Georg Bardl

Evaluation of adhesive binders for the development of yarn bonding for new stitch-free non-crimp fabrics

Non-crimp fabrics (NCFs), especially multi-axial warp-knitted fabrics, are used as reinforcement materials for fiber-reinforced composites. The manufacturing of multi-axial warp-knitted fabrics by a conventional stitch bonding process to produce NCF has several disadvantages, such as filament damage, low production speed, yarn disorientation, etc. In order to overcome the existing limitations, the idea of using an adhesive binder to attach the fabric layers is a promising approach, so that the use of stitching yarns can be eliminated. The fundamental investigations presented in this paper show that the selection of the binder material has a major influence on the parameters of the textile products. Whereas the tested hotmelt adhesives offer a short curing time and a small but nevertheless sufficient bonding strength between bonded yarns, the tested reactive adhesives show a bonding strength up to 10 times higher, but at a considerably longer curing time. The reason for the different bonding strength is identified in the different penetration into the yarns. The experiments also show a significant influence of the fiber type and sizing, which needs to be taken into account when selecting fabric binders.

Adhesive Systems for the Production of Multi-Layer Bonded Fabrics for Composite Applications

Nowadays Non-Crimp Fabrics (NCF) are of substantial use in the field of technical textiles. Due to their lightweight, multilayer set-up, NCF became to an important factor for several technology sectors, i. e. automotive, wind energy and civil engineering. In order to eliminate known drawbacks of current manufacturing technologies, to enhance mechanical properties and to increase production speed of such NCF, a novel technology is proposed. This manufacturing technique is based on the adhesive bonding of layers made of high-performance fibres. Different adhesives were investigated to check their wettability and adhesion properties in relation to the high-performance fibres made of carbon or glass. Furthermore, the interface between the adhesive and a classical matrix for fibre-reinforced plastics was examined.

Warp Knitted Textile-Based Sensors for In-Situ Structural Health Monitoring of Wind Turbine Blades

The structural health monitoring of large-scaled fiber-reinforced composite components plays a crucial role for the further advancement of lightweight design approaches for a large-range application spectrum. Using textile-based and technological integrated stress sensors within the composite’s textile reinforcement, the detection of serious structural damages on early stages as well as an in-situ monitoring of mechanical loading conditions in inaccessible areas within immediate distance of the load-bearing layers of the subsequent composite component can be realized by those in situ condition monitoring systems, enabling the possibility of just in time maintenance or even local repairs before full structural failures occur.

Robot-guided eddy current measurement of yarn orientation change during stepwise 3D draping

The production of high-performance carbon fiber-reinforced plastics (CFRP) involves the draping of the carbon fiber fabrics to a 3D shape, a process which changes the orientation of the load-bearing fibers in the fabric and therefore has a high impact on the strength of the final composite part. This paper investigates the change in yarn orientation during the 3D-draping process of biaxial carbon-fiber non-crimp fabrics to a hemispherical shape. The draping process is partitioned in several steps, after each of which the yarn orientation in the fabric is measured by a robot-guided eddy current scanning system. The results show that the greatest change in yarn orientation occurs in the final stages of the draping. Furthermore, the yarn orientation change is not linear – in some regions, later draping steps reverse the yarn orientation change from earlier steps. These results are of high importance for a better controlling of the textile draping process.