Marion Merklein

Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany

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Publications (88)39.62 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Demonstrated that textured tool possessed a lower friction coefficient than the nontextured tool.•Demonstrated that the amount of reduction depends on the relative orientation between the sliding direction and the sheet orientation.•The flat-on-cylindrical test apparatus effectively simulated the critical bending area in the sheet metal stamping operation.
    Tribology International 01/2015; 81. · 2.17 Impact Factor
  • Sebastian Suttner, Marion Merklein
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    ABSTRACT: Increased requirements for sheet metal parts and the use of advanced high-strength steels and other materials with lightweight potential set new standards for material characterization methods. Especially in the automotive sector with complex, multi-stage forming processes, new challenges are placed to model the real material behavior numerically. Thus, the requirements can be met to the numerical design of forming processes, advanced knowledge in the field of material characterization is needed. Therefore characterization methods under cyclic load are used. Two possibilities to investigate the cyclic behavior of the material are the tension-compression test and the cyclic shear test. The differences in the material properties of sheet metals during a reversal of load are marked by the Bauschinger effect and lead to a decrease of the beginning of plastic yielding. In this paper, the cyclic material behavior of different materials is characterized with experimental tension-compression tests and compared to the results of cyclic shear tests from a modified ASTM simple shear test preparation. The aim is the analysis of the Bauschinger effect through the identification of the kinematic hardening model according to Chaboche and Rousselier for the investigated materials. Moreover an estimation of the characteristic of the Bauschinger effect is presented.
    IDDRG 2014 Conference; 06/2014
  • Kolja Andreas, Marion Merklein
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    ABSTRACT: Cold forging enables mass production of steel based components. High loads within cold forging presuppose high loadable tool materials. This is why apart from tool steels cemented carbides are mainly used as tool materials. Due to brittleness of these materials, fatigue is one of the major limits of tool life. Tool manufacturing requires a combination of hard machining and subsequent machining steps. For hard machining of complex tool geometries electrical discharge machining (EDM) represents the industrial standard. The thermal influenced surface layer has to be removed by post and fine machining steps. The resulting surface integrity has a major influence on the internal strength of a tool. Correlations between tool manufacturing, surface properties and tool behavior will gain knowledge for an optimized tool production. In this context, scope of the present paper are the investigation and description of the interactions between tool manufacturing and resulting surface properties for tools made of cemented carbide and tool steel. Within the article, the surface properties caused by a conventional process chain consisting of EDM and polishing are quantified. In addition, these results are compared to an adapted process chain with an integrated peening process. The results reveal that the conventional and the adapted process chain lead to similar surface topographies and roughness values. However, the integration of a peening process shifts the residual stress level towards higher compressive stresses.
    Production Engineering 03/2014; 8(1-2).
  • Sebastian Rösel, Marion Merklein
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    ABSTRACT: Within this paper a new approach to enhance the process window in sheet metal hydroforming processes will be presented. The key idea of the technology is the local adaption of the properties of the active fluid medium. In this case the magnetorheological fluid (MRF) Basonetic® 5030 is used and the fluid behavior is changed due to a partially applied external magnetic field. Based on the new property distribution the medium can be used as forming and sealing medium at the same time. The results are compared to the values reached with mineral oil. The presented work covers all necessary steps for a successful application of the technology. After the presentation of the used fluids, a material characterization and the tools, which are developed for this reason, as the sealing limits for two different configurations are determined. Based on these investigations forming operations are carried out at the related process parameters to show up the potential of the MRF. At the end a numerical model is built up and validated for both fluids used to offer a qualified tool for process design.
    Production Engineering 03/2014; 8(1-2).
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    ABSTRACT: Tailored Blanks is the collective for semi-finished sheet products which are characterised by a local variation of the sheet thickness, sheet material, coating or material properties. With these adaptions the tailored blanks are optimised for a subsequent forming process or the final application. In principle four different approaches can be distinguished to realise tailored blanks: joining materials with different grade, thickness or coating by a welding process (tailor welded blanks), locally reinforcing the blank by adding a second blank (Patchwork blanks), creating a continuous variation of the sheet thickness via a rolling process (tailor rolled blanks) and adapting the material properties by a local heat treatment (tailor heat treated blanks). The major advantage of products made from tailored blanks in comparison to conventional products is a weight reduction. This paper covers the state of the art in scientific research concerning tailored blanks. The review presents the potentials of the technology and chances for further scientific investigations.
