In order to investigate the validity on a size requirement for
KIc testing in the proposed revision of ISO12135,
W-a≥1. 1 (
KQ⁄σ
ys)
2 , and on that in the present standard of ISO12135,
W-a,
a,
B≥2. 5 (
KQ⁄σ
ys)
2, we analytically investigated the effect of plasticity at the crack tip on a provisional fracture toughness
KQ calculated from the force, at which a force-displacement curve (
F-
V curve) intersects a secant line given in accordance with the above standard. The nonlinear component of the
F-
V curve is the sum of two parts, one due to the plasticity at the crack tip and the other to actual crack extension. 3-dimensional elastic-plastic finite element analyses of CT specimens with varying sizes have been performed to calculate
KQpl, which means
KQ obtained as a result of the plasticity at the crack tip without the crack extension. In the case of standard specimen (
W⁄
B=2,
a⁄
W=0. 5) , the correlation between
KQpl and ligament size (
W-
a) was approximately given by
W-
a=1. 5
KQ⁄σ
ys)
2 . It was found that the present standard leads to a plane strain fracture toughness
KIc with a crack extension more than about 1%of the initial crack length, provided that
W-
a≥2. 5 (
KQ⁄σ
ys)
2 . Meanwhile, in the case of the proposed revision of ISO12135, it was shown to recognize
KQpl as
KIc, although the size requirement of
W-
a≥1. 1 (
KQ⁄σ
ys)
2 was met.
抄録全体を表示