Amplitude-modulated lock-in vibrothermography for NDE of polymers and composites

Active and passive thermography for defect detection in polymer joints

“…from local changes in material stiffness or a higher mechanical loss angle by interfacial friction [21,22]. When the ultrasonic waves are amplitude modulated, the defect sites are initial points of thermal waves with the same modulation frequency as the ultrasonic waves, which may also be analysed by the lock-in method [23]. As the thermal waves emerge from the defect sites in ULT, the depth range is highly increased compared to the reflective measurements in OLT.…”

Local defect resonance for sensitive non-destructive testing

“…In all experiments, the acoustic power produced was kept within mW-range.The thermal response of the defects was visualized and measured with an IR-camera (IRCAM Equus 327K, NETD 15-20 mK). To enhance signal-to-noise ratio lock-in methodology [8] was applied to obtain phase images of defects. Figure 5 shows the results of LDR vibrothermography of a rectangular (2 x 2 cm 2 ) insert at 1.2 mm depth in a (300 x 300 x 5 mm 3 ) CFRP specimen.…”

Lockin-Thermography: Principles, NDE-applications and trends

“…Weakness means that the stress/strain-diagram is locally changed so that the curve has a different shape or has hysteretical effects due to internal friction when loose boundaries in a crack move parallel and in contact with each other and generate heat. Such effects have been investigated initially by ultrasonic pulses and thermography [23,24] and later with modulated ultrasound as a source for Lockin-Thermography [25], a technique often called "Ultrasound LockinThermography" (ULT). Strong ultrasound at typically 20 kHz is injected into the sample (figure 9) and generates heat at Fig.…”