Thermomechanical Fatigue Analysis of a Rocket Engine Thrust Chamber made with Additive Manufacturing

Luís Miguel Nobrega Rebelo

Key information

Authors:

Luís Miguel Nobrega Rebelo (Luís Miguel Nobrega Rebelo)

Supervisors:

Luís Filipe Galrão dos Reis (Luís Filipe Galrão dos Reis); Augusto Manuel Moura Moita de Deus (Augusto Manuel Moura Moita de Deus)

Published in

December 10, 2024

Abstract

The thrust chambers of liquid rocket engines are designed to withstand extreme temperatures and pressures. Reusable engines are starting to be the paradigm in the industry, and correctly predicting their fatigue life alongside modeling the most common structural failure mode (the so-called doghouse effect) is still a difficult task. In this work, two different geometries are employed, making use of geometric symmetries to reduce computational cost, and two distinct materials and loading conditions are investigated. A one-way coupled thermomechanical simulation is performed. First, thermal loads varying in time and axial direction are applied onto a non-linear transient numeric model, with the resulting thermal field being imported onto a non-linear structural model. With the thermal expansion and applied pressure loads, the deformation of the part is studied. The mechanical material model used in the analyses is calibrated based on experimental uniaxial tensile tests and includes temperature-dependent elastoplasticity coupled with combined cyclic hardening and ductile damage initiation criteria. Later, the mechanical analyses are performed for several cycles of operation, with the accumulated strain being used to calculate the expected fatigue life using a strain-life method, considering low cycle fatigue and ratcheting phenomena. The dependence of fatigue life from loading conditions, materials and geometry is analyzed. It is found that 3D geometries and harsher operational conditions lead to a decrease in fatigue life prediction. Ultimately, this model is a first step towards predicting the location of crack initiation, as determined by experimental studies performed on other engines. Improvements to the model are suggested.