This paper presents comprehensive studies on sensor performance of an embedded Extrinsic Fabry Perot Interferometer (EFPI) fiber optic strain sensor in an aerospace grade composite system to support fiber optic smart structures (FOSS) development for Structural Health Monitoring (SHM) System. A major portion of this study is focused on establishing the accuracy of the embedded EFPI sensors in a graphite epoxy composite material system at different stress levels under quasi-static loading conditions. The NASA Dryden calibrated EFPI's were used for accurate measurements. Two collocated surface-mounted strain gages and a calibrated surface-mounted EFPI sensor are used to validate the calibrated embedded EFPI sensor. Experimental results suggest that once calibrated, the embedded and surface-mounted EFPI sensors provide robust, reliable and accurate measurement for values up to ~5,400 με higher than sensor's durability limit ~3,000 με at 106 cycles. This validation provides evidence that the sensing information emanating from FOSS can be used to monitor accurate health information.
We investigated a thermal nondestructive evaluation (NDE) technique based on thermography that uses optical fiber thermal sensors to detect damage within a laminated graphite epoxy composite specimen. Composite samples manufactured for testing had fiber optic sensors embedded between layers and thermocouples attached to the exterior. A simulated impact system was used to induce damage of varying degrees into the samples and the damage was confirmed with C-span. The experimental procedures in addition to the test data obtained are presented. The results confirm that the fiber optic thermal sensors can not only detect the presence of damage, but can measure the severity of damage as well.
We investigated a thermal nondestructive evaluation (NDE) technique based on thermography that uses optical fiber sensors to detect damage within a laminated graphite epoxy composite specimen. Two sets of composite samples were used for testing, one set had fiber optic sensors imbedded between the layers and the other set did not. Thermocouples were attached to the front and back surfaces of all coupons for comparison. Damage was initiated in the samples at various levels with a simulated impact system and damage was confirmed with X-ray. Results suggest that the thermal approach is more sensitive to damage than the X-ray evaluation used. The test apparatus in addition to the results obtained from both sets of samples are presented.
Experimental results on mechanical behavior of Extrinsic Fabry-Perot Interferometric Fiber Optic Strain Sensors (EFPI-FOSS) are presented in this paper. The goal of this study was to determine the accuracy, strength characteristics, and durability properties of both bare (non-embedded) EFPI sensors, and embedded EFPI optical fiber sensors in either a neat resin or aerospace grade composite laminate. Experimental results suggest that the embedded EFPI sensors provide reliable strain measurements for values exceeding 10,000 (mu) (epsilon) under static loading conditions. A major portion of this study focused on evaluating the long term tension-tension fatigue behavior of optical fiber sensors. Test data suggest the EFPI sensors provide reliable data up to 1 million cycles at fatigue strain levels below 3,000 (mu) (epsilon) . For fatigue strain levels above this value, failure of the fiber optic sensor was observed. While the sensor failed it did not influence the strength and fatigue life of the composite coupons. Considering the design strains used in aerospace components, these results provide evidence that the EFPI sensors will survive during the life of typical aerospace structures.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.