In this study, a mechanical shaker operating at low frequencies is demonstrated to be a viable excitation source for
vibrothermography. Additionally, a low-cost transduction approach based on commercially available piezoelectric
materials (PZT) is investigated. These PZT transducers are assessed for their excitation efficiency to allow crack
detection in metallic structures. Cracks as small as 1 mm are detected using the mechanical shaker regardless of a beam
structure orientation or crack location. Although the low-cost
PZT-based transduction approach had sufficient excitation
power to generate vibration, localized heat generation was not observed at crack locations.
This paper investigates the use of finite element to model frictional heating based vibrothermography for the detection of
fatigue cracks in steel specimens. First, a finite element modal analysis is carried out to predict the optimal excitation
frequencies. Some thermographic experiments using an infrared camera are carried out to help updating a coupled
thermo-mechanical model built to simulate the thermographic inspection process and to explain the heat generation and
transfer related to it. Experimental investigations also confirmed that the technique is able to detect cracks as short as 0.1
mm. The developed model is able to simulate the thermographic inspection process with a maximum error of 2.13 % on
the temperature distribution. The Fourier transform applied to numerical data reveals that the temperature evolution at
the crack face changes according to the excitation frequency and is modulated due to the nonlinearity induced by the
crack. The model also serves to confirm that the test is non-destructive since the calculated stress at the crack tip is less
than the specimen material's yield stress.
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