Reference Strain Structure: Multiaxial Strain Sensor for Real-Time Estimation of Flexible Dynamics Based on Fiber Bragg Sensor Arrays

This article presents the design, analysis, and experimental demonstration of a fiber Bragg-based multiaxial sensor reference strain structure (RSS) for real-time estimation of the 3D shape of a structure subject to biaxial bending plus torsion. The proposed device could be installed on a slender structure, such as a launch vehicle, and enables measurement of the multiaxial deflection and estimation of the 3D shape of the structure in real time based on both beam theory and modal methods. The proposed approach enables the extraction of additional degree of freedom (DOF) information from 3DOF nodes using strain interpolation and addresses important limitations of existing methods for real-time estimation of deflection and structural vibrations during flight. Update rates in the order of tens of kHz are possible with current fiber Bragg grating (FBG) technology, making the RSS practical for monitoring and control of flexible structures during flight. The proposed approach builds on previous effort fiber optic sensor system (FOSS) that enabled estimation of 1D acceleration in real time at any point on a slender structure based on an FBG array. In addition, a method is presented to extract strain mode shapes of a target structure without the need of a finite element model of the main structure the RSS is attached to. The proposed methods have been experimentally validated under both static and dynamic load conditions, by comparing RSS predictions against finite element model predictions and measurements from a 3D optical metrology system.