The correlation of microstructure and fracture mechanism to acoustic emission detection in railway track materials under tensile load

Acoustic Emission Technique (AET) is an advanced non-destructive testing (NDT) procedure that utilises elastic waves and is recorded using similar types of sensors. This study studied three types of railroad steel with different structures: Hadfield steel (Fully austenitic), R260 rail steel (Fully pearlitic) and thermite welded joints (Partial pearlitic). The laboratory used a tensile test and a Nano 30 AE sensor to examine the correlation between the material’s structural changes during the receiving force and the generated acoustic emission signal. The AE signal increased exponentially (linearly) as the material entered the elastic region, with its maximal value occurring at the material’s yield stress, and the AE signal decreased exponentially as the material approached the plastic region. R260 shows minor amplitude and hits due to its fine structure and nearly defect-free microstructure, differing from the other two, which found more hits. Hadfield has a significant crack at the grain boundary due to carbide precipitate while thermite welded; most cracks came from internal defects or impurities dispersed. Fractographic analysis shows that every specimen’s failure type is identical. R260 and thermite welded have similar structures and show brittle failure, which differs from Hadfield, which shows ductile behaviour and found deformation twin.