Mário Duarte de Araújo

Effect of Mutual Bonding of Textile Layers on Thermal Insulation and Thermal Contact Properties of Fabric Assemblies

This paper deals with thermal insulation and thermal contact properties of woven fabric assemblies used to produce mens jackets. An important part of the paper is the description of the new computer-controlled instrument, the Alambeta, to measure insulation and thermal contact properties of fabrics. The heat flow passing between the textile sample and measuring head during thermal contact is measured directly by a special thin sensor, whose thermal inertia is similar to that of human skin. Thus, the instruments warm-cool feeling sensitivity aproximates human skin. Spotbonding the outer fabric interlining and lining together reduces the total thermal resistance of the assembly and simultaneously increases (makes cooler) thermal absorptivity, a new parameter used to describe the warm-cool feeling of fabric. The meaning of this pa rameter, which mainly reflects the surface properties of the fabrics and whose level does not depend on experimental conditions, is explained in detail. The effect of temperature drop on the thermal properties of the fabric assemblies is also investigated. The increased resulting thermal conductivity with the average temperature of the assembly is a consequence of the increased portion of the heat transferred through the system by radiation.

Simulation of the Effect of Air Gaps between the Skin and a Wet Fabric on Resulting Cooling Flow

As the moisture content of a fabric increases, the relative water vapor permeability (the relative heat flow responsible for the cooling of the body) also increases and the fabric temperature drops due to the evaporation of the water from the surface of the fabric. In this work on the experimental study of water vapor permeability of wet fabrics, the effect of air layers between the skin of the wearer and the fabric on the total relative cooling heat flow (cooling effect) experienced by the skin of the garment wearer is investigated. It was found out that when layers of 2- and 4-mm thickness were introduced between the skin and the fabric, the relative water vapor permeability or relative cooling heat flow was smaller than when the fabric was in direct contact with the skin, and in this case it did not depend significantly on the fabric moisture content.

Mechanical properties of composite materials made of 3D stitched woven-knitted preforms

This article presents an experimental investigation carried out to understand the mechanical behavior of composite materials made of 3D stitched woven-knitted basalt fabrics. The innovative preforms used consist of two outer layers of a plain woven fabric combined with two inner layers of weft-knitted fabrics. The weft-knitted fabrics selected for the study were varied plain knit, 1 × 1 rib, Milano, and interlock. The fabric layers were stitched together with Kevlar yarns. These 3D stitched preforms were impregnated with polyester resin using resin transfer molding, and the corresponding composites obtained were tested under tensile, bending, and impact loads. The results obtained show that the type of knitted structure significantly influences the mechanical performance of the 3D stitched woven-knitted composites. The composite using interlock structure as the inner layers has the best results concerning energy absorption and tensile strength. The varied plain knit structure has proved to be the best suited to impart stiffness as it provides the highest Young’s modulus among the above four knitted structures.

Self-monitoring Composite Rods for Sustainable Construction

This paper presents the development and properties assessment of braided reinforced composite rods (BCR) able to both reinforce and monitor the stress state of concrete infrastructures. The research study aims at understanding the tensile behaviour and self-monitoring ability of composite rods reinforced by a textile structure – braided structure with core reinforcement – for civil engineering applications, namely for concrete internal reinforcement, as a steel substitute, in order to improve structures safety and sustainability. Seven types of braided composite rods have been produced using an author patented technique based on a modified conventional braiding machine. The tensile properties of the braided reinforced composite rods were evaluated in order to identify the type(s) of fibre(s) to be used as core reinforcement. BCR have been tested under bending while the variation of the electrical resistance was simultaneously monitored.

Optimization of Dry and Wet Heat Transfer through Textile Structures

This work reports on research being carried out in the area of functional knitted fabrics with a special structure incorporating hydrophobic fibres near to the skin and suction channels of hydrophilic fibres to suck moisture from the skin on the hydrophilic layer away from the skin; in this way, comfort is maximised in active wear as the fabric does not feel wet near to the skin.

The Comparison of the Thermal Behaviour of Leisure and Sports Clothing Using Conventional and New Textile Materials

This work reports on research being carried out in the area of functional knitted fabrics with a special structure incorporating hydrophobic fibres near to the skin and suction channels of hydrophilic fibres to suck moisture from the skin on the hydrophilic layer away from the skin; in this way, comfort is maximised in active wear as the fabric does not feel wet near to the skin.

Development of GF/PP Towpreg Woven Fabrics for Composite Reinforcements

In the present work, glass fibre polypropylene (GF/PP) woven fabrics were manufactured from cost-effective flexible thermoplastic towpregs produced by a developed dry coating process. The paper describes the modifications made on the developed coating line to allow producing thermoplastic towpregs able to be woven in textile equipments. The produced fabrics were observed under optical microscopy and submitted to tests in order to evaluate their textile-like properties, glass fibre content and flexibility. Composites processed from those fabrics by compression moulding were also submitted to mechanical testing in order to assess their performance. The obtained experimental results have shown that the woven fabrics produced are cost-effective and present properties good enough to be applied in large-scale commercial markets (e.g. automotive). Future research efforts will be carried to try decreasing the towpreg frictional properties and the amount of polymer lost during the textile processing and improving the feeding technology to warp yarns directly from a creel.

Fibrous Reinforcements for Composite Materials: Producing and Modelling

This paper presents some of the recent research work taking place in the development of complex shape preforms using weft-knitting and braiding technologies for technical applications, especially for composite materials reinforcement. A FEA model has been used for the prediction of the deformation behaviour and related mechanical properties of weft knitted fabrics and corresponding composite material. A plain weft knitted fabric, based on the simple loop structure, is simplified and represented by a 2D hexagonal structure constructed by the non-linear truss elements. The characteristics of the truss elements for FEA simulation are obtained from experimental results through an analytical method when a loop is converted to a FEA model. The elongation deformation is simulated in one, two and multi directions. The model can also be used to calculate a plain weft-knitted fabric to be deformed to fit a 3D mould with a spherical form.