Browsing by Author "Simsir, Caner"

Now showing 1 - 8 of 8

Citation - Scopus: 2
Anisotropic Transformation Strain and Its Consequences on Distortion During Austenitization
(Amer Soc Testing Materials, 2012) Simsir, Caner; Lubben, Thomas; Hunkel, Martin; Hoffmann, Franz; Zoch, Hans-Werner
The distribution of segregations, which is introduced in the continuous casting process and modified during succeeding manufacturing steps, is considered as an important "distortion potential carrier" for chemically banded steels. This article presents a recently developed mathematical model for integration of the effect of prior forming and cutting operations into heat-treatment simulations by considering "anisotropic transformation strain (ATS)." The model was justified experimentally by simulating the heating and austenitization of dilatometer specimens machined from the forged discs with distinct orientations with respect to the banded microstructure. After the verification, it is used in conjunction with former experimental work to demonstrate that the distribution of fiber flow is one of the important reasons of the dishing of carburized discs. The model provides promising results for process chain simulation to predict the heat-treatment distortion that cannot be predicted with currently available models.
Citation - WoS: 8
Citation - Scopus: 9
A Comprehensive Study of the Effect of Scanning Strategy on In939 Fabricated by Powder Bed Fusion-Laser Beam
(Elsevier, 2024) Dogu, Merve Nur; Ozer, Seren; Yalcin, Mustafa Alp; Davut, Kemal; Obeidi, Muhannad Ahmed; Simsir, Caner; Brabazon, Dermot
This study provides a comprehensive investigation into the effects of different scanning strategies on the material properties of IN939 fabricated using the PBF-LB process. The scanning strategies examined included alternating bi-directional scanning with rotation angles of 0 degrees, 45 degrees, 67 degrees, and 90 degrees between adjacent layers (named as shown), as well as alternating chessboard scanning with rotation angles of 67 degrees and 90 degrees (named as Q67 degrees and Q90 degrees). The results revealed that the 45 degrees and 67 degrees samples had the highest relative density, while the 0 degrees and Q67 degrees samples showed the highest average porosity. Moreover, various types of cracks, including solidification, solid-state, and oxide-induced cracks, were observed. Among the bi-directional scan samples, the 0 degrees sample displayed the most extensive cracking and the highest sigma max residual stress values in both XZ and XY planes. Conversely, the 45 degrees and 67 degrees samples exhibited fewer cracks. Notably, the lowest sigma max residual stress in the XZ planes among the bidirectional scan samples was observed in the 67 degrees sample. Additionally, microstructural analyses indicated differences in grain size and morphology, among the samples. Texture analysis indicated that the 0 degrees and 90 degrees samples exhibited strong cube textures, whereas the texture intensity weakened for the 45 degrees and 67 degrees samples. Moreover, the alternating chessboard scanning strategy led to rougher surfaces (higher Sa and Sz values) compared to the alternating bi-directional scanning strategy, regardless of the rotation angles. Furthermore, the microhardness values among the samples showed minimal variance, ranging between 321 + 14 HV and 356+ 7 HV.
Citation - WoS: 37
Citation - Scopus: 40
Dynamic strain aging in DP steels at forming relevant strain rates and temperatures
(Elsevier Science Sa, 2017) Bayramin, Berkay; Simsir, Caner; Efe, Mert
Mechanical testing of dual phase (DP) steels at low strain rates (10(-3) s(-1)) have shown that they are susceptible to dynamic strain aging (DSA) between 100 degrees C-400 degrees C. During industrial forming processes at intermediate strain rates (1-10(2) s(-1)), the local temperatures may rise to the DSA range due to deformation heating which may disturb the exceptional formability of these steels. In this study, two grades of DP steel (DP590 and DP800) are tested at thermomechanical conditions relevant to forming and the effects of DSA on the formability are established. Test results show that the DSA controls the deformation between 200 degrees C-300 degrees C through serrations in the stress-strain curves of both grades. With increasing strain rates (up to 1 s(-1)) and temperatures, DSA intensifies and results in severe drops in uniform and total ductility with negative strain rate sensitivity, indicating poor formability at these conditions. A detailed analysis of the serrations coupled with dislocation density measurements by x-ray analysis suggests that the serrations can be linked to a periodic microstructural feature.
Citation - WoS: 6
Citation - Scopus: 6
Excessive Damage Increase in Dual Phase Steels Under High Strain Rates and Temperatures
(Sage Publications Ltd, 2021) Cobanoglu, Merve; Ertan, Rasim K.; Simsir, Caner; Efe, Mert
Damage formation in dual phase steels is a complex process and it may be sensitive to the deformation conditions and mechanisms. In this study, the damage parameter is measured and compared under quasi-static and industrial forming conditions (temperatures: 25 vs 200, 300 degrees C and strain rates: 10(-3)vs 10 s(-1)) for DP590 and DP800 steels. Resonance frequency and ultrasonic sound velocity techniques are utilized for the measurements to test the effectiveness and validity of each technique. At a given strain, the damage values can be up to 700% higher at industrial forming conditions, under which dynamic strain aging (DSA) controls the deformation behavior. DSA results in lower formability and is the likely mechanism responsible from the abnormal damage evolution. Measured damage parameters are also confirmed with the void fraction characterization by microscopy, which also provided details on the void shape and distribution with respect to the deformation conditions.
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.
Citation - WoS: 7
Citation - Scopus: 9
Parameter Identification for an Armstrong-Frederick Hardening Law for Supercooled Austenite of Sae 52100 Steel
(Elsevier, 2010) Wolff, Michael; Suhr, Bettina; Simsir, Caner
The mechanical properties of the supercooled austenite phase are sensitive parameters for the prediction of distortion of the components during heat treatments as the inelastic deformation occurs mostly on the soft austenite phase. Recent studies clarified that one of the overlooked issues related with the thermomechanical behavior of supercooled austenite during heat treatment and welding is its complicated cyclic hardening behavior (cf. Simsir et al., Acta Materialia, 2010). Based on those concerns, this article presents an optimization method for determination of temperature-dependent parameters for an Armstrong-Frederick model with combined non-linear kinematic and isotropic hardening, which can potentially pull the quality of simulations through. The results indicate that the proposed approach yields satisfactory results for simulation of heat treatments and welding even with a small and imperfect experimental data pool. (C) 2010 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Simulation and Optimization in Materials Technology
(Hindawi Ltd, 2014) Guerrero, Martha; Simsir, Caner; Deus, Augusto; Sarler, Bozidar
[No Abstract Available]
Citation - WoS: 9
Citation - Scopus: 14
Simulation of Quenching: a Review
(Amer Soc Testing Materials, 2012) Gur, C. Hakan; Simsir, Caner
Quenching is an important part of the production chain of steel components. The final properties of the product are largely determined during this stage, and this renders quenching as one of the most critical stages of production, requiring design and optimization specific to the product. The simulation of quenching requires the solution of a multi-scale/multi-physics problem with complex boundary conditions because of the simultaneously occurring heat transfer, phase transformation, and mechanical interactions. The aim of this paper is to provide an updated review of research studies on the simulation of quenching. The subject is covered from the pioneering work up to very recent advances in the field, with special emphasis on future research needs for improving the industrial usage of heat treatment simulations.