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Due to their advantageous characteristics, shape memory alloys (SMAs) are prominent representatives in smart materials. They can be used in application fields such as soft robotics, biomimetics, and medicine. Within this work, a fiber–elastomer composite with integrated SMA wire is developed and investigated. Bending and torsion occur when the SMA is activated because of the anisotropic structure of the textile. The metrological challenge in characterizing actuators that perform both bending and torsion lies in the large active deformation of the composite and the associated difficulties in fully imaging and analyzing this with optical measurement methods. In this work, a multi-sensor camera system with up to four pairs of cameras connected in parallel is used. The structure to be characterized is recorded from all sides to evaluate the movement in three-dimensional space. The energy input and the time required for an even deflection of the actuator are investigated experimentally. Here, the activation parameters for the practical energy input required for long life with good deflection, i.e., good efficiency, were analyzed. Different parameters and times are considered to minimize the energy input and, thus, to prevent possible overheating and damage to the wire. Thermography is used to evaluate the heating of the SMA wire at different actuation times over a defined time. [ABSTRACT FROM AUTHOR]

The ring spinning technology is widely used in the textile industry to produce high‐quality yarn. One of the challenges for higher productivity is the limited spindle speed due to friction in its conventional ring/traveler twisting system. However, it was recently shown that a superconducting magnetic bearing twisting system might overcome this limitation due to significantly reduced friction, which allows the use of higher spindle speeds and thereby increases productivity. To analyze the impact of speed increments on the yarn formation, it is crucial to model the yarn balloon dynamics. This is of particular importance as new challenges arise for such high‐speed processes, including the increase in yarn tension due to higher centrifugal forces and increased air resistance of the yarn itself. Therefore, in this work, a model based on a chain of springs and masses as an alternative to traditional continuous models was developed. In the proposed model, each mass corresponds to a yarn segment, while the springs represent the interactions between adjacent segments. This discrete approach allows for a simplified simulation of the three‐dimensional yarn balloon dynamics, leading to a reduced computational load, which allows to analyze the yarn path more easily under different conditions. [ABSTRACT FROM AUTHOR]

While carbon fibers (CFs) are still the most attractive reinforcement material for lightweight structures, they are mostly manufactured using crude oil-based process chains. To achieve a higher eco-efficiency, the partial substitution of polyacrylonitrile (PAN) by renewable materials, such as lignin, is investigated. So far, this investigation has only been carried out for batch manufacturing studies, neglecting the transfer and validation to continuous CF manufacturing. Therefore, this work is the first to investigate the possibility of partial substituting lignin for PAN in a continuous process. Lignin/PAN-blended CFs with up to 15 wt.-% lignin were able to attain mechanical properties comparable to unmodified PAN-based carbon fibers, achieving tensile strengths of up to 2466 MPa and a Young's Modulus of 200 Pa. In summary, this study provides the basis for continuous Lignin/PAN-blended CF manufacturing. [ABSTRACT FROM AUTHOR]

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.

This study focuses on the development of an advanced high heating rate thermobonding process for the manufacture of preforms and the metrological characterisation of the process. The process involves passing hot air, driven by pressure differential, through a textile stack consisting of several plies of a quadraxial fabric coated with a binder. Heat is transferred into the stack and into the binder by forced convection, melting the binder. The process is used in the same way to cool the stack and binder so that the plies are bonded together. The pressure differential compacts the stack. The comprehensive methodological characterisation of the process includes first determining the air permeability of the stack and thus the volume flow of air as a function of the number of plies stacked. Further characterisation focuses on a comprehensive determination of the heating behaviour in the individual plies as a function of time, using thermocouples and thermal imaging to determine the temperatures of hot air and textiles. These are compared and related using a mathematical approach as different values have been found. The results indicate high heating rates, reducing process time by at least 85% compared to previous binder activation methods. In addition, the cantilever method assesses the flexural stiffness of the processed stacks and shows a twofold improvement in bond strength compared to uncompacted stacks. Results and discussions include orifice based volume flow determination, thermography calibration, mathematical modelling, stiffness of bonded textile plies, process comparison, process control and potential energy savings. [ABSTRACT FROM AUTHOR]

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]

The aim of this research is to improve the impact strength of thermoplastic composites manufactured from recycled carbon fiber (rCF). For this purpose, the development of a novel multi-material, micro-scale hybridized and low-cost hybrid yarn by blending aramid fibers with rCF and polyamide 6 (PA 6) fibers through the processing route of carding, drawing and flyer spinning is reported in this paper. In addition, two other hybrid yarns were produced from rCF/PA 6 and aramid/PA 6 for comparison with the multi-material rCF/aramid/PA 6 hybrid yarn. Finally, the tensile, flexural and impact properties of composites based on the developed rCF/aramid/PA 6 multi-material hybrid yarn were compared with those of composites reinforced only with rCF and aramid fiber. The results of the Charpy impact test showed that the inclusion of 24 volume percentage aramid fiber increased the impact strength by 70% compared to the composite reinforced with rCF alone. The multi-material hybrid yarn consisting of rCF/aramid/PA 6 fibers shows good potential for designing a hybrid composite with tailored tensile, flexural and impact resistant properties. [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]