Posts Tagged ‘Composites’

CIBOR: The future in composites

CiBOR (www.ncibor.org), The National Center of Innovation for Biomaterials in Orthopaedic Research, conducts research and develops certified prototypes of medical products made from composite materials.

Next Generation Fibre Reinforced Composites

Introduction

Composite fibre products are not new. The first composite material known was made in Egypt around 3,000 years ago when clay was reinforced with straw to build walls. With the advent of metals, the use of natural fibre for reinforcing declined. The rise of composite materials began during the 1960s when glass fibres in combination with tough rigid resins could be produced on a large scale. Fibre Composites consist of polymers (plastics) reinforced with carbon, glass and/or Aramid (Kevlar) fibres. These materials are up to 6 times stronger than steel and concrete at a fraction of the weight. They are also non-corroding, non-magnetic and can be designed to locate strength and stiffness where it is needed. The potential cost advantages are significant.

Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure.

Why Use Composites?

To satisfy the increasing demand for housing and infrastructure, industry and government are constantly looking for building materials and structures that are strong, economical, and easy to assemble and durable. Fibre composites satisfy these requirements.

Specific advantages of fibre composites in structural engineering include:

More appropriate and economical structures:

Case histories demonstrate that in many applications (even with today’s material costs and processing technologies) fibre composites are directly competitive in initial cost, substantially less expensive in terms of installed cost, and far less costly in maintenance.

More attractive structures:

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Because of the high strength, low weight and excellent design flexibility, fibre composite structures are commonly smaller, easier to blend in with the environment and more pleasing to the eye.

More environmentally friendly structures:

The high corrosion resistance of fibre composites eliminates the need for chemical treatment (as required for most timbers), or protection by toxic paints (as with steel). Consequently there is less danger of leaching of dangerous chemicals into the environment.

Composite materials are also becoming more sustainable:

Significant effort is being made in the development of polymer resins made from plant oils. Soy based resins are already in use for non-structural components, and natural fibres such as flax are being used to create sustainable composites from renewable resources.

A Nickel-Carbon-Fibre Composite for Large Adaptive Mirrors

The next generation of ground-based optical telescopes is currently under development. These telescopes will have primary mirrors of 30-50m in diameter and are termed Extremely Large Telescopes (ELTs). Most design studies for ELTs have identified the need for an integrated large adaptive mirror ranging in size from 2-4 metres and either flat, convex or concave in profile. Currently there is a move towards large, ultra-thin glass mirrors, however these are fragile, costly to produce and unlikely to be made to the sizes required for ELTs, needing a less desirable segmented arrangement of smaller mirrors to obtain the required diameter.

An alternative solution could be to use carbon-fibre composite (CFC) substrates – these are very robust even at high length to thickness aspect ratios and are scalable to the maximum sizes proposed. Some of the benefits in using CFC material are its low density, high stiffness and good thermal stability – these properties and others can be optimized for the project in question by careful choice of the fibre/resin ply matrix and design of the laminate lay-up sequence.

Carbon Fibre Reinforced Composite Car

Carbon dioxide emissions and world hydrocarbon fuel reserves means that there is considerable interest in technologies that reduce fuel consumption for passenger cars. In the area of vehicle design, body weight is the most important target for improvement, as a reduction in the weight of a vehicles body means that a smaller engine, and a lighter drive train and assembly can be used. So that various studies have indicated a potential for savings of up to 65% by using carbon fibre composites instead of steel wherever possible.

The Aero-Stable Carbon Car (ASCC) programme has been investigating the limitations to maximizing fuel economy in a lightweight car manufactured using carbon fibre composites (CFC). Current lightweight composite vehicles, such as racing cars, use a monocoque stressed-skin design for both weight and manufacturing cost reasons.

The monocoque approach having been discarded, a more efficient design that does not need to transfer large loads through panel joints, is to use a very stiff framework of complex shaped beams and struts, covered by thin panels, bonded using low stiffness adhesives. This approach also offers benefits in vehicle assembly and fitting, since loading and attachment points can be provided on the framework and the panels can be attached near the end of the process to provide clear access through frame apertures.

