FREN DİSK-BALATA MEKANİZMASININ ÜÇ BOYUTLU GERİLME ANALİZİ

Bu çalışmada bir otomobil disk fren mekanizması için üç boyutlu termoelastik gerilme analiziyapılmıştır. Disk/balata çifti için silindirik koordinatlarda ısı iletim denklemi türetilmiştir. Isı iletimdenklemini balata ve disk için çözebilmek için sınır ve ilk şartlar belirlenmiştir. Balata ve disk arasındakisürtünme katsayısı sıcaklığa ve zamana bağlıdır. Sıcaklığa ve zamana bağlı sürtünme katsayısını dikkatealmak için termal analizde iteratif bir yöntem geliştirilmiştir. Hareket denklemi türetilmiş, sabit hızdagiden aracın frenleme anından itibaren doğrusal olmayan şekilde yavaşlayarak durma anına ulaştığıgörülmüştür. Sıcaklığın artması sürtünme katsayısında azalmaya ve durma zamanında artışa sebepolmuştur. Balata ve disk arasında sürtünme nedeniyle oluşan toplam ısı akısı hesaplanmıştır. Isı akısıbalata ve disk yüzeylerine ısı paylaşım oranı düşünülerek uygulanmıştır. Silindirik koordinatlardatermoelastik gerilme-gerinim bağıntıları türetilmiştir. Bu bağıntıların denge denklemi içerisine konulmasıile birlikte Navier denklemleri elde edilmiştir. Isı iletim ve Navier denklemlerinin hesaplamalı olarakçözülebilmesi için sonlu elemanlar metodu kullanılmıştır. Disk/balata çifti için sıcaklık dağılımları veeşdeğer von-Mises gerilmeleri hesaplanmıştır. Frenleme basıncının ve balata fiziksel özelliklerinindisk/balata fren mekanizmasında oluşan sıcaklık ve eşdeğer gerilme değerlerine olan etkileriincelenmiştir. Sonuçlar balata malzemesi özelliklerinin disk/balata çifti için sıcaklık ve gerilmeleri dikkatedeğer ölçüde etkilediğini göstermiştir. Isı iletim katsayısı, yoğunluğu ve ısı kapasitesi yüksek olan bir baltamalzemesi kullanımı disk üzerindeki gerilmeleri azaltarak aşınma ve kırılma gibi durumlarınönlenmesinde önemli rol oynayabilir.

Three Dimensional Stress Analysis of a Brake Disc-Pad Mechanism

In the present study, three-dimensional thermoelastic stress analysis is carried out for the automobile disc brake mechanism. Heat conduction equation is derived at cylindrical coordinate system for the disc/pad couple. In order to solve the heat conduction equation for the pad and disc, boundary and initial conditions are specified. The coefficient of friction between the pad and disc is temperature and time dependent. In order to take into account temperature and time dependent coefficient of friction, iterative method is developed in thermal analysis. Equation of motion is derived and it is observed that vehicle travelling at constant speed reaches the moment of stop with decelerating nonlinearly. Total heat flux due to the friction between pad and disc is calculated. Heat flux is applied to the surface of the pad and the disc considering heat partition ratio. Thermoelastic stress-strain relations are derived at cylindrical coordinates. Navier equations are obtained by substituting these relations into equations of equilibrium. In order to solve the heat conduction and Navier equations computationally, the finite element method is used. Temperature distributions and equivalent von-Mises stresses for the disc/pad couple are calculated. Influences of brake pressure and physical properties of the pad upon the values of temperature and equivalent stress are examined. Results indicate that properties of pad material lead to remarkable influence on temperature and stress for disc/pad couple. Utilization of pad material with high conductivity, density and specific heat capacity may play a significant role on avoiding wear and fracture situations by reducing stresses on the disc.

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