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Fatigue crack detection on structural steel members by using ultrasound excited thermography
Author(s) -
Plum Robin Marc
Publication year - 2015
Publication title -
stahlbau
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.268
H-Index - 19
eISSN - 1437-1049
pISSN - 0038-9145
DOI - 10.1002/stab.201590162
Subject(s) - thermography , citation , forensic engineering , art history , structural engineering , engineering , computer science , library science , art , physics , optics , infrared
In the field of non-destructive testing (NDT), ultrasound excited thermography has been recognised as a promising technique that was successfully applied to metals, fibre composites and many more engineering materials in order to detect cracks, delaminations and other types of internal flaws. Dating back to the late 1970s, the idea of high-frequency vibration excitation of structural members combined with monitoring the surface temperature by means of infrared thermography aims at the localised energy dissipation at defect regions and its thermal detection. The purpose of this thesis is to investigate the potential use of ultrasound excited thermography for detecting surface breaking fatigue cracks in thick-walled components relevant to steel construction. The presented research is motivated by a lack of fast and imaging crack detection methods in the field and the growing acceptance and technological progress of active thermography techniques. After introducing the concept of ultrasound excited thermography or vibrothermography, its current state of the art is described by means of a comprehensive literature review focusing on research activities towards crack detection on metals. Owing to the interdisciplinarity of the test method, all relevant technical subdisciplines from the excitation of plate vibrations via potential heat generation mechanisms and heat transfer to infrared thermography are outlined. The experimental work starts with the manufacture and fatigue loading of suitable plate specimens made from low-carbon steel S355, mostly in the high cycle fatigue regime, to generate throughthickness cracks with specified depths. Using a modified high-power ultrasonic welding generator, basic dependencies of the defect heating on frequency, coupling location and excitation duration are clarified at first. Besides of an estimation of realistic detection limits depending on the plate thickness, main issues such as the relation between vibration intensity and defect heating, wear and damage due to repeated ultrasound insonification and the influence of a static preload are addressed in detail. A procedure for 3D scanning of vibration mode shapes using a single-point laser vibrometer is developed in order to predict the frictional power dissipation based on crack face displacements. In-situ crack detection is simulated on a hot-rolled girder featuring multiple cracks. The efficiency of several prototypes of a portable excitation device is evaluated.