The connection technology based on high temperature silica fiber optic sensor

et al. 2016

Sensors

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This paper presents a simple methodology to perform a high temperature coupled thermo-mechanical test using ultra-high temperature ceramic material specimens (UHTCs), which are equipped with chemical composition gratings sensors (CCGs). The methodology also considers the presence of coupled loading within the response provided by the CCG sensors. The theoretical strain of the UHTCs specimens calculated with this technique shows a maximum relative error of 2.15% between the analytical and experimental data. To further verify the validity of the results from the tests, a Finite Element (FE) model has been developed to simulate the temperature, stress and strain fields within the UHTC structure equipped with the CCG. The results show that the compressive stress exceeds the material strength at the bonding area, and this originates a failure by fracture of the supporting structure in the hot environment. The results related to the strain fields show that the relative error with the experimental data decrease with an increase of temperature. The relative error is less than 15% when the temperature is higher than 200 °C, and only 6.71% at 695 °C.

“…Table 1 lists the curve fitting parameters with a 95% confidence interval. Similar quadratic thermal responses have been recorded in other studies [40,48,49,50]. …”

Section: Experimental Results and Analysissupporting

confidence: 89%

Application of CCG Sensors to a High-Temperature Structure Subjected to Thermo-Mechanical Load

et al. 2016

Sensors

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“…Figure a also shows the quadratic curve fitting of the experimental data, and Table lists the curve fitting parameters with a 95% confidence interval. Similar quadratic thermal responses were recorded in other works present in open literature . The average value of the parameter K T 1 from Table can be used to calculate the average strain transfer coefficient β (Table ) from Equation .…”

Section: Temperature and Strain Response Characteristics From The Testssupporting

confidence: 54%

“…The wavelength shift of the CCGs due to the strain corresponds to Δ λ ε , and it is affected by the strain and wavelength of CCGs, as well as the elastic‐optic effect . The theoretical relation of the strain sensitivity coefficient with the center wavelength and the strain variation is

\frac{Δ λ_{ε}}{λ_{B}} = Δ ε_{s} β K_{ε} .

where the center wavelength λ B is the Bragg wavelength, Δ ε s is the global strain of the structure, and it includes the thermal and structural strains.…”

Section: Methodsmentioning

confidence: 99%

“…The wavelength shift of the CCGs due to the strain corresponds to Δλ ε , and it is affected by the strain and wavelength of CCGs, as well as the elastic-optic effect. [44] The theoretical relation of the strain sensitivity coefficient with the center wavelength and the strain variation is [39,45,46]…”

Section: Methodsmentioning

confidence: 99%

“…Similar quadratic thermal responses were recorded in other works present in open literature. [39,46,49,50] The average value of the parameter K T1 from Table 1 can be used to calculate the average strain transfer coefficient β (Table 2) from Equation 1. After the strain transfer coefficient β is obtained, the global strain of the structure can be calculated by using Equation 3, based on the response signal from the CCGs.…”

Section: Superalloymentioning

confidence: 99%

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Measurement of high‐temperature strains in superalloy and carbon/carbon composites using chemical composition gratings

et al. 2016

Strain

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This paper describes an experimental and signal processing technique to perform high temperature tests on superalloy (INCONEL) and carbon/carbon structures using silica‐based chemical composition gratings (CCGs). The results obtained from applying this technique at 940°C in superalloys and 950°C for carbon/carbon (C/C) composites are benchmarked against data obtained from four different methods. The results show that the wavelength responses of the CCGs bonded on the superalloy and on the C/C plate increase nonlinearly with increasing temperatures. The temperature‐dependent strain transfer coefficients recorded during the superalloy tests show quite stable results below 600 °C and tend to slightly decrease thereafter. The values of the strain transfer coefficients below 1000 °C are significantly affected by the thermal expansion coefficient of the substrate material and the interface. We demonstrate that the strain transfer coefficient calculation method used in this paper is not suitable for low and/or negative expansion material. The results of the relative errors show that the CCGs‐F method based on the quadratic dependence of the wavelength shift versus the temperature appears to be the best to estimate the mechanical strains within the interval of temperatures considered and the measurement accuracy. The relative errors measured between 200 °C and 1000 °C are less than 5%.

Measurement of the high-temperature strain of UHTC materials using chemical composition gratings

et al. 2016

Meas. Sci. Technol.

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This paper proposes a simple bonding and measuring technique to realise silica-based chemical composition gratings' (CCGs) high temperature applications on hot structures. We describe a series of experiments on CCGs to measure the thermal and mechanical response characteristics of ultra-high temperature ceramic (UHTC) materials when the maximum temperature is above 1000°C. Response characteristics are obtained at the heating and cooling stages. Results show that the wavelength response of the CCGs bonded on the UHTC plate increases non-linearly with increasing temperatures, but decreases almost linearly with decreasing temperatures. The temperature-dependent strain transfer coefficients are calculated theoretically and experimentally; results show that the values of strain transfer coefficients below 1000°C are significantly affected by the thermal expansion coefficient of the substrate material and the interface. The strain transfer coefficient value tends to vary slowly between 0.616 and 0.626 above 700°C.