FATPARM

Bulk Data Entry

FATPARM - Fatigue Analysis Parameters

Description

This bulk data entry can be used to define parameters required for a Fatigue Analysis.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
FATPARM	ID	TYPE	MAXLFAT
	STRESS	COMBINE	CORRECT	STRESSU	PLASTIC	SURFSTS
	RAINFLOW	RTYPE	GATEREL
	PRPLD	CHK
	MDMGMDL	DM1	DM2	DM3
	CERTNTY	SURVCERT
	SPWLD	METHOD	CORRECT	SURVCERT	THCKCORR	NANGLE
	SMWLD	METHOD	CORRECT	SURVCERT	THCKCORR
	FOS	FOSTYPE
	RDMGMDL	DM1	DM2	DM3
	RANDOM	FACSREND	SREND	NBIN	DS	TEXP	STSUBID

Field

Contents

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 = Stress Life
EN = Strain Life
FOS = Factor of Safety Analysis - see comment 8

Default = SN

(NSTRESS is also supported for Stress Life for compatibility)

MAXLFAT

Controls the activation of Multiaxial Fatigue Analysis.

Default = NO (YES or NO)

STRESS

Indicates that parameters are to follow which define how the stress is used in fatigue calculation.

COMBINE

Default = ABSMAXPR

(ABSMAXPR = Abs Max Principal

MAXPRINC = Max Principal

MINPRINC = Min Principal

VONMISES = von Mises

SGVON = Signed von Mises

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)

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).

For brittle materials, "Absolute maximum principle" is recommended.

For ductile materials, "Signed von Mises" is recommended.

CORRECT

Mean stress correction method. See comments 5, 6, and 7.

For TYPE = SN, valid options are:

Default = GOODMAN (NONE, GOODMAN, GERBER, GERBER2, or SODERBE)

For TYPE = EN, valid options are:

Default = SWT (NONE, MORROW, MORROW2, or SWT = Smith-Watson-Topper)

STRESSU

FE analysis Stress Tensor Unit. The Unit is necessary because the S-N/E-N 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 S-N curve. See comment 9.

Default = MPA (MPA, PA, PSI, or KSI)

PLASTIC

This parameter is only applicable for TYPE = EN.

For TYPE = SN, is not used.

For TYPE = EN, valid options are:

Default = NEUBER (NONE or NEUBER)

SURFSTS

Activation flag. If solid elements are defined in FATDEF, stress on the surface of the solid elements are used for damage assessment. For Multiaxial Fatigue Analysis, 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.

Default = NO for Uniaxial Fatigue Analysis or YES for Multiaxial Fatigue Analysis

(YES or NO)

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. See comment 1.

LOAD = Load-time history
STRESS = Stress-time history

Default = LOAD

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 = 0.0 (0.0 ≤ Real < 1.0)

PRPL

Flag that indicates proportional load treatment information is to follow.

CHK

Check Proportional Load.

Currently only applicable to a single load case in FATEVNT. If NO, even a single load case multiaxial fatigue analysis will use Non-Proportional Load Fatigue Analysis.

Default = YES (YES or NO)

MDMGMDL

Flag that indicates Multiaxial Damage Model information is to follow.

DMi

Damage models to be used in multiaxial fatigue analysis. Multiple damage models can be specified in the three DMi fields, the sequence is irrelevant.

For TYPE = SN, valid options are:

Default = GOODMAN and FINDLEY (GOODMAN, FINDLEY)

For TYPE = EN, valid options are:

Default = SWT and FS (SWT = Smith-Watson-Topper, FS, BM)

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 S-N curve. See comment 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.

Default = RUPP (RUPP or blank)

CORRECT

Mean stress correction indicator.

Default=NONE (FKM or NONE)

SURVCERT

Certainty of survival.

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

THCKCORR

Thickness correction flag.

Default=YES (YES or 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.

Default = VOLVO (VOLVO or blank)

CORRECT

Mean stress correction indicator.

Default = NONE (FKM or NONE)

SURVCERT

Certainty of survival.

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

THCKCORR

Thickness correction flag.

Default = YES (YES or 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

This field can be used to select the Factor of safety analysis type.

Default = DANGVAN

RDMGMDL

Indicates Random Response Damage Model information is to follow.

DMi

Damage models to be used in Random Response fatigue analysis. Multiple damage models can be specified in the three DMi fields, the sequence is irrelevant.

Default = DIRLIK (DIRLIK, LALANNE, NARROW, or 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). See comment 10.

Default = 8.0 (Real > 0.0 or blank)

SREND

Can be 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. See comment 11.

Default = 100 (Integer > 0 or blank)

Can be used to directly define the width of the stress ranges.

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

TEXP

Total Exposure time of the initial source time domain Random Loading Sample.

Default = 1.0 (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)

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.

4.	Certainty of Survival is based on the scatter of the S-N/E-N curve. It is used to modify the S-N/E-N 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.	CORRECT=GERBER2 improves the GERBER method by ignoring the effect of negative mean stress.

6.	CORRECT=MORROW2 improves the MORROW method by ignoring the effect of negative mean stress.

7.	CORRECT=SODERBE is slightly different from GOODMAN, the mean stress is normalized by yield stress instead of ultimate tensile stress.

Se = Sa / (1 - Sm / Sy)

Where, Se is equivalent stress amplitude, Sa is stress amplitude, Sm is mean stress, and Sy is 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 = 2RMS StressFACSREND. RMS stress is output from Random Response Subcase.

11.	The width of the stress ranges is calculated as DS = SREND/NBIN.

12.	This card is represented as a loadcollector in HyperMesh.