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									  Non-destructive evaluation of metal and composite targets
         using an infrared line-scanning technique
                           Christopher Smith, Matthew J. Rowley, Curt Dvonch, Mary Fulton
                       Infrared Development and Thermal Testing Laboratory, James Madison University
                                                                     Advised by Dr. Jonathan J. Miles
                                              SPIE Defense and Security Symposium – Thermosense XXVII
                                                                           Tuesday, 29 April 2005


  1. Power cord for illuminator
                                                                          Summary / Abstract
  2. Illuminator control box                                              A thermal, non-destructive evaluation (NDE) technique has been employed by ThermTech
  3. Power supply to illuminator
  4. Test plate
                                                                          Services in cooperation with NASA Langley Research Center that allows for quantitative
  5. Motor and lift cable                                                 measurements of wall thickness in steam boilers. The same technique was applied in this
  6. Camera mount                                             1           investigation to analyze aluminum, steel, carbon-epoxy, and carbon-carbon sample plates
  7. Data acquisition computer with Video Savant
  8. M-drive to control motor speed and illumination
                                                                          to locate “manufactured” defects within the specimen. By analyzing the induced surface
                                                                          temperature variations, and processing images collected with an infrared imager, it can
                                                                          be determined where there exist hidden defects. Post data acquisition, a line-by-line
                                                                          subtraction methodology is utilized to discard irrelevant information, displaying a re-
                   3
                                                                          created image to visualize the defects. The overall goal of this project is to provide a proof
                                                                          of concept for a portable, hand-operated thermographic line scanner that utilizes
            8                                                             uncooled microbolometer-based infrared imaging.
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                        Figure 1. Experimental setup.
                                                   5




                          Figure 1. Experimental setup.


                                                                        Figure 4. Subtracted images (thinnest composite plate)
Experimental Design                                                           with the Merlin (left) and BAE (right) data.


Thermtech Services provided a test apparatus                            Results / Analysis                                                            Figure 3. Flowchart of experimental process.

(shown above) to support data collection. A test
                                                                        Software was developed to create visualizations of the test sample. A line-by-line
sample is placed perpendicular to the ground by
                                                                        subtraction method was utilized to normalize an image with respect to baseline conditions,
two clamps connected to the aluminum frame. The
                                                                        the technique is described in Figures 2 and 3. A line prior to heating is subtracted from the
lift moves at constant velocity, between 0.5 and 5.0
                                                                        same line after heating. This technique generates a pixel array set that represents an
in/s after a brief acceleration. The quartz illuminator,
                                                                        analysis of defects. An Indigo Systems Merlin Stirling-cooled imager was used to generate
with a range of 8.5 to 11.3 watts, provides a line
                                                                        a baseline, results from analysis of data acquired with a BAE microbolomer were
input of thermal energy across a test specimen. The
                                                                        compared. The similarity in performance of detecting defects in a target, as depicted in
steps used in experimental testing are displayed as
                                                                        Figures 4 and 5, shows that the uncooled technology performs comparably.
a flowchart in Figure 3. A total of six test samples
were loaned to JMU by HEAT, Inc. and NASA in
support of the research. The sample materials were
steel, aluminum, carbon epoxy, and carbon-carbon.
                                                                                                                                               B                                            C




                                                                                                                                                                                   D




       Figure 4. Simple representation of how lines were chosen.
                                                                                        Figure 5. Backside of the aluminum plate (left), Merlin image (center), and BAE processed image Surfer (right).


                 Figure 2. Linescan schematic description.
                                                                        “Before” and “After” lines of pixel values were subtracted to determine a “density” value
                                                                        along a particular line. The “Density” values represent intensity of defect at a particular
Conclusions                                                             location. A “Plate” value was determined by the same process at a location without defect.
                                                                        The “Ratio” was calculated to compare areas with and without defect. The ratio values
This investigation compared performance of                              generated with cooled and uncooled instruments are comparable.
uncooled infrared imaging technology to larger,
cooled instruments. The application of micro                               Merlin Camera                            SCC500H Camera                            The data shown in Table 1
bolometers to the existing NDE thermographic                       Location Density Plate Ratio              Location Density Plate                Ratio      demonstrate the effectiveness of
line-scan technique is feasible while using a                         A      269 228 1.18                       A       4880 4128                  1.18       using an uncooled microbolometer
smaller, portable version of the scanning system.                     B      605 200 3.03                       B      11536 4000                  2.88       for this type of application in which
The uncooled technology can be used to identify                       C      331 234 1.41                       C       6448 3984                  1.62       line-scanning is applied to conduct
defects in metal and composite structures with                                                                                                                non-destructive evaluation of metal
                                                                      D      458 192 2.39                       D       8496 4080                  2.08
acceptable reliability and resolution.                                                                                                                        and composite structures.
                                                                             Table 1. Density, plate, and ratio values for aluminum plate

								
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