Dorel Banabic

Universitatea Tehnica Cluj-Napoca | UT Cluj · "CERTETA" Research Center

The chapter presents the formation of the Romanian industrial system starting with the nineteenth century until the end of the First World War. The historical context of the development of the Romanian industrial environment is mentioned, the politicians who influenced this development as well as the industrial policies from the end of the nineteen...

This chapter presents the evolution of research in Romania on the mechanics (the mechanics of rigid solids, deformable solids in elastic, elastoplastic or plastic behavior regimes, the theory of mechanical vibrations, fluid mechanics) but also closely related problems such as the theory of mechanisms, contact mechanics, construction of hydraulic eq...

A fundamental category of historical civilization is the traditional popular civilization. This represents a multi-millenary synthesis, resulting from the grafting, on the ancient autochthonous background, of some elements mediated by ethnic contacts, temporary or long. These were caused by heterogeneous influences, caused by numerous and diverse p...

The chapter is structured in four parts. In the first part, the beginning of industrialization in Romania is presented. The industrialization of Romania begins in the first part of the eighteenth century, when the demand for mineral resources (coal and iron) of the western European countries increased considerably. These resources began to be explo...

The chapter presents a synthesis of the evolution of technical education in Romania. The first attempts from the beginning of the nineteenth century to found an engineering education are presented, starting with the School of Surveying and Civil Engineers in Moldova (1813) and Wallachia (1818). Later these schools evolved into a French form of engi...

The chapter briefly presents the biographies of the most representative personalities who made contributions in the field of engineering born in Romania, of Romanian origin or who worked on the territory of Romania.

According to the current development of commercial vehicles, a novel structure of the double-layer exhaust pipe with gap was designed. Hydroforming through the combination of internal and external pressures (HIEP) was proposed to form the complex structure of the new exhaust pipe. The double-layer tube without gap was used as the initial tube blank...

In this paper, the response surface methodology (RSM) and finite element (FE) simulation were applied to optimize the push-bending process parameters of the thin-walled tube with polyurethane mandrel. The objective of the present work is to predict the optimal set of process parameters including the length to diameter ratio of the mandrel (L/D), th...

It is impossible to obtain the forming limit curve (FLC) by full zone hydraulic forming test under quasi-static (QS) condition since the liquid will leak from the notches of the specimen once the pressure increases. In this study, a novel method is proposed to investigate the frictionless full zone hydraulic FLC of AA5A06 under high strain rate (HS...

Reliable sheet metal forming simulations depend on accurate descriptions of real process conditions. These conditions include material behavior, lubrication systems, tool deformations, press dynamics, and more. Research on material models is the most mature area for describing these conditions in a reliable way. Several advanced and flexible models...

Thin-walled bent tubes with small bending radius are one of the key components used in airspace and aerospace launch vehicles and various electrical equipment. Traditional forming technology for such bent tubes is the welding of two stamped half bends, which cannot meet the high reliability demand anymore, so forming technology for the seamless ben...

In this paper, the response surface methodology (RSM) and finite element (FE) simulation were applied to optimize the push-bending process parameters of the thin-walled tube with polyurethane mandrel. The objective of the present work is to predict the optimal set of process parameters including the relative length of the mandrel ( L / D ), the fri...

This paper reviews the most recent models for description of the anisotropic plastic behavior and formability of sheet metals. After a brief review of classic isotropic yield functions, recent advanced anisotropic criteria for polycrystalline materials of various crystal structures and their applications to cup drawing are presented. Next, the disc...

For reduction of vehicle weight and higher fatigue property, the hot-rolled dual-phase steel 700DP was developed to produce wheel disc with multistage stamping process. The wheel disc is one critical component of wheel system whose forming precision is extensively concerned. The critical area of the part characterizes nonlinear strain path during t...

The manuscript presents some aspects of Professor Marciniak's life as well as a synthesis of his main contributions in metal forming.

Thin-walled (D/t > 30; D, initial outer diameter; t, initial wall thickness) bent tubes with large diameter (D > 100 mm) and small bending radius (R/D < 3; R, centerline radius) are difficult to form integrally using traditional bending methods. In this paper, using a novel loading method, a modified push-bending (MPB) process with polyurethane as...

