Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 246

Fig. 3.56 Number of bending cycles of a twisted wire rope 12 mm—WS6936 - IRWC—sZ,
Weber and Wehking ( 2013 )

3.2.4 Reverse Bending

Müller ( 1961 ) and Jehmlich ( 1985 ) established that about the half the number of
bending cycles will be reached for reverse rather than for simple rope bending.
Newer tests from Feyrer and Jahne ( 1991a ) show that this result is only valid for a
small range of test conditions. These tests were carried out on bending fatigue
machines with a test sheave arrangement as shown in Fig. 3.30 .
Figure 3.57 shows the ratio of the numbers of reverse and simple bending
cycles up to breakage taken from these tests, as well as from tests carried out by
Müller ( 1961 ) and Jehmlich ( 1985 ). However, it has been taken into consideration
that Jehmlich's definition of a bending cycle was different from the standard one.
From the regression calculation, the number of reverse bending cycles is

a 2

D
d

N rev ¼ a 0 N a 1
sim

: ð 3 : 61 Þ

The constants a i for the numbers of bending cycles up to discard or breakage
are listed in Table 3.16 (Sect. 3.4.3 ). The standard deviation for the ratio of the
numbers of bending cycles N rev /N sim is lg s = 0.132 and lg s A = 0.084.
The regression equation with its constants relates to the 12 parallel strand wire
ropes 8 9 19 in ordinary lay and lang lay with fibre cores FC and steel cores WRC
used in the tests. The ratio of the number of reverse and simple bending cycles is a
little greater for the six strand ropes used in the tests carried out Müller and