# Example of SN Interpolation Schemes

Suppose that you defined an SN curve that has the following two consecutive data points:
No. of Cycles (N) Log (N) Alternating Stress (S) Log (S)
1000 3 50,000 psi 4.699
100,000 5 40,000 psi 4.602
For a stress of 45,000 psi, the program reads the number of cycles based on the SN interpolation scheme as follows:
 Log-Log SN Curve. The X- and Y-axes represent the logarithm of the number of cycles and the stress, respectively. The program takes the logarithm of 45000 (which is 4.653) and performs linear interpolation. Using this procedure, the number of cycles is 103.944 = 8,790. Semi-Log SN Curve. The X-axis represents the logarithm of the number of cycles and the Y-axis represents the stress. At stress value of 45,000 psi, the program performs linear interpolation and calculates the number of cycles as 104=10,000. Linear SN Curve. The X- and Y-axes represent the number of cycles and the stress, respectively. At a stress value of 45,000 psi, the program performs linear interpolation and calculates the number of cycles as 50,500.