S-N Curve Calculator

Reviewed By: Patrick Myers (BSME)

Enter the stress range, the material constant K, and the material constant m into the SN Curve Calculator. The calculator will evaluate the SN Curve.

S-N (solve 1 of 4)

Fit K (m known)

Fit m & K (two points)

Enter any 3 values to calculate the missing variable

Stress Range

Material Constant K (cycles · [stress unit]^m)

Material Constant m SN Curve (number of cycles to failure)

SN Curve Formula

The following formula is used to calculate the SN Curve.

N = K * S^-m

Variables:

N is the number of cycles to failure
S is the stress range
K is the material constant K
m is the material constant m

To calculate the SN curve, raise the stress range to the power of -m (equivalently, divide by the stress range raised to m), then multiply by the material constant K.

How to Calculate SN Curve?

The following steps outline how to calculate the SN Curve.

First, determine the stress range.
Next, determine the material constant K.
Next, determine the material constant m.
Next, gather the formula from above: N = K * S^-m.
Finally, calculate the SN Curve.
After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

stress range S = 400

material constant K = 4.472136×10⁶ (cycles · [stress unit]^m)

material constant m = 0.25

N = K * S^-m = 4.472136×10⁶ * 400^-0.25 ≈ 1,000,000 cycles