If there is a typical engineering material that is associated in the public's mind with modern engineering practice, it is structural steel. This versatile construction material has several characteristics, or properties, that we consider metallic: (1) It is strong and can be readily formed into practical shapes. (2) Its extensive, permanent derformability, or ductility, is an important asset in permitting small amounts of yielding to sudden and severe loads. Many Californians have been able to observe moderate earthquake activity that leaves windows (of relatively brittle glass) cracked while steel support framing still functions normally. (3) A freshly cut steel surface has a characteristic metallic luster, and (4) a steel bar shares a fundamental characteristic with other metals: it is a good conductor of electrical current. Although structural steel is an especially common example of metals for engineering, a little thought produces numerous others [such as gold, platinum, lead and tin].
An alloy is a metal composed of more than one element. Engineering alloys include the cast-irons and steels, aluminum alloys, magnesium alloys, titanium alloys, nickel alloys, zinc alloys and copper alloys. For example, brass is an alloy of copper and zinc.
Taken from Introduction to Materials Science for Engineers, James F. Shackelford, Prentice Hall, Inc., New Jersey.
Rarely do we find metallic elements in the `free' state. For example, consider native silver. Silver has been mined for eons and has always been popular in jewelry and for coinage. Only in the past hundred years however, has the demand for silver been so great. The reason for this demand is the use of silver in the photography industry, which takes advantage of silver's reactivity to light. Native Silver is rare and much silver is produced from silver-bearing minerals such as prousite, pyrargyrite, galena, etc. Specimens of Native Silver usually consist of wires that are curved and intertwined together, making an inspiring mineralogical curiosity. The reference source URL is a commercial supplier of mineral specimens. The image has Copyright1995,1996 by Amethyst Galleries, Inc..
Society gets its metals from an ore, not from the natural element found in nature. Ores are often a combination of the metallic element and a non-metallic element. Consider, for example, Galena. Galena, PbS, is a common and popular mineral for rock hounds. Its characteristic cubes, distinctive cleavage and high density make it easy to identify and a favorite in high school geology labs. The structure of Galena is identical to that of halite, NaCl. The two minerals have the same crystal shapes, symmetry and cleavage. Some Galena may contain up to 1% silver in place of lead. The large volume of Galena that is processed for lead produces enough Silver as a by product in the production of Galena, the leading ore of Silver. The reference source URL is a commercial supplier of mineral specimens.
Shown on the left is the basic oxygen furnace used in the production of steel. Other steel production images are also available at this URL from Corus Education. Corus is a company that manufactures, processes and distributes steel products and services to customers worldwide. For additional information on the making of steel, visit either of the following web pages: The Steel Society; or 'What's a Matter-U".
The basic oxygen furnace is just one method for producing steel. One way to make something useful is to pour the liquid metal directly into a crucible or mold and let it solidify. However, there are alternative processes such as the condensation of evaporated metallic elements; or the consolidation of micron-size particles! Some of these alternate processes are explored in the companion web page, AltProcess.htm
Here is where the metal aluminum, once 'won' from the earth, finds useful application. The aluminum alloy used in the production of beverage cans contains manganese and is highly hardenable. This means that when worked (or hammered!), the aluminum becomes harder or 'more resistant' to further deformation. The all aluminum-can is one of the most convenient and cost-effective containers ever developed for delivering beverages to consumers. If you would like to know how a beverage can is made from aluminum plate more than one-foot thick, I invite you to explore the following web pages. Discover just how amazing the aluminum beverage can really is. The reference source URL is The Aluminum Association.
A close-up image of the rocker assembly on a mountain bike appears below. The reference source URL is Marin Bikes. If you would like to know more about the materials selection options for making a bicycle frame, please link to either of the following: Technical White Paper; or, University of Washington web pages: Bicycle Materials Case Study.
Another interesting component of the bicycle, usually made from a metallic alloy, is the spoke. The Web Pages of Belgian spoke manufacturer Sapim provide some insight to producing super lightweight, bladed spokes. For example, the small CX-Ray blades, of extremely high tensile strength (due to a special forging process), cut wind resistance markedly. A materials engineer (or mechanical engineer with materials expertise) would be involved with the following issues regarding the design and fabrication of advanced bicycle spokes:
The complexity of the design and selection of metals and alloys used in a high-temperature, aggressive environment is illustrated in this image (left). I believe this is a heat exchanger, perhaps in a petro-chemical plant. I found this image while doing a search for NDI (Non-Destructive Inspection) information, so the source is not directly relevant to the metals and alloys web pages. Nevertheless, I could not resist including it! The reference URL is Q.A.T.E., a Australasian quality assurance and testing engineering firm which manufacturers and resales NDI products.
There is a class of alloys called shape memory alloys. These alloys provide the engineer a means of restoring a bent metal wire to some trained alternate shape. These SMA's have applications ranging from frames for optical glasses to repair parts for the human body. For example, fine NiTi (containing approximate equal parts of nickel and titanium) shape memory or superelastic wires can be woven into cylindrical shapes for various applications. One such application is vascular stents to reinforce blood vessels in the human body. The stent is crushed and inserted through a cannula into the proper location in the blood vessel. Upon warming above its transformation temperature, the stent returns to its trained cylindrical shape and provides reinforcement to the walls of the blood vessel. If you would like to see a stent in-service in a blood vessel, go to the Biomaterials link on these pages. If you would like to know more about shape memory alloys, go to the web pages of Johnson-Mathis, the source of the image.
By the way, how do you think the common coin is made? This is a common metal device familiar to us all. Consider; what metal(s) and alloy(s) do you think are used in the fabrication of a dime? This is an excellent topic to search on the Internet. How is a dime fabricated? The process is termed 'coining' if this will help.
The materials engineer is often involved in a function called failure analysis. The materials engineer that deals with metals and alloys is most often asked to participate in the analysis of structural and mechanical failures. For further information about this most interesting aspect of materials engineering, please visit the Failure Analysis web pages at this site.
Concept of Structure
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