FATPARM

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

Format


(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)
`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`
	`RNDPDF`	`PDF1`	`PDF2`	`PDF3`
	`RANDOM`	`FACSREND`	`SREND`	`NBIN`	`DS`		`STSUBID`
	`SWEEP`	`NF`	`DF`	`STSUBID`
	`PSEUDO`	`NPV`	`NOISETHR`	`MXHOTSPOT`	`NACTDMG`
	`NPLNCRT`	`NPLN`
	`SOLDER`	`METHOD`	`AVG/ELEM`
	`MCRVS`	`UPEXTPL`	`HGHINTPL`
	`FOS`	`METHOD`	`TGLIFE`
	`STFAIL`	`STATNC`	`CHK`

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 DANGVAN Dang Van Safety Factor Analysis 8 SOLDER Solder Fatigue 20
`MAXLFAT`	Controls the activation of Multiaxial Fatigue Analysis. UXL (Default) Activates Uniaxial Fatigue MXL Activates Multiaxial Fatigue
`PSEUDO`	Flag which activates Pseudo Damage method for Fatigue Calculations. For additional information, refer to Pseudo Damage Method in the User Guide.
`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 CRTPLN Critical Plane approach 26
`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) INTPLTN Interpolation of multiple SN curves (applicable to multiple SN curves defined on MATFAT via SNTBL). 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 field is only applicable for `TYPE`=EN. NEUBER (Default) For `TYPE`=SN, it is not used. For `TYPE`=EN, NEUBER is the only valid option.
`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.
`GRD`	Stress gradient effect. GRDCD Critical distance method. GRDFKM FKM guideline method. Blank No stress gradient effect. Note: If GRDCD or GRDFKM is specified, the `SURFSTS` field is automatically set to GP for nodal stress.
`SCBFKM`	Combined Stress to calculate stress-gradient in FKM stress gradient method. 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. Refer to Unit Systems for more information.
`LENUNIT`	Unit of length. Refer to Unit Systems for more information. 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, the length unit is MM If Stress unit is Pa, the length unit is M If Stress unit is PSI or KSI, the 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 LOAD (Default) Load-time history 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.
`CHK`	Check if the loading is Proportional Load in Multiaxial Fatigue Analysis. Proportional loading means that multiaxial loading is in-phase. 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
`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. 21 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/ELEM`	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. ELEM Creep strain or creep energy density of each element in interface layers is used in damage calculation.
`MCRVS`	Continuation line which indicates that the following options are applicable to the definition of multiple SN curves (which are defined via `SNTBL` continuation on MATFAT).
`UPEXTPL`	Controls the extrapolation of SN curves. YES NO (Default)
`HGHINTPL`	This option is applicable when multiple Haigh diagrams are defined on MATFAT. This option controls the interpolation of multiple Haigh diagrams. 24 HAIGHCR (Default) Interpolation on a constant stress ratio line. HAIGHCM Interpolation on a constant mean stress line. blank
`FOS`	Flag indicating that Safety Factor Analysis is activated. 22, 23
`METHOD`	Method for Safety Factor (SF) calculation. CR (Default) Constant stress ratio CM Constant mean stress SCALE Activates Back-calculation to calculate scaling factor 25 blank
`TGLIFE`	This is the target life at which the Safety Factor is evaluated. This is also the target life for which Back-calculation (SCALE method) is used to calculate the scaling factor. No default (Real)
`STFAIL`	Flag indicating that information about Static Failure check is to follow.
`STATNC`	Identifies how static failure transition cycle is defined. STRESS This option defines stress amplitude threshold using `ALPHA``UTS` (values based on MATFAT). A cycle corresponding to the threshold amplitude is the static failure transition cycle `Nc_stat`. If `CHK` field is not set to NOCHK, the SN slope at static failure region (`b0`) is determined by `UTS` and `ALPHA``UTS` (unless `b0` is defined). If internally calculated `b0` is 0.0, damage of stress amplitude higher than or equal to `ALPHA`*`UTS` is 1.0. LIFE(Default) This option directly defines transition cycle with `Nc_stat` in MATFAT. If `CHK` is not set to NOCHK, for the SN curve: SN slope at static failure region is determined by `UTS` and Stress amplitude corresponding to `Nc_stat` by default. If `b0` is defined explicitly on MATFAT, the defined `b0` is used for the SN slope in the static failure region. If `b0`=0.0, the damage value is 1.0 at life = `Nc_stat`, and damage for life shorter than `Nc_stat` is greater than 1.0.
`CHK`	This field controls the behavior of static failure check. 27 CONT (Default) SN curve is modified based on static failure check. NOCHK Static failure checking is not active. STOP If static failure is reached, then further evaluation of this fatigue event is stopped.

