REDISTRIBUTION OF STRESSES FROM MANUFACTURING OPERATIONS DURING SERVICE LOADS AND THEIR EFFECT ON FATIGUE LIFE OF BUILT-UP STRUCTURES

When manufacturing built-up structures different operations like joining, forming and casting will introduce residual stresses, which will interact with subsequent service loads applied to the structure and also influence growth of cracks in critical locations. This overview addresses the fatigue design of structures considering the effects of residual stresses caused by manufacturing. The redistribution of residual stresses during operation, the derivation of stress-intensity factors for cracks in residual stress fields and techniques to study growth of cracks in structures containing residual stress fields will be discussed. Joining of components by welding will be discussed in detail. Welding will introduce residual stresses in the structure due to localized plastic deformation caused by strong temperature gradients, with normally, tensile peaks in the welded region where cracks often are initiated due to the stress concentration. The presence of tensile residual, mean, stresses in regions with stress concentrations make welds susceptible to fatigue crack growth, which has lead to the development of special design codes for welded joints. The background for such codes and different strategies for the fatigue design will be addressed. Some recent applications will be discussed in detail, growth of cracks in spot welded car components, in flash butt welded railway rails and in stress coined holes in plates