Civil Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10679/312

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Browsing by Institution Author "BEBEK, Özkan"

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    Automated flow rate control of extrusion for 3D concrete printing incorporating rheological parameters
    (Elsevier, 2024-04) Ahi, Oğulcan; Ertunç, Özgür; Bundur, Zeynep Başaran; Bebek, Özkan; Civil Engineering; Mechanical Engineering; ERTUNÇ, Özgür; BUNDUR, Zeynep Başaran; BEBEK, Özkan; Ahi, Oğulcan
    The use of inline quality assessment technologies is of great importance in meeting the consistent extrusion requirements of 3D concrete printing (3DCP) applications. This paper presents a system to regulate extrusion speed and maintain the flow rate at a target value during 3DCP processes. The system is based on a new equation that combines printing parameters and the material's rheological properties in the printing process. The proposed control strategy is designed to effectively function with various cement-based mixtures. Validation tests demonstrate that the proposed system can maintain an instantaneous flow rate within a certain range and eventually achieve a constant flow rate. During operation, the flow rate is consistently maintained around the targeted value with an average error rate of 6.7 percent. The flow rate control mechanism shows promise as a reliable and efficient solution for achieving precise and constant flow rates, regardless of the cement mix design used.
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    A comparative evaluation of sepiolite and nano-montmorillonite on the rheology of cementitious materials for 3D printing
    (Elsevier, 2022-10-03) Aydın, Eylül Mina; Kara, Ahmet Burhan; Bundur, Zeynep Başaran; Özyurt, N.; Bebek, Özkan; Gulgun, M. A.; Civil Engineering; Mechanical Engineering; BUNDUR, Zeynep Başaran; BEBEK, Özkan; Aydın, Eylül Mina; Kara, Ahmet Burhan
    Through the last decade, methods of digital manufacturing of concrete gained a significant interest compared to conventional concrete. The main challenge in additive manufacturing (3D printing) is to design a highly thixotropic cementitious system. This study aims to investigate the use of sepiolite as a rheology modifier as a novel approach to improve the thixotropic behavior and adapt cementitious systems to 3D printing. To understand the influence of sepiolite on rheological properties, a comparative evaluation with nano-montmorillonite was established. The effectiveness of clay addition was also investigated in fly-ash amended cement-based materials. The rheological analysis was done on cement-paste samples containing both clays in terms of their effects on thixotropy, structural build-up, and recovery. A preliminary printability assessment was done with a lab scale printer having a ram extruder. The results show that the incorporation of clays increased the dynamic yield stress and time-dependent evolution of static yield stress. Moreover, the addition of clays improved the thixotropic behavior of cement-based systems, particularly those containing fly-ash. Herein, the sepiolite was found to be more effective compared to nano-montmorillonite in terms of improving thixotropy, structural build-up and recovery. The results showed that use of fly-ash enhances the printability of the mix for the specified extruder and the samples containing 1% nano-montmorillonite or 0.5% sepiolite can be printed. The positive effects of sepiolite were attributed to opposing surface charges of the clay layers and its micro-fibrous microstructure. The findings in this study enabled an in-depth understanding of the rheology and printability of fly-ash amended clay containing printable cement-based mortars.
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    Designing redundant cable-driven parallel robots for additive manufacturing using end-effector compliance index
    (IEEE, 2023) Kara, Burhan; Qureshi, Muhammad Sarmad; Bundur, Zeynep Başaran; Bebek, Özkan; Civil Engineering; Mechanical Engineering; BUNDUR, Zeynep Başaran; BEBEK, Özkan; Kara, Burhan; Qureshi, Muhammad Sarmad
    This paper presents a methodology for optimizing cable anchor points for cable-driven parallel robots (CDPRs) for specific additive manufacturing tasks. Much of a CDPR's workspace is generally not used for printing tasks. The unused workspace of the CDPR can be sacrificed to gain greater control to fulfill the printing task. In this paper, the CDPR is designed for a specific task to achieve the best printing results. To find the optimum robot size, the stiffness of the end-effector and mean cable tension are analyzed. The end-effector compliance index (ECI) is proposed to assess the stiffness of the end-effector within the workspace. The ECI uses cable directions to determine the compliance of a given robot pose. From simulation results, a relation to get optimum CDPR frame size is achieved for both suspended and constrained type CDPRs. The proposed method can be used to design low-cost cable-driven robots for additive manufacturing.