Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 291

simple bending reverse bending

Fig. 3.83 Definition of simple and reverse bending for angles between the sheave axis,

DIN15020

X n i
N i

¼ 1 : ð 3 : 70 Þ

In this, n i is the number of cycles under the load i, the wire rope is stressed and
N i is the endurance number under the load i.
In one working cycle or trip the wire rope is often stressed by numbers of
the three standard loading elements w i ( and
). For the tensile force S j , the number of working cycles Z j can then
be calculated using the following equation

¼ X

3

1
Z j

w i
N i

¼ w sim
N sim

þ w rev
N rev

þ w com

N com :

ð 3 : 92 Þ

i¼1

In very rare cases where a running wire rope is also loaded by fluctuating
tension cycles, the number of tension cycles can be calculated using the equations
in Sect. 2.6 (up to now, only for ropes Warr.-Seale 6 9 36-IWRC). With these, the
further quotient w tens /N tens can be included in ( 3.92 ), though at present there are no
test results known which make allowances for this addition of damage ratios.

3.4.4.2 Collective Factor

In many cases the ropes in rope drives are loaded by a collective of forces S i .
With the force S i can be got the number of bendings N i or the number of
working cycles Z i respectively. For a collective of numbers of working cycle with
different forces the total number of working cycles will be