The shape and size of a component has great effect on the choice of the processing unit which ultimately effects the choice of the material.

There are some materials which can be finished to close tolerance while others cannot

To select a suitable material for specific conditions, all mechanical properties, e.g., toughness, hardness, strength, etc. guide us.

Method of processing of the material also affects the properties of a component, e.g., forged components can be stronger than the casted components

When the desired material supply is limited, thena costly material which is available inample quantity may be chosen.

Selection according to different parameters such as :

Procedure for materials selection:

are elements that have free valence electrons which are responsible for their good thermal and electrical conductivity.

Inorganic, non-metallic crystalline compounds, usually oxides,carbides, nitrides, borides, and silicides

A combination of two or more materials to achieve better properties than that of the original materials.

is a long chain molecule made up of many repeating units, called monomers.

Materials that are utilized in high-technology (or high-tech)applications are sometimes termed ___________.

This means consideration of such properties as strength, stiffness, hardness, ductility, toughness, fatigue resistance, wear properties, etc.

This means considering the environment to which the material will be exposed and the possibility of corrosion.

This means consideration of such properties as specific heat capacity, linear coefficient of expansion and thermal conductivity.

For example,does the material need to be a good conductor of electricity or perhaps an insulator?

Does the material need to have soft or hard magnetic properties or perhaps be essentially non-magnetic?

For example,does the material need to be capable of a good surface finish, have dimensional stability, be flat, have a particular size, etc

 the ability of a material to resist deflection when loaded

is the progressive loss of material from surfaces as a result of contact with other surfaces

4 Mechanisms for wear :

On an atomic scale, even smooth surfaces appear rough and thus when two surfaces are brought together; contact is made at only a fewpoints.

_____________________ is used when material is removed from a surface by contact with hard particles; sliding resulting in the pushing out of the softer material by the harder material.

When rubbing between surfaces takes place in a corrosive environment, surface reactions can take place and reaction products formed on the surfaces

is a process by which the surface of a material is weakened by cyclic loading, which is one type of general material fatigue

a device supporting a mechanical element and providing its movement relatively to another element with minimum power loss.

____________ of a material isa measure of the ability of a material to conduct heat

have relatively low fatigue strength and this can limit their use to low-load conditions.

Polymers have thermal expansivities much greater than metals and so can present problems, e.g. a higher running clearance between surfaces is needed.

They have a large, positive susceptibility to an external magnetic field.

They have a weak, negative susceptibility to magnetic fields.

They have a small, positive susceptibility to magnetic fields.

Materials which retain their magnetism and are difficult to demagnetize.

Easy to magnetize and demagnetize. Used for making temporary magnets.

need to have rounded corners,no abrupt changes in section and gradual sloping surfaces