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The researchers presented the functionality of their technology using a bicycle top tube demonstrator at the
The researchers presented the functionality of their technology using a bicycle top tube demonstrator at the "Research for the Future" joint stand at the 2019 Hanover Trade Fair.
( Source: K. Juschkat/konstruktionspraxis)

fiber composite Smart sensors detect damage to e-bikes

| Editor: Florian Richert

Scientists from the Institute for Structural Lightweight Construction at Chemnitz Technical University and the Merge federal excellence cluster have developed a technology that detects damage in fibre-reinforced plastics during component production.

Fibre-reinforced plastic composites (FKV) are characterised by low weight, high stability, and easy processing and are already being used in sectors such as aviation or mechanical engineering. However, damage in fibre-reinforced plastics is not always immediately visible. This entails risks, especially in the area of mobility.

Detect damage before complete failure

A new technology developed as part of a joint project at Chemnitz University of Technology is now providing a remedy. Scientists from the Institute for Structural Lightweight Construction and the Federal Cluster of Excellence Merge, together with their partners, have set up a process chain that allows the flexible embedding of so-called "smart sensors" already during the actual component production. In combination with a corresponding evaluation unit, the sensors ensure that damage to the component is detected before it even fails completely.

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Load and damage detection for the e-bike

The researchers presented the functionality of this technology using a bicycle top tube demonstrator at the Hannover Messe 2019. The top tube connects saddle and handlebar of a so-called pedelecs, a version of the electric bicycle. It is also an important component in load and damage detection - whether during regular maintenance or after a fall.

"This additional sensor function is particularly promising in the field of electromobility," explains Torsten Vogel, a researcher at the Institute for Structural Lightweight Construction at Chemnitz Technical University. He specifies: "Experts see the greatest development potential for integrated sensor technology in two-wheeler mobility because both in terms of environmental protection and energy efficiency, the bicycle is still the most suitable vehicle. As an e-bike, it is ideal for urban and suburban traffic. There, it provides an emission-free option for transporting individuals and is currently experiencing a correspondingly high market growth."

Reduce maintenance and condition monitoring efforts

According to analyses, the fleet vehicles of large companies or cities, in particular, are a rapidly growing, promising area of two-wheel mobility. An integrated sensor system with automated monitoring is, therefore, an optimal solution to keep the costs for maintenance and condition monitoring of the wheels as low as possible. It is also conceivable that this system could be used in other structures, such as automobiles, which are predominantly exposed to crash loads.

Previously separate production steps merge to form a material-efficient production process

"A major focus of the research project was the cost-effectiveness of production - a factor that could be guaranteed by the participants through the development of an integrated process chain," explains Vogel. The new process begins with the joining of the starting material, which consists of several thermoplastic FKV layers, and its thermal forming. A laser then exposes a small pocket for the sensor in the resulting component. The sensor in the form of a strain gauge is then inserted in an automated process. It can convert mechanical quantities into a measurable change in the electrical resistance and thus display the corresponding loads. Component production is completed by resealing the sensor pocket and adding reinforcing structures to stabilize the top tube by injection molding. Subsequently, an intelligent acceleration sensor is applied to the functional demonstrator to determine the shock acceleration.

Cooperation partners from the region support project

"Due to the promising objectives in the areas of safety and efficiency and the prospect of a broad implementation of the new technology, we were able to win numerous regional cooperation partners for the research project - an additional benefit for Saxony as a production and development location," Vogel proudly describes. The partners include Hugo Stiehl GmbH, which specializes in plastics processing; Nordmetall GmbH, an engineering firm that is mainly involved in determining parameters for numerical simulations (e.g. Forming and Crash Simulation); AMAC ASIC- und Mikrosensoranwendung Chemnitz GmbH, which develops various sensors and complete system solutions based on them; EKF Automation GmbH, which is active in the field of automation, robotics and special mechanical engineering; and the Fraunhofer Institute for Material and Beam Technology (IWS), which conducts application-oriented research and development in laser and surface technology. Project funding was provided by the Sächsische Aufbaubank - Förderbank - (SAB) and the European Regional Development Fund (EFRE).

Plastic sensors manufactured by microinjection moulding process

Scientists from the Federal Excellence Cluster Merge and the Institute for Structural Lightweight Construction are investigating complex lightweight structures that not only combine different materials but also integrate microelectronics, such as sensors or actuators, directly into structural components. In particular, the development of the necessary manufacturing processes is an essential part of their research work. For example, they have succeeded for the first time in developing a technology that makes it possible to manufacture plastic sensors only a few millimetres in size using the so-called microinjection moulding process. Their direct integration into semi-finished products based on plastics offers the advantage of material compatibility, which simplifies the material connection in the component, e.g. compared to metal-plastic combinations.