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Nondestructive Testing, 4. Thermography

: Netzelmann, Udo

Ullmann's Encyclopedia of Industrial Chemistry. 7th Edition
Weinheim: Wiley-VCH, 2011
ISBN: 978-3-527-32943-4
ISBN: 9783527306732
8 pp.
Book Article
Fraunhofer IZFP ()
thermal nondestructive testing; thermography; signal processing

In thermal nondestructive testing, interactions of heat flows with the internal structures of test objects are used to detect defects or to characterize coatings. The dominant concept is active thermography, in which additional heat is applied to the test object in an appropriate way to generate thermal contrast. Various heat sources and detectors are employed The most useful information is obtained when heat is applied as a short single pulse or by periodic modulation (dynamic thermography). Then the characteristic thermal penetration is governed by material properties such as thermal diffusivity. Contrast formation from defects is determined by the thermal effusivity, which is the square root of the product of thermal conductivity, mass density, and specific heat capacity. As defects like cracks, inclusions, and pores usually have a different effusivity than the matrix, application of thermal testing is versatile. The techniques can be applied to nearly all materials.