The AA5083 alloy is already being used in applications that require lightweight construction and moderate strengths. In order to carry out accurate simulations of the superplastic forming of this alloy, the used constitutive models should be able to predict the deformation and thinning behavior during the forming process. In this paper, we compare the dome height and pole thickness evolution during gas bulge forming using different AA5083 constitutive material models. The models considered have different levels of complexity and are fitted using either tensile or biaxial experimental data. The simulation results are also compared with experimental data from literature. In addition, recommendations are made for developing accurate material models for the considered AA5083 alloy.

Superplastic forming of the rectangular edge welded envelope consisting of two rectangular sheets welded along their periphery is considered. The diameter of the cylindrical shell manufactured turns out to be considerably less as compared with the initial width of the rectangular edge welded envelope to be formed superplastically. The deforming of the envelope is effected in a free state, i.e. without fixing the edges of the envelope. Finite element analysis of the stress state is effected by using ANSYS software. Time dependencies of the dome height and width of the envelope are obtained for two cases: plane strain state and plane stress state. The following three stages of the deforming process have been established. Elastic bending of the envelope takes place at the first stage, when the dome height is sharply increasing while the width of the envelope is considerably diminishing. Second stage corresponds to the stationary superplastic flow when the dome height and width of the envelope are changing not so much. The third stage is characterizing by increasing the width of the envelope with the increase in the dome height up to its maximum value. The commercial titanium alloy VT14 (Ti-4,2Al-2,7Mo-1,2V) is used in experiments. The comparison of the analytical predictions with corresponding finite element solutions as well as with experimental data is made.

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1 Институт проблем сверхпластичности металлов РАН, ул. Ст. Халтурина, 39, 450001, г.Уфа 2 Уфимский государственный нефтяной технический университет, ул. Космонавтов, 1, 450062, г.Уфа Рассмотрен процесс сверхпластической формовки трехслойной конструкции, состоящей из листа наполнителя, помещенного между двумя листами обшивки, под действием давления инертного газа, подаваемого в технологические зазоры между листами. Основное внимание уделяется учету влияния параметров модели Пэжины на временные характеристики процесса формовки. Предложена математическая модель процесса, основанная на использовании основных гипотез безмоментной теории оболочек. Полученные результаты сопоставлены с результатами решения краевой задачи вязкопластичности, полученными в среде ANSYS. Сделан вывод и применимости предлагаемого упрощенного подхода к анализу основных технологических параметров процесса. Ключевые слова: моделирование; сверхпластическая формовка; трехслойная конструкция; напряженно-деформированное состояние; ANSYS.Superplastic forming of 3-sheet structure consisting of the core sheet placed between two face sheets is considered. Deforming of the 3 sheets structure is effected due to the action of an inertia gas which is supplied between the sheets. Main attention is paid to taking into account the influence of parameters of Perzyna's model on the time characteristics of the process involved. Analytical model of the process under study is based on the main assumptions of the thin shell theory. The results obtained are compared with corresponding finite element solutions of the boundary-value problem in the mechanics of viscoplasticity that are found by means of usage of ANSYS program. The conclusion is made that the analytical approach suggested is suitable in analyzing the time characteristics of the technological process under study.

A method is proposed which allows one to search for a solution to inverse problems of identifying constitutive relations from the results of technological experiments. The method uses simplified mathematical models of technological plastic metal forming processes based on the membrane theory of shells, which allows for calculations of material constants K and m entering Backofen's constitutive relation for superplasticity from the results of experiments carried out directly on a technological equipment. The method differs from others by the fact that for its implementation results of only two test formings of hemispherical domes at a constant gas pressure are sufficient. The set of experimental data include gas pressure, forming time and thickness in the pole of the dome. The method consists of three steps: calculation of initial material constants K and m; fitting of coefficient m* until the coincidence of computed value of the thicnkness at the dome pole with experimentally determined value; correction of the value of constant K*. Finite-elements simulations of superplastic forming (SPF) are done by means of ANSYS software. Computational model of material is considered in the framework of creep theory. Time dependencies of relative dome height and relative thickness of semispheres at the dome pole using approximate formulas and simulations using ANSYS are plotted. The method is verified on an example of superplastic forming of semispheres with 35 mm radius from sheet blanks of titanium alloy VT6 (analogue of Ti-6Al-4V) with thickness of 1 mm to a cylindric matrix with diameter 70 mm and height 35 mm with entry radius of 1 mm at two constant values of gas pressure 0.5 and 0.7 MPa. The forming temperature was equal to 900°C. As a result of validation, agreement of experimental and computational data acceptable for engineering calculations has been obtained. Предложена методика, позволяющая искать решение обратных задач идентификации определяющих соотношений по результатам технологических экспериментов. В методике использованы разработанные упрощенные матема-тические модели технологических процессов обработки давлением, построенные на основе безмоментной теории оболочек, позволяющие вычислять постоянные материала K и m, входящие в определяющее соотношение сверх-пластичности Бекофена, по результатам экспериментов, которые проводятся непосредственно на технологическом оборудовании. Методика отличается от известных, тем, что для ее реализации достаточно результатов только двух тестовых формовок полусферических куполов при постоянном значении давления газа. Набор экспериментальных данных включает: давление газа, время формовки и толщину в полюсе купола. Методика состоит из трех этапов: расчет начальных значений постоянных материала K и m; подбор величины показателя m* до совпадения расчет-ного значения толщины в полюсе купола с экспериментально полученным значением; корректировка величины постоянной К*. Конечно-элементное моделирование процесса СПФ выполнено в среде программного комплекса ANSYS. Численная модель мате...