(vi) Toughness
The ability of a material to resist fracture under impact loads; i.e. loads suddenly applied. This may be measured by means of an impact test, which determines the mechanical energy required to fracture a standard shape of sample of the material.
(vii) Malleability
This is a property very similar to ductility. A malleable material may be beaten or rolled into plates without fracture. The malleability of a material may be affected by such treatment, because of a phenomenon a known as "work hardening". The permanent deformation produced tends to set up internal stresses so that further strain causes fracture. These internal stresses can often be relieved by suitable heat treatment known as 'annealing, which also restores malleability.
(vii) Hardness
The ability of a material to resist penetration or wear. The hardness of the surface of a material may be made than of the main body of the material by suitable heat treatment in the presence of certain other materials. The hardness may be measured in terms of the pene- tration of the surface by a standard pointed shape of a standard hard