Bir B segment araç için ön gövde çarpma parçalarının tasarımı
Desing of front body crash components for B segment small car
Yazar: CEVRİYE NUR KÖSE
Danışman: PROF. DR. HÜSEYİN ÇİMENOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Otomotiv endüstrisinde sürücü ve yolcu emniyetinin sağlanması araç ön gövdesinde yüksek mukavemetli ve darbe emici yapıların oluşturulmasını gerekli kılmıştır. Bununla birlikte hem otomobil üreticilerinin hem de kullanıcılarının talepleri göz önünde bulundurulduğunda araç ön gövde parçalarının geliştirilmesi ve iyileştirilmesine yönelik çalışmalar gündeme gelmiştir.
Otomobil ön gövde parçalarının önden çarpma durumlarında belirli bir enerjiyi absorplaması gerektiği regülasyonlarla belirtilmiştir. Araçların bu regülatif değerleri sağlaması ön gövde parçalarında daha kalın kesitlerin ve mukavemetli malzemelerin kullanılması gerekliliği ortaya çıkmıştır. Bu parçalarda kullanılan daha kalın kesitler araç ağırlığının artışına ve buna bağlı olarak yakıt tüketiminin artması, yolcu kapasitesinin azalması ve CO2 emisyon seviyesinin regülatif olarak belirtilen değeri desteklememesi ile sonuçlanmaktadır. Bu durumda bu parçalar için kullanılan geometrilerin ve malzemelerin geliştirilmesine zemin hazırlamıştır.
Bu çalışmada benchmark ve literatür araştırmaları sonucunda otomobil ön gövde parçaları olan tampon, ana ray ve çarpma kutusu için uygun olabilecek geometriler ve malzemeler belirlenmiştir. Belirlenen tasarımlar üzerinde iyileştirme çalışmaları yapılarak en uygun geometri oluşturulmuş ve malzeme seçimi yapılmıştır. Tampon, çarpma kutusu ve ana ray için uygun geometrilerin belirlenmesi sonrasında ön gövde grubunun değerlendirilmesi yapılmıştır. 
Bu tez çalışmasında öncelikle çalışmanın hedefleri; literatür ve benchmark çalışmaları sonrasında "%15 daha hafif, darbe emme enerjisi yüksek ve roll form metodu ile üretilecek geometrilerin belirlenmesi ve doğru malzemenin tayin edilmesi" olarak belirlenmiştir. Bu hedeflere ulaşabilmek adına tasarım metodolojisi oluşturulmuştur. Çalışmalara konsept tasarımı ile başlanmıştır. Sonraki aşamalarda ise ana ray, çarpma kutusu ve tampon için alternatif tasarım çalışması yapılarak olabilecek muhtemel geometriler belirlenmiştir. Bu geometriler için malzeme – kalınlık matrisi oluşturulmuştur. Temel seviyede yapılan tasarım ve analiz çalışmaları sonrasında taslak parça geometrisi belirlenmiştir. Bu geometriler için üç temel presip belirlenerek tasarım ve analiz sürelerini optimize edebilmek için bu prensipler doğrultusunda ilerlenmiştir. Analiz çalışmaları esnasında belirlenen bu prensiplerin doğrulaması da yapılmıştır. İlerleyen aşamalarda çekme testleri  yapılarak analizlere girdi teşkil edecek malzeme saptanmıştır. Sonrasında parçanın üretim metodu da göz önünde bulundurularak tasarım iyileştirilmiştir. Üç parça içinde parçalardan beklenen mekanik özellikler düşünülerek en uygun malzeme ve kalınlık belirlenmiştir.
Tüm bu aşamalar sonrasında ise parçaların birbiri ile olan ilişkileri incelenmiş ve değerlendirilmiştir. Tasarımda güncellemeler yapılarak son seviye analiz çalışmaları yapılmıştır. 
Test, tasarım çalışmaları ve analiz sonuçları değerlendirildiğinde; darbenin ilk karşılaştığı parça olan tamponun düşük hızlarda kendisinden sonra gelen çarpma kutusu ve ana rayların etkilenmemesi için daha mukavemetli malzeme seçilmesi gerektiği analizlerde gözlemlenmiştir. Daha mukavemetli malzeme seçimi daha ince kesitlerin kullanımına imkan vermiştir. Böylece tampon parçasında ağırlık azaltılması sağlanmıştır. Ayrıca roll form metodu ile üretilebilmesi için parça geometrisi incelenmiş ve tamponun kenar radyusları kaldırılmıştır. Tamponun görevi düşünülmüş ve hem mekanik özellikler hem de roll form üretim tekniğine uygun olduğu için Docol 1400 malzemesi seçilmiştir. Bu malzemenin seçimi ile bu parçada daha ince bir kalınlık kullanılmıştır. Çarpma kutusu için yapılan analiz çalışmaları sonrasında düşük hızlarda çarpışma olaylarında ana rayların etkilenmemesi için tetikleyici tasarımı yapılmıştır. Tetikleyici tasarımı sonrasında yapılan analizlerde darbe enerjisi emiliminde iyileşme olduğu gözlemlenmiştir. Yapısal olarak en önemli parçalardan biri olan ana raylar için de sıralı ve kademeli deformasyonun sağlanması adına tetikleyici tasarımı yapılmıştır. Analiz sonrasında belirlenen burkulma modları ile tetikleyicilerin yerleri belirlenmiş ve deformasyon yönlendirilmiştir. Böylece çarpma esnasında darbe enerjisinin yolcu ve sürücü bölgesine iletilmesi engellenerek yolcu ve sürücü güvenliği sağlanmıştır. Ana rayların roll form metodu ile üretilecek olmasıda uygun geometrilerin belirlenmesinde etkili olmuştur. 
