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Good image and superb looks, low weight and high strength are characteristics everybody immediately thinks of. But particularly with carbon, mistakes made in construction or manufacturing can lead to considerable component defects. For a better understanding, Zedler made a quick side trip to explaining the material.
Carbon is a compound structure of graphite and a matrix material serving as carrier (thermosetting and thermoplastic plastics). Graphite is used in the form of fibres. The individual fibres can be as short as 0,5 millimetres in order to add strength to injected plastic components. Usually, weaves of long individual filaments are put into a mould which is casted with as little filling material as possible, as the latter does not provide any additional strenght itself. This is the way, carbon parts are usually composed. The typical looks, however, are accomplished by a varnished top coat which is only of cosmetic importance. Already the appropriate use of the material in construction is decisive for the quality of the product. This is, because carbon - unlike other materials - does not have fixed material parameters. These are determined by shaping it in a material-fitting way and factors like number and alignment of the layers lying on top of the other.
Another source of trouble is manufacturing with considerable quality diversification being a possible consequence. Because of this, glaring variations of the life span are often determined in fatigue tests. Therefore manufacturers should consistently conduct 100-percent-controls. In these controls, results should be documented by allocation of the serial number. Anomalies of serial products can be detected with the aid of strength tests. An interesting additional advantage is that after an accident, conclusions about possible damages can be drawn by conducting comparison tests. Faulty structures deliberately worked in, which can be judged by taking an x-ray after an accident, are still being tested.
Nevertheless: carbon parts ideally constructed, whose fibres are material-fittingly only strained in the pre-determined direction, theoretically has an unlimited life span. Bad products made by negligent manufacturers or wrong use can damage the reputation of a principally good material. The conclusion to be drawn from all these facts is that carbon parts are expensive and not always unproblematic.
In general, Dirk Zedler considers the use of carbon for certain parts critical. Rims have a bad coefficient of friction with the brake pads, the stopping distance is increased considerably. Seat posts and fork steering columns are easily damaged by clamp slots.
Another problem is the insecurity arising from improper assembly or damages caused by crash or accident, as pre-existing defects of a part visually often cannot be detected. Carbon parts to not bend, they break. Also corrosion can harm carbonframes when aluminium parts laminated into the frame (e.g. threads) are not taken enough care of and blossom. At this point, it has to be pointed out that carbon parts must never be greased at the clamping area! Varnished clamping areas often make life difficult for mechanics. In case of doubt, you should gradually grope your way to suffient clamping force with the aid of a torque handle. Carbon stems have hardly any advantages over well made aluminium parts. Carbon saddles have to be chosen very carefully with regard to shape and comfort.
Ossweiler Blaettle, 2019/03/28