A right angle bracket arm experiences a downward normal force F(t) which cycles continuously between a minimum of 100 Lbs to a maximum of 400 Lbs. The machined part is made from 4140 steel, quenched & tempered at 800°F (Table A-21). Determine the factor of safety of the 5/8- inch diameter shaft at point A based on a life >10 million cycles using the DE - ASME-Elliptic Fatigue Failure Theory. Consider 90 % reliability and room temperatures. Assume stress concentrations, Kf = Kt = 1.7 and Kfs = Kts = 1.4 at point A. List governing equations and show all work.
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 right angle bracket arm experiences a downward normal force F(t) which cycles continuously between a minimum of 100 Lbs to a maximum of 400 Lbs. The machined part is made from 4140 steel, quenched & tempered at 800°F (Table A-21). Determine the factor of safety of the 5/8- inch diameter shaft at point A based on a life >10 million cycles using the DE - ASME-Elliptic Fatigue Failure Theory. Consider 90 % reliability and room temperatures. Assume stress concentrations, Kf = Kt = 1.7 and Kfs = Kts = 1.4 at point A. List governing equations and show all work.
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