Experimental study of corrosion fatigue behaviour of welded steel structures

Earlier research has shown that stress-raisers at weld geometry, misalignment and post-weld tensile residual stresses caused by the welding process are the major sources of fatigue cracks initiations and propagation in welded steel structures. The problem becomes more pronounced in the presence of corrosive environment, and the rate of crack propagation becomes exceedingly high and finally the structure fails. It has been observed in this study that fatigue crack propagation in the corrosive medium is strongly influenced by weld-geometry parameter (weld-toe undercut) which played a significant role in reducing the fatigue life and fatigue strength of butt-welded structures, and accelerated the time to propagate to failure. From the limited experiments performed in this study, it has been found that the threshold stress intensity factor of butt-welded structures attains a much lower value in corrosive environment than in air environment and its effect needs to be included in fatigue assessment. It is observed that a more rigorous mathematical model can be determined only when relevant important parameters (such as parameters relating to stress ratios, stress concentrations caused by weld-joint geometry variations, type and rate of loading, residual stresses and threshold properties of the material strength) are known.