Carbon fiber: Cutting-edge technology serving mobility
Carbon fiber’s properties and the clinical connection for wheelchair users
Motion Composites was created from the desire to improve the wheelchair industry by taking advantage of carbon fiber’s excellent physical attributes. When the company’s founders explored this sector, they immediately saw that the industry would greatly benefit from using carbon fiber.
*The following text was written by Sarah Matson, OT Reg., of Ontario.
A brief history
Carbon Fiber fiber was first discovered by Roger Bacon of Ohio in 1958. The high-potential strength of carbon fiber was realized in a process discovered by Leslie Phillips, a British engineer, in 1964. For the last 50 years, carbon fiber has been used commercially, mainly in the manufacture of high-end sporting goods and vehicles. The National Academy of Engineering named composite materials, including carbon fiber, one of the 20 greatest engineering achievements of the 20th century.
What is a composite material?
A composite material is a combination of two or more materials differing in form or composition that retain their identities. — National Academy of Engineering
What is carbon fiber?
Carbon fibers are filaments smaller than a human hair consisting mainly of carbon atoms. Several thousand filaments are bundled and used on their own or woven into a fabric. A composite is created when carbon fiber fabric is mixed with a matrix of plastic resin. This strong and light composite material, commonly referred to as carbon fiber, is used to manufacture vehicles, sporting goods and Motion Composite wheelchairs.
Carbon fiber property
High specific strength
Specific strength is also called strength-to-weight ratio or strength/weight ratio. It is calculated by dividing the material’s strength (force per unit area at failure) by its density. Carbon fiber has a remarkably high specific strength compared to metals (see graph below).
A wheelchair made with carbon fiber will be just as strong or stronger while also weighing less than a wheelchair made of titanium or aluminum. There is clinical evidence to support the use of wheelchairs made of the lightest material available for upper limb function preservation (1–4).
A 2002 study found that older adults who do not use their manual wheelchair report chair weight as a primary reason (5).
There is also some evidence that a lighter chair is easier to propel (6).
The primary benefit of a lightweight wheelchair is that it will be easier to lift. This is especially important to users or caregivers, who are required to lift the chair in/out of the car, up stairs or when traveling.
Carbon fiber has superior fatigue resistance compared to metals. This means that components made of carbon fiber will resist the repetitive stress of everyday use longer. Motion Composites’ carbon fiber wheelchairs withstood double the minimum number of cycles required on the NSI/RESNA* fatigue strength test of durability.
Exceptional durability means a more reliable, safer wheelchair with fewer repairs and superior cost effectiveness over the lifetime of the chair. This is important to the end user and funding agencies.
Durability and safety mean less risk of chair nonuse. A 1993 study looking at predictors of assistive technology abandonment found a 39% abandonment rate among wheelchair users (7). In this study Phillips found that devices were more likely to be abandoned when consumers felt they did not perform well. Factors listed as affecting performance included safety and durability.
*The American National Standards Institute and The Rehabilitation Engineering and Assistive Technology Society of North America work together to contribute to the public welfare by overseeing the creation, assertion and use of norms and guidelines and by developing assistive technology standards.
Low thermal expansion
Carbon fiber will expand or contract much less in hot or cold conditions compared to materials like steel and aluminum. This is a desirable quality for a piece of equipment that must operate in a wide range of temperatures.
Less expansion and contraction of the wheelchair materials means consistent interaction between the frame components, ensuring a smooth and comfortable ride regardless of weather.
Carbon fiber is one of the most corrosion-resistant materials available.
Wheelchairs made of a material that resists corrosion will be durable and cost effective over time.
Carbon fiber myths
- Rehabilitation Engineering & Assistive Technology Society of North America (RESNA). 2012. Position on the Application of Ultralight Manual Wheelchairs [position paper]. Retrieved from: RESNA: www.resna.org/resources/position_papers.dot. (2011). Position on the Application of Ultralight Manual Wheelchairs [position paper].
- Paralysed Veterans of America Consortium for Spinal Cord Medicine (2005). “Preservation of upper limb function following spinal cord injury: A clinical guideline for health-care professionals.” Journal of Spinal Cord Medicine, 28(5):434–470.
- Boninger ML, Koontz AM, Sisto SA, Dyson-Hudson TA, Chang M, Price R et al. Pushrim biomechanics and injury prevention in spinal cord injury: Recommendations based on CULP-SCI investigations. J Rehabil Res Dev 2005;42(3 Suppl 1):9–20.
- Requejo P, Mulroy, Haubert, et al. Evidence-Based Strategies to Preserve Shoulder Function in Manual Wheelchair Users with Spinal Cord Injury. Top Spinal Cord Injury Rehabilitation. 2008; 13(4): 86–119.
- Mann WC, Goodall S, Justiss MD, Tomita M. Dissatisfaction and nonuse of assistive devices among frail elders. Assist Technol 2002;14:130–9. [PubMed: 14651251]
- Cowan RE, Nash MS, Collinger JL, Koontz AM & Bonninger ML (2009). Impact of surface type, wheelchair weight and axle position on wheelchair propulsion by novice older adults. Archives of Physical Medicine and Rehabilitation, 90(7): 1076–1083.
- Phillips, B., & Zhao, H. (1993). Predictors of assistive technology abandonment. Assistive Technology, 5(1), 36–45.