MATFAT
Bulk Data Entry Defines material properties for fatigue analysis.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

MATFAT  MID  UNIT  LENUNIT  
STATIC  YS  UTS 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SN  SRI1  B1  NC1  B2  FL  SE  
FINDLEY  TFP  MSS1  MSS2  MSS3  MSS4  A/R 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SPWLD  MSS1  MSS2  MSS3  MSS4  R  A/R  
SR1_SP1  B1_SP1  NC1_SP1  B2_SP1  FL_SP1  SE_SP1  
SR1_SP2  B1_SP2  NC1_SP2  B2_SP2  FL_SP2  SE_SP2  
SR1_SP3  B1_SP3  NC1_SP3  B2_SP3  FL_SP3  SE_SP3 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SMWLD  MSS1  MSS2  MSS3  MSS4  A/R  
SR1_SM1  B1_SM1  NC1_SM1  B2_SM1  FL_SM1  SE_SM1  
SR1_SM2  B1_SM2  NC1_SM2  B2_SM2  FL_SM2  SE_SM2 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SMWLD  NORMAL  MSSN1  MSSN2  MSSN3  MSSN4  A/R  
SR1_SMN1  B1_SMN1  NC1_SMN1  B2_SMN1  FL_SMN1  SE_SMN1  
SR1_SMN2  B1_SMN2  NC1_SMN2  B2_SMN2  FL_SMN2  SE_SMN2 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SMWLD  SHEAR  MSSSH1  MSSSH2  MSSSH3  MSSSH4  A/R  
SR1_SMSH  B1_SMSH  NC1_SMSH  B2_SMSH  FL_SMSH  SE_SMSH 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SNTBL  REFTYPE  logSE  Nc1  Nc  FINDLEY  STSTYPE  
REFVAL1  A1  B1  A2  B2  A3  B3  
A4  B4  A5  B5  etc.  
REFVAL2  A1  B1  A2  B2  A3  B3  
A4  B4  A5  B5  etc.  
REFVAL3  A1  B1  A2  B2  A3  B3  
A4  B4  A5  B5  etc.  
etc. 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

STFAIL  ALPHA  Nc_stat  b0  
HAIGH  A/R  
S1  M1  S2  M2  S3  M3  
S4  M4  etc.  
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

STRESS  SCALE  OFFSET 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

EN  Sf  b  c  Ef  np  Kp  Nc  
SEe  SEp  SEc  A/R  
tfp  gfp  bg  cg  CoefKp90  Coefnp90  MXLMSTRN  
FSParm  BMParm 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

FOS  Tfl  Hss  STHETA  SSHEAR 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

STSGRD  CRTDIS  FKM_aG  FKM_bG  TFKM 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

SOLDER  Wp  Wcrp  b1w  Cp  b1e 
Definitions
Field  Contents  SI Unit Example 

MID  Material identification
number that matches the identification number on a MAT1 Bulk Data Entry. No default (Integer > 0) 

UNIT  Defines the units of
stress values specified on the YS,
UTS, SRI1,
FL, Sf, and
Kp fields. Refer to Unit Systems for more
information.


LENUNIT  Unit of length. Refer to
Unit Systems for more information.


STATIC  Indicates that static material properties are defined in the following fields.  
YS  Yield strength. 1 (Real > 0.0, or blank) 

UTS  Ultimate tensile strength.
1 (Real > 0.0, or blank) 

SN  Indicates that fatigue material properties for SN analysis are following.  
SRI1  Fatigue strength
coefficient. It is the stress range intercept of the
SN curve at 1 cycle on a loglog scale. No default (Real > 0.0) 

B1  The first fatigue strength
exponent. It can be input in two ways.
No default (Real ≠ 0.0) 

NC1  In onesegment SN curve,
this is the cycle limit of endurance (see NC1 in
Figure 1). In twosegment SN curve, this is the transition point (see NC1 in Figure 3). No default (Real ≥ Nc_stat) 

B2  The second fatigue
strength exponent. It can be input in two ways.
Default = 0.0 (Real) 

