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Fig. 2.34 Tension-torsion fatigue endurance of stranded wire ropes as a function of cyclic
rotation, Ridge ( 2010 )
fluctuating twist. The twist angle range is—for a constant middle tensile force
S m —approximately proportional to the tensile force range 2S a . They have carried
out fatigue tests with a stress level where a high rope endurance has to be expected
if there would be no fluctuating twist. Together with the fluctuating twist the
numbers of load cycles are only about N = 50,000 for ropes with cast sockets as
terminations. With Oplatka's clamp-sockets which allow slight movements of the
wires and thus reduce the longitudinal stresses from the rope twist, they get more
than ten times the number of load cycles for relatively short ropes.
Chaplin ( 2002 ) started his investigations in this field by defining the demand for
a special testing machine which would enable rope endurance to be evaluated
when the rope is stressed by constant or fluctuating twist in combination with
constant or fluctuating tensile stress. Now Chaplin ( 2005 ) has reported that the new
testing machine functions. He has presented first results in a diagram with the axis
not scaled, because the results—belonging to a sponsor—are still confidential.
Ridge ( 2010 ) reported from extensive wire rope tension-torsion tests—that
means tests with wire ropes under fluctuating tensile force and fluctuating twist
angle. In that tests the tensile force and the twist angle varies in phase. The three
tested wire ropes are
Seale 6 9 19—IWRC—1,770—bright—d = 19 mm
Warr.Seale 6 9 36—IWRC—1,770—zinc—d = 19 mm
Warr.Seale 6 9 41—IWRC—1,770—zinc—d = 77 mm.
The result of the tension-torsion tests is shown in Fig. 2.34 . The tests have been
done with fluctuating twist angles between 0 and 1,400/100d. In the legend, M is
mean load, LR is load range (both expressed as a % of the rope's measured UBL),
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