Numerical simulation tools are increasingly used for developing novel composites and composite reinforcements.
The aim of this paper is the application of digital elements for the simulation of the mechanical behaviour of textile
reinforcement structures by means of a finite element analysis. The beneficial computational cost of these elements
makes them applicable for the use in large models with a solution on near micro-scale. The representation of
multifilament yarn models by a large number of element-chains is highly suitable for the analysis of structural and
geometrical effects. In this paper, a unit cell generating method for technical reinforcement textiles, using digital
elements for the discretization, is introduced.
For the development of a new generation non-crimp fabrics (NCF) made of carbon fibres, a feasibility study of
different characterisation methods and surface treatments of the used carbon fibres needs to be performed. In
order to join the carbon fibre layers with the binder for realising this new type of NCF, the surface topography and
functionality of the fibres have to be analysed first. The wettability of the binder to the carbon fibre surface is of prime
significance and needs to be enhanced. Here, the enhancement is carried out by improving the surface energy
using atmospheric plasma of compressed air, argon and nitrogen. It is also proposed to improve the surface energy
through chemical techniques.
Wound assessment has become an important issue in the wound treatment procedure. One important indicator of the wound status is the pH value. Our approach to assess this quantity is through use of a fiber sensor coated with a pH-responsive hydrogel, which functions as a sensitive layer for impedance measurements. An advantage of this is its integratability into wound dressings using standard textile technologies. The pH characteristic shows a pH-dependent behavior of the absolute impedance at certain frequencies. The fabrication technology and sensor characteristics are discussed. The values of almost 14% impedance change demonstrate the potential for improvement by optimizing fabrication technologies. The presented sensor meets all requirements necessary for wound pH assessment
Due to its excellent biocompatibility, Chitosan is a very promising material for degradable products in biomedical
applications. The development of pure chitosan microfibre yarn with defined size and directional alignment has
always remained a critical research objective. Only fibres of consistent quality can be manufactured into textile
structures, such as nonwovens and knitted or woven fabrics. In an adapted, industrial scale wet spinning process,
chitosan fibres can now be manufactured at the Institute of Textile Machinery and High Performance Material
Technology at TU Dresden (ITM). The dissolving system, coagulation bath, washing bath and heating/drying were
optimised in order to obtain pure chitosan fibres that possess an adequate tenacity. A high polymer concentration
of 8.0–8.5% wt. is realised by regulating the dope-container temperature. The mechanical tests show that the
fibres present very high average tensile force up to 34.3 N, tenacity up to 24.9 cN/tex and Young’s modulus up
to 20.6 GPa, values much stronger than that of the most reported chitosan fibres. The fibres were processed into
3D nonwoven structures and stable knitted and woven textile fabrics. The mechanical properties of the fibres and
fabrics enable its usage as textile scaffolds in regenerative medicine. Due to the osteoconductive properties of
chitosan, promising fields of application include cartilage and bone tissue engineering.
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.
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.
The present research work was carried out to develop the prediction models for blended ring spun yarn evenness and tensile parameters using artificial neural networks (ANNs) and multiple linear regression (MLR). Polyester/cotton blend ratio, twist multiplier, back roller hardness and break draft ratio were used as input parameters to predict yarn evenness in terms of CVm% and yarn tensile properties in terms of tenacity and elongation. Feed forward neural networks with Bayesian regularisation support were successfully trained and tested using the available experimental data. The coefficients of determination of ANN and regression models indicate that there is a strong correlation between the measured and predicted yarn characteristics with an acceptable mean absolute error values. The comparative analysis of two modelling techniques shows that the ANNs perform better than the MLR models. The relative importance of input variables was determined using rank analysis through input saliency test on optimised ANN models and standardised coefficients of regression models. These models are suitable for yarn manufacturers and can be used within the investigated knowledge domain.
Despite significant weight and performance advantages over metal parts, today’s demand for fiber-reinforced polymer composites (FRPC) has been limited mainly by their huge manufacturing cost. The combination of dry textile preforms and low-cost consolidation processes such as resin transfer molding (RTM) has been appointed as a promising approach to low-cost FRPC manufacture. This paper presents an advanced weaving technique developed with the aim to establish a more cost-effective system for the manufacture of dry textile preforms for FRPC. 2D woven fabrics with integrated net shape selvedge can be obtained using the open reed weave (ORW) technology, enabling the manufacture of 2D cut patterns with firm edge, so that oversize cutting and hand trimming after molding are no longer required. The introduction of 2D woven fabrics with net shape selvedge helps to reduce material waste, cycle time and preform manufacturing cost significantly. Furthermore, higher grade of automation in preform fabrication can be achieved.
A single step electrospinning of chitosan and chitosan derivative-chitosan lactate nanofibres was studied in this paper.
Chitosan was dissolved into acetic acid to produce structure-stable nanofibres. The effect of chitosan concentration
and the content of acetic acid on the fibre diameter and morphology of nanofibres were studied in detail. The
dynamic viscosity and surface tension of the electrospinning chitosan solutions were systematically studied as well.
Based on the fundamental study on electrospinning chitosan in acetic acid, a chitosan derivative, chitosan lactate,
was added to produce nanofibre in a pH-friendly aqueous environment. Chemical and morphological analyses
demonstrated that chitosan lactate will positively influence the formation of nanofibres in higher pH condition
although the morphology should be improved.
This article reports the results of investigations carried out to produce yarns consisting of staple carbon fiber (CF) obtained from process waste for the manufacturing of composites suitable especially for thermoset applications. For this purpose, a comparative analysis is done on processability between 100% staple CF and 60 weight% staple CF mixed with 40 weight% PVA fibers in carding, drawing and spinning process. The hybrid yarns are produced by varying twist level. The PVA fibers of the hybrid yarn are then dissolved using hot water treatment. The mechanical properties of yarns consisting of 100% staple CF and hybrid yarns consisting of staple CF and PVA before and after hot water treatment are investigated. Furthermore, test specimen is also prepared by impregnating 100% staple CF yarn and the hybrid yarns (after the dissolving of PVA) with epoxy resin. The results of the tensile test of the yarns in consolidated state reveals that the hybrid yarn produced with 80 T/m after hot water treatment exhibits approximately 75% of the tensile strength of virgin filament tow, and it is expected that the hybrid yarns can be applied for the manufacturing of thermoset based composites for load bearing structures.