In this study, a novel method was proposed to evaluate high strain rate (HSR) formability of Al-Cu-Mg 2B06-O sheets by impact hydroforming (IHF). IHF was suitable to manufacture hard-to-form sheets, since it combined the advantages of flexible liquid and impact impulse loading. Both 2D and 3D HSR formability curves were established to describe the...

This paper presents a historical perspective on the development of the model that was initially proposed by Prof. Marciniak in 1965 for calculating the Forming Limit Curves (FLC's) of metallic sheets. Based on a pre-existing geometric and/or structural non-homogeneity of the metallic sheet, it is at present the most widely used framework for the th...

This paper presents an investigation on the determination of forming limit curves (FLCs) by finite element simulations. The numerical FLCs are determined applying the criteria of strain localization in simulations of the Nakazima formability tests. Two methods to determine the onset of localized necking have been compared. The first criterion is ba...

Recent advances in the modelling of metals encompass modelling of metals structural inhomogeneity, damage, porosity, twinning/untwining and non-local and second order effects. This presentation is focused on modelling the void growth in ductile fractures. The growth and coalescence of microscopic voids are the main mechanisms in ductile fracture of...

In sheet metal forming simulation, a flow curve and a yield criterion are vital requirements for obtaining reliable numerical results. It is more appropriate to determine a flow curve by using biaxial stress condition tests, such as the hydraulic bulge test, than a uniaxial test because hardening proceeds higher strains before necking occurs. In a...

Virtual manufacturing concepts have been adopted by most of the industrial companies, including the small and medium ones, to face the global competition and deal with the top challenges of manufacturing industry, i.e. improving the quality, reducing the delivery time and decreasing the costs. However, most of the virtual manufacturing methodologie...

This work presents results of investigations on the determination of strain localization in sheet forming. Nakajima formability test has been chosen for the experimental studies and numerical analysis. The onset of localized necking has been determined using the criteria studied in the authors' earlier works, based on the analysis of the principal...

This paper presents a comparison of two criteria of strain localization in experimental research and numerical simulation of sheet metal forming. The first criterion is based on the analysis of the through-thickness thinning (through-thickness strain) and its first time derivative in the most strained zone. The limit strain in the second method is...

High strain rate (HSR) forming has been found to be able to enhance the formability of sheet metals like electro-magnetic forming. Impact hydroforming (IHF) is proposed, in which the sheet is formed with high-pressure pulse combining hydroforming and HSR forming. An IHF bulge test setup was designed, 5A06 aluminium sheet was tested with strain rate...

Metal/polymer/metal sandwich sheets have recently attracted the interests of industries like automotive industry. These sandwich sheets have superior properties over single-layer metallic sheets including good sound and vibration damping and light weight. However, the formability of these sandwich sheets should be enhanced which requires more resea...

The spatial distribution of contact orientations and anisotropy in granular assemblies stand for the directional features of contacts and contact forces. Contact anisotropy and contact force anisotropy are two fundamental concepts for microscopic and macroscopic mechanics of granular materials. In this paper, a kind of diagrammatic description for...

This paper presents the investigation on detection of strain localization in experimental research and numerical simulation of sheet metal forming. Experimental tests and numerical simulations of the Nakazima test have been performed for the DC04 grade steel sheet. The onset of localized necking has been determined using the criterion based on anal...

Bondal is the denomination of a vibration damping sandwich sheet, which is mainly used in automotive industry for sound and vibration damping. In this paper, the formability of this sheet was investigated by conducting different types of experiments such as uniaxial tensile, hydraulic bulge, Nakazima and T-peel tests. Furthermore, SEM analyses have...

The aim of this study is to analyze formability of three-layer metal/polymer/metal sandwich sheets. For this purpose, forming limit curves (FLCs) of sandwich sheets with particular configurations were determined using two different approaches, namely an anisotropic GTN model and a modified M-K model. Both GTN and M-K models use mechanical prope...

