K.B. Cheng

Electromagnetic shielding effectiveness of copper/glass fiber knitted fabric reinforced polypropylene composites

The main objectives of this research work are to develop conductive knitted fabric composite materials and to determine their electromagnetic shielding effectiveness (EMSE). Polypropylene is the matrix phase and glass fibers are the reinforcement phase of the composite material. Copper wires are incorporated as conductive fillers to provide the electromagnetic shielding properties of the composite material. The amount of copper in the composite material is varied by changing the yarn composition, fabric knit structure and stitch density. The EMSE of various knitted fabric composites is measured in the frequency range of 300 kHz to 3 GHz. The variations of EMSE of knitted fabric composites with fabric structure, stitch density and yarn compositions are described. Suitability of conductive knitted fabric composites for electromagnetic shielding applications is also discussed.

Electromagnetic Shielding Effectiveness of Stainless Steel/Polyester Woven Fabrics

This paper presents a preliminary study of the development of stainless steel/polyester woven fabrics for electromagnetic shielding applications. To facilitate weaving of stainless steel wires and to reduce material costs, initially blended yarns of stainless steel and polyester staple fibers are produced by a ring spinning method, then woven into a variety of structures. Using a coaxial transmission set-up, the electromagnetic shielding effectiveness (EMSE) of these fabrics is determined in the frequency range of 300 kHz to 3 GHz. Variations of EMSE with the woven structures, number of layers, and blend ratio of stainless steel to polyester in the yarns are described. The new textile material may be suitable for shielding home electronics and electrical appliances from electromagnetic fields.

Friction core-spun yarns for electrical properties of woven fabrics

This paper reports a study to develop a spinning method of open-end friction core-spun yarn (OFCY) and its conductive fabric for shielding the electrostatic discharge and electromagnetic applications. To facilitate weaving of stainless steel (SW) and to reduce the material cost, initially OFCY yarn was made from SW core and polyester (PET) and stainless steel staple (SS) fibers, produced by a DREF III open-end friction spinning method. The core-spun yarns were woven into a variety of woven structures, which are made from semi-automatic loom, successfully. The conductive fabrics could be suitable for shielding home electronic and electrical appliances, cellular phones, and digital devices from electromagnetic fields. The variations of EMSE, and ESD of the woven fabric structure, and blend ratio of stainless steel yarns are also described. It has been shown that the EMSE and ESD attenuation of the woven fabric can be tailored in a number of ways including fabric structure, density, and the amount of conductive filler material.

Electromagnetic Shielding Effectiveness of the Twill Copper Woven Fabrics

Twill copper fabrics (3/1) were produced using a single cylinder handloom jacquard weaving machine. The effect of varying weft density, warp density, wire diameter, and lay-up angle on electromagnetic shielding effectiveness was studied. The electromagnetic shielding effectiveness (EMSE) of various copper woven fabrics was obtained using a coaxial transmission line holder in the frequency range of 144–3000 MHz. With an increase in the number of conductive fabric layers, warp density, and weft density, an increase in shielding effectiveness is observed. With an increase in wire diameter, a decrease in shielding effectiveness has been observed.

Electrical and impact properties of the hybrid knitted inlaid fabric reinforced polypropylene composites

A range of conductive knitted fabric reinforced polypropylene composites have been developed and their electromagnetic shielding effectiveness (EMSE), electrostatic discharge (ESD) and impact properties have been investigated. Carbon and aramid fibers are used as the reinforcement phase in the composites, while copper and stainless steel wires are incorporated as conductive fillers to provide the ESD and EMSE properties of the composite materials. The hollow spindle spinning system has been used to make SS/PP, Cu/PP, SS/C/PP, Cu/C/PP and Cu/K/PP uncommingled yarns. The double plain knitted fabric and its inlaid fabrics were fabricated from the yarns using a 5G traverse knitted machine. Changing the yarn composition, fabric knit structure, and stitch density varies the amount of copper and stainless steel conductive fillers in the composites. 4 layer cross-ply laminates were laid-up by hand, then formed into 3-mm thick conductive thermoplastic composites using a compression molding. It was observed that the EMSE and ESD of the composites increase with increasing the incident frequency, especially at higher frequency range. The effects of inlaid ends, materials and yarn constitutions on the EMSE of the conductive thermoplastic composites were investigated. The results indicate that the composites can be used for the purpose of electromagnetic shielding and ESD attenuation, as well as for some microwave applications.

