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In industrial components operating at high temperatures, although the uni-axial external tensile load is applied, local multi-axial stress field is caused due to the locality of stress field such as plastic constraint, which is related to the structural brittleness. In previous paper, using a round bar specimen with a circular notch which causes the local multi-axial stress field due to the plastic constraint, the effect of local multi-axial stress on the creep crack growth rate has been investigated for creep-ductile and brittle materials such as Cr-Mo-V and W-added 12Cr steels1,2). On the basis of these resluts, the concept of structural brittleness was proposed1,2). Furthermore, in weldments, it has been shown that the local multi-axial stresses are also caused due to the plastic constraint induced by a decrease in hardness of the heat affected zone as compared with that of a base metal and weld metal by conducting the creep crack growth tests using the welded joint of C(T) specimen and finite element analyses3,4). Under these situations, it is important to conduct the characterizations of the creep crack growth rate and its life under the multi-axial stress field to predict the life of creep crack growth5).
However,