Stress Measurement System
As part of NASA's Aircraft Structural Integrity program (see
page 68), Langley Research Center teamed with Stress Photonics
Inc., Madison, Wisconsin to develop an infrared-based stress
measurement system for use in nondestructive evaluation of materials
and structures. Stress Photonics has commercialized the technology
and incorporated it into the DeltaTherm 1000 (DeltaTherm 1000
is a trademark of Stress Photonics Inc.) system.
The DeltaTherm 1000 stress measurement system combines digital
signal processing technology with an infrared camera.
Both the NASA system, intended for inspection of aircraft
structures to detect cracks and disbonds, and the commercial
unit make use of the fact that all materials change temperature
when compressed or expanded. In solid materials, this effect
is known as thermoelasticity. Thermelectric Stress Analysis (TSA)
employs special infrared detectors and signal processing equipment
to image temperature changes that correspond to the dynamic stresses
in a structure; modern TSA systems can measure temperature changes
as small as one-thousandth of a degree Centigrade.
Stress Photonics' DeltaTherm 1000 is an infrared differential
thermography system for TSA and thermal nondestructive evaluation.
The system is used to verify mathematical models of a design,
demonstrate the effects of loadings on the design, measure stress
concentrations and stress intensity factors in load-bearing components,
and survey a structure for potential problem sites. It combines
digital signal processing technology with a special infrared
camera to provide instantaneous thermal images and live TSA (differential)
images. Data collected from the infrared camera is processed
at 434 frames a second; processed images are sent to a computer
and/or to a video monitor for immediate display.
Used in nondestructive evaluation of materials and structures,
the system images temperature changes that correspond to dynamic
stresses in a structure.
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