, Ninic method
The base of Ninic method is covered in [Nin06] and [NS07]. Its original formula can be rewritten to:
,
where the material parameters aN and bN are set as:
,
.
When this solution was tested, we found that a similar application of SWT mean stress formula as performed by Spagnoli's method is desirable in order to get more appropriate results. The final form of the criteria as implemented in PragTic thus was rewritten to:
.
Note, that the Spagnoli's v.MD and Ninic's criteria differ only in the b parameter. The criterion is new, so there is relevant comparison to other methods excluding the FatLim Database. The paper by Ninic and Stark [NS07] covers relatively broad range of data, but systematic confusion in U.S. and British tons and incomplete data of Findley's experiments [Fin53] do not allow to rely on it.
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 |
|
|
[-] |
ratio of fatigue limits ( |
|
|
|
[MPa] |
amplitude of normal stress on the plane examined |
|
|
|
[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
This help file has been generated by the freeware version of HelpNDoc
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