In this research, a new approach has been introduced for the identification of GTN damage model parameters. The response surface methodology was used for design of experiments and also for the calculation of the optimum values of the GTN model parameters. For the calibration of the parameters, the values of the major and minor limit strains were me...

The purpose of this study is to investigate the variation of the required punch load during the deep drawing process under different friction conditions. In this regards, several deep-drawing tests of cylindrical cups were conducted under four friction conditions at the tool–blank interface. The first case was the dry deep-drawing, considered as a...

During the forming of flat sheet metal into a more complex shape, a number of plastic instabilities may occur subsequently. A ‘plastic instability’ occurs when the zone of plastic deformation is suddenly confined to a smaller zone. The first plastic instability which usually occurs in forming processes is the onset of diffuse necking, in which plas...

Ductile fracture in metals and metallic alloys is due to the evolution of microscopic voids during plastic deformation. Voids nucleate around foreign inclusions or at grain boundaries and grow in regions with large triaxial stresses. Larger voids promote the formation of bands of localized deformation where new small voids are nucleated, thus formi...

Due to the rolling process, sheet metals generally exhibit a significant anisotropy. In fact, the rolling process induces a particular anisotropy characterised by the symmetry of the mechanical properties with respect to three orthogonal planes. Such a mechanical behaviour is called orthotropy. The intersection lines of the symmetry planes are the...

The main objective of the paper consists in elaborating a unified framework that allows the theoretical assessment of sheet metal formability. Hill’s localized necking model and the Extended Maximum Force Criterion proposed by Mattiasson, Sigvant, and Larsson have been selected for this purpose. Both models are thoroughly described together with th...

In sheet metal forming simulation, flow curve is a vital ingredient for reliable numerical results. It is more appropriate to determine the flow curve using biaxial stress state tests such as hydraulic bulge test instead of uniaxial test because hardening proceeds to higher strains. With a uniaxial test, higher strains are extrapolated which might...

The growth and coalescence of voids in sheet metals are not only the main active mechanisms in the final stages of fracture in a necking band, but they also contribute to the forming limits via changes in the normal directions to the yield surface. A widely accepted method to include void effects is the development of a Gurson-type model for the ap...

Hot gas pressure forming is one of the sheet metal forming processes. One of the drawbacks of this method is non-uniform thickness distribution in final parts. In this paper a new method is proposed to control thickness distribution in this process by dividing the process's die into two segments. Due to lead's considerable strain rate dependency in...

Developing microcracks in final tube is one of the serious challenges in cold tube pilgering process. In this paper to predict the exact location of this microcracks and effects of process parameters on distribution of them, finite element analysis in conjunction with damage mechanics is used. For this purpose Lemaitre model with and without consid...

In the last decades, numerical simulation has gradually extended its applicability in the field of sheet metal forming. Constitutive modeling and formability are two domains closely related to the development of numerical simulation tools. This paper is focused, on the one hand, on the presentation of new phenomenological yield criteria developed i...

Crosslinked polyurethane-ureas based on a mixture of 4,4′-dibenzyl diisocyanate, poly(ethylene adipate) glycol, diethylene glycol (DEG) and trimethylol propane (TMP) were synthesized with various ratios of DEG and TMP. The combination within the network structure of the chemical crosslinks generated by TMP and the cohesive strength of urethane and...

This paper is focused on the performance evaluation of two theoretical models that can be used to predict the Forming Limit Curve (FLC) for an AA6016-T4 aluminium alloy sheet. The FLC is calculated based on the Marciniak-Kuczynski (M-K) model and the Modified Maximum Force Criterion (MMFC) using the Hill '48, Barlat '89 and BBC 2005 yield criteria,...

In the last decades, numerical simulation has gradually extended its applicability in the field of sheet metal forming. Constitutive modelling and formability are two domains closely related to the development of numerical simulation tools. This paper is focused, on the one hand, on the presentation of new phenomenological yield criteria developed...

The aim of the study is to identify the microstructure and voids evolution during the aluminium AA6016-T4 sheet deformation up to 93 % in order to perform deformation simulation for future applications. The deformed samples were cut in the rolling direction and to an angle of 45 and respectively 90 degrees to the rolling direction. The low deformed...

