Pierre Yves Manach

• PhD
• Professor (Full) at University of Southern Brittany

In the electronics industry sector, different types of parts made out of copper alloys are used, such as metal supports (lead frames), on which the chips are assembled. These parts are produced using progressive dies, with several blanking and bending stages. There is a huge interest to numerically predict these multistage forming processes, to dec...

The aim of this study is to investigate the balance between 2D and 3D (or twist) springback of copper-based thin sheets after a deep drawing process. Such materials are widely used in the manufacturing of electric and electronic components, but getting an accurate final geometry is usually difficult due to springback. Three copper-based materials a...

Shear testing holds a peculiar place in sheet metal characterization for multiple reasons. Indeed, as opposed to tension or bi-axial expansion, the principal strains of such a deformation change their direction, non-linearly, as a test proceeds. It is, in general, also impossible for an experimental setup to reproduce theoretical conditions. The ki...

After forming by plastic deformation, it’s rare that the part produced retains its shape perfectly after removing the tools, the shape and dimensions that the tools imposed on it. This change in shape is mainly due to springback. This study focuses on the springback of U-shaped channels made of thin sheets of beryllium copper alloy 0.1 mm thick. Th...

The purpose of this paper is to simulate a complex forming process with parameters identified from tensile and shear tests. An elastic-plastic model is retained which combines a Hill’s 1948 anisotropic criterion and plastic potential using a non-associated flow rule. Firstly, a mechanical characterization is made with homogenous tests like tensile...

Dual phase steels are largely used to form automotive structural parts by deep drawing involving complex loading paths, which influence the material mechanical behavior and formability, as well as subsequent service life. The aim of this paper is to investigate the calibration of a strain path change model from an experimental database involving si...

Rigid plastic material models are suitable for modeling metal forming processes at large strains where elastic effects are negligible. A distinguished feature of many models of this class is that the velocity field is describable by non-differentiable functions in the vicinity of certain friction surfaces. Such solution behavior causes difficulty w...

The main objective of the present paper is to compare, by means of a problem leading to a closed-form solution, the qualitative behavior of solutions based on three strain hardening laws: Swift’s law, Ludwik’s law, and Voce’s law. The boundary value problem involves the maximum friction law as one of the boundary conditions. Such features of the so...

This study deals with the occurrence and numerical prediction of Portevin-Le Châtelier (PLC) instabilities during a forming process at room temperature. In a first part, the mechanical behavior of an aluminium alloy (5000 series) thin sheet is investigated in tension and simple shear under quasi-static conditions and at room temperature. As PLC eff...

The objective is to propose an accurate method for determining the forming limit curves (FLC) for ultra-thin metal sheets which are complex to obtain with conventional techniques. Nakazima tests are carried out to generate the FLCs of a pure copper and a copper beryllium alloy with a thickness of 0.1 mm. Because of the very small thickness of the s...

The bending process of an industrial connector is considered and investigated via numerical simulation using a crystal plasticity finite element model (CPFEM). The process consists of sequentially bending a 0.1 mm thick copper-based alloy (CuBe2) with progressive tools into a miniature cylindrical connector of around 1 mm in diameter. The paper foc...

Several alloys are subjected to plastic instabilities that are due to the interaction between dislocations and solutes. Among them, Lüders bands and the Portevin–Le Chatelier (PLC) effect are of particular interest as they complicate the industrial use of many commercial alloys. They involve a repeated softening that results in mesh sensitivity and...

To investigate the impact of the variations of different input parameters in the multi-stage hot forging process of a shackle, an analysis is carried out through numerical simulations of the whole manufacturing process. Due to the complexity of the process and the large number of factors influencing the thermo-mechanical forming process, the invest...

The present study focuses upon the numerical investigation of fracture initiation of austenitic stainless steel, AISI 304L, during a forming process leading to an expansion strain path. Hence, a combined experimental and numerical approach was tested. Monotonic tensile tests up to fracture were carried out. Load-extensometer displacement curves and...

