Mekatronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/255

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Citation Count: Yalçın, F., Öztürk, A., Gülgeç, M. (2016). A parametric study on the elastic-plastic deformation of a centrally heated two-layered composite cylinder with free ends. Archives Of Mechanics, 68(3), 203-228.
A parametric study on the elastic-plastic deformation of a centrally heated two-layered composite cylinder with free ends
(Polish Acad Science Inst. Fundamental Technological Research, 2016) Yalçın, F.; Öztürk, A.; Gülgeç, Müfit; 4168
In this paper, an elastic-plastic deformation of a centrally heated two-layered composite cylinder with free ends subjected to uniformly distributed internal energy generation within an inner cylinder is studied using Tresca's yield condition and its associated flow rule. Stress, strain and displacement distributions in the composite cylinder made of elastic-perfectly plastic material are derived considering the influence of geometric parameters as well as material properties such as yield strength, modulus of elasticity, Poisson's ratio, coefficient of thermal conduction and coefficient of thermal expansion. Yielding starts at the outer boundary or at the axis corresponding to an 'edge regime' of Tresca's prism in both cases. Propagations of the plastic regions are studied due to an increase of a heat generation
Citation Count: Evci, C., Gülgeç, M. (2012). An experimental investigation on the impact response of composite materials. International Journal of Impact Engineering, 43, 40-51.
An experimental investigation on the impact response of composite materials
(Pergamon-Elsevier Science Ltd, 2012) Evci, Celal; Gülgeç, Müfit; 243247; 4168
Due to the improved impact performance characteristics, composites are widely used in engineering and military applications to absorb the impact energy. Determination of impact response of composite materials provides the engineer and the manufacturer with critical knowledge to understand the failure criteria, initiation of the first failure and damage growth through the laminates. This study covers the investigation of impact damage growth and determination of Hertzian failure and maximum force thresholds in three different types of composites. Unidirectional E-Glass, woven E-Glass and woven Aramid composite samples with dimensions of 100 x 100 mm are subjected to low velocity impact with an instrumented impact test system. Rebound, on-set of perforation and perforation limits of composites are found out. Also, energy profile diagrams of both unidirectional and plain weave E-Glass composites are obtained. According to test results, woven composites are found to be superior to unidirectional composites in the protection limit of low velocity impact. It is also observed that damage growth in woven composites is restricted within a smaller area. Impact tests conclude that strength of the composite materials under dynamic loading increases considerably compared to static loading case as a result of strain rate sensitivity.
Citation Count: Öncü, H., Schmidt, K.W. (2013). An integrated scheduling and control model for multi-mode projects. Flexible Services And Manufacturing Journal, 25(1-2), 230-254. http://dx.doi.org/10.1007/s10696-012-9138-3
An integrated scheduling and control model for multi-mode projects
(Springer, 2013) Hazır, Öncü; Schmidt, Klaus Werner; 4168
In today's highly competitive uncertain project environments, it is of crucial importance to develop analytical models and algorithms to schedule and control project activities so that the deviations from the project objectives are minimized. This paper addresses the integrated scheduling and control in multi-mode project environments. We propose an optimization model that models the dynamic behavior of projects and integrates optimal control into a practically relevant project scheduling problem. From the scheduling perspective, we address the discrete time/cost trade-off problem, whereas an optimal control formulation is used to capture the effect of project control. Moreover, we develop a solution algorithm for two particular instances of the optimal project control. This algorithm combines a tabu search strategy and nonlinear programming. It is applied to a large scale test bed and its efficiency is tested by means of computational experiments. To the best of our knowledge, this research is the first application of optimal control theory to multi-mode project networks. The models and algorithms developed in this research are targeted as a support tool for project managers in both scheduling and deciding on the timing and quantity of control activities
Citation Count: Ozturk, Ali; Gulgec, Mufit, "Analytical Solution of Thermal Stresses in a Functionally Graded Solid Cylinder within Parabolic Continuous Grading", Mechatronics and Computational Mechanics, Vol. 307, pp. 364-, (2012)
Analytical Solution of Thermal Stresses In A Functionally Graded Solid Cylinder Within Parabolic Continuous Grading
(Trans Tech Publications LTD, 2012) Öztürk, Ali; Gülgeç, Müfit; 4168
This paper presents analytical solutions of the thermal stresses in a functionally graded solid cylinder with fixed ends in elastic region. These thermal stresses are due to the uniform heat generation inside the cylinder. Material properties of the functionally graded (FG) cylinder vary radially according to a parabolic form. The material properties are assumed to be independent of the temperature which are yield strength, elasticity modulus, thermal conduction coefficient, thermal expansion coefficient and Poisson's ratio. The solutions for the thermal stresses are valid for both homogeneous and functionally graded materials.
