Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 289

N cor ¼ N f N1 f N2 f N3 f N4 : ð 3 : 88 Þ

f N1 is the endurance factor for the influence of the rope lubrication. For the wire
rope without any lubrication the endurance is extremly reduced. From bending
tests of Müller ( 1966 ) for ropes without lubrication the endurance factor is about
f N1 = 0.2.
If the wire ropes will be re-lubricated during the rope life, the endurance factor
is according (5.56) and ( 3.57 ) for the breaking number of bending cycles

f N1 ¼ 0 : 0316 N 0 : 307 ð 3 : 56a Þ

and for the discarding number of bending cycles

f N1 ¼ 0 : 0682 N 0 : 248

: ð 3 : 57a Þ

A

In ( 3.56a ) and ( 3.57a ), the number of bending cycles N and N A should be only
used in special maintenance.
f N2 is the endurance factor for the influence of side deflection. The equation in
Table 3.15 for the side deflection has been derived from Schönherr ( 2005 ) out of
her voluminious investigation for the breaking number of bending cycles. The
equation of Schönherr represent also the few first endurance factors from Neu-
mann ( 1987 ) up to the rope discarding and therefore can be used for discarding
numbers of bending cycles too.
f N3 is the endurance factor for the influence of the pressure in sheave grooves.
On the base of round steel grooves with the radius r = 0.53 d the number of
bending cycles can be corrected with the endurance factor f N3 , for other groove
radius, for grooves out of plastic and for form grooves.
The factors f N3 for the form grooves come from investigations of Holeschak
( 1987 ) on existing elevators. He evaluated his factors supposing a car load of 75 %
of the nominal load. Using this factor for a standard loading of 50 % of the
nominal car load, no big failure will be made. Newer tests of Berner ( 2011 ) are
only of principle interest.
An other endurance reduction by pressure occurs under multi layer rope
winding on a drum. From the tests of Briem ( 2002 ) and Weiskopf et al. ( 2005 ),
Weiskopf ( 2007 ) a relation for the endurance factor f N3 has been evaluated.
The endurance factor f N4 for the bending of twisted wire ropes has been derived
from a extensive investigation of Weber ( 2013 ).
The endurance factors f N has been evaluated in simple bending fatigue tests.
Therefore they are only really valid for the calculation of the number of simple
bendings. For the reverse bending cycles and the fluctuating tension and bending
cycles these factors are only conditionally qualified. For the calculation of the
number of reverse bending cycles it seams useful in the 1.edition to correct