Probabilistic Assessment of High-Energy Acoustic Emission Events During Tensile Deformation of Thermally Exposed S235 Structural Steel

Thermal exposure can modify the tensile response of structural steel and the acoustic-emission (AE) activity recorded during deformation. This study presents a stage-resolved probabilistic analysis of high-energy AE events in S235 steel tested as received and after nominal furnace exposure to 700, 900, or 1100 °C for 40, 80, or 120 min, followed by still-air cooling. Twenty specimens with archived stage-resolved AE records were analysed from a 30-test mechanical programme. Each record was divided into pre-yield, yielding, plastic deformation to ultimate tensile strength, and post-UTS localization/fracture stages. High-energy events were defined using stage- and channel-specific thresholds derived from the 90th percentiles of room-temperature specimens. For Channel 1, the adjusted odds were higher after exposure to 700 and 1100 °C than at room temperature (OR = 5.36 and 6.71), whereas the 900 °C estimate was positive but uncertain (OR = 3.60; 95% CI: 0.93–13.93). Stage III showed higher odds than Stage I (OR = 3.54; 95% CI: 2.15–5.84). Analyses using 85th- and 95th-percentile thresholds preserved the positive temperature estimates and higher Stage II–III odds. Leave-one-specimen-out refits confirmed stable Stage II, Stage III, and 1100 °C associations, while 700 and 900 °C were more specimen-sensitive. The framework remains exploratory and measurement-configuration-specific; sparsely represented conditions are descriptive.