The aim of this work is to determine the forming limit curves (FLC) of ultra-thin sheets of pure copper by a time-dependent method based on the analysis of the strain rate, and to use the macroscopic rupture criteria to predict these curves in order to evaluate the formability of the sheets. Many criteria make it possible to predict the onset of ne...

Automotive manufacturers have shown a growing interest in an integrated design approach, considering the coupling and interactions of different design phases, as it saves time and increases part reliability. In particular, the residual stresses induced by the forming process of metallic sheets affect the service life. Therefore, the accuracy of the...

Aluminum alloys raise a growing interest in the automotive industry as they represent a fair compromise of strength, density and formability. However their use is critically hindered by the occurrence of the Portevin-Le Chatelier effect that is not yet accurately predicted by numerical simulations. Based on experimental investigations, an attempt t...

Single point incremental sheet forming (SPIF) is a process of manufacturing parts that leads to low prices of manufactured parts and high productivity. However, surface finish and forming time are responses that still need to be optimized to get better surface quality and less forming time. In the present paper, two techniques, the Taguchi grey rel...

Lüders bands and the Portevin–Le Chatelier effect are both due to plastic flow instabilities that affect a wide variety of metallic materials. The present study focuses on understanding these behaviors. Field kinematic measurements combined with the comparison of two specimen sizes are used here to characterize the Al–Mg alloy AA5086, by investigat...

There has been a longtime and steady interest for the influence of strain path changes on the forming and formability of metallic sheets. First from an experimental point of view, leading to a classification of strain path changes according to their severity, related to the microstructural changes at the grain scale and stress stagnation or even de...

This study is dedicated to the experimental characterisation and phenomenological modeling of the bake hardening effect of a thin steel sheet, to predict the static dent resistance and perform an experimental validation on a bulged part. In a first step, rectangular samples are submitted to a thermo-mechanical loading to characterise the bake harde...

L'objectif de ce travail est d'étudier l'influence des lois de comportement sur la simulation numérique d'essais d'emboutissage inverse des tôles minces en acier inoxydable AISI 304L. Plusieurs modèles ont été considérés pour prédire les effets combinés d'anisotropie et d'écrouissage, ainsi que les changements des trajets de déformation. L'identifi...

This study deals with forming and springback of U-shaped channels made of copper alloy thin sheets. Three materials are considered: pure Cu, copper-beryllium CuBe2 and copper-iron CuFe2P alloys. All these materials are supplied under sheets of thickness around 0.1mm. Their mechanical behavior is investigated in monotonic uniaxial tension, loading-u...

To evaluate a priori the amount of strain path changes in forming processes in order to adjust the complexity of constitutive equations, it is necessary to develop forming tests at the laboratory scale sensitive to strain paths changes. In this work, a micro-forming experiment is designed in order to perform reverse deep drawing tests on ultra-thin...

The Swift test was originally proposed as a formability test to reproduce the conditions observed in deep drawing operations. This test consists on forming a cylindrical cup from a circular blank, using a flat bottom cylindrical punch and has been extensively studied using both analytical and numerical methods. This test can also be combined with t...

This work adopts elastic–plastic/damage coupling in order to describe tensile behavior with validation on the deep-drawing test of a DP980 Dual Phase steel sheet. The damage model used is the Gurson–Tvergaard–Needleman (GTN model). The hardening laws used are those of Swift (non-saturating law), Voce (saturating law), Hockett-Sherby (saturating law...

Experimental and numerical cup drawing process has been investigated on 0.65 mm zinc sheets. The cup exhibits anisotropic earrings due to the material microstructure. The material formability is studied through elliptical bulge tests in the rolling, diagonal and transverse direction. High anisotropy of the formability is observed. The numerical sim...

