Suppose you have a 4340 steel plate in fully variable axial loading with an axial load ranging from 15000 N to -15000 N. The plate is 5mm thick, 20mm high and 50mm long. The plate has a hole in the middle and is 5mm in diameter. Its fatigue strength is 0.76 and its Notch sensitivity is 0.95. As the strength of this part is 173 MPa, determine the life of the part. (Sut = 1080 MPa, Kt = 2.7)
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.
Suppose you have a 4340 steel plate in fully variable axial loading with an axial load ranging from 15000 N to -15000 N. The plate is 5mm thick, 20mm high and 50mm long. The plate has a hole in the middle and is 5mm in diameter. Its fatigue strength is 0.76 and its Notch sensitivity is 0.95. As the strength of this part is 173 MPa, determine the life of the part. (Sut = 1080 MPa, Kt = 2.7)
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