Electrically conductive fibers are required for various applications in modern textile technology, e.g., the manufacturing of smart textiles and fiber composite systems with textile-based sensor and actuator systems. According to the state of the art, fine copper wires, carbon rovings, or metallized filament yarns, which offer very good electrical conductivity but low mechanical elongation capabilities, are primarily used for this purpose. However, for applications requiring highly flexible textile structures, as, for example, in the case of wearable smart textiles and fiber elastomer composites, the development of electrically conductive, elastic yarns is of great importance. Therefore, highly stretchable thermoplastic polyurethane (TPU) was compounded with electrically conductive carbon nanotubes (CNTs) and subsequently melt spun. The melt spinning technology had to be modified for the processing of highly viscous TPU–CNT compounds with fill levels of up to 6 wt.% CNT. The optimal configuration was achieved at a CNT content of 5 wt.%, providing an electrical resistance of 110 Ωcm and an elongation at break of 400%.

Abstract:In this work, typical high-performance yarns are oxy-fluorinated, such as carbon fibers, ultra-high-molecular-weight polyethylene, poly(p-phenylene sulfide) and poly(p-phenylene terephthalamide). The focus is on the property changes of the fiber surface, especially the wetting behavior, structure and chemical composition. Therefore, contact angle, XPS and tensile strength measurements are performed on treated and untreated fibers, while SEM is utilized to evaluate the surface structure. Different results for the fiber materials are observed. While polyethylene exhibits a relevant impact on both surface and bulk properties, polyphenylene terephthalamide and polyphenylene sulfide are only affected slightly by (oxy-)fluorination. The wetting of carbon fiber needs higher treatment intensities, but in contrast to the organic fibers, even its textile-physical properties are enhanced by the treatment. Based on these findings, the capability of (oxy-)fluorination to improve the adhesion of textiles in fiber-reinforced composite materials can be derived.

a b s t r a c tThe paper introduces a novel finite deformation thermomechanical interface approach, containing a realistic physical description of the delamination behavior of heterogeneous materials at their designated failure layer. Considering the interfacial layer as consisting of breaking connections between different materials of a heterogeneous structure, when loaded above their connective strength, the model approach introduces a damage type formulation, reflecting the state of delamination. The paper introduces not only the model formulation, it also contains its numerical treatment and its validation on testing examples. The physical background of the interface approach leads to a simple determination of the interfacial model parameter, which is demonstrated at an aramid yarn pull out experiment using HNBR rubber at elevated temperatures.

The integration of shape memory alloys (SMAs) into textile-reinforced composites produces a class of smart materials whose shape can be actively influenced. In this paper, Ni-Ti SMA wires are inserted during the weaving of a glass fiber reinforcement textile. This “active” reinforcement is then combined with an elastomeric matrix to produce a highly flexible composite sheet, which maintains high rigidity in the longitudinal direction. By activating the SMAs, high deflection ratios of up to 35% (relative to the component's length) are achieved. To adjust the composite's deflection to defined values, a closed-loop control is set up to adjust the current flow through the SMA wires. A control algorithm is designed and evaluated for several test cases. The high deformability and the controllable behavior show the high potential of these materials for applications such as aerodynamic flow control, automation and architecture.

Shape memory alloys (SMA) are a promising material class for active lightweight structure applications with movement functionality. Due to their high activation energy potential and good processability in wire shape, they are well suited for application in actively deformable, fibre-reinforced composite structures. In order to generate large deflections from the limited deformation potential of SMA, detailed analysis of the deformation mechanisms is required. In this work, a bionic approach is pursued, investigating the characteristics of locomotion systems of insects. A simplified joint concept is derived from the cockroach knee and implemented using flat knitting technology. A composite joint is manufactured with a resin infusion process and experimentally verified in regards to its motion behaviour. The presented results show good deformation behaviour with large deformation angles up to 60°, suggesting large potential for further development of the presented approach.