Static Tensile Properties in Plain Specimen with Artificial Defects : Examination by Successive Observation in SEM Servopulser

Abstract

Characteristics of crack initiation and propagation in tensile tests were investigated for Ti-6Al-4V and S45C. Successive observations were made in a SEM servopulser to clarify the relationship between tensile deformation and crack initiation. The main results are summarized as follows. (1)Microcracks appear in a large deformed area in Ti-6Al-4V and in a strongly shear-deformed area in S45C. (2)Net stressσ_net in both materials is nearly equal to σ_B of plain specimens. This means that the most of minimum section deformed plastically under the stress nearly equal to σ_B. (3)The coalesence of two holes occurred through the process of crack initiation and propagation in the strongly deformed area between the two holes in Ti-6Al-4V. (4)With decreasingρ, the hole deformation parameter h_c/d of crack initiation increases. When ρis constant, h_c/d is almost constant, independent of the notch depth(ρ : notch radius, d : initial diameter of hole, h : height of hole, h_c : h at crack initiation).