Calibration of cast-in fibre Bragg gratings for internal strain measurements in cast aluminium by using neutron diffraction

Heilmeier, Florian; Koos, Robert; Hornberger, Peter; Hiller, Jochen; Weraneck, Klaus; Jakobi, Martin; Koch, Alexander W.; Volk, Wolfram

doi:10.1016/j.measurement.2020.107939

Cited by 6 publications

(7 citation statements)

References 24 publications

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“…This elongation change of the fiber in axial direction as a combination of mechanical and thermal strain and can be calculated according to equation 2. The proportionality constant is denoted by κ [4]. This describes the interface influences between the glass fiber and the alloy.…”

Section: Fiber-bragg-gratingmentioning

confidence: 99%

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Analysis of the melting and solidification process of aluminum in a mirror furnace using Fiber-Bragg-Grating and numerical models

Bauer,

Erber,

Fuchs

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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In the search of an adequate real time strain measurement method in aluminum casting, the use of Fiber-Bragg-Grating (FBG) is being investigated with great interest. In order to do so, the behaviour of glass fiber sensors in a liquid aluminium alloy at temperatures up to 750°C is experimentally analysed in a laboratory environment. For better process understanding a simulation of the fiber alloy composite is conducted. FBG is an optical measurement method, which uses engraved Bragg reflectors in a 125 µm in diameter thick glass fiber. This reflector transmits most of the wavelengths but only reflects one specific wavelength. This specific wavelength can be measured and changes due to the axial strain on the grating by the fluid alloy reaction and by the changes in temperature. Using a so-called mirror furnace, several experiments with the fiber alloy composite are evaluated. These measurements are also the basis for the further understanding of hot tearing. The data gathered during the measurement campaign - both numerical and experimental - is used to parameterize a simulation. As a result, the understanding of the fiber alloy composite behaviour is expanded and a digital twin is modeled with MATLAB’s partial differential equation toolbox.

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Section: Fiber-bragg-gratingmentioning

confidence: 99%

“…However, such measurements can only be carried out and conducted within a laboratory environment. An alternative way of measuring both temperature and strain at the same time is the use of optical methods [4]. FBGs is such a method to perform experiments in the liquid phase of aluminum…”

Section: Introductionmentioning

confidence: 99%

Analysis of the melting and solidification process of aluminum in a mirror furnace using Fiber-Bragg-Grating and numerical models

Bauer,

Erber,

Fuchs

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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“…For a distinct evaluation of the strain transition from aluminium to fibre, we used the implicit finite element (FE) simulation given in Figure 9, as already presented in [13]. In order to model the interaction properly, the simulation starts with the cooling of the aluminium body, which forces compression strains onto the fibre-see Figure 10.…”

Section: Simulationmentioning

confidence: 99%

“…We extended the model by defining a step-wise increasing load σ onto the upper surface of the aluminium body as depicted in Figure 9a. For an additional evaluation on how the occurring porosity within the specimen affects the strain transition, the aluminium body contains voids, which are simulated by a random deletion of nodes in the FE-mesh, as already described by Heilmeier et al [13]. The mesh with deleted nodes is shown in Figure 9b, while Figure 9c shows a detailed view of the voids on the model's surface.…”

Section: Simulationmentioning

confidence: 99%

“…First calibration efforts, conducted by comparing strain measurements on the inside as well as on the outside of tensile specimens [10], showed that the calibration factor of the FBG differs from the factor obtained from the free fibres as determined by Jülich et al [11]. In the effort to calibrate cast-in FBGs during casting [13] and uniaxial straining [10], Heilmeier et al shows a wide dispersion of calibration factors. Obviously, cast-in FBGs behave differently compared to free FBGs, which can be precisely calibrated.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Strain Transition Properties between Cast-In Fibre Bragg Gratings and Cast Aluminium during Uniaxial Straining

Heilmeier

Koos

Singer

et al. 2020

Sensors

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Current testing methods are capable of measuring strain near the surface on structural parts, for example by using strain gauges. However, stress peaks often occur within the material and can only be approximated. An alternative strain measurement incorporates fibre-optical strain sensors (Fiber Bragg Gratings, FBG) which are able to determine strains within the material. The principle has already been verified by using embedded FBGs in tensile specimens. The transition area between fibre and aluminium, however, is not yet properly investigated. Therefore, strains in tensile specimens containing FBGs were measured by neutron diffraction in gauge volumes of two different sizes around the Bragg grating. As a result, it is possible to identify and decouple elastic and plastic strains affecting the FBGs and to transfer the findings into a fully descriptive FE-model of the strain transition area.We thus accomplished closing the gap between the external load and internal straining obtained from cast-in FBG and generating valuable information about the mechanisms within the strain transition area.It was found that the porosity within the casting has a significant impact on the stiffness of the tensile specimen, the generation of excess microscopic tensions and thus the formation of permanent plastic strains, which are well recognized by the FBG. The knowledge that FBG as internal strain sensors function just as well as common external strain sensors will now allow for the application of FBG in actual structural parts and measurements under real load conditions. In the future, applications for long-term monitoring of cast parts will also be enabled and are currently under development.

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Monitoring strain evolution and distribution during the casting process of AlSi9Cu3 alloy with optical fiber sensors

Bian

Bauer²,

Stadler³

et al. 2023

Journal of Alloys and Compounds

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Calibration of cast-in fibre Bragg gratings for internal strain measurements in cast aluminium by using neutron diffraction

Cited by 6 publications

References 24 publications

Analysis of the melting and solidification process of aluminum in a mirror furnace using Fiber-Bragg-Grating and numerical models

Analysis of the melting and solidification process of aluminum in a mirror furnace using Fiber-Bragg-Grating and numerical models

Evaluation of Strain Transition Properties between Cast-In Fibre Bragg Gratings and Cast Aluminium during Uniaxial Straining

Monitoring strain evolution and distribution during the casting process of AlSi9Cu3 alloy with optical fiber sensors

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