Topic of the Month September 2008

No hollow achievement: hollow glass fibres embedded in carbon fibre reinforced plastic could be the key to safer products.
Photo by EPSRC

The use of composites is a successful approach when it comes to developing a set of technologically sophisticated properties for structural applications. Especially in the field of fiber reinforcement of materials and their processing, current research and development has resulted in exciting innovations that can provide optimized features and useful functionality for applications in a wide range of industries. More precisely, in the context of lightweight construction, durability, safety and design, users can benefit from new technology solutions that focus on the product range within the value chain of the wire and Tube exhibitions, making these products fit for the applications of the future.

Let’s start with a definition …

Composites are based on the intelligent combination of different materials, creating a new set of properties that cannot be provided by any single one of the materials involved. This concept, which is e.g. also employed by nature for wood and bones, aims at the targeted optimization of the required properties for a wide range of technology applications and permits the merging of apparently conflicting characteristics into a single material system. For example, composites may convince by their reliability in sophisticated semi-finished products, parts and components with high mechanical strength or extreme rigidity, despite their low weight. The principle of fiber reinforcement – e.g. through the inclusion of glass, carbon or aramid fibers – is especially useful for plastic-based materials in order to provide them with better specific, i.e. weight-related, properties than comparable components made of steel, aluminum or titanium while also allowing significant weight savings. These can amount to up to 60 per cent for steel.

Especially the world of fiber-reinforced plastics – or FRPs – keeps surprising the users with marketable innovations that, due to their frequently broad range of possible uses, translate directly into positive economic data of the industry. According to market research by Industrievereinigung Verstärkte Kunststoffe e.V. (AVK) in Frankfurt am Main, the European FRP industry grew by about 6.2 per cent in 2006. The total produced quantity of fiber-reinforced plastics over the same period in Europe reached more than 1.1 million tons.

Continuous fibers were industrially produced in the USA back in 1935 as reinforcement for material systems; soon afterwards, the term fiberglass established itself as a keyword for a material that reliably covers a wide range of requirements. Today, more than 70 years later, the innovation potential of this material class is still far from being exhausted.

The following paragraphs describe selected technological developments that demonstrate the engineering competence made possible with fiber-reinforced plastics. Interesting stimulus is especially provided for applications that can benefit from extended geometries, complex shapes and integrated safety features.

Lightweight, reliable and sustainable: Load-bearing construction elements

In July 2008, Europe’s first steel-FRP composite bridge was completed in the German town of Friedberg, Hessia. The overpass, which is 27 meters long and five meters wide, was designed and constructed within a multi-year cooperation project between the Hessian State Office for Roads and Transportation and the Institute of Building Structures and Structural Design of the University of Stuttgart. Criteria for this novelty included, among others, the advanced properties of this material class – fiber-reinforced plastics are considered robust and durable, have good ecologic characteristics and offer a wide creative margin for the implementation of particularly lightweight and efficient structures.

“Fiber-reinforced plastics will play a major role in bridge construction,” confirms Wolfgang Scherz, President of the HLSV. “While conventional reinforced concrete bridges are associated with long construction periods and equally long obstructions of traffic, a construction has been found for the bridge in Friedberg that is largely prefabricated, then transported to the site as a whole and lifted into place.” The follow-up costs also support the material selection. After all, conventional bridges require comprehensive maintenance already after 15 to 20 years. In contrast, the bridge made of fiberglass composites is expected to survive a period of up to 50 years without any repair.

Three-dimensional, complex and cross-industry: Components in defined shapes

The WOVENIT method from VISIOTEX GmbH is a new process for the manufacturing of textile structures in complex shapes which, when combined with suitable resin systems, can be used to build three-dimensional composite parts or components. For this purpose, the company developed a technology that integrates three textile manufacturing methods on a single machine and in a single process: weaving, weft and warp knitting. Formerly, structured fiber composite parts were mostly manufactured as individually made manual laminates, which is known as a time-consuming and expensive process.

In contrast, the new method permits precise series production at an industrial scale. In combination with the resin injection molding process and the corresponding resin systems, it enables the production of fiber composite materials on the basis of special technical fibers such as glass, carbon and aramid fibers. In addition to semi-finished products with defined discoid and tubular geometries, this process also enables the manufacturing of parts with more complex shapes, such as calottes, casings and profiles.

Intelligent, innovative and trendsetting: Self-healing tubes

The detrimental effects of component failures are widely known – expensive loss of production, annoying downtimes, long inspection intervals or even safety hazards are only a few but telling examples. In this context, fiber-reinforced materials can also set technologically relevant highlights. Scientists from the University of Bristol have presented an innovative technology in the context of their research project “Bleeding Composites”, which permits the self-repair of cracks and damage in composite components. According to project manager Dr. Ian Bond, epoxy resin that is embedded in hollow glass fibers will leak out in case of damage, closing and sealing the affected area in conjunction with a hardener.

Moreover, the color of the resin/hardener system differs from that of the base material, which serves as a visible indicator for any material damage that has occurred. This makes it easier for the technicians to detect cracks and other damage during scheduled maintenance and inspection of components and plants and to properly repair such damage or to replace the affected components entirely. The method that was developed by the British scientists is expected to be ready for the market by 2012.

Satisfy your curiosity and discover the helpful features of these FRP composites for your applications – for example through material and process substitution, functional integration or technology transfer.

Dr.-Ing. Christoph Konetschny
Materials Consultant and Nano Expert

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