FL  Fatigue Limit. No damage
occurs if the stress range is less than FL (see
FL in Figure 1 and
Figure 3). 6 (Real ≥ 0.0, or blank) 

SE  Standard Error of
Log(N). Default = 0.0 (Real ≥ 0.0) 

FINDLEY  Constant k in the Findley
model Default = 0.3 (Real > 0.0) 

TFP  Shear Fatigue Strength
coefficient (
${\tau}_{f}^{\text{'}}$
) based on range. This value should
be twice the value defined for TFP on the
EN continuation line. Default = Blank (Real > 0.0) 

MSSi  Mean Stress Sensitivity
parameters for mean stress correction based on FKM Guidelines. These
are used only if the UCORRECT field of the
STRESS continuation line, on
FATPARM, is set to
FKM/FKM2 or the
MCi fields of the MCORRECT
continuation line, on FATPARM, is set to
FKM. 11
Note: MSS1, MSS3, and
MSS4 can be blank only if all of them
are blank. If one of them is specified, then all four
MSS1, MSS2,
MSS3, and MSS4
should be input.


A/R 
Defines the interpretation of the defined SN
curve.


SPWLD  Indicates that the fatigue material properties for spot weld fatigue analysis are to follow. The following seam weld properties are only applicable to the Volvo method.  
MSSi  Mean Stress Sensitivity
parameters for mean stress correction based on FKM Guidelines. These
are used only if the UCORRECT field of the
SPWLD continuation line on
FATPARM is set to FKM or
FKM2. 11
Note: MSS1, MSS3, and
MSS4 can be blank only if all of them
are blank. If one of them is specified, then all four of
MSS1, MSS2,
MSS3, and MSS4
should be input.


R  Indicates the Stress
Ratio, R, at which the Spot Weld SN curve is input 2
11 Default = 0.0. or 1.0 

A/R 
Defines the interpretation of the defined SN
curve.


SR1_SPi  Fatigue strength
coefficient. It is the stress range intercept of
SN curve at 1 cycle in loglog scale. Here i=1, 2, 3 represent sheet 1, sheet 2, and nugget, respectively in spot weld fatigue analysis. For default 12 (Real > 0.0) 

B1_SPi  The first fatigue strength
exponent. It is the slope of the first segment of
SN curve in loglog scale. Here i=1, 2, 3 represent sheet 1, sheet 2, and nugget, respectively in spot weld fatigue analysis. For default 12 (Real < 0.0) 

NC1_SPi  In onesegment
SN curve, this is the cycle limit of
endurance (NC1 in Figure 1). In twosegment SN curve, this is the transition point (NC1 in Figure 3). Here i=1, 2, 3 represent sheet 1, sheet 2, and nugget, respectively in spot weld fatigue analysis. For default 12 (Real ≥ 1000.0) 

B2_SPi  The second fatigue
strength exponent. It is the slope of the second segment of
SN curve in loglog scale. Here i=1, 2, 3 represent sheet 1, sheet 2, and nugget, respectively in spot weld fatigue analysis. Default = 0.0 (Real < 0.0 ) 

FL_SPi  Fatigue Limit. No damage
occurs if the stress range is less than FL
(FL in Figure 1 and
Figure 3). 6 Here i=1, 2, 3 represent sheet 1, sheet 2, and nugget, respectively in spot weld fatigue analysis. (Real ≥ 0.0, or blank) 

SE_SPi  Standard Error of
Log(N). Here i=1, 2, 3 represent sheet 1, sheet 2, and nugget, respectively in spot weld fatigue analysis. Default = 0.0 (Real ≥ 0.0) 

SMWLD  Indicates that the fatigue material properties for seam weld fatigue analysis are to follow. The following seam weld properties are only applicable to the Volvo method.  
MSSi  Mean Stress Sensitivity
parameters for mean stress correction based on FKM Guidelines. These
are used only if the UCORRECT field of the
SPWLD continuation line on
FATPARM is set to FKM or
FKM2. 11
Note: MSS1, MSS3, and
MSS4 can be blank only if all of them
are blank. If one of them is specified, then all four of
MSS1, MSS2,
MSS3, and MSS4
should be input.


