Whether you’re a mechanical engineering student or simply brushing up on your technical knowledge, it’s important to understand the mechanical properties of materials used in engineering.
Knowing this information helps you quickly choose the best materials for your design based on various factors including: load capacity, elasticity, hardness, strength and much more.
The purpose of this article is to break down the mechanical properties that make each material unique. By becoming familiar with these terms, you’ll be able to differentiate between materials and assess their usefulness for your design project.
What is a Material?
A material is any substance we use to make things: wood, glass, steel, plastic, gold, brass, to name just a few.
In the case of metals, brilliant engineers have devised ways to mix some of these materials together to create new desired mechanical properties like more strength, more flexibility, lighter weight or better durability. We’ll cover these properties in the next section.
The new materials are referred to as alloys or composites depending on the methods used.
List of Mechanical Properties
Here are some of the most common mechanical properties that define different types of materials, followed by more detailed descriptions for each:Strength (six types)DuctilityBrittlenessToughnessHardnessDurabilityMalleabilityHardenabilityCreepElasticityThermal Expansion
The strength of a material can be evaluated based on either the amount of load it can take before fracturing or becoming deformed.
There are six main subcategories of strength:Compressive strength. The ability of a material to withstand a load that reduces its size. Think of it as the material being squeezed.Shear strength. The ability of a material to withstand loads that cause the materials internal structure to slide against itself.Tensile (or ultimate) strength. The ability of a material to withstand a load that stretches it or pulls it apart, without fracturing.Yield strength. The ability of a material to withstand a load that stretches it or pulls it apart, without becoming deformed.Elastic strength. A material’s capacity to recover to its original shape after being stressed.Fatigue strength. A material’s ability to withstand repeated and/or fluctuating stresses (like loading and unloading).
The ability of a material to become deformed, and retain that deformed shape without breaking, when a load is applied to it. Silly putty is an example of a ductile material.
You can stretch it quite a bit before it breaks, and it will more or less retain the new shape.
This mechanical property refers to the ability of a material to shatter without becoming significantly deformed. Glass and ceramics are examples of brittle materials that don’t become deformed so much as shatter upon impact. It is the opposite of ductility.
Toughness refers to how good a job a material does at resisting fracturing under stress. Toughness contains components of strength and ductility. For example, despite its high ductility, silly putty is not tough since it easily becomes deformed when stretched (hence it has very little strength).
On the other hand, strong yet brittle material like ceramic can also be considered not tough.
A rubber shoe sole can be considered a tough material since it contains both strong and ductile properties.
This mechanical attribute refers to the ability of a material to resist localised abrasion or indentation as a result of external stress. In other words, it’s the ability to withstand scratches and dents.
A diamond is an example of a hard material.
The ability of a material to withstand load or stress for a long time. The stress can be heat, pressure, wear and tear, damage or other forms of stress.
Similar to ductility, this mechanical attribute refers to a material’s ability to become deformed (but not fractured) and retain that shape when compressed or squeezed. Lead is an example of a material that is malleable but not ductile. You can hammer it into different shapes, but when you pull it, it fractures.
Hardenability refers to a material’s ability to become harder under heat treatment, usually used to describe steel alloys. It’s easier to make alloys containing higher amounts of carbon harder using heat than it is to make alloys with lower amounts of carbon harder using the same heat treatment.
Creep is a material’s tendency to become deformed over time. High temperatures usually speed up creep, but creep can also occur at room temperature albeit more slowly. An example where you don’t want creep is in jet engines. The extremely high heat would cause many common materials to experience creep very quickly. Therefore it is important to use materials that are extremely creep resistant.
This mechanical property refers to a material’s ability to return to its original shape when a stressor is removed. A rubber band is an example of a highly elastic material.
When you stretch a rubber band and then let go, it easily returns to its original shape.
Thermal expansion is the tendency of a material to change in shape, area or volume due to changes in temperature. An example of a material that experiences thermal expansion is asphalt that expands and cracks in hot weather.
Mechanical properties of common materials
Let’s take a look at the mechanical properties of some of these widely used common materials:Carbon FiberSteelStainless SteelPolycarbonateFiberglassTitaniumPLACopperBrassAluminium
Mechanical Properties Of Carbon Fiber
Carbon fiber refers to a long chain of carbon atoms that are bonded together. In terms of material properties, carbon fiber has:High tensile strengthHigh strength to weight ratioLow thermal expansion
These properties make carbon steel popular for use in industries where materials need to be lightweight but strong - such as motorsports, aerospace engineering and the military.
The downside to carbon fiber is that it is somewhat brittle, and can easily crack or shatter on impact.
Mechanical Properties Of Steel
Steel is an alloy containing iron and carbon. There are many types of steel, with varying levels of iron, carbon and other metals, and each of these has slightly different properties. But for the most part, the common properties for most types of steel include:High tensile strengthHigh hardnessHigh yield strengthHigh weight to strength ratioHigh ductility
These properties make steel the ultimate material to use in building construction. In fact, steel has the highest strength-to-weight ratio of any material used in the construction of buildings.
However, unless it is treated, steel can become corroded easily..
