Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 231

This equation belongs to
the nominal strength R 0 = 1770 N/mm 2

the nominal rope diameter d = 16 mm

the bending length l = 60 d

the rope cores FC and IWRC

the number of strands for parallel lay rope 8

With the Eqs. ( 3.51 ), ( 3.51a ), ( 3.52b ) and ( 3.54f ), the influence of the nominal
strength R 0 , the nominal rope diameter d, the bending length l and the number of
strands of the parallel ropes can be introduced in this Eq . ( 3.49 ). Furthermore with
Eq. ( 3.49a ) beside the mean number of bending cycles N the number of bending
cycles N 10 can be expressed. With that the number of bending cycles for any
nominal strength R 0 , nominal rope diameter d and bending length l is

þ b 2 lg D
d

lg N ¼ b 0 þ b 1 þ b 3 lg D
d

S
d 2 0 : 4 lg

R 0
1770

lg

ð 3 : 55 Þ

þ lg f d þ lg f L þ lg f C

With

d in mm nominal rope diameter

D in mm sheave diameter

S in N rope tensile force

in N/mm 2 R 0 nominal tensile strength

l in mm bending length

The constants b i for the wire ropes of the important rope constructions listed in
Table 3.14 . The endurance factors f d ,f L and f C are presented in Table 3.14a .

3.2.3 Further Influences on the Number of Bending Cycles

3.2.3.1 Zinc Coating

Woernle and Müller have carried out a great number of bending fatigue tests to
compare the endurance of wire ropes with bright or zinc coated wires. All the wire
ropes tested were lubricated before starting the tests. The result of these tests is shown
in Fig. 3.43 . There was practically no difference recorded between the bright and the
zinc coated ropes, irrespective of whether the wire ropes tested had ordinary lay or
lang lay. Zimerman and Reemsnyder ( 1983 ) came to the same result.