Numerical Simulation Of Guided Waves In Thin Walled Composite Structures.

Abstract

The success of guided waves (GW) in the area of nondestructive evaluation/testing (NDE/NDT) has spurred their utilization in structural health monitoring (SHM). GW present promising possibilities in developing SHM systems as they can travel long distances over the structure’s surface, and also through its thickness. In addition to damage detection, GW are capable of providing the overall degradation state of the material in terms of stiffness change.

Wave propagation has been studied extensively for isotropic materials, but studies for composite structures are still in the beginning stages. A good understanding of the GW propagation is required to build robust and reliable SHM systems. It has been shown that Local Interaction Simulation Approach (LISA), a numerical method based on finite difference transformations, is capable of efficiently and accurately modeling GW generation, propagation, and damage interaction in engineering structures. First, the basic theoretical development for the University of Michigan Local Interaction Simulation Approach (UM-LISA) is presented. Then LISA is extended to model three-dimensional (3D) multi-layered orthotropic structures with nonuniform cell aspect ratios. The iterative equations for the simulations are extended for orthotropic materials in a non-principal axis frame, which will benefit in modeling generic laminated composite structures. The validation studies are performed against experimental data.

UM-LISA is further developed to model the piezoelectric actuator effects. The iterative equations are extended for piezoelectric materials by taking into account the electromechanical coupling of the governing equilibrium equations. New constitutive and compatibility conditions are considered to account for the coupling in the electrical and mechanical parameters. The iterative equations calculate mechanical displacements in an explicit time marching scheme, whereas the electric potentials are calculated using an implicit scheme. Studies are carried out to demonstrate the improvements in modeling GW generation using piezo-coupled version of the UM-LISA framework. These studies demonstrate the advantages of UM-LISA as an advanced multiphysics numerical framework to model GW generation and propagation in thin-walled composite structures.