Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye
Tezin Onay Tarihi: 2017
Öğrenci: GÖKSU GÜRER
Danışman: CEMİL HAKAN GÜR
Özet:The aim of this thesis is to develop a procedure based on the multi-axial fatigue theories that can be used at the design stage for minimizing fretting fatigue failures of the railway axles. The premature fretting fatigue failure of the press-fitted wheel-axle assembly was investigated by means of mechanical and metallurgical methods. First, the loading path obtained through finite element analysis was implemented into the stress-based multiaxial fatigue models to predict possible sites of crack initiation. Then, the computed multiaxial fatigue index of the identified loading path was compared with the reduced fatigue limit presented by the Kitagawa analysis to describe the threshold conditions for fretting fatigue initiation and to define the onset of fatigue crack propagation. The stress intensity factor and the tangential stress at the permissible defects were determined by using the weight functions. The results of the analyses were compared to and verified with those obtained from the metallurgical investigations of the full-scale 34CrMo4 axles failed during service. The effects of the microstructure, the contact surface, and the applied press-fit interference on the initiation of fretting fatigue cracks were discussed. The possible mechanical and metallurgical treatments to improve the fretting fatigue resistance were presented. The consistency between the results of fractographic investigations and numerical analyses reveals that the proposed procedure can be used as an effective tool to assess the risk of fretting damage through uniaxial coupon tests. This procedure also gives designers an opportunity to evaluate the effects of the selected assembly and geometry parameters on fretting fatigue before conducting expensive and time-consuming full-scale axle tests which are requested by international standards.