Study On The Fracture Behavior And Fracture Model Of Corroded Cold-bent Thin-walled Steel Plate

The development of steel structure material,the cold bending thin-wall steel as a kind of has many advantages of lightweight steel,compared with thick wall steel steel quantity is little,the price is cheap,light quality,and have sufficient strength and stability,is widely applied in all kinds of industrial construction and civil construction,but in use process for many years,cold-formed thin-walled steel generally can produce serious corrosion phenomenon because of the protective hard,causing difficult to predict the fracture accident,harm to life and property.In this paper,the thin steel with rusted cold bending which has been used in the industrial plant for many years is selected as the research object,and the mechanical properties and fracture prediction of the specimens are studied by means of experimental research,finite element simulation and theoretical analysis.The main contents are as follows:(1)Will be in the demolition of industrial plant specimen made of standard specimen,were selected tablet sites and corners where two kinds of specimens,to extract the rust after cleaning degree of polishing in lab for tensile test specimens,obtained a series of basic mechanical properties of the specimens,the specimens of load deformation curve and fracture load,fracture displacement,such as data,discusses different parts of the relationship between corrosion rate and mechanical properties of the specimens.The results show that the pitting greatly shortens the yield platform of the specimen and reduces ductility performance.The fracture deformation at the bending Angle is only 20% of that at the flat plate,and the strength of the specimen is reduced due to comprehensive corrosion.And compared with ordinary hot-rolled steel,the effect of corrosion on cold-rolled steel is more serious.(2)Combined with tensile test specimens of the corresponding data obtained,based on the actual shape of the finite element model as the basis of accurate numericalsimulation,the introduction of SMCS and VGM fracture criterion,the specimen surface of the material parameters,and to establish a model of isoline chart,generally known specimen cracking from the maximum size of rust pit begin to produce stress concentration caused by rust pit makes the fracture occurs only in the corrosion pits around a small piece of special parts,pitting and stress concentration of the specimens more clearly.(3)Using the ABAQUS finite element software to establish flat parts of the pitting and general corrosion model,the corner part model,pitting specimen by rust pit depth change simulation,simulated by the net change of cross section area of general corrosion specimens,on the basis of not rust mechanical properties of the specimens,obtained from the model related to the fracture criterion of three parameters(MISES stress and the equivalent plastic strain,hydrostatic stress),pitting and general corrosion conditions,rust pit depth and their relationship,the net section area in the relationship.The results show that with the increase of rust pit depth and the net area,the increase of the three data showed regular,between the corresponding function,respectively established rust pit depth and mechanical parameters of fitting function,net area and mechanical parameters of fitting function,put forward the correction coefficient of mechanical parameters,generation into two fracture criterion,is put forward under the pitting and general corrosion state flat parts and corners area a total of four groups of fracture correction criterion,this criterion is applicable to pitting corrosion condition of cold-formed thin-walled steel fracture and general corrosion fracture prediction.