Definitions
Endurance Limit
As the alternating stress gets smaller, the material can take more stress cycles before it fails due to fatigue. The endurance limit is the highest alternating stress that does not result in fatigue failure. In other words, if the alternating stress is equal to or lower than the endurance limit, the number of stress cycles to cause failure becomes very large (practically infinite). The endurance limit is usually defined for zero-mean alternating stresses. The endurance limit is also called the fatigue limit. Some metals do not have a measurable endurance limit.
Alternating Stress
The alternating stress is defined as (s
max - s
min)/2 where s
max and s
min are the maximum and minimum stresses respectively.
Stress Range
Stress = (smax - smin)
Mean Stress
Mean stress = Sm = (smax + smin)/2
Mean stress correction
Stress Ratio
Stress ratio = smin/smax
Fatigue Life
Fatigue life, at a given alternating stress level and mean, is the number of cycles required to cause failure due to fatigue.
Fatigue Strength
The stress at which fatigue failure occurs after a given number of loading cycles.
Related Topics
Fatigue Analysis
Fatigue Events
Performing Fatigue Analysis
Fatigue Plots