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 5mm side ligament (specimen-CN5) and the side-notched specimens with the ratios of the ligament to notch depth, 5mm/22.5mm, 10mm/20mm, and 20mm/15mm (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
Ji, whereas δ
i's and
Ji's of other specimens have shown about the same values, where δ
i and
Ji 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.
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