Makine Mühendisliği Bölümü

Permanent URI for this communityhttps://hdl.handle.net/20.500.12416/19

Browse

Now showing 1 - 6 of 6

Citation - WoS: 11
Citation - Scopus: 10
Effect of Constitutive Material Model on the Finite Element Simulation of Shear Localization Onset
(Elsevier, 2020) Yilmaz, Okan Deniz; Oliaei, Samad Nadimi Bavil
One of the most challenging problems in the field of machining is to determine the onset of shear localization. The consequences of the emergence of shear localized chips are fluctuations in the machining forces, tool wear, deterioration of the surface quality and out-of-tolerance machined components. Several constitutive material models are developed for the simulation of shear localization during machining, especially for Ti6Al4V. However, the accuracy and capability of the proposed models for the prediction of shear localization onset have not been investigated yet. In this study, the effect of different constitutive material models in the prediction of shear localization onset has been investigated. Different material models are studied including the Johnson-Cook (J-C) material model with Cockcroft-Latham damage model, J-C material model with a J-C damage model, models based on modified J-C material models (MJ-C) with strain softening terms, and material model with power-law type strain hardening and strain rate sensitivity, with polynomial thermal softening and polynomial temperature-dependent damage. The results of the finite element models are verified using orthogonal cutting experiments in terms of chip morphology and machining forces. Metallography techniques are used along with SEM observations to elucidate the distinction between continuous and shear localized chips. The results of this study indicate that three models are capable of predicting shear localization onset. However, when compared to the experiments, where a critical cutting speed of 2.8 m/min is obtained for shear localization onset, the results revealed that the model proposed by Sima and Ozel (2016) which is a model based on MJ-C model with temperature-dependent overarching modifier and temperature-dependent material model parameters is more accurate for the prediction of shear localization onset during machining Ti6Al4V. This model is shown to reveal a good prediction for the machining forces as well.
Citation - Scopus: 3
Electrochemical Discharge Machining: Trends and Development
(Elsevier, 2021) Akar, S.; Perveen, A.
The fabrication of microscale products revolutionizes the way manufacturing industries work today and has become the demand of current era due to their applications in various fields like microfluidics, biomedical testing systems, and microelectromechanical systems. Current research interest of manufacturing industries has shifted toward micromanufacturing process development. Electrochemical discharge machining (ECDM) is one of such recently developed process well known for its capability to machine both conductive as well as nonconductive materials. This process evolved from combination of electrodischarge machining and electrochemical machining. This hybrid machining process becomes an attractive technology due to its process simplicity and application in fabrication of microscale features and three-dimensional structures. This chapter will be focusing on the state-of-the-art review of the ECDM processes and its recent development. Various form of this process such as ECDM turning, ECMD-milling, and ECDM grinding will be presented in this chapter. Based on the research found in the literature, limitation associated with ECDM process will be demonstrated, and future research trend for overcoming these drawbacks will be narrated. © 2021 Elsevier Inc. All rights reserved.
Citation - WoS: 12
Citation - Scopus: 16
Fast Fluorometric Enumeration of E. Coli Using Passive Chip
(Elsevier, 2019) Cogun, Ferah; Yildirim, Ender; Boyaci, Ismail Haklu; Cetin, Demet; Ertas, Nusret; Kasap, Esin Nagihan; Dogan, Uzeyir
In this report, a passive microfluidic chip design was developed for fast and sensitive fluorometric determination of Escherichia coli (E. coli) based on sandwich immunoassay. Initially, magnetic nanoparticles (MNPs) and chitosan modified mercaptopropionic acid capped cadmium telluride (CdTe) quantum dots (QDs) were functionalized with E.coli specific antibody to form a sandwich immunoassay with the E. coli. The magnetic separation and preconcentration of the E.coli from the sample solution was performed in the vial. Conjugation of QDs to the magnetically captured E. coli and washing were performed using a passive type of microchip. The microfluidic chip consists of four microchambers connected to each other by microchannels which act as capillary valves. Signal measurement was performed at the last chamber by using a hand-held spectrofluorometer equipped with a fiber optic reflection probe. The selectivity of the method was tested with Enterobacter aerogenes (E. aerogenes) and Salmonella enteritidis (S. enteritidis), it was observed that these bacteria have no interference effect on E.coli determination. The calibration curve was found to be linear in the range of 10(1)-10(5) cfu/mL with a correlation coefficient higher than 0.99. The limit of detection was calculated as 5 cfu/mL. The method was successfully applied to spiked tap and lake water samples. The results suggest that the developed method is applicable for on-site E. coli detection and offers several advantages such as large dynamic range, high sensitivity, high selectivity and short analysis time.