    Journal of Materials Processing Technology 02/2014; 214(2):151–164. · 1.95 Impact Factor
  • Marion Merklein, Sebastian Suttner, Adam Schaub
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    ABSTRACT: The requirement for products to reduce weight while maintaining strength is a major challenge to the development of new advanced materials. Especially in the field of human medicine or aviation and aeronautics new materials are needed to satisfy increasing demands. Therefore the titanium alloy Ti-6Al-4V with its high specific strength and an outstanding corrosion resistance is used for high and reliable performance in sheet metal forming processes as well as in medical applications. Due to a meaningful and accurate numerical process design and to improve the prediction accuracy of the numerical model, advanced material characterization methods are required. To expand the formability and to skillfully use the advantage of Ti-6Al-4V, forming processes are performed at elevated temperatures. Thus the investigation of plastic yielding at different stress states and at an elevated temperature of 400°C is presented in this paper. For this reason biaxial tensile tests with a cruciform shaped specimen are realized at 400°C in addition to uniaxial tensile tests. Moreover the beginning of plastic yielding is analyzed in the first quadrant of the stress space with regard to complex material modeling.
    Key Engineering Materials 01/2014; 622-623:273-278.
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    ABSTRACT: The Laser Beam Melting (LBM) process technology within the family of Additive Manufacturing technology is characterized by its ability to fabricate fully dense 3D structures directly from micro-sized metal powder. With the current state of the art, Ti-6Al-4V has been processed using LBM machine systems constituting a laser with a beam diameter of about 100 μm. In order to fabricate structures with smaller wall thicknesses, processing of Ti-6Al-4V is attempted on the LBM machine system, Realizer SLM 50 consisting of a laser with a beam diameter 10 μm. The proposed paper presents the development of process parameters for fabricating fully dense Ti-6Al-4V 3D structures using the LBM machine system, Realizer SLM 50. Further experiments are carried out to determine the wall thickness and mechanical properties achievable using the selected process parameters. Analysis and scientific arguments are presented to explain the influence of building direction and heat treatment on mechanical properties.
    Physics Procedia 01/2014; 56:90–98.
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    ABSTRACT: The paper deals with the testing and modelling of metals response when subjected to sheet forming operations. The focus is both on the modelling of hardening behaviour and yield criteria and on the description of the sheet metal formability limits. Within this scope, the paper provides a critical review of the models available today for predicting the material behaviour at both industrial and scientific level, and the tests needed to identify the models’ material parameters. The most recent advances in the field are also presented and discussed with particular emphasis on the challenges the sheet metal forming community is now facing.
    CIRP Annals - Manufacturing Technology 01/2014; · 2.25 Impact Factor
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    ABSTRACT: With respect to multistage forming processes the material behaviour and the history of the strain path during the process is of special interest for the improvement of the numerical prediction of forming processes. While different researchers investigated the Bauschinger effect during a load reversal and biaxial loading with pre-strained specimens, in this paper the yield locus evolution in the first quadrant of the principles stress space under biaxial loading of a modified cruciform specimen without test interruption is presented. The movement of the yield surface centre caused by kinematic hardening is approximated by an alternative approach based on experimental results.
    CIRP Annals - Manufacturing Technology 01/2014; · 2.25 Impact Factor
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    Kolja Andreas, Marion Merklein
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    ABSTRACT: In forming industry the tool is fundamental for the profitability, as it determines efficiency of cold forging process. In this regard, the tool surface has a distinctive influence on the tribological conditions and thus on the occurring tool stresses. The present study investigates the influence of different fine machining strategies on the tribological performance of cold forging tools made of WC-Co cemented carbide by applying the double cup extrusion test.The results reveal that a peened surface causes higher friction in the forming process compared to polished tool surfaces up to 100%. For polishing a minimum in friction is found for the diamond grit D 6 μm with a friction factor of m = 0.03.
    Procedia CIRP. 01/2014; 13:61–66.
