Thermal Shock Study of Sapphire Fiber Bragg Gratings Embedded in Ceramic Matrix Composites

doi:10.16553/j.cnki.issn1000-985x.2026.0093

Abstract

Abstract: Aero-engine guide vanes operate under high-temperature gas flow and rapid thermal shock environments. Real-time monitoring of their internal temperature and strain states is important for thermal-structural safety assessment and lifetime evaluation. To address the difficulty of embedded multi-parameter measurement using conventional electrical sensors under high-temperature， strong vibration， and strong electromagnetic interference， this study proposed a temperature-strain synchronous monitoring method based on sapphire fiber Bragg gratings （SFBGs） for guide vanes made of ceramic matrix composites （CMCs）. Low-loss coupling and fusion splicing between sapphire fiber and multimode silica fiber were achieved through end-face polishing， axial-offset fusion splicing， and discharge-current optimization. Cascaded dual SFBGs with center wavelengths of 1 530 and 1 540 nm were fabricated using the femtosecond laser phase-mask method. The -3 dB bandwidths of the two SFBGs are 0.56 and 0.68 nm， and the signal-to-noise ratios are 11.21 and 9.34 dB， respectively. High-temperature performance test show that the SFBG exhibits a stable quadratic function temperature response from room temperature to 1 200 ℃， with determination coefficients of 0.999 47 and 0.999 68 during heating and cooling， respectively. An SFBG was embedded into a specimen made of CMCs for high-temperature strain calibration text. The results show that after temperature compensation， the test results of SFBG in 0 με to 3 000 με are consistent with the test results of high-temperature extensometer， and the relative error is less than 5%. In this study， the cascaded dual SFBGs were further embedded inside a guide vane， and 23 thermal shock cycles were conducted under a 1 200 ℃ high-speed， high-temperature gas flow environment. The temperature-strain synchronous measurement inside the guide vane is realized， and the feasibility of embedding SFBG into the CMCs guide vane to realize thermal shock monitoring is preliminarily verified.

Key words: sapphire fiber Bragg grating; ceramic matrix composite; guide vane; high-temperature sensing; strain measurement; thermal shock

CLC Number:

O782.9

ZHANG Chenxin, ZHOU Feng, ZENG Yuqi, TAN Huzhou, ZHANG Yifei, LIU Xianming, JIANG Yajun. Thermal Shock Study of Sapphire Fiber Bragg Gratings Embedded in Ceramic Matrix Composites[J]. Journal of Synthetic Crystals, 2026, 55(8): 1222-1230.

Figures/Tables 10

Fig.1 Schematic diagram of high-temperature testing system

Fig.2 （a） Optical fiber end face microscope； sapphire fiber end faces after grinding with 1 μm abrasive paper （b） and polishing with 0.5 μm polishing paper （c）

Fig.3 Fusion splicing morphology of sapphire fiber and multimode silica fiber. （a） Before fusion splicing；（b） during fusion splicing；（c） after fusion splicing

Fig.4 Sapphire fiber fusion splicing loss test. （a） Test system；（b） transmitted optical power curves under different discharge currents

Fig.5 Spectral test results of cascaded dual SFBGs. （a） Reflection spectrum；（b） demodulator monitoring interface

Fig.6 Fitting curves of temperature and SFBG wavelength （a） and SFBG high-temperature calibration and its fitting curve （b）

Fig.7 High-temperature strain test results. （a） Comparison of SFBG sensor and high-temperature extensometer text；（b） relative error

Fig.8 Schematic illustration of CMCs structure and SFBG sensor arrangement. （a） Simulation diagram of temperature field distribution of guide vane；（b） schematic illustration of sensor arrangement

Table 1 Experimental parameters of component-level test bench for aero-engine components under extreme environments

Parameter	Value	Unit
Oxygen flow rate	130.0	L/min
Kerosene flow rate	4.0	L/h
Air supply pressure	0.80	MPa
Kerosene supply pressure	0.63	MPa
Oxygen supply pressure	0.93	MPa
Gas-flow velocity	600	m·s^-1

Fig.9 Thermal shock response curves of embedded cascaded dual SFBGs in guide vane. （a） Temperature response curve induced by thermal shock；（b） strain response curve induced by thermal shock

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