Taşıt el fren kablolarında kullanılan metal bağlantı elemanının yorulma davranışının incelenmesi
Investigation of fatigue behaviour of metallic bracket on parking brake cable
Yazar: SERDAR DALFİDAN
Danışman: PROF. DR. HALUK EROL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Katı Cisimlerin Mekaniği Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Başta otomotiv sektöründe olmak üzere, endüstriyel alanlardaki tasarım ve geliştirme süreçlerinde karşılaşılan problemler, büyük ölçüde zaman kaybını, yüksek maliyeti ve iş yükünü beraberinde getirmektedir. Ayrıca ürün tasarım ve geliştirme sürecinde, seri üretim koşullarında karşılaşılan problemleri önceden tespit edip önlem alabilmek, araştırma ve geliştirme sürecinde nihaî karar alma aşamasındaki süreci hızlandırmakta ve kuruluşların rekabet gücünü arttırmaktadır.   
Tasarım ve geliştirme sürecinde karşılaşılan zaman kaybı ve yüksek maliyet gibi etkenler, bu sürecin deneme yanılma yerine, nümerik metot ve bilgisayar destekli mühendislikle yönetilmesini zorunlu kılmaktadır. Nümerik metotlar ve bilgisayar destekli mühendislik çalışmaları, seri koşullarda karşılaşılabilecek problemleri önceden tespit edip, daha tasarım aşamasında bu tip problemlerin önüne geçmeyi amaçlamaktadır.  
Tez çalışması ile sürücü güvenliğini önemli ölçüde etkileyen ve aracın olmazsa olmazı el fren kablo sistemindeki bağlantı elemanlarının yorulma davranışlarının incelenmesi ve yapılmış olan bilgisayar destekli mühendislik ile mevcut bağlantı elemanlarının iyileştirilmesi amaçlanmıştır. Bu sayede tasarım veya geliştirme sürecindeki deneme yanılma yöntemi ile elde edilmeye çalışılan nihaî sonuca, daha kısa zamanda ve az maliyetle ulaşılacaktır. Çalışma sonucunda ortaya çıkacak olan ürünün validasyon dönemi, yüksek verimlilik ile tamamlanmıştır.  
El fren kabloları (PKB, Parking Brake Cable), bir ucu el fren kolunun birincil (primary) kablosuna, diğer ucu tekerlekte bulunan disk veya kampanaya (otomobil özelliğine göre) bağlanan, sadece çekme kuvvetini ileten ve bu sayede, disk ve kampanadaki fren yayını harekete geçirerek park frenlemesini sağlayan araç güvenlik elemanlarıdır. El fren kabloları, şasi altında belirli bir rota izleyerek, el fren kolu ve tekerlek arasındaki bağlantıyı doğrudan sağlamaktadır. Araç üzerindeki bu rotanın oluşturulması ve el fren kablolarının araç şasisine bağlanması, farklı tasarım ve malzemedeki bağlantı elemanlarının kullanılmasıyla gerçekleşmektedir. Bu bağlantı elemanları, hareket halindeki araçlarda, tekerlekteki süspansiyon hareketi sonucunda meydana gelen harmonik hareketlerden doğrudan etkilenmektedir. Bu süspansiyon hareketleri, bağlantı elemanlarında farklı doğrultularda yüklerin oluşmasına ve elemanların 
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yorulmasına sebep olmakta; bu yorulmalar ise bağlantı elemanlarının zamanla belirli noktalardan kırılmalarına ve çatlamalarına sebep olmaktadır. Bu kırılma ve çatlamalar, el fren telinin performansının düşmesine ve dolayısıyla sürücü güvenliğini de riske atılmasına sebep olmaktadır.  
Araçların süspansiyon sistemlerinin birbirinden farklı olması ve kullanılan el fren kablolarının araç şasisinde aldığı rotanın her araçta farklılık göstermesi, farklı tasarımlarda bağlantı elemanlarının kullanımını da zorunlu kılmaktadır.  
Tez çalışmasının ilk aşamasında, her bir parçanın birbiri ile olan bağıl davranışları incelenmiştir. İç çelik tel ile iç tüp, iç tüp ile dış koruyucu tüpün beraber çalışması sonucu oluşan eğilme rijitliği ve sönümleme davranışı tespit edilmiştir. Bu tespitlerin ardından rotanın bilgisayar ortamında (CAD, Computer Aided Design) modeli oluşturulmuş ve sonlu elemanlar methodu (FEA, Finite Element Analysis) ile bilgisayar ortamında modeli kurulmuş ve analiz edilmiştir. Belirlenen rota ve süspansiyon hareketinde, yorulma deneyi yapılmış ve bağlantı elemanının üzerinde oluşan gerinimler (Strain, Birim Şekil Değiştirme) tespit edilmiştir. SEM'den alınmış olan  veriler, deneysel verilerle doğrulanmış, ardından bilgisayar ortamında yorulma analizi ile hasar tespiti yapılmıştır. Yapılmış olan hasar tespitleri ile farklı malzeme ve/veya tasarımdaki bağlantı elemanlarının ömürleri karşılaştırılarak ihtiyacı karşılayacak olan nihaî modelin tespit edilebilirliği amaçlanmıştır.

Abstract:
The study is related with most common problems facing in most of industries, particularly in automative industry, cause time loss, high cost and workload for the companies in design and development process. In addition, to forecast problems facing in serial production mostly and to take precaution for them during design and development term leads to accelerate to reach precise results and take a decision accordingly. This also aids competitive capacity of companies in most of indusrties.  
