ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
The most obvious method of changing the stress
ratio is by loading a tubular specimen axially with
pressure acting on the pistons is borne by the rod
connecting the pistons. This will reduce the axial
stress in the cylinder wall to zero (assuming no
friction between piston and cylinder) without af-
fecting the tangential stress. In actcsol practice,
one piston can be replaced by a fixed end. By
using a piston of larger net area than the opposite
cylinder end, compressive axial stresses can be
introduced into the cylinder walls without altering
the tangential stresses. This arrangement is shown
in Fig. 7.3. By using thin-walled cylinder approxi-
mations, the stress ratio is given by the equation
ut 2d (d + t)
...... -
Oa d2 - D2
_- ~
IJ N C L A S S I FIE D
ORNL-LR-OWG 2849
PISTON
__-- SPECIMEN
_--- - PISTON ROD
__-- -PISTON
Fig, 7.2. Apparatus for Producing Tangential
Stress in a Tubuhr Specimen.
114
(Note that the diamefer n of the piston rod does nat
enter into the calculation of the stress ratio.)
ut 2d (d t t)
- - -. ...............
"a D2
In the event that it is necessary to extend the piston
rod through the top end of the cylinder (to provide Q
thermocouple well, for example), the arrangement
shown in Fig. 7.4b may be considered. The stress
ratio is given by the equation
6t 2d (d + t)
_- ............... -
"a D2 - b2
UNCLASSI FlED
ORNL-LR-DWG 2850
Fig. 7.3. Apparatus for Producing Compressive
Axial Stresses in a Tubular Specimen
Altering the Tangential Stresses.