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Summary
The objective of a meridional yield rupture test is
to determine the internal pressure, which will cause
yielding, and rupture of a Bellows. An accurate evaluation
of the yield pressure is quite important since it is
this value, rather than rupture, which usually provides
the limiting criteria for establishing suitable operating
pressure. The test specimen should have a minimum of
three convolutions to minimize the effects of the end
attachments. Identification of the Bellows should be
established as per parameters of prototype specified.
b) Test Procedure
Place the Bellows in any suitable fixture, the Bellows
fixed in the straight position, which will effectively
seal the ends during pressurization, and most importantly,
will prevent any movement of the ends during testing.
The fixture must also safely restrain the Bellows when
rupture occurs. The test medium should be limited to
water as a safety precaution.
Pressurize the specimen in steps, returning to zero
pressure after each step, up to at least twice the yield
pressure. There after the specimen may be pressurized
continuously until rupture occurs. The initial pressure
intervals should not exceed 10% of the anticipated yield
pressure. A constant holding time at pressure should
be established for each step throughout the yield point
determination. As a minimum, the width or space between
each convolution at the pitch diameter, should be measured
and record before and after each pressure step. Instrumentation,
such as a pressure time recorder, strain gauges, or
other conventional means may be used to get valuable
information.
c) Conclusions
Both meridional yielding (bulging of flat sides of the
convolutions and circumferential yielding of the root
diameter will be experienced in test of this type. Although
a plot of permanent deformation versus pressure will
resemble that of a simple tensile stress-strain curve,
a well defined yield point does not usually appear.
Beyond the yield point gross distortion, root collapse
and ultimate failure will occur.
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