TRUCK SERVICE MANUAL
Center of Oscillation
If a body oscillates about a horizontal axis which does
not pass through its center of gravity, there will be a point on
the line drawn from the center of gravity perpendicular to the
axis, the motion of which will be the same as if the whole
mass were concentrated at that point. This point is called the
center of oscillation.
When a body revolves in a curved path, it exerts a
force called the centrifugal force upon the arm or cord which
restrains it from moving in a straight (tangential) line.
A bevel, or a corner or edge removed, a relief.
Changing the shape of steel parts by compressing,
stretching, bending, or twisting, using stresses beyond the
yield point and temperatures below the critical range. Cold-
drawn steel is finished by being drawn through a die, while
cold-rolled steel is finished between rollers.
Outline or profile of an object.
Applied to the internal-combust; on, four-cycle engine,
a cycle comprises four strokes for each piston (1, intake; 2,
compression; 3, explosion; 4, exhaust) performed during two
revolutions of the crankshaft. An interval or period of time
occupied by one round or course of events, recurring in the
same order in a series.
Ability to withstand stretch without rupture. Ductility is
usually measured by the percentage of elongation, after
rupture over a gauge length laid off on a specimen before
stretching, or by the reduction of area of the original cross
section of a specimen when tested in tension.
A crankshaft may be in perfect static balance, but if it is
mounted in bearings and revolved at high speed great
vibration may develop which would soon cause failure of
engine bearings and possibly cause breakage of the shaft
itself due to fatigue action.
Dynamic unbalance means that the weight sums of
diagonally opposite portions are not equal. Take, for
example, a pulley that is in perfect balance. Visualize the
pulley mounted on a shaft supported by bearings. Attach a
weight to the outer periphery on one edge of the pulley, then
attach an exact counterweight to the opposite side of the
pulley on the opposite edge. The pulley continues to be in
static balance as evidenced by the fact that it turns freely and
stops with the counterweights either up, down, or in any other
position; but if the pulley is revolved at a high rate of speed its
evidenced by the vibration. This dynamic unbalance is
eliminated in a crankshaft first by determination of the heavy
points and next by drilling into these points until the necessary
amount of metal and weight has been removed.
The term "elastic limit" is unfortunately used very
loosely in general practice. In scientific usage the term is
used to denote the highest unit stress at which material will
completely recover its form after the stress is removed.
In the physical laboratory this term is used to denote
the number of cycles of repeated stress withstood by a
specimen before failure.
Factor of Safety
Working stresses should never exceed the elastic limit.
They are generally based on the ultimate strength of the
material. The ratio of the ultimate strength of a given material
to the allowable working strength called the "Factor of Safety".
CTS-2128-L Page 8
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