Wire Ropes, Elements and Definitions - Wire Ropes: Tension, Endurance, Reliability - page 22

Fig. 1.18 Rotary bending
strength for different
corrosion times, wire
diameter d = 2 mm,
Jehmlich ( 1969 )

490

470

450

wire ʴ = 2 mm

430

410

390

370

350

330 0

100 200 400 500

300

corrosion time in h

According to ( 1.3d ), the rotary bending strength for new wires with tensile strength
R m = 1,770 N/mm 2 and wire diameter d = 1mm is r Rot = 500 N/mm 2 .
According to ( 1.3c ), Wolf ( 1987 ) found the mean rotary bending strength for
different wires to be between r Rot ¼ 510 N/mm 2 and 730 N/mm 2 for wires with
diameters between 0.8 and 1.0 mm taken from wire ropes and tested under the
same conditions.
The fatigue strength is reduced for wires with zinc coating, Reemsnyder ( 1969 ),
and especially for wires with a thick zinc coating, Apel and Nünninghoff ( 1979 ).
For normal zinc-coated wires, Briem ( 2000 ) also found that fatigue endurance is
reduced in relation to bright wires. On the other hand, the corrosion that should be
prevented by the zinc coating. Corrosion reduces the fatigue strength enormously,
as can be seen in Fig. 1.18 , Jehmlich ( 1969 ).
The fatigue strength of wires depends on their various contents and method of
manufacture. With the loss of cross-section during repeated wire drawing, the
repetitive tensile strength r t,Rep first increases and then decreases. The maximum
repetitive strength exists for a cross-section loss between about 60 and 80 %,
Becker ( 1977 ).
Unterberg ( 1967 ) found that aged wires have increased fatigue strength. After
being artificially aged for three weeks at a temperature of 90 C, a wire (diameter
d = 3.1 mm, measured tensile strength R m = 1,760 N/mm 2 ) has an 11 % higher
rotary bending strength r Rot .
For wires made of corrosion resistant steel X5CrNi18-10, Nr 4301, Luo ( 2002 )
found the mean tensile strength amplitude to be r t ; A = 290 N/mm 2 with the
middle stress r m = 356 N/mm 2 . The diameter of the wire is d = 2 mm and the
stressed wire length l = 125 mm. The tensile strength is R m = 840 N/mm 2 .
The influence of the tensile strength and the fluctuating strength of wires on the
tensile endurance of wire ropes is still unknown. For the bending endurance of
wire ropes the influence of tensile strength R 0 is presented in detail in Sect. 3.2.2 .
The complete results—without considering the influence of wire fatigue

strength—is given by ( 3.51b ) and for a part result in Fig. 3.36 .