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    ABSTRACT: Simple shear tests are widely used for material characterization especially for sheet metals to achieve large deformations without plastic instability. This work describes three different shear tests for sheet metals in order to enhance the knowledge of the material behavior under shear conditions. The test setups are different in terms of the specimen geometry and the fixtures. A shear test setup as proposed by Miyauchi, according to the ASTM standard sample, as well as an in-plane torsion test are compared in this study. A detailed analysis of the experimental strain distribution measured by digital image correlation is discussed for each test. Finite element simulations are carried out to evaluate the effect of specimen geometries on the stress distributions in the shear zones. The experimental macroscopic flow stress vs. strain behavior shows no significant influence of the specimen geometry when similar strain measurements and evaluation schemes are used. Minor differences in terms of the stress distribution in the shear zone can be detected in the numerical results. This work attempts to give a unique overview and a detailed study of the most commonly used shear tests for sheet metal characterization. It also provides information on the applicability of each test for the observation of the material behavior under shear stress with a view to material modeling for finite element simulations.
    International Journal of Solids and Structures 12/2013; · 2.04 Impact Factor
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    ABSTRACT: Accumulative roll bonding (ARB), as a method for production of ultrafine grained materials, is frequently supposed to be easily transferable to established industrial production lines. In literature, however, common sheet dimensions used for ARB in a laboratory scale are between 20 and 100 mm in width. In order to quantify the potential of upscaling the ARB process to a technological relevant level, sheets of AA1050A with an initial sheet width of 100–450 mm were accumulative roll bonded up to 8 cycles. In this regard, three different rolling mills of distinct dimensions were used for processing of the sheet material. The influence of process parameters and the reproducibility of the process, in terms of mechanical properties and homogeneity of the sheets, were studied by means of mechanical and microstructural characterization. Both appear to be largely independent on the sheet size and the rolling mill utilized for production. Only small deviations after the first cycles could be detected, vanishing in subsequent cycles due to the features of microstructural evolution. The finally obtained results indicate a high potential for industrial application of ARB and illustrate the possibility to upscale the process to a level necessary for that purpose.
    Journal of Materials Science 12/2013; 48(24). · 2.31 Impact Factor
  • Tobias Gnibl, Sebastian Suttner, Marion Merklein
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    ABSTRACT: In order to predict the warm formability of friction stir welded aluminum sheets, a new approach for the mechanical characterization at elevated temperature is presented in this paper. Based on warm tensile test and biaxial tensile test local properties of base material and weld nugget material were determined by using specimens with reduced measuring areas. Special characterization specimens are designed according to the weld zone dimensions and numerically optimized to guarantee homogeneous stress distribution. Identified material parameters were used to build up local material models based on approximated flow curves and an anisotropic yield function. The ability of predicting the formability performance of welded sheets was finally evaluated by the validation of numerical simulations with experimental results in dome stretching tests.
    AIP Conference Proceedings; 12/2013
  • T. Kroiß, U. Engel, M. Merklein
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    ABSTRACT: In this paper a comprehensive approach is presented for the consideration of the interactions between process, tool and machine during the design of cold forging tools and processes by simulation. The interactions occur due to the high forming loads in cold forging and yield considerable deflections of press and tooling system. These, in turn, influence the workpiece dimensions. The entire approach comprises an efficient determination of the deflection characteristic of stroke-controlled press and tooling system and its condensed modeling in combination with the FE simulation of a cold forging process. Building on that, an analytic process model is developed that is based on a set of variant simulations. It permits an optimization of the values of influencing parameters to achieve high workpiece accuracy without subsequent adjusting effort. Initially, the analytic process model required a high number of variant simulations. By acquiring knowledge on the specific process behavior in an analysis of effects and interactions a considerable reduction of simulation runs by a factor of almost 12 was achieved in the case study on full forward extrusion. The approach is supplemented by an analytic model of the die load. In addition, scatter and uncertainties of target values depending on the ones of the influencing parameters can be estimated by applying the Monte Carlo method to the analytic process model.
    Journal of Materials Processing Technology. 07/2013; 213(7):1118–1127.
  • M. Merklein, M. Biasutti
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    ABSTRACT: A new stand-alone biaxial testing machine with out-of-plane loading system has been developed to study the anisotropic plastic behavior of metal sheets on cruciform specimens. In this apparatus a single screw driven actuator is used and the variation of the load ratio along the two main directions is achieved by adjusting the geometry of a link mechanism. This design firstly combines the advantages of biaxial displacement devices, typically mounted in a universal tensile tester, with stand-alone machines and by at the same time providing a solution to the limitations associated with each of these types. The used specimen is discussed and compared through numerical simulations to a prominent geometry proposed in the literature. Experiments are presented and the results are implemented in identifying classical and advanced yield criteria and though represented as yield surfaces.
