A numerical study on planar gradient acoustic impedance matching for guided ultrasonic wave detection

Abstract

Increasing the service-life of engineering structures such as aeroplanes is a major issue in order to enhance their cost-effectiveness and to reduce the carbon footprint. One possibility to achieve this goal is to determine the current structural health state and to derive respective measures in order to increase the structure’s technical reliability. For doing so, a structural health monitoring system consisting of both an actuator and a sensor network may be applied. Whereas the actuator induces a wave field of guided ultrasonic waves, the measuring data of the sensors allows to determine the health state of the respective structure. However, both actuators and sensors in most cases distort these wave fields. This distortion may lead to false-detection of damage: both the number and severity of damage may be over- or underestimated. The former leads to an unnecessary high effort for retrofitting the structure, whereas the latter reduces the structure’s technical reliability. Several measures exist in order to avoid such false-detections. In the present contribution, focus is set on reducing the distortion of the wave field which is caused by an embedded sensor. The reduced distortion of the wave field is achieved by an acoustic impedance matching with a functionally graded material which is based on a mechanical model. The approach additionally results in amplified measuring signals of the sensor. The applicability of the proposed approach is shown by means of a numerical study.

An approach for improving SHM systems with GUW detection and embedded sensors by a planar gradient acoustic impedance matching

“…Similarly to Rottmann et al [15], the best results are achieved for interphase configuration with a gently rising acoustic impedance such as quadratic-and cubic-interphase followed by linear-and square root-interphase. Only at 60 kHz, this linear interphase shows a different behaviour which needs further investigation but is not part of this work.…”

“…Here, (i) represents the wavefield which is reflected by the sensor/interphase and (ii) represents the wavefield which is transmitted through the interphase into the sensor. The evaluation was analogous to the one in Rottmann et al [15]. For all configurations, the envelopes of the displacement data were calculated and compared with the displacement data of the reference configuration (no interphase).…”

“…Within this work, the existing numerical model for planar gradient acoustic impedance matching from Rottmann et al. [15] has been extended and used for higher frequencies, helping to understand the frequency dependency of the interphase. The results show (i) a reduction of the reflections (disturbances) from the sensor for the whole frequency range and (ii) an amplification of the transmission into the sensor (signal measured by the sensor) for certain frequencies.…”

“…Time increment, mesh size were chosen to satisfy the Courant-Friedrichs-Lewy condition. For further details of the model, please refer to Rottmann et al [15].…”

A numerical approach for determining the optimal position of a single damper for damping a distinct eigenfrequency of multi‐body systems

“…Applications in mechanical engineering involve damping of composite structures such as laminated sandwich structures [8]. It should be emphasized that such additional damping needs to be incorporated into methods of structural health monitoring in order to prevent these methods from false-detection of damages [9,10]. Whereas for some special cases an analytical or semi-analytical calculation of optimal damper placement and optimal damping value is possible, for real-world applications a numerical investigation is necessary.…”