Mekanik el fren sistemi sonlu elemanlar analiz modelinin deformasyon testleri ile doğrulanması ve tasarım iyileştirme çalışması
Verification of the finite element analysis model of the mechanical hand brake system with deformation tests and design optimization
Yazar: EMRE BAYDUR
Danışman: DOÇ. DR. ATAKAN ALTINKAYNAK
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Konstrüksiyon Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Deformasyon = Deformation ; Fren sistemleri = Brake systems ; Geometri optimizasyonu = Geometry optimisiation ; Sonlu elemanlar analizi = Finite element analysis

Özet:
İnsanlık tarihindeki gelişim basamakları göz önünde bulundurulduğunda şüpesiz ki tekerleğin icadı büyük bir adımdır. Özellikle binek hayvanların evcilleştirmesi ile başlayan mobilite, tekerleğin icadı ile daha da artmış, böylece insanlık yaşam alanını farklı bölgelere taşıyarak bilginin taşınması ve yığılması sürecini hızlandırmıştır. Bu ilerleme süreci öyle bir noktaya gelmiştir ki insanlar haraketin kaynağı olan enerjinin sağlanmasını binek hayvanlardan buharlı makinalara, sonrasında ise fosil yakıt kaynaklı ve daha güçlü içten yanmalı motorların kullanılmasına evirmişlerdir. Enerjinin bu denli kullanılır seviyelere çıkması ile birlikte, kontrolü de tam anlamıyla sağlamak amacıyla, haraketin istenilen zamanda durdurulması ihtiyacı ve bu yönde gelişitirme süreçleri serüveni başlamıştır. Bu gereklilik ile birlikte durdurma bir diğer adıyla frenleme mekanizmalarının tarihi de başlamaktadır. 
İlgili tez çalışmasında frenleme sistemlerinden el fren/park fren mekanizması üzerine çalışılmıştır. Araç pasif güvenlik elemanı kategorisine girmekte olan mekanik el fren mekanizmaları araç park halinde iken, haraket etmesini engellemek amacı ile kullanılmaktadır. Özellikle eğimli arazide taşıtın sabit bir pozisyonda kalmasını belirli standartlar çerçevesinde sağlamak, ilgili park fren mekanizmasının temel görevidir. Bunun yanısıra aktif güvenlik elemanı olarak görev alan ve araç haraket halindeyken hızını düşürmek amacıyla kullanılan ayak fren sisteminde yaşanacak bir  arıza anında, risk azaltıcı destek fren sistemi olarak kullanılması da beklenmektedir.
Tez çalışmasında odaklanılan kısım mekanik el fren mekanizmasının yanal yük uygulanması durumundaki yer değiştirme miktarının azaltılmasıdır. Bu çalışmanın hedef iyileştirme değeri, 400 N'a kadar çıkan yanal yük altındaki deformasyonun %10 mertebesinde iyileşirilmesidir. Mevcut tasarımın yer değiştirmesinin ölçüldüğü pozitif ve negatif yönlü yanal basma testleri gerçekleştirilerek, sistemin yer değiştirme miktarı, çalışma boşluğu ve parça deformasyonları olarak  2 temel girdi biçiminde raporlanmıştır. Çalışma süresince odaklanılacak temek konu, parçalardaki gerinimler kaynaklı olan yer değiştirmeler olup, çalışma boşluklarının iyiyleştirilmesi ilgili tezin kapsamı dışındadır. Birden fazla numune ile yapılan testlerde ortalama değerler çıkartılarak, uygulanan yük/yer değiştirme grafikleri oluşturulmuştur. Sonrasındaki adımda mekanik el fren mekanizmasının, 3 boyutlu modeli Siemens NX 12 programı ile oluşturularak, test cihazındaki sınır şartlarının uygulanması ile Ansys Workbench modeli kurulmuş ve sonlu elemanlar yöntemi ile yapısal analizler koşturulmuştur. Test sonuçları ile bilgisayar ortamındaki analiz sonuçlarının birbirini maksimum % 5 hata oranında doğrulaması sağlandıktan sonra ilgili test ve parça grubunun dijital ikizinin oluşturulma süreci tmaamlanmıştır. 
Bir sonraki aşamada, dijital ikizi oluşturulan mekanik el fren sistemi şekil optimizasyonu ve imalat/maliyet/uygulanabilirlik odaklı mühendislik yaklaşımları ile birlikte yanal basma mukavemeti açısından geliştirilmeye tabi tutulmuştur. Yeni geometri dijital ortamda %5'den daha az hata oranı ile çalışmakta olan sonlu elemanlar analiz modeli ile tekrardan yükleme altına alınmış ve elde edilen yer değiştirme sonuçlarında %10 mertebelerinde iyileşme olduğu görülmüştür. İlgili geometrinin imalatı ve tekrardan teste alınması süreçleri bu tez kapsamında olmayıp, çalışma mevcut hedefine ulaşmış bir şekilde tamamlanmıştır. Bunun yanı sıra, tez çalışmasında iyileştirme kapsamında olmayan dikey basma testleri de dijital ortama yine benzer hata oranları ile taşınmış olup, ilgili tasarım önerisi sonucunda bu yöndeki deformasyon miktarında ciddi bir değişim görülmemiştir.

