Mechanical Properties Of Steel Foams And Buckling Behaviors Of Steel Foam Columns Under Axial Compression

Steel foams possess a unique combination of structural and functional properties.The density,elastic modulus and yield strength can be altered by changing the prosity and pore structure,which introduces a new degree of freedom in its applications.If designed with care,the resulting steel foam component can have higher stability and bearing capacity.Full-scale applications of steel foams will greatly promote the development of steel structures.The research of steel foams is gradually extending from material science field to engineering structure applications;however,studies on mechanical properties of steel foams are mainly focused on the monotonic uniaxial compression performance,and the research of properties of steel foam members is still rare up to now.Based on the relevant research work of manufacturing technology and mechanical properties of steel foams,a large amount of experimental and numerical investigations were carried out to study the preparation processes,mechanical properties and buckling behaviors of steel foam columns under axial compression in this dissertation.The main research works covered in this dissertation include:(1)Among the processing methods of metal foams,the space holder technique is more suited to metals with high melting points.The porosity is regarded as the single most important physical property of metal foams.Steel foams were produced by the space holder technique,and a model equation for calculating the porosity was established based on the study of the relationship between porosity and the spacer content.Steel foams with only micropores were produced using starch as space holder,and the relationship between mechanical properties and microstructures were studied in detail.Then,a cylindrical steel foam sample with large size was produced in factory workshops,which was used in the research of material mechanical properties and buckling behaviors of steel foam columns under axial compression.(2)The uniaxial compression,uniaxial tension,compression loading and unloading tests of steel foams were carried out.The elastic and plastic poisson ratios were obtained and a typical stress-strain curve of steel foams was determined.In addition,the damage evolution law of steel foams was studied.(3)Steel foam specimens under 11 different cyclic loading patterns were tested,and the cyclic hardening behavior and failure deformation were studied.Based on the test results,the corresponding material parameters for the Chaboche model were obtained,which were verified by nonlinear analysis results in the finite element analysis.(4)Experimental investigations were carried out to clarify the global buckling behavior of steel foam columns.Totally 22 columns were tested,and based on the results,the bearing capacity was studied.The finite element model was established,which was validated by comparing the numerical simulation results with experimental results.A large number of columns were calculated by using the finite element model,and the global buckling strengths of totally 418 columns were obtained.Then,the effects of residual stresses,constitutive model and material mechanical properties on the global buckling behavior of steel foam columns were analyzed.In addition,new column curves for steel foams were proposed by the nonlinear fitting from numerical results,which were based on the expression form of column curve formulae in the current Chinese codes.(5)A total of 17 short steel foam columns were tested to investigate the local buckling deformation and bearing capacity.The finite element model was established,and validated by comparing the numerical simulation results with test results.A total of 303 short steel foam columns were calculated by using the finite element model.Then,the effects of different parameters on the local buckling behavior of steel foam plates were analyzed,including the ratio of width to thickness of plate,constitutive model and interactive restraint effects between plates.Furthermore,the width-thickness ratio limitations for steel foam plates in short steel foam columns were proposed based on the yield criterion.