F₁ F₂- F₂ A B с F3 -F3 D E F
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.
The total axial load acting at the centroid at on the leftmost rib would be 2F2 and the total axial load acting at the centroid at section C would be 2F3
A) Assume that the axial member is in equilibrium and the applied forces are an unknown load F1, F2 = 11 kN , F3 = 9 kN , and F4 = 6 kN . Calculate the internal resultant normal force at section B.
B) Calculate the internal resultant normal force at section D.
C)Suppose the axial member has a circular cross section with a diameter of dB = 16 cm at section B and a diameter of dD = 8 cm at section D. What is the average normal stress in the section with the maximum magnitude stress?
Given Data:
- Applied forces: F1 (unknown), F2 = 11 kN, F3 = 9 kN, F4 = 6 kN
- Diameter at section B (dB) = 16 cm (or 0.16 m)
- Diameter at section D (dD) = 8 cm (or 0.08 m)
We need to find for each part of the problem:
A) Calculate the internal resultant normal force at section B:
B) Calculate the internal resultant normal force in section D:
C) Calculate the average normal stress in the section with the maximum magnitude stress:
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