Digital cameras are rapidly supplanting film, even for very high speed and ultra high-speed applications. The benefits of these cameras, particularly CMOS versions, are well appreciated. This paper describes how a pair of synchronized digital high-speed cameras can provide full-field dynamic deformation, shape and strain information, through a process known as 3D image correlation photogrammetry. The data is equivalent to thousands of non-contact x-y-z extensometers and strain rosettes, as well as instant non-contact CMM shape measurement. A typical data acquisition rate is 27,000 frames per second, with displacement accuracy on the order of 25-50 microns, and strain accuracy of 250-500 microstrain.
High-speed 3D image correlation is being used extensively at the NASA Glenn Ballistic Impact Research Lab, in support of Return to Flight activities. This leading edge work is playing an important role in validating and iterating LS-DYNA models of foam impact on reinforced carbon-carbon, including orbiter wing panel tests. The technique has also been applied to air blast effect studies and Kevlar ballistic impact testing. In these cases, full-field and time history analysis revealed the complexity of the dynamic buckling, including multiple lobes of out-of-plane and in-plane displacements, strain maxima shifts, and damping over time.
On February 1, 2003, the Space Shuttle Columbia broke apart during reentry resulting in loss of seven crewmembers and craft. For the next several months an extensive investigation of the accident ensued involving a nationwide team of experts from NASA, industry, and academia, spanning dozens of technical disciplines.
The Columbia Accident Investigation Board (CAIB), a group of experts assembled to conduct an investigation independent of NASA concluded in August, 2003 that the cause of the loss of Columbia and its crew was a breach in the left wing leading edge Reinforced Carbon-Carbon (RCC) thermal protection system initiated by the impact of thermal insulating foam that had separated from the orbiters external fuel tank 81 seconds into that mission's launch. During reentry, this breach allowed superheated air to penetrate behind the leading edge and erode the aluminum structure of the left wing which ultimately led to the breakup of the orbiter.
Supporting the findings of the CAIB, were numerous ballistic impact testing programs conducted to investigate and quantify the physics of External Tank Foam impact on the RCC wing leading edge material. These tests ranged from fundamental material characterization tests to full-scale Orbiter Wing Leading Edge tests. Following the accident investigation, NASA turned its focus to returning the Shuttle safely to flight. Supporting this effort are many test programs to evaluate impact threats from various debris sources during ascent that must be completed for certifying the Shuttle system safe for flight. Digital high-speed cameras were used extensively to document these tests as significant advances in recent years have nearly eliminated the use of film in many areas of testing. Researchers at the NASA Glenn Ballistic Impact Laboratory have participated in several of the impact test programs supporting the Accident Investigation and Return-to-Flight efforts.
This paper summarizes the Columbia Accident and the nearly seven month long investigation that followed. Highlights of the NASA Glenn contributions to the impact testing are presented with emphasis on the use of high speed digital photography to document theses tests.
The major concern in advancing the state-of-the-art technologies for hypersonic vehicles is the development of an aeropropulsion system capable of withstanding the sustained high thermal loads expected during hypersonic flight. Even though progress has been made in the computational understanding of fluid dynamics and the physics/chemistry of high speed flight, there is also a need for experimental facilities capable of providing a high heat flux environment for testing component concepts and verifying/calibrating these analyses. A hydrogen/oxygen rocket engine heat source has been developed at the NASA Lewis Research Center that is capable of providing heat fluxes up to 450 W/cm<SUP>2</SUP> on flat surfaces and up to 5,000 W/cm<SUP>2</SUP> at the leading edge stagnation point of a strut in a supersonic flow stream. Gas temperatures up to 3050 K can also be attained. Two recent experimental programs conducted in this facility are discussed.