Characterization of Piezoelectric Stack Actuators for Vibrothermography

Abstract

Vibrothermography, also known as Sonic IR and thermosonics, is an NDE technique for finding cracks and flaws based on vibration-induced frictional rubbing of unbonded surfaces. The vibration is usually generated by a piezoelectric stack actuator which transduces electrical energy into large amplitude mechanical vibrations. The amplitude and impedance transfer characteristics of the transducer system control the vibration of the sample. Within a linear contact (no tip chatter) model, the interaction between the transducer system and the specimen can be characterized using the theory of linear time-invariant (LTI) systems and electro-mechanical Norton equivalence. We present quantitative measurements of the performance of piezoelectric stack actuators in a vibrothermography excitation system and investigate the effect of actuator performance and specimen characteristics on the induced vibration in the specimen. We show that the system resonances generated because of metal-metal contact of specimen and actuator are broken by adding a couplant between specimen and actuator. Finally, we give criteria for actuator and couplant selection for vibrothermography.

Detection of multiple thin surface cracks using vibrothermography with low-power piezoceramic-based ultrasonic actuator—a numerical study with experimental verification

“…Similarly, Rizi et al [5] used the same finite element analysis procedure to qualitatively study the heating mechanisms in defected areas. A few authors such as Vaddi et al [17] studied the effect of adding ultrasonic piezoelectric stack actuators in the vibrothermographic excitation system. However, there are not yet any studies which couple the electrical model of ultrasonic transducers into the thermomechanical model of the specimen under inspection in order to form a more comprehensive and realistic thermo-electromechanical model.…”

Low-power vibrothermography detection technique for surface cracks on composite sucker rod

“…Han et al [21] experimentally verified the effectiveness of VT for turbine blade crack detection and found the enhancement of crack detectability by acoustic chaos. Holland et al [22,23] quantitatively evaluated the performance of piezoelectric stack actuators in a VT excitation system and investigated the effect of actuator performance and specimen characteristics on the excitation effect. Zhang et al [24] confirmed the impact of engagement force on crack frictional heating by an ultrasonic gun with a maximum power of 1.25 kW.…”

Vibration modeling for vibrothermography

“…A broadband excitation system was used to generate vibrations at the desired frequencies in the specimen [Vaddi (2011)]. A layer of cardstock material was used as a couplant between transducer tip and the specimen to eliminate transducer-specimen combined system resonances [Vaddi et al (2011)]. A laser vibrometer measured the specimen vibrations while a calibrated infrared camera was used to measure the temperature rise in the coating.…”

“…The use of cardstock or a similar compliant material between transducer and specimen breaks specimen-transducer system resonances [Vaddi et al (2011)]. It also reduces nonlinearity and the potential for unpredictable "chaos" at the tip-specimen contact.…”