The bracket shown in the figure is bolted a ceiling beam to support a fluctuating vertical load imposed on it. The bolts are -in coarse-thread SAE grade 7, tightened to recommended preload for nonpermanent assembly. The stiffnesses have already been computed and are kp= 8 Mlb/in and km = 18 Mlb/in. %3D
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
![The bracket shown in the figure is bolted a ceiling beam to
support a fluctuating vertical load imposed on it. The bolts are
5
in coarse-thread SAE grade 7, tightened to recommended preload
8
for nonpermanent assembly. The stiffnesses have already been
computed and are kp= 8 Mlb/in and km
18 Mlb/in.
Laad line
A
D.
Seady stress o
(a) Assuming that the bolts, rather than the welds, govern the
strength of this design, determine
the safe repeated load that can be imposed on this assembly
using the Goodman criterion with the load line in the Figure
and a fatigue design factor of 2.5.
(b) Compute the static load factors based on the load found in
part (a).
(ie. Yielding factor of safety,
Load factor of safety and
Factor against joint separation)
Altemating strosso,](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F89d31404-901c-4cb4-8788-ffc7f5a8d5c1%2F65950613-22a2-4049-9437-9212d899b61e%2Foyxh53q_processed.png&w=3840&q=75)
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