Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 235

The reason for this may be that the re-lubrication reduces the friction between
the wires and the strands which then results in a reduction of the fluctuating
secondary tensile stresses. On the other hand, a broken wire only bears the load
again after a certain length which means that the neighbouring wires will be more
highly stressed. The result of these findings may show that for smaller stresses the
first influence and for higher stresses the second influence is predominant.
In all the bending fatigue tests described, the wire ropes were lubricated before
and, in the case of re-lubrication, during the tests with a viscous mineral oil
without any additives and with a viscosity 1.370-1.520 cSt, 40 C. The amount of
lubricant—transported by a pump and dripped onto the rope—is very small. To
find the lowest limit of lubricant needed, the quantity of lubricant was reduced
from test to test in a series of bending tests. In the last test where the endurance
was not reduced, the amount of lubricant used was only 1.8 g/m for 100,000
bending cycles of the 16 mm wire rope, see Sect. 1.4 .

3.2.3.4 Round Groove

If the radius of the round groove is greater than half the rope diameter, the wire
rope will be ovalised and the pressure in the bottom of the groove is high on the
wire rope running over the sheave. Therefore the number of bending cycles
decreases with the increasing ratio r/d of groove radiusr and the rope diameter d.
The ratio of the breaking number of bending cycles as a function of the ratio r/d
has been evaluated by Woernle ( 1929 ), Müller (1954), Shitkow and Pospechow
( 1957 ), Wolf ( 1987 ) and Unterberg ( 1991 ). Their results are shown in Fig. 3.47 .
Unterberg's results in particular show that—as expected—the greatest rope
endurance has been found for the ratio r/d m = 0.5 of the groove radius and the

= 300N/mm 2
= 100N/mm 2
= 200N/mm 2
= 394N/mm 2
= 246N/mm 2
= 159N/mm 2
= 600N/mm 2

Woernle s z

1,5

Müller
Shitkow
Unterberg
Unterberg
Unterberg
Wolf

1

0.5

r
d

=0,53

0

0,4 0,517 0,6

rel. groove radius r / d actual

0,5 0,7 0,8 0,9 1

Fig. 3.47 Influence of the groove radius on the breaking number of bending cycles