Investigating the Thermo-Physiological Comfort Properties of Weft-Knitted Smart Structures Having a Negative Poisson’s Ratio

Smart auxetic structures are gaining attention in various areas such as architecture, clothing (sports and protective), civil, and medical applications owing to their negative Poisson’s ratio. Compared to ordinary structures, these structures have better properties (shear resistance, formability, energy absorbance, and robust fracture strength). Auxetic structures show the exceptional property of becoming wider in one direction when stretched from another direction. In this research, three different auxetic weft-knitted structures were fabricated using nylon, polyester, acrylic, and cotton yarns on a Shima Seiki flat-knitting machine. The physical properties, negative Poisson’s ratio, and thermo-physiological comfort properties of these fabrics were checked. Negative Poisson’s ratio strain curves of the developed fabrics were plotted; all fabrics, except for nylon, show the negative Poisson’s ratio (NPR). The NPR decreases with increased strain in the longitudinal direction, and polyester exhibits a maximum value of NPR −0.4 in line structure at 30 mm extension. Results also revealed that structures made with nylon and polyester yarns exhibit a better value of air permeability than acrylic and cotton, while acrylic provides the best thermal resistance values than other materials in line structure and polyester yarn shows better overall moisture management capacity (OMMC) performance in zigzag structures.

Mechanical performance of 3D woven jute/green epoxy composites with novel weaving patterns

Green composites have ecofriendly features that are technically and economically feasible while minimizing the pollution. It refers to the combination of degradable fibers mostly cellulosic materials and natural resins to develop green composites. Since mechanical performance of such structures is a concern for industry, by playing with the position and pattern of yarns in woven fabric, these properties can be optimized. This research focuses on the development and characterization of novel 3D woven jute/green epoxy composites having hybrid interlocking patterns. Four conventional derivatives of 3D woven fabrics i.e. orthogonal layer to layer (OLL), orthogonal through thickness (OTT), angle interlock layer to layer (ALL), angle interlock through thickness (ATT) and three novel 3D woven fabrics i.e. H1 (combination of OTT and ATT binder yarns), H2 (combination of OTT and ALL binder yarns), H3 (combination of orthogonal layer to layer warp and weft interlock called as bi-directional interlock) were developed using different binding patterns on dobby loom. Tensile, flexural, and short beam shear tests were performed to check the mechanical performance of the developed composites. OTT composite structure showed the highest values of tensile strength, modulus, and maximum force both in warp and weft directions as compared to the other 3D interlock structures, due to least interlacement/crimp of binder yarn. While ATT composite exhibited the highest value of flexural strength and modulus both in warp and weft directions due to through thickness angle binder yarns. H3 composite showed the highest values of force and short beam shear strength in warp direction.

Compression and recovery behavior of three-dimensional woven spacer composites

Three-dimensional woven spacer composites have great potential for use in different parts of automobiles and construction application due to their better mechanical performance. In literature, time-dependent compression and recovery behavior of three-dimensional woven spacer composites was not studied. In this study, three-dimensional woven spacer composites (three thickness levels) were evaluated under static and dynamic (time-dependent) compression and recovery. The static compressive strength of composites was reduced with the increase in sample thickness. Also, the highest amount of energy was absorbed during the fracture of 4 mm (Comp4) thick composite, followed by 10 mm (Comp10) and 20 mm (Comp20) thick composites. Compressibility (%) and resiliency (%) was highest in Comp4 but recovery (%) was a bit lower as compared to the Comp10 and Comp20, while recovery (%) was highest in 10 mm thick composite as compared to the 4 mm and 20 mm thick samples. Moreover, higher value of permanent deformation in thickness with time was observed in Comp20 showing higher creep followed by Comp4 and Comp10. Furthermore, Comp4 showed the highest values of work done during cyclic compression loading–unloading testing, presenting highest toughness.

Optimization of 3D woven preform for improved mechanical performance

For structural design applications, through-thickness characteristics of reinforcement played a vital role, which is why 3D woven preforms are recommended for such applications. These characteristics are mainly dependent on the fiber and yarn positioning in reinforcement. Although research has been conducted for characterizing woven composites, special attention has not been made on weave pattern parameter which directly affects the mechanical performance of composites. In this research work, 3D orthogonal layer to layer and through thickness woven structures with different interlocking patterns have been thoroughly studied for their mechanical properties, thickness, air permeability and areal density. Natural fibers when used with biodegradable matrix find use in structural, as well as low to medium impact applications for automobiles. Jute yarn was used to produce four-layered 3D woven structures, as synthetic fibers will not give a biodegradable composite part. The focus of this study is to optimize weave pattern, which is robust in design, degradable preforms and easy to reproduce. The main objective of this research focused on the effectiveness of weaving patterns on physical and mechanical properties as well as to optimize the weave pattern for optimum performance. Grey relational analysis was used for the optimization of the robust weave pattern. The results showed that hybrid structures can be useful for improving the properties of the orthogonal layer to layer and through thickness woven structures. It was also noted that weft-way 3D woven structures can provide comparable mechanical properties with warp-way 3D woven structures.

