A 28mm diameter round steel bar is 0.4m long. It is placed concentrically within a brass tube which has an outside diameter of 40mm and an inside diameter of 30mm. The length of the brass tube exceeds that of the round steel bar by 0.12mm. Rigid plates are placed on the ends of the tube through which an axial compressive force is applied to the compound bar. Determine the compressive stresses in the bar and tube due to force of 60 kN. Use 200 GPa for modulus of elasticity of steel and 90 GPa for modulus of elasticity of brass.
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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