Sonuç olarak, yapılan tasarım çalışmaları sonrasında roll form metodu da göz önünde bulundurularak belirlenen geometriler üzerinde tetikleyici tasarımı yapılmış ve deformasyon yönlendirilmiştir. Ayrıca doğru malzeme ve kalınlık seçimi ile de gövde parçalarında ağırlığın azaltıldığı ve darbe emme enerjisinin arttığı görülmüştür.

Abstract:
In automotive industry, use of high strength and shockabsorber structure is made essential on vehicle front body because of providing driver' s and passenger' s safety. Besides; vehicle front body components are to be developed and improved according to both automanufacturers and automobile drivers. 
Regulation is emphasized that vehicle front body components have to absorb at frontal collision situation. Materials that have harder, thicker and high strength properties are used on front body components for providing regulation. Vehicle weight is increased because of using thick section on front body components; therefore, fuel consumption increases , passenger capacity decreases and CO2 emission level does not support regulation. As a result, geometry of front body components is to be developed and improved. In addition, material selection is very important in this area.
In this study, applicable geometries and materials that are used in automotive industry were determined for front body components which were crashbox, front bumper and main rails according to benchmark studies and literature research. Designs which were determined were developed so that the best geometry was selected and study belonging to material selection was completed for this geomerty. Front body components were evaluated after design studies were completed with material selection.
In this case, firstly literature investigations and benchmark activities were done on B segment vehicles. After these activities, basic geometries belonging to front body crash components which were crash boxes, main rails and front bumper were designed. And then impact absorption energy at the time of front collision was evaluated according to Federal Motor Vehicle Safety Standards and Regulations 208 Occupant Crash Protection. At he same time impact absorption energy belonging to basic geometries was analyzed by analysis computer programme. In this study, DS / CATIA V5 computer programme was used for design studies. In addition, HyperMesh Pre-processor computer programme was used for mesh activities which were done before analysis activities. After mesh activities, HyperView Post-precessor computer programme was used for analysis studies. Finally Radioss computer programme was used for evaluating result of analysis studies. The result of impact absorption energy which was determined by FMVSS 208 regulation was compared with the result of analysis computer programme. The results showed that impact absorption energy belonging to basic design of front body crash components did not provide the regulation which was determined for having this weight and B segment vehicle. These results were taken as a reference. Benchmark studies and literature investigations were done on B segment vehicle by a private computer benchmark programme for determining new design targets.
After benchmark studies and literature invesitgations, targets of study were determined as selection of the best material and the most applicable geomerty that should be producted with roll form method and had lighter body than the others. In addition, it should have high strength and high shock absorption energy. Design methodology was made for both reaching study targets and studying effective. This methodology had got six steps. First step belonging to design activites started as concept design that was done for each of components according to bechmark studies and literature investigations Materials which were used on front body crash components were determined. Alternative geometries were prepared for crash boxes, main rails and front bumper. And then material and thickess matrix was prepared for these geometries which were crash boxes, main rails and front bumper. Draft geometries were determined according to result of design and analysis studies. Basic principles were determined for this geometry and studies were proceed with these principles which were confirmed during analysis studies. Second step, material characterization studies which were tensile tests were done because of the fact that the results were used in analysis program as an input. Third step, design was improved according to roll form production method, and it was targeted that new geometries were lighter than first geometries. So that design improve activities were done. Fourth step, connection of components with each other and other components which were situated in same front body package were viewed. After analyzing, new geometries belonging to front body crash componentes were updated. Fifth step, material selection was done for reduction of front body weight. At the same time, thicness was determined for components. So that it was provided that lighter geometry was designed. The last step, the new geometries belonging to front bumper, main rails and crash boxes were analysed. The analysis study was done at low speed and high speed. It was seen that when low speed collosion happened, crash boxes and front bumper were deformed, and main rails were not deformed.In addition, when high speed collosion happened, impact absorption energy was better than first geometry. And it was seen that both weight was reduced on fornt body crash components and impact absorption energy was improved by comprasion first design.
When the result of study, design activities and analysis were evaluated; it was seen that bumper was important component and firstly impact faced with bumper which was used high strength materials because of the fact that main rails and crash boxes were not affected negative at low speed. In addition, bumper was evaluated and it was seen that if this component was produced with roll form method, side radius coul be removed. Docol 1400 material was used on this component because of both mechanical properties and roll form method feasible. Thus, thin section was used on this component. After analysis studies, trigger design was done for crash boxes because of the fact that main rails were not affected negative low speed. Analysis was made again and it was seen that impact absorption energy was improved for this component. Trigger design was also done for main rails which were the most important structural parts for providing serial and fraction deformation. Trigger' s location was determined according to the result of buckling analysis. After this study, deformation was directed with trigger. Thus, impact energy was blocked, safety of passengers and drivers was ensured. In additon, front body weight was reduced with using different materials and thin section. And consequently, environmental pollution was reduced and it is aimed reduction of CO2 gases emission. At the same time, fuel consumption which is always very important for both producer and consumer was reduced and improved.
In conclusion, after design activities were completed according to roll form production method, trigger design was done on components and deformation was directed. In addition, right material was selected and thickness was decreased so that weight reduction studies were completed; on the other hand, impact absorption energy were increased. Final design, Docol 1400 material and 1.00mm thickness was used on front bumper component. So that high strength structure was built for this component. DP600 steel and 1.6mm thickness was used on crash boxes. Thin section was created for this component. Finally, DP780 steel and 1.8mm thickness was used on main rails. In this way, impact absorption energy was improved and weight of front body was reduced by comprasion first design.