Factors such as time loss and high cost facing in design and development term oblige to manage this process by means of numerical methods and computer aided engineering instead of empiric (trial and error) methods. Numerical methods and computer aided engineering aim to determine problems facing mostly in serial production and to prevent these kind of problem further in design and development term.  
Intended to study with this thesis is investigation of metallic bracket using in parking brake cables which is mostly important for drivers and passengers and common system on vehicles. Investigation of fatigue on these metallic bracket is done by means of computer aided engineering in order to reach precise result in short time and with low cost. The validation term of this product was completed by high yield.  
Parking Brake Cable (PKB) is a type of pull cable whose one side is assembled to primery cable of hand lever via equalizer and the other end side is assembled to drum or disc (changing according to vehicle model) exists in wheels. These cables transfer only traction force and block rotation of cable by means of closing parts of drum by pulling brake spring in drums or discs. Thereby, they provide parking brake in vehicles.   
Parking brake cables are consist of many different kind of component such as cable end fitting, conduit end fitting, conduit, inner cable, metallic or plastic bracket etc. We can classify components of parking brake cables according to relation with function of parking brake cables as directly and indirectly. As inner cable, conduit, conduit and cable end fittings are considered as related with function directly, metallic and plastic brackets are considered as related with function indirectly.
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These cables provide connection between hand brake levers and wheels by following a route on vehicles. Generate of this route and assembly of brake cable to frame of vehicles are provided by usage of supporting parts (brackets) in different designs, sizes and materials. In vehicles on the move, harmonic motions of suspension lead to loads in different direction over brackets depend on road condition (such as hollow or bump on ways etc.). These kind of loads occuring in different direction and showing an alteration induce fatigue over brackets, hence cause bracket fractures and cracking. These fractures and crackages lead to decline of performans and loss of functions parking brake cables. Mostly, these events jeopardize vehicles safety and bring about customer complaints. 
Differentiation in suspension systems and in routes of parking brake cables on frames in every each vehicles are obliged to use brackets in different size and design. Decision of design, size and material of bracket is generally difficult and hard to foresee. These difficulties necessitate more know-how or numerical system usage such as finite element analysis by means of computer aided engineering.  
The main study on the thesis is to simulate fatigue behaviour on one spesific bracket choosen from real vehicle with spesific route and suspension movement and to investigate it by means of computer aided enginnering and to validate it in real conditions.  The simulation in real condition will be created in oscillation test bench which is giving harmonic movement in stable frequency instead of random movement.  
Invetigation of fatigue behaviour of metallic bracket is consists of three milestones which are " system CAD (Computer Aided Design) and FEA (Finite Elemant Analysis)  modeling", "data acquisition and processing" and "tests and validation". During this study, first target is investigation of many relative parameters of parts and detection of their behaviour on cables.   
Firstly, rigidity of conduit which are consist of  inner steel armer, inner tube and cover is the most important parameter for simulation in finite element analysis. Beside rigidity, damping factor of conduit is also other important parameter in order to simulate system properly. These two parameters were determined as experimental by creating force vs displacement graphic for spesific conduit length. As rigidity of conduit was calculated by means of deflection equations, damping factor of conduit was calculated by means of energy reduction of conduit due to internal friction of structure. These two paratemers are playing role directly on movement of conduit and specify fatigue loading over critical bracket.   
Secondly, route and suspension behaviour was investigated to gain knowledge about routing and system. Route and suspension behaviour of system using in real vehicle was choosen for the study. In order to create numerical modal in finite element analysis, CAD datas of system should be created initially. In the study, conduit and metallic brackets are the critical and effective components that are  needed to created CAD modal as input of finite element modal. CAD modal for conduit which is composite structure was created as 3D silindirical tube by basing of phcsical
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geometry. CAD modal of metallic brackets were selected as mid-surface shell data in order to get homogenious and stable data from bracket in fatigue behaviour.   
Component models created in CAD modal was used in FEA model in order to simulate experimental oscillation model. Finite element analysis is the highlight step of study regarding to creating numerical method properly. Because this modal will be fundamental of our study and future study which same method is integrated in. Consequently, fatigue behaviour on bracket was detected by means of finite element method and numerical method for its spesific route and suspension behaviour virtually.  
Thirdly, experimental oscillation model was created as phsically in order to clarify finite element method. Oscillation model was created with spesified route and bracket which are critical. Strain gauge was used to collect data from critical bracket during oscillation movement on experimental bench. Three direction gauge was used to collect data from three direction and these datas were progressed in order to obtain usefull data for study.  
Finally, data obtained from finite element analysis as virtual and collected form oscillation test as phsically were evalauted regarding to data compatibility and results shows that nearly % 90 compatibility was achieved in the study. It means that finite element modal was created properly and simulates phsical oscillation modal. Datas obtained from finite element method were used as input for fatigue numerical modal in order to determine fatigue damage and life of critical metallic bracket. Results showed that fatigue damage is under 1 which means metallic bracket is safety in oscillation modal.   
Briefly, these steps and studies will be mainly validation process of design and development term. In phases of new study for different vehicle modals or similiar system, foresight of bracket fractures will contribute to creating of correct and easy design; analyses of routes and brackets without producing bracket phsically. Finite element analysis will be contribute to diminish customer compliments even in phases of new development study. In this way, companies will save both cost and time consumption on itself productions. This saving is already must in terms of automotive sector.     
Consequently, by the means of these simulations and methods, variances of design are able to be foreseed and significant design parameters are able to determined via different programs. Brackets and conduits which have different size, geometry and material are able to be entegrated on finite element modal in order to optimize critical components. In addition, these steps are able to be implemented for other kind of similiar system such as transmission cables (push-pull cables) in order to simulate transmission side oscillation movement. Thereby this study will be fundamental for future studies include similiar cable system.