Phosphor thermometry for surface temperature measurements of composite materials during fire test

This study presents the implementation of phosphor thermometry method to obtain pointwise surface temperature measurements of a carbon fibers reinforced polymers composite exposed to a flame. Phosphor thermometry has previously been used to measure surface temperature in relevant applications, mainly on metallic materials. In the present study, it has been applied to measure the backside temperature of a carbon fiber Poly Phenylene Sulfide (PPS) polymer composite exposed to a flame, in order to analyze the feasibility, the limits and the advantages of the method compared to infrared thermography. Mg₄FGeO₆:Mn⁴⁺ thermographic phosphor is coated on the back side of the composite sample and excited with a 10 Hz repetition rate Nd:YAG laser at 355 nm. The time-resolved phosphorescence signals are processed with the lifetime approach to determine the temperature. A coating of small thickness allows the surface temperature to be measured up to 400 °C, and it is shown that this coating has no effect on the heat exchange at the surface. The comparison between the phosphor thermometry results with the ones obtained with an infrared camera shows an interesting methodology to determine the infrared emissivity of the sample at high temperature.