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Featured researches published by Alper Güner.


Key Engineering Materials | 2009

Analysis of the Hydraulic Bulge Test with FEA Concerning the Accuracy of the Determined Flow Curves

Alper Güner; Alexander Brosius; A. Erman Tekkaya

This work covers the finite element analysis of geometric and process parameters in hydraulic bulge tests in terms of the accuracy of the evaluated flow curve. The important parameters are identified and varied to cover the whole range of possible uses. The effects of these parameters are analyzed for three representative materials: aluminium, mid-strength steel, and high-strength steel. The flow curves of the materials for each set of parameters are calculated by using the results of the simulations and the membrane theory. It is seen that even with simulation results, it is not always possible to obtain the input flow curve, especially towards the end of the test. The dimensions of the sheet and the tooling affect the plastic strain development and geometry of the bulge, leading to errors in computed flow curves. In order to observe the effect of the material flow from the flange on the determined yield stresses, the function and position of the drawbeads are also examined. These parameters, together with the method used to calculate the radius of the bulge, determine the accuracy of the calculated flow curve. Guidelines for an accurate flow curve determination regarding the test set-up and calculation methods are given.


Cirp Annals-manufacturing Technology | 2016

Enhanced granular medium-based tube and hollow profile press hardening

Hui Chen; Sigrid Hess; Jan Haeberle; Sebastian Pitikaris; Philip Born; Alper Güner; Matthias Sperl; A. Erman Tekkaya

Abstract Active and passive control strategies of internal pressure for hot forming of tubes and hollow profiles with granular media are described. Force transmission and plastic deformation of granular medium is experimentally investigated. Friction between tube, granular medium and die, and the external stress field are shown to be essential for the process understanding. Wrinkling, thinning and insufficient forming of the tube establishes the process window for the active pressure process. By improving the punch geometry and controlling tribological conditions, the process limits are extended. Examples for the passive pressure process reveal new opportunities for hot forming of tubes and hollow profiles.


Key Engineering Materials | 2014

Effects of Weld Line in Deep Drawing of Tailor Welded Blanks of High Strength Steels

Thomas Mennecart; Alper Güner; Nooman Ben Khalifa; A. Erman Tekkaya

Due to the increase of lightweight design in car bodies, there is a raise in use of tailored welded blanks (TWB). With these blanks it is possible to strengthen the car body where it is necessary. This can lead to less weight. In the case of tailored welded blanks, there is a weld line, which influences the deep drawing behavior significantly during forming. In the presented results two different high strength steels (HCT980X and HCT600X) are welded together. One forming operation is performed, in which the weld line is positioned differently. The results show the influence of the weld line on the forming behavior which is realized by the comparison of deep drawn monolithic parts with the deep drawn tailored welded blanks. While the monolithic parts could be formed without failure, the forming of tailored welded blanks was accompanied by cracks in dependency to the weld line orientation and the applied load in this region. The results also show that the failure occurs in the base material and that the weld line is not damaged by the applied load. After the characterization of the base materials and the weld material, a numerical modelling of the whole TWB could be realized in this work. Two different ways of modelling techniques of the weld line are compared and the necessity of the consideration of the weld line properties is demonstrated. Furthermore, in consideration of the weld line properties in the FE-Model, it is possible to show that the weld line resists the forming operation without failure.


NUMISHEET 2014: The 9th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes: Part A Benchmark Problems and Results and Part B General Papers | 2013

Incremental analysis of springback and kinematic hardening by the variation of tension during deep drawing

H. ul Hassan; Alper Güner; N. Ben Khalifa; A. E. Tekkaya

Springback is considered as one of the major problems in sheet metal forming. It leads to assembly defects and cause a huge amount of cost for tool modifications. In this work a tool for incremental analysis of springback analysis has been presented. Development of springback with punch travel has been analyzed for the simple U draw-bend geometry, tunnel geometry with open base and modified tunnel geometry with closed base and variable flange height. The effect of tension variation in the sheet with punch travel has been considered as the steering parameter for the springback and various profiles of varying tension are studied, which would generate different tensile forces in sheet. It is found that the tension in the part in the last quarter of punch travel has a profound effect on the springback reduction as compared to the traditionally applied constant BHF. Two selected kinematic hardening models, namely Yoshida-Uemori(YU) model and Armstrong-Frederick(AF) model are used to study the coupled effects o...


