Fatigue life evaluation of a bus charging door bracket

Year 2026, Volume: 32 Issue: 1, 10 - 22, 01.02.2026

Samet Karabulut Ahmet Özcan , Ahmet Baha Inal

https://doi.org/10.5505/pajes.2025.61168

https://izlik.org/JA97LR67MD

Abstract

This study presents a comprehensive evaluation of the fatigue performance of two different bracket designs used in the charging door mechanism of an M3-class electric bus-one made from Aluminum 6061-T6 and the other from ST52 structural steel. Both brackets were subjected to constant-amplitude cyclic loads derived from real service data. Fatigue life predictions were conducted using finite element analysis (FEA) and two stress-based approaches: the Soderberg criterion and the Smith-Watson-Topper (SWT) method. FEA of the Aluminum 6061-T6 bracket revealed von Mises stress levels ranging between 170–204 MPa, which approach the material’s yield strength of 208 MPa. The Soderberg result (1.717>1) did not meet the safe design criterion, which was further validated by the occurrence of fracture during field application. The fatigue life predicted by the SWT method was 9.81 × 10^9 cycles. The alternative bracket design made from ST52 steel yielded more favorable results with lower stress levels
(100–115 MPa). For this design, the Soderberg value was found to be 0.485 (< 1), indicating a structurally safe configuration. Additionally, a fatigue life of 3.87×10^11 cycles was obtained using the SWT method, and approximately 10^6 cycles according to FEA-consistent with the infinite life threshold reported in the literature. The findings highlight the critical influence of material selection and structural geometry on fatigue performance. The ST52 steel bracket demonstrated superior performance in terms of both safety and durability, providing a methodological basis for fatigue-resistant design in electric bus components.

Keywords

Fatigue Life , Finite Element Analysis (FEA) , SmithWatson-Topper Method , Soderberg Approach

Bir otobüs şarj kapaği braketinin yorulma ömrü değerlendirmesi

https://izlik.org/JA97LR67MD

Abstract

Bu çalışma, M3 sınıfı bir elektrikli otobüsün şarj kapağı mekanizmasında kullanılan iki farklı braket tasarımının biri Alüminyum 6061-T6, diğeri ST52 yapısal çeliğinden üretilmiş yorulma dayanımı açısından kapsamlı bir değerlendirmesini sunmaktadır. Her iki braket, gerçek servis verilerinden elde edilen sabit genlikli çevrimsel yüklere maruz bırakılmıştır. Yorulma ömrü tahminleri, sonlu elemanlar analizi (FEA) ve iki farklı yöntem olan gerilme temelli Soderberg kriteri ile gerilme temelli Smith-Watson-Topper (SWT) yöntemi kullanılarak gerçekleştirilmiştir. Alüminyum 6061-T6 braketi için yapılan FEA,
170–204 MPa aralığında von Mises gerilmeleri ortaya koymuş; bu değerler malzemenin 208 MPa’lık akma sınırına oldukça yakındır. Soderberg sonucu (1.717>1) güvenli tasarım kriterini karşılamamış ve bu durum saha uygulamasında meydana gelen kırılmayla da doğrulanmıştır. SWT yöntemiyle elde edilen yorulma ömrü ise 9.81 × 10^9 çevrim olarak hesaplanmıştır. ST52 çeliğinden imal edilen alternatif braket tasarımı ise daha düşük gerilme seviyeleri (100–115 MPa) ile daha avantajlı sonuçlar vermiştir. Bu tasarım için Soderberg değeri 0.485<1 olarak bulunmuş ve güvenli bir yapı olduğunu göstermiştir. Ayrıca SWT yöntemiyle 3.87×10^11 çevrimlik yorulma ömrü elde edilmiş, FEA analizine göre ise yaklaşık 10^6 çevrim sonucuna ulaşılmış ve literatürdeki sonsuz ömür eşiğiyle uyum sağlanmıştır. Elde edilen sonuçlar, malzeme seçimi ve yapısal geometrinin yorulma performansı üzerindeki kritik etkisini ortaya koymaktadır. ST52 çeliğinden üretilen braket hem güvenlik hem de dayanıklılık açısından üstün performans sergilemiş ve elektrikli otobüs bileşenlerinde yorulma dayanımına yönelik tasarım sürecine katkı sağlayacak metodolojik bir temel sunmuştur.

Keywords

Yorulma Ömrü , Sonlu Elemanlar Analizi (FEA) , Smith-Watson-Topper Yöntemi , Soderberg Yaklaşımı

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