The aim of this study is to investigate the forming limits of an ultra-thin copper sheet (0.1mm thickness) that is used for connection applications. The first step consists in characterising the mechanical behaviour under different strain paths, up to necking and final rupture, such as uniaxial and biaxial tension, in order to investigate the large...

This study presents an experimental investigation of the heat treatment of 34CrNiMo6 steel used for shackles. Indeed, industrial requirements impose specific mechanical properties to the materials which constitute shackles. The aim of this work is to propose a method to relate heat treatment parameters and the resulting mechanical properties. Instr...

The Swift test was originally proposed as a formability test to reproduce the conditions observed in deep drawing operations. This test consists on forming a cylindrical cup from a circular blank, using a flat bottom cylindrical punch and has been extensively studied using both analytical and numerical methods. This test can also be combined with t...

The present work aims to study the constitutive models' influence on the reverse deep drawing simulation of cylindrical cups. Several constitutive laws were considered to predict the combined effects of anisotropy as well as the changes in strain path direction of the stainless steel. To this end, a number of models were used, worth mentioning amon...

The kinematic contribution to the hardening of ultra-thin metallic sheets characterized by monotonic and reversed simple shear tests is of high interest in the sheet metal forming industry, because of its influence on the accurate prediction of springback. However, ultra-thin sheets are very sensitive to buckling when submitted to shear stress beca...

The main objective of this study is to characterize the mechanical behaviour of an Al-Mg alloy in conditions close to those encountered during sheet forming processes, i.e. with strain path changes and at strain rates and temperatures in the range 1.2×10−3–1.2×10−1 s−1 and 25–200°C, respectively. The onset of jerky flow and the interaction of dynam...

Plenary lecture of the Benchmark 3 Numisheet 2016

These results can be used to check coupled thermal and mechanical constitutive laws

A 3D finite element analysis has been carried out of the whole manufacturing process of a shackle involving the steps of closed-die forging and de-flashing of the extremity jaws, the open-die forging of the central body, and the ram bending of the crown. Thermal effects related to the transportation from the gas furnace to the mechanical press and...

This work deals with the numerical prediction at different temperatures and under tension and simple shear of the Portevin-Le Châtelier (PLC) effect. The Estrin-Kubin-McCormick constitutive model was extended in a phenomenological way in order to take into account the influence of temperature and plastic anisotropy. The identification procedure use...

Plastic instabilities like Portevin-Le Châtelier were quite thoroughly investigated experimentally in tension, under a large range of strain rates and temperatures. Such instabilities are characterized both by a jerky flow and a localization of the strain in bands. Similar phenomena were also recorded for example in simple shear [1]. Modelling of t...

Micro-forming of ultra-thin sheet metals raises numerous challenges. In this investigation, the predictions of state-of-the-art crystal plasticity (CP) and phenomenological models are compared in the framework of industrial bending-dominated forming processes. Sheet copper alloys 0.1mm-thick are considered, with more than 20 grains through the thic...

Accurate prediction of springback is a long-standing challenge in the field of warm forming of aluminium sheets. The objective of this benchmark is to predict the effect of temperature on the springback process through the use of the split-ring test [1] with an Al-Mg alloy. This test consists in determining the residual stress state by measuring th...

The forming tools are commonly assumed as rigid in the finite element simulation of sheet metal forming processes. This assumption allows to simplify the numerical model and, subsequently, reduce the required computational cost. Nevertheless, the elastic deformation of the tools can influence considerably the material flow, specifically the distrib...

In the expanding context of device miniaturization, forming processes of ultra thin sheet metals are gaining importance. Numerical simulation of these processes requires accurate material modeling. In this study, both the phenomenological modeling approach and the crystal plasticity finite element method (CPFEM) are considered. Theoretical definiti...

Simulations of sheet metal forming processes are nowadays of common use in the manufacturing industry and mostly performed with commercial finite-element softwares. Though remarkable improvements on the reliability of these simulations have been achieved over the last decades, the material modeling remains an essential aspect to be upgraded. On one...

