Revision of Commonly Used Loop Knots Efficiencies

J. Šimona, V. Dekýšb, P. Palčekc aDepartment of Applied Mathematics, Faculty of Mechanical Engineering, University of Žilina, Univerzitná 8215/1, 010 26 Žilina, Slovakia bDepartment of Applied Mechanics, Faculty of Mechanical Engineering, University of Žilina, Univerzitná 8215/1, 010 26 Žilina, Slovakia cDepartment of Materials Engineering, Faculty of Mechanical Engineering, University of Žilina, Univerzitná 8215/1, 010 26 Žilina, Slovakia

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In a number of professions, human life hangs on a knotted rope. However, until now only a poor attention of scientists has been paid to the properties of knots. The main objective of the presented research is to provide an in-depth revision of commonly used loop knot efficiencies employing modern experimental technologies and correct statistical processing. In the first part of the paper, the common mistakes in the available information sources were pointed out and the correct way of assessing the loop knot efficiency was proposed. Subsequently, correct statistical calculus was derived to evaluate mean knot efficiency and confidence interval. Efficiencies of eight commonly used loop knots loaded in several geometries were precisely measured, evaluated, and analyzed. Special attention was paid to avoid misleading conclusions based on experiments of low statistical power. Loop knot efficiency is not a constant, but it depends at least on the static breaking strength of a rope. The process of knot breakage was recorded by high-speed infrared thermal imaging. Analyses showed that the temperature of the most exposed parts of a knot could reach polyamide melting point. Finally, the microfilament analysis using electron microscopy was carried out to understand the breakage process on the microscopic level.

DOI:10.12693/APhysPolA.138.404 topics: knot efficiency, rope, tensile tests, thermal imaging, electron microscopy\\vs*{10pt}