Twelve months ago the German Association for Materials Research and Testing (DVM) had held a first workshop on “Service strength in bicycle construction” in cooperation with DIN, the German Institute for Standardization. The feedback had been positive enough to organise a follow-up workshop. It had was managed by the meanwhile founded working team “bicycle safety” with Dr. Eric Groß of Technische Universität Hamburg-Harburg, Siegfried Neuberger of the German two-wheel-industry association and the bicycle expert Dirk Zedler of lngenieur- und Sachverständigenbüro Zedler, as members.
The workshop offered a wide range of issues. The contributors were experts, mainly from research and industry. 53 percent of the 70 attendees came from the industry, one from the aircraft manufacturer Airbus, 27 percent from universities or institutes and 10 percent registered as experts. No more than one percent of the attendees was from the trade sector, the other attendees being classified as ”miscellaneous“. From this partitioning one could already expect high-quality speaches.
Carbon Findings
Some of the contributors started by explaining the structure of carbon materials: Besides die cast components with short carbon fibres, it is primarily the fibre composite components with long fibres that are well known. The finished components are made with a more or less high share of handicraft of fibres and the matrix as thermoset material.
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From this material structure one can draw two conclusions: First, it can be stated that not all components are equally suitable for being used for construction with carbon fibre material. Structures that can induce load cases on large component surfaces are particulary suitable. The extremely high fatigue strength allows very high numbers of load cycles.
Secondly, there is no such thing as ”the“ component, as due to the wide spread usage on the models the components handcrafted to a large extent are actually individual items.
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Dirk Zedler, Ingenieur- und Sachverständigenbüro für Fahrradtechnik, Ludwigsburg: “Many problems with bicycle components made of CRP arise from false expectations of the customers and a lack of knowledge of the mechanics in the cycle shop. Continuing training for dealers and mechanics are absolutely necessary; the specialised press is in charge of delivering profound and realistic reports and the final customer must be provided with clear instructions when he obtains his product.”
Conclusion
Carbon differs from other materials used for the construction of bicycle frames or components. This must be taken into account during construction as well as during manufacture and quality control including the extensive tests and test procedures. The special characteristics of the composite materials must, however, be considered to some extent by the standards, as well. The first steps in this direction have already been made: On the occasion of the meeting of the CEN TC-333 (Technical Committee for Cycles) in September 2009 it was stated that special attention should be drawn to composite materials, even with regard to the standards already in force. But the experts of the sector have already been sensibilised by the DVM workshop. This pushes a lot the issue of carbon as construction material in the cycle construction as well as bicycle safety in general.
Author: Jörg Kreinjobst
