ETD system

Electronic theses and dissertations repository


Tesi etd-11072019-095011

Thesis type
Tesi di laurea magistrale
Development and verification of improved Metallic and Ceramic Materials Demise Models for ground risk prediction software tools
Corso di studi
relatore Prof. Filippeschi, Sauro
Parole chiave
  • Clean Space Initiative
  • Metallic and Ceramic materials
  • Ablation Model
  • Atmospheric re-entry
  • Design for Demise
Data inizio appello
Secretata d'ufficio
Riassunto analitico
The emerging Design for Demise (D4D) approach in the context of uncontrolled re-entries from Space, is urgently requiring the necessity of more sophisticated and reliable prediction software tools able to reproduce materials degradation -or “ablation”- processes when subjected to the harsh conditions of atmospheric re-entries from Low Earth Orbits (LEO).
As a background, the mitigation of risk for life and property on the ground in the context of uncontrolled re-entries of space debris or defunct satellites as part of the European Space Agency (ESA) Clean Space initiative.
Objective of this thesis is the development of a numerical model aiming at describing the destructive behaviour of Metallic and Ceramic materials when subjected to atmospheric re-entry scenario. The model is applied to a selection of material samples featuring representative characteristics of aerospace structures; Aluminium Alloy 7075, Grade 5 Titanium Ti6AI4V, Stainless Steel 316L and Silicon Carbide.
The general thermal problem is treated through the resolution of a 1-D heat conduction equation, in which the effect of gas-surface interactions, such as catalysis and oxidation, are accounted in order to generate a more accurate modelling. In this regard, a semi-empirical approach is adopted in order to model these latter processes.
The results of the implemented materials demise model are compared and verified using experimental data of the testing campaign executed at the Institute of Space Systems (IRS) of the University of Stuttgart, during which different materials were characterized in terms of their aerothermal “demisability” using simulated uncontrolled atmospheric entry conditions generated in Plasma Wind Tunnel facilities.
As proved experimentally, the extremely demisable behaviour of Aluminium Alloy 7075 is obtained also numerically in terms of time required to reach the critical condition of melting; however, the complexity of the melting process, in particular the coupling between phase change and surface oxidation results in high degree of uncertainties in the material behaviour.
Similarly, hardly demisable materials such as Grade 5 Titanium and Silicon Carbide are reproduced with an acceptable degree of accuracy.
Therefore, it is here implemented a numerical ablation model able at predicting, at a certain extent and under definite approximations, whether a material, is going to undergo to thermal degradation as compared to re-entry times typical of LEO orbits.