Radial stiffness is an essential characteristic in many rope applications, for example on multi layer winch drums, where the rope is subjected at the same time to the pulling force of the traction winch and to the compression of the adjacent layers.

An excessive wire rope deformation can generate a heavy flange shear stress, while an excessive wire stiffness can cause a drum hoop stress.

In both cases, severe damage to the winch may occur.

Radial stiffness correlates pressure and radial deformation following the definition

where P is the pressure to which the wire rope is subjected and Δd/d is the variation of the wire rope diameter.

Redaelli conducted several experiments to measure the radial stiffness of different wire rope constructions, as summarized in the graph below.

For each curve, two main areas can be identified: the main ratio of the diameter variation is obtained during the first stage of compression, while after having reached a certain deformation value, the diameter variation slows down and the curves show similar slopes.

Six and seven strands fiber core wire ropes are the most sensitive to the compression effect, while the special compacted ropes (Flexpack and independent wire rope core) have a much higher diameter stability towards pressure.

It has to be noted that after each pressure cycle the wire rope denotes a certain degree of permanent deformation.

This permanent deformation is particularly significant after the first cycle, while after a few cycles the rope diameter shows a stabilization.