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3. ENDURANCE LIMIT

4. ENDURANCE LIMIT
 Whenever a cyclic (repetitive) load is
applied on the material, If the
material shows no evidence of
fracture then this property of the
material is called, “Endurance Limit”
 While if the material shows any
evidence of fracture during the
loading this property is called,
“Fatigue Limit”

5. ENDURANCE LIMIT
 The conventional fatigue testing has
been concerned primarily with the
testing of specimens with smooth
surfaces under the conditions of
rotating-bending or uniaxial tension-
compression cycling.
 The results of these tests are
presented in the form of plots of
stress verses the number N of stress
cycles required to cause the fracture.

6. ENDURANCE LIMIT
 These plots are called δ-N diagrams, it
was suggested by “WhÖler”. These
diagrams are also called, “S-N
diagrams” in some literatures. It is
shown in the figure.
 Usually in mild steel or certain other
steels, an endurance limit is observed.

7. ENDURANCE LIMIT
 Actually when the cyclic load is applied on
the material stress decreases and once a
point is arrived where the stress becomes
constant, means there is no further
decrease in stress with the increase of N.
 However many materials do not exhibit a
clear cut endurance limit, but δ-N curves
continues downward as N increases.