Composites

Exploring Materials Engineering



Composites

Composites: materials, usually man-made, that are a three-dimensional combination of at least two chemically distinct materials, with a distinct interface separating the components, created to obtain properties that cannot be achieved by any of the components acting alone.
Composites are combinations of two materials in which one of the materials, called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other materials called the matrix phase. The reinforcing material and the matrix material can be metal, ceramic, or polymer. Typically, reinforcing materials are strong with low densities while the matrix is usually a ductile, or tough, material. If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. The downside is that such composites are often more expensive than conventional materials. Examples of some current application of composites include the diesel piston, brake-shoes and pads, tires and the Beechcraft aircraft in which 100% of the structural components are composites.
Taken from The Science and Design of Engineering Materials; by J.P. Schaffer, A. Saxena, S.D. Antolovich, T.H. Sanders, Jr. and S.B. Warner, published by IRWIN [now McGraw-Hill], Chicago.
As a general overview of composites and composite applications, I suggest this source . Some tutorials about "Composite Materials" are found on the Internet, but they are limited in scope. For example, visit this Composites-by-Design site. Also, one may find it useful to look over the glossary of terms on the following Hexcel Corporation web pages. This may provide useful insight. For information specific to polymer composites, try the University of Southern Mississippi web pages.

Recreational equipment is heavily dependent on materials technology. For example, consider a snowboard. Snowboards are fabricated from advanced composite materials. An example is illustrated below. The reference source URL is Rossignol Snowboards. The Rooster snowboard (vintage 1998) is a free-riding, twin-tip board with a cap and a full wrap around edge. These boards are stiff and torsionally rigid so one can rail them at high speed and launch and land the hugest airs. Look at the intricate design shown in the sectional view. For more information on composite snowboard materials and construction, visit the abc-of-snowboarding web pages at the following URL.



Shown below are various structural composite members. They consist of glass fibers incorporated in a polymeric resin matrix. When the resin cures to a hard state, it is strengthened by the reinforcement. The shape of the finished part is dependent on a mold, die or other tooling that controls the geometry of the composite during processing. Shown are aerospace applications, like the Space Boom and a High Velocity Aircraft. The reference URL for this image was Owens Corning. Select the 'Composites Solutions' link to get more information. For other applications of structural composite materials, visit the web pages of TPI Composites. For space and satellite applications, refer to this JOM Journal of Materials article.

A structural composite often begins with lay-up of prepreg. The choice of fiber will influence the basic tensile and compressive strength and stiffness, electrical and thermal conductivity, and thermal expansion of the final pre-preg material. The cost of the composite is also strongly influenced by the fiber selected. The reference source URL is Cytec Corporation

Below is a scanning electron micrograph (SEM) of a graphite composite golf club shaft. The graphite reinforced golf club shaft has been cross sectioned and polished, and the micrograph shows an area where damage occurred while sectioning. For more about carbon, fiber-reinforced composite structures, visit these Columbia University web pages. However, these web pages were 'hacked' and have not been brought back to service. Consider an alternative SEM site. The Centre for Microscopy and Microanalysis at the University of Queensland, Australia, is an interdisciplinary research and service facility dedicated to an understanding of the structure and composition of all materials at atomic, molecular, cellular and macromolecular scales. Its 'Nanoworld' web pages offer a gallery of interesting scanning electron microscopic images. Materials related images begin about Fig. 59, page 03, at the following URL; but one may very well be interested in viewing some of the other 300+ images. Have fun!

To illustrate one aspect of the interest of the materials engineer in composites, consider the following. A micrograph of a vacuum processed, void-free glass-fiber/epoxy composite is illustrated on the left. On the right, a special probe is being used to determine how much force it takes to get the fiber to 'slip away' from the matrix under a compressive load. From load versus deflection information, one can quantify the structural integrity of the composite; or assess the quality of the processing steps used in the manufacture of the composite. Two academic programs with research focus on composite materials are represented by these images. The cross-section is from the web pages of UC-Berkeley; and the fiber testing image is from the web pages of theUniversity of Southern California: Center for Composite Materials.

The composite of the USC research image, illustrated above, is an aluminum alloy composite reinforced with aluminum oxide fibers ~ 12µm in diameter. This is termed a metal-matrix composite. For more information about MMC's, visit the following Mechanical Engineering Memagazine, July 2001 feature article: 'packaged for the road'.

The strength of the resin/fiber composite depends primarily on the amount, arrangement and type of fiber (or particle) reinforcement in the resin. Typically, the higher the reinforcement content, the greater the strength. In some cases, glass fibers are combined with other fibers, such as carbon or aramid, to create a "hybrid" composite that combines the properties of more than one reinforcing material. In addition, the composite is often formulated with fillers and additives that change processing or performance parameters. For information about the materials engineering approach to designing with composites , you are encouraged to visit the following The University of Western England (I kid you not!) web pages.

A mountain bike is another piece of recreational equipment that is dependent on advanced material's technology. The mountain bike utilizes composite materials; but it also is an integration of a number of other structural materials (ie, metals, elastomers [rubber!], etc). It is, thus, a composite system. These bikes can weigh less than 16 pounds and still meet the rigors of the sport. The reference source URL is Marin Bikes. For specific information about materials used in the construction of a bicycle, read the following white paper.

The integration of ceramic, metallic, plastic and semiconductor materials is a necessary requirement to the fabrication of the micro-electronics package, shown below, left. This is a composite system whose function is to provide interface between the central IC (Integrated Chip) and the other items on, for example, a PCB (printed circuit board). The package has been de-capped (ie, a hole made in the top) to reveal the inside of the package. Decapsulation of integrated circuits is described in the following URL. Another example of a generalized, composite system, using a number of complementary materials, is shown on the right, below. Can you guess the function of the system? Certainly this is not an example of a composite material. It has been included to emphasize the point that many classes of materials are frequently used in combination to make engineering devices, components or structures to best serve society. The reference source URL for the mystery system is Philips Research.



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Please send any comments to Patrick P. Pizzo, Professor Emeritus, Materials Engineering
Created by Dr. Pizzo on August 1, 1997.
Last Revision, December 06, 2012