Papers by Author: Abel D. Santos

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Authors: J. Bessa Pacheco, Abel D. Santos
Abstract: The sheet metal bending is one of the metal forming processes with the simplest geometric interpretation and usually a 2D analysis is considered. The bend over a sheet metal blank consists of a V shape forming by using a punch, with a certain nose radius, forcing the plate against an open die, with a V section. The forming result is a part with an angle obtained between the V legs, flanges, which is known as bending angle. The operation to get the required V angle is called air bending, or free bending. The most common used machines for this forming process are press brakes, special long presses, where the tools, punch and die, are attached to. With the spread use of CNC machines, and their computer control capabilities, most of them using graphical user interface (GUI), became important to get the required shape at first trial. Beyond the required bending angle obtained with just one hit, it is also important to position the gauge system in order to get the successive flange lengths to complete the programmed shape. The main variables controlled by the CNC are the punch penetration inside the die and the position of the back gauge, which is determined by the bend allowance. However this penetration is not the only responsible for the resulting bending angle and the gauging position is not the only responsible for the flange length. Additionally, the radius inside the V shape edge, known as bending radius, influences the geometry and correspondingly the bend allowance. Some authors believe that the punch nose radius has direct influence, both in the bending angle and bend allowance. In this paper, results are presented describing the use of finite element analysis as an aid in the prediction of the inside bending radius, that influences both punch penetration for the final bending angle and the bend allowance for the final flange length. From the air bending analysis, a natural inside bending radius is presented as an important variable in these kind of processes, as well as its minor dependence on the punch nose radius.
Authors: A.P.B. Tufaile, Abel D. Santos, Y. Souche, V. Novosad
Authors: L.G.C. Melo, Abel D. Santos
Authors: Pedro Teixeira, Abel D. Santos, J. César de Sá, Augusto Barata da Rocha
Abstract: The optimisation of sheet metal processes by using numerical simulations has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving, in many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries. The introduction of new materials brought new challenges to sheet metal forming processes. The behaviour observed with conventional steels may not be applied when using high-strength steels or aluminium alloys. Numerical codes need to model correctly the material and different constitutive equations must be considered to describe with greater accuracy its behaviour. This enhancement of material description may provide a better prediction of the forming limits, enabling an assessment of the influence of each forming parameter on the necking occurrence and the improvement of press performance. This paper presents two numerical approaches for failure prediction in sheet metal forming operations: one is the implementation of the Lemaitre’s ductile damage model in the Abaqus/Explicit code in accordance with the theory of Continuum Damage Mechanics and the other is the traditional use of FLDs, usually employed as an analysis of the finite element solution in which the necking phenomenon is carried out in the framework of Marciniak-Kuczinsky (M-K) analysis coupled with the conventional theory of plasticity. The previous strategies and corresponding results are compared with two experimental failure cases, in order to test and validate each of these strategies.
Authors: Ana Reis, Abel D. Santos, J.F. Duarte, A.B. Rocha, Say Yi Li, E. Hoferlin, Albert Van Bael, Paul van Houtte, Cristian Teodosiu
Authors: Augusto Barata da Rocha, Abel D. Santos, Pedro Teixeira
Abstract: The use of Finite Element Simulation allows accurate predictions of stress and strain distributions in complex stamped parts. The onset of necking is strongly dependent on the strain paths imposed to the parts and therefore the prediction of localized necking can be a difficult task. Numerical models of plastic instability have been used to predict such behavior and recent and more accurate constitutive models have been applied in these calculations. In many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries, the optimization of sheet metal processes, through the use of numerical simulations, has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving. This paper makes an analysis of the evolution of strain gradients in stamped parts. The combination of Finite Element Analysis with a Plastic Instability Model, developed to predict localized necking under complex strain paths, shows that it is possible to predict failure with precision. Several constitutive laws are used and comparisons are made with experiments in stamped benchmark parts. Considering non linear strain paths, as detected in stamped parts, more accurate failure predictions are achieved. The work described in this paper shows the need to include a post processor analysis of failure, capable of predicting the behavior of the material under non linear strain paths. Taking this phenomenon into account, it is shown that it is possible to increase the accuracy of the onset of localized necking prediction.
Authors: Abel D. Santos, J.F. Duarte, Ana Reis, Pedro Teixeira, A.B. Rocha, A. Ajmar, M. Bertero, S. Saporita
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