Study On Buckling And Warping Deformation Of Steel Strip

With the development of aerospace, automobile, appliance and other high-end manufacturing industry, there are more and more demand on the quality of strip product. The flatness that affects the product competitiveness and market share becomes the major quality indexes. The generation theory and control technology become the research frontier and focus at home and abroad. Based on National Science Foundation project "Basic Research on Residual Stress Control of Temper Rolling and tension leveling Process for High Strength Steel", the generation mechanism and deformation behavior of buckling and warping for steel strip are studied by using the theoretical analysis, numerical simulation and experiment test. There are to develop and perfect the theory and technology of flatness. The main work and achievements are as follows:(1) According to the generation mechanism, a new summarization and classification is put forward for flatness and straightness defects. The mechanical model of generation process for buckling and warping deformation are established. The general analytical calculation model and solution algorithm which can consider the anisotropy of steel strip are derived and established. The spline finite element method is introduced for solving the buckling and warping deformation under effect of initial strain and external load. The visible calculation software is built up by using MATLAB. Through calculation and comparison, the calculation results of the two methods are agreed with each other, and they all can meet the research needs for flatness.(2) Application of the analysis model of buckling and warping deformation, three important issues in the field of flatness defect generation which are caused by different initial strain in plastic pressure processing of steel strip are studied.①The anisotropy and its influence on flatness and straightness defects of steel strip after rolling are studied.The relationship between critical load, critical wavelength, the path of post-buckling for buckling deformation and warping deformation with the degree of anisotropy are obtained, and the effect laws of anisotropy on flatness and straightness defects are revealed.②Four new explanations from the point of initial strain and external load are put forward for different kinds of oblique buckling, Included initial strain, diagonal and antisymmetric distribution of tensile and compressive stress with shear stress, centre wave with diagonal distribution of tensile and compressive stress and centre wave with shear stress.The mechanical models are established, and they are solved by spline finite element method. The critical condition, the path of post-buckling and their effect factors, effect laws are obtained.③The mechanical model of reverse C-warping, which is one of the complex warping deformations, is established. The warping behavior are analysed, and the deformation laws are obtained which agrees with the reverse C-warping of industrial production. The control technology and measures are proposed, and the industrial applications achieve success.(3) Structural change of steel strip for shearing process will cause flatness changes. The apparent straight strip that has "potential" shape defects will yield various warping deformations after a shearing process. The generation mechanism and deformation behavior of this warping are studied, and the relationship between warping value of small size strip and "potential" shape defects is obtained. The mechanical model of C-warping converting to L-warping is established, and the formula of converting relation is obtained, which is verified by field experiment.