A/R 
Defines the interpretation of the defined SN
curve.


SR1_SMi  Fatigue strength
coefficient. It is the stress range intercept of
SN curve at 1 cycle in loglog scale. Here i=1, 2 represent bending SN and membrane SN, respectively in seam weld fatigue analysis. For default 13 (Real > 0.0) 

B1_SMi  The first fatigue strength
exponent. It is the slope of the first segment of
SN curve in loglog scale. Here i=1, 2 represent bending SN and membrane SN, respectively in seam weld fatigue analysis. For default 13 (Real < 0.0) 

NC1_SMi  In onesegment
SN curve, this is the cycle limit of
endurance (NC1 in Figure 1). In twosegment SN curve, this is the transition point (NC1 in Figure 3). Here i=1, 2 represent bending SN and membrane SN respectively in seam weld fatigue analysis. For default 13 (Real ≥ Nc_stat) 

B2_SMi  The second fatigue
strength exponent. It is the slope of the second segment of
SN curve in loglog scale. Here i=1, 2 represent bending SN and membrane SN, respectively in seam weld fatigue analysis. Default = 0.0 (Real ≤ 0.0) 

FL_SMi  Fatigue Limit. No damage
occurs if the stress range is less than FL
(FL in Figure 1 and
Figure 3). 6 Here i=1, 2 represent bending SN and membrane SN respectively in seam weld fatigue analysis. (Real > 0.0, or blank) 

SE_SMi  Standard Error of
Log(N). Here i=1, 2 represent bending SN and membrane SN respectively in seam weld fatigue analysis. Default = 0.0 (Real ≥ 0.0) 

SMWLD  Indicates that the fatigue material properties for seam weld fatigue analysis are to follow. The following seam weld properties are only applicable to the Joint Line method. 15  
NORMAL  Flag indicates that the SN curve properties in this block are for Normal Stress. 15  
MSSNi  Mean Stress Sensitivity
parameters for mean stress correction for Normal Stress SN curve
based on FKM Guidelines. These are used only if the
UCORRECT field of the
SMWLD continuation line on
FATPARM is set to FKM or
FKM2. 11
Note: MSS1, MSS3, and
MSS4 can be blank only if all of them
are blank. If one of them is specified, then all four of
MSS1, MSS2,
MSS3, and MSS4
should be input.


A/R  Defines the interpretation
of the defined Normal Stressbased SN curve.


SR1_SMNi  Fatigue strength
coefficient for Normal Stressbased SN curve. It is the stress range
intercept of SN curve at 1 cycle in loglog scale. Here i=1, 2 represent transverse SN and longitudinal SN, respectively for Normal Stressbased SN curve in seam weld fatigue analysis. For default, 13 (Real > 0.0) 

B1_SMNi  The first fatigue strength
exponent for Normal Stressbased SN curve. It is the slope of the
first segment of SN curve in loglog scale. Here i=1, 2 represent transverse SN and longitudinal SN, respectively for Normal Stressbased SN curve in seam weld fatigue analysis. For default, 13 (Real < 0.0) 

NC1_SMNi  In onesegment SN curve,
this is the cycle limit of endurance for Normal Stressbased SN
curve (NC1 in Figure 1). In twosegment SN curve, this is the transition point for Normal Stressbased SN curve (NC1 in Figure 3). Here i=1, 2 represent transverse SN and longitudinal SN, respectively for Normal Stressbased SN curve in seam weld fatigue analysis. For default, 13 (Real > Nc_stat) 

B2_SMNi  The second fatigue
strength exponent for Normal Stressbased SN curve. It is the slope
of the second segment of SN curve in loglog scale. Here i=1, 2 represent transverse SN and longitudinal SN, respectively for Normal Stressbased SN curve in seam weld fatigue analysis. Default = 0.0 (Real < 0.0) 

