![]() This type of extension or contraction depend on the coefficient of linear expansion of the rope. This relation accelerate until a condition of permanent extension is reached and finally of the rope without further loading. If the load continues to increase the extension will increase faster than the load. This mean a small increase of load cause a lager extension than it would be in the elastic elongation area. Load that cause tension in the steel wire rope, which exceeding the yield point of the material, the linear relation, due to phase 2, between stress and strain. General E-module of the rope construction Elasticity limit are defined as the largest strain where the rope return to its original length when unloaded. ![]() By load exceeding this limit extension according to phase 3 take place. The elastic extension is valid until the proportionality or elasticity limit is reached. If exact E-module olf a certain rope is necassary a modulus test have to be done at that rope. According to manufacturing factors, wire dimensions and a lot of other factors the E-module various between different wire ropes of the same construction and dimension. The modulus of elasticity varies with different rope constructions. The elastic extension can be calculated as followed (Hookes law):Įlastic extension (mm) = (W x L) / (E x A)Ī = area of rope - circumscribed circle (mm2) To steel wire ropes the E-module is more of a construction constant than a material constant. The proportionality factor normally is a material constant called Modulus of Elasticity (E-module). ![]() It is not possible to quote any exact values for various constructions but the following approximate values can be used to give reasonably accurate results.įollowing Phase 1, the rope extends in a manner which complies approximately with Hookes Law, i.e. stress is proportional to strain. The initial extention can not be accurately determined and depend on, apart from the strand or the rope construction, the various load and the current load frequency. When sufficientely large bearing areas have been generated on adjacent wires, to withstand the circumferential compressive loads, this mechanically created extension ceases and the extension in phase 2 commences. This reduction in diameter creates an excess length of wire which is accommodated by a lengthening of the helical lay. When loading a new product, extension is created by the bedding down of the assembled wires with a corresponding reduction in overall diameter. This phase of extension of the rope depend on the construction of the rope and can be explained as following: Due to this a new rope, which are exposed to overloading, will go through phase 1 and 2 before the third phase (permanent extension) begin. The phases are connected to eachother and cause a course of event in all ropes that are exposed to gradual increased load. Phase 3, on the other hand, can be caused by wrong choose of rope or lack of rope inspection. Phase 1 and 2 are highly important because they represent a part of the qualities of the rope. Phase 3: permanent extension (thermal elongation and contraction, rotation, wear and corrosion) Properties of Extension of Steel Wire RopesĪny assembly of wires spun into a helical formation (either as a strand or a wire rope), when subjected to a tensile load, can extend in three seperate phases, depending on the magnitude of the applied load:
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