Comments

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.
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.
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.
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.
UCORRECT=GERBER2 improves the GERBER method by ignoring the effect of negative mean stress.
UCORRECT=MORROW2 improves the MORROW method by ignoring the effect of negative mean stress.
UCORRECT=SODERBE is slightly different from GOODMAN, the mean stress is normalized by yield stress instead of ultimate tensile stress.
$S_{e} = \frac{S_{a}}{(1 - \frac{S_{m}}{S_{y}})}$
Where,

$S_{e}$

Equivalent stress amplitude

$S_{a}$

Stress amplitude

$S_{m}$

Mean stress

$S_{y}$

Yield stress
The STRESS, RAINFLOW and CERTNTY continuation lines are ignored in Dang Van factor of safety analysis (TYPE=DANGVAN).
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.
Refer to Unit Systems for more information.
The Upper limit of the stress range is calculated as SREND = 2*RMS Stress*FACSREND. RMS stress is output from Random Response Subcase.
The width of the stress ranges is calculated as DS=SREND/NBIN.
Vibration fatigue analysis (random response fatigue and sine sweep fatigue) is supported for both SN and EN fatigue analysis. Selection of uniaxial fatigue/multiaxial fatigue does not apply in vibration fatigue. Supported combined stress type in vibration fatigue are signed vonMises stress, absolute maximum principal stress, and critical plane.
Weld fatigue is not supported in sine sweep fatigue. Weld fatigue is supported in random response fatigue.
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.
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.
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.
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.
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.
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.
When TYPE=SOLDER, the METHOD field following SOLDER continuation line should be specified.
When METHOD is one of SYEDW, SYEDEPS, and DARV, creep material (MATVP) should be used for solder joints in the underlying analysis.
Safety factor is based on target stress (endurance limit) and is supported for uniaxial and multiaxial stress life (SN) fatigue. Safety factor is the ratio of target stress amplitude to stress amplitude of a cycle found in stress history. The minimum safety factor is reported from all the stress amplitudes during rainflow counting. If the minimum safety factor is greater than 1.0, then the structure is considered safe under the stress history. Safety factor is calculated either with constant mean stress or constant stress ratio.
The FOS I/O Option Entry should be specified for safety factor output. Safety factor output is also supported for multiple SN curves/Haigh diagram (SNTBL on MATFAT) for SN fatigue.
Interpolation options for multiple Haigh diagrams via the HGHINTPL flag are supported for metal SN fatigue analysis. Uniaxial and multiaxial SN fatigue are supported. Static, Transient, Random Response, and Sine-Sweep Fatigue Analysis are supported.
Back-calculation for Fatigue is available to calculate scaling factor for a particular Target life (TGLIFE). It can be activated by requesting FOS output, followed by setting the target life in the TGLIFE field of the FOS continuation line. The METHOD field should be set to SCALE for back-calculation. The results are supported in the H3D and OPTI formats.
The Critical Plane approach (COMBINE=CRTPLN) for stress combination is supported for the following:
1. Random Fatigue (SN and EN)
2. Sine-Sweep Fatigue (SN and EN)
3. Sine-Sweep on Random, Sine on Random, and Multiple Sine Tones Fatigue (SN)
SN curve modification due to surface finish, surface treatment, and fatigue strength reduction factor only apply to cycles greater than the static failure transition cycle in SN curves.
This card is represented as a load collector in HyperMesh.