Large Deformation Shape Sensing Using a Nonlinear Strain to Displacement Method

This paper presents a three-dimensional strain-to-displacement transformation method based on a nonlinear modal formulation, suitable for cases of large structural deformations. The method is first demonstrated numerically on a complex beam-like structure test case. A sensitivity study presents the effects of different solution parameters, such as the number of modes and sensors used and the measurement noise. The method is then applied to an experimental test case of the Pazy wing that undergoes very large deformations of 50% span. The wing is equipped with fiber optic strain sensors and a motion-tracking camera system that provides the reference displacement data. The modal data are extracted experimentally, and the scheme is validated using data from a structural loading test. The method is used in a wind tunnel test to map the wing's deformations from measured strain data. Results are compared to those of a linear modal strain-to-displacement transformation method and to displacements computed by direct integration of the measured strains. The process is shown to yield superior results in cases of large deformations.