fatigue Flashcards
1
Q
define fatigue
A
the growth of cracks due to cyclic loading, occurs below yield stress
2
Q
define cyclic loading
A
the repeated application of varying stresses, ‘continual’ loading
3
Q
What are the three stages of fatigue
A
- initiation, stress concentration points create small cracks, parallel to shear stress
- propagation, growth of cracks
- failure
4
Q
How do you reduce fatigue in stage I
A
- reduce grain size
- surface finish
- shape, rounded
5
Q
How do you work out is a specimen is going to fail
A
Goodman:
Sa/Se + Sm/Sut = 1
Soderburg:
Sa/Se + Sm/Sy = 1
> 1 = failure
Sa = alternating stress
Se = insurance limit
Sm = mean stress
Sy = yield stress
Sut - ultimate tensile stress
6
Q
Equation for mean stress
A
σm = (σmax + σmin) / 2
7
Q
Equation for amplitude
A
σa = (σmax - σmin) / 2
8
Q
What does a fully reversed cyclic load mean
A
σm = 0
σa = se
