Browsing by Author "Celik, A."

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    ArticlePublicationOpen Access
    Experimental and numerical modal characterization for additively manufactured triply periodic minimal surface lattice structures: Comparison between free-size and homogenization-based optimization methods
    (Wiley, 2023-06) Özdemir, Mirhan; Simsek, U.; Kuşer, Engin; Gayir, C. E.; Celik, A.; Şendur, Polat; Mechanical Engineering; ŞENDUR, Polat; Özdemir, Mirhan; Kuşer, Engin
    Homogenization-based topology optimization (HMTO) is one of the most extensively used grading methods to generate functionally graded lattice structures (FGLs). However, it requires a precharacterization of the lattices, which is time-consuming. As a remedy, free-size optimization-based graded lattice generation (FOGLG) is explored as an alternative method to generate the FGLs. This article builds on the authors’ previous work in which the HMTO and FOGLG approaches are studied to improve the dynamic characteristic of a design by using a single lattice type, namely, double gyroid (DG) structure. To show applicability of the proposed methods, different lattice types including diamond (D), gyroid (G), and I-WP are employed to create FGLs herein. The frequency response analysis is performed, and the results from HMTO and FOGLG are compared in terms of their accuracy and efficiency. The optimized designs are then reconstructed by relative density mapping (RDM) and enhanced relative density mapping (ERDM) methods. The fabricated test samples made of cobalt–chromium using the direct metal laser melting (DMLM) technique are then experimentally validated using a laser vibrometer. The results reveal that HMTO and FOGLG can be used on the lattice types with a variety of configurations and relative densities.
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    A novel design framework for generating functionally graded multi-morphology lattices via hybrid optimization and blending methods
    (Elsevier, 2023-05-25) Özdemir, Mirhan; Simsek, U.; Kiziltas, G.; Gayir, C. E.; Celik, A.; Şendur, Polat; Mechanical Engineering; ŞENDUR, Polat; Özdemir, Mirhan
    Owing to its excellent mechanical properties, triply periodic minimum surfaces (TPMS) lattice structures have recently gained more interest in engineering applications. The superior properties of these structures make it easier to achieve engineering design goals such as strength and weight. However, technological advancements compel the designer to enhance the traditional TPMS design qualities. Hybridization of different lattice types emerges as a strong candidate for enhancing overall design performance. Therefore, a hybrid optimization scheme based on genetic algorithms (GA) and anisotropic homogenization-based topology optimization is considered to generate a functionally graded multi-morphology for a Messerschmitt–Bölkow–Blohm (MBB) beam design in this paper. The GA is performed to identify the best lattice morphology, including Diamond (D), Gyroid (G), I-WP, and Primitive (P), and their relative densities prior to topology optimization (TO). Once the best lattice morphology of the design domain is obtained via the GA, the homogenization-based topology optimization is applied to grade the multi-morphology lattice to improve the design performance further. The final step is the reconstruction of the graded multi-morphology using a novel blending algorithm. The reconstructed MBB beams are made of cobalt-chromium (CoCr) alloy and are then manufactured using the laser sintering method, direct metal laser melting (DMLM) technique. Destructive metallographic and non-destructive metrological techniques are utilized to assure manufacturing quality. An impact hammer test is conducted on the fabricated beams to validate and compare the proposed graded multi-morphology geometry with graded and uniform single lattice morphologies. Experimental results show that the stiffness of the graded multi-morphology structure designed by the proposed hybrid optimization is 4.5 % and 13.0 % higher than the graded form of D and P-type single lattice morphologies, respectively. Also, it is observed that the graded form single lattice morphologies deliver superior performance than their uniform encounters namely D and P-type lattice structures.