Bulk Data Entry Defines fatigue loading parameters.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
FATLOAD ID TID LCID LDM Scale Offset LHFORMAT CHANNEL
SWEEP SR SRUNIT
HARMO Fi MAGi
LDHIST BGNSTP ENDSTP

Definitions

Field Contents SI Unit Example
ID Each FATLOAD card must have a unique ID. This identifier may be referenced by a FATEVNT definition.

No default (Integer > 0)

TID TABFAT or TABLEDi entry identification number.

References TABFAT ID:

If LCID references a Linear static subcase, TID should be a positive integer (Integer > 0) or blank. It can only be blank when SQNTL field is set on the FATEVNT entry.

If LCID references Transient or Random Response subcase, TID should be blank.

References TID on ASSIGN,DAC or ASSIGN,RPC:

If LCID references a Linear static subcase, TID should be a positive integer (Integer > 0). This TID should match the TID on ASSIGN,DAC or ASSIGN,RPC entries. If both TABFAT and ASSIGN,DAC have same TID, then the load history from TABFAT is not used, and is just ignored.

References TABLEDi ID:

If LCID references a Frequency Response subcase, then, TID references a TABLEDi table which defines a magnification load table.

If TID is left blank for Sine Sweep Fatigue analysis, then a scale factor of 1.0 is applied automatically to the Frequency Response output used for Sine Sweep calculations.

(Integer > 0 or blank)

LCID Subcase identification number of a Linear Static, Transient, Frequency Response, Random Response, or Multibody Dynamics (MBD) subcase. 3

No default (Integer > 0)

LDM The magnitude of the FEA load in the same units as those for the time history. It is ignored in fatigue analyses based on a transient analysis subcase. 2

Default = 1.0 (Real)

Scale Scale factor applied to the load or time history. It is ignored in fatigue analyses based on a transient analysis subcase.

Default = 1.0 (Real)

Offset Offset applied to the load or time history. It is ignored in fatigue analyses based on a transient analysis subcase.

Default = 0.0 (Real)

LHFORMAT Identifies the format of the load history information defined via TID field.
blank (Default)
DAC
The TID field identifies load history information from the corresponding .dac file which is referenced via ASSIGN,DAC entry. The TID on this FATLOAD should match with the corresponding TID on ASSIGN,DAC entry.
RPC
The TID field identifies load history information from the corresponding .rpc file which is referenced via ASSIGN,RPC entry. The TID on this FATLOAD should match with the corresponding TID on ASSIGN,RPC entry. Additionally, for RPC format, the channel should be identified by the CHANNEL field on this FATLOAD entry.

CHANNEL Identifies the channel which is used for the load history definition for the RPC format. This field is mandatory, if the LHFORMAT field is set to RPC.

Default = blank (Integer > 0)

SWEEP Flag indicating that the options for Sweep test are to follow.
SR Sweep rate. 4

No default (Real ≥ 0.0)

SRUNIT Unit of sweep rate.
OCTPM
Octave per minute
HZPS
Hertz per second

No default

HARMO Continuation line indicating the sine tone properties for Sine-on-Random Fatigue Analysis or fatigue calculation from Multiple Sine Tones Fatigue Analysis.
Fi Sine tone frequencies.

No default (Real)

MAGi Magnification factor to frequency response stress at the specified frequency (Fi).

If 0.0, the sine load at this frequency is ignored.

Default = 1.0 (Real)

LDHSIT Continuation line indicating the first output time step and the last output time step of a stabilized cycle in the underlying nonlinear analysis.
BGNSTP The first output time step of a stabilized cycle in the underlying nonlinear analysis.

Default = 1 (Integer)

ENDSTP The last output time step of a stabilized cycle in the underlying nonlinear analysis.

Default = blank (The last output time step)

1. This magnitude is used as a scale factor to normalize the finite element stresses/strains to obtain the stress/strain distribution due to a unit loading.
2. The equation below depicts how LDM, Scale and Offset values work together to scale the FEA stress tensor at time $t$ :

If SQNTL flag on FATEVNT is blank (default), all FATLOADs referenced on a particular FATEVNT are applied simultaneously.

The stress tensors at each time $t$ from each FATLOAD, for the entire fatigue event are calculated as:
${\left({\sigma }_{ij}\left(t\right)\right)}_{event}=\sum _{l=1}^{n}\left[\frac{{\left({\sigma }_{ij.FEA}\right)}_{l}}{LD{M}_{l}}\left(P{\left(t\right)}_{l}Scal{e}_{l}+Offse{t}_{l}\right)\right]$

Subsequently, Rainflow counting is conducted using ${\left({\sigma }_{ij}\left(t\right)\right)}_{event}$ to calculate the equivalent stress amplitude and mean stress. This is used to calculate damage and life for this fatigue event.

If SQNTL flag on FATEVNT is set, all FATLOADs referenced on a particular FATEVNT are applied sequentially, instead of simultaneously.

The stress tensors at each time $t$ from each FATLOAD are calculated as:(1)
${\left({\sigma }_{ij}\left(t\right)\right)}_{load}=\frac{{\left({\sigma }_{ij}\right)}_{l}}{LD{M}_{l}}\left(P{\left(t\right)}_{l}Scal{e}_{l}+Offse{t}_{l}\right)$
Where,
${\left({\sigma }_{ij}\left(t\right)\right)}_{event}$
Superposed stress tensor for the entire fatigue event, as a function of time $t$ .
${\left({\sigma }_{ij}\left(t\right)\right)}_{load}$
Stress tensor for the fatigue load, as a function of time $t$ .
$l$ represents FATLOAD entries defined on a particular FATEVNT and ranges from 1 to $n$ , where $n$ is total number of FATLOADs referenced on the particular FATEVNT entry of interest.
${\left({\sigma }_{ij.FEA}\right)}_{l}$
Stress tensor from static analysis for a FATLOAD entry, $l$ (TID referencing a TABFAT entry is only used for Static subcases. TID should be blank for Transient Analysis-based Fatigue Analysis).
$LD{M}_{l}$ , $P{\left(t\right)}_{l}$ , $Scal{e}_{l}$ , and $Offse{t}_{l}$
Corresponding LDM, TABFAT, Scale, and Offset field values for each FATLOAD entry, $l$ .
3. A referenced MBD subcase allows Fatigue Optimization using the ESL method. Fatigue Analysis is not supported for this solution, only optimization is supported.
4. If SR=0.0, then sweep does not occur. In this case, the damage at the first frequency (from FREQi entries) is calculated. Final damage is reported after being multiplied by T# in FATSEQ. Similarly, for the case of a single loading frequency being used in the FRF subcase, the damage is calculated at that frequency and the final damage is reported after multiplying by T# in FATSEQ.
5. When time history of underlying nonlinear analysis result is directly used as a load history in fatigue analysis, load history between BGNSTP and ENDSTP is only used in fatigue analysis. This feature can be used to choose stabilized cycle or to remove setup load of the nonlinear analysis.
6. This card is represented as a load collector in HyperMesh.