Sunday, 25 September 2016

Carbon Frame Life Span

Almost three decades have passed since the emergence of carbon fibre and while the material dominates all but the low end of the road bike market, the reputation of carbon fibre still seems marred by the industry’s early efforts. The first carbon bikes (such as Look’s KG86) were far from robust or reliable. Carbon tubing was bonded to aluminium lugs and while the frames were significantly lighter than their steel counterparts, it was a devastating mismatch of materials. Galvanic corrosion (and to a lesser extent, UV exposure) would defeat the epoxies in use at the time and the frames would fall apart.

How about today? Do carbon frames have a shelf life? Should you be worried about your carbon frame wearing out? Scott Nielson has worked with carbon fibre for over a decade, starting with Trek, and is now the vice president of research and development and engineering at Enve. “If you look at carbon materials in general,” he said, “they’re very good in fatigue, much better than any aluminium or steel would be. If done properly, a frame could last you forever.” The reason for such confidence is the extraordinary durability of carbon fibre. “Composites do not behave like metals,” explained Chuck Texiera. “In fact, they don’t actually fatigue like metals in the same classic sense of the word. The fatigue life of the fibre itself is just about infinite.

Carbon bike frame is a matrix of two different materials: the carbon fibres which give the frame its structural strength, and the resin which binds the carbon together. They each have different properties, both physically and chemically, which determine the frame’s structural integrity. “It is truly a matrix,” said Grelier (Scott Bicycle). “The resin is the material that joins all the fibres together. They have to match each other really well, then you will have a better material.” It is an understanding of the interplay between the two components of the composite that has developed in recent years, improving the quality of the reliability of carbon composites.

The carbon fibres used are very strong, but the resin needed to hold them together is potentially susceptible to degradation over time. Thomas Leschik, chief technology officer at Lightweight highlights this degradation as a factor which will alter the frame’s properties. Resins used in carbon-fibre composites are heat-sensitive and manufacturers recommend that bikes are not kept in hot environments such as inside cars. But again this is not likely to be an issue except in extreme cases: curing of carbon frames takes place at well over 100°C and it’s unlikely that this temperature would be reached once the frame leaves the factory.

UV radiation is another potential cause of degradation of the resin. But carbon frames are routinely painted with UV-resistant lacquers and paints and modern resins are designed to have intrinsic UV and temperature resistance too. Prolonged exposure to intense sunlight might lower the lifetime of your frame. “Somebody riding every day in the desert and having 12 hours’ full sun exposure and extreme heat would have a different effect than an average rider,” says Thomas Trapp, head of engineering at Focus Bikes.

The weakness of carbon composites 

While carbon fibre composites have a high strength to weight ratio, they are highly susceptible to high loads over a small area, such as an impact. Once the integrity of the composite is compromised, the matrix essentially starts to crumble and must be repaired or replaced. In the absence of any impact, the matrix can deteriorate with use, but it takes an extremely long time. “The epoxy matrix will at some point start to form little cracks,” explained Chuck Texiera, “and then over time it will just have the connectivity of the fibre. So really what’s happening, over really extended periods of time, you can expect the stiffness of the frame to change ever so slightly but it’s such a small number. We can measure it but I really wouldn’t think it would be perceivable. But it takes hundreds of thousands of cycles to even get to that. Two years would be far too short for that to occur with any kind of typical age group racer.”

Improving the impact resistance of carbon composities

The impact resistance of carbon composites has improved in recent years to the point where MTBers are now truly embracing the material. The advances are largely due to innovations in resin technology. “We have the materials that are stiff enough,” said Benoit Grelier, “but the goal is now to work with some materials that have strength in case of an impact. We have had some good results by playing with the resin and nano-components.” “Standard resin is like oil and nano-resin is like water,” explained Grelier. “If you throw oil onto a mesh, it won’t go inside because it is thicker, whereas the water will go directly inside the mesh. If I use a nano-resin, it will go deeper into the fibres and the final bonding will be better.” Chuck Texiera has seen the same kind of results. “The fibre is quite good and quite tough and it actually hasn’t changed much in thirty years,” he said. “It’s the resin systems that have continued to evolve, become tougher, to fill in voids and create better bridging. But there’s still room for improvement.” Scott Nielson agrees. “They’ve been working on nanomaterials for years and now we’re seeing new materials coming out that are taking advantage of some of those nano-enhancement or nano-tougheners. It’ll be interesting to see what happens. I think it’s a good start but there’s a long way to go for those materials to really truly yield a dramatic improvement.”


Composites: Composites is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components.

Resin: Resin is a hydrocarbon secretion that comes from many different types of plants. It also comes from many types of coniferous trees, like pine trees. Generally, resins are insoluble in water. Although resin is most often used in its natural form, synthetic resins are also popular, and make the base for things like epoxies, polyesters and silicone. Resin, whether natural or synthetic, usually dries to a hard, transparent or opaque consistency.

Cycling Weekly 2016/08/11

Ride On!

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