延性き裂進展に伴うき裂先端領域における局部破壊条件 : 試験片形状の影響

概要

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The effects of specimen geometry on the initiation and growth of ductile fracture from fatigue precrack have been investigated. Tests were made on the center-notched specimens with 5 mm side ligament (specimen-CN5) and the side-notched specimens with the ratios of the ligament to notch depth, 5 mm/22.5 mm, 10 mm/20 mm, and 20 mm/15 mm (specimen-SN5, -SN10, and -SN20, respectively). Of these specimens, the stress triaxiality was largest in Specimen SN5 and smallest in CN5. 3 point bend specimens and CT specimens were also used as the standard specimens. Specimen-CN5 has shown the largest δ_i and Specimen-SN5 the smallest δ_i and J_i, whereas δ'_<i s> and J'_<i s> of other specimens have shown about the same values, where δ_i and J_i are COD and J at ductile crack initiation, respectively. Though the effect of specimen geometry on the ductile crack "initiation" was obvious in the above results, the effect on ductile crack "growth" was not clear in the present tests. The result that COD at the crack tip decreased from δ_i to δ_p as the crack grew from the precrack tip was explained by considering the effect of plastic strain-stress triaxiality history at each point of fracture until ductile fracture occurred at that point.
1982-05-15