Paper describes blast-proof structures

A system modelled in a paper authored by theoretical physicists at the University at Buffalo demonstrates that it may one day be possible to protect civil structures and ships from extremely powerful impacts.

A system modelled in a paper authored by theoretical physicists at the University at Buffalo (UB) demonstrates that it may one day be possible to protect bridges, ships, skyscrapers, highway structures and even automobile bumpers from extremely powerful impacts.

In the paper, ‘Thermalising an Impulse,’ Surajit Sen, Ph.D., UB associate professor of physics, Felicia S. Manciu and Marian Manciu, describe a system that is capable of reducing the amplitude of a physical impact it receives by at least 95 to 98 percent.

The work shows, Sen said, that it may be possible to turn the dissipated energy from a shock wave into usable thermal energy. It also suggests that in a similar way, energy may be able to be harnessed from natural phenomena, such as ocean waves and geothermal sources.

Sen said that the work provides an important step in the physics of how shock waves travel through granular systems.

‘Granular materials, such as sand or soil, have long been used in shock-absorbing systems, but they have had only mixed results,’ said Sen. ‘Impulses simply will pass through systems where sizes of individual grains are about the same. In systems like ours, where grain sizes are altered in specific ways, a granular assembly can efficiently absorb the impulse.’

The shock-absorption system modelled by the UB physicists consists of a long, cone-shaped chain of spheres. The sphere positioned closest to the expected source of a shock is the largest, while each subsequent sphere is slightly smaller; the sphere closest to the structure – the building, bridge or ship – that the system is designed to protect would be the smallest of all.

‘The design is such that if a large shock hits the wide end of this tapered cone-shaped chain, then the shock would be broken down into an extremely large number of tiny shocks that would be received at the tapered end of the chain,’ he said.

Sen and his colleagues performed the research by first developing a model of the tapered-chain system and then by precisely solving Newton’s equations of motion on a computer to describe the dynamics of the tapered chain system.

The calculations reportedly demonstrate that by tailoring the way in which the spheres are tapered, the size of the spheres and the length of the chain, the system could reduce the amplitude of literally any size shock for any type of material.

‘The crux of the argument is that as mass gets reduced, the energy of the impulse gets distributed so that no single sphere is carrying too much energy,’ Sen said.

Sen envisions a shock-absorption material or a structural material, such as brick, in which these chains of spheres are embedded. At the same time, he said, the theoretical calculations provide a strong basis for the reuse of the mechanical energy of an absorbed shock wave. A similar reuse of impulses from nature, such as geological activities and ocean waves, also might be possible, Sen said.

‘It could create a situation where not only could structures be made shock-absorbent, but it might be possible for the building, the ship or the bridge that received the impact to take advantage of that energy for its own internal systems,’ he added.