R. Alagirusamy

A Review on Carbon Epoxy Nanocomposites

Carbon nanotubes are the major component of nanotechnology and a considerable area of research, due to their outstanding physical and mechanical properties. Since their discovery in 1991, extensive research has been carried out to understand and exploit these unique properties in the form of composites for various applications. But the main challenge lies in transferring the properties of carbon nanotubes to the nanocomposites successfully. In this paper, recent research in the field of carbon nanotubes reinforced epoxy composites and carbon epoxy three phase composites are reviewed.

Hybrid Yarns and Textile Preforming for Thermoplastic Composites

Abstract In the recent years, the use of textile structures made from high performance fibers is finding increasing importance in composites applications. In textile process, there is direct control over fiber placements and ease of handling of fibers. Besides economical advantages, textile technologies also provide homogenous distribution of matrix and reinforcing fiber. Thus textile performs are considered to be the structural backbone of composite structures. Textile technology is of particular importance in the context of improving certain properties of composites like inter-laminar shear and damage tolerance apart from reducing the cost of manufacturing. Textile industry has the necessary technology to weave high performance multifilament fibers such as glass, aramid and carbon, which have high tensile strength, modulus, and resistance to chemicals and heat into various types of preforms. Depending upon textile preforming method the range of fiber orientation and fiber volume fraction of preform will vary, subsequently affecting matrix infiltration and consolidation. As a route to mass production of textile composites, the production speed, material handling, and material design flexibility are major factors responsible for selection of textile reinforcement production. This opens a new field of technical applications with a new type of semifinished material produced by textile industry. Various types of hybrid yarns for thermoplastic composites and textile preforming methods have been discussed in detail in this issue. Information on manufacturing methods, structural details and properties of different hybrid yarns are presented and critically analyzed. Characterization methods used for these hybrid yarns have been discussed along with the influence of different processing parameters on the properties being characterized. The developments in all areas of textile preforming including weaving, knitting, braiding, stitching and nonwovens techniques are presented and discussed along with the characterization techniques for these preforms. The techniques used for manufacturing composites using hybrid yarns and textile preforms are discussed along with the details on compaction behavior of these structures during consolidation process. The structure of hybrid yarns and the textile preforms have direct influence on the properties of the composite made from them. The reported literature in this aspect is discussed in detail. In the end, the potential application areas and their trends for thermoplastic composites are discussed and analyzed.

Knitted preforms for composite applications

Knitted structures occupy a special position in composite preforming due to their inimitable characteristics. An insight into the knitted structures with respect to their composite preforming characteristics is presented in this article. Directionality of knitted structures and requirements of high performance fibers for knitting have been discussed. Contourability, net-shape preforming, high dynamic mechanical properties along with easy and rapid manufacturability are the important features of knitted structures to match the composite preform requirements. In this article, the work done in the above areas of research have been critically reviewed.

Polyesters and polyamides

Part 1 Polyester and polyamide fundamentals: Polyester resins Polyamide fibres Manufacture of polyester fibres Manufacture of polyamide fibres Poly (lactic acid) fibres (PLA) Environmental impact of polyester and polyamide textiles. Part 2 Improving functionality of polyesters and polyamides: Specialty fibres from polyester and polyamides Property enhancement through blending Weaving technology for manufacturing high performance fabrics Advances in coloration of polyester textiles Flame retardant polyester and polyamide textiles Advances in functional finishes for polyester and polyamide textiles The impact of nanotechnology on polyester and polyamides. Part 3 Applications of fibrous polyesters and polyamides: Polyester fibre-apparel applications Medical applications Sports applications Automotive applications Applications of polyesters and polyamides in civil engineering.

Commingled and Air Jet-textured Hybrid Yarns for Thermoplastic Composites

Hybrid yarns have reinforcing and matrix-forming filaments combined together in order to reduce the problems associated with high melt viscosity of thermoplastic matrices. Among hybrid yarns, commingled and air-textured yarns, which are produced with air jets have demonstrated high flexibility and good mixing of constituent filaments. Many research findings have been reported on the structure and properties of intermingled and air-textured yarns having low-modulus apparel-grade filaments. The relationships between air jet, filament yarn, and the processing parameters are critically reviewed. It is emphasized that there is an immediate need to study the mixing behavior of combination of high- and low-modulus filaments in air jet, which has not been investigated in detail in the published literature, in order to improve the mixing of these filaments. The methods used to characterize hybrid yarns are discussed. The need to study and improve the stability of the hybrid yarns in terms of maintaining the level of mixing of constituent filaments across the cross section is also established.

