Guided Wave Propagation and Damage Interaction in Isotropic and Composite Structures.

Abstract

Guided wave structural health monitoring methods offer many of the capabilities needed to move from a schedule-based maintenance paradigm to a more cost-effective condition-based system. This dissertation explores several key aspects of guided wave propagation and damage interaction in both isotropic and composite structures. First, a reliable method of computing displacement time histories from guided wave excitation is presented. This formulation, based on the Global Matrix Method, is directly applicable to composite laminates. It improves upon previous methods that were unable to properly separate inbound and outbound wave solutions. Second, a comprehensive wave propagation simulation tool is presented that combines the best features of the Global Matrix Method and the recently developed local interaction simulation approach (LISA). This LISA hybrid model accurately captures guided wave generation from both piezoceramic and piezocomposite actuators. Wave propagation results from the new model compare favorably with semi-analytical models for both isotropic plates and composite laminates. Following that, the dissertation describes the application of the LISA hybrid model to examine guided wave interaction with holes in plate structures. Simulations are used to analyze the influence of various damage parameters, such as hole radius and depth, and the results are compared with experimental measurements. The effect of hole orientation relative to fiber direction in composite laminates is also explored. Subsequently, the dissertation examines guided wave interaction with low-velocity impact damage in composite laminates. Diagnostic imagery of laboratory-produced impact damage is presented to help characterize the size, shape, and composition of the damage. Experimental results from guided wave interrogation of the damage region are also presented. Together, these are used to evaluate various methods to model the impact damage in LISA. Finally, this dissertation introduces a damage characterization tool based on the matching pursuit method. The new algorithm uses a library of LISA simulations that capture the effects of various damage sizes and locations. The ability of the algorithm to locate damage is demonstrated in both 1-D and 2-D scenarios.