Shear rigidity of woven fabrics is an important property that defines the behaviour of fabrics when they are required to conform to three dimensional forms, including the human body in the case of ...apparel textiles or preforms and prepregs used for production of fibrous polymer composite components. Typically, shear rigidity is measured using complicated and expensive equipment. This paper presents the study of the influence of weave patterns on the shear behaviour of fabrics using a simple and precise testing method. The shear behaviour of eleven cotton fabrics in total, utilizing different weaving patterns and different yarn densities was investigated. Specimens of different dimensions were also tested to determine the influence of the specimen dimensions on the measured characteristics. The investigation resulted in a correlation between the shear behaviour and the different weaving patterns. Specifically, it was shown that weave patterns that are closer to the plain weave (firm weaves) are more restricting to the yarn rotation than loser weave patterns. Furthermore, the results show the relationship between shear behaviour and specimen dimensions as well as yarn density. Increasing the length of the specimens (the dimension of the specimen parallel to the direction in which the shearing force is applied) or decreasing the width of the specimens (the dimension of the specimen vertical to the force application) also leads to an increase of the shear rigidity.
Scientifically defined in 1880 by the Curie brothers, piezoelectricity - from the Greek piezein, meaning to press (squeeze), and ilektron, meaning amber, a material with electrostatic properties - is ...a phenomenon with many applications. The related piezoelectric materials have been undergoing a long-lasting evolution over the years until today. The field of organic and inorganic piezoelectric materials is continuously expanding in terms of new substances used, new structures, and new applications. The seven chapters of this book present modern aspects and technological advances in the field of piezoelectric materials and applications. To present a balanced view of the field, some chapters focus on new piezoelectric materials and structures, while others examine interesting applications of piezoelectric sensors, energy harvesters, and actuators.
Piezoelectric textile fibres are important for wearable energy harvesting applications. Piezoelectric melt-spun fibres have been under investigation starting with 2010. While most of research has ...been carried out on fibres produced from polyvinylidene fluoride (PVDF) which is a widely researched piezoelectric polymer, attempts have been carried out at developing fibres from polypropylene (PP) which has mostly been researched when used in cellular form. Moreover, the piezoelectric behavior of the fibres has until now been characterized, only by the voltage produced by the fibres when they are tested under open circuit conditions. The research presented in this paper, investigated yarn specimens made of polypropylene mixtures with multiwalled carbon nanotubes (MWCNTs) regarding the electric power produced by the yarns. Measurement of the power was carried out using equipment developed by the research team and previously used to measure the power produced by monofilament piezoelectric textile yarns. The result of the current research indicate that the piezoelectric behavior of PP yarns is not affected essentially affected by the addition of MWCNTs and illustrate potential areas for further research of the behavior of piezoelectric PP yarns.
The ability of certain dyestuffs to change colour in a predictable and reversible way with the change in temperature is a property that can be well utilized in smart textiles. Accurate and repeatable ...determination of the chromatic response of the dye stuff and as an extension of the textile material dyed using these dyes in a significant step towards developing such smart textiles. In this regard the current research project proposes a method for investigating the thermochromic properties of textiles using a custom made testing setup, that includes a digitally controlled heating and cooling equipment as well as a set up to obtain the chromatic response of the textiles every 0.5 °C. Moreover, the proposed set up allows for the investigation of heating/ cooling cycling of the specimens, to confirm the repeatability of the chromatic response of the specimens.
Polymers such as polyvinylidene difluoride, polypropylene and polyamide-11 show great promise for providing light-weight, flexible and fibrous piezoelectric materials that can be integrated into ...technical textile fabric structures for energy harvesting applications. Durability is an important parameter for the textiles and especially for functional and smart materials. This research work provides an insight on the piezoelectric behaviour of polypropylene, polyamide-11 and polyvinylidene difluoride in terms of peak-to-peak voltage generation capabilities after washing at 40°C with the addition of detergent as described in test method BS EN ISO 105-C06:2010. It was observed that the peak-to-peak voltage generated by polypropylene monofilaments retained similar values with only slight differences, while the monofilaments of polyvinylidene difluoride and polyamide-11 showed higher peak-to-peak voltage generation after washing. These changes have been explained using the changes in the crystallinity and phase, as determined by Fourier transform infrared spectroscopy analysis.
Piezoelectric, melt spun, textile fibres as multifunctional materials appeared recently, and they are under thorough investigation and testing in order to define their performance and behaviour. ...Although piezoelectricity was first reported in 1880 and the piezoelectric behaviour of organic polymers materials has been known since 1969, the fibrous form of the piezoelectric materials under consideration opens new technological horizons; however, it introduces novel restrictions and further complex parameters are involved in their study. The major issue of the current research work is the study of the actual capacity of the piezoelectric fibres, i.e. the electric power produced following mechanical stimulation of the individual fibre. The measurements were made possible after the development of the necessary specific equipment. The test results enabled the ranking of the various types of the piezoelectric fibres according to the respective power generation. The main difference in this research approach is the measurement of the power generated by the fibres. Measurement of the power generated by an electrical power source (in the case of energy harvesting applications which is the prime interest of this research project) is an important characteristic as the requirements of various applications are expressed in units of power. Stating the voltage produced during mechanical deformation of the fibres is not enough (cf. voltage produced due to electrostatic phenomena on textiles where the voltage is in the range is the several kV, but the power is not enough to power a light-emitting diode).
