Requirements Computer Aided Material Selection

The requirements for a computer program to undertake selection by the classical procedure are much more general and much less well defined. The starting point is a product design specification (PDS) which is a functional and formal statement of what is required from the product to be designed, not a description of the product. The PDS contains a material design specification (MDS) which, like the PDS, is incomplete and ill defined. The computer must match this MDS to descriptions of existing materials and materials specifications (MS) which may be incomplete and reflect various levels of confidence. The result of the analysis may be a requirement to modify the PDS, to develop or new material, or to acquire additional information concerning specific materials.

A computer system capable of selecting materials requires :

a) The ability to deal with simple and complex data structures;

b) Powerful structures for data acquisition and updating by augmentation and modification;

c) The ability to manage sparse data;

d) The ability to compare incomplete descriptions;

e) The ability to distinguish the relationships, and sometimes lack of relationships, between materials, or parameters nominally in the same classification; and

f) The ability to be easily extensible.

The system should take into consideration:

• The duty or function of the component;
• The manufacturing route;
• The materials properties;
• Shape, dimensions and failure mode; and
• The relative cost of the materials, manufacturing routes and product designs.

In addition, the system requires certain user characteristics so that it may be operated by designers, and engineers and free the materials engineer from long-term difficult and strategic problems. It should following:

• Be fast in usage;
• Require a minimum of learning;
• Be accessible : at different levels to suit different levels of user;
• Have text and graphical output; and
• Have recording facilities.

Various procedures for optimised decision-making have been proposed including linear programming and numerical algorithms. There is a tendency to rely on ranking methods, which allocates a rank of 0 to 3 for each material property. This introduces an imprecision.