Statik und Dynamik

In order to enhance Structural Health Monitoring of engineering structures, an appropriate modelling of the underlying structures as e. g. bridges or wings is necessary. Amongst other things this includes relevant (pre-)damages as cracks, delaminations, imperfect bonding, etc. which have to be incorporated at the so-called micro- or mesoscale of the structure. However, given the overall dimensions of typical engineering structures a discrete modelling of these (pre-)damages is not feasible at the macro-/structural scale. Thus, a scale-bridging is necessary to capture the structural behaviour. One promising approach to incorporate (pre-)damages at the microscale while maintaining a numerically manageable model of the overall structure is the sub-structure technique which will be used in the current project. Since a Structural Health Monitoring using the aforementioned numerical models strongly relys on useful measurement data it is of tremendous interest to determine the optimal number and the optimal position of the respective sensors. Hence, this topic is also addressed in the current contribution.

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.