FATLOAD

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`

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, 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

Comments

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.
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:(1)
${(σ_{i j} (t))}_{e v e n t} = \sum_{l = 1}^{n} [\frac{{(σ_{i j . F E A})}_{l}}{L D M_{l}} (P {(t)}_{l} S c a l e_{l} + O f f s e t_{l})]$

Subsequently, Rainflow counting is conducted using ${(σ_{i j} (t))}_{e v e n t}$ 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:(2)
${(σ_{i j} (t))}_{l o a d} = \frac{{(σ_{i j})}_{l}}{L D M_{l}} (P {(t)}_{l} S c a l e_{l} + O f f s e t_{l})$

Where,

${(σ_{i j} (t))}_{e v e n t}$

Superposed stress tensor for the entire fatigue event, as a function of time $t$ .

${(σ_{i j} (t))}_{l o a d}$

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.

${(σ_{i j . F E A})}_{l}$

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).

$L D M_{l}$ , $P {(t)}_{l}$ , $S c a l e_{l}$ , and $O f f s e t_{l}$

Corresponding LDM, TABFAT, Scale, and Offset field values for each FATLOAD entry, $l$ .
A referenced MBD subcase allows Fatigue Optimization using the ESL method. Fatigue Analysis is not supported for this solution, only optimization is supported.
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.
This card is represented as a load collector in HyperMesh.