# Theory of Failure List of Questions with Answers

1. σ_1 is the only stress to use to find the factor of safety by the maximum normal stress theory of failure
• True
• False
2. A load is changing on a part from 1,000 lb to 5,000 lb, the average and range loads are
• 6,000 lb and 4,000 lb
• 5,000 lb and 1,000 lb
• 3,000 lb and 2,000 lb
• 1,000 lb and 5,000 lb
3. A part is loaded under service stress for 25,000 reversals, then under a higher stress for 35,000 reversals until failure. If the total life under the larger stress alone is 36,000 reversals, what is the estimated life under the service load?
• 900,000 reversals
• 37,000 reversals
• 50,000 reversals
• 60,000 reversals
4. Brittle materials fail in yielding
• True
• False
5. By applying 10,000 in.lb torque to this non-rotating shaft, the torque reactions are
• T1=5,000 in.lb; T2=5,000 in.lb
• T1=6,000 in.lb; T2=4,000 in.lb
• T1=4,000 in.lb; T2=6,000 in.lb
• None of the above
6. For a ductile material, the yield stress in shear is the same as it is for tension
• True
• False
7. For a loaded part, the state of stress is σ_x=2,000 psi, σ_y=-8000 psi, τ_xy=0. If σ_yp=45,000 psi, what is the factor of safety using the maximum normal stress theory of failure?
• 5.625
• 22.5
• 4.5
• 7.5
• True
• False
9. For a shaft that is transmitting 145 HP while turning at 1,200 rpm, the torque is
• 760.2 in.lb
• 6722 in.lb
• 7615.5 in.lb
• 2235.3 in.lb
10. For a shaft under torque, the only type of deformation that will result is the rotation of the cross-sections with respect to each other
• True
• False
11. For a brittle material, there are two curves for the stress-strain relationship–one for the tension and the other for compression.
• True
• False
12. If a part fails by yielding, it will sustain permanent deformation
• True
• False
13. In order to apply one of the failure theories to estimate the factor of safety, we have to
• use the state of stress
• find the principal stresses
• calculate the maximum shear stress
• find the yielding stress of the material
14. Maximum shear theory of failure only applies to brittle materials
• True
• False
15. Stress concentration factors are functions of
• Geometry
• Material
16. Stress concentration factors must be applied when we are using brittle materials
• True
• False
17. The principal stresses for a part are σ_1=20 MPa, σ_2=5 MPa. What is the factor of safety using the Mises Henckey theory of failure if σ_yp=100 MPa?
• 6.1
• 6.5
• 5.55
• 8.23
18. The shear stress on a cross-section of a shaft under torsion is linearly proportional to its radius
• True
• False
19. A torque applied to one end of a shaft, while the other end is keyed against rotation. The torque along the shaft will be proportional to the length
• True
• False
20. Ultimate stress is the same as yielding stress
• True
• False
21. When solving for the factor of safety in a combined steady and alternating loading situation, stress concentration factors must be applied for both average and range stresses.
• True
• False