Premise: To determine if rope diameter has any effect on the brake holding power of a #206 Crossing hitch (Munter hitch).
Test mass = 40kg (two 20kg barbell gym weights were used to create a 40kg test mass).
Load cell: Linescale 3 (running latest firmware).
Set to 'relative zero' prior to each test series.
Sensor scan rate (cycle rate) set to 40hz (to make it easier to read the LCD screen).
Carabiner: Rock exotica 'Pirate' (I chose this carabiner because it has a perfect round cross sectional profile).
NOTE: All tests conducted with a single strand of rope formed into a #206 crossing hitch (Munter hitch).
Measured kN values represents the force required to hold the 40kg mass in static equilibrium.
The test mass was carefully lowered in position to allow the Munter hitch to become consistently and gradually loaded.
(ie the test mass was not dynamically dropped to induce a sudden shock load).
TEST SERIES #1 (Single rope strand - Munter hitch set to lowest brake power geometry)
EN564 6.0mm Sterling accessory cord
Test 1: 0.08kN
Test 2: 0.06kN
Test 3: 0.07kN
Test 4: 0.07kN
Test 5: 0.07kN
Test 6: 0.07kN
EN892 dynamic 9.1mm Beal 'Joker'
Test 1: 0.05kN
Test 2: 0.06kN
Test 3: 0.07kN
Test 4: 0.06kN
Test 5: 0.05kN
EN892 dynamic 11.0mm Edelrid
Test 1: 0.04kN
Test 2: 0.05kN
Test 3: 0.05kN
NFPA Sterling HTP static rope 13mm
Test 1: 0.03kN
Test 2: 0.05kN
Test 3: 0.04kN
Test 4: 0.03kN
Conclusion:
The results suggest a trend... in that the brake force induced by the #206 Italian/Munter hitch
scales with increasing rope diameter.
A possible explanation for this is that larger diameter rope has a larger surface contact area bearing across the carabiner.
EDIT NOTE 1:
Image of test configuration added.
I encourage others to run tests to compare results.
If others are interested in performing tests, I would suggest using similar spec ropes/cordage.
I chose to use EN certified ropes/cords - because this is the type of material used by climbers, rope access technicians, and rope rescue technicians.
EDIT NOTE 2:
I have improved the image quality of the test rig - and to clarify that the load cell
measured the force required to hold the load in static equilibrium.
I used two 20kg barbell gym weights to create a 40kg test mass.
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The following tests were carried out with the same rope specimen.
(EN892 Beal Joker 9.1mm).
I chose to test with a Beal 'Joker' 9.1mm rope because it is likely one of the most commonly used climbing ropes.
These tests compared the relative brake power to hold a load
in static equilibrium in various geometries.
In each test, I carefully lowered the test mass into position without any sudden shock loading.
I also 'relaxed' the test rope after each test by untying and then retying the Munter hitch (tying it exactly the same each time).
The load cell was set to relative zero prior to loading. The latest firmware was used, and set to 40hz scan cycle rate.
Even with all these precautions, I still had variance in the results - although within what I would have expected for the Munter hitch geometry.
Refer to attached images for details of test rig configurations.
TEST SERIES #2
SIngle strand rope testing
EN892 dynamic rope Beal Joker 9.1mm
Munter hitch set to highest brake power geometry.
Test 1. 0.04kN
Test 2. 0.05kN
Test 3. 0.03kN
Test 4. 0.03kN
TEST SERIES #3
Double strand rope testing
EN892 dynamic rope Beal Joker 9.1mm
Munter hitch set to lowest brake power geometry.
Test 1. 0.04kN
Test 2. 0.06kN
Test 3. 0.05kN
Test 4. 0.05kN
TEST SERIES #4
Double strand rope testing
EN892 dynamic rope Beal Joker 9.1mm
Munter hitch set to highest brake power geometry.
Test 1. 0.02kN
Test 2. 0.01kN
Test 3. 0.01kN
Test 4. 0.03kN
