Section 7.5.1. Test Conditions
Structural hardware testing can be a form of comparative
testing during the development phase.
That means that the test conditions do not always have to be an exact
simulation of service conditions as long as the variables considered are tested
the same way. However, it is strongly
recommended that service conditions be approximated as closely as
possible. How closely the test
conditions have to resemble service conditions depends upon the predictability
of the effect of a change in conditions.
The following guidelines are applicable to structural hardware
testing for damage tolerance. First,
the specimen should contain the design and manufacturing details that are the
subject of the investigation. The load
should be properly distributed at the point of interest. Second, if the purpose is to validate a piece of structure for damage tolerance, then
load sharing, load interaction, and load transfer among different
members should be simulated or otherwise accounted for. Type of loading (bending, tension) should be
as in service, or be such that the stress distribution at the critical location
is as in the actual structure. Special
care should be taken that no undesired bending is introduced due to load
eccentricities. This requires intelligent
grip design. It may also require some
special structure to distribute the loads properly from these areas into the
specimen. Third, the nominal stress at
the critical location should be as in service.
Experiments should be performed on a flight-by-flight basis with landing
loads included. A reasonable number of stress levels should be used. The stress sequence within a flight should
be representative of service usage (see Section 5) or arranged in
lo-hi-lo sequence. Block loading should
not generally be applied.