Crashworthiness Characterisation of the Car Front Bumper System Based on FEA Analysis

This thesis investigated different designs and material selections of vehicle front bumper system to improve the vehicle crashworthiness during the low impact speed (impact velocity=15km/h, 9.32mph) via FEA simulations. The primary purpose is to identify the most important parameters directly related to the improvement of crashworthiness using numerical parametric study. It is found the cross-section profile, curvature shape, material of the bumper beam, together with the connection to the crash box have been all identified that directly influence the crashworthiness performance of the front bumper system. The bumper system, including the sub-components such as bumper beam, crash box, and the connection methods were carried all the parameters, including a number of folds, curvature shapes and spot welds were in-built while creating them into the CAD models using Solidworks. The final assembled complete bumper system is then imported into the ANSYS for further geometry checks and adjustment. Solver Autodyn is used to perform the FEA simulation, and numbers of results files were generated. Results files such as force reaction, plastic work, and equivalent stress, normal stress was all exported it into the Excel for parametric analysis and discussions. Cross-section Profile-Out of proposed Single fold (fold 1) and Triple fold(fold 3) bumper beam profiles, Double fold (fold 2) bumper beam profile presented the best results of force reaction on both smoothness and force value, while the plastic work remained almost identical to profile fold 1 and 3 gained. Fold 2 profile is considered as a good performer since this profile regulated the deformation behaviour of the beam resulted in a smooth increasing force reaction curve. Where the force reaction curve on both fold 1 and fold 3 were fluctuated dramatically due to catastrophic structural failure. Material-In between structural steel and aluminium alloy used in the bumper beam, while the structural steel made bumper beam achieved good force reaction and plastic work. Switched to aluminium can achieve similar force reaction trend and rate with Cross-section neglectable amount of plastic work reduced. Particularly the weight of the bumper beam is dropped down to 5.357 kg while maintaining similar crashworthiness performance to the structural steel. Crash box Crash box connection- The bonded connection is considered as an ideal scenario and was xvii Sensitivity: Internal favoured in much other literature due to it simplifies the connection setting in the FEA environment since it automatically considers it as perfect contact. Three alternative connection methods were therefore proposed to simulate the more realistic scenario. It defined as welding connection that is constituted by a number of spot welds at left, right, top and bottom of the crash box. Since the bonded method contains no spot welds, a method of weld L+R was indicated by totally 4 spot welds appeared at both left and right side of the crash box. On top of this, 4 additional spot welds were added to the top and bottom of the crash box. Totally 4 spot welds were added only to both the top and bottom of the crash box to extend the comparison. While both bonded and weld L+R methods suffered from buckling effect to the crash box, particularly concentrated at the left and right side with high equivalent and normal stresses. It is discovered weld full method provided promising results by reducing the buckling effect to both left and right faces of the crash box, and also managed to lower the equivalent stress down to 336.48MPa and normal stress on the connection surface down to 66MPa. Weld T+B also observed similar performance when compared with both bonded and weld L+R methods. While registered with very small amount of equivalent and normal stresses, the buckling effect is significantly reduced. This thesis contributed the knowledge to the improvement of vehicle front bumper system. Particularly to the failure mode of both bumper beam and crash box, and offered the related optimisation.N/

Bilgisayar destekli çarpışma analizi ile otomobil ön tampon optimizasyonu

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu çalışmada, pasif taşıt güvenliğinin en önemli yapı elemanı olan ön tampon sisteminin kaza esnasında emdiği enerji ve yolcu kabinine aktardığı tepki kuvveti sonuçları farklı sac kalınlıkları için araştırılmıştır. Ön tampon sistemi elemanlarının en iyi sonuçları sağlayan kalınlık değerlerinin bulunması amaçlanmıştır. Bu amaçla birebir ölçekli bir taşıt ön tampon sistemi ve basitleştirilmiş bir taşıt gövde kafesi modellenmiş ve ardından bu sistemin 64 km/h hızla rijit duvara önden çarpması bilgisayar destekli olarak analiz edilmiştir. Ön tampon sisteminin ve kafes yapının SEM, gelişmiş sonlu eleman analiz paket programı olan ANSYS'in Explicit Dynamics modülünde oluşturulmuş ve tampon kirişi ile darbe emicilerin et kalınlıkları değiştirilerek 25 adet analiz gerçekleştirilmiştir. Bu analizlerde elde edilen ön tampon sisteminin emdiği enerji ve kafes yapıya gelen tepki kuvveti sonuçları yorumlanmış ve bu sonuçların arasından optimizasyona en uygun olanları seçilmiştir. Optimizasyon problemini tanımlayan fonksiyonlar bu verilere göre oluşturulmuş ve bu problem MATLAB programında çözdürülerek en yüksek emilen enerji / tepki kuvveti oranını sağlayan darbe emicinin kalınlık değeri bulunmuştur.In this study, the energy absorbed by the front bumper system, which is the most important structural element of passive vehicle safety, during the accident and the reaction force results transferred to the passenger cabin were investigated for different sheet thicknesses. The aim of the front bumper system elements is to find the thickness values which provide the best results. For this purpose, a one-scale vehicle front bumper system and a simplified vehicle body cage were modeled, and then computer-aided analysis of this system with 64 km/h rigid wall front crash was performed. FEM of the front bumper system and cage structure was created in the Explicit Dynamics module of ANSYS, an advanced finite element analysis package program, and 25 analyzes were performed by varying the wall thicknesses of the shock absorbers with the bumper beam. The energy absorbed by the front bumper system and the reaction force results from the cage structure are interpreted and the data set that is most suitable for optimization among these results is selected. The functions describing the optimization problem are constructed according to this equation and the problem is solved in the MATLAB program and the thickness value of the impact absorber providing the highest absorbed energy / reaction force ratio is found