Fatigue strength of gusset welded joints under simulated program loading of overhead travelling crane

A survey of the degradation in overhead travelling cranes was performed, Fatigue cracks were often detected in highly stressed regions in cranes that had been in use for fifteen years or more. Service stresses of an overhead travelling crane with a lifting capacity of 50 kN were monitored and analyzed by the rain-flow method, A fatigue test of gusset welded joints made of SM490A steel was carried out under both constant loading and program loading determined based on service stress monitoring. The fatigue life of the gusset welded joints is dominated by crack initiation rather than propagation. The crack growth rate of the welded joints under program loading is correlated with an effective stress intensity factor range, Delta K-Rem, estimated based on linear accumulation of the stress intensity factor range which takes into account residual stress at each step in a block, The prediction of fatigue propagation life using Delta K-Rem agrees with the experimental result in the range of error up to 15%, when the crack length is less than 20 mm.