Title: High-temperature strain monitoring of stainless steel using fiber optics embedded in ultrasonically consolidated nickel layers

Abstract

Fiber optic sensors have long been considered for use in structural health monitoring of components because of their small size, high accuracy, and their ability to perform spatially distributed strain measurements when embedded within a component or on its surface. The typical method for transferring strain from the component to the fiber is to use an epoxy, which may not survive extended exposure to high temperatures, thus necessitating a more elaborate technique to embed the fibers. This work represents a first step towards using additive manufacturing techniques to embed fiber optic sensors on stainless steel components for high-temperature strain monitoring, including quantification of the differential thermal strains that develop between the fiber and the steel substrate. Copper-coated optical fibers were embedded in nickel layers on top of a stainless steel substrate using an ultrasonic additive manufacturing technique. The embedded fibers showed minimal signal attenuation and clear compressive strain after embedding. Heating the embedded fibers in steps to temperatures of 300 °C–400 °C resulted in measured strains with values between the expected thermal strain in stainless steel and nickel. Finite element simulations confirm the measured strain values and show that the thermal strain depends on the thickness of the nickel layersmore » deposited on top of the stainless steel substrate. While the fibers failed before reaching temperatures of 500 °C, it is suspected that these failures occurred due to a combination of (1) the lack of strain relief, (2) the high-temperature oxidation of the fiber's copper coating, and (3) improper sizing of the machined channel in which the fiber is placed prior to embedding. If proper coating selection and sizing of the channel can prevent the failures observed in this work, the next step would be to monitor strain during mechanical loading at high temperatures.« less

Authors:

Petrie, Christian M.  ^[1];

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Sridharan, Niyanth  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-9682-8261"
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Hehr, Adam ^[2]; Norfolk, Mark ^[2]; Sheridan, John ^[3]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Fabrisonic LLC, Columbus, OH (United States)
3. Sheridan Solutions, Saline, MI (United States)

Publication Date:

2019-07-23

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1545217

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Smart Materials and Structures

Additional Journal Information:

Journal Volume: 28; Journal Issue: 8; Journal ID: ISSN 0964-1726

Publisher:

IOP Publishing

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 42 ENGINEERING