Fiber composite anchoring pins for the connection of several components
An additive joining technique developed at the University of Stuttgart makes it possible to connect individual components with each other positively using fiber-reinforced pins without the need for post-processing steps in the manufacturing process or foreign materials in the part. The technology thus opens up new possibilities both in the connection of individual components and in interlaminar component reinforcement.
In order to connect two fiber-reinforced solid bodies with each other, the state-of-the-art method currently used is adhesive or rivet connections.
These connections, especially the adhesive connections, are usually supported by a surface treatment of at least one of the two components, which can result in damage to the component even during production. In the case of any occurring tension loading, a riveted connection can even be the weakest point of an entire component group.
In this process, which has been developed at the University of Stuttgart, anchoring elements, so called “tufting pins”, are applied to the component at the same time as the supporting textile structure. A needle guiding the fiber material is pierced through the textile preform into the foam (supporting material) (figure 1A). The fiber material remains in the foam as a loop when the needle is pulled out. During the impregnation of the textile preform, the matrix penetrates not only the flat textile, but also the puncture holes in the foam and wets the loops.
After cross-linking of the matrix material, the foam is dissolved, and a fiber composite component is created – two or three dimensional – with integrated connecting elements (figure 1B). The pins either protrude into a component interior to be filled or jut out of the two-dimensional layer. By interlocking two facing elements, a form-fit within a joint can be achieved.
The number of pins per unit area, their size, orientation, and arrangement can be flexibly adjusted to create a connecting element that can be individually tailored to the component group.
- Reinforcement of FRP components and joints
- Force flow and transmission in the composite component continuously ensure resistance to temperature fluctuations due to material homogeneity in the connection
- High quality and reproducibility guaranteed by automated process
- Two-dimensional and three-dimensional components can be produced using flat or slotted foam
Fields of application
Example: Rear edge bonding of wind power rotor blades and aircraft wings
In particular, the connection of rear blade edges of rotor blades (wind turbines), but also the joint between the inner shear webs and the outer skin, are three-dimensionally loaded structural component areas. Currently, these connections are glued directly (figure 2). Thickened thermoset resin systems are used, which do not guarantee a form-fit of the joint. If shear loads occur in the bonded areas, there is thus a possibility of shearing off, whereby the bonded joint detaches and the component fails.
The wings of a wind turbine or an airplane consist of fiber-reinforced plastic, sometimes also of a sandwich structure with cover layers of fiber-reinforced plastic and an enclosed foam or honeycomb core. The implementation of the reinforcing pins as an additional component element would thus be a firmly bonded possibility of creating a form-fit within the adhesive bond to prevent shear failure.
The intention is to provide the two half-liners to be connected with reinforcing pins which interlock with each other when the half-liners are glued together (figure 3). The interlocking would create a three-dimensionally reinforced joint that can also be subjected to three-dimensional loads such as thrusts and shears. As can be expected, the strength of the adhesive bonds of such components could be greatly increased.
The fiber loops of the reinforcing pins can already be automatically inserted during the textile stacking process into defined areas while producing the half-liners. A Z-reinforcement, a connection between the individual textiles and in particular the sandwich layers, is thus simultaneously created in the entire component. Using such an interlaminar connection, the strength properties of a component are demonstrably improved, especially those exposed to load changes with deflections in which the layers are subjected to thrusts against each other.
Consequently, by adding the reinforcement pins which are presented here to the component structure, a fatigue-resistant high-performance component could be created.