Life prediction of thermally highly loaded components: modelling the damage process of a rocket combustion chamber hot wall

Abstract

During their operational life-time, actively cooled liners of cryogenic combustion chambers are known to exhibit a characteristic so-called doghouse deformation, pursued by formation of axial cracks. The present work aims at developing a model that quantitatively accounts for this failure mechanism. High-temperature material behaviour is characterised in a test programme and it is shown that stress relaxation, strain rate dependence, isotropic and kinematic hardening as well as material ageing have to be taken into account in the model formulation. From fracture surface analyses of a thrust chamber it is concluded that the failure mode of the hot wall ligament at the tip of the doghouse is related to ductile rupture. A material model is proposed that captures all stated effects. Basing on the concept of continuum damage mechanics, the model is further extended to incorporate softening effects due to material degradation. The model is assessed on experimental data and quantitative agreement is established for all tests available. A 3D finite element thermo-mechanical analysis is performed on a representative thrust chamber applying the developed material-damage model. The simulation successfully captures the observed accrued thinning of the hot wall and quantitatively reproduces the doghouse deformation.

Lifetime prediction of a rocket combustion chamber wall by a viscoplastic damage model

“…The hot gas temperature is T hg = 3435 K and the maximum calculated hot gas wall temperature is about 950 K. In order to avoid damage concentration at the outer cooling channels additional water cooling is applied. The applied material parameters for the material model were identified based on [1,6]. The damage distribution of the testing sample after 20 cycles (cf.…”

Reliability as an Independent Variable Applied to Liquid Rocket Engine Hot Fire Test Plans

“…In each hot-fire operation, the hardware is degraded by the two fundamental failure mechanisms, stress-increased (cyclic) and strength-reduced (time dependent), which result in the failure mode wear, erosion, creep, and fatigue, including crack initiation and propagation, and thermal shock caused by cyclic high-temperature ranges as well as cyclic mechanical stress/strain amplitudes [18,19].…”

“…The weighting factors 1 and 2 are assumed to be equal (both are 0.5) in this study, but advanced physics-of-failure (POF) analysis models for the various subassemblies may determine more accurate values by varying the stress-increased and strength-reduced loading of the subassembly and component designs. One of these advanced POF analysis models is under final evaluation for the failure modes present in liquid rocket engine combustion chambers [19].…”

“…EQM tot EQM bogey EQM rem , HW tot HW bogey HW rem (19) where EQM bogey is the required EQM to support the BRDT, and EQM rem is the remaining EQM needed to complete the overall RAIV methodology hot-fire test scope defined by Eq. (6).…”

“…(6). Equation (19) can be modified with the corresponding life capability in order to define the required number of hardware sets as given in Eq. (20) (20) where EQM bogey is the required EQM for the BRDT with corresponding bogey EQL (EQL bogey ), and EQM rem is the remaining EQM to complete the overall RAIV methodology hot-fire test scope with corresponding median EQL (EQL med ) based on the 0.5 percentile.…”