The influence of thermal expansion of a composite material on embedded polarimetric sensors

Abstract

Abstract. Some of the most critical issues of the influence of the thermal expansion of composite materials on embedded polarimetric sensors for measurements of strain and temperature are studied in this paper. A composite material sample with polarimetric fiber sensors embedded in two distinct layers of a multi-layer composite structure is fabricated and characterized. The polarimetric fiber sensors used in this study are based on panda type fiber and polarization maintaining photonic crystal fiber (PM-PCF). The temperature sensitivities of polarimetric fiber sensors with acrylate buffer coated and buffer stripped polarization maintaining optical fibers are measured in free space and compared to those for embedded in the composite material. It is found that a polarimetric fiber sensor with an acrylate coating embedded in the composite material shows the same response as the one in free space while the coating-stripped fiber polarimetric sensor shows significant temperature sensitivity when embedded in the composite material. This is due to the stress-induced change in birefringence created by the thermal expansion of the composite material, while in the case of a buffer coated fiber, the effect is considerably reduced as the thermal stress is largely eliminated by the buffer coating. The results obtained in this study demonstrated that thermal expansion of the composite material are the main source of error in strain and temperature measurement using embedded polarimetric fiber sensors and that more accurate strain and temperature measurements can be obtained with buffer coated polarimetric fiber sensors.

Experimental Study and Analysis of a Polymer Fiber Bragg Grating Embedded in a Composite Material

“…The composite material sample is fabricated by using a hand lay-up method with glass fibre fabrics (E-glass) as the reinforcement and a general purpose unsaturated polyester resin as the matrix material [11][12][13]. The orientations of the glass fibres were unidirectional (0/0) to each other.…”

“…However most of the studies were focused on the use of fiber sensors to measure the temperature and strain during the curing process and also during structural tests [7][8][9][10]. Our recent studies established that the thermal expansion effects of the composite material considerably affect the performance of the embedded sensors and result in a cross sensitivity in sensing parameters [11][12][13]. Therefore it is important to differentiate the influence of temperature of the composite material and thermal expansion induced effects on the embedded fiber sensor.…”

“…It has been reported earlier that FBGs written in micro structured fibers can be used for measurement of temperature and thermally induced strain in the composite materials simultaneously [14][15]. Polarimetric fiber sensors based on polarization maintaining photonic crystal fibers can also be used to measure thermal effects in composite materials [12,13]. However these approaches involve complex fabrication techniques and instrumentation requirements.…”

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

“…The specific type of polarimetric sensor using micro-structured polarization maintaining highly-birefringent photonic crystal fiber (PM-HB-PC)F is proven to have very low temperature sensitivity in free space [20,21]. But we have shown that it acquires a significant response with temperature when embedded in a composite material, due to the stress-induced change in birefringence created by the thermal expansion of the composite material [22]. It is logical therefore to assume that this sensor could be used as a basis for measuring thermal strain and thus thermal expansion.…”

Influence of lamination process on optical fiber sensors embedded in composite material

“…The fiber coating layer can be responsible for the behavior of the fiber inside a composite material [18]. The sidehole fiber was covered by a hard coating layer and transversal pressure was easily transmitted to the sensing fiber, introducing changes in its birefringence.…”