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NDT.net Issue - 2017-12 - Articles
NDT.net Issue: 2017-12
Publication: 7th European-American Workshop on Reliability of NDE; Sep 4 – 7, 2017, Potsdam, Germany (Reliability 2017)
Session: Posters
ARTICLE

POD Improvement of Defects in Fibre Reinforced Plastics by Use of Multiply Flash Thermography with Variable Pulse Parameters

Giovanni Schober15, Christian Kolb10, Marcel Werner3, Daniel Hoffmann9, Stefan Kremling9
SKZ - Das Kunststoff-Zentrum28, Würzburg, Germany

Abstract: In the field of non-destructive testing (NDT), active flash thermography is state of the art. There, the test object is heated with a short intense thermal pulse, e.g. by means of powerful flashbulbs, radiant heaters or lasers and the heat wave propagates into the object. Defects influence the heat wave propagation and thus the temperature distribution on the object surface. Further developments have been focused on the increase of pulse energy of the excitation sources to enhance the penetration depth and the thermal contrast of defects. However, in the case of plastic components the higher amount of heat may damage the object’s surface. Therefore multiple flash thermography offers a promising approach for increasing the probability of detection of defects. As a result of a currently ongoing research project between Hensel-Visit and SKZ, for the first time, it is possible to generate six sequential pulses with adjustable pulse duration between 100 μs and 3 ms and a temporal distance starting at 25 ms by using one single device. A systematic study of the mentioned parameters was carried out. The parameters of each pulse of the sequence influence its spectrum and the maximal surface temperature of the sample. Therefore, components consisting of carbon-fibers embedded in an epoxy resin matrix with artificial defects of different sizes and depth positions within the sample were investigated. As a result, the maximum surface temperature of the sample can be considerably reduced by applying consecutive pulses with the same total energy as one high-energy pulse at a constant temperature difference between the damaged and undamaged area. Furthermore the penetration depth of the resulting thermal waves can be increased by influencing the excitation spectrum. Due to the new possibility of adjusting the temporal distance between several pulses and their length by a cut off mechanism, coded signals can be applied prospectively for receiving detailed depth information. In summary, multiple pulse thermography will enhance the probability of detection of defects in the future. 1. State

Keywords: reliability (285),
*Keywords are freely formed keywords from the authors and thus you may Search also for similar terms.

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