In this study, the influence of the blank-holding force (BHF) on the drawing force (DF) in the deep-drawing process of cylindrical and square cups has been investigated experimentally. For this purpose, different constant and variable BHFs have been applied to AA6016-T4 aluminum alloy and DC04 steel sheets during the forming process. It has been ob...

A new procedure for the experimental determination of the FLCs has been proposed. The procedure is based on the hydraulic bulging of two specimens. The upper blank has a pair of holes pierced in symmetric positions with respect to the center, while the lower blank acts both as a carrier and a deformable punch. By modifying the dimensions and recipr...

In the deep drawing process, the blank-holding force (BHF) is an important process parameter affecting the energy consumption and the successful production of parts. In the present work, both experiments and finite element simulations have been conducted to investigate the influence of constant and time variable BHF on drawing force (DF) and thickn...

Constitutive models for dominant mechanisms in hot forming are proposed. These models consider inter-granular deformation, grain boundary sliding, grain boundary diffusion and grain growth. New stress-strain rate relationships are proposed to predict deformation due to grain boundary sliding and grain boundary diffusion. Besides a Taylor type polyc...

In this paper, an anisotropic formulation of the Gurson-Tvergaard-Needleman (GTN) damage model is used for simulating the deep-drawing of a rectangular box made from an AA6016-T4 metallic sheet. The model is implemented as a VUMAT routine in the ABAQUS/Explicit finite-element code. The material parameters involved in the constitutive relationships...

The accuracy of the forming limit curves reported by the Marciniak-Kuczynski model as well as the quality of the predictions provided by the FE programs depend on the yield criterion that describes the anisotropic plastic behavior of the sheet metal. Two identification procedures of Barlat89 and BBC2005 are used in this paper. The first procedure i...

Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. The influence of thickness reduction on the microstructure was studied by scanning electron microscopy. Microstructure evolution was ch...

In this paper, the forming limit curve of an AA6016-T4 sheet metal is constructed using Gurson-Tvergaard-Needleman (GTN), Marciniak-Kuczynski (M-K) and Modified Maximum Force Criterion (MMFC) models. The mechanical behavior of the matrix material is described using Hill’48 quadratic yield criterion and an isotropic hardening rule. The accuracy of t...

In this paper, the effect of equal-channel angular pressing parameters including die channel angle (ϕ), die outer corner angle (ψ), fillet radius (r), friction coefficient between billet and punch (µ) and friction factor between billet and die (m) on the equivalent plastic strain of AA6061 alloy is investigated. In this regard, the equal-channel an...

The accuracy of the finite element simulation of sheet metal forming processes is mainly influenced by the shape of the yield surface used in the mechanical model and, in particular, by the number of input values used in the identification of the yield surface. This paper investigates the effect of the input values used for identifying the BBC 2005...

In the sheet metal forming processes, the inherent unavoidable noise in material property, which can vary inside and between batches as well as between suppliers, constitutes an important source of uncertainty which could result in rejection of some formed parts. In the process design phase, a successful tool for the sensitivity analysis proved to...

The current trend in the automotive industry consists in decreasing the weight of the car body to reduce the fuel consumption and the air pollution. This can be done by using low-density materials such as the aluminium alloys having good formability. A frequently used aluminium alloy in the manufacturing of the car body components is AA6016-T4. The...

We report on our attempts to build a theoretical model for determining forming limit diagrams (FLD) based on limit analysis that, contrary to the well-known Marciniak and Kuczynski (M-K) model, does not assume the initial existence of a region with material or geometrical inhomogeneity. We first give a new interpretation based on limit analysis for...

Hydraulic bulging experiments are performed in order to evaluate the mechanical parameters of cold rolled steel (DC04) and aluminium alloy (EN AW 6016-T4) sheet materials. The biaxial yield stresses, and the biaxial anisotropy coefficients are derived from the biaxial stress-strain curves and the ratio between the strains in the transverse and in t...

During the development of a central platform that connects measuring systems, simulators and fabrication machinery through internet, helping the metal forming process chain, the biggest challenge turned out to be something surprising. The biggest challenge was not finding the correct technology to communicate a high load of data through the interne...

