Structural damage diagnosis using stereolithography, experimental modal analysis and finite element analysis

The increasing complexity and challenging missions of advanced aerospace, mechanical, marine and transportation (civil and military) structures demand the development of hybrid analytical/experimental modeling and simulation techniques capable of monitoring their health and assessing the damage they undergo. Damage diagnosis and assessment are complicated procedures that in recent years have brought interest and challenging opportunities to the research community. It consists of detecting damage, locating it, and assessing its severity.; In a health monitoring process, a pre-damage base line is always needed to provide a reference in order to perform a comparison with the post-damage case. A base line is defined as the model that yields, to a certain approximation, the response of a pre-damaged structure. In most real life situations, such a base line is absent.; Finite element analysis, though a powerful tool, when properly used, does not provide such a base line with acceptable confidence. Simulating a structure by modally testing it gives a better match than FEM.; The current research uses this integrated system of state-of-the-art technologies, furnishing a prototype structural damage assessment system integrating stereolithography modeling, experimental modal analysis, dimensional analysis, reverse engineering and finite element analysis.; Stereolithography (SL) models are used for various reasons; of particular importance is the fact that stereolithography material has properties that are suitable for mechanical testing. In addition, the ease of producing complex models in a short period of time and the ability to simulate damage makes SL suitable for this application.; Experimental modal analysis plays a major role in the inspection of structures as a means of non-destructive evaluation. The measurement tool of choice for modal parameters, in most cases, is the Laser Doppler Vibrometer (LDV), which has the advantage of being non-contact and hence has little or no effect on the modal parameters of the tested structure.; Dimensional analysis is used to deduce relations between structures of different materials and in some cases of different sizes too. These scaled governing equations are used to calculate the expected frequencies for an undamaged structure; deviation from this frequency serves as a first check for damage.; In some situations, CAD files of a certain structure might not be available. In such a case, a structure can be reverse engineered to obtain the geometrical file necessary to produce the FEM and SL model.; Finite element analysis (FEA) comes into play to validate experimental results and to offer understanding of structural vibration behavior. The insight that FEA provides is of great importance in planning a modal test, for example choosing measurement points away from nodal points or nodal lines.; Strain energy method is found to be one of the most successful damage parameters and hence is used in this study. The baseline formation, however, can be applied to other methods.