Classical Procedure

Functional Analysis

Functional analysis is a formal way of specifying material properties, starting from the function of a component. It involves following:

1. specification of the functions of the component;

2. specification of the requirements of the component; and

3. Specification of the requirements of the material properties.

Function

The overall function of the product being designed must be specified as broadly as possible to permit for the greatest number of options in design. Where there are various functions all must be specified. 'This latter requirement is necessary even while the choice of material has been necessitated by the failure of a material to perform one specific function, because a change in the material to make it capable of fulfilling one function may make it incapable of fulfilling another. For example, using a higher tensile steel to carry an increased load may result in brittle fracture under shock.

Component Requirements

When the functions have been established the component requirements can be identified. For example, the one-piece box mentioned above must be capable of being opened and closed an indefinite number of times. In specifying component requirements it is important to remember that it must be possible to produce the article in the required form, and that the component must withstand the environment in which it is operating, at least for its designed life.

Materials Property Requirements

From the component requirements the materials-property requirements can be established. The material for the one-piece box must have an almost infinite resistance to high strain fatigue in air at room temperature. This is obtainable from a polypropylene component manufactured in a specific way.

The material property requirements, established by the functional analysis, may be quantitative or qualitative. For example, the material for an automobile exhaust must be sufficiently strong and rigid to withstand weight and gas pressure.

Quantitative requirements must be established by analysis of the design and operating conditions. In comparison, the requirement to resist corrosion and oxidation is qualitative. Property requirements may also be classified as essential and desirable. The strength requirement in the material for the exhaust is essential. Environmental resistance is often sacrificed to minimize initial cost (even when, as in this example, a more resistant material may be economically superior over the total life of an automobile).

Materials Requirement Check-list

The next stage is the formulation of a 'materials requirement check-list'. The reader should not be discouraged by the length and complexity of this list. It will

in many cases become evident that whole ranges of properties (and materials) may safely be ignored at first glance. For example, if the component is required to transmit or refract light the choice of material is immediately limited to a glass, mineral or polymer and the design and property specification is thus restricted. If electrical conductivity is significant, choice is limited to conducting metals, resistive or semi-conducting materials or insulators.