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Glossary
M10-94400-1
on original cross-sectional area without taking into ac-
count changes in area due to applied load. This some-
times is called conventional or engineering stress. True
stress is equal to the load divided by the instantaneous
cross-sectional area through which it acts.
Stress Amplitude.
One-half the range of fluctuating stress developed in a
specimen in a fatigue test. Stress amplitude often is used
to construct an S-N diagram.
Stress Concentration Factor.
Ratio of the greatest stress in the area of a notch or other
stress raiser to the corresponding nominal stress. It is a
theoretical indication of the effect of stress concentrators
on mechanical behavior. Stress concentration factor usu-
ally is higher than the empirical fatigue notch factor or
strength reduction ratio, because it does not take into ac-
count stress relief due to local plastic deformation.
Stress Ratio.
Ratio of minimum stress to maximum stress in one cycle
of loading in a fatigue test. Tensile stresses are consid-
ered positive and compressive stresses negative.
Stress Relaxation.
Decrease in stress in a material subjected to prolonged
constant strain at a constant temperature. Stress relaxa-
tion behavior is determined in a creep test. Data often is
presented in the form of a stress vs time plot. Stress re-
laxation rate is the slope of the curve at any point.
B-30
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