Materials | 2016

Deep Drawing of High-Strength Tailored Blanks by Using Tailored Tools

Thomas Mennecart; Hamad ul Hassan; Alper Güner; Noomane Ben Khalifa; Mohamad Hosseini

In most forming processes based on tailored blanks, the tool material remains the same as that of sheet metal blanks without tailored properties. A novel concept of lightweight construction for deep drawing tools is presented in this work to improve the forming behavior of tailored blanks. The investigations presented here deal with the forming of tailored blanks of dissimilar strengths using tailored dies made of two different materials. In the area of the steel blank with higher strength, typical tool steel is used. In the area of the low-strength steel, a hybrid tool made out of a polymer and a fiber-reinforced surface replaces the steel half. Cylindrical cups of DP600/HX300LAD are formed and analyzed regarding their formability. The use of two different halves of tool materials shows improved blank thickness distribution, weld-line movement and pressure distribution compared to the use of two steel halves. An improvement in strain distribution is also observed by the inclusion of springs in the polymer side of tools, which is implemented to control the material flow in the die. Furthermore, a reduction in tool weight of approximately 75% can be achieved by using this technique. An accurate finite element modeling strategy is developed to analyze the problem numerically and is verified experimentally for the cylindrical cup. This strategy is then applied to investigate the thickness distribution and weld-line movement for a complex geometry, and its transferability is validated. The inclusion of springs in the hybrid tool leads to better material flow, which results in reduction of weld-line movement by around 60%, leading to more uniform thickness distribution.


Applied Mechanics and Materials | 2015

Analysis of Drawbead Behaviour for Sandwich Sheets in Sheet Forming Simulation

Siu Ping Li; Alper Güner; A. Erman Tekkaya

Lightweight sandwich sheets represent an alternative in the framework of body lightweight construction. They are made of metal face sheets which form a shear-resistant bond with the thermoplastic core layer. The present work describes the drawbead behavior of sandwich sheets and how it can be modelled in a numerical simulation. Drawbeads are used to control the rate of material flow into the die cavity and are located in the binder area. In the numerical simulation they are either modelled as physical drawbeads or replaced by an equivalent drawbead in which a certain drawbead restraining force (DBRF) is specified as a boundary condition. The values of DBRF can be obtained in a strip test, via numerical simulation or predicted with the aid of a drawbead model. In the current study, strip tensile tests through different physical drawbeads are conducted for sandwich materials. With the obtained variables, restraining forces and thinning values, the results from numerical simulations can be evaluated. Once an optimal simulation approach is found, a parameter study can be conducted to analyze the main influencing factors on drawbead behavior. The results from this study can be leveraged to create a semi-empirical drawbead model.


Key Engineering Materials | 2014

Dry Shearing of Micro-Alloyed Steels

Frank Steinbach; Alper Güner; A. Erman Tekkaya

In the production process of sheet metal parts, oil is widely used as lubricant, not only in sheet metal forming but also in shearing and blanking. Due to environment, health and cost reasons, the absence of lubricants is an aim for future production as it has initiated for machining in the last years. For lubricant-free shearing, it has to be known if there is an influence on the process itself when using oil or not. To find this out, experiments are carried out with a small testing device installed in a tensile testing machine and a blanking tool installed in a servo press. With the small device it is possible to make a piercing process with a circle punch of 16 mm diameter. The blanking tool produces a larger cut part with different holes and open cuts. Without lubricant, there is no difference in the maximum shearing force for the small device while the stripping force is higher and the cut edge zones differs slightly. Using oil or not has a small effect on the force using the blanking tool.


THE 8TH INTERNATIONAL CONFERENCE AND WORKSHOP ON NUMERICAL SIMULATION OF 3D SHEET METAL FORMING PROCESSES (NUMISHEET 2011) | 2011

Characterization of Initial Anisotropy of Sheet Metals Employing Inhomogeneous Strain Fields

Alper Güner; C. Soyarslan; Alexander Brosius; A. Erman Tekkaya

The realistic finite element simulation of sheet metal forming processes necessitates the accurate characterization of plastic behavior of the sheet. For this purpose different experiments and specimen geometries are used in the field of sheet metal characterization to supply information to the increasing number of sophisticated constitutive models demanding many parameters. This work proposes an inverse procedure that reduces the number of needed experiments by utilizing the distribution of strains in the identification of the initial yield locus of sheet metals. The procedure includes the optical measurement of strains on a flat specimen with a varying cross‐section. The geometry of the specimen allows obtaining a distribution of strains rather than a uniform deformation. The measured deformation field is compared with the numerical results which use the YLD2000‐2D yield criterion and the difference is tried to be minimized in an inverse framework using the Levenberg‐Marquardt algorithm. The proposed me...


International Journal of Solids and Structures | 2012

Characterization of anisotropy of sheet metals employing inhomogeneous strain fields for Yld2000-2D yield function

Alper Güner; C. Soyarslan; Alexander Brosius; A.E. Tekkaya


International Journal of Mechanical Sciences | 2012

A cyclic twin bridge shear test for the identification of kinematic hardening parameters

Qing Yin; C. Soyarslan; Alper Güner; Alexander Brosius; A.E. Tekkaya

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A. Erman Tekkaya

Technical University of Dortmund

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Alexander Brosius

Technical University of Dortmund

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A. E. Tekkaya

Technical University of Dortmund

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C. Soyarslan

Hamburg University of Technology

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Thomas Mennecart

Technical University of Dortmund

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Noomane Ben Khalifa

Technical University of Dortmund

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Qing Yin

Technical University of Dortmund

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A.E. Tekkaya

Technical University of Dortmund

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Frank Steinbach

Technical University of Dortmund

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