NPL’s role in developing polymer composites metrology for use in today’s state-of-the art structures

NPL’s role in developing polymer composites metrology for use in today’s state-of-the art structures by Michael Gower Recorded July 2006Celebrating Science is a series of lectures given by NPL scientists or external speakers designed to inspire and inform us about the amazing research done both at NPL and other institutions worldwide. More: www.npl.co.uk

Advanced Composites as high-end engineered materials

The quest for using light-weight structural materials, which also have the necessary strengths, especially in aerospace industry, led to the development of the modern fiber reinforced laminated composite materials in the late 70′s. While light weight metals such as aluminum or its alloys were widely used in the industry, they still lacked the necessary strengths and stiffness’s required in high strength applications. These limitations of pure materials or alloys were overcome by embedding fibers of glass, carbon, Boron and other substances in a metal or polymer matrix paving the way for an era of advanced man made materials of high strength. The fundamental idea of reinforcement of a weaker matrix material with tougher fibrous materials has, however, always existed since primitive times and is still being used in a variety of ways- in simple to complex engineering application domains. Mud mixed with jute or straw are still being used for building construction in certain societies, with an intuitive understating of the improvement in structural behavior. Reinforced cement concrete was invented with similar ideas, as hardened concrete though having a high compressive strength can resist negligible tensile loads. Mild steel bars with a good bond in the concrete matrix are designed to take all the tensile forces while concrete resisted compression. With this fundamental idea, the use of reinforced concrete became a huge success in the construction industry, which until then was facing the difficulty of supporting larger structural spans without resorting to the construction of arches.

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In a similar manner, fiber reinforced composites are the choice of engineers for advanced applications, e.g., making the body of a spacecraft, for making the supporting frame work of an antenna in space, etc., where the desirable engineering properties (performance) rather than the cost of manufacturing the material is the prime consideration.

The advantage of composite materials is normally expressed through the stiffness/weight ratio achievable while comparing with an equivalent metallic structural component. Some of the well known everyday materials, e.g., like ‘Fiber glass’, are made of glass fiber reinforced plastics. Other well known fiber materials are carbon (graphite), Kevlar (made by Dupont), and Boron fibers.

Graphite-epoxy composites, (also called carbon fiber composites), for instance, are very standard composites used widely. Kevlar fibers have very high strength and special composites are made with them, e.g., as aircraft parts, bullet proof vests, etc. Increasing use of the composites can be seen in infrastructure, sports goods (sail boats, bicycles, etc.), bio-medical (special implants), automotive, space, and innumerable other industries as well.

Manufacturing process:

Composites are of various types, via, those with randomly distributed fibers, and, secondly, laminate. An example of the former type is the case of a crash helmet. Generally randomly distributed fibered products are molded and cured. The process of making laminates on the other hand is more involved. Firstly, uni-directionally laid fibers embedded in the matrix material are manufactured in the form of tapes called pre-pegs. Any piece of a finite length cut from such a tape is known as a lamina. To achieve uniform directional properties, laminas are laid over each other in different pre determined directions and fused together to form laminates. Thus structural materials of desired directional properties can be manufactured.

Structural forms, design and analysis (Challenge for the Engineer)

The basic structural components can generally be grouped into beams, plates and shells. Other shapes in the form of cylindrical or conical shapes are custom made. The challenge for the designer lies in the fact that unlike a conventional structural material like steel, fiber reinforced composites are orthotropic requiring the determination of nine basic elastic constants as against two required for a homogeneous isotropic material like steel or aluminum. The mechanical behavior of a laminated composite is complex and requires a good understanding of the concepts from the theory of anisotropic elasticity. Thus for an analyst grounded in the subjects of mechanics and engineering the analysis of composite behavior presents an excellent challenge and a fertile ground for carrying out research and development.

However, the composite industry is now well developed, significantly big and mature. A large body of industry-related as well as academically oriented literature exists in the form of books, journals and other periodicals. Much information can be traced through the internet medium as well.

Polymer Carbon Nanotube Composites: The Polymer Latex Concept

Product Description
This book provides readers with a comprehensive toolbox for dispersing single-walled and multiwalled carbon nanotubes in thermoplastic polymer matrices. The book starts with an overview of all known techniques for dispersing CNTs in thermoplastic polymers and then concentrates on one of the most versatile techniques known nowadays: the so-called latex technology. Also discussed are the basic principles of this latex technology, the role of the matrix viscosity on pe… More >>

Polymer Carbon Nanotube Composites: The Polymer Latex Concept