Measurement of thermal elongation induced strain of a composite material using a polarization maintaining photonic crystal fiber sensor

A measurement scheme to measure a composite material's thermal elongation induced strain using a buffer stripped Polarization Maintaining Photonic Crystal Fiber (PM-PCF) sensor is investigated in this paper. A composite material sample with an embedded PM-PCF based polarimetric fiber sensor is fabricated and characterized. It is found that the buffer stripped PM-PCF polarimetric sensor which is temperature insensitive in free space, shows significant phase change when embedded in the composite material due the thermal elongation of the composite material. The temperature induced phase change of buffer stripped PM-PCF polarimetric sensors embedded in carbon-epoxy, E glass-epoxy, E glass-unsaturated polyester resin composite material samples is measured and the results are used to determine the thermal elongation induced strain over a temperature range from 0 °C to 65 °C. The experimentally measured thermal elongation induced strain of the same samples are found to be 3.648 × 10−5 ɛ/°C, 1.52 × 10−5 ɛ/°C, and 2.42 × 10−5 ɛ/°C. The Coefficient of Thermal Expansion (CTE) estimated theoretically using composite laminate theory shows good agreement with that derived using the PM-PCF sensor. The present investigation offers a simple non destructive method to determine thermal elongation induced strain in composite structures. It is shown that the method allows the measurement of thermal expansion for those composite materials having negligible residual strain and moisture expansion.