Study On Axial Mechanical And Stress Relaxation Performance Of Wire Ropes

As an important part of hoisting equipment in the ultra-deep mine,a wire rope has significant influence on the life and efficiency of the hoisting system.The mechanical performance of the lifting wire rope can directly affect the lifting capacity of the hoisting equipment.In addition,the mechanical performance will change in the long-term loading process of the lifting wire rope,which will affect the reliability of the mine hoist.Funded by the National Key Basic Research Program of China(No.2014CB049403),the present thesis studies the axial mechanical performance of the wire rope strand considering inter-wire contact,and analyzes the stress relaxation behavior of the wire rope strand subjected to tensile or bending loads.Moreover,the wire rope tensile tests are conducted.The above research is eager to provide a certain theoretical reference for the design and selection of lifting wire ropes in the ultra-deep mine.The main contents of the thesis are as follows:Firstly,the mathematical model of wire rope strand subjected to axial tension and torsion loads is established,and solved with a semi-analytical method(SAM).Meanwhile,the above model and method are verified.The results show that the axial mechanical performance of the wire rope strand can be solved quickly and accurately with the said SAM,whose efficiency is much higher than that of the finite element method.The axial strain of the outside wire,contact pressure,contact deformation and half contact width between the central and outside wires increase with increasing torsion load during the axial torsion process.Moreover,the contact between the central and outside wires,and the transverse radial contraction of the outside wire can lead to a slight decrease in the helix radius of the outside wire centerline.Further,based on creep and relaxation theories of the material,the finite element model for the stress relaxation of spiral triangular strand(STS)subjected to the axial tensile load is established.And the tensile model is verified.The simulation shows that non-uniform distributions of von Mises stress in the middle cross-sections of STS can be aggravated through the increment of the lay angle and outside wire diameter.The increment of relaxation time leads to a uniform stress distribution of STS,but increases the relaxation extent of the inter-wire contact zone and central wire.STS with a larger axial tensile strain,lay angle and outside wire diameter will bring out a larger von Mises stress and equivalent creep strain.In addition,based on the Modified Time Hardening model,the finite element model for the stress relaxation of single strand wire ropes subjected to bending loads is established,and the bending model is verified.The numerical results show that high stress and creep strain zones of the wire are distributed symmetrically on both sides of the neutral layer,where no stress relaxation occurs.A small elastic modulus or a large Poisson’s ratio is helpful to reduce the maximum von Mises stress and maximum equivalent creep strain of the wire rope.Increasing the lay angle or outside wire diameter will cause a large von Mises stress and equivalent creep strain.Finally,tensile tests are conducted to study the tensile performance of wire ropes by using electronic multifunctional testing machine,and the breaking tensile force of wire ropes are measured.The experimental results show that with the increase of tensile velocity,the measured breaking force increases gradually.The steel core has an ability to resist breaking force in comparison with the fibre core,and the surface heat treatment can effectively change the tensile properties of the wire rope.Steel wire material and surface heat treatment have great influence on the fracture morphology of the steel wire.