Carbon fibres – carbon composites
Innovation came out even in the trend of materials used for the production of bicycle frames and other components. Carbon composites are currently used in a large extend, especially because of their properties.
Duratec company produces composite monocoques with the use of a unique technology AFCF developed inDuratecDevelopmentCenter. High Modulus (HM) graphitised fibres are also used. Hugh modulus of fibres means that they are produced from finer carbon fibres with higher “Young modulus” – higher stiffness and strength. The higher the module, the higher the price of material and the better mechanical properties (see below) (link to AFCF)
Advantages of carbon composite use: low weight, high stiffness, great absorbing properties of strokes, high life span, very positive fatigue life (see the picture below), a very compact and attractive design coming out of the structure and type of fibres used.
Which material to choose for your bike? The above-mentioned advantages allure to choose a composite, but a regular user should be aware of disadvantages connected with using composites. They are irreparability and impossibility to service the bike.
We particularly emphasise this fact as our clients are used to “full service” which means that it is possible to have the frame rebuilt some years later (remove polish and varnish) and use it again. However, if you choose a composite it is impossible to ensure this service! It goes hand in hand with its irreparability. Rapture of fibres, fracture of tube or another damage of structure which we are not able to repair yet can occur in case of an accident, fall etc.
Price differences of carbon frames: We often encounter a question “Why prices of carbon frames range from CZK 18, 000 to CZK 80,000?” It is possible to differ from the very start of the manufacturing process. Difference can be found in the manufacturing material itself which is composite and it influences the resulting handling of a bike. The price is naturally higher when carbon from reputable brands as Hexcel or Toray (Japan) which guarantee the certification of material is used, but it also guarantees its quality and parameters defined in the standards. The price of material also depends on technical demands, on the so-called Young’s module of elasticity of a given material. As it has already been mentioned, the higher the demands are, the higher the price is. The difference in price can also be influenced by a chosen manufacturing technology of frames which is constantly developing. Development costs are covered from the sales of products which influences the final price of a product. In development it is about the development of manufacturing technology and the development of a technical design of a product. Required strength and stiffness of a frame construction depends on experience of a designer who proportions the frame and thus influences its features, particularly by the structure and number of cuttings per one piece of frame. To get a better idea we can state that model Cult CR3 consists of about 200 of cuttings. By lowering the number of cuttings the amount of used material is reduced and this reduction influences mechanic - riding features as well. The number of cuttings also reduces time needed for laying the cuttings and thus makes the production cheaper. The next factors influencing price can include the possibility to use the mould repeatedly and next the classic costs indicators as serial production, price of manpower, overheads etc.
TECHNICAL INFORMATION FOR THE CURIOUS
Characteristics of composite: material of two or more constituents with different properties which together give the final product new properties. At carbon composite, one of the substances is carbon fibres which give the product strength and second substance is a binder (the most frequent are polymer binders). The type of carbon fibres used influences the final mechanic properties of composite.
Characteristics of carbon fibres: There are many marketing bubbles concerning carbon fibres and technologies of processing these fibres. Their aim is to convince the public to buy a product. However, real differences in material are quite simple. The parameter of comparison is Young’s modulus of elasticity. Most carbon fibres are sold with module of elasticity of 33 MSI. These fibres can have smaller diameter which results in higher strength of cross-section. The modulus of a fibre referred to as Intermediate Modulus (IM fibres) is 42 MSI. The advantage of using higher MSI fibres is the use of smaller amount of material to reach the same stiffness and thus a lighter construction! However, IM fibres are more expensive because of higher demands on their production. It is possible to reach higher stiffness than in IM fibres by reducing the diameter of a fibre but increasing its thickness. HM fibres (High Modulus – 55 MSI and higher) which are rather expensive and brittle come into existence this way.
Carbon fibres are supplied in various sizes determined in thousands (K) of fibres – 1K, 3K, 6K, 12K, 24K, 50K and others. These fibres are woven into a fabric of different patterns – the most commonly used is 3K. Duratec uses UD (unidirectional) fibre the most often.