The design and development of a high-speed digital imaging system

Abstract

The goal of this research was to develop a high-speed digital imaging system is a for optically recording dynamic experimental mechanics events. Optical imaging ' valuable tool in the field of experimental mechanics because it yields full-field information about the stresses and displacements which develop in a material under steady-state or transient conditions. The first main design requirement for the system was to have an exposure time of less than fifty nanoseconds in order to avoid streaking of the images. Also, variable interframe times ranging from two to one hundred microseconds were required so that an appropriate time window of the event can be captured. The second main design function required that adequate spatial separation of each of the images be obtained. Finally, the recording medium had to preserve full, undisturbed gray-scale information and allow post-experiment image enhancement and processing to be performed. This last requirement translated into digital storage of the images. The high-speed digital imaging system that has been developed utilizes an acousto-optic deflector, or Bragg cell, to accomplish the necessary spatial separation of the images to be captured. The system employs a pulsed argon laser for its light source and uses a combination of charge-injection device cameras and a frame grabber to capture the images. The system was first evaluated by capturing static images of a test and a photoelastic compression specimen. The next evaluation phase involved grid capturing dynamic images of the stress waves travelling through a photoelastic impact specimen. The essential requirements for any high-speed recording system and the characteristics of existing systems are reviewed first, followed by a discussion of the essential elements of the new system. A detailed description of the arrangement and interaction between the system components is then presented, followed by the results from the evaluation experiments that have been performed. Finally, some comments concerning the further work needed to make the system fully operational are provided.