Wire Ropes Under Tensile Load - Wire Ropes: Tension, Endurance, Reliability - page 152

respectively k T1 = 2.76, with a certainty of 95 % at the most 10 % respectively
1 % of the wire ropes are broken at the number of load cycles

N 10 ¼ 0 : 38 N respectively N 1 ¼ 0 : 184 N :

For the Warrington-Seale ropes with 6-strands and steel core IWRC, the
relation between the wire rope stress and the specific force is

r z ¼ 2 : 195 S

d 2 :

Of the wire ropes with steel core, the 6-strand Warrington-Seale ropes reach a
much higher number of load cycles than both of the 8-strand Warrington ropes
compared in the last column of Table 2.9 . Even for the same specific forces, the 8-
strand Warrington rope with fibre core has shown a higher endurance than both of
those with steel cores. For the same wire rope stress, Reemsnyder ( 1972 ) also
found that wire ropes with fibre cores had an advantage as far as endurance is
concerned.

2.6.3.4 Round Strand Wire Ropes with Metal Sockets

The results of tension-tension fatigue tests on wire ropes with metal sockets are
listed in the Table 2.10 . These results are presented because wire ropes with metal
sockets are frequently used and because it is very informative to see the endurance
results with metal sockets under different conditions. Most of the results come
from Müller ( 1962 , 1963 , 1966 as well as other unpublished results). For all his
tests, the lower specific force was about S lower /d 2 = 20 N/mm 2 . He found that the
parallel lay wire ropes always have much higher endurance than cross lay ropes
although the cross lay ropes with the same wire lay angle in all wire layers have
the advantage of having theoretically the same tension in the different wire layers.
The reason for the smaller endurance of the cross lay ropes may just be due to the
pressure between the crossing wires.
There is not much variation in the number of load cycles of the cross lay ropes
FNC + 6 9 19, 6 9 37 and 6 9 61 whereby the higher number of wires tends to
show an advantage. The simple wire rope FNC + 6 9 7 has a slightly higher
endurance. Here again, the reason may be that there are no crossing wires. This
may overcome the disadvantage of the thicker wires. In all cases, he found that the
lubrication gave higher endurance. This result comes from the smaller second
tensile stress, see Sect. 2.1.4 .