FATPARM

Format

Definitions

Comments

1. 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.
2. 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.
3. 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 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.
5. UCORRECT=GERBER2 improves the GERBER method by ignoring the effect of negative mean stress.
6. UCORRECT=MORROW2 improves the MORROW method by ignoring the effect of negative mean stress.
7. UCORRECT=SODERBE is slightly different from GOODMAN, the mean stress is normalized by yield stress instead of ultimate tensile stress.(1)
   $$S_e=\frac{S_a}{\left(1-\frac{S_m}{S_y}\right)}$$
   Where,

   $S_e$

   Equivalent stress amplitude

   $S_a$

   Stress amplitude

   $S_m$

   Mean stress

   $S_y$

   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 = 2*RMS Stress*FACSREND. RMS stress is output from Random Response Subcase.
11. The width of the stress ranges is calculated as DS=SREND/NBIN.
12. Random Response Fatigue analysis is supported for both SN and EN Fatigue Analysis. For EN fatigue, currently Uniaxial fatigue and COMBINE=VONMISES are only supported.
13. For Sine Sweep Fatigue:
    • Currently, only von Mises is supported for the COMBINE field.
    • Only Uniaxial Fatigue analysis is supported.
    • SN and EN for Solid and Shell elements are supported.
    • Weld Fatigue is not supported.
    • Only one FATLOAD is allowed on a FATEVNT entry
14. 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.
15. 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.
16. 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.
17. This card is represented as a load collector in HyperMesh.