FL_SMNi  Fatigue Limit for Normal
Stressbased SN curve. No damage occurs if the stress range is less
than FL (FL in Figure 1 and Figure 3). 6 Here i=1, 2 represent transverse SN and longitudinal SN, respectively for Normal Stressbased SN curve in seam weld fatigue analysis. (Real > 0.0, or blank) 

SE_SMNi  Standard Error of Log(N)
for Normal Stressbased SN curve. Here i=1, 2 represent transverse SN and longitudinal SN, respectively for Normal Stressbased SN curve in seam weld fatigue analysis. Default = 0.0 (Real > 0.0) 

SMWLD  Indicates that the fatigue material properties for seam weld fatigue analysis are to follow. The following seam weld properties are only applicable to the Joint Line method. 15  
SHEAR  Flag indicates that the SN curve properties in this block are for Shear Stress. The Shear Stress block is optional for Joint Line Seam Weld method. 15  
MSSSHi  Mean Stress Sensitivity
parameters for mean stress correction for Shear Stress SN curve
based on FKM Guidelines. These are used only if the
UCORRECT field of the
SMWLD continuation line on
FATPARM is set to FKM or
FKM2. 11
Note: MSS1, MSS3, and
MSS4 can be blank only if all of them
are blank. If one of them is specified, then all four of
MSS1, MSS2,
MSS3, and MSS4
should be input.


A/R  Defines the interpretation
of the defined Shear Stressbased SN curve.


SR1_SMSH  Fatigue strength
coefficient for Shear Stressbased SN curve. It is the stress range
intercept of SN curve at 1 cycle in loglog scale. For default, 13 (Real > 0.0) 

B1_SMSH  The first fatigue strength
exponent for Shear Stressbased SN curve. It is the slope of the
first segment of SN curve in loglog scale. For default, 13 (Real < 0.0) 

NC1_SMSH  In onesegment SN curve,
this is the cycle limit of endurance for Shear Stressbased SN curve
(NC1 in Figure 1). In twosegment SN curve, this is the transition point for Shear Stressbased SN curve (NC1 in Figure 3). For default, 13 (Real > Nc_stat) 

B2_SMSH  The second fatigue
strength exponent for Shear Stressbased SN curve. It is the slope
of the second segment of SN curve in loglog scale. Default = 0.0 (Real < 0.0) 

FL_SMSH  Fatigue Limit for Shear
Stressbased SN curve. No damage occurs if the stress range is less
than FL (FL in Figure 1 and Figure 3). 6 (Real > 0.0, or blank) 

SE_SMSH  Standard Error of Log(N)
for Shear Stressbased SN curve. Default = 0.0 (Real > 0.0) 

SNTBL  Flag to define multiple SN curves 17.  
REFTYPE  Reference type identifying
the type of multiple SN curve definition.
No default 

logSE  Standard Error of
log(Stress) Default = 0.0 (Real > 0.0) 

Nc1  Fatigue transition point.
After this point, fatigue strength is offset by the surface
correction factor. Before this point, fatigue strength is
proportionally reduced. Default = NC (Real > Nc_stat) 

Nc  Endurance limit. Number of
cycles at which damage can be considered zero. Default = 1.0E+8 (Real > 1.0E+5) 

FINDLEY  Constant k in the Findley
model. Default = 0.3 (Real > 0.0) 

STSTYPE  Stress type.


REFVALi  Reference values for which
each curve is defined. Depending on REFTYPE,
reference values can be either Mean stress, Rratio or Life. No default 

Ai  Depending on
STSTYPE, Ai values can be one of stress
amplitude, stress range, or max stress. No default 

Bi  Depending on
REFTYPE, Bi values can be
life (REFTYPE=MEAN or
RRATIO) or mean stress
(REFTYPE=LIFE). No default 

STFAIL  Flag indicating that material properties regarding static failure are to follow.  
ALPHA  Scale factor to determine the stress amplitude threshold to
trigger static failure. The stress amplitude threshold is ALPHA*UTS. Default = 0.9 (0 < Real ≤ 1.0) 

Nc_stat  Number of cycles at which static failure transition occurs.
Default = 1000 (0 < Integer < NC1) 

b0  Slope for static failure region. Default = Blank (b0 ≤ 0.0) 

HAIGH  Flag indicating that the Haigh diagram is to follow to define static failure region.  
Si  Stress Amplitude or Stress Range (depending on
A/R field). Default = Blank (Real > 0.0) 

Mi  Mean Stress. Default = Blank (Real) 

A/R  Determines the interpretation of the SN curve.


