Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 215

Fig. 3.32 Rope-bending fatigue machine, Feyrer and Hemminger (1983)

The real research work using rope-bending machines began much later in the
early 20th century. The researchers construct their own rope-bending machines,
usually on the principle shown in Fig. 3.27 . Rope-bending-machines have been
devised, for example, by Benoit ( 1915 ), Scoble ( 1920 ), Woernle ( 1929 ), Shitkow
( 1957 ), Wiek ( 1976 ), Jehmlich ( 1985 ), Waters and Ulrich ( 1990 ) and the latest
from Vogel and Nikic ( 2004) .
In most of the rope-bending machines, the rope is guided very simply with a
large traction sheave which remains unaltered during all the tests and a rope-
testing sheave with a smaller diameter. These test sheaves can normally be
replaced easily for testing different ropes and sheave diameters. In the newer
machines, the traction sheave and the test sheave are in overhung position. This
construction makes it possible just to lay the rope samples on to the sheave and to
exchange the test sheave quickly. Even more important, however, is the easy
accessibility of the rope bending zones, so that the wire breaks can be counted
without difficulty during the course of the test.
A rope-bending machine with overhung sheaves is shown in Fig. 3.32 . The
tensile force per rope is achieved through leverage with weights over a lever arm
with knife edge suspension. In rope-bending machines for very large rope tensile
forces and in rope-bending machines for testing bending combined with fluctu-
ating tensile forces, the rope forces are induced using hydraulic cylinders.
In all the newer rope-bending machines, the bending frequency and the stroke
can be varied. The machines are fitted with two of the usual devices for counting
the bending fatigue cycles accurately and a device for measuring the crank rev-
olutions per minute. Additionally, they have a counting device which switches the
machine off when the desired number of bending cycles has been reached so that it
is possible to estimate the state of the rope, for instance, to count the wire breaks.