Y. Obara
Kumamoto University
INTRODUCTION
In order to examine the effect of the stress corrosion, the
uniaxial compression tests in a chamber are conducted on Kumamoto
andesite, changing the surrounding non-atmospheric environment of
rock. The environments used in this paper are water vapor and
acetone, ethanol, methanol as organic gas and hydrogen as
inorganic gas. Furthermore, the experiments, which surrounding
environment is changed from water vapor to hydrogen or hydrogen to
water vapor, are performed. From the experimental results, it is
concluded that not only strength but also hysteresis of rock
change, depending on the environment, and that the water is the
most effective agent that promotes the stress corrosion among the
materials used in this research.
In the experiment of changing surrounding environment, two
cyclic loading was performed in two kinds of surrounding
environment, using one specimen. Namely, after one kind
environment was maintained for 6 hours, the first loading was
carried out until the volumetric strain reached about -2000×l0-6
after starting dilatancy. Subsequently, the gas in the chamber was
replaced to another. After the environment was maintained for 6
hours, the second loading was performed until the rock specimen
was fractured. The pressure in the chamber during loading is a
constant value that is little bit smaller than the atmospheric
pressure. The gases used in this experiment are water vapor and
hydrogen.
The stress-strain curves in the case that the environment in the
chamber is changed from water vapor to hydrogen are shown in
Fig.1. Assuming that fracture occurs when the volumetric strain
reaches 2000×l0-6, the strength of andesite in water vapor can be
estimated 60 to 70MPa from the extension of the stress-volumetric
strain curve. It is considered that this value is reasonable,
comparing that on the water vapor pressure 103Pa. After changing
environment to hydrogen, the stress-strain curves pass through the
starting points of unloading. However, the inclination or
curvature of stress-strain curves is changed over stress level of
the first loading. Especially, the lateral strain is remarkable.
Furthermore, the strength in hydrogen environment is estimated
about 115MPa. Then this value becomes large in comparison with
that estimated in water vapor environment. According to the
results described above, it is concluded that the surrounding
environment of rock changes not only strength but also hysteresis
of rock, and that the water is the most effective agent that
promotes the stress corrosion among the materials used in this
research.
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