STRESS  Flag indicating that stress scaling and offset parameters are to follow. 26  
SCALE  Scale factor to scale stress before damage calculation. Default = 1.0 (Real) 

OFFSET  Offset value to offset stress before damage
calculation. Default = 1.0 (Real) 

EN  Indicates that fatigue material properties for EN analysis are following.  
Sf  Fatigue strength
coefficient. No default (Real > 0.0) 

b  Fatigue strength
exponent. No default (Real < 0.0) 

c  Fatigue ductility
exponent. No default (Real < 0.0) 

Ef  Fatigue ductility
coefficient. No default (Real > 0.0) 

np  Cyclic strainhardening
exponent. No default (Real > 0.0) 

Kp  Cyclic strength
coefficient. No default (Real > 0.0) 

Nc  Reversal limit of
endurance. One cycle contains two reversals. 6
Default = 2.0E8 (Real > 1.0E5) 

SEe  Standard Error of Log
(elastic strain). Default = 0.0 (Real ≥ 0.0) 

SEp  Standard Error of Log
(plastic strain). Default = 0.0 (Real ≥ 0.0) 

SEc  Standard Error of Cyclic
StressStrain curve. 25 Default = 0.0 (Real ≥ 0.0) 

A/R  Defines the interpretation
of the defined EN curve.


tfp  Shear Fatigue Strength
coefficient (
${\tau}_{f}^{\text{'}}$
) based on amplitude. This value
should be one half of the value defined for tfp
on the SN continuation line. Default = Blank (Real > 0.0) 

gfp  Shear Fatigue Ductility
coefficient (
${\gamma}_{f}^{\text{'}}$
) Default = Blank (Real > 0.0) 

bg  Shear Fatigue Strength
exponent (
${b}_{\gamma}$
) Default = $b$ (Real ≤ 0.0) 

cg  Shear Fatigue Ductility
exponent (
${c}_{\gamma}$
) Default = $c$ (Real ≤ 0.0) 

CoefKp90  Coefficient value (see
Plasticity model for strainbased Fatigue Analysis in the User
Guide). Default = 1.2 (Real > 0.0) 

Coefnp90  Coefficient value (see
Plasticity model for strainbased Fatigue Analysis in the User
Guide). Default = 1.0 (Real > 0.0) 

MXSTRN  Maximum Strain value for
StrainLife Approach. The default value is 0.02 (corresponds to 2%
strain). In multiaxial fatigue analysis, this value is used as maximum allowable strain in the plasticity model regardless of whether the load is proportional or nonproportional. If accumulated strain is greater than this value, OptiStruct does not calculate actual damage but assigns a larger value of damage (10.0). In uniaxial fatigue, 10% of this value (0.2% by default) is used as maximum possible strain amplitude. If strain amplitude is greater than 10% of this value, a warning message will be issued. Actual damage is still calculated. Default = 0.02 (Real > 0.0) 14 

FSParm  Constant k for the
FatemiSocie model. Default = 0.3 (Real ≥ 0.0) 

BMParm  Constant S for the
BrownMiller model. Default = 1.0 (Real ≥ 0.0) 

FOS  Indicates that material properties for factor of safety analysis are defined in the following fields.  
Tfl  Torsion fatigue limit. A
Real or Integer value can be specified. If an integer is input, then
it references the ID of a TABLES1 Bulk Data Entry
that defines the intersection points. The Xvalues represent
Hydrostatic Pressure, and Yvalues represent Shear. 10 No default (Real > 0.0 or Integer) 

