Multi-scale Modeling And Simulation On Damage In Heterogeneous Materials Of Ultra-high Steel Wire Drawing

Cold drawn pearlitic wires is widely used in large construction projects due to its high strength and simple production process.It is also the only nano-crystalline material used in engineering yet.In many years,the performance of steel wires are enhanced significantly by improving the drawing process.However,few scholars studies which kind of microstructure billet is more suitable for pearlitic wires production.In order to improve the quality of pearlite steel wire from the source,the damage evolution process of sheet pearlite micro-aggregates in the middle layer of steel wire during drawing process is investigated from the micro-point of view,and the internal stress distribution and damage distribution are analyzed.The methods and indexes for evaluating the internal damage of pearlite steel wire are put forward to provide theoretical guidance for the choices of steel billet.The main work and conclusions in this paper are as follows:A layered pearlite micro-element model was established based on the pearlite detailed structure image obtained by electron scanning microscopy.The material parameters of the ferrite were determined through uniaxial tensile tests and a damage constitutive model was developed based on the mechanical performance of the cementite during the drawing process.Then a numerical model of lamellar pearlite micro-aggregates was developed,which was verified by the simulation of uniaxial tension.According to the actual damage of ultra-high steel wire drawing,the GursonTvergaard-Needleman(GTN)model was selected as the macroscopic multi-passing damage constitutive of steel wire;The stress field,strain field and damage field of the steel wire in the drawing process were obtained by numerical simulation of the six-step drawing model.The results show that in the process of drawing,the radial stress of steel wire decreases first and then increases.The radial strain shows a trend of non-uniform distribution with the increase of drawing number.The damage distribution gradually concentrates to the core with the progress of drawing.Through the analysis of the drawing direction of the wire core,the front end of the wire is the most damaged area in the forming process,that is,the macroscopic most unfavorable area.Based on the macro-scale simulation results of steel wire in drawing process,the stress and constraints of pearlite micelle at different positions are extracted.The displacement time history is selected as dynamic control loading condition of infinitesimal model in drawing process.The results of damage evolution in the infinitesimal model of lamellar pearlite are obtained.The results show that the cementite in the pearlite bears the main tensile stress during the drawing process.After the six-step drawing processes,a damage zone,perpendicular to the laminar direction,is formed in the center of the pearlite.The width of the damage zone is related to the length of the shortest cementite in the pearlite.Finally,the damage assessment method in pearlite is put forward,and the definition and algorithm of damage assessment index are given.The damage evolution process of pearlite with different structural parameters,such as different ratio in the same total width of cementite and ferrite laminates,or different angle between laminates and drawing direction,is simulated by using the control variable method.The damage evolution process of pearlite at different locations in steel wire is studied.The assessment for different working condition is performed using the developed damage evaluation indexes.The results show that,to a certain extent,decreasing the ratio of lamellar width and increasing the lamellar angle are beneficial to decrease the damage evolution rate of pearlite.The location of the pearlite micelle has the greatest influence on its damage assessment index,and the most serious pearlite damage occurs at core of the steel wire.