Surface Fatigue Crack Growth In Vessels And Welds. Measurement Methods And Analysis Of Large Cracks
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Fatigue crack propagation results obtained in four-point bending at base metal, heat affected zone and weldment of butt welds made of pressure vessel steel BS 4360-50D (C-Mn steel) are reported. Low cycle fatigue tests were performed in air at RT at a range of stress ratio R between O,l and 0,7. The shape of surface cracks was continuously recorded using potential drop methods. At very low stress ratios crack closure was observed. The results were presented in the form of propagation curves da/dN vs. A K. Threshold values were also recorded; they decreased with increasing R values. The crack growth rate results for the CT specimens of weld and parent metal fall into a narrow band with the weldment results being the fastest at high K^ns values and parent plate data the slowest. HAZ results generally lie between the weld and the base metal data.