Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 212

Fig. 3.28 Symbols for
standard loading elements
and numbers of bending
cycles

SIMPLE BENDING

N
N

sim

straight bent straight or

bent straight bent

REVERSE BENDING

N
N

rev

bent straight reverse bent

FLUCTUATING TENSION AND
BENDING

N
N

comb

s traight, tensile force enlarged

bent
straight, tensile force reduced

The rope can be bent with a simple bending test) or (with several test sheaves)
as reverse bending. In Fig. 3.28 , both simple and reverse bending is defined and
the symbols used are taken from the OIPEEC Recommendations, OIPEEC Bul-
letin 56 (1988). In addition to this, combined fluctuating tension and bending is
introduced in Fig. 3.28 . Combined fluctuating tension and bending means that the
tensile force will be enlarged before the rope is bent and reduced again afterwards.
In this case the longitudinally fluctuating wire stresses are composed of those of
the rope bending and those of the changing tensile force. These combined fluc-
tuating stresses are much higher than in the case of simple bending under a
constant tensile force. Therefore this combined fluctuating bending and tensile
force reduces the rope endurance enormously.
In Fig. 3.28 the number of bending cycles are defined by two different indices.
The indices sim, rev and com are introduced for the case that the characterising
indices are not available for printing.
For testing the number of simple bending cycles, the rope stroke
h is of importance. If the stroke h is smaller than the rope contact bow u with the test
sheave, then for each machine cycle the rope is bent by one simple rope bending.
The number of machine cycles Z is equal to the number of the rope's simple
bending cycles . The bending length l on two bending zones h is

ð 3 : 38 Þ

If the rope stroke h is greater than the rope contact bow u with the test sheave,
then for each machine cycle the rope is bent twice. For the number of machine