Monitoring and instantaneous evaluation of fatigue crack using integrated passive and active laser thermography

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>This study proposes an integrated passive and active laser thermography (IPALT) system comprising a continuous wave (CW) laser and an infrared (IR) camera for fully noncontact monitoring and instantaneous evaluation of a fatigue crack in a metallic structure. The IPALT system operates in two phases: (1) passive thermography (PT) mode, and (2) active thermography (AT) mode. The PT mode monitors the fatigue crack initiation by measuring the thermoelastic effects on the fatigue crack tip in real time using the IR camera. Once the crack tip is identified, the AT mode is automatically triggered, and the corresponding fatigue crack is precisely quantified using the CW laser and the IR camera. Through this effective crack monitoring system under operating conditions, time dependent crack propagating behavior analysis, as well as early crack detection, can be achieved. The feasibility of the proposed IPALT system is experimentally validated by monitoring a metallic structure under a 10 Hz cyclic loading. The validation tests indicate that fatigue crack initiation is detected at 10,000 cycles by the PT mode, and the fatigue crack length is quantified as 10.45 mm with an accuracy of 99.43% compared to the microscope observed ground truth of 10.51 mm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel integrated passive and active thermography (IPALT) system is proposed for real-time fatigue crack monitoring of metallic structures under operating conditions. </LI> <LI> The IPALT system retains and combines the advantages of both passive and active thermography techniques, and was experimentally validated through fatigue crack monitoring and quantification on a metallic structure. </LI> <LI> Monitoring and inspection can be performed in a completely noncontact, nondestructive, and nonintrusive manner. </LI> <LI> Automated visualization and quantification of a fatigue crack can be accomplished through the proposed single data acquisition and processing platform without interrupting the operating target structure or expert intervention. </LI> <LI> The fatigue crack monitoring and evaluation can be accomplished by only using current-state thermal images, making it possible to minimize false-alarms caused by environmental or operational variations. </LI> </UL> </P>