How to Calculate a Stress Intensity Factor

Write out the formula, or formulas, needed for determining the stress. The specific formula will depend on the method being employed and the factor you are determining. Typically, all formulas use the letter “K” to represent the stress intensity factor.

Measure the crack length. Use an appropriate unit of measure based on the size of the crack so that you can get the most accurate measurement. You may need to use millimeters or smaller depending on how small the crack is.

Determine the fracture toughness. This information is based on the type of material and may be supplied by the manufacturer.

Determine the size and geometry of the crack. In most formulas this is represented by a lowercase “g.”

Calculate the energy release rate. There is a separate formula for this and the result is represented by the letter “G.” To calculate "G," divide “K” by the plane stress conditions which are represented by the letter “E.”

Factor the amount of stress being placed on the building material. This could be represented as nominal far field stress, applied stress, ancillary stress or boundary stress. You may need to factor for multiple types of stress and multiple degrees of stress applied to the material. Each one will be represented by a different symbol.

Find and factor any other variables needed for the specific equations.

Plug the variables into your formula and solve to determine what “K” is. The result is the stress intensity factor.

Repeat the steps as many times as needed to find the lowest stress intensity factor possible for the strength and integrity of the building material to remain intact.