Wire Ropes Under Tensile Load - Wire Ropes: Tension, Endurance, Reliability - page 146

Fig. 2.40 Number of load
cycles N, wire rope C, Warr.
8 9 19-IWRC-zZ, resin
socket

99
%

2S a /d 2 = 246 N/mm 2
S lower /d 2 = 252 N/mm 2
N = 82 700
I gs = 0.038

95

90

80

70

60

50

40

30

20

10

5

1

10 5 2 3 4 5 7 2

number of load c ycles N

were each tested under nominally identical conditions as shown in Figs. 2.39 and
2.40 , Feyrer ( 1995 ).
Raoof and Hobbs ( 1994 ) found on the contrary that it was preferable to use the
Gumbel distribution for the number of load cycles in the tension fatigue tests on
stranded ropes tested repeatedly under the same conditions.
Unfortunately, the numbers of load cycles they counted are in the region of
N = 355,000-1,636,000 which is where finite life fatigue strength ends. Also, with
its difficult relation to the regression, the Gumbel distribution does not describe
their test results better than the logarithm normal distribution would have done.
Castillo et al. ( 1990 ) proposed using the Weibull distribution with three
parameters to describe the number of load cycles for repeated tension tests with the
same conditions. This distribution has the disadvantage that many more tests
would be needed to evaluate the three parameters and, above all, these parameters
cannot be combined simply with a regression calculation.

2.6.3 Results of Tension Fatigue Test-Series

2.6.3.1 Spiral Wire Ropes with Resin Sockets

Wehking and Klöpfer ( 2000 ) in Stuttgart, and Casey ( 1993 ) and Paton et al. ( 2001 )
in East Kilbride, Glasgow have completed extensive tension fatigue investigations