Structural analysis of thermal fatigue failures on rocket combustion chambers by the finite element method

Accurately estimating the thermal stress and strain levels in rocket combustion chambers is an important factor for increasing their safety and reliability. At the NAL, two thermal fatigue failures have occurred in water cooled combustion chambers. This paper examines the cause of the failures and chamber deformations using an inelastic structural analysis incorporating the Finite Element Method (FEM). Both the analytical crack initiation life at low cycle fatigue conditions and analytical deformation determined using a crack initiation model agreed with observed results obtained by a Scanning Electron Microscope (SEM) and with the eye. Another analysis indicates that modifying the cooling channel design would increase the crack initiation life. It was also shown that FEM structural analysis is an effective method for estimating thermal stress and strain levels in rocket combustion chambers.