Estimation of residual fatigue life of high-strength steel welded joints based on diffuse ultrasound

Fatigue significantly affects the durability and capacity of high-strength steel welded joints (WJs) in engineering. Despite the capability of ultrasonic-based methods to issue early warnings for fatigue crack initiation and effectively monitor crack expansion, estimating residual life before surface cracks poses a considerable challenge. This study introduces a novel method that relies on the correlation coefficient of the ultrasonic energy density, α , to estimate the residual life of WJs before surface cracks become evident. The fatigue damage of 20 butt- and cross-WJs of Q690qENH and Q960E, subjected to different fatigue stresses, was monitored using α . The results revealed a cubic polynomial relationship between α and the number of fatigue cycles when a sample experienced early fatigue damage. Consequently, we introduced an α - N early fatigue damage monitoring curve. The zero value of its second derivative functioned as an early warning indicator, and the corresponding life of the sample was recorded as ζ . Finally, a warning of 20%–50% of the fatigue life for WJs made of two high-strength steels was attainable. A linear relationship between ζ and fatigue stress, denoted as the ζ - S curve, facilitated residual life estimation before surface cracks developed. The blind test produced an approximately ± 10 % error with 4 samples. • Developed early fatigue damage monitoring model for high-strength steel WJs based on diffuse ultrasound. • Achieving early-life warning for high-strength steel WJs, targeting 20% to 50% of their total fatigue life. • Proposed a prediction model that predicts the early warning life percentage for high-strength steel WJs. • Realized estimating residual fatigue life in high-strength steel WJs before surface cracks.