One of the prerequisites when there is need for high mechanical properties in a composite laminate structure is straight fiber alignment. In the vacuum infusion process the state-of-the-art reinforcements have been Non Crimp Fabrics (NCFs) which Ahlstrom is producing with the well-proven warp knitting technology. These fabrics, however, suffer to a greater or lesser degree from pronounced fibre undulation. With this as a background, Ahlstrom set a target of developing a production technology for reinforcements that would leave the yarns straight, while simultaneously providing processing properties that customers would be willing to accept, at a competitive price level.
Ahlstrom, supported by the FIMECC LIGHT programme, has been able to develop a new type of reinforcement that is anticipated to fulfil the objectives. The new unidirectional glass fiber reinforcement offers superior fatigue resistance and exceptional mechanical performance which is confirmed by extensive testing. After successful initial tests, the first version of this new reinforcement was launched on the market at the end of 2013. Currently the new product AceBladeTM is under customer evaluation and certification. In addition there is a patent pending.
The actual development work was carried out exclusively within Ahlstrom. Bringing this new material to market demands extensive testing of chemical compatibility of the materials, and of the processing characteristics and mechanical performance of the laminates. This has been supported by a Tampere University of Technology MSc thesis on binder compatibility analysis, and by an Aalto University PhD investigation into fatigue performance of laminates made of NCF and new reinforcements.
Stitched reinforcements are widely introduced in thick laminate sections like in spar caps for Wind Turbine Blades, as they are compatible with the infusion process and due it’s handling conditions. However, stitching is limiting their mechanical performance. Non-stitched, non-woven UD-fabrics have been attempted but have suffered from extremely poor permeability and handling characteristics. This compromise between performance and processing, drove Ahlstrom to seek a non-stitched solution compatible with the infusion process
The target application is wind energy blade structures, where ever-growing dimensions ask for extreme mechanical performance combined with lightness. The new reinforcement addresses the market need for longer and lighter blades. Through delivery of higher strength and stiffness as well as improved fatigue properties, longer and lighter blades can be manufactured with AceBladeTM. Estimated global usage of all fiber reinforcements for wind turbine industry alone is more than 200 kilotons per year and this newly developed material is expected to replace part of it. Other composite structures will also benefit from the new reinforcement type. Indeed, the product family will grow in near future.
Rainer Bergström, Ahlstrom Glassfibre Oy
Ahlstrom Glassfibre Oy, Tampere University of Technology, Aalto University