d. Steel columns having slenderness ratios of less
Therefore, some permanent set occurs in the lock
groove due to the loads imposed by the 100 percent
than 40 are not subject to critical bending failure but will
inspection of the locks. This load capacity becomes
fail first in compression. The maximum compressive
increasingly higher as the bearing area increases
load which the piston can resist is:
because of "Brinelling." Also, this capacity becomes
greater because the deformed metal obtains some
support from the end sleeve.
c. The load capacity under certain sudden
unsustained loads is greater than the permissible
bearing loads within the elastic region. The criteria used
for inspection is that the unit shall not unlock under the
suddenly applied load, 800 pounds in this case. This
load should not be used as the operating load in actual
78. End Sleeve and Locking Mechanism. a. The
installation. Because plastic deformation is encountered
end sleeve has external threads for connecting the
and the metal becomes confined by surrounding
thruster to the mechanism to be actuated. A hexagonal
material, design calculations become impractical. The
flange is located at the rear of the threaded projection.
most reliable solution is, therefore, obtained by
The locking mechanism for the thruster consists of three
experiment. Figure 72 shows a series of load-deflection
kidney-shaped keys (fig. 71) which are equally spaced
curves obtained by testing the locking keys in a fixture.
around the circumference of the end sleeve.
It will be noted that the curve is almost linear up to 800
pounds, which is the load required in the specifications.
Figure 71. Locking key for thruster.
b. Due to the space limitations of thrusters of this
small size, the key lock design becomes most critical.
Figure 72. Load deflection curves for keylock
In the design of this thruster, a very shallow groove is
mechanism.
provided for the lock keys in the end cap. Although this
is not a desirable situation and makes for difficulty in the
d. To insure that the material between the slots for
lock design, space limitations dictated its use. The key
the locking keys will not tear because of tension loads
lock is far superior to the ball lock design used in earlier
while the unit is locked, the minimum thickness of
designs for the initial locks, although its load capacity is
material for walls of the sleeve is calculated:
not fully realized when a shallow groove is used. The
keys tend to seat when subjected to the loads specified.
† Safety factor.
88
