at 900MPa, and failure at 1,100MPa, 200% higher than commonly used aerospace composite materials. 

NTPT’s composite materials also featured in the presentation given by Dr Jonathan Fuller of the University of Bristol, UK. Fuller spoke about Bristol's High Performance Ductile Composites Technology programme, which has an objective of overcoming conventional materials’ lack of ductility. Fuller is working on the bicycle handlebar – professional cyclists will often refuse carbon fibre-epoxy bars because of their brittle nature, and the risk of injury it presents. Fuller explained that the programme is developing a thin ply sensor to coat the handlebars that will alert the user to any overload on the composite structure. The sensor, a glass-carbon hybrid, changes appearance when a layer fractures or delamination occurs. Tests carried out using these sensors on high-end bicycle handlebars showed that the damage became visible, under an applied load of 2,700N, at 1,750N. The programme has also developed a hybrid self-repair patch to cover cracks in the material, which gives the same warning as the sensor. 

At the market

Rockwood Composites, UK, and its spin-off hockey specialist ZEEK delivered a joint talk regarding the manufacture and marketing of composite products for sport. Mark Crouchen of Rockwood explained the company’s manufacturing process using compression and bladder moulding. 

His colleague at ZEEK, Marcel Schuurkes, primarily focused on the impact of composites on the sports market. ZEEK’s main product, the Z-1.0 hockey stick, is manufactured by hand using a patented one-piece moulding process. The product is made mostly of carbon fibre, with the blade made up of multiple layers of composites wrapped around a foam core. ZEEK says its stick combines strength, lightness and flexibility for better performance and usability.

A particularly interesting point brought up by Schuurkes, which sparked conversation between audience and speaker, was how composite equipment has sometimes been banned by a sporting governing body, or the body has altered the rules of the sport to accommodate new equipment. 

‘It’s one thing to make a really great product, and introduce it to a market where it out-performs everything, but it could be banned,’ Schuurkes said, citing a composite baseball bat developed and introduced in the mid-1990s that was deemed too dangerous because of the speed a ball would travel when struck. The product was banned for safety reasons, but now composite bats are manufactured to perform within the boundaries of safety and regulations. 

Schuurkes spoke about the development of the wood-aluminium and composite ice hockey sticks that replaced the wooden stick, allowing for a more powerful shot and the ability to engineer specific properties, such as breaking point. ‘With the introduction of these sticks, some companies ceased to exist. Even companies that produced other gear were in trouble, as the cash cow was the stick, and the stick dropped away, drying up the R&D funding. It changed the whole landscape of the market.’ 

Action and advances

Moving away from brands and manufacturers, Rosie Manning, graduate of Mechanical Engineering at the University of Nottingham, UK, presented her final year project, a body brace to allow Ben White, a paraplegic skydiver, greater control when flying. Manning explained how White’s original brace was restrictive, and did not allow him to launch from his wheelchair, rather having to be dragged in and out of the wind tunnel in a demeaning manner. ‘The goal of this project was to design, validate, manufacture and test a lower body exoskeleton that could be worn by paraplegic skydivers. One of the main aims was to provide both support, but also allow for as much movement control as possible so the user could achieve the desired level of skill as an able bodied skydiver,’ Manning said. 

Manning carried out tests with an experienced skydiver to measure angles, force and torques when performing various manoeuvres common in competitive skydiving. These results were used to design the brace to ensure optimal performance when flying. The final product is made of tencate E720 resin, carbon twill, glass twill and titanium joints at the hip. The carbon fibre has an ultimate tensile strength of 621MPa, and a maximum von Mises stress of 378MPa. The brace was manufactured by taking plaster casts of Ben’s legs and laying up the composite materials on these casts before the vacuum bag process. The brace was then assembled. 

Manning’s improved brace allows White greater control over his limbs when flying, with the titanium hinges at the waist granting easy mobility when moving from front to back, allowing him to launch from his wheelchair, making entering and exiting wind tunnels far easier. 

Jaime Ferrer-Dalmau of Entropy Resins EU spoke about the company’s bio-based and recyclable composites largely for use in extreme sports such as surfing. Entropy has developed a system called Super Sap, a sustainable epoxy resin that can be made from surfboards and other recycled fibre based products to create epoxy thermosets. The process uses acidic water at 95oC, and is described by Ferrer-Dalmau as very low on energy. The composite material is placed into the solution for one hour until the thermoplastic is solubilised and the fibre is separated. The material is then pulled apart, the valuable fibres separated and put aside, and the thermoplastic is precipitated through neutralisation. The thermoplastic takes on a solid form, and is recovered for re-use in the manufacture of surfboard fins. 

Elite materials, elite sport

Stefan Mohr, Team Leader for R&D Predevelopment Racquet Sport at global sporting goods company Head, outlined its many branches in various sports, including diving, winter sports and tennis, and talked about the materials used to make high performance racquets. They contain 180g of complex carbon and glass fibre composite, 30g of steel, 40g of PU-parts in the handle and grip, 20g of lacquer, 30g of plastic in the form of grommets and 15g worth of strings made of a combinations of plastics and natural gut. The racquet head can withstand up to 30kN of implosion force, and up to 2kN in peak forces from ball impact. Mohr highlighted that the racquet must also be deal with external influences such as impact with the court and net.

In their closing remarks, Dr Peter Giddings and Matt Scott of the National Composites Centre (NCC) recounted their 2016 Olympic story of providing the Australian cycling team with four chainrings that were pre-formed in seven hours. Traditionally, these parts are manually laid up, stacking materials by hand to form the composite product. In this case, the NCC used automated fibre placement (AFP). Material is fed, laid and cut into narrow unidirectional strips, and is heated using laser homogeniser optics before being pressed onto the previous layer. The layer then cools once the press has moved on, and the process is repeated. 

The NCC said that using AFP over the manual process offers a 90% reduction in lay-up time. It offers what Giddings and Scott called a pyramid cycle design, which included rapid inquiry response, manufacturing expertise with AFP, access to an advanced thermoplastic preforming facility and an improvement over existing manufacturing. 

Composites in Sport is set to return in 2018 for an extended two-day event.