Abstract
In this study, the response of fiber Bragg gratings (FBGs) embedded in cast aluminum parts under thermal and mechanical load were investigated. Several types of FBGs in different types of fibers were used in order to verify general applicability. To monitor a temperature-induced strain, an embedded regenerated FBG (RFBG) in a cast part was placed in a climatic chamber and heated up to 120 within several cycles. The results show good agreement with a theoretical model, which consists of a shrink-fit model and temperature-dependent material parameters. Several cast parts with different types of FBGs were machined into tensile test specimens and tensile tests were executed. For the tensile tests, a cyclic procedure was chosen, which allowed us to distinguish between the elastic and plastic deformation of the specimen. An analytical model, which described the elastic part of the tensile test, was introduced and showed good agreement with the measurements. Embedded FBGs - integrated during the casting process - showed under all mechanical and thermal load conditions no hysteresis, a reproducible sensor response, and a high reliable operation, which is very important to create metallic smart structures and packaged fiber optic sensors for harsh environments.
Highlights
Monitoring of functional parts is of great interest and could help to improve the lifetime of these parts or to avoid failures in advance [1,2]
To monitor a temperature-induced strain, an embedded regenerated fiber Bragg gratings (FBGs) (RFBG) in a cast part was placed in a climatic chamber and heated up to 120 °C within several cycles
Cast parts with embedded Type-I and Type-II fs-FBGs were machined to tensile test specimens and subsequently cyclic tensile tests were performed
Summary
Monitoring of functional parts is of great interest and could help to improve the lifetime of these parts or to avoid failures in advance [1,2]. Is acting on the fiber, and on the FBG, the Bragg wavelength will change Both therefractive index and grating period are sensitive to temperature and strain. Due to the fact that the radius of the aluminum in our case is at least one order of magnitude larger than the radius if the fiber (b >> a), the Equations (6) and (8) can be simplified to εzz ∼= (αalu − α f iber)∆T, Note that in this case, the strain and internal pressure are independent of the radii and are dominated by the difference of the CTEs. According to Equations (6) and (8), the axial and radial strains induced by the aluminum depend nonlinearly on temperature because temperature-dependent parameters for Young’s moduli, Poisson’s ratios and thermal expansion coefficients should be used in the extended temperature range considered here.
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