Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 233

Fig. 3.44 Number of
bending cycles of two wire
ropes, lubricated and
degreased, Müller ( 1966 )

8
6
4
2
0
10 6

°
R=0.53d

60

D= 25d

10 5

6x(1+7+(7+7)+14)
+ 7x (1+6)

10 4

6x(1+6+(6+6))+1H

10 3

0 10 20 3 k 4

rope tensile force S

tests. The eff ec t of the re-lubr ica tion was to increase the mean number of bending
cycles from N ¼ 246 ; 000 to N ¼ 392 ; 000 The standard deviation for logarithm
distribution is lg s = 0.038 and lg s = 0.047, based on the bending length 45d.
A larger number of bending fatigue tests, both with and without re-lubrication,
were carried out with seven parallel strand ropes with the rope diameters between
12 and 16 mm, Feyrer ( 1998 ). Figure 3.46 shows the ratio of the breaking numbers
of bending cycles N m /N with (index m) and without re-lubrication (no index). By
regression calculation, the breaking number of bending cycles with re-lubrication
is

N m ¼ 0 : 0316 N 1 : 307 : ð 3 : 56 Þ

and the discarding number of bending cycles with re-lubrication is

N Am ¼ 0 : 0682 N 1 : 248 : ð 3 : 57 Þ

A

Normally, the number of bending cycles will be increased by the re-lubrication.
However, if the wire rope without re-lubrication only reaches the numbers of
bending cycles N = 80,000, respectively, N A = 50,000, there is no increase in
endurance to be expected. Moreover, up to these limits the numbers of bending
cycles may be even reduced by re-lubrication, Fig. 3.46 .