of safety of 2.0. (3) Ti-5Al-2.5Sn titanium alloy
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.
![A cylindrical 1045 steel bar (see the figure below) is subjected to repeated compression-
tension stress cycling along its axis. If the load amplitude is 23,000 N, calculate the
minimum allowable bar diameter (in mm) to ensure that fatigue failure will not occur.
Assume a factor of safety of 2.0.
Maximum stress, S (MPa)
700
600
500
400
300
200
100
0
4340 steel
104
Ti-5Al-2.5Sn titanium alloy
70Cu-30Zn brass
EQ21A-T6 Mg alloy
105
1045 steel
Ductile cast iron
107
2014-T6 Al alloy
108
10⁹
106
Cycles to failure, N
Data taken from the following sources and reproduced with permission of ASM
International, Materials Park, OH, 44073: ASM Handbook, Vol. I, Properties and Selection:
Irons, Steels, and High-Performance Alloys, 1990; ASM Handbook, Vol. 2, Properties and
Selection; Nonferrous Alloys and Special- Purpose Materials, 1990; G. M. Sinclair and
W. J. Craig, "Influence of Grain Size on Work Hardening and Fatigue Characteristics of Alpha
Brass," Transactions of ASM, Vol. 44, 1952.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Faf033eb0-5213-479e-b20c-cfd2190955a4%2Fc636535f-93ae-40bf-a06a-a963249b1c9b%2Fetxjobl_processed.png&w=3840&q=75)
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