Hss  Hydrostatic stress
sensitivity. No default (Real > 0.0) 

STHETA  Safe zone angle. If the
angle of a point in the domain is lower than the Safe zone angle, it
is considered safe (FOS is 1.0e20). 10 Default = 0.0 (Real ≥ 0.0) 

SSHEAR  Shear Threshold for the
Safe zone. If the microscopic shear stress is lower than this value,
it is considered safe (FOS is 1.0e20). 10 Default = 0.0 (Real ≥ 0.0) 

STSGRD  Indicates that material properties for stress gradient effect are defined in the following fields.  
CRTDIS  Critical Distance for
Critical Distance method in Stress Gradient Effect.
(Real) 

FKM_aG 
${a}_{G}$
value in FKM stress gradient effect.
Default = 0.5 (Real) 

FKM_bG 
${b}_{G}$
value in FKM stress gradient effect.
Default = 2700 (Real) 

TFKM  TABLES1
ID to define notch correction factor with respect to the related
stress gradient in FKM stress gradient effect. If
TFKM is specified, the relationship between
related stress gradient and notch factor defined by
TFKM takes precedence over
FKM_aG and FKM_bG.
Default = Blank (Integer) 

SOLDER  Optional continuation line to define solder fatigue material property data.  
Wp  Plastic work density for
Failure in DIFFCTE method. 16 Default = 0.0019 (Real > 0.0) 

Wrcp  Creep energy density for
failure in SYEDW method. 24 Default = 0.0019 (Real > 0.0) 

b1w  Exponent of SYEDW
method. Default = 1.0 (Real) 

Cp  Inverse of creep ductility
in SYEDEPS method. 24 Default = 0.0513 (Real > 0.0) 

