The key mechanical properties are tensile strength, toughness, hardness, and elasticity. Their importance depends on the product’s function, expected forces, working environment, and likely mode of failure.
In A3.1 Material classification and properties, material selection involves matching measurable properties to a design specification. Designers must identify how a component will be loaded and what type of deformation or failure must be prevented.
| Mechanical property | Meaning and significance in material selection | Example application |
|---|---|---|
| Tensile strength | The maximum tensile stress a material can withstand before breaking. It matters when a component experiences pulling or stretching forces. | Steel suspension-bridge cables require high tensile strength. |
| Toughness | The ability to absorb energy and undergo plastic deformation before fracturing. It is represented by the total area under a material’s stress-strain curve. | A protective helmet must absorb impact energy without sudden fracture. |
| Hardness | Resistance to scratching, indentation, abrasion, and localized plastic deformation. It matters for surfaces exposed to wear. | Cutting tools and drill bits require hard working surfaces. |
| Elasticity | The ability to return to the original dimensions after a force is removed, provided the elastic limit has not been exceeded. | Springs and flexible sports equipment must recover their original shape. |
A designer normally considers several properties together. For example, a tool may need a hard edge to resist wear but also sufficient toughness to prevent brittle fracture during impact. Processing method, cost, mass, sustainability, and availability must then be considered alongside mechanical performance.
A common misconception is that strength and toughness are the same. A strong material resists high stress, whereas a tough material absorbs substantial energy before fracture; a material can be strong but brittle.
In an IB response, do not merely list properties. For a command term such as explain, define the property, connect it to the forces or failure mode, and justify why it suits a specific product or component.