The output of the simulation is very sensitive to the constitutive equations that describing the anisotropic behaviour of the sheet metal. From this point of view, the mathematical formulation of the yield criterion as well as the number of the mechanical parameters used in the identification procedure has the most significant influence. The paper...

In the hydraulic bulge tests, dies with both circular and elliptical apertures were used. A recently proposed methodology was used to determine the equivalent stress—strain curves by bulging through elliptical dies. This methodology combines an analytical approach with the experimental data measured by an ARAMIS system. In the hydraulic bulge test...

Fluid pressure is the most important parameter in hydroforming deep drawing process. In this manuscript, we present the results obtained from FE modelling using genetic algorithm to determine the optimum fluid pressure for the production of a two-stepped workpiece in the deep drawing hydroforming process. It is suggested that a two-stepped workpiec...

A constitutive model is proposed for simulations of hot metal forming processes. This model is constructed based on dominant mechanisms that take part in hot forming and includes intergranular deformation, grain boundary sliding, and grain boundary diffusion. A Taylor type polycrystalline model is used to predict intergranular deformation. Previous...

The accuracy of the forming limit curves predicted by the Marciniak-Kuczynski model depends on the type and flexibility of the constitutive equations used to describe the mechanical response of the sheet metal. From this point of view, the yield criterion has the most significant influence. The paper presents a comparative analysis referring to the...

The paper describes a new experimental procedure for the determination of the curves relating the equivalent stress and equivalent strain of sheet metals by means of the hydraulic bulge tests through elliptical dies. The procedure is based on an analytical model of the bulging process and involves the measurement of only two parameters (pressure ac...

Virtual manufacturing concepts have been adopted by most of the industrial companies, including the small and medium ones, to face the global competition and deal with the top challenges of manufacturing industry, i.e. improving the quality, reducing the delivery time and decreasing the costs. However, most of the virtual manufacturing methodologie...

The paper deals with constitutive modelling of highly anisotropic sheet metals. It presents FEM based earing predictions in cup drawing simulation of highly anisotropic aluminium alloys where more than four ears occur. For that purpose the BBC2008 yield criterion, which is a plane‐stress yield criterion formulated in the form of a finite series, i...

Driving simulators are tools used for driver education, behavioural evaluation and to prove new systems. In order to be effective, the driving simulators have to provide correct and realistic cues. Due to the research conducted at the Chair of Mechatronics from University of Duisburg-Essen, on human machine interface, a low cost driving simulator w...

The variability of the so called noise factors greatly influences the results of any forming process (deep-drawing, stretching, etc.). By taking into account this variability, the number of the rejected parts and the manufacturing costs will decrease. The aim of this work is to evaluate the variability of the mechanical parameters of a DC04 steel s...

The paper is focused on the determination of the biaxial stress-strain curves by hydraulic bulging tests with circular die using a new methodology. This methodology is based on a modified version of Kruglov's formula for the calculation of the polar thickness that takes into account the non-uniformity of the strain distribution on the dome surface....

This paper presents a new methodology for the determination of the biaxial stress – strain curves by hydraulic bulging tests with circular die. In order to validate the methodology, the authors have performed both stepwise and continuous bulging experiments. The pressure, polar height and curvature radius have been measured in different stages of t...

The paper analyzes the dispersion of the mechanical parameters and its influence on the forming limit curves of sheet metals. The tests have been made for the case of the DC01 steel sheets. The dispersion of the mechanical parameters has been observed during the experimental research. On the basis of this dispersion, a forming limit band has been c...

This paper presents synthetically the most recent models for description of the anisotropic plastic behavior. The first section gives an overview of the classical models. Further, the discussion is focused on the anisotropic formulations developed on the basis of the theories of linear transformations and tensor representations, respectively. Those...

In the current section an overview of different Finite Element (FE) formulations used for sheet metal forming simulation, now and in the past, will be given. The theories of FE-simulation of large deformation problems will be briefly touched upon herein, but for thorough presentations the reader is referred to the many existing text books on the su...