Flame retardant polymer composites

In this review article, different approaches of enhancing flame retardancy of polymeric composite material and their effect on different composite properties are analysed critically. The mechanisms of fire spreading on composite materials are also discussed. Flame retardancy of polymeric composite material can be enhanced either by enhancing the fire performance of constituents of composite i.e. matrices and reinforcing agents or by providing a protective flame retardant (FR) coating around the composite material. Fire performance of reinforcing material is improved by treating with FR-chemicals while the fire performance of polymer matrices can be improved by incorporating micro and nano FR-fillers or by introducing FR-compound into polymer backbone. The flammability of micro and nano filler added polymeric composites and newly developed polymer derivatives and their effect on composite properties like mechanical, thermal have been discussed. However, the development of flame retardant polymer composite is still at nascent stage and for further development, it is necessary to work on the development of non-health hazardous, environment friendly flame retarding agents which will be able to enhance the fire performance of composite materials at very low concentration levels.

Mechanical properties of natural fibre-reinforced composites

Natural fibres were initially used in composite materials to predominately improve bulk and reduce cost rather than improving mechanical properties. But the environmental problems associated with the production and use of synthetic fibres have changed the scenario. In the previous decade, natural fibres have been extensively used as reinforcement materials for both synthetic and bio-degradable matrices. Natural fibre reinforcements have mostly improved flexural and impact properties, but tensile strength improvement has been marginal and has been an area of investigation. Many attempts have been made towards improving mechanical properties, with efforts directed at improving the interface, newer methods of production of composites, new modelling techniques etc. In this detailed review, an attempt is made to critically analyse the various research efforts directed towards improving the mechanical properties of natural fibre reinforced composites.

Development and Characterization of GF/PET, GF/Nylon, and GF/PP Commingled Yarns for Thermoplastic Composites:

Commingling is becoming an important method for developing thermoplastic composites, which demonstrate significant advantages over thermoset composites in several applications including aerospace, marine, sporting, and automotive industries. Although the commingling technique has a very high potential to produce towpregs with a good blending of matrix and reinforcing fibers, it has been reported that these towpregs tend to de-mingle due to nonuniform stretching during textile and other preforming processes, leading to the segregation of stiffer reinforcing fibers and matrix-forming fibers, which in turn results in poor mechanical properties. Therefore, the current research focuses on the enhancement of stability and homogeneity of commingled yarns during subsequent processing. An attempt has been made to study the effect of the commingling process variables, namely air pressure and volume fraction of matrix-forming fibers on the structure and properties of Glass/Polypropylene, Glass/Polyester, and Glass/Nylon commingled yarns. In this paper, nips are classified into different categories based on their structure. The causes of occurrence and their effect on the commingled yarn properties are identified. Other parameters including nip frequency, nip length, and degree of interlacing are also studied in relation to the process parameters. The results show that commingling process parameters as well as the type of matrix-forming fibers significantly affect the structure and properties of commingled yarns.

Coating of conductive yarns for electro-textile applications

Conductive yarns are used for integration of sensors and other electronic devices with textile fabrics through weaving, knitting, braiding or embroidery processes. In the lifetime of the textile also several washing cycles might occur. These processes involve rubbing which may lead to displacement of conductive fibres, causing short circuiting between the neighbouring conductive fibres. Also the textile products made with conductive fibres may have to work in the presence of water, where the exposed conductive fibres can get short circuited. In this work, an attempt has been made to protect silver-coated polyamide yarns with polypropylene (PP). This is done through wrapping the PP staple fibres around the silver-coated polyamide yarns through friction spinning and melting the PP sheath fibres in an oven. The influence of twist in the conductive yarns, amount of PP coating and the oven temperature during coating process on the tenacity, electrical insulation in the presence of water and flexibility properties of the coated yarns are studied. The PP coated yarns with plied conductive yarn in the core provide better flexibility but need higher amount of coating to provide complete electrical insulation in the presence of water as compared to those yarns with single conductive yarn in the core.

Prediction of internal pressure profile of compression bandages using stress relaxation parameters

The efficacy of compression therapy using compression bandages is highly dependent on the level of compression applied and the sustenance of the pressure during the course of treatment. This study attempts to predict the pressure profile generated by compression bandages using constitutive equations describing relaxation behavior of viscoelastic materials. It is observed that this pressure profile is highly correlated with the stress relaxation behavior of the bandage. To model the pressure profile, the stress relaxation behavior of compression bandages was studied and modeled using three mechanical models: the Maxwell model, the standard linear solid model and the two-component Maxwell model with a nonlinear spring. It was observed that the models with more component values explained the experimental relaxation curves better. The parameters used for modelling relaxation behavior were used to describe the pressure profile, which is significantly dependent on the longitudinal stress relaxation behavior of the bandage, using the modified Laplaces law equation. This approach thus helps in evaluating the bandage performance with time during compression therapy as novel wound care management.