Bending cables with different torque

An ongoing discussion is the influence of the torque of clamps. Earlier in this blog I found out that higher torque prevents cable connections from slipping.

Some people claim: Higher torque damages the cable. I wanted to check the effect on cyclic bending.

I took two pieces of 10 mm, 6 x 19 (fiber core) cable. 

The load was a weight of 80 kg.

I applied a torque of 9 Nm  to the first and 30 Nm to the second sample.

9 Nm is the torque stated by the Euronorm EN 13411-5, A. 30 Nm is at the yield point of the bail material.

I checked after 1000, 2000 and 3000 cycles under the clamp.

Here are the results:

 

 Higher torque creates less wire breaks.

 Interesting is that the breaking load was the same with both cables.

I tested a cable where I cut one strand (about 19 wires) with a grinder: 51 kN breaking load.

To check the change in the material I took a cable and loaded it with 1500 cycles, with 10 wires broken.

The breaking load was 29 kN.

I assume that the bending cyclic process damages a cable more than only the broken wires indicate.

Here is the overview: cyclic loaded  aganist not loaded (grinded).

 Conclusion:

The influence of torque in cyclic bending situations is low. 

(Wire breaks occur later, but breaking load is similar).

Cyclic bending should be avoided if high loads are expected.