Ultrasonic Wave Propagation in Aerospace Structures: Highly Efficient Simulation with a Minimal Model

Kurzfassung

Continuous monitoring of the state of a structure could provide a great benefit for many aspects of maintenance, repair and overhaul (MRO) of aircraft and can be an enabler for condition based maintenance. One approach to realize structural health monitoring (SHM) is based on actuator-sensor networks to excite and receive ultrasonic waves. Signal changes indicate damage, but can also be used to identify the location and type of a defect. Simulations of wave propagation could be beneficial to support development and design of SHM systems. However, currently no suitable tools exist due to the size and complexity of aerospace structures in combination with the required high frequencies. An innovative simulation technique is proposed to provide approximate solutions at selected points of the structure with drastically reduced computational cost compared to established numerical methods. In this paper an overview of this minimal model including necessary pre-processing steps is given. This is followed by a validation of the analytical approach with the help of numerical and experimental result. In a first step, wave propagation and interaction inside an aluminum plate is analyzed. Results of the proposed method are compared to calculations with the finite element method (FEM) and measurements with a laser vibrometer. Signals of all three methods agree very well and only a few minor deviations point toward some shortcomings of the minimal model in its current state. But at the same time, the huge performance advantage of the analytical model becomes apparent, as calculation are about three orders of magnitude faster as the FEM. To validate the minimal model on a more complex structure, experimental measurements on a plate consisting of carbon fiber reinforced polymer (CFRP) are used. Good agreement of the results can be observed, but discrepancies are present. This is since modelling of composites is more challenging as they induce different anisotropy effects.