Abstract:
Considering the stages of development in human history, the invention of the wheel is inarguably a big step. Mobility, which started especially with the domestication of riding animals, increased even more with the invention of the wheel, enabling large objects to be relocated and strengthened the hand of humanity at the point of transporting life to different regions. This progress process has come to such a point that people have evolved the supply of energy, which is the source of movement, primarily to combustion reactions in steam boilers, and then to the use of fossil fuel-based and more powerful internal combustion engines, rather than passenger animals. With the influx of movement and energy into life, the adventure of stopping the ongoing movement at the desired time has begun in order to ensure full control. With this requirement, the history of stopping, also known as braking mechanisms, begins. 
In the related thesis study, the hand brake/parking brake mechanism, which is one of the braking systems, was studied. Mechanical handbrake mechanisms, which fall under the category of passive safety elements, are used to prevent the vehicle from moving when it is parked. The main task of the relevant parking brake mechanism is to ensure that the vehicle remains in a fixed position, especially on sloping land, within the framework of certain standards. In addition to this, it is expected to be used as an anti-risk, reducing support brake system in the event of a failure in the foot brake system, which is used as an active safety element and is used to reduce the speed of the vehicle while it is in motion. 
The focus of the thesis study is to reduce the amount of displacement of the mechanical handbrake mechanism when lateral load is applied. The target improvement value of this study is 10% improvement of the average deformation in the amount of lateral load up to 400 N. Positive and negative lateral compression tests, in which the deformation of the existing mechanism was measured, were carried out and the displacement amount of the system was reported as two basic inputs as working gap and deformation. The main focus during the study is the strain-induced displacements of the parts, and the improvement of the running clearance is out of the scope. The amount of displacement obtained as a result of a load of up to 400 N applied to the mechanism in both positive and negative directions was measured. In the next step, the 3D model of the mechanical handbrake mechanism was created with the Siemens NX 12 program, the Ansys Workbench model was established by applying the boundary conditions in the test device, and structural analyzes were run with the finite element method. After ensuring that the test results and the results of the analysis in the computer environment confirm each other at the level of 5%, the process of creating the digital twin of the relevant test and part group was completed. 
To decrease the running time of finite element model, some simplifications were applied to the structure. First of all, cosmetic parts, such as button and lather grip were eliminated from model. Also, push rod and button spring mechanism that is used to guarentied the tension on the system were canceled from the Ansys model. Secondly, number of elements on the FEA model was decreased with the implementation of middle surface sheet modelling. Most of the part in the system were manufactured from sheet metals by progressive presses so changing of the part from solid to sheet was done clearly and did not face with any warpage problem on the model. Additionaly, rivets between the upper and lower levers were modelled as a deformable beam to decrease the running time. With the application of this simplification methods, running time of the analysis was decreased to half an hour. 
Defining of the boundary condition is also another important parameter to reach the targed error rate. In the production of the mechanical hand brake mechanis, specific oils are used to decrease the friction between the braket and lever parts. To simulate the lateral tests, contacts between the static and rotated pars were modelled as frictional contact so FEA model was classified as a non-lineer. In addition to that, material data were taken from Cavo Automative and modelled as bi-lineer material model. Both type of friction and material modelling strategies analysis were changed lineer to non-linner FEA model. 
Comparison of the FEA results and test results shows that, there was not plastic deformation on the mechanism under the 400 N lateral loading both in positive and negative directions. Together with, there were a weak path on the upper and lower levers so deformation of the arms is derived from that exact locations. To increase the lateral stiffness of the mechanism, this weak zone should be studied.
In the next stage, the mechanical hand brake system, which is digitally twinned, has been developed in terms of lateral compression strength together with shape optimization and manufacturing + cost-oriented engineering approaches.The new geometry was reloaded with the finite element analysis model, which was working with less than 5% error rate in the digital environment, and it was observed that there was an improvement of the order of 10% in the displacement results obtained.The manufacturing and retesting processes of the relevant geometry are not within the scope of this thesis, and the study has been completed in a way that has reached its current goal. 
When the current and optimized designs were compromised to each other, stiffness of the parts at the lateral direction was increased with the help of bump structures. Number of rivets, materials and connection type were not exchanged to improve the performans. Shape optimization tool on the Ansys workbench program was used to generate new geometry submissions but it is reliazed that the maturity level of the beta version of shape optimization tool is not edequate yet. Amount of improvement is around %11 up to 200 N lateral loading and after that value, benefit ratio is decreasing slowly. Average improment is proper with the targed of the study.
In addition, the vertical compression tests, which were not within the scope of improvement in the thesis study, were transferred to the digital environment with similar error rates, and as a result of the relevant design proposal, no significant change was observed in the amount of deformation in this direction. 
In conclusion, verification of the finite element analysis model of the mechanical hand brake system with deformation tests and design optimization study was put across. Bench tests are modelled with in the % 5 average error rate and performance of current model was improved %10 with the implementation of some improvements on the upper and lower lever parts. In addition to these, sit upon bench test was also simulated and effect geometry changes on this direction was also reported. Due to the high margin, decreases the performance of mechanical hand brake mechanism at sit upon test can be acceptable.