Four material characteristics
Stiffness/elasticity concerns the lengthening or shortening of a material under loading. Stiffness is resistance to change in length; elasticity is the ability to return to original size and shape. Stiffness is measured formally by the modulus of elasticity, which is the slope of the straight line portion of the stress-strain curve: the steeper, the stiffer.
Strength is a measure of a material’s ability to accept a load. The maximum strength of a material (usually tested in tension rather than compression) is represented by the highest point on the stress-strain curve.
Ductility/brittleness is the extent a material deforms or elongates before fracturing. A highly ductile material is taffy-like, and its stress-strain curve extends far to the right. A very brittle material is chalk-like; its curve ends abruptly after reaching maximum strength.
Toughness is an overall measure of a material’s ability to absorb energy before fracture. It is represented by the total area under the stress-strain curve.
