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Author: Duran, DenizWoS Q: Q2

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    Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Predicting and Measuring Surface Enlargement in Forward Rod Extrusion
    (Asme, 2016) Duran, Deniz; Ozdemir, Izzet
    Surface enlargement during bulk metal forming processes is one of the key parameters controlling the tribology at the tool-workpiece interface. Not only the surface roughness evolution but also the integrity of the lubricant layer critically reposes on surface enlargement. As an attempt to address this issue, in the first part of this work, a general, deformation gradient based surface enlargement description is implemented in a commercial finite element program. In the second part, forward rod extrusion tests with different area reductions are conducted using customized steel workpieces in which cylindrical copper rods are embedded through the depth. By sectioning the extruded parts and by identifying the position of the copper rods on the lateral surface, average surface enlargement values could be measured locally at different positions along the extrudate. Comparison of experiments and numerical predictions reveal that the deformation gradient based description performs reasonably well in capturing surface enlargement profiles both qualitatively and quantitatively.
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    Conference Object
    Citation - WoS: 10
    Citation - Scopus: 12
    A Flow Stress Model for Steel in Cold Forging Process Range and the Associated Method for Parameter Identification
    (Springer London Ltd, 2018) Simsir, Caner; Duran, Deniz
    Detailed thermo-mechanical characterization of DIN 16MnCr5 covering the process range of cold forging applications (0.01 s(-1) 40 s(-1), 25 A degrees C Ta 400 A degrees C) by compression tests revealed flow stress instabilities associated with dynamic strain aging (DSA) which cannot be reproduced by conventional flow stress models. As a remedy, a flow stress model capable of capturing sharp changes in flow stress, strain hardening, and strain rate sensitivity is proposed. Then, a method for parameter identification is presented which can deal with inhomogeneous deformation heating of the specimen at relatively high-strain-rate tests. The presented method involves response surface-based numerical optimization of the flawed compression tests coupled with finite element (FE) simulation. The proposed flow stress model and the extracted parameters are validated in a forward rod extrusion process without using any case-specific determined parameters in FE simulation. A natural agreement is obtained between the experimental and the predicted results in terms of both the force-displacement curve and the part geometry. The authors think that the flow stress instabilities encountered in the cold forging process range may have further consequences in other inverse analysis attempts such as friction coefficient or critical damage parameter determination and that the proper treatment of material data as put forth in this study can improve the predictive capability of process modeling.