The weight of series production road bikes that are ready for use has meanwhile decreased to less than six kilograms, whereas the weight of the cyclist can be 100 kg and more. Thus the typical ratio between carrying structure and bearing load with factor 8 to 18 is very unfavourable compared to other vehicles and carrying structures.
Apart from the indeterminacy of the load to be transported the usage parameters vary a lot according to the user. The range includes the amateur cyclist who rides occasionally relaxed on smooth tarred roads, the road racer whose explosive sprints actually result in a twisting of the material as well as the downhillers and freeriders who burden their bicycles to and beyond the limits by long jumps and by crossing huge obstacles when riding their bicycles in the most challenging terrains.
Another unfavourable parameter for the usage of fibre compound materials with bicycles is the fact that contrary to other branches professionals do not construct and build for professionals, but that the components and bicycles made of fibre compound materials with their open technique meet more or less skilled non-professionals. It’s quite typical that good road racing cyclists think themselves to be good mechanics, what is actually not always the case. This leads more and more to damage, in particular with these materials.
Due to the fact the the fabrication of the sophisticated CFR constructions requires a lot manual operations and due to the intense cost pressure in the sector, bicycle parts, frames and forks are almost all fabricated in the Far East. A rather small number of manufacturers undertake the production for the big number of brands. Therefore, constant product quality can only be ensured by committed suppliers at high expenses. These are reasons enough for the second workshop of the DVM work group bicycle safety (chairman: Prof. M. Hanselka, LBF) to deal with test procedures and quality assurance methods in consideration of CFRP materials.
The first day three general lectures tuned in the participants on the range of topics and inspired the table talks of the joint dinner in the highly praised ambience of the Funkturm Berlin.
The second day contributors from research, industry and test institutes shed light on the topics manufacturing aspects, quality methods, test methods and test procedures in practice.
The perfect selection of contributors granted a look behind the scenes of the CFRP production status from the bicycle sector to Formula One.
As a result it could be stated that there are certain basic approaches that are worth being adopted at reasonable expenses. State and knowledge of the testing technology in the bicycle sector including relevant, available standards were compared to that of research at the university institutes. On this occasion it became clear once again that the load assumptions based on really assessed data need to be reworked in consideration of types of damage in practice. To date this has only been implemented by individual companies or university institutes. An exchange of experiences has, however, not yet got started.
Destructive test methods were explained as much as the various possibilities of non-destructive methods. In particular with regard to the latter it became clear that there are various possiblities, but only a few that are usable for bicycles. One reason for that is the insufficient documentation of initial states in the production, as a consequence of which reliable verifications in this country can only be carried out at high expenses and are therefore out of all proportion to the value of the component.
The interest of the 70 attendees from five nations was apparently very high and reflected in the committed discussions of the one and a half day long event. It was positively stated by insiders of the sector that the opinions had been exchanged with a rare frankness.
Among the bicycle manufacturers on the spot this frankness led to the conclusion that certain kinds of problems were not individual incidents. In this regard collaborations of the interested parties can be expected. To participants of the research it became clear that these conditions need to be adjusted due to the financial restrictions to which the testing and quality assurance of the bicycle manufacturers are subject.
In summary it can be stated that the workshop bicycle safety is an important event for the sector that gives impetus and that will be beneficial for the Eupean standardisation that has partly got stuck. The extension from one to one and a half day and the incorporation of a tour through a renowned institute, in this case through Federal Institute for Materials Research and Testing, were the correct decision and will ensure a continuation of the workshop.
Author: Dirk Zedler, graduate engineer, Ingenieur- und Sachverständigenbüro für Fahrradtechnik, Ludwigsburg