# FATPARM

Bulk Data Entry Used to define parameters required for a Fatigue Analysis.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
FATPARM ID TYPE MAXLFAT PSEUDO
STRESS COMBINE UCORRECT STRESSU PLASTIC SURFSTS GRD SCBFKM
UNIT LENUNIT
RAINFLOW RTYPE GATEREL
PRPLD CHK
MCORRECT MC1 MC2 MC3 MC4
CERTNTY SURVCERT
SPWLD METHOD CORRECT SURVCERT THCKCORR NANGLE
SMWLD METHOD CORRECT SURVCERT THCKCORR
FOS FOSTYPE
RNDPDF PDF1 PDF2 PDF3
RANDOM FACSREND SREND NBIN DS   STSUBID
SWEEP NF DF STSUBID
PSEUDO NPV NOISETHR MXHOTSPOT NACTDMG
NPLNCRT NPLN
SOLDER METHOD AVG/MAX
MCRVS UPEXTPL

## Definitions

Field Contents SI Unit Example
ID Each FATPARM card must have a unique ID. The FATPARM Subcase Information Entry may reference this identifier.

No default (Integer > 0)

TYPE Fatigue analysis type that is defined.
SN (Default)
Stress Life
EN
Strain Life
FOS
Factor of Safety Analysis 8
SOLDER
Solder Fatigue

MAXLFAT Controls the activation of Multiaxial Fatigue Analysis.
UXL (Default)
MXL

PSEUDO Flag which activates Pseudo Damage method for Fatigue Calculations. 16
STRESS Indicates that parameters are to follow which define how the stress is used in fatigue calculation.
COMBINE The sign on the Signed von Mises, Signed Tresca, Signed Max Shear is taken from the sign of the Abs Max Principal value.

For Stress Life, combined stress value is used; For Strain Life, combined strain value is used.

For Strain Life, shear strain components are engineering shear strain (two times tensor shear strain).
ABSMAXPR (Default)
Abs Max Principal - recommended for brittle materials
MAXPRINC
Max Principal
MINPRINC
Min Principal
VONMISES
von Mises
SGVON
Signed von Mises - recommended for ductile materials
TRESCA
Tresca
SGTRESCA
Signed Tresca
SGMAXSHR
Signed Max Shear
XNORMAL
X Normal
YNORMAL
Y Normal
ZNORMAL
Z Normal
XYSHEAR
X-Y Shear
YZSHEAR
Y-Z Shear
ZXSHEAR
Z-X Shear

UCORRECT Mean stress correction method for Uniaxial Fatigue Analysis. 5 6 7 15
Valid options for TYPE=SN:
NONE
GOODMAN (Default)
Goodman model
GERBER
Gerber model
GERBER2
Gerber model (negative mean stress is ignored)
SODERBE
Soderberg model
FKM
FKM Guidelines (all four Regimes)
FKM2
FKM Guidelines (only Regimes 2 and 3)
Valid options for TYPE=EN:
SWT (Default)
Smith-Watson-Topper model
MORROW
Morrow model
MORROW2
Morrow model (negative mean stress is ignored)
NONE

STRESSU FE analysis Stress Tensor Unit. The Unit is necessary because the SN/EN curve (MATFAT card) might be defined in different unit, and FEA stress needs to be converted before looking up the fatigue life for a given stress level on the SN curve. 9
MPA (Default)
PA
PSI
KSI

PLASTIC This parameter is only applicable for TYPE=EN.
NONE
NEUBER (Default)

For TYPE=SN, is not used.

SURFSTS Surface stress options.
MBRN
Membrane stress
GP
Nodal stress 17 18 19
Blank
No surface stress for Uniaxial Fatigue and MBRN for Multiaxial Fatigue Analysis.

For Multiaxial Fatigue Analysis, by default, a membrane is created to calculate damage of the free surfaces in the model, and this is visible as an AUTO_SKIN component in the H3D file.

GRDCD
Critical distance method.
GRDFKM
FKM guideline method.
Blank
Note: If GRDCD or GRDFKM is specified, then SURFSTS field is automatically set to GP for nodal stress.

VONMISES (Default)
von Mises stress
ABSMAXPR
Absolute maximum principal stress.
Blank

UNIT Flag indicating that the next field defines the unit for length in fatigue analysis.

