Rail neutral temperature monitoring using non-contact photoluminescence Piezospectroscopy: A field study at high-speed rail track

Abstract

A novel non-contact stress sensing method using the photoluminescence piezospectroscopy (PLPS) method was applied in full-scale field test at high-speed rail tracks. The fluorescence spectra of the aluminum oxide (α-Al2O3) were collected from different locations on bare thermite weld surface for about 1.5 days. Prominent α-Al2O3 signals (i.e., R1/R2 peaks) were observed with the very short measurement time of 0.01 s, which is preferable in mobile sensing applications. The kernel spectrum estimation (KSE) method was developed as a postprocessing technique to determine R1/R2 peak locations accurately. The R1/R2 time histories showed strong correlation with those of strain gauges mounted on the rail near the thermite welds. The piezospectroscopy coefficients were determined at −30.01 cm−1/GPa for R1 and –32.11 cm−1/GPa for R2, calibrated with the strain gauge measurements. Prior to the field test, a laboratory test was conducted to determine the R1/R2 zero-stress states using a pulverized thermite weld sample. The zero-stress state was determined at 14,404.99 cm−1 for R1 and 14,434.09 cm−1 for R2. Using these parameters, rail neutral temperature was determined at full-scale high-speed tracks based on the absolute rail stress measured with PLPS without additional field calibrations.