    Journal of Materials Processing Technology. 06/2013; 213(6):939–946.
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    ABSTRACT: Complex material models used for the numerical representation of forming processes need in addition to tension and compression tests also shear tests to completely analyse the behaviour of the material under different loading conditions. There are two concepts of shear test – one uses symmetrical specimens with two shear zones (according to Miyauchi) the other one specimens with a single shear zone. In both cases, a homogeneous distribution of the strain in the shear zone is essential for the validity of the shear test. Therefore, the length and width of the shear zone in a single shear specimen made from high strength steel according to the ASTM standard geometry were varied. Analysing the resulting strain distribution numerically an optimised sample geometry with a more uniform strain distribution than the ASTM standard was achieved. The numerical results were also validated with experimental shear tests.
    SheMet 2013; 01/2013
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    ABSTRACT: Aluminum alloy AA6016 was accumulative roll bonded up to eight cycles and investigated regarding formability by bending tests. Due to the limited bendability of accumulative roll bonding (ARB) processed materials, a tailored laser heat treatment was performed along the bending edge before forming. This tailored laser heat treatment causes a local recrystallization and recovery of the bending samples at the deformation zone, which locally increases ductility and allows higher bending angles achievable with lower forming forces. Between the recrystallized heat treated zone and the unaffected ultrafine-grained (UFG) base material, a gradient in grain size with a bimodal region is formed. This observed microstructural profile is confirmed by local mechanical testing measuring the hardness and strain rate sensitivity by nanoindentation techniques.
    Metallurgical and Materials Transactions A 06/2012; 43(9). · 1.73 Impact Factor
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    ABSTRACT: Microbending experiments of brass foils were conducted and demonstrated clear size effects, i.e., the normalized bending moment increased with the reduction of foil thickness. The experiments were modeled using the classical plasticity model and three strain-gradient plasticity models. A modified Nix–Gao model was proposed to consider the number of twins across the thickness direction in strain hardening. It was found that the proposed model could better predict the normalized bending moment for both fine-grain and coarse-grain foils and the proposed equation for material intrinsic length could better capture the physics of material deformation. Furthermore, micro-hardness distributions in the bending area were measured and obvious lower-hardness region was found in the middle layer of fine-grain foils instead of coarse-grain foils. This indicates that the modified Nix–Gao model and the assumption of fully plastic bending worked better for coarse-grain foils than for fine-grain foils.
    Journal of Materials Processing Technology - J MATER PROCESS TECHNOL. 03/2012;
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    ABSTRACT: Aluminium alloy AA6016 was accumulative roll bonded up to eight cycles in order to produce an ultrafine-grained microstructure. The formability of these sheets was investigated by means of bending tests. Furthermore the influence of a local laser heat treatment at the bending edge is observed. The strength of the UFG samples is increased by a factor of around two compared to the conventionally grained T4 condition which also results in up to 50 % higher punch forces needed for bending of ARB processed samples. An anisotropic bending behaviour is observed. By applying a tailored laser heat treatment along the bending edge prior to the bending tests a local recrystallization and recovery at the deformation zone of the samples is achieved. Thus, ductility is increased locally whereby bending to an angle of 80° is possible with lower forming forces compared to the non-heat treated specimens. The results are compared to previous studies on mechanical properties and formability investigations of ARB processed AA6016.
    Key Engineering Materials 02/2012; 504-506:575-580.
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    ABSTRACT: Ever increasing demands on functional integration of high strength light weight products leads to the development of a new class of manufacturing processes. The application of bulk forming processes to sheet or plate semi-finished products, sometimes in combination with conventional sheet forming processes creates new products with the requested properties. The paper defines this new class of sheet-bulk metal forming processes, gives an overview of the existing processes belonging to this class, highlights the tooling aspects as well as the resulting product properties and presents a short summary of the relevant work that has been done towards modeling and simulation.
    CIRP Annals - Manufacturing Technology 01/2012; 61(2):725-745. · 2.25 Impact Factor