MM
Millimeter
KM
Kilometer
M
Meter
CM
Centimeter
MI
Mile
FT
Foot
IN
Inch
Blank
Length unit is determined using the Stress unit, based on the following rules:
If Stress unit is MPa, then length unit is MM
If Stress unit is Pa, then length unit is M
If Stress unit is PSI or KSI, then length unit is IN

RAINFLOW Indicates that parameters required for Rainflow counting are to follow. This flag and its related parameters will be used only when the TYPE field is set to SN or EN.
RTYPE Rainflow data type. 1
STRESS
Stress-time history

GATEREL Relative fraction of maximum gate range. The reference value is the maximum range multiplied by GATEREL and used for gating out small disturbances or "noise" in the time series.

Default = 0.2 (0.0 ≤ Real < 1.0)

PRPLD Flag that indicates proportional load treatment information is to follow.
YES (Default)
OptiStruct will check if the loading from the single load case on FATEVNT is a proportional load or not for multiaxial fatigue analysis. If multiple load cases are defined on FATEVNT, the loading is assumed to be non-proportional and the YES option does not apply.
NO
Proportional load check is deactivated even for a single load case definition on FATEVNT for multiaxial fatigue analysis. The solution will always go through the non-proportional fatigue code.

For more information, refer to Multiaxial Fatigue Analysis in the User Guide.

MCORRECT Flag that indicates Multiaxial Mean Stress Correction information is to follow.
MCi Mean Stress Correction to be used in Multiaxial Fatigue Analysis. Multiple mean stress correction models can be specified in the four MCi fields, the sequence is irrelevant.
Valid options for TYPE=SN:
GOODMAN (Default)
Goodman model
FINDLEY (Default)
Findley model
FKM
FKM Guidelines (all four Regimes)
Valid options for TYPE=EN:
SWT (Default)
Smith-Watson-Topper model
FS (Default)
Fatemi-Socie model
BM
Brown-Miller model
MORROW
Morrow model

CERTNTY Indicates that parameters that define certainties in fatigue analysis are to follow. This flag and the following parameter will be used only when the TYPE field is set to SN or EN.
SURVCERT Certainty of survival based on the scatter of the SN curve. 4

Default = 0.5 (0.0 < Real < 1.0)

SPWLD Flag indicating that the following parameters are used for spot weld fatigue analysis.
METHOD Spot weld fatigue analysis method.
RUPP (Default)
blank

UCORRECT Mean stress correction indicator for Uniaxial Fatigue Analysis.
NONE (Default)
FKM
FKM Guidelines (all four Regimes)
FKM2
FKM Guidelines (only Regimes 2 and 3)

SURVCERT Certainty of survival.

Default = SURVCERT value on CERTNTY continuation line (0.0 < Real < 1.0)

THCKCORR Thickness correction flag.
YES (Default)
NO

NANGLE Number of angles to be examined on the sheet and nugget.

Default = 20 (Integer > 0)

SMWLD Flag indicating that the following parameters are used for seam weld fatigue analysis.
METHOD Seam weld fatigue analysis method.
VOLVO (Default)
Activates the Volvo method.
JNTLINE
Activates the Joint line method.
blank

UCORRECT Mean stress correction indicator for Uniaxial Fatigue Analysis.
NONE (Default)
FKM
FKM Guidelines (all four Regimes)
FKM2
FKM Guidelines (only Regimes 2 and 3)

SURVCERT Certainty of survival.

Default = SURVCERT value on CERTNTY continuation line (0.0 < Real < 1.0)

THCKCORR Thickness correction flag.
YES (Default)
NO

FOS Indicates that the following parameters are for Factor of Safety analysis (TYPE=FOS). This flag and following parameter will be used only when the TYPE field is set to FOS.
FOSTYPE Used to select the Factor of safety analysis type.

