The demands of the automotive industry for weight saving design have led to the construction of lightweight auto bodies. However, at the same time, drivers want greater comfort and safety but this need calls for additional weight. As a result of this demand, high-strength lightweight steels have been developed to improve vehicle passive safety, decrease weight and lessen fuel consumption.
© Fotolia, 2012
High strength combined with high ductility and toughness is made possible by increasing the so called "strain hardening behaviour". However, no in depth investigation of this behaviour had ever been undertaken.
STRAINHARD was a Research Fund for Coal and Steel (RFCS) project that began in July 2004 and lasted for three years. With European Union (EU)-funding of €711,962, it investigated the behaviour of these different types of lightweight steels already used in cars. The project's ultimate aim was to understand the structure of these steels and their behaviour in different conditions such as in heat and under high stress.
The project had three main objectives. Firstly, parameters on strain hardening behaviour such as temperature, stress state and strain rate were examined. With the obtained results, the team then evaluated and improved existing strain hardening models. Microstructures with an extraordinary strain hardening behaviour were then identified. Finally, by combining the strain hardening behaviour with the microstructure characteristics, microstructures with extraordinary strain hardening behaviour were identified.
STRAINHARD was coordinated by the Rheinisch-Westfälische Technische Hochschule in Aachen, Germany but had research and industry partners in Spain, France and Germany . "In essence, STRAINHARD was a research project but results could in the future contribute to the design of microstructures in new lightweight steel," says Thorsten Labudde from lead partner, Aachen University. "Component crash tests performed in the project's last phase showed promising results and could pave the way for the increased use of these steel grades and future commercialisation," he adds.
The project has not only improved knowledge on strain hardening behaviour; it could lead to economic, raw material and energy savings due to lighter vehicles and higher fuel efficiency becoming the norm. Light weight steel is also cheaper to use in car construction than plastic. And crucially, safety could be improved as a result of better crash performance due to the ability to investigate, simulate and predict the steel's behaviour.
Results of STRAINHARD have been shared with steelmakers, automotive suppliers and carmakers, delivering deeper knowledge in the forming and crash behaviour of light weight steels. This knowledge enables the tailor-made application of steels contributing to both passive safety and light weight design.
Such light weight steels will be crucial for the body of the electric car, which requires lightweight design. "The change from conventional to electric cars will not only be crucial for the sector, but offers new opportunities for design and material choice," concludes Labudde.