b) 10o Fig 8 SEM of the cross-section of creep ruptured sample under 180 MPa(a)total morphology, (b)dimples and voids, (c),(d) three-neighbouring voids an obvious brittle rupture morphology, seen in Fig. 9a. can be determined among the voids generated, respec Lots of slim dissociation steps resulting from narrow sor- tively, under 110, 130 and 180 Mpa. On the one hand, bite laths can be found on the cross-section Meanwhile. as is discussed above. the wide and shallow voids with di creep voids can also be observed in Fig. 9b. However, the ameter of about 10 um(Fig. 10d)may be accounted for amount of voids which have grown in a wide and shal- the low toughness of the weld seam. On the other hand, low form is far less than that on the cross-section under the larger distribution density of the creep voids under 180 MPa. Although a small amount of dimples can be 110 MPa than that generated under 130 MPa may be ad observed in Fig. 9b as well, they are not the dominant fac- counted for the lower hardness of the weld seam. Thus, tors of rupture. This phenomenon may be attributed to the fractograph of the ruptured sample under 110 MPa the highest hardness and residual stress in HAZ of T92. presents an intermediate micromorphology between that Figure 10 displays the fractograph of creep ruptured under 180 and 130 Mpa, which indicates its intermediat sample under 110 MPa. An obvious macroscopic disso- properties of weld seam. ation step rather than macroscopic creep voids can be detected in fig. 10a. Meanwhile, it can be learned that the Finite element method results reduction in area y is less than 5%. Actually, magnified by 500 times, the zoom is filled with randomly distributed FEM is the most widely used computational simulation creep voids, seen in Fig. 10b. Furthermore, neighbouring method for its superiorities as convenience, effectiveness voids also have the potential to coalesce into larger ones, accuracy, etc, and is always applied in physical field anal as shown in Fig. 10c. However, at least three differentials yses including thermal field, force field, magnetic field, Including vo pth, void area a nd distribution density etc and their coupled fields. 3-37In this case, the residual @2010 Blackwell Publishing Ltd Fatigue Fract Engng Mater Struct 34, 83-9690 Y. GONG et al. Fig. 8 SEM of the cross-section of creep ruptured sample under 180 MPa (a) total morphology, (b) dimples and voids, (c), (d) three-neighbouring voids. an obvious brittle rupture morphology, seen in Fig. 9a. Lots of slim dissociation steps resulting from narrow sor￾bite laths can be found on the cross-section. Meanwhile, creep voids can also be observed in Fig. 9b. However, the amount of voids which have grown in a wide and shal￾low form is far less than that on the cross-section under 180 MPa. Although a small amount of dimples can be observed in Fig. 9b as well, they are not the dominant fac￾tors of rupture. This phenomenon may be attributed to the highest hardness and residual stress in HAZ of T92. Figure 10 displays the fractograph of creep ruptured sample under 110 MPa. An obvious macroscopic disso￾ciation step rather than macroscopic creep voids can be detected in Fig. 10a. Meanwhile, it can be learned that the reduction in area ψ is less than 5%. Actually, magnified by 500 times, the zoom is filled with randomly distributed creep voids, seen in Fig. 10b. Furthermore, neighbouring voids also have the potential to coalesce into larger ones, as shown in Fig. 10c. However, at least three differentials including void depth, void area and distribution density can be determined among the voids generated, respec￾tively, under 110, 130 and 180 Mpa. On the one hand, as is discussed above, the wide and shallow voids with di￾ameter of about 10 μm (Fig. 10d) may be accounted for the low toughness of the weld seam. On the other hand, the larger distribution density of the creep voids under 110 MPa than that generated under 130 MPa may be ac￾counted for the lower hardness of the weld seam. Thus, the fractograph of the ruptured sample under 110 MPa presents an intermediate micromorphology between that under 180 and 130 Mpa, which indicates its intermediate properties of weld seam. Finite element method results FEM is the most widely used computational simulation method for its superiorities as convenience, effectiveness, accuracy, etc., and is always applied in physical field anal￾yses including thermal field, force field, magnetic field, etc. and their coupled fields.35–37 In this case, the residual c 2010 Blackwell Publishing Ltd. Fatigue Fract Engng Mater Struct 34, 83–96