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The Investigation of Energy Absorption Characteristics of Tpu Tpms Structures Subjected To Impact Loading
(01. Izmir Institute of Technology, 2023) Bakıcı, Çetin; Taşdemirci, Alper
In this thesis, the energy absorption capability of a schwarz based TPMS structure both experimentally and numerically was invetigated. In the product, TPU material and FDM printer was used. Instead of the regular schwarz primitive cell structure, which has been frequently examined in the literature, the sandwich structure design was prepared with the geometry selected from the region between two cells was used and its advantages were compared. In the selection of the TPMS structure, both its high energy absorption capability per unit weight and its geometry suitable for mass production in the future was important. A hyperelastic material TPU and a printer suitable for its production were selected to show deformation behaviour of the structure against multiple loading. After material characterization with TPU specimens, the determined printer parameters were kept constant, and single and multiple cell structures were produced. Static and dynamic tests were performed, and single and multiple-cell structures were modeled and validated in the LS-DYNA finite element package program. It was observed that as the strain rate increases, the structures densification point also decreased and the first peak force and the energy absorption per unit weight (SAE) increase. In addition, it was observed that the deformation behaviour of single and multiple-cell structures were rate dependent. It has been observed that the structure with 9 cells absorbs 20% more energy than the structure with unit cell, which is 9 times higher than the unit cell structure due to the interaction of cells. The developed structure was numerically exposed to blast loads following Nato Stanag 4569 standart. In this standart, from the defined of the injury criteria,on the lower and upper tibia joint should experienced force values lower than 2.6 kN and 5.4 kN respectively. From the numerial simulations, it was found that the structure was able to mitigate the blast load transmitted to the during the accaptable limits.
The Investigation of the Static and Dynamic Crushing Behavior of an Energy Absorbing Biomimetic Armor
(Izmir Institute of Technology, 2017) Akbulut, Emine Fulya; Taşdemirci, Alper; Güden, Mustafa
In this study, an innovative thin-walled energy absorbing structure was manufactured following by biomimicry rules and produced from AISI 304L stainless steel sheet material by deep drawing method. Manufacturing process was modelled in two stages to produce the numerical specimen containing residual stress/strain and thickness distribution using commercial software LS-DYNA. The balanus being a sea creature, consisting of an inner core structure and an outer shell structure, is the inspiration of this study. The balanus was compared to the other conventional geometries in terms of the energy absorption capacity and determined as highly advantageous configuration. Quasi-static crushing and drop weight experiments were conducted and modelled numerically. The observations indicated that the carried load by the balanus is greater than the arithmetic total of the carried load by the inner core and the outer shell separately due to the interaction effect. Besides, energy absorbing performance of the balanus improved under dynamic loading since the outer shell confines the inner core during the deformation and developed the energy absorption performance of it while the energy absorbing capacity of the other two decreased. After the end of the experimental studies, the energy absorption partitions between the components of the balanus were studied numerically and it was observed that the energy absorbing capacity of the balanus increases with increasing deformation velocity due to the strain rate sensitivity effect of the material and the differences of energy partition ratio between the two components decreases.
Development of Aluminum Honeycomb Cored Carbon Fiber Reinforced Polymer Composite Based Sandwich Structures
(Izmir Institute of Technology, 2016) Okur, Mehmet Ziya; Tanoğlu, Metin
Lightweight composite sandwich structures are composed of composite structures that are laminated between thin stiff facesheets bonded to a thicker lightweight core. These structures have high potatial to be used in civil engineering applications, marine, aerospace industry etc. applications due to their high strength to weight ratios and energy absorption capacity. In these structures, the bending loads are generally carried by the force couple formed by the face sheets while the shear loads are carried by the lightweight core materials. Main purpose of the core material is to provide a high moment of inertia. Therefore, under flexural loading, sandwich panels have higher specific mechanical properties relative to the monocoque structures. Also, the core resists transverse forces and stabilizes the laminates against global buckling and local buckling. The resulting structure provides increased buckling resistance and its rigidity. In this study, sandwich composite structures were developed with carbon fiber reinforced polymer composite facesheets and the cores made by Aluminum (Al) based honeycomb with various thicknesses. Carbon fiber/epoxy composite facesheets were fabricated with non-woven unidirectional (UD) fabrics (with 0o/90o orientation) and epoxy resin by vacuum infusion technique. Al honeycomb layers were sandwiched together with carbon/epoxy facesheets using a thermosetting adhesive. Mechanical tests were carried out to determine the mechanical behavior of face sheets, aluminum cores and the composite sandwich structures. Effect of core thickness on the mechanical properties of the sandwich structures was investigated.

Master Degree / Yüksek Lisans Tezleri

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