Study of Innovative Techniques for Structural Health Monitoring

This thesis aims at developing new methodologies to determine the structural integrity of aeronautical components. The increasing use of composite materials, which present damage initiation and evolution different from the homogeneous ones, requires the development of new techniques to determine the performance of the most critical components. Structural health monitoring (SHM) is a field of research which aims at developing new methods to perform this task. One of the main concerns is given by initially barely visible impact damage (BVID), which can grow during operational time and eventually lead to catastrophic failures. The monitoring can be accomplished both with active and passive methods. In this thesis the part of SHM which concerns the development of algorithms for damage and impact detection is addressed. First a damage detection approach based on the proper orthogonal decomposition (POD) is developed. Analyses on different components are performed, in particular detecting defects without needing any baseline. Particularly important is the application of the proposed approach to a stiffened panel, which has not been deeply analysed in literature. The second part of the thesis concerns impact detection and force reconstruction. In particular the attention is focused on large mass impacts, which can produce geometrical nonlinearities in the dynamics of the system. Finally a novel impact location algorithm, based on the POD is proposed. This represents a novelty in impact location algorithms, which have previously been focused on the triangulation method. In particular the proposed approach is not dependent on the wave velocity, which is a major limitation in the application of the triangulation on composite panels. Remarkable results are obtained in this thesis. In particular experimental verifications are performed on damage detection using only data coming from a damaged system and on force reconstruction on a composite panel