b1e  Exponent of
SYEDEPS method. Default = 1.0 (Real) 
Figures
Comments
 UTS or YS is used in mean stress correction (SN) and surface finish correction (SN and EN). If both UTS and YS are defined, UTS will be used. It is not allowed that both UTS and YS are blanks.
 SN data defined in
the MATFAT card is expected to be obtained from standard
experiments that are fully reversed tests on mirrorpolished specimens. Fully
reversed tests imply that the stress ratio (
$R={S}_{\mathrm{min}}/{S}_{\mathrm{max}}$
) is equal to 1.0. Therefore, any SN curve input
on MATFAT entry should be obtained with a stress ratio
(R) equal to 1.0.Note: Only in the case of Spot Weld SN curve, the R field on the SPWLD continuation line can be used to indicate the stress ratio at which the input SN curve is obtained.
 In SN approach,
including Spot Weld and Seam Weld, OptiStruct
calculates damage based on the Stress Range. If the SN curve
is defined based on Stress Amplitude, OptiStruct
converts the Amplitudebased SN curve to a Rangebased
SN curve. ECHO will print the converted
SN curves. SN curves are defined in
Stress range  Cycle form. Stress range is the algebraic difference between the
maximum and minimum stress in a cycle. SN curve is expressed
as:$${S}_{r}=SRI1{({N}_{f})}^{b}$$Where,
 ${S}_{r}$
 Stress range
 $SR1$
 Fatigue strength coefficient
 ${N}_{f}$
 Cycle number
 $b$
 Fatigue strength exponent
Note: For a special case, wherein the following two conditions are satisfied for SN Fatigue (Uniaxial and Multiaxial): SRI1 is greater than 2*UTS, and
 Stress amplitude after mean stress correction is greater than
90% of UTS.
Then, the equation used to calculate Fatigue Damage and Life is different from the SN curve mentioned above. Therefore, you may notice a sudden increase in the value of damage for an element when the above two conditions are satisfied for it. This is done to allow for the higher possibility of failure when the corrected mean stress is so close to UTS of the material, and additionally takes into account the situation where the value of SRI1 is extremely high (greater than 2*UTS).
 In EN approach,
OptiStruct calculates damage based on the Strain
Amplitude. If the EN curve is defined based on Strain Amplitude, OptiStruct converts the Rangebased EN
curve to an Amplitudebased EN curve. ECHO will print the
converted EN curves. EN curves are defined
in Strain amplitude  Reversal form. Strain amplitude is half of the algebraic
difference between the maximum and minimum strain in a cycle, and one strain
cycle contains two reversals. EN curve is expressed as:
$${\epsilon}_{a}=\frac{{S}_{f}^{\text{'}}}{E}{(2{N}_{f})}^{b}+{\epsilon}_{f}^{\text{'}}{(2{N}_{f})}^{c}$$Where,
 ${\epsilon}_{a}$
 Strain amplitude
 ${S}_{f}^{\text{'}}$
 Fatigue strength coefficient
 $E$
 Young's modulus
 ${N}_{f}$
 Cycle number
 $b$
 Fatigue strength exponent
 ${\epsilon}_{f}^{\text{'}}$
 Fatigue ductility coefficient, and c is the fatigue ductility exponent
 Empirical formula can be used to
estimate SN/EN data from ultimate tensile
strength (UTS) and Young's modulus (
$E$
):
Table 1. Estimated SN Data from Empirical Formula*(* Source: YungLi Lee, Jwo. Pan, Richard B. Hathaway and Mark E. Barekey. Fatigue testing and analysis: Theory and practice, Elsevier, 2005) Material SRI1 b1 Nc1 b2 Steel 4.263*UTS 0.125 1E6 0.0 Aluminum alloys (UTS<336MPa) 2.759*UTS 0.062 5E8 0.0 Aluminum alloys (UTS≥336MPa) 0.131*UTS^{1.526} 0.3790.175*log(UTS) 5E8 0.0 Table 2. Estimated EN Data from UTS and E**(** Source: Anton Baumel and T. Seeger, Materials Data for Cyclic Loading, Elsevier, 1990) Unalloyed and LowAlloy Steels Aluminum and Titanium Alloys ${\sigma}_{f}^{\text{'}}$ 1.5*UTS 1.67*UTS $b$ 0.087 0.095 ${\epsilon}_{f}^{\text{'}}$ 0.59 $\Psi $ 0.35 c 0.58 0.69 K' 1.65*UTS 1.61*UTS n' 0.15 0.11 $$\Psi =\left\{\begin{array}{l}1.0\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{0.17em}}UTS/E\le 3\times {10}^{3}\\ 1.357125*UTS/E\text{\hspace{1em}}UTS/E>3\times {10}^{3}\end{array}\right\}$$  For onesegment SN
curve (b2=0.0), if FL is blank, the
fatigue limit is the stress range at Nc1. If both
Nc1 and FL are defined, the more
conservative value (larger damage) will be used (Figure 1).
For twosegment SN curve, if FL is blank, the fatigue limit is 0.0.
When fatigue optimization is performed, fatigue limit FL of SN data and reversal limit Nc of EN data will be ignored in order to get continuous changes in fatigue results when stress/strain changes.
 If tfp or gfp are not available, OptiStruct calculates this automatically. See FatemiSocie Model in the User Guide.
 Although tfp is defined in EN, it can be used both in EN (FS model) and SN (Findley). tfp should be defined based on the amplitude.
