Findley method
The origin of the Findley criterion goes back to the fifties of the last century [Fin57]:
In contrast to the McDiarmid criterion where the coefficient in the equation were set on the basis of extensive test batch evaluation, the coefficients are derived from pure uniaxial tests here. The critical plane is set by a maximization of the left hand side of the equation above – the method is MD based. The computation of both material variables aF and bF is based on two maximizations performed in fully reversed tension and in fully reversed torsion, which lead to:
Papadopoulos omits this criterion in his comparison set [PDG97] due to its sensitivity to the mean torsion loading. Nevertheless, the criterion is cited in other papers [CS01], thus it is also included in PragTic. Its results within the FatLim database [FatLim Database] show inappropriate mean stress effect.
Nomenclature:
|
Mark |
Unit |
PragTic variable |
Meaning |
|
|
[MPa] |
shear stress amplitude on an examined plane |
|
|
|
[MPa] |
TENS-1, BEND-1 |
fatigue limit in fully reversed axial loading |
|
|
[MPa] |
maximum normal stress on the plane examined |
|
|
|
[MPa] |
TORS-1 |
fatigue limit in fully reversed torsion |
Methods & Options & Variables of Calculation – Edit
Decomposition
Elasto-plasticity
- No – currently no option implemented
Solution option
- Searched planes <0~BS algorithm, 1~globe analogy, 2~random>
- Number of scanned planes
- Optimize <1~yes, 0~no>
- Only every x-th data-point taken from load history
- Evaluate envelope curve only <1~yes, 0~no>
Solution variable
- Minimum damage – this option is not active for this high-cycle fatigue method
Material parameters
|
E |
[MPa] |
tensile modulus |
|
NU |
[-] |
Poisson’s ratio |
|
TENS-1 |
[MPa] |
fatigue limit in fully reversed push-pull (or plane bending) |
|
TORS-1 |
[MPa] |
fatigue limit in fully reversed torsion |
Result detail variables
Damage fatigue index is computed, not the damage as a reciprocal value to number of cycles or repetitions
FDD1 NCX x-coordinate of the normal line vector of the critical plane
FDD2 NCY y-coordinate of the normal line vector of the critical plane
FDD3 NCZ z-coordinate of the normal line vector of the critical plane
FDD4 ALFA angle between the normal lines to the critical plane and to the free surface
© PragTic, 2007
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