Papuga PI method

Warning: The method description is not correct. I have found a bug in its definition (which also caused the improper behaviour by brittle materials). I am sorry but I do not want to present detailed description until I write about that to International Journal of Fatigue. The method itself gives better results for the new definition.

This is an integral version of the equivalent stress used also in the Papuga PCr method. It seemed to give better results in [Ppg05], but further inspection and verification lessens its value significantly [PR06].

The form of the criterion is:

Results of the criterion seem to be acceptable for:

The tests on grey cast iron in [Ppg05] show that brittle materials (the lower limit here) are not covered correctly and the same can be observed, if the results in the FatLim Database are examined. The upper limit above separates cases, where the effect of normal stress is very small or even negative. Further development, testing and analysis of the criterion is necessary.

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]		mean (average value of maximum and minimum values) normal stress on the plane examined
	[MPa]	TORS-1	fatigue limit in fully reversed torsion

Methods & Options & Variables of Calculation – Edit

Decomposition

- Whole load path

Elasto-plasticity

- No – currently no option implemented

Solution option

- Searched planes <0~BS algorithm, 1~globe analogy, 2~random>

- Number of scanned planes

- 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 MAXDP maximum of damage parameter

FDD2 NCX x-coordinate of the normal line vector of the plane with MAXDP

FDD3 NCY y-coordinate of the normal line vector of the plane with MAXDP

FDD4 NCZ z-coordinate of the normal line vector of the plane with MAXDP

FDD5 ALFA angle between the normal lines to the critical plane and to the free surface

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