Thermographic techniques for the detection of cracks in metallic components

Abstract

The presentation will show that thermographic NDT, which has long been associated with the detection of sub-surface in-plane faults in composites or coatings, also has great potential to compete with DPI and MPI for the detection of cracks in metallic components. Work on three thermographic NDE techniques that have been developed to locate and image cracks in metallic components will be reviewed. These techniques are: thermosonics (sonic IR, ultrasonically stimulated thermography); laser spot thermographic imaging and pulsed eddy current stimulated (induction) thermography. The three techniques will be explained and examples will be given of their performance in imaging well characterised cracks. Factors concerning the practical and reliable implementation of the techniques will be discussed.

Defect detection in laser powder deposition components by laser thermography and laser ultrasonic inspections

“…Laser thermography, also known as pulsed laser spot thermography, has been successful in identifying cracks and other flaws in regular sized components (components in the order of cms size) [6]. It has effectively been applied to industries requiring high quality components such as the aerospace industry [7].…”

“…Predicative modelling was performed to identify automated techniques to detect and to quantify the size of defects based upon findings that defected regions such as cracks and porosity have lower thermal conductivity and affect the flow of heat throughout the inspection specimen [6]. Based upon a fine scale LPD track, heat flow was modelled for a laser pulse across a 300µm LPD track's deposition profile.…”

Detection of cracks in laser deposited coatings by laser spot thermography

“…Nevertheless, these methods have contact character and are quite time-consuming, so an alternative form of quality control are being searched for. Many authors regard the active thermography as alternative NDT approach, which fulfill foregoing expectations of non-contact and fast control [3,4,5,6]. The methods of active thermography such as lock-in or pulse thermography are widely used for example to detect delaminations, porosity and inhomogenities of composite materials in aerospace industry [7,8].…”

Surface crack detection using infrared thermography and ultraviolet excitation

“…Active thermography can be performed by using different excitation techniques, all with pros and cons. Excitation techniques such as laser, white light, induction heating and ultrasonic are found in the literature [3][4][5]. The physical principles are to some extent different between the techniques and the methods are either based on pulsed, continuous or modulated excitation.…”