Micro-forming of ultra-thin sheet metals raises numerous challenges. In this investigation, the predictions of state-of-the-art crystal plasticity (CP) and phenomenological models are compared in the framework of industrial bending-dominated forming processes. Sheet copper alloys 0.1mm-thick are considered, with more than 20 grains through the thic...

Hole-flanging which is the manufacturing operation used to form an integral collar around the periphery of a hole in a metal sheet is investigated. In this work, a 2-mm-thick 1000 series aluminium alloy sheet which is widely used in industrial applications was considered. The process is studied by means of numerical simulations and compared with ex...

The effect of volume fraction and hardness of martensite on the Bauschinger effect in Dual Phase (DP) steel was investigated for strain levels close to those observed in automotive stamping. Five different grades of DP steel were produced by controlled heat treatment allowing the examination of the Bauschinger effect for three different volume frac...

This study deals with the multi-stage forming process of a sling shackle, investigated with the use of finite element simulation.

The objective of this paper is to characterize the mechanical behavior of an ultra-thin stainless steel, of 0.15-mm thickness, that is commonly used in the manufacturing of miniature connectors. The main focus is the relationship between some microstructural features, like grain size and surface roughness, and the macroscopic mechanical behavior in...

This paper shows that non-linearity of mechanical behaviour of metal in the elastic regime has an influence on the forming process. Discrete Dislocation Dynamics simulations show that pure elastic behaviour is altered when reversible dislocation displacements occur even in the very beginning of the elastic stage. The influence of such a non-lineari...

Thèse de doctorat, Institut National Polytechnique de Grenoble

The aim of this work is to investigate numerically the springback of U-shaped elongated parts made of ultra-thin stainless steel after deep-drawing, and in particular to focus on twisting. A dedicated rig was designed, with a scale factor of 1/10 compared to devices already presented in literature for elongated parts of length around 1 m. Moreover,...

The warm deep drawing of circular AA5754-O aluminium alloy blanks was investigated both experimentally using specially designed equipment and numerically using a fully coupled thermo-mechanical finite element model. Cylindrical cups were prepared with a heated die and blank-holder. The split-ring test was used to measure the effects of the temperat...

La miniaturisation de nombreux produits et systèmes entraine le développement permanent de micro -systèmes électro mécaniques (M.E.M.S). En raison de leurs taux de production élevés, les procédés de mise en forme demeurent la solution technologique la plus courante pour la fabrication de ces pièces miniatures. Toutefois, en raison des dimensions et...

The mechanical behavior of 5000 series aluminium alloy sheets has been investigated in simple shear, in order to highlight the influence of strain rate and temperature on the occurrence of plastic instabilities. Indeed, as in tension, Portevin-Le Chatelier effect is also observed in simple shear and the aim of this study is to investigate the chara...

Twisting of metallic sheets is one particular mode of springback that occurs after drawing of elongated parts, i.e. with one dimension much larger than the two others. In this study, a dedicated device for drawing of elongated parts with a U-shaped section has been designed on purpose, in order to obtain reproducible data. Very thin metallic sheet,...

Journée 2014 de la SF2M Ouest

Local strain and temperature of an AA5754-O aluminum alloy sheet have been full-field measured during monotonous tensile tests carried out at room temperature. Sharp strain increases and temperature bursts which are locally generated by the Portevin-Le Chatelier phenomenon have been measured at the same point for two strain rates: V2 = 1.9 × 10−3 s...

Twisting is one of the deformation mode occurring after springback and characterized by a torsion of a part around the axis aligned with its highest dimension. This phenomenon is experimentally difficult to highlight, because its occurrence has been evidenced in the case of elongated parts, when one of the part dimensions is much higher than the ot...

