Study on FCG of EH36 and EH690 Dissimilar Steel Welded Joints Based on the RA - AF Method of acoustic emission

This study investigates fatigue crack growth(FCG) in EH36/EH690 dissimilar steel welded joints using acoustic emission (AE) technology. Three specimen types EH36-HAZ, EH690-HAZ, and weld metal(WS) were subjected to fatigue testing under different stress ratios (R=0.1, 0.3 and 0.5) using compact tension (CT) specimens. AE characteristic parameters, including cumulative energy, RA value (Risetime/Amplitude), and AF value (Average Frequency), in conjunction with RA-AF correlation analysis, were employed to elucidate crack propagation mechanisms. The results indicate thatFatigue life of all specimens significantly improves as the R increases, while crack growth rate (da/dN) demonstrates an exponential increase with the rise in stress intensity factor amplitude (ΔK). AE cumulative energy analysis successfully identifies two substages (IIa and IIb) within the stable crack growth phase by detecting variations in the slope. The transition point ΔK decreases with higher R while maintaining material-dependent hierarchy (EH690-HAZ > WS> EH36-HAZ).RA-AF analysis demonstrates a maximum 10% decrease in the proportion of shear cracks as the R increases, suggesting that crack growth is predominantly tensile under high stress conditions. The activation of material defects can lead to a transition from pure tensile fracture modes to mixed tensile-shear fracture modes.