Wire Ropes, Elements and Definitions - Wire Ropes: Tension, Endurance, Reliability - page 9

Fig. 1.5 Wire arrangement for the fatigue tests, zones of maximum stress amplitude in the wire
cross-section, stress amplitudes and middle stresses

Fig. 1.6 Stress course during
a load cycle

load cycle N = 1

˃ a

˃ a

˃ upper

˃ m

˃ lower

0

time t

For these test methods, the principle wire arrangement in the test machines is
shown in Fig. 1.5 . The fluctuating longitudinal stress affects different zones of the
wire cross-sections. The wire cross-sections with the zones of the highest fluctu-
ating longitudinal stress are shown in Fig. 1.5 below the wire arrangements. The
highest stressed zones are shaded. The highest fluctuating longitudinal stress is
taken as the nominal fluctuating stress.
For fatigue strength (infinite life), instead of the stress the symbols r are written
with indices as capital letters.
In Fig. 1.5 , the stress amplitude r a and the middle stress r m are listed for
general cases in fatigue tests. Figure 1.6 shows the stress course over one load