Crack Propagation Mechanism And Experimental Study Of AZ31B Magnesium Alloy During Straightening

Magnesium alloy,as a light alloy,has the characteristics of high specific strength,low density and high damping.Because of its excellent mechanical properties,magnesium alloy is widely used in logistics,aerospace,electronic information and other industrial fields.With the rapid development of industrial informatization,more stringent requirements are put forward for the performance of magnesium alloy materials.The magnesium alloy material industry as a whole is developing in the direction of good machinability,stable technological performance,high efficiency and high quality.However,the straightening of magnesium alloy plate is the key link in the processing and molding process of magnesium alloy plate.Under the action of straightening rollers,the plate undergoes repeated tensile-compressive stress changes,resulting in stress concentration at the edge defects of magnesium alloy plate,which leads to the initiation and propagation of cracks at the tip of the defects,and in severe cases,the plate will break and fail during the straightening process.This subject is supported by the Shanxi Provincial Science and Technology Major Project(20181102016)-"Intelligent High-strength Wide and Thick Plate Finishing Line Complete Equipment" to carry out plate straightening research.Therefore,in this paper,the initiation,propagation mechanism and evolution law of edge defect cracks in AZ31 B magnesium alloy sheet during straightening were studied.The main research work of this paper is as follows:(1)Based on the elastic-plastic bending deformation and straightening theory of plates,the elastic-plastic bending deformation mechanical model is established to explore the mechanical characteristics of stress-strain,curvature and bending moment of plates during bending deformation are explored.According to the theory of fracture mechanics,the common crack propagation mechanism and the change of stress field at crack tip are expounded.(2)With the help of ABAQUS finite element analysis software,the straightening model of magnesium alloy plate with original notch at the edge is established,and different straightening process schemes are set.The changes of equivalent stress,displacement,direction and path of crack propagation in the straightening process are explored,and the straightening effect of different process schemes is evaluated with flatness as an index.(3)GTN damage model is introduced into the failure simulation of ABAQUS straightening process,and the effects of straightening inlet reduction,straightening speed and notch geometry size on crack propagation are studied,and the crack propagation of plates with original defects at edges is further analyzed.(4)Design the experimental scheme,and compare and verify the simulation.Explore the trend of crack cracking and crack length expansion under four experimental process schemes.Through the above research work,this paper aims to provide reliable data and theoretical support for the straightening process in the production process of magnesium alloys,and help magnesium alloy sheet manufacturers to improve production efficiency and quality.