In this study, beamformers consisting of phased sensor or actuator arrays are used in the nondestructive evaluation of homogeneous and heterogeneous structural components. Beamforming can be used to detect, locate, and quantify damage by suitably applying weights and time or phase delays to the tapped signals from a sensor array and/or actuator array in a narrow frequency band to obtain the desired directional sensitivities and optimal array gains. Some aspects about beamforming and wave propagation are discussed as a prelude to the experimental investigation. Design considerations for the phased arrays are also examined. The advantages of using adaptive over conventional beamforming are demonstrated with Frost constraint- and pilot signal-based adaptive techniques. Data from steel and composite plates are analyzed using propagating elastic waves and phased arrays of sensors and/or actuators. Damage, which can be characterized as a local change in impedance, is diagnosed by using propagating elastic waves as they are sensitive to small changes in impedance and do not require a large number of input/output transducers. Beamforming of sensor and/or actuator arrays is carried out to characterize damage in steel and composite plates by comparing the directivity patterns associated with the damage and baseline data.

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Polymer based piezoelectric composite materials can be readily integrated within laminated composite structures to provide sensing and actuating capabilities. In this study composite films of ferroelectric ceramic/polymer materials have been developed and characterized as in-situ multi purpose sensing elements for the nondestructive monitoring of fiber reinforced composites. In this paper the response of embedded composite films to simulated acoustic emission signals will be presented and discussed.Results show the ability of the composite sensors to detect signals from acoustic emission sources over a wide bandwidth.

The superior engineering properties of fiber reinforced polymer matrix composites, primarily the high strength-to-weight ratio, make them suitable to applications ranging from sporting goods to aircraft components (e.g. helicopter blades). Unfortunately, consistent fabrication of components with desired mechanical properties has proven difficult, and has led to high production costs. This is largely due to the inability to monitor and control polymer cure, loosely defined as the process ofpolymer chain extension and cross-linking. Even with stringent process control, slight variations in the pre-polymer formulations (e.g. prepreg) can influence reaction rates, reaction mechanisms, and ultimately, product properties. In an effort to optimize the performance ofthermoset composites, we have integrated fiber optic probes between the plies of laminates and monitored cure by Raman spectroscopy, with the eventual goal ofprocess control. Here we present real-time measurements oftwo high performance aerospace composites cured within an industrial autoclave.

This study investigates the nonlinear dynamic failure characteristics of a notched cantilever beam using numerical finite element models and experiments with various displacement loads at the root of the beam. Damage states of the beam are represented as quasi-static equilibrium points and, subsequently, all significant damage events are modeled as bifurcations (qualitative changes) in the set of stable equilibria for the structure-damage system using a set of low-order normal forms. When analytical models are used to interpret trends in data from the beam as it undergoes different routes to failure, the state-space relationship between estimated crack length and rate of change of crack length exhibits elastic-plastic transitions, which depend on the effects of damage accumulation and the load history. It is suggested that these transitions could be used as a series of milestones for rendering a prognosis. It is demonstrated that nonlinear normal forms do simulate a variety of damage evolution phenomena using a few key parameters, which must be evaluated in future works.