Page 432 - Mechanical Behavior of Materials

Section 9.4 Fatigue Testing 433

Figure 9.12 The R. R. Moore rotating beam fatigue testing machine. (From [Richards 61]
p. 382; reprinted by permission of PWS-Kent Publishing Co., Boston.)

Figure 9.13 A reciprocating cantilever bending fatigue testing machine based on controlled
deflections from a rotating eccentric. (From [Richards 61] p. 383; reprinted by permission of
PWS-Kent Publishing Co., Boston.)

specimen. For all forms of rotating bending test, the cyclic stress has a mean value of zero. This
is because the distance from the neutral axis of bending to a given point on the specimen surface
varies symmetrically about zero as the circular cross section rotates.
A rotating crank can be used in a reciprocating bending test to achieve a nonzero mean stress,
as shown in Fig. 9.13. Geometric changes in the apparatus that effectively alter the length of the