Measurement of Coefficient of Thermal Expansion of Composite Structures Using Fiber Bragg Grating Sensor

The coefficient of linear thermal expansion is a material property indicative of the extent to which a material expands on heating. Structural design necessitates the determination of the Coefficient of Thermal Expansion (CTE) to avoid the issues arising due to thermal expansion after structural assembly during service life. Various conventional measurement techniques for determining CTE, namely dilatometry, interferometry, and thermomechanical analysis. This paper presents an alternate method for CTE measurement using Fiber Bragg Grating (FBG) sensors. The FBG sensor is surface bonded on the test specimen in the required directions of CTE measurement and is subjected to increasing temperature changes in a temperature-controlled chamber. The reflected wavelength measured from FBG during the experiment will be the sum of wavelength shifts due to the thermally induced strains on the structure in addition to the temperature-induced shift. In order to determine the strains due to the thermal expansion of the structure, the effect of wavelength shift due to temperature on the structure is compensated using a bare FBG sensor (not bonded to the specimen) to calculate the thermally induced strains. This paper reports the experimental work to characterize different CFRP specimens made of BHOR and AS914 prepregs. The paper will discuss the preparation of test specimens, sensor installation methods, and experimental results for various materials.