A latch is made from steel with 490 Bhn, a machined finish, and a yield strength of 100 ksi. Assume 95% reliability and operating temperature of 250 F. The latch design is as shown in the figure below. The latch force ranges from 9 lbf to 14 lbf. r=in. K=1.7 0.1094 in. High-carbon steel, 490 Bhn, machined finish a) Find em, ea for this loading condition. (Hint: find the mean and alternating force, then calculate mean and alternating stresses, and then make the table) b) If the overloading is such that the σea = constant, what is the safety factor? If the safety factor is less than 1, find the number of cycles to failure. Include a sketch that illustrates your calculations.
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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