Structural health monitoring of composite materials will lead to a significant safety and economic impact on the aircraft
and aerospace industries. Ultrasonic guided wave based methods are becoming popular because of an excellent
compromise between coverage area and sensitivity for localized damage detection. The transducers currently used in
composite health monitoring are designed mostly in an empirical manner. The work presented in this paper provides an
analytical procedure to study the wave excitation phenomenon in composite laminates. A hybrid semi-analytical finite
element method and global matrix method is used to obtained the guided wave modal solutions. A normal mode
expansion technique is then used to simulate the guided waves excited from a surface mounted piezoelectric transducer
with transient loading. Parametric studies are performed to obtain the guided wave mode tuning characteristics and to
study the influence of piezoelectric wafer geometry on wave excitation. In an inverse problem, an appropriate loading
pattern can be designed to achieve selective guided wave mode excitation for improved sensitivity and/or penetration
power in the health monitoring of composites. A wave field reconstruction algorithm based on normal mode expansion
is also introduced in this paper. This method is also very computationally efficient compared with the commonly used
finite element method in wave field excitation simulation.
An optimized sensor design and sensor placement strategy will be extremely beneficial to both safety ensuring and cost reduction considerations of structural health monitoring systems. A new framework for structural health monitoring sensor placement optimization was recently developed at Pennsylvania State University based on genetic and evolutionary computation. The formulation of the optimization problem is to minimize the damage misdetection rate as well as to minimize the number of sensors by searching the optimized patterns of sensor placement topology on the feasible region of the structure being monitored. Two types of SHM sensors are considered. One is a single sensor scenario; the other is an actuator-damage-sensor scenario. The program was applied to a sample sensor placement problem of an aging aircraft wing. Optimized sensor placement designs are obtained. The tradeoff relationship between the sensor performance, sensor number, and the overall sensor network performance are also presented in this paper.
Sensor development and signal processing are two key issues in structural health monitoring (SHM). A process of PVDF annular array sensor design via guided ultrasonic wave propagation, excitation, and wave damage interaction modeling is presented in this paper. A sample problem to monitor the occurrence and progression of simulated corrosion damage in an aluminum plate is studied. An effective guided wave mode for easy corrosion depth assessment was selected based on guided wave propagation analysis. Three dimensional finite element method (FEM) analyses were performed to study the wave field excited from PVDF annular arrays and sectioned annular arrays in the aluminum plate. Annular arrays with enhanced mode selection capabilities were permanently bonded to a 1mm aluminum plate. Simulated corrosion damage with progressive corrosion depths was successfully detected in the structure using wave mode based signal analysis and feature extraction. The relation between the damage depth and the reflection wave amplitude from the signal were studied with both numerical simulation and experiments.