Understanding mechanical failure of graphite rocket nozzle throats under thermal stresses


Nigar B., Dönmez S., Çöker D. , Özerinç S.

Aerospace Science and Technology, vol.119, 2021 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 119
  • Publication Date: 2021
  • Doi Number: 10.1016/j.ast.2021.107152
  • Title of Journal : Aerospace Science and Technology
  • Keywords: Graphite, Fracture, Crack propagation, Extended finite element analysis, Rocket nozzle

Abstract

© 2021 Elsevier Masson SASMechanical failure of graphite nozzle throats is a common problem of rocket engines. The extreme operating conditions constitute the main cause of the problem, resulting in thermal shock-induced cracking. However, the exact mechanisms of crack initiation and propagation are not well-understood. This study presents a detailed investigation of the problem by combining computational fluid dynamics simulation of the supersonic flow, finite element modeling of the thermal shock, and extended finite element method-based (XFEM) analysis of the cracking behavior. The results show that most cracks initiate at the flow surface and propagate parallel to the surface in the form of Mode II cracks. Partitioning the nozzle into an assembly of graphite segments reduces the peak stresses and slows down the crack propagation and resulting failure. The efficiency of this partitioning approach strongly depends on the proper selection of clearances between the segments. The findings clarify the failure mechanisms of graphite nozzle throats and provides key information towards superior throat designs with higher fracture resistance.