Wearable electronics have evolved from electronic components secured on the human body with straps and belts to partial electronic components integration onto textile structures. Cables and standard ...components defeat the purpose of the wearable approach by being bulky, rigid and especially not being able to withstand standard textile cleaning/care methods (washing, dry-cleaning, etc.). New 3D textile structures can provide a promising solution. In this research project, we examined the capacitive behaviour of specially prepared 3D weft knitted textile fabrics. The samples knitted specially for this project incorporated conductive outer layers and an insulating inner layer. The outer layers form the plates of the capacitor and the insulating layer plays a role of the dielectric material between the two plates. The structure of these 3D knits allows for inherent capacitive behaviour of the material. These 3D weft-knitted fabrics can be produced on usual existing knitting machines, without any need of dedicated, specialized or expensive equipment. The expected values of the capacitance, based on theoretical calculations, satisfactorily approach the values derived from the measuring process. The ability to customize the structure and hence the capacitance of the 3D fabrics-based capacitors is a positive point towards the design of the textile-based electronics systems in the future. Therefore, the development of textile capacitors based on the 3D fabrics is expected to be an essential contribution to the integration of the wearable system concept.
Piezoelectric polymer materials have been under investigation since the 1970’s starting with the discovery of the piezoelectric effect in PVDF films by Kawai. Since then the piezoelectric effect has ...been detected among other polymers in polyureas, polyamides, and polypropylene and their copolymers. While the investigation of the piezoelectric effect was largely carried out on the film form of the polymers since 2010 interest has developed into the production methods, properties and applicability of melt spun piezoelectric textile fibres made of these polymers. The application of piezoelectric fibres could have a significant impact in wearable textiles as sensors, actuators, or energy harvesting modules. Current research is mostly centred onto production methods and fibre crystallinity characterization. The research carried out in this PhD by publication project is concerned with piezoelectric textile fibres as electrically active elements. As such the research focused on the electrical behaviour of the fibres. The work carried out was threefold. Specifically, wearable textile materials undergo cleaning/ care treatments that are intrinsic to their function as wearables. These treatments may include washing, dry cleaning or sponging. Washing (cleaning treatment in a solution mainly containing water and an appropriate detergent at an elevated temperature or room temperature) is a common cleaning method. The effects of washing cycles on melt spun piezoelectric fibres remain under-investigated. For the first part of the research, piezoelectric melt spun fibres (PVDF, PP and PA-11) with two different cross sections (circular and rectangular), were mechanically stimulated by a rotating fin that impacted the fibres periodically. The resulting Vp-p (peek to peek voltage), was measured on the original fibres and on the fibres following one wash cycle (adapted BS EN ISO 105-C06), using an oscilloscope. Based on the results of this part of the research it was shown that the washing cycle effected the voltage response of the fibres depending on the fibre cross section and the fibre composition. The results of the research were presented in a paper titled “Investigation of the durability and stability of piezoelectric textile fibres” published in the Journal of Intelligent Materials Systems and Structures. For the second part of the research, it was noted that according to the existing literature the research approach for the determination of the electrical response of the fibres utilized exclusively the measurement of the voltage produced by mechanical excitation of the fibres, in open circuit conditions. This approach is not sufficient to satisfactorily characterise the electrical behaviour of the fibres as power generating elements. By contrast, a sufficient measurement is the power production of the fibres as this also includes a measurement of the current produced. In order to supply these measurements a testing apparatus/ methodology was developed. The apparatus consists of a measuring station where the voltage and current produced are measured, and a means for periodic mechanical stimulation of the specimens. The equipment was used to determine the power generated by piezoelectric melt spun fibres (PVDF, PP and PA-11) with two different cross sections (circular and rectangular). The results of the research were presented in a paper titled “On the Measurement of the Electrical Power Produced by Melt Spun Piezoelectric Textile Fibres” published in the Journal of Electronic Materials. Finally, considering the underlying premise of integration of fully textile based electronic components into textile substrates (e.g. wearable applications), 3D knitted fabrics that incorporated piezoelectric melt spun fibres were investigated with regards to their capacitive behaviour. Four different fabric structures were examined (different composition of the outside layers and different thickness). The capacitive behaviour of the samples was modelled based on the specific structural characteristics of the fabrics and the actual properties were determined using an Impedance Analyzer. Based on the results it was found that the theoretical model for the calculation of the capacitance of the samples appeared to be an acceptable approximation for the behaviour of the fabrics. Also, the ability to customise the required capacitance to suit the applications by specifying the dimensions of the 3D fabric and/or the density, the thickness or even the material of the interlaced fibres has also been shown to be possible. Moreover, reviewing the results of a resonance test for a purely textile based parallel LC circuit, it was shown that it is possible to implement resonant circuits that are convenient for basic electronic applications (i.e. oscillators, filters, etc.). The results of the research were presented in a paper titled “Three-dimensional weft-knitted textile fabrics-based capacitors” published in the Journal of the Textile Institute. This research project touched on some of the less thoroughly investigated research areas connected to the efficiency and durability of piezoelectric melt spun fibres and structures, with innovative results such as the development/ construction of the equipment that can be used for the measurement of the power produced by piezoelectric textile fibres as well as the investigation of the capacitive behaviour of the 3D knitted fabrics incorporating piezoelectric textile fibres and the conclusion that resonance is possible to achieve in a purely textile LC parallel circuit.
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