how-engineering-materials-are-classified

Here’s How Engineering Materials Are Classified

February 15, 2023 - Ellie Gabel

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Engineers are concerned with optimizing materials, creating structures and machines that withstand usage and maximize their purpose. How engineering materials are classified helps professionals pick the most suitable for each project they tackle. To make the best material selection, knowing how their qualities separate them is essential.

Every material has the chance to be substantial depending on how engineers utilize them. Materials may need to bear heavy loads without deflection — and most importantly, they cannot break or wither. Engineers use these major categories to discern what’s best for their creations.

Metals and Alloys

Engineering materials have major categories that branch off into smaller designations. Metals and alloys make up one of the two most extensive umbrellas. Metals have the capability of changing their shape. This ductility and malleability make them widely versatile. Once engineers design that shape, it can stay that way permanently. Engineers use alloys to enhance metals above their standard capabilities to:

  • Make their electromagnetic characteristics stronger
  • Enhance grain size
  • Change electrical properties

The benefits of metals stack as they have high electrical and thermal conductivity. With the added benefit of added alloys, melting and mixing them to form upgraded materials is a simple process to take advantage of different hardnesses and luster. Some of the most common engineering metals and some of their uses include:

  • Silver for circuit boards
  • Copper for pipe fittings
  • Gold for connecting wires in cellphones
  • Aluminum for car engines
  • Iron for steel girders
  • Zinc to form brass for musical instruments
  • Lead for typesets
  • Tin for metal bearings

All metals fall into the two subcategories of this classification — ferrous and non-ferrous.

Ferrous Metals

These are magnetic metals containing iron and carbon. The negative is they are prone to rust when exposed to moisture. Sometimes, they have other elements, such as phosphorous and sulfur, in small quantities to change the metal’s qualities.

Ferrous metals usually contain a couple of further subcategories, including cast iron and steel. Steel is an iron alloy with up to a 2% concentration of carbon. This creates a more robust material since iron is soft by nature. The more carbon it gets, the stronger it becomes. Cast iron is a stronger ferrous metal, containing carbon contents between 2-6%, though this causes it to be more brittle. Each could be broken down even further, reaching into more curated uses for each material. 

Other ferrous metals include wrought iron and stainless steel, an alternative containing chromium which prevents it from rusting.

Non-Ferrous Metals

These are non-magnetic since iron is not part of their primary content. They have a high resistance to rust and corrosion. Since they can withstand high temperatures, it makes them ideal for medical engineers. Sterilizing medical materials like surgical blades is easier with metals as a whole.

Non-Metals

Non-metals can take the form of any state of matter — solid, liquid or gas. This includes elements like hydrogen and silicon — a metalloid — are poor conductors of heat or electricity and do not have the ductility of metals. 

The benefit they do have is that non-metals can join to create compounds. Like how alloys can strengthen metals to provide alternative characteristics, compounds are when chemicals bond together to form a new material. These materials make the subsections for non-metals — organic and inorganic.

Organic Non-Metals

Carbon is what makes organic compounds. They are highly complex and exist from living things like wood, leather, rubber and plastic. They do not dissolve in water, making them ideal for specific engineering environments. 

Under this section are organic polymers that are lightweight and low-cost. Materials like plastics, adhesives and fibers fall into this category. They have high plasticity and are naturally inert, making them highly moldable.

Inorganic Non-Metals

Inorganic materials are not found in nature and do not contain carbon. Some standard engineering materials that are inorganic non-metals include cement, minerals and glass. Just as steel and cast iron are subsections of ferrous metals, inorganic non-metals continue to divide into more specific components.

Ceramics and glass are nonmetallic and inorganic, with excellent thermal and electrical insulating properties and low conductivity. They include stones, abrasives and heavy clayware. This group can withstand a great deal of wear and tear and corrosion. Their high melting temperatures are great for engineering purposes, from spark plugs to bricks. 

Other Classifications

Though most engineers put materials under these designations, a few variations and developments in the field place more recent innovations in their separate categories. This includes composites, which combine multiple materials to create something ideally stronger, lighter and less expensive.

There are also smart engineering materials and innovations like acoustic metamaterials that are more market specific.

First, some choose not to classify engineering materials by metals and non-metals — some prefer to organize them by purpose. This would separate everything into structures like dams, machines like electric motors and devices like photoelectric cells. The main distinctions are creations without moving parts, inventions with moving parts and more modern technologies, respectively.

There are also biomaterials, which include combinations of materials mentioned above, like ceramics and polymers, but engineers specifically design them to interact with biological systems. Medical engineers primarily use these materials to treat or repair tissues or provide diagnoses with materials like artificial proteins. 

An example of a biomaterial would be sutures made from animal sinew. Biomaterials can either be bioerodible and decompose when implanted or biostable, which have a solid resistance to the biological environment they’re installed in, such as dental implants.

Engineering Material Classifications

Though there are many sections to engineering material classifications, they all help engineers discover which materials are best for each project. Many undertakings require diverse materials with varying properties — some are more homogeneous. This will help anyone crossing a bridge or witnessing a wind turbine. Every material going into that formation was considered to optimize it to work most efficiently.

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Author

Ellie Gabel

Ellie Gabel is a science writer specializing in astronomy and environmental science and is the Associate Editor of Revolutionized. Ellie's love of science stems from reading Richard Dawkins books and her favorite science magazines as a child, where she fell in love with the experiments included in each edition.

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