Compared to most synthetic fibers, natural fibers are low-cost, are easier to handle, have good specific mechanical properties, and require only around 20–40% of the production energy. Using natural materials and modern construction techniques reduces construction waste and increases energy efficiency while promoting the concept of sustainability. Several drawbacks of natural composites which would be even more pronounced in their use in infrastructure include their higher moisture absorption, inferior fire resistance, lower mechanical properties and durability, variation in quality and price, and difficulty using established manufacturing practices when compared to synthetic composites. Many researchers have been working to address these issues, with particular attention paid to the surface treatment of fibers and improving the fiber/matrix interface. Because of their positive economic and environmental outlook, as well as their ability to uniquely meet human needs worldwide, natural composites are showing a good potential for use in infrastructure applications.

Critical review of recent publications on use of natural composites in infrastructure

Critical Review of Recent Publications on Use of Natural Composites in Infrastructure

Because of their wide abundance, their renewable and environmentally benign nature, and their outstanding mechanical properties, a great deal of attention has been paid recently to cellulosic nanofibrillar structures as components in nanocomposites. A first major challenge has been to find efficient ways to liberate cellulosic fibrils from different source materials, including wood, agricultural residues, or bacterial cellulose. A second major challenge has involved the lack of compatibility of cellulosic surfaces with a variety of plastic materials. The water-swellable nature of cellulose, especially in its non-crystalline regions, also can be a concern in various composite materials. This review of recent work shows that considerable progress has been achieved in addressing these issues and that there is potential to use cellulosic nano-components in a wide range of high-tech applications.

Cellulosic nanocomposites: a review

Biodegradable Soy Protein Isolate-Based Materials: A Review

In the context of sustainable development, considerable interest is being shown in the use of natural fibres like as reinforcement in polymer composites and in the development of resins from renewable resources. This paper focuses on eco-friendly and sustainable green composites manufacturing using resin transfer moulding (RTM) process. Flax fibre reinforced bioepoxy composites at different weight fractions (40 and 55 wt%) were prepared in order to study the effect of water absorption on their mechanical properties. Water absorption test was carried out by immersion specimens in water bath at room temperature for a time duration. The process of water absorption of these composites was found to approach Fickian diffusion behavior. Diffusion coefficients and maximum water uptake values were evaluated; the results showed that both increased with an increase in fibre content. Tensile and flexural properties of water immersed specimens were evaluated and compared to dry composite specimens. The results suggest that swelling of flax fibres due to water absorption can have positive effects on mechanical properties of the composite material. The results of this study showed that RTM process could be used to manufacture natural fibre reinforced composites with good mechanical properties even for potential applications in a humid environment.

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Water Absorption Behaviour and Its Effect on the Mechanical Properties of Flax Fibre Reinforced Bioepoxy Composites

Fully biodegradable high strength composites or 'advanced green composites' were fabricated using yearly renewable soy protein based resins and high strength liquid crystalline cellulose fibers. For comparison, E-glass and aramid (Kevlar®) fiber reinforced composites were also prepared using the same modified soy protein resins. The modification of soy protein included forming an interpenetrating network-like (IPN-like) resin with mechanical properties comparable to commonly used epoxy resins. The IPN-like soy protein based resin was further reinforced using nano-clay and microfibrillated cellulose. Fiber/resin interfacial shear strength was characterized using microbond method. Tensile and flexural properties of the composites were characterized as per ASTM standards. A comparison of the tensile and flexural properties of the high strength composites made using the three fibers is presented. The results suggest that these green composites have excellent mechanical properties and can be considered for use...

Advanced 'green' composites

In the aviation industry, materials are being developed to improve the performance of jet engines. TiAl is used in turbine blades because of its high strength at high temperatures and its light weight. However, due to the difficulty of machining TiAl, additive manufacturing has been expected in recent years. Electron-beam-melted TiAl4822 has a unique layered microstructure composed of duplex-like fine-grain layers and a band of coarser γ-grains. This unique microstructure is known to bring about the anisotropy of mechanical properties. This study investigated the effects of building direction on creep properties. The creep test was conducted in accordance with the ASTM standard. The creep life of an additive manufacturing specimen was longer than that of a cast specimen due to the higher percentage of lamellar structure in the former. A specimen with building angle θ = 0° (vertical direction) had the longest creep life, which is attributed to the deformation of layers. When the building angle is θ = 45° or 90°, slip occurs between the layers, resulting in the formation of a large void along the vertical grain boundary of the γ band, which may cause high creep elongation. 

Effect of build direction on creep properties of TiAl4822 alloy additively manufactured by electron beam melting

TiAl (Titanium aluminide) alloy is attracting attention in the automobile and aviation industries as a promising lightweight heat-resistant alloy material. Parts used in the high-temperature environment must have ductility and toughness at room temperature in addition to high strengths at high-temperature, because some alloys such as TiAl alloy is known as a difﬁcult material for casting and machining. Recently, manufacturing process using AM (addi tive manufacturing) have been studied to avoid these problems. In this research, the effect of the energy density during AM process on surface roughness and strengths of the built parts was studied by changing build parameters. As the energy density increased, the porosity and surface roughness decreased. The higher energy density tended to increase the proportion of lamellar structure. It was found, however, that the increase in lamellar structure does not necessarily lead to the improvement in tensile and creep strengths at 750°C. As a result, the constant energy density of 15 J/mm 3 showed better tensile and creep properties than those of the standard parameter. The results suggested that it is important to optimize the parameters according to the required properties of the parts.

Kazuhiro Mizuta

Papers

Advanced 'green' composites

Effect of build direction on creep properties of TiAl4822 alloy additively manufactured by electron beam melting

Effect of process parameters on microstructure and high-temperature strengths of titanium aluminide alloy fabricated by electron beam melting