The fatigue crack growth rate in HT80 base plate and welded joints has been measured using compact tension specimens, and examined by means of fracture mechanics and electron fractography.
The lowest fatigue crack growth rate was obtained in the heat-affected zone and the highest rate in the stress-relieved weld metal. In the weld metal, the compressive residual stress affected the crack growth rate and reduced the effective stress intensity factor range ΔK_eff.
The fatigue crack growth rate coincided almost completely with the microscopic growth rate calculated from the striation spacing for base metal and heat-affected zone. The fatigue crack growth rate for both weld metal and stress-relieved weld metal was, however, higher than the microscopic growth rate in the present stress intensity factor range. It is supposed that this discrepancy is caused by the fracture accompanied with dimples and striations. The relation between the dimple size, d_s(mm), and the stress intensity factor range, ΔK(kg/mm^3/2), has been obtained as follows, d_s=1.4×10^-5·(ΔK)