Mechanical Properties Of Stainless Steel
Stainless steel is an alloy of steel that was developed to help make steel more resistant to corrosion by adding chromium to that alloy. Therefore, in addition to being corrosion-resistant, it exhibits many of the same properties as steel including:High tensile strengthHigh hardnessHigh yield strengthHigh strength to weight ratio.High ductility
The downside of stainless steel is that it's not very cost-effective, and that’s why you see it used in smaller items like silverware sets.
Mechanical Properties Of Polycarbonate
Polycarbonate (PC) is a type of plastic that is inherently transparent. It is a robust and amorphous thermoplastic polymer with great performance. It is simple to work with, mold, and thermoform. PC is well-known for sustaining color and strength over time.
Some of the characteristics of polycarbonate are:
High impact resistance
High tensile strength
High dimensional durability
Excellent electrical & thermal insulator
Easy to fabricate and machine
It is used in a wide range of products including compact disc players and safety helmets as well as in automotive headlight lenses and roof and glazing purposes.
The downsides of Polycarbonate are that it is extremely scratchable. As a result, transparent surfaces, such as the polycarbonate lenses in a pair of glasses, are usually coated with a scratch-resistant coating.
Mechanical Properties Of Fiberglass
Fiberglass is a material formed from very thin glass fibers. It is stronger by weight than many metals, non-magnetic, non-conductive, and transparent to electromagnetic waves. It requires very little maintenance, is fire resistant, an excellent electrical insulator, and is weatherproof.
The common properties for fiberglass include:High tensile strengthDimensional stabilityHigh thermal enduranceExcellent impact strengthHigh durability
The best feature of fiberglass is its capacity to be molded into a variety of complex shapes. This explains why fiberglass is so popular in bathtubs, boats, airplanes, roofs, and other uses. Disadvantages include the necessity for frequent re-gel coating and the possibility of airborne fibers irritating asthma patients.
Mechanical Properties Of Titanium
Titanium metal is an extremely durable metal for industrial applications since it is corrosion-resistant, as well as lightweight and strong. It is 40% lighter than steel but twice as strong as high-strength steel. As a result, titanium is used in a variety of industries, including aviation and aerospace. Some of the characteristics and properties of titanium include:High StrengthLow DensityHighest strength-to-density ratioHigh ductilityNatural resistance to rust and corrosionLow thermal expansionHigh melting point
These properties make it ideal for use in a wide range of aerospace and naval applications such as airplanes, spaceships, missiles, and ships of all sizes. Due to its non-reactivity with skin and bone, it is used in prosthetics as well. The downsides of titanium include the difficulty of casting and that is generally more expensive than other types of metals.
Mechanical Properties Of Polylactic Acid (PLA)
PLA (polylactic acid) is a biodegradable and recyclable polyester derived from renewable feedstock. PLA has grown in popularity as a result of its low cost of production from renewable resources.
PLA is the most commonly used plastic filament material in 3D printing due to its shrink rate. Some common properties for most polylactic acid include:Low shrink rateGood thermal processabilityExcellent flexural strength
Due to permeability problems with PLA, it is still regarded as inferior for long-term food storage applications.
Mechanical Properties Of Copper
Copper (Cu) is a highly ductile metal that is an exceptional conductor of electricity and heat. Copper is found in nature in its free metallic form. The electrical, marine, defense, construction, architecture, and jewellery industries all use it. Some of the characteristics and properties of copper include:
Ductile and Malleable
High heat conductivity
Excellent electrical conductivity
High corrosion resistance
Some of the downsides of copper include its high cost as compared to fiber optic cables, it is more susceptible to corrosion as compared to optical fiber and has a shorter life expectancy. Copper is more vulnerable to electrical interference than fiber optics, resulting in a less clear transmission. Fiber optic cable also has a reduced shock danger than copper wire.
Mechanical Properties Of Brass
Brass is a copper-zinc alloy with variable proportions that may be used to achieve different mechanical, electrical, and chemical characteristics. It's well-known for its durability and workability. Modern brass is composed of 67 percent copper and 33 percent zinc. Some of the characteristics and properties of brass include:
Good thermal conductivity
Low melting point
Easy to cast
Brass is utilized in a variety of products because of its unique characteristics, including pipework, weatherstripping and other architectural trim pieces, screws, heaters, musical equipment, and weapon cartridge casings. Brass requires a lot of care due to its proclivity for a blackish tarnish.
Mechanical Properties Of Aluminium
Aluminium is the most abundant metal and the third most abundant element globally, accounting for 8% of the earth’s crust. Aluminum is the most commonly used metal after steel due to its flexibility. Aluminium is used to make cans, foils, cooking utensils, aircraft components, etc. Some of the characteristics of Aluminium include:Low densityExcellent electrical and thermal conductivityResistant to corrosionEasily cast, machined, and shapedNon-magneticIt has the second-highest malleability and the sixth-highest ductility among all metals.
Some of the downsides of aluminium include its high cost with respect to other metals like steel, welding of aluminium needs special procedures, which are expensive and take longer than other methods. And in comparison, to steel, it is more readily dented and scratched.