Default = DANGVAN

RNDPDF Indicates Random Response Probability Density Function information is to follow. 12
PDFi Random Response Probability Density Functions to be used in Random Response fatigue analysis. Multiple functions can be specified in the three PDFi fields, the sequence is irrelevant.
DIRLIK (Default)
LALANNE
NARROW
THREE

RANDOM Indicates that parameters for Random Response Fatigue are to follow. This flag and the following parameters will be used only when the LCID field references a Random Response Analysis Subcase.
FACSREND Calculates the upper limit of the stress range (SREND). 10

Default = 8.0 (Real > 0.0 or blank)

SREND Used to directly specify the upper limit of the stress range.

Default = SREND based on FACSREND (Real > 0.0 or blank)

NBIN Calculates the width of the range of stress ranges for which the probability is calculated. 11

Default = 100 (Integer > 0 or blank)

DS Used to directly define the width of the stress ranges.

Default = DS based on NBIN (Real > 0.0 or blank)

STSUBID References the subcase ID of a Static Subcase to account for mean stress correction with any loading that leads to a mean stress different from zero.

Default = blank (Integer > 0 or blank)

SWEEP Flag indicating that options for Sweep Fatigue analysis are to follow. 13
NF
Integer
Number of frequencies to be examined between the first and last frequency of the Frequency Response subcase.
NFREQ (Default)
NF is set equal to number of frequencies of the Frequency Response Subcase (based on FREQi entries).

DF Frequency increment from first to last frequency of the frequency response subcase. If DF is defined, NF is ignored. 14

Default = blank (Real)

STSUBID References the subcase ID of a Static Subcase to account for mean stress correction with any loading that leads to a mean stress different from zero.

Default = blank (Integer > 0 or blank)

PSEUDO Flag indicating options for Pseudo Damage method.

For additional information, refer to Pseudo Damage Method in the User Guide.

NPV Number of peak-valley pairs in approximated load histories.

For additional information, refer to Pseudo Damage Method in the User Guide.

Default = 3 (Integer)

NOISETHR Threshold for termination of an element cluster. An element cluster is allowed to continue expanding even if positive slopes are encountered between two elements, as long as the difference in pseudo damage between the two elements falls below NOISETHR. If the differences in pseudo damage at the cluster boundary is higher than NOISETHR, then the cluster expansion is terminated.

For additional information, refer to Pseudo Damage Method in the User Guide.

Default = 1.0E-8 (Real > 0.0)

MXHOTSPOT Number of hotspot clusters.

Default = 1% of the total number of elements of the entire model, or 2000, whichever is lower (Integer > 0)

NACTDMG Number of elements where the actual damage is calculated in a cluster.

Default = 20 (Integer > 0)

NPLNCRT Continuation line which indicates that critical plane calculation parameter for Multiaxial Fatigue analysis is to follow.
NPLN Number of planes that damage is assessed on in Multiaxial fatigue analysis. The last two planes that are assessed are always 45 degrees and 135 degrees planes.

Default = 20 (8 < Integer < 92)

SOLDER Continuation line to activate solder fatigue analysis.
METHOD Method for solder fatigue analysis.
DIFFCTE
Solder fatigue method based on mismatch of local Thermal Expansion Coefficient (CTE).
SYEDW
Creep energy density method (proposed by Syed).
SYEDEPS
Creep strain method (proposed by Syed).
DARV
Creep energy density method (proposed by Darveaux).

No default

AVG/MAX Controls how creep strain or creep energy density is used in damage calculation.
AVG (Default)
Creep strain or creep energy density is averaged over volume of interface layers in damage calculation.
MAX
Maximum creep strain or creep energy density of interface layers is used in damage calculation.

MCRVS Continuation line which indicates that the following option is for the definition of multiple SN curves (which are defined via SNTBL continuation on MATFAT).
UPEXTPL Controls the extrapolation of SN curves (see the User Guide for more information).
YES
NO (Default)

