Study On Fretting Damage Behaviors And Fretting Fatigue Life Estimation Of Steel Wires

Fretting wear and fretting fatigue occurs among neighboring strands and among contactingwires in hoisting rope during lifting in coal mine, which accelerates the fatigue fracture of steelwires, thereby reduces the endurance strength of the rope, and thus affects the rope reliability andproduction safety in coal mine. Therefore, studies on fretting damage behavior and frettingfatigue life estimation of steel wires are significant to prolong the rope service life and toenhance the rope reliability.6×19+IWS rope is taken as the objective of study in this thesis. Load-carrying conditionsof hoisting rope at the sheave tangent point at the start and end of a lifting cycle are explored bystatic analysis. Simulink simulation models are built based on dynamic models of the ropetension during the lifting cycle. The roles of maximum hoisting velocity, hoisting acceleration(deceleration), and terminal load on peak tensions and tension amplitudes of the rope during thelifting cycle are investigated. Simulation results show that overall ranges of the rope tensionvary from2102.1N to18762.1N and from191.1N to16851.1N at the start and end of thelifting cycle, respectively. During lifting, overall ranges of maximum peak tension, maximumtension amplitude, minimum peak tension and minimum tension amplitude are9793.3N-19896.9N,176N-4817.6N,1240N-19821.3N, and39.5N-2366N, respectively.Mathematical relationships between tensions and tension amplitudes of the rope and frettingfatigue parameters of steel wires, and corresponding Simulink simulation models are establishedemploying the rope theory and contact mechanics. The effects of hoisting parameters onfretting fatigue parameters during the whole lifting cycle are discussed. Simulation resultsshow overall ranges of various fretting fatigue parameters almost all present the expanding orupward expanding trends with increasing hoisting parameters during the whole lifting cycle.Overall ranges of wire tension, contact load and relative displacement between wires changefrom1.5N to175.6N, from0.2N to452.1N and from0.2μm to99.6μm, respectively.The stresses and deformations of6×19+IWS rope are explored employing the finite elementmethod. Detailed analysis of the three-layered strand under axial extension is carried out usingconcise boundary conditions and sub-modeling technique. Effects of friction of coefficient andmaterial model on stress distributions and radial deformations are analyzed. The results showthat stresses along wire surfaces and wire deformations both present distributions of quadraticcurves. Various stresses on the cross-section of rope in the axially middle location all exhibitsymmetric distributions. The stresses on cross-sections of the straight strand and spiral strandboth decrease along the radially outward direction, respectively. Neighboring spiral strands exhibit the largest difference in deformations of contacting wires. Variations of coefficient offriction, material model and strand axial extension strain all cause distinct stress levels of variouswires, abrupt changes of stress near contact zones of contacting wires of adjacent wire layers,and radial deformations.Three-dimensional Hertzian contact theory is introduced to investigate the effects ofcrossing angle and contact load on the contact widths and maximum contact pressure. Theevolution of fretting wear depth of wires crossed at different angles during fretting wear and thecorrelation model between fretting wear depth and fretting parameters are established. Theresults demonstrate that different crossing angles and contact loads both cause distinct contactwidths and maximum contact pressure. Experimental values of wear depths of steel wirescrossed at angles of90°and18°in tests with different fretting parameters show good agreementwith corresponding predicted values, which validates the fretting wear evolution model.The roles of fretting amplitude, strain amplitude and contact load on fretting fatiguebehaviors of steel wires in low cycle fatigue are investigated employing the homemade frettingfatigue test apparatus. The results show that different fretting fatigue parameters inducesdistinct coefficients of friction, fretting regimes, wear mechanisms, fretting fatigue lives, crackinitiation and propagation characteristics during the fretting fatigue tests. Those elements offretting fatigue behaviors interact with each other.Fretting fatigue behaviors of perpendicularly crossed steel wires without damage and withwear gaps are studied using finite element method. The effects of fretting fatigue parameters onfretting regimes and stress distributions on contact surfaces are explored. Multiaxial fatiguecriteria are employed to investigate roles of fretting parameters on crack initiation characteristicson the tensile wire surface during the initial fretting stage. The linear elastic fracture mechanicsand method for a power function curve fitting are used to establish quantitative relationshipsbetween fretting fatigue lives of tensile wire and cyclic stress, contact load and fretting amplitude,respectively. The results show that different fretting fatigue parameters induce distinct frettingregimes, stress distributions and abrupt changes of stresses near trailing edges in two cases.Crack initiation on the contact surface of tensile wire becomes more difficult and easier withincreasing contact load and increasing fretting amplitude, respectively. Predicted fatigue livesare in good agreement with experimental values, which validates the theoretical model.