Machine Design Fatigue
Identify the true statements regarding fatigue and combined loadings. (Check all that apply.) - (correct
Answer) - In determining the endurance limit, the Marin factors for surface condition, sizing, and
bending should be used.
If axial loads occur as part of the combined loading, the alternating component of stress should be
divided by 0.85.
Select all of the statements that are true regarding the Smith-Watson-Topper criterion. - (correct
Answer) - nf = Se(σa+σm)σa√Seσa+σmσa
The Smith-Watson-Topper criterion is based on theory rather than empirical results.
The Smith-Watson-Topper criterion is primarily associated with the strain-life method.
To ensure that the _____ is not lost in a variable stress diagram, begin on the snapshot with the largest
(or smallest) stress and add previous history to the right side. - (correct Answer) - hidden cycle
For the case of pure shear, which of the following is correct when replacing Sy in the failure criteria
equations? - (correct Answer) - Ssy = 0.577Sy
Morrow - (correct Answer) - Reasonably accurate for steels with the true fracture strength, or the fatigue
strength coefficient
matches
Smith-Watson-Topper - (correct Answer) - Very good for aluminum and reasonably good for steel.
matches
Goodman - (correct Answer) - Commonly used for cases where excessive design conservatism is
acceptable.
Walker - (correct Answer) - If the fitting parameter, γ, is known, it is considered the best match to
experimental predictions.
Select all of the following statements that are true regarding the Palmgren-Miner rule. - (correct Answer)
- ∑niNi∑niNi = c
The parameter c is usually found to be between 0.7 and 2.2.
Identify the true statements regarding fatigue and combined loadings. (Check all that apply.) - (correct
Answer) - In determining the endurance limit, the Marin factors for surface condition, sizing, and
bending should be used.
If axial loads occur as part of the combined loading, the alternating component of stress should be
divided by 0.85.
Select all of the statements that are true regarding the Smith-Watson-Topper criterion. - (correct
Answer) - nf = Se(σa+σm)σa√Seσa+σmσa
The Smith-Watson-Topper criterion is based on theory rather than empirical results.
The Smith-Watson-Topper criterion is primarily associated with the strain-life method.
To ensure that the _____ is not lost in a variable stress diagram, begin on the snapshot with the largest
(or smallest) stress and add previous history to the right side. - (correct Answer) - hidden cycle
For the case of pure shear, which of the following is correct when replacing Sy in the failure criteria
equations? - (correct Answer) - Ssy = 0.577Sy
Morrow - (correct Answer) - Reasonably accurate for steels with the true fracture strength, or the fatigue
strength coefficient
matches
Smith-Watson-Topper - (correct Answer) - Very good for aluminum and reasonably good for steel.
matches
Goodman - (correct Answer) - Commonly used for cases where excessive design conservatism is
acceptable.
Walker - (correct Answer) - If the fitting parameter, γ, is known, it is considered the best match to
experimental predictions.
Select all of the following statements that are true regarding the Palmgren-Miner rule. - (correct Answer)
- ∑niNi∑niNi = c
The parameter c is usually found to be between 0.7 and 2.2.
