Understanding Infrared Thermography Reading 3

Material surface characteristics, as in any other thermographic application.
are critical to test effectiveness. Materials with high and uniform surface
emissivity are ideally suited for evaluation by infrared materials discontinuity
detection. When evaluating samples with low or nonuniform emissivity, the
thermographer has several alternatives. The first is to apply a removable, thin,
high ernissivity coating, Another is to use an image subtraction routine as
previously discussed in Chaptcr 3. This greatly reduces emissivity artifacts
without affecting the material. Most materials successfully evaluated by
infrared materials discontinuity detection are composed of layers of metals.
plastics, composites or combinations of all three. The surfaces may be metal
or plastic and the core structure may be solid, amorphous or geometrically
configured (i.e. a honeycomb structure). Assembled layered sections (i.e.
aircraft lapped sections) are also tested thermographically. The surfaces of
the test amples facing the scanner are usually uniform in appearance and
finish, although emissivity is low and surface scratches are frequently present.
Keywords:
Emissivity artifact (Reflectivity)
Charlie Chong/ Fion Zhang