TRUCK SERVICE MANUAL
Fatigue of Metals
The action which takes place in metals causing failure
after a large number of applications of stress. Fatigue failures
are characterized by their suddenness and by the absence of
general deformation in the piece which fails. A wire broken by
bending backward and forward is a characteristic fatigue
Cause of Fatigue Failure
The cause of a fatigue failure may be attributed to a
repetition of stresses which exceed the elastic limit of the
steel. This may be subdivided as follows:
1. Defective raw material.
2. Defective heat treatment.
3. Defective design.
4. Defective machining.
Truck Operator's Responsibility
3. Rough handling and driving.
4. Road conditions.
The different classes of fit of shafts in their holes most
generally used are as follows:
Shrink Fit-For parts which have to be fitted together by
means of an application of heat to expand the hole, at which
time the shaft is inserted. On cooling the hole contracts,
making a perfect union which requires no keys or other
anchors of any kind. The bores are always machined to a
smaller diameter than that of the shaft.
Force Fit --For parts which have to be fitted together by
means of a press; they must be keyed if they are to be
subjected to a twisting force.
Driving Fit --For parts which have to be fitted together
with a soft hammer, but which can be afterwards
Push Fit --For parts which have to be fitted together by
hand without special force, and without having perceptible
shake when assembled, they should remain motionless in
Sliding Fit --For all parts which in functioning have to
slide constantly on one another, without turning.
Running Fit --For parts which in functioning have to
revolve constantly one in the other, at a medium speed and
with very little play.
Easy Running Fit --Parts revolving with a relatively
large amount of play.
A narrow band of material, frequently in shop practice
used to designate a radius on a shaft or other part.
The groove cut in taps and reamers to form the cutting
edge and allow room for chips.
Is the resistance to motion which takes place when one
body is moved upon another, and is generally defined as
"That force which acts between two bodies at their surface of
contact, so as to resist their sliding on each other."
Gauge or Gage
Master, Standard or Reference; terms applying to a
nearly perfect gauge used for calibration of working gauges.
A gauge having two sizes, the difference between them
representing the tolerance or allowable variation. One size
must go into or over the work being checked, and the other
size must not go. These gauges are frequently referred to in
shop practice as "tolerance gauges" and as "go" and "no go"
CTS-2128-L Page 9
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