Page 354 - Introduction to Marine Engineering

Chapter 16

Engineering materials

A knowledge of the properties of a material is essential to every
engineer. This enables suitable material choice for a particular
application, appropriate design of the components or parts, and their
protection, where necessary, from corrosion or damage.

Material properties

The behaviour of a metal under various conditions of loading is often
described by the use of certain terms:
Tensile strength. This is the main single criterion with reference to metals.
It is a measure of the material's ability to withstand the loads upon it in
service. Terms such as 'stress', 'strain', 'ultimate tensile strength*, 'yield
stress' and 'proof stress' are all different methods of quantifying the
tensile strength of the material.
Ductility, This is the ability of a material to undergo permanent change in
shape without rupture or loss of strength.
Brittleness, A material that is liable to fracture rather than deform when
absorbing energy (such as impact) is said to be brittle. Strong materials
may also be brittle.
Malleability. A material that can be shaped by beating or rolling is said to
be malleable. A similar property to ductility.
Plasticity. The ability to deform permanently when load is applied.
Elasticity. The ability to return to the original shape or size after having
been deformed or loaded.
Toughness. A combination of strength and the ability to absorb energy or
deform plastically. A condition between brittleness and softness.
Hardness. A material's ability to resist plastic deformation usually by
indentation.

Testing of materials
Various tests are performed on materials in order to quantify their
properties and determine their suitability for various engineering