Composite wing box deformed-shape reconstruction based on measured strains: Optimization and comparison of existing approaches

The reconstruction of the displacement field of a structure (shape sensing) has become crucial for the Structural Health Monitoring of aerospace structures and for the progress of the recently developing morphing structures. As a consequence, shape sensing techniques based on discrete surface strains measurements have seen a consistent expansion in the last few years. In this paper, the three main shape sensing methods, the Modal Method, the Ko’s displacements theory and the inverse Finite Element Method, are presented. The most recent and also novel improvements are discussed and added to the methods’ formulations. Then, the three methods are numerically applied to a complex aerospace structure such as that of a composite wing box experiencing bending and twisting deformations. For the first time, a detailed investigation on the optimal strain sensors configuration is performed for all the three techniques simultaneously. Finally, the methods’ performances, in terms of accuracy of the reconstruction and of number of required sensors, are compared. The three methods show different characteristics that make them suitable for different applications, depending on the level of accuracy and the number of strain information required. The iFEM is proven to be the more accurate but the more demanding in terms of required sensors; the Ko’s displacement theory is capable of giving a rough estimation of the displacement field, but requires a small amount of sensors; the Modal Method represents a trade-off between the other two in terms of accuracy and number of sensors required.