Citation - WoS: 12
Citation - Scopus: 15
Investigation of Surface Roughness in Laser-Assisted Hard Turning of Aisi 4340
(Elsevier, 2021) Sadeghi, Mohammad Hossein; Akar, Samet; Khatir, Farzad Ahmadi
In recent years, new materials such as titanium, nickel alloys, and high-strength steels have been widely used in medical, nuclear, and other industries. Since the manufacturing of different components from these materials has always been associated with the machining process, the use of hard machining in their production is unavoidable. The short life of the cutting tool, the poor quality of the machined surfaces, and the long machining time are some of the challenging issues involved in the traditional machining of these materials. Therefore, researchers have investigated new machining techniques to increase the efficiency and quality of produced parts. Thermal-assisted machining, especially laser-assisted machining is one of the promising methods of machining difficult-to-machine materials. However, this process faces some challenges in terms of the achievable surface integrity of the machined surfaces. This research studies the effect of cutting and thermal parameters on the surface roughness in the laser-assisted turning (LAT) process of AISI 4340 hard steel with a hardness of 560 HV. The results illustrated that by selecting a proper combination of process parameters, the damage caused by the heat penetration into the workpiece can be minimized and the advantages of LAT can be benefited from. (C) 2020 The Authors. Published by Elsevier Ltd.
Citation - Scopus: 4
Microchannels for Microfluidic Systems
(Elsevier, 2020) Nasseri, B.; Akar, S.; Naseri, E.
Microfluidic systems (which are also known as microchannel devices) are an important and versatile practical apparatus applicable in different areas of science and technology. The appropriate design of microfluidic system demands the accurate calculation of the parameters of the microfluidic device. The channels used in microfluidic systems are critical compartments of the device, which affect the efficiency of the system. The purpose of this chapter is to survey the microchannels and their characteristics in microfluidic systems. After a detailed discussion of microchannels, their applications for non-living phantoms for cardiovascular, neuroscience and respiratory studies will be discussed. In the biomedical applications of microchannels the areas such as cell studies e.g. cytoskeleton behavior, cell-to-cell interaction detecting of cell derived moieties are important. Also cellular level tissue engineering, such as cell vaso-occlusion in tissue biomimicking is described. © 2021 Elsevier Inc. All rights reserved.
Citation - WoS: 10
Citation - Scopus: 12
Molecular Dynamic Approach To Predict Thermo-Mechanical Properties of Poly(Butylene Terephthalate)/Caco3 Nanocomposites
(Elsevier, 2021) Boga, Cem; Akar, Samet; Pashmforoush, Farzad; Seyedzavvar, Mirsadegh
Thermo-mechanical properties of poly(butylene terephthalate) polymer reinforced with carbonate calcium nanoparticles have been investigated using molecular dynamics simulations. Detailed analyses have been conducted on the effects of nanofiller content, at concentration levels of 0-7 wt%, on the mechanical properties of PBT, i.e. Young's modulus, Poisson's ratio and shear modulus. Thermal properties, including thermal conductivity and glass transition temperature, have been determined using Perl scripts developed based on nonequilibrium molecular dynamics and a high temperature annealing procedure, respectively. Experiments have been performed to verify the accuracy of the results of MD simulations. The CaCO3/PBT nanocomposites were synthesized using melt blending and mold injection techniques. The uniaxial tensile test, thermal conductivity, differential scanning calorimetry and x-ray diffraction spectroscopy measurements were conducted to quantify the thermo-mechanical properties of such nanocomposites experimentally. The results showed significant improvements in the mechanical properties by addition of CaCO3 nanoparticles due to strong binding between rigid particles and PBT polymer and high nucleation effects of nanoparticles on the matrix. Thermal conductivity and glass transition temperature of nanocomposites represented a consistent increase with the ratio of CaCO3 nanoparticles up to 5 wt% with an enhancement of 38% and 36% with respect to that of pure PBT, respectively.

Browse

Browsing Makine Mühendisliği Bölümü by browse.metadata.publisher "Elsevier"