1.1 Material Selection — Part 3: Mechanical properties

What are mechanical properties?

Properties relating to how a material reacts when subjected to various forces.

What are the two types of deformation?

Temporary (elastic) deformation and permanent (plastic) deformation.

What is strength?

The ability of a material to withstand force without breaking or permanently bending.

What is compressive strength?

The ability of a material to withstand pushing forces that attempt to crush or shorten it.

What is shear force?

A force that subjects a material to a sliding action across its surfaces.

What is torsional force?

A force applied to a material that attempts to twist it.

What is elasticity?

The ability of a material to flex, bend or deform and return to its original shape when the applied forces are removed.

What is plasticity?

The ability of a material to permanently change shape when forces are applied without cracking or breaking.

What are the two key terms associated with plasticity?

Malleability and ductility.

What is malleability?

The ability of a material to deform in different directions under compressive forces such as hammering, pressing or rolling without cracking or breaking.

What is ductility?

The ability of a material to be drawn into a longer, thinner form, such as wire, under tensile force.

What is the difference between malleability and ductility?

Malleability involves deformation under compression, whereas ductility involves being drawn into a longer, thinner form under tension.

What important relationship does CCEA give between ductility and malleability?

All ductile materials are malleable, but not all malleable materials are ductile.

What is toughness?

The ability of a material to withstand sudden shocks or blows.

How does the Izod impact test work?

A pendulum swings and strikes a specimen containing a 45° notch. The material absorbs energy from the impact.

Why must test specimens be the same size in an Izod test?

The energy absorbed during fracture depends partly on the size of the material, so specimens must be the same size for a fair comparison.

What is hardness?

The ability of a material to resist indentation.

What is the Mohs scale?

A scale used to rank the scratch resistance/hardness of materials.

How do indentation hardness tests work?

A hard object is forced into the surface of a material, and the hardness value is determined from the size or depth of the indentation.

Name the three main indentation hardness tests.

Brinell, Vickers and Rockwell.

What is durability?

The ability of a material to withstand wear and tear and deterioration caused by weathering.

Why are metals particularly relevant when considering durability?

Metals are prone to corrosion, which is a chemical breakdown of the surface.

What is brittleness?

The tendency of a material to break or shatter before it undergoes significant deformation.

What is the general relationship between brittleness and strength?

Brittle materials generally have high compressive strength but low tensile strength.