Safety Factor of Shaft :Machine Design

Click For Summary
SUMMARY

The discussion focuses on calculating the safety factor of a solid bar made of Class 40 cast iron, measuring 8 inches long and 2.5 inches in diameter, subjected to a torque of 75,000 lbf-in and an axial compressive load of 165,000 lbf. The calculated maximum stress is 33.6 kpsi, while the shear stress is 24.5 kpsi. The safety factor is determined to be approximately 4.17, calculated using the formula nf = Allowed/Actual, where the allowable compressive strength is 140 kpsi. The relevance of principal stresses and Mohr's Circle in this context is also discussed.

PREREQUISITES
  • Understanding of stress calculations, specifically axial and shear stress
  • Familiarity with Class 40 cast iron material properties
  • Knowledge of safety factor calculations in mechanical design
  • Basic principles of Mohr's Circle for stress analysis
NEXT STEPS
  • Study the application of Mohr's Circle for determining principal stresses
  • Research the mechanical properties of different cast iron classes
  • Explore advanced safety factor calculations in complex loading scenarios
  • Learn about torque and axial load interactions in mechanical components
USEFUL FOR

Mechanical engineering students, design engineers, and professionals involved in structural analysis and material selection for mechanical components.

speedy21cvb
Messages
1
Reaction score
0

Homework Statement


An 8” long, 2.5” diameter, solid bar of Class 40 cast iron is subjected to both a torque of 75,000 lbf-in and an axial compressive load of 165,000 lbf. If these two loads can increase at a constant ratio, calculate the safety factor.

Homework Equations


\sigmax=F/A
\tauxy=Tr/J
nf= Allowed/Actual
For class 40 cast iron:
Sut=42.5 kpsi
Suc=140 kpsi

The Attempt at a Solution


\sigmax=165000/4.91=33.6 kpsi
\tauxy=75000*1.25/(\pi*2.54/32=24.5 kpsi

Take the higher stress of 33.6 kpsi.
nf=140kpsi/33.6kpsi= 4.1667I did it this way, however afterwards I thought about the principal stresses. Would I need to solve for the principal stresses present in the shaft under this loading? We used mohrs circle in class, does this apply? This is my first post, I'm finally going to stop being proud and ask for help :) Please let me know if my formatting is incorrect.

-Chris Van Buren, Mechanical Engineer Student, Georgia Tech
 
Physics news on Phys.org
speedy21cvb wrote:[/color] "Would I need to solve for the principal stresses present in the shaft under this loading? Does this apply?"[/color]

speedy21cvb: That sounds like a good plan.
 

Similar threads

Strength calculations of threaded spindle.
  • · Replies 1 ·
Replies
1
Views
5K