The formability is the capability of sheet metal to undergo plastic deformation to a given shape without defects. The defects have to be considered separately for the fundamental sheet metal forming procedures of deep-drawing and stretching. The difference between these types of stamping procedures is based on the mechanics of the forming process....

In the paper the authors propose an improved version of the Modified Maximum Force Criterion (MMFC) initially developed by Hora and his co-workers. The most appealing characteristic of this model is the fact that no assumptions related to the existence of voids or other defects are needed. The MMFC model is based on the hypothesis that a plane-stra...

Nowadays, the finite element analysis (FEA) is playing a main rule in fields of sheet metal forming for designing processes and dimensioning parts. The most frequent yield criteria used in the FE commercial programs for the sheet-metal-forming simulation, like AUTOFORM, PAMSTAMP, etc., are Hill’48 for common steels or Barlat’89 and various BBC mode...

The improvement proposed in the frame of this paper consists in adding two material constants to the MMFC model. Their values are determined by enforcing a couple of experimental constraints on the model. In this way, the quality of the theoretical predictions can be improved. As proven by the numerical tests, the most appropriate constraints are r...

We take a general plane stress, orthotropic, sixth order homogeneous polynomial and impose upon it conditions for in-plane isotropy. We obtain a four parameter yield function that takes as input the yield stress along the rolling direction, the average r-value of the sheet, the balanced-biaxial yield stress and a shape parameter. This last paramete...

An aluminum sheet, AA5182, is modeled (as rigid-plastic) with two yield criteria that, for all practical purposes, generate almost identical yield surfaces for this alloy. Yet, the differences between the two in limit strain prediction using the MK model are noticeable, pointing to a hyper-sensitivity of the MK model to the input data. It is shown...

The paper presents an analysis of a recently proposed failure criterion for thin sheets. According to Aretz [1], this criterion becomes numerically unstable for yield surfaces with locally constant exterior normal fields. Here we make more precise statements about the nature of this instability, asses the predictive capabilities of the criterion, a...

A simple method for including a normal to the plane of the sheet stress component in the M-K model is proposed. The plane stress characteristic of the model is preserved. The new model allows for studying the influence of the fluid pressure upon the forming limit strains of orthotropic thin sheets. In practice it is observed that the formability of...

The nonuniform height profiles of deep-drawn cylindrical cups is caused by the plastic anisotropy of the blank sheet. Which locations on the yield surface determine uniquely the earing profile is still an unsolved problem. Present (phenomenological) theories take into consideration only the directional properties of the sheet (r-value and yield str...

The Marciniak and Kuczynski computational model, [1], for predicting the forming limit strains during biaxial stretching of thin sheets with positive strain ratios assumes tangential strain continuity at the interface between the groove and the bulk zones. We question here whether this continuity holds true for the entire loading history in the cas...

The double curvatures encountered in aerospace skin components require significant plastic strain levels to achieve final form. In order to obtain the required part geometry and final temper strength, while avoiding failure, multistage-processing is employed. For components that are more difficult to form this requires three stretching stages and t...

During the last three decades, numerical simulation has gradually extended its applicability in the field of sheet metal forming. Constitutive modelling is one of the domains closely related to the development of numerical simulation tools. The paper is focused on the development of new phenomenological yield criteria developed in the CERTETA resea...

The paper presents a plane-stress yield criterion in the form of a finite series that can be expanded to retain more or less terms, depending on the volume of experimental data. Due to its structure, the model is suitable for a variety of practical applications. An identification procedure consisting in the minimization of an error-function is used...

The finite element analysis (FEA) is getting more and more important in fields of sheet metal forming for process design and parts' dimensioning. But the reliability and the quality of the numerical results strongly depend on the model that has to be built for the calculations. Especially the modelling of the elastic-plastic material behaviour is o...

A recently proposed sixth order polynomial yield function, [1], is applied in conjunction with the Marciniak and Kuczynski (M-K) model, [2-3], to the prediction of forming limit strains. We review the equations of the M-K model and for the particular case of plane strain loading integrate them in explicit form. We thus show that the plane strain li...