The meanings of malleable, ductile and brittle are quite easy to explain. and some can be illustrated on a stress strain graph:
Malleable material can be beaten into shape.
Brittle materials break often without warning. They have little elasticity and do not stretch easily.
Tough materials can deform plastically and absorb a lot of energy before breaking. This is indicated on the graph below by the area under the graph for the tough material being larger than that area for the not so tough material.
Stiff materials have a high Young's modulus. It takes large forces and stresses to stretch them a little.
The strength of a material is it's ability to withstand stress(
) Strong materials can withstand large stresses. They may still stretch, but it will take a large force to break them.
The ultimate tensile stress is the stress a material experiences when it breaks.
The phenomenon of 'necking' is illustrated below.
The hardness of a materiial is it's ability to withstanddeformation on impact.