Twisting of metallic sheets is one particular mode of springback that occurs after drawing of elongated parts, i.e. with one dimension much larger than the two others. In this study, a dedicated device for drawing of elongated part with a U-shaped section has been designed on purpose, in order to obtain reproducible data. Very thin metallic sheet,...

Les distorsions de la forme géométrique d’une pièce en tôle métallique mince sont liées aux contraintes résiduelles existantes après le retrait des outils de mise en forme. Le vrillage est un mode de déformation particulier, caractérisé par la torsion autour d’un axe parallèle à la plus grande dimension de la pièce. La difficulté expérimentale rela...

In the present work, the jerky flow in an Al-Mg alloy during simple shear tests for various strain paths and temperatures is studied. Direct observations of the sample surface using digital image correlation is used to investigate the type and the dynamics of Portevin-Le Châtelier (PLC) bands as a function of shear strain and temperature. The influ...

The aim of this work is to identify the limits of the hole-flanging process under different conditions. A 3D finite element model was developed to predict failure in hole-flanging process for sheet aluminium alloys. The Gurson–Tvergaard–Needleman (GTN) coupled damage model and the Bao-Wierzbicki (BW) uncoupled damage model were used. The parameter...

Local strain and temperature of an AA5754-O aluminum alloy sheet have been full-field measured during monotonous tensile tests carried out at room temperature. Sharp strain increases and temperature bursts which are locally generated by the Portevin-Le Chatelier phenomenon have been measured at the same point for two strain rates: V2=1.9×10 −3 s −1...

Les alliages Al-Mg sont connus pour présenter un effet Portevin-Le Châtelier (PLC) à température ambiante, caractérisé par des oscillations sur la courbe d'écoulement et une déformation plastique localisée dans des bandes au cours de la déformation globale. Les courbes d'écoulement d'un alliage AA 5754-O lors d'essais de cisaillement simple sont ét...

Le couplage thermomécanique dû à l'existence de transformations de phases dans les Alliages à Mémoire de Forme n'est pas encore complètement compris et des études expérimentales sont encore nécessaires. Cet article propose une étude thermomécanique des AMF NiTi lors d'un essai homogène de cisaillement. Au cours de ces essais, des mesures simultanée...

Nowadays, aluminium alloys are increasingly used in the automotive industry, since they allow weight reduction in body-in-white. However, aluminium alloys are known for being more prone to springback phenomenon than conventional steels. The numerical simulation has a key role in the study of aluminium forming processes and its defects prediction. H...

This study deals with the new strategy currently implemented in DD3IMP in-house code to describe the forming tools using Nagata patches. The strategy is based on the use of the Nagata patch interpolation to generate smooth contact surfaces over coarse faceted finite element meshes. The description of the adopted algorithm is briefly presented, high...

Deep drawing is one of the most important operations used in sheet metal forming. Within this, forming of cylindrical cup is one of the most widely studied deep drawing processes since it allows analysing the effect of different process parameters in phenomena such as earing, springback and ironing. In fact, during the deep drawing of a cylindrical...

NiTi Shape Memory Alloys are being increasingly used in the fields of aeronautical, structural engineering and biomedical applications. To design such products, knowledge of thermomechanical properties of the material is of great importance. Most of the experimental characterizations have been achieved in tension using wires, strips or bone-shaped...

The jerky flow in an Al-Mg alloy is studied during simple shear tests at room temperature and various strain rates. Direct observations of the sample surface using digital image correlation allow the study of the type and the dynamics of bands associated to plastic instabilities as a function of shear strain and shear strain rate. The paper feature...

The bending process of an aluminium alloy and a high‐strength steel is analysed using the cylindrical bending test of Numisheet 2002 (Proceedings of the 5th International conference and workshop on numerical simulation of 3D sheet forming processes, 2002, Jeju Island, South Korea). Despite its simplicity, it is now well known that this test is diff...

This study focuses on the numerical simulation of roller hemming of an aluminium alloy sample with a curved geometry; this non-planar geometry is obtained by a prestrain procedure similar to deep drawing process. Material characterization was performed through tensile and simple shear tests at different orientations on the sheet plane. The influenc...

