Small Defect Analysis

Traditional theories of fatigue evaluation based on either stress concentration factors or stress intensity factors are applicable to defects which can be seen with the naked eye, defects larger than about 1mm. Small artificial notches, such as surface defects like corrosion pits and scratches, naturally occuring defects and nonmetallic inclusions are all of practical importance. As the defect size decreases, traditional theories are longer accurate and special techniques must be used.

Enter as much data as you know. If it is not enough, you will be asked for more. Fields with a light blue/gray background represent the minimum required data to begin calculations. Other data may become necessary as calculation proceeds. Pressing the button provides help in the form of an equation or default information for a parameter.

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Stresses or strains can be entered as either the maximum and minimum values or as the alternating stress and mean stress. Remember that the alternating stress is only one half of the stress range. A safety factor will be computed whenever the stresses or strains are entered. You can also enter a safety factor and the allowable stresses will be computed. In this case, you must select an option for the mean stress. For example you can select a value for the maximum or minimum stress. Alternatively, you could choose a mean stress or stress ratio.

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Maximum   Smax or emax =
Minimum   Smin or emin =
OR
Alternating   Sa or ea =
Mean   Sm or em =
OR
Safety Factor n =
Mean Stress Definition =

Material

This analysis requires either the material hardness or ultimate strength. The other material properties will be estimated from one of these two properties if they are not entered. You may also look for properties in the stress-life material finder.

Name
Type
Hardness
OR
Ultimate Strength Su =
Elastic Modulus   E =
Fatigue Limit   SFL =

Defect Size and Shape

Small defects are often 3 dimensional and irregularly shaped. The square root of the projected area, √ Area  is a good measure of defect size. You may enter √ Area  directly or you can select the defect shape and enter it's dimensions.


hole
inclusion
porosity

microcrack
scratch
indentation

d1 =
d2 =
OR
√ Area  =

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