Browsing by Author "Kapci, Mehmet Fazil"

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Accurate Prediction of Residual Stresses in Machining of Inconel 718 Alloy through Crystal Plasticity Modelling
(Afyon Kocatepe Üniversitesi, 2023) Kesriklioglu, Sinan; Kapci, Mehmet Fazil; Büyükçapar,Rıdvan; Çetin , Barış; Yılmaz, Okan Deniz; Bal, Burak; 0000-0002-2914-808X; 0000-0003-3297-5307; 0000-0002-2550-7911; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kesriklioglu, Sinan; Kapci, Mehmet Fazil; Büyükçapar, Rıdvan; Bal, Burak
Determination and assessment of residual stresses are crucial to prevent the failure of the components used in defense, aerospace and automotive industries. The objective of this study is to present a material method to accurately predict the residual stresses induced during machining of Inconel 718. Orthogonal cutting tests were performed at various cutting speeds and feeds, and the residual stresses after machining of Inconel 718 were characterized by X-ray diffraction. A viscoplastic self-consistent crystal plasticity model was developed to import the microstructural inputs of this superalloy into a commercially available finite element software (Deform 2D). In addition, same simulations were carried out with classical Johnson - Cook material model. The simulation and experimental results showed that the crystal plasticity based multi-scale and multi-axial material model significantly improved the prediction accuracy of machining induced residual stresses of Inconel 718 when compared to the existing model, and it can be used to minimize the surface defects and cost of production trials in machining of difficult-to-cut materials.
An atomistic study on the HELP mechanism of hydrogen embrittlement in pure metal Fe
(PERGAMON-ELSEVIER SCIENCE LTD, 2024) Hasan, Md Shahrier; Kapci, Mehmet Fazil; Bal, Burak; Koyama, Motomichi; Bayat, Hadia; Xu, Wenwu; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
The Hydrogen Enhanced Localized Plasticity (HELP) mechanism is one of the most important theories explaining Hydrogen Embrittlement in metallic materials. While much research has focused on hydrogen's impact on dislocation core structure and dislocation mobility, its effect on local dislocation density and plasticity remains less explored. This study examines both aspects using two distinct atomistic simulations: one for a single edge dislocation under shear and another for a bulk model under cyclic loading, both across varying hydrogen concentrations. We find that hydrogen stabilizes the edge dislocation and exhibits a dual impact on dislocation mobility. Specifically, mobility increases below a shear load of 900 MPa but progressively decreases above this threshold. Furthermore, dislocation accumulation is notably suppressed at around 1 % hydrogen concentration. These findings offer key insights for future research on Hydrogen Embrittlement, particularly in fatigue scenarios.
Edge dislocation depinning from hydrogen atmosphere in α-iron
(Acta Materialia Inc, 2024) Kapci, Mehmet Fazil; Yu, Ping; Liu, Guisen; Shen, Yao; Li, Yang; Bal, Burak; Marian,Jaime; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
Understanding the dislocation motion in hydrogen atmosphere is essential for revealing the hydrogen-related degradation in metallic materials. Atomic simulations were adopted to investigate the interaction between dislocations and hydrogen atoms, where the realistic hydrogen distribution in the vicinity of the dislocation core was emulated from the Grand Canonical Monte Carlo computations. The depinning of edge dislocations in α-Fe at different temperatures and hydrogen concentrations was then studied using Molecular Dynamics simulations. The results revealed that an increase in bulk hydrogen concentration increases the flow stress due to the pinning effect of solute hydrogen. The depinning stress was found to decrease due to the thermal activation of the edge dislocation at higher temperatures. In addition, prediction of the obtained results was performed by an elastic model that can correlate the bulk hydrogen concentration to depinning stress.
