Aerospace Materials Testing

All the various types of materials commonly used inshould be non-flammable or of low flammability
airframes, their applications, and their advantages and(magnesium burns fiercely when exposed to fire, but
disadvantages, common airframe manufacturingneeds very high temperatures to ignite it). It should
methods... They all need to be subject to testing andpresent no other safety hazard, such as toxicity, in
quality standards.use, manufacture or repair. All this needs verification
The materials used in structural areas of airframeby aerospace materials testing.
construction must have adequate strength withIt should be readily available and at reasonable cost,
minimum weight, in other words a highand should be suitable for manufacturing using
strength-to-weight ratio (SWR). This is not the onlystandard processes. Where a material's properties are
consideration, however. Stiffness of the material isparticularly useful, new processes can sometimes be
often as important as its strength, and other factorsdevised to make its use more practical.
need to be considered as well. The material must beIt should not be highly susceptible to fatigue, or must
consistent and predictable in its properties, so thatbe used at stress levels low enough to ensure an
we know what behaviour to expect from it. Allacceptable life.
materials vary slightly in their basic properties, so it isIt must have good stiffness for a given weight.
normal to take the lowest or worst properties, plusIt must retain adequate strength at the
an appropriate factor of safety, when using them intemperatures to which it will be subjected, particularly
design. This gives a reasonable guarantee that thewith materials used in supersonic aircraft, or in certain
material properties will not be worse than theregions of the aircraft.
specified properties. Reasonable guarantee still meansSo these requirements limit the types of materials
that materials testing is desirable.used in airframes, but there are still many options
The material should ideally be homogeneous (havingavailable to the designer. Usually, the particular needs
the same properties in all parts and in all directions),lead directly to one or a small group of materials, but
although the way a particular material is processednew aerospace alloys and new ways of working can
may mean this is not possible. Aluminium alloys arechange the situation. The following groups of
frequently rolled to produce plate and thin sheets,materials meet the requirements listed above, and
and this means the material properties may beare used for the main structure of an
different in different directions. Sheet is assumed toairframe:aluminium and magnesium alloys (light alloys)
have consistent properties in all directions, but platesteelstitanium and titanium alloys nickel alloysplastics
does not. If the properties are affected in this way,and composites
the final properties must be predictable, and theIt is difficult to draw exact comparisons between
rolling direction clearly marked on the plate, to leavedifferent materials, because there are so many
the material in a useful state.different factors to consider. For example, some
Aerospace metals must not suffer seriousresist tension better than others; some resist
deterioration from corrosion caused by exposure tocompression better. Even different types of
the weather, sea water or any chemicals that theyaluminium alloys are preferred for different types of
come into contact with. The effect of stress is likelyloads. We can get some idea of how different
to accelerate the effects of corrosion. Similarly,materials compare by considering their
non-metals should not be prone to significantstrength-to-weight ratio... and of course by testing
degradation under these environments. The materialthem... aerospace materials testing.