Nonlinear Response of a Thin Panel in a Multi-Discipline Environment: Part I—Experimental Results

Abstract

High-speed aircraft structures are susceptible to the extreme and transient effects of the associated aerodynamic environment. These structures can experience a myriad of limit states—yield, fatigue, creep, buckling, and the response is very often path-dependent. Hypersonics, defined as flight speeds greater than Mach 5 (Heppenheimer, NASA Technical Report, NASA SP-2007-4232, September 2007) where aerodynamic heating drives the analysis and design, often causing appreciable structural concerns, is a flight regime with very little practical experience. While the NASA Space Shuttle Orbiter and other space-access vehicles routinely transit the Mach 5 barrier, long-duration air-breathing flights represent but a scant portion of past flight-test programs. As a result, the aerospace industry accounts for the associated uncertainties in the structural response through overly-conservative, and often program-deleterious, design assumptions. The USAF Research Laboratory, Structural Sciences Center (SSC), is investigating and developing analysis methods to predict the changing, nonlinear response of hypersonic hot-structures; however, there is a lack of relevant flight-test and experimental data useful for validating these developing structures-centric methods. The SSC recently began a series of thorough wind-tunnel experiments to provide quality, full-field experimental data for a simple, clamped nominally flat panel exposed to supersonic flow, shock boundary-layer interactions (SBLI) and heated flow. External heating sufficient to buckle the test article during supersonic wind tunnel experiments is being explored. Early results are presented in the present study. Additionally, wind tunnel conditions will be sought that lead to panel snap-through dynamics. The present study documents the evolution of the experiments, emphasizing the nonlinear response of the panel in preparation for upcoming wind-tunnel experiments. Also discussed are the characteristics of the experimental conditions leading to the nonlinear structural response, and the full-field displacement, pressure and thermal results necessary for model validation. Part II of this study will present the results of a numerical study of the same structure in the supersonic environment.