Tensile fracture tests of specimens having a single blind hole were carried out in order to investigate the mechanism of ductile fracture originating in a surface defect. Although a crack was initiated at the hole edge, the true stress-true strain curve of the holed specimen approximately coincided with that of the plain specimen with no hole untill the true stress reached a maximum value. In the deformation stage of the specimen after this stress value was reached, the growth behavior of the crack was not affected by the deformation of the hole. On the basis of these phenomena, parameter f
ac was defined by the ratio of crack area to minimum cross section of the specimen at which the true stress reached the maximum value, and the effect of hole size on the fracture ductility was examined using the parameter f
ac. The ture strain ε
c at the point of maximum true stress showed good correlation with the parameter f
ac, and the shear mode growth of the crack started unstably at this point. The relation between the fracture ductility ε
f and the parameter fαc was predicted from the relation between ε
c and f
ac and from the growth behavior of the crack. This relation coincided with the experimental results, and it was found that the fracture ductility ε
f of the present experiment is determined mainly by the starting conditions of unstable fracture and the growth behavior of the crack.
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