Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 267

100
[%]

for birth distribution

80

60

for Poisson distribution

40

Seale, Filler Warrington
8x19 IWRC and FC
sZ and zZ, lubricated
d = 12 mm, D/d = 12.5, 25 and 63
steel hardened r = 0.53 d
Chi-square test

20

ʱ = 0.01

0

0.1 10.0

mean number of wire breaks B 6

1.0 100.0

Fig. 3.76 Percentage of the wire break distributions explained by Poisson- or by birth-

distribution, Ren ( 1996 )

3.2.9.3 Discarding Number of Wire Breaks

As shown in Fig. 3.69 , the number of wire breaks on a reference bending length
L = 30 d were recorded during a number of series of bending fatigue tests. The
results of these counts show that the number of wire breaks B30 found by inter-
polation was reached at 80 % of the rope endurance. From these numbers of wire
breaks found for different groups of wire ropes of the same construction, the
discarding number of wire breaks has been evaluated by regression calculation and
reasonable limits to be

2
g 2

2
g 3

2 2

:

S
d 2

d
D

S
d 2

d
D

B A30 ¼ g 0 g 1 ð 3 : 83 Þ

where S is the rope tensile force in N, d is the rope diameter in mm, and D is the
sheave diameter in mm.
The discarding number of wire breaks on the small reference length L = 6 d,
chosen in order to detect concentrations of breaks, is given by definition as

B A6 ¼ 0 : 5 B A30 : ð 3 : 84 Þ

The constants g i for the ropes with different constructions listed in Table 3.18
(Sect. 3.4.5 ) are based on more safe limits than for the first form, Feyrer ( 1984 ).
Furthermore, in Jahne's test results (1992) there is no longer any trace of the small
difference between Seale ropes and Warrington and Filler ropes.
The discarding numbers of wire breaks from ( 3.83 ) and ( 3.84 ) are valid for
outside visible wire breaks on wire ropes running in simple bending over sheaves