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There are O-rings for movement and for airtight in O-rings. O-ring for movement is used to protect to penetrate the dust
or the alien substance into cylinder. O-ring for airtight is used to maintain airtight. Airtight of O-ring is controlled by
squeeze rate and the gap between external diameter of groove and internal diameter of cylinder. Squeeze rate of O-ring is
controlled by internal diameter of groove. Gap between external diameter of groove and internal diameter of cylinder is
controlled by the external diameter of groove. Stresses of O-ring are depended on the squeeze rate, gap and internal
pressure. O-ring for airtight is under uniform squeeze rate and internal pressure with constant gap. And then stress
distributions are very complicated. Therefore stresses of O-ring are almost analyzed by experiment.
To study the stress distributions of O-ring by experiment, 3-dimensional photoelastic experiment had better be used. To
study stress distributions of O-ring by 3-dimensional photoelastic experiment, loading device is very important. Loading
device should are functions, which uniform squeeze rate and internal pressure etc, can be applied, and the uniform
squeeze rate can be controlled.
Therefore, in this research, the loading device with functions explained above was developed. The validity of the loading
device was confirmed by the stress distributions of O-ring, the configuration change of O-ring and the contact length of
O-ring etc.. When squeeze rate is constant, the contact length of upper of the deformed O-ring is almost equal to that of
lower of the deformed O-ring. When the internal pressure is applied to O-ring under uniform squeeze rate, the contact
length of upper of O-ring is increased with the increment of the internal pressure by little. The contact length of lower of
O-ring is constant irrespective of the increment of the internal pressure.
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