GCRIS

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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.
Dynamic Crushing Behavior of Sandwich Panels With Bio-Inspired Cores
(Izmir Institute of Technology, 2017) Güzel, Erkan; Taşdemirci, Alper; Güden, Mustafa
In the current study, a new approach was shown to develop an innovative loadcarrying and energy absorbing structure which can fulfill the requirements in the fields of automotive, defense and aerospace. Two different topics which have been in great demand in the recent times were combined: sandwich structures and bio-inspiration. Balanus which is a barnacle living along the seashores and on the ships’ surfaces was taken under examination to design a novel sandwich structure core geometry. The designed geometry was manufactured with deep drawing process. The sandwich structures were produced with different face sheets using a pattern to ensure the repeatability of the crushing tests. Firstly, the advantage of the bio-inspired core over the conventional core geometries was shown with a numerical study. Then, the crushing tests were conducted at both quasi-static and dynamic loading rates. Further, the effects of foam filling, confinement, inertia and strain rate sensitivity on the crashworthiness performance of the proposed structure were investigated. In addition to the experimental studies, numerical analyses were also performed using LS-DYNA 971. In the numerical studies, manufacturing process of the core geometry was also modeled to count in the residual stress/strain so that a good proximity was obtained between the experimental and numerical results. Moreover, the penetration and perforation behaviors were inspected. Utility of the proposed geometry where a high resistance is needed against dynamic crushing was demonstrated. Finally, several suggestions were proposed for the future works to elaborate the present study.
Static and Dynamic Deformation Behavior of Combined Geometry Aisi 304l Stainless Stell Shells
(Izmir Institute of Technology, 2015) Şahin, Selim; Taşdemirci, Alper; Güden, Mustafa
In this study, the static and dynamic crushing behavior of combined geometry shells consisting of hemi-spherical and cylindrical segments were studied both experimentally and numerically. The proposed geometries were manufactured by deep drawing. Due to the nature of the deep drawing process, specimens inherited significant amount of residual stress/strain and thickness variation along the cross-section was observed. Thus, the manufacturing process was also numerically modeled explicitly. Quasi-static compression and dynamic drop weight tests were conducted both experimentally and numerically. The plastic deformation of the combined geometry shells started with the inward dimpling of the hemi-spherical segment and progressively continued deforming with the asymmetric or axisymmetric folding in cylindrical segment depending on the radius to thickness ratios and strain rates. The failure/fracture was observed in the thicker specimens at dynamic strain rates and that caused decreases in specific absorbing energy (SAE) levels. In addition, the energy partitions between the hemi-spherical segments increased at higher loading rates. Furthermore, the inertia and rate sensitivity influenced the crushing response of cylindrical segment more than that of hemi-spherical segment and inertia effect was more pronounced than the rate sensitivity at higher loading rates. Considering the thermal effects in the crushing behavior of the combined geometry shells, it was shown that the mean crushing load lowered as the temperature increased. Additionally, the percentages of increase in the crushing load were limited at lower temperatures for varying loading rates. It was shown that as the absolute temperature increased the percentage of increase in crushing load was significantly increased due to the change in deformation mode.

Master Degree / Yüksek Lisans Tezleri

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