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Author: Oliaei, Samad Nadimi BavilScopus Q: Q1

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    Citation - WoS: 12
    Citation - Scopus: 11
    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.
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    Article
    Citation - WoS: 19
    Citation - Scopus: 21
    Plateau Honing of a Diesel Engine Cylinder With Special Topography and Reasonable Machining Time
    (Elsevier Sci Ltd, 2020) Sadizade, Babak; Araee, Alireza; Oliaei, Samad Nadimi Bavil; Farshi, Vahid Rezaeizad
    Deep valleys and flattened peaks are essential characteristics of the finished cylinder bore surface, which is known as the plateau surface. Generally, a honing process is done in three steps to achieve a plateau surface, which is costly and time-consuming and acts as a bottleneck for cylinder block machining line. The real challenge is to select optimum levels of honing process parameters to achieve desired surface characteristics with minimum machining time. The aim of this study is to examine the influence of the input parameters of the honing process on the surface texture of diesel engine cylinder bore. The Rk family parameters are used for surface roughness evaluation and the honing crosshatch angle, in accordance with engine design requirements, which was fixed for all experiments. Optimization by means of the desirability function technique allowed determining most appropriate conditions to desirable roughness (surface quality) and/or minimize machining time (productivity). Based on the findings of this study the conventional three-stage honing process has been replaced by the two-stage process. Using the proposed two-stage honing process the intended plateau surface in cylinder bores are achieved and a remarkable reduction in the honing process time is obtained. Consequently, the process efficiency is improved significantly.
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    Article
    Citation - WoS: 9
    Citation - Scopus: 10
    Strain Engineering of Germanium Nanobeams by Electrostatic Actuation
    (Nature Portfolio, 2019) Ayan, Arman; Turkay, Deniz; Unlu, Buse; Naghinazhadahmadi, Parisa; Oliaei, Samad Nadimi Bavil; Boztug, Cicek; Yerci, Selcuk
    Germanium (Ge) is a promising material for the development of a light source compatible with the silicon microfabrication technology, even though it is an indirect-bandgap material in its bulk form. Among various techniques suggested to boost the light emission efficiency of Ge, the strain induction is capable of providing the wavelength tunability if the strain is applied via an external force. Here, we introduce a method to control the amount of the axial strain, and therefore the emission wavelength, on a suspended Ge nanobeam by an applied voltage. We demonstrate, based on mechanical and electrical simulations, that axial strains over 4% can be achieved without experiencing any mechanical and/or electrical failure. We also show that the non-uniform strain distribution on the Ge nanobeam as a result of the applied voltage enhances light emission over 6 folds as compared to a Ge nanobeam with a uniform strain distribution. We anticipate that electrostatic actuation of Ge nanobeams provides a suitable platform for the realization of the on-chip tunable-wavelength infrared light sources that can be monolithically integrated on Si chips.