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Öğe A comparison of recent metaheuristic algorithms for crashworthiness optimisation of vehicle thin-walled tubes considering sheet metal forming effects(Inderscience Enterprises Ltd, 2017) Karagöz, Selçuk; Yıldız, Ali RızaIn this paper, recent optimisation techniques have been used to improve crash performance of a thin-walled tube considering influence of the forming history. In the optimisation study, weight and amount of the energy absorption of the thin-walled tubes are chosen as objective function and constraint, respectively. Radial basis functions (RBFs) metamodelling technique was used to approximate the structural responses selected in crash and forming analyses. The performances of recent optimisation algorithms which are particle swarm algorithm, cuckoo search algorithm, gravitational search algorithm (GSA), hybrid gravitational search-nelder mead algorithm (HGSANM), league championship algorithm (LCA), firefly algorithm, bat algorithm, interior search algorithm (ISA) and imperialist competitive algorithm (ICA) were investigated to find the optimal thin-walled tube design. The lowest mass of the components is obtained at 1000 function evaluation number (FEN) using hybrid GSA.Öğe EFFECT OF FORMING HISTORY ON CRASHWORTHINESS OF A SPOT-WELDED AND DOUBLE-HAT ELLIPTICAL THIN-WALLED TUBE(2019) Beytüt, Hüseyin; Karagöz, Selçuk; Özel, SerkanThin-walled structures (TWTs) are widely used in automotive and aerospace industries due to their easy formability, high energy absorption capacity, low cost, and lightweight advantages. In this study, considering the forming history, the crashworthiness of spot-welded and double-hat shaped elliptical TWT was numerically investigated under dynamic axial load, by the finite element method (FEM). In addition, a bead-shaped trigger mechanism was added to the TWT to reduce the peak crushing force. Non-uniform thickness distribution (thickening or thinning of some elements), plastic strain and work hardening may occur during forming. To investigate the effect of the forming history on crashworthiness, the sheet metal was formed by single-acting deepdrawing process and forming data were mapped to the TWT. The results showed that forming history has an effect on the crashworthiness of the tube. With deep-drawing results mapped to the tube, energy absorption decreased by 5.218% and peak crushing force decreased by 3.614%. Numerical simulations were conducted by using the nonlinear finite element codes RADIOSS/explicit.Öğe EFFECT OF HEAT TREATMENT AND CROSS SECTION ON THE CRASHWORTHINESS OF 51CRV4 SPRING STEEL(Bursa Uludağ Üniversitesi, 2019) Dindar, Çiğdem; Beytüt, Hüseyin; Karagöz, SelçukIn this study, the 51CrV4 spring steel was used as crash box material and its crashworthiness was investigated. Crash boxes with cylinder and rectangular geometries were designed in SolidWorks and nonlinear finite-element analysis was performed in HyperWorks software. In addition, 51CrV4 spring steel was subjected to three different heat treatments and their mechanical properties were determined by tensile and hardness tests. The crashworthiness of structure was evaluated taking into account the total energy absorbed, peak force and the specific energy absorbed. It has been observed that heat treatment and geometric changes have a serious impact on crashworthiness.Öğe INVESTIGATION ON VEHICLE CRASH ANALYSIS CONSIDERING SHEET METAL FORMING HISTORY(TMMOB Makina Mühendisleri Odası, 2015) Yıldız, Ali Rıza; Karagöz, SelçukDepending on the increasing number of vehicles in recent years, accidents resulting in serious injuries and death increased significantly and this situation made it necessary to design and manufacture vehicles with extra safety cautions. Frontal collision accidents are one of the most common types of vehicle accidents. In this study, crash performances of the energy absorbers are investigated numerically with using finite element method. For this purpose, energy absorbers with different geometrical characteristics are designed and tested to develop a new crash box which has better crash performance than initial design.Öğe Optimization of thin-wall structures using hybrid gravitational search and Nelder-Mead algorithm(Carl Hanser Verlag, 2016) Yıldız, Ali Rıza; Kurtulus, Enes; Demirci, Emre; Yıldız, Betül Sultan; Karagöz, SelçukIn literature, a lot of research works have been presented on crashworthiness in order to develop crash performance of vehicles and thin-wall structures. In this research, a new hybrid optimization algorithm based on gravitational search algorithm and Nelder-Mead algorithm is introduced to improve crash performance of vehicles during frontal impact. The results show that the hybrid approach is very effective to develop crash performance of the vehicle components and thin-wall structures.Öğe Yüksek performanslı taşıt güvenlik sistemlerinin geliştirilmesi(Bursa Teknik Üniversitesi, 2016) Karagöz, Selçuk; Yıldız, Ali RızaBu tez çalışması kapsamında, otomobillerde bulunan pasif güvenlik sistemlerinin çarpışma performansları bilgisayar programları ile analiz edilmiştir. Ayrıca gerçek koşullara daha yakın sonuçlar alabilmek için, sac metalden üretilen pasif güvenlik elemanının üretimi esnasında, soğuk sac şekillendirme sonucu meydana gelen artık gerilmelerin ve kesitteki kalınlık değerlerinin değişimi de hesaba katılmıştır. Bu sayede daha doğru sonuçlar elde edilebilmiştir. Bu çalışmanın diğer bir ayağı olarak da üzerinde çalışılan pasif güvenlik sistemi olan enerji yutucu için ilk olarak geometrik boyutlarına sınır şartları verilerek bazı değişkenler atanmış ve bu boyut aralıkları için optimizasyonu yapılarak darbe emici sistemin çarpışma performansı arttırılmıştır. Bunun ardından optimizasyon değişkenlerine sistemin üretimi esnasında maruz kaldığı şekil değişimi parametreleri eklenerek optimizasyon çalışması yapılmış ve gerçek sonuçlara daha yakın, çarpışma performansı daha yüksek bir darbe emici bulunarak tez çalışması tamamlanmıştır.
