STRUCTURAL ANALYSIS OF MECHANICAL COMPONENTS UNDER THERMAL LOADS: AN INDUSTRY-ORIENTED APPROACH

This thesis investigates the structural behavior of mechanical components in presence of thermal loads. In many engineering situations there are evidences of failures related to parts that are not free to expand, and a carefully evaluation of stress and strain field related to the temperature distribution is crucial to prevent costly and catastrophic effects, or to provide suitable fire-resistive devices. In the first part of the work the mechanisms which give rise to thermal stresses are investigated. In order to assess some basic problem solving techniques that can be of practical use in an industry-oriented approach, simplified models are developed. Material behavior under cyclic loading conditions has been investigated to individuate the best strategy to modeling cyclic plasticity and to obtain accurate life predictions in presence of thermal fatigue. Examples concerning metallurgical plants and naval engineering are investigated in the second part of the thesis, where the interpretative models previously developed are shown to be capable of well describe the behavior of the components during operational conditions. Analytical and numerical models adopted to define stress levels and damage mechanisms are developed in order to guarantee a computational effort compatible for the daily industrial practice. The proposed thermo-mechanical analyses allow to detect some optimization parameters (related to both selected material and geometrical shape) that permits a longer life to be achieved. Furthermore, an experimental validation of the adopted methodologies is performed for a naval application, where temperature variation, as well as displacements induced by temperature gradients, have been monitored

In questa tesi viene analizzato il comportamento strutturale di componenti meccanici soggetti a carichi di tipo termico. Rotture e cedimenti di organi meccanici, dalle conseguenze a volte catastrofiche e costose, sono spesso correlate a fenomeni di riscaldamento localizzato. Un'accurata analisi delle tensioni termiche in condizioni operative è dunque fondamentale per poter prevenire tali inconvenienti. Lo studio delle deformazioni indotte da carichi termici è inoltre di estrema importanza nella progettazione di dispositivi antincendio. Nella prima parte della tesi si esaminano i principali meccanismi che portano all'insorgenza di tensioni termiche, le conseguenze derivanti da carichi ripetuti e l'interazione tra temperatura e proprietà dei materiali. Gli aspetti metodologici sviluppati sono successivamente applicati all'analisi di strutture meccaniche di derivazione siderurgica e navale, in cui simulazioni numeriche e calcoli di tipo analitico sono supportati da rilievi sperimentali