Wednesday, October 27, 2010

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!

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

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  1. Been given a "Fuji SL 1 Carbon frame with the "Ritchey Carbon seat post epoxied into it!

    How do i break the seal without damaging the frame?

    i am 81cm but at moment the seat post only reaches 74cm, so need to solve problem to put the frame to use

  2. Good stuff!

    I'd love to read what he says about hand-built versus mass-produced, custom versus stock, ride quality versus stiffness versus mass, and reality versus marketing on trends in carbon frame design (BB30, tapered head tubes, ultra-thin seat stays, ISPs), and even on the advantage of carbon over steel or Al other than the obvious weight number (and versus Al, the difference is only a few hundred grams at most).

  3. P.S. On that previous question, it seems to me carbon fiber is held together with epoxy, so removing an epoxies seat post would be an issue. Could be post be cut and capped with a seat mast, like Ritchey's, or if that's too heavy, Woodman's?

  4. -> parrabuddy, sounds like you have quite the seatpost problem! Sometimes galvanic corrosion occurs between carbon fiber and aluminum. This corrosion could effectively bond the post into the frame. If the post is indeed epoxied in... the only way to remove it would be to machine out the post...not your standard procedure!

    ->djconnel, you have a loaded question! With regard to standard versus custom geometry ... the manufacturing methods vary drastically. Custom builders need to be flexible in their manufacturing process where major manufacturers don't. One benefit to custom is you get to communicate directly with the designer/builder ...good luck finding the builder(s) of mass produced bikes.

    ->all, feel free to contact me through my website!

  5. Anonymous1:30 PM

    Great interview!

  6. I enjoyed reading the interview and it had a lot of great information. However, it appears that Matt flipped the definitions of isotropic vs anisotropic materials. Isotropic materials have the same properties in all directions, whereas anisotropic materials have properties that vary with direction. No big deal, I just wanted to point out the mistake.

  7. Anonymous9:05 PM

    I'm not sure I appreciate how Matt uses the terms he does, but maybe he's trying to speak to the layman.
    The failure mode of carbon fiber reinforced polymers is a brittle failure. The ability to absorb stress without permanent deformation is strength, and the ability to resist fracture is toughness - also can be referred to as the ability to "absorb energy".
    Matt's example of a carbon bicycle failing from sudden impact forces is based on the strain rate, not because the material is "brittle".

    The use of the correct terms to describe mechanical behavior is helpful.

  8. Chris -> Thank you for the correction. My mistake for each use of iso and anisotropic materials. Isotropic materials have equal properties in all directions (metals). Anisotropic materials have unique strengths in different directions.

    Anonymous -> You are very correct in your definitions of material properties. I will add, that the term "toughness" has many definitions depending on the industry and test method used to measure it. In composites, toughness can be a measurement of material elongation, Izod/Charpy impact strength, and compression strength after impact, and many more.

    Thank you both for your correction & contribution.

    -Matt Appleman

  9. It's pretty amazing that Appleman can go from building turbines to bike frames! My buddy is a avid biker -- I definiently share this article with him. Thanks!
    Austin Cash Advance Blogger

  10. Thanks for the tech talk but speaking to us that have no engineering background. I was wondering if you could expand on djconnel's question of how a custom bike builder differs from mass production?

  11. @Anonymous

    Do you realize you've just specified yourself into being wrong?

    Yes, resistance to impact and other "higher" strain rate phenomena is best described by toughness and dynamic toughness values.

    However lower toughness materials (like glass type ceramics) are traditionally described as being "brittle materials" in many sources.

    To make matters worse, the act of increasing the strain capabilities and thus energy absorptive abilities of brittle materials is called toughening.

    Also, there are several engineering strength parameters, several of which go well into the yield zone of a material and deal with stress until rupture. Ultimate tensile strength for one.

  12. Cool tech stuff.

    From a rider's perspective I am a fan of carbon fiber. I became aware of some of it's properties when I switched my steel fork to a carbon on my steel Waterford bicycle. The difference in road shock absorption was amazing!

    @Matt Appleman: The trend with bike design is to go light and have big tube dimensions. I understand this, but also think it would be nice if there was also a choice for more aerodynamic bikes. I feel aerodynamics is far more important than weight for performance (racing).

  13. There are two main ways custom bike builders differ from mass production:
    1- Construction methods vary greatly, a book could be written on this subject! Custom builders have flexible processes versus mass production uses high volume and expensive tooling.

    2- Service and Design! Custom builders speak directly to and design the bike specifically for you... the customer! You work WITH the builder of the bike and have input on how the bike will look, feel, and ride. Good luck discussing your frame design with the engineer, designer, manufacturing technician, and painter in a mass production environment.


Thank you. I read every single comment.