Damage detection by applying statistical methods to PZT impedance measurements

An effective integrated structural health monitoring system must include a method of sensing and a process of damage identification that are optimized to work together. The result is a system that provides an automated and quantified assessment of damage present in a structure. Two candidates for such a symbiosis of sensing and damage identification are impedance-based measurement and statistical process control. The impedance-based structural health monitoring method uses a high frequency signal to excite a structure through a bonded piezoelectric patch and measures the impedance response of the excited structure across a frequency spectrum. In structural damage cases such as threads loosening or a crack developing, the structure in question will begin to show a change in impedance. Once measured, a damage sensitive feature from this impedance change can be statistically quantified into different damage cases by statistical process control. This paper addresses impedance measurements from experimental structures and a subsequent statistical method for quantitatively determining when the impedance signature of the structures has changed significantly enough to warrant the classification of "damaged". Simple features and hypothesis testing algorithms are explored in an effort to create real-time solutions and reduce the complexity of damage identification for future use in low resource integrated structural health monitoring systems.