Experimental testing, analysis and optimization of aerospace structures and components

Design of aerospace structures is a very complicated process entailing experimental measurements, numerical analysis and optimization for each of the different disciplines involved in the project. Experimental measurements must always be carried out to validate any modeling assumption made in the design process. However, there are at least three critical issues in the experimental analysis of aerospace structures: (i) to precisely measure deformations and strains developing from different loading conditions; (ii) to reliably estimate the level of damage experienced by the structure; (iii) to reliably assess constitutive behavior of new materials utilized in purpose of enhancing structural efficiency. Information gathered from experimental tests are of fundamental importance in all cases where new components must be developed starting from previously existing structural configurations or innovative materials must be utilized in order to improve the performance of the structure. Furthermore, during the life cycle of aerospace structures, periodic inspections and verifications of the components must be conducted to guarantee the required level of structural safety. In the stage of conceptual design it is necessary to carry out extensive experimental investigations on the materials and components included in the structure finally developed. Therefore, experimental techniques and testing protocols should provide designers with information the most complete and accurate as it is feasible, especially when the measured data are inputted to numerical models simulating the behavior of the structure. For example, full-field measurements based on optical techniques can be used to determine three-dimensional distribution of deformation and strain, to contour shapes, and to properly identify boundary conditions. Full-field experimental data can also be taken as target values in inverse problems where the objective is to identify structural or aerodynamic behavior. As far as it concerns the assessment of the level of structural integrity and safety, experimental techniques must be specifically suited for the different levels of structural complexity entailed by material inhomogeneity and anisotropy and, in general, material and geometric non-linearity. In some cases, the nature of the material undergoes significant modifications during the service of structure with obvious implications on the global structural response of the vehicle whose configuration may become completely different from that originally considered by the designers. For this reason, experimental techniques for surface inspection must be complemented or even replaced by other methods such as X-rays, neutron diffraction, ultrasounds, acoustic emission, thermography, electron microscopy, etc able to pick information inside solid bodies. This chapter presents some applications of experimental techniques to the study of mechanical behavior of aerospace components. In particular, full-field optical techniques will be utilized to determine the displacement field and buckling strength of two real components: a landing light glazing and a stringer stiffened composite fuselage panel of commercial airliners. Some examples of mechanical characterization of composite materials for aerospace use also will be illustrated in the paper. Besides experimental techniques, important aspects concerning numerical methods for modeling, analysis and multidisciplinary optimization of aerospace structures also are discussed in the paper.