Wire Ropes, Elements and Definitions - Wire Ropes: Tension, Endurance, Reliability - page 7

Fig. 1.4 Evaluation of the
yield strength R p0.2 according
to EN 10002-1

R p0.2

hysteresis loop

extension

0.2

the wire has to be unloaded and loaded again. As a result, a hysteresis loop occurs
as seen in Fig. 1.4 . A middle line of this hysteresis defines the elasticity module
E = Dr/De. To evaluate the yield strength R p0.2 , a parallel to the middle line of
the hysteresis has to be drawn through the residual extension e r = 0.2 % on the
abscissa. Then the yield strength R p0.2 is found as an ordinate where the parallel
meets the stress extension line.
To determine stresses, strengths and elasticity modules, the cross-section A of
the unloaded wire has to be measured very precisely. (Unlike EN 10002-1, the
symbol A is used here for the cross-section.) The error in measurement of the
cross-section should be 1 % at the most. For round wires the cross-section has to
be calculated from two wire diameters d measured perpendicular to each other.
To fulfil this accuracy requirement for the cross-section, the wire diameter d
should be measured with a maximum deviation of 0.5 %. With commonly used
measuring instruments this accuracy requirement can only be achieved for thicker
wires. For thin wires and for profile wires, the cross-section can be evaluated by
weighing. With the wire weight m in g, the wire length l in mm and the density q,
the cross-section is then

A ¼ m

l q :

ð 1 : 1 Þ

The density for steel is normally q = 0.00785 g/mm 3 . However, because of the
great carbon content of wires used for wire ropes it is to use q = 0.00780 g/mm 3 .
The total extension of steel wires for ropes amounts to about e t = 1.5-4 % and
the yield strength R p0.2 is about 75-95 % of the measured tensile strength R m . For
wires taken out of ropes and straightened, the total extension is about
e t = 1.4-2.9 % and the yield strength R p0.2 is about 85-99 % of the tensile
strength R m , Schneider and Lang ( 1973 ).