21st International Congress on Sound and Vibration (ICSV) July 13–17, 2014, Beijing, China
COMPUTATIONAL AND EXPERIMENTAL INVESTIGATIONS OF ULTRASONIC WAVE PROPAGATION IN SANDWICH PANELS WITH HETEROGENEOUS CORE LAYERS U. Gabbert1 , S. M. H. Hosseini2 and S. Duczek1 1
Otto-von-Guericke-University Magdeburg, Universit¨atsplatz 2, 39106 Magdeburg, Germany, {ulrich.gabbert, sascha.duczek}@ovgu.de, http://www.uni-magdeburg.de/ifme 2 University of Rostock, Albert Einstein Str. 2 , 18059 Rostock, Germany,
[email protected], http://www.welisa.uni-rostock.de
Keywords: Fictitious Domain Method, Finite Element Method, Sandwich Plates, Wave Propagation Analysis, Laser Scanning Doppler Vibrometry.
The on-line monitoring of the structural integrity of thin walled lightweight structures is of steadily growing interest in several industrial areas, such as civil engineering, mechanical engineering, naval architecture, etc. Its main purpose can be seen in increasing the safety and in decreasing the maintenance costs. The application of ultrasonic guided waves is considered as an appropriate means for damage detection since their propagation is sensitive towards small damages, where reflections, refractions, and mode conversions may occur, which are distinct indications for the structural health state. But the application of such waves in cellular lightweight sandwich panels is still a demanding task. The wave behavior in such materials as well as their interaction with damages is not well understood, and, consequently, their application for health monitoring reasons is also not well accepted. It is also a great challenge to simulate the wave propagation in such complex materials. The required computational costs exceed the possibilities of today’s standard FEA software tools. Hence, an effective higher order finite element approach based on a combination of the spectral element method (SEM) and the finite cell method (FCM) called spectral cell method (SCM) - has been developed, which seems to be an efficient method to simulate the ultrasonic wave propagation in sandwich panels with a heterogeneous core layer (honeycomb, foam, hollow spheres etc.). In the paper the modelling approach as well as simulation results are presented. To demonstrate the ability of ultrasonic waves to detect damages in heterogeneous materials and to validate the simulation results also experimental measurements are presented. For this purpose a 3D laser scanning vibrometer has been employed to study the wave propagation and their interaction with material discontinuities. In addition, computer tomography images are shown to visualize the inner structure of the panel in a region of interest where strong wave interactions due to failures in the material can be observed.
