SNDATA

Stress-Life Method Material Fatigue Data

Description: Specifies material property data needed for fatigue analysis. This entry is used if a MAT1, MAT2, MAT8, MAT9, or MAT12 entry is specified with the same MID.

Format:

Example:

Field	Definition	Type	Default
MID	Identification number of a MAT1, MAT2, MAT8, MAT9, or MAT12 entry.	Integer > 0	Required
B	S-N curve slope. See Remark 3.	Real > 0.0	See Remark 2
SU	Intercept stress level. Typically taken as the material ultimate stress. See Remark 3.	Real > 0.0	See Remark 2
N0	Intercept cycles. See Remark 3.	Integer > 0	1000
KF	Factor applied to compensate for life reduction effects such as finish, corrosion, and notch effects. See Remark 3.	Real > 0.0	1.0
BE	Slope after endurance limit. See Remark 4.	Real > 0.0	0.1*B
SE	Endurance limit. See Remark 3.	Real ≥ 0.0	0.2*SU

Remarks:

1. SNDATA entries must all have unique set identification numbers.
2. VFATIGUE and FATIGUE entries provide defaults to SNDATA. Values not specified on SNDATA entries will be replaced with ones from the VFATIGUE or FATIGUE entry STRESS continuation.
3. The S-N curve shown in Figure 1 is characterized by the following equations:

   If

   

   If

   

   where,

   is the number of cycles to failure

   is the amplitude of input stress (S_max - S_min)/2

   is the number of failure cycles at the endurance limit

   and the slope B shown in Figure 1 is calculated by:

   

4. A small slope is required to prevent infinite life. See Figure 1.

   

   Figure 1. Stress-Life Curve Format