Material Properties

Background

Materials are the building blocks of our designed world. These materials must be found and processed before they are used. Some of these materials occur in nature and others are synthetic or man-made.

Materials can be categorized in many ways. Natural materials can be organic or inorganic, renewable or nonrenewable. Organic materials come from living things like trees, animals, and plants. Inorganic materials come from mineral deposits like stone, metals, and ceramics. Renewable materials can be grown, therefore replaced. Nonrenewable materials cannot. Once they have been used up… they are gone.

When engineers are choosing materials to use in a product or structure, they must consider the properties of the material, as well as other factors like price, availability, environmental impact, health hazards, appropriateness, and durability.

Many times there will be multiple materials that could be used for a given project.

Try this… take a look at the shirt you are wearing. What material is it made of? What about your pants, socks, and shoes? They are not all made of the same material. Your shirt may be polyester, your pants cotton, and your shoes will have different materials; likely nylon and polyester or leather and rubber for the soles.

Material Properties

Material properties are extremely important in selecting a material. Imagine having an umbrella made of cardboard. What would happen when you try using it in the rain? Why wouldn’t you want to have a pillow made of concrete? Why don’t beverage companies make cans from platinum? Material properties must be considered when designing products and structures. Countless people have wasted a great deal of money over the years due to poor material choices and on occasion, people have been injured and killed.

Basic mechanical properties will be examined in class, including strength, fatigue, toughness, hardness, ductility, brittleness, elasticity, and plasticity. Mechanical properties determine how a material responds to force. They affect the material's strength. Other types of properties include acoustical, chemical, electrical, magnetic, optical, physical, and thermal properties.

For this unit, the main focus will be on mechanical properties, but the other types are very important to engineers as well. Acoustical properties determine how a material reacts to sound waves; a few examples are acoustical transmission (a materials ability to transmit sound waves) and reflectivity (a materials ability to reflect sound waves… some materials will absorb the energy while others bounce the waves off).

Chemical properties determine how a material will react to one or more chemicals in the outside environment. Some common chemical properties include chemical activity, corrosion resistance, and solubility.

Electrical and magnetic properties determine how a material will react to electrical and magnetic forces; such as electrical conductivity and magnetic permeability (also known as magnetic conductivity).

Optical properties determine how a material will react to light waves. These properties include color, optical transmission, and reflectivity.

Physical properties are characteristics of a material such as size, shape, density, moisture content, and porosity.

Thermal properties determine how a material will react to heating and cooling. Thermal properties include thermal conductivity, thermal shock resistance (how well a material can handle a sudden or significant change in temperature), thermal expansion, melting point, and boiling point.

Mechanical Properties

A material’s strength is its ability to keep its shape, even when a force is applied. Four kinds of force may be applied to a material. Tension is a force that pulls on a material. Compression is the opposite of tension. It’s a force that pushes on or squeezes a material. Torsion is a force that twists a material. The twisting force itself is called torque. The last force, shear force is created when one part slides in one direction and the other part slides in the opposite direction.

Fatigue is the progressive and localized damage that occurs when a material is subjected to cyclic loading (repeated flexing or bending). Fatigue strength refers to a materials ability to resist failure after repeated bending or flexing. If you have ever taken a paper clip and bent it back and forth, it will eventually snap from too much stress.

Toughness is the capacity of a material to absorb energy without breaking. Think about a bad piece of steak. If you keep chewing and the fibers of the meat don’t break down easily, we would say the meat is tough.

Hardness is a material's ability to resist being scratched or dented. Diamonds are the hardest material known. Products like saw blades and drill bits must be hard, otherwise, they would not have the ability to cut through materials. Some drill bits made of steel are used to bore holes in steel. To do this, the steel bit must be harder than the steel that is being drilled.

A material that can be twisted, bent, or pressed without breaking is said to be ductile. Metals can be quite ductile. Pots and pans begin as a flat sheet and are formed into the desired shape. A wire is made from a thick rod which is “drawn” through increasingly smaller dies to make the desired size.

A material that lacks ductility is said to be brittle. Brittle materials are inflexible, easily shattered or broken, and will not deform without breaking. A good example is window glass. If you have ever seen a window get hit by a rock or baseball, it shatters.

Ductile materials are either elastic or plastic. A material that can be bent or stretched and then returned to its original shape is said to be elastic. Elasticity is the quality of being flexible. Plasticity is similar. Materials with plasticity stay deformed even after a force that shapes them has been removed. The material that we call plastic was named after this property, but there are a number of other materials with this characteristic.

Related Careers

The field of engineering plays a monumental role in today’s world. Engineering has been called the “invisible” or “stealth” profession. Everything around you and that you use every day has been engineered in some way yet you may not see the engineers behind the scenes or know much about engineering.

You have math and science classes and both are basic to engineering. But, engineers take math and science from paper and the lab to invent, design, and build things that matter (technology). They are team players with independent minds who ask, “How can we develop a better recycling system to protect the environment, design a school that can withstand an earthquake, or create cutting-edge special effects for the movies?” By dreaming up creative and practical solutions, engineers are changing the world all the time.

There are many different areas of engineering. It is a profession which applies scientific principles to the design, construction, and maintenance of engines, cars, machines, etc. (mechanical engineering), buildings, bridges, roads, etc. (civil engineering), electrical machines and communication systems (electrical engineering), chemical plant and machinery (chemical engineering), aircraft (aeronautical engineering), or military fortifications and communications (military engineering).

The larger field above can be broken down even further. Aside from those, there are interdisciplinary and specialized fields in engineering. These include agricultural, biological, bioengineering and biochemical, structural, energy, industrial, nuclear, and petroleum engineering, as well as mechatronics and nanoengineering.

These careers are demanding and typically require a minimum of a 4 year (bachelors) degree. Often students looking to enter this field will opt to minor in a field related to the type of engineering they are pursuing. The average starting salary for an engineer is around $65,000 (2018) and with experience can easily rise well over $100,000 a year.

Admissions requirements for undergraduate engineering schools include a solid background in mathematics (algebra, geometry, trigonometry, and calculus) and science (biology, chemistry, and physics), with courses in English, social studies, and humanities.

Engineers should be creative, inquisitive, analytical, and detail oriented. They should be able to work as part of a team and to communicate well, both orally and in writing. Communication abilities are important because engineers often interact with specialists in a wide range of fields outside engineering.