Investigation of the Main Factors Affecting the Fatigue Life of Structural Casting Parts in Heavy Commercial Vehicle Brake Systems

Abstract

In the study, factors affecting the fatigue life of the bridge, which is one of the main casting components of an air disc brake used in heavy commercial vehicles, were investigated to enhance its service life. Considering all the boundary conditions affecting the brake under real operating conditions, a two-level factorial experimental design method was used for the three factors predicted to have the most effect on fatigue life and two different levels were determined for each factor and specimens were produced. Structural analyses were conducted using the finite element method to identify critical regions with high stresses on the part. In the tests, to capture the moment of crack initiation, a tripwire was applied to the areas where the stress was high and the part failure was expected, as determined by numerical methods. Prepared test samples were subjected to fatigue testing until mechanical damage occurred and cycles where cracks formed were analysed in detail. As a result of the analysis, the two factors found to have the greatest impact on the fatigue life of the bridge were identified as "pearlite ratio" and the "combination of caliper orientation and bridge casting cavity". It was observed that the fatigue life of bridge samples with a high perlite ratio increased up to 3.1 times compared to low-perlite samples and when an appropriate combination of caliper orientation and bridge casting cavity was selected, it increased up to 3.4 times.

Keywords

• heavy commercial vehicle
• brake system
• structural casting component
• fatigue test
• cycling loading test
• finite element analysis

Yapısal Döküm Parçaların Yorulma Ömrünü Etkileyen Ana Faktörlerin Ağır Ticari Araç Fren Sistemlerinde İncelenmesi

Öz

Çalışmada, ağır ticari araçlarda kullanılan havalı disk frenin ana döküm parçalarından biri olan köprünün servis ömrünün arttırılabilmesi için yorulma ömrüne etkiyen faktörler incelenmiştir. Fren parçasına, gerçek çalışma koşullarında etki eden tüm sınır koşulları göz önüne alınarak, yorulma ömrüne en çok etki edeceği öngörülen üç faktör için iki kademeli faktöriyel deney tasarımı yöntemi kullanılmış ve her bir faktör için iki farklı seviye belirlenerek numune üretimleri gerçekleştirilmiştir. Parça üzerindeki gerilmelerin yüksek olduğu kritik bölgelerin belirlenmesi amacıyla sonlu elemanlar yöntemi kullanılarak yapısal analizler gerçekleştirilmiştir. Testlerde, çatlağın ilk oluştuğu anda yakalanması için sayısal yöntem ile belirlenen, gerilmenin yüksek olduğu ve parçaların kırılması beklenen bölgelere tuzak teli uygulanmıştır. Hazırlanan test numuneleri mekanik hasar meydana gele kadar yorulma testine tabi tutulmuş ve çatlak oluşan çevrimler detaylı analiz edilmiştir. Analiz sonucunda köprü parçasının yorulma ömrüne en fazla etki eden iki faktör sırası ile “perlit oranı” ve “kaliper yönü ile köprü döküm gözünün kombinasyonu” olarak bulunmuştur. Perlit oranı yüksek olan köprü numunelerinin yorulma ömürlerinin, düşük olan numunelere göre 3,1 kata kadar; uygun kaliper yönü ve köprü döküm gözü kombinasyonu seçildiği durumda ise 3,4 kata kadar arttığı tespit edilmiştir.

Anahtar Kelimeler

• ağır ticari araç
• fren sistemi
• yapısal döküm parça
• yorulma testi
• tekrarlı yükleme
• sonlu elemanlar analizi

Kaynakça

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