Rope wear in climbing and in laboratory
Commission for Materials and Techniques, Italian Alpine Club
attraction of particles towards the rope, charged by static electricity. Damage due to wear occurs primarily on the surface of rope, the sheath. A study performed by the CMT has shown that the sheath plays an important role in the whole resistance of the rope. In fact, both components (sheath and core) contribute to energy absorption, though their elongation under load is different, depending on construction. The sheath, whose weight is about 30% of the rope, contributes by about 30% to the static breaking load. Dodero tests carried out after cutting the sheath of the rope showed a dynamic resistance decrease from, typically, 8-9 falls to only 1 fall. The reduction in the peak force during the first fall arrest was moderate, but the corresponding increase in elongation was obviously large enough to cause permanent deformations which piled up during subsequent falls. Therefore, to weaken the sheath means to seriously reduce the dynamic performances of the rope. It is plain that superficial abrasions of rope, easily noticeable with naked eye, correspond to breakage of part of the filaments (PHOTOS 1A and 1B). The reduction of the static breaking load of a rope can be fairly well correlated to the total number of broken filaments.
By visual inspection, only the specimens related to 49 descents with Figure-of-Eight were noticeably damaged. In fact, even with the naked eye
the presence of broken
filaments causing the characteristic superficial down of the sheath was well visible (PHOTOS 2A,2B,2C,2D). Breaking tests done on several strands showed a reduction in breaking strength of about 35%, in very good agreement with the percentage of broken yarns counted on the strands. This result caused concern, due to the important contribution of the sheath to the total rope strength; this concern was confirmed by tests on the Dodero. Indeed (TABLE.1), after about fifty descents with Figure-of-Eight the dynamic resistance of the rope ( that is the number falls sustained at the Dodero) is reduced by about 1/3.
definite and plai
One thing we clearly know: the main cause of rope wear is the combined effect of the rubbing against rocks, mechanical stresses (carabiners and belaying devices), dust and small crystals that penetrate the sheath. The number of metres climbed matters, not the age of the rope.
Research carried out by the CMT  and elsewhere has provided an interesting contribution to the understanding of the complicated mechanisms that produce the decay of rope performance. However, it hasnít produced enough information to improve the evaluation of rope deterioration in quantitative terms. At present, the only valid information in this context is given by the research carried out during the í90s by Pit Schubert . By testing ropes used in climbing and mountaineering, Schubert was able to quantify the decay in dynamic performance of a rope as a function of the length of its run in climbing sites or in the mountains.
In the first research, the static breaking load on an edge was reported as a function of use (expressed in metres) in different conditions, the way it was used (climbing, abseiling, both) and the environment (limestone or granite). The use of an edge corresponds to the way the ropes really break in mountaineering; the use of static tests instead of dynamic tests is still under evaluation today, however the results clearly showed the dominant effect of abrasion and mechanical stress (abseiling, friction on rock and carabiners) on the deterioration of a rope. The importance of the environment was also shown: different decay curves can be plotted for ropes used in granite and limestone.
In the second research, the decay of the dynamic performance of the rope was evaluated, based on the analysis of about thirty ropes used by climbers and mountaineers in different conditions. Itís interesting to point out that these tests were done on the Dodero, using classical and sharp orifice edges with different curvature radii: the relative reduction of the number of sustained falls was about independent of the type of edge used (PLOT 2 see annex power point presentation).
Present work of the CMT
The results of the dynamic tests, made on the Dodero according to UIAA standards, show that new and used ropes generate about the same holding force on the first fall. This means that wear does not affect elongation on the first fall, but leads to plastic deformation and/or breakage of filaments, which produce cumulative effects in the subsequent falls.
Itís important to point out that the results - particularly those referring to artificial wear - are in a very good agreement with Pit Schubertís (PLOT 3, see annex power point presentation). This seems to confirm the validity of procedure adopted by the CMT for artificial wear. This comparison is possible because Schubertís curve is valid for standard Dodero as well as for sharp- edge Dodero tests.
In conclusion, may we remind the reader that our data refer to numbers of falls held on the Dodero, that is in a test where the rope is clamped at one end. In real life, dynamic belay normally occurs in holding a fall; this means that the characteristics of a rope are less important than on the Dodero
Annex po power poitn presentation.
TABLE 1 Ė Number of rappels and rope strength PLOT 1 - Dynamic strength of rope vs. number of rappels and device PLOT 2 - Dynamic strength of rope vs. rope run in climb/abseil (Pit Schubertsís data) TABLE 2 - Artificial wear and dynamic strength TABLE 3, 4, 5, 6 - Dynamic strength vs. rope run in climbing / Various ropes PLOT 3 - Artif. wear and rock climbing. Comparison with Pit Schubertís data