Lock-in thermal test with corrected optical stimulation

ABSTRACT

Among the Non-Destructive Testing (NDT) techniques available today, Active Infrared Thermal Testing (AIRTT) is certainly one of the most flexible and promising. The goal of this work was to compare the results obtained with a common Lock-in Thermal Test (LTT) and the same test using a true sinusoidal stimulation obtained through a closed-loop controller. The results showed a poor dynamic response of the common system and a lack of proportionality between the reference signal and the generated optical stimulation. To improve its response, it was implemented a PID controller using a light sensor to close the feedback loop. The amplitude images obtained with this controller showed a significant improvement in the results. Defects invisible with the common LTT were now identifiable. The phase images obtained using the controller with feedback revealed higher sensitivity with lower noise. Despite only one system was tested, the results show that the optical stimulation used in LTT is not very accurate and can/should be improved and, that a sensitivity 2.5 times higher than the common LTT was achieved with a real sinusoidal stimulation.

Abbreviation: NDT: Non-Destructive Tests; AIRTT: Active Infrared Thermal Testing; LTT: Lock-in Thermal Test; cLTT: common LTT; PID: Proportional, Integral and Derivative; CFRP: Carbon Fibre Reinforced Polymers; TTT: Transient Thermal Tests; LDR: light-dependent resistor; PMMA: Poly(methyl methacrylate)

KEYWORDS:

• Applied mechanics
• defect detection
• lock-in
• non-destructive testing
• thermography

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was funded by Fundação para a Ciência e a Tecnologia Project UIDB/50022/2020, UIDP/50022/2020

Notes on contributors

António Ramos Silva

António Ramos Silva, holds a Masters and a PhD in Mechanical Engineering from University of Porto, Faculty of Engineering (2010 and 2016 respectively) and a degree in Mechanical Engineering from Porto Polytechnic Institute. He is currently an invited professor at University of Aveiro (Portugel), Porto Polytechnic Institute of Engineering (Portugal) and Faculdade de Engenharia da Universidade do Porto (Portugal) and a researcher at INEGI - Institute of Science and Innovation in Mechanical and Industrial Engineering.

Mário Vaz

Mário Augusto Pires Vaz is an associate professor with tenure in the Department of Mechanical Engineering, Faculty of Engineering, UP. Holds a PhD in laser interferometry techniques for experimental mechanics, from the UP, in 1995; In 1985 he joined INEGI, an interface university institute. He coordinates European projects carried out in consortium with companies such as Bosch, Aerospatiale and British Aerospace, Alenia, SAGEM, Thales, among others. During that period was involved in the construction of  devices for non-destructive inspection of composite materials based on interferometric technics. Head of the Laboratory of Optics and Experimental Mechanics (LOME) since 2000. Past president of the Portuguese Society of Biomechanics and Past President of the EURASEM European Society for Experimental Mechanics.

Sofia Leite

Sofia Leite is a clinical psychologist with a research career in developmental psychology, biometrics, data analysis, and artificial intelligence. After working in the fields of neuroscience, neuro-feedback, and biofeedback at Faculty of Psychology University of Porto, and in the field of human-computer interaction at Microsoft Portugal, she completed a PhD thesis in biomedical engineering/artificial intelligence at Faculty of Engineering University of Porto. She is now an integrated researcher at CINTESIS, Faculty of Medicine University of Porto, working with medical data, and linking all the above disciplines.

Joaquim Gabriel

Joaquim Mendes, holds a PhD in Industrial Electronics from University of Minho (2003), a Master in Computer & Industrial Engineering from Universidade do Porto (UPorto), a Post-graduation in Automation and Management of Industrial Processes, and a degree in Mechanical Engineering. He is currently Associated Professor at Faculdade de Engenharia da Universidade do Porto (Portugal), researcher at INEGI - Institute of Science and Innovation in Mechanical and Industrial Engineering.