The brittle fractures of low carbon steels containing notches or microcracks occur easily under high strain rates. In this report, test pieces in which Al
2O
3 was dispersed in iron were examined by a tensile tester under a strain rate range of 10
−4∼10
−2 l/sec. The dependence of the strain rate on the yield stress and conditions of the stress concentration owing to inclusions under the strain rates range was investigated by means of transmission electron-microscopy. Ashby’s dislocation model with voids formation around the particles was also discussed in terms of dislocations and voids around the inclusions.
The results obtained are as follows:
(1) Al
2O
3 particles were uniformly dispersed in iron. The average diameter of inclusions is about 5 μ. The distances between the inclusions for the test pieces containing 4 wt%Al
2O
3 and 2 wt%Al
2O
3 were about 22 μ and 35 μ respectively.
(2) The brittle fracture of the specimens containing 4 wt%Al
2O
3 occurred at a strain rate of 10
−2 l/sec. The cause may be attributed to the formation of micro-cracks around the inclusions (Al
2O
3 type) due to the stress concentration.
(3) The micro-cracks around the inclusions in the tensile-fractured specimens under the strain rate of 10
−2 l/sec and the voids in the tensile-fractured specimens under the strain rate range of 10
−4∼10
−3 l/sec were observed by means of transmission electron microscopy.
(4) The size of the voids in the tensile-fractured specimens under the strain rate of 10
−4 l/sec was bigger than that of the specimens under the strain rate of 10
−3 l/sec.
(5) The dependence of the strain rates on the yield stress (τ
y) is expressed as
(This article is not displayable. Please see full text pdf.)
where \dotε is strain rate and
A,
B and
C are constants.
View full abstract