|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Tecniche numeriche per l’analisi a fatica termo meccanica applicate allo sviluppo di componenti motore|
|Titolo in inglese||Numerical methodologies for the structural validation of engine components based on low cycle thermal-fatigue criteria|
|Settore scientifico disciplinare||ING-IND/14 - PROGETTAZIONE MECCANICA E COSTRUZIONE DI MACCHINE|
|Corso di studi||INGEGNERIA INDUSTRIALE E DEL TERRITORIO|
|Data inizio appello||2019-09-25|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
Durante le attività di ricerca è stata sviluppata una metodologia per la verifica strutturale di collettori di scarico per motori a combustione interna. Il fenomeno studiato e ritenuto fondamentale per l’affidabilità riguarda le sollecitazioni termiche e la fatica a basso numero di cicli.
During the Ph.D. research activity, a methodology for the structural analysis of the exhaust manifolds of an internal combustion engine has been proposed. In particular, the thermal loading and the related thermal fatigue damage mechanism are addressed. The method has been applied during the study of a new Ferrari project of melted exhaust manifold which includes the turbine involute. The particular complex geometry of the component derives from the project constrains in terms of engine performance and sound targets which define the length and the cross section of the different exhaust system parts and the twin-scroll architecture of the turbocharger assembly. Several Finite Element simulations have been performed to obtain a virtual approval of the component geometry, in advance with respect to the component manufacturing, in order to identify and prevent possible structural failures. The numerical analysis accurately follow the experimental approval procedure which considers different warming and rapid cooling cycles to mimic typical engine operating conditions. Two particular aspects of the developed numerical methodology are described in details: the elasto-plastic behaviour of the material at high temperatures, a damage criterion for thermal fatigue. Based on Ferrari expertise derived by previous experimental and numerical analysis of other exhaust manifolds, the increase of the equivalent plastic strain registered for a single thermal cycle (delta PEEQ) has been adopted as damage criterion for the low cycle thermal fatigue analysis. On one side, this criterion is easy to be adopted since only the static (tensile test) material properties have to be included in the Finite Element models. On the other side, no general target values of delta PEEQ exist and the numerical forecasts have to be compared with specific values derived from experimental correlations performed by Ferrari considering different failures registered during the development of similar components. The adopted criterion has revealed itself to be well correlated with the experimental evidences thus limiting the number of tests necessary for the component approval. The geometry modifications introduced following the Finite Element results have firstly prevented untimely structural failures and then allowed an optimization of the component geometry useful to reach the target number of cycles.