 If tfp is not defined for SN, OptiStruct calculates this automatically. See Findley Model in the User Guide.
 The Tfl field can be used to define either a value (constant slope) or a table (multiple slopes) to specify the Failure zone. Additionally STHETA and SSHEAR fields can be used to determine safezones for FOS calculation.
 See Mean Stress Correction in the Fatigue section of the User Guide for more information.
 If SRI_SPi,
B1_SPi, and NC1_SPi are not defined
for Spot Weld Fatigue, then the following values are used as the default for the
SN curve.
 Sheet 1: SRI_SP1=28218.0 MPa, B1_SP1=0.34, NC1_SP1=2000000.0
 Sheet 2: SRI_SP2=28218.0 MPa,
B1_SP2=0.34,
NC1_SP2=2000000.0
These default SN curves are based on a stress ratio (R) equal to 0.0
Only sheet damage (sheet 1 and sheet 2) at spot weld locations will be analyzed regardless of the value of SPTFAIL field on PFATSPW entry.
Mean stress correction for R=0.0 will be carried out using FKM guidelines regardless of the value of CORRECT field on SPWLD continuation line on FATPARM entry.
 If SRI_SWi,
B1_SWi, and NC1_SWi are not defined
for Seam Weld Fatigue, then the following values are used as the default for the
SN curve.
 Bending SN curve: SRI_SW1=3254.0 MPa, B1_SW1=0.1429, NC1_SW1=2000000.0
 Membrane SN curve: SRI_SW2=6094.0 MPa,
B1_SW2=0.2270,
NC1_SW2=2000000.0
These default SN curves are based on a stress ratio (R) equal to 1.0
 In uniaxial fatigue, the calculated damage needs further checking, because the excessive strain implies that original analysis (static or transient) result could be beyond linear range.
 For the Joint Line Seam Weld method,
two SN curve blocks are available for input.
The first block (starting from field NORMAL on the SMWLD continuation line), defines the SN curves based on Normal Stress. There are two SN curve lines for this, the first is for Transverse Stress SN curve, and the second is for Longitudinal Stress SN curve. The Transverse Stress SN curve is mandatory, while the Longitudinal Stress SN curve is optional (if not input, then Fatigue Damage/Life is not calculated for Longitudinal Stress).
The second block (starting from field SHEAR on the SMWLD continuation line), defines the SN curve based on Shear Stress. This second block is optional (if not input, then Fatigue Damage/Life is not calculated for Shear Stress).
 The default value for the SnAgCu solder is in MPa units.
 SNTBL continuation line defines multiple SN curves/Haigh diagram for stresslife approach. Only one instance of SNTBL is allowed in a MATFAT entry.
 SNTBL option is supported in uniaxial and multiaxial fatigue. It is generally supported for static, transient, and vibration load fatigue (including random, sinesweep, sineonrandom, sinesweeponrandom, etc.).
 If a single Haigh diagram is defined, no damage will be calculated. Damage will be reported as 0.0. Only safety factor will be calculated if FOS output is requested.
 If multiple SN curves/Haigh diagrams are defined, safety factor is calculated with an internally created target Haigh diagram.
 If multiple SN curves are defined, and mean stress correction is not INTPLTN, an SN curve with stress ratio =1 or mean stress =0 must be specified.
 If multiple Haigh diagrams are defined, mean stress correction must be INTPLTN.
 In multiaxial SN, any mean stress correction for tensile stress (FKM or GOODMAN) will trigger INTPLTN for damage due to tensile stress if multiple SN curves/Haigh diagrams are defined.
 The default value if for SnAgCu solder represented by the hyperbolic creep material. The default value for Wcrp is in MPa units. In damage calculation, the default value for Wcrp is converted to that of userdefined stress units in FATPARM.
 The Standard Error of Cyclic
StressStrain curve is defined via the SEc field for EN
fatigue. The value of SEc is used to modify the cyclic
strength coefficient as: $$K\text{'}=K\text{'}*{10}^{\left(z*n\text{'}*SEc\right)}$$Where,
 $K\text{'}$
 Cyclic strenght coefficient.
 $n\text{'}$
 Strain Cyclic hardening exponent.
 z
 z value of normal distribution calculated using the certainty of survival.
 The updated stress value is
calculated as follows after SCALE and
OFFSET are applied. The unit of OFFSET
is the same as the stress unit defined on the MATFAT entry.
This feature is currently not supported for vibrational fatigue and Dang Van.
updated combined stress = combined stress*SCALE + OFFSET
updated combined strain = combined strain*SCALE + OFFSET/E
 Temperaturedependent Haigh Diagrams are supported via the MATFATT Bulk Data Entry.
 This card is represented as a material in HyperMesh.