A 1.5-in-diameter bar has been machined from an AISI 1050 cold-drawn bar having a yield strength of 84 kpsi and ultimate strength of 100 kpsi. This part is to withstand a fluctuating tensile load varying from 0 to 16 kip. Knowing a fatigue stress-concentration factor K, is 1.85 for 106 or larger life. The Marin factors are: K₂= 0.8; K=1; K=K=K₂=K=1. Estimate the factor of safety guarding against fatigue and static failures using the Gerber and Langer failure criteria.
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.
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