Towards a Coupled Loads-Response-Life Prediction Framework for Hypersonic Structures in Combined Extreme Environments

Abstract

This study presents a novel computational framework to improve life prediction capabilities for hypersonic aerospace platforms where evaluating the performance of these structures in extreme environments remains a challenge. Here, thermo-mechanical loading histories determined from analyses that couple aerodynamic loads and structural deflections drive high-fidelity continuum models of the structural member, and results from the continuum model in turn drive critical-plane models of fatigue crack nucleation and growth. This approach readily enables complex features of the loading, geometry, and material response to be incorporated by the structural response and life predictions. Results shown here demonstrate the capabilities of this framework, including: representative thermomechanical and acoustic loadings from ascent to cruise conditions through to descent, the full structural response history, and damage indications that incorporate the full thermocyclic history. Preliminary studies on a challenge structural panel indicate that the ascent and descent phases of the flight profile represent the primary drivers for large residual deflections (on the order of the skin thickness), that remain present in subsequent flights and that may degrade aerodynamic and structural performance. Furthermore, the highly cyclic and transient response present in the acoustic loading phase contributes strongly to localized fatigue damage. Nomenclature b= compressibility exponent C p = pressure coefficient F c = compressible flow transformation function H = enthalpy k = parameter representing compressibility and heat transfer effects M = Mach number m = viscosity power law exponent, η/η e = (T /T e ) m n = velocity power law exponent, U/U e = (y/δ) (1/n) P r = Prandtl number p = pressurẽ p = rms fluctuating pressure q = ρU 2 /2, dynamic pressure r = P r 1/3 , turbulent flow recovery factor T = temperature U = velocity y = normal distance into boundary layer from wall γ = ratio of specific heats δ = boundary layer thickness δ 1 = boundary layer displacement thickness η = viscosity λ = viscous/velocity power law exponent ρ = density φ(ω) = power spectral density ω = frequency, rad/s Subscripts a = attached flow aw = adiabatic wall e = edge of boundary layer s = separated flow w = wall Superscripts * = reference enthalpy condition

Characterizing the Role of Plasticity in Structural Response to High Speed Flows

“…The model showed reasonable agreement with experiments and computations for a limited number of cases. The elastic-thermoviscoplastic response of a stiffened panel in hypersonic flow was examined in [10]. The panel was modeled using thin shell elements and aerodynamic loads were calculated using piston theory.…”

“…The impact of material plasticity on the response of aerospace structures subjected to thermomechanical loads was considered in [8][9][10]. Reference [8] describes an early exploratory study in which a viscoplastic material model was combined with an aerothermoelastic model.…”