This paper deals with surface defects of automobile outer panels, which alter significantly the vehicle quality. Such defects occur during springback, after forming or flanging steps, and are characterized by concave depression of small amplitude over the convex shape of the part. The aim of this work is to reproduce at the laboratory scale a surfa...

NiTi Shape Memory Alloys are being increasingly used in the fields of aeronautical, structural engineering and biomedical applications. To design such products, knowledge of thermomechanical properties of the material is of great importance. Most of the experimental characterizations have been achieved in tension using wires, strips or bone-shaped...

The effect of the clearance-thickness ratio on the hole-flanging process was investigated to determine the occurrence of ironing. A 2 mm thick 1000 series aluminium alloy sheet was considered. An elastic-plastic finite element model using remeshing option was developed. Experiments were conducted to verify the reliability of the developed finite el...

Surface defects are small concave imperfections that can develop during forming on outer convex panels of automotive parts like doors. They occur during springback steps, after drawing in the vicinity of bending over a curved line and flanging/hemming in the vicinity of the upper corner of a door. They can alter significantly the final quality of t...

Hole-flanging is a sheet metal forming process which is often used to produce a flange around holes. Many industrial applications require a longer flange that can be used for example to increase bearing surface or to increase the number of threads that will fit in a tapped hole. Ironing is usually used during such process to increase the flange hei...

The mechanical behavior of mild and dual phase steel sheets is investigated at room temperature in quasi-static conditions under different strain paths: uniaxial tension, simple shear and balanced biaxial tension. The aim is to characterize both the anisotropy and the hardening, in order to identify material parameters of constitutive equations abl...

Sheet metal forming involves planar stress states, in the sheet plane, like in tension and simple shear, or stress states characterized by a gradient in the thickness, like in bending. In this latter case, material limit prediction derived from an instability criterion is no longer valid. In this work, a criterion based on a critical void volume fr...

Several surface defects can develop on automotive exterior panels during the forming operations. They alter the vehicle aesthetic and their severity increases with the decrease of sheet thickness. These defects are difficult to characterize experimentally and reproduce numerically because of their depth below 0.5 mm and the complexity of the parts...

This study deals with the mechanical behaviour and material modelling of an AA5754-O alloy at elevated temperature. Experimental shear tests were performed from room temperature up to 200°C, and the material behaviour has been identified with both shear and tensile tests, as a function of temperature. To analyse the influence of temperature during...

Photomechanics 2011. Brussel.

An elasto-plastic finite element model was used to predict the occurrence of ironing in hole-flanging process. Experiments were conducted on sheet aluminum alloy to verify the reliability of the developed finite element model. Deformed shape, flange geometry and punch load were analyzed to quantify flange thinning and to study the effect of ironing...

The goal of this investigation is to gather experimental data on the hemming of concave or convex edge-curved surface samples, to study the influence of geometry and pre-strain on roll-in and load, as well as to assess the validity of the numerical simulation of the process. A specific experimental set-up was designed to study classical and roll-he...

Surface defects can develop on automotive exterior panels after drawing and flanging steps, during springback and may alter significantly the vehicle quality. These defects are characterized by a small depth below 0.5mm and are then difficult to detect numerically. This study focuses on the surface defects for two parts: an industrial upper corner...

The split-ring test provides a simple benchmark for correlating springback obtained by finite element analysis (FEA) with experimental measurements. This test consists in cutting a ring specimen from a full drawn cup and then to split the ring longitudinally along a radial plane. The difference between the ring diameters, before and after splitting...

This study deals with the experimental and numerical investigation of springback in an aluminium alloy at different temperatures. An experimental split-ring test is performed on a AA5754-O alloy using a laboratory drawing device. The influence of temperature during forming over springback is measured from room temperature to 200°C. The temperature...