Findley method v. Socie

where only the Basquin's elastic part of the fatigue deformation curve is included. The left-side corresponds to a common Findley damage parameter being a linear combination of shear stress amplitude and maximum normal stress. Original Socie's proposal prefers the MSSR concept, i.e. Ca symbol stands for the maximum amplitude of the shear stress on the plane, where its maximum occurs and Nmax maximum normal stress is derived on the same plane.

PragTic introduces the ability to switch to the MD concept among the Solution option parameters. Socie proposes to look only for the maximum cycle for deduction of N number of cycles, which is accepted here (Decomposition: Maximizing load ranges), but should be changed later in the next versions to common Palmgren-Miner sumation of damage.

Note: Note the b parameter in the model. Due to the shear load character, the parameter introduced there should be bt. This is nevertheless quite rarely available, thus Socie decided to keep the parameter, which is valid for an axial loading. Be aware that the equality of the exponent parameters in both load modes is not confirmed experimentally and significant differences could be found. PragTic currently does not allow to use different exponents for different load modes, so you have to accept this reported simplification.

Mark	Unit	PragTic variable	Meaning
Nmax	[MPa]		maximum normal stress on a plane during a cycle
Ca	[-]		shear stress amplitude on a plane during a cycle
	[MPa]	TAU_F	fatigue strength coefficient in torsion
b	[-]	EXP_B	fatigue strength exponent
c	[-]	EXP_C	fatigue ductility exponent
k	[-]	C_FIN	material coefficient in the Findley model
N	[-]		number of cycles to crack initiation

- Maximizing load ranges - only the maximum shear stress amplitude and maximum normal stress are looked for over the entire load history. Such solution can be quite unsuitable for a random loading or a loading with distinctly varying load levels.

Note: The Neuber-like methods allowing input of elastic stresses and strains into the fatigue damage calculation for multiaxial solution are not implemented in PragTic. The only allowed input thus is the input of transient analysis, where the elastic-plastic constitutive rules were applied in the non-linear elastic-plastic FE-solution.

- Shear component description <0~MCCM, 1~LCM, 2~by normal line> - fill in zero, please - the MCCM solution is used as default currently. Any other choice will not be reflected in the computation.

E	[MPa]	tensile modulus
NU	[-]	Poisson’s ratio
TAU_F	[MPa]	fatigue strength coefficient in torsion
EXP_B	[-]	fatigue strength exponent
C_FIN	[-]	k material parameter