Groovy solution to explosion protection

Cutting grooved patterns into building materials can make them much more resistant to the huge shockwaves of explosions or earthquakes, Californian team finds

Shock protection is a vital consideration for many types of building. Whether the risk is from potential terrorist attack to public spaces, industrial explosion or natural disaster, keeping people safe is of primary concern to engineers designing and building such structures.

Undergraduate researchers in the structural engineering laboratory of Prof Veronica Eliasson at the University of California San Diego made two related discoveries that could lead to major changes in how buildings are protected.

explosion protection
Two-dimensional side view of the logarithmic spiral layout of explosion obstacles

In the journal Multiscale and Multidisciplinary Modelling, Experiments and Design recent graduates Christina Scafidi and Alexander Ivanov explain that their research initially focused on the best way to lay out physical obstacles to shockwaves. They found that obstacles laid out in a logarithmic spiral – a pattern repeated many times in nature, such as in shelves and the swirl of galaxies, were best able to diminish the energy of shockwave and reduce overall damage.

Subsequently, they discovered that cutting three semi-circular grooves into each side of the obstacle materials made the obstruction even more effective attenuating shock.

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The team built a “shock tube” out of aluminium and acrylic polymer to propagate a shockwave travelling at Mach 1.2, and then used an ultrahigh speed camera to analyse how the test materials inside the tube behaved when struck by the shockwave. They found that the grooves seem to diminish the reflected shockwave that occurred when the initial wave hits the spire of obstacles and bounced back, with sensors mounted in the tube recording less than half of the peak pressure when the grooved spiral of obstacles was used. However, their results were conclusive for the initial transmitted shockwave.

“This research can be used in military applications and civil applications too, to design materials and buildings to better withstand high-intensity blasts,” said Scafidi, a structural engineer. “The coal industry has had many fatal accidents and we believe this research presents a strong case for protecting the workers from blast waves that can easily propagate throughout an entire coal mine,” added Ivanov, who recently graduated in aerospace engineering. “If the entire wall of the coal mine could be lined with these solid geometric obstacles, it could provide a cheap way to protect all of the workers in the mine.”