Structural Response and Service Life Prediction Concerns in the Design of Hypersonic Flight Vehicle Hot-Structure

Abstract

Strength sizing of hypersonic vehicles requires the inclusion of temperature as that additional critical variable that sets it apart from the analyses of conventional aircraft. At high Mach numbers, aerodynamic and propulsion limitations restrict the maneuverability of hypersonic aircraft and increasing Mach number radically reduces the aerodynamic efficiency of wings. In turn, the external loads on the airframe are reduced. However, due to the higher temperature environment, which also reduces the strength of conventional structural materials, it is unclear as to which of these loading conditions actually sizes the structure. A further complication is the fact that for many materials the yield and ultimate strength vary differently with temperature, so both limit and ultimate loading conditions which correspond respectively to yield and ultimate material strengths, require consideration. An assessment has been made in identifying gaps in structural analysis and life prediction methods as applied to reusable, integrated structures for sustained operations in a hypersonic environment. The subject assessment has been performed through a phased program approach conducted by the AFRL. The Phase I program reviewed previous high supersonic and hypersonic vehicle programs with considerations of their service environment impacts on the design of the airframe. The Phase II program objective was to build upon the efforts of the Phase I program in continuing to identify gaps in structural analysis and life prediction methods as applied to reusable, integrated structures for sustained operations in a hypersonic environment. The Phase II program exploited these gaps through the detailed design and analyses exercises on four individual airframe panels of a conceptual Mach 5.0-7.0 Hypersonic Cruise Vehicle (HCV) that met the objectives of the analyses areas that the Air Force Research Lab is focused upon. A review of the Phase II program along with suggestions for future thrusts in the area of predictive capability for operational hypersonic aircraft structure to be conducted in the Phase III program is provided.