Abstract
Aims of research. This paper deals with the problem of determining the radius of the neutral surface of the bending strip at the same time the action of tensile stresses. Methods. In the development of technological processes of sheet bending and the calculation of the initial billet (sweep), most often considered a flat stress state and preference is given to the theory of pure bending, providing uniform curvature of the individual layers of metal under the action of the bending moment and neglecting the action of transverse tensile forces. However, in reality, bending is always accompanied by sliding of the metal along the deforming tool, causing the appearance of friction forces and creating a complex loading in the form of plastic bending with stretching in the metal, which will additionally displace the neutral surface, forcing the experienced one to adjust the technology of manufacturing bent parts. Provides an overview and analysis of the most famous works dedicated to the topic, specifying the distribution of the contact stresses from the inner surface to the center of curvature and developed the theory of complex bending, which allows to specify the radius of the neutral surface in conditions of stretching of the flexible strip of the additional tangential stresses. Results. The results obtained will allow to simulate the stress state of the metal in the development of technological processes of sheet stamping and, in particular, to assess the specific braking force during the bending (straightening) of the strip in the process of pulling through the thresholds and brake edges of the die tooling to eliminate possible defects in the elongated parts and to clarify the dimensions of the workpiece and the finished profile.
Highlights
This paper deals with the problem of determining the radius of the neutral surface of the bending strip at the same time the action of tensile stresses
In the development of technological processes of sheet bending and the calculation of the initial billet, most often considered a flat stress state and preference is given to the theory of pure bending, providing uniform curvature of the individual layers of metal under the action of the bending moment and neglecting the action of transverse tensile forces
In reality, bending is always accompanied by sliding of the metal along the deforming tool, causing the appearance of friction forces and creating a complex loading in the form of plastic bending with stretching in the metal, which will displace the neutral surface, forcing the experienced one to adjust the technology of manufacturing bent parts
Summary
В работе рассматривается вопрос определения радиуса нейтральной поверхности изгибаемой полосы при одновременном действии растягивающих напряжений. Полученные результаты позволят смоделировать напряженное состояние металла при разработке технологических процессов листовой штамповки и, в частности, оценить конкретное усилие торможения при изгибе (спрямлении) полосы в процессе перетягивания через перетяжные пороги и тормозные ребра штамповой оснастки для устранения возможных дефектов вытягиваемых деталей, а также уточнить размеры заготовки и готового профиля. При изгибе с растяжением радиальные напряжения чистого изгиба справедливо можно рассматривать в качестве контактных напряжений пластического формоизменения, возникающих в зоне соприкосновения заготовки с деформирующим инструментом σr σк [6]: ρн rнар rвн exp σк σT
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