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FEATURE ARTICLE

High-speed Imaging of Shock Waves, Explosions and Gunshots

New digital video technology, combined with some classic imaging techniques, reveals shock waves as never before

Gary Settles

Shock waves were recognized as a natural phenomenon more than a century ago, yet they are still not widely understood. They are responsible for the crash of thunder, as well as the bang of a gunshot, the boom of fireworks, or the blast from a chemical or nuclear explosion. But these are not just loud noises. Sound waves can be thought of as the weaker cousins of shock waves in the air: They are both pressure waves, but they are not the same.

Figure 1. High-speed photography freezes in time...Click to Enlarge Image

Shock waves play important roles in modern physics and engineering, military operations, materials processing and medicine. Historically, the study of shock waves has taught us much about the properties of gases and material responses to a sudden energy input, and has contributed to the development of gas lasers and the field of plasma dynamics.

Recent attacks by terrorists using improvised explosive devices have reinforced the importance of understanding blasts, explosions and the resulting shock waves. These waves can be powerfully damaging in their own right, but in addition, studying them can help to quantify their originating explosions and can provide insight into how buildings and airplanes can be hardened to resist damage resulting from such blasts.

Their almost-total invisibility has given shock waves a mystique that has been exploited by Hollywood in countless scenes where explosions send heroes diving for cover. Like sound waves, shock waves are as transparent as the air through which they travel. Usually they can only be seen clearly by special instruments under controlled conditions in the laboratory. 

Now, however, our research group has taken modern high-speed videography equipment and combined it with some classical visualization methods to image shock waves from explosions and gunshots in more realistic environments. This allows us to capture the development and progress of these wave fronts on a scale that has not been possible in the past.




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