Use the Fatigue SN Curves tab to define SN curves for a fatigue study. SN curves are used in fatigue studies only. Some materials in the material library have fatigue SN curves already defined. These materials are identified by a suffix (SN) attached to the end of their names in the material list of the material library.
The Fatigue SN Curves tab is only available when SolidWorks Simulation is added in.
Source
Sets the interpolation scheme and the source of the data.
Interpolate 
Sets the scheme for interpolating alternating stresses against the number of cycles of SN curve.

Loglog.
Logarithmic interpolation (base 10) for the number of cycles and the alternating stress. This option is recommended for SN curves with few data points that are widely scattered on both axes unless the curve is better fit by another interpolation scheme.
 Semilog. Linear interpolation for stress and logarithmic for number of cycles. This option is recommended for SN curves with relatively small stress range compared to variation in the number of cycles unless the curve is better fit by another interpolation scheme.
 Linear. Linear interpolation for both stress and number of cycles. This option is recommended for SN curves with many data points unless the curve is better fit by another interpolation scheme
Example
In some cases, the SN curve is available in the form of an equation that is obtained by fitting the experimental data. In such cases, if the equation matches one of the interpolation schemes, it may be adequate to define only the extremes of the curve as data points and use the proper interpolation scheme.

Define 
Define curve data manually. Select from up to ten curves in the menu. 
Derive from material elastic modulus 
Derive the SN curve automatically based on ASME SN curves and the moduli of elasticity of the reference material and the active material. The source SN shows in the Preview area.

Based on ASME Austentic Steel curves
 Based on ASME Carbon Steel curves
The SN curve is derived by dividing each stress value of the reference SN curve by the modulus of elasticity of the reference ASME material and multiplying it by the modulus of elasticity of the current material. The associated numbers of cycles remain unchanged.

Table data
Lists curve data. Available only when
Define is selected in the
Source box.
Stress Ratio (R) 
Available only when Custom defined is selected under Select material source. 
Units 
Alternating stress units. If you are typing values in, make sure to select the desired units that you want to use before entering the values.

Curve data table 
Enter pairs of number of cycles and alternating stress values if you are defining the curve manually. If the curve is derived based on a reference ASME SN curve, the scaled curve is listed. You can use copy and paste to populate the table.

File 
Imports curve data from a file. Available only when Custom defined is selected under Select material source. 
View 
Displays a graph of the current data in the table. 
Delete 
Deletes the selected data row. Available only when Custom defined is selected under Select material source. 
To apply the same SN curve to bodies with different materials, in the fatigue study tree rightclick
Parts , and select
Apply Fatigue Data to All Bodies.