Page 169 - Biaxial Multiaxial Fatigue and Fracture

154 1 LIU AND H. ZENNER

1

0.4

0.2

0 I I I I I
0 0.2 0.4 0.6 0.8 1
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Fig. 4. Effect of the mean shear stress on the fatigue limit for cyclic normal stress

Fig. 5. Effect of the mean normal stress on the fatigue limit for cyclic shear stress

For the case of an alternating shear stress with a superposed static normal stress, the
fatigue limit is decreased by the superposed static positive normal stress (tension). A
superposed negative static normal stress (compression) increases the fatigue limit to a limiting
value, Fig. 5. If the negative static stress exceeds a certain value, the fatigue limit decreases
again with increasing compressive mean stress. The influence of the mean stress essentially
comprises the effects of the equivalent mean shear stresses and the equivalent mean normal