# Mechanical properties of matter

Mechanical properties of matter are the behavior of matter under action of an external force.

Materials are things used in the construction of structures like buildings bridges, dams, etc. Before a material is put to use the following mechanical properties should be considered; strength, stiffness, ductility, brittleness and elasticity.

Strength: It is the ability of a material to resist forces that want to deform it.
Is the ability of a material to resist breaking when stretched, compressed or sheared.

The strength depends on
i) Dimensions of the material, in that a large force is applied in order to bend a material of large diameter.

ii) Nature of the substance
Materials of same size but of different substance require different force to be broken. E.g. a large force is applied to a steel rod compared to a piece of wood of the same size.

iii) Magnitude of force applied

Stiffness (toughness): Is the ability of a material to resist bending or to resist forces, which try to change its shape or size so that it is not flexible. A material which is more stiff always needs a large force in order to bend e.g. wood is more stiff than rubber

Ductility: Is the ability of a material to deform when a force is applied.
Is the ability of a material to be changed/rolled/hammered/pressed/bent or stretched into other shapes with out breaking.

Ductile materials can be hammered, bent or drawn into various shapes with out breaking.
A Ductile material is one, which stretches elastically then plastically before it breaks when tensile force acts on it

Examples;
Wet clay, plasticine, Metals, steel, e.t.c.

Properties of ductile material.
i) can be molded into any shape.
ii) can be bent without breaking. Because of the above properties of ductile materials, they can be rolled into sheets drawn into wires or worked into other useful shapes without breaking.

Brittleness: Is the ability of a material to break suddenly without bending.
A brittle material is one, which bends very little, then suddenly cracks without undergoing plastic deformation.
When a brittle material breaks, its pieces fit together almost exactly and can be glued back.
Properties of brittle material

i) Can bend very little and suddenly break without undergoing plactic deformation.
ii) Cannot be molded into any shape.

Examples;
Glass, chalk, stones, concrete, cast iron bricks, alloys like brass, and bronze.

Elasticity: Is the ability of a material to recover its original shape and size after a deformation force has been removed.

The material stretches due to the particle being pulled further apart from one another.
A material, which does not recover its original shape and size but is deformed permanently, is plastic.

Examples;
Rubber, steel, e.t.c.