13 Matt Appleman On Carbon Fiber

Appleman Bicycles in Orange County, CA is the brainchild of Matt Appleman. After an injury called an end to his 10 year long bike racing career, he decided to pour the knowledge gained through his college Composites Engineering degree and work experience into building carbon fiber bikes.  Today, he builds custom carbon fiber bikes to suit the stiffness needs of a rider. The base price for a frame, fork, and headset is $3,500 and this includes a standard "three panel" paint job.

Besides bicycles, Matt has worked in the aerospace and wind energy industries. "From 150 ft, 13,000 lb wind turbine blades, to 2 lb bike frames... I've used composites to build them all!" he would tell you.

Matt is a follower of my blog and recently contacted me to express his extreme satisfaction (or dissatisfaction) with my website. After having learned his credentials, I chanced upon the opportunity to shoot him a couple of simple questions on CF without getting into an erudite discussion. His reply is as below. If you have further questions after reading it, feel free to contact Mike through his website or start a discussion here.


Me : Matt, you must be quite confident in carbon fiber's material properties for bicycle applications. I too believe in its benefits when properly applied. But when it shows its limitations, the consequences aren't so good. For the rest of us, tell us what makes a carbon fiber frame weak?

MA : Well it depends on a bunch of factors.

1) Material Properties : The inherent weakness of carbon fiber is that it is brittle.  Carbon fiber composites have low elongation (typically 1-1.5%).  The brittleness of carbon fiber can be seen from sudden impact forces like riding into a curb or large pot hole.  These impact forces can bend the frame/fork to the point of catastrophic failure.  The frame needs to be sufficiently strong to absorb impacts and transmit the force throughout the frame.

2) Design (or lack thereof) : The “layup schedule” or the number of layers and direction of carbon fiber is the most important aspect to building a strong bicycle.  For structure, bicycles use unidirectional carbon fiber meaning that all of the fibers run in the same direction (an isotropic material).  Woven fabrics are typically cosmetic.

Unidirectional carbon fiber is  30 times stronger in the fiber direction than perpendicular to the fibers. The angle of the fiber directly affects the strength of a frame!

There are many forces applied to a bicycle while riding it and each tube resists a unique set of forces. Each tube requires a unique diameter, number of layers, and fiber directions.  The true beauty of composites is that you can pick the direction of the strength.  To save weight, material only needs to be added in a select number of directions.  A carbon fiber frame with tubes designed with equal strength in all directions (anisotropic) would weigh at least twice as much and be overbuilt!  Unfortunately, frames often fail because of forces not considered when designing the layup schedule.  There is always a balance of weight and strength.

3) Manufacturing Methods : Then there are manufacturing methods. There are a 101 ways to manufacture a carbon fiber frame, but no matter how the frame is made, air voids can be present.  Air is the true enemy of composites.  Air can be trapped between layers of carbon fiber during the layup process.  If the air is not removed prior to the resin curing, a void will form.  For reference, a void content of <3% is considered acceptable in most composite industries.  The void is a stress riser that enables cracks and delaminations to propagate.  Whether failure occurs depends on the size and location void. 

Me : How do your bikes take care of this weakness issue?

MA : Appleman Bicycles uses high strength carbon fibers and toughened epoxy resin.  The carbon fiber is pre-impregnated with the resin to provide consistent  resin content and low weight.

By using a multitude of angles, the layup holds tubes together while transmitting loads and forces throughout the frame.  The loads are distributed along the length of the tube as well as throughout the cross-section producing an extremely lightweight and robust structure.

During my time working in the wind energy and aerospace composite industries, I’ve witnessed and developed hundreds of cure schedules.  Using my background, I designed new cure schedules specific for my process of building bicycles.  By using heat and pressure, air is extracted from the laminate prior to the resin curing.  After the air is removed, consolidation of the layers of carbon fiber is realized until the resin is cured.


Me : Thank you for your time!


SEE MUCH MORE RELATED READING ON THIS BLOG :

Effect of BVID On Carbon Fiber Bike Frames 
Broken Steerer Tube : Composites Are Not Perfect
Aspect Ratios & The Spirit of Cycling as a Sport

Cannondale Six 13's Bi-Axial Braid Solution

How TIME Makes Carbon Fiber Reinforced Bike Parts

Nanotechnology Application In Bicycles : How Good?

Why Some Carbon Fiber Is So Cheap?

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1 Metallurgical Failure Analysis

Part failures are a common story in world of cycling - be it metal or composite parts. If you have ever experienced a metal part failure yourself that was a factor in any injury, have that part sent to someone knowledgeable in metallography.

Metals have existed for thousands of years and both their theory and their analysis have been perfected through science. Mainstream carbon composites sprang up during the 50's and 60's so understanding them is still bit of a niche field. But who hasn't bent or welded a metal part in their garage at some point in time?

Speaking of metal failures, agencies exist today that not only can analyze a specimen of a failed part blown thousands of times larger by microscopes but they can also perform chemical and impact tests on the part to determine if the composition of the metal was as per the specifications, and whether attributes related to heating - such as the thermal alteration during welding and cutting - had any part to play in the breakage.

A nice overview of these processes was provided recently by the ME Magazine. With this brief introduction, it may help you decide whether its something you want to pursue through an expert if the injury case is significant. This route may cost a good amount of money but both accuser and the accused can come to an agreement as to who was at fault in a technical and professional manner. One example of a case where metallurgic expert lent his insight to the victim of a bicycling accident was explored in one of my previous blog posts here. 

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5 Robic's Crash Scene

The scene of Jure Robic's fatal crash that left him dead is below. I was a bit late to the news but boy was I shocked to hear this. One day a great champion, next day, your number is up. I wonder if Robic had the chance to spend time with all the people he cared for before he passed on. 

Life's so short and precious that often I wonder about all the things you miss when you spend all your damn time and life around a dum bicycle, you know. I mean, so many other things matter more in life, doesn't it? 

Please take care out there while you exercise. While we mull at the loss, here's an interview that NYTimes did with Robic back in 2006.

31 Braking Induced Fork Failure

Here's another image of one of those braking induced fork failures that crop up from time to time. This was sent to me by a reader. The entire story of how the accident occured is mentioned on this blog.

Because of the lack of telescopic front suspensions like those nice mountain bikes have, rigid forks take the full brunt of a combination of two forces. One is the braking force that acts longitudinally backward to direction of motion but this has a component along the axis of the fork as well. The other is the force due to braking load transfer towards the front of the bike. This force acts inline with the fork axis. In essence, the two forces add together. I'm fairly certain that the quantity of this directed force along the fork is strongly dependent on the wheelbase of the bike and the rake angle of the fork. Lower wheelbases equate to more load transfer. Higher rake angles must also promote higher fork forces.

Undersized, thin walled tubes, such as forks, do not act kindly to hard braking forces. An example of this kind of buckling along with its physics was provided sometime back on my blog.

Thanks for reading. Have an enjoyable weekend and exercise safely.

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