Numerous studies and practices show that the main reason affecting the service life of steel wire rope is "fatigue failure". The so-called "fatigue failure" is due to the formation of "fracture sources" within the steel wire rope under the action of alternating stress. These "fracture sources" gradually develop and expand, and finally lead to wire fracture (commonly known as "fatigue broken wire"). This kind of "fatigue fracture" has no obvious plastic deformation and has the characteristics of sudden, which is very harmful to the wire rope. Therefore, for a long time, people began to reduce or eliminate the stress of the wire rope to enhance the "fatigue resistance" performance of the wire rope, so as to improve the service life of the wire rope.
In order to eliminate or reduce the stress of wire rope, it is necessary to objectively analyze and understand the various stresses in the wire rope. In this respect, many researchers at home and abroad have made a lot of theoretical and practical research and made great achievements. However, the stress of steel wire rope is very complex, and it needs further efforts to accurately describe the stress of wire rope and the relationship between stress and "fatigue limit".
According to various discussions, the stress of steel wire rope can be basically divided into two categories: one is the stress produced in the manufacturing process of steel wire rope; the other is the stress produced in the process of using steel wire rope.
Stress formed in wire rope manufacturing
The steel wire in the steel wire rope is made by drawing. In the process of drawing, the residual drawing stress should be formed in the steel wire; when the steel wire is read into strand and then twisted into rope, the twisting stress will also be produced. Therefore, there are two kinds of stress in the manufacturing process of wire rope: residual drawing stress and twisting stress.
Residual drawing stress
There are three forms of residual drawing stress
1) Residual tensile stress
In the process of drawing steel wire, due to the difference of die angle, lubrication condition and cooling condition, the displacement and deformation difference of each layer of "grain fiber" appear in the steel wire during deformation, so the tensile stress is produced in the longitudinal direction of steel wire. This tensile stress will partially form residual tensile stress in the residual steel wire.
Residual bending stress
In the process of drawing, when the steel wire is bent in the roller and drum of the wire drawing machine, the bending stress remains in the steel wire. Especially when the diameter of the drum and the diameter of the steel wire do not match (that is, the bending ratio is not consistent), the residual bending stress is more obvious. In addition, if the exit center of the mold and the tangent point of the steel wire in the drum are not on the natural horizontal tangent line, the formation of bending stress will also be intensified.
When the pulley type wire drawing machine is used to draw steel wire, the steel wire will twist around its own axis and form torsion stress.
Twist stress
There are also three forms of twist stress
Torsional stress
Bending stress
Tensile stress
Stress of wire rope in operation
There are mainly two kinds of working state of wire rope according to the way of stress: one is the working state under the action of tension load, even in this case, the stress of wire rope is very complicated. Because the wire rope itself has various forms of motion under tension load, the different forms of power transmission will have different degrees of influence on the size and direction of tension. For the convenience of research, only the stress state of wire rope under static tension load is considered. The other is the working state when the wire rope bypasses the rope pulley or drum. In this case, in addition to the friction of the rope pulley, the wire rope mainly receives the bending of the rope pulley in the tension state.
In this paper, the stress of wire rope is analyzed under these two working conditions.
Stress of wire rope under tension load only
When the wire rope is under tension load, because the steel wire and the strand rope are in the spiral state, they will be subject to the comprehensive action of tension, radial extrusion, bending and torsion at the same time.
Relationship between tensile load of steel rope and force of steel wire and strand
Contact stress in wire rope
Torsion moment and torsion stress
Bending moment and bending stress