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Particularly in terms of carbon fiber (CF) rovings and further high performance fibers, it is a highly demanding task to clamp technical yarns with low elongations at break during high-speed tensile tests due to their sensitivity to shear stress. For fibers to be tested, a low elongation at break results in short testing times and requires high acceleration. In this paper, four different yarn grips that can be applied with various test machines will be introduced and compared to a wedge screw grip. By using most sensitive CF rovings, advantages and disadvantages of these gripping devices will be qualitatively evaluated by means of testing machines with test speeds of up to 20 m/s and strain rates of up to 200 s−1, respectively. Hence, the reproducibility and precision of test results were considerably enhanced by optimizing the geometry and mass of yarn grips. Moreover, theoretical approaches and calculations for the design of yarn grips suitable for test speeds of up to 100 m/s will be presented.

Warp knitting creates very challenging dynamics due to its high production speeds. On the one hand, this makes it method of choice for many products in various fields. On the other hand, not all materials are suitable for such high productivity. With the current generation of machines being limited to only achieve their maximum speed of around 4,400 min−1 with highly elastic yarns, it is desired to gain a deeper insight into yarn behavior in such highly dynamic environments. Among other influences, resonance effects gain high significance as they may result in high loads on the used materials; therefore, yarn breakages interrupt the production and decrease the quality of the product. To extend the material choice, especially high-performance fibers, for high productivity, a deep understanding of the intrinsic properties of the yarn is required. In particular, the viscoelastic properties are of importance. This study proposes a method to determine these characteristics using the dynamic mechanical analysis method. For the purpose of finding the damping in the transversal direction to the yarn axis, the variant of free oscillation is chosen. For the trials, a high-speed camera is suspended above a testing rig. On this rig, a yarn sample is clamped and then displaced from its rest position. The resulting oscillation is recorded and later extracted from the video. From the decrement of the maxima of the amplitude and corresponding time intervals, the damping factor is determined. It decreases with higher initial deflection. Summarised the developed trial setup proved suitable for the determination of the viscoelastic properties in transversal direction. [ABSTRACT FROM AUTHOR]

This paper presents the simulation-based development of a novel knitted design of textile heating structures based on dedicated serial-parallel circuits for heating (DSPCh) using silver-plated yarns processed via knitting technology. The DSPCh approach features dedicated and spatially bounded sub-circuits, ensuring even heat distribution and resilience against circuit failures in smart textiles with heating functionality. The study finds that the conductor arrangement and knitting pattern significantly affect the heating performance. DSPCh structures achieve even more heat distribution than serial and parallel circuit designs. Due to its binding, the developed basic pattern based on the right–left knit is less electrically conductive than that based on the right–right knit. Results show that DSPCh structures exhibit a favorable heat level and uniform heat distribution suitable for wearable textiles close to the body. The comparison with other circuit designs demonstrates higher temperatures of maximum 132°C and temperature differences up to 100 K, making DSPCh structures suitable for functional underwear. In addition, the experiments reveal that the heating performance is minimally degraded after standard machine-washing and care protocols. The investigations demonstrate that the DSPCh structures are suitable for actively heatable functional underwear, and simulation tools can aid in predicting temperatures and heat distribution for various textile designs. [ABSTRACT FROM AUTHOR]

Considering their energy and resource efficiency, fiber-reinforced plastics (FRPs) have been displacing metals and metal alloys for lightweight constructions. During the semiautomated manufacturing process of FRPs, and in particular during the laying of reinforced fabric layers, foreign bodies are enclosed within them, which in turn reduce the mechanical performance of FRPs. The research project presented in this article investigated if the loss in mechanical properties, such as tensile, flexural, and impact strengths, depends on the position of defined local defects, polytetrafluorethylene (PTFE) in this case, in the thickness direction of FRPs. In order to achieve this aim, PTFE was placed in different layers of reinforcing fabric before infusion. Subsequently, the mechanical performance of the fabricated FRPs was tested and evaluated. On the basis of the experiment, it can be concluded that the loss in mechanical properties was maximal if PTFE was laid in the middle position of FRPs in the thickness direction.

There is a considerable need for research to fully exploit the application potential of adaptive fiber-reinforced plastics based on functional materials, in particular with regard to industry-specific solutions. Hence, this paper presents the development of a locomotion mechanism based on fiber-elastomer composites with shape memory alloys. In order to attain this goal, shape memory alloys were textile-technically integrated into the reinforcing fabric in the weft direction using flat knitting technology. The functionalized reinforcing fabrics was infused by the vacuum assisted resin infusion with an elastomeric silicone matrix system. Later, an extensive electro-thermal-mechanical characterization of the fiber-elastomer composites by varying electrical power caused by the varying voltage amplitude was completed. The fiber-elastomer composites were then shaped in a cross-country ski as an example of locomotion mechanism. Finally, the forward movement of the cross-country skiers was realized by activating the shape memory alloy in the left and right leg. [ABSTRACT FROM AUTHOR]