Citation Count: Öztürk, A.; Gülgeç, Müfit (2013). "Determination of onset of yield due to material properties in a heat generating two-layered compound cylinder", Applied Mechanics and Materials, Vol. 327, pp. 22-27.
Determination of onset of yield due to material properties in a heat generating two-layered compound cylinder
(2013) Öztürk, A.; Gülgeç, Müfit; 4168
In this theoretical study, based on Tresca's yield criterion and its associated flow rule, the elastic deformation of a centrally heated compound cylinder with fixed ends is investigated analytically by taking into consideration not only the geometrical but also the material parameters such as yield strength, modulus of elasticity, Poisson's ratio, thermal conductivity and coefficient of thermal expansion. These material parameters are assumed to be independent of the temperature. The compound cylinder is assumed to be very long such that axisymmetric condition exists. Both of the constituent materials of the two layers are supposed to be elastic-perfectly plastic materials. There is heat generation in the interior solid cylinder but no heat generation in the outer hollow cylinder. Both of the cylinders are assumed to be bounded perfectly at the interface. Elastic stress analysis is performed to prevent yield in the compound cylinder. © (2013) Trans Tech Publications, Switzerland.
Citation Count: Yalçın, F.; Ozturk, A.; Gulgec, M. ko“Effect of the Material Properties on the Yielding of the Two-Layered Composite Cylinder with Free Ends”, 13th International Conference Computational and Mathematical Methods in Science and Engineering (CMMSE-2013), June 24- 27 2013, Almería, Spain.
Effect of the Material Properties on the Yielding of the Two-Layered Composite Cylinder with Free Ends
(2013) Yalçın, F.; Öztürk, A.; Gülgeç, M.; 4168
Citation Count: Evci, C., Gülgeç, M. (2014). Effective damage mechanisms and performance evaluation of ceramic composite armors subjected to impact loading. Journal Of Composite Materials, 48(26), 3215-3236. http://dx.doi.org/10.1177/0021998313508594
Effective damage mechanisms and performance evaluation of ceramic composite armors subjected to impact loading
(Sage Publications Ltd, 2014) Evci, Celal; Gülgeç, Müfit; 243247; 4168
Researches on the armor systems composed of composite materials with ceramic frontal face and polymer-based back-support are continuously developing further. This study, which mainly covers the impact behavior of ceramic composite armors, is a two-stage research. The first stage involves the investigation of component-level impact characteristics and failure mechanisms of the ceramic composite armors. At this stage, low-velocity impact behavior of ceramics and fiber-reinforced composites is investigated. Impact test results revealed that impact loading is of dynamic nature and strength of the composite materials under dynamic loading increases considerably as a result of strain rate sensitivity, which makes them the right choice to be used in conjunction with ceramics in armor systems. The second stage examines the ballistic impact behavior and ballistic performance of the armor systems. The extent and pattern of impact damage related to projectile velocity are determined for the armor components and the armor itself.
