Noncontact mobile sensing for absolute stress in rail using photoluminescence piezospectroscopy

A novel noncontact, mobile sensing technique to measure absolute stress in rail using photoluminescence piezospectroscopy is presented. Photoluminescence piezospectroscopy is a vibrational spectroscopy technique for chemical identification and stress measurement by focusing low-power laser on a substance surface. Thermite welding is a major welding method for continuous welded rail, which produces iron (Fe) and aluminum oxides (Al₂O₃) after aluminothermic reaction. Photoluminescence piezospectroscopy was used as a noncontact stress sensing method since photoluminescence piezospectroscopy has an excellent detectability for alpha-phase aluminum oxide (α-Al₂O₃). Using a portable photoluminescence piezospectroscopy system, a prominent α-Al₂O₃signal was collected from the bare surface of thermite weld samples. A loading frame test was conducted to determine the piezospectroscopic coefficient of α-Al₂O₃in thermite weld. A pulverization method is introduced to determine absolute stress from an existing rail sample. The experimental results show many advantages of this method over traditional methods to measure stress in rail as a mobile sensing method.