You are required to size member FI of the truss shown at right using Western lumber with the following properties: • Yield stress in compression: 2100 psi • Yield stress in tension: 1300 psi • Modulus of elasticity 1700 ksi. Use a factor of safety of 2.0. For the selected section: c. Calculate the stress and the strain in member FI d. Calculate the deflection of member FI; specify if elongation or shortening.
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.
You are required to size member FI of the truss shown at right using Western lumber with the following properties:
• Yield stress in compression: 2100 psi
• Yield stress in tension: 1300 psi
• Modulus of elasticity 1700 ksi.
Use a factor of safety of 2.0.
For the selected section:
c. Calculate the stress and the strain in member FI
d. Calculate the deflection of member FI; specify if elongation or shortening.
given
loads act at point A, B, C and D is 2000lb in magnitude
Yield stress in compression: 2100 psi
• Yield stress in tension: 1300 psi
• Modulus of elasticity 1700 ksi.
Use a factor of safety of 2.0.
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