Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites

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

In the 1970s, high chromium (9–12%Cr) ferritic/martensitic steels became candidates for elevated temperature applications in the core of fast reactors. Steels developed for conventional power plants, such as Sandvik HT9, a nominally Fe–12Cr–1Mo–0·5W–0·5Ni–0·25V–0·2C steel (composition in wt-%), were considered in the USA, Europe and Japan. Now, a new generation of fission reactors is in the planning stage, and ferritic, bainitic and martensitic steels are again candidates for in-core and out-of-core applications. Since the 1970s, advances have been made in developing steels with 2–12%Cr for conventional power plants that are significant improvements over steels originally considered. The present study will review the development of the new steels to illustrate the advantages they offer for the new reactor concepts. Elevated temperature mechanical properties will be emphasised. Effects of alloying additions on long-time thermal exposure with and without stress (creep) will be examined. Information ...

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Elevated temperature ferritic and martensitic steels and their application to future nuclear reactors

Despite the large number of recent reviews on green composites, limited investigation has taken place into the most appropriate applications for these materials. Green composites are regularly referred to as having potential uses in the automotive and construction sector, yet investigation of these applications reveals that they are often an inappropriate match for the unique material attributes of green composites. This review provides guidelines for engineers and designers on the appropriate application of green composites. A concise summary of the major material attributes of green composites is provided; accompanied by graphical comparisons of their relative properties. From these considerations, a series of complementary application properties are defined: these include applications that have a short life-span and involve limited exposure to moisture. The review concludes that green composites have potential for use in a number of applications, but as with all design, one must carefully match the material to the application.

Green composites: A review of material attributes and complementary applications

A series of tensile tests were conducted on a Lloyd LRX tensile testing machine for numerous natural fibers deemed potential candidates for development in composite applications. The tensile tests were conducted on the fibers jute, kenaf, flax, abaca, sisal, hemp, and coir for samples exposed to moisture conditions of (1) room temperature and humidity, (2) 65% moisture content, (3) 90% moisture content, and (4) soaked fiber. These seven fibers were then tested for the four conditions and the mechanical properties of tensile strength, tensile strain to failure, and Young's modulus were calculated for the results. These results were then compared and verified with those from the literature, with some of the fibers showing distinctly promising potential. Additionally, a study on the effect of alkalization using 3% NaOH solution was carried out on flax, kenaf, abaca, and sisal to observe impact that this common fiber pre-treatment process has on fiber mechanical properties. The result of the investigation indicated that over treatment of natural fibers using NaOH could have a negative effect on the base fiber properties. It is consequently apparent that a treatment time of less than 10 min is sufficient to remove hemicelluloses and to give the optimum effect.

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Tensile Testing of Cellulose Based Natural Fibers for Structural Composite Applications

An experimental study of damage accumulation in balanced CFRP laminates due to repeated impact

The vacuum infusion process has been found to be very versatile for making large composite structures. During the resin impregnation process, the vacuum causes the nucleation and formation of air bubbles from gasses dissolved in the resin. One solution to this would be a degassing process prior to infusion. Recent experiments have shown that a degassing process, conducted in batches with a small quantity of a bubble nucleation agent (Scotch–Brite) and an air sparging method could reduce void formation in the vacuum infusion process. At 90 mbar, this method of degassing may remove 40–50% of the dissolved gas. However, despite reducing the level of dissolved gas, some micro-bubbles remain suspended due to the viscosity of the resin and contribute to void formation. While these results were quite encouraging, there is a need to design a system to ensure a continuous supply of degassed resin as a better way forward. In a continuous degassing system, it is necessary to establish the relationship between the degassing process quality and void content reduction from the perspective of strength and performance, besides signifying the most viable method of degassing.

Bubble free resin for infusion process

Changes in the dielectric relaxations of water in epoxy resin as a function of the extent of water ingress in carbon fibre composites

Applications of high-frequency dielectric measurements (300 kHz to 3 GHz) to the non-destructive examination (NDE) of composite structures are discussed Preliminary data indicate that the method, previously used for aluminium bonded structures, can be applied to bonded carbon fibre composite structures Water ingress into the bond structure was observed to influence both the time- and the frequency-domain data Comparison of exposed and dry joints demonstrated that a good correlation exists between changes with time in the dielectric properties of the composites and the extend of water uptake in the matrix Parallel gravimetric measurements were also performed Diffusion of water into the composite structures is discussed in terms of various models This paper demonstrates that this NDE method may be used for assessment of the water content in the matrix and has general applicability to the study of carbon-reinforced matrix materials

William M. Banks

Papers

Tensile Testing of Cellulose Based Natural Fibers for Structural Composite Applications

An experimental study of damage accumulation in balanced CFRP laminates due to repeated impact

Bubble free resin for infusion process

Changes in the dielectric relaxations of water in epoxy resin as a function of the extent of water ingress in carbon fibre composites

Non-destructive examination of composite joint structures: a correlation of water absorption and high-frequency dielectric propagation