Toughness: The ability of the material to absorb energy till the breaking or  rupture taken place is known as toughness

Hardness: It is the resistance offered by the material against scratch or  Abrasion. Higher the yield stress, higher is the hardness

Brittleness: If post elastic strain or plastic strain is less than 5% than it is      brittle Material a material is said to be brittle when it cannot  be drawn out    by tension to smaller section

Eg: Cast iron, high carbon steel, concrete, stone, glass etc.