The influence of heat treatment on the behavior of fatigue crack growth in welded joints made of S355 under bending loading

摘要

The work concerns on the results of the tests of the growth of the fatigue crack experiment. All specimens were subjected to bending at constant load using S355 steel. Rectangular cross-section specimens were weakened by external notches and fillet welded joints. The tests were carried out under cyclic bending without and with mean load values. Additionally, the impact of heat treatment on fatigue lifetime was investigated. Crack initiation and propagation stages were observed on the specimens' surface using a light microscope. This research also shows microstructures with cracks of welded connectors and with changes in the material after heat treatment as well as their effect on the fatigue lifetime of joints. The highest durability was demonstrated by specimens without heat treatment. On the other hand, a similar fatigue crack growth mechanism was observed in different weld types. The numerical analysis also explains similar fatigue crack growth mechanism by equivalent stress intensity factors values. The fatigue life of welded specimens without heat treatment for both stress R-ratios was higher than for specimens after heat treatment.