Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Taşdemirci, AlperSubject: search.filters.subject.Acrylonitrile Butadiene Styrene

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  • Master Thesis
    On the Selection of Material Model for the 3d Printed Plastics
    (01. Izmir Institute of Technology, 2021) Yorulmazlar, Berika; Taşdemirci, Alper
    In this study, the behavior of suitable material models which fulfil the need of representation of static and dynamic constitutive behavior ABS plastic produced with Fused Deposition Modeling (FDM) method was investigated. The accuracy of material model strongly depends on the accurate determination of its constants. These constants were obtained by conducting quasi-static and high strain rate experimental studies. The high strain rate tests of FDM built ABS samples were performed using split-Hopkinson pressure bar (SHPB) and split-Hopkinson tension bar (SHTB) and gas gun set-ups. Numerical models were conducted by using the commercial explicit finite element code LS-DYNA 971. Raw data obtained from experiments at low and high strain rates, were reduced and defined in material models. ΜΑΤ_24, ΜΑΤ_81, ΜΑΤ—187 material models were considered in numerical models to investigate the constitutive behavior of the FDM b^ilt ABS material. Good correlation was observed between the numerical and experimental data with the use of selected material models. Then, Generalized Incremental Stress-State dependent damage Model (GISSMO) was selected to characterize the failure behavior of the FDM built ABS. Parameters and curves that defines the state necking and failure occurs at, were found by using optimisation tool, LS-OPT. After observing successful match between the numerical and experimental forcedisplacement curves, GISSMO parameters were defined in SHTB and gas gun numerical models. The results showed good correlation for also the gas gun and SHTB tests in terms of failure behavior, eventually. These imply that GISSMO has the potential to predict necking and localization of deformation of the 3D-printed ABS plastics for different load cases.
  • Master Thesis
    Dynamic Crushing Behaviour of Cactus Geometry Inspired Core Structure
    (Izmir Institute of Technology, 2019) Balya, Ozan; Taşdemirci, Alper; Güden, Mustafa
    Cactus geometry inspired core structure was manufactured with the fused deposition modelling method by a 3D printer using Acrylonitrile Butadiene Styrene (ABS) material filament. The characterization of ABS was made by performing compression tests to take some parameters for numerical models. Numerical preliminary studies were carried out by using the areal density concept and direct-impact Hopkinson pressure bar test method to compare the cactus geometry with the conventional ones in point of the specific energy absorption capacity (SEA). It was understood that from the preliminary work, the cactus inspired structure is intriguing to investigate the dynamic crushing behaviour at least. Quasi-static, drop weight and direct-impact Hopkinson pressure bar tests were conducted to comprehend the energy absorption and crushing behavior in all cases, then to investigate the strain rate and inertia effects on the structure. Implicit and explicit numerical models were made by using LS-DYNA software to validate experiments and to set a precedent for future works. It was seen that the result of numerical models is in harmony with that of experiments excluding the non-fracture structure at the quasi-static implicit model. Moreover, although quasi-static compression gave the structure more stable deformation behavior compared to drop weight impact, higher energy absorption capability was observed on drop-weight tests. In addition, the strain rate effect is more forceful in point of loading carrying capacity compared to the inertia effect despite the fact that it provides the development of buckling and damage formation.