Aerospace design with aerospace materials.  

Aerospace design is an iterative process. You start with the definition of a function and draw on your knowledge and experience in formulating a tentative design. You then refine this by a systematic process.

Materials selection is an integral part of design. And because the principles of mechanics, dynamics and so forth are all well established and not changing much, whereas new materials are appearing all the time, innovation in design is frequently made possible by the use of new materials. Designers have at their disposal metals, ceramics, polymers, and combinations of them to form composites. Each class of material has its own strengths and limitations, which the designer must be fully aware of.

At and near room temperature, metals have well-defined, almost constant, moduli and yield strengths (in contrast to polymers, which do not). And most metallic alloys have a ductility of 20% or better. Certain high-strength alloys (spring steel, for instance) and components made by powder methods, have less - as little as 2%. But even this is enough to ensure that an unnotched component yields before it fractures, and that fracture, when it occurs, is of a tough, ductile, type. But - partly because of their ductility - metals are prey to cyclic fatigue and, of all the classes of materials, they are the least resistant to corrosion and oxidation.

Aerospace materials  

In designing with ductile materials, a safety factor approach is used. Metals can be used under static loads within a small margin of their ultimate strength with confidence that they will not fail prematurely.

Ceramics cannot. Brittle materials always have a wide scatter in strength, and the strength itself depends on the time of loading and the volume of material under stress. If the pin of a pin-jointed frame, made of metal, fits poorly, then the metal deforms locally, and the pin beds down, redistributing the load. But if the pin and frame are made of a brittle material, the local contact stresses nucleate cracks which then propagate, causing sudden collapse