Strain Life Curves Flashcards
What is considered crack initiation for the Strain-Life method?
Crack is 1-2mm
What does the Strain-Life method measure?
The time taken to initiate a crack
What types of conditioning are there?
Cyclic softening
Cyclic hardening
What is the name for non-cyclic loading?
Monotonic loading
How does a strain curve compare to a stress curve?
They are very similar, but strain curves take plasticity into account
What steps are involved in the Strain-Life method?
-Look at the whole component, cycle etc
-Stress concentration
-Hysteresis curve
-Stress-strain curve
-Strain life curve
Give some examples of factors which could affect data quality
-Material composition and heat treatment
-Specimen preparation
-Quality of test machine (control systems, calibration, fixtures, data captures etc)
What does the Morrow Correction for Mean Stress do?
Moves the elastic cycle up/down depending on mean stress
What is the limitation of the Morrow Correction?
It only applies to elastic curves
What does the Smith Watson Topper Correction do?
Corrects for mean stress
What is the nominal stress and strain?
The applied stress and strain - would be at there if the stress concentration wasn’t
What is local elastic/plastic stress and strain?
Stress and strain next to notch root
How can the notch root local stresses and strains be derived?
- Measurement from a strain gauge
- Elastic-plastic FE modelling
- An empirical rule
Which is the best derivation method for notch root local stresses and strains?
An empirical rule, eg Neuber’s rule
What is Neuber’s rule?
K(epsilon).K(sigma) = (K(t))^2
What is the useful rearrangement of Neuber’s rule and why is it useful?
(K(t))^2.s.e = sigma.epsilon
The terms on the left are usually known
What are e and s in Neuber’s rule?
e = nominal strain
s = nominal stress
Where is the plastic strain range on a hysteresis loop?
Along the stress = 0 line inside the loop
How do fatigue limit and plastic strain range relate?
The larger the plastic strain range, the lower the fatigue limit
What is point 1 in the graphical solution for local sigma and epsilon?
s and e- the material response diverges from the linear stress-strain line
What is point 2 in the graphical solution for local sigma and epsilon?
K(t)s and K(t)e
The point of intersection of the Neuber equation structural response and the linear stress-strain line
What is point 3 in the graphical solution for local sigma and epsilon?
The solution point - epsilon and sigma
The intersection of the material response and the structural response
