Laser excited thermography – Simulation based determination of detection thresholds in aluminum welds depending on geometrical and excitation properties

Mund, Malte; Technische Universität Braunschweig; Germany

Mund, M.; Technische Universität Braunschweig; Germany
Blass, D.; Technische Universität Braunschweig; Germany
Dilger, K.; Technische Universität Braunschweig; Germany

ID: ECNDT-0366-2018
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Session: Thermography and Thermosonics Techniques 2
Room: H1
Date: 2018-06-15
Time: 10:50 - 11:10

Active thermography has become a widely used technique in nondestructive material testing. However, the testing results strongly depend on the excitation technique. Especially optical excitation sources are frequently used as they allow contactless measurements and have advantages concerning the access. Halogen lamps as well as flash lamps are the preferred excitation sources as they are cost efficient and easy to integrate into the testing system. However, those excitation sources heat the whole surface of the test object resulting in a very insensitive excitation and therefore they are limited in detecting crack-like defects. To overcome this disadvantage, laser excited thermography has become an alternative to the traditional optical heat sources.
The lasers used to heat the specimens partially create heat flows on the surface. Those heat flows can be used to detect crack-like defects that are perpendicular to the surface. The suitability of those methods has been shown in various studies, but the limitations have not been explored yet. Therefore this study aims to determine the limitations of laser excited thermography to detect crack like defects in aluminum based on a FEM-approach. Therefore a parametric FE-model of a laser scanning process has been developed that covers the characteristics of an experimental heating process.
Consequently, this model is used to simulate the heating process and to determine theoretical process limitations for crack detection depending on geometrical as well as heating parameters. Based on the simulation results, the theoretical detection thresholds are defined and an outlook on the consequences for the laser excited thermography is given.