Development and characterization of three-dimensional woven fabric for ultra violet protection

Purpose

The purpose of this paper is to investigate the effect of materials, three dimensional (3D) structure and number of fabric layers on ultraviolet protection factor (UPF), air permeability and thickness of fabrics.

Design/methodology/approach

Total 24 fabrics samples were developed using two 3D structures and two weft materials. In warp direction cotton (CT) yarn and in weft direction polypropylene (PP) and polyester (PET) were used. Air permeability, thickness and UPF testings were performed and relationship among fabric layers, air permeability, thickness and UPF was developed.

Findings

UPF and thickness of fabrics increases with number of fabric layers, whereas air permeability decreases with the increase in number of fabric layers. Furthermore, change of multilayer structure from angle interlock to orthogonal interlock having same base weave does not give significant effect on UPF. However, change of material from polyester (PET) to polypropylene (PP) has a dominant effect on UPF. Minimum of three layers of cotton/polyester fabric, without any aid of ultraviolet radiation (UV) resistant coating, are required to achieve good. Cotton/polyester fabrics are more appropriate for outdoor application due to their long-term resistance with sunlight exposure.

Originality/value

Long-term exposure to UV is detrimental. So, there is need of proper selection of material and fabric to achieve ultraviolet protection. 3D fabrics have yarns in X, Y as well as in Z directions which provide better ultraviolet protection as compared to two dimensional (2D) fabrics. In literature, mostly work was done on ultraviolet protection of 2D fabrics and surface coating of fabrics. There is limited work found on UPF of 3D woven fabrics.

Study of electro-thermal properties of pyrrole polymerised knitted fabrics

This paper presents the results of research work carried out to investigate the heating properties of nylon knitted fabric impregnated with a polymerised solution of polypyrrole. The inspection of the molecular polypyrrole electro-conductive pathways responsible for the heating effect of the knitted fabric was investigated using a scanning electron microscope. Further to this, the heat generated by the polypyrrole impregnated fabric was observed under varying power supply terminal separation distances in order to understand the relationship between the length of the polypyrrole electro-conductive fabric and the level of heat generated. The sample with the lowest terminal separation distance i.e. 5 × 1 cm2 produced more localized heat and reached a temperature level of 114℃ in less than three minutes. Additionally a thermo-mechanical characterisation of this knitted heating material was carried out against varying levels of strain and compression. The maximum stress and ultimate strain values of both treated and untreated samples were found to be similar. However, it was observed that the extensibility of the samples affected the generation of heat. The suitability of knitted fabric impregnated with polymerised polypyrrole heating elements for in-car applications where the heating elements may be next to skin was also discussed. The investigation concluded that polypyrrole heating fabric is suitable for next-to-body heating applications which can be engineered by controlling the optimum electrical pathways provided by the network of polypyrrole molecular chains together with the correct power supply levels to work under a defined fabric strain range. The purpose of the current research is to provide a new material that could help to develop heating fabrics with improved textile properties.

Thermo-Mechanical Behavior of Textile Heating Fabric Based on Silver Coated Polymeric Yarn

This paper presents a study conducted on the thermo-mechanical properties of knitted structures, the methods of manufacture, effect of contact pressure at the structural binding points, on the degree of heating. The test results also present the level of heating produced as a function of the separation between the supply terminals. The study further investigates the rate of heating and cooling of the knitted structures. The work also presents the decay of heating properties of the yarn due to overheating. Thermal images were taken to study the heat distribution over the surface of the knitted fabric. A tensile tester having constant rate of extension was used to stretch the fabric. The behavior of temperature profile of stretched fabric was observed. A comparison of heat generation by plain, rib and interlock structures was studied. It was observed from the series of experiments that there is a minimum threshold force of contact at binding points of a knitted structure is required to pass the electricity. Once this force is achieved, stretching the fabric does not affect the amount of heat produced.