Research On Mechanical Properties Of Braided Wire Rope For Traction Subjected To Tension-Torsion Combined Load

Braided wire rope is vital for stringing conductors with tension in overhead transmission lines.Its structure and characteristics determine the safety and reliability of the stringing construction.In view of the urgent need for the failure mechanism and life prediction of braided wire rope in the construction of green environmental protection power grid,we studied the mechanical properties of braided wire rope under tension,torsion and combined loads of tension-torsion using theoretical analysis,numerical simulation and experimental methods.It is of great significance to improve the structure of the wire rope and improve its service life.YS9-8×19 braided wire rope is taken as the objective of study in this thesis.The structure and braiding technology of it were analyzed,and its forming process was deeply discussed.The basis of the assumption of elliptical helix in space for strand of rope was analyzed from its braiding forming principle.We explored the structure of a wire rope and its strands,and obtained the key parameters to characterize the structure.Based on the three modeling methods of reverse engineering,surface intersection and space spiral equation of strand unit,the research on geometric model construction of double elliptical spiral symmetrical braided wire rope was carried out.Comparing the efficiency of the three methods and the accuracy of the model,the modeling method based on the space spiral equation of the strand unit had certain advantages in the construction of the geometric model of the braided wire rope.The causes of external torsion of braided wire rope were discussed deeply from the contact deviation angle and contact condition between the wire rope and the groove of the traction reel and the release pulley.Taking the force of micro-section wire rope on the reel groove as the research object,the external torque expression of the wire rope generated in the traction process was derived.Based on the geometric model of braided wire rope,the geometrical relationship between the strands and the related mechanics theory were used to study the internal torsion of the wire rope,and the internal torque expression of it was derived.On this basis,the torsional stiffness was proposed to characterize the anti-torsional behavior of the wire rope.The stiffnessof YS9-8×19 braided wire rope was obtained by torsion test.The results show that the clockwise has better torsional characteristics than anticlockwise of the braided wire rope under the same torsional load.Considering the characteristics of large deformation,non-linearity and multi-contact of braided wire rope under load,the numerical simulation of YS9-8×19braided wire rope under tension,torsion and combined loads of tension-torsion was carried out using explicit algorithm to find the distribution law of stress and deformation of wires.Simulation results show that the stress in strands evolves from uniform distribution to local stress concentration along the length of the rope with the increase of tension load.Each strand deforms and gradually moves toward the center of the section.With the similarities and differences between the torsion direction and the lay direction of the strands,the wires in the strands tend to be loosened or tightened and the wires are deformed by tension or compression under torsion load.It is larger than the equivalent stress value of the independent load under the tensile-torsional composite load.The existence of the torsional load can resist the axial deformation of the rope.The twisting direction has little effect on the axial deformation of the rope,but it can cause the internal wire to produce different forms of force and accelerate the failure of the wire rope.With the help of universal testing machine,torsion testing machine and self-developed torsion assistant device,the experimental study of braided wire rope under tension,torsion and combined load of tension-torsion was carried out respectively.The test results show that the numerical simulation of the whole rope is superior to the analytical method in solving the load problem of braided wire rope.The torque of the wire rope under clockwise torsional load is slightly greater than the torque under anticlockwise torsional load.The existence of torsion resists the axial deformation of the braided wire rope and reduces its flexibility.The phenomenon is more obvious with the increase of torsional angle.Torsion can change the force state of the wire rope,and the uneven force of the strands and wires will accelerate the failure.The test results are in good agreement with the numerical simulation results,which verifies the rationality of the construction of the braided wire rope geometrymodel and the validity of the numerical simulation.