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Meet About Carbon Fiber

Carbon Fiber

Carbon fiber properties and the clinical

connection for wheelchair users

Sarah Matson OT Reg (Ont)

Clinical Educator Motion Composites

veloce-Carbon

Carbon Fiber

A brief history

Carbon 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 Philips, a British engineer, in 1964. Carbon Fiber - Clinical Connections.pdf
For the last 50 years carbon fiber has been used commercially mainly in the manufacture of high-end sporting goods and vehicles.

Carbon Fiber - Clinical Connections2

The National Academy of Engineering named composite materials, including carbon fiber, one of the 20 greatest engineering achievements of the 20th century.

Carbon Fiber - Clinical Connections3

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.

Carbon Fiber - Clinical Connections4

What is CARBON FIBRE?

Carbon fibers are filaments smaller than a human hair (top photo) consisting mainly of carbon atoms. Several thousand filaments are bundled and used on their own or woven into a fabric (middle). 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 (bottom).

Carbon Fiber - Clinical Connections5Carbon Fiber - Clinical Connections6

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).

Clinical Connectionto

High Specific Strength

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 - Clinical Connections7

Carbon Fiber Property:

Exceptional Durability

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.

Clinical Connection

Exceptional 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 non-use. 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.

Carbon Fiber Property:

No welding

Carbon fiber is not welded but rather molded into the desired shape

The heat treatment of metals can lower their strength considerably, up to 40% at welds

Motion Composites’ carbon fiber wheelchair side frames and crossbrace pieces are seamless and do not have joints (photo).

Motion Composites uses clamps around the carbon fiber structure instead of drilling through the frame and using bolt assembly.

Clinical Connection to

No Welding

A one-piece (monocoque) frame means less movement within the frame components, which results in improved propulsion efficiency.

The elimination of joints or welds yields a solid, seamless finish that is preferred for cleaning and infection control, especially in a multi-user environment.

The elimination of joints, drilling and bolt assembly contributes to the reduction in chair weight and improves durability.
Carbon Fiber - Clinical Connections8

Carbon Fiber Property:

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

Clinical Connection

Low Thermal Expansion

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 Property:

Corrosion Resistance

Carbon fiber is one of the most corrosion-resistant materials available

Clinical Connection

Corrosion Resistance

Wheelchairs made of a material that resists corrosion will be durable and cost effective over time.

Carbon Fiber Myths

Performs poorly in cold temperatures

Carbon fiber components are used extensively in aircraft and satellites, which are exposed to temperatures that range from
superheated to near absolute zero. Carbon fiber’s low thermal expansion properties make it ideal for extreme temperature changes.

Breaks or chips easily

Carbon Fiber technology has greatly improved over the last decade. It is now used in high impact applications such as baseball bats.

Catastrophic damage

Other carbon fiber wheelchairs and sporting goods (bikes, hockey sticks, etc.) have had a reputation for catastrophic damage that render the product unusable. The strength of a carbon fiber component is a function of its design. Since a layer of carbon fiber is strong only in one direction, some carbon fiber products (e.g., hockey sticks) are designed to flex and are therefore more susceptible to breakage. Depending on how the carbon fiber is laid and aligned, extraordinary strength in torsion, compression and flexion can be achieved. The Motion Composites design team worked for three years to determine the best fiber alignment for durability, lightness and propulsion efficiency.

 

References

1. 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].

2. 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.

3. 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.

4. 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.

5. 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]

6. 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.

7. Phillips, B., & Zhao, H. (1993). Predictors of assistive technology abandonment. Assistive Technology, 5(1), 36-45.