1. The fatigue life for a certain alloy at stress levels of σ1, σ2, and σ3 is 10,000, 50,000, and 500,000 cycles, respectively. If a component of this material is subjected to 2500 cycles of σ1 and 10,000 cycles of σ2, estimate the remaining lifetime in association with cyclic stresses at a level of σ3.
2. Polymer fatigue failures may include significant heating. Why is this more of a problem for polymers than for metals?
3. Explain why the fatigue life (Nf) of a polymer should decrease with increasing frequency.
8. Why is fatigue generally less of a problem with ceramics and glasses than with metals and polymers?
9. What role does a notch or flaw play in determining the total fatigue life of a component?
10. Sketch the cyclic dependent material response under stress control and strain control for cyclic hardening and cyclic softening materials.
11. List three general categories of surface treatment that can increase fatigue life, and provide one example of a specific process for each category.
12. What is the relationship between the stress concentration factor kt and the fatigue notch factor kf?
13. What is the significance of the cyclic stress-strain curve? How is the cyclic stress-strain curve determined?
14. Goodman and Gerber are empirical relationships for the mean stress effect. Under what conditions are these relationships applied and what are their limitations?
15. Given the data in the above figure for AISI 4340 steel, express the Basquin relationship.
|
Alloy
|
Yield stress, ksi
|
Tensile strength, ksi
|
|
A
|
100
|
160
|
|
B
|
100
|
110
|
|
C
|
60
|
110
|
16. Given the above monotonic tensile data for three alloys, predict whether the alloy will cyclically harden or cyclically soften.