Is Friction in a knot dangerous? No. Its a modern urban legend

Recently there was a discussion on facebook about this knot:

One reason was mentioned why to put a thimble where you could just do this:

"Rope on rope equals friction. That friction generates heat and that can be devastating to the rope integrity."

If you load this knot then the rope may cut/melt through the loop. 

Ok, My approach is: Test it.

I built a Cyclic load  machine:

It looks very complicated but it loads the knot with 1 kN.

After 4.000 times loading I did the breaking load test.

 

 It broke at 20,58 kN.

As a comparison I tested an unused rope. It broke at 22,24 kN:

I decided to do the ultimate "fatigue" test. I cyclic loaded the knot between10 kN and 1 kN.

I checked the rope after 1200 cycles:

They look damaged, but the core is not visible.

At 1500 cycles I stopped. 

Although the core was not visible I think everybody would have discarded the rope.

Then I tested the breaking load:

 21 kN.

So there was no difference between a new rope and this rope.

It is a modern urban legend that the rope will become damaged in this application only by loading it in rope access.