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Experimental study of Portevin–Le Châtelier bands on tensile and plane strain tensile tests

Sene N. A., Balland P., Bouabdallah K.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 1

94--102

EN

The aim of this article is to show that it is possible to create an experimental database to better model Portevin–Le Châtelier (PLC) phenomenon with two kinds of solicitation. Indeed, two kinds of specimen are tested: conventional tensile specimens and specimens designed for plane strain tensile test. In order to better understand this phenomenon and above all to put away any geometry effect, two materials are tested: one without PLC bands (AU4G) that is used as reference and AlMg3 which is well known for its PLC bands. The image correlation tool is used to analyse the creation and the spread of PLC bands. Characteristic parameters of the bands are then measured: width, angle, transported strain, strain rate, and velocity. The originality of this paper is first to show that PLC bands are present during plane strain tensile test and then to characterize the bands thanks to image correlation. These experimental databases could be very useful for those who develop models on PLC phenomenon.

2

Influence of heterogeneities introduced into the modelling of a ring compression test

Bizet L., Charleux L., Balland P., Tabourot L.

Archives of Civil and Mechanical Engineering

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2017

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Vol. 17, no. 2

365--374

EN

This paper analyses the influence of heterogeneities introduced into the constitutive model of Aluminium alloy 6060. Two types of modelling are hereby presented: a standard phenomenological homogeneous model and a compartmentalized hybrid model, the formulation of which is based on the physical phenomena underlying plasticity. The mechanical parameters needed to establish such models are determined by two different experimental tests: a uniaxial tensile test and a ring compression test. The ability of such models to simulate a forming operation that differs from the operation used to determine their parameters will then be discussed.

3

Constitutive modelling effect on the numerical prediction of springback due to a stretch-bending test applied on titanium T40 alloy

Maati A., Tabourot L., Balland P., Ouakdi E. H., Vautrot M., Ksiksi N.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 4

836--846

EN

Nowadays, numerical simulation by finite element analysis is an essential tool that allows performing virtually sheet metal forming processes, and therefore to reproduce various phenomena such as springback (SB) and necking that are generated by plastic deformation. However, the quality of the model used to represent the mechanical behaviour is a determining factor for the realism of numerical simulations. To perform well, the model must reproduce all the properties of the material such as the anisotropy and the strain hardening induced by plastic deformation. The main purpose of this work is to show, by means of numerical simulations, the influence of constitutive modelling on the prediction of the degree of SB in the case of a stretch bending test. Tests have been carried out on titanium sheets which have a wide range of applications for high tech industries because of specific mechanical and physical properties. At the same time, we have investigated the dependence of some process parameters such as the clamping force on SB. In order to prove the accuracy and reliability of the proposed finite element model, experimental data were used to compare with the numerical results.

4

Numerical study of the micro-formability of thin metallic materials: virtual micro-forming limit diagrams

Sene N., Balland P., Arrieux R.

Archives of Civil and Mechanical Engineering

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2011

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Vol. 11, no 2

421-435

EN

This paper presents the determination of virtual micro-forming limit diagrams from two types of numerical simulations based on the finite element method: one with modelling of the full tool for microdeep drawing and a thin blank with geometric imperfections, based on a defined roughness; and a second called "reduced simulation" where different deformation paths were simulated with appropriate boundary conditions by introducing the same type of geometric imperfections on aluminium 1050A (99.5%). A new test for detecting the onset of necking, called the "change of slope" criterion has been defined. Several methods based on histograms to represent the distributions of major and minor strains, have been used to determine the strain at the onset of necking. The numerical micro-forming limit diagrams (MFLD) were then compared to one obtained experimentally.

PL

W pracy przedstawiono wyznaczenie wirtualnej krzywej odkształceń granicznych dla mikroformowania blach aluminiowych 11050A (99,5%), na podstawie dwóch rodzajów numerycznych symulacji opartych o metodę elementów skończonych. Pierwszy to modelowanie, z geometrycznymi modelami narzędzi procesu mikro wytłaczania cienkiego półfabrykatu z geometryczną niejednorodnością wprowadzoną za pomocą zdefiniowanej chropowatości. Drugi, nazwany "uproszczoną symulacją", w którym różne drogi odkształcania były symulowane za pomocą odpowiednich warunków brzegowych wprowadzając tego samego typu niejednorodność geometryczną. Dla wykrywania początku utraty stateczności został zaproponowany nowy test nazwany kryterium zmiany nachylenia. Dla wyznaczenia odkształceń początku utraty stateczności zastosowano różne metody oparte o reprezentację rozkładu odkształceń głównych za pomocą histogramów. Wyznaczona numerycznie krzywa odkształceń granicznych dla mikroformowania (MFLD) została porównana z krzywą doświadczalną.