A thermal, non-destructive evaluation (NDE) technique has been employed by ThermTech Services, Inc. in cooperation with NASA Langley Research Center that allows for quantitative measurements of wall thickness in steam boilers. By determining the thickness of the walls, one can easily determine how much thinning has occurred due to corrosion. This type of NDE can be applied to the inspection of wings and fuselages on aircraft and spaceflight vehicles including the shuttle. The NDE technique employs the linear movement of a heat source (lamp) and an infrared imager that is situated at a fixed distance behind the heat source. The instruments are aligned on a platform that moves up and down across the outer surface of a test sample. By analyzing the induced surface temperature variations, and processing images collected with the infrared imager, it can be determined where material loss of the tubes has occurred. After an image sequence has been collected, a line-by-line subtraction methodology is utilized to discard irrelevant information so that defects are displayed in a re-created image. The overall goal of this project is to provide a proof of concept for a portable, hand-operated thermographic line scanner that would provide an alternative to the existing mass- and power-intensive instrument that utilizes a cooled infrared imager. In this project, two different microbolometers are first analyzed using different metal- and carbon epoxy-based targets to determine which provides better resolution for detection of subsurface, manufactured defects. The feasibility of using uncooled bolometer technology to support the development of a portable instrument to conduct this type of NDE technique was proven.
A fiber-optic/infrared (F-O/IR), non-contact temperature measurement system was characterized, and the existing technique for data collection improved, resulting in greater repeatability and precision of data collected. The F-O/IR system is a dual-waveband measurement apparatus that was recently enhanced by the installation of a tuning fork chopper directly into the fiber optical head. This permits a shortened distance between fiber and detector pair, and therefore a stronger signal can be collected. A simple closed box with the inside painted flat black was constructed and used to prevent stray radiation and convection, thus minimizing undesired effects on the measurement process. Analyses of the new data sets demonstrate that system improvements provide a cleaner and more reliable data collection capability. The exponential relationship between detector output voltage and object temperature indicates that the instrument is operating within its nominal range.
The overall goal of this project was to develop a reliable technique to measure the temperature of Kapton HN, an aluminized polymer material being studied for potential future NASA missions. A spectral model that emulates the instrument was also developed in this study. Our measurements and characterization of KaptonÒ HN will be incorporated into the spectral model in order to determine the sensitivity of the instrument to background radiation, spectral emittance of Kapton HN, and other parameters that may affect thermal measurements.
A dual-waveband, fiber-optic/infrared (F-O/IR) temperature measurement system was enhanced with incorporated optical chopping and applied to measure the surface temperature of a coated (aluminized) Kapton HN sample. The F-O/IR system provides a non-contact means for accurate membrane temperature measurement without distorting surface contour. An FTIR spectrometer was used to measure the absorptance and reflectance properties of the Kapton HN sample. A long-wave IR scanner was used to validate and enhance results obtained from the spectrometer and predict temperature dependence of optical properties. Data are presented that demonstrate the feasibility to apply the F-O/IR system for non-contact temperature measurement of highly reflective surfaces at low temperatures.