Experimental and Molecular Dynamics Simulation-Based Investigations on Hydrogen Embrittlement Behavior of Chromium Electroplated 4340 Steel
(ASMETWO PARK AVE, NEW YORK, NY 10016-5990, 2021) Dogan, Ozge; Kapci, Mehmet Fazil; Esat, Volkan; Bal, Burak; 0000-0003-3297-5307; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Dogan, Ozge; Kapci, Mehmet Fazil; Bal, Burak
In this study, chromium electroplating process, corresponding hydrogen embrittlement, and the effects of baking on hydrogen diffusion are investigated. Three types of materials in the form of Raw 4340 steel, Chromium electroplated 4340 steel, and Chromium electroplated and baked 4340 steel are used in order to shed light on the aforementioned processes. Mechanical and microstructural analyses are carried out to observe the effects of hydrogen diffusion. Mechanical analyses show that the tensile strength and hardness of the specimens deteriorate after the chrome-electroplating process due to the presence of atomic hydrogen. X-ray diffraction (XRD) analyses are carried out for material characterization. Microstructural analyses reveal that hydrogen enters into the material with chromium electroplating process, and baking after chromium electroplating process is an effective way to prevent hydrogen embrittlement. Additionally, the effects of hydrogen on the tensile response of alpha-Fe-based microstructure with a similar chemical composition of alloying elements are simulated through molecular dynamics (MD) method.
Investigation of Hydrogen Diffusion Profile of Different Metallic Materials for a Better Understanding of Hydrogen Embrittlement
(Gazi Üniversitesi, 2023) Kapci, Mehmet Fazil; Bal, Burak; 0000-0003-3297-5307; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
In this study, hydrogen diffusion profiles of different metallic materials were investigated. To model hydrogen diffusion, 1D and 2D mass diffusion models were prepared in MATLAB. Iron, nickel and titanium were selected as a material of choice to represent body-centered cubic, facecentered cubic, and hexagonal closed paced crystal structures, respectively. In addition, hydrogen back diffusion profiles were also modeled after certain baking times. Current results reveal that hydrogen diffusion depth depends on the microstructure, energy barrier model, temperature, and charging time. In addition, baking can help for back diffusion of hydrogen and can be utilized as hydrogen embrittlement prevention method. Since hydrogen diffusion is very crucial step to understand and evaluate hydrogen embrittlement, current set of results constitutes an important guideline for hydrogen diffusion calculations and ideal baking time for hydrogen back diffusion for different materials. Furthermore, these results can be used to evaluate hydrogen content inside the material over expensive and hard to find experimental facilities such as, thermal desorption spectroscopy.
A phenomenological hydrogen induced edge dislocation mobility law for bcc Fe obtained by molecular dynamics
(ELSEVIER, 2024) Baltacioglu, Mehmet Furkan; Kapci, Mehmet Fazil; Schön, J. Christian; Marian, Jaime; Bal, Burak; 0000-0002-7389-9155; 0000-0001-6476-0429; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Baltacioglu, Mehmet Furkan; Kapci, Mehmet Fazil; Bal, Burak
Investigating the interaction between hydrogen and dislocations is essential for understanding the origin of hydrogen-related fractures, specifically hydrogen embrittlement (HE). This study investigates the effect of hydrogen on the mobility of ½<111>{110} and ½<111>{112} edge dislocations in body-centered cubic (BCC) iron (Fe). Specifically, molecular dynamics (MD) simulations are conducted at various stress levels and temperatures for hydrogen-free and hydrogen-containing lattices. The results show that hydrogen significantly reduces dislocation velocities due to the pinning effect. Based on the results of MD simulations, phenomenological mobility laws for both types of dislocations as a function of stress, temperature and hydrogen concentration are proposed. Current findings provide a comprehensive model for predicting dislocation behavior in hydrogen-containing BCC lattices, thus enhancing the understanding of HE. Additionally, the mobility laws can be utilized in dislocation dynamics simulations to investigate hydrogen-dislocation interactions on a larger scale, aiding in the design of HE-resilient materials for industrial applications.
The role of hydrogen in the edge dislocation mobility and grain boundary-dislocation interaction in alpha-Fe
(PERGAMON-ELSEVIER SCIENCE LTDTHE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2021) Kapci, Mehmet Fazil; Schoen, J. Christian; Bal, Burak; 0000-0003-3297-5307; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak; Kapci, Mehmet Fazil
The atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of alpha-Fe, specifically 1/2<111>{110} and 1/2<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. The results reveal that the presence of hydrogen decreases the velocity of the dislocations -in contrast to the commonly invoked HELP (Hydrogen-enhanced localized plasticity) mechanism-, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stress-strain behaviour which can initiate brittle fracture points. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.