A Preliminary Study On Buckling Deformation Of Thin Sheet Metals Featured With Typical Geometric Characteristics

Generally,sheet metals tend to buckle under in-plane compressive loads.Local buckling,as a rising research topic,has been regarded as the main reason for causing sheet wrinkling during the stamping forming process.Meanwhile,a new kind of sheet metal forming technology called Buckling Forming is expected to be developed if the buckling deformation can be predicted and controlled accurately.Compared with stamping process,buckling forming needs no tools and much fewer forming loads.The final shape of a product is mainly determined by the tools during stamping process,while the final output is essentially dependent to the geometric characteristics of the sheet metal during buckling forming.Hence,the research on buckling deformation of sheet samples with different geometric characteristics is the fundamental of buckling forming frame.A series of sheets with typical characteristics were designed and cut for studying their configurations after buckling deformation under uniaxial or biaxial loads.Analytical models,simulations via finite element method and buckling deformation experiments were performed subsequently in this work.The details are as following:Firstly,flat-thin sheets were designed and cut into different “patterns”.Buckling deformation experiments were launched,and the results demonstrated that buckling forming could be used to generate threedimensional structures with various shapes,which would be a reference for further buckling structure designs.In the meantime,the results are virtually critical to the following investigations concerning geometric parameters relationships.Secondly,two kinds of typical structures,even-width and unevenwidth were tested under uniaxial-loading.The analytical models of geometric parameters were derived to describe both loading and unloading processes respectively.Cosine contour were assumed during loading process and constant or inconstant equivalent stress model were applied during unloading process separately.These results were compared to each other and the optimized models were established as well.The analytical solutions fit well with experimental data.Moreover,the relationships of geometric parameters between the two-dimensional patterns and the deformed three-dimensional structures could be discussed with the consequences of the analytical solutions.Finally,FEA simulations were operated on buckling deformation,where the hardening models were especially discussed about their effects on springback calculations.Some common hardening models were introduced and their calculated results were compared with experimental data.For the test material of stainless steel 304,Chaboche N3L0 model revealed better predictions than others.For instance,the simulation prediction errors of the height,length and angle of a typical sample KL2# were-3.2%,0.4% and-3.6% respectively.