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dynamic testing and on composites testing in general. As
previously mentioned, composites exhibit significant en-
ergetic response to loading, but this can be observed both
in damaging and purely elastic conditions.
In the simplest sense, imaging the infrared emission
from a specimen can provide useful qualitative informa-
tion about location and evolution of heating and damage
during a test, as seen in Figs. 1 and 2. With appropriate cal-
ibration, it can also be used to directly measure surface
temperature, but this must be approached with caution re-
garding the factors that affect measurements. First, mate-
rials that are chemically or visually similar can have
significantly different values of emissivity, which determine
the intensity of infrared light released by the specimen.
Second, emissivity can vary with temperature: This is gen-
erally a subtle change for polymers, but when monitoring
metals at high temperatures, serious changes can be ob-
served due to the formation of oxide layers. Finally, almost
all specimens reflect radiation from the surrounding envi-
ronment, so readings from an unshielded test area at am-
bient temperature can be affected simply by reflected
radiation from people walking around the laboratory.
On a more advanced level, one that is rapidly gaining
traction within the research sector, the University of
Southampton pioneered a new technique of thermoelastic
stress analysis (TSA), which can be applied to all types of
materials, using cameras with much higher sensitivity.
Here, the relationship between temperature and mechan-
ical dilation analyzes the stress distribution in a system, by
comparing the surface temperature difference between two
load levels. Stress mapping generated in this manner can
be conducted in parallel with strain mapping generated
using digital image correlation, and these two independ-
ent techniques are then used for mutual verification. To
date, this approach has been used most effectively with
high-performance cameras, to maximize data extracted
from very high speed tests. Although this research is
largely academic, it is paving the way for application of less
expensive equipment to more routine studies of damage
evolution in the future.
Moving to higher capacity
The aerospace sector has not been mentioned thus far
with regard to new areas of composites testing, and has his-
torically been criticized by some researchers for its conser-
vative approach. Flight-ready technology takes a long time to
pass through approvals, but that does not correspond to a
lack of applied research activity. A large part of aerospace
manufacture’s R&D development work is centered on com-
posites. In addition to developing their production technolo-
gies, these groups are working to identify robust, repeatable
approaches for dynamic performance evaluation. Mean-
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