Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Publisher: search.filters.publisher.SAGE Publications Inc.Subject: search.filters.subject.Dimensional stability

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  • Article
    Citation - WoS: 13
    Citation - Scopus: 17
    Design of Dimensionally Stable Composites Using Efficient Global Optimization Method
    (SAGE Publications Inc., 2019) Aydın, Levent; Aydın, Olgun; Artem, Hatice Seçil; Mert, Ali
    Dimensionally stable material design is an important issue for space structures such as space laser communication systems, telescopes, and satellites. Suitably designed composite materials for this purpose can meet the functional and structural requirements. In this paper, it is aimed to design the dimensionally stable laminated composites by using efficient global optimization method. For this purpose, the composite plate optimization problems have been solved for high stiffness and low coefficients of thermal and moisture expansion. Some of the results based on efficient global optimization solution have been verified by genetic algorithm, simulated annealing, and generalized pattern search solutions from the previous studies. The proposed optimization algorithm is also validated experimentally. After completing the design and optimization process, failure analysis of the optimized composites has been performed based on Tsai-Hill, Tsai-Wu, Hoffman, and Hashin-Rotem criteria.
  • Article
    Citation - WoS: 19
    Citation - Scopus: 19
    Comparison of Stochastic Search Optimization Algorithms for the Laminated Composites Under Mechanical and Hygrothermal Loadings
    (SAGE Publications Inc., 2011) Aydın, Levent; Artem, Hatice Seçil
    The aim of the present study is to design the stacking sequence of the laminated composites that have low coefficient of thermal expansion and high elastic moduli. In design process, multi-objective genetic algorithm optimization of the carbon fiber laminated composite plates is verified by single objective optimization approach using three different stochastic optimization methods: genetic algorithm, generalized pattern search, and simulated annealing. However, both the multi- and single-objective approaches to laminate optimization have been used by considerably few authors. Simplified micromechanics equations, classical lamination theory, and MATLAB Symbolic Math toolbox are used to obtain the fitness functions of the optimization problems. Stress distributions of the optimized composites are presented through the thickness of the laminates subjected to mechanical, thermal, and hygral loadings.
  • Article
    Citation - WoS: 15
    Citation - Scopus: 18
    Modeling of Diffusion in Closed Cell Polymeric Foams
    (SAGE Publications Inc., 1999) Alsoy Altınkaya, Sacide
    Closed-cell foams made of polymers have the lowest thermal conductivity of any currently available insulation material other than vacuum insulation systems. The increase of foam conductivity with age occurs as air diffuses into the foam while the blowing agent diffuses out, thus modifying the cell gas composition. Also, the change in cell gas composition influences the dimensional stability of the foams. To predict the long term aging behavior and dimensional stability of these foams, the diffusion characteristics of the different components need to be known. Several models exist in the literature which describe diffusion in foams. The most popular of these models are reviewed, and effective diffusivities predicted from one model are compared with experimental data. An unsteady state model is then proposed and solved numerically using a finite difference scheme. The numerical solution algorithm is developed to efficiently solve the large number of coupled equations resulting from this model. The uptake curves predicted from both the unsteady-state model and a discrete model (Bart and Du Cauze De Nazelle, 1993) are compared with available experimental data for the polystyrene-nitrogen system. From the analysis of uptake curves generated for different numbers of cells, the effective diffusivity of the PS/N2 system is predicted. Also, the effect of initial cell gas composition and cell size on both the long term aging profile and dimensional stability of polyurethane foam is considered. The proposed model can easily be extended to include the influence of blowing agent concentration on diffusivity in the polymer phase and the isotherm describing the distribution of blowing agent between the gas and polymer phases.