A steel spring can be replaced by a composite structure that is up to 70% lighter while retaining properties tailored to a specific application. The technology was developed by a team at Lublin University of Technology. The springs could be used not only in automotive and e-mobility applications, but also in vibrating machinery. The solution has already completed its first commercialisation step and a pilot series is now being sent to companies for real-world testing.
‘Our solution breaks away from traditional geometric concepts. By using composite materials instead of steel, we can modify the properties while significantly reducing weight — by as much as 70% compared with steel equivalents,’ says Prof. Patryk Jakubczak of Lublin University of Technology.
The research team developed a spring made entirely from polymer composites reinforced with carbon, glass or aramid fibres. It is not simply a conventional coil or leaf spring reproduced in another material. The design uses a different geometry and exploits the properties of composites through in-plane deformation and controlled buckling.
By arranging the composite layers and fibres appropriately, engineers can determine at the design stage how the spring will behave, including the force required to deflect it and the amount of deformation it can withstand. The force-deflection relationship can also be shaped to create, for example, a progressive response. This makes it possible to tailor the spring to a specific application.
The composite is corrosion-resistant, electrically insulating and unaffected by magnetic fields. These characteristics open the door to applications beyond conventional mechanical systems.
‘Composite springs can be used primarily in the automotive industry, bicycles and e-mobility, where weight reduction is very important, but also where the ability to tune mechanical properties matters,’ Jakubczak says. ‘During the project we also found significant potential in machinery, particularly vibrating equipment such as feeders, conveyors and vibrating tables.’
Wheelchairs, including electric models, are another possible application because lower weight must be combined with comfort-related performance. In vibrating machinery, the low mass of the composite reduces inertia, while the material also offers good vibration-damping properties.
Work on replacing steel springs with composite alternatives has been under way globally for decades. In 1982, SAE described a 3.6 kg Liteflex composite leaf spring that replaced an 18.6 kg steel component. Before deployment it completed 58 million fatigue cycles in laboratory tests and more than 5 million kilometres of vehicle testing.
Composite springs are already commercially available in markets including the United States and Germany. According to Jakubczak, however, many competing solutions rely on a fixed catalogue of springs with predefined parameters, forcing machine designers to adapt their equipment to available components. The Lublin team wants to reverse that process by designing the spring around the requirements of a specific machine.
‘Our innovation lies in the ability to shape the spring’s properties according to what machine designers actually need. Every production line has unique parameters — mass, required frequency, number of supports and geometric constraints. We can tailor the spring so that it is as efficient as possible in that exact application,’ he explains.
The team has already built demonstrators and tested them in laboratory conditions. It is now carrying out application-specific tests. A steel spring cannot always be replaced directly by a composite one; in some cases additional calculations and changes to mounting or attachment methods are required.
The process is easier when equipment is designed from scratch, because engineers can account for the spring’s parameters and operating principle from the beginning. The technology has already gone through its first commercialisation and the team is preparing another batch for a company that will test the springs under real operating conditions.
The technology draws on methods previously developed at Lublin University of Technology for the aviation sector. ‘The properties proved so distinctive and the microstructure of the composites so repeatable and controllable that we can now successfully adapt the solution for mass use in other industries,’ Jakubczak says.
The project is being commercialised through the PRIME programme of the Foundation for Polish Science. The project, titled ‘Composite springs for use in motor vehicles’, received PLN 313,900 in support from the European Funds for a Modern Economy programme. PRIME focuses not on further laboratory research, but on market validation, conversations with potential customers and preparing the technology for commercial deployment.
‘The challenge is convincing the market. Steel springs are well known, effective and reliable, but that does not mean they are the only possible solution. We need business partners willing to participate in R&D, and that requires time, materials and a willingness to experiment on both sides,’ Jakubczak concludes.
