CALCE Webinar - Fiber Optic Conjugate Stress Sensor for Prognostic Health Monitoring (PHM)

Tuesday, November 26, 2019
11:00 a.m.-12:00 p.m.

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Abstract

Materials used in aerospace vehicles, offshore assemblies, civil structures, and consumer products can all show degraded performance due to fatigue. Many PHM techniques in literature rely on sensing techniques that capture crack formation and crack growth throughout a structure’s lifetime. However, at CALCE we are using fiber optic sensors to target fatigue damage precursors, i.e. microstructural evolution that precedes visible damage. To achieve this, a fiber optic conjugate stress sensor (FOCSS) has been developed to track changes in the stress-strain hysteresis, a known damage precursor indicator. Conjugate stress sensing relies on two co-located extensometers of different stiffness. Then with an appropriate transfer function, the stress-strain relation (tangent stiffness) of the host structure can be estimated from the strains in each extensometer.

One of the advantages of the FOCSS is that it enables crack detection and impact detection techniques as well as stiffness monitoring. This webinar will present the initial capabilities of the FOCSS, i.e. impact and crack detection, then move to stiffness detection. In stiffness detection, monotonic tensile tests of copper have been performed with the FOCSS accurately monitoring the stress-strain state of the copper coupon. Finite element and spring models developed for the transfer function from sensor strains to host stress-strain state will also be presented. The presentation will conclude with the state of the current focus with the FOCSS, capturing fatigue hysteresis, though experimental verification has proven tricky as the bonding between the sensor and the host needs to be improved moving forward.

About the Presenter: Jonathan Kordell is a mechanical engineering PhD candidate at the University of Maryland co-advised by Professors Abhijit Dasgupta and Miao Yu. The bulk of his research focuses on sensors for prognostic health monitoring, though he has experience in multiaxial vibration analysis and single axis vibration fatigue of electronic assemblies. As an undergraduate at the University of Maryland, he also conducted research into acceleration mitigation techniques for armored vehicles exposed to high magnitude impacts. Mr. Kordell graduated with a B.S. and M.S. in mechanical engineering from the University of Maryland in 2016 and 2019, respectively.

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