Development of Conductive Knitted- Fabric-Reinforced Thermoplastic Composites for Electromagnetic Shielding Applications

This paper presents a feasibility study to develop conductive knitted-fabric-reinforced thermoplastic composites for electromagnetic shielding applications. Polypropylene is the matrix phase, and glass fibers are the reinforcement phase of the composite material. Stainless steel wires and staple yarns are incorporated as conductive fillers to facilitate the electromagnetic shielding properties of the composite material. Owing to their high stiffness, knitting of glass fibers and stainless steel wires is very difficult. To facilitate the knitting, uncommingled yarns comprising stainless steel wires, glass, and polypropylene fibers are produced using a hollow spindle spinning method. Different kinds of weft knitted fabrics are produced, which are subsequently consolidated into composite materials using a compression molding method. The electromagnetic shielding effectiveness (EMSE) of various knitted composites is measured in the frequency range of 300 kHz to 3 GHz. The variations of EMSE of knitted composites with the fabric structure, stitch density, number of plies, and amount of stainless steel are described. The suitability of the knitted composites developed in this study for electromagnetic shielding applications is also discussed.

Analytical procedure for the prediction of elastic properties of plain knitted fabric-reinforced composites

Abstract This paper presents an analytical method for predicting the elastic properties of plain-knitted fabric-reinforced composites. Firstly, a geometrical model suitable for expressing the orientation of knitted fabric has been identified. Equations have been developed for estimating the fibre content of the composite. The effects of yarn linear density and knitted fabric stitch density on the fibre content of the composite are predicted. Based on the laminated plate theory, a ‘cross-over model’ has been proposed. As the name suggests, this model considers the cross-over of curved yarns of knitted fabric. Owing to their curved fibre architecture, the knitted fabric composites are heterogeneous with resin and fibre-rich regions. The elastic properties of the composite were determined by combining the effective elastic properties of the curved yarns and the resin-rich regions. Elastic properties of knitted fabric composites with different fibre contents were computed. The analytical method has been validated by comparing one set of experimental results with the predictions. The applicability and limitation of this model have been discussed.

Effects of Spinning Conditions on Structure and Properties of Open-End Cover-Spun Yarns

Critical settings and their effects on the properties of open-end cover spun yams produced by a novel system are explained. The yams are constructed from open-end rotor spun (OER) yarns and textured polyester yarns combined within the yarn formation zone of the rotor during the open-end rotor spinning process. The end result is a textured yarn wrapped as a sheath around an OER yarn core, in which the wraps per meter distribution is uniform, the yarn remains soft, and tensile properties are better than for an equivalent OER yarn.

Processing and microstructures of 3D woven-fabric composites incorporating solid rods

This work has two objectives. The first is to examine the processability of incorporating pultruded rods in three-dimensional woven fabrics. A weaving set-up for this purpose has been developed. The second objective is to characterize the microstructures of the composites and to assess the merits and limitations associated with the rods. Three types of fabric have been made in this study. The first is a 3-axis orthogonal type combining the rods in the axial direction. The second type has a similar structure except that the rods are also used in the widthwise direction. The third is the addition of two off-axis weaving yarns to the first type, resulting in a 5-axis structure. Material processing involves rod pultrusion, fabric formation, and resin impregnation. Both Kevlar and carbon tows have been used in the rods and weaving yarns. A series of specimens with varying bundle size of the weaving yarns have been made. No pressing force was applied during resin transfer molding to preserve the as-formed fabric configuration. According to the micrographs, the rods are essentially free of distortion, while two kinds of local deformation have been identified in the yarns. Unit cells are selected to describe interior microstructures of the materials. Fiber distribution along each direction and matrix distribution in interbundle and intrabundle spaces have been examined on the basis of measured fabric dimensions. The influence of the pitch length on the distributions of fiber and matrix has been analyzed by assuming constant yarn areas. Unique features in processing/microstructure relationships resulting from the presence of the rods have been discussed.

Flexural behavior of three-axis woven carbon/carbon composites

This work examines the processing characteristics and flexural behavior of 3D woven carbon/carbon composites. Two types of the composites have been made, both having 3-axis orthogonal structures. The first combines solid rods along the axial direction. The rod, 1 mm in diameter, is composed of unidirectional carbon fibers and a phenolic resin. The second is a conventional type composed of carbon yarns in all axes. Both preforms were then impregnated by the phenolic resin. Matched molds were used to enhance fiber packing and to cure the resin under a hot press. The green composites were then heat-treated at various temperatures ranging from 200° through 1000° C. The second set of specimens was made by applying multi-cycle impregnation and carbonization. Flexural tests were carried out for these two sets of specimens. Their responses to the load and the induced damage behavior have been examined. The use of rods enhances fiber packing and reduces fiber crimp, leading to higher material performance. Decomposition of the resin due to the heat-treatment results in weak interfacial bonding and compressive failure in axial yarns. The efficiency of densification has been examined. The induced damage configurations vary significantly in these specimens, as a result of the processing. Some unique modes associated with the 3D structure are discussed.