| High performance, light-weight composites and other multifunctional materials are being used in many engineering applications, however, reliability is a critical issue because a damage event will compromise the integrity of composite structures and lead to ultimate failure. In composites, the energy is absorbed through various fracture processes, resulting in more complex forms of damage including fiber failure, matrix cracking and delamination. The development of robust structural health monitoring (SHM) framework, which comprises efficient detection, identification and quantification techniques to characterize the presence of multiscale damage in heterogeneous structural systems is a critical area of research, and requires considerable attention.; A comprehensive framework has been developed including damage characterization in composites, advanced signal processing for damage detection, and optimal sensor placement. A refined global/local laminate analysis technique is used for the characterization of damage in composites. Damage identification is conducted using elastic waves and miniaturized piezoelectric sensors. A new design methodology for optimal sensor placement has been developed based on the requirements of sensing certainty and sensor density. An analytical method has been developed to model the material attenuation of the composite medium to formulate a relationship between sensing region, sensor observation angle, fiber orientation, and damage size. A hierarchical approach has been adopted to improve the monitoring technique for further quantification of delaminations patterns. A signal processing technique based on the matching pursuit decomposition has been further extended to extract newly generated spectral components due to the nonlinearity in the received signal. Time-of-flight analysis has been performed on decomposed components of transient datasets to quantify defect. An advanced machine-learning based classifier, known as Support Vector Machines, has also been developed to detect and classify the signature characteristics due to the presence of various types of defects like delaminations, drilled holes, notches, saw-cut etc. in composite structures so that the status of the structure can be ascertained. Experiments have been conducted using a variety of nondestructive evaluation (NDE) techniques, including pulse echo, thermography, to visualize the presence of damage. |
