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Distributed Optical Sensing in Composite Laminate End-Notched Flexure Tests

LEEANNA MEADOWS, RANI SULLIVAN, VIPUL RANATUNGA, KEITH VEHORN, KEVIN BROWN and STEVE OLSON

Abstract


The end-notched flexure test (ENF) evaluates the mode-II interlaminar fracture toughness (GIIc) for unidirectional fiber-reinforced polymer matrix composite laminates. To obtain correct GIIc values, care must be taken to locate the crack tip and verify that the growing crack front is straight. This is often done by performing an ultrasonic scan between each crack growth which is very time consuming. This paper presents a method for locating the growing crack front by observing the changing stain field through embedded distributed optical fiber sensors. To establish a repeatable fabrication methodology, manufacturing techniques for embedding the optical fibers during the laminate layup process are investigated. Specimens with and without embedded fibers are tested to verify that the embedded fibers do not affect the resulting GIIc values. True crack growth values are compared to the optical fiber data to validate the sensors’ ability to map the growing crack front shape.

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