Citation Count: Öztürk, A., Gülgeç, M. (2011). Elastic-plastic stress analysis in a long functionally graded solid cylinder with fixed ends subjected to uniform heat generation. International Journal of Engineering Science, 49(10), 1047-1061. http://dx.doi.org/10.1016/j.ijengsci.2011.06.001
Elastic-plastic stress analysis in a long functionally graded solid cylinder with fixed ends subjected to uniform heat generation
(Pergamon-Elsevier Science Ltd, 2011) Öztürk, Ali; Gülgeç, Müfit; 4168
Elastic-plastic deformation of a solid cylinder with fixed ends, made of functionally graded material (FGM) with uniform internal heat generation is investigated, based on Tresca's yield criterion and its associated flow rule, considering four of the material properties to vary radially according to a parabolic form. These four material properties are yield strength, modulus of elasticity, coefficients of thermal conduction and thermal expansion, assumed to be independent of temperature as Poisson's ratio which is taken as constant. The materials which compose the functionally graded cylinder are supposed to be elastic-perfectly plastic materials. Expressions for the distributions of stress, strain and radial displacement are found analytically in terms of unknown interface radii. After determining these radii numerically by means of Mathematica 5.2, the distributions are plotted versus dimensionless radius, increasing heat generation, to compare the FGM cylinder with the homogeneous one. The numerical values used in this work for material parameters are arbitrarily chosen to point out the effect of the non-homogeneity on the stress distribution. The results obtained show that the stress distribution, as well as the development of plastic region radii, is influenced substantially by the material non-homogeneity
Citation Count: Gulgec, Mufit; Evci, Celal, "Functionally Graded Hollow Cylinder Under Pressure and Thermal Loading: Effect of Material Parameters on Stress and Temperature Distributions", International Journal of Engineering Science, 123, pp. 92-108, (2018).
Functionally Graded Hollow Cylinder Under Pressure and Thermal Loading: Effect of Material Parameters on Stress and Temperature Distributions
(Pergamon-Elsevier Science LTD, 2018) Evci, Celal; Gülgeç, Müfit; 4168
This study presents an analytical solution of stresses and displacements in a long functionally graded (FGM) hollow cylinder subjected to uniform heat generation and internal pressure. Thermo-elastic material properties of FGM cylinder continuously vary in radial direction along the thickness with a power function. The temperature distribution is assumed to vary as a function of the radial coordinate and in steady state. Stress formulation approach is employed using the Airy stress function to derive the analytical solution. In the failure analysis of FGM cylinder, Coulomb-Mohr theory is applied for the ceramic phase whereas Tresca yield criterion is used for the metal phase. The stress analysis reveals that stresses in FGM cylinder decrease considerably, compared to the homogenous one, for a particular interval of material parameters. Radial displacement analysis in FGM cylinder supports the results obtained from stress analysis. (C) 2017 Elsevier Ltd. All rights reserved.
Citation Count: Öztürk, A., Gülgeç, M. (2013). Influence of the material properties on the elastic-plastic deformation in a heat generating composite solid cylinder. Journal of the Faculty of Engineering and Architecture of Gazi University, 28(2), 283-292.
Influence of the material properties on the elastic-plastic deformation in a heat generating composite solid cylinder
(Gazi University, Fac Engineering Architecture, 2013) Öztürk, Ali; Gülgeç, Müfit; 30494; 4168
Based on Tresca's yield criterion and its associated flow rule, the elastic-plastic deformation of a centrally heated composite cylinder with fixed ends is investigated by considering the influence of geometric parameters as well as material properties such as yield strength, modulus of elasticity, Poisson's ratio, coefficient of thermal conduction and thermal expansion. In the study, stress, strain and displacement distributions in the composite cylinder made of elastic-perfectly plastic material are derived. Stress distribution and evolution of plastic regions in the composite are presented for different levels of heat generation in the core.
Citation Count: Hazir, Oencue; Haouari, Mohamed; Erel, Erdal, "Robust scheduling and robustness measures for the discrete time/cost trade-off problem", European Journal of Operatıonal Research, Vol. 207, No. 2, pp. 633-643, (2010)
Robust Scheduling and Robustness Measures for the Discrete Time/Cost Trade-Off Problem
(Elsevier Science BV, 2010) Hazır, Öncü; Erel, Erdal; Haouari, Mohamed; 4168
Projects are often subject to various sources of uncertainties that have a negative impact on activity durations and costs. Therefore, it is crucial to develop effective approaches to generate robust project schedules that are less vulnerable to disruptions caused by uncontrollable factors. In this paper, we investigate the robust discrete time/cost trade-off problem, which is a multi-mode project scheduling problem with important practical relevance. We introduce surrogate measures that aim at providing an accurate estimate of the schedule robustness. The pertinence of each proposed measure is assessed through computational experiments. Using the insights revealed by the computational study, we propose a two-stage robust scheduling algorithm. Finally, we provide evidence that the proposed approach can be extended to solve a complex robust problem with tardiness penalties and earliness revenues. (C) 2010 Elsevier B.V. All rights reserved.

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