The effect of welding on the fatigue crack growth rate in a structural steel

Abstract

Fracture mechanics principles have been used to study the effects of welding on the rate of fatigue crack growth (FCG) in a low-carbon structural steel. The steel concerned is used widely in the fabrication of the structural framework of passenger buses. Tests were carried out on the base metal (BM), heat affected zone (HAZ) and weld metal (WM). Both the near threshold and midrange regimes of crack growth were studied. In the midrange regime, the FCG rate was highest in the HAZ and lowest in the WM. Near the threshold, the FCG rate was highest in the BM and lowest in the WM. The results are explained in terms of microstructural changes due to welding, welding residual stresses, and fracture mechanisms. Recommendations to reduce the incidence of fatigue cracking have been made.