1. RTYPE=LOAD is valid when there is only one static load case defined in an event. If the event contains multiple static load cases, RTYPE will automatically be set to STRESS because there will be stress super-positioning among different load cases; doing rainflow counting on load-time history could not deal with it.
2. When RTYPE=LOAD, load-time history will be cycle counted using the rainflow cycle counting method. The cycle counting results (load Ranges and Means) will be scaled by combined FEA stress. Doing rainflow counting on load-time is much faster than doing it on stress-time (RTYPE=STRESS), especially when the load-time history is complex and contains a large number of time points, but it is less accurate.
3. When RTYPE=STRESS, stress-time history will be cycle counted using the rainflow cycle counting method. The stress-time history has the same length as load-time, while each point of the stress time is the combined stress value where the stress tensor is FEA stress scaled by y point value of the corresponding load-time history.
4. Certainty of Survival is based on the scatter of the SN/EN curve. It is used to modify the SN/EN curve according to the standard error parameter (SE) defined in fatigue property of material card (MATFAT). A higher reliability level requires a larger certainty of survival.
5. UCORRECT=GERBER2 improves the GERBER method by ignoring the effect of negative mean stress.
6. UCORRECT=MORROW2 improves the MORROW method by ignoring the effect of negative mean stress.
7. UCORRECT=SODERBE is slightly different from GOODMAN, the mean stress is normalized by yield stress instead of ultimate tensile stress.(1)
${S}_{e}=\frac{{S}_{a}}{\left(1-\frac{{S}_{m}}{{S}_{y}}\right)}$
Where,
${S}_{e}$
Equivalent stress amplitude
${S}_{a}$
Stress amplitude
${S}_{m}$
Mean stress
${S}_{y}$
Yield stress
8. The STRESS, RAINFLOW and CERTNTY continuation lines are ignored in a factor of safety analysis (TYPE=FOS).
9. If UNITS or DTI UNITS is present, the default value of STRESSU is determined by UNITS or DTI UNITS entry (UNITS entry takes precedence over DTI UNITS). If UNITS, DTI UNITS, and STRESSU are not provided, the default value of STRESSU is MPA. If UNITS or DTI UNITS issued.

10. The Upper limit of the stress range is calculated as SREND = 2*RMS Stress*FACSREND. RMS stress is output from Random Response Subcase.
11. The width of the stress ranges is calculated as DS=SREND/NBIN.
12. Random Response Fatigue analysis is supported for both SN and EN Fatigue Analysis. Multiaxial Fatigue is not currently supported for Random Response Fatigue Analysis. For EN fatigue only, COMBINE=VONMISES is supported.
13. For Sine Sweep Fatigue:
• Currently, only von Mises is supported for the COMBINE field.
• Only Uniaxial Fatigue analysis is supported.
• SN and EN for Solid and Shell elements are supported.
• Weld Fatigue is not supported.
• Only one FATLOAD is allowed on a FATEVNT entry
14. If Frequency Response results are not available at a frequency calculated based on DF, then the Frequency Response results are interpolated from the nearest two results.
15. The UCORRECT field is only applicable for Uniaxial Fatigue Analysis (Static, Transient, Random, and Sine Sweep Fatigue). It is not applicable in Multiaxial Fatigue Analysis. For Multiaxial Fatigue analysis, the MCORRECT continuation line is used for Mean Stress correction methods.
16. The units for Elastic Modulus (E) and Rigidity Modulus (G) in the material data are obtained from the stress unit field (STRESSU) in the FATPARM card, in general. In the case of SN fatigue, the units for Elastic Modulus in the material data is obtained from the stress unit field (STRESSU) in the FATPARM card, when the critical distance is activated.
17. The SURFSTS=GP option is supported for SN, EN, and FOS Fatigue Analysis and optimization. It is also only supported for solid elements. Optimization is available and RTYPE on DRESP1 can be set to FATIGUE. PTYPE should be PSOLID or ELEM, and ATTA should be FOS.
18. When SURFSTS=GP, XELSET and XELEM (if available) options on FATDEF are considered first to exclude any elements from the elements defined via ELSET/PROP continuation lines on FATDEF. Grids are then populated from the remaining elements. Then XGSET and XGRID (if available) on FATDEF are applied to exclude any grids.
19. When SURFSTS=GP, and if multiple properties are associated with a single grid, then GPSTRESS of the grid used in Fatigue Analysis is averaged GPSTRESS at the grid. If multiple materials are associated with a node, refer to Surface Damage in the User Guide for more information.
20. When TYPE=SOLDER, the METHOD field following SOLDER continuation line should be specified.
21. When METHOD is one of SYEDW, SYEDEPS, and DARV, creep material (MATVP) should be used for solder joints in the underlying analysis.
22. This card is represented as a load collector in HyperMesh.