Implementation of Fiber Optic Sensing System on Sandwich Composite Cylinder Buckling Test

Abstract

The National Aeronautics and Space Administration (NASA) Engineering and Safety Center Shell Buckling Knockdown Factor Project is a multicenter project tasked with developing new analysis-based shell buckling design guidelines and design factors (i.e., knockdown factors) through high-fidelity buckling simulations and advanced test technologies. To validate these new buckling knockdown factors for future launch vehicles, the Shell Buckling Knockdown Factor Project is carrying out structural testing on a series of large-scale metallic and composite cylindrical shells at the NASA Marshall Space Flight Center (Marshall Space Flight Center, Alabama). A fiber optic sensor system was used to measure strain on a large-scale sandwich composite cylinder that was tested under multiple axial compressive loads up to more than 850,000 lb, and equivalent bending loads over 22 million in-lb. During the structural testing of the composite cylinder, strain data were collected from optical cables containing distributed fiber Bragg gratings using a custom fiber optic sensor system interrogator developed at the NASA Armstrong Flight Research Center. A total of 16 fiber-optic strands, each containing nearly 1,000 fiber Bragg gratings, measuring strain, were installed on the inner and outer cylinder surfaces to monitor the test article global structural response through high-density real-time and posttest strain measurements. The distributed sensing system provided evidence of local epoxy failure at the attachment-ring-to-barrel interface that would not have been detected with conventional instrumentation. Results from the fiber optic sensor system were used to further refine and validate structural models for buckling of the large-scale composite structures. This paper discusses the techniques employed for real-time structural monitoring of the composite cylinder for structural load introduction and distributed bending-strain measurements over a large section of the cylinder by utilizing unique sensing capabilities of fiber optic sensors.

One-wire reconfigurable and damage-tolerant sensor matrix inspired by the auditory tonotopy

“…Good contact between the prosthetic gel liner and the residual limb is critical for the health of amputees. The ability to measure pressure and temperature at this interface can help patients adapt to the prosthetic socket more effectively, especially as the residual limb volume changes (42). By considering the shape of the prosthetic socket and the desired temperature measurement points, we can easily develop a custom multimodal TSM, packaged with polydimethylsiloxane, that is well suited for the needs of amputees, as illustrated in Fig.…”

“…The accurate measurement of wing position, displacement, and deformation during flight and its response to wing gusts and atmospheric turbulence is critical for wing shape control and to avoid loss of flight control (45). The fiber optic sensing system (FOSS) developed by NASA (39,42) has shown great potential in wing monitoring due to its lightweight, ease of installation, and dense measurement points. The working principle of FOSS can be found in text S2.…”

“…Moreover, it can also be combined with a small strain gauge to measure areas that are inaccessible to FOSS. A comparison between the TSM based on strain gauges and FOSS is described in text S2 and table S1 (42). To validate the function of the strain TSM, we carried out experiments using a wing model equipped with nine TSUs (Fig.…”

Test and Analysis of a Buckling-Critical Large-Scale Sandwich Composite Cylinder

“…Instrumentation used to monitor the structural response during loading included: 28 electrical displacement transducers, 256 electrical-resistance strain gages, approximately 16,000 fiber-optic strain sensor locations, 9 eight lowspeed digital image correlation (DIC) photogrammetry systems 10 to measure full-field strains and displacements on the entire OML, and six high-speed DIC systems to measure OML strains and displacements during the dynamic